The recovery of a shallow lake within an agricultural landscape of Minnesota—an interdisciplinary approach to understanding change

Abstract

AbstractPerleberg DJ, Anderson JP, Streitz AR. 2023. The recovery of a shallow lake within an agricultural landscape of Minnesota—an interdisciplinary approach to change. Lake Reserv Manage. XX:XXX–XXX.This case study of Lake Shaokatan, Minnesota, reveals how long-term climate, hydrology, water chemistry, and macrophyte data can explain and predict shallow lake phase shifts. After decades of agricultural landscape nutrient loadings, lake and watershed management efforts successfully reduced summer mean total phosphorus and chlorophyll a concentrations to levels that met standards set specifically for shallow lakes in the Northern Glaciated Plains ecoregion (0.09 mg/L and 0.03 mg/L, respectively). The lake “flipped” from a turbid, phytoplankton-dominated phase (<20% macrophyte occurrence) to a clear, macrophyte-dominated phase (annual average of 90% occurrence), and the Minnesota Pollution Control Agency removed it from the state’s impaired waters list. A paired groundwater and lake water quality investigation was critical in understanding how increased precipitation might affect lake water quality, the relationship between groundwater and surface water in this system, and how compounds such as chloride and phosphorus are transported through the watershed. Lakewide macrophyte occurrence has been sustained for at least 7 yr. While abundant macrophyte growth helps maintain a clear water state, it can also create recreational boating issues. Lake managers question how long the lake will remain in the present clear phase as lake users weigh the recreational and aesthetic differences between the 2 phases.Keywords: Chloridegroundwaterlong-term monitoringmacrophyteMinnesotamonitoring wellsnutrient impairmentshallow lake management AcknowledgmentsWe are indebted to the numerous staff from MDNR and MPCA who conducted field surveys and assisted with data management. We thank them and our agencies’ leadership for recognizing the value of long-term, multidiscipline monitoring. J. Lauer, S. Kloiber, and E. Smith provided review and helpful comments that improved this article.Disclosure statementNo potential conflict of interest was reported by the author(s).