Reduced Phytoplankton Biomass Research Articles

Clay‐Turbid Interactions May Not Cascade—A Reminder for Lake Managers

Abstract Food web management is a frequently used lake restoration method, which aims to reduce phytoplankton biomass by strengthening herbivorous zooplankton through reduction of planktivorous fish. However, in clay‐turbid lakes several factors may reduce the effectivity of food web management. Increasing turbidity reduces the effectivity of fish predation and weakens the link between zooplankton and phytoplankton. Therefore, the effects of fish stock manipulations may not cascade to lower trophic levels as expected. Additionally, in clay‐turbid conditions invertebrate predators may coexist in high densities with planktivorous fish and negate the effects of fish reductions. For instance, in the stratifying regions of the clay‐turbid Lake Hiidenvesi, Chaoborus flavicans is the main regulator of cladocerans and occupies the water column throughout the day, although planktivorous Osmerus eperlanus is very abundant. The coexistence of chaoborids and fish is facilitated by a metalimnetic turbidity peak, which prevents efficient predation by fish. In the shallow parts of the lake, chaoborids are absent despite high water turbidity. We suggest that, generally, the importance of invertebrate predators in relation to vertebrate predators may change along turbidity and depth gradients. The importance of fish predation is highest in shallow waters with low turbidity. When water depth increases, the importance of fish in the top‐down regulation of zooplankton declines, whereas that of chaoborids increases, the change along the depth gradient being moderate in clear‐water lakes and steep in highly turbid lakes. Thus, especially deep clay‐turbid lakes may be problematic for implementing food web management as a restoration tool.

The Role of Filtering Zooplankton in De-Eutrophication of Water Bodies

The filtration capacity of large-size cladoceras is examined. Cladoceras Simocephalus vetulus with a biomass of 1.6 g/l in flow-through ecosystems isolated from ichthyifauna can reduce phytoplankton biomass from 2.89 to 0.12 mg/l within 1 h. Particularly, the biomass of blue-green algae Anabaena spiroides decreases from 0.14 to 0.01 mg/l, and their filaments shorten. In the period when phytoplankton biomass in the water body was at maximum, the activity of cladoceras (biomass of 2.1 g/l) resulted in a decrease in this biomass in flow-through ecosystems by a factor of 13.6 (down to 0.34 mg/l). The decrease in phytoplankton biomass in flow-through ecosystems facilitated changes in its composition in the water body (an increase in the share of green algae) and was accompanied by an increase in water transparency.

Nutrient pressures and ecological responses to nutrient loading reductions in Danish streams, lakes and coastal waters

The Danish National Aquatic Monitoring and Assessment Programme (NOVA) was launched in 1988 following the adoption of the first Danish Action Plan on the Aquatic Environment in 1987 with the aim to reduce by 50% the nitrogen (N) loading and by 80% the phosphorus (P) loading to the aquatic environment. The 14 years of experience gathered from NOVA have shown that discharges of total N (TN) and P (TP) from point sources to the Danish Aquatic Environment have been reduced by 69% (N) and 82% (P) during the period 1989–2002. Consequently, the P concentration has decreased markedly in most Danish lakes and estuaries. Considerable changes in agricultural practice have resulted in a reduction of the net N-surplus from 136 to 88 kg N ha −1 yr −1 (41%) and the net P-surplus from 19 to 11 kg P ha −1 yr −1 (42%) during the period 1985–2002. Despite these efforts Danish agriculture is today the major source of both N (>80%) and P (>50%) in Danish streams, lakes and coastal waters. A non-parametric statistical trend analysis of TN concentrations in streams draining dominantly agricultural catchments has shown a significant ( p<0.05) downward trend in 48 streams with the downward trend being stronger in loamy compared to sandy catchments, and more pronounced with increasing dominance of agricultural exploitation in the catchments. In contrast, a statistical trend analysis of TP concentrations in streams draining agricultural catchments did not reveal any significant trends. The large reduction in nutrient loading from point and non-point sources has in general improved the ecological conditions of Danish lakes in the form of increased summer Secchi depth, decreased chlorophyll a and reduced phytoplankton biomass. Major changes have also occurred in the fish communities in lakes, with positive cascading effects on water quality. In Danish estuaries and coastal waters only a few significant improvements in the ecological quality have been observed, although it is expected that the observed reduced nutrient concentrations are likely to improve the ecological quality of estuaries and coastal waters in Denmark in the long term.

Feeding by black fly (Diptera:Simuliidae) larvae causes downstream losses in phytoplankton, but not bacteria

Experimental removal of early instar black fly larvae from 3 oligotrophic lake-outlet streams in southern Quebec showed that larvae reduced phytoplankton biomass, but had little effect on bacterioplankton biomass. The rates of decline in bacterioplankton and phytoplankton biomass with distance downstream from 6 lake outlets were determined before the insecticide Bacillus thuringiensis var. israelensis was used to remove black fly larvae from 3 of the streams. The rates of decline in bacterioplankton and phytoplankton biomass were measured again after the larvae were removed, and the differences in the rates of decline between before and after were used as indicators of the rates of biomass ingestion by the black fly larvae. The proportion of bacterioplankton ingested/m stream length was <0.081%/m in all streams, but the proportion of phytoplankton ingested/m stream length was 0.35%/m and 0.24%/m in 2 of the 3 manipulated streams. Downstream declines in both bacterioplankton and phytoplankton persisted in the absence of black fly larvae. Factors other than black fly feeding (such as biofilm adhesion and ingestion by other filter-feeders) were responsible for 50 to 90% of the total downstream loss rate of bacteria, whereas factors other than black fly feeding were responsible for 0 to 55% of the total downstream loss rate of phytoplankton. Apparently, free-living bacteria were not ingested to a great extent by black fly larvae in these oligotrophic lake-outlet streams, and the link between bacteria in the plankton and their potential black fly predators seemed weak. The relative importance of algivory over bacterivory is expected to be greater in eutrophic lake-outlet streams, where the ratio of bacterial C to phytoplankton C is smaller than in oligotrophic lake-outlet streams, and in systems with a greater abundance of later-instar larvae, which are less efficient at capturing bacteria than early instar larvae.

Predicting benthic microalgal oxygen and nutrient flux responses to a nutrient reduction management strategy for the eutrophic Neuse River Estuary, North Carolina, USA

In response to recent water quality declines, caused by excessive nitrogen (N) loading, a 30% reduction of N inputs into the Neuse River Estuary (NRE) has been mandated by the North Carolina State Legislature. Water quality model predictions as well as nutrient bioassays indicate that a 30% reduction in N will result in a 15% reduction in phytoplankton biomass (as chlorophyll a) in the NRE. Using previously published NRE light extinction coefficient component data and NRE irradiance data, we calculated that the average NRE compensation depth (<1% surface irradiance) would deepen by 13 cm following a 15% reduction in phytoplankton biomass. Hydrographic and bathymetry data were used in a Geographical Information System to plot the resulting increase in euphotic sediment surface area based on the predicted change in the compensation depth. The newly created euphotic sediment surface area represents 4.47 × 10 6 m 2 which is 20% larger than the average sediment surface area in the euphotic zone during the study period (1998–2000). Previous NRE work revealed that euphotic sediment in the NRE support autotrophic benthic microalgal communities (BMC) that alter oxygen and nutrient fluxes. To further quantify this effect, we conducted a series of light versus dark incubations of NRE sediments collected from above (shallow euphotic areas < 1 m water depth) and below (deep aphotic areas > 3.5 m water depth) the compensation depth. Sediment oxygen demand (SOD), nutrient flux and organic matter content were significantly lower in shallow water cores compared to their deep-water counterparts. Furthermore, the illuminated shallow cores demonstrated a 45% decrease in SOD compared to shallow cores incubated in the dark. The combined effect of the projected increase in BMC habitat coupled with the reduction in SOD and nutrient flux associated with BMC represents an overlooked and potentially important benefit of reduced N inputs that could accelerate water quality recovery in the NRE.

Seasonal coupling between ciliate and phytoplankton standing stocks in the South Slough of Coos Bay, Oregon

The standing stocks of ciliates and phytoplankton together with physical variables (temperature and density) were measured biweekly from March 6, 1999, to March 22, 2000, in the marine-dominated region of the South Slough, the southern arm of the Coos Bay estuary (Oregon, United States). The abundance and biomass of naked ciliates correlated significantly with phytoplankton 5 μm phytoplankton fraction from diatoms in the spring-summer period to flagellates during this fall-winter period. Temperature could explain 49% of the variation of ultraphytoplankton and naked ciliate biomass across seasons and may be important in determining the rate of the ciliate numerical response to increases in ultraphytoplankton and its assimilation into ciliate biomass. High standing stocks of ciliates, their strong coupling with ultraphytoplankton across seasons, and the relatively higher contribution of ciliate carbon to the ciliate and >5 μm phytoplankton carbon pool in the October–March period suggest that ciliates are a significant component to the South Slough food web and may be particularly important during seasons of reduced phytoplankton biomass.

Pathways of Increased Water Clarity After Fish Removal from Ventura Marsh; a Shallow, Eutrophic Wetland

We investigated the pathways by which water clarity increases following fish removal by evaluating the effects of a benthivorous fish reduction in a large, shallow, eutrophic, wetland in a predominately agricultural watershed in Iowa, U.S.A. Phytoplankton was phosphorus limited prior to manipulation. After a substantial fish removal was obtained, water clarity increased as a result of decreased suspended sediment and phytoplankton biomass. Trophic cascading, mitigated by release from fish predation and decreased physical interference from suspended sediments, appears to determine water clarity. Inorganic suspended solids declined immediately after fish were removed but the biomass of Daphnia and Ceriodaphnia did not increase until a few weeks after fish removal. High grazing by zooplankton likely reduced phytoplankton biomass during the height of the clear-water phase. Phytoplankton appeared to be limited by zooplankton grazing for approximately two months before reverting to bottom-up control. An increase in suspended sediment and/or increased predation pressure on zooplankton, due to the return of juvenile carp, appears to account for the decline of larger-bodied zooplankters and the switch back to bottom-up control. Macrophyte diversity and density increased substantially after the initiation of the clear-water phase.

Does resuspension prevent a shift to a clear state in shallow lakes during reoligotrophication?

Water managers often debate whether resuspension of sediment with high organic matter and water content accumulated during eutrophication delays improvement of water clarity after reduction of external nutrient loading. Using data from 15 shallow (mean depth &lt;5 m) eutrophic lakes surveyed during 8–12 yr, we show that the reduction in phytoplankton biomass after external loading reductions of phosphorus or changes in the abundance of planktibenthivorous fish was accompanied by a proportional or nearly proportional reduction in detritus and inorganic suspended solids. The reduction occurred irrespective of lake size (0.1–40 km2), extent of phytoplankton biomass reduction (up to 10‐fold), and despite dominance of sediments with high water and organic content. Therefore, we conclude that recovery of shallow lakes after nutrient loading or fish stock reduction is apparently not significantly delayed by resuspension of organic or inorganic matter accumulated in the sediment during eutrophication.

Influence of simulated bivalve biodeposition and microphytobenthos on sediment nitrogen dynamics: A laboratory study

Suspension‐feeding eastern oysters, Crassostrea virginica, were once abundant in Chesapeake Bay and may then have exerted top‐down control on phytoplankton and also reduced turbidities, thereby increasing light available to benthic plants. Alternatively, oysters may have simply recycled inorganic nutrients rapidly back to the water column, with no long‐lasting reduction in phytoplankton biomass resulting from oyster feeding activity. To help distinguish between these scenarios, we explored changes in nitrogen fluxes and denitrification in laboratory incubations of sediment cores held under oxic and anoxic conditions in response to loading by pelletized phytoplankton cells, an experimental analog for oyster feces and pseudofeces. When organics were regenerated under aerobic conditions, typical of those associated with oyster habitat, coupled nitrification‐denitrification was promoted, resulting in denitrification of ~20% of the total added nitrogen. In contrast, under anoxic conditions, typical of current summertime conditions in main‐stem Chesapeake Bay where phytoplankton is microbially degraded beneath the pycnocline, nitrogen was released solely as ammonium from the added organics. We postulate that denitrification of particulate nitrogen remaining in oyster feces and pseudofeces may enhance nitrogen removal from estuaries. In aerobic incubations with sufficient light (70 µmol m-2 s-1), a benthic microalgal/cyanobacterial community grew that not only absorbed the inorganic nitrogen released from the added organics but also fixed N2. This result suggests that an ecosystem dominated by benthic primary production may develop in shallow waters when reduced turbidity associated with bivalve feeding increases light penetration to a level that can sustain benthic microalgal production.

Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences

Although algal blooms, including those considered toxic or harmful, can be natural phenomena, the nature of the global problem of harmful algal blooms (HABs) has expanded both in extent and its public perception over the last several decades. Of concern, especially for resource managers, is the potential relationship between HABs and the accelerated eutrophication of coastal waters from human activities. We address current insights into the relationships between HABs and eutrophication, focusing on sources of nutrients, known effects of nutrient loading and reduction, new understanding of pathways of nutrient acquisition among HAB species, and relationships between nutrients and toxic algae. Through specific, regional, and global examples of these various relationships, we offer both an assessment of the state of understanding, and the uncertainties that require future research efforts. The sources of nutrients poten- tially stimulating algal blooms include sewage, atmospheric deposition, groundwater flow, as well as agricultural and aquaculture runoff and discharge. On a global basis, strong correlations have been demonstrated between total phos- phorus inputs and phytoplankton production in freshwaters, and between total nitrogen input and phytoplankton pro- duction in estuarine and marine waters. There are also numerous examples in geographic regions ranging from the largest and second largest U.S. mainland estuaries (Chesapeake Bay and the Albemarle-Pamlico Estuarine System), to the Inland Sea of Japan, the Black Sea, and Chinese coastal waters, where increases in nutrient loading have been linked with the development of large biomass blooms, leading to anoxia and even toxic or harmful impacts on fisheries re- sources, ecosystems, and human health or recreation. Many of these regions have witnessed reductions in phytoplankton biomass (as chlorophyll a) or HAB incidence when nutrient controls were put in place. Shifts in species composition have often been attributed to changes in nutrient supply ratios, primarily N:P or N:Si. Recently this concept has been extended to include organic forms of nutrients, and an elevation in the ratio of dissolved organic carbon to dissolved organic nitrogen (DOC:DON) has been observed during several recent blooms. The physiological strategies by which different groups of species acquire their nutrients have become better understood, and alternate modes of nutrition such as heterotrophy and mixotrophy are now recognized as common among HAB species. Despite our increased un- derstanding of the pathways by which nutrients are delivered to ecosystems and the pathways by which they are assimilated differentially by different groups of species, the relationships between nutrient delivery and the development of blooms and their potential toxicity or harmfulness remain poorly understood. Many factors such as algal species presence/ abundance, degree of flushing or water exchange, weather conditions, and presence and abundance of grazers contribute to the success of a given species at a given point in time. Similar nutrient loads do not have the same impact in different environments or in the same environment at different points in time. Eutrophication is one of several mechanisms by which harmful algae appear to be increasing in extent and duration in many locations. Although important, it is not the only explanation for blooms or toxic outbreaks. Nutrient enrichment has been strongly linked to stimulation of some harmful species, but for others it has not been an apparent contributing factor. The overall effect of nutrient over- enrichment on harmful algal species is clearly species specific.

Nutrient and grazing factors in relation to phytoplankton level in a eutrophic shallow lake: the effect of low macrophyte abundance

The ability of submerged macrophytes to moderate the structure of food webs with respect to lake eutrophication management has been intensively studied in recent years. Many lake managers have adopted the option of increasing macrophyte abundance in order to restore eutrophic waters, with a view to improve water quality, increase water transparency and reduce phytoplankton biomass. These studies are mostly based upon the comparison of macrophyte-rich and macrophyte-free waters. There is less quantitative information on how different levels of macrophyte abundance, in particular very low levels, influence ecosystem structure, or vice versa, within the same ecosystem. This paper takes a multivariate statistical approach to examine ecosystem function with low macrophyte abundance (ca. 5%) in the context of nutrient–phytoplankton–zooplankton interaction in a eutrophic shallow lake. It shows that with low levels of macrophyte coverage, phytoplankton biomass was only limited by nutrient (TP and Si) availability, whilst nutrient (Si) as well as grazing (zooplankton and Daphnia) factors were both limiting phytoplankton levels in macrophyte-free waters. With respect to interactions between Daphnia and chlorophyll-a, the results suggest that low macrophyte cover does not result in a reduction of phytoplankton biomass due to the presence of Daphnia. Rather, low macrophyte cover provides a refuge that maintains constant Daphnia predation, so reducing chlorophyll-a fluctuation. These results add credence to the causal interpretation of different interactions amongst nutrients, phytoplankton and zooplankton at very low macrophyte densities.

Reduction of the Trophic Status of a Water Body with the Use of Large-Size Zooplankton

It is shown that large-size zooplankton can be used as a natural filter in flow-through plants for reducing the trophic status of water bodies and improve water transparency. Experiments in Chistye Prudy pond in the period of blue-green algae blooming show large-size zooplankton to reduce phytoplankton biomass in the pond throughout the period of phytoplankton growth. Daphnia magna specimens (with a biomass of 92 to 3450 mg/l) in lothic ecosystems are found to reduce the biomass of dominating Anabaena spirodes blue-green algae when this biomass attains its maximum.

INTERACTIVE EFFECTS OF PREDATION AND DISPERSAL ON ZOOPLANKTON COMMUNITIES

Communities of coexisting organisms are formed by both dispersal among habitat patches in a region and local interactions within patches. The supply of colonists from the regional pool has the potential to alter the outcome of local interactions by providing species that fill different ecological roles. I examined the consequences of invasion by fish (juvenile Lepomis macrochirus) and insect (Notonecta undulata) predators on ex- perimental plankton communities that were either connected to or isolated from the regional pool of zooplankton species. The effects of predators on zooplankton composition and diversity depended on dispersal by members of the regional zooplankton species pool. Fish and notonectids reduced the abundance of large zooplankton and thereby facilitated invasion by new species from the surrounding region. Both predators reduced zooplankton species richness in the absence of dispersal, while fish had positive effects and notonectids had no effects with rapid dispersal. Fish facilitated invasion by more species than they excluded, while similar numbers of species invaded with notonectids as were driven extinct. The effects of predators on planktonic trophic structure (zooplankton size structure and biomass, phytoplankton biomass) were independent of the level of dispersal. Both predators reduced zooplankton mean body size, but only fish enhanced phytoplankton density. Invasion by members of the regional species pool slightly increased zooplankton mean body size and reduced phytoplankton biomass; however, the effects were small and independent of the predator treatment. Predator-facilitated invasion of new species altered the effects of pred- ators on zooplankton species composition and diversity, but not on plankton trophic struc- ture. The results suggest that spatial heterogeneity in predator abundance promotes regional coexistence among zooplankton. Connection to a diverse regional species pool via dispersal may therefore be important for determining the impact of local interactions such as predation on communities.

Interactive Effects of Predation and Dispersal on Zooplankton Communities

Communities of coexisting organisms are formed by both dispersal among habitat patches in a region and local interactions within patches. The supply of colonists from the regional pool has the potential to alter the outcome of local interactions by providing species that fill different ecological roles. I examined the consequences of invasion by fish (juvenileLepomis macrochirus) and insect (Notonecta undulata) predators on experimental plankton communities that were either connected to or isolated from the regional pool of zooplankton species. The effects of predators on zooplankton composition and diversity depended on dispersal by members of the regional zooplankton species pool. Fish and notonectids reduced the abundance of large zooplankton and thereby facilitated invasion by new species from the surrounding region. Both predators reduced zooplankton species richness in the absence of dispersal, while fish had positive effects and notonectids had no effects with rapid dispersal. Fish facilitated invasion by more species than they excluded, while similar numbers of species invaded with notonectids as were driven extinct. The effects of predators on planktonic trophic structure (zooplankton size structure and biomass, phytoplankton biomass) were independent of the level of dispersal. Both predators reduced zooplankton mean body size, but only fish enhanced phytoplankton density. Invasion by members of the regional species pool slightly increased zooplankton mean body size and reduced phytoplankton biomass; however, the effects were small and independent of the predator treatment. Predator-facilitated invasion of new species altered the effects of predators on zooplankton species composition and diversity, but not on plankton trophic structure. The results suggest that spatial heterogeneity in predator abundance promotes regional coexistence among zooplankton. Connection to a diverse regional species pool via dispersal may therefore be important for determining the impact of local interactions such as predation on communities.

Complementary impact of copepods and cladocerans on phytoplankton

The differences in the impact of two major groups of herbivorous zooplankton (Cladocera and Copepoda) on summer phytoplankton in a mesotrophic lake were studied. Field experiments were performed in which phytoplankton were exposed to different densities of two major types of herbivorous zooplankton, cladocerans and copepods. Contrary to expectation, neither of the two zooplankton groups significantly reduced phytoplankton biomass. However, there were strong and contrasting impacts on phytoplankton size structure and on individual taxa. Cladocerans suppressed small phytoplankton, while copepods suppressed large phytoplankton. The unaffected size classes compensated for the loss of those affected by enhanced growth. After contamination of the copepod mesocosms with the cladoceran Daphnia, the combined impact of both zooplankton groups caused a decline in total phytoplankton biomass.

Zooplankton grazing dynamics: top‐down control of phytoplankton and its relationship to an estuarine habitat

AbstractTop‐down control of algal blooms was investigated in the Swan–Canning Estuary, to determine whether the resident zooplankton community was able to substantially reduce phytoplankton biomass through grazing, or whether high phytoplankton biomass effectively inhibited grazing. In situ grazing by zooplankton at two depths in the water column was measured over a diel period on six occasions and examined in relation to the biotic and abiotic habitat conditions.Measured weight‐specific ingestion rates varied with phytoplankton and zooplankton species composition, but were significantly greater at the surface than at 5 m, close to the bottom (ranges of 1·59 to 252·41 and 0·51 to 28·99 µg phytoplankton C µg zooplankton C−1 day−1, respectively). There was no evidence of significant diel changes in ingestion rates of zooplankton. Phytoplankton biomass removed by in situ community grazing ranged between 0·9 and 45·0% of standing stock per hour. The maximum loss occurred when phytoplankton biomass ranged from 249·0 to 320·8 µg phytoplankton C l−1. Zooplankton grazing impact was negatively associated with high phytoplankton and low dissolved oxygen in bottom waters. The implications of, and mechanisms associated with, top‐down control of algal biomass in this estuary are discussed in relation to plankton succession and the physical environment. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Effects of reduced load in the River Danube on nutrients and phytoplankton dynamics in the flood-relief channel New Danube (Vienna, Austria)

Spatio-temporal distributions of plant nutrient concentrations, turbidity, chlorophyll-a and phytoplankton biomass are evaluated for a 10-year dataset from both impoundments of the New Danube flood-relief channel at Vienna, including measurements from the main River Danube. Concentrations of phosphorus primarily are influenced by groundwater transfer of water and nutrients from the main river into the two impoundments, percolating through the gravel substratum of a newly constructed island separating the Danube from the New Danube. Variations of phosphorus input in turn affect the amounts of chlorophyll-a and phytoplankton developing in the impoundments. In the Danube, turbidity depends mainly on discharge, but in the New Danube, although influenced by wind and wave action, turbidity is basically associated with direct inputs from the river when flood-gates are opened. When the channel was first filled with water, all variables had concentration gradients down its 21-km length. Over time, trophic levels have fallen considerably, from hypertrophic to oligo-mesotrophic, with a concurrent reduction of phytoplankton biomass. Species composition of algae has changed to a lesser extent.

Effects of Phosphorus Reduction on Water Quality: Comparison of Alum-Treated and Untreated Portions of a Hypereutrophic Lake

ABSTRACT The effects of a reduction in total phosphorus concentration on the water quality and plankton community structure in a 86-ha hypereutrophic sandpit lake with high internal phosphorus loading were assessed by dosing an isolated 4.6-ha section of the lake with 34,065 L (dose = 10 mg Al·L−1) of liquid aluminum sulfate (alum). During the three summers following treatment, hypolimnetic total dissolved phosphorus, epilimnetic total phosphorus, and eplimnetic total nitrogen were decreased by 97%, 74%, and 36%, respectively, in the treated section. Secchi depth was 134% greater in the treated area. Alum treatment also increased the volume of usable fish habitat by 22%, as the depth of the 3.0-mg/l dissolved oxygen isocline was 52% deeper in the treated portion than in the untreated portion. Total phytoplankton biovolume decreased by 40% and chl a concentration by 65% in the treated area. Although cyanophytes continued to dominate in die treated area, there was a shift in relative abundance from cyanophytes to bacillariophytes and chlorophytes, especially during the second summer after treatment. By the second post-treatment summer, daphnid biomass increased substantially and there was a subtle shift in relative abundance from copepods to daphnids. Overall, alum was extremely effective in controlling sediment phosphorus release rates and lowering water column phosphorus concentrations and thus improving water clarity, reducing phytoplankton biomass, shifting phytoplankton species composition from cyanophyte dominance toward bacillariophytes and chlorophytes, increasing daphnid biomass, and increasing usable fish habitat.

Phytoplankton Composition and Biomass in the Offshore Waters of Lake Erie: Pre- and Post- Dreissena Introduction (1983–1993)

Phytoplankton was collected in all basins of Lake Erie during 42 cruises during the spring and summer from 1983 to 1993—a period that spans the Dreissena mussel invasion. Two potential impacts of Dreissena on the phytoplankton community of the western, central, and eastern basins of Lake Erie were evaluated: Was selective feeding occurring as observed in Saginaw Bay and were reductions in biomass evident in the offshore regions of the three basins of Lake Erie? In the western basin, significant summer decreases in Chlorophyta, Bacillariophyta, Cyanobacteria, and total phytoplankton biomass were observed after Dreissena introduction. Similarly in the spring, Bacillariophyta and total phytoplankton biomass and chlorophyll a concentrations decreased significantly. Since several divisions of phytoplankton did not decrease in phytoplankton biomass in the western basin, and spring Cyanobacteria biomass increased significantly while other divisions decreased in biomass, selective feeding on the phytoplankton community was suggested. Where significant reductions in biomass were observed in the offshore waters of the western basin, they were approximately 50% of the reduction observed at the nearshore sites in Lake Erie by other workers. Dreissena impact on the phytoplankton community of the pelagic waters of the central and eastern basin appeared to be minimal. Pre- and post- Dreissena total phytoplankton biomass and chlorophyll a concentrations were not significantly different or increased significantly after the Dreissena invasion. Biomass of several divisions of phytoplankton significantly increased after Dreissena introduction in the central and eastern basins. These included Bacillariophyta (central basin), Cyanobacteria (central and eastern basin), Chrysophyta (eastern basin), Chlorophyta biomass (eastern basin) and phytoplankton biomass (central basin) and chlorophyll a (central basin) in the spring, and Chrysophyta (eastern basin) and Cryptophyta biomass (central basin) in the summer. Generally, a reduction in phytoplankton biomass would be expected as a result of Dreissena grazing, not an increase in biomass. Dreissena-mediated changes in phytoplankton have generally occurred in shallow, well-mixed lakes, ponds, and embayments, not in deeper waters such as the central and eastern basins of Lake Erie.

The Optical Water Quality of Cannonsville Reservoir: Spatial and Temporal Patterns, and the Relative Roles of Phytoplankton and Inorganic Tripton

ABSTRACT Longitudinal and temporal distributions of optical properties, and the relative role of selected light attenuating constituents in regulating light penetration, in Cannonsville Reservoir, NY, in 1995 are documented. The analysis is supported by field measurements of light penetration; die angular distribution of irradiance (reflectance); and the spectral quality of penetrating light; laboratory measurements of turbidity, chlorophyll, gelbstoff, and microscopy-based individual particle size and elemental chemistry, and calculations of absorption and scattering coefficients and their components. Longitudinal gradients in attenuating components, and therefore optical properties, prevailed along the main axis of the reservoir; light attenuation and the relative role of scattering decreased with the approach to the dam. Large temporal variations in optical characteristics occurred. These dynamics were mostly controlled by variations in phytoplankton biomass in spring and early summer, when the reservoir was full, but resuspended inorganic tripton (non-phytoplankton particles; suspensoids) became the regulating component as the reservoir was drawn down. Quantitative optical frameworks (models) are applied to simulate light penetration conditions that would have prevailed for scenarios of reductions in phytoplankton biomass and/or inorganic tripton.