North Temperate Lakes

North American lakes with heavy infestations of nuisance macrophytes (e.g.- Eurasian watermilfoil, Myriophyllum spicatum) are often associated with slow growing populations of bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides).  Reducing macrophyte densities has often been suggested as one way of improving fish growth in such lakes.  We conducted a series of planning and modeling exercises to optimize the design of a multi-lake study designed to test the effects of macrophyte harvesting on growth of bluegill and largemouth bass.  From a large group of candidate lakes, we selected thirteen lakes in southern and central Wisconsin for study.  These had slow growing bluegill populations and were dominated by watermilfoil and other fine-leafed macrophytes.  In 1994, macrophytes were mechanically removed from approximately 20% of the littoral zone in four lakes selected for experimental manipulation.  The other nine lakes served as unmanipulated controls.  Macrophytes were removed in a series of deep channels spaced evenly around the lake with a macrophyte harvester retrofitted with a deep cutting bar to remove macrophytes at the plant-sediment interface at depths deeper than those reached with a commercial harvester.

Surprises - large, unexpected changes from apparently small causes -- are common in systems of people and nature. Are these surprises a consequence of the complexity or nonlinearity of natural-social systems? Or can they be explained by simpler processes? Our research addresses this question for systems composed of lakes, their shoreline (riparian) vegetation and land use, and social and economic organizations of lake users. We will study the self-organization of lake users and associated characteristics of shoreline and lake ecosystems. We will determine whether thresholds in riparian organization set the stage for an important class of surprises - collapses of economically important game fish stocks. We will test the possibility that nonlinear dynamics can be used to design manipulations that remove invading crayfish from a lake. If successful, our experiment will cause a self-sustaining removal of an invasive species - a path-breaking ecological restoration.