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A synoptic assessment of water quality in two Great Lakes connecting channels
Citation:
Wick, M., T. Angradi, M. Pawlowski, D. Bolgrien, J. Launspach, J. Kiddon, AND M. Nord. A synoptic assessment of water quality in two Great Lakes connecting channels. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 45(5):901-911, (2019). https://doi.org/10.1016/j.jglr.2019.08.001
Impact/Purpose:
Impact Statement Comprehensive assessments of water quality in Great Lakes’ connecting channels are necessary to support the management of these important systems and to protect downstream lakes. Because the St Marys River and the Huron-Erie corridor have never been systematically assessed management decisions are based on data from relatively few sampling sites that may not represent condition of the systems. This report is the first use of probability surveys to assess water quality at systems-scales. Water quality in connecting channels is as good or only slightly worse than upstream lake may be protective of downstream lakes. However, connecting channels with much poorer condition than downstream lakes may jeopardize conditions in those lakes. The challenge of using assessment data for management decisions because of the lack of connecting channel-specific thresholds is discussed.
Description:
Great Lakes connecting channels (GLCC) have not been included in United States regional-scale surveys. We conducted a probabilistic water quality assessment of two GLCC, the St. Marys River, and the Lake Huron-Lake Erie Corridor (HEC) in 2014-2015. We compare the channels to each other and to the up- and down-river Great Lakes with data from an assessment of the Great Lakes nearshore conducted in 2015. We assessed the condition of each GLCC as good, fair, or poor by applying the most protective water quality thresholds for the downriver lake. St. Marys River rated mostly fair for total phosphorus (TP) and chlorophyll a, and concentrations were generally intermediate to nearshore Lake Superior and Lake Huron. St. Marys River had large proportions of area with poor conditions for Secchi depth; nearshore Lakes Superior and Huron were mostly in good condition for this indicator. Area-weighted mean concentrations of TP and chlorophyll a in the HEC were more like nearshore Lake Huron than Lake Erie. For those indicators, most of the area of the HEC was rated good, more than the nearshore of Lakes Huron or Erie. Applying Lake Huron thresholds in the HEC, condition estimates for TP and chlorophyll a for the HEC were like Lake Huron but were worse than Lake Huron when applying downriver Central Lake Erie thresholds. Appropriate thresholds for the GLCC should align with assessment objectives and be at least as protective as thresholds for the downriver lake. Future iterations of this assessment will allow evaluation of water quality trends in the GLCC.
