Vertical partitioning of the phytoplankton assemblage in ultraoligotrophic Crater Lake, Oregon, U.S.A.

SUMMARY 1. The summertime phytoplankton assemblage in abysmally deep (Z_max: 589 m) Crater Lake, Oregon, consists of over 100 species, which are variously distributed in the upper 200 m of the vertical water column. The depth distribution of the lake's three most prevalent species follows a predictabk pattern: Nitzschia gracilis in the 0–20 m stratum, Tribonema sp. at mid–depth (80–20 m), and Stephanodiscus hantzschii in the lowermost stratum (160–200 m). These major species, which account for approximately 80% or more of the lake's total phytoplankton biomass and primary production, exist under atypical temperature, light, and nutrient conditions.
2. The spatial distribution of phytoplankton in Crater Lake resembles a three-tier structure. Unlike most lakes, where the entire phytoplankton communities exist in less disparate environmental conditions, or are vertically mixed periodically by storm events and seasonal lake turnover. the Crater Lake community is partitioned into stratified environments.
5. The disparate and unusual characteristics of these environments, and the hydrological and limnological stability of the lake basin, are perhaps important factors regulating the diversity, dominance. and partitioning of the lake's phytoplankton populations.     

The phosphorus economy of a hypertrophic seepage lake in Scania,south Sweden groundwater influence

The phosphorus dynamics and economy of Lake Bysjön, a hypertrophic seepage lake in Scania, southern Sweden, were investigated during 1973–1977. The mean dissolved inorganic phosphorus concentration (1973–1977) was 580 µg · l^–1. There were no correlations between dissolved inorganic P, total organic P, dissolved organic P, particulate P and phytoplankton biomass. Groundwater inflow and lake water outflow through the ground are the most important factors for maintaining a constant water volume. Groundwater seepage is also important for water quality. Groundwater inflow, together with planktonic activity, keeps the P concentration high in the lake water.     

Size-fractionated phytoplankton biomass and its implications for the dynamics of an oligotrophic tropical lake

1. Size-fractionated phytoplankton biomass was examined in relation to the hydrodynamics of tropical Lake Alchichica from 1999 to 2002.
2. Alchichica is a warm monomictic lake, in which mixing takes place from late December to early March. The lake is oligotrophic (mean total chlorophyll- a concentration 4.2 ± 4.2  μ g L⁻¹) and its phytoplankton biomass is dominated (72.3 ± 16.4%) by large individuals (>2  μ m). The degree of dominance of the large size class (nano- and microplankton) over the small size class (picoplankton) throughout the year is mainly determined by the availability of silicate and the Si/N ratio in the hypolimnion prior to the mixing period.
3. This is the first record of an oligotrophic tropical lake dominated by large size fractions of phytoplankton. Because of this dominance, the fate of most primary productivity is rapid sedimentation to the bottom followed by decomposition that promotes an anoxic hypolimnion.
4. Our findings in tropical Lake Alchichica challenge the idea that oligotrophic waters are dominated by small phytoplankton, as has been well established for the oligotrophic ocean and temperate lakes.     

Contribution of grazing in phytoplankton overall losses in a shallow French lake

SUMMARY 1. Based on data for ¹⁴C-primary production and biomass changes in a small and shallow lake (Créteil Lake, France), overall phytoplankton losses were calculated through an annual cycle (November 1985-October 1986). The summer period in 1986 is compared with two other summer periods in 1985 and 1980, these two years corresponding to extreme levels of algal biomass.
2. Independent from the trophic state of the lake, phytoplankton populations were dominated by small-sized species (<20 μm); their high growth rate (maximal in May and June: 0–8 day⁻¹) was characteristic of nanoplanktonic natural populations.
3. The positive correlation between phytoplankton losses and production indicates a close coupling between growth and loss processes.
4. With a high filtering rate (0.22 day⁻¹ as an annual average), zoo-plankton impact is considerable at any time of the year but especially in late summer, when grazing losses exceeded primary production.
5. Despite the uncertainty concerning the meaning of ¹⁴C-primary production, the persistence of small algae throughout the year implies that a great part of the phytoplankton production was harvested by grazers which led to a recycling of organic matter within the water column.     

The effect of small zooplankton on the microbial loop and edible algae during a cyanobacterial bloom

SUMMARY 1. We studied the effect of the small crustacean zooplankton on heterotrophic micro-organisms and edible phytoplankton in a eutrophic lake during a cyanobacterial bloom.
2. Small (15 L) enclosures were filled with natural or screened (100 μm) lake water and incubated for 5 days in the lake. Screening removed crustacean zooplankton but the initial density of rotifers and phytoplankton remained the same in control and removal treatments. Changes in the abundance and biomass of bacteria, autotrophic picoplankton (APP), heterotrophic nanoflagellates (HNF) and ciliates were measured daily.
3. The crustacean zooplankton, dominated by the small cladoceran Chydorus sphaericus , did not affect cyanobacteria, the main phytoplankton group during the experiment.
4. The removal of the crustacean zooplankton induced a higher abundance of ciliates and reduced that of the HNF, indicating the importance of ciliates in controlling HNF in this system.     

Production and chlorophyll concentration of epipelic and epilithic algae in fertilized and nonfertilized subarctic lakes

The production and chlorophyll concentration of epipelic and epilithic algae was measured during four years (1972–1975) in two shallow, Swedish subarctic lakes. One lake (Lake Hymenjaure) was fertilized with phosphorus or a combination of phosphorus and nitrogen while the other (Lake Stugsjön) served as a reference. The benthic algae in both lakes were dominated by Cyanophyceae of the same species during the whole investigation. The chlorophyll concentration of epipelic and epilithic algae was 100 and 20 mg·m^–2 respectively and fairly constant during the season. In 1974–1975 there was a significant increase in chlorophyll concentration of the benthic algae in Lake Hymenjaure, probably as a response to the poorer light climate in the lake due to a large phytoplankton development. The annual benthic production was 3.4–7.2 gC·m^–2 and it was not enhanced by the fertilization. Compared to the other primary producers (phytoplankton and macrophytes) the benthic algae constituted 70–83% of the total production in Lake Stugsjön. In Lake Hymenjaure, however, the importance of the benthic algae decreased from 50 to 22% of the total due to the great increase in phytoplankton production induced by the lake fertilization.     

Fluxes of free amino acids in three Danish lakes

SUMMARY. 1. Heterotrophic assimilation rates and concentrations of dissolved free amino acids (DFAA) were followed during diel studies in the eutrophic Lake Mossø, Lake Esrom and Lake øm in spring and summer in 1982. In all three lakes, three to four fold diel variations in concentrations and assimilation rates were measured. These fluctuations appeared to be iindependent of phytoplankton and bacteria production. Pools of DFAA varied from 380 nM (Lake Mossø) to 2430 nM (Lake ørn), with serine, glycine, alanine and ornithine as dominant free amino acids.
2. When similar water samples were incubated in a natural light-dark cycle or in total darkness, different pools of DFAA were measured in light and dark.
3. Decomposition of organic matter or zooplankton activity (rather than e.g. phytoplankton exudates) appear to be responsible for the concentration changes.
4. Observed discrepancies between simultaneous concentration changes and assimilation rates are discussed in relation to the applied tracer procedure and the concentration measurements.
5. Assimilation of DFAA sustained from 6% to 25% of the bacterial carbon requirement, corresponding to 2–12% of the phytoplankton production in the lakes.     

Relationships between the biomass and production of bacterio- and phytoplanktonic communities

Quantitative ratios of the biomasses of bacterio- and phytoplankton, interrelation of their production characteristics, and association of the functional characteristics with environmental factors were studied for Lake Khanka, the Yenisei River, and the Krasnoyarsk Reservoir. The ratio between the biomasses of bacterioplankton (B_b) and phytoplankton (B_p) in these water bodies was shown to vary within the range exceeding three orders of magnitude. Bacterioplankton biomass was relatively stable and varied from sample to sample by an order of magnitude. In more than 50% of the samples (total sample number, 495), bacterioplankton biomass exceeded that of the phytoplankton. The average B_b/B_p ratios for Lake Khanka, Yenisei River, and Krasnoyarsk Reservoir were 5.1, 2, and 1.4, respectively. Increased B_b/B_p ratios were found to correlate with elevated specific (per unit biomass) phytoplankton production. This finding indicated additional supply of biogenic elements to phytoplankton due to their recycling by bacterial communities. The ratio between bacterioplankton and phytoplankton production for Lake Khanka varied from year to year (0.07 to 0.76). For the Yenisei River and the Krasnoyarsk Reservoir these ratios were on average 0.19 and 0.27, respectively. According to the literature data for other water bodies, bacterial production may reach from 10 to over 100% of the primary production. The equilibrium density of bacterioplankton (maximal density of the population) in Lake Khanka was ~1.5 times higher than in the Yenisei River and the Krasnoyarsk Reservoir due to higher content of suspended mineral matter and associated organo-mineral detritus in the lake. The interaction between dissolved organic compounds sorbed on the surface of mineral particles results in chemical alteration of biochemically stable substrate into compounds which may be assimilated by aquatic microorganisms.     

A note on Lake Goang, an unusual acid lake in Flores, Indonesia

SUMMARY. 1. Lake Goang has a pH of 2.5. Associated with this low pH are high concentrations of sulphate, chloride, iron and aluminium. There are no fish in the lake.
2. A single species of Heterococcales was found in the phytoplankton.
3. The zooplankton consists of one species of rotifer and a stalked species of Vorticella.
4. The shallow water fauna consists of two species of nematodes, at least two larval Diptera, one trichopteran, a zygopteran, a small crab ( Sundatelphusa ) and a cyclopoid copepod ( Paracyclops ).
5. During January an oily slick appears and is deposited as asphalt around the shore of the lake.     

Nutrient retention and transformation in relation to hydraulic flushing rate in a small impoundment

SUMMARY. The fluxes of water, chloride, silicale and various forms of nitrogen and phosphorus into and out of a 3925 ha impoundment (Lake Taiquin) in north Florida were examined over a 3 year period. Annual hydraulic flushing rates for the lake varied by a factor of more than 2 during the study period and provided an opportunity to examine the effect of flushing rate on nutrient cycling within the lake. The results support the hypothesis that nutrient retention and transformation in lakes and impoundments with high flushing rates (> 1 year^-1) are appreciably influenced by annual variations in flushing rates. Higher fractions of input silicate and total phosphorus were retained by Lake Taiquin during the years with average flushing rates (8 year^-1) than during a year with abnormally high flushing rate (16 year^-1). Nitrogen was not appreciably retained during any of the three study years, and thus N: P ratios in the lake outflow were higher than in the inflow.
Phytoplankton productivity was appreciably higher (70%) during the year with the higher flushing rate, apparently in response to higher reactive phosphorus concentrations in the lake and perhaps to a higher standing crop of phytoplankton during that year. Reactive phosphorus and dissolved inorganic nitrogen inputs could account for only about 30% and 25%, respectively, of the phosphorus and nitrogen required to support observed photosynthetic rates in all three study years. Recycling of nutrients apparently accounted for most of the remainder, although nitrogen fixation could not be ruled out as a factor in the nitrogen budget.     

乌梁素海冰封期浮游植物分布特征及其与水质指标的关系北大核心CSCD

为揭示寒旱区冰封期富营养化湖泊水体中浮游植物群落结构及其与水质指标的响应关系,该研究以乌梁素海为对象,于2019年1月在湖区设立12个采样点采集水样及浮游植物,通过对浮游植物定性定量检测和水体理化性质测定分析,以明确冰封期乌梁素海浮游植物群落结构空间变化特征及主要水质指标的分布规律;结合RDA分析和Pearson相关性分析揭示了浮游植物与水质指标的响应关系,为水体富营养化程度评估及防控提供理论依据。结果显示:(1)冰封期乌梁素海12个样点的水质指标特征差异明显,各水质指标从北到南具有不同的变化趋势。(2)冰封期乌梁素海共检出浮游植物61种,其中隐藻门的丰度最高(4.76×10^(6)个·L^(-1)),甲藻门的生物量最高(18.09 mg·L^(-1)),但湖区不同位置的优势浮游植物类群有所差异,北湖区蓝隐藻和伪鱼腥藻丰度明显高于南湖区。(3)不同种类的浮游植物在空间分布上存在明显的差异,且在P3样点的多样性最低,P8样点的多样性最高,并发现中、下湖区物种类型多且组成较为均匀。(4)浮游植物的丰度与TP呈显著正相关关系,生物量与TP呈极显著正相关关系,多样性指数与TP呈正相关关系。研究表明,冰封期乌梁素海水体处于中等营养水平,水体中总磷(TP)含量是影响浮游植物物种丰度和生物量的主要影响因子;寒旱区冰封期富营养化湖泊浮游植物分布特征为北湖区隐藻门、蓝藻门和甲藻门占优势;南湖区中绿藻门丰度最高。     

Seasonal pattern in nutrient limitation and grazing control of the phytoplankton community in a non-stratified lake

1. The relative importance of zooplankton grazing and nutrient limitation in regulating the phytoplankton community in the non-stratified Lake Kvie, Denmark, were measured nine times during the growing season.
2. Natural phytoplankton assemblage bioassays showed increasing importance of nutrient limitation during summer. Growth rates at ambient nutrient concentrations were continually below 0.12 per day, while co-enrichment with nitrogen (N) and phosphorus (P) to above concentration-saturated conditions enhanced growth rates from May to the end of July.
3. Stoichiometric ratios of important elements in seston (C : N, C : P, N : P), in lake water (TN : TP), in external loading (TN : TP) and in internal loading (DIN : DIP) were measured to determine whether N or P could be the limiting nutrient. TN : TP molar ratio of both lake water, benthic fluxes and external loading suggested P limitation throughout the growing season. However, seston molar ratios suggested moderate P-deficiency only during mid-summer.
4. Abundance and community structure of the zooplankton varied considerably through the season and proved to be important in determining the responses of algal assemblages to grazing. High abundance of cladocerans and rotifers resulted in significant grazing impact, while cyclopoid copepods had no significant effect on the phytoplankton biomass.
5. Regeneration of ammonium and phosphate by zooplankton were periodically important for phytoplankton growth. A comparison of nutrient regeneration by zooplankton with nutrient inputs from sediment and external sources indicated that zooplankton may contribute significantly in supplying N and P for the growth of phytoplankton.     

Seasonal and interannual variability in the taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake,Oregon

Taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake, Oregon, were examined during time periods between 1984 and 2000. The objectives of the study were (1) to investigate spatial and temporal patterns in species composition, chlorophyll concentration, and primary productivity relative to seasonal patterns of water circulation; (2) to explore relationships between water column chemistry and the taxonomic composition of the phytoplankton; and (3) to determine effects of primary and secondary consumers on the phytoplankton assemblage. An analysis of 690 samples obtained on 50 sampling dates from 14 depths in the water column found a total of 163 phytoplankton taxa, 134 of which were identified to genus and 101 were identified to the species or variety level of classification. Dominant species by density or biovolume included Nitzschia gracilis, Stephanodiscus hantzschii, Ankistrodesmus spiralis, Mougeotia parvula, Dinobryon sertularia, Tribonema affine, Aphanocapsa delicatissima, Synechocystis sp., Gymnodinium inversum, and Peridinium inconspicuum. When the lake was thermally stratified in late summer, some of these species exhibited a stratified vertical distribution in the water column. A cluster analysis of these data also revealed a vertical stratification of the flora from the middle of the summer through the early fall. Multivariate test statistics indicated that there was a significant relationship between the species composition of the phytoplankton and a corresponding set of chemical variables measured for samples from the water column. In this case, concentrations of total phosphorus, ammonia, total Kjeldahl nitrogen, and alkalinity were associated with interannual changes in the flora; whereas pH and concentrations of dissolved oxygen, orthophosphate, nitrate, and silicon were more closely related to spatial variation and thermal stratification. The maximum chlorophyll concentration when the lake was thermally stratified in August and September was usually between depths of 100 m and 120 m. In comparison, the depth of maximum primary production ranged from 60 m to 80 m at this time of year. Regression analysis detected a weak negative relationship between chlorophyll concentration and Secchi disk depth, a measure of lake transparency. However, interannual changes in chlorophyll concentration and the species composition of the phytoplankton could not be explained by the removal of the septic field near Rim Village or by patterns of upwelling from the deep lake. An alternative trophic hypothesis proposes that the productivity of Crater Lake is controlled primarily by long-term patterns of climatic change that regulate the supply of allochthonous nutrients.     

芜湖市镜湖轮虫群落结构分析及水质的生态学评价

2003年1—12月,对芜湖市镜湖轮虫群落结构的周年动态进行了研究,并分析了轮虫密度与有关生态因子间的关系。经鉴定,共发现轮虫55种,隶属于15科21属。密度优势种为裂痕龟纹轮虫(Anuraeopsis fissa)、暗小异尾轮虫(Trichocerca pusilla)、前额犀轮虫(Rhinoglena frontalis)、红多肢轮虫(Polyarthra remata)、长三肢轮虫(Filinia longise-ta)、广布多肢轮虫(Polyarthra vulgaris)和多须伪前翼轮虫(Proalides tentaculates),而生物量优势种为前节晶囊轮虫(Asplanchna priodonta)、多须伪前翼轮虫和暗小异尾轮虫。全年轮虫的总密度与水温、叶绿素a浓度及小型纤毛虫密度具有显著的相关性;温度对全年轮虫总密度的影响最大,叶绿素a浓度对春、冬季轮虫总密度影响最大,小型纤毛虫密度对夏季轮虫总密度影响最大,而水温是影响秋季轮虫总密度的主要因素。根据污染指示生物、物种多样性指数和Q值并结合水理化性质对治理后的镜湖水质所进行的初步评价表明,经清淤、截流和换水等措施治理后,小湖区应偏属寡污-β中污至β中污型水体,大湖区属于β中污型水体;目前镜湖水体处于中营养后期—富营养化初期阶段。       

Paleopigment evidence of competition between phytoplankton and a cyanobacterial algal mat in a meromictic lake near Toronto,Ontario Canada

Crawford Lake, a meromictic lake located near Toronto, Canada, was cored to determine if algal pigments preserved in its sediments would make it possible to infer past changes in lake productivity over the last five hundred years. From 1500 to 1910 A.D. the sediments display extremely high levels of oscillaxanthin and myxoxanthophyll while chlorophyll derivatives and total carotenoids were relatively low. As the lake became increasingly more eutrophic in the latter part of the twentieth century, this relationship reversed itself. Competition for light between the deep dwelling cyanobacteria in the algal mat on the lake's bottom (8–14 m) and phytoplankton in the overlying surface layers of the water column (5–7 m) was attributed to the observed reduction in oscillaxanthin and myxoxanthophyll as Crawford Lake eutrophied. Because the major cyanobacteria in Crawford Lake are benthic mat forming Lyngbya and Oscillatoria, and not phytoplankton, competition for light with the overlying phytoplankton is critical in determining the total quantity of oscillaxanthin and myxoxanthophyll preserved in the lake's profundal sediments. These findings have major implications for the use of cyanobacterial pigments as indicators of lake trophic status in lakes where benthic algal mats are present.     

Eutrophication processes regulated by a plunging river inflow

Lake Rotoiti (North Island, New Zealand) is a deep mesotrophic lake that has declined in water quality over the last 30 years. The main river entering the lake was identified as the primary enrichment source, but its interaction with the surrounding lakewater varied with season and time of day. During winter the river was colder than the lake and penetrated 6–8 km into the main basin as an underflow. In summer the river often entered as a plunging inflow during the early morning, but it warmed during the day, and in the afternoon entered the lake as a buoyant jet that flowed directly to a nearby outlet river. From continuous temperature measurements in the inflow and lake surface it was estimated that the river plunged and penetrated the lake as an interflow or underflow for 60.2% of the year. This translated into 31% of the N and 64% of the P loading on the lake. The river also injected phytoplankton into the main basin of Lake Rotoiti, including populations of bloom-forming cyanobacteria. The underflow was the dominant term in calculating the hydraulic flushing time of the main basin, and also made a large contribution of dissolved oxygen to the subsurface waters. These complex interactions between Lake Rotoiti and its inflowing river were controlled by small temperature differences ( < 3 °C, and had wide-ranging implications in the eutrophication process.     

Recruitment of Total Phytoplankton,Chlorophytes and Cyanobacteria from Lake Sediments Recorded by Photosynthetic Pigments in a Large,Shallow Lake (Lake Taihu,China)

Recruitment of total phytoplankton, chlorophytes and cyanobacteria from lake sediments to the water column was studied using photosynthetic pigments at one site (1.5 m) in Lake Taihu, a large shallow lake in China. Samples were taken weekly from the migration traps installed on the bottom from March to May 2004. Abundance of total phytoplankton, chlorophytes and cyanobacteria were represented by Chlorophyll (Chl) a, b, and phycocyanin (PC), respectively. Over the three months, total phytoplankton, chlorophytes, and cyanobacteria corresponding to 48.9%, 68.9% and 316.2% of their initial concentrations in surface sediments were recruited in Lake Taihu. However, compared with their increase in pelagic abundance over the same period, the recruitment accounted for a rather small inoculum. Accompanying the recruitment, total phytoplankton and chlorophytes declined and cyanobacteria increased in the upper 0–2 cm sediments; colonies of Microcystis aeruginosa in the water column enlarged from small size with several cells to large colonies with hundreds of cells. Thus, overwintering and subsequent growth renewal of pelagic phytoplankton merits further study and comparison with benthic survival and recruitment. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of physical refuges on fish–plankton interactions

1.Refuges that reduce fish-induced mortality of zooplankton are considered to be key factors in controlling phytoplankton growth in lake ecosystems. In order to better understand the role of physical refuges for zooplankton on zooplanktivorous fish-plankton relationships, an enclosure experiment was run in a mesotrophic lake. Even-link systems (zooplankton and phytoplankton) and odd-link systems (zooplanktivorous fish, zooplankton and phytoplankton) were established. We also established an odd-link system with a physical refuge for zooplankton where fish predation was limited in the upper half of the enclosure.
2.Fish negatively affected density and mean body length of herbivorous zooplankton and total zooplankton, filtering rates with some intermediate effects in the presence of the refuge. A clear refuge effect was observed for the dominant herbivore, Ceriodaphnia . On the other hand, the refuge seemed to increase the vulnerability of those taxa that aggregated in upper layers of the water column. Grazing was thus reduced in both odd-link systems.
3.The lack of significant correlation between nutrient availability and phytoplankton biomass in enclosures suggested a top-down control of algal growth in our experimental systems. In both odd-link systems ('fish' and 'refuge') phytoplankton biomass was significantly enhanced, and transparency was reduced in comparison with the even-link system.     

The composition and abundance of phytoplankton in Lake Bukoni,western Uganda

Lake Bukoni is one of the crater lakes in western Uganda. Investigations into this lake is limited compared to other African lakes. Data on phytoplankton ecology in the lake are lacking. Phytoplankton consists of a community of photosynthetic, microscopic plants adapted to suspension in water. They constitute ‘hidden flora’ which make an important contribution to the primary productivity of a water mass. Some phytoplankton taxa, among them species belonging to Cyanophyta, are known to influence ecological transformations and to cause health hazards in water bodies that are used by humans. From July 2004 to December 2005, phytoplankton was collected from two sites (inshore and offshore) in Lake Bukoni. An inverted microscope, Sedgwick counting chamber and multiple tally denominator were used to quantify the phytoplankton. Phytoplankton was dominated by nonheterocystous cyanoprokaryotes especially Lyllgbya limnetica followed by the diatoms Synedra ulna and Fragillaria mutabilis. The inshore site had more phytoplankton species. Differences in phytoplankton diversity and density were mainly attributed to mixing and presence of macrophytes. The occurrence of large numbers of cyanoprokaryotes poses a potential health hazard to the local people who utilize the water from Lake Bukoni. The dominance of cyanoprokaryotes might result in ecological transformations like loss of biodiversity.     

Temporal dynamics in epipelic, pelagic and epiphytic algal production in a clear and a turbid shallow lake

SUMMARY 1. Pelagic and epipelic microalgal production were measured over a year in a pre-defined area (depth 0.5 m) in each of two lakes, one turbid and one with clear water. Further estimates of epiphytic production within reed stands were obtained by measuring production of periphyton developed on artificial substrata.
2. Total annual production of phytoplankton and epipelon was 34% greater in the turbid lake (190 g C m⁻² year⁻¹) than in the clearwater lake (141 g C m⁻² year⁻¹). However, the ratio of total production to mean water column TP concentration was two fold greater in the clearwater lake.
3. Phytoplankton accounted for the majority of the annual production (96%) in the turbid lake, while epipelic microalgal production dominated (77%) in the clear lake. The relative contribution of epipelic algae varied over the year, however, and in the turbid lake was higher in winter (11–25%), when the water was relatively clear, than during summer (0.7–1.7%), when the water was more turbid. In the clearwater lake, the relative contribution of epipelon was high both in winter, when the water was most clear, and in mid-summer, when phytoplankton production was constrained either by nutrients or grazing.
4. Compared with pelagic and epipelic primary production, epiphytic production within a reed stand was low and did not vary significantly between the lakes.
5. The study supports the theory of a competitive and compensatory trade-off between primary producers in lakes with contrasting nutrient concentrations, resulting in relatively small differences in overall production between clear and turbid lakes when integrating over the season and over different habitats.