Summer Phytoplankton Biomass Research Articles

Nutrient and chlorophyll a variability at six stations associated with mussel farming in Pelorus Sound, 1984–85

Abstract The large nutrient and chlorophyll a concentration variability in Pelorus Sound resulted from the complex hydrodynamic regime operating on the three major nutrient sources—sediment remineralisation, advection from Cook Strait, and the river inflows. Concentrations changed over time periods which ranged from short (minutes to hours), associated with the passage of tidal fronts and isolated patches of water, to long (days to months) associated with floodwater, retention times, and oceanic exchange. Spatial variability indicated that high nitrogen (N) concentrations and phytoplankton biomass in the inner sounds were associated with rainfall whereas the highest levels in the outer sounds were associated with sediment remineralisation, oceanic exchange, and the seasonal pattern in Cook Strait. Exceptions occurred when high phytoplankton biomass produced in the inner sounds was flushed out of the sounds following a storm event. Low N concentrations and phytoplankton biomass in summer throughout Pelorous Sound coincided with low rainfall and low concentrations in Cook Strait, and may have resulted in a food shortage for the cultivated mussels within Pelorous Sound at that time. Accumulation of N in the bottom waters of poorly flushed embayments resulted in deep chlorophyll a maxima developing below the level of the mussel farms. Internal waves on the halocline provided vertical displacement of both nutrients and phytoplankton biomass by up to 6 m independent of the tidal cycle, periodically moving this food source within the depth range of the cultivated mussels in those embayments.

The Seasonal Dynamics and Composition of Photosynthetic Picoplankton Communities in Temperate Lakes in Ontario, Canada

AbstractThe seasonal abundance and composition of photosynthetic picoplankton (0.2‐2 μm) was compared among five oligotrophic to mesotrophic lakes in Ontario. Epilimnetic picocyanobacteria abundance followed a similar pattern in all lakes; maximum abundance (2‐4 × 105 cells · ml−1) occurred in late summer following a period of rapid, often exponential increase after epilimnetic temperatures reached 20 °C. In half of the lakes picocyanobacteria abundance was significantly correlated with temperature, while in other lakes the presence of a small spring peak resulted in a poor correlation with temperature. In all lakes there was a significant correlation between epilimnetic abundance and day of the year. Correlations with water chemistry parameters (soluble reactive phosphorus, total phosphorus, particulate C: P and C: N) were generally weaker or insignificant. However, in the three lakes with the highest spring nitrate concentrations, a significant negative correlation with nitrate was observed. During summer stratification, picocyanobacteria abundance reached a maximum within the metalimnion and at or above the euphotic zone (1% of incident light) in all lakes. These peaks were not related to nutrient gradients.The average total phytoplankton biomass ranged from 0.5 g m−3 (wet weight) in the most oligotrophic lake to 1.4 g m−3 for the most mesotrophic with picoplankton biomass ranging from 0.01 g m−3 to 0.3 g m−3. Picocyanobacteria biomass comprised 1 to 9 % of total phytoplankton biomass in late summer, but in one year for one lake represented a maximum of 56%. Other photosynthetic picoplankton (unidentified eukaryotes, Chlorella spp. Nannochloris spp.), although less abundant (103 cells · ml−1) than picocyanobacteria, represented biomass equal or greater than that of the picocyanobacteria in spring and early summer. On average, half of the photosynthetic picoplankton biomass was eukaryotic in the more coloured lakes, while in the clear lakes less than 20% was eukaryotic. Among the lakes there was a significant positive correlation between the average light extinction coefficient and the proportion of eukaryotic biomass of the picoplankton.In mesotrophic Jack's Lake, the contribution of picoplankton to the maximum photosynthetic rate ranged from 10 to 47% with the highest values in the spring (47%) and late summer (33%), as a result of eukaryotic picoplankton and picocyanobacteria respectively. Picocyanobacteria cell specific growth rates were high during July (0.6‐0.8 day−1) and losses were close to 80% of the growth rate. Thus, despite low biomass, photosynthetic picoplankton populations appeared to turn over rapidly and potentially contributed significantly to planktonic food webs in early spring and late summer.

Seasonal Changes in Chlorophyll‐containing Picoplankton Populations of Ten Lakes in Northern England

AbstractKey features of photosynthetic picoplankton populations were compared during 1988 in ten lakes in northern England ranging from oligotrophic to slightly eutrophic; two of the three eutrophic lakes were shallow and lacked a thermocline. Measurements were made at 0.5 m depth of temperature, total chlorophyll a, chlorophyll‐containing picoplankton cell density, mean picoplankton cell volume and percentage of phycoerythrin‐rich cells in the total picoplankton population. All lakes showed maxima for total chlorophyll concentration and picoplankton cell density in mid‐ to late summer. The maximum value for picoplankton density ranged from 3.4 × 103 (Esthwaite Water) to 1.3 × 106 cells ml−1 (Ennerdale Water).There was a significant negative relationship (p < 0.05) between log10 of maximum picoplankton cell density and maximum total chlorophyll, the latter being taken as an indicator of lake trophic status. The ratio of maximum to minimum picoplankton density during the year in a particular lake ranged from 39 to 2360 and showed no obvious relationship to lake type. Overall, the seasonal range in picoplankton density was about one order of magnitude greater than the range in total chlorophyll a, but there were considerable differences between lakes.Phycoerythrin‐rich picoplankton as a percentage of total picoplankton reached a maximum in summer in all lakes. Values were always very low (<5%) in the two shallow eutrophic lakes, but reached 97% and over in the four most oligotrophic lakes. In two of the oligotrophic lakes, Wast‐water and Ennerdale Water, phycoerythrin‐rich picoplankton was a major component of the summer phytoplankton biomass.

Effects of planktivorous fish mass mortality on the plankton community of Lake Mendota, Wisconsin: implications for biomanipulation

Massive mortality of planktivorous fish had a dramatic impact on plankton community dynamics of Lake Mendota, Wisconsin, USA. After fish mortality, the larger Daphnia pulicaria replaced the smaller Daphnia galeata mendotae, resulting in greater grazing pressure on phytoplankton. This was accompanied by a much longer spring clear-water period and lower summer phytoplankton biomass compared to years before the fish mortality. Analysis of historical data (from the mid-1970’s) showed that previous fluctuations in planktivorous abundance had similar effects on Daphnia abundance and species composition, and on spring phytoplankton biomass. However, the mid-1970’s fish fluctuations had no detectable effect on summer phytoplankton. Concentrations of phosphorus were much higher in the 1970’s (spring P 80–135 μg 1−1 ’) than in the 1980’s (spring P 19–36 μg 1−1) and it is possible that high P concentrations may reduce trophic cascade effects on summer phytoplankton communities. This suggests that the success of biomanipulation programs may be dependent on lake nutrient status.

Bacterioplankton and Organic Carbon Dynamics in the Lower Mesohaline Chesapeake Bay

The mesohaline portion of the Chesapeake Bay is subject to annual summertime hypoxia and anoxia in waters beneath the pycnocline. This dissolved oxygen deficit is directly related to salinity-based stratification of the water column in combination with high levels of autochthonously produced organic matter and a very high abundance of metabolically active bacteria. Throughout the water column in the lower, mesohaline part of the bay, between the Potomac and Rappahannock rivers, near the southern limit of the mainstem anoxia, bacterial abundance often exceeded 10 x 10 cells per ml and bacterial production exceeded 7 x 10 cells per liter per day during summer. Bacterial biomass averaged 34% (range, 16 to 126%) of the phytoplankton biomass in summer. These values are equal to or greater than those found farther north in the bay, where the oxygen deficit is more severe. Seasonal variations in bacterial abundance and production were correlated with phytoplankton biomass (lag time, 7 to 14 days), particulate organic carbon and nitrogen, and particulate biochemical oxygen demand in spring; but during summer, they were significantly correlated only with dissolved biochemical oxygen demand. During summer, dissolved biochemical oxygen demand can account for 50 to 60% of the total biochemical oxygen demand throughout the water column and 80% in the bottom waters. There is a clear spring-summer seasonal shift in the production of organic matter and in the coupling of bacteria and autochthonous organic matter. The measurement of dissolved, microbially labile organic matter concentrations is crucial in understanding the trophic dynamics of the lower mesohaline part of the bay. The absolute levels of organic matter in the water column and the bacterial-organic carbon relationships suggest that a lower bay source of organic matter fuels the upper mesohaline bay oxygen deficits.

The seasonal productivity cycle of phytoplankton and controlling factors in Lake Constance

Annual phytoplankton productivity in Lake Constance is about 300 g C m−2, a value typical for mesoeutrophic lakes. Seasonal variations in phytoplankton biomass and productivity are exceptionally great because of a sequence of factors controlling the production process. During winter productivity is controlled by low energy inputs and high respiratory losses due to deep water column mixing. Biomass is low and water transparancy high. The spring phytoplankton growth is triggered by the thermal stabilization of the water column. The summer phytoplankton biomass maximum mainly depends on phosphorus availability. However, biomass yields comprise only 15–20% of values to be expected from the Redfield ratio because large proportions of POM are detritus and non-algal biota. Moreover, sedimentation during the second half of the year removes biomass from the euphotic zone. Water transparency and thus vertical distribution of algal photosynthesis is highly dependent on phytoplankton biomass. Self-shading causes considerably smaller seasonal variations in areal biomass and photosynthetic rates than in volume-based values. By light-shade adaptation effects of seasonal fluctuations in mean daily surface radiance fluxes on algal photosynthesis can to a significant extent be compensated for. At any given level of biomass daylength is the major determinant of daily production rates.

Effects of low concentrations of heavy metals on plankton community dynamics in a small, shallow, fertile lake

Significant differences in phytoplankton abundance developed among identical, untreated 2.3-m 3 enclosures, maintained in a shallow, fertile lake in northern Italy for 14 days in June 1981. Differences in soluble reactive phosphorus concentration were significant after 7 days and developed more rapidly if the water columns were isolated from the sediment. Three replicate enclosures were used per treatment in experiments carried out between November 1981 and June 1983 to investigate heavy metal toxicity. This enabled between-treatment variation caused by the heavy metal additions to be distinguished from within-treatment variation caused by containing the water column within enclosures. For plankton abundance and physico-chemical variables, the within-treatment coefficient of variation exceeded ±50% if experiments were >3 weeks. Containment within enclosures affected the ecosystem differently in different seasons but, in general, planktonic populations resembled those in the lake. Cadmium, copper and mercury additions of between 10 and 100 μg l −1 had little immediate effect upon phytoplankton biomass in summer. In winter, marked reductions occurred in the first 2 days of the experiment. Zooplankton was more sensitive than phytoplankton to the heavy metals in summer, cladoceran and rotifer populations declining precipitously, shortly after heavy metal addition in each experiment. Copepods were the most heavy-metal-tolerant zooplankters. As the direct toxicity of the heavy metals subsided, there was disruption of zooplankton predation and nutrient regeneration. In summer, reduced grazing by heavy-metal-sensitive zooplankton caused algae to proliferate, whereas in winter, inorganic nutrients, which accumulated in the treatments due to heavy-metal-induced decreases in plankton biomass, later supported larger populations of algae than would otherwise have occurred. Low nutrient concentrations in summer probably reflected rapid uptake in productive conditions. Mercury persisted in the water for a shorter period than did either cadmium or copper, and accumulated more rapidly in periphyton. Copper remained longest in the water column and was largely associated with suspended particulate material. Cadmium also persisted in the water column but remained largely in solution. Heavy metal accumulation in sediment was not evident, but may have been masked by high background concentrations.

The inadequacy of existing chlorophyll- a/phosphorus concentration correlations for assessing remedial measures for hypertrophic lakes

Because large reductions in phosphorus loading are required to cause small decreases in mean summer phytoplankton biomass, inaccuracies exist in (1) predicting lake phosphorus concentrations from phosphorus loading models and mean and maximum chlorophyll- a from lake phosphorus concentrations and (2) representative sampling to estimate true phosphorus loading and true mean and maximum chlorophyll- a. Remedial measures to reduce external phosphorus loads—and hence lower in-lake phosphorus concentrations from some 600 mg/m 3 to much lower values of some 100 mg/m 3—will result in the reduction of long-term (several years average) mean—and, more significantly, maximum—open-water summer chlorophyll- a concentrations. However, despite the application of these remedial measures, perturbations in phytoplankton biomass will remain such that, on any particular day during the open-water period, short-term algal blooms or scums will still be sufficiently intense for long-term improvements not to be clearly evident to the casual recreational user of the lake.

Le contrôle de la variabilité à court terme du phytoplancton estuarien: stabilité verticale et profondeur critique

Hourly series of summer phytoplankton biomass (ATP and chlorophyll a) and photosynthetic capacity (14C assimilation and ATP increase in saturating light) were sampled in the lower St. Lawrence Estuary during the summer of 1977. Vertical stability of the water column was estimated by the Richardson number. From the results it is concluded that the mean level of biomass is an inverse function of critical depth, likely linked to the neap-spring tidal cycle (Mf). On the other hand, the fine fluctuations of biomass and photosynthetic activity were related to vertical stability, which varies according to the semi-diurnal tidal cycle (M2). A simple model was developed on the basis of Sverdrup's critical depth, combining the M2 fluctuations in stability (degree of vertical mixing) to Mf variations in critical depth. Net biomass increases, observed in a nonturbid stabilized water column, cannot be explained by the growth rates computed from 14C assimilation, but they are consistent with the measured rates of ATP production. Spectral analyses of time series of temperature and Richardson number suggest that low frequency water column stability variations amplify the spatial heterogeneity of a reacting parameter such as phytoplankton. On the other hand, a passive scalar such as temperature does not respond to these low frequency variations of stability. It follows that the study of stability spectra may give some insight into the low frequency control of phytoplankton dynamics. Key words: phytoplankton, St. Lawrence Estuary, variability, vertical stability, critical depth, Richardson number, Kendall's cross correlation, spectral analysis