Periphyton Ecology in Great Basin Rivers: Winter Blooms, Hyporheic Exchange Effects, and Reservoir-Tailwater Productivity

University of Nevada, Reno

Periphyton Ecology in Great Basin Rivers: Winter Blooms, Hyporheic Exchange Effects, and Reservoir-tailwater Productivity

A dissertation in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Sciences and Health

Clinton J. Davis

Christian H. Fritsen / Dissertation Advisor

August 2012

THE GRADUATE SCHOOL

We recommend that the dissertation prepared under our supervision by

CLINTON JOHN DAVIS

entitled

Periphyton Ecology In Great Basin Rivers: Winter Blooms, Hyporheic Exchange Effects, And Reservoir-Tailwater Productivity

be accepted in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Christian H. Fritsen, Ph.D., Advisor

Sudeep Chandra, Ph.D. , Committee Member

Laurel Saito, Ph.D., Committee Member

Robert Qualls, Ph.D., Committee Member

Jeffrey Baguley, Ph.D., Graduate School Representative

Marsha H. Read, Ph. D., Dean, Graduate School

August, 2012

Abstract

Recent surveys have revealed a preponderance of evidence that strong periphyton- nutrient interactions occur in Great Basin rivers. These initial field efforts have, to some extent, determined the occurrence, coverage and magnitude of these periphyton blooms.

Localized studies are warranted that focus on quantifying ecologically relevant rates (e.g. accrual, primary production, growth rates) and environmental conditions related to bloom events. Three observational studies were conducted in Great Basin rivers focusing on various spatial and temporal dynamics of periphyton blooms.

The first study provides a detailed description of a recurring winter bloom in the

Truckee River, CA-NV. Results show that despite near-freezing temperatures and low light, the bloom appears as a result of slow but steady growth that experiences minimal losses for an extended period (>100 days). Further, net ecosystem production during the winter bloom can account for approximately a third of the annual net ecosystem production.

The second study is an investigation of the potential influence of vertical hyporheic exchange on periphyton assemblages in the main channel of a montane reach and a desert reach in the Truckee River. No convincing evidence was found that periphyton assemblages were affected by exchange processes at the riffle-pool scale in either reach.

A sufficient flux of nutrients from other sources (e.g. water column, N2 fixation, internal cycling within mats) supports balanced periphyton growth.

Third, a reservoir-tailwater system in eastern Nevada appears to provide the optimal conditions for periphyton that maximizes areal rates of primary production. Periphyton-

ii nutrient interactions were exceptionally strong due to a combination of reservoir operations and a favorable environmental setting in the semi-arid landscape. Estimated primary production rates ranked among the highest reported for streams worldwide and appeared to be constrained to maximum rates by self-regulating mechanisms.

iii

Dedication

I dedicate this dissertation to my Mother, Carol L. Davis, who provided enduring support throughout the many endeavors I have embarked on in the past 33 years. To-date the greatest achievement has been a PhD, which I undoubtedly share with her. I truly wish she could have been with me for the final push to the goal-line so that she could share the extraordinary feeling of accomplishment and pride. Thanks Mom, for the sacrifices you made and selfless dedication in supporting me through it all. You are, and will continue to be, greatly missed.

Acknowledgements

Many people and institutions supported me along the path to dissertation completion. My

“home-away-from-home” has been the Desert Research Institute in Reno, Nevada which provided me with a pristine environment to grow as a young researcher. Beyond the ample resources that were made available, there was always consistent support from DRI staff, faculty and students to assist in all aspects of my graduate research experience. I owe many thanks to my primary advisor, Dr. Chris Fritsen (DRI-DEES), whose passion for science-based inquiry could not help but rub off on me in addition to being an engaging teacher, patient mentor, effective writing coach and, after more than 10 years of working together, most certainly a strong collaborator and a good friend. My progression as a scientist has also benefited greatly from the mentorship and friendship of Dr. Sudeep

Chandra (UNR) with whom I spent many hours discussing science, policy, and life in general. I also owe much appreciation to Drs. Jerry Qualls, Laurel Saito, and Jeffrey

Baguley (UNR) for being excellent committee members via helping refine my research products and guiding me through the realities of professional development. I would not have been able to effectively organize, collect and process data without the patient training (often repeatedly!) and advice from Jeramie Memmott. Eric Wirthlin contributed immensely by assisting with field and lab work, as well as a being a fellow passenger on the roller-coaster ride of experiences that graduate work entails. My first interdisciplinary collaboration was marked with success in working closely with Ramon

Naranjo (DRI-DHS), in which many long hours in the field and lab not only improved my understanding of shallow groundwater hydrology, but also led to another great

v collaboration and solid friendship. Finally, I could not have achieved any of this without the unwavering support from my family (Carol, Rod, Matt), extended Caires family

(Joyce and Ken) and my incredible wife, Annie, who were all wholeheartedly invested in my professional and personal progression throughout the graduate years. We did it!!!

Table of Contents Abstract ...... i Dedication ...... iii Acknowledgements ...... iv List of Tables ...... ix List of Figures ...... xi Chapter 1 ...... 1 Introduction ...... 1 References ...... 3 Chapter 2 ...... 5 Abstract ...... 6 Introduction ...... 7 Methods ...... 8 Study sites description ...... 8 Chemical and physical conditions ...... 9 Periphyton biomass, nutrient content, and assemblage composition ...... 10 Accrual rates and specific growth rates ...... 11 Community metabolism ...... 12 Photosynthesis-irradiance experiments ...... 13 Ecosystem metabolism ...... 15 Statistical Analyses ...... 16 Results ...... 17 Physical and chemical conditions ...... 17 Periphyton biomass, community composition, and nutrient balance ...... 18 Community metabolism ...... 20 Accrual rates and Specific growth rates ...... 21 Ecosystem metabolism ...... 22 Discussion ...... 22 Biomass, community composition, and nutrient balance ...... 22 Accrual rates and specific growth rates ...... 25

vii

Community metabolism ...... 26 Winter’s contribution to annual net production ...... 27 Acknowledgements ...... 28 References ...... 29 Chapter 3 ...... 47 Abstract ...... 48 Introduction ...... 49 Methods ...... 51 Study sites description ...... 51 Instrumentation and monitoring ...... 51 Periphyton accumulation, nutrient content, and assemblage composition ...... 52 Primary production ...... 54 Results ...... 56 Physical and chemical conditions ...... 56 Periphyton accumulation, nutrient content, and assemblage composition ...... 57 Primary production ...... 58 Specific growth rates ...... 58 Discussion ...... 59 Key insights to guide future hyporheic exchange studies ...... 61 Conclusions ...... 63 Acknowledgements ...... 63 References ...... 64 Chapter 4 ...... 74 Abstract ...... 75 Introduction ...... 76 Study System ...... 77 Methods ...... 78 Water Quality ...... 78 Ecosystem Metabolism ...... 79 Periphyton ...... 80

viii

Results ...... 82 Dissolved Oxygen and Temperature ...... 82 Ecosystem Metabolism ...... 82 Nutrient Concentrations and Ratios ...... 83 Periphyton Biomass, Nutrient Content, and Community Composition ...... 84 Discussion ...... 85 Comparison of SFHR tailwater productivity to other semiarid streams ...... 85 Potential self-regulation and maximum production ...... 87 Identification of extremely productive reservoir-tailwater systems ...... 90 Acknowledgements ...... 91 References ...... 92 Chapter 5 ...... 102 Summary and Synthesis ...... 102 Why are such “strong” periphyton-nutrient interactions apparent in Great Basin rivers? ...... 102 References ...... 106

List of Tables

Chapter 2

Table 1. Description of sampling dates and research design for the 2009-10 winter bloom study...... 32 Table 2. Water quality and habitat variables (mean and % coefficient of variation) at each site during the winter study (November 2009 to February 2010). Site (distance from Lake Tahoe), OP (orthophosphate), NH4+ (ammonium), NOx (nitrate+nitrite), DIN (dissolved inorganic nitrogen)...... 33 Table 3. Two-way ANOVA results for periphyton metabolism, brick biomass, and temperatures (log-transformed data). Analyses applied sites (56 km, 80 km, 97 km, 125 km) and bloom phase (early, middle, late) as fixed factors. Bloom phases categorized as early bloom (October 31 st to December 15 th ), middle bloom (December 16 th to January 31 st ) or late bloom (February 1 st to February 20 th )...... 34 Table 4. Mean differences from Tukey’s pairwise comparisons for brick biomass (µg chl a cm -2) between sites and bloom phases. Bold indicate significant differences (p < 0.05)...... 35 Table 5. Comparison of relevant winter studies of stream periphyton conducted at temperate latitudes...... 36

Chapter 3

Table 1. Dissolved nutrients (µM) at 56 km in surface-water (Surface) and pore-water zones of upwelling (UW) and downwelling (DW) during periphyton studies in spring and summer 2008...... 69 Table 2. Dissolved nutrients (µM) at 176 km in the surface-water (Surface) and pore- water in zones of upwelling (UW) and downwelling (DW) during periphyton studies in summer 2008...... 69 Table 3. Photosynthesis-irradiance (PE) experimental summary. Maximum biomass B specific photosynthetic rate (P m), specific growth rate (µ)...... 73

Chapter 4

Table 1. Site reaeration rates and associated metabolic rates (GPP, ER, NEM)...... 98 Table 2. Nutrients (micromolar) and ratios (mole:mole) in SFR–SFHR during spring and summer 2009...... 99 Table 3. Periphyton densities of biomass, particulate nutrients and ratios. Mean ± SE . 100

Table 4. Summary of maximum rates of productivity reported in desert streams and tailwaters. Discharge at or near time of metabolism measurements unless otherwise indicated...... 101

List of Figures

Chapter 2

Figure 1. Periphyton monitoring sites (2000-04) along the Truckee River, CA-NV. Four sites (yellow circles) selected for winter bloom study (2009-10) that represent a gradient of biomass accumulation (i.e. increasing downstream). Map modified from California Department of Water Resources (1991)...... 38 Figure 2. Average daily discharge (USGS gauge 10348000) in the Truckee River 80 km downstream from Lake Tahoe, CA (A) and daily solar irradiance from the Western Regional Climate Center station located at the Desert Research Institute, Reno, NV (B). Shaded area indicates the temporal window of study...... 39 Figure 3. Hourly temperature logged at each site (A-D) in the Truckee River in the autumn-winter 2009-2010...... 40 Figure 4. Mean (± 1 SE) time-series of biomass (chla) accrual on bricks and cobble (Epil) and biomass present during chamber and photosynthesis-irradiance (PE) experiments at each site. Dashed lines indicate transitions between early, middle, and late bloom phases. Asterisks (*) along x-axis indicate time points when biomass on cobble were significantly higher than biomass on bricks...... 41 Figure 5. Mean (± 1 SE) relative abundance (RA) and relative biovolume (RB) of dominat diatom taxa in brick assemblages. Diatoma (A-D), Gomphoneis (E-H), and Nitzschia (I-L)...... 42 Figure 6. Mean (± 1 SE) nutrient content ratios of periphyton on bricks and cobble (Epil). POC:PN (A-D), POC:PP (E-H), and PN:PP (I-L)...... 43 Figure 7. Mean (± 1 SE) epilithic metabolism (gross primary production, GCP, community respiration, CR, and net community metabolism, NCM) during three phases of bloom development (early, middle, late) at each site (A-D). Bars with the same letter are not significantly different...... 44 Figure 8. Accrual rates on bricks and cobble (epilithic) (A) and specific growth rates ( µ) estimated from chambers during the bloom (B) and early bloom specific growth rates estimated from brick PE experiments, epilithic chambers, brick biovolume accrual, brick chla accrual and epilithic chla accrual (C). Mean ± 95% CI ...... 45 Figure 9. Mean (± 1 SE) net ecosystem metabolism (NEM) for different seasons in 2008- 2009 water year at 122 km, Truckee River, Nevada...... 46

Chapter 3

Figure 1. Hyporheic study sites in the Truckee River within a montane reach at 56 km (A) and semi-arid reach at 176 km (B). Periphyton studies conducted in localized

xii upwelling (UW) and downwelling (DW) exchange zones within each reach. Arrows indicate flow direction...... 66 Figure 2. Average daily discharge for the 2007-2008 water-year near Farad, CA (USGS gauge 103446000) and near Nixon, NV (USGS gauge 10351700) representing flow at 56 km and 176 km, respectively. Shaded areas indicate temporal window of periphyton studies...... 67 Figure 3. Temporal dynamics of vertical hydraulic gradient (VHG) in predicted upwelling (UW) and downwelling (DW) zones at 56 km and 176 km. Shaded areas indicate temporal window of periphyton studies...... 68 Figure 4. Mean biomass (± SE) of brick and epilithic assemblages in predicted upwelling (UW) and downwelling (DW) zones at 56 km in spring, 56 km in summer , and 176 km in summer...... 70 Figure 5. Mean nutrient balance (± SE) of periphyton on bricks...... 71

Figure 6. Relative biovolume of diatoms (N 2-fixing, non-N2-fixing), cyanobacteria (N 2- fixing, non-N2-fixing), and “green” filamentous algae at 56 km in spring (A) and summer (B), and 176 km in summer (C)...... 72 Figure 7. Specific growth rates (µ) (± 95% CI) estimated from brick chla accrual and brick PE experiments...... 73

Chapter 4

Figure 1. Daily discharge statistics (USGS gauge 10320000) from 1988 to 2008 for the South Fork Humboldt River below reservoir. Arrows indicate timing of periphyton sampling and metabolism estimates...... 96 Figure 2. Diel temperature, dissolved oxygen and dissolved oxygen saturation in the South Fork Humboldt River downstream of the reservoir...... 97

Chapter 1

Introduction

General Statement of Problem and Significance

Freshwater ecosystems throughout the world are being impacted by a variety of

anthropogenic activities. Direct discharge of effluents from industry and wastewater

treatment, as well as non-point source inputs from agricultural and urban areas are

increasing loads of toxins and nutrients to aquatic environments (Carpenter et al., 1998).

Water has been increasingly controlled and regulated in most watersheds. These

alterations have resulted in hydrologic regimes that exhibit unnatural dynamics in flow

(Poff et al., 1997). These impacts to freshwater environments can impose drastic changes

to ecosystem structure and function.

Algae represent an evolutionarily diverse group of photoautotrophic organisms that are

responding to the rapid environmental change in aquatic systems. Increased nutrient

loads have fueled higher rates of primary production, resulting in the accumulation of

high standing stocks of biomass or ‘blooms’ of algae (Biggs, 1996). Bloom magnitude

(e.g. biomass L -1 or cm -2) has been used as a basic metric, in conjunction with nutrient concentrations, to track the ecological process of eutrophication in water-bodies.

Fundamental understanding of the spatial and temporal dynamics of algal blooms is of primary importance to evaluate and monitor the impacts of anthropogenic eutrophication.

Several surveys have recently been completed on the spatial and temporal dynamics of periphyton (attached algae) blooms in three major rivers of the Great Basin located in

2 western Nevada: Truckee River (Davis, 2007), Carson River (Fritsen et al., 2006), and

Walker River (Davis et al., 2009). Summer blooms of attached filamentous ‘green’ algae and associated epiphytes (i.e. diatoms, cyanobacteria) have been documented in these

Great Basin rivers and generally conform to the conceptual model defined by the dynamics of nutrient regime and flood frequency (Biggs, 1995). However, it has become apparent that several aspects of bloom phenomenon in the Great Basin’s major rivers require further investigation:

1) The Truckee River has an annual winter bloom of attached diatoms that is

comparable in magnitude to the summer bloom of filamentous ‘greens’. Generally it is

expected that standing stocks of periphyton are much lower in the winter compared to

summer (Biggs, 1996), however late-autumn to winter maxima have been documented

(Uehlinger, 1991). Less information exists related to ecologically relevant rates during

these cold-season bloom events, such as the metabolic rates (photosynthesis, respiration)

that determine production rates, which in turn establish the accrual rate of periphyton

biomass.

2) High standing stocks of periphyton biomass within reaches of the Truckee River are

spatially variable and are often associated with relatively low nutrient concentrations

(especially dissolved nitrogen), thus the potential role of smaller spatial scale processes

(<1000 m) may explain biomass patterns. The interaction between stream surface-water

and the saturated sediments and interstitial water directly beneath (broadly defined as the

hyporheic zone) creates a dynamic ecotone of physical and chemical characteristics that

can influence the structure and function of biotic communities in benthic habitats

(Boulton, 1993). A longitudinal gradient in the nutrient balance (nitrogen:phosphorus)

3 within the Truckee River offers a chance to determine the effects of hyporheic exchange on periphyton structure and function in reaches of different in-stream nutrient concentrations and balance.

3) A reservoir-river system in the semi-arid region of eastern Nevada appears to meet

the optimum environmental conditions (i.e. light, nutrients, temperature, flow) to

maximize productivity. Preliminary data of bloom magnitude, areal coverage, and

relative dissolved oxygen changes in the South Fork Humboldt River, NV, highlight its

likelihood as a tailwater system exhibiting maximum rates of production such that self-

regulating mechanisms (e.g. self-shading, space) are the only constraints on production

rates.

References

Biggs, B.J.F. 1995. The contribution of flood disturbance, catchment geology and land- use to the habitat template of periphyton in stream ecosystems. Freshwater Biology 33:419-438. Biggs, B.J.F. 1996. Patterns in benthic algae of streams. Pages 31-56 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal ecology in freshwater benthic ecosystems. Academic Press, San Diego, California. Boulton, A.J. 1993. Stream ecology and surface hyporheic hydrologic exchange: implications, techniques, and limitations. Australian Journal of Marine and Freshwater Research 44:553-564. Carpenter, S.R., N.F. Caraco, D.L. Correll, R.W. Howarth, A.N. Sharpley, and V.H. Smith. 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecological Implications 8:559-568. Davis, C.J. 2007. Periphyton dynamics and environmental associations: Truckee River, CA-NV, USA. (Master’s Thesis) University of Nevada Reno. ProQuest/UMI, Ann- Arbor, Michigan. Publication No. 14477636. Davis, C.J., J. Memmott, and C.H. Fritsen. 2009. Walker River periphyton. In M.W. Collopy, J.M. Thomas (editors). Restoration of a desert lake in a agriculturally dominated watershed: the Walker Lake Basin. Final report to the Bureau of Reclamation. Reno, NV.

Fritsen, C.H., Z. Latham, J. Memmott, C.J. Davis, and A. Rost. 2006. Dissolved oxygen dynamics in the Carson River, Nevada: Results from field programs during the summers of 2003 and 2004. Desert Research Institute. Poff, N.L., J.D. Allan, M.B. Bain, J.R. Karr, K.L. Prestegaard, B.D. Richter, R.E. Sparks, and J.C. Stromberg. 1997. The natural flow regime. Bioscience 47:769-784. Uehlinger, U. 1991. Spatial and temporal variability of periphyton biomass in a prealpine river (Necker, Switzerland). Archive Fur Hydrobiologie 123:219-237.

Chapter 2

Ecology of a winter diatom bloom in a montane-desert river

Clinton J. Davis 1 AND Christian H. Fritsen 2 Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 USA [email protected] [email protected]

This paper was submitted to Freshwater Science on February 18, 2012

Abstract

Ecological processes (e.g. primary production and biomass accumulation) are often assumed to be at their minimum in the winter due to abiotic constraints (low temperatures and irradiances). However, a notable winter bloom of diatoms has been observed and documented in the Truckee River, CA-NV, USA. Longitudinal accrual rates, specific growth rates, community metabolism, and assemblage nutrient balance measures were undertaken to evaluate the relative magnitude of these processes and potential ramifications in regards to ecosystem energetics and material cycling. Standing stocks generally increased downstream (up to 60 µg chlorophyll a cm -2) in conjunction with

accrual rates (up to 0.92 µg chlorophyll a cm -2 day -1) and specific growth rates (up to

0.15 divisions day -1). Photosynthesis always exceeded respiration in epilithic

communities, indicating a continual net gain in energy (both spatially and temporally)

throughout the winter bloom. Net autotrophy at the ecosystem-scale was also

demonstrated in a high biomass reach and emphasized the potential significance of the

winter bloom in regard to the annual primary production. Seasonal estimates indicate

that the winter months (November to January) contribute approximately 37% of the

yearly net ecosystem production in the Truckee River, thus underscoring the importance

of evaluating ecological processes during winter to truly understand the complete

energetics and mass-balance of aquatic systems.

Introduction

Consideration of seasonal changes in ecological systems is a fundamental aspect of

ecological studies. Streams and rivers can experience major seasonal changes in key

drivers (such as temperature, light, and discharge) that impact key ecological processes.

Winter at temperate latitudes can impose extreme conditions on stream communities as

solar radiation and temperatures drop. Reduced temperatures slow the physiology of

organisms and can induce ice formation that impacts in-stream conditions that may

physically affect stream organisms and populations (Prowse 2005). Due to these

conditions, winter is typically perceived as a period of reduced activity or dormancy for

aquatic communities (Alekseev et al. 2007). Despite this perception, the importance of

understanding assemblages in winter (e.g. habitat use, survival, physiology) has become

increasingly recognized (Huusko et al. 2007).

Several studies have revealed temperate streams’ capacities for supporting high

periphyton biomass in winter. Periphyton biomass in winter has been assessed in the

context of establishing spatial and temporal patterns associated with non-point source

pollution (Delong and Brusven 1992) and hydrological factors (Uehlinger 1991),

evaluating nutrient limitation (Bothwell 1985, Gustina and Hoffmann 2000) and light

limitation (Rounick and Gregory 1981), and estimating rates of primary production

(Ostrofsky et al. 1998). These studies counter the general perception of periphyton

standing stocks being low in streams during winter (Biggs 1996) due to reduced

temperatures (DeNichola 1996) and low irradiances (Hill 1996).

Beyond recognizing the potential for substantial winter biomass in streams, there is

limited information regarding the growth dynamics of winter blooms. The current study

assesses periphyton growth in a montane-desert river during high magnitude blooms in

winter. Longitudinal accrual rates, specific growth rates, community metabolism, and assemblage nutrient content show the relative magnitude of changes in benthic structure and growth kinetics in winter. We describe appreciable inputs of autochthonous carbon into the river ecosystem during the winter due to diatom production. Biomass losses are minimal relative to net production in several reaches such that eutrophic-levels of biomass are attained and maintained. The relative importance of winter production for the Truckee River system is evaluated by estimating seasonal contributions to annual net ecosystem metabolism within a high productivity-high biomass reach. Ultimately, this study stresses the importance of quantifying ecological structure and processes during winter to truly elucidate complete energetic and mass-balance of materials in aquatic systems.

Methods

Study sites description

The Truckee River is located at the western edge of the Central Basin and Range

province in the western US. It spans both montane and semi-arid environmental

conditions along its 190 km course from Lake Tahoe, California to its terminus at

Pyramid Lake, Nevada. Typically the system experiences low flood frequency as

scouring flows only arrive during the snow-melt in spring (April to June), which is

9 followed by an extended period of stable flow. Discharge releases from upstream reservoirs (Prosser, Stampede, Boca) are continually manipulated to sustain downstream agriculture, municipalities, and recreational opportunities.

Previous periphyton monitoring at 11 sites (2000 -04, Davis 2007) revealed that

biomass increased from 56 km to 125 km downstream of Lake Tahoe during the annual

winter bloom and enabled the selection of four study sites along a gradient in biomass in

winter (~ 5, 10, 20, 40 mean µg chl a cm -2) (Figure 1). The 56 km site is in a canyon near the transition from montane to semi-arid conditions with modest anthropogenic impacts from upstream development. The 80 km site is slightly upstream from the urban setting of Reno, Nevada (population ~ 225,000) but is likely impacted by non-point pollution from upstream septic tanks and road run -off. Downstream, the 97 km site (in Sparks,

Nevada; population ~ 90,000) is impacted by non-point pollution and a point source from

a man-made drainage system connected to northern communities. The 125 km site is

further impacted by treated sewage effluent from the Truckee Meadows Wastewater

Treatment Facility and a polluted tributary (Steamboat Creek). The environmental

setting of the Truckee River combined with these pollution sources results in a

longitudinal nitrogen:phosphorus gradient whereby the nutrient balance shifts from

phosphorus limitation of algal growth upstream to nitrogen limitation downstream (Green

and Fritsen 2006).

Chemical and physical conditions

Discrete water chemistry samples were collected each time periphyton was sampled.

Water grab-samples were subsampled, filtered and frozen until analysis using flow-

10 injection analysis based on Lachat QuikChem methods for orthophosphate (OP, Liao

+ 02002), nitrate plus nitrite (NO x, Pritzlaff 2000), and ammonium (NH 4 , Prokopy 2003).

Stream temperature was logged hourly using iButton temperature loggers (iBTags, Alpha

Mach Inc.) secured to stream-bed. Solar irradiance (W m -2) data were retrieved online from the Western Regional Climate Center station located at the Desert Research

Institute, Reno, NV (http://www.wrcc.dri.edu/weather/nnsc.html).

Periphyton biomass, nutrient content, and assemblage composition

Bricks were used as artificial substrates (surface area = 442 cm 2) via clustering within a

habitat that had similar depth (0.25 -0.5 meter), substrate (cobble/pebble), and light regime (0% riparian cover). The near-bed current velocities (20 mm above brick surface) were moderate (0.21 -0.49 m s -1). A subset of bricks (n = 5) were randomly collected weekly at each site for the first month (subsequently every 2-3 weeks, depending on accrual rates, Table 1), placed in sealed plastic containers and transported to the lab for scrubbing, homogenizing and subsampling for periphyton biomass (chlorophyll a, chla), nutrient content (particulate organic carbon, particulate nitrogen, particulate phosphorus), and algal community composition. Epilithic assemblages growing on cobble upstream of brick clusters (~80 m reach) were randomly collected (n = 3-5) and processed for the same suite of parameters.

Chla subsamples were vacuum filtered onto filters (Whatman GF/F) that were placed

into borosilicate glass scintillation vials in a -80°C freezer for storage until analysis. Chla

concentrations were determined via fluorometry following Welschmeyer (1994) in a

Turner Designs model 10AU fluorometer calibrated with chlorophyll a from Anacystis

11 nidulans (Sigma Corp.). Chla content was checked spectrophotometrically (Parsons et al.

1984) for quality assurance. Particulate organic carbon (POC) and particulate nitrogen

(PN) subsamples were filtered onto pre-combusted GF/F filters, dried for 24 h and stored

with desiccant until analysis using a Perkin Elmer 2400 series II CHN/SO analyzer

system. Particulate phosphorus (PP) subsamples were filtered onto HCl rinsed pre-

combusted GF/F filters and dried before digesting to extract organic and inorganic

fractions which were determined via colorimetric methods (Diamond 2001).

Homogenized periphyton samples were subsampled for microscopy and preserved by

addition of gluteraldehyde. Two of the five brick samples from each time point were

randomly selected for enumeration. All diatom and soft-algae were counted in a Palmer-

Maloney chamber and identified to genus-level using a tiered magnification method that

entailed scanning the whole chamber at 100X magnification for large taxa (>200 µm),

followed by a minimum of 5 views at 400X for small taxa (<200 µm). The tiered

counting allowed for a minimum of 400 natural units (cell, filament, or colony) identified

in each sample. Taxonomic identity of diatoms was confirmed at 1000x magnification via

permanent slide mounts using Naphrax© medium. All counts were standardized to the

area sampled for biovolume ( µm3 cm -2). Biovolume estimates for each contributing taxa were determined by assigning formulas outlined by Hillebrand et al. (1999). Assemblage composition was evaluated using proportional values for abundance (relative abundance,

RA) and biovolume (relative biovolume, RB) instead of absolute densities.

Accrual rates and specific growth rates

Accrual rates of biomass ( µg chla cm -2 d-1) was calculated at each site by averaging the

-2 accrual rate between each sampling point in the time-series, accrual = (µg chla cm t – µg

-2 chla cm t-1) / (dt – dt-1), where t is the time point and d is day of accrual. Growth rates

were estimated by least-squares fit of accrual time-series data during the period of

increasing biomass by applying the equation y = a*ekt , where y is the chla density ( µg

chla cm -2) at day t, a is the initial chla density, and k is the net growth rate. Net growth rate was converted to specific growth rates (µ, divisions day -1) by the expression, k = µ/ln

2. Immigration of algal cells during the initial 5 to 10 d of accrual (thus not actually

active growth) was accounted for by excluding the first time-series point from growth

rate estimations. Specific growth rates based on biovolume accrual were also estimated

for brick biofilms using similar approaches. Specific growth rates based on net accrual

rates were used for comparison to growth rates determined via short-term metabolic

measurements on epilithic assemblages in chambers and photosynthesis-irradiance

experiments on brick assemblages.

Community metabolism

Metabolic rates of epilithic assemblages were estimated three times during the bloom

by monitoring dissolved oxygen inside 2 L Cambro © chambers. Two or three cobble

were collected haphazardly near brick clusters before dawn and placed in darkened

chambers in order to depress dissolved oxygen below saturation (e.g. 80% saturation) to

improve signal detection and avoid bubble formation. The light and dark chambers (3

replicates treatment -1) were subsequently incubated in-stream over short-term periods

(1.5 -3 h) during the mid-day conditions of ambient temperature and light. Changes in

13 dissolved oxygen in chambers yielded estimates of gross primary production by epilithic communities (GCP) by adding the community respiration (CR) from dark treatments to net hourly metabolism measured in light treatments (Bott 2006). Hourly metabolic rates from chambers were scaled to daily estimates (e.g. net community metabolism, NCM) by integrating hours of daylight, while CR was scaled to 24 h period. Light levels (PAR) were logged continuously during the chamber incubation period using a Licor QSL-2100.

Chambers were kept dark and on ice until access to the lab to scrub, homogenize and subsample for chla. Biomass-specific rates (µg C µg chla -1 day -1) of GCP during the

early bloom were converted to doubling times by estimating carbon to chlorophyll a using the slope from a regression of POC versus chla.

Photosynthesis-irradiance experiments

Photosynthesis as a function of irradiance (PE) was measured using short-term

incubations (1.85 to 2.5 h) on periphyton scraped from bricks collected during the early

bloom phase (Table 1). Bricks were collected in the morning and transported

immediately to the lab in sealed plastic containers filled with stream water and placed in

coolers filled with stream water to maintain ambient conditions. Five aliquots of the

scrapped/rinsed periphyton slurry (1 mL) were subsampled in order to normalize uptake

14 rates to biomass and the remaining 70 mL was spiked with NaH CO 3 to attain a final

activity of 0.28 to 0.49 µCi mL -1. Radioisotope concentrations in periphyton slurry were

determined from triplicate 0.05 mL aliquots that were fixed with 0.05 mL ethanolamine

before adding scintillation cocktail. Aliquots (2mL) were pipetted into 24 glass

scintillation vials and placed into a temperature controlled aluminum block (± 1 -2ºC

14 ambient) fitted with neutral density screening to attain 24 different irradiances spanning a wide range (7 -400 µEinstein’s m -2 sec -1) emitted from a 500 W tungsten halogen lamp.

Irradiances were measured using a 4 π scalar irradiance meter (Biospherical Instruments

QSL-2100). Three control vials wrapped in foil were incubated in the water bath

throughout the experiment in order to subtract background radioactivity from 14 C uptake in light treatments. Experiments ended by turning off the light and adding concentrated

HCl. Vials were subsequently dried on a heating block in a fume hood to remove residual inorganic 14 C. Scintillation fluid was added and radioactivity was determined using a Beckman Coulter LS6500 multipurpose scintillation counter.

Carbon fixation rates were calculated using the general approach of Strickland and

Parsons (1972). Total dissolved inorganic carbon was estimated for each site (11 -21 mg l-1) following Wetzel and Likens (2000) indirect method using field temperature and pH

values collected the day of experiment and the monthly average of alkalinity (7 -10 years)

(NDEP 2009). Curve fitting software, TableCurve 2D (version 5.01/2011, Systat

Software Inc., San Jose ) was used to fit the chla normalized uptake rates to a hyperbolic

tangent function (Jassby and Platt 1976) by the expression:

B B B P = P m tanh ( αI/ P m)

B -1 -1 B where P is the biomass-specific photosynthetic rate (µg C µg chla h ), P m is the maximum biomass specific photosynthetic rate (µg C µg chla-1 h-1) , α is the initial linear

slope of the curve, and I is the irradiance. Daily rates of carbon fixation (µg C µg chla -1

-1 B day ) were calculated by assuming P m was maintained throughout the entire daylight

B -2 period (given that P m was reached at relatively low irradiances, 80 to 120 µEinsteins m

15 sec -1). Specific growth rates were estimated assuming carbon to chla was equal to the regression slope of POC vs chla.

Ecosystem metabolism

Winter’s contribution to annual net productivity were estimated by calculating gross

primary productivity (GPP), ecosystem respiration (ER), and net ecosystem metabolism

(NEM) at 122 km (USGS gauge 10350340) using data collected by the Truckee

Meadows Water Reclamation Facility (Cities of Reno and Sparks, Nevada). Hourly

sonde data collected by the Truckee Meadows Water Reclamation Facility at 122 km

during the previous water year (October 1, 2008 to September 30, 2009) was used to

estimate ecosystem metabolism. The water year encompassing the winter periphyton

study (2009 to 2010) was not analyzed due to large gaps in measurements (4 months) in

winter and spring.

Diel oxygen curve methods using the single-station approach were applied to estimate

-2 - rates of production and respiration (Odum 1956). Net ecosystem metabolism (g O 2 m h

1) is defined as:

NEM( t) = z(d C/d t – k[Cs – C])

-3 where C is the dissolved oxygen concentration (g O2 m ), Cs is the concentration at

-3 -1 saturation (g O 2 m ), k is the oxygen reaeration coefficient (h ) that has been corrected to

the ambient stream temperature, and z is the average depth (m) of the stream reach.

Reaeration rates were estimated using the night-time drop of oxygen concentration

method (Hornberger and Kelly 1975). Estimates of daily metabolism were excluded

from further analysis if night-time regressions were not significant ( p >0.05). Reaeration

16 rates estimated from night-time regressions were compared to empirically derived estimates for the same reach (Nowlin 1987) to ensure reliability of this estimation approach. Ecosystem respiration was estimated by calculating the average hourly rate of

NEM at night. Gross primary production integrated during daylight hours was the sum of hourly rates of NEM and ER. Metabolism rates were converted to areal estimates by establishing empirical relationships between channel width, velocity, and discharge.

Daily averages of NEM were calculated for winter (November, December, January; n =

38 days), spring (February, March, April; n = 16 days),), summer (May, June, July; n =

57 days), and fall (August, September, October; n = 68 days).

Statistical Analyses

Sampling points were categorized as early bloom (October 31 st to December 15 th ), middle bloom (December 16 th to January 31 st ) or late bloom (February 1 st to February 20 th ).

Two-way ANOVA followed by post-hoc Tukey’s multiple comparison tests were used to

evaluate the effect of site and bloom phases (early, middle, late) on temperature, brick

biomass and community metabolism. Data were log (x+1) transformed to meet the

assumptions of homogenous variances and approximate normality (Zar 1999).

Restricted access at 97 km during the late bloom due to high flows resulted in estimating

brick biomass using the previous week’s epilithic biomass to ensure a balanced design

that could evaluate the interaction of site and bloom period. Tukey’s comparisons were

not reported for 97 km during the late bloom due to this biomass estimation approach.

Brick and cobble biomass were compared at each sampling time using one-way ANOVA,

followed by Tukey’s pairwise comparisons, for each site. Biomass on cobbles used in the

17 measurement of community metabolism was compared to cobble collected for accrual patterns using one-way ANOVA, followed by Tukey’s pairwise comparisons, for each site. Effects were considered significant at p < 0.05.

Results

Physical and chemical conditions

The study began immediately after the last rain event in autumn (23 October 2009),

with the final collections occurring during the onset of the spring run-off from mountain

snowpack (20 February 2010). Discharge was at an annual low (2.2 -7.8 m 3 s-1) during the study with a median flow ~ 5 m 3 s-1 (Figure 2A). Solar irradiance was at the annual low during the same period (median = 2358 W m -2) (Figure 2B). Mean stream temperature increased slightly downstream (2.1 to 5.4 °C) (Table 2), however site and bloom phase were not a significant source of variation in temperature (Table 3).

Temperatures declined gradually during November to freezing or near-freezing temperatures by early December (Figure 3). Near-freezing conditions (≤ 1°C) were sustained for 2 wk at 56 km and 80 km, 3 wk at 97 km, and 1 wk at 125 km. The only site to actually freeze-over completely was 97 km. Orthophosphate generally increased

+ downstream while NH 4 and NO x were usually low (<1 µM) at 56 km, 80 km, and 97 km

+ (Table 2). Greater than 3-fold increases in OP, NH4 and NO x characterized the 125 km

site as the most nutrient enriched reach. Dissolved nutrient balance, DIN:OP, in the

water column was typically less than 16, suggesting nitrogen limiting conditions

throughout all reaches during the study.

Periphyton biomass, community composition, and nutrient balance

Biomass on bricks increased from November to January at 80 km, 97 km, and 125 km, attaining maximum standing stocks (15 to 60 mean µg chl a cm -2) in 70 to 90 d (Figure

4B-D). Two-way ANOVA of brick biomass revealed significant differences between

sites and bloom phases as well as a significant interaction between sites and bloom phase

(Table 3). Brick biomass showed evidence of significant differences within each site at

80 km, 97 km and 125 km between bloom phases (Table 4). In contrast, brick biomass at

56 km exhibited no significant change between bloom phases and attained lower maximum standing stocks (1.4 µg chl a cm -2) (Figure 4A). System-wide increases in discharge combined with the senescing understory within thick diatom felts, induced sloughing at all downstream reaches which reduced biomass to less than 6 µg chl a cm -2 near the middle of February. Standing stocks on bricks at 80 km and 125 km were reduced to significantly lower biomass during the late bloom compared to densities during the early bloom at these sites.

Between site comparisons revealed that brick biomass was significantly higher at 80 km and 125 km compared to 56 km and 97 km during the early bloom and middle bloom

(Table 4). Brick biomass was significantly higher, however, during the middle bloom at

125 km compared to 80 km and at 97 km compared to 56 km. Late bloom comparisons showed that standing stocks on bricks at 125 km were significantly higher than 80 km.

Brick biomass accrual generally followed the same spatial and temporal patterns as epilithic biomass (Figure 4). All sites during the early bloom had significantly higher

epilithic biomass compared to bricks for 1 to 5 wk (Figure 4). In contrast, brick biomass

19 during the middle bloom was often significantly higher than epilithic biomass at 80 km,

97 km, and 125 km. Epilithic and brick biomass was comparable at all sites by the late bloom.

Algal composition stabilized relatively quickly (14-28 d) on the bricks and was

consistent throughout the bloom for the majority of common genera. In general, relative

abundances at all sites were continuously dominated by Nitzschi a spp. (>20% RA), especially at 97 km and 125 km where relative abundances peaked at 35 -40% (Figure 5I-

L). Diatoma monoliformis was consistently low ( ~ 5% RA) during the initial 30 days of

accrual at the 56 km, 80 km and 97 km sites (Figure 5A -D). D. monoliformis gradually

increased to a plateau at 56 km and 80 km (10% RA) and increased to substantial

proportions (>25% RA) at 97 km after the ice cover receded in late December. The stalk-

forming diatom Gomphoneis minuta had consistently low abundances (<5% RA) at most

sites except at 125 km where it sustained ~ 5% RA for 50 days (Figure 5 E -H).

The relative biovolume (RB) of algal assemblages stabilized and remained low (<5%)

for most of the commonly occurring genera. D. monoliformis RB paralleled RA magnitudes and accrual patterns at all sites (Figure 5A-D). G. minuta contributed notable proportions (>10%) to biovolume across all sites, particularly at 80 km and 125 km

(Figure 5F,H). G. minuta increased to a climax in biovolume contributions after 25 d at

56 km (15%) and 97 km (35%) then declined (Figure 5E,G).

The nutrient balance of periphyton during the winter bloom was restricted to a relatively narrow range (Figure 6). Periphyton POC:PN varied between 7.6 to 17, but generally stabilized between 8 to 10 in all reaches for assemblages growing on both bricks and cobble (Figure 6A -D). Periphyton POC:PP ranged between 76 to 210 (Figure

6E -H). Brick assemblages had lower POC:PP for the first 30 d at 80 km and 125 km

(Figure 6F,H). In contrast, brick assemblages at 56 km and 97 km sustained slightly

lower POC:PP (~ 90 to 100) relative to cobble assemblages (~ 130 to 190) throughout

the winter bloom (Figure 6E,G). PN:PP in brick assemblages maintained slightly lower

ratios (~ 5 to 15) compared to cobble assemblages ( ~ 15 to 20) (Figure 6I -L). Similar to

POC:PP, brick PN:PP approached cobble PN:PP within a month at 80 km and 125 km,

while brick assemblages remained lower than cobble at 56 and 97 km.

Community metabolism

Metabolic rates were constrained to a relatively narrow range throughout the bloom for

2 -1 2 -1 GCP (0.25 -1.1 g O 2 m day ), CR (0.15 -0.49 g O 2 m day ), and NCM (0.12-0.69 g O 2 m2 day -1) (Figure 7). Site and bloom phase was a significant source of variation in GCP

and NDM, in comparison to only site in CR (Table 3). The interaction of site and bloom

phase was significant in GCP (p = 0.001) and NCM (p = 0.002), and marginally

significant in CR (p = 0.056). GCP was not significantly different during the early bloom

phase at 80 km, 97 km, and 125 km (Tukey’s HSD, p> 0.05) in comparison to

significantly lower rates upstream at 56 km (Tukey’s HSD, p < 0.05) (Figure 7A). GCP

was significantly higher at 125 km compared 56 km and 97 km during the middle bloom.

During the late bloom 97 km was significantly higher than 56 km and 80 km (Tukey’s

HSD, p < 0.05). CR between sites were not significantly different during any phase of

the bloom based on Tukey’s HSD pairwise comparisons (Figure 7B), in contrast to the

significance indicated by the analysis of variance. NCM was significantly higher at 80

km and 125 km compared to 56 km during the early bloom (Figure 7C). During the

21 middle bloom NCM at 125 km was significantly higher than all upstream sites, while by the late bloom both 97 km and 125 km exhibited significantly higher NCM compared to

56 km and 80 km.

Biomass on cobble collected for estimating community metabolism was typically not significantly different (one-way ANOVA) from the biomass on cobble collected for the accrual time-series (Figure 4). Early bloom estimates of community metabolism at 80 km and 125 km, however, did have significantly higher biomass. Middle bloom estimates of community metabolism at 125 km also had significantly higher biomass compared to cobble collected for accrual.

Accrual rates and specific growth rates

Accrual rates for brick and epilithic biomass were highest at 125 km (0.91 -0.92 µg chl a cm -2 day -1) followed by 80 km (0.20 -0.37 µg chl a cm -2 day -1), 97 km (0.09 -0.22 µg chl

a cm -2 day -1), and 56 km (brick only, 0.02 µg chl a cm -2 day -1) (Figure 8A). Epilithic accrual at 56 km could not be determined due to a poor least-squares fit of accrual time- series.

Specific growth rates based on the chamber metabolic approach increased downstream and usually were comparable within each reach throughout the bloom (Figure 8B). Much slower µ occurred during the middle phase when biomass was highest. Growth rates increased substantially after sloughing during the late phase and increased downstream.

The 56 km reach maintained relatively low but consistent µ (~ 0.04 divisions day -1) throughout the study. Brick PE experiments yielded higher µ estimates than the epilithic chambers (Figure 8C). Overall, the fastest µ occurred at 125 km (0.09 to 0.15 divisions

22 day -1), though comparable rates were documented at 97 km (0.08 -0.12 divisions day -1).

Slightly lower and narrower range of µ was documented at 56 km (0.02 -0.04 divisions

day -1) and 80 km (0.03 -0.04 divisions day -1). Growth rates based on k using various

parameters (brick chla, brick biovolume, epilithic chla) showed substantial variability

within each site (Figure 8C) and often exceeded the more direct measures of growth rate.

Ecosystem metabolism

The average daily NEM was positive during all seasons except summer (Figure 9)

2 when ER exceeded GPP. Spring and winter had comparable daily averages ( ~ 6 g O 2 m day -1) and were higher than fall and summer. Summer consistently showed negative

NEM (GPP

122 km during the 2008-009 water-year was 41% in spring, 37% in winter, and 22% in fall.

Discussion

Periphyton biomass and nutrient balance

The current study provides data and new insights into a river’s capacity for supporting extremely high algal biomass during winter. Appreciable amounts of periphyton biomass were documented in the Truckee River compared with many temperate streams studied during winter (Table 5). Uehlinger (1991) reported comparable winter biomass in a prealpine river at a location receiving inputs of nutrients from agricultural and sewage treatment facilities. Discharge was 2-times higher in that system, but an extended period

23 of stable flows without incidences of bed-moving floods allowed for accumulation of high standing stocks of winter periphyton, which was also observed in the current study of the Truckee River.

Standing stocks did differ on brick and cobble within each site at certain times. Lower

biomass on bricks during the early bloom are expected due to the artificial surface being

recently deployed, however comparable levels were eventually attained at all sites.

Discrepancies in the magnitude of maximum biomass on cobble (2-fold lower than

bricks) and the timing (e.g. one to two weeks earlier at 80 km and 125 km) can be

attributed to several aspects of the study design. Cobble were collected randomly from

multiple habitats upstream from brick clusters, thus it included variable velocities that

readily influence standing stocks (Biggs 1996). In contrast, bricks were clustered in moderate velocities (0.21 to 0.49 m sec-1) in order to reduce the potential influence of current velocities on the observed patterns when comparing sites. A monotonic increase in biomass (chla) as a function of increased near-bed velocities has been shown for mucilaginous diatom assemblages (Biggs et al. 1998), thus the cobble may have been collected mostly from habitats with slower near-bed velocities compared to brick clusters.

Slower near-bed velocities would have restricted the mass transfer of nutrients though the boundary layer of the dense, coherent growth form of the winter diatom felts. Restricting the transfer of nutrients into the diatom felts constrains the maximum biomass attainable.

Therefore, the standing stocks of biomass likely differed on brick and cobble within each site as the bloom progressed due to these near-bed velocity differences influencing the biomass accumulation.

The maximum chlorophyll densities attained in 3 of 4 reaches in the Truckee exceeded that proposed by Welch et al. (1988) to be an undesirable or “nuisance” condition for periphyton biomass (>10 µg chl a cm -2). Cold temperatures maintain high levels of dissolved oxygen (>8 mg L -1) throughout the bloom, however, so impairment of aquatic life use due to low oxygen appears unlikely. Degradation of the river’s aesthetic value also may not be a concern given the anticipated reduction in recreational uses in winter compared to warmer seasons. Designating the winter bloom as a “nuisance” may therefore not be warranted based on these typical criteria, however the magnitude of biomass accumulated undoubtedly impacts the system. Understanding the factors controlling the winter bloom is of particular concern when considering system-wide energetics and material cycling.

Nutrient enrichment is typically considered when investigating algal blooms in rivers and streams (Borchardt 1996). Water column DIN:OP indicated that all reaches were potentially nitrogen limited (Redfield 1958). Nutrient availability was quite low for both

DIN and OP in all reaches except 125 km. Observed nutrient concentrations at 56 km, 80 km, and 97 km were also below the expected saturation levels that maximize growth rates for OP (0.52 µM) and DIN (6 µM) (Rier and Stevenson 2006). In comparison, the nutrient content of periphyton generally indicated balanced growth. POC:PN was consistently near optimum (5 to 10, Hillebrand and Sommer 1999) and POC:PP was generally near optimum (90 to 185, Hillebrand and Sommer 1999) in all reaches throughout the bloom. PN:PP was generally near optimum (13 to 22) for cobble assemblages in all reaches. However, periphyton PN:PP growing on bricks at 56 km, 97 km, and 125 km indicated potential nitrogen limitation (less than 13, Hillebrand and

Sommer 1999). Altogether, winter periphyton growth at 56 km may have been limited by nitrogen while growth of thicker mats at 80 km and 97 km was more likely to be colimited by both nitrogen and phosphorus.

Accrual rates and specific growth rates

Accrual rates and specific growth rates displayed variable responses to increases in

downstream nutrient availability. The highest biomass accrual rate, 0.92 µg chl a cm -2 day -1, coincided with an increase in the supply of dissolved inorganic nutrients at 125 km from non-point and point (wastewater effluent) sources. This accrual rate is comparable to rates reported during summer in an agricultural/suburban influenced spring-fed stream

(Spring Creek, Pennsylvania, Godwin and Carrick 2008) that has ~ 24-fold more nitrogen as nitrate and ~ 4 -fold less phosphorus as phosphate. Despite much lower concentrations

+ of dissolved nutrients at 80 km compared to 125 km (9 -fold less OP, 3 -fold less NH 4 and

3-fold less NO x) the accrual rate was similar. In comparison, specific growth rates

generally followed an increasing trend downstream. Growth rates became comparably

low across all the downstream sites when biomass densities attained eutrophic levels (>10

µg chla cm -2) during the middle phase of the bloom. In contrast to downstream, biomass density remained consistently low at 56 km such that growth rates were stable throughout the winter study.

A comparable study evaluating growth rates of winter periphyton along a downstream gradient in nutrients was conducted by Bothwell (1985) in the Thompson River system

(Table 5). Despite temperatures near 0ºC, growth rates were close to maximum for these relatively low biomass assemblages (1 -3 µg chl a cm -2) given particularly low levels of

26 phosphorus (~ 0.09 µM P). Specific growth rates in the Thompson River generally increased downstream as phosphorus availability increased, ranging from 0.05 to 0.22 divisions d -1 based on accrual and 0.04 to 0.32 divisions d -1 based on PE experiments. In comparison, winter periphyton in the Truckee showed a slower and narrower range for growth rate estimates, 0.02 to 0.15 divisions d -1. Truckee DIN concentrations were

generally ~ 5 -fold to 7 -fold lower than the Thompson River system, thus nitrogen may

have constrained growth rates. The fastest growth rates occurred at 125 km where the

average DIN concentration was 6.2 µM, which is slightly above the value expected for

growth rate saturation (Rier and Stevenson 2006). Similar to the conclusion of Bothwell

(1985) for the Lower Thompson, winter growth at 125 km in the Truckee was likely near

the maximum rate that can be attained given the constraints of low temperature and

reduced irradiances.

Community metabolism

Metabolic rates and energy balance in epilithic communities were influenced by consistently cold temperatures (<10°C). Winter GCP in the Truckee was generally low

-2 -1 -2 -1 (<1.0 g O 2 m day ) compared to previous estimates in fall (2.2 -4.6 g O 2 m day ) and

-2 -1 summer (3 -9 g O 2 m day ) (Uehlinger and Brock 2005). These seasonal differences

can largely be explained by temperature differences, as colder temperatures should

reduce metabolic rates. Respiration was reduced to a greater degree (relative to

photosynthesis) such that positive NCM was evident at all sites throughout the winter

bloom. A consistent net gain in carbon/energy throughout the winter accumulated as

periphyton biomass at downstream sites.

Standing stocks remained consistently low despite positive NCM at 56 km. Biomass removal by the activity of overwintering macroinvertebrates (e.g. consumption, dislodgement) may decrease periphyton biomass. Benthic macroinvertebrates were not enumerated during the current study, however previous longitudinal collections in the

Truckee by various agencies indicates a greater relative abundance of “scrapers” (i.e. grazers) at upstream sites (10 to 15% more) (TetraTech 2004). Higher abundances of grazers at 56 km could effectively decrease periphyton biomass via dislodgement even if ingestion rates were depressed due to cold temperatures (as implied by low respiration rates). Grazing pressure from small-bodied invertebrates can effectively control high magnitude algal blooms during summer in eutrophic rivers (Sturt et al. 2011), however top -down control during winter blooms remains to be shown.

Winter’s contribution to annual net production

Winter blooms of the magnitude reported in this study equate to a substantial load of organic matter to the river during a temporal period that is typically at an annual minimum for most temperate systems (Tank et al. 2010). Analysis of seasonal contributions to annual net ecosystem metabolism in the Truckee River revealed that winter months (November to January) can contribute ~ 37% of the annual net gain in energy. Winter production can largely be stored as attached periphyton throughout the extended period of stable flows. Catastrophic sloughing of biomass was likely due to senescence of understory cells combined with elevated discharge. Exported winter biomass represents a substantial loading of material to downstream reaches within a relatively short time-frame.

Determining the fate and consequences of winter periphyton biomass should be of particular concern for effective water quality management because of potential impacts to biogeochemical cycles. Accumulated biomass only temporarily retains essential macronutrients (carbon, nitrogen, and phosphorus) in particulate forms. Sloughed biomass feeds microbial processes (which increase ecosystem respiration) further exacerbating nightly minima in dissolved oxygen during warmer seasons.

Decomposition and mineralization of particulate nitrogen from sloughed biomass may provide limiting nutrients during subsequent blooms in spring and summer, particularly in the nitrogen limited reaches downstream (Green and Fritsen 2006). Alternatively, organic matter from winter blooms could provide additional energy (carbon) and nitrate for denitrification processes in the streambed (McMillan et al. 2010), thereby providing a beneficial ecosystem service via permanently removing nitrogen from the system.

Altogether, winter blooms could have extended influence on system energetics and nutrient cycling, well beyond the winter season.

Acknowledgements

We thank and acknowledge the supporting laboratory staff and graduate students in the

Desert Research Institute’s Systems Microbial Ecology Lab (Jeramie Memmott, Eric

Wirthlin, Diane Momberg); and the prior works and collaborations with Alan McKay and

Jim Brock that helped shape this study. This study was funded by EPA grant 83277801-1 awarded to A. McKay. We also commend the continual monitoring efforts by the

Truckee Meadows Water Reclamation Facility (Cities of Reno and Sparks, Nevada)

29 which provided the dissolved oxygen and temperature data needed for estimates of ecosystem metabolism.

References

Alekseev, V.R., O. Ravera, and B. de Stasio. 2007. Introduction to Diapause. Pages 3-10 in V.R. Alekseev, B. Stasio, and J. Gilbert (editors). Diapause in aquatic invertebrates theory and human use. Springer Netherlands, Netherlands. Biggs, B.J.F. 1996. Patterns in benthic algae of streams. Pages 31-56 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal ecology in freshwater benthic ecosystems. Academic Press, New York, New York. Biggs, B.J.F., D.G. Goring, and V.I. Nikora. 1998. Subsidy and stress responses of stream periphyton to gradients in water velocity as a function of community growth form. Journal of Phycology 34:598-607. Borchardt, M.A. 1996. Nutrients. Pages 183-227 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal Ecology: Freshwater Benthic Ecosystems. Academic Press, New York, New York. Bothwell, M.L. 1985. Phosphorus limitation of lotic periphyton growth rates: An intersite comparison using continuous-flow troughs (Thompson River system, British Columbia). Limnology and Oceanography 30:527-542. Bothwell, M.L. 1988. Growth rate responses of lotic periphytic diatoms to experimental phosphorus enrichment: the influence of temperature and light. Canadian Journal of Fisheries and Aquatic Sciences 45:261-270. Bott, T.L. 2006. Primary productivity and community respiration. Pages 263-290 in F.R. Hauer and G.A. Lamberti (editors). Methods in Stream Ecology, 2 nd edition. Elsevier, New York. Davis, C.J. 2007. Periphyton dynamics and environmental associations: Truckee River, CA-NV, USA. (Master’s thesis) University Nevada Reno. ProQuest/UMI, Ann -Arbor , Michigan. Publication No. 14477636. Delong, M. D., and M.A. Brusven. 1992. Patterns of periphyton chlorophyll a in an agricultural nonpoint source impacted stream. Water Resources Bulletin 28: 731 -741. DeNichola, D.M. 1996. Periphyton responses to temperature at different ecological levels. Pages 149-181 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal ecology in freshwater benthic ecosystems. Academic Press, New York, New York. Diamond, D. 2001. Determination of total phosphorus by flow injection analysis (acid persulfate digestion method). Quickchem® Method 10-115-01-1-E:16. Lachat Instruments. Loveland, Colorado. Godwin, C.M., and H.J Carrick. 2008. Spatiotemporal variation of periphyton biomass and accumulation in a temperate spring-fed stream. Aquatic Ecology 42:583-595.

Green, M.B., and C.H. Fritsen. 2006. Spatial variation of nutrient balance in the Truckee River, California -Nevada. Journal of the American Water Resources Association 42:659-674. Gustina, G.W., and J.P. Hoffmann. 2000. Periphyton dynamics in a subalpine mountain stream during winter. Arctic, Antarctic, and Alpine Research 32:127-124. Hill, W.R. 1996. Effects of light. Pages 121 -148 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal ecology in freshwater benthic ecosystems. Academic Press, New York, New York. Hillebrand, H., C.D. Durselen, D. Kirschtel, U. Polligher, and T. Zohary. 1999. Biovolume calculation for pelagic and benthic microalgae. Journal of Phycology 35:403-424. Hillebrand, H., and U. Sommer. 1999. The nutrient stoichiometry of benthic microalgal growth: Redfield proportions are optimal. Limnology and Oceanography 44:440-446. Hornberger, G.M., and M.G. Kelly. 1975. Atmospheric reaeration in a river using productivity analysis. Journal of Environmental Engineering 101:729-739. Huusko, A., L. Greenberg, M. Stickler, T. Linnansaari, M. Nykänen, T. Vehanen, P. Louhi, and K. Alfredsen. 2007. Life in the ice lane: the winter ecology of stream salmonids. River Research and Applications 23: 469–491. Jassby, A.T., and T. Platt. 1976. Mathematical formulation of the relationship between photosynthesis and light for phytoplankton. Limnology and Oceanography 21:540- 547. Liao, N. 2002. Determination of orthophosphate in waters by flow injection analysis colorimetry. Quickchem® Method 10-115-01-1-M:17. Lachat Instruments. Loveland, Colorado. McMillan, S.K., M.F. Piehler, S.P. Thompson, and H.W. Paerl. 2010. Denitrification of nitrogen released from senescing algal biomass in coastal agricultural headwater streams. Journal of Environmental Quality 39:274-281. NDEP (Nevada Division of Environmental Protection). 2009. Truckee River Basin. Available at http://ndep.nv.gov/BWQP/truckeemap.html. Accessed in December 2009. Nowlin, J.O. 1987. Modeling nutrient and dissolved-oxygen transport in the Truckee River and Truckee Canal downstream from Reno, Nevada: U.S. Geological Survey Open-File Report 87-4037. Odum, H.T. 1956. Primary production in flowing waters. Limnology and Oceanography 1:102-117. Ostrofsky, M.L., D.E. Weigel, C.K. Hasselback, and P.A. Karle. 1998. The significance of extracellular production and winter photosynthesis to estimates of primary production in a woodland stream community. Hydrobiologia 382:87-96. Parsons, T.R., Y. Maita and C.M. Lalli. 1984. Determination of chlorophylls and total carotenoids: Spectrophotometric method. Pages 101-112 in T.R. Parsons, Y. Maita and C.M. Lalli (editors). A manual of chemical and biological methods for seawater analysis. Pergamon Press, Oxford. Pritzlaff, P. 2000. Determination of nitrate/nitrite in surface and wastewaters by flow injection analysis. Quickchem® Method 10-107-04-1-C:15. Lachat Instruments. Loveland, Colorado.

Prokopy, W.R. 2003. Determination of ammonia by flow injection analysis. Quickchem® Method 10-107-06-2-C:10. Lachat Instruments. Loveland, Colorado. Prowse, T.D. 2005. River-ice hydrology. In M.G. Anderson (editor) Encyclopedia of Hydrological Sciences, Volume 4. John Wiley and Sons, West Sussex, United Kingdom. Redfield, A.C. 1958. The biological control of chemical factors in the environment. American Scientist 46:205-221. Rier, S.T., and R.J. Stevenson. 2006. Response of periphytic algae to gradients in nitrogen and phosphorus in streamside mesocosms. Hydrobiologia 561:131-147. Rounick, J. S., and S.V. Gregory. 1981. Temporal changes in periphyton standing crop during an unusually dry winter in the streams of the Western Cascades, Oregon. Hydrobiology 83:197-205. Strickland, J.D.H, and T.R. Parsons. 1972. A practical handbook of seawater analysis, 2 nd edition, Bulletin 167. Fisheries Research Board of Canada, Ottawa. Sturt, M.M., M.A.K. Jansen, and S.S.C. Harrison. 2011. Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river. Freshwater Biolog 56:2580-2593. Sumner, W.T. and S.G. Fisher. 1979. Periphyton production in Fort River, Massachusetts. Freshwater Biology 9:205-212. Tank, J.L., E.J. Rosi-Marchall, N.A. Griffiths, S.A. Entrekin, and M.L. Stephen. 2010. A review of allochthonous organic matter dynamics and metabolism in streams. Journal of the North American Benthological Society 29:118-146. Tetra Tech. 2004. Biological condition index development for the Truckee River: benthic macroinvertebrate assemblage. Prepared for Nevada Division of Environmental Protection by Tetra Tech, Inc., Owings Mills, Maryland. (Available from: Nevada Division of Environmental Protection, Bureau of Water Quality Planning, 333 W. Nye Lane, Carson City, Nevada 89706 USA.) Uehlinger, U. 1991. Spatial and temporal variability of the periphyton biomass in a prealpine river (Necker, Switzerland). Archiv fur Hydrobiologie 123: 219-237. Uehlinger, U., and J.T. Brock. 2005. Periphyton metabolism along a nutrient gradient in a desert river (Truckee River, Nevada, USA). Aquatic Sciences 67:507-516. Welch, E.B., J.M. Jacoby, R.R. Horner, and M.R. Seeley. 1988. Nuisance biomass levels of periphytic algae in streams. Hydrobiologia 157:161-168. Welschmeyer, N. 1994. Fluorometric analysis of chlorophyll a in the presence of chlorphyll b and pheopigments. Limnology and Oceanography 38:1985-1992. Wetzel, R.G., and G.E. Likens. 2000. Limnological Analyses, 3 rd edition. Springer, New York. Zar, J.H. 1999. Biostatistical Analysis, 4 th edition. Prentice Hall, New Jersey.

Table 1. Description of sampling dates and research design for the 2009-10 winter bloom study.

Site Biomass Accrual Community Metabolism PE curve Substrate Days between Bloom Date Substrate N Date (2 or 3 per Treatments Replicates Date sampling Phase chamber) 31-Oct-2009 to 56 km Brick 11,8,16,9,42,36 5 Early 19-Nov-2009 Cobble Light, Darks 3 4-Dec-2009 20-Feb-2010

Cobble 3 to 5 Middle 16-Jan-2010

Late 20-Feb-2010

6-Nov-2009 to 80 km Brick 7,9,7,7,9,5,16,21,24 5 Early 22-Nov-2009 Cobble Light, Darks 3 29-Nov-2009 12-Feb-2010

Cobble 3 to 5 Middle 29-Dec-2009

Late 12-Feb-2010

2-Nov-2009 to 97 km Brick 6,8,7,7,21,14,25,12 5 Early 23-Nov-2009 Cobble Light, Darks 3 30-Nov-2009 10-Feb-2010

Cobble 3 to 5 Middle 4-Jan-2010

Late 10-Feb-2010

1-Nov-2009 to 125 km Brick 9,6,7,9,5,8,8,20,27 5 Early 17-Nov-2009 Cobble Light, Darks 3 1-Dec-2009 16-Feb-2010

Cobble 3 to 5 Middle 31-Dec-2009

Late 16-Feb-2010

Table 2. Water quality and habitat variables (mean and % coefficient of variation) at each site during the winter study (November 2009 to February 2010). Site (distance from Lake Tahoe), OP (orthophosphate), NH4+ (ammonium), NOx (nitrate+nitrite), DIN (dissolved inorganic nitrogen).

Variable 56 km 80 km 97 km 125 km

OP (µM) 0.19 (21) 0.17 (53) 0.46 (160) 1.5 (65)

+ NH 4 (µM) 0.46 (35) 0.65 (24) 0.70 (30) 2.2 (66)

NO X, (µM) 0.68 (127) 1.3 (55) 0.86 (76) 4.0 (100)

DIN:OP 6.2 (83) 12 (42) 11 (75) 6.2 (99)

Temperature (°C) 2.1 (81) 2.8 (84) 3.5 (67) 5.4 (43)

Velocity (m s -1) 0.21 (34) 0.32 (22) 0.49 (17) 0.28 (17)

Table 3. Two-way ANOVA results for periphyton metabolism, brick biomass, and temperatures (log-transformed data). Analyses applied sites (56 km, 80 km, 97 km, 125 km) and bloom phase (early, middle, late) as fixed factors. Bloom phases categorized as early bloom (October 31 st to December 15 th ), middle bloom (December 16 th to January 31 st ) or late bloom (February 1 st to February 20 th ).

Source df GCP NCM CR Brick Chla Temperature

F p F p F p F p F p Site 3 28.0 0.000 33.1 0.000 8.87 0.000 34.7 0.000 2.4 0.119 Bloom Phase 2 5.03 0.015 5.40 0.012 2.30 0.122 73.2 0.000 1.24 0.321 Site x Bloom Phase 6 5.21 0.001 4.91 0.002 2.43 0.056 14.8 0.000 0.25 0.955

Table 4. Mean differences from Tukey’s pairwise comparisons for brick biomass (µg chl a cm -2) between sites and bloom phases. Bold indicate significant differences (p < 0.05).

56-early 56-middle 56-late 80-early 80-middle 80-late 97-early 97-middle 125-early 125-middle

80-early 4.4 97-early 3.0 -4.0 125-early 4.5 2.7 4.0

56-middle 3.4 80-middle 6.1 4.7 97-middle 4.6 -3.6 5.2 125-middle 9.2 4.1 5.5 7.0

56-late 3.3 2.8 80-late -3.4 -4.5 -7.8 97-late na na na na 125-late 4.4 5.4 -3.2 -5.9

Table 5. Comparison of relevant winter studies of stream periphyton conducted at temperate latitudes.

Maximum Winter Growth Rates Biomass

Study Winter Warm Specific Growth Net Study Factors Location Watershed Area Latitude Study Months Winter Net Accrual Reference Primary Discharge season Rate Metabolism of Interest Focus

2 3 -1 -2 -2 -1 -2 -1 (km ) (m s ) (µg chla cm ) (µg chla cm day ) (divisions day-1) (g O 2 m d )

Stevenson Gustina and January to Light and N/P Brooke Creek, 5.2 44°30’N 0.0005-0.0025 * 125 * * * Hoffmann Biomass April limitation Vermont USA (2000)

Necker River, February to Uehlinger Hydrologic 126 47°21’N 10-20 90 80 * * * Biomass Switzerland March (1991) factors

Rounick and Oregon streams October to * 45° ’N * * 7 * * * Gregory Biomass Light (5), USA March (1981)

Fort River, July to Sumner and Massachusetts, * 42°19’N * 13.6 4.5 * * -1.4 Metabolism Seasonal December Fisher (1979) USA

Delong and Lapwai Creek, May to 665 46°27’N 0.02-1.6 38 30 * * * Brusven Biomass Seasonal Idaho, USA February (1992)

Sandy Run, January to Ostrofsky et Primary Pennsylvania, 9.3 41°36’N * 50 18 * * * Seasonal September al. (1998) production USA 36

Maximum Winter Growth Rates Biomass

Study Winter Warm Specific Growth Net Study Factors Location Watershed Area Latitude Study Months Winter Net Accrual Reference Primary Discharge season Rate Metabolism of Interest Focus

2 3 -1 -2 -2 -1 -2 -1 (km ) (m s ) (µg chla cm ) (µg chla cm day ) (divisions day-1) (g O 2 m d )

North, South , Lower 430 (North), February to Bothwell Phosphorus Thompson 56,000 50°41’N * 3 * 0.05-0.32 * Growth rate 280 (South) April (1985) gradient Rivers, British Columbia, CA

South Thompson, January to Bothwell 56,000 50°41’N 280 (South) * * * 0.08-0.26 * Growth rate Phosphorus British November (1988) Columbia, CA

Truckee River, Growth November to Current California- 7,900 39°51’N 4.7 * 60 0.02-0.10 0.02-0.15 0.12-0.69 Rate, High Biomass February Study Nevada, USA Metabolism 37

Figure 2. Average daily discharge (USGS gauge 10348000) in the Truckee River 80 km downstream from Lake Tahoe, CA (A) and daily solar irradiance from the Western Regional Climate Center station located at the Desert Research Institute, Reno, NV (B). Shaded area indicates the temporal window of study.

12 56 km A 9

0 12 80 km B

3 C) ° 0

12 97 km C 9 Temperature(

0 12 125 km D

Figure 3. Hourly temperature logged at each site (A-D) in the Truckee River in the autumn-winter 2009-2010.

Figure 4. Mean (± 1 SE) time-series of biomass (chla) accrual on bricks and cobble (Epil), biomass present during chamber (Chamber) and photosynthesis-irradiance (PE) experiments at each site. Dashed lines indicate transitions between early, middle, and late bloom phases. Asterisks (*) along x-axis indicate sampling points when biomass was significantly different on bricks compared to cobble during winter accrual.

Figure 5. Mean (± 1 SE) relative abundance (RA) and relative biovolume (RB) of dominat diatom taxa in brick assemblages. Diatoma (A-D), Gomphoneis (E-H), and Nitzschia (I-L). 42

25 56 km 250 56 km Brick Epil 25 56 km A E I 20 200 20 15 150 15 10 100 10 5 50 5 0 0 0 25 80 km B 250 80 km F 25 80 km J 20 200 20 15 150 15 10 100 10 5 50 5 0 0 0

25 97 km 97 km PN:PP

POC:PN 97 km C POC:PP 250 G 25 K 20 200 20 15 150 15 10 100 10 5 50 5 0 0 0 25 125 km D 250 125 km H 25 125 km L 20 200 20 15 150 15 10 100 10 5 50 5 0 0 0

Figure 6. Mean (± 1 SE) nutrient content ratios of periphyton on bricks and cobble (Epil). POC:PN (A-D), POC:PP (E-H), and PN:PP (I-L). 43

Figure 7. Mean (± 1 SE) epilithic metabolism (gross primary production, GCP, community respiration, CR, and net community metabolism, NCM) during three phases of bloom development (early, middle, late) at each site (A-D). Bars with the same letter are not significantly different.

Figure 8. Accrual rates on bricks and cobble (epilithic) (A) and specific growth rates ( µ) estimated from chambers during the bloom (B) and early bloom specific growth rates estimated from brick PE experiments, epilithic chambers, brick biovolume accrual, brick chla accrual and epilithic chla accrual (C). Mean ± 95% CI

7.5 122 km )

-1 5.0 day

2 2.5 m 2 0.0

-2.5 NEM (g O (g NEM

-5.0

-7.5 Fall Winter Spring Summer

Figure 9. Mean (± 1 SE) net ecosystem metabolism (NEM) for different seasons in 2008- 2009 water year at 122 km, Truckee River, Nevada.

Chapter 3

Investigating the potential influence of hyporheic exchange on periphyton structure and function in a montane-desert river

Clinton J. Davis

Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 USA [email protected]

Abstract

The potential influence of hyporheic exchange on periphyton assemblages was investigated in a montane-desert river in the Great Basin (Truckee River, CA-NV, USA).

Contrasting vertical exchange zones (upwelling and downwelling) in two riffle-run reaches (montane and desert) were identified after mapping vertical hydraulic gradients using shallow wells. Growth-related rates (accrual, primary production) and composition

(taxonomic, nutrient content) of periphyton were evaluated in contrasting exchange zones in spring and summer. Both reaches showed that periphyton structure and function were generally equivalent regardless of exchange direction. Slow flux rates likely limited the hyporheic effects on periphyton, despite 10-fold higher dissolved nitrogen in the streambed. Patchiness in upwelling exchange (<1 m) may limit the detection of periphyton response to smaller spatial scales (i.e. cobble) in the Truckee River.

Introduction

Interaction between stream surface-water and saturated sediments and pore-water

directly beneath- broadly defined as the hyporheic zone- creates a dynamic subsystem of

physical and chemical processes (Grimm et al., 2006). Hyporheic zones can be “hot-

spots” of metabolic activity that influence temporal and spatial patterns of nutrient

cycling, particularly nitrogen (McClain et al., 2003). Benthic communities on the

streambed surface are expected to respond to the upwelling water from the hyporheic

zone that has been enriched with dissolved nutrients released or transformed via

biogeochemical transformations (Boulton, 1993).

Direct influence of hyporheic exchange on periphyton, however, has been demonstrated in relatively few lotic systems (e.g. Sycamore Creek, Middle Fork Flathead River).

Periphyton assemblages responded to contrasting zones of hyporheic exchange

(discharge, recharge) at the benthic interface by changes in biomass (Pepin and Hauer,

2002), community composition (Henry and Fisher, 2003) and primary productivity

(Valett et al., 1994). Fluxes of nitrogen-rich pore-water in Sycamore Creek increased accumulation rates by an order of magnitude resulting in higher standing stocks and faster recovery post-flood (Valett et al., 1994). Significantly different standing stocks and different assemblages in contrasting exchange zones were only recently reported for a larger scale system (discharge = 50 to 160 m 3 sec -1) in the Middle Fork Flathead River

(Wyatt et al., 2008). Thus, the potential effects of exchange on periphyton have not been demonstrated in a mid-sized, alluvial river.

The Truckee River is a mid-sized river that spans both montane and semi-arid conditions. Studies of periphyton ecology in the Truckee River have focused on spatial and temporal dynamics of periphyton standing stocks, community composition (Davis,

2007) and periphyton metabolism (Uehlinger and Brock, 2005). High standing stocks of periphyton biomass are spatially variable and are associated with relatively low nutrient concentrations, especially dissolved nitrogen. The potential role of smaller-scale processes, such as hyporheic exchange, may explain reach-scale spatial patterns.

Furthermore, a longitudinal gradient in the nutrient balance (nitrogen:phosphorus) (Green and Fritsen, 2006) offers a chance to determine the potential effects of hyporheic exchange on periphyton assemblage structure and function in reaches of different in- stream nutrient concentrations and balance.

The current work focused on periphyton accrual rates, taxonomic composition, nutrient content and primary productivity in zones of contrasting vertical exchange (upwelling vs. downwelling) within a riffle-run sequence in montane and desert reaches of the Truckee

River. Specific hypotheses focused on the effect of nutrient flux in upwelling compared to downwelling zones such that 1) upwelling zones have higher growth rates and biomass, 2) down-welling zones have higher proportions of N 2-fixing algal taxa in

comparison to upwelling zones, 3) upwelling zones support periphyton with balanced

nutrient content, 4) upwelling zones have higher rates of primary productivity, and 5)

exchange zones in the montane reach have the largest differences in periphyton structure

and function due to depleted nitrogen and phosphorus in the water column.

Methods

Study sites description

Two reaches of the Truckee River were selected for hyporheic studies. A higher

elevation, montane reach was chosen approximately 56 km downstream from Lake Tahoe

(Figure 1A) near Fleisch, California. A lower elevation, semi-arid reach was also chosen

approximately 176 km downstream of Lake Tahoe (Figure 1B) near Little Nixon,

Nevada. The montane reach at 56 km is representative of moderately impacted,

oligotrophic reaches of the Truckee River that are typically depleted in dissolved

nitrogen/phosphorus and experiences minimal periphyton growth (<10 µg chla cm -2). In contrast, the semi-arid reach at 176 km represents the more human-impacted, eutrophic reaches of the Truckee River that are usually replete with dissolved phosphorus and supports rather excessive periphyton biomass (>50 µg chla cm -2) (Davis 2007).

Instrumentation and monitoring physical-chemical conditions

Piezometers (2.54 cm diameter observation wells) with a 20 cm screened interval

starting 10 cm from bottom were installed to approximately 1 m depth in the streambed

to allow characterization of the vertical hydraulic gradient and sampling of pore-water

throughout each study reach. Several additional mini-piezometers (Rapid Creek

Research, Boise Idaho) were also installed to various streambed depths (20-150 cm).

Vertical hydraulic gradient (VHG) was calculated, VHG = ∆h/ ∆z, where ∆h is the

difference in head between the water level in the piezometer and the level of the stream

surface and ∆z is the depth from the streambed to the mid-point of the screened section at

52 the bottom (Dahm et al., 2006). A positive VHG indicates upwelling and negative VHG indicates downwelling.

VHG was monitored biweekly using a depth sounder to measure water levels. Pore-

water was sampled monthly from piezometers using Tygon tubing attached to a hand-

pump. Pore-water samples were kept on ice until filtration (47 mm Nucleopore) in lab

and frozen until analysis using flow-injection based on Lachat QuickChem methods for

orthophosphate (OP) (Liao, 2002), nitrate plus nitrite (NO x) (Pritzlaff, 2000), and

+ ammonium (NH 4 ) (Prokopy, 2003).

Periphyton accumulation, nutrient content, and assemblage composition

Contrasting exchange zones of downwelling (DW) and upwelling (UW) were identified within the study reach such that other benthic habitat conditions were comparable. Bricks were deployed as artificial substrates (surface area = 442 cm 2) for periphyton colonization via clustering within a habitat that had similar depth (0.25 -0.5 meter), substrate (cobble/pebble), and light regime (0% riparian cover). The near-bed current velocities (20 mm above brick surface) were moderate (0.18 -0.54 m s -1). Brick clusters at 56 km were near piezometer P26 (DW zone) and piezometer 46 (UW zone) (Figure

1A). Brick clusters at 176 km were near piezometer P3 (DW zone) and piezometer 16

(UW zone) (Figure 1B). A subset of bricks (n = 3) were randomly collected weekly, placed in sealed plastic containers and transported to the lab for scrubbing, homogenizing and subsampling for periphyton biomass (chlorophyll a, chla), nutrient content

(particulate organic carbon, particulate nitrogen, particulate phosphorus), and algal community composition. Epilithic assemblages growing on cobble upstream of brick

53 clusters in close proximity (~5 m) were randomly collected (n = 3) and processed as a composite sample for the same suite of parameters as bricks.

Chla subsamples were vacuum filtered onto (Whatman GF/F) which were placed into borosilicate glass scintillation vials in a -80°C freezer for storage until analysis. Chla concentrations were determined via fluorometry (Welschmeyer, 1994) using a Turner

Designs model 10AU fluorometer calibrated with chlorophyll a from Anacystis nidulans

(Sigma Corp.). Chla content was checked spectrophotometrically (Parsons et al., 1984) for quality assurance. Particulate organic carbon (POC) and particulate nitrogen (PN) subsamples were filtered onto pre-combusted GF/F filters, dried for 24 h and stored with desiccant until analysis using a Perkin Elmer 2400 series II CHN/SO analyzer system.

Particulate phosphorus (PP) subsamples were filtered onto HCl rinsed pre-combusted

GF/F filters and dried before digesting to extract organic and inorganic fractions which were determined via colorimetric methods (Diamond, 2001).

Homogenized periphyton slurries were subsampled for microscopy and preserved by addition of gluteraldehyde. All diatom and soft-algae were counted in a Palmer-Maloney chamber and identified to genus-level using a tiered magnification method that entailed scanning the whole chamber at 100X magnification for large taxa (>200 µm), followed

by a minimum of 5 views at 400X for small taxa (<200 µm). The tiered counting allowed for a minimum of 400 natural units (cell, filament, or colony) identified in each sample.

All counts were standardized to the area sampled for biovolume ( µm3 cm -2). Biovolume

estimates for each contributing taxa were determined by assigning geometric formulas

(Hillebrand et al., 1999).

Net accrual rate within each exchange zone was calculated by least-squares fit of accrual time-series data during the period of increasing biomass by applying the equation y = a*ekt , where y is the chla density ( µg chla cm -2) at day t, a is the initial chla density,

and k is the net growth rate. Net growth rate was converted to specific growth rates (µ,

divisions day -1) by the expression, k = µ/ln 2. Immigration of algal cells during the initial

4 to 7 d of accrual (thus not actually active growth) was accounted for by excluding those

data from growth rate estimations.

Primary production

Photosynthesis as a function of irradiance (PE) was measured using short-term

incubations (~2 h) on periphyton scrapped from bricks collected in each exchange zone

in order to estimate primary production. Bricks were collected in the morning and

transported to the lab in sealed plastic containers filled with stream water and placed in

coolers filled with stream water to maintain ambient conditions. Five aliquots of the

scraped/rinsed periphyton slurry (1 mL) were subsampled in order to normalize uptake

14 rates to biomass and the remaining 70 mL was spiked with NaH CO 3 to attain a final

activity of 0.36 to 1.8 µCi mL -1. Radioisotope concentrations in periphyton slurry were

determined from triplicate 0.05 mL aliquots that were fixed with 0.05 mL ethanolamine

before adding scintillation cocktail. Aliquots (2 mL) were pipetted into 24 glass

scintillation vials and placed into a temperature controlled aluminum block (± 1 -2ºC

ambient) fitted with neutral density screening to attain 24 different irradiances (8.5 -460

µEinstein’s m -2 sec -1) emitted from a 500 W tungsten halogen lamp. Irradiances were

measured using a 4 π scalar irradiance meter (Biospherical Instruments QSL-2100).

Three control vials wrapped in foil were incubated in the water bath throughout the experiment in order to subtract background radioactivity from 14 C uptake in light treatments. Experiments ended by turning off light and adding concentrated HCl. Vials were subsequently dried on a heating block in fume hood to remove residual inorganic

14 C. Radioactivity was determined using a Beckman Coulter LS6500 multipurpose scintillation counter.

Carbon fixation rates were calculated using established approaches (Bott, 2006). Total dissolved inorganic carbon was estimated for each site (8.5 -18 mg L -1) following an indirect method (Wetzel and Likens, 2000) using field temperature and pH values collected the day of experiment and the monthly average of alkalinity (7 -10 years)

(NDEP, 2009). Curve fitting software, CurveExpert Basic (version 1.4)) was used to fit the chla normalized uptake rates to a hyperbolic tangent function (Jassby and Platt, 1976) by the expression:

B B B P = P m tanh ( αI/ P m)

B -1 -1 B where P is the biomass-specific photosynthetic rate (µg C µg chla h ), P m is the maximum biomass specific photosynthetic rate (µg C µg chla-1 h-1), α is the initial linear slope of the curve, and I is the irradiance. Daily rates of carbon fixation ( µg C µg chla -1

-1 B day ) were calculated by assuming P m was maintained throughout the daylight period.

Specific growth rates were estimated assuming carbon to chla equal to the slope from the

regression of POC vs chla.

Results

Physical and chemical conditions

Discharge at 56 km was mostly stable (9 m 3 sec -1) during the spring 2008 accrual study, however by late March/early April flows almost doubled as run-off from snowmelt increased (Figure 2). Spring run-off concluded by early June and base-flow conditions were extremely stable throughout the summer at 56 km (17 m 3 sec -1) and 176 (6 m 3 sec -

1).

VHGs were initially upwelling (positive) in the predicted UW zone at 56 km in spring

and summer (Figure 3) but shifted to downwelling (negative) during both accrual studies.

Similarly, the UW zone at 176 km shifted from upwelling to downwelling during the

summer study. In comparison, predicted DW zones generally remained downwelling

throughout the accrual studies at both 56 km and 176 km.

Surface-water at 56 km had consistently low OP (~ 0.14 µM) while pore-water in UW

and DW zones were often > 2-fold higher than surface OP in both spring and summer

(Table 1). Dissolved inorganic nitrogen in surface-water at 56 km was mostly NO x and

was 1-2 orders of magnitude higher in spring (~1.46-5.95 µM) compared to summer

+ (0.03-0.23 µM). Similarly, NH 4 was 4-fold higher in surface-water at 56 km in spring

(0.56-0.75 µM) compared to summer (0.15-0.17 µM). In comparison, pore-water was variable but generally had an order of magnitude higher NO x in both the UW zone (3.66-

10.29 µM) and DW zone (1.88-6.41 µM). Ammonium concentrations in the pore-water

were comparable to the surface at 56 km, except in early summer (end June) when both

+ UW and DW zones had an order of magnitude more NH 4 (~3.5 µM).

Surface-water at 176 km maintained elevated OP during the summer, typically with 2- fold higher concentrations in the streambed (Table 2). Pronounced decreases in dissolved nitrogen at 176 km were documented in surface-water for NO x (0.84 to 0.08 µM) and

+ NH 4 (0.69 to 0.17 µM). Pore-water concentrations were generally higher than surface-

+ water in both the UW and DW zone for both NO x (1.34-5.89 µM) and NH 4 (1.80-3.27

µM). At the beginning of the summer study (end June) the DW zone at 176 km

+ contained the maximum reported concentrations of OP, NO x, and NH 4 .

Periphyton biomass accumulation, nutrient content, and assemblage composition

Intra-site patterns of periphyton accrual on bricks were extremely similar in UW and

DW zones at 56 km in both spring and summer (Figure 4). Standing stocks were comparable in the exchange zones in spring at 56 km except day 35 when nearly 2-folder higher biomass had accumulated in the UW zone (3.67 µg chla cm -2) than the DW zone

(1.87 µg chla cm -2). Summer accrual at 56 km was equivalent in contrasting exchange

zones.

Standing stocks at 176 km diverged on day 19 as the UW zone attained higher biomass

(10.80 µg chla cm -2) versus the DW zone (8.09 µg chla cm -2), and subsequently

maintained greater biomass for remaining 12 d of the study. Epilithic biomass was

generally similar in contrasting exchange zones however standing stocks were nearly 2-

fold greater in the UW zone at 56 km in spring (ca. 4 vs 2 µg cha cm -2).

Intra-site patterns of periphyton nutrient content were usually comparable in UW and

DW zones (Figure 5). UW zones displayed only sporadic periods (~7 d) of greater

58 carbon content relative to nitrogen and phosphorus (i.e. higher POC:PN or POC:PP) but variability was quite high at those time-points.

Non N 2-fixing diatoms dominated the assemblage composition (>90% relative biovolume) in both exchange zones at 56 km in spring (Figure 6A). Encyonema and

Nitzschia comprised the highest proportions (24-60%) on day 35, as well as day 47 (16-

39%) at 56 km in spring. In contrast, summer assemblages at 56 km in both exchange zones became increasing dominated (> 40%) by diatom genera, Epithemia and

Rhopalodia , which potentially house endosymbiotic cyanobacteria capable of N2-fixation

(Figure 6B). Summer assemblages at 176 km exhibited similar composition changes with non-N2 fixing diatoms dominating by day 8 before shifting to ~80% N 2-fixing

diatoms ( Epithemia sorex ) (Figure 6C). After 31 days the assemblage at 176 km became increasingly comprised of filamentous ‘green’ taxa ( Cladophora and Oedogonium ).

Primary production

PE experiments on brick assemblages at 56 km in spring (day 47) revealed 2-fold faster

B B P m in the DW zone (Table 3). In contrast, summer assemblages had comparable P m in exchanges zones (~ 0.30 µg C µg chla -1 hr -1) at 56 km (day 19). Brick assemblages at

B 176 km in summer (day 9) had nearly 3-fold faster P m in the DW zone.

Specific growth rates

Specific growth rates (µ) ranged from 0.07 to 0.18 divisions day -1 based on brick chla accrual and from 0.04 to 1.04 divisions day -1 based on PE experiments (Figure 7).

Growth rates in contrasting exchange zones were mostly similar, whether considering

59 rates based on brick chla accrual or PE experiments (Figure 7). An exception was in summer at 176 km when PE-based µ was nearly 7-fold faster than the brick chla µ in the

DW zone (1.04 vs. 0.15 division day -1) and 3-fold faster in the UW zone (0.54 vs. 0.18

divisions day-1).

Discussion

Periphyton assemblage attributes were largely equivalent in contrasting exchange zones

in both the montane and semi-arid reaches of the Truckee River. Standing stocks and

biomass accrual were strikingly similar in exchange zones. Assemblage composition was

comparable in exchanges zones and was typically dominated by N 2-fixing taxa. Nutrient

content and resulting stoichiometry of periphyton assemblages were also similar in

exchange zones. Rates of primary productivity were also comparable between exchange

zones at each site. Thus, the current work shows little evidence for hyporheic exchange

influencing periphyton structure and function in both montane and desert reaches of the

Truckee River.

Pore-water was enriched relative to surface water with dissolved nitrogen (ca. 10-fold)

and phosphorus (ca. 2-fold higher), however, flux rates may not have been adequate to

impact periphyton assemblages at the streambed surface. For example, in summer at 176

km the average upwelling flux of dissolved nitrogen was estimated at 0.28 mmoles N

day -1 m-2 (using the average porewater DIN, 3.38 mmole m -3, and UW discharge rate reported by Naranjo et al. (2012), 8.6 x 10 -7 m3 sec -1 m2). Accumulation of particulate nitrogen in the UW zone was 4 mmoles m -2 day -1, so the UW flux could only account for

60 ca. 7% of the nitrogen budget for periphyton in the UW zone. Upstream at 56 km in summer the average upwelling flux of dissolved nitrogen was estimated at 0.06 to 61 mmoles N day -1 m-2 (using the average porewater DIN, 7.06 mmole m -3, and estimated

UW discharge rate, 10 -7 to 10 -6 m3 sec -1 m2). Accumulation of particulate nitrogen in the

UW zone at 56 km was 4.3 mmoles m -2 day -1, thus the UW flux could only account for 1 to 14% of the nitrogen budget for periphyton in the UW zone in summer. Additionally,

VHG values in UW zones were often only slightly positive and readily shifted to negative with slight changes in stage. These “pulses” from the hyporheic would have influenced periphyton at the streambed surface for only brief periods (days), however, the net effect on assemblages may have been masked at the scale of measurements (weekly).

Some anecdotal evidence observed during on-going monitoring of piezometers suggests that nutrient enriched upwelling water could influence periphyton at 176 km. Thick felts of stalk diatoms were observed in February 2009 in an extremely shallow (< 0.20 m depth) mid-riffle region, just upstream of the predicted upwelling zone investigated during summer 2008. These specific locations correspond to areas at the 176 km site that had consistently vertical upwelling fluxes (Naranjo et al., 2012).

Periphyton nutrient content indicated that nutrient conditions in both exchange zones were conducive for balanced growth. POC:PN mostly indicated optimal growth conditions (5 to 10) as did POC:PP (90 to 185) (Hillebrand and Sommer, 1999). PN:PP was also generally near optimum (13 to 22), however, growth during the early stages of accrual at 56 km in spring and 176 km in summer were likely experiencing nitrogen limitation (< 13) (Hillebrand and Sommer, 1999). Nitrogen limitation was most likely alleviated at 56 km in spring by the elevated NO X in the surface water, while nitrogen

61 availability at 176 km in summer may have improved through increases in the prevalence of taxa capable of N2-fixation (e.g. Epithemia sorex ). Thus, an adequate source of nitrogen for balanced growth of periphyton in the Truckee River appears to be mostly derived from sources other than hyporheic flux.

Key insights to guide future hyporheic exchange studies

The design and overall methodology of the current study has several noteworthy strengths and weaknesses to consider. First, considerable effort was invested in instrumenting and characterizing the hydraulic exchanges throughout the riffle-pool sequence at both study locations. Spatial heterogeneity at fine scales is expected due to changes in both substrate and bed topography (Baxter and Hauer, 2000), so defining the locality and extent of exchange zones is critical in order to gain assurance in measured benthic biota responses. Our efforts allowed the identification of contrasting exchange zones in the Truckee River that had similar habitats (e.g. depth, substrate, velocity) in order to evaluate periphyton dynamics. Availability of similar habitats in contrasting exchange zones, however, was extremely limited within each study reach, thus preventing the incorporation of randomization or replication into the study design.

Previous studies investigating the effects of hyporheic exchange on periphyton have increased replication (i.e. more sites with contrasting exchange) by mapping physical, chemical, and biological parameters at a discrete time at the expense of incorporating temporal dynamics. The current study sacrificed spatial replication in order to capture the temporal dynamics of periphyton structure and function in contrasting exchange zones.

Several key insights emerged from the current work to help guide future studies investigating the potential influence of hyporheic exchange on periphyton in the Truckee

River or comparable systems. First, extensive semi-quantitative mapping of periphyton growth characteristics (e.g. color, thickness, condition) using a viewing bucket should be combined with quantitative measures (e.g. biomass, taxonomic enumeration, metabolism) throughout several reaches (Grimm et al., 2006). Secondly, time should be budgeted to allow for monitoring the dynamics of vertical exchange across varying hydrological events (e.g. spates, floods) and extremes (i.e. base-flow vs. high flow) to ensure a reasonable understanding of exchange dynamics across the study reach. Finally, evaluating the effects of exchange at the plot scale may not have been appropriate in the

Truckee River given patchiness that exist in upwelling zones (Naranjo et al., 2012).

Effects of hyporheic exchange on periphyton in the Truckee River may be more tractable at the cobble-scale, similar to patterns in the Middle Fork Flathead River (Wyatt et al.,

2008). Future efforts should investigate the potential for finer scale (< 1 m) periphyton responses in the Truckee River or comparable systems.

The scale of exchange needed in order to “influence” periphyton assemblages is a

fundamental aspect of hyporheic studies. The scale of exchange in Sycamore Creek

documented by Valett et al. (1994), for example, was particularly dramatic such that

appreciable spikes (2-3 fold) in dissolved nitrogen were detectable in the surface water

near upwelling zones where surface discharge was relatively low (0.01 to 0.04 m 3 sec -1)

(Valett et al., 1994). Artificially high surface flows are maintained for extensive periods

(>100 days) in the Truckee River, thereby potentially limiting the relative influence of

hyporheic exchange on periphyton. Seasonal low-flows (e.g. early winter) or drought

63 conditions that impose much lower surface flow in the Truckee River could increase the relative flux in upwelling zones. Investigating the effects of hyporheic exchange during different hydrologic conditions seems warranted.

Conclusions

The current study did not provide quantified evidence that hyporheic exchange was

directly influencing periphyton dynamics in the Truckee River. Despite pore-water being

highly enriched with dissolved nutrients relative to depleted surface waters, the hyporheic

flux probably was not sufficient to deliver enriched pore-water to periphyton in the study

plots for any appreciable time that would be detectable in the assemblage measurements.

Periphyton growth in both the montane and semi-arid study reaches of the Truckee

appears to be largely supported by nutrient sources other than hyporheic exchange.

Acknowledgements

I would like to thank and acknowledge the supporting laboratory staff and graduate

students in the Desert Research Institute’s Systems Microbial Ecology Lab (Jeramie

Memmott and Andy Rost); and the prior works and collaborations with Alan McKay and

Jim Brock that helped frame this study. This study was funded by EPA grant 83277801-

1 awarded to Alan McKay. A special thanks to Ramon Naranjo with whom I worked

closely on these hyporheic studies, in particular, in mapping hydraulic gradients and

sampling water chemistry. R. Naranjo also provided the GIS map (Figure 1) for the

study sites.

References

Baxter, C.V., and F.R. Hauer. 2000. Geomorphology, hyporheic exchange, and selection of spawning habitat by bull trout (Salvelinus confluentus). Canadian Journal of Fisheries and Aquatic Sciences 57:1470-1481. Bott, T.L. 2006. Primary productivity and community respiration. Pages 663-690 in F.R. Hauer and G.A. Lamberti (editors). Methods in Stream Ecology, 2 nd edition. Elsevier Academic Press, New York, New York. Boulton, A.J. 1993. Stream ecology and surface hyporheic hydrologic exchange: implications, techniques, and limitations. Australian Journal of Marine and Freshwater Research 44:553-564 Dahm, C.N., H.M. Valett, C.V. Baxter, W.W. Woessner. 2006. Hyporheic Zones. Pages 119-142 in F.R. Hauer and G.A. Lamberti (editors). Methods in Stream Ecology, 2 nd edition. Elsevier Academic Press, New York, New York. Davis, C.J. 2007. Periphyton dynamics and environmental associations: Truckee River, CA-NV, USA. (Master’s Thesis) University of Nevada Reno. ProQuest/UMI, Ann- Arbor, Michigan. Publication No. 14477636. Diamond D. 2001. Determination of total phosphorus by flow injection analysis (Acid persulfate digestion method). QuikChem® Method 10–115–01–1–E:16. Lachat Instruments. Loveland, Colorado. Green, M.B. and C.H. Fritsen. 2006. Spatial variation of nutrient balance in the Truckee River, California-Nevada. Journal of the American Water Resources Association 42:659-674. Grimm, N.B., C.V. Baxter, and C.L. Crenshaw. 2006. Surface-subsurface interactions in streams. Pages 761-782 in F.R. Hauer and G.A. Lamberti (editors). Methods in Stream Ecology, 2 nd edition. Elsevier Academic Press, New York, New York. Henry, J.C. and S.G. Fisher. 2003. Spatial segragation of periphyton communities in a desert stream: causes and consequences for N cycling. Journal of the North American Benthological Society 22:511-527. Hillebrand H., C.D. Durselen, D. Kirschtel, U. Pollingher, and T. Zohary. 1999. Biovolume calculation for pelagic and benthic microalgae. Journal of Phycology 35: 403-424. Hillebrand H. and U. Sommer. 1999. The nutrient stoichiometry of benthic microalgal growth: Red– field proportions are optimal. Limnology and Oceanography 44:440- 446. Jassby, A.T., and T. Platt. 1976. Mathematical formulation of the relationship between photosynthesis and light for phytoplankton. Limnology and Oceanography 21:540- 547.

Liao, N. 2002. Determination of orthophosphate in waters by flow injection analysis colorimetry. QuikChem® Method 10–115–01–1–M:17. Lachat Instruments. Loveland, Colorado. McClain, M.E., E.W. Boyer, C.L. Dent, S.E. Gergel, N.B. Grimm, P.M. Groffman, S.C. Hart, J.W. Harvey, C.A. Johnston, E. Mayorga, W.H. McDowell, and G. Pinay. 2003. Biogeochemical hot spots and hot moments at the interface of terrestrial and aquatic ecosystems. Ecosystems 6:301-312. Naranjo, R.C., R.G. Niswonger, M. Stone, C. Davis, and A. McKay. 2012. The use of multiobjective calibration and regional sensitivity analysis in simulating hyporheic exchange. Water Resources Research 48: W01538, doi:10.1029/2011WR011179. Parson, T.R., Y. Maita, and C.M. Lalli. 1984. A Manual of Chemical and Biological Methods for Seawater Analysis, 1 st edition. Oxford Pergamon Press, New York, New York. Pepin, D.M., and F.R. Hauer. 2002. Benthic responses to groundwater-surface water exchange in 2 alluvial rivers in northwestern Montana. Journal of the North American Benthological Society 21:370-383. Pritzlaff, P. 2000. Determination of nitrate/nitrite in surface and wastewaters by flow injection analysis. QuikChem® Method 10–107–04–1–C:15. Lachat Instruments. Loveland, Colorado. Prokopy, W.R. 2003. Determination of ammonia by flow injection analysis. QuikChem® Method 10–107–06–2–C:10. Lachat Instruments. Loveland, Colorado. Uehlinger, U. and J.T. Brock. 2005. Periphyton metabolism along a nutrient gradient in a desert river (Truckee River, Nevada, USA). Aquatic Sciences 67:507-516. Valett, H.M., S.G. Fisher, N.B. Grimm, and P. Camill. 1994. Vertical hydrologic exchange and ecological stability of a desert stream ecosystem. Ecology 75:548-560. Welschmeyer, N. 1994. Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnology and Oceanography 38:1985-1992. Wetzel, R.G. and G.E. Likens. 2000. Limnological Analyses. Springer-Verlag, New York, New York. Wyatt, K.H., F.R. Hauer, and G.F. Pessoney. 2008. Benthic algal response to hyporheic- surface water exchange in an alluvial river. Hydrobiologia 607:151-161.

A B

Figure 1. Hyporheic study sites in the Truckee River within a montane reach at 56 km (A) and semi-arid reach at 176 km (B). Periphyton studies conducted in localized upwelling (UW) and downwelling (DW) exchange zones within each reach. Arrows indicate flow direction.

50 56 km 40

-1 30 s

3 20 m 10

0 50 176 km Jul-08 Oct-07 Oct-08 Apr-08 Jan-08 Jun-08 Feb-08 Mar-08 Nov-07 Dec-07 Aug-08 Sep-08

40 May-08

-1 30 s

3 20 m 10

0 Jul-08 Apr-08 Oct-08 Oct-07 Jun-08 Jan-08 Feb-08 Mar-08 Nov-07 Dec-07 Aug-08 Sep-08 May-08

Figure 2. Average daily discharge for the 2007-2008 water-year near Farad, CA (USGS gauge 103446000) and near Nixon, NV (USGS gauge 10351700) representing flow at 56 km and 176 km, respectively. Shaded areas indicate temporal window of periphyton studies.

Figure 3. Temporal dynamics of vertical hydraulic gradient (VHG) in predicted upwelling (UW) and downwelling (DW) zones at 56 km and 176 km. Shaded areas indicate temporal window of periphyton studies.

Table 1. Dissolved nutrients (µM) at 56 km in surface-water (Surface) and pore-water zones of upwelling (UW) and downwelling (DW) during periphyton studies in spring and summer 2008.

Parameter Surface UW (70-100 cm depth) DW (50-60 cm depth)

14-Feb 20-Mar 3-Apr 9-Jul 5-Aug 28-Feb 21-Mar 3-Apr 25-Jun 31-Jul 14-Feb 21-Mar 3-Apr 25-Jun 31-Jul

OP 0.16 0.17 0.11 0.14 0.09 0.40 0.58 0.42 0.57 0.80 0.24 0.24 0.38 0.50 0.25

NO x 1.46 5.95 2.22 0.03 0.23 3.66 8.48 4.91 7.71 10.29 1.88 3.74 6.41 4.07 6.04 NH + 0.56 0.66 0.75 0.15 0.17 0.11 0.96 0.31 3.67 1.35 0.19 0.25 0.03 3.76 <0.07 4

Table 2. Dissolved nutrients (µM) at 176 km in the surface-water (Surface) and pore-water in zones of upwelling (UW) and downwelling (DW) during periphyton studies in summer 2008.

Parameter Surface UW (100 cm depth) DW (50 cm depth)

7-Jul 4-Aug 26-Jun 30-Jul 26-Jun 30-Jul

OP 1.64 1.15 2.62 2.88 13.08 1.62

NO x 0.84 0.08 2.61 1.34 5.89 1.11 NH + 0.69 0.17 1.80 1.93 3.22 3.27 4

Figure 4. Mean biomass (± SE) of brick and epilithic assemblages in predicted upwelling (UW) and downwelling (DW) zones at 56 km in spring, 56 km in summer , and 176 km in summer.

56 km 56 km DW Brick UW Brick 56 km 40 300 40 250 30 30 200 20 150 20 100 10 10 50 0 0 0

56 km 56 km 56 km 40 300 40 250 30 30 200

20 150 20

100 PN:PP POC:PP POC:PN 10 10 50

0 0 0 176 km 176 km 176 km 40 300 40 250 30 30 200

20 150 20 100 10 10 50

0 0 0

Figure 5. Mean nutrient balance (± SE) of periphyton on bricks.

N-fixing Diatoms N-fixing Cyanobacteria non N-fixing Diatoms non N-fixing Cyanobacteria 56 km Greens 100% A 80%

60%

40%

20%

0% DW UW DW UW 35 days 47 days 56 km 100% B 80%

60%

40%

20%

0% DW UW DW UW DW UW

Relative Relative Biovolume 20 days 25 days 31 days

176 km 100% C 80%

60%

40%

20%

0% DW UW DW UW DW UW 8 days 19 days 31 days

Table 3. Photosynthesis-irradiance (PE) experimental summary. Maximum biomass specific B photosynthetic rate (P m), specific growth rate (µ).

River B Exchange Temperature P m ± 95% CI µ ± 95% CI Distance Date α R2 zone (°C) -1 -1 -1 (km) (µg C µg chla hr ) (divisions day )

56 25-Mar DW 6 0.005 0.57±0.22 0.85 0.11±0.04 25-Mar UW 6 0.002 0.25 ± 0.06 0.92 0.04 ± 0.01 ± ± 23-Jul DW 18 0.001 0.29 ± 0.05 0.96 0.04 ± 0.01 23-Jul UW 18 0.001 0.33 ± 0.03 0.99 0.03 ± 0.00 ± ± 176 11-Jul DW 24 0.015 5.30±0.42 0.99 1.04±0.08 11-Jul UW 24 0.006 1.90 ± 0.18 0.99 0.54 ± 0.05

Brick chla Brick PE 1.2

1.0 ) -1 0.8

0.6

0.4 (divisions day (divisions

Specific growth Specific growth rate 0.2

0.0 DW UW DW UW DW UW Spring Spring Summer Summer Summer Summer 56 km 56 km 56 km 56 km 176 km 176 km

Figure 7. Specific growth rates (µ) (± 95% CI) estimated from brick chla accrual and brick PE experiments.

Chapter 4

HIGH RATES OF PRIMARY PRODUCTIVITY IN A SEMI-ARID TAILWATER: IMPLICATIONS FOR SELF-REGULATED PRODUCTION

CLINTON J. DAVIS, CHRISTIAN H. FRITSEN, ERIC D. WIRTHLIN, and JERAMIE C. MEMMOTT Desert Research Institute, Reno, NV, USA

This paper was published on-line in River Research and Applications on August 18, 2011.

Abstract

Reservoir-river systems in desert environments may provide the optimal combination of environmental conditions (e.g. light, nutrients, temperature, and flow) that maximizes primary production in downstream reaches. Stream metabolism was measured using an open-system approach each month during spring-summer in a semi-arid tailwater (South Fork Humboldt

River) in the central Great Basin, USA. Spatial and temporal differences in metabolic rates were evident despite tailwater reaches sustaining comparable standing stocks of periphyton (> 10 µg

-2 -2 chl a cm ) during this growing season. Primary productivity was highest (15 to 36 g O 2 m day -1) in July, supporting previous studies that have described arid regulated/unregulated streams as ultra-productive. Substrate availability when combined with self-shading and hypoxic conditions created a system that was likely near the maximal productivity that stream systems can achieve because of the self-regulating attributes that thick periphyton mats impose upon themselves as they reach high biomass and maximal production rates.

Introduction

Primary production in streams is primarily dependent on light (incident and transmitted), nutrient availability (e.g. phosphorus), temperature and, to a lesser degree, flow (Lamberti and Steinman,

1997; Mulholland et al ., 2001). The optimum combination of these environmental factors that maximizes primary production of stream systems may only occur in a limited number of streams throughout the world. Reservoir tailwater systems in arid environments, such as the western US, may provide such a combination of environmental conditions.

The western US contains many tailwater reaches that are often characterized as clear-water, high nutrient systems with relatively stable flows that pass through riverine corridors with minimal riparian cover. Upstream reservoirs function to entrap sediments and particulate matter and increase water clarity in the downstream reaches. Moreover, their hypolimnetic releases often have elevated nutrient concentrations (nitrogen and phosphorus) that can help fuel algal production in these clear waters (Lowe, 1979). Released water is often cold, especially below deep reservoirs (Ward and Stanford, 1979). Stable releases from reservoirs may maintain flow and dampen flood occurrences (that often remove autotrophic biomass) such that ideal conditions for biomass accumulation and productivity may occur.

High standing stocks of periphyton and macrophytes have been repeatedly documented in tailwaters, but are often only noted secondarily in case studies of cold-water fisheries (Lowe,

1979). Despite the evidence of high tailwater productivity, to the authors’ knowledge, no studies have actually examined tailwaters in regards to the environmental conditions that maximize production.

In the current study, we show how a semi-arid tailwater system provides environmental conditions that allow maximum primary production to be realized such that the rates of production become more constrained by self-regulating mechanisms (e.g. self-shading, space).

A high elevation reservoir-river system in the semi-arid region of eastern Nevada, U.S. appears to meet the optimum environmental conditions to maximize productivity. In summer 2009 we measured ecosystem metabolism using a single-station, open system approach in the tailwater reaches of the South Fork Humboldt River. The nutrient regime, periphyton biomass and community composition were also assessed in conjunction with metabolism to provide further chemical and biological context for metabolic rates.

Study System

The South Fork Humboldt River (SFHR) is located in the central Basin and Range province (40°

40’N, 115° 45’W). The climate of the catchment is semi-arid with relatively little precipitation

(<300 mm annually) and large temperature variation during summer characterized by high daytime (July mean = 32°C) and low nighttime temperatures (July mean = 9.2°C). Sagebrush is the dominant vegetation of this cool desert region, though sparse riparian vegetation includes willow species. The SFHR hydrograph is typical of a snow-melt driven system with flows peaking during run-off in late-spring/early summer (end June), then declining to base flow by late summer/early autumn (end August). The South Fork Reservoir (SFR) was built in 1988 upstream (36 km) from the confluence of the SFHR with the Humboldt River and filled by 1995.

The SFR drainage area is 2325 km 2 and stores ca. 5.18 x 10 7 m3 of water (Sater et al. , 1994). The

SFR is operated as a “flow in flow out” system, in that the hypolimnetic outflow (ca. 14 meter

78 depth in the reservoir) into the SFHR is managed to closely match upstream inflows so that downstream water rights and wildlife habitat are minimally impacted.

Methods

Water Quality

Longitudinal synoptic surveys of nutrients were conducted in the spring and summer 2009 to characterize spatial trends throughout the reservoir-river system and included both reaches upstream (5.5 km) and downstream (0.75 km, 10 km, 19.5 km) of the reservoir dam. Nutrients in the SFR hypolimnion (12.5 meter depth) were also sampled within a week of sampling these river reaches. All samples were filtered (0.4 µm pore polycarbonate filter) and then frozen

immediately until flow injection analysis for orthophosphate (OP), nitrate plus nitrite (NO x), and

+ ammonium (NH 4 ) using standard Lachat QuikChem methods (OP, 10-115-01-1-M (Liao,

+ 2002); NH 4 , 10-107-06-2-C (Prokopy, 2003); NO x, 10-107-04-1-C (Pritzlaff, 2000)). Unfiltered samples were frozen for total nitrogen (TN) and total phosphorus (TP) until analysis using dual manual digests and colorimetric methods (TP, 10-115-01-4-B (Tucker and Jones, 2007b); TN,

10-107-04-4-B (Tucker and Jones, 2007a)).

Short-term deployments (24 to 72 hours) of oxygen and temperature sensors (YSI 600 xlm sonde, Yellow Springs, Ohio) occurred in June, July, and August within three tailwater reaches

(0.75 km, 10 km and 19.5 km) in order to estimate productivity and document biologically influenced environmental parameters. All probes were calibrated before and after deployments according to the recommendations of the manufacturer.

Ecosystem Metabolism

The exchange rate of oxygen between air and water is required to make accurate estimates of metabolic rates in streams. Reaeration coefficients, k oxygen , were derived from two methods; the

commonly used energy dissipation model (EDM) based on channel hydraulics (Tsivoglou and

Neal, 1976) and regression of the night-time drop of oxygen concentration (Hornberger and

Kelly, 1975). A recent study found that these indirect reaeration methods generally performed

well after comparing and contrasting various methods in 21 reaches of variable channel width,

catchment area, and water quality (Aristegi et al. , 2009).

Reaeration coefficients based on the EDM method were calculated from estimates of channel

depth, water velocity, discharge, and reach slope. The average depth and velocity for SFHR

study reaches were derived from the discharge transects at each site while slope was calculated

from digital elevation maps.

The night-time drop of oxygen concentration is an indirect reaeration method based on the

assumption that as the saturation deficit increases so does the diffusion from air, so night-time

oxygen dynamics are solely driven by respiration and reaeration. Based on this, one can plot the

rate of change in oxygen concentration versus the saturation deficit to obtain a linear regression

with a slope equivalent to the reaeration coefficient.

Diel oxygen curve methods using the single-station approach was applied to estimate rates of

production and respiration (Odum, 1956). Net ecosystem metabolism is defined as NEM(t) =

z(d C/dt – k[ Cs-C]), where C is the dissolved oxygen concentration, Cs is the concentration at

saturation, k is the reaeration coefficient, and z is the average depth of the reach. Ecosystem

respiration (ER) was estimated by calculating the average hourly rate of NEM at night. Gross

primary production (GPP) integrated during daylight hours was the sum of hourly rates of NEM

80 and ER. Metabolic rates were calculated using both reaeration methods to attain an estimated range of rates. Metabolic rates were not groundwater-corrected (Hall and Tank 2005) which adds some additional uncertainty to metabolic estimates.

Periphyton

Sampling for periphyton occurred in June, July, and August 2009 within three reaches of the

SFHR tailwater. Sampling reaches were clustered around three access points 0.75 km, 10 km, and 19.5 km downstream from the reservoir. At each location periphyton samples were collected along 10 meter intervals that were longitudinally spaced along approximately 80 meters of the reach. Within each interval, the distance of the sample from bank (where the samples were collected) was a randomized percentage of the river width. If a location could not be sampled based on field safety protocols, it was noted and that sample was allocated towards the next interval. This operation procedure resulted in 21 to 24 periphyton samples.

Epilithic, episammic, or epipelic samples were collected depending on the dominate substrate encountered. Epilithic samples consisted of 1 to 2 cobbles or 3 to 5 gravel substrates. Attached algae were scrubbed from the cobble and gravel using steel brushes and rinsing with filtered stream water. The axes (x, y, z) of each cobble or gravel were measured to determine the area sampled (mean = 117 +/- 5 (SE) cm -2). Epipelic and episammic samples were collected in three

petri dishes of sand/silt and pooled (total area = 53 cm -2). Large, unmovable boulders were

treated the same as unwadeable sampling points. Periphyton samples were placed on ice and in

the dark until processing.

Periphyton slurries were mechanically homogenized and sub-sampled for chlorophyll a (chl a), ash-free dry mass (AFDM), particulate organic carbon/particulate nitrogen (POC/PN), total particulate phosphorus (TPP) and algal identification/enumeration. Analysis of phosphate

81 content of periphyton in episammic and epipelic samples are complicated by the interference from ferric iron in the milled sediments. Due to these analysis difficulties, only chlorophyll a was sub-sampled from episammic and epipelic samples.

Chlorophyll a samples were vacuum filtered onto Whatman GF/F glass fiber filters and frozen

(-80°C). Chlorophyll a concentrations were determined via fluorometry using the Welschmeyer

(1994) method using a Turner Designs model 10AU fluorometer calibrated with chlorophyll a from Anacystis nidulans (Sigma Corp.). AFDM samples were vacuum filtered onto pre- combusted (500°C for 1 hour) GF/F filters, dried, and stored with desiccant. The AFDM was determined gravimetrically using standard methods (Clesceri et al. , 1998).

POC/PN samples were vacuum filtered onto pre-combusted (500°C for 1 hour) GF/F filters, dried, and stored with desiccant until analysis using a Perkin Elmer 2400 Series II CHNS/O system. TPP samples were filtered onto acid-rinsed GF/F filters, dried, and digested to extract organic and inorganic fractions which were determined colorimetrically using the method outlined in the Lachat QuikChem® Method 10-115-01-1-E (Diamond, 2001).

Blended periphyton slurries were subsampled for microscopy and preserved by addition of gluteraldehyde. All diatom and soft-algae genera were identified to genus-level and counted in a

Palmer-Maloney cell using a tiered magnification method that entails scanning the whole chamber at 100x magnification for large taxa (>200 µm), scanning minimum of 5 views at 200x

for medium-size taxa (200 to 50 µm), and minimum of 5 views at 400x for small taxa (<50 µm).

The tiered counting allowed for >400 “natural units” identified. Biovolume estimates were

determined by assigning formulas outlined in current literature (Hillebrand et al. , 1999). All counts were standardized to the area sampled using biovolume ( µm3 cm -2).

Results

Discharge downstream from SFR in 2009 paralleled the 10-yr median with peak flows (ca. 15 m 3 sec -1) in early-mid June then gradually declined throughout July until base-flows (< 1 m 3 sec -1)

being attained by the end of August (Figure 1). However, the peak discharge in 2009 was near

the 90 th percentile, 30 m 3 sec -1, on June 20 th following a heavy rain event. Field collections in

2009 coincided with the peak flows in June, slightly above base-flow in July, and at base-flow in

August.

Dissolved Oxygen and Temperature

Temperature and DO dynamics were not extremely variable over a daily time-scale downstream of the reservoir until July and August (Figure 2). Dissolved oxygen in July at 10 km had large swings, 4 to 18 mg L -1 (52% to 245% saturation) and broader temperature range, 13 to

24 °C. Dissolved oxygen at 19.5 km also had large swings, from 4 to 19 mg L -1 (48% to 258% saturation) and broad temperature ranges, 16 to 23 °C, in July. The 10 km site exhibited the lowest DO concentration recorded and the most extreme DO swings, 1 to 18 mg L -1 (17% to

244% saturation) in August, while the temperature range remained similar to those in July (15 to

23 °C). A reduced DO range at 19.5 km in August compared to July was measured, ranging from 3.9 to 12.9 mg L -1 (45% to 172% saturation). Temperature in August remained similar to

those in July (14 to 21 °C) at 19.5 km.

Ecosystem Metabolism

Reaeration coefficients in the 10 km reach ranged from 3.4 to 26 day-1 and 1.1 to 11 day -1 in the 19.5 km reach (Table 1). This range of reaeration coefficients is comparable to those expected for a low gradient, slow flowing stream (Grace and Imberger, 2006).

-2 -1 -2 -1 GPP estimates varied between 5.1 to 24 g O 2 m day at 10 km and 3.6 to 36 g O 2 m day at

-2 -1 19.5 km (Table 1). In comparison, ER varied between 4.7 to 12 g O 2 m day at 10 km and 2.1

-2 -1 -2 -1 to 20 g O 2 m day at 19.5 km. NEM was 0.40 to 12 g O 2 m day at 10 km and -0.84 to 16 g

-2 -1 O2 m day at 19.5 km. GPP, ER and NEM had comparable ranges at both sites in July and

August, with higher estimates in June at 10 km compared to 19.5 km. The highest GPP, which

corresponded with the peak autotrophic state (highest NEM) was in July and exhibited a similar

range at both sites.

Nutrient Concentrations and Ratios

Orthophosphate concentrations had a lower range throughout the system in April, May and

July (0.09 to 1.2 µM) compared to June and August (1.0 to 4.6 µM), with the lowest and highest

OP occurring in the reservoir hypolimnion in April and August, respectively (Table 2). TP was

generally more consistent across sites and months however a large increase (1.7 to 6.3 µM)

occurred between July and August at 0.75 km that also corresponded with a clear downstream

decrease in the tailwater reaches.

Dissolved forms of nitrogen were generally low throughout the system (1.3 +/- 0.39 (SE) µM

+ + NH 4 ; 1.2 +/- 0.38 (SE) µM NO x). NH 4 did show a large 2 µM increase in June within the

hypolimnion and at 0.75 km, and an additional 4 µM increase in August in the hypolimnion. NO x exhibited a downstream decrease in May and June, and was extremely low in July (0.17 to 0.70

µM) (except for the high concentrations in the hypolimnion of the reservoir (8.4 µM)). TN was moderately low across sites and months (mean 27 +/- 2.7 (SE) µM) with the highest concentrations generally occurring in April and May. Ratios of dissolved nitrogen and phosphorus (DIN:OP) were low (0.3 to 16), while TN:TP had a much broader range (4 to 70).

Periphyton Biomass, Nutrient Content, and Community Composition

Periphyton biomass in June decreased downstream (Table 3), though all averages were at

densities considered to be eutrophic (> 10 µg chl a cm -2). A month later, the 19.5 km reach had extremely high biomass (>71 µg chl a cm -2), while the biomass at the 0.75 km and 10 km

reaches were comparable to those in June. By late summer, chl a decreased at 0.75 km and 19.5

km, but remained high at 10 km (31 µg chl a cm -2).

Seasonal and longitudinal patterns for AFDM paralleled those for chl a, with values of AFDM consistently exceeding 5 mg cm -2. The autotrophic index (AFDM:chl a) ranged between 212 to

419. These values are indicative of an assemblage dominated by algae compared to organic

matter (plus heterotrophic organisms) in the periphyton matrix (Wetzel 1979).

Particulate nutrients were relatively consistent for POC (226 +/- 19 SE µmole cm -2), PN (24

+/- 1.9 µmole cm -2) and TPP (1.6 +/- 0.14 µmole cm -2). However there were some minor spatial and temporal variations (Table 3). Particulate nutrients were low at 0.75 km in August and high at 19.5 km in July. Periphyton POC, PN, and TPP content were strongly correlated with each other as well as to AFDM and chla (Pearson’s r >0.90). The balance of these particulate constituents was relatively consistent across sites and months (C:P = 146 +/- 4.7; C:N = 9.1+/-

0.12; N:P = 16 +/- 0.53) and remained relatively close to the Redfield C:N:P (106:16:1).

Periphyton taxa varied spatially and temporally in the SFHR tailwater. Directly below the

SFR dam (0.75 km) the epilithic periphyton was largely composed of the filamentous chlorophyte, Cladophora , throughout the entire summer of 2009. Epiphytic diatoms- particularly

Cocconeis , Rhoicosphenia , and Diatoma - also comprised a large proportion of the periphyton biovolume in July and August at 0.75 km. The highest proportion of cyanobacteria occurred at

10 km. Heterocyst-forming filamentous genera, Nostoc and Calothrix , were dominat at 10 km in

June. Epithemia (a diatom genus which houses N 2-fixing symbionts) was found in high proportions at 10 km in July (25 to >50%) and August (>25%). The 19.5 km reach contained a large proportion of Cladophora in June, but became increasingly populated by diatoms, particularly Epithemia and Gomphoneis , throughout July and August.

Discussion

The SFR is a rather ‘young’ reservoir (ca. 20 years) and it appears that eutrophication processes

have developed over a relatively short time period. High concentrations of phosphorus from the

in-flow (1.5 µM TP), internal loading of phosphorus associated with the seasonally anoxic

hypolimnion (Nürnberg 1984), and mineralized nitrogen from N 2-fixing phytoplankton (Fritsen et al . 2010) subsequently provides the balance of nutrients needed to fuel extremely high productivity in this tailwater system. Uptake of these nutrients is rapid upon release into the

+ SFHR (e.g. 97% NO x, 91% NH 4 , and 70% OP taken up within 0.75 km in July), thus higher proportions of N2-fixing cyanobacteria in the downstream periphyton likely sustains high productivity and standing stocks of biomass in the lower reaches given adequate phosphorus supply.

Comparison of SFHR tailwater productivity to other semiarid streams

Our results corroborate previous investigations (Table 4) which have shown that high primary productivity occurs in streams in desert/semi-arid environments (see summary by Bunn et al. ,

2006). However, to the authors’ knowledge the current study is the first estimate of primary productivity in relatively low discharge, semi-arid tailwaters. Maximum rates of GPP in the

SFHR tailwater are comparable to those reported for small unregulated, semi-arid systems,

86 however, discharges in those systems are an order of magnitude lower (e.g. <0.10 m 3 sec -1). The increase in GPP with decreases in discharge has been reported in comparisons across biomes

(Lamberti and Steinman, 1997) and within a particular system (Acuña et al. , 2011). Thus, the

SFHR tailwater is exhibiting rather high GPP given relatively high discharge. The most comparable size semi-arid system (Upper Salmon River, Idaho, USA) has an order of magnitude

-2 -1 -2 -1 lower maximum GPP (1.6 g O 2 m day ) than the SFHR (15 to 36 g O 2 m day ). Hence, the

observed biomass and extensive production processes in the SFHR tailwater system invoke key

questions regarding the system attributes than can lead to extremely high primary production in a

lotic system.

Autotrophic assemblage types and biomass vary in these highly productive streams (Table 3).

These productive systems are characterized as having biomass contributions from various

periphyton patch-types (epipelic, epilithic, epiphyton), as well as macrophytes. Positive

correlations between autotrophic biomass and production have been reported in cross-system

metabolism studies (Bernot et al ., 2010), however the ultra-productive streams in our semiarid

system comparison (e.g. Chicamo, South Fork Humboldt) have the lowest standing stocks. The

apparent negative correlation between biomass and production rates could be attributed to higher

biomass-specific GPP for these ultra-productive systems. However, large quantities of loosely

attached, floating Cladophora -epiphyte mats were observed in the SFHR when GPP was highest

(July and August). Acuña et al. (2011) recently reported a large fraction of the GPP (up to 90%)

-2 -1 in a productive Pampean stream (22 g O 2 m day ) could be attributed to floating algal mats.

Similarly, despite loss of attachment and degraded appearance these floating mats accumulated

in low gradient sections of the SFHR and could have increased ecosystem GPP significantly.

Potential self-regulation and maximum production

There are probably few exogenous factors that limited the productivity and subsequent algal biomass accumulation in the SFHR system. The productivity, on areal basis, may be limited by the amount of available substrate (space). The lack of freshets (the flows and sediment subsequently mobilized by such events), equates to fewer disturbances due to scouring and thus allows for accumulation of loosely attached biomass that occupies the surface area of the stream and competes for resources (light, nutrients). Additionally, resource pools of dissolved inorganic carbon needed to maximize photosynthesis may be limiting in such thick algal mats (Hill and

Middleton 2006), as it becomes depleted throughout each daylight period. Replenishment of DIC pools could occur during night-time respiration, however at the cost of extreme depletion of the oxygen pool.

Hypoxia is a consistently over-looked factor that most certainly impacts the physiological condition of periphyton such that the self-imposed stresses of the dense algal growth are likely to occur as the nightly respiration depletes oxygen to extremely low levels for extensive periods

(e.g. less than 1 mg L -1 for 7 hours at 10 km in August). Dissolved oxygen minima are often not

reported in stream metabolism studies- especially when chamber methods are applied.

Neglecting to report or quantify these hypoxia events potentially excludes critical water quality

information that may be influencing metabolic rates. Moreover, information regarding the

varying effects of both low and high oxygen concentrations on periphyton metabolism is likely

needed to better understand self-regulation in these ultra-high productive systems.

The balance of nutrients in the periphyton and the water column has been used to identify the

possible resource limitations for algal growth (Redfield, 1958; Healey and Hendzel, 1980). The

balance of C:N:P within the periphyton are indicative of relatively homeostatic, near-balanced

88 nutrient conditions throughout the SFHR. Most C:P ratios were 90 to 185, which has been proposed by Hillebrand and Sommer (1999) to indicate an adequate nutrient balance within actively growing microalgal cells. All C:N ratios were similarly within or near the optimum range of 5 to 10 and N:P ratios were within or near the proposed optimum range of 13 to 22

(Hillebrand Sommer 1999). To attain optimum N:P ratios for maximum growth rates, the periphyton in downstream reaches are likely meeting required nutrients from processes within the biofilms (e.g. decomposition-recycling, N2-fixation). In contrast to the periphyton, the nitrogen:phosphorus balance of the SFR-SFHR system (based on the water column constituents) indicated a potentially nitrogen-limited system (N:P <16).

Several lines of evidence support the assertion that self-regulating mechanisms likely

controlled the maximum rate of production that was attained during our study period. First, the

lower reaches of the SFHR consistently supported Cladophora -epiphyte mats that were thick (20 to 60 cm) and extremely dense (>50 g AFDM m -2). Self-shading has been recognized and evaluated as a constraint on areal rates of photosynthesis of benthic algae (Higgins et al., 2008;

Dodds et al . 1999; Hill and Boston 1991) in several systems with similar attributes and biomass.

Vertical attenuation coefficients can be estimated through the estimation of diffuse absorption/scattering coefficients (Kirk 1994) and we applied a simplified version of the vertical attenuation of light, Kd(z) = ad(z), to attain a conservative estimate of light attenuation in the

SFHR periphyton mats at the time of the highest production rates (July). We estimated an normal absorption coefficient, a(PAR), in the SFHR periphyton mats by assuming a spectrally integrated optical absorption coefficient of 0.01 m2 mg chlorophyll a-1 (Davies-Colley et al.

1986) and a chlorophyll a volume of 792 mg m-3 (at 10 km) or 1224 mg m -3 (at 19.5 km) (based on average areal chlorophyll a density multiplied by depth (m)) to attain estimates of 7.9 m -1 and

-1 12.2 m for a(PAR). Next, we calculated the diffuse absorption coefficient, ad(z), by dividing the normal absorption coefficient by the average cosine of an equally diffuse down-welling light

-1 field, µd(z) (assuming θ = 45º, µd(z) = 0.53) (Kirk 1994). The Kd(z) was estimated at 15 m at

10 km and 23 m -1 at 19.5 km in July during the highest productivity period. The SFHR light attenuation estimates are comparable to those previously reported for Cladophora dominated mats (20 to 30 m -1, Higgins et al. 2006). Based on our conservative estimates, 2.7% and

0.0001% of down-welling irradiance reached the base of the SFHR periphyton mats at 10 km

and 19.5 km, respectively. Furthermore, earlier theoretical work by Nielsen (1957) estimated the

absolute maximum quantity of chlorophyll a in a photic layer (down to where the light is reduced to 1%) is 300 mg chlorophyll a m-2. It is of particular concern that this theoretical maximum biomass value is comparable to the present measures of chlorophyll a density in the SFHR

(Table 3) such that the biomass supported is likely to determine and help self-regulate the euphotic zone in this periphyton dominated system.

For self-regulation to occur in such systems, nutrients should be present in adequate supply to maintain the production and biomass accrual to the degree that internal self-regulating mechanisms occur. The nutrient balance in the water and periphyton indicated that nutrients are indeed utilized rapidly from the water column such that concentrations in the river below the hypolimnetic release become low- yet the balance of the macronutrients in the periphytic biomass indicates adequate nutrient supply to attain balanced growth.

In addition to self-regulation of biomass through self-shading mechanisms, gas utilization and exchange could have been a factor in determining the maximum production rate and the amount of biomass that could be sustained through any given day. Oxygen is known to compete with

CO 2 at the site of carbon fixation in the enzyme RUBISCO. Oxygen gas saturation values of ca.

250 % during the day may have led to competition for RUBISCO and the potential for ‘empty’ photosynthesis would have been high. Carbon concentrating mechanisms (CCMs) must be employed to mitigate such high DO/low DIC conditions, however studies are lacking that directly link the energetic and nutrient costs of CCMs to ecologically relevant processes such as periphyton productivity.

In summary, the SFHR system appears to have attained maximum production such that self- regulating mechanism became limiting given that we 1) observed 100% coverage of stream-bed surface area, 2) measured adequate nutrient ratios (C:N:P) based on periphyton nutrient content,

3) evaluated the high likelihood of self-shading based on our modeled light attenuation within periphyton mats which were comparable to previous studies of periphyton self-shading, and 4) showed that standing stocks of chlorophyll a in the SFHR are equivalent to the theoretical

maximum quantity of chlorophyll a m-2.

Identification of extremely productive reservoir-tailwater systems

It is difficult to speculate on the number of reservoir-river systems in existence that actually fit

the criteria for ideal characteristics that maximize productivity similar to that in the SFR-SFHR.

Developed countries have inventories of reservoirs in databases such as the National Inventory

of Dams (NID) compiled by the U.S. Army Corps of Engineers. General dam/reservoir

information such as physical features (e.g. storage, surface area) and regulatory purpose (e.g.

irrigation, hydroelectric) are available in the NID such that a query can identify candidate

reservoirs within the semi-arid regions of the U.S. However, information regarding low level

outlet or deep release operations in conjunction with nutrient conditions in the reservoir is

needed to anticipate whether reservoir releases are likely to support high rates of production in

the receiving tailwater reaches. Identifying the presence and operations of low level outlets is

91 not readily determined in the NID database. Furthermore, selection of mesotrophic-eutrophic reservoirs is also restricted due to the limited availability of water quality data that is typically provided by federal and state agencies for a given water-body. Nutrient concentrations in influent streams, if available, could also be analyzed as these have been shown to have considerable influence on the nutrient status of the receiving reservoir (Bott et al. 2006).

Watershed land-use can have a strong correlation with reservoir nutrient status (Jones et al .

2004) so quantifying land-use utilizing geographic information systems may be another approach for identifying candidate reservoir-tailwater systems that may provide the environmental setting downstream to maximize system primary production.

Acknowledgements

The authors are grateful to the Nevada Division of Environmental Protection for funding support and the Great Basin Community College for logistical support in completing this study. We thank the Nevada Division of State Parks for assisting with access to the sampling locations. Ken

McGwire assisted with addressing the expected biomass variance and related uncertainty in the periphyton sampling design. Thank you to Amy Boykin for helping us with sample processing in the field and lab.

References

Acuña V, Vilches C, Giorgi A.2011. As productive and slow as a stream can be–the metabolism of a Pampean stream. Journal of the North American Benthological Society 30 : 71–83. Aristegi L, Izagirre O, Elosegi A. 2009. Comparison of several methods to calculate reaeration in streams, and their effects on estimation of metabolism. Hydrobiologia 635 : 113–124. DOI: 10.1007/s10750–009–9904–8. Benenati EP, Shannon JP, Blinn DW, Wilson KP, Hueftle SJ. 2000. Reservoir–river linkages: Lake Powell and the Colorado River, Arizona. Journal of the North American Benthological Society 19 : 742–755. Bernot MJ, Sobota DJ, Hall RO, Mulholland PJ, Dodds WK, Webster JR, Tank JL, Ashkenas LR, Cooper LW, Dahm CN, Gregory SV, Grimm NB, Hamilton SK, Johnson SL, McDowell WH, Meyer JL, Peterson B, Poole GC, Valett HM, Arango C, Beaulieu JJ, Burgin AJ, Crenshaw C., Helton AM, Johnson L, Merriam J, Niederlehner BR, O’Brien JM, Potter JD, Sheibley RW, Thomas SM, Wilson K. 2010. Inter-regional comparison of land-use effects on stream metabolism. Freshwater Biology 55: 1874–1890. DOI: 10.1111/j.1365-2427.2010.02422.x Bott TL. 2006. Primary productivity and community respiration. In: Methods in Stream Ecology , 2nd edition, Hauer FR and Lamberti GA (eds). Elsevier: New York; 263– 290. Bott TL, Montgomery DS, Arscott DB, Dow CL. 2006. Primary productivity in receiving reservoirs: links to influent streams. Journal of the North American Benthological Society 25 : 1045–1061. Brock JT, Royer TV, Snyder EB, Thomas SA. 1999. Periphyton metabolism: a chamber approach. In The Controlled Flood in Grand Canyon , Webb RH, Schmidt JC, Marzolf GR, Valdez RA (eds). Geophysical Monograph 110; American Geophysical Union; 217–224. Bunn SE, Balcombe SR, Davies PM, Fellows CS, McKenzie–Smith FJ. 2006. Aquatic productivity and food webs of desert river ecosystems. In Ecology of Desert Rivers , Kingsford R. (eds). Cambridge University Press: Cambridge, UK; 76–99. Chester H, Norris R. 2006. Dams and flow in the Cotter River, Australia: effects on instream trophic structure and benthic metabolism. Hydrobiologia 572 : 275–286. DOI: 10.1007/s10750–006–0219–8 Clesceri LS, Greenberg AE, and Eaton AD. 1998. Standard Methods for the Examination of Water and Wastewater, 20 th ed. American Public Health Association, American Water Works Association, Water Environment Federation. Cushing CE, Wolf E.G.1984. Primary production in Rattlesnake Springs, a cold desert spring–stream. Hydrobiologia 114 :229–236. Davies-Colley RJ, Pridmore RD, and Hewitt JE. 1986. Optical properties of some freshwater phytoplanktonic algae. Hydrobiologia 133 :165–178. Diamond D. 2001. Determination of total phosphorus by flow injection analysis (Acid persulfate digestion method). QuikChem® Method 10–115–01–1–E:16. Lachat Instruments. Loveland, Colorado.

Dodds WK, Biggs BJ, Lowe RL. 1999. Photosynthesis-irradiance patterns in benthic microalgae: variations as a function of assemblage thickness and community structure. Journal of Phycology 35 :42–53. Elmore HL, West WF. 1961. Effects of water temperature on stream reaeration. Journal of the Sanitary Engineering 91 : 59–71. Fisher SG. 1995. Stream Ecosystems of the western United States. In River and Stream Ecosystems , Cushing CE and Cummins KW (eds). Elsevier Science: The Netherlands; 61–88. Fritsen CH, Davis CJ, Wirthlin ED, Smith DW, Momberg DK, Memmott JC. 2010. South Fork Reservoir and South Fork of the Humboldt River Reports to Nevada Department of Environmental Protection. Guildford SJ, Hecky RE. 2000. Total nitrogen, total phosphorus, and nutrient limitation in lakes and oceans: Is there a common relationship? Limnology and Oceanography 45 : 1213–1223. Hall RH, Tank JL. 2005. Correcting whole–stream estimates of metabolism for groundwater input. Limnology Oceanography Methods 3: 222–229. Healey FP, Hendzel LL. 1980. Physiological indicators of nutrient deficiency in lake phytoplankton. Canadian Journal of Fisheries and Aquatic Science 37 :442–453. Higgins SN, Hecky RE, Guildford SJ. 2006. Environmental controls on Cladophora growth dynamics in eastern Lake Erie: application of the Cladophora growth model (CGM). Journal of Great Lakes Research 32: 629–644. Higgins SN, Hecky RE, Guildford SJ. 2008. The collapse of benthic macroalgal blooms in response to self-shading. Freshwater Biology 53 : 2557–2572. Hill WR, Boston HL. 1991. Community development alters photosynthesis-irradiance relations in stream periphyton. Limnology and Oceanography 36 : 1375-1389. Hill WR, Middleton RG. 2006. Changes in carbon stable isotope ratios during periphyton development. Limnology and Oceanography 51 :2360–2369. Hillebrand H, Durselen CD, Kirschtel D, Pollingher U, Zohary T. 1999. Biovolume calculation for pelagic and benthic microalgae. Journal of Phycology 35 : 403–424. Hillebrand H, Sommer U.1999. The nutrient stoichiometry of benthic microalgal growth: Red– field proportions are optimal. Limnology and Oceanography 44 :440–446. Hornberger GM, Kelly MG. 1975. Atmospheric reaeration in a river using productivity analysis. Journal of Environmental Engineering 101 : 729–739. Jones JR, Knowlton MF, Obrecht DV, Cook EA. 2004. Importance of landscape variables and morphology on nutrients in Missouri reservoirs. Canadian Journal of Fisheries and Aquatic Sciences 61 : 1503-1512. Karl DM, Dore JE, Hebel DV, Winn C. 1991. Procedures for particulate carbon, nitrogen, phosphorus, and total mass analyses used in the US–JGOFS Hawaii Ocean time series program. In Marine Particles: Analysis and Characterization , Hurd DC, Spencer D (eds). American Geophysical Union, Geophyscial Monograph 63 : 71–77. Kirk JO. 1994. Light and Photosynthesis in Aquatic Ecosystems , 2 nd edition. Cambridge University Press: Cambridge, UK; 509 pp. Lamberti GA, Steinman AD. 1997. A comparison of primary production in stream ecosystems. Journal of the North American Benthological Society 16 : 95–104.

Liao N. 2002. Determination of orthophosphate in waters by flow injection analysis colorimetry. QuikChem® Method 10–115–01–1–M:17. Lachat Instruments. Loveland, Colorado. Lowe RL. 1979. Phytobenthic ecology and regulated streams. In The Ecology of Regulated Streams , Ward JV, Stanford JA (eds). Plenum Press: New York; 25–34. Minshall GW. 1978. Autotrophy in stream ecosystems. Bioscience 28 :767–771. Minshall GW, Peterson RC, Bott TL, Cushing CE, Cummins KW, Vannote RL, Sedell JR. Stream Ecosystem Dynamics of the Salmon River, Idaho: An 8 th -Order System. Journal of the North American Benthological Society 11 : 111–137. Mulholland PJ, Fellows CS, Tank JL, Grimm NB, Webster JR, Hamilton SK, Marti E, Ashkenas L, Bowden WB, Dodds WK, McDowell WH, Paul MJ, Peterson BJ. 2001. Inter–biome comparison of factors controlling stream metabolism. Freshwater Biology 46 : 1503– 1517. Munn MD, Brusven MA. 2004. The influence of Dworshak Dam on epilithic community metabolism in the Clearwater River, U.S.A. Hydrobiologia 513 : 121–127. Nielsen ES. 1957. The Chlorophyll Content and Light Utilization in Communities of Plankton Algae and Terrestrial Higher Plants. Physiologia Plantarum 10 : 1009–1021. Nürnberg GK. The prediction of internal phosphorus load in lakes with anoxic hypolimnia. Limnology and Oceanography 29: 111–124. Odum HT. 1956. Primary production in flowing waters. Limnology and Oceanography 1:102–117. Parson TR, Maita Y, Lalli CM. 1984. A Manual of Chemical and Biological Methods for Seawater Analysis, 1st ed. Pergamon Press: New York, New York. Pritzlaff P. 2000. Determination of nitrate/nitrite in surface and wastewaters by flow injection analysis. QuikChem® Method 10–107–04–1–C:15. Lachat Instruments. Loveland, Colorado. Prokopy WR. 2003. Determination of ammonia by flow injection analysis. QuikChem® Method 10–107–06–2–C:10. Lachat Instruments. Loveland, Colorado. Redfield AC. 1958. The biological control of chemical factors in the environment. American Scientist 46 : 205 Sater EM, Reuter JD, Goldman CR. 1994. Seasonal nutrient limitation at four high latitude, shallow reservoirs of the Tahoe Basin and Northern Nevada. University of California, Davis: Davis CA. Stevens LE, Shannon JP, Blinn DW. 1997. Colorado River benthic ecology in Grand Canyon, Arizona, USA: Dam, tributary, and geomorphological influences. Regulated Rivers: Research and Management 13 : 129–149. Tucker S, Jones D. 2007a. Determination of total nitrogen in manual persulfate digests. QuikChem® Method 10–107–04–4–B:26. Lachat Instruments. Loveland, Colorado. Tucker S, Jones D. 2007b. Determination of total phosphorus in manual persulfate digests. QuikChem® Method 10–115–01–4–B:16. Lachat Instruments. Loveland, Colorado. Tsivoglou EC, Neal LA. 1976. Tracer measurement of reaeration: III. Predicting the reaeration capacity of inland streams. Journal of the Water Pollution Control Federation 48 : 2669–2689.

Uehlinger U, Kawecka B, Robinson CT. 2003. Effects of experimental floods on periphyton and stream metabolism below a high dam in the Swiss Alps (River Spol). Aquatic Sciences 65 : 199–209. DOI: 10.1007/s00027–003–0664–7. Velasco J, Millian A, Vidal–Abarca MR, Suarez ML, Guerrero C, Ortega M. 2003. Macrophytic, epipelic, and epilithic primary production in a semiarid Mediterranean stream. Freshwater Biology 48 : 1408–1420. Ward JV, Stanford JA. 1979. Ecological factors controlling stream zoobenthos with emphasis on thermal modification of regulated streams. In The Ecology of Regulated Streams , Ward JV, Stanford JA (eds). Plenum Press: New York; 35–55. Welschmeyer N. 1994. Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnology and Oceanography 38 : 1985–1992. Wetzel RL. 1979. Periphyton measurements and applications. In Methods and measurements of periphyton communities , Wetzel RL (ed). American Society for Testing and Materials. ASTM STP 690:3–33.

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0 JFMAMJJASOND

90TH PERCENTILE 2009 MEAN MEDIAN 10TH PERCENTILE

Figure 1. Daily discharge statistics (USGS gauge 10320000) from 1988 to 2008 for the South Fork Humboldt River below reservoir. Arrows indicate timing of periphyton sampling and metabolism estimates.

Figure 2. Diel temperature, dissolved oxygen and dissolved oxygen saturation in the South Fork Humboldt River downstream of the reservoir.

Table 1. Site reaeration rates and associated metabolic rates (GPP, ER, NEM).

Distance

downstream -2 -1 -2 -1 -2 -1 Month Reaeration coefficient, day -1 GPP, g O m day ER, g O m day NEM, g O m day from dam 2 2 2 (km)

EDM Night EDM Night EDM Night EDM Night

June 10 26 17 21 16 12 9.2 9.4 6.9 19.5 11 7.5 6.3 5.1 3.8 3.8 2.5 1.2 July 10 21 12 24 14 12 8.4 12 5.7 19.5 3.2 11 15 36 8.1 20 7.3 16 August 10 3.4 8.6 5.1 11 4.7 10 0.40 0.91 19.5 1.1 11 3.6 12 2.1 13 1.5 -0.89

Table 2. Nutrients (micromolar) and ratios (mole:mole) in SFR –SFHR during spring and summer 2009.

Distance DIN:O Month downstream from TP TN OP NH + NO TN:TP 4 x P dam (km)

April -5.5 1.5 36 1.1 0.6 0.2 0.8 24 SFR Hypo 0.09 0.1 0.1 2.3 0.75 0.8 56 0.23 0.15 0.17 1.3 70 10.0 0.6 21 0.64 0.24 0.14 0.6 33 19.5 1.5 49 0.57 0.43 1.41 3.2 32

May -5.5 1.5 22 1.1 0.6 1.6 2.0 15 SFR Hypo 1.4 48 0.62 1.0 1.1 3.3 35 0.75 1.0 38 1.24 2.31 0.97 2.7 40 10.0 0.73 0.40 0.34 1.0 19.5 1.0 20 0.68 0.36 0.45 1.2 21

June -5.5 1.6 17 1.6 1.2 1.1 1.5 11 SFR Hypo 1.2 21 1.0 4.7 2.1 6.9 17 0.75 1.8 48 1.59 4.29 1.97 3.9 27 10.0 1.4 19 1.10 0.16 0.19 0.3 14 19.5 1.3 7 1.01 0.08 0.50 0.6 5

July -5.5 1.6 17 2.0 1.1 0.2 0.6 11 SFR Hypo 1.7 26 1.1 1.2 8.4 8.6 16 0.75 1.1 14 0.33 0.11 0.23 1.0 13 10.0 2.2 34 0.83 1.02 0.17 1.4 16 19.5 0.4 20 0.22 0.69 0.70 6.2 47

August -5.5 0.4 14 0.54 0.8 0.1 1.7 36 SFR Hypo 2.6 28 4.6 9.6 1.3 6.1 11 0.75 6.3 27 2.76 2.14 2.67 1.7 4 10.0 3.4 35 1.53 0.97 0.27 0.8 10 19.5 0.3 20 0.45 0.82 6.52 16.2 59

Table 3. Periphyton densities of biomass, particulate nutrients and ratios. Mean ± SE

Distance Autotrophic downstream Chla AFDM POC (µmole PN TPP Month N Index POC:TPP POC:PN PN:TPP from dam (µg cm -2 ) (mg cm -2 ) cm -2 ) (µmole cm -2 ) (µmole cm -2 ) (AFDM:Chla) (km) June 0.75 21 36 ± 7 5.8 ± 0.79 261 ± 68 223 ± 34 25 ± 3.5 1.6 ± 0.23 137 ± 7 8.8 ± 0.42 16 ± 0.95 10 22 29 ± 13 5.0 ± 1.9 247 ± 16 175 ± 66 17 ± 6.4 1.0 ± 0.43 175 ± 6 11 ± 0.24 17 ± 0.61 19.5 24 19 ± 4 3.5 ± 0.58 249 ± 23 117 ± 17 11 ± 1.5 1.0 ± 0.09 109 ± 11 10 ± 0.24 11 ± 0.92

July 0.75 24 29 ± 6 5.7 ± 1.3 212 ± 18 213 ± 48 25 ± 5.3 1.6 ± 0.37 145 ± 7 8.3 ± 0.16 18 ± 0.69 10 23 19 ± 2 5.9 ± 0.81 314 ± 18 213 ± 27 21 ± 2.4 1.4 ± 0.19 161 ± 7 10 ± 0.24 16 ± 0.72

19.5 23 71 ± 10 22 ± 3.2 320 ± 25 617± 99 56 ± 9.1 4.8 ± 0.71 137 ± 11 11 ± 0.39 12 ± 0.80

August 0.75 24 5 ± 1 1.7 ± 0.26 419 ± 48 60 ± 8 8.3 ± 1.1 0.51 ± 0.07 136 ± 26 7.5 ± 0.34 17 ± 2.7 100

10 24 31 ± 9 9.0 ± 2.3 311 ± 8 302 ± 79 37 ± 9.4 2.2 ± 0.60 148 ± 16 8.2 ± 0.11 18 ± 1.8 19.5 23 15 ± 2 5.3 ± 0.73 375 ± 20 173 ± 26 22 ± 3.3 1.0 ± 0.13 167 ± 23 7.4 ± 0.37 22 ± 2.9

Table 4. Summary of maximum rates of productivity reported in desert streams and tailwaters. Discharge at or near time of metabolism measurements unless otherwise indicated.

Maximum Stream Name, 3 -1 Autotrophic Biomass Stream Type Reference Productivity Q (m s ) Method Autotrophic Assemblage -2 Location -2 -1 (g carbon m ) (g O 2 m day )

Semiarid Velasco et al., Chamber, short-term Chicamo, Spain 84.5 0 to 0.07 Chara vulgaris 20 stream 2003 oxygen change

Epilithic cyanobacteria/chlorophyte 7.4

Epipelic diatoms 3.5

Total 31

South Fork Humboldt Semiarid Single-station, diurnal Current study 15 to 36 2 Cladophora, epiphytic diatoms 26 River, NV, USA tailwater oxygen change 101 Macrophytes na

Rattlesnake Springs, Semiarid Cushing & Two-station, diurnal 23.7 a 0.01 to 0.05 Periphyton 128 b Washington, USA stream Wolf, 1984 CO 2/pH change

Sycamore Creek, Mulholland et Two-station, diurnal Arid stream 15.04 0.03 Filamentous algae 94 b Arizona, USA al., 2001 oxygen change

Semiarid 0.06 to 0.7 Two-station, diurnal Deep Creek, ID, USA Minshall, 1978 10.2 a Periphyton, macrophytes na stream (annual mean) oxygen change

Upper Salmon River , Semiarid Minshall et al., 16 Chamber, diurnal 1.6 Diatoms 42 b ID, USA stream 1992 (base flow) oxygen change

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Chapter 5

Summary and Synthesis

Three observational studies improved the conceptual model for the dynamics of periphyton blooms in Great Basin rivers. Research highlighted a high degree of potential periphyton-nutrient interaction in Great Basin rivers that generates recurring, excessive blooms at various spatial and temporal scales. First, winter blooms of diatoms can appear in reaches with non-point or point source nutrient inputs due to slow but steady growth in conjunction with minimal losses (e.g. death, sloughing, herbivory), and subsequently that winter production can contribute appreciably to annual system energetics. Second, finer- scale nutrient inputs from vertical hyporheic exchange appear to have little direct influence on periphyton bloom dynamics in montane or semi-arid reaches of the Truckee

River. Finally, reservoir-tailwater systems in the semi-arid setting of the Great Basin provide the optimum environmental conditions (i.e. light, flow) that maximize periphyton-nutrient interactions such that productivity is maximized. Evaluating these periphyton bloom phenomena in various environmental contexts contributes critical information regarding the realized and potential impacts on Nevada rivers which are experiencing regime shifts.

Why are such “strong” periphyton-nutrient interactions apparent in Great Basin rivers?

Periphyton blooms have occurred in Great Basin rivers in the past, though the duration and magnitude of these blooms have likely shifted to an alternative state. The

103 environmental setting of Great Basin rivers has changed to a riverine landscape that is ideal for supporting excessive periphyton growth. Watershed topography combined with a legacy of modified riparian areas, disrupted hydrologic regimes, altered nutrient balances, and weakened trophic interactions have created in-stream habitat that favors extensive periphyton blooms in Great Basin rivers.

Relatively abrupt transitions in catchment topography (when combined with the associated climatic shifts) may provide the physical template that facilitates periphyton blooms in Great Basin rivers. Great Basin watersheds can typically be characterized as progressing rapidly from steep, constrained valleys in the mountains to lower gradient, unconstrained semi-arid reaches. Historically coarse bed-load (i.e. cobble, boulders) in these unregulated rivers would likely have been transported downstream with some regularity by bed-load moving floods caused by spring runoff from the mountains.

Cobble transported to the lower reaches provides a stable surface to support excessive periphyton growth (Cattaneo et al., 1997). Additionally, closer proximity to a montane water source increases the duration of wet periods in semi-arid reaches such that periphyton can grow and accumulate in more favorable light and temperature conditions located downstream. A larger watershed with greater distance between the montane and semi-arid reaches in the river network would limit the direct linkage between upper and lower catchments. Reduced linkage to bed-load material in the upper catchment could result in unstable sandy substrates in the lower catchment that limit periphyton production (Atkinson et al., 2008).

Hydrologic regimes in the past were likely the primary factor controlling periphyton dynamics in the Great Basin’s lotic systems via naturally occurring disturbance events.

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These unregulated flows probably displayed a wider variability with regard to the frequency, magnitude and duration of natural hydrologic events such as flooding and drought (Poff et al., 1997). Hydrologic events typically confine the temporal window allowed for the accumulation of periphyton growth, either by removing biomass during floods or stranding during droughts (Biggs, 1996).

Today the flows in most Great Basin rivers are largely regulated for human benefit, while at the same time improving habitat conditions for periphyton blooms. Downstream water-use is dependent on a steady supply year round, thus flows are often tightly regulated by adjusting releases from mountain reservoirs. Maintaining stable flows for extended periods (>100 days) allows time for extensive periphyton biomass accumulation

(Biggs, 1996). Also, flood control limits the disturbance capacity that could potentially scour periphyton communities, restricting the magnitude and duration of blooms.

Degradation of riparian zones along Great Basin rivers may also have improved in- stream conditions for periphyton blooms. Historically, riparian forests shaded low elevation reaches, however, land-use changes (e.g. urbanization, agriculture) and climate change have resulted in removal or degradation of riparian zones (Chambers and Miller

2004). Modified hydrologic regimes have impaired the life-history strategies of many riparian species (e.g. cottonwood) resulting in reduced recruitment. Reduction of the riparian canopy likely increased periphyton growth by improving the light conditions

(Hill, 1996) and elevating the water temperatures (DeNichola, 1996).

Prior to human settlement, periphyton in Great Basin rivers probably relied on episodic natural non-point sources of nitrogen and phosphorus. Terrestrial material from the surrounding landscape delivered along various flow-paths (e.g. overland, shallow

105 subsurface) during rain and snow-melt events provided a major source of nutrients.

These irregular loads of nitrogen and phosphorus were likely supplied for relatively short periods and probably did not support periphyton growth for extended periods. A more continuous natural source of phosphorus in Great Basin rivers is from the underlying and eroded soils from streambanks derived from P-rich granitic and volcanic rock (Alvarez and Seiler, 2004). Naturally high phosphorus concentrations enable periphyton taxa capable of nitrogen fixation (e.g. cyanobacteria or cyanobacteria symbionts) to thrive and contribute a biologically-derived source of nitrogen to periphyton in Great Basin rivers.

Biological nitrogen fixation is temperature sensitive, however, so this source of nitrogen is restricted to warm seasons (Marcarelli and Wurtsbaugh, 2006).

Humans have altered the nutrient regimes of Great Basin rivers to the point of almost continuous nutrient supply. Effluent discharges from wastewater treatment facilities represent a concentrated point source of nitrogen and phosphorus that originates from communities positioned throughout all elevations in the watershed. Furthermore, that effluent can become a non-point source when used as a water-source sprayed onto agricultural fields and municipal areas (Alvarez and Seiler, 2004). Reservoirs impose another potential point-source, particularly if managed using hypolimnetic releases that may be nutrient-rich due to biogeochemical reactions in the bottom sediments (Beutel and Horne, 1999). Non-point sources are numerous throughout some catchments as a result of run-off from surrounding land-use that includes golf courses, pasture, agriculture, and impervious surfaces in built environments. Current nutrient regimes in

Great Basin rivers are defined by multiple and, often, continual point inputs of nitrogen and phosphorus that can fuel recurring periphyton blooms.

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Top-down control of periphyton by higher trophic levels (e.g. grazing macroinvertebrates) was likely weakened with changes in the catchments of the Great

Basin. Life-histories that had evolved in these montane-arid systems were disrupted by changes to the hydrologic regime (Brittain and Saltveit, 1989). Thermal tolerances in lower reaches may have been exceeded as stream temperatures increased due to reduced riparian cover. An onslaught of pollution (e.g. nutrients, organic waste, toxins) has added additional stress to sensitive species, allowing the opportunity for more pollution tolerant species to thrive. Loss of efficient grazers, in particular, may have effectively released periphyton from a strong force of control. A subsequent feedback also may have developed where periphyton released from grazer control experience summer blooms, thereby creating hypoxic condition that further stress grazing invertebrate populations.

References

Alvarez, N.L., and R.L. Seiler. 2004. Sources of phosphorus to the Carson River upstream from Lahontan Reservoir, Nevada and California, water years 2001-02. Carson City, Nevada: U.S. Geological Survey. Atkinson, B.L., M.R. Grace, B.T. Hart, and K.E.N. Vanderkruk. 2008. Sediment instability affects the rate and location of primary production and respiration in a sand-bed stream. Journal of the North American Benthological Society 27:581-592. Beutel, M.W., and A.J. Horne. 1999. A review of the effects of hypolimnetic oxygenation on lake and reservoir water quality. Journal of Lake and Reservoir Management 15: 285-297. Biggs, B.J.F. 1996. Patterns in benthic algae of streams. Pages 31-56 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal ecology in freshwater benthic ecosystems. Academic Press, New York, New York. Brittian, J.E., and S.J. Saltveit. 1989. A review of the effect of river regulation on mayflies (Ephemeroptera). Regulated Rivers: Research & Management 3: 191-204. Catteneo, A., T. Kerimian, M. Roberge, and J. Marty. 1997. Periphyton distribution and abundance on substata of different size along a gradient of stream trophy. Hydrobiologia 354:101-110.

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DeNichola, D.M. 1996. Periphyton reponses to temperature at different ecological levels. Pages 149-181 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal ecology in freshwater benthic ecosystems. Academic Press, New York, New York. Hill, W. 1996. Effects of light. Pages 121-148 in R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal ecology in freshwater benthic ecosystems. Academic Press, New York, New York. Marcarelli, A.M. and W.A. Wurtsbaugh. 2006. Temperature and nutrient supply interact to control nitrogen fixation in oligotrophic streams: An experimental examination. Limnology and Oceanography 51: 2278-2289. Poff, N.L., J.D. Allan, M.B. Bain, J.R. Karr, K.L. Prestegaard, B.D. Richter, R.E. Sparks, and J.C. Stromberg. 1997. The natural flow regime. Bioscience 47:769-784.