Andrew R. Dzialowski

Effects of sediment resuspension on nutrient concentrations and algal biomass in reservoirs of the Central Plains

Abstract Historically, lake and reservoir management has focused on controlling external nutrient loading. However, it is becoming increasingly clear that internal mechanisms, such as the episodic resuspension of benthic sediments, can also contribute to the processes of eutrophication. We conducted laboratory bioassay experiments to determine how resuspended sediments affected nutrient concentrations and algal biomass in four eutrophic reservoirs of the Central Plains. Surficial sediments and surface water were collected from each reservoir and returned to the laboratory where they were added to 1-L bioassay bottles at five turbidity concentrations (0, 50, 150, 250, and 500 NTUs). Sediments in the bioassay bottles were resuspended daily, and algal biomass (measured as relative fluorescence) was measured for 11–14 days. Resuspended sediments at the lowest experimental turbidity concentration, 50 NTUs, had highly significant effects on algal biomass in each of the sediment resuspension bioassays. Algal biomass appeared to increase following experimental sediment resuspension due to an increase in available nutrients and/or the establishment of algae (meroplankton) from the sediment. Overall, our results highlight the importance of considering internal mechanisms when developing reservoir management and restoration plans for these important ecosystems.

Predicting sediment phosphorus release rates using landuse and water-quality data

Abstract.  We developed a series of models using landuse and water-quality variables to predict sediment P release rates under anoxic conditions in reservoirs. We collected sediment cores from 17 reservoirs in the Central Plains region of the USA, and we measured nutrient release rates under anoxic conditions in laboratory incubation studies. We used corresponding landuse and water-quality data from the reservoirs to develop regression models for predicting P release rates. We used variables that relate directly to trophic state, including % cropland in the watershed, which explained the greatest amount of variation in release rates. P release rates tended to be higher in reservoirs that had greater % cropland in the watersheds. We developed additional predictive models using surface total P concentrations and Secchi disk depths. Trophic state was also a good predictor of release rates because more P was released from hypereutrophic reservoirs than from mesotrophic or eutrophic reservoirs. The median release rates for reservoirs representing different trophic state classes (e.g., mesotrophic, eutrophic, and hypereutrophic) were very similar to those previously reported for natural lakes. Our models can be used to predict sediment release rates in individual reservoirs of concern or to screen a large number of reservoirs to help direct resources to those systems that are most vulnerable to internal loading. Models based on landuse characteristics are particularly valuable because these data can be obtained from computer-based assessments and do not require labor-intensive field sampling.

Effects of non-algal turbidity on cyanobacterial biomass in seven turbid Kansas reservoirs

Abstract One of the most visible consequences of eutrophication in freshwater lakes is an increase in the biomass of cyanobacteria. While growth of cyanobacteria has been shown to be coupled to water column concentrations of total phosphorus (TP) in natural lakes, the ecological behavior of cyanobacteria in turbid impoundments is less well understood. Patterns of cyanobacterial biovolume in 7 turbid Kansas (USA) reservoirs exhibited overlap with published data from natural lakes in North America. Non-algal turbidity (NAT) influenced the relationship between cyanobacteria and TP in these systems. Relative to yields predicted from natural lakes, the biomass of cyanobacteria per unit TP was typically higher in the reservoirs, except in those systems that had exceptionally high levels of NAT (>∼2.0 2/m) where observed concentrations were mostly lower than predicted. A more consistent pattern was observed with respect to the effects of NAT on yields of chlorophyll-a per unit TP in the reservoirs: across almost the entire NAT gradient, observed chlorophyll-a concentrations were typically lower than those predicted from natural lakes. Taken together, our results confirm that NAT plays an important role in regulating relationships between TP and phytoplankton biomass in reservoir ecosystems.

Experimental effect of consumer identity on the invasion success of a non-native cladoceran

An important goal of ecologists is to identify the characteristics of native communities that help to either promote or resist the invasion of non-native taxa. In this study, experimental mesocosms were used to determine how the richness and species identity of freshwater consumers influenced the invasion success of Daphnia lumholtzi (DL), a cladoceran that has successfully invaded aquatic habitats throughout the United States. Three species of native zooplankton were used to create a gradient of richness in replicated mesocosms that included all species in monoculture, all two species combinations, and all three species together. DL was then added to each mesocosm and its biomass was monitored over time. While additional research is needed to better determine how richness affects the invasion success of DL, the presence of native zooplankton resulted in reduced levels of DL biomass in all treatments relative to the zooplankton free controls. One species (Daphnia magna, DM) was able to reduce the biomass of DL to lower levels than the other two species. DL also appeared to be unable to establish or persist over time in mesocosms with DM, unlike in mesocosms with the two other species. These species–specific effects on invasion success appeared to be related to DM’s ability to reduce algal biomass to lower levels than the other two species. Therefore, while the presence of native zooplankton helps to reduce the biomass of DL once it is introduced into novel systems, the degree to which DL is able to establish and maintain populations over time within individual systems will likely depend on the presence or absence of particular species that can have particularly strong impacts on invasibility. Using such data, we may be able to predict which habitats are most likely to be invaded based on the presence or absence of individual native species.

Comparisons of zooplankton and phytoplankton in created shallow water habitats of the lower Missouri River: implications for native fish

Shallow water habitat (SWH) is important for riverine fish and their invertebrate prey, yet the availability of SWH has declined in many systems due to human impacts. We evaluated the potential ecological benefits of restoring SWH by comparing zooplankton and phytoplankton from created backwaters (a floodplain feature connected to the river on the downstream end but disconnected at the upstream end) and chutes (a side channel of the river that diverts flow from the main channel through the chute and back into the main channel) on the lower Missouri River. We tested the hypothesis that backwaters support higher abundances of zooplankton and phytoplankton than chutes using data that were collected during the summer of 2010. As predicted, backwaters had more diverse cladoceran communities and greater abundances of rotifers, copepod nauplii, adult copepods, and cladocerans than chutes. Total algal biovolume was the same in chutes and backwaters; however, phytoplankton taxa richness was higher in backwaters, and there was a greater biovolume of green algae (Chlorophyta), Crypotophyta, cyanobacteria, and Euglenophyta in backwaters than in chutes. Differences in zooplankton and phytoplankton between backwaters and chutes appeared to be related to slower current velocities, longer retention times, and lower levels of turbidity and total suspended solids in backwaters. While chutes have the potential to provide greater habitat diversity than the mainstem, there were no differences in water quality or phytoplankton abundance, community structure, or diversity between these two habitats. Combined, our results suggest that created backwaters initially provide a greater potential food resource for native fishes. However, additional research is needed to determine whether chutes can also develop beneficial shallow water features over a longer period of time.

Effects of invasive zebra mussels on phytoplankton, turbidity, and dissolved nutrients in reservoirs

Few experiments have quantified the effects of invasive zebra mussels (Dreissena polymorpha) on man-made reservoirs relative to other aquatic habitats. Reservoirs, however, are the dominate water body type in many of the states that are at the current front of the zebra mussel invasion into the western United States. The objective of this research, therefore, was to determine how zebra mussels affected phytoplankton, turbidity, and dissolved nutrients in water that was collected from three Kansas reservoirs that varied in trophic state (mesotrophic to hypereutrophic), but all experienced frequent cyanobacterial blooms. Laboratory mesocosm experiments were conducted to document the effects of zebra mussels on cyanobacteria and general water quality characteristics in the reservoir water. Zebra mussels significantly reduced algal biomass, and the total biovolume of cyanobacteria (communities were dominated by Anabaena) in each reservoir experiment. The effects of zebra mussels on other major algal groups (diatoms, flagellates, and green algae) and algal diversity were less consistent and varied between the three reservoir experiments. Similarly, the effects of zebra mussels on nutrient concentrations varied between experiments. Zebra mussels increased dissolved phosphorus concentrations in two of the reservoir experiments, but there was no effect of zebra mussels on dissolved phosphorus in the mesotrophic reservoir experiment. Combined, our results strongly suggest that zebra mussels have the potential to significantly impact reservoirs as they continue to expand throughout the western United States. Moreover, the magnitude of these effects may be context dependent and vary depending on the trophic state and/or resident phytoplankton communities of individual reservoirs as has similarly been reported for natural lakes.

Rapid Buffer Assessment Fails to Predict and Classify Wetland Floristic Quality in Oklahoma

Rapid field assessment indicators of ecological stress and disturbance may or may not reflect actual biological conditions. We tested the ability of rapidly assessed buffer quality to predict and classify wetland floristic quality across 106 sites in Oklahoma, USA. We used buffer zone metrics from a national-level rapid assessment tool (USA-RAM) to evaluate applicability at the state level. The rapid assessment relying on buffer quality did not relate predictably (linearly) with floristic quality, but the relationship improved after ecoregional stratification. Focusing on the Central Great Plains ecoregion with 55 wetlands sampled, we found 16 floristically intact sites and 13 floristically altered sites based on multivariate testing of the Floristic Quality Assessment Index and several component metrics. Distributions of buffer metrics across these sites were similar between the floristically intact and altered classes, suggesting potential for misclassification of wetland biological condition using rapid buffer assessment. Some of the disconnect may be attributed to bias in the buffer measurements and to using a national assessment protocol at the state level. Buffer metrics in the USA-RAM may offer little insight about wetland biological condition in some regions, and the use of such metrics should only complement direct bioassessments and not substitute for them.

Invasive zebra mussels alter zooplankton responses to nutrient enrichment

Abstract.  The effects of nutrient enrichment on aquatic ecosystems have been well documented, but less is known about how these effects vary in response to additional stressors. I used experimental mesocosms to assess how nutrient enrichment affected zooplankton density and community structure in the presence and absence of invasive zebra mussels (Dreissena polymorpha). The density of several pelagic zooplankton taxa increased in response to nutrient enrichment, but these increases were offset or reduced in mesocosms that contained zebra mussels. At least at the beginning of the experiment, zebra mussels reduced the amount of algae that developed in response to nutrient enrichment and potentially were in competition with pelagic zooplankton. In contrast, zebra mussels did not reduce the total density of zooplankton in the absence of nutrient enrichment. Instead, the density of several littoral taxa increased in mesocosms with zebra mussels, presumably because they were able to use attached algae that also developed in mesocosms with zebra mussels. Combined, these results suggest that the overall effects of nutrient enrichment on plankton communities should be considered in the context of multiple stressors including the presence or absence of invasive species.

Experimental Impacts of Fish on Small and Large Cladocerans under Eutrophic Conditions

The impacts of fish and nutrient enrichment on the biomass of small and large cladoceran species were studied in mesocosms under eutrophic conditions. Fish shifted the ratio between small and large species to favour small cladocerans compared to control mesocosms, while nutrient enrichment favoured large cladocerans. Both fish vital activity and nutrient enrichment increased total and blue-green algae concentrations. While chlorophyll concentrations increased in response to fish and nutrient enrichment, there were no significant effects of fish on total cladoceran biomass and the relative proportion of large species due to high variability among replicates within treatments. However, fish and nutrient enrichment affected average total cladoceran biomass and the biomass of large species compared to control conditions.

Effects of zebra mussels on cladoceran communities under eutrophic conditions

The purpose of this study was to determine how zebra mussels affected cladoceran community structure under eutrophic conditions. We conducted a mesocosm study where we manipulated the presence of zebra mussels and the presence of large-bodied Daphnia (Daphnia magna and Daphnia pulicaria). We also conducted a complimentary life-table experiment to determine how water from the zebra mussel treatment affected the life history characteristics of the cladoceran species. We anticipated that small- and large-bodied cladoceran species would respond differently to changes in algal quality and quantity under the effects of zebra mussels. Large-bodied Daphnia successfully established in the zebra mussel treatment but failed to grow in the control. We did not observe positive relationships between food concentrations and cladoceran abundances. However, the phosphorus content in the seston indicated that food quality was below the threshold level for large-bodied cladocerans at the beginning of the experiment. We believe that zebra mussels quickly enhanced the phosphorus content in the seston due to the excretion of inorganic phosphorus, thus facilitating the development of large-bodied Daphnia. In conclusion, our results suggest that zebra mussels can alter the phosphorus content of seston in lakes and this can affect the dynamics of crustacean zooplankton.