Little Rock Lake (Wisconsin): Perspectives on an experimental ecosystem approach to seepage lake acidification

Ecosystem-level experiments are essential in assessing the effects of environmental perturbations like acidification. To date in North America, such experiments have been rare and geographically limited to drainage lakes in south-western Ontario and to streams in the northeastern US. Seepage lakes, which are the dominant hydrologic type in large regions of the US, have received limited attention from many perspectives, including whole-system manipulation. The Little Rock Lake Acidification Project was initiated to expand insights from previous acidification experiments with whole drainage lakes to a seepage lake system. It involves the gradual acidification of a small (18 ha), seepage lake in northcentral Wisconsin. The lake has been divided into a treatment and reference basin using a flexible, inert barrier; and the treatment basin is being acidified in steps of 0.5 pH units/2 yr period from a starting pH of 6.1 to a final pH of 4.6 (roughly the average pH of rain in this region). The goals are to document the biological and chemical changes which occur, to identify the direct and indirect mechanisms which regulate responses, and to expand insights to a class of lakes previously understudied. In this paper, we describe the history and rationale of the project and we discuss in general terms the utility and constraints of whole-ecosystem manipulations.