Richard A. Lillie

LAND USE, WATER CHEMISTRY, AQUATIC VEGETATION, AND ZOOPLANKTON COMMUNITY STRUCTURE OF SHALLOW LAKES

Landscape-lake interactions, including anthropogenic effects in modern hu- man-dominated landscapes, are essential elements of our understanding of aquatic com- munity ecology. This study links land use (six categories) to the aquatic environment (30 water chemistry, lake morphology, and vegetation variables) and to zooplankton community richness (32 common taxa) and composition in 73 small and shallow lakes of southeastern Wisconsin, USA. The sites differed most according to two environmental variables (prin- cipal components analysis (PCA) ordination): the presence/absence of riparian vegetation and the water source (whether ground or atmospheric). Shallow lakes in different land use categories (reference, urban, and agricultural) differed significantly in terms of the two major environmental variables, especially presence of riparian and aquatic vegetation. Reference sites were characterized by the most vegetation and the highest zooplankton richness. Agricultural sites with wide riparian vegetative buffer strips (>30 m) had sig- nificantly more zooplankton taxa than agricultural lakes with narrow buffer strips. A non- metric multidimensional scaling (NMS) ordination of zooplankton community composition suggested a single community among land use categories, with some variation related to vegetation and the water source. The first NMS axis was correlated with PCA1 axis (veg- etation) and with zooplankton taxon richness, and the second axis was correlated with PCA2 (water source). The third axis was not strongly correlated with any of the measured en- vironmental factors, suggesting that an unmeasured factor related to disturbance was also important in determining taxon composition. Our analysis supports the hypothesis that zooplankton community structure (taxon richness and composition) is indirectly associated with land use, via the effect of land use on vegetation and the hydrological continuum.

Habititat Architecture of Myriophyllum spicatum L. as an Index to Habitat Quality for Fish and Macroinvertebrates

ABSTRACT Plant architecture, described on the basis of the number, morphometry, and arrangement of stems, branches, and leaves, exhibits temporal and spatial variability within species. In order to assess the extent of this variability within an individual lake, the distribution and architecture of Myriophyllum spicatum was measured on five dates during 1990 in Fish Lake, Wisconsin. These data were used to develop an index of plant habitat quality and quantity to describe 1) horizontal visibility within macrophyte beds, 2) the amount of shading afforded by the surface canopy, 3) the amount of available habitat for macroinvertebrate attachment, 4) the relative amount of protection afforded fish by the plants, and 5) the degree of crowding or compaction among plants. The methodology employed in developing this index could be adaptable to other aquatic plants. Temporal changes in the architecture of M. spicatum during the growing season and differences in architecture within one macrophyte bed in Fish Lake w...

ZOOPLANKTON COMMUNITIES OF RESTORED DEPRESSIONAL WETLANDS IN WISCONSIN, USA

Wisconsin has lost approximately 2 million hectares of wetland since statehood (1848). Through the combined efforts of state and federal agencies and private groups focused primarily on wetland restoration for waterfowl habitat management or compensatory mitigation, a fairly substantial gain in wetland area has been achieved. Much of the wetland restoration effort in Wisconsin has occurred on formerly agricultural lands. However, due to the nature of the past disturbance and possible residual effects not corrected by simply returning surface waters to these lands, there is some question regarding the resultant wetland quality or biological integrity. In an effort aimed at developing tools to measure wetland gains in terms of quality or ecological integrity, the Wisconsin Department of Natural Resources (WDNR) initiated a study of biological communities on restored wetlands in Wisconsin. In this paper, we report on the community of microcrustaceans and arthropods that can be collected with a plankton net in open water in wetlands. We examined zooplankton community structure in restored wetlands in terms of richness, taxonomic representation, and Daphnia sexual reproduction and related these metrics to attributes on wetlands representing least-disturbed conditions and agriculturally impacted wetlands. We sampled 56 palustrine wetlands distributed across Wisconsin. These wetland sites were categorized as agricultural, least-impacted, and restored (recently withdrawn from agricultural usage). The wetlands were reasonably homogeneous in many ways, so that taxon richness was not correlated with basin origin, presence of adjacent roads, presence or absence of fish, water chemistry, or the size of the open water. We identified a total of 40 taxa. Taxon richness was significantly lower in agricultural sites (average of 3.88 taxa per site) compared to that of least-impacted sites (7.29 taxa) and restored sites (7.21 taxa). Taxon richness of restored sites was significantly correlated with time since restoration. The data indicate that taxon richness changes from a value typical of agricultural sites to the average richness of least-impacted sites in about 6.4 years. The total taxon list for 8 agricultural sites (14 taxa) was significantly smaller than the average value for randomly chosen sets of 8 least-impacted sites (20.4 taxa). Agricultural and least-impacted sites tended to have the same common taxa. Many taxa of chydorid cladocerans and cyclopoid copepods that were rare in least-impacted sites did not occur in the agricultural sites, nor did fairy shrimp occur in agricultural sites. Daphnia populations only produced males in least-impacted and restored sites. Further research is needed to identify the mechanism(s) responsible for the reduced species richness and lack of sexual reproduction in agricultural wetland sites. Likely factors include eutrophication, turbidity, or chemical contamination. We conclude that restoration of wetland watersheds works. Withdrawal of the watershed from agricultural usage is followed by an increase in taxon richness, and the sites resembled least-impacted sites in about 6–7 years.

A model of bluegill-largemouth bass interactions in relation to aquatic vegetation and its management

Abstract Dense, slow growing populations of bluegill sunfish are common in lakes where heavy vegetation prevents thinning of bluegill numbers by their primary predator, the largemouth bass. Since bass can effectively prey on bluegill only along the periphery of dense macrophyte beds, mowing vegetation to create additional edge may improve growth rates and size structure of both species. While this concept is straightforward, determining the optimal vegetation configuration for the two species is difficult because mechanisms such as feeding, competition, and mortality together determine the population response and may interact in complex ways. This paper describes a model that simulates the interactions of bluegill, largemouth bass and their invertebrate prey in the context of vegetation structure. The model is calibrated to data from a heavily vegetated temperate lake and is used to examine the fish response to additional edge created by mowing channels through plant beds. Bass growth rates and numbers increased after most simulated vegetation removals because their access to prey increased. Bluegill grew fastest when about 30% of the vegetation was cut, but responded negatively to mowing more than about half the plants. Bluegill responded to the manipulations more by changing growth rates, while bass responded more by increasing numbers. Moderate plant removals accomplished by mowing many narrow channels are most likely to simultaneously benefit both species. The model synthesizes current understanding of the relationship between macrophytes, bluegill and largemouth bass, and suggests which vegetation manipulations are most informative to test in large scale experiments.

Influence of macroinvertebrates and macrophytes on waterfowl utilization of wetlands in the Prairie Pothole Region of northwestern Wisconsin

Waterfowl and limnological data were monitored on Waterfowl Production Area (WPA) wetlands in northwestern Wisconsin over a 6-yr period (1983–88) to determine the impact of macroinvertebrates and macrophytes on waterfowl utilization. Interrelationships between limnological conditions and Waterfowl Breeding Pair Densities (BPDs reported as pairs/ha water surface) were analyzed using correlation and general linear model analysis techniques.

Influence of Dense Growth of Eurasian Watermilfoil on Lake Water Temperature and Dissolved Oxygen

ABSTRACT Over a five year period we compared summer temperature and dissolved oxygen (DO) at 10 sites within dense beds of Myriophyllum spicatum L. to an unvegetated reference site in a moderately eutrophic Wisconsin lake. Average surface temperatures in the Eurasian watermilfoil beds were significantly elevated in two of the five years, while bottom temperatures were significantly depressed each year. Dissolved oxygen concentrations in surface layers of the bed were elevated by at least 1 mg L−1 during roughly 30–40% of site-date visits, while DOs in the bottom layers were depressed on the average more than 50% of monitoring visits. Both depressed DOs and low DOs (< 3.0 mg L−1) in bottom layers were positively correlated with average annual air temperatures but were not directly related to variations in milfoil biomass. Dissolved oxygen and temperature appeared to be most severely impacted at shallow, densely vegetated sites close to shore.

Physical-chemical influences on vernal zooplankton community structure in small lakes and wetlands of Wisconsin, U.S.A.

We sampled zooplankton communities from 54 small water bodies distributed throughout Wisconsin to evaluate whether a ‘snap-shot’ of zooplankton community structure during early spring could be used for the purpose of differentiating lakes from wetlands. We collected a single set of zooplankton and water chemistry data during a one-month time window (synchronized from south to north across the state) from an open water site in each basin as a means to minimize and standardize sampling effort and to minimize cascading effects arising from predator–prey interactions with resident and immigrant aquatic insect communities. We identified 53 taxa of zooplankton from 54 sites sampled across Wisconsin. There was an average of 6.83 taxa per site. The zooplankton species were distributed with a great deal of independence. We did not detect significant correlations between number of taxa and geographic region or waterbody size. There was a significant inverse correlation between number of taxa and the concentration of calcium ion, alkalinity and conductivity. One pair of taxa, Lynceus brachyurus and Chaoborus americanus, showed a significant difference in average duration of sites of their respective occurrence. All other pairs of taxa had no significant difference in average latitude, waterbody surface area, total phosphorus, total Kjeldahl nitrogen, alkalinity, conductivity, calcium ion, sulfate, nitrate, silicate or chloride. Taxa were distributed at random among the sites – there were no statistically significant pairs of taxa occurring together or avoiding each other. Multivariate analysis of zooplankton associations showed no evidence of distinct associations that could be used to distinguish lakes from wetlands. Zooplankton community structure appears to be a poor tool for distinguishing between lakes and wetlands, especially at the relatively large scale of Wisconsin (dimension of about 500 km). The data suggest that a small body of water in Wisconsin could be classified as a wetland if it persists in the spring and summer for only about 4 months, and if it is inhabited by Lynceus brachyurus, Eubranchipus bundyi, and if Chaoborus americanus and Chydorus brevilabris are absent.

Influence of Sediment and Groundwater on the Distribution and Biomass of Myriophyllum spicatum L. in Devil's Lake, Wisconsin

ABSTRACT Influences of physical and chemical characteristics of sediments and of groundwater inputs on the distribution and biomass of Eurasian milfoil, Myriophyllum spicatum L., were studied in Devils Lake, Wisconsin. Sediment cores from inside and outside M. spicatum beds were analyzed for density, particle size composition, and moisture, organic, elemental, and nutrient contents. Groundwater direction, volume, and nutrient concentration were determined using seepage meters. Whereas sediment composition appears to be inadequate to support dense growth of macrophytes, localized groundwater inputs may be important in regulating the distribution and biomass of M. spicatum in Devils Lake.

Morphological Characteristics of the Aquatic Macrophyte, Myriophyllum spicatum L., in Fish Lake, Wisconsin

ABSTRACT Several morphological attributes of individual Myriophyllum spicatum L. plants were studied during three summers in Fish Lake, Dane County, Wisconsin to document spatial and temporal dynamics. Measurements were taken from twelve randomly-selected plants at each of four depth intervals along two transects on five dates during each year from 1990 to 1992. Density, length, foliation, and biomass attributes of stems and branches were each influenced somewhat differently by depth and location. Plants growing in deep water were long and thin, while plants growing in shallow water were shorter and more robust, with greater relative amounts of foliation. Plants at most locations increased in length, but percent of total plant length (and biomass) comprised of foliated stem decreased over time.

Usefulness of natural regions for lake management : analysis of variation among lakes in northwestern Wisconsin, USA

A map of summer total phosphorus in lakes was compiled recently for a three-state area of the upper Midwest for purposes of identifying regional patterns of total phosphorus in lakes and attainable lake trophic state. Spatial patterns in total phosphorus from approximately 3000 lakes were studied in conjunction with maps of geographic characteristics that tend to affect phosphorus balance in lakes to identify regions of similarity in phosphorus concentrations in lakes or similarity in the mosaic of values as compared to adjacent areas. While degrees of relative homogeneity are apparent at many scales, the map was designed at a scale that would yield regions with sufficient homogeneity to be useful for lake management throughout the area. In this study, data from 210 lakes in a 1560-mi2 area in northwestern Wisconsin, sampled by the Wisconsin Department of Natural Resources in the spring of 1988 (subsequent to the compilation of the phosphorus map), were examined to: (1) substantiate the existence of the regions depicted on the map in northwest Wisconsin, (2) determine the nature and relative precision of the regional boundaries, (3) determine the relative importance of natural and anthropogenic watershed characteristics, lake types, lake area, and lake depth in explaining within-region differences in lake phosphorus, and (4) demonstrate how the regions might be used by local lake managers.