CHANGES IN BENTHIC ALGAL COMMUNITY STRUCTURE FOLLOWING AN UNPREDICTABLE STREAM-WIDE DESICCATION EVENT

Theodore Bambakidis

A Thesis

Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

August 2009

Committee:

Rex L. Lowe, Advisor

J. Patrick Kociolek

Robert Huber

ii

ABSTRACT

Rex L. Lowe, Advisor

Global climate models predict future temperature and precipitation conditions that will increase the likelihood of unpredictable drought in currently perennially-flowing stream ecosystems. In this study, an experiment using artificial streams examined the impact that unpredictable desiccation and rehydration have on lotic periphyton community structure. 23 day-old periphyton communities were slowly desiccated and rehydrated over the course of two weeks, and changes in cell density and community composition were analyzed. Results indicated that a catastrophic loss of cell density occurred during desiccation, as most diatoms were eliminated and blue-green and green algal densities were severely depressed. The remaining desiccated periphyton community was dominated by blue-green, and to a lesser extent, green algae. After a

24-hour rewetting period, a 3-fold increase in cell density occurred and blue-greens continued to dominate the community. Immigration analysis indicated that immigrant cells could not have been solely responsible for the increase in cell density, suggesting that reproduction was more important during recovery. Cell health data revealed unique kingdom-specific responses to desiccation: diatom cells were empty, green algae exhibited some cellular damage, and blue- green algal cells were mostly healthy. The results of this study suggest that in streams that lack any history of seasonal desiccation, catastrophic loss of all periphyton occurs during drought, but blue-green and green algae are relatively better at surviving and recovering from desiccation than diatoms. iii

ACKNOWLEDGMENTS

This work would not have been possible without financial support from the University of

Michigan Biological Station (UMBS) and Bowling Green State University. I would like to thank the many people that helped me at different stages of this project: Troy Keller at Columbus State

University and UMBS for his helpful suggestions and logistical support at the stream lab;

Yangdong Pan at Portland State University, and Tom Neeson at the University of Michigan, for their patience and willingness to help me with NMDS and R; my fellow graduate students in the

Lowe Lab, Jen Ress and Meg Woller-Skar, for their helpful suggestions and valuable friendship.

I would also like to thank my committee members. Robert Huber taught an invaluable course on multivariate statistics, and ingrained in me the wonder and power of the philosophy of science.

Pat Kociolek spawned the idea for this project, and supported earlier fieldwork. I would also like to thank Pat for his encouragement, endless enthusiasm, and for posing questions rather than providing answers. Finally, I would like to thank my major advisor, Rex Lowe, for both helping and challenging me, and teaching me to become a better scientist. Thanks to him, I will forever

“think like a diatom!”

iv TABLE OF CONTENTS

Page

INTRODUCTION …………………………………………………………………………. 1

METHODS …………………………………………………………………...... 4

Study Site ………………………………………………………………………...... 4

Experimental Design ………………………………………………………………. 4

Artificial Streams …………………………………………………………... 4

Experimental Manipulations ……………………………………………….. 5

Sampling …………………………………………………………………… 6

Laboratory Analysis ………………………………………………………………... 6

Data Analysis ………………………………………………………………………. 8

RESULTS ………………………………………………………………………………….. 10

Changes in Cell Density ……………………………………………………………. 10

Changes in Community Composition ……………………………………………… 11

Relationships Among Samples …………………………………………………….. 12

Relationships Between Samples and Species ……………………………………… 13

Immigration ………………………………………………………………………… 13

DISCUSSION …………………………………………………………………………….... 15

Desiccation Effects ………………………………………………………………… 15

Changes in Cell Density ……………………………………………………. 15

Changes in Community Composition ……………………………………… 17

Diatoms …………………………………………………………….. 17

Soft-bodied Algae ………………………………………………….. 19 v

Recovery …………………………………………………………………………… 21

Conclusions ………………………………………………………………………… 24

LITERATURE CITED …………………………………………………………………….. 26

APPENDIX A. FIGURES AND TABLES ………………………………………………… 32

APPENDIX B. COMMUNITY DATA SET ………………………………………………. 41

vi

LIST OF FIGURES AND TABLES

Figure/Table Page

1 Map of the study site in northern Micigan, USA …………………………………... 32

2 Experimental design at the UMBS Stream Research Facility ……………………... 33

3 Range diagram of median cell density for control and treatment groups ………….. 34

4 Percent change in cell density of the dominant Healthy taxa in all samples ………. 35

5 Median relative abundance of the dominant Healthy periphyton taxa …………….. 36

6 Non-metric multidimensional scaling ordination plot of all samples with

species vectors ……………………………………………………………………... 37

7 Range diagram of median cell density of immigrants ……………………………… 38

8 Median relative abundance of immigrant taxa in each health class ……….. ………. 39

9 Proportional contribution of Healthy immigrants …………………………………. . 40

1

INTRODUCTION

Streams and rivers are spatially and temporally dynamic ecosystems. Their upstream dependence on both external (e.g. precipitation, snowmelt, allochthonous inputs) and internal

(e.g. flow dynamics, substrate movement, autochthonous production) abiotic and biotic processes make downstream habitats uniquely sensitive to upstream perturbations on a multitude of spatial and temporal scales. Spates are often considered to be a major abiotic perturbation that dramatically alters lotic communities (Resh et al. 1988). Such hydrological events can severely change substrate structure, shift flow patterns, and remove a majority of stream biota, effectively

“resetting” the stream community (Resh et al. 1988, Peterson and Stevenson 1992, Peterson

1996).

In contrast, desiccation events occur at the other extreme of the hydrological continuum, and the complete absence of surface moisture may make such an event more biologically destructive than its continuously-flowing counterpart. Such drought conditions deserve particular attention in the context of global climate change. The latest reports by the

Intergovernmental Panel on Climate Change showed recent reductions in winter alpine snowpack and annual rainfall concomitant with increases in mean terrestrial surface temperature and evapotranspiration rates for most of North America (IPCC 2007a, 2007b). Model simulations predict further decreases in northern hemisphere snow cover, alpine glacier volume, and subtropical and mid-latitude rainfall; and increases in heat waves, extreme storm events, and the frequency of heavy precipitation events.

These observed and predicted climactic changes have important implications for lotic ecosystems. One consequence of a warmer climate is the reduction in the proportion of precipitation that falls as snow (Vicuna and Dracup 2007). Many stream ecosystems depend 2 upon heavy winter snowfall to create a slowly-melting snowpack, which in turn maintains downstream discharge levels during warmer months. When this snowpack is perennially depleted and not adequately replenished by winter snowfall, stream discharge may be severely reduced and even subside by mid-summer. This phenomenon is already occurring with increased severity in Mediterranean and montane ecosystems (Miller et al. 2003). Although deciduous and boreal biomes historically lack distinct wet- and dry-seasons and are typically less reliant on alpine snowpack, they may also soon experience drought conditions. Increased temperature and evapotranspiration rates, combined with unpredictable and extreme weather events, may increase the likelihood of unpredictable drought in these biomes. Additionally, these expanded drought conditions are often exacerbated as expanding municipality and agricultural needs further draw upon freshwater resources.

Understanding the role of desiccation events in structuring lotic communities is therefore critically important to stream ecologists. While numerous studies have examined the fate of benthic macoinvertebrates during droughts (e.g. Boulton and Lake 1992, Closs and Lake 1994,

Stanley et al. 1994, Miller and Golladay 1996, del Rosario and Resh 2000, Boulton 2003), relatively few investigators have focused on stream primary producers (Peterson 1987, Benenati et al. 1998, Robson 2000, Mosisch 2001, Robson and Matthews 2003, Stanley et al. 2004,

Ledger et al. 2008). This paucity of research is particularly noteworthy given the recent shift toward developing Periphyton Indices of Biotic Integrity in water quality monitoring programs by federal, state, and local agencies in the United States (e.g. USGS National Water Quality

Assessment Program, USEPA Environmental Monitoring and Assessment Program; Lazorchak et al. 2000, Peck et al. 2001). As relatively immobile producers, benthic algae occupy a unique position between the abiotic physiochemical environment and the biotic community in stream 3 food webs. Consequently, their fate during physical disturbance events, such as desiccation, has direct implications for higher trophic levels and stream food webs in general. Thus, in anticipation of global climate change forecasts and in recognizing the increasingly important role of periphyton to water quality managers, information about the impact of desiccation on lotic benthic algal communities is critical.

The objectives of this study were to (i) examine the effect that a singular, unpredictable stream-wide desiccation event has on the periphyton community of a historically perenially- flowing ecosystem; and (ii) document any subsequent changes in the periphyton community when water is reintroduced. While perennial seasonal desiccation already occurs in arid and semi-arid lotic ecosystems, this study sought to understand how benthic algal communities will respond to a novel and unpredictable drought event in presently perennially-flowing systems because the increased likelihood of such a phenomenon is forecasted by future climate scenarios.

4

METHODS

Study Site

This experiment was conducted at the University of Michigan Biological Station Stream

Research Facility (UMBS-SRF) in northern lower Michigan, USA (45°33'49.39"N,

84°45'3.26"W; Figure 1). This region in the Upper Great Lakes lies within the northern deciduous and boreal forest transition zone, and is geologically characterized by post-glacial moraines and well-drained acidic sandy soils. Most forest cover is secondary growth due to widespread logging and burning in the early 20th century.

The UMBS-SRF is located along the East Branch of the Maple River, a first-order stream that drains the epilimnion of Douglas Lake from the Maple Bay outlet. This relatively pristine, low-gradient stream flows through secondary successional forests, contains a predominately sandy substrate, and is rich in tannic acid (Stevenson 1983, Pan and Lowe 1995). Almost the entirety of the upstream habitat flows within the protected UMBS nature preserve.

Experimental Design

Artificial Streams

Water from the East Maple River was pumped from the middle of the stream, through a pipe beneath a concrete pad at the UMBS-SRF, and was then returned downstream to the river.

Sixteen artificial stream channels were constructed using 2.75 m long polyvinyl chloride household rain gutters and placed less than 10 cm apart in the middle of the concrete pad (Figure

2). The streams were raised above the pad and evenly divided between two wooden tables.

Window screen was clipped to the top of the streams to simulate light attenuation found at more 5 deeply submerged benthic habitats. Additionally, a clear plastic sheet was placed approximately

45 cm above the channel surface to prevent rainwater infiltration and splash disturbance.

Seventeen 4.9 by 4.9 cm (24.01 cm2) unglazed ceramic tiles were placed in a row 10 cm apart in the center of each channel. A double-layer of women’s stockings were placed on the inlet pipe above each channel and were changed daily; these were used as filters to limit the importation of coarse and fine particulate organic matter and grazers. Flow commenced on July 2 2008 (Day 1) at a discharge of 100 cm3 s-1 in each channel and was sustained in all channels for 22 days.

During this time, the natural East Maple River flora colonized the ceramic tiles. By Day 22, a dense periphyton community was established on both the ceramic tiles and inter-tile (i.e. channel bottom) substrata.

Experimental Manipulations

Streams were divided into control and treatment groups (Figure 2). On Day 23, the discharge in treatment streams was decreased to approximately 70% of original discharge, to 70 cm3 x s-1, while control streams remained unchanged at 100 cm3 x s-1. The treatment group continued to experience a gradual decrease to approximately 30% of original discharge on Day 25, and a subsequent decrease to zero on Day 27. After the cessation of flow, the treatment channels were allowed to completely desiccate for 10 days, while the control group continued to experience a discharge of 100 cm3 x s-1. On Day 37, water was reintroduced to the desiccated treatment channels and slowly increased over a period of two hours to reach the initial (and control) discharge of 100 cm3 x s-1.

6

Sampling

Samples were collected from all streams at three times during the course of the experiment. On

Day 23, samples of the periphyton community were collected from each stream just before the first decrease in discharge (“Established”). The second sampling date occurred on Day 37, after the treatment group had experienced complete desiccation for 10 days (“Desiccated”). Finally, the last samples were collected on Day 38, approximately 24 hours after discharge resumed in the treatment channels (“Recovery”).

Tiles were sequentially numbered from 1 (upstream) to 17 (downstream) in each channel.

For each sample, four tiles were selected using a random number generator in an effort to minimize any effect that tile order had on the periphyton assemblages, and tiles 1 and 17 were always omitted from sampling. The four tiles were placed in an enamel pan, and all periphyton was removed using a toothbrush, razorblade, and squirt bottle filled with stream water. The scraped periphyton was then poured into a labeled 500 mL glass jar and immediately placed in a freezer for quick cooling.

Laboratory Analysis

At the conclusion of each sampling event, sample jars were removed from the freezer and preserved with 50% reagent grade glutaraldehyde solution to achieve a final sample concentration of approximately 2-3% glutaraldehyde solution. The preserved samples were then stored for further analyses at Bowling Green State University.

In the laboratory, the volume of each sample was measured to the nearest milliliter, poured into a half-gallon household blender, and blended for 15 seconds to homogenize the 7 sample and break apart any long filaments. Immediately after homogenization, approximately a

10 ml aliquot of sample was pipetted from the suspended sample into a 15 ml centrifuge tube.

The volume of the subsample was recorded to the nearest 0.1 ml, and it was then centrifuged for

10 minutes. After centrifugation, the supernatant glutaraldehyde solution was removed, deionized water was added, and the subsample was again centrifuged. This centrifuge-decant- rise cycle was repeated a minimum of 4 times to remove glutaraldehyde from the subsample.

The volume of the subsample after the final rinse cycle was recorded.

To aid in the identification of live algal cells, a second aliquot of material was removed from several samples. These aliquots followed the same rinse cycle detailed above, but were then boiled in concentrated nitric acid to remove all organic material. The resulting suspension of cleaned diatom frustules was rinsed and mounted on glass microscope slides using Naphrax® mounting medium. Diatoms were identified to species level using Krammer and Lange-Bertalot

(1986, 1988a, b, 1991), Patrick and Reimer (1966, 1975), Krammer (1997, 2002), and Siver et al.

(2005).

Each subsample was then agitated for approximately 10 seconds, and 0.01 ml was drawn and placed in a Palmer-Maloney nannoplankton counting chamber. Random fields of view were scanned until at least 600 cells were identified and enumerated to species level on an Olympus

BX-51 compound microscope at 400-800X magnification. Diatom taxa were identified using knowledge of the species composition from the fixed-medium analysis (above), and also Cox

(1996). Non-diatom taxa were identified using Prescott (1973), Prescott et al. (1975, 1977,

1981), and Komárek and Anagnostidis (1999, 2005).

Cleaned material was deliberately not used when analyzing community structure. While such fixed material is commonly used to identify diatoms, this procedure was avoided due to the 8 nature of this study. Specifically, it was particularly important to identify which diatoms and other algal taxa were still alive and bearing cytoplasm, and which were not, during the desiccation event. Only an approach that used uncleaned material could accurately reveal any differential tolerance or survival among algal taxa during desiccation.

Therefore, the health of every enumerated cell was evaluated by examining the protoplasmic content and color. Four categories were established to describe the relative health status of each cell. Those with >90% of their normal protoplasm (sensu Cox, 1996) were

“Healthy”. Cells with a slight reduction in protoplasmic content (50-90% of normal protoplasm) and/or with moderate discoloration were categorized as “Slightly-damaged”. Cells that exhibited a large reduction in protoplasm (10-49% of normal protoplasm) and/or major discoloration were categorized as “Constricted”. Finally, cells that had little or no protoplasmic content (<10% of normal protoplasm) were categorized as “Empty”.

To estimate the contribution of immigration to the recovery community, 1000 ml of influent stream water was collected from each treatment stream (n=8). Samples were settled, decanted, and concentrated, and the immigrant cells were identified and enumerated in the same manner as the collected benthic samples.

Data Analysis

Algal assemblage data were scaled and transformed from abundance data, cells x 0.1 ml-1, to cells x cm-2 (Appendix I). This was performed to standardize taxa densities on a per-area basis.

Kruskal-Wallis nonparametric analysis of variance was used to examine differences in total cell density between all treatment and control samples. Post hoc Nemenyi multiple comparison tests were used to reveal significant differences in median cell density between samples (α = 0.05, df 9

= 42, k = 6) (Zar 1999). The identical statistical tests were performed on the cell immigrant data to examine differences in cell density (cells x ml-1) between the four cell health classes (α = 0.05, df = 24, k = 4).

Non-metric multidimensional scaling (NMDS) was used on natural-log (ln x+1) transformed cell density data to examine the differences in algal assemblage structure between treatments and health classes by ordering all samples in 2-dimensional space based upon assemblage dissimilarity. NMDS was performed using the “Vegan” community ecology package for the R statistical computing program v. 2.8.1 on Macintosh OS 10.5.6 (function

“metaMDS”, Bray-Curtis distance measure, 300 iterations, 2 dimensions; Oksanen et al. 2008).

Analysis of Similarity (ANOSIM) was performed on the Bray-Curtis dissimilarity matrix to test whether species assemblages were significantly different based upon the a priori classification of samples into treatment groups. Vector-fitting correlations between species abundances and NMDS axis scores were performed to identify which species were most responsible for the underlying sample distances on the NMDS plot.

10

RESULTS

Changes in Cell Density

The density of cells in the benthos changed with time and by treatment over the course of the experiment. Median total cell densities (i.e. total of all health classes) were 2.8 x 107 and 2.7 x

107 cells x cm-2 for control and treatment established samples, respectively. After the desiccation event, controls experienced a slight decline in density, but treatments were significantly reduced to 8.7 x 105 cells x cm-2, a 31-fold decrease representing a 97% loss of median cell density

(Figure 3). After streams were rehydrated, treatment cell density rose to 3.0 x 106 cells x cm-2, a

3-fold increase representing a 240% gain in median cell density from the desiccated treatment samples (Figure 3).

Cell densities of individual taxa were analyzed to see if the decline in density affected some taxa more than others. The diatoms Fragilaria capucina var. mesolepta (Rabenhorst)

Rabenhorst and Staurosira construens Ehrenberg were completely absent in the desiccated samples and never returned during recovery, while Staurosira venter (Ehrenberg) Bukhtiyarova was nearly lost in desiccated samples and declined even more during recovery (Table 4). The dominant blue-green taxa Chroococcus sp. 1, Chroococcus sp. 2, Chroococcus sp. 3, and

Pseudanabaena catenata Lauterborn were not lost but did experience a major decline in cell density in desiccated samples (Table 4). Unlike the diatoms, however, the blue-greens

Chroococcus sp. 2 and P. catenata increased in cell density in the recovery samples (Table 4).

11

Changes in Community Composition

Although desiccated and recovery samples experienced a significant loss in cell density, it is important to determine if the relative proportion of taxa in the community changed between established, desiccated, and recovery samples. Established samples were dominated by the chain-forming diatoms S. construens, S. venter, and F. capucina v. mesolepta, with the blue- green taxa Chroococcus sp. 1, Chroococcus sp. 2, Chroococcus sp. 3, and P. catenata comprising a relatively smaller proportion of the community (Table 5). In desiccated samples, however, these diatom taxa were completely absent, and P. catenata behaved similarly by experiencing a six-fold decrease in median relative abundance between established and desiccated samples (median relative abundance = 18% and 3%, respectively; Table 5). In contrast, the coccoid blue-greens exhibited major increases in median relative abundance from established to desiccated samples, with more than a four-fold increase in Chroococcus sp. 1

(median relative abundance = 6% and 25%, respectively), more than a 13-fold increase in

Chroococcus sp. 2 (median relative abundance = 2% and 27%, respectively), and a five-fold increase in Chroococcus sp. 3 (median relative abundance = 3% and 15%, respectively) (Table

5).

The resumption of flow further altered the relative abundance of some taxa, but not others. The dominant diatoms remained absent in the recovery samples, but the filamentous blue-green P. catenata exhibited a 7-fold increase in relative abundance between desiccated and recovery samples (median relative abundance = 3% and 22%, respectively) (Table 5). The coccoid blue-greens Chroococcus sp. 1, Chroococcus sp. 2, and Chroococcus sp. 3 all 12 experienced a 2- to 3-fold decline in relative abundance between desiccated and recovery samples (Table 5).

Relationships Among Samples

Non-metric multidimensional scaling (NMDS) found a two-dimensional solution that explained

93% of the variance in the sample distance matrix (Figure 6). Samples were clustered based on control and treatment groups, cell health, and differences in cell density.

All controls clustered around the origin. Healthy and empty assemblages appeared to form distinct clusters, while slightly-damaged and constricted assemblages tended to intermix below Axis 1 (Figure 6).

Treatment groups responded differently according to health class. All empty assemblages clustered with their controls around the origin. Most constricted assemblages remained near the origin, but desiccated and recovery assemblages clustered farther away below

Axis 1. Healthy desiccated and recovery assemblages clustered away from the origin along negative Axis 1 and mostly above positive Axis 2, but established assemblages remained near the origin. Slightly-damaged desiccated assemblages clustered away from the origin along negative Axis 1 and Axis 2, but recovery assemblages were somewhat closer to the origin

(Figure 6).

Results from the ANOSIM indicated that desiccated and recovery treatment samples were significantly different from all controls and the established treatment group (p < 0.001).

13

Relationships Between Samples and Species

Axis 1 was driven primarily by the relative abundance of Achnanthidium minutissimum

(Kützing) Czarnecki (r = 0.89) and Chroococcus sp. 2 (r = - 0.59). Axis 2 was driven primarily by the relative abundance of Chroococcus sp. 1 (r = 0.57) and Geminella mutabilis (Brebisson)

Wille (r = -0.30). Correlations between NMDS axis scores and species abundance data revealed the taxa that were most associated with differences in sample distance (Figure 6). All empty assemblages, both treatment and control, were dominated by the diatoms A. minutissimum, S. construents, S. venter, Cyclotella ocellata Pantocsek, Cymbella excisiformis Krammer, F. capucina v. mesolepta, Cocconeis placentula Ehrenberg, and Planothidium frequentissimum var. rostratum (Ostrup) Lange-Bertalot. Treatment groups were associated with distinct suites of algal taxa depending on their health class. Slightly-damaged desiccated and recovery assemblages were both most associated with the green alga Mougeotia sp. 1. Constricted desiccated and recovery assemblages were both most associated with the green algae

Cladophora glomerata Linneaus (Kützing), G. mutabilis, and Ulothrix subtillissima Rabenhorst.

Healthy desiccated and recovery assemblages were most associated with the blue-green algae

Chroococcus sp. 1, Chroococcus sp. 2, Chroococcus sp. 3, Pseudanabaena catenata,

Merismopedia tenuissima Lemmermann, and Oscillatoria simplicissima Gomont (Figure 6).

Immigration

The median cell density of imported cells was 424 cells x ml-1. Classification of immigrants on the basis of cell health revealed that the density of empty cells (218 cells x ml-1) was significantly greater than healthy (57 cells x ml-1), slightly-damaged (53 cells x ml-1), and constricted (80 cells x ml-1) cells, respectively (Figure 7). Community composition also varied 14 with cell health. Blue-greens comprised the majority of healthy assemblages, while slightly- damaged, constricted, and empty classes were dominated by diatoms (Table 8).

To determine the role that immigration had in re-establishing the recovery community, immigration cell density was compared to the standing-crop benthic algal cell density. Although total immigrant cell density was 424 cells x ml-1, only 57 cells x ml-1 of the total were healthy, and hence only this subset could presumably successfully colonize and contribute to the recovery community. Accordingly, over the 24-hour recovery period a total of 4.88 x 108 healthy cells were imported into each stream. If we assume that (i) imported cells were evenly distributed across the entire wetted stream bottom, including submerged areas between the tiles, and (ii) all imported cells successfully attached to the benthos, then immigration added 3.62 x 105 cells x cm-2 to the standing-crop benthic algal community. Recall that an increase of 2.10 x 106 cells x cm-2 occurred from desiccated to recovery samples (Figure 3). Therefore, the added 3.62 x 105 cells x cm-2 immigrants accounted for only 17% of the observed increase in cell density from desiccated to recovery (Figure 9A). Similarly, recall that total standing-crop benthic algal density was 2.97 x 106 cells x cm-2 in recovery samples (Figure 3). Here, the additional 3.62 x

105 cells x cm-2 immigrants accounted for only 12% of the recovery standing-crop benthic algal cell density (Figure 9B).

15

DISCUSSION

Desiccation Effects

The results of this experiment suggest that an unpredictable desiccation event altered periphyton community structure. Both the cell density and community composition of treatment streams were significantly different relative to controls, and cell health classifications revealed unique responses at species and broader taxonomic levels.

Changes in Cell Density

Cell density peaked early in established samples and subsequently declined in desiccated and recovery samples for both treatments and controls. Treatment streams, however, exhibited a significant loss of cell density by nearly two orders of magnitude. Such a significant decline in cell density is often in response to hydrological shear stress during spates, and referred to as a sloughing event (Biggs and Thompson 1995). The present study, however, found a loss of periphyton in response to desiccation. Previous studies have shown that periphyton assemblages can respond to desiccation by being removed from the substratum (Peterson 1987, Mosisch

2001, Ledger et al. 2008). Ledger et al. (2008) found that loose mats of Melosira were sloughed off during the first year of repeated desiccation events, and were subsequently replaced by closely-adhering unicellular diatom taxa (e.g. Gomphonema spp.). Mosisch (2001) reported significant decreases in epilithic algal biomass and chlorophyll a during a desiccation experiment in a subtropical Australian stream. In this study, a group of adnate diatoms dominated the mature periphyton community, but became nearly absent in the desiccated streams. Unlike

Ledger et al. (2008), prostrate unicellular diatoms did not persist during the desiccation event.

Peterson (1987) found that diatom desiccation resistance largely depended upon the pre- 16 desiccation flow regime. Fast-current and slow-current assemblages were subjected to identical desiccation treatments. Fast-current assemblages showed little change in community structure, while slow-current assemblages exhibited a significant decrease in diatom biomass and density due to desiccation. Peterson (1987) argued that mucilage production might have played a role in desiccation resistance. Mucilage production has been found to aid in diatom immigration, binding, and cell accrual in fast-current habitats (Stevenson 1983, Peterson 1987, 1996a), and

Peterson (1987) reasoned that increased mucilage that is normally advantageous in fast-current habitats is also beneficial during desiccation because it increases water and nutrient retention.

Unfortunately, comparisons to this study are limited because Peterson (1987) failed to report the current velocities at which high mucilage production occurred.

While the loss of benthic algal biomass and cell density during desiccation has been documented in this study and others, the mechanism of this loss is poorly understood. Clearly, hydrological shear stress was not a factor in this study because discharge subsided, rather than increased, during the course of this experiment. One possible mechanism for periphyton loss during desiccation is algal drift. Previous studies have documented benthic algal drift in lotic ecosystems, but mostly in the context of diurnal periodicity in the abundance and taxonomic composition of drift flora (e.g. Müller-Haeckel 1976, Hamilton and Duthie 1987, Stevenson and

Peterson 1991). Early work by Blum (1954) attributed peak daytime drift activity to increased cell buoyancy from higher light intensity, photosynthetic rates, and oxygen bubble accumulation, although this hypothesis has since been challenged (e.g. Barnese and Lowe 1992). Other workers have suggested that grazer feeding activity and movement may promote drift by dislodging cells (Lamberti et al. 1987, Stevenson and Peterson 1989), and species-specific immigration, emigration, and successional processes may regulate algal drift (Stevenson and 17

Peterson 1991, McCormick and Stevenson 1991, Peterson 1996b). Although the present study did not sample stream drift, and therefore lacks any direct evidence for this mechanism of cell loss, drift still could have been played an important role in the desiccation response. Benthic algae may have been able to detect a deteriorating physical environment (e.g. decreased flow velocity, collapse of mat architecture, slow emersion) and responded by detaching and emigrating downstream in search of a more favorable (i.e. hydrated) habitat. To my knowledge, such an autogenic mechanism for desiccation-induced drift has neither been suggested nor investigated, and future desiccation studies should measure drift communities to see whether an increase in benthic algal drift occurs as streams slowly desiccate.

Changes in Community Composition

Diatoms

While a significant loss of cell density occurred during desiccation, not all algal taxa responded similarly. Overall, diatoms exhibited a greater decline in both cell density and relative abundance compared to soft-bodied algae. Health class data support this overall trend, as the relative abundance of healthy diatom species peaked in the established community, but subsequently declined to zero with the onset of desiccation. In contrast, constricted and empty diatom species peaked in relative abundance in desiccated and recovery samples. This shift in diatom health from live to dead cells represents a major die-off of diatoms during desiccation.

This is not surprising, as previous studies have suggested that diatoms have a low tolerance for desiccation. Douglas (1958) documented a severe decline in diatom abundance during prolonged drought in an English stream, and Peterson (1987) and Mosisch (2001) similarly found that diatom assemblages were unable to survive desiccation (Section i., this paper). 18

It is important to stress that although a growing body of literature has documented the apparent inability of lotic diatom assemblages to survive unpredictable desiccation, unique diatom floras are known to exist in dry habitats such as caves, river and lake spray zones, and dry rocks. Krasske (1929), for example, found that species of Eunotia, Melosira, and Navicula occur on dry rocks. Dry-habitat diatoms may also exhibit physiological adaptations to survive desiccation. For example, two species of Melosira, M. dickiei and M. roseana, possess thick inner plates (i.e. “innenschalen”) that may be an adaptation to prevent moisture loss (Koble

1932) or protect from increased salt concentration (Hustedt 1938). Additional adaptations by aerophilous diatoms include decreased cell size and copious oil storage (Patrick 1948). The present study, however, found neither aerophilic taxa nor any of the physiological adaptations reported by previous investigators. This may be due to the experimental nature of this study.

Drought-tolerant diatoms have been reported from samples collected in situ, where presumably a naturally occurring flora had existed in those dry habitats for some time. Conversely, this study subjected a perennial lotic periphyton community to desiccated conditions in order to see which, if any, taxa could survive. A plausible explanation is that not all diatoms (i.e. lotic taxa) possess physiological adaptations, such as innenschalen and high oil production, to persist during desiccation; or, if such changes could be triggered in any diatom, they do not arise under the experimental conditions of this study.

Previous investigators have stressed the importance of desiccation history in the response of periphyton to drought (Robson and Matthews 2004, Ledger 2008). Repeated desiccation events may restructure the periphyton community by selectively removing poorly attached and chain-forming diatoms, while simultaneously increasing the relative abundance of desiccation- tolerant taxa. Ultimately, periodic and predictable seasonal desiccation may create unique 19 assemblages that contain either desiccation survivalists, quickly recovering taxa, or both. Such assemblages may presently be endemic to arid and semi-arid ecosystems where perennial seasonal desiccation occurs, but absent from ecosystems experiencing consistent year-round discharge. This study was conducted in the latter ecosystem in an effort to examine the impact of an unpredictable desiccation event that is likely to occur according to future climate forecasts.

Consequently, this singular desiccation event prohibited any long-term selection of the periphyton community for survivalists, but instead found that lotic diatoms in perennially- flowing streams are unable to survive desiccation.

Soft-bodied Algae

Soft-bodied algae (i.e. blue-green and green algae) also exhibited a decline in cell density.

Unlike diatoms, however, blue-greens in particular were not completely removed from the benthos, and actually increased in relative abundance to comprise the majority of the remaining periphyton community. Specifically, coccoid blue-green taxa were a relatively small proportion of the healthy periphyton community in established samples, but increased greatly to account for over half of the healthy cells in desiccated samples. Filamentous green algae also appeared to survive desiccation better than diatoms, but were less healthy than blue-greens, dominating the slightly-damaged and constricted asemblages during desiccation.

Previous studies have shown that soft-bodied algae are able to survive desiccation events

(Benenati et al. 1998, Robson 2000, Robson and Matthews 2004). Blue-green algae, in particular, have been shown to be successful in high temperature and light environments, allowing them to out-compete diatoms and dominate periphyton assemblages (Vannote et al.

1980, Duncan and Blinn 1989). Blue-greens are also known to occupy extreme habitats such as 20 hot springs and hypersaline lakes (Komárek 2003), as well as subaerial environments such as seep walls and waterfall splash zones (Casamatta et al. 2006, Johansen et al. 2007, J. Ress unpublished data). These extreme habitats are not unlike a slowly drying benthic habitat, where the temperature rises, solutes concentrate, and moisture becomes limited.

Blue-green and green algae may be able to withstand drought conditions better than diatoms due to their unique morphological and physiological traits. The mat architecture of filamentous green algae, such as Cladophora glomerata (Linneaus) Kützing, enables them to retain moisture during desiccation (Usher and Blinn 1990, Blinn et al. 1995). Morison and

Sheath (1985) observed cell wall thickening in Klebsormidium rivulare (Kützing) Morison and

Sheath in an effort to reduce water loss. Davis (1972) provided a review on the ability of algae to survive desiccation. Green and blue-green algae showed the greatest resistance to desiccation by employing a variety of strategies, many of which include changes in pigmentation.

Carotenoid pigments in akinetes and resting cells, bluish vacuolar pigments in Zygnematalean green algae, and yellow, brown, or red mucilaginous sheaths in blue-greens all serve to reduce light intensity in high-light environments. Mucilaginous sheath formation is especially ubiquitous among the blue-green algae (Prescott 1973, Komárek 2003), which may help to slow the rate of drying (Davis 1972, Robson 2000). These strategies, however, were often found in algal “surviving structures” such as zygotes, akinetes, cysts, and propagules (but also vegetative cells). While the present study did not find any of these specialized structures, the observation of blue-green dominance and green algae tolerance during desiccation corroborates the findings of several investigators. For example, species of Oscillatoria survived desiccation for 5 to 7 days

(Hess 1962) and 88 years (Becquerel 1942) (Davis 1972). Mougeotia parvula Hassall (Evans 21

1959: unknown), Geminella terricola Petersen (Petersen 1935: 1 year) and Ulothrix species

(Bristol 1920: 24 weeks, Trainor 1970: 10 years) also survived desiccation (Davis 1972).

The absence of survival structures in the present study might be a result of the failure of the sampling regime to capture the time when these structures were being produced. Such structures might be found if submerged taxa were collected, slowly desiccated in the laboratory, and observed periodically to document the response over the course of hours to days. It should be noted, however, that many of the above studies were conducted in non-aquatic habitats such as soil, terrestrial leaf litter, and ephemerally hydrated substrata. Accordingly, the aforementioned responses to desiccation simply might not have occurred in this study. Rather, the lack of observable physiological changes in green algae and blue-green algae may be attributable to the absence of any previous desiccation history. Like innenschalen and copious mucilage production in subaerial diatom assemblages, green and blue-green assemblages in non- aquatic habitats may commonly produce pigments and enter resting stages as relatively normal strategies of coping with predictable, periodic desiccation. Without such a history of desiccation, however, lotic communities may not have the ability to immediately employ physiological responses to desiccation, or may lack them entirely.

Recovery

While the reintroduction of water in desiccated streams did not significantly alter periphyton cell density or community composition, some interesting changes were detected. Total cell density increased 3-fold in the 24-hour rehydration period, and an increase in cell density of healthy blue-greens, especially Chroococcus sp. 2 and Pseudanabaena catenata, and slightly-damaged and constricted green algae were largely responsible for this phenomenon. The failure of 22 diatoms to reappear during recovery and relative return of blue-greens suggests that soft-algae in general are not only better able to survive desiccation, but they can quickly recover once water returns to the habitat.

Algal recolonization can occur from two sources: immigration and reproduction.

Distinguishing between these two mechanisms of recolonization is important because the former process would produce a community that is relatively similar to the pre-desiccation community, while the latter would rebuild a community comprised of those taxa that survived desiccation. In this study, I attempted to differentiate between these two processes by collecting quantitative samples of the immigrant pool. Recall that a large number of immigrants entered the streams, but the significant majority of them were empty, dead cells. I assumed that only healthy immigrants could contribute to the periphyton community by successfully attaching to the benthos. This healthy subset of immigrants was dominated by blue-green algae, while unhealthy assemblages (i.e. slightly-damaged, constricted, and empty) were dominated by diatoms. If these healthy blue-green algae were the only immigrants that could presumably contribute to the recover community, then I would expect them to increase in cell density in the recovery benthic algal community. That is indeed what I found: an increase in blue-green cell density in the recovery samples.

Reproduction, in contrast, is more difficult to directly measure. Indirect evidence suggests that immigration was not the main source of the recovery community. First, the contribution of healthy immigrants comprised a small proportion of the recovery benthic algal community. Second, and perhaps more importantly, the cell density of healthy immigrants was a small fraction of the total increase in cell density from desiccated to recovery communities.

These results suggest that reproduction, rather than immigration, was primarily responsible for 23 the increase in cell density during recovery. Whether rapid reproduction only occurred in the newly attached immigrants, or in the benthic algae that survived desiccation, or both, is unclear.

Overall, both processes resulted in an increase in the density of blue-green algae.

Although benthic algal cell density increased after streams became hydrated, the recovery time of 24-hours might have been too short to reveal the full dynamics of recovery from desiccation. Previous studies have detected changes in community structure shortly after rewetting (Robson 2000), although must studies collected the first rewetted samples a week after the reintroduction of water (Robson and Matthews 2004). Robson (2000) observed active thalli of Stigonema and Hapalosiphon species that were capable of growth within 24 hours of rewetting in the laboratory, although it is unclear whether the investigator actually found an increase in cells or only rehydrated cells. Robson and Matthews (2004) observed a measurable periphyton response after one week of rehydration, and found that desiccated streams with wet pools responded more quickly than streams with dry pools, suggesting that pools serve as an important source of immigrants when flow resumes. A substantial amount of periphyton regrowth, however, may take much longer. After 18 weeks of rehydration, Benenati et al. (1998) found that periphyton biomass on previously desiccated rocks was only 35% of the controls, although the daily fluctuations in discharge of the Colorado River probably had a major influence on periphyton regrowth. Mosisch (2001) found that it would take at least 30 days for resubmerged diatom assemblages to recover to pre-desiccation levels.

Evidence of post-desiccation recovery of the benthic algal community is an important result of this experiment. It would have been informative, however, to extend the recovery time beyond 24-hours, perhaps to 7 days or more. Ideally, a long-term rehydration experiment would reveal exactly how periphytion communities reestablish following desiccation. Multiple 24 treatments of varying desiccation and rehydration lengths could be used to examine how benthic algal communities respond to and recover from desiccation, and these treatments could also be used predict the relationship between desiccation duration and the time needed for the community to recover. Such information would be extremely valuable to stream ecologists and watershed managers.

Finally, one of the most interesting results of this experiment was the different response to desiccation and recovery on a broad phylogenetic level. Three different kingdoms of organisms exhibited three distinct responses to desiccation (Figure 6). Diatoms (Stramenopila) appeared to be unable to survive desiccation. Green algae (Plantae) suffered during desiccation, but continued to persist. Finally, blue-green algae (Monera) appeared to be relatively successful at maintaining healthy cells, surviving desiccation, and reestablishing in the recovery community. These distinct responses may indicate ancient evolutionary differences in how organisms cope with extremes in moisture, light, and nutrients. These results will hopefully motivate other investigators to further explore this phenomenon, as studies from the molecular to ecological levels could reveal the mechanisms underlying the patterns in this study, and have important implications for organisms throughout the tree of life.

Conclusions

The results of this study suggest that unpredictable stream-wide desiccation alters benthic algal community structure by (i) removing a significant proportion of the benthic algal community; and (ii) shifting community composition from diatom to blue-green dominance. Furthermore, short-term recovery is (iii) dominated by blue-green algae, and (iv) driven more by reproduction than immigration. The loss of diatoms during desiccation and their failure to recover supports a 25 growing body of literature which suggests that aquatic diatoms are poorly adapted to withstand desiccation (e.g. Douglas 1958, Peterson 1987, Mosisch 2001, Ledger et al. 2008). Conversely, soft-bodied algae, particularly blue-greens, have been shown to be relatively tolerant of desiccation in lotic ecosystems (e.g. Davis 1972, Morison and Sheath 1985, Benenati et al 1998,

Robson 2000), and recover quickly when flow resumes.

As global climate change creates novel and unpredictable desiccation events in presently perennially-flowing streams, this study suggests that blue-green algae, and to a lesser extent green algae, may come to dominate benthic habitats. This is particularly concerning because stream food webs may seasonally shift from abundant, nutritious food sources (e.g. diatoms) to nutrient-poor, unpalatable food sources (e.g. blue-green and green algae). Further studies of stream-wide desiccation in presently perennially-flowing ecosystems are critically important to understanding how stream food webs will react to the first occurrence of seasonal desiccation.

Understanding the sequence and mechanisms of shifts in benthic algal community structure during both desiccation and rehydration will help prepare stream ecologists and watershed managers for the future management of increasingly precious and vulnerable freshwater ecosystems.

26

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32

APPENDIX A. FIGURES AND TABLES

1. Map of the study site in northern Michigan, USA.

A map of Michigan, USA showing the location (*) of the University of Michigan Biological Station Stream Research Facility (UMBS-SRF)

33

2. Experimental design at the UMBS Stream Research Facility.

The experimental design at the UMBS-SRF. Channels were numbered from 1-16 and alternated between control and treatment groups.

34

3. Range diagram of median cell density for control and treatment groups.

Range diagram of median cell density for control and treatment groups at each sampling time. Values are calculated from the total cell density of all four health classes. Different letters (e.g. a, b) indicate significant differences from the Kruskal-Wallis nonparametric analysis of variance and Nemenyi multiple comparison tests.

35

4. Percent change in cell density of the dominant Healthy taxa in all samples.

Established-Desiccated Desiccated-Recovery Chroococcus sp. 1 -98.8 -14.3 Chroococcus sp. 2 -98.0 68.7 Chroococcus sp. 3 -96.8 -15.4 Pseudanabaena catenata -99.9 569.5 Staurosira venter -99.6 -1.9 Fragilaria capucina var. mesolepta -100.0 0.0 Staurosira construens -100.0 0.0

These taxa occurred in ≥10% of all samples and ≥25% of each treatment subgroup.

36

5. Median relative abundance of the dominant Healthy periphyton taxa.

Established Desiccated Recovery All Samples Control Treatment Control Treatment Control Treatment Chroococcus sp. 1 10 (1-41) 6 (3-14) 10 (2-13) 4 (2-11) 25 (13-40) 13 (1-23) 13 (5-41) Chroococcus sp. 2 4 (1-66) 2 (1-6) 2 (1-2) 4 (2-11) 27 (2-67) 4 (2-22) 9 (5-14) Chroococcus sp. 3 6 (0-68) 3 (1-7) 3 (1-13) 2 (0-10) 15 (8-46) 2 (1-6) 7 (6-68) Pseudanabaena catenata 16 (1-40) 18 (2-31) 14 (8-35) 15 (5-19) 3 (1-6) 18 (8-29) 22 (5-40) Staurosira venter 10 (0-26 9 (2-22) 5 (0-11) 19 (7-23) 0 14 (4-26) 0 Fragilaria capucina v. mesolepta 8 (1-33) 8 (1-13) 7 (3-33) 5 (2-25) 0 14 (3-24) 0 Staurosira construens 12 (1-42) 11 (2-21) 12 (4-28) 21 (9-42) 0 8 (1-17) 0

Median relative abundance and range (in parentheses) of the dominant Healthy periphyton taxa in all samples. Values are further subdivided by sample time and treatment. These taxa occurred in ≥10% of all samples and ≥25% of subgroups.

37 6. Non-metric multidimensional scaling ordination plot of all samples with species vectors.

Non-metric multidimensional scaling ordination plot (samples in species space) of all samples coded by treatment group and health state. E = Established; D = Desiccated; R = Recovery. Capital letters (i.e. E, D, R) indicate treatment samples, and lowercase letters (i.e. e, d, r) indicate control samples. Color coding: green = Healthy; yellow = Slightly-damaged; brown = Constricted; grey = Empty. Blue vectors are the results of vector-fitting analysis. The vector points to the direction of the most rapid change in abundance, and the length of the vector is proportional to the correlation coefficient. Species abbreviations: “Pla ros” = Planothidium rostratum; “Fra mes” = Fragilaria capucina var. mesolepta; “Sta ven” = Staurosira venter; “Sta con” = Staurosira construens; “Cyc oce” = Cyclotella ocellata; “Cym exc” = Cymbella excisiformis; “Coc pla” = Cocconeis placentula; “Ach min” = Achnanthidium minutissimum; “Mou sp 1” = Mougeotia sp. 1; “Ulo sub” = Ulothrix subtilissima; “Gem mut” = Geminella mutabilis; “Cla glo” = Cladophora glomerata; “Osc sim” = Oscillatoria simplicissima; “Chr sp 2” = Chroococcus sp. 2; “LGB 2” = LGB 2; “Chr sp 1” = Chroococcus sp. 1; “Mer ten” = Merismopedia tenuissima; “Pse cat” = Pseudanabaena catenata. 38 7. Range diagram of median cell density of immigrants.

Range diagram of median cell density of immigrant cells separated into Health classes. Different letters (e.g. a, b) indicate significant differences from the Kruskal-Wallis nonparametric analysis of variance and Nemenyi multiple comparison tests.

39 8. Median relative abundance of immigrant taxa in each health class.

Healthy Median relative abundance (%) LGB 9 56 (44-63) Chroococcus sp. 2 36 (4-58) Chroococcus sp. 1 21 (12-96) Psuedanabaena catenata 9 (7-11) Scenedesmus quadricauda 5 (4-17)

Slightly-damaged Fragilaria capucina v. mesolepta 36 (13-59) Staurosira construens 24 (13-33) Cocconeis placentula 23 (7-30) Achnanthidium minutissimum 19 (6-58) Synedra rumpens 12 (7-25)

Constricted Fragilaria capucina v. mesolepta 15 (4-31) Achnanthidium minutissimum 14 (5-36) Staurosira construens 13 (6-34) Cocconeis placentula 12 (7-25) Gomphonema sp. 1 10 (4-16)

Empty Cyclotella ocellata 29 (21-34) Achnanthidium minutissimum 16 (9-42) Cocconeis placentula 16 (11-28) Staurosira venter 6 (1-8) Fragilaria capucina 4 (2-5)

Median relative abundance and range (in parentheses) of the most abundant immigrant taxa in each health class. These taxa occurred in ≥10% of all samples and ≥25% of subgroups. (Note: Medians were calculated separately and may not add to 100 in each health class).

40 9. Proportional contribution of Healthy immigrants.

The proportional contribution of Healthy immigrant cells to (A) the total gain in cell density from Desiccated to Recovery samples; and (B) the total cell density in Recovery samples.

41 APPENDIX B. COMMUNITY DATA SET

Median cell density of all taxa separated by sample, treatment, and health. Data are in cells x cm-2. "Sli-dam" = Slightly-damaged. Established-Control Healthy Sli-dam Constricted Empty Bacillariophyta (diatoms) Achnanthes lacunarum Hustedt Achnanthes rosenstockii Lange-Bertalot 42672 43163 Achnanthes submarina Hustedt Achnanthidium deflexum (Reimer) Kingston 44668 44637 Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki 33355 43670 42135 84309 Achnanthidium minutissimum (Kützing) Czarnecki 647607 333265 513203 1623402 Amphipleura pellucida (Kützing) Kützing 46030 45621 49516 66709 Amphora michiganensis Stoermer & Yang 43654 Amphora perpusilla Grunow 61345 41637 44668 49516 Aneumastus tuscula f. minor Andresen, Stoermer, & Kreis, Jr. Brachysira microcephala morphotype 2 (Grunow) Compere 38649 43654 41658 45144 Cavinula scutelloides (W. Smith) Lange-Bertalot Cocconeis placentula Ehrenberg 38649 81780 69378 373595 Cyclotella gamma Sovereign Cyclotella ocellata Pantocsek 214235 162641 302631 7678665 Cymatopleura solea (Brebisson) W. Smith Cymbella cistula (Ehrenberg) Kirchner 87307 38649 44161 Cymbella cuspidata Kützing 43670 Cymbella cymbiformis Agardh 154816 174614 45621 44668 Cymbella excisiformis Krammer 263017 183929 181966 91242 Cymbella laevis Nageli in Kützing Cymbella naviculiformis Auerswald 38649 38649 55688 Cymbella tumida (Brebisson in Kützing) Van Heurck Diatoma tenuis Agardh 232083 40660 45621 45144 Diatoma vulgaris Bory Diploneis oblongella (Naegeli in Kützing) Ross Encyonema auerswaldii Rabenhorst 38013 43654 Encyonema semilanceolatum Krammer 40660 53412 42672 Encyonema silesiacum (Bleisch) Mann 33355 Encyonopsis cesatii (Rabenhorst) Krammer 38649 43654 Epithemia turgida (Ehrenberg) Kützing Eucocconeis flexella (Kützing) Meister 41637 Eunotia bilunaris (Ehrenberg) Mills Eunotia implicata Norpel, Alles, & Lange-Bertalot Eunotia minor (Kützing) Grunow in Van Heurck Fragilaria capucina Desmazieres 581022 60060 164653 208187 Fragilaria capucina var. mesolepta (Rabenhorst) Rabenhorst 734323 147119 66709 160235 Gomphonema acuminatum Ehrenberg 76027 43654 45621 45621 Gomphonema angustatum var. sarcophagus (Gregory) Grunow 38649 40143 Gomphonema gracile Ehrenberg 44668 88045 72003 77297 Gomphonema intricatum Kützing Gomphonema parvulum (Kützing) Kützing 85344 43654 60982 62973 Gomphonema sp. 1 64945 41637 43654 66709 Gomphonema subclavatum (Grunow) Grunow 41637 Gyrosigma strigilis (W. Smith) Cleve Hippodonta capitata (Ehrenberg) Lange-Bertalot 40660 44668 76222 Hippodonta linearis (Ostrup) Lange-Bertalot, Metzeltin & Witkowski 42

Established-Control Healthy Sli-dam Constricted Empty Karayevia clevei (Grunow) Round and Bukhtiyarova 40660 52679 115946 Martyana sp. 1 43163 45144 Melosira varians Agardh 106823 Meridion circulare (Greville) Agardh 33355 Meridion circulare var. constrictum (Ralfs) Van Heurck 44668 44668 Navicula brockmannii Hustedt 33355 cf. Navicula cryptocephala Kützing 44161 48042 Navicula gastrum (Ehrenberg) Kützing 41637 41637 43383 Navicula radiosa Kützing 86305 42672 42672 44668 Navicula reinhardtii Lauby 41637 Navicula sp. 1 54173 36002 252928 Navicula trivialis Lange-Bertalot Neidium dubium (Ehrenberg) Cleve Neidium productum (W. Smith) Cleve Nitzschia acicularis (Kützing) W. Smith Nitzschia inconspicua Grunow 39011 Nitzschia paleacea Grunow 612471 247702 222207 180181 Nitzschia sp. 3 45621 48533 Pinnularia latevittata Cleve Plagiotropis lepidoptera var. proboscidea (Cleve) Reimer Planothidium frequentissimum var. magnum (Straub) Lange-Bertalot 43654 43153 Planothidium rostratum (Ostrup) Lange-Bertalot 44147 41658 64945 133307 Reimeria sinuata (Gregory) Kociolek & Stoermer 44668 Sellaphora disjuncta (Hustedt) Mann Sellaphora pupula (Kützing) Mereschkowsky 33355 Sellaphora rexii Potapova & Ponader 33355 Staurosira construens Ehrenberg 1273549 160235 87340 130709 Staurosira venter (Ehrenberg) Bukhtiyarova 839560 115868 98079 160235 Staurosirella pinnata (Ehrenberg) Williams & Round 46030 38649 43163 Staurosirella pinnata var. lancettula (Schumann) Siver & Hamilton 41637 44668 Stephanodiscus niagarae Ehrenberg Surirella biseriata Brebisson & Godey Synedra acus Ehrenberg 115946 33355 72003 67478 Synedra rumpens Kützing 110655 33355 44637 Synedra ulna (Nitzsch) Ehrenberg 98079 61996 40143 38649 Tabellaria fenestrata (Lyngbye) Kützing 40660 43654 55326

Chlorophyta (green algae) Ankistrodesmus falcatus (Corda) Ralfs 43654 Cladophora glomerata (Linnaeus) Kützing Closterium spp. (Nitzsch) 42135 Cosmarium spp. Corda 44147 44668 Euastrum lapponicum var. protuberans Prescott Geminella mutabilis (Brebisson) Wille 3816689 Haematococcus lacustris (Girod) Rostafinski Mougeotia sp. 1 (Agardh) Wittrock 43654 85344 53412 44668 Mougeotia sp. 3 (Agardh) Wittrock 46030 Mougeotia sp. 4 (Agardh) Wittrock 85344 182484 43

Established-Control Healthy Sli-dam Constricted Empty cf. Oedogonium inconspicuum Hirn 256033 480704 69378 48042 Oedogonium sp 1 Pediastrum boryanum (Turpin) Meneghini Pediastrum tetras (Ehrenberg) Ralfs Pleurotaenium sp 1 44637 Scenedesmus dimorphus (Turpin) Kützing 43654 Scenedesmus quadricauda (Turpin) Brebisson 87340 38649 Scenedesmus sp. 2 43654 Scenedesmus sp. 3 33355 Selenastrum minutum (Naegeli) Collins 43654 Spirogyra sp. 1 Staurastrum spp. (Meyen) 41637 Ulothrix subtilissima Rabenhorst 1014820 Ulothrix variabilis Kuetzing 2029640 102928 45621 106823 Zygnema sp. 1

Cyanophyta (blue-green algae) Anabaena sp. 2 Chroococcus sp. 1 Nageli 699023 Chroococcus sp. 2 Nageli 213646 Gloeocapsa sp. 1 Kützing Gomphosphaeria aponina Kützing Hapalosiphon intricatus West & West LGB 2 267058 LGB 9 961408 Merismopedia tenuissima Lemmermann 44668 Oscillatoria simplicissima Gomont Pseudanabaena catenata Lauterborn 2128060 Spirulina major Kützing

Chrysophyta (chrysophytes) Chlorellidiopsis separabilis Pascher 266837 Pleurogaster oocystoides Prescott 37496 44

Established-Treatment Healthy Sli-dam Constricted Empty Bacillariophyta (diatoms) Achnanthes lacunarum Hustedt Achnanthes rosenstockii Lange-Bertalot 45891 83924 Achnanthes submarina Hustedt Achnanthidium deflexum (Reimer) Kingston 30259 64908 Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki 47291 18555 43927 60661 Achnanthidium minutissimum (Kützing) Czarnecki 517956 309450 372730 1518327 Amphipleura pellucida (Kützing) Kützing 113145 47291 41962 Amphora michiganensis Stoermer & Yang 75200 37110 18555 Amphora perpusilla Grunow 90681 49267 47291 Aneumastus tuscula f. minor Andresen, Stoermer, & Kreis, Jr. 24515 Brachysira microcephala morphotype 2 (Grunow) Compere 49888 32923 54430 56572 Cavinula scutelloides (W. Smith) Lange-Bertalot Cocconeis placentula Ehrenberg 47291 41962 51932 330703 Cyclotella gamma Sovereign Cyclotella ocellata Pantocsek 282862 122574 269662 7397232 Cymatopleura solea (Brebisson) W. Smith 18555 Cymbella cistula (Ehrenberg) Kirchner 89253 44111 Cymbella cuspidata Kützing 33238 Cymbella cymbiformis Agardh 178449 91782 88222 73544 Cymbella excisiformis Krammer 157526 121321 169717 127692 Cymbella laevis Nageli in Kützing Cymbella naviculiformis Auerswald 47291 Cymbella tumida (Brebisson in Kützing) Van Heurck Diatoma tenuis Agardh 93182 49029 41962 71944 Diatoma vulgaris Bory Diploneis oblongella (Naegeli in Kützing) Ross Encyonema auerswaldii Rabenhorst 41962 18555 18555 Encyonema semilanceolatum Krammer 24515 37110 Encyonema silesiacum (Bleisch) Mann 31333 Encyonopsis cesatii (Rabenhorst) Krammer 30259 18555 18555 Epithemia turgida (Ehrenberg) Kützing Eucocconeis flexella (Kützing) Meister Eunotia bilunaris (Ehrenberg) Mills Eunotia implicata Norpel, Alles, & Lange-Bertalot 18555 Eunotia minor (Kützing) Grunow in Van Heurck Fragilaria capucina Desmazieres 156666 92776 120112 189165 Fragilaria capucina var. mesolepta (Rabenhorst) Rabenhorst 749888 251772 125886 169717 Gomphonema acuminatum Ehrenberg 40611 56572 51232 41501 Gomphonema angustatum var. sarcophagus (Gregory) Grunow 65092 37110 45891 Gomphonema gracile Ehrenberg 74221 90002 83924 140497 Gomphonema intricatum Kützing Gomphonema parvulum (Kützing) Kützing 71944 56572 55666 116128 Gomphonema sp. 1 37564 32923 47291 91782 Gomphonema subclavatum (Grunow) Grunow 33238 Gyrosigma strigilis (W. Smith) Cleve Hippodonta capitata (Ehrenberg) Lange-Bertalot 129497 67757 Hippodonta linearis (Ostrup) Lange-Bertalot, Metzeltin & Witkowski 45

Established-Treatment Healthy Sli-dam Constricted Empty Karayevia clevei (Grunow) Round and Bukhtiyarova 44111 45891 49029 Martyana sp. 1 45001 64749 56572 Melosira varians Agardh 113145 64749 49029 Meridion circulare (Greville) Agardh Meridion circulare var. constrictum (Ralfs) Van Heurck 64749 Navicula brockmannii Hustedt cf. Navicula cryptocephala Kützing 55169 41962 65058 Navicula gastrum (Ehrenberg) Kützing 21535 46591 Navicula radiosa Kützing 44111 74177 Navicula reinhardtii Lauby Navicula sp. 1 45891 184082 Navicula trivialis Lange-Bertalot Neidium dubium (Ehrenberg) Cleve Neidium productum (W. Smith) Cleve Nitzschia acicularis (Kützing) W. Smith Nitzschia inconspicua Grunow 24515 Nitzschia paleacea Grunow 713355 292951 206450 332222 Nitzschia sp. 3 275346 64749 50342 Pinnularia latevittata Cleve 24515 Plagiotropis lepidoptera var. proboscidea (Cleve) Reimer Planothidium frequentissimum var. magnum (Straub) Lange-Bertalot 56572 45891 83924 64749 Planothidium rostratum (Ostrup) Lange-Bertalot 56572 54430 35903 91402 Reimeria sinuata (Gregory) Kociolek & Stoermer 44111 Sellaphora disjuncta (Hustedt) Mann Sellaphora pupula (Kützing) Mereschkowsky 45891 44111 18555 Sellaphora rexii Potapova & Ponader 47291 37564 Staurosira construens Ehrenberg 1235109 269662 189165 371034 Staurosira venter (Ehrenberg) Bukhtiyarova 642188 169717 141874 210745 Staurosirella pinnata (Ehrenberg) Williams & Round 163419 45701 Staurosirella pinnata var. lancettula (Schumann) Siver & Hamilton 129497 88222 Stephanodiscus niagarae Ehrenberg 43037 Surirella biseriata Brebisson & Godey Synedra acus Ehrenberg 45001 45891 46570 60661 Synedra rumpens Kützing 50778 47291 30813 60756 Synedra ulna (Nitzsch) Ehrenberg 129497 73544 24515 47291 Tabellaria fenestrata (Lyngbye) Kützing 91782 45891

Chlorophyta (green algae) Ankistrodesmus falcatus (Corda) Ralfs 37110 Cladophora glomerata (Linnaeus) Kützing Closterium spp. (Nitzsch) 41962 Cosmarium spp. Corda 30259 Euastrum lapponicum var. protuberans Prescott Geminella mutabilis (Brebisson) Wille 275346 Haematococcus lacustris (Girod) Rostafinski Mougeotia sp. 1 (Agardh) Wittrock 47291 48160 56572 Mougeotia sp. 3 (Agardh) Wittrock 74221 Mougeotia sp. 4 (Agardh) Wittrock 98059 46

Established-Treatment Healthy Sli-dam Constricted Empty cf. Oedogonium inconspicuum Hirn 280275 41962 106840 137673 Oedogonium sp 1 Pediastrum boryanum (Turpin) Meneghini 56572 Pediastrum tetras (Ehrenberg) Ralfs Pleurotaenium sp 1 Scenedesmus dimorphus (Turpin) Kützing 54219 Scenedesmus quadricauda (Turpin) Brebisson 74221 34313 Scenedesmus sp. 2 18555 Scenedesmus sp. 3 41962 Selenastrum minutum (Naegeli) Collins Spirogyra sp. 1 Staurastrum spp. (Meyen) Ulothrix subtilissima Rabenhorst 1308753 545507 83924 125886 Ulothrix variabilis Kuetzing 888644 Zygnema sp. 1 37110

Cyanophyta (blue-green algae) Anabaena sp. 2 37110 Chroococcus sp. 1 Nageli 776393 Chroococcus sp. 2 Nageli 92279 Gloeocapsa sp. 1 Kützing 169717 Gomphosphaeria aponina Kützing 88222 Hapalosiphon intricatus West & West LGB 2 337566 47291 LGB 9 Merismopedia tenuissima Lemmermann 64018 Oscillatoria simplicissima Gomont Pseudanabaena catenata Lauterborn 1331534 Spirulina major Kützing

Chrysophyta (chrysophytes) Chlorellidiopsis separabilis Pascher Pleurogaster oocystoides Prescott 47

Desiccated-Control Healthy Sli-dam Constricted Empty Bacillariophyta (diatoms) Achnanthes lacunarum Hustedt 15185 24150 34373 Achnanthes rosenstockii Lange-Bertalot 27676 51330 24150 26099 Achnanthes submarina Hustedt Achnanthidium deflexum (Reimer) Kingston 24150 39963 Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki 22557 60739 Achnanthidium minutissimum (Kützing) Czarnecki 239321 214707 331475 1376483 Amphipleura pellucida (Kützing) Kützing 17672 36279 26771 Amphora michiganensis Stoermer & Yang 27442 15185 17672 17672 Amphora perpusilla Grunow 21426 34373 39517 87146 Aneumastus tuscula f. minor Andresen, Stoermer, & Kreis, Jr. 17672 17672 Brachysira microcephala morphotype 2 (Grunow) Compere 21643 25665 20668 26771 Cavinula scutelloides (W. Smith) Lange-Bertalot 26099 Cocconeis placentula Ehrenberg 25882 48556 321621 Cyclotella gamma Sovereign Cyclotella ocellata Pantocsek 47935 24907 37871 1591799 Cymatopleura solea (Brebisson) W. Smith 17186 Cymbella cistula (Ehrenberg) Kirchner 26099 54885 Cymbella cuspidata Kützing 17186 Cymbella cymbiformis Agardh 24150 17672 48299 26099 Cymbella excisiformis Krammer 17672 24150 56335 95114 Cymbella laevis Nageli in Kützing 17186 Cymbella naviculiformis Auerswald 27442 15185 37871 Cymbella tumida (Brebisson in Kützing) Van Heurck Diatoma tenuis Agardh 17672 25882 Diatoma vulgaris Bory Diploneis oblongella (Naegeli in Kützing) Ross Encyonema auerswaldii Rabenhorst 26099 27442 Encyonema semilanceolatum Krammer 33076 27909 Encyonema silesiacum (Bleisch) Mann 24150 26099 Encyonopsis cesatii (Rabenhorst) Krammer 25665 Epithemia turgida (Ehrenberg) Kützing Eucocconeis flexella (Kützing) Meister Eunotia bilunaris (Ehrenberg) Mills 35344 Eunotia implicata Norpel, Alles, & Lange-Bertalot Eunotia minor (Kützing) Grunow in Van Heurck Fragilaria capucina Desmazieres 389686 104396 30369 153989 Fragilaria capucina var. mesolepta (Rabenhorst) Rabenhorst 248202 88361 32371 61815 Gomphonema acuminatum Ehrenberg 39341 21886 28906 Gomphonema angustatum var. sarcophagus (Gregory) Grunow 25882 34373 34859 Gomphonema gracile Ehrenberg 17672 19810 34101 45554 Gomphonema intricatum Kützing Gomphonema parvulum (Kützing) Kützing 16428 25124 17186 34373 Gomphonema sp. 1 17672 24150 24150 51878 Gomphonema subclavatum (Grunow) Grunow Gyrosigma strigilis (W. Smith) Cleve Hippodonta capitata (Ehrenberg) Lange-Bertalot 21669 21669 25665 Hippodonta linearis (Ostrup) Lange-Bertalot, Metzeltin & Witkowski 48

Desiccated-Control Healthy Sli-dam Constricted Empty Karayevia clevei (Grunow) Round and Bukhtiyarova 77110 Martyana sp. 1 51330 15185 26099 Melosira varians Agardh Meridion circulare (Greville) Agardh Meridion circulare var. constrictum (Ralfs) Van Heurck Navicula brockmannii Hustedt cf. Navicula cryptocephala Kützing 21886 20425 39386 Navicula gastrum (Ehrenberg) Kützing 24150 27442 48299 Navicula radiosa Kützing 25882 25665 15185 53017 Navicula reinhardtii Lauby Navicula sp. 1 15570 20668 27442 132768 Navicula trivialis Lange-Bertalot Neidium dubium (Ehrenberg) Cleve Neidium productum (W. Smith) Cleve 17186 Nitzschia acicularis (Kützing) W. Smith 16428 Nitzschia inconspicua Grunow 20425 Nitzschia paleacea Grunow 73383 20911 34501 41863 Nitzschia sp. 3 Pinnularia latevittata Cleve 17672 Plagiotropis lepidoptera var. proboscidea (Cleve) Reimer 27442 Planothidium frequentissimum var. magnum (Straub) Lange-Bertalot 35344 20668 17672 Planothidium rostratum (Ostrup) Lange-Bertalot 27909 36036 17429 166851 Reimeria sinuata (Gregory) Kociolek & Stoermer 13954 Sellaphora disjuncta (Hustedt) Mann Sellaphora pupula (Kützing) Mereschkowsky 27909 27442 Sellaphora rexii Potapova & Ponader 13954 17672 Staurosira construens Ehrenberg 912988 161495 215587 351536 Staurosira venter (Ehrenberg) Bukhtiyarova 793755 365385 311199 380442 Staurosirella pinnata (Ehrenberg) Williams & Round 73521 30369 27442 35344 Staurosirella pinnata var. lancettula (Schumann) Siver & Hamilton 70689 25796 82327 20425 Stephanodiscus niagarae Ehrenberg 17186 Surirella biseriata Brebisson & Godey Synedra acus Ehrenberg 35102 15185 24907 Synedra rumpens Kützing 75373 26099 50219 25124 Synedra ulna (Nitzsch) Ehrenberg 35344 24150 26099 Tabellaria fenestrata (Lyngbye) Kützing 24150 24150

Chlorophyta (green algae) Ankistrodesmus falcatus (Corda) Ralfs Cladophora glomerata (Linnaeus) Kützing 30369 Closterium spp. (Nitzsch) 26099 14570 Cosmarium spp. Corda 13954 26099 Euastrum lapponicum var. protuberans Prescott Geminella mutabilis (Brebisson) Wille Haematococcus lacustris (Girod) Rostafinski Mougeotia sp. 1 (Agardh) Wittrock 22314 22314 17672 Mougeotia sp. 3 (Agardh) Wittrock 54885 Mougeotia sp. 4 (Agardh) Wittrock 49

Desiccated-Control Healthy Sli-dam Constricted Empty cf. Oedogonium inconspicuum Hirn Oedogonium sp 1 Pediastrum boryanum (Turpin) Meneghini 17672 Pediastrum tetras (Ehrenberg) Ralfs Pleurotaenium sp 1 Scenedesmus dimorphus (Turpin) Kützing 27442 Scenedesmus quadricauda (Turpin) Brebisson 52058 34692 26554 Scenedesmus sp. 2 Scenedesmus sp. 3 26099 Selenastrum minutum (Naegeli) Collins Spirogyra sp. 1 52198 Staurastrum spp. (Meyen) Ulothrix subtilissima Rabenhorst 326539 51559 17186 Ulothrix variabilis Kuetzing Zygnema sp. 1

Cyanophyta (blue-green algae) Anabaena sp. 2 Chroococcus sp. 1 Nageli 172087 Chroococcus sp. 2 Nageli 167031 30369 Gloeocapsa sp. 1 Kützing Gomphosphaeria aponina Kützing 78297 Hapalosiphon intricatus West & West LGB 2 102659 31393 LGB 9 83726 24150 Merismopedia tenuissima Lemmermann 36116 Oscillatoria simplicissima Gomont 153989 Pseudanabaena catenata Lauterborn 628231 Spirulina major Kützing

Chrysophyta (chrysophytes) Chlorellidiopsis separabilis Pascher Pleurogaster oocystoides Prescott 50

Desiccated-Treatment Healthy Sli-dam Constricted Empty Bacillariophyta (diatoms) Achnanthes lacunarum Hustedt 635 1642 Achnanthes rosenstockii Lange-Bertalot 975 975 Achnanthes submarina Hustedt 1950 805 Achnanthidium deflexum (Reimer) Kingston 1634 Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki 1626 1626 3010 Achnanthidium minutissimum (Kützing) Czarnecki 3174 5155 34322 89412 Amphipleura pellucida (Kützing) Kützing 1181 Amphora michiganensis Stoermer & Yang 1181 3692 2769 Amphora perpusilla Grunow 3692 3675 Aneumastus tuscula f. minor Andresen, Stoermer, & Kreis, Jr. Brachysira microcephala morphotype 2 (Grunow) Compere 1078 1788 Cavinula scutelloides (W. Smith) Lange-Bertalot 1269 Cocconeis placentula Ehrenberg 3692 1904 10187 Cyclotella gamma Sovereign Cyclotella ocellata Pantocsek 4723 1626 1626 177058 Cymatopleura solea (Brebisson) W. Smith Cymbella cistula (Ehrenberg) Kirchner 1497 1642 Cymbella cuspidata Kützing 2769 Cymbella cymbiformis Agardh 1642 4878 9555 Cymbella excisiformis Krammer 4878 5130 22917 Cymbella laevis Nageli in Kützing Cymbella naviculiformis Auerswald 2156 Cymbella tumida (Brebisson in Kützing) Van Heurck Diatoma tenuis Agardh 3692 3285 Diatoma vulgaris Bory Diploneis oblongella (Naegeli in Kützing) Ross Encyonema auerswaldii Rabenhorst 975 4700 Encyonema semilanceolatum Krammer 1642 3285 Encyonema silesiacum (Bleisch) Mann 1403 Encyonopsis cesatii (Rabenhorst) Krammer 975 Epithemia turgida (Ehrenberg) Kützing 225 Eucocconeis flexella (Kützing) Meister Eunotia bilunaris (Ehrenberg) Mills Eunotia implicata Norpel, Alles, & Lange-Bertalot Eunotia minor (Kützing) Grunow in Van Heurck 430 Fragilaria capucina Desmazieres 8951 14209 Fragilaria capucina var. mesolepta (Rabenhorst) Rabenhorst 4180 11227 49457 Gomphonema acuminatum Ehrenberg 1626 975 3823 Gomphonema angustatum var. sarcophagus (Gregory) Grunow 635 2769 Gomphonema gracile Ehrenberg 1634 3900 Gomphonema intricatum Kützing Gomphonema parvulum (Kützing) Kützing 1626 3692 2216 6286 Gomphonema sp. 1 1872 3807 Gomphonema subclavatum (Grunow) Grunow Gyrosigma strigilis (W. Smith) Cleve 3692 Hippodonta capitata (Ehrenberg) Lange-Bertalot 908 3010 Hippodonta linearis (Ostrup) Lange-Bertalot, Metzeltin & Witkowski 51

Desiccated-Treatment Healthy Sli-dam Constricted Empty Karayevia clevei (Grunow) Round and Bukhtiyarova 1269 1702 Martyana sp. 1 975 1626 1950 Melosira varians Agardh 1975 Meridion circulare (Greville) Agardh Meridion circulare var. constrictum (Ralfs) Van Heurck Navicula brockmannii Hustedt 1269 cf. Navicula cryptocephala Kützing 4667 1626 Navicula gastrum (Ehrenberg) Kützing 1309 2769 Navicula radiosa Kützing 975 3252 Navicula reinhardtii Lauby Navicula sp. 1 1626 975 1138 5168 Navicula trivialis Lange-Bertalot Neidium dubium (Ehrenberg) Cleve 1181 Neidium productum (W. Smith) Cleve Nitzschia acicularis (Kützing) W. Smith Nitzschia inconspicua Grunow 3692 Nitzschia paleacea Grunow 1300 1078 Nitzschia sp. 3 Pinnularia latevittata Cleve 3692 Plagiotropis lepidoptera var. proboscidea (Cleve) Reimer Planothidium frequentissimum var. magnum (Straub) Lange-Bertalot 975 1950 Planothidium rostratum (Ostrup) Lange-Bertalot 3309 Reimeria sinuata (Gregory) Kociolek & Stoermer 3285 Sellaphora disjuncta (Hustedt) Mann Sellaphora pupula (Kützing) Mereschkowsky Sellaphora rexii Potapova & Ponader Staurosira construens Ehrenberg 4875 15411 69625 Staurosira venter (Ehrenberg) Bukhtiyarova 3252 2925 6827 29909 Staurosirella pinnata (Ehrenberg) Williams & Round 635 3630 Staurosirella pinnata var. lancettula (Schumann) Siver & Hamilton 1642 1626 Stephanodiscus niagarae Ehrenberg Surirella biseriata Brebisson & Godey Synedra acus Ehrenberg 2769 2481 Synedra rumpens Kützing 451 1300 Synedra ulna (Nitzsch) Ehrenberg 3692 975 2359 Tabellaria fenestrata (Lyngbye) Kützing 2769 4669

Chlorophyta (green algae) Ankistrodesmus falcatus (Corda) Ralfs Cladophora glomerata (Linnaeus) Kützing 7385 3285 6360 3692 Closterium spp. (Nitzsch) Cosmarium spp. Corda 1498 975 1181 Euastrum lapponicum var. protuberans Prescott Geminella mutabilis (Brebisson) Wille 12674 2437 3402 3542 Haematococcus lacustris (Girod) Rostafinski 3692 Mougeotia sp. 1 (Agardh) Wittrock 2769 6569 5692 1626 Mougeotia sp. 3 (Agardh) Wittrock 7076 3582 Mougeotia sp. 4 (Agardh) Wittrock 2769 6569 4283 52

Desiccated-Treatment Healthy Sli-dam Constricted Empty cf. Oedogonium inconspicuum Hirn 2538 1269 2028 4502 Oedogonium sp 1 Pediastrum boryanum (Turpin) Meneghini Pediastrum tetras (Ehrenberg) Ralfs Pleurotaenium sp 1 Scenedesmus dimorphus (Turpin) Kützing 2769 Scenedesmus quadricauda (Turpin) Brebisson 2197 1497 Scenedesmus sp. 2 7385 Scenedesmus sp. 3 Selenastrum minutum (Naegeli) Collins Spirogyra sp. 1 Staurastrum spp. (Meyen) 3231 600 Ulothrix subtilissima Rabenhorst 47640 3488 635 Ulothrix variabilis Kuetzing 3173 Zygnema sp. 1

Cyanophyta (blue-green algae) Anabaena sp. 2 Chroococcus sp. 1 Nageli 8306 Chroococcus sp. 2 Nageli 4221 12017 Gloeocapsa sp. 1 Kützing 3692 Gomphosphaeria aponina Kützing 39702 Hapalosiphon intricatus West & West 3173 LGB 2 8415 635 635 LGB 9 3887 635 Merismopedia tenuissima Lemmermann 3252 Oscillatoria simplicissima Gomont Pseudanabaena catenata Lauterborn 2053 Spirulina major Kützing

Chrysophyta (chrysophytes) Chlorellidiopsis separabilis Pascher 1950 Pleurogaster oocystoides Prescott 53

Recovery-Control Healthy Sli-dam Constricted Empty Bacillariophyta (diatoms) Achnanthes lacunarum Hustedt 27132 31976 Achnanthes rosenstockii Lange-Bertalot 31770 29395 Achnanthes submarina Hustedt 31563 42505 Achnanthidium deflexum (Reimer) Kingston 27218 Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki 27175 27222 76322 Achnanthidium minutissimum (Kützing) Czarnecki 130956 330805 660205 2133316 Amphipleura pellucida (Kützing) Kützing 29601 40835 26946 42913 Amphora michiganensis Stoermer & Yang 29344 27226 31513 27218 Amphora perpusilla Grunow 31976 44860 27222 131507 Aneumastus tuscula f. minor Andresen, Stoermer, & Kreis, Jr. 31462 Brachysira microcephala morphotype 2 (Grunow) Compere 27132 27218 29597 Cavinula scutelloides (W. Smith) Lange-Bertalot 31462 Cocconeis placentula Ehrenberg 31462 29395 95156 362419 Cyclotella gamma Sovereign Cyclotella ocellata Pantocsek 44860 31976 123514 1830507 Cymatopleura solea (Brebisson) W. Smith Cymbella cistula (Ehrenberg) Kirchner 27226 19264 Cymbella cuspidata Kützing Cymbella cymbiformis Agardh 43214 54263 38212 27226 Cymbella excisiformis Krammer 63952 54452 94690 107987 Cymbella laevis Nageli in Kützing 31976 49633 Cymbella naviculiformis Auerswald 31513 24781 Cymbella tumida (Brebisson in Kützing) Van Heurck 27132 Diatoma tenuis Agardh Diatoma vulgaris Bory Diploneis oblongella (Naegeli in Kützing) Ross Encyonema auerswaldii Rabenhorst 31563 31563 31563 24781 Encyonema semilanceolatum Krammer 22430 27222 56558 29344 Encyonema silesiacum (Bleisch) Mann Encyonopsis cesatii (Rabenhorst) Krammer 27226 Epithemia turgida (Ehrenberg) Kützing 27132 Eucocconeis flexella (Kützing) Meister Eunotia bilunaris (Ehrenberg) Mills 25414 Eunotia implicata Norpel, Alles, & Lange-Bertalot 95928 Eunotia minor (Kützing) Grunow in Van Heurck 31976 Fragilaria capucina Desmazieres 140123 58469 53892 27132 Fragilaria capucina var. mesolepta (Rabenhorst) Rabenhorst 517141 139446 134847 214478 Gomphonema acuminatum Ehrenberg 45071 31563 31976 Gomphonema angustatum var. sarcophagus (Gregory) Grunow 27226 63952 29391 Gomphonema gracile Ehrenberg 56569 44678 Gomphonema intricatum Kützing 27218 Gomphonema parvulum (Kützing) Kützing 29597 31462 63952 Gomphonema sp. 1 22430 32877 27226 81524 Gomphonema subclavatum (Grunow) Grunow 27222 Gyrosigma strigilis (W. Smith) Cleve 27132 Hippodonta capitata (Ehrenberg) Lange-Bertalot 27218 27218 27226 Hippodonta linearis (Ostrup) Lange-Bertalot, Metzeltin & Witkowski 54

Recovery-Control Healthy Sli-dam Constricted Empty Karayevia clevei (Grunow) Round and Bukhtiyarova 27226 31513 29601 85558 Martyana sp. 1 43120 38528 31563 45027 Melosira varians Agardh 62923 22430 Meridion circulare (Greville) Agardh 58789 Meridion circulare var. constrictum (Ralfs) Van Heurck 22430 Navicula brockmannii Hustedt 54452 27218 cf. Navicula cryptocephala Kützing 29348 24828 47450 44860 Navicula gastrum (Ehrenberg) Kützing 24824 19264 Navicula radiosa Kützing 29597 19264 29395 19264 Navicula reinhardtii Lauby 31976 Navicula sp. 1 27132 51326 227735 Navicula trivialis Lange-Bertalot 22430 Neidium dubium (Ehrenberg) Cleve Neidium productum (W. Smith) Cleve Nitzschia acicularis (Kützing) W. Smith 22430 Nitzschia inconspicua Grunow 22430 Nitzschia paleacea Grunow 49562 56122 54452 43214 Nitzschia sp. 3 Pinnularia latevittata Cleve 31976 29348 Plagiotropis lepidoptera var. proboscidea (Cleve) Reimer 22430 Planothidium frequentissimum var. magnum (Straub) Lange-Bertalot 22430 27203 65107 Planothidium rostratum (Ostrup) Lange-Bertalot 27226 176039 Reimeria sinuata (Gregory) Kociolek & Stoermer 27175 Sellaphora disjuncta (Hustedt) Mann 27226 Sellaphora pupula (Kützing) Mereschkowsky 27132 Sellaphora rexii Potapova & Ponader Staurosira construens Ehrenberg 217868 512485 668449 818594 Staurosira venter (Ehrenberg) Bukhtiyarova 342338 680332 746119 762212 Staurosirella pinnata (Ehrenberg) Williams & Round 31976 29297 54452 Staurosirella pinnata var. lancettula (Schumann) Siver & Hamilton 27226 72555 26946 54350 Stephanodiscus niagarae Ehrenberg Surirella biseriata Brebisson & Godey Synedra acus Ehrenberg 63952 63952 54404 31462 Synedra rumpens Kützing 45542 85558 104235 92053 Synedra ulna (Nitzsch) Ehrenberg 22430 32877 Tabellaria fenestrata (Lyngbye) Kützing 31719

Chlorophyta (green algae) Ankistrodesmus falcatus (Corda) Ralfs 31462 Cladophora glomerata (Linnaeus) Kützing 65754 Closterium spp. (Nitzsch) Cosmarium spp. Corda 24781 25363 Euastrum lapponicum var. protuberans Prescott 31462 Geminella mutabilis (Brebisson) Wille Haematococcus lacustris (Girod) Rostafinski Mougeotia sp. 1 (Agardh) Wittrock 134581 157011 54492 27226 Mougeotia sp. 3 (Agardh) Wittrock 43191 Mougeotia sp. 4 (Agardh) Wittrock 54436 43191 55

Recovery-Control Healthy Sli-dam Constricted Empty cf. Oedogonium inconspicuum Hirn Oedogonium sp 1 Pediastrum boryanum (Turpin) Meneghini 108526 54436 Pediastrum tetras (Ehrenberg) Ralfs 31976 63952 Pleurotaenium sp 1 Scenedesmus dimorphus (Turpin) Kützing 23198 31462 Scenedesmus quadricauda (Turpin) Brebisson 96773 42913 31462 27218 Scenedesmus sp. 2 Scenedesmus sp. 3 Selenastrum minutum (Naegeli) Collins Spirogyra sp. 1 57792 Staurastrum spp. (Meyen) 31462 27218 Ulothrix subtilissima Rabenhorst Ulothrix variabilis Kuetzing 89721 Zygnema sp. 1

Cyanophyta (blue-green algae) Anabaena sp. 2 27218 Chroococcus sp. 1 Nageli 435487 Chroococcus sp. 2 Nageli 107784 Gloeocapsa sp. 1 Kützing Gomphosphaeria aponina Kützing 99353 Hapalosiphon intricatus West & West LGB 2 62923 LGB 9 488463 Merismopedia tenuissima Lemmermann 81677 Oscillatoria simplicissima Gomont Pseudanabaena catenata Lauterborn 530829 Spirulina major Kützing

Chrysophyta (chrysophytes) Chlorellidiopsis separabilis Pascher Pleurogaster oocystoides Prescott 56

Recovery-Treatment Healthy Sli-dam Constricted Empty Bacillariophyta (diatoms) Achnanthes lacunarum Hustedt 3224 4995 Achnanthes rosenstockii Lange-Bertalot 3224 Achnanthes submarina Hustedt 9990 Achnanthidium deflexum (Reimer) Kingston 4818 Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki 6583 17541 Achnanthidium minutissimum (Kützing) Czarnecki 8724 16709 117047 614881 Amphipleura pellucida (Kützing) Kützing Amphora michiganensis Stoermer & Yang 3224 3224 Amphora perpusilla Grunow 7120 4995 13054 Aneumastus tuscula f. minor Andresen, Stoermer, & Kreis, Jr. 7120 Brachysira microcephala morphotype 2 (Grunow) Compere 4479 11862 Cavinula scutelloides (W. Smith) Lange-Bertalot Cocconeis placentula Ehrenberg 4818 18948 85093 Cyclotella gamma Sovereign 7120 Cyclotella ocellata Pantocsek 4741 29642 665932 Cymatopleura solea (Brebisson) W. Smith Cymbella cistula (Ehrenberg) Kirchner 5307 4995 Cymbella cuspidata Kützing Cymbella cymbiformis Agardh 24974 34396 Cymbella excisiformis Krammer 44953 63975 Cymbella laevis Nageli in Kützing 7120 7120 7391 Cymbella naviculiformis Auerswald 4741 7256 Cymbella tumida (Brebisson in Kützing) Van Heurck Diatoma tenuis Agardh Diatoma vulgaris Bory 3224 Diploneis oblongella (Naegeli in Kützing) Ross 3190 Encyonema auerswaldii Rabenhorst 3224 6379 Encyonema semilanceolatum Krammer 4479 4479 Encyonema silesiacum (Bleisch) Mann Encyonopsis cesatii (Rabenhorst) Krammer 5857 Epithemia turgida (Ehrenberg) Kützing Eucocconeis flexella (Kützing) Meister Eunotia bilunaris (Ehrenberg) Mills Eunotia implicata Norpel, Alles, & Lange-Bertalot Eunotia minor (Kützing) Grunow in Van Heurck 4995 4610 Fragilaria capucina Desmazieres 6720 22920 Fragilaria capucina var. mesolepta (Rabenhorst) Rabenhorst 12386 37896 117039 Gomphonema acuminatum Ehrenberg 6058 13440 Gomphonema angustatum var. sarcophagus (Gregory) Grunow 7234 8144 Gomphonema gracile Ehrenberg 5721 12894 Gomphonema intricatum Kützing 6720 7120 Gomphonema parvulum (Kützing) Kützing 3190 13440 22157 Gomphonema sp. 1 7120 40481 Gomphonema subclavatum (Grunow) Grunow Gyrosigma strigilis (W. Smith) Cleve Hippodonta capitata (Ehrenberg) Lange-Bertalot 3851 5594 Hippodonta linearis (Ostrup) Lange-Bertalot, Metzeltin & Witkowski 3224 57

Recovery-Treatment Healthy Sli-dam Constricted Empty Karayevia clevei (Grunow) Round and Bukhtiyarova 4955 6920 Martyana sp. 1 8986 4972 9483 Melosira varians Agardh 9569 3207 Meridion circulare (Greville) Agardh 3224 Meridion circulare var. constrictum (Ralfs) Van Heurck 6720 Navicula brockmannii Hustedt cf. Navicula cryptocephala Kützing 9483 6066 Navicula gastrum (Ehrenberg) Kützing 3224 5594 Navicula radiosa Kützing 4479 8958 Navicula reinhardtii Lauby Navicula sp. 1 4479 37309 Navicula trivialis Lange-Bertalot 4995 Neidium dubium (Ehrenberg) Cleve Neidium productum (W. Smith) Cleve Nitzschia acicularis (Kützing) W. Smith Nitzschia inconspicua Grunow 7120 Nitzschia paleacea Grunow 3190 3224 7120 Nitzschia sp. 3 Pinnularia latevittata Cleve 4479 Plagiotropis lepidoptera var. proboscidea (Cleve) Reimer Planothidium frequentissimum var. magnum (Straub) Lange-Bertalot 4972 13438 Planothidium rostratum (Ostrup) Lange-Bertalot 3224 14613 Reimeria sinuata (Gregory) Kociolek & Stoermer 6193 Sellaphora disjuncta (Hustedt) Mann 8958 Sellaphora pupula (Kützing) Mereschkowsky 5172 Sellaphora rexii Potapova & Ponader 4479 Staurosira construens Ehrenberg 8958 33190 91812 181462 Staurosira venter (Ehrenberg) Bukhtiyarova 3190 17963 64282 122238 Staurosirella pinnata (Ehrenberg) Williams & Round 4741 9483 19472 Staurosirella pinnata var. lancettula (Schumann) Siver & Hamilton 4741 11591 19341 Stephanodiscus niagarae Ehrenberg Surirella biseriata Brebisson & Godey 7120 4479 Synedra acus Ehrenberg 14782 4610 7120 4995 Synedra rumpens Kützing 4868 7391 Synedra ulna (Nitzsch) Ehrenberg 4479 7391 14782 Tabellaria fenestrata (Lyngbye) Kützing 6720

Chlorophyta (green algae) Ankistrodesmus falcatus (Corda) Ralfs Cladophora glomerata (Linnaeus) Kützing 9888 Closterium spp. (Nitzsch) Cosmarium spp. Corda 4610 4868 Euastrum lapponicum var. protuberans Prescott Geminella mutabilis (Brebisson) Wille 23707 9483 Haematococcus lacustris (Girod) Rostafinski 4479 Mougeotia sp. 1 (Agardh) Wittrock 8958 21970 11715 Mougeotia sp. 3 (Agardh) Wittrock 15466 6720 Mougeotia sp. 4 (Agardh) Wittrock 7120 13179 13567 58

Recovery-Treatment Healthy Sli-dam Constricted Empty cf. Oedogonium inconspicuum Hirn 20089 4972 7391 19341 Oedogonium sp 1 7391 7391 Pediastrum boryanum (Turpin) Meneghini Pediastrum tetras (Ehrenberg) Ralfs Pleurotaenium sp 1 Scenedesmus dimorphus (Turpin) Kützing Scenedesmus quadricauda (Turpin) Brebisson 6066 6379 6379 Scenedesmus sp. 2 Scenedesmus sp. 3 Selenastrum minutum (Naegeli) Collins Spirogyra sp. 1 Staurastrum spp. (Meyen) Ulothrix subtilissima Rabenhorst 18965 40501 4868 9577 Ulothrix variabilis Kuetzing 18965 Zygnema sp. 1

Cyanophyta (blue-green algae) Anabaena sp. 2 Chroococcus sp. 1 Nageli 7120 9990 Chroococcus sp. 2 Nageli 7120 7391 Gloeocapsa sp. 1 Kützing 7256 Gomphosphaeria aponina Kützing 28482 Hapalosiphon intricatus West & West LGB 2 7120 7120 LGB 9 18965 9483 3224 Merismopedia tenuissima Lemmermann 9569 Oscillatoria simplicissima Gomont 40649 39958 Pseudanabaena catenata Lauterborn 13743 Spirulina major Kützing 9990

Chrysophyta (chrysophytes) Chlorellidiopsis separabilis Pascher Pleurogaster oocystoides Prescott