Photosynthetic activity of phytoplankton and its relation to environmental factors in hypersaline Mono Lake,California

The photosynthetic activity of phytoplankton in hypersaline Mono Lake, California was measured over the three year period, 1983–1985. The maximum chlorophyll-specific rate of carbon uptake (P_m ^B) and the light-limited slope (alpha) were derived from laboratory measurements of photosynthesis vs. irradiance (P-I) relationships. Annual estimates of primary production were 340–540 g C m^-2 yr^-1. Production was two to three times higher during the spring of 1983 than in the springs of 1984 and 1985; higher standing biomass of algae occurred in 1983. While P_m ^B rates followed water temperatures and varied over 40-fold over the year, integral primary production varied less since periods of high P_m ^B occurred when algal biomass was low. Sixty-eight percent of the seasonal variation in the P_m ^B was explained by a regression on temperature (53%), chlorophyll a (12%), and the carbon:chlorophyll a ratio (3%). Light-saturated and light-limited rates of photosynthesis generally covaried, evidenced by the strong seasonal correlation between P_m ^B and alpha. Sixty-one percent of variation in alpha was explained by a regression on P_m ^B, temperature, grazing, water column stability, and self-shading. There was no correlation of carbon uptake with ambient levels of inorganic nitrogen. The regression coefficient of the dependence of P_m ^B on the seasonal temperature trend was much larger than that determined from individual samples incubated at several different temperatures; this indicates that uptake is limited by more than low temperatures in the spring. Regression equations including only temperature, chlorophyll and depth were sufficient to estimate patterns of seasonal and year to year variation in integral primary productivity.     

Micronutrient and phosphorus limitation of phytoplankton abundance in Gem Lake,Sierra Nevada,California

Nutrient addition experiments conducted during the ice-free seasons of 1983 and 1984 in Gem Lake, an alpine lake in the Sierra Nevada mountains of California, indicate that algal biomass is limited by phosphorus, in combination with iron or copper. Phosphorus additions were always required to stimulate growth, but did not do so when phosphorus was the only nutrient added. Simultaneous additions of phosphorus and iron resulted in increased levels of chlorophyll, particulate carbon, particulate nitrogen and particulate phosphorus. Simultaneous additions of phosphorus and copper resulted in increases in chlorophyll, particulate nitrogen and particulate phosphorus, not in particulate carbon. Neither iron nor copper by itself stimulated growth.Particulate N : P ratios from all seasons in Gem Lake suggest that simultaneous micronutrient and phosphorus limitation exists throughout the summer, when nutrient and biomass levels remain low; limitation by phosphorus alone may appear in the fall and spring, when biomass and major ion concentrations increase dramatically.     

Dynamics of phytoplankton detritus in a shallow,eutrophic lake (Lake Loosdrecht,The Netherlands)

A study was made of the mortality and aerobic decomposition of light- and phosphorus-limited cultures of Oscillatoria limnetica, a dominant phytoplankton species in shallow, eutrophic Lake Loosdrecht (The Netherlands). When placed in the dark at 20 °C, most cells died and lysed within twelve days. The labile organic matter was completely decomposed within three weeks. Absorbance spectra indicated that blue green algae may contributed significantly to the refractory dissolved substances in the lake. Refractory particulate matter constituted from 7 to 24% of the biomass of O. limnetica, depending on the growth rate before incubation in the dark. The decomposition rate of this fraction was 0.005 d^–1. On a basis of a steady-state model of the dynamics of phytoplankton detritus, the areal organic dry weight concentration of the detritus in the lake is ca. 60 g m^–2. This means the quantities of detritus in the seston and epipelon are about equal.     

The role of periphytes in the shift between macrophyte and phytoplankton dominated systems in a shallow, eutrophic lake (Lake Taihu, China)

Based on experiments of periphyte response to different trophic levels and their impact on macrophyte production,it was found that the periphyte biomass increased with the nutrient con-centrations. Increased trophic level and periphyte biomass resulted in decreased macrophyte photo-synthesis. It was suggested that the periphytes could cause resilience and hysteresis in the system shifts between macrophyte and phytoplankton domination. Other factors,such as fish farming,storm induced waves and mechanical destruction,and high water levels could be the perturbations during the system shifts,but these are not the key factors. Instead,the nutrient loading and periphyte abundance could determine the shift in lake ecosystem between macrophyte and phytoplankton domination. This finding could theoretically elucidate the mechanism of ecosystem shifts between macrophyte and phytoplankton domination.     

The role of periphytes in the shift between macrophyte and phytoplankton dominated systems in a shallow, eutrophic lake (Lake Taihu, China)

Based on experiments of periphyte response to different trophic levels and their impact on macrophyte production, it was found that the periphyte biomass increased with the nutrient concentrations. Increased trophic level and periphyte biomass resulted in decreased macrophyte photosynthesis. It was suggested that the periphytes could cause resilience and hysteresis in the system shifts between macrophyte and phytoplankton domination. Other factors, such as fish farming, storm induced waves and mechanical destruction, and high water levels could be the perturbations during the system shifts, but these are not the key factors. Instead, the nutrient loading and periphyte abundance could determine the shift in lake ecosystem between macrophyte and phytoplankton domination. This finding could theoretically elucidate the mechanism of ecosystem shifts between macrophyte and phytoplankton domination.     

Coupling of phytoplankton and detritus in a shallow,eutrophic lake (Lake Loosdrecht,The Netherlands)

An oscillating steady state is described of phytoplankton, dominated by Prochlorothrix hollandica and Oscillatoria limnetica, and sestonic detritus in shallow, eutrophic Lake Loosdrecht (The Netherlands). A steady-state model for the coupling of the phytoplankton and detritus is discussed in relation to field and experimental data on phytoplankton growth and decomposition. According to model predictions, the phytoplankton to detritus ratio decreases hyperbolically at increasing phytoplankton growth rate and is independent of a lake's trophic state. The seston in L. Loosdrecht contains more detritus than phytoplankton as will apply to many other lakes. The model provides a basis for estimating the loss rate of the detritus, including decomposition, sedimentation and hydraulic loss. In a shallow lake like L. Loosdrecht detritus will continue to influence the water quality for years.     

Primary production of phytoplankton in Lake Valencia (Venezuela)

Lake Valencia is heavily polluted by waste water of domestic, agricultural and industrial origin. The high organic load may have produced important changes in the limnological properties. Cyanobacteria dominated in numbers and biomass (over 90% throughout the year). Chlorophyll-a content averaged 37.7 + 15 μg · 1⁻¹. Maximum concentrations of 50–80 μg · 1⁻¹ were found near the inflows affected by organically polluted affluents. There has been a 50% reduction in the euphotic zone in only 13 years. The maximum rate of gross photosynthesis per hour at light saturation was determined within the uppermost 1-meter layer. The highest value was 16,290 mg O₂ · m⁻³ · h⁻¹. Lake Valencia is among the most productive lakes in the world, with areal net photosynthesis averaging 7.5 g C · m⁻² · d⁻¹.     

Microbial food web in a large shallow lake (Lake Balaton, Hungary)

Seasonal variations of phyto-, bacterio- and colourless flagellate plankton were followed across a year in the large shallow Lake Balaton (Hungary). Yearly average chlorophyll-a concentration was 11 µg 1^–1, while the corresponding values of bacterioplankton and heterotrophic nanoflagellate (HNF) plankton biomass (fresh weight) were 0.24 mg 1^–1 and 0.35 mg 1^–1, respectively. About half of planktonic primary production was channelled through bacterioplankton on the yearly basis. However, there was no significant correlation between phytoplankton biomass and bacterial abundance. Bacterial specific growth rates were in the range of 0.009 and 0.09 h^–1, and ended to follow the seasonal changes in water temperature. In some periods of the year, predator-prey relationships between the HNF and bacterial abundance were obvious. The estimated HNF grazing on bacteria varied between 3% and 227% of the daily bacterial production. On an annual basis, 87% of bacterial cell production was grazed by HNF plankton.     

Vertical distribution of phytoplankton in Lake Xolotlán (Managua)

A study of the vertical distribution of phytoplankton was carried out at the end of the rainy season (October–November), when wind activity is lower and the probability for phytoplankton stratification is enhanced. Samples were taken every other day at 0, 0.5, 1.0 m and, thereafter, for every meter up to the bottom. The number of individuals and their biomass were determined for each sampling depth and expressed as wet weight and chlorophyll-a, respectively. The results indicate that there were no significant differences (ANOVA one way, P<0.05) with regard to the vertical distribution of phytoplankton biomass over the 15 m of the water column. This result reflects the polymictic condition of Lake Xolotlán (Managua).     

The influence of the diel climatic cycle on the depth-time distribution of phytoplankton and photosynthesis in a shallow equatorial lake (Lake Baringo,Kenya)

Lake Baringo is a shallow equatorial lake. This paper reports a diel study of the depth-time distribution of phytoplankton and photosynthesis at one location in Lake Baringo on 10 March 1989. The water column shows a pattern of diurnal stratification probably accentuated by the high turbidity of the water and therefore rapid attenuation of solar energy. This stratified pattern breaks down at night due to atmospheric cooling and the regular onset of winds in the early evening. The phytoplankton is dominated byMicrocystis aeruginosa with some associated epiphytes. It concentrates in the narrow euphotic zone during the diurnal period of stratification due to buoyancy of theMicrocystis; evening breakdown of the thermocline results in the phytoplankton being mixed throughout the water column. A series of measurements of photosynthesis throughout the diurnal period gives an areal rate of 3.8 g O₂ m⁻² d⁻¹. The relationship between this value and the level of fish exploitation in Lake Baringo is discussed. The diel cycle in Lake Baringo is interpreted as dominating over any seasonal limnological cycle in the lake.     

Primary producer dynamics associated with evaporative concentration in a shallow,equatorial soda lake (Lake Elmenteita,Kenya)

Lake Elmenteita (0°27S, 36°15E) lies on the floor of the rift valley at 1776 m above sea level in Kenya. As a consequence of lower than average rainfall, the mean depth decreased from 1.1 to 0.65 m during the study period (February 1973 to August 1974). The initiation of major biological changes coincided with a period of rapid evaporative concentration in 1973 (February to April) when the conductivity increased from 19.1 to 27.0 mmhmos cm^-1. Spirulina platensis, Spirulina laxissima and Anabaenopsis arnoldii decreased in abundance precipitously in parallel with large declines in chlorophyll a concentration and phytoplankton photosynthetic rates. Once the overall abundance of phytoplankton had declined and the transparency had increased, primary productivity by benthic algae increased significantly. Paradiaptomus africanus, the only copepod living in the lake, was abundant in February and March 1973, but was gone by May. Eight hypotheses to explain these changes are evaluated and converge on the suggestion that a rate of change of salinity greater than 5 mmhmos cm^-1 per month and a salinity exceeding 25 mmhmos cm^-1 cannot be tolerated by P. africanus and adversely effects the nitrogen fixer, A. arnoldii. Furthermore, the loss of P. africanus and oxygenation of the sediments by benthic algae reduce the rate of recyling of nutrients which alters phytoplankton abundance and species composition.     

Seasonal pattern of ammonium (methylamine) uptake by phytoplankton in an oligotrophic lake

Our primary objective was to determine if a relationship existed between seasonal change in phytoplankton and high affinity for (K _m) or uptake rates (V _maX) of ammonium which might explain seasonal phytoplankton succession in oligotrophic ecosystems. We measured ammonium uptake using [¹⁴C]-methylamine and estimatedK _m andV _max using Hanes Plots at 2-week intervals during 6 months of thermal stratification in Mountain lake, Virginia (37° 22 N, 80° 32 W). Community composition, nutrient levels, and other variables were determined in all uptake experiments. A second objective was to determine if ammonium was preferentially utilized over nitrate and to characterize further the ammonium transport system.V _max increased steadily from May until the end of July, each increase coinciding with major changes in the phytoplankton community. Cryptophyceans dominated in May, chlorophyceans in June and July, and cyanophyceans from the end of July to late October. With cyanophycean dominance,V _max declined until chlorophyceans reestablished dominance in late October. By contrast,K _m values increased from May to the end of July, but thereafter showed no correlation. Acetylene reduction experiments showed no nitrogen fixation during late summer and fall when blue-green algae were present. Preference for ammonium was implied also by negative nitrate reductase assays. Overall, the coincidence ofV _max andK _m values for [¹⁴C]-methylamine uptake and changing phytoplankton community structure suggests the possibility that successive algal communities may be changing as a result of specific species differences in ammonium affinity and uptake rates.     

Species composition and phytoplankton biomass in a tropical African lake (Lake Awassa,Ethiopia)

The species composition and phytoplankton biomass of Lake Awassa, Ethiopia were studied from September 1985 to July 1986 in relation to some limnological features of the lake. During the study period, three phases of thermal stratification were recognized: a period of unstable stratification and near-complete mixing was followed by a stable stratification period and another period of complete mixing. Complete mixing was associated with cooling of air temperature with an influx of cool rain and high rainfall. The underwater light penetration showed a similar pattern over the whole period with the highest in the red, and the lowest in the blue spectral region. Euphotic depth varied between 1.6 and 3.0 meters with the highest measurements corresponding to the stable stratification period. PO₄-P concentrations ranged between 23 and 45 µg l^–1 and NO₃-N concentrations varied between 7 and 14 µg l^–1 during the study period. Both nutrients showed increasing values associated with mixing periods and/or the rainy season.A total of 100 phytoplankton species were identified with 48% of the taxa represented by green algae, 30% by blue-green algae, 11% by diatoms, and the rest by chrysophytes, dinoflagellates, cryptomonads and euglenoids. The dominant phytoplankton species were Lyngbya nyassae, Botryococcus braunii and Microcystis species. Seasonal biomass variation was pronounced in the first two species but not in Mycrocystis. Phytoplankton biomass increased following the mixing period in December, and thermal destratification during May to July which was also a period with high rainfall and relatively high nutrient concentration. While the seasonal variation of the total phytoplankton community in Lake Awassa was relatively low (coefficient of variation < 20%), it was higher in some of the individual component species.     

Trophic status of Tilitso,a high altitude Himalayan lake

The trophic status and water quality of Lake Tilitso (4920 m above sea level) in a high altitude region in central Nepal were surveyed in September, 1984. The lake is rather large with a maximum depth of 95 m and a surface area of 10.2 km². The lake water was turbid due to glacier silt and the euphotic layer was only 5 m deep. The nutrient concentration was very low with total phosphorus concentration 1–6 μg l⁻¹, and DTN concentration 0.10–0.22 mg l⁻¹. The phytoplankton biomass and chlorophyll-a concentration were also low. Primary production was estimated to be about 12 mg C m⁻² d⁻¹. The concentrations of particulate matter and most cations and bacterial number were higher in the epilimnion than in the hypolimnion. The trophic status of this lake was estimated as ultraoligotrophic.     

Plankton dynamics in a high mountain lake (Las Yeguas,Sierra Nevada,Spain). Indirect evidence of ciliates as food source for zooplankton

A detailed sampling programme during the ice-free season (July–September) in the oligotrophic lake Las Yeguas (Southern Spain) has shown a well-defined time lag between phytoplankton and zooplankton maximum standing stocks, the former displaying a peak (23 μgC l^-1) just after the ice-melting, and the latter by the end of September (80 μgC l^-1). A ratio of autotrophs to heterotrophs lower than 1 which lasted more than two thirds of the study period may suggest a high algal productivity per unit of biomass. The estimated strong top-down regulation of phytoplankton by zooplankton indicates an efficient utilization of resources. A comparative analysis between the available food supply and the critical food concentration that is necessary to maintain the population of Daphnia pulicaria (which constitutes up to 98% of the heterotrophic biomass) proves this species to be food-limited in the lake under study. To explain the dominance (and development) of such large-bodied cladoceran population, we discuss the possibility of the utilization of naked protozoan ciliates (Oligotrichidae) as a complementary high quality food source, and the exploitation of benthic resources through a coupled daily migration behaviour.     

Long-term phytoplankton changes in a shallow hypertrophic lake,Albufera of Valencia (Spain)

A long-term phytoplankton study was carried out in the Albufera of Valencia, a shallow hypertrophic lake (surface area 21 km², mean depth 1 m, total inorganic nitrogen load 155 g m^-2 y^-1, total inorganic phosphate load 15 g m^-2 y^-1) from 1980 to 1988. The lake functions as a reservoir for the surrounding rice cultivation. From 1940's to 1988, its phytoplankton assemblage has been altered from a mesotrophic to a hypertrophic character, as consequence of the increasing pollution. For 1980–88, annual variations in the phytoplankton were less pronounced than seasonal changes. The hypertrophic and morphometric features of the lake favoured the stability of the phytoplankton assemblage and chlorophyll a levels during the study period. Seasonal and horizontal distribution of the total phytoplankton abundance and biomass were highly influenced by the hydrological cycle of the lagoon. Compared with other shallow nutrient rich lakes, the Albufera of Valencia is similar to the shallow hypertrophic lakes of the Netherlands.     

The effect of lake restoration measures on the physical,chemical and phytoplankton variables of Lake Bled

Monthly changes of physical, chemical and biological variables due a combination of artificial inflow of clean water, removal of hypolimnetic water, and diversion of sewage were studied in Lake Bled from December 1980 to December 1982.During the winter period 1981/82 the species composition of the phytoplankton changed. New species replaced those observed in previous years. We conclude that the combined effect of these three lake restoration measures was responsible for the sudden disappearance ofOscillatoria rubescens D.C. A marked decrease in some nutrients and an increase in temperature and oxygen concentration also occurred.     

Long-term phytoplankton changes in an artificially divided,top-down manipulated humic lake

Lake Große Fuchskuhle (Brandenburg, Germany) is a naturally acidic bog lake that was artificially divided into four basins by large plastic curtains for biomanipulation experiments in 1990. Different numbers of perch were added to each compartment beginning in the spring of 1993. The species composition and abundance of phytoplankton, pH, nutrient concentrations, dissolved organic carbon (DOC) and chlorophyll a content were analyzed at regular intervals during 1991 and 1998. The division of the lake resulted in divergent developments in the physical and chemical environment of the compartments. This study compared the phytoplankton assemblages of the Northeast- (NE) and Southwest- (SW) basins which differed strongly in chemistry during the investigation period. Divergent developments in phytoplankton species composition in both basins can be explained by changes in physical and chemical conditions (bottom-up effects). Increased pH values and DOC concentrations probably favoured mass developments of the dinoflagellate Gymnodinium uberrimum since 1993, while increased nutrients (dissolved inorganic carbon, total nitrogen and especially total phosphorus) as well as further changes in pH and DOC led to the dominance of the raphidophyte Gonyostomum semen in 1998. This bloom was characterized by extreme biomasses of up to 143 mg l^–1 wet weight, corresponding with high chlorophyll a concentrations of up to 413 g l^–1 at the same time. In contrast, no significant relationship between experimental manipulations by piscivorous fish stocking (top-down effects) and phytoplankton biomass were observed.     

The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana,Croatia)

The shallow Lake Vrana was studied over a 1-year period, special attention being paid to the phytoplankton. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. The regular annual development observed was in species contribution to total biomass rather than in seasonal changes in species composition. The assemblage was dominated by Cosmarium tenue Arch. and Synedra sp. In winter and in spring the phytoplankton assemblage was dominated by Cosmarium tenue and high contribution of Synedra sp. was observed during the summer and autumn. Results suggest that concentrations of inorganic nitrogen and phosphorus were critical in regulating phytoplankton biomass and species dominance.     

Seasonal dynamics of phytoplankton and phytobenthos,and associated chemical interactions,in a shallow upland lake (Malham Tarn,northern England)

Seasonal changes of phytoplankton were followed over 3 years (1985–87) in a shallow, unstratified and calcareous upland lake.The phytoplankton was of low to moderate abundance and generally dominated by phytoflagellates. Seasonality involved a winter minimum of abundance, a spring maximum of diatoms, and often brief increases in summer that included blue-greens, especially the colonial Gloeotrichia echinulata. Some components were of benthic origin. Seasonal growth of the main component of the phytobenthos, Chara globularisvar. virgata, caused a regular summer depletion in lake water of Ca²⁺ and HCO₃ ^- (alkalinity) by associated CaCO₃ deposition, and a more extreme (and unusual) depletion of K⁺. Chemical analysis of Chara biomass and of underlying sediments indicated a large benthic nutrient stock, much surpassing that represented by the phytoplankton. Growth in this biomass, and the magnitude of water-borne inputs, influenced the removals of Ca²⁺, K⁺ and inorganic N. The phytoplankton was probably limited by a low-P medium, to which co-precipitation of phosphate with CaCO₃ may have contributed. A vernal depletion of Si was probably limiting to diatom growth, and appeared to be mainly induced by benthic rather than planktonic diatoms. Examples of long-term change in composition of the phytoplankton and phytobenthos are noted and discussed in relation to the interaction of these components, nutrient enrichment, and possible alternative stable states.