Water Quality Conditions and Patterns on the Grand Portage Reservation and Grand Portage National Monument, Minnesota: Implications for Nutrient Criteria Development and Future Monitoring

Lafrancois, B; Watkins, M; Maki, R

Lakes and streams are important natural features in northeastern Minnesota, and their protection is of management interest for the Grand Portage Band of Minnesota Chippewa and Grand Portage National Monument. In 1999, the Grand Portage Band began monitoring water quality intensively in 15 lakes and eight streams, in preparation for developing nutrient criteria. We used the resulting eight-year dataset to provide insights for 1) developing local nutrient criteria for Reservation waters, and 2) developing additional monitoring activities for Grand Portage Creek, through the National Park Service (NPS) Great Lakes Inventory and Monitoring Network. Specifically, we aimed to characterize existing water quality conditions in Grand Portage lakes and streams, evaluate variation among lakes and streams, explore seasonal patterns, relate current water quality conditions to state and federal standards, identify relationships between nutrients and trophic response variables, consider options for setting nutrient criteria, and provide recommendations related to site selection, sampling frequency, and parameter selection for future NPS monitoring of Grand Portage Creek. Grand Portage lakes and streams tended to be dilute, with intermediate nutrient levels, low transparency, and high dissolved organic carbon concentrations. Streams showed more seasonal variation than lakes, being strongly influenced by hydrologic patterns. The chemistry of Grand Portage Creek was similar to the overall average for Reservation streams. The water quality of Grand Portage lakes differed significantly from that of other lakes in Minnesota’s Northern Lakes and Forests (NLF) ecoregion. In particular, Grand Portage lakes were smaller, shallower, more acidic, and more highly stained. Subgroups of Grand Portage lakes were identified, but group divisions were not distinct. Although the Reservation landscape is relatively undisturbed, some exceedences of state or federal reference criteria were noted. Chloride concentrations in two lakes and one stream were higher than average, which may suggest contamination from local roadways. Concentrations of total nitrogen and total phosphorus were higher than expected for lakes and streams of the NLF ecoregion, and Secchi depths were shallower; such patterns are likely attributable to the humic, dystrophic nature of Grand Portage waters rather than to anthropogenic enrichment. Relationships between nutrients and trophic response variables were somewhat difficult to interpret, perhaps because nutrients were not present in readily bioavailable forms, or because algal responses were limited by high dissolved organic carbon concentrations and resulting low light conditions. Options for establishing reference criteria for Reservation waters were reviewed in the context of the present analysis and recent paleolimnological studies in Reservation lakes. The Grand Portage Band’s monitoring efforts on Grand Portage Creek fit well with the objectives of NPS Great Lakes Inventory and Monitoring Network. The Band’s program addresses NPS core water quality variables (e.g., temperature, pH, dissolved oxygen, and specific conductance) as well as more advanced variables. The sampling regime is frequent enough to capture dominant seasonal and interannual patterns in water quality. Future NPS monitoring on Grand Portage Creek should target other aspects of stream hydrology and biological integrity, such as stream discharge, benthic algal biomass, benthic communities, and stream habitat structure. Finally, future monitoring on Grand Portage Creek should account for climate-related changes to stream hydrographs and dissolved organic carbon inputs.

Water Quality Conditions and Patterns on the Grand Portage Reservation and Grand Portage National Monument, Minnesota: Implications for Nutrient Criteria Development and Future Monitoring

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