Groundwater Interactions with Holland Lake, MN

Abstract

Holland Lake, a small but deep mesotrophic lake in the Twin Cities Metropolitan Area, has been considered by the Minnesota Department of Natural Resources, Division of Fisheries, for stocking with brown trout. Holland Lake, with a surface area of 0.14 km:2 (35 acres) and a maximum depth of about 18.8 m (61 ft) consists of two shallow bays covered with rooted macrophytes and a deep main basin. The deep basin is thermally suitable for brown trout. However, due to a high oxygen depletion rate in summer, the lake becomes anoxic below the surface mixed layer. The field study conducted in the summer of 1999 by the authors concluded that several mechanisms, all regarding some sort of horizontal advection process, could explain the observed high dissolved oxygen (DO) depletion rates: transport of detrital material from the shallow bays, density currents combined with sediment oxygen demand in the shallow bays and flushing effect by groundwater flow through the lake. Density currents from the shallow bays were attributed to the temperature regimes of the shallow bays. To aid in the design of an aeration system for the lake, a new field study was conducted in the summer of 2000 to quantify the potential groundwater flow through the lake, especially through the shallow bays. The field study included the measurement of groundwater piezometric heads underneath the lake bed using a potentiomanometer and DO concentrations and temperatures of groundwater. In addition, the water temperature profiles were measured at several locations in the shallow bays to investigate the potential for density currents.