Duluth Area Lakes Water Quality Assessment: Caribou, Grand, and Pike Lakes - 1999; Pike Lake Fall Overturn Studies - 1996-1998

Abstract

Minnesota is divided into seven regions, referred to as ecoregions, as defined by soils, land surface form, natural vegetation and current land use. Since land use affects water quality, it has proven helpful to divide the state into regions where land use and water resources are similar. Data gathered from representative, minimally-impacted (reference) lakes within each ecoregion serve as a basis for comparing the water quality and characteristics of other lakes. Caribou, Grand, and Pike Lakes are located on the northern edge of the Duluth Metropolitan Area (Figure 1) in the Northern Lakes and Forests Ecoregion (Figure 2). Caribou Lake has an area of 569 acres (230 hectares), and a maximum depth of 21 feet (6.4 meters). The majority of the lake is less than 10 feet deep, and is dominated by emergent and submergent aquatic vegetation. Grand Lake has an area of 1742 acres (705 ha). Baby Grand Lake flows into Little Grand, which flows into Grand Lake. Similar to Caribou, much of Grand Lake (~ 95%) is less than 10 feet (3 m) deep, and vegetation dominates the shoreline and near-shore areas. Pike Lake has an area of 508 acres (206 ha), and is much deeper. The maximum depth is 60 feet (~18 m), and most of the lake is between 20-50 feet deep (6-15 m). These lakes all have relatively developed shorelines and are likely to experience increased development pressure in the next decade. They have also experienced some degree of water quality problems in the past. Efforts are underway to improve wastewater treatment on two of these lakes. Construction of a sanitary sewer was recently (1999) begun around Pike Lake, and a constructed wetland wastewater treatment system servicing a cluster of nine (9) lakeshore homes was installed at Grand Lake in late 1995. The present study was conducted because local units of government desired additional water quality information on these Duluth area lakes for planning purposes. The Pike Lake Association also desired some follow-up work for comparison to a previous MPCA study (Bauman 1994), and to better define current lake water quality prior to the installation of a sanitary sewer in the basin.