Karen A. Wilson

Managing Macrophytes to Improve Fish Growth: A Multi-lake Experiment

Abstract Macrophyte harvesting often has been suggested as a way to improve fish growth and size structure in lakes with high densities of submergent macrophytes and stunted fish populations. However, previous experimental tests have provided no clear consensus on whether the technique works for management. We conducted a series of whole-lake manipulations to test the effects of macrophyte removal on growth of bluegill and largemouth bass. We selected four lakes in southern and central Wisconsin for experimental manipulation and nine others for controls. In August 1994, we removed macrophytes from approximately 20% of the littoral zone by cutting a series of evenly spaced, deep channels throughout each treatment lake. In the first year after manipulation, we observed substantially increased growth rates of some age classes of both bluegill and largemouth bass in treatment lakes relative to controls. Growth rates of other age classes were less responsive to manipulation. We observed increased bluegill and ...

Effects of restoration and reflooding on soil denitrification in a leveed Midwestern floodplain.

River floodplains have the potential to remove nitrate from water through denitrification, the anaerobic microbial conversion of nitrate to nitrogen gas. An important factor in this process is the interaction of river water with floodplain soil; however, many rivers have been disconnected from their historic floodplains by levees. To test the effect of reflooding a degraded floodplain on nitrate removal, we studied changes in soil denitrification rates on the Baraboo River floodplain in Wisconsin, USA, as it underwent restoration. Prior to this study, the site had been leveed, drained, and farmed for more than 50 years. In late fall 2002, the field drainage system was removed, and a gate structure was installed to allow controlled flooding of this site with river water. Soil moisture was extremely variable among zones and months and reflected local weather. Soil organic matter was stable over the study period with differences occurring along the elevation gradient. High soil nitrate concentrations occurred in dry, relatively organic-poor soil samples and, conversely, all samples with high moisture soils characterized by low nitrate. We measured denitrification in static cores and potential denitrification in bulk samples amended with carbon and nitrogen, one year before and two years following the manipulation. Denitrification rates showed high temporal and spatial variability. Static core rates of individual sites ranged widely (from 0.00 to 16.7 microg N2O-N x [kg soil](-1) x h(-1), mean +/- SD = 1.10 +/- 3.02), and denitrification enzyme activity (DEA) rates were similar with a slightly higher mean (from 0.00 to 15.0 microg N2O-N x [kg soil](-1) x h(-1), 1.41 +/- 1.98). Denitrification was not well-correlated with soil nitrate, organic matter content, or moisture levels, the three parameters typically thought to control denitrification. Static core denitrification rates were not significantly different across years, and DEA rates decreased slightly the second year after restoration. These results demonstrate that restored agricultural soil has the potential for denitrification, but that floodplain restoration did not immediately improve this potential. Future floodplain restorations should be designed to test alternative methods of increasing denitrification.

Rusty crayfish (Orconectes rusticus) movement within and between habitats in Trout Lake, Vilas County, Wisconsin

The exotic rusty crayfish, Orconectes rusticus, has invaded northern Wisconsin watersheds and is causing severe ecological alterations. We investigated the processes of rusty crayfish dispersal and movement within Trout Lake, Vilas County, Wisconsin, using a mark and recapture technique. We examined the effects of crayfish size, gender, and original location on distance traveled. Some O. rusticus moved up to 221 m in 2 d, but most crayfish remained in their original habitat (distances ranged from 0–58 m). Distances traveled were similar for both male and female crayfish. Crayfish size did not affect the patterns of movement. Crayfish did not travel greater distances over time, which may be an artifact of 2 groups of crayfish: those that stayed in their local habitat and those that moved far distances. Comparisons with published dispersal and movement data suggest that large movements are observed occasionally in both lotic and lentic habitats. For rusty crayfish, these movements have important implications for invasion rates.

Landscape-scale Variation in Taxonomic Diversity in Four Groups of Aquatic Organisms: The Influence of Physical, Chemical, and Biological Properties.

We evaluated several factors influencing the taxonomic richness of macrophytes, benthic invertebrates, snails, and fish in a series of northern Wisconsin lakes. We chose the study lakes to decouple the potential effects of ionic strength of lake water and stream connection, two factors that are usually highly correlated and therefore have been confounded in previous studies. In addition, our study lakes covered a wide range in a variety of characteristics, including residential development, abundance of exotic species, nutrient concentrations, predator abundance, and lake size. Species richness within each of the four taxonomic groups was significantly positively related to ionic strength (as measured by specific conductance); we also found secondary associations with other variables, depending on the specific group of organisms. The relationship between richness and lake area was dependent on the specific conductance of the lake and the vagility of the organisms; less vagile groups of organisms showed stronger and steeper species–area relationships in low-conductivity lakes. Further, after variance owing to specific conductance was removed, the presence of stream connections was positively related to species richness for fish, snails, and macrophytes as well as familial richness in benthic invertebrates. Our results indicate that lakes with relatively more groundwater input have lower extinction rates for all four groups of taxa and that lakes with stream inlets and outlets have enhanced immigration rates for fish, snails, benthic invertebrate families, and macrophytes. These findings link processes of immigration and extinction of four groups of organisms of varying vagility to landscape-level hydrologic characteristics related to the glacial history of the region.

A Resilience Approach Can Improve Anadromous Fish Restoration

Most anadromous fish populations remain at low levels or are in decline despite substantial investments in restoration. We explore whether a resilience perspective (i.e., a different paradigm for understanding populations, communities, and ecosystems) is a viable alternative framework for anadromous fish restoration. Many life history traits have allowed anadromous fish to thrive in unimpacted ecosystems but have become contemporary curses as anthropogenic effects increase. This contradiction creates a significant conservation challenge but also makes these fish excellent candidates for a resilience approach. A resilience approach recognizes the need to maintain life history, population, and habitat characteristics that increase the ability of a population to withstand and recover from multiple disturbances. To evaluate whether a resilience approach represents a viable strategy for anadromous fish restoration, we review four issues: (1) how resilience theory can inform anadromous fish restoration, (2) how...

Macrophyte Structure and Growth of Bluegill (Lepomis macrochirus): Design of a Multilake Experiment

Experimental manipulations of whole ecosystems can be a powerful test of ecological understanding. In particular, ecosystem-scale manipulations can evaluate basic ecological ideas in ways that complement comparative studies, models, and smaller-scale experiments (Carpenter et al., 1995a). From an applied perspective, ecosystem experiments can also give unique insights into what works at a scale directly relevant to managers (Kitchell, 1992). When management actions are coupled with scientific studies of the response of the ecosystem, learning may lead to improved management practices (Gunderson et al., 1995). Here we present early results of an experiment to test the idea that nuisance macrophytes can be managed to enhance fish growth.