Robert W. Pillsbury

Shifts in Benthic Algal Community Structure and Function Following the Appearance of Zebra Mussels (Dreissena polymorpha) in Saginaw Bay, Lake Huron

Zebra mussel, Dreissena polymorpha (Pallas), proliferation in Saginaw Bay, Lake Huron is associated with increased water clarity and increased light levels on benthic substrata in the littoral zone. We hypothesized that the filtering activities of Dreissena and associated increases in light penetration should affect the structure and function of benthic algae in the bay. Monthly quantitative benthic algal samples were collected from natural substrata by SCUBA in the littoral zone of the bay through the growing seasons of 1991 (initial Dreissena colonization), 1992 and 1993 (post-Dreissena colonization). Algal community structure was examined microscopically and productivity rates were measured using carbon-14 in sealed acrylic chambers in situ. Our data demonstrate that, following Dreissena proliferation, light penetration, benthic algal biomass, chlorophyll concentrations and rates of benthic primary productivity have increased. These changes coincided with a shift from diatom domination of the benthic algal community to a flora dominated by filamentous green algae (Zygnematales). We suggest that these shifts have the potential to affect benthic food webs within littoral zones of the Great Lakes.

The pH-independent effect of aluminum on cultures of phytoplankton from an acidic Wisconsin lake

Negative correlations between aluminum and planktonic algal abundance have been reported in acidic lakes. Natural assemblages of phytoplankton from a low-pH, low-Al lake (Franklin Lake, WI) were grown in semi-continuous cultures consisting of four treatments at pH 5.7 with 0.0, 50, 100, and 200 µg Al L−1 and one treatment at pH 4.7 with no Al added. Asterionella ralfsii var. americana (a common diatom plankter in acidic lakes) grew well at both pH 4.7 and 5.7 when no Al was added but declined in all other treatments and so may be useful as an indicator of acidic, low monomeric-Al conditions. Other common plankters that showed this pattern included: Arthrodesmus indentatus, Ar. octocornus, Ar. quiriferus, Staurastrum arachne var. curvatum, S. longipes var. contractum, and S. pentacerum. Common taxa showing no toxic effects of Al were Dinobryon bavaricum, Peridinium limbatum, Stenokalyx monilifera, Elaktothrix sp. and Oedogonium sp. We hypothesize that metal toxicity as a pulse at spring snowmelt could dramatically change algal succession in moderately acidic lakes. The experimental results agreed well with field observations. These types of experiments are useful for predicting the responses of natural phytoplankton communities to increases in Al concentration.

The Green Alga, Cladophora , Promotes Escherichia coli Growth and Contamination of Recreational Waters in Lake Michigan

A linkage between Cladophora mats and exceedances of recreational water quality criteria has been suggested, but not directly studied. This study investigates the spatial and temporal association between Escherichia coli concentrations within and near Cladophora mats at two northwestern Lake Michigan beaches in Door County, Wisconsin. Escherichia coli concentrations in water underlying mats were significantly greater than surrounding water (p < 0.001). Below mat E. coli increased as the stranded mats persisted at the beach swash zone. Water adjacent to Cladophora mats had lower E. coli concentrations, but surpassed EPA swimming criteria the majority of sampling days. A significant positive association was found between E. coli concentrations attached to Cladophora and in underlying water (p < 0.001). The attached E. coli likely acted as a reservoir for populating water underlying the mat. Fecal bacterial pathogens, however, could not be detected by microbiological culture methods either attached to mat biomass or in underlying water. Removal of Cladophora mats from beach areas may improve aesthetic and microbial water quality at affected beaches. These associations and potential natural growth of E. coli in bathing waters call into question the efficacy of using E. coli as a recreational water quality indicator of fecal contaminations.

Factors Affecting the Distribution of Wild Rice (Zizania palustris) and the Associated Macrophyte Community

A recent decline in wild rice (Zizania palustris) wetlands has been observed. We assessed the factors significant in understanding the distribution of Z. palustris and the surrounding macrophyte community. Sixty historic wild rice wetlands that currently display a wide range of rice densities were sampled in Wisconsin and Minnesota (USA). Chemical and physical factors and aquatic plants densities were measured. Data were analyzed using Canonical Correspondence Analysis in which the following trends were found. Wetlands that exhibited the greatest loss of Zizania tended to have higher levels of residential development within their watershed, ammonia, pH and depth. The aquatic plant community also shifted to plants that likely benefited from increases in light and pollinators. Increased agriculture was correlated with higher nutrient levels and increases with floating plants that can acquire nutrients directly from the water column. This study suggests optimal conditions for wild rice as well as the aquatic plant communities that are associated with these conditions. This paper demonstrates that Zizania (and other aquatic plants) may be very sensitive to small changes within their watershed that are typical of moderate development. Future management strategies should include consideration of these land-use patterns.

Benthic algal response to invasive mussels in Saginaw Bay: a comparison of historical and recent data

Benthic algal communities in the Laurentian Great Lakes (USA and Canada) have been strongly affected by the invasion of dreissenid mussels. Early (1990–1995) studies in Saginaw Bay, Lake Huron, demonstrated a shift from light to nutrient (phosphorus, P) limitation of benthic algae, and large changes in benthic algal community composition once zebra mussels (Dreissena polymorpha) became established. We conducted benthic algal sampling and a nutrient enrichment experiment at a historic sampling site to quantify benthic algae under current environmental conditions and to compare current results with historical data. Benthic algal P-demand was apparently saturated immediately post-invasion, but in subsequent years, algal growth on artificial substrata was consistently P-limited (p always <0.005), perhaps as a result of declining mussel abundance. Epilithic benthic algal community composition displayed large interannual changes, perhaps in response to mussel-induced alteration of light availability and natural changes in substratum characteristics at this site.

PINNULARIA ALDENII SP. NOV., A DIATOM FROM ACIDIC HABITATS IN NORTHERN MICHIGAN

A new species of Pinnularia (P. aldenii) is described from the surface sediment samples of brown-water, acidic lakes and bogs in the upper-peninsula of Michigan (USA) based upon light and scanning electron microscopy examination. Survey of existing environmental data suggests this taxon is an acidobiont found mainly in waters with high levels of dissolved organic carbon.

Determining Site-Specific Toxicity of Copper to Daphnids and Fishes in a Brown-Water Ecosystem

ABSTRACT We examined the influence that wetland brown water had on the toxicity of copper to aquatic species in Swamp Creek basin, Wisconsin. Copper was added to Swamp Creek water and to laboratory-prepared reconstituted water and tested for toxicity using daphnids (Ceriodaphnia dubia and Ceriodaphnia reticulate), larval fathead minnows (Pimephales promelas), and larval walleye (Stizostedion vitreum). The toxicities of copper in Swamp Creek water, which contained dissolved organic carbon (DOC), were significantly lower than in water with no DOC. Therefore in successive experiments. using cultured C. dubia as the test organism, we experimentally reduced DOC in Swamp Creek water. We established that increased concentrations of DOC and hardness increased the odds of survival of C. dubia in the presence of potentially lethal concentrations of copper. In the Swamp Creek watershed which contains brown water and in watersheds where DOC concentrations are substantial, DOC, and hardness could be the principal factors in developing site-specific criteria involving copper and perhaps other metals.