NITROGEN RECYCLING in the CHOWAN RIVER 1 Donald W

NITROGEN RECYCLING IN THE CHOWAN RIVER

Donald W. Stanley 1 , Research Associate, Zoology John E. Hobbie 2 , Professor of Zoology

Department of Zoology N.C. State University Raleigh, N. C. 27607

I Present address: Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina 27514. 3 LPresent address: The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543.

The work upon which this publication is based was supported by funds provided by the Office of Water Research and Technology, U.S. Department of the Interior, through The University of North Carolina Water Resources Research Institute, as authorized under the Water Resources Research Act of 1964, as amended.

Project No. B-077-NC Agreement No. 14-31-0001-5097 December, 1976

TABLE OF CONTENTS Page ACKNOWLEDGMENTS ...... iv ABSTRACT ...... v LISTOFFIGURES ...... vi LIST OF TABLES ...... viii SUMMARY AND CONCLUSIONS ...... ix RECOMMENDATIONS ...... xiii

INTRODUCTION ...... a*.... 1 A.Background...... , 1 B . Objectives and Research Plan ...... 2 C . The Chowan River and Its Drainage Basin ...... 3 METHODS ...... 9 A.Sampling ...... 9

B . Carbon andt Nitrogen Uptake Experiments ...... 9 C . Nutrient Analyses and Algal Biomass ...... 12 RESULTS AND DISCUSSION ...... 14 A . Seasonal Patterns ...... 14 1. Nitrogen Concentrations ...... 14 2 . Phytoplankton Composition and Biomass ..... 23 3 . Photosynthesis and Inorganic Nitrogen Uptake . . 26 B . Kinetics of Photosynthesis and Nitrogen Uptake . 30 1. Temperature Effects ...... 30 2 . Light Effects and Die1 Uptake ...... 30 3 . Nitrogen Concentration Effects ...... 35 a . Enrichment Experiments ...... 35 b . Nitrate-Ammonia Interaction ...... 39 C . Annual Input and Output of Nitrogen ...... 40 D . Annual Carbon and Nitrogen Uptake ...... 46 E . Nitrogen Recycling ...... 52 REFERENCES ...... 56

iii ACKNOWLEDGMENTS

This study was made possible by a grant from the North Carolina Water Resources Research Institute to J. E. Hobbie, Zoology Department, North Carolina State University, Raleigh. Several people were associated with the project in various ways. Bruce Dornseif, William Bowden, Charles Balducci, and Adrianne Zlotowitz provided help with the sampling, field experiments, and laboratory analyses. Mr. Grover Cook, co- ordinator of The ChowantRiver Study, cooperated in providing work space for the project in a portable field laboratory located near Winton, N.C. Dr. Jay Langfelder of the Center for Coastal and Marine Studies at N.C. State University made available to us other field laboratory and sleeping facilities. Dr. A.M. Witherspoon's laboratory provided estimates of algal species composition and abundance in samples collected every other week from the four sampling sites. Dr. Charles Daniels of the U.S. Geological Survey provided river flow data. Total Kjeldahl nitrogen analyses were performed in the laboratory of Dr. Michael Overcash of the Biological and Agricultural Engineering Department at N.C. State University. We aref especially grateful to Dr. Richard Volk of N.C. State Univer- sity, in whose laboratory all the samples were analyzed by mass spectrometry. Dr. John Miller served as principal investigator during the last six months of the project, following J. E. Hobbie's resignation from the University to accept a position with the Marine Biological Laboratory, Woods Hole, Massachusetts. ABSTRACT

The repeated occurrence of nuisance algal blooms in the Chowan River during the past few summers may have been caused by increased nitrogen loading in the river. That possibility prompted this study of the relationship between nitrogen and algal growth in the river. The lower Chowan River, located in northeastern North Carolina, is actually a freshwater tidal estuary emptying into Albemarle Sound. As is typical for this region, dissolved inorganic nitrogen concentrations in the Chowan are high in winter and low in summer. This pattern results from a combination of high rates of input from land runoff in the winter and high rates of removal by rapidly growing algae in the summer. Dissolved organic nitrogen is the most abundant form of nitrogen in the river, and the concentrations decrease downriver, suggesting that it is transformed to other forms within the river. Annual algal production in the river was around 100 g over 90% of which occurred between May and October, a period when blue-green, dinoflagellate and green algae made up most of the algal biomass. Annual inorganic nitrogen uptake, measured by ls~isotope techniques, was 33 g NHq.-Nmm-2 and 12 g -2 NO 3- Ngm . Carbon-nitrogen ratios calculated from these data are low, probably because of nitrogen assimilation by bacteria in the samples and because of luxury uptake of nitrogen by the phytoplankton. During winter rapid flushing rates, low light intensities and low temperatures are the most important factors limiting algal photosynthesis and nitrogen uptake in the river. During summer inorganic nitrogen became limiting as nitrate and ammonia levels fell below 50 pg N liter-', the concentration found necessary for maximum uptake. However, rapid regeneration of ammonia permitted rapid algal growth throughout the summer despite the low concentrations. LIST OF FIGURES Page The Chowan River drainage basin in southeastern Virginia and northeastern North Carolina. Sampling stations are Edenhouse (E), Colerain (C) , Harrells- ville (H), andWinton(~) ...... 4 Discharge for the Chowan River at Winton, N.C. The average rates for each day are plotted ...... 6 Chowan surface water temperatures and depth of penetration of 1% of the surface light, at the Winton station...... 8 Nitrate and ammonia concentrations at the Winton and Harrellsville stations ...... ,.... 15 Nitrate and ammonia concentrations at the Colerain and Edenhouse stations, ...... 16 Particulate nitrogen concentrations at the Winton and Harrellsville stations ...... 19 Particulate nitrogen concentrations at the Colerain and Edenhouse stations...... 20 Dissolved organic nitrogen concentrations at the Winton and Harrellsville stations ...... 21 Dissolved organic nitrogen concentrations at the ColerainandEdenhousestations...... 22 Seasonal variation in algal wet weight biomass and species composition at the Winton and Harrellsville stations...... 24 Seasonal variation in algal wet weight biomass and species composition at the Colerain and Edenhouse stations...... ,...... 25 Midday rates of algal photosynthesis and nitrate and ammonia uptake for surface samples from the Winton and Harrellsville stations ...... 27 ~iddairates of algal photosynthesis and nitrate and ammonia uptake for surface samples from the Colerain and Edenhouse stations ...... 28 Effect of increasing temperature on rates of algal photosynthesis and nitrate and ammonia uptake at three Chowan River stations: Edenhouse (E), Colerain (C), and Harrellsville (H)...... 31 Page 15. Effect of increasing light intensity on photosynthesis and nitrate and ammonia uptake at the Colerain station on 15 June 1975...... 32 16, Die1 pattern of photosynthesis and nitrate and ammo~iauptake at the Winton station on 31 August- 1 September 1975...... 36 17. Effect of increasing nitrate and ammonia concentration on the uptake rates of these nutrients at three Chovian stations ...... 37

18. Effect of increasing ammonia cor~centrationon the fraction of DIN uptake that is nitrate...... 41 19. Inflow, uptake, and outflcw of nitrate and ammonia in the lotlTer Chowan River between Nove,mber 1974 and November 1975. Size of the blocks is proportional to the quantity of nitrogen...... 53 20. Total annual input, assimilation, and output of nitrogen for the lower Chowan River between 1 November 1974 and 31 October 1975 ...... 55

vii

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SUMMARY AND CONCLUSIONS

This project studied the utilization and recycling of nitrogen in the lower Chowan River, North Carolina. The Chowan River Basin drains approximately 12,600 km2 in southeastern Virginia and northeastern North Carolina. One objective was to determine how significant recycling of the nitrogen nutrients is for algal growth in the river. Second, we wished to determine what factors limit algal growth in the Chowan at different times of the year. A final objective was to generate information that could be used in models that would simulate biological processes (e.g., algal growth) in the river. Specific findings were: 1. In the lower Chowan (the section of river included in this study between Winton and the mouth at Edenhouse) flow often exceeds 15,000 cfs in winter but is usually less than 3,000 cfs in summer when tributary inflow is lowest. Thus, flushing times for the lower Chowan are typically 50 days or more in the summer, compared to 10 days or less in winter. Water temperatures range from around 5'~in January to near 30'~ in August. Light penetration in the river water is so limited by high turbidity that the depth of penetration of 1%of the surface light seldom exceeds 2 m. 2. At the four stations sampled, nitrogen levels were typical of estuarine systems in this region. Nitrate concentrations were high in winter and low during the summer. This seasonal pattern results from a combination of high rates of input from land runoff in the winter and high rates of removal by rapidly growing algae in the summer. Ammonia concentrations had less seasonal variation and were usually lower than the nitrate concentrations. Particulate nitrogen levels remained high throughout the year, but even in the summer when algal biomass was highest over 50% of the particulate nitrogen was detrital. Although the data on dissolved organic nitrogen (DON) are incomplete, they do show that DON is the most abundant form of nitrogen in the river and that the concentrations decrease downriver. It is likely that uptake and remineralization of DON occurs in the river. 3. Diatoms were the most abundant algae during the winter, whereas dinoflagellate, blue-green and green algae made up most of the biomass during the summer. Measurements every other week during 1975 showed that algal biomass was much higher in summer than winter. Even so, the peak summer biomass was no higher than in other lakes and estuaries of the region. However, in 1975 blooms were not encountered in the lower Chowan like those which had occurred in the summers of 1972-1974 4. Similarly, algal photosynthesis and nitrogen uptake rates were higher in summer than in winter and were typical for the region. Annual algal production in the river was around 100 g CamW2, over 90% of which occurred between May and Octo- ber. In nearby estuaries where rates were measured, the annual algal production was about the same as it was in the Chowan River during 1975. Annual inorganic nitrogen uptake, measured by 15~isotope techniques, was 33 g NH~-N-~-~and 12 g NO -~*m-~. 3 Carbon-nitrogen ratios calculated from these data are low, probably because of nitrogen assimilation by bacteria and because of luxury uptake of nitrogen by the phytoplankton. 5. River flow exerts a very stong control on algal biomass in the Chowan River during the winter. This was illustrated vividly in July 1975 when algal biomass declined rapidly during a short-lived period of high river flow. Biomass subsequently rose again to normal summer levels as soon as the river flow returned to normal. 6. Temperature and light fluctuations also cause part of the high seasonal variability in algal growth in the river, and both of these factors appear to limit algal growth at all times of the year. Light limitation is especially severe in winter because of high turbidity. Based on experiments, we conclude that temperature alone, in the absence of other limitations, is responsible for a 6 to 10-fold seasonal change in the rates of algal growth and nitrogen assimilation. Both carbon and nitrogen uptake are also limited by low light intensities in the Chowan. Even on the brightest summer days, algal growth is only about 20% as rapid as it would be if light pene- trated all the way to the bottom of the river. 7. Nitrogen concentration, on the other hand, limits algal growth in the Chowan only during the summer. We base this conclusion on evidence from nitrogen enrichment experiments which showed that as long as ammonia or nitrate levels in the river remain higher than 50 pg liter-l, nitrogen should not be limiting to algal growth. Summer was the only period when dissolved inorganic nitrogen levels fell below this concentration. 8. Our nitrate and ammonia uptake data show that ammonia is used preferentially, especially when ammonia concentrations are high. As a result, nitrate becomes important as a nitrogen nutrient only during the summer when ammonia levels are low. 9. We estimated total amounts of nitrogen entering and leaving the lower Chowan River between 1 November 1974 and 31 October 1975. Some 69% of the incoming nitrogen was dissolved organic nitrogen (DON), 18% was dissolved inorganic nitrogen (DIN) , and the remaining 13% was particulate nitrogen (PN). However, only about 64% of the incoming DON left the river at Eden- house. This loss was nearly matched by gains in DIN and PN, suggesting that some DON is assimilated by microorganisms or absorbed by sediments in the river and subsequently regenerated as inorganic nitrogen. 10. The annual output of DIN from the Chowan watershed was 0.11 g ~#m-~*~r-',which is similar to most watersheds in the Southeast. This indicates that at present the Chowan basin as a whole is not discharging unusually high quantities of nitrogen into the river. 11. Discrepancies between amounts of DIN available in the inflow and the amount of DIN assimilated indicate rapid nitrogen cycling within the river during summer. For example, during June and August 1975, 75 times as much nitrogen was assimilated (per month) as came in. Clearly, most of the nitrogen that is assimilated during the summer comes from recycling processes such as regeneration of DIN from dead organic matter in the water and sediments. Unfortunately, there is little that can be done to slow down these processes except to reduce the total amount of nitrogen entering the river. 12. During the summer factors such as light, temperature, and flow are more favorable to algal growth than at any other time of the year. Therefore, because the summertime input of

"new" nitrogen from the watershed is so low (e,g., 400 kg Ne day-') any additional input should significantly increase the algal biomass.

xii 1. In the lower Chowan, most of the algal growth occurs in the summer when dissolved inorganic nitrogen concentrations are often analytically undetectable and when the rate of input of nitrogen from upstream is at least an order of magnitude lower than it is in winter. This is not a paradox, because most of the summer nitrogen demand is met by recycling nitrogen already in the river water and sediments. Apparently, most of this recycled nitrogen comes from the decomposition of organic matter previously deposited in the river sediments. Thus, it is probably not practical to try to use nitrogen concentration alone as a criterion upon which to base regula- tions for controlling eutrophication in the river. 2. It has been estimated that the discharges from one nitrogen fertilizer plant on the banks of the lower Chowan amount to about 200 to 500 kg ~#da~-'. This is equivalent to less than 10% of the average daily input from the rest of the river's watershed during the winter. However, during the summer both the river flow and nitrogen concentrations are so low that this one discharge nearly doubles the nitrogen load in the river. Clearly, this example illustrates that in the future additional inputs must be very closely regulated, especially during the summer. 3. The data suggest that one of the greatest threats to the lower Chowan River is any action that would decrease the flushing rate, especially during the summer when it is already low. Conceivably, this could result from activities such as construction of causeways or dams near the river's mouth that would restrict water flow or circulation, or upstream removal of large quantities of water during the summer. 4. Little is known about recycling of nutrients in rivers. If the Chowan is at all typical, then we can say that an algal bioassay technique is worthless for predicting the algal growth potential in shallow rivers. This technique tells what the

xiii growth potential is based on the total nutrients in solution. In shallow rivers, the regeneration of nitrogen from the sediments can actually provide 75 times more nitrogen over the course of the summer.

xiv INTRODLTCTION A. Background Rapid and dramatic biological changes in the lower Chowan River during the early 1970's stimulated interest in a detailed study of the entire river. In particular, the nuisance algal growths that developed in much of the river in 1972 severely restricted fishing, both commercial and sport, recreation and navigation. Nuisance algal growths, or algal "blooms", occur when algae can obtain large amounts of nutrients, especially nitrogen and phosphorus. These nutrients come into the Chowan River from many sources including wastewater discharges by towns and overland runoff and drainage from agricultural and urban areas. In addition, it was discovered in 1972 that a new source, a fertilizer plant on the banks of the Chowan at Tunis, North Carolina, was adding large amounts of nitrogen to the river. This discharge was stopped by state action, and no severe algal blooms developed in the river during the next few years. Then, in the early summer of 1976 the nuisance blooms reappeared. At about the same time it was discovered that high nitrogen water was seeping from the Tunis fertilizer plant into the river. Thus, there is circumstantial evidence that an increase in nitrogen levels in the Chowan is responsible for triggering the nuisance blooms. In response to this situation, the North Carolina Depart- ment of Natural and Economic Resources (NCDNER) in 1973 authorized a thorough investigation of the Chowan River. This Chowan River Study has two primary objectivest 1) to determine the effects of point and non-point source discharges on water quality in the river; and 2) to develop mathematical models for a water quality management plan that will predict the impact of increased discharges and new discharges in the Chowan basin. A study plan was developed which included water quality measurements by the NCDNER Division of Environmental Management, flow measurements by the U.S. Geological Survey, and special- ized projects by university researchers. These cooperative projects included a study of the effects of aquatic macro- phytes on the storage and release of nitrogen and phosphorus, a study of the kinds and numbers of algae in the river, and a study of the utilization and recycling of nitrogen nutrients in the river (data presented in this report), In addition, two modeling projects have utilized information from these studies to develop mathematical simulations of the biological dynamics of the Chowan as affected by increased nutrient loading.

B. Objectives and Research Plan One objective of this study was to determine the extent of recycling and regeneration of nitrogen nutrients in the Chowan River. A three-step procedure was followed in pursuing this goalr 1. The input of nitrogen into the lower Chowan River was calculated by multiplying nutrient concentrations in the water by river flow. These daily estimates were summed to give total monthly and total annual input. 2. The assimilation of ammonia and nitrate by algae and bacteria in the river water was measured at two-week intervals, starting in April 1975. The data were integrated over time and space to give total assimilation in the lower Chowan (Winton to Edenhouse segment) per month and per year. 3. Recycling rates were calculated by comparing assimilation rates to input rates OM a short-term (monthly) and a long- term (annual) basis. A second objective was to study the relationships between light intensity, temperature and inorganic nitrogen concentration and algal growth in the river. Factorial experiments were conducted which related both the rates of algal growth (as measured by photosynthesis) and the rates of nitrogen uptake to combinations of various water temperatures, light intensities and nutrient concentrations. Analysis of the data from these experiments permitted us to draw some conclusions as to which factors were controlling algal growth in the river at various times of the year. Finally, the third objective was to generate information that could be used in models that would simulate biological processes (e.g., algal growth) in the river. The factorial experiments described above fulfilled this objective in that they gave quantitative relationships between the biological processes (e.g., rate of nitrogen uptake by algae) and environmental conditions (e.g., water temperature, light, and nitrogen concentration) .

C. The Chowan River and Its Drainage Basin

The Chowan River drains approximately 12,000 km2 in southeastern Virginia and northeastern North Carolina. The Chowan River proper extends 80 km from the confluence of the Blackwater and Nottoway Rivers near the North Carolina-Virginia border south to its mouth in Albemarle Sound near Edenton, North Carolina (Fig. 1). Another important tributary is the Meherrin River which empties into the Chowan about 20 km below the Blackwater-Nottoway confluence. Because Albemarle Sound is sheltered from the Atlantic Ocean by a series of barrier islands, lunar tides in the lower Chowan seldom exceed 15 cm, These barrier islands also prevent seawater from intruding into the western half of Albemarle Sound; thus the entire Chowan is freshwater. Wind is an important factor affecting flow rates and direction in the lower Chowan. Between Winton and the mouth at Edenhouse, the river's cross-sectional area increases by nearly 10-fold, yet the volume of flow is estimated to increase by only 10% since about 10% of the total watershed lies between Winton and Edenhouse. As a result the Chowan flows very sluggishly near the mouth and during periods of low tributary Fig. 1. The Chowan River drainage basin in southeastern Virginia and northeastern North Carolina.

4 inflow, southerly winds may actually result in upstream flow for short periods (C, Daniels, personal communication). Typically the river flow is highest in winter (around 15,000 cfs) and lowest in summer (often less than 1,000 cfs) . During 1975 there was one outstanding exception to this pattern. It occurred in July when the flow exceeded 50,000 cfs for a short period during unusually rainy weather (Fig. 2). Under normal flow conditions flushing times for the lower Chowan can range from less than 10 days during the winter to over 50 days during the summer, In 1975 the average flow rate was 6,849 cfs and the average flushing time was 26 days (Table 1). The average depth of the lower Chowan is about 4 m and the water is usually well mixed. It is highly turbid because of suspended detritus and strongly colored from humic material. The 1%light level often is less than 1 m deep and seldom exceeds 2 m (Fig. 3). Water temperatures range from about 5'~ in January to nearly 30°C in August (Fig. 3). 2 The Chowan basin has a sparse population (20.6/km ) , totaling only 260,000, of which nearly 80% live in rural areas. The regional economy is primarily agricultural, with tobacco as the major crop. Towns in the drainage area are small (all less than 10,000 population).

Table 1. Summary of morphornetric and hydrographic parameters for the lower Chowan River

Drainage area (kmL) 2 River area (km ) Volume (m3 ) Mean depth (m) Annual discharge (m3 ) Flushing rate (yr-l) TEMPERATURE ("c)

DEPTH OF 1 % LIGHT LEVEL (m) METHODS A. Sampling

Between November 1974 and November 1975 surface water samples were collected every two weeks from piers at four stations along a 65 km stretch of the lower Chowan River between Winton and the river's mouth at Edenhouse (~ig.1) . Within 2 h after collectii~n,these samples were taken to a field laboratory at Winton where all nitrogen and carbon assimilation experiments were conducted and where nutrient and algal biomass sub-samples were taken. The nutrient samples were frozen with dry ice and stored frozen. The algal samples were preserved with Lugolts acetic acid solution. At each sampling station the surface water temperature was measured with a mercury thermometer and sub-surface light intensity was measured at 0.2 m depth intervals by means of a submarine quantum meter (Lambda Instruments Co. Model LI-185). This instrument measures only photosynthetically available radiation (i.e. , 400 - 700 nrn wavelength band) , which is equal to about 50% of the total solar radiation (Strickland 1958).

B, Carbon and Nitrogen Uptake Experiments

Phytoplankton photosynthesis was estimated by the carbon-14 technique of Steemann-Nielsen (1952). Samples of river water were incubated in 125-ml ground-glass-stoppered bottles with 1 to 3 ml of a 2 >~i/ml solution of N~H"CO After incu- 3 * i~ationthe phytoplankton were killed with Lugol's acetic acid solution (~ollenweider1974) and filtered onto 0.45 ym pore size membrane filters (Millipore HA). The filters were dried and stored until their radioactivity could be determined with a Beckman planchette counter. Meanwhile, carbonate alkalinity was measured by the method of Karlgren (1962), which involves titrating a 50-ml water sample with 0.02 N HC1 to an endpoint pH of 5.4, where the Saurebindungsvermogen (SBV) indicator undergoes a dis- tinct color change from green to clear gray to red. During the titration nitrogen gas bubbles through the sample in a sintered glass funnel, so as to hold the C02 tension low, thus forcing a complete shift in the carbonate-bicarbonate- carbon dioxide equilibrium towards carbon dioxide. Carbonate alkalinity was calculated as follows:

- (HC~~-HC~~)* (N) a (1,000) A' - v meq,liter, where HC~"equals the ml of acid used to titrate the sample, HC1b equals the ml of acid used to titrate a blank of 50 ml of boiled, distilled water; N is the normality of the acid used, and v equals the volume (ml) of sample titrated. Available carbon ( 12Cavail) was then calculated as

The factors fl, f2, and f which vary with pH, are used for 3 ' calculating concentrations of C02, HCO;, and CO= Tables of 3 ' values for the factors at different pH leve3.s can be found in Karlgren's (1962) paper. A glass electrode pH meter (Corning Model 10) was used to measure pH of the Chowan samples. Finally, photosynthesis rates were calculated as followsr

where 14~assimequals the corrected counts per minute of the sample and the count per minute of isotope added to the bottle is I4cadd. The factor 1.06 corrects for the heavier carbon- 14 isotope, and the milligrams inorganic carbon per liter available for photosynthesis is 12cavail. The length of the incubation period is h. The 15~tracer technique was used to measure uptake of ammonia and nitrate in samples of river water. The procedure was similar to that used by Dugdale and Goering (1967). First, a known amount of 15N-labeled Na15N0 or 15~~4~1was 3 added to the water in 1-liter ground-glass-stoppered bottles. The amount of labeled compound normally added was 14 yg 15N as ammonia or nitrate. After incubation, the 15N samples were killed with Lugol's acetic acid solution and filtered onto Whatman GF/C glass-f iber filters, which were then dried and stored in a dessicator. Later, particulate material on the filters was converted to molecular nitrogen by Dumas combus- tion (~arsdateand Dugdale 1965). The 15~~'4~ratio of the resulting N2 was determined with a mass spectrometer, the ratio was converted to atom per cent 15N, and the enrichment over the normal atom per cent I5N (0.37) of the organic material was calculated, The amount of nitrogen taken up was calculated as follows;

mg N * liter-' *h-l = (PN) (Af) . (h) (Ai)

The total amount of particulate nitrogen (PN) on the filter was determined by a method described below. The atom per cent excess 15N of the ammonia or nitrate fraction in the sample at the beginning of the experiment just after the isotope was added is Ai. The atom per cent excess 15N in the particulate nitrogen (PN) on the filter at the end of the experiment is Af. The length of the incubation period in hours is h. 14c and incubat ions were carried out simultaneously in a set of four temperature-controlled water baths placed outdoors at the Winton laboratory site. Two of the tanks were held at the ambient river temperature, one loOc higher and one 10'~lower. Five light levels (loo%, 55%, 33%, 12%, and 5% of the ambient illumination) were produced by wrapping sample bottles with layers of gray Fiberglas screening. This screening equally transmits all wavelengths in the range 400 nm to 700 nm. Usually, incubations were begun at 1000 and ended at 1400 EST. Photosynthesis was measured on every sampling date between November 1974 and November 1975, but nitrogen uptake was measured only between April and November 1975. Each photosynthesis experiment consisted of: (two replicates of each light intensity) X (three temperatures) X (four stations), for a total of 120 14~samples. The 15N experiments always included a set of samples consisting ofr (two replicates of two light intensities; ambient and dark) X (15~0 and l5N~4) 3 X (4 stations) run at ambient river temperature. A variety of extra 15~experiments were conducted from time to time. On some occasions, for example, samples were incubated at all three temperatures. Sometimes uptake rate vs. nutrient concentration was determined by innoculating sets of samples with various amounts of the isotope, usually 3 pg, 7 pg, 14 yg, and 42 pg 15N.

C. Nutrient Analyses and Algai Biomass

Soon after the incubations were begun, samples for total Kjeldahl nitrogen, dissolved nitrogen, particulate nitrogen, and algal biomass were prepared. Whatman GF/C glass-fiber filters were used to seperate particulate and dissolved nitrogen samples. These filtered samples, along with samples of whole water, were quick-frozen (using dry ice) in polyethylene bottles and stored frozen until nutrients could be analyzed. The filters were dried and stored in a dessicator. Plankton samples were preserved with Lugol's acetic acid solution. Nitrate and nitrite were analyzed by standard methods outlined in Strickland and Parsons (1968). Ammonia was measured by a modification of the Solorzano method (Solorzano 1969) , as described in Liddicoat et al. (1975) . Particulate nitrogen on the filters was measured in a Coleman Nitrogen Analyzer* Between May and November 1975 total Kjeldahl nitrogen (TKN) was measured by means of procedures that are outlined in Standard Methods (1971). Values for dissolved organic nitrogen (DON) were obtained by subtracting PN and NH4 from the TKN values. Plankton samples were counted by the Utermohl sedimentation technique (Lund et al. 1958) with an inverted microscope. Algal bio,mass was calculated from the number of individuals per liter and the esti,mated average volume of each species; a specific gravity of one was assumed. RESULTS AND DISCUSSION

A. Seasonal Patterns

1. Nitrogen Concentrations

Nitrate levels in the Chowan River are high in the late winter and low during the summer. For example, at Colerain the nitrate concentration was around 400 sg N*liter-' during January and February 1975 (Fig. 5). By July and August the nitrate had decreased to less than 10 ag ~aliter-l. Then, in September and October 1975 the nitrate began to increase again, apparently climbing toward another winter peak, The same seasonal pattern occurred at the three other sampling stations (Figs. 4 and 5), but the winter-to-summer decline was less pronounced at the upstream stations than at the river mouth. There are at least two factors which cause nitrate levels to fluctuate seasonally in the Chowan. The first is varying upstream input of nitrate. Gilliam and Lutz (1972) studied the nitrogen in the ground water of the Coastal Plain and found that the nitrate in the runoff greatly increased as soon as the crops were harvested and the ground water was recharged by the fall rains. Thus, input of nitrate from the Chowan Basin is much greater in winter than in summer. The second factor affecting nitrate levels in the river is biological activity of micro-organisms (algae and bacteria) in the water and sediments. This will be discussed later in more detail, but can be summarized here. Because environmental factors affecting algal growth (e.g., temperature and light intensity) are more favorable in summer, more nitrate is removed from the water by the growing algae in summer than in winter. Nitrate levels in the Chowan are similar to those in other coastal systems of the Mid-Atlantic Region. For example, Hobbie repeatedly found highest nitrate during the winter (approximately 300 yg ~aliter-I)for the Pamlico and Neuse WINTON

HARRELLSVILLE AMMONIA NITRATE r

Fig. 4. Nitrate and ammia concentrations at the Winton and Harrellsville s-t;ations, - - -. .. .- --- I NITRATE '.

Fig, 5. Nitrate and ammonia concentrations at the Colerain and Edenhouse stations. River estuaries (Hobbie 1974, Hobbie 1975). In both estuaries nitrate was very low during the summer. This same seasonal pattern was noted for the Chesapeake Bay by Carpenter et al. (1969) , although there the winter concentrations were somewhat higher than in the North Carolina estuaries, presumably because of considerable pollution in the upper part of the bay. Of all the nitrogen fractions measured in the Chowan, nitrite was by far the least abundant. Concentrations ranged from undetectable em,less than 1 pg NSliter-I) to only about 14 >g N * liter-', Furthermore, there were no seasonal or spatial trends in the nitrite concentrations. The data are not presented graphically, but are included in Appendix A. Similarly, Hobbie (1975) found no more than about 20 pg ND liter-' as nitrite at any time in the Neuse River Estuary. Indeed, nitrite is not common in natural waters except in situations where ammonia is being oxidized to nitrate or where nitrate is being denitrified to ammonia. Even then, however, nitrite concentrations do not usually build up, since these transformations are relatively rapid and complete, In comparison to nitrate, ammonia levels in the Chowan showed less seasonal variation and were usually lower than the nitrate concentrations. At Colerain the range was from around 100 pg liter-I in January to less than 10 pg liter-I in July (Fig. 5). As in the case of nitrate, these ammonia levels seem typical for natural systems in this region (Hobbie 1974, 1975; Carpenter et al. 1969) , Most other lakes and estuaries that have been studied also show little or no clear-cut seasonal pattern in ammonia concerArations. This fact is cited as evidence that ammonia is rapidly regenerated in the water and sediments of aquatic systems. In a subsequent section we will present other evidence from 15~tracer studies that this is indeed the case in the lower Chowan River at some times of the year, Particulate nitrogen (PN) includes all living organic nitrogen and detrital nitrogen in particles that are retained on a filter that has a pore size of about 0.5 ,urn. Particulate nitrogen levels were relatively high during winter and summer in the Chowan and lower in spring and fall (Figs. 6 and 7). Highest values were around 400 sg N-liter-' and the lowest were about 75 gg Noliter-'. Thus, PN is an important nitrogen fraction in the river because it represents a significant part of the total nitrogen input and because it is continuously being broken down into inorganic forms, primarily ammonia, that can be used by the phytoplankton. Unfortunately, the rate of this breakdown remains unknown. Apparently, most of the PN in the river is detrital. During the 1975 summer the average algal biomass was around 15 mg wet wgtmliter-' (see next section). This is equivalent to approximately 100 pg N liter-', assuming a carbon-nitrogen ratio of 7rl and a wet weight-to-carbon conversion of 0.05 (Strickland 1958). Thus, since the summer PN levels were often over 200 pg ~mliter-l,at least 50% of it must have been detrital. During the winter, almost all of the PN was detrital since algal biomass was very low then (equivalent to less than 10 pg N-liter-') compared to the total PN concentrations, which were 100 pg N *liter-' or more (~igs.6 and 7) . Dissolved organic nitrogen (DON) makes up a high per- centage (Figs. 8 and 9) of the total nitrogen input to the Chowan. Between June and November 1975 the concentrations averaged approximately 600 pg Noliter-' and ranged from 200 to 1200 sg N-liter-'. Often this was 10 to 100 times the amount of dissolved inorganic nitrogen present (ammonia, nitrite, and nitrate). Except during June and August DON concentrations were also higher, by a factor of 2 to 5 times, than the PN levels. However, there was no clear pattern in the DON levels. Likewise, Hobbie found that in the Neuse River and Pamlico River estuaries DON was usually the most abundant form of nitrogen (range 70 - 350 yg Nwliter-') but that the concentrations did not appear to correlate very well with any other parameters (Hobbie 1974, 1975) I I I I I I I I I 0000 0 0 0 0 000 0 0 0 0 em- z * ca * tr3lll-N 9ff kl3111 N 3; L- 1-

N F M AMJ J 1974 1975 Fig. 8. Dissolved organic nitrogen concentrations at the Winton and Harrellsville stations. DON

DON I

Fig. 9. Dissolved organic nitrogen concenwa~~u~lsar the Colerain and Edenhouse stations. 2. Phytoplankton Composition and Biomass

In the Chowan, diatoms made the greatest contribution to the algal biomass during the winter, whereas dinoflagellates, blue-green, and green algae formed most of the summer biomass (Figs. 10 and 11) . At the river ,mouth (Edenhouse station), for example, diatoms, mostly species of Melosira, usually accounted for over 75% of the total biomass in samples collected between November and May. Following a rapid decline in diatom abundance in the late spring, blue-green algae (e.g., Microcystis, Anabaena, Aphanozomenon) and dinoflagellates (Peridinium) began to predominate, together making up as much as 80% of the biomass from June through October. Green algae (Coelosphaerium, Microasterias, Scenedesmus), and Eugleno- phyta were present in smaller quantities throughout the year, and Chrysophyta were observed in a few samples. This pattern is about the same as that which Whitford (1958) described as being typical for North Carolina Coastal Plain lakes and ponds. He noted that there seemed to be a correlation between the winter-to-summer shift from diatoms to green and blue-green algae and changes in water temperature, but cautiously added that the interaction of many factors determines the relative abundance of any one species. Algal biomass in the river was lowest during winter (average less than 1 mg0liter-' wet weight) and highest in summer (average about 15 mg*liter-' wet weight) . However, as shown in Figs. 10 and 11 , several of the summer samples con- tained large numbers of one or two species which raised the total biomass to as high as 37 mg*liter-I (e.g., 30 June 1975 at Colerain station). In this case a species of Peridinium accounted for more than half the total wet weight. Later, in August, large numbers of Peridinium along with two species of blue-greens (in the genera Synechoccus and Aphanozomenon) produced unusually high biomass peaks of about 21 and 19 mga liter-' at Harrellsville and Winton respectively (Fig. 10). In comparison to data that has been compiled from other Fig. 10. Seasonal variation in algal wet weight biomass and species composition at the Winton and Harrellsville stations. I d 1 I I I I I L BIOMASS COLERAIN

BA 4

N DIJ FMAMJ J ASON 1974 1975

Fig. 11. Seasonal variation in algal wet weight biomass and species composition at the Colerain and Edenhouse stations. lakes and estuaries in North Carolina, the Chowan biomass levels during 1975 were not unusual. After surveying 69 natural lakes and inpoundments in the state, Weiss and Kueneler (1976) found that most had between 1 and 6 rng.liter-' of algal biomass during the summer. Also, although the seasonal patterns are different, the Chowan and the Pamlico River Estuary have similar quantities of phytoplankton. In the Pamlico the wet weight biomass averages around 5 to 10 mge liter-' except during brief periods in the late winter when blooms of Peridinium triquetrum raise the biomass to around 50 rng*liter-' (Hobbie 1972) . It should be noted, however, that during the course of this study we did not encounter any blooms in the Chowan like those which occurred in the summers of 1972-1974, However, recently C. Balducci (personal communication) collected samples at the Colerain station during the early summer of 1976 when an algal bloom covered the water surface with a visible layer of blue-green algae, mostly Anabaena and Microcystis species. In these surface samples, the algal biomass was as high as 100 mg.liter-l.

3. Photosynthesis and Inorganic Nitrogen Uptake

Algal photosynthesis (which is indicative of growth rate) in the lower Chowan was lowest in January and February and highest in the summer months. At Colerain, for example, the -1 h-l in February rates ranged from less than 1 pg Cmliter 1975 to over 125 ~g c *litere1ah-' in July 1975. Although there was considerable day-to-day variation in these midday photosynthesis rates due to short-term environmental fluctuations, the Colerain data in Fig. 13 clearly show the gradual buildup of algal activity that occurred in the river between April and July and then the gradual decline between September and December. This same cycle occurred at all four of the stations and the summertime maximum rates were about the same at all stations (Figs. 12 and 13). PHOTOSYNTHESIS

N DIJ FMAMJJ ASON

Fig. 12. Midday rates of algal photosynthesis and nitrate and ammonia uptake for surface samples from the Winton and Harrellsville stat ions. PHOTOSYNTHESIS

AMMONIA & NITRATE UPTAKE

Fig. 13. Midday rates of algal photosynthesis and nitrate and ammonia uptake for surface samples from the Col.erain and Edenhouse stations. There was one unusual dip in the summertime algal photosynthesis which was most noticeable at the two up-river stations, Winton and Harrellsville, At these stations, the rates fell rapidly during July 1975 to about 10% of the May and June rates, but then increased again in August to the typical summertime rates (about 125 pg c *literm1ah-') . This short-lived but precipitous decline did not occur at Eden- house and Colerain (Fig. 13)$where, instead, the high rates of photosynthesis persisted throughout July and August. The most likely cause of this anomaly was the unusually high river flow, which peaked at nearly 50,000 cfs in mid-July 1975. This was 10 to 20 times the normal flow for that time of year and was the highest flow during the entire 1975 calendar year ,(Fig. 2). Consequently, there was a severe washout of the algae in the Winton-Harrellsville region. Farther down-river the cross-sectional area of the Chowan increases much more rapidly than the volume of water carried, so that flow rates do not vary nearly so much at the mouth as farther upriver. This probably explains why the washout was not noticeable at the Colerain and Edenhouse stations. This example illustrates the strong effect that flow rate can have on the quantity of algae in a river like the Chowan. Another example of the effect was reported by Hobbie (1971) for the Pamlico River Estuary, where the 1968 Peridinium bloom was temporarily washed out of the river following heavy rains. In addition to river flow rate there are several other important factors that influenced the seasonal pattern of algal growth in the Chowan. Among these are solar radiation, water temperature and nutrient availability, all of which will be examined quantitatively in a later section of this report. As expected, nitrogen uptake by the plankton followed the same seasonal pattern as photosynthesis. There is no nitrogen uptake data between November 1974 and March 1975. However, nitrogen uptake was probably low then so that the lack of measurements for that period has little effect on our understanding of the seasonal cycle and calculations of total annual assimilation of nitrogen in the river. For example, assuming that carbon and nitrogen uptake rates approximated the Redfield et al. (1963) CIN atomic ratio of 7r1, we estimated wintertime values for nitrate and ammonia uptake to be less than 1 jag Neliter -l-h-' on most days. By mid-summer, the measured rates had risen to about 10 yg N9 liter-' ah-' of ammonia and 4 pg N a liter-' sh-' of nitrate. Then as algal growth rates and biomass decreased during Sep- tember and October, nitrogen uptake rates also decreased.

B. Kinetics of Photosynthesis and Nitrogen Uptake

1. Temperature Effects Te,mperature fluctuations caused part of the great seasonal variability in algal growth rates in the Chowan. Experi- ments showed that both photosynthesis and nitrogen uptake increased as water te,mperature increased. For example, in one experi,ment in August 1975, photosynthesis approximately doubled (Q10=2 .0) between 8'~and 18Oc. In concurrent experiments, ammonia and nitrate uptake rates tripled (Q10=2.8-3.3) (Fig. 14). The QlOvsseemed to remain about the same over the whole range of temperatures occurring in the river during the year. Therefore, we conclude that temperature alone, in the absence of severe ltmitation by other factors, was responsible for a 6-to-10 fold seasonal difference in the rate of algal growth and nitrogen assimilation.

2. Light Effects and Die1 Uptake A typical set of data for photosynthesis and nitrogen uptake vs. light at different te,mperatures are shown in Fig. 15. As the light increased, the photosynthetic rate rose to a maximum and then re,mained constant or decreased somewhat at higher light intensities, This decline at high light intensities, called 'inhibition', was ,most severe at the lowest PHOTOSYNTHESIS

I I I I I AMMONIA UPTAKE

NITRATE UPTAKE /E C Q,,= 3.3 E Q,,= 3.0

4 8 12 16 20 24 28 TEMPERATURE (OC )

Fig. 14. Effect of increasing temperature on rates of algal photosynthesis and nitrate and ammonia uptake at three Chowan River stations: Edenhouse (E), Colerain (C) , and Harrellsville (H). PHOTOSYNTHESIS ( Colerain 9 15 June, 1975

AMMONIA & NITRATE UPTAKE (@olerain) 15 June, 1975

Nitrate 20%

SOLAR RADIATION ( ly minute-' )

Fig. 15. Effect of increasing light intensity on photosynthesis and nitrate and ammonia uptake at the Colerain station on 15 June 1975. water temperature. Similarly, ammonia and nitrate uptake rates first increased with increasing light to a saturation level and then declined at higher intensities. Here again, the degree of light inhibition was inversely related to light intensity (data not shown) . Our data for nitrogen uptake vs. light are similar to others that have been plotted for marine phytoplankton assemblages and for single species of algae in culture. The curves take the shape of rectangular hyperbolas, up to the point of light saturation. They may be described by the following equationr

where V is the rate of nitrogen uptake (pg N liter-' * h-l) , Vd is the dark uptake rate, Vmax is the maximum, light saturated uptake, and I is light intensity. The light intensity corresponding to $vmaX is 10,5: it is called the light half-saturation constant (MacIssac and Dugdale 19'72). Chowan I values, estimated from graphs like Fig. 15, 0.5 usually were around 0.05 lya min-' . MacIssac and Dugdale (1969) reported I 0.5 values around 0.005 - 0.02 lyomin-' for phytoplankton in the tropical Pacific Ocean, but Bates (1976) found that I0 varied, depending on the previous light history of the algal cells. Shade-adapted cells of some species had a lower I 0.5 than sun-adapted cells. Nevertheless, even on cloudy days nitrogen uptake at the surface of the Chowan must be light saturated, whereas light intensity must almost always limit the uptake in the deeper waters of the river, where light levels fall below 0.05 ly* min-l. For example, if the surface intensity were 1.0 lys min-' (typical for a sunny summer day at noon), then the 0.05 lye min-' level would be at a depth of approximately 0.8 rn. This is based on an extinction coefficient of 3.5, a typical value for the Chowan (see Appendix A), Thus, under even the most favorable light conditions, at least 80% of the planktonic algae in the river (average depth 4.5 m) would be light limited, if we assume a homogeneous vertical distribution of the biomass. The data in Fig. 15 also show that in darkness there is considerable nitrogen uptake, but no algal photosynthesis, by plankton in the Chowan. At 20'~ the dark uptake of both ammonia and nitrate was approximately one-half the maximum rate. Similarly, Bates (1976) observed significant dark uptake of ammonia and nitrate in algal cultures, as did Packard (1973) , MacIssac and Dugdale (1972) , and Dugdale and Goering (1967) in marine phytoplankton. It seems paradoxical that light stimulates nitrogen uptake by algae, but that dark uptake, nevertheless, is commonly observed. Falkowski (1975) found that ATP generated during photosynthesis is used in the translocation of nitrate across the cell membrane. See Healey (1973) for a detailed discussion of the dependence of nitrate uptake on light. This might explain the similarity in the curves of photosynthesis vs. light and nitrate uptake vs. light. Note, for example, that both processes exhibited I values of around 0.5 0.05 ly*min-l in the Chowan, and that both rates were inhib- ited at high light levels. On the other hand, Grant and Turner (1969) and Packard (1973) have suggested that energy for dark nitrate uptake and reduction to ammonia can be derived from respiration. Thus, as Bates (1976) surmised from this evidence, there could be two nitrate uptake mechanisms in algaet one that operates only in the light and derives its energy from photophosphorylation, and a second that derives its energy from cellular respiration. Clearly, however, these hypotheses need confirmation. By means of several die1 studies, we sought to describe the pattern of photosynthesis and inorganic nitrogen uptake in the Chowan over a 24-h period. Samples of river water were collected every three hours and incubated under ambient light and constant temperature. Since different samples were used for each 3-h segment of the experiment, algal biomass was not constant from one incubation to the next. However, the variation was usually less than 25% of the mean of all eight samples, and therefore did not drastically alter the shape of the die1 rate curves. The results of one of these die1 experiments (Fig. 16) again illustrates the importance of dark nitrogen uptake. Although ammonia and nitrate uptake both rose and fell with changes in solar radiation, the uptake did not cease at dusk, but rather continued throughout the night at approximately 50% of the midday rates. In fact, integration of these rate curves showed that over 30% of the total nitrogen uptake on this late August day occurred at night. Of course, at other times of the year when the nights were longer, the relative importance of dark uptake would be even greater. Furthermore, this experiment described the pattern at the water surface. As was indicated earlier, when the rates are integrated over depth as well as time, the importance of dark nitrogen uptake is magnified (see also Section D below).

3. Nitrogen Concentration Effects a. Enrichment Experiments On several occasions we measured the response of nitrogen assimilation to increased concentrations of ammonia and nitrate. Various amounts of 15~-labellednitrate or ammonia were added to a series of well-mixed samples which were incubated and analyzed for nitrogen uptake in the normal way (see Methods). In some experiments the increased nutrient concentration stimulated uptake rates, but more often there was no effect. For example, on 10 August 1975 nitrate appeared to be satu- rating at the ambient concentration, which was about 30 pg No liter-' (~ig.17) . Ammonia uptake, on the other hand, was stimulated by increasing the ammonia concentration. The increase I I I I I I I I I I '7 I SOLAR RADIATION $J 5 500-

PHOTOSYNTHESIS

680 pgC -day"

AMMONIA & NITRATE UPTAKE. 1-J 1-J 4 - 2

30 PHOTOSYNTHESIS : NITROGEN UPTAKE

20- -

10 - -

I 1-1-1-1- 0900 1300 1700 2100 r 0100 - 0500 - 31 August 1975 (EDT) 1 September

Fig. 16. Die1 pattern of photcsynthesis and nitrate and ammonia uptake at the Winton station on 31 August-1 September 1975 I I I 4MMONIA UPTAKE 0 August, 1975

NITRATE UPTAKE 10 August, 1975

/--/H // 0

Fig. 17. Effect of increasing nitrate and ammonia concentration on the uptake rates of these nutrients at three Chowan stations. was most noticeable at the Harrellsville station, rising from 3 .5 yg N liter-' h-' at ambient concentration to a maximum rate of around 10 pg N-liter-' ah-' at a concentration of 60 pg N liter-'. It is important to note, however, that this positive response to nitrogen enrichment was observed only in a few of the summer experiments while at other times of the year ambient concentrations of ammonia and nitrate were relatively high (over 50 pg Nsliter-') and there was no stimu- lation by added nutrient. In many cases, the expression

has been found to describe the relationship between algal uptake of nitrate and ammonia and the concentrations of the nutrients (e.g., MacIssac and Dugdale '972). The terms of the equation, which describes a rectangular hyperbola, ares V = velocity of uptake of ammonia or nitrate (pg Naliter-'ah-') ; 'max = maximum velocity of uptake; S = concentration of the nutrient (pg N liter-') ; Kt = the nutrient concentration at which V = $vmaX. As MacIssac and Dugdale (1972) noted, the constant is designated Kt or transport condtant to emphasize that a mathematical and not necessarily biochemical equivalence to Michaelis-Menten kinetics is involved. Although there is considerable variation, most measurements, including our own for the Chowan, have indicated a Kt of about 14 pg N liter-' for both nitrate and ammonia uptake by phytoplankton. For example, measurements of Kt for ammonia in coastal Peruvian waters gave values of 9 - 28, with a mean of 15.5 pg l liter-' (~ac~ssacand Dugdale 1969) . Lehman et al. (1975) compiled Kt values froiri a variety of marine and freshwater studies. The values in their table ranged from 2 - 140 pg liter-I for nitrate and from 2 - 70 pg Naliter-' for ammonia with most values falling near the lower end of the range. In the Chowan experiments, Kt for ammonia and nitrate uptake was usually in the range 5 - 20 pg Naliter-l' (e.g., Fig. 17). The results of our measurements suggest that nitrate and ammonia become severely limiting to algal growth when the concentrations fall below about 50 ug IV0liter-I (~ig. 17). In fact, the concentrations were often below this level during July and August, 1975 (Figs. 4 and 5). Conse- quently, we conclude that higher summertime nitrogen levels in the river would cause more rapid algal growth.

b. Nitrate-Ammonia Interaction Comparison of the nitrate and ammonia uptake data shows that most of the time ammonia was assimilated more rapidly than nitrate. For example, at Edenhouse ammonia was used ten times, or more, faster than nitrate on many days (Fig. 13) . Furthermore, the rate of nitrate uptake exceeded that of ammonia on only a few of the sampling days. This difference, despite the fact that usually there was more nitrate than ammonia present in the water, suggests preferential assimilation of ammonia. Of course, preferential assimilation of ammonia in the presence of nitrate has been observed or inferred from data for a variety of aquatic systems studied previously. Marine phytoplankton growing in artificially enriched seawater used ammonia in preference to nitrate (Eppley et al. 1969, Eppley and Rogers 1970, McCarthy and Eppley 1972) . The same phenomenon was observed in field studies of phytoplankton in the Peru Current (MacIssac and Dugdale 1969) . McCarthy (1972) also concluded that ammonia was the preferred nitrogen nutrient for phytoplankton in the Chesapeake Bay Estuary. It is believed that this nearly universal preference is related to the fact that in order to utilize nitrate an energy expendi- ture is required for both induction of the enzyme system (to reduce intracellular nitrate to ammonia) and for reduction of the nitrate to ammonia (Eppley et al. 1969). 39 In order to better illustrate the effect that ammonia concentration has on nitrate uptake in the Chowan, we have plotted the fraction of the total nitrogen uptake that was nitrate (i.e., nitrate uptake divided by the sum of nitrate uptake and ammonia uptake) vs. the ammonia concentration (Fig. 18). The points on this graph form a curve whose shape suggests that at ammonia levels greater than about 30 pg Nm liter-' over 90% of the inorganic nitrogen taken up will be ammonia. Interestingly, the shape of this curve is almost identical to the one McCarthy et al. (1975) presented for the Chesapeake Bay. As these workers noted, this kind of plot should not be interpreted to mean that ammonia concentrations below 30 pg l liter-' will necessarily induce nitrate uptake, but rather demonstrates that in excess of this concentration little if any nitrate is utilized even when available.

C. Annual Input and Output of Nitrogen The amount of DIN, DON, and PN flowing into and out of the lower Chowan River was calculated for each day of the sampling year by multiplying nitrogen concentrations times river flow rates. Dr. C. Daniels of the U.S. Geological Survey provided estimates of the river flow (daily mean cfs) at Winton and Edenhouse (Daniel 1975) . Since we measured nutrient concentrations every other week, it was necessary to interpolate (linearly) between measured data to obtain concentration estimates for the days between samplings. The calculated inputs and outputs were summed by month for each nitrogen fraction (Table 2) . Even though PN and DON flux followed no seasonal pattern, there was a strong seasonal difference in the amount of nitrogen (total) entering the lower Chowan. Generally, the highest flux rates were during the winter months (e.g., 1126 tonnes input in January) whereas the summer months tended to have low input and low output rates (184 tonnes input in 20 60 100 AMMONIA CONCENTRATION

Fig. 18. Effect of increasing ammonia concentration on the fraction of DIN uptake that is nitrate.

41 Table 2. Monthly input (at Winton) and output (at Edenhouse) of nitrogen (tonnes) in the lower Chowan River

WINTON Month -DIN -DON Total NOV 1.8 31.2 44.6 DEC 39.8 128.3 191 -3 JAN 261.7 704 7 1126.5 FEB 193.6 596 - 3 864.7 MAR 294.7 961.5 1444.0 APR 132.7 359.1 561 a3 MAY 4.4.8 170.2 272.1 JUN 14.4 61.5 109.4 JUL 142.8 1129.1 1442.4 AUG 9-7 132.9 184.2 SEP 111.6 493.4 683.8 OCT 43.6 245 5 316.4 ANNUAL

EDENHOUSE Month DIN DON Total -NH4 N02 - - -- NOV -1.3 10.6 24.7 DEC 47.7 92.0 198 -0 JAN 748 7 480.2 1421.2 FEB 357 8 335 1 777.0 l"tAR 707.9 887.3 1928 -9 APR 210.9 396 0 74.2.1 MAY 21.8 139 2 206.1 JUN 10.2 39 * 1 81.2 JUL 72.0 391 07 AUG 4.1 3 73.3 SEP 437-1 6 4.4. .5 OCT 264.3 382.5 ANNUAL August, for example). It was the combination of high river flow with high inorganic nitrogen concentrations in the winter versus low flows and low DIN concentrations in the summer that caused the great seasonal variation in total nitrogen flux rates. The most abundant form of nitrogen entering the river was DON which accounted for 69% (5013 tonnes) of the total annual nitrogen input able 2). Actually, this may be an underestimate, because we assumed that winter DON concentrations were the same as the measured summer levels. We based this assumption on the finding by Hobbie (1974, 1975) that DON levels do not vary seasonally in the nearby Pamlico and Neuse River Estuaries. The second most abundant fraction was the dissolved inorganic nitrogen. Of the 1291 tonnes DIN input at Winton, about two-thirds (862 tonnes) was nitrate and one-third was ammonia (415 tonnes). Nitrite made an insignificant contribution (14 tonnes) to the total annual DIN input, Finally, the remaining 935 tonnes of nitrogen that moved past Winton was particulate nitrogen. Comparison of the input and output of the various nitrogen fractions suggests that there may be considerable utilization of DON by microorganisms in the lower Chowan. While input of DON exceeded output, the reverse was true for both DIN and PN. Specifically, only about two-thirds of the incoming DON left the river at Edenhouse (5013 tonnes input vs. 3194 tonnes output). On the other hand, this loss of 1819 tonnes was nearly matched by gains in DIN and PN. The DIN increased by 1064 tonnes and PN increased by 385 tonnes, so that the net input-output of nitrogen appears to be almost balanced (Table 2). One possible explanation for this simul- taneous loss of DON and gain in DIN and PN is that part of the incoming DON is assimilated by algae and bacteria in the river and sediments and subsequently regenerated in the river as inorganic nitrogen. There could also be adsorption of the DON onto sediments. The assimilatory transformation would explain the continued availability of DIN in the river during the sWf.lmerwhen algal uptake of nitrate and ammonia greatly exceeds the downstream input of these forms (see next section). Despite the indication in Table 2 that nitrogen input and output in the lower Chowan are nearly equal, we must point out that there are several fluxes that are not included in this balance. One is precipitation directly onto the river, In some lakes with small watersheds, precipitation is the most important source of nitrogen (Likens 1975, Wetzel 1975). For the Chowan we made an estimate of this input by multiplying surface area of the river between Winton and Eden- 6 2 house (97.3 x 10 m ) times the average annual precipitation (125 cm*yr-l)times estimated nitrogen content of the rain- water (98 pg ~eliter-') (Harrison 1974) in this region. By this estimate the gain from precipitation is about 22 tonnes per year, or 0.6% of the estimated total input. Thus, in the Chowan, as in most estuaries and lakes with proportionally large drainage areas (Hobbie et al. 1975, Likens 1975), direct input from precipitation is a relatively unimportant nitrogen source. A second input not included in our balance is tributary inflow between Winton and Edenhouse. There is 10% of the total Chowan drainage basin lying between these two points, and the addition of 10% of the nitrogen at Winton (or 724 tonnes) would alter the budget only slightly. Finally, there is a third nitrogen source that we have not taken into account, although it has received much attention as a possible factor in the eutrophication of the Chowan. It is the fertilizer manufacturing plant on the river's bank just below the Winton station. The seepages from this plant into the river have been estimated to be 200 - 500 kg ~.da~-'(G. Cook personal communication) or about 75 - 185 tonnes*yr-l.This amounts to about 10% of the total DIN input, and is probably most significant during the summer when the natural input is very low (e.g.,10 tonnes DIN in August 1975). At that time, the plant seepage of 6 - 15 tonnessmonth-l would nearly double the total DIN input to the river. The annual output of DIN from the Chowan watershed was 0 .11 g ~~m-~nyr-l,which is a little less than that of the Tar-Pamlico River basin and apparently about the same as most in the Southeast. Hobbie et al. (1975) estimated the NH4-N and NO -N input to the Pamlico at 2804 tonnes.yr-l from a 11,128 km 2 drainage basin, or 0.32 g N *m-2*yr-1. Farther -N south, Windom et al. (1975) measured the output of NO 3 and NH4-N from nine rivers between Georgetown, South Carolina and Jacksonville, Florida. The sum of the annual discharges from these rivers was 12,740 tonnes ~1~myr-lfrom a combined water- 2 shed of approximately 217,000 km , or 0.06 g N mm-2*yr-l. Furthermore, the Chowan basin output was near the lower end of the range of estimates compiled by Likens and Bormann (1974) for a diverse group of so-called "undisturbed" forest ecosystems. These comparisons suggest that the Chowan basin as a whole is not discharging unusually high quantities of nitrogen into the river. There is increasing evidence that tidal estuaries like the Chowan can tolerate higher nutrient loading than some lakes because of higher flushing rates in the estuaries. Previous studies have shown that estuaries and even some lakes with rapid flushing rates do not fit Vollenweider's proposed relationship between specific nutrient loading (g ~*rn~of lake surface) and degree of eutrophication (Vollenweider 1968). For example, Dillon (1975) showed that even though nutrient loadings are very high in some lakes, they are not eutrophic because a high flushing rate counteracts the high loading. Both Flemer et al. (1970) for the Patuxent Estuary and Harri- son (1974) for the Pamlico River Estuary found that the DIN input far exceeded Vollenweider's maximum permissible load for the onset of severe eutrophication. For the Pamlico, the

input was around 12 g DIN em-2*yr-1 compared to Vollenweider's estimate of 2 g DIN*m-2ayr-1 as the maximum load for a lake the same depth. Similarly, in the lower Chowan we found that the annual DIN input was 1'1 g ~*m-~*~r-'.Yet this river is not as severely eutrophic as the proposed relationship would predict because the river was flushed 13.6 times (annual flow/river volume) in 1975. %US, the DIN loading was less than 1 g ~*m-~for each flush. As others have concluded, we believe that rapid flushing is the main reason why estuaries are less sensitive than mast lakes to the relatively high loading rates. It would seem, then, that one of the greatest threats to the lower Chowan River is any action that would decrease the flushing rate, especially during the summer when it is already low and when other factors are most favorable for algal growth. Conceivably, this could result from activities such as construction of causeways or dams near the river's mouth that would restrict water flow or circulation, or upstream removal of large quantities of water during the su'mmer .

B, Annual Carbon and Nitrogen Uptake To facilitate comparisons between nitrogen input and nitrogen assimilation in the river, we extrapolated our surface hourly uptake rates to depth-integrated daily and annual rates. The procedure was to first compute for each sampling date the uptake of carbon and nitrogen per m2 of river surface; then we interpolated between these estkmates the rates corresponding to days between samplings. The next step was to sum, for each station, a11 the daily rates to give estimates of monthly and annual uptake per m2 of river surface. Finally, we multiplied these areal rates times the river surface area for estimates of total carbon and nitrogen assimilation in the river (tonne~*~r-'). The depth-integrated die1 estimates were computed by a numerical integration technique similar to that of Fee (1973). Briefly, the technique involves combining in an interpolative scheme measured relationships for uptake rate vs. light, light vs. water depth, and light vs. time of day. The first step was to divide the water column into vertical segments, each 0.2 m khick,and to divide the day into one-hour intervals. Then, for a given time interval, the average light intensity at each depth interval (I,) was calculated by the following equation1

where I, is the average surface light intensity for that hour (from field pyrheliometer data), n is the vertical extinction coefficient in the river (Appendix A), and z is the water depth in meters. Next, photosynthesis and nitrogen uptake rates corresponding to each depth were obtained from rate vs. light intensity curves (e.g., Fig. 15) for that date. These curves were generated from the incubator experiments described above. Finally, summing these rates for each vertical segment gave the hourly areal rate (mg C or mg ~*m-'Sh-~). The procedure was repeated for each hour of the day, and the hourly integrals were summed to give the rates per unit area (Appen- dix F). As Fee noted, this technique assumes that the relationship of photosynthesis to light does not vary during the day. Also, in the present case, we assume that the water column is well mixed so that the vertical distribution of algal cells is homogeneous. Another possible source of error in our procedure involves the absence of solar radiation data for the days between sampling trips. Lack of this information forced us to estimate uptake on days between measurements by linear interpolation rather than by computing the daily integrals from the actual amount of light received at the river. That would lessen the underestimate that could occur from interpolation if, for example, we happened to sample a series of unusually cloudy days in sequence, Certainly, in future studies of this type careful attention should be paid to collecting adequate solar radiation data, especially if the rate measurements are made infrequently. This integration showed that phytoplankton carbon production in the lower Chowan is about the same as it is in nearby estuaries where annual rates have been determined. From 108 g ~*m-~#yr-lat Edenhouse the annual rates decreased slightly upriver to 96 g C*m-2*yr-1 at Winton (Table 3) . Elsewhere along the coast of North Carolina algal production -2 has been estimated to be 50 - 115 g C*m eyr-' in estuaries near Beaufort (Thayer 1971) and 40 - 80 g C*m-2myr-1 in the Pamlico River Estuary (Copeland et al. 1969). Examples of measured annual rates in other areas include 88 g C Omm2 for the Columbia River mouth in the northwest, 107 g C *m-' for . the Wacasassa Estuary on the west coast of Florida, and 193 - 330 g C*m-' for the Patuxent River estuary in Maryland (all examples cited in Thayer 1971). Thus, in 1975, a year when noxious algal blooms did not develop in the lower Chowan, the river's annual phytoplankton production was not unusually high in comparison with these other tidal estuaries. Several studies have shown that ratios of the uptake of carbon to the uptake of nitrogen by phytoplankton are highly variable and usually are lower than the ratios of the concentration of carbon to nitrogen found within algal cells. The most commonly used chemical ratio for algal cells, 6t1 (by weight) was given by Redfield, et al. (1963) . Others have found that the ratio can change as the nutritional environment of the cells changes. Parsons et al. (1961), for example, reported a range of ratios from 4 to 9, and Thomas (1964) observed an increase in the ratio from 5.4 to 16.8 in pure cultures of Dunaliella primolecta as the medium became increas- ingly nitrogen deficient. Nevertheless, carbon to nitrogen uptake ratios, especially if the rates were depth integrated, are usually less than even the lowest of these cellular rates. In one study, Eppley et al. (1973) found that the ratio of carbon to nitrogen uptake integrated over the euphotic zone was often less than 3:1 in the north Pacific. In another Table 3. Annual carbon and nitrogen uptake at four stations in the lower Chowan River

i- * NITROG.EN UPTAKE PHOTOSYNTHETIC STATION CARBON UPTAKE NH4-N NO -N SUM 32 (g Nam *JTF1) *

EDENHOUSE

COLERAIN

HARRELLSVILLE

WINTON

* numbers in parentheses are mg C *literm1ayr-' ' numbers in parentheses are mg ~*liter-'.~r-' study in the subtropical Pacific, Goering et al. (1970) measured ratios less than 1.0 for the depth-integrated uptake rates. These workers speculated that the cause of the low ratios might be heterotrophic uptake of nitrogen by bacteria that were retained on the filters used in the 15~uptake experiments. Similarly, in the Chowan River C:N uptake ratios are often less than 6:1 when calculated from time and depth integrated data. To illustrate the effect of time and depth on the calculation of these ratios, we compared C:N uptake in the Chowan expressed three waysc 1) uptake at the river surface during a short (3 h) time interval, 2) surface uptake per day, and 3) depth-integrated uptake per day. On a short term basis, as exemplified by a die1 experiment (Fig. 16), C:N uptake varied from 60:1 early in the morning to 0.0 after dark. However, when the carbon and nitrogen uptake rates were integrated for the whole day, the CrN ratio was about 10:1, somewhat higher than the expected 611 ratio. However, in this experiment the algae spent no time in darkness during the day as they would in the well mixed Chowan. Therefore, lower ratios might be expected when the rates are depth integrated, since nitrogen uptake, but not photosynthe~is,occurs in the dark. Indeed, the ratios calculated from depth-integrated daily uptake data are lower. Table 4 lists these ratios for the Edenhouse station where they ranged from 0.7 to only 6.9 during the one-year sampling period. There is no obvious pattern in the numbers that might suggest an explanation for the low ratios. Certainly; bacterial uptake is a real possibility in a system like the Chowan where there is considerable detrital material suspended in the water. Pre- sumably, most of the detritus-bacteria aggregate material is retained on the filters used in the 15~uptake experiments. Clearly, we need an experimental technique that would enable us to distinguish between algal and bacterial nitrogen uptake in these measurements. Luxury uptake of nitrogen by the phytczpkkton is another Table 4. Photosynthesis, nitrogen uptake, and calculated C:N uptake ratios for each sampling date at the Edenhouse station. All rates are depth-integrated: to convert to uptake/liter, divide by 4600

NITROGEN UPTAKE PHOTOSYNTHETIC UPTAKE BELOW C UPTAKE DATE CARBON UPTAKE NH4-N NO3-N SUM 1%LIGHT LEVEL N UPTAKE

l9Nov, 1974 0.26 0.06 0.01 0.07 63 3-7 1 Dec 0 .l5 0.01 0.03 0.04 54 3-6 14 Dec 0.04 0.01 0.01 0.02 49 - 5 Jan, 1975 0.05 0.02 0.01 0.03 58 - 20 Jan 0.01 0.01 0.02 0.02 - - 9 Feb 0.01 0.01 0.01 0.02 - - 23 Feb 0.04 0.01 0.01 0.02 51 - 9 Mar 0.01 0.01' 0.01 0.02 - - 23 Mar 0.04 0.01 0.01 0.02 68 2.0 6 Apr 0.03 0 .03 0.01 0.04 31 0.8 20 Apr 0.12 0.08 0.01 0.09 78 1.5 4 May 0.14 0.13 0.01 0.14 79 1.O 19 May 0.20 0.09 0.01 0.10 76 2.0 1 Jun 0.31 0.22 0.02 0.24 79 1.3 15 Jun 0.56 0.60 0.14 - 0.74 58 0-7 28 Jun 0 .86, 0.21 0.06 0.27 60 3 2 14 JU~ 0.28 0.15 0.01 0.16 74 25 ~ul 1.34 0.15 0.12 0.27 77 ;:: 10 AU~ 0.63 0.12 0.06 0.18 55 3-5 31 Aug 0.77 0.04 0.07 0.12 59 6 9 14 Sep 0.74 0.09 0.05 0.14 60 5-2 28 Sep 0.46 0.16 0.24 0.40 67 1.2 12 Oct 0.18 0.03 0.01 0.04 73 5-0 25 0ct 0 .17 0 .03 0.01 0.04 77 4.5 1 16 NOV 0.10 0.01 0.01 0.02 54 5.0 I factor that may be partly responsible for the low carbon: nitrogen uptake ratios for the Chowan samples. The term luxury uptake means that the algae take up more nutrient than they need for growth and metabolism and store the excess nutrient within the cell. Usually, luxury uptake is most noticeable when nutrient concentrations in the water increase from very low levels to higher levels. It may be that excess nitrogen is also taken up by the algal cells during darkness, in anticipation of the need for high cell reserves for the next day.

E, Nitrogen Recycling The seasonal patterns of input and uptake of DIN in the river were completely out of phase (Fig. 19). In January 1975, for example, input was 12 times higher than uptake. By April input had decreased and uptake had increased so that the two were about equal, while later in the summer the uptake rate per month was as high as 75 times the input rate (August). In brief, DIN uptake exceeded input every month from May through October 1975. This pattern suggests rapid nitrogen recycling within the river during summer. Otherwise, high phytoplankton productivity could not have persisted throughout the summer once the input of nitrate and ammonia fell to such low levels. During June and August, in particular, the DIN turnover times (time required for ambient nutrient to be completely removed from the water by algal assimilation. in the absence of additional supply) were as low as 3 to 10 hours. Such short turnover times are strong evidence for a local origin of large quantities of DIN in the river. There are several mechanisms by which nitrogen is recycled within the river, One is simply the remineralization of PN from dead algal cells. Evidently, this process occurs rapidly in summer since PN concentrations did not increase drastically despite th'e slow river flushing and rapid algal I NFLOW UPTAKE OUTFLOW

...... 0...... :.:.:.:.>..... ------

------

------a ------a ------

H P ------y'J y'J ------

a El

ig ------..... 0 ig NIT. AMM. NIT. AMM. NIT. AMM. INFLOW UPTAKE OUTf LOW 415 TOTAL 862 (tonnes) -1277

Fig. 19. Inflow, uptake, and outflow of nitrate and ammonia in the lower Chowan River between November 1974 and November 1975. Size of the blocks is proportional to the quantity of nitrogen. growth rates. Another obvious source of DIN is breakdown of part of the large pool of incoming DON. In the Chowan, differences between input and output suggest that this fraction could have supplied as much as 1800 tonnes of the DIN assimilated between June and November 1975. Undoubtedly, much of this regeneration occurs from the river sediments, as has been shown for other estuaries and lakes (Harrison 1974, Keeney 1972) . Total annual input, assimilation, and output of nitrogen for the lower Chowan are shown in Fig. 20. Input from the watershed accounted for 31% of the nitrogen that was assimilated in the river water. The remaining 2875 tonnes of assimilated DIN came from regeneration within the river. Apparently, most of the DIN that was regenerated was ammonia, since 7.3 times as much ammonia was assimilated as came in. Nitrate assimilation, on the other hand, was about 1.3 times the input. Thus, in terms of management of the Chowan Basin, it is important to consider both the amount of new nitrogen input and the rates of recycling within the river. Obviously, the input of new nitrogen in the long run sets an upper limit to the algal biomass that can develop. Fortunately, most of this input occurs in the winter when other growth factors like temperature and light are unfavorable. However, it has been shown that nutrient remineralization rates increase with increasing temperature (Hale 1975) and, theref ore, are most rapid in summer. The effect of this is an increase in the summer supply of nitrate and ammonia, which in turn boosts the maxiTnum possible algal biomass. In addition, the decomposition of organic matter associated with rapid re,minerali- zation of nutrients creates high oxygen demands and supports the growth of large quantities of bacteria. Both of these side effects are potentially troublesome in the Chowan River, especially since low oxygen concentrations are most likely to develop during the summer when river flow is low and vertical mixing of the water column is poorest. I INPUT FROM WATERSHED

DON

OUTPUT TO ALBEMARLE SOUND

Fig. 20. Total annual input, assimilation, and output (in tonnes) of nitrogen for the lower Chowan River between 1 November 1974 and 31 October 1975. REFERENCES

American Public Health Association. 1971. Standard Methods for the Examination of Water and Wastewater. A.P.H.A., New York. 769 pp. Barsdate, R.J. and R.C. Dugdale. 1965,"Rapid conversion of organic nitrogen to N2 for mass spectrometry: An auto- mated Dumas procedure. " Anal. Biochem. 13: 1-5. Bates, S.S. 1976. "Effects of light and ammonium on nitrate uptake by two species of estuarine phytoplankton." Limnol . Oceanogr . 21 1212-218. Carpenter, J.H., D.W. Pritchard, and R.C. Whaley. 1969. "Observations of eutrophication and nutrient cycles in some coastal plain estuaries." pp. 210-221. In Eutro- phication; Causes, Consequences, correctives. National Academy of Sciences. Copeland, B.J., K.R. Tenore, and D.B. Horton. 1969. "Oligo- haline regime." pp. 789-828. In H.T. Odum, B.J. Cope- land, and E .A. McMahan. (Eds. ) Coastal Ecological Systems of the United States. The Conservation Foundation, Washington, D.C. Daniel, C. C . 1975. "Flow model of the Chowan River Estuary, North Carolina. " U .S . Geological Survey (unpublished) Interim Report. Raleigh, N.C. 9 pp. Dillon, P.J. 1975. "The phosphorus budget of Cameron Lake, Ontario: The importance of flushing rate to the 'degree of eutrophy of lakes." Limnol. Oceanonr. 20828-39. Dugdale, R.C. and J.J. Goering. 1967. "Uptake of new and regenerated forms of nitrogen in primary productivity." Limnol. Oceanonr. 121 196-206. Eppley, R.W., J.N. Rogers, and J.L. McCarthy. 1969. "Half- saturation constants for uptake of nitrate and ammonium by marine phytoplankton." Limnol. Oceanogr. 14:912-920. Eppley, R.W. and J.N. Rogers. 1970. "Inorganic nitrogen assimilation of Ditylum brightwellii, a marine plankton diatom." J, Phycol. 6:344-351. Eppley, R.W., E.H. Ringer, E.L. Vernick, and M.M. Mullin. 1973. "A study of plankton dynamics and nutrient cycling in the central gyre of the North Pacific Ocean." Limnol. Oceanogr. 18:534-551, Falkowski, P.G. 1975. "Nitrate uptake in marine phytoplankton: comparison of half-saturation constants from seven species." Limnol. Oceanogr. 20: 412-417.

Fee, E.J. 1973. "Modeling primary production in water bodies: A numerical approach that allows vertical inhomogeneities." J. Fish. Res. Bd. Canada 30:1469-1473. Flemer, D.A., D.H. Hamilton, C.W. Keefe, and J.A. Mihursky. 1970. "The effects of thermal loading and water quality on estuarine primary production." Report to Office of Water Resources Research, Washington, D.C., 217 pp.

Gilliam, Jaw. and J.F. Lutz. 1972. "Loss of fertilizer nutrients from soils to drainage waters. 11, Nitrogen concentrations in shallow groundwater of the North Carolina coastal plain." Water Resources Research Insti- tute, U.N.C., Report No. 55, Chapel Hill, 25 pp. Goering, J.J,, D.D. Wallen, and R.M. Nauman. 1970. "Nitrogen uptake by phytoplankton in the discontinuity layer of the eastern subtropical Pac ific Ocean. " Limnol. Oceanogr. 158 789-796. Grant, B.R. and I.M. Turner. 1969. "Light stimulated nitrate and nitrite assimilation in several species of algae," Comp. Biochem. Physiol. 291995-1004. Hale, Stephen S. 1975. "The role of benthic communities in the nitrogen and phosphorus cycles of an estuary," pp. 291-308. In F.G. Howell, J.B. Gentry, and M.H. Smith (eds.) Mineral Cycling in Southeastern Ecosystems. NTIS, U.S. ERDA CONF-740513. Harrison, W.G. 1974. "Nitrogen budget of a North Carolina estuary." PhD. Thesis, Department of Zoology, North Carolina State University, Raleigh. 172 pp. Healey, F.P. 1973. "Inorganic nutrient uptake and deficiency in algae." Crit. Rev. Microbial. 3:69-113. Hobbie, J.E. 1971. "Phytoplankton species and populations in the Pamlico River estuary of North Carolina." Water Resources Research Institute, Univ, of North Carolina Report No. 56, Chapel Hill, 147 pp. Hobbie, J.E. 1972. "Phosphorus and eutrophication in the Pamlico River Estuary, North Carolina." Water Resources Research Institute , Univ. of North Carolina Report No. 65, Raleigh, 86 pp. Hobbie, J.E. 1974. "Nutrients and eutrophication in the Pamlico River Estuary, North Carolina: 1971-1973." Water Resources Research Institute, Univ. of North Carolina Report No. 100, Raleigh, 239 pp. 57 Hobbie, J.E. 1975 "Nutrients in the Neuse River Estuary." Sea Grant Publication Univ. of North Carolina SG-75-21. Raleigh, 183 pp. Hobbie, J.E., B.J. Copeland, and W.G. Harrison, 1975. "Sources and fates of nutrients of the Pamlico River Estuary, North Carolina." pp. 287-302. In L.E. Cronin (Ed.) Estuarine Research, Vol. I. Academic Press, New York. Karlgren, L. 1962. "Vattenkemiska analy~metoder.~Revised mimeographed edition. Limnology Inst., Uppsala, Sweden, 118 pp. Keeney, D.R. 1972. "The fate of nitrogen in aauatic ecosystems." Eutrophication ~nformazion~roiram, Univ. of Wisconsin; Madison, Literature Review'Mo. 3, 59 pp. Lehman, J.T.! D.B. Botkin, and G.E. Likens. 1975. "The assumptions and rationales of a computer model of phytoplankton population dynamics." Limnol. Oceanogr. 20: 343-364, Liddicoat, M.I.! S. Tibbitts, and E.I. Butler. 1975 "The determination of ammonia in seawater." Limno1,Oceanogr. 20r131-132. Likens, G.E. 1975. "Nutrient flux and cycling in freshwater ecosystems.,,'pp. 314-348. In F.G. Howell, J.B. Gentry, and M.H. Smith (Eds.) Mineral Cycling in Southeastern Ecosystems. NTIS, U .S ERDA CONF-740513. Likens, G.E. and.F.H. Bormann. 1974. "Linkages between terrestrial and aquatic ecosystem^.^ Bioscience 24~447-456.

Lund, J.W., C, Kipling, and E.D. LeCren. 1958. "The inverted microscope method of estimating algal numbers and the statistical basis of estimations by counting." Hydro- biolo~ia11 :143-170. McCarthy, J.J. 1972. "The uptake of urea by natural populations of marine phytoplankton." Limnol. Oceanogr. 17r738-748. McCarthy, J.J. and R.W. Eppley. 1972. "A comparison of chemical, isotopic, and enzymatic methods for measuring assimilation in marine phytoplankton." Limnol. Oceanogr. 17: 371-382. McCarthy, J.J., W.R. Taylor, and J.L. Taft. 1975. "The dynamics of nitrogen and phosphonus cycling in the open waters of the Chesapeake Bay." 'AmericanChemical Society Sym- posium Series No. 18: Marine Chemistry in the Coastal Environments. MacIssac, J.J. and R.C. Dugdale. 1969. "The kinetics of nitrate and ammonia uptake by natural populations of marine phytoplankton." Deep-sea Research 16r45-57. MacIssac, J.J. and R.C. Dugdale. 1972. "Interactions of light and inorganic nitrogen in controlling nitrogen uptake in the sea." Deep-Sea Research 19: 209-232. Packard, T.T. 1973. "The light dependence of nitrate reductase in marine phytoplankton." LLimno1. Oceanogr. 18t466-469. Parsons, T.R., KO Stephens, and J.D.H. Strickland, 1.961. "On the chemical composition of eleven species of marine phytoplankters." J, Fish. Res. Bd, Canada 18~1001-1016. Redfield, A.C., B.H. Ketchum, and F.A. Richards, 1963. "The influence of organisms on the composition of seawater." In M.A. Hill (Ed,) The Sea, Vol. 2, pp, 27-79. Inter- science, New York, Solorzano, L. 1969. "Determination of ammonia in natural waters by the phenylhypochlorite ,method." Limnol. Oceanogr. 14%799-801. Steemann-Nielsen, E. 1952. "The use of radioactive carbon (14-C) for ,measuring organic carbon production in the sea." JO Cons. Expl, Mer. 18:117-140. Strickland, J.D.H. 1958. "Solar radiation penetrating the ocean: A review of require,ments, data and methods of measure,ment, with particular reference to photos nthetic productivity." J. Fish. Res. Bd. Canada 15:453- E93. Strickland, J.D.H. and T.R. Parsons. 1968. A Practical Hand- . Bull, Fisheries Res. Bd,

Thayer, G,W. 1971. "Phytoplanktorl production and the distribution of nutrients in a shallow unstratified estuarine system near Beaufort, North Carolina." Chesapeake Sci- ence 12: 240-253. P Thomas, W.H. 1964. "An experimental evaluation of the 14c method for measuring phytoplankton production, using cultures of Dunaliella primolecta Butcher." Fish. Bull. 63: 273-292. Vollenweider, R .A. 1968. I1Scientific fundamentals of the eutrophication of lakes and flowing waters, with particular reference to nitrogen and phosphorus as factors in eutrophication, " O .E. C .D. DAS/CSI/~~.27. 159 pp. Vollenweider , R .A. 1974. Primary Production in Aquatic Environments. IBP Handbook No. 12. Blackwell Scientific Publications, London. 225 pp. Weiss, C.M. and E.J. Kuenzler. 1976. "The trophic state of North Carolina lakes." Water Resources Research Institute Univ. of North Carolina, Report No. 119, Raleigh, 224 pp. Wetzel, R.G. 1975. Limnolom. W.B. Saunders, Philadelphia. 743 PP* Whitford, L,A. 1958. "Phytoplankton in North Carolina lakes and ponds." Journal Elisha Mitchell Scientific Society 748 143-157. Windom, H.L., W.M. Dunstan, and W.S. Gardner. 1975. "River input ofbhorganicphosphorus and nitrogen to the southeastern salt-marsh estuarine environment." pp. 309-313. In F.G. Howell, J.B. Gentry, and M.H. smith (Eds.) Mineral Cycling in Southeastern Environments. NTIS, U.S. ERDA CONF-740513, APPENDICES

A. Hydrographic and nutrient data for lower Chowan River stations ...... 62

C. Algal wet weight bio,mass . . . , . . , . . , . . , . 73 Dm Algal photosynthesis data ...... 78

F. Depth-integrated daily uptake of carbon, nitrate, and ammonia ...... = 123 G. Cumulative uptake of carbon, nitrate, and ammonia . . 126 APPENDIX A. HYDROGRAPHIC AND NUTRIENT DATA FOR LOWER CHOWAN RIVER STATIONS

ABBREVIATIONS AND UNITS

STA = Station E: Edenhouse C: Colerain H: Harrellsville W: Winton

TEMP = River Water (surface) Temperature (OC)

EXT = River Water Extinction Coefficient (m-l)

ALK = Alkalinity (mg C liter-1)

NO2 = Nitrite Nitrogen (pg N liter-')

NO3 = Nitrate Nitrogen (pg N liter-l)

NHq = Ammonia Nitrogen (pg N ' liter-l)

PN = Particulate Nitrogen (pg N liter-') APPENDIX A. (continued)

DATE -STA -TEMP -EXT -ALK NO? 19 Nov 74 2.3 9.17 1.99 - - - 2.2 4.86 0.92 2.6 4.58 1.04 0.84 0.66 1.27 1.15 1.22 1.27

1 Dec 74 3.8 9.724 2.03 - - - 4.0 4.740 1.36

2.6 5.435 2.83 3.11 3.44 2.71 2.52 2.94

14 Dec 74 10.2 8.740 4.61 - 7.487 5.43 3.3 4.438 3.88

2.1 4.788 2.44

5 Jan 75 9.8 9.016 3.26 2.94 5.7 4.953 3.36 APPENDIX A. (continued)

EXT ALK NO NO PN DATE -STA TEMP - pH - -2 -3 NH, - 3.12 466.2 299.6 103 C 7.6 5.1 7.3 6.570 24.50 541.8 96.6 273 23.94 539.0 96.6 247 E 7.8 3.3 7.0 4.862 14.00 343.0 42.3 230 14.14 365.4 44.8 %HI1 . 20 Jan 75 W 5.0 11.5 6.5 4.815 1.41 2.44

9 Feb 75 W 7 6.2 7.1 3.205 0.56 337.5 0.84 241.9

23 Feb 75 W 9.0 4.2 7.0 2.735 0.36 283.6 - 87 0.73 249.0 - 98 H 10.2 - 6.6 2.955 0.95 247.4 81.5 120 0.76 217.4 0.81 108 111 C 9.3 - 6.8 3.333 0.59 481.6 60.1 97 1.26 389.5 17.5 9 1 APPENDIX A. (continued)

-DATE -STA -TEMP -EXT -ALK E 9.5 - 3.269

9 Mar 75 W 6.5 4.4 3.798

5.7 - 3.038

8.0 - 2.734

8.0 - 2.431

23 Mar 75 W 11.8 7.1 3.105

11.8 - 2.628

12.2 7.1 2.034

11.5 - 3.026

6 Apr 75 W - 5.75 2.042

10.0 - 3.062

10.3 5.75 1.913

10.5 - 2.272 -DATE -STA -TEMP -EXT -ALK 20 Apr 75 W 14.5 4 3.511

15.2 - 4.063

15.4 5.75 2.709

14.5 - 2.709

4 May 75 W 18.0 4.2 5.288

18.4 3.8 4.132

18.9 3.6 3.46

17.7 4.0 2.91

19 May 75 W 20.9 2.9 4.942

H 21.4 2.7 5.127

C 21.9 3.3 4.138

E 21.4 5.4 3.522 APPENDIX A. (continued)

-DATE -STA -TEMP -EXT -ALK 1 June 75 W 26.0 2.6 4.15

H 26.0 2.9 5.74

C 25.1 3.0 5.10

E 25.2 3.3 4.47

15 June 75 W 25.7 3.54 6.71

26.8 - 5.62

- - 5.37

E 25.6 2.71 6.74

28 June 75 W 27.5 2.8 7.218

H 27.5 - 8.383

C 26.0 - 7.442 AE PENDlX A. (con t inued)

DATE STA TEMP l!!! ALK NO NO PN - - - -2 -3 NH, -

14 July 75 W - - 7.0 4.567 1.88 2.14

25 July 75 W 24.5 - 6.0 10.164 2.41 54.9 2.70 58.2

10 Aug 75 W 28.0 2.8 7.0 4.8073 11.42 35.0 9.2 279 8.96 34.2 7.6 269 268 H 28.4 - 7.0 4.5068 7.27 24.4 5.8 35 2 1.26 11.1 3.6 337 334 C 28.3 3.0 7.6 2.2934 9.42 4.2 15.6 30 9 7.27 7.2 10.9 312 29 2 APPENDIX A. (continued)

DATE STA TEMP ALK NO NO - - - - -2 -3 NH, E 28.1 1.9913 15.43 13.9 41.4 13.24 13.4 33.3

31 Aug 75 W

14 Sept 75 W

28 Sept 75 W

C APPENDIX A. (continued)

DATE -STA -TEMP -EXT -ALK E 23.5 - 3.5107

12 Oct 75 . W - - 4.6950

H - - 3.3536

C 20.0 4.11 2.6829

E 20.0 - 3.0183

25 Oct 75 W 18.0 2.88 4.5068

H 19.2 3.17 4.1697

2.4307

2.5891

APPENDIX B. TOTAL KJELDAHL NITROGEN DATA

DATE STATION" TKN DATE STATION TKN (pa liter-l) (ua N-liter-') 15 Jun, 1975 E 50 14 Sep, 1975 E 1100 C 800 C 930 H 1200 H 920 W 880 W 940

-1 i-.I 28 Jun, 1975 .a 480 28 S~P,1975 2, 500 C 870 C 1030 H 970 H 1670 w 1010 W 980 14Jul,1975 E 940 12 Oct, 1975 E 960 C 540 C 1333 H 1280 H 1400 W 1040 W 7 40 25 Jul, 1975 E 1130 25 Oct, 1975 E 590 C 900 C 950 H 1160 H 1230 W 1310 W 4-90 28 Nov, 1975

a. E = Edenhouse C = Colerain H = Harrellsville W = Winton APPENDIX C . ALGAL WET WEIGHT BIOMASS IN THE LOWER. CHOWAN RIVER

BAC = BACILLARIOPHYCEAE CYA = CYANOPHYCEAE CHL = CHLOROPHYCEAE DIN = DINOPHYCEAE CHR = CHRY SOPWCEAE EUG = E GLENOPHYCEA CRY = CRYPTOPHYCEAE, UNK = UNKNOWN

DATE STATION DEPTH WET WGT. (mg liter-') (meters) BAC CHL CHR CRY CYA DIN EVG UNK TOTAL

19 Nov 1974 W 19 Nov 1974 C 19 Nov 1974 E 19 Nov 1974 E 19 Nov 1974 E 19 Nov 1974 E 19 Nov 1974 E 19 Nov 1974 E -3 19 Nov 1974 E W 1 Dec 1974 1 Dec 1974 1 Dec 1974 1 Dec 1974 1 Dec 1974 1 Dec 1974 1 Dec 1974 1 Dec 1974

14 Dec 1974 W S 0.13 0.06 0.00 0.04 0.02 0.00 0.01 0.01 0.25 14 Dec 1974 H S 0.32 0.12 0.00 0.07 0.03 0.00 0.01 0.03 0.56 14 Dec 1974 C S 2.33 0.24 0.00 0.18 0.17 0.00 0.00 0.04 2.95 14 Dec 1974 E S 1.77 0.44 0.00 0.08 0.06 0.00 0.00 0.07 2.42

5 Jan 1975 W S 0.09 0.02 0.00 0.04 0.00 0.06 0.04 0.00 0.26 5 Jan 1975 H S 0.20 0.00 0.00 0.03 0.00 0.00 0.01 0.01 0.24 5 Jan 1975 C S 8.50 0.40 0.00 0.46 0.05 0.00 0.00 0.10 9.52 5 Jan 1975 E S 1.38 0.10 0.03 0.05 0.00 0.00 0.00 0.03 1.59 mmmm 30-4-.... 0444

OONrl rlrlmN 0000 0000 dddd dddd

N4ON Nc00N ooorl.... 0000 0000 dddd

QQOO QOOO rlooo 4 0 0 0 0000 0000 4004 rlooo.... dddd dddc; 0 0 0 0

ONOQ 0000 dddd

mmNQ 004N oood...

0040 ooorl 0000 0000.... dddd 0000

NcOrlN rld-mo.... OOON

mmmm mmmm

mmmm mmmm mmmm mmL?ln hhhh hhhh mmmmhhhb hhhh mmmm mmmm m m m m rlrlrlrl 4444 4rlrlr-l rl 44rl aaaa 44-44 mmmm mmmm mmmm 0000 NNNN NNNW APPENDIX C . (continued)

DATE STATION DEPTH WET WGT. (mg liter-') (meters) BAC CHL CHR CRY CYA DIN EUG UNK TOTAL

4 May 1975 W S 0.05 0.18 0.01 0.35 0.01 0.45 0.00 0.03 1.08 4 May 1975 H S 0.18 0.07 0.01 0.88 0.00 0.65 0.40 0.07 2.25 4 May 1975 C S 2.71. 1.05 0.84 0.64 0.24 0.00 1.14 0.14 6.76 4 May 1975 E S 0.86 0.09 0.00 0.05 0.06 0.00 0.00 0.03 1.09

19 May 1975 W S 19 May 1975 H S 19 May 1975 C S 19 May 1975 E S

1 Jun 1975 1 Jun 1975 1 Jun 1975 1 Jun 1975 4 Ln 15 Jun 1975 15 Jun 1975 15 Jun 1975 15 Jun 1975

28 Jun 1975 W S 28 Jun 1975 H S 28 Jun 1975 C S 28 Jun 1975 E S

14 Jul 1975 W S 14 Jul 1975 H S 14 Jul 1975 C S 14 Jul 1975 E S

25 Jul 1975 W S 0.79 0.03 0.00 0.00 3.69 0.00 0.19 0.02 4.72 25 Jul 1975 H S 0.56 0.00 0.00 3.86 0.10 1.10 0.00 0.02 5.65 25 Jul 1975 C S 1.02 0.09 0.05 0.47 0.11 0.00 0.00 0.10 1.84 25 Jul 1975 E S 0.66 1.03 0.00 1.25 7.68 5.50 0.56 0.56 37.23 APPENDIX C . (continued)

DATE STATION DEPTH WET WGT. (mg liter-') (meters) BAC CHL CHR CRY CYA DIN EUG UNK TOTAL

10 Aug 1975 10 Aug 1975 10 Aug 1975 10 Aug 1975

31 Aug 1975 31 Aug 1975 31 Aug 1975 31 Aug 1975

31 Aug 1975 31 Aug 1975 31 Aug 1975 31 Aug 1975 31 Aug 1975 31 Aug 1975 31 Aug 1975 1 Sep 1975 1 Sep 1975 1 Sep 1975

14 Sep 1975 14 Sep 1975 14 Sep 1975 14 Sep 1975

28 Sep 1975 28 Sep 1975 28 Sep 1975 28 Sep 1975 mhlm omm... ON*

ooorl 0 0 0 w

rlmoco ooom ooorl....

me0 omm ddd

\Dmhl* orlmo dddd

rlrl*co www ommm omm... dddd dddd OrlN

500 moo mmmm mmmm w N mom

mmmm mmmm hhhh h h h h mmmm mmmm rlrlrlrl rlrlrlrl UUUU UUUU u u u u uuuu 0 0 0 0 0000 NNNN wwww rl rl rl rl rl rl rl rl ana$ 0 hrl APPENDIX D. (continued)

Date: 1 Dec 74 Date: 14 Dec 74

Incubation Started: 12:30 Incubation Started: 1:00 Ended : 5:05 Ended : 5:15 Mean Io: 0.30 Mean Io: 0.32 Time : EST TTme : EST TEMP LIGHT PHOTO -S TA TEMP LIGHT PHOTO 15.77 16.33 8.63 4.26 - 33.62 35.20 21.05 13.22 13.73 14.30 9.05 4.88 13.83 15.86 13.79 14.27 12.67 APPENDIX D. (continued)

Date: 5 Jan 75

Incubation Started: 1:27 Ended : 5:10 Mean I,: 0.27 Time : EST

STA TEMP - - LIGHT PHOTO LIGHT PHOTO

1.157 100 5.891 1.096 33 8.194 0.704 12 6.486 0.492 5 3.288 3.114 100 23.505 1.889 33 17.003 1.073 12 12.521 0.279 5 5.875 5.289 100 43.963 2.902 33 32.938 1.459 12 17.113 0.492 5 7.644 0.577 100 1.832 0.602 33 2.330 0.519 12 1.559 0.387 5 0.853 1.864 100 10.019 1.391 33 8.854 0.743 12 6.638 0.224 5 2.852 4.109 100 22.288 2.952 33 17.841 1.440 12 11.358 0.461 5 3.211 APPENDIX D. (continued)

Date: 20 Jan 75

Incubation Started: 12: 15 Ended : 5:15 Mean 1,: 0.025 Time : EST

-STA -TEMP LIGHT PHOTO. -STA TEMP LIGHT PHOTO APPENDIX D. (continued)

Date: 9 Feb 75

Incubation Started: 12:30 Ended : 5:15 Mean Io: 0.34 Time : EST

-STA TEMP LIGHT PHOTO -STA LIGHT PHOTO 0.23 0.70 0.37 0.23 1.22 1.18 0.76 0.38 2.22 1.84 0.86 0.43 0.15 0.26 0.30 0.20 0.74 0.92 0.65 0.27 1.91 1.54 0.63 0.38 APPENDIX D. (continued)

Date: 23 Feb 75

Incubation Started: 11:46 Ended : 6:05 Mean Io: 0.30 Time : EDT

-STA TEMP LIGHT PHOTO -STA TEMP LIGHT PHOTO OWNmOWN~OmNmOmNmOWN~OWNLn omrl omrl omrl omrl omrl omrl rl I+ 4 rl rl rl APPENDIX D. (continued)

Date: 23 March 75

Incubation Started: 12:44 Ended : 5:15 Mean 1,: 0.75 Time : EDT

STA TEMP - - LIGHT PHOTO -S TA -TEMP LIGHT PHOTO -uate: 6 April 75

Incubation Started: 12:05 Ended : 6:08 Mean Io: - Time : EDT -STA TEMP LIGHT PHOTO -STA TEMIJ LIGHT PHOTO 0.379 C 3 100 0.351 0.561 33 0.528 1.220 12 0.953 1.334 5, 1.053 3.271 14 100 4.069 5.688 33 6.814 4.401 12 5.941 3.107 5 4.289 9.177 25 100 15.600 10.540 33 17.159 6.003 12 12.152 4.473 5 10.062 1.291 E 3 100 0.049 1.651 33 0.389 2.129 12 0.742 2.154 5 0.894 5.398 14 100 3.977 7.717 33 6.838 6.064 12 4.845 4.846 5 4.100 15.714 25 100 14.983 16.425 33 15.474 10.286 12 12.050 7.953 5 8.989 APPENDIX D. (continued)

Date: 20 April 75

Incubation Started: 11:35 Ended : 4:20 Mean I,: 1.1 Time : EDT -ST A -TEMP LIGHT PHOTO -S TA -TEm' LIGHT PHOTO 0.66 C 9 100 2.96 33 6.64 12 5.99 5 6.79 15 100 15.56 33 12.30 12 7.43 5 22.13 28 100 30.21 3 3 16.11 12 6.64 5 1.12 E 9 100 5.66 3 3 12.90 12 11.06 5 8.24 15 100 23.45 3 3 21.48 12 10.32 5 28.86 2 8 100 44.27 33 25.16 12 11.26 5 AFPEhiIX D. (continued)

Date: 4 May 75

Incubation Started: 12:05 Ended : 5:05 Mean 1,: 0.97 Time : EDT

-STA -TEMP LIGHT PHOTO -ST A TEMP LIGHT PHOTO APPENDIX D. (continued)

Date: 19 May 75

Incubation Started: 11:15 Ended : 4:25 Mean I,: 0.31 Time : EDT -STA -TEMP LIGHT PHOTO -STA TEMP LIGHT PHOTO APPENDIX D. (continued)

Date: 1 June 75

Incubation Started: 12:15 Ended : 4:15 Mean Io: 0.60 Time :EDT

-STA -TEMP LIGHT PHOTO -STA TEMP LIGHT PHOTO

26.48 C 11 39.76 38.84 24.05 90.09 89.06 52.28 12.14 148.73 106.57 49.25 29.47 44.00 67.08 62.61 40.78 130.39 121.95 79.52 20.09 222.78 165.96 85.48 44.20 APPENDIX D. (continued)

Date: 15 June 75

Incubation Started: 11:20 Ended : 3 :25 Mean 1,: 1.05 Time : EDT

-STA -TEMP LIGHT -STA TEMP LIGHT PHOTO W 10 100 3 3 12 5 100 3 3 12 5 100 3 3 12 5 100 3 3 12 5 100 3 3 12 5 100 3 3 12 5 APPENDIX D. (continued)

Date: 28 June 75

Incubation Started: 12:35 Ended : 5:05 Mean I,: 0.43 Time : EDT

-STA TEMP LIGHT PHOTO -STA LIGHT PHOTO 5.2 7.8 10.9 11.1 50.1 61.0 44.9 19.0 105.2 87.4 44.2 17.1 7.2 12.6 16.7 13.1 69.6 92.5 64.8 36.1 131.5 141.0 65.4 24.9 APPENDIX D. (continued)

Date: 14 July 75

Incubation Started: 11:35 Ended : 10°C-2:40, 24OC-2:37, 34°C-2:35 Mean Io: 0.22 Time : EDT

TEMP LIGHT PHOTO -Tm LIGHT PHOTO APPENDIX D. (continued)

Date: 25 July 75

Incubation Started: 12:13 Ended : 2:15 Mean Io: 0.70 Time : EDT

-STA TEMP LIGHT PHOTO -STA -TEMP LIGHT PHOTO APPENDIX D. (continued)

Date: 10 Aug 75

Incubation Started: 12:00 Ended : 2:15 Mean I,: 0.56 Time : EDT

-TEMP LIGHT PHOTO -STA . TEMP LIGHT PHOTO APPENDIX D. (continued)

Date: 31 Aug 75

Incubation Started: 12:08 Ended : 2:10 Mean I,: 0.89 Time : EDT

-STA TEMP LIGHT PHOTO LIGHT PHOTO om~mom~mom~mom~mom~mom~m omrl om4 omrl om4 omrl omrl 4 rl rl rl rl rl APPENDIX D. (continued)

Date: 28 Sept 75

Incubation Started: 12:07 Ended : 2:12 Mean Io: 0.90 Time : EDT

-STA -TEMP LIGHT PHOTO -STA TEMP LIGHT PHOTO 0.77 0.98 0.70 0.63 1.4 1.4 1.2 1.0 2.7 2.5 1.3 - 3.7 7.4 6.3 4.0 9.6 11.8 8.0 6.1 18.1 18.4 11.4 1.8 APPENDIX D. (continued)

Date 12 Oct 75

Incubation Started: 12: 24 Ended : 2:36 Mean Io: 0.92 Time : EDT

STA TEMP LIGHT PHOTO STA TEMP PHOTO - - - - - LIGHT

C APPENDIX D. (continued)

Date: 25 Oct 75

Incubation Started: 12: 00 Ended : 2:05 Mean 1,: - Time : EDT

TEMP LIGHT PHOTO -STA TEN? LIGHT PHOTO 100 7.1 33 - 12 3.4 5 2.5 100 7.8 33 6.5 12 4.7 5 2.9 100 7.3 3 3 5.8 12 4.9 5 3.2 100 4.5 33 24.7 12 24.9 5 24.2 100 42.6 33 42.8 12 23.1 5 15.0 100 53.8 33 42.4 12 18.9 5 28.8 APPENDIX D. (continued)

Date: 16 Nov 75

Incubation Started: 11:47 Ended : 2:00 Mean Io: 0.64 Time : EST -STA -TEMP LIGHT PHOTO .. -STA TEMP -LIGHT PHOTO C 6 100 55 33 12 5 100 55 33 12 5 100 55 33 12 5 100 55 3 3 12 5 100 55 33 12 5 100 55 33 12 5 APPENDIX E. 15~~~~~~~~UPTAKE DATA FOR CHOWAN STATIONS

Abbreviations and Units

STA = River Station TEMP = Incubation Temperature (OC) - LIGHT = Incubation light intensity as per cent of ambient (Io) light intensity (ly/min) ADDED 15-NO = Nitrate addition to incubation ' bottle as ug l liter ADDED 15-NH4 = Ammonia addition to incubation

bottle as vg- l liter UPTAKE NO3 = ug Nmliter-1 ,h-l UPTAKE NH4 = pg N'liter -1.h-l APPENDIX E. (continued)

Date: 6 April 75 15-NO3 15-NH4 Incubation Started: 12:OO 11:55 Ended : 6:lO 6:lO Time : EDT

STA TEMP LIGHT ADDED UPTAKE ADDED UP TAKE - - 15-NO3 NO3 15-NH4 NH4 W 3 -APPENDIX E. (continued) Dare: 6 April 75

STA TEMP LIGHT ADDED UPTAKE ADD ED UPTAKE - - 15-NO3 NO3 15-NH4 NH4 APPENDIX E. (continued)

Date: 20 April 75 15-NO3 15-NH4 Incubation Started: 11: 25 11 :20 Ended : 4:10 4: 10 Mean Io: 1.1 1.1 Time : EDT

TEMP LIGHT ADDED UP TAKE ADDED UPTAKE - 15-NO3 NO 3 15-NJ34 NH4 9 100 0.04 28 - 15 100 0.06 28 0.99 3 3 0.07 28 1.40 12 0 28 1.34 5 0 2 8 1.19 2 8 100 0.16 28 - 9 100 0.06 2 8 0.015 15 100 0 0.35 3 3 0.01 0.45 12 0.02 0.15 5 0.02 0.44 2 8 100 0 0.98 9 100 0.11 2 8 0.68 15 100 0.15 2.31 33 0.27 2.77 12 0.26 2.75 5 0.21 2.87 100 0.89 5.77 9 100 0.30 28 0.74 100 0.66 2.26 33 0.73 2.71 12 0.78 - 5 0.85 3.02 100 1.83 4.68 APPENDIX E. (continued)

Date: 4 May 75 15-NO3 15-NH4 Incubation Started: - 12 :00 Ended : - 5:OO Mean 1,: - 0.84 Time : EDT

S TA TEMP LIGHT ADDED UPTAKE ADD ED UPTAKE - - 15-NO3 NO 3 15-NH4 NH4 100 100 100 100 100 100 DARK DARK DARK DARK 10 0 100 100 100 10 0 100 10 0 100 DARK DARK DARK DARK 100 100 100 100 100 100 100 100 DARK DARK DARK DARK 100 100 APPENDIX E . (continued)

Date: 4 May 75

TEMP LIGHT ADDED UPTAKE ADDED UP TAKE 15-NO3 NO3 15-NH4 NH 4

100 23.3 100 100 100 100 100 DARK DARK DARK DARK 100 100 APPENDIX E. (continued)

Date: 19 May 75 15-NO3 15NH4 Incubation Started: 11 :00 11 :00 Ended : 4:15 4:15 Mean Io: 0.30 0.30 Time : EDT

TEMP LIGHT ADDED UPTAKE ADDED UPTAKE - 15-NO3 NO3 15-NH4 NH4 7 100 28 0.22 14 0.83 2 0 100 2 8 2.02 14 3.68 20 3 3 28 1.41 14 4.10 20 12 28 Q. 35 14 3.50 2 0 5 28 - 14 1.86 30 100 28 3.08 14 2.77 7 100 28 0.06 14 0.48 20 100 28 0.25 14 3.33 2 0 3 3 28 0.19 14 3.33 20 12 28 0.06 14 2.97 2 0 5 28 0.06 14 1.59 30 100 28 0.37 14 5.64 7 100 28 0.03 14 0.41 2 0 100 29 0.11 14 2.40 20 3 3 28 0.10 14 2.53 20 12 28 0.05 14 2.29 20 5 2 8 0.02 14 1.62 30 100 28 0.13 14 4.48 7 100 2 8 - 14 0.33 20 100 2 8 - 14 2.92 20 33 2 8 - 14 3.03 20 12 2 8 0.08 14 1.56 20 5 28 0.07 14 1.94 30 100 28 0.44 14 -

APPENDIX E. (continued)- Date: 1 June 75 15-NO3 15NH4 Incubation Started: - 12:OO Ended : - 4:lO Mean I,: - 0.60 Time : EDT

STA TEMP LIGHT ADDED UP TAKE ADDED UPTAKE - - - 15-NO3 NO3 15-NH4 NH4 W 20 100 100 100 10 0 TK DARK H 20 100 100 100 10 0 TK DARK C 20 100 100 100 100 TK DARK E 20 100 100 100 100 TK DARK APPENDIX E. (continued)

Date: 15 June 75 15-NO3 15-NH4 Incubation Started: 11 :10 - Ended : 3:25 - Mean I,: 1.05 - Time : EDT

S TA TEMP LIGHT ADDED UPTAKE ADDED UP TAKE - - - 15-NO3 NO 3 15-NH4 NH4 100 3 3 12 5 TK DARK 100 33 12 5 TK DARK 100 3 3 12 5 TK DARK 100 33 12 5 TK DARK APPENDIX E. (continued)

Date: 15 June 75 15-NO3 Incubation Started : - Ended : - 3: 25 Mean Io: - 1.05 Time EDT

S TA TEMP LIGHT ADDED UPTAKE ADDED UP TAKE - - 15-NO3 NO 3 15-NH4 NH4 W 20 100 - 100 - 100 - 100 - TK - DARK - 100 9.73 100 10.54 100 9.92 100 9.29 TK 0.94 DARK 7.80 100 10.63 100 12.41 100 12.11 100 10.20 TK 0.06 DARK 10.44 100 13.39 100 14.03 100 13.34 100 10.90 TK 0.15 DARK 13.70 -APPENDIX E. (continued) Date: 28 June 75 15-NO3 15-NH4 Incubation Started: 12 :45 - Ended : 4:55 - Mean Io: 0.43 - Time : EDT

STA TEMP LIGHT ADDED UPTAKE ADDED UP TAKE 15-NO3 NO 3 15-NH4 NH4

100 33 12 5 DARK 100 100 100 33 12 5 DARK 100 100 100 100 100 100 100 100 DARK 100 33 12 5 DARK 100 100 APPENDIX E. (continued)

Date: 28 June 75 15-NO3 15-NH4 Incubation Started: - 12 :45 Ended : - 4:55 Mean Io: - 0.43 Time : EDT

TENP LIGHT ADDED UPTAKE ADDED UPTAKE 15-NO3 NO 3 15-NH4 NH4

20 100 2.97 100 3.80 100 4.83 100 6.03 DARK 2.65 20 100 0.04 100 3.74 100 2.68 100 2.62 DARK 0.54 20 100 2.67 100 4.41 100 6.01 100 5.31 DARK 2.74 20 100 5.79 100 4.32 100 5.28 100 4.90 DARK 0.72 APPENDIX E . (continued) - Date: 14 July 75 15-NO3 15-NH4 Incubation Started: 12:OO 12:05 Ended : 4:00 4 :00 Mean Io: 0.40 0.39 Time : EDT

TEMP LIGHT ADDED UPTAKE ADDED UP TAKE 15-NO3 NO3 15-NH4 NH4

100 14 0.0 7 2.4 100 2 8 0.08 28 2.6 100 42 0.09 42 2.6 100 56 0.11 56 2.6 100 14 0.07 14 3.4 DARK 14 - 14 1.7 100 14 0.0 7 0.0 100 28 0.0 2 8 4.7 100 4.2 0.0 42 1.3 100 5.6 0.0 56 0.1 100 14 0.0 14 7.6 DARK 14 0.0 14 2.1 100 14 2.4 7 5.1 100 28 2.5 28 7.9 100 42 2.5 42 8.3 100 56 2.2 56 9.0 100 14 3.4 14 6.0 DARK 14 3.8 14 0.0 100 14 0.08 7 5.1 100 28 0.07 28 3.9 100 42 0.07 42 5.2 100 56 0.09 56 5.0 100 14 0.04 14 7.4 DARK 14 0.0 14 0.8 APPENDIX E. (continued)

Date: 25 July 75 15-NO3 15-NH4 Incubation Started: 12:05 12:03 Ended : 2:20 2:20 Mean 1,: 0.68 0.68 Time : EDT

STA TEMP LIGHT ADDED UP TAKE ADDED UP TAKE - - 15-NO3 NO 3 15-NH4 NH4 100 100 100 100 100 DARK 100 100 100 100 100 DARK 100 100 100 100 100 DARK 100 100 100 100 100 DARK APPENDIX E. (continued)

Date: 10 Aug 75 15-NO3 15-NH4 Incubation Started : 12 :O5 12:15 Ended : 2:25 2:25 Mean 1,: 0.54 0.53 Time :EDT

STA TEMP LIGHT ADDED UP TAKE ADDED UPTAKE - 15-NO3 NO 3 15-NH4 NH4

W 14 6.12 7 3.92 2 8 5.87 28 6.69 42 5.27 4 2 5.91 5 6 6.07 5 6 7.24 42 - 42 - 4 2 - H 14 6.89 7 3.35 2 8 - 2 8 - 42 7.30 42 9.37 56 6.74 56 8.80 42 - 42 - 42 - C 14 1.47 7 5.42 2 8 1.50 28 6.18 42 - 42 5.85 56 - 5 6 5.53 42 - 42 - 42 - E 14 - 7 3.83 28 - 2 8 4.31 4 2 - 42 4.68 56 0.13 56 4.76 42 - 42 - 42 - APPENDIX E. (continued)

Date: 31 Aug 75 \ 15-NO3 15-NH4 Incubation Started: 12: 20 12 :20 Ended : 2:16 2:16 Mean I, : 0.89 0.89 Time : EDT

TEMP LIGHT ADDED UPTAKE ADDED UPTAKE - 15-NO3 NO 3 15-NH4 NH4

25 100 7 7.19 3.5 2.70 100 14 7.10 7 - 100 2 8 6.02 2 8 1.97 100 4 2 5.94 42 - 100 5 6 6.02 5 6 - DARK 14 - 14 3.39 25 100 7 - 3.5 1.56 10 0 14 - 7 - 100 2 8 - 2 8 - 10 0 42 - 42 - 100 5 6 - 5 6 - DARK 14 2.91 14 3.99 25 100 7 2.27 3.5 1.43 100 14 2.80 7 3.38 100 2 8 2.17 2 8 4.06 100 42 2.01 42 4.22 100 56 1.69 5 6 4.40 DARK 14 - 14 1.59 E. (continued) -APPENDIX -- Date: 14 Sept 75 15-NO3 Incubation Started: 1:05 Ended : 3:17 Mean I, : 0.89 Time : EDT

ST A TEMP LIGHT ADDED UP TAKE ADDED UP TAKE 15-NO3 NO 3 15-NH4 NH4

100

100 APPENDIX E. (continued)

_I_- Date: 28 Sept 75 15-NO3 15-NH4 IncubationStarted: 12:21 12:18 Ended : 2:23 2 :23 Mean Io: 0.90 0.90 Time : EDT

STA TEMP LIGHT ADDED UPTAKE ADDED UPTAKE - - 15-NO3 NO 3 15-NH4 NH4 E. (continued) ---APPENDIX - - Date: 12 Oct 75 15-NO3 15-NH4 Incubation Started: 12:19 12:22 Ended : 2:27 2:27 Mean I,: 0.93 0.93 Time : EDT

STA TEMP LIGHT ADDED UP TAKE ADDED UPTAKE -- - 15-NO3 NO3 15-NH4 NH4 APPE~IXE. (continued) --

Date: 16 Nov 75 15-NO3 15-NH4 Incubation Started: 11:57 12:05 Ended : 2:10 2:lO Mean Io: 0.66 0.67 Time : EST

STA TEMP LIGHT ADDED UPTAKE ADD ED UPTAKE - 15-NO3 NO 3 15-NH4 NH 4 100 14 DARK 100 55 3 3 12 5 DARK 100 DARK 100 DARK 100 5 5 3 3 12 5 DARK 100 DARK 100 DARK 100 5 5 3 3 12 5 DARK 100 DARK 100 DARK

3 3 12 5 DARK 100 DARK APPENDIX F. DEPTH-INTEGRATED DAILY UPTAKE OF CARElOh., NITRATE, AND AMMONIA

DATE STATION PHOTOSYNTHETIC NITROGEN UPTAKE" c UPTAKE CARBON UPTAKE N UPTAKE (mg C m-2 . day-1) (mg N m- 19 Nov

1 Dec

14 Dec

5 Jan

20 Jan

9 Feb

23 Feb

9 Mar

23 Mar

6 Apr

20 Apr APPENDIX F . (continued) DATE STATION PHOTOSYNTHETIC NITROGEN UPTAKE C UPTAKE CARBON UPTAKE SUM N UPTAKE (mg ~~rn-~~da~'1) 4 May

19 May

1 Jun

15 Jun

28 Jun

14 Jul

25 Jul

10 Aug

31 Aug

14 Sep

28 Sep

12 Oct APPENDIX F. (cc~tinued)

DATE STATION PHOTOSYNTHETIC NITROGEN UPTAKE C UPTAKE CARBON UPTAKE NO3 NH SUM N UPTAKE (mg~~rn-~.da~-')(mgNam-'mday-l)

Oct E C H W Nov E

a Data in parentheses are not measurements but rather estimates based on a carbon-to-nitrogen assimilation ratio of 7:l. The estimated total DIN uptake is in turn assumed to be 90% ammonia and 10% nitrate. APPENDIX e;. CUMULATIVE UPTAKE OF CARBON, NITRATE, AND AMMgNIA

STATION FROM TO PHOTOSYNTHETIC NITROGEN UPTAKE CARBON UPTAKE N03 NH4 SUM (g c m-2) (g N m-2)

19 Nov 1 Dec r l 1 I

It 11

11 11 1 Dec 14 Oec 11 11

It I1

11 I! 14 Dec 5 Jan 11 I1

I1 I1

11 I1 5 Jan 20 Jan 11 11

I1 I1

11 II 9 Feb 23 Feb 11 11

I1 I1

I1 II 23 Feb 9 Mar 11 I1

11 11

11 11 9 Mar 23 Mar 11 11

11 I1

!I 11 23 Mar 6 Apr II 11

I1 11

11 11 6 Apr 20 Apr 11 11

I! I1

I1 11 20 Apr 4 May I! I!

11 II

11 11 4 May 19 May 11 11

11 II

II I1 APPENDIX G. (continued)

PHOTOSYNTHETIC NITROGEN UPTAKE STAT 1021 FROM TO CARBON UPTAKE SUM N03 NH4 (g C* rn2) (g ~*rn-~)

19 May 1 June I1 I1

1I I1

I1 11 1 Jun 15 Jun I1 I1

I1 11

11 I1 15 Jun 28 Jun 11 11

11 II

II 11 28 Jun 14 Jul 11 I1

11 11

11 I1 14 Jul 25 Jul I1 11

11 I1

II I1 25 Jul 10 Aug 11 II

11 11

11 It 10 Aug 31 Aug 11 I1

I1 11

II 11 31 Aug 14 Sep 11 11

II I1

II 11 14 Sep 28 Sep 11 I1

11 I1

11 I1 28 Sep 12 Oct 11 I1

I1 1I

I1 11 12 Oct 25 Oct I1 11

I1 11

I1 11 25 Oct 16 Nov 11 I1

I1 11