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Trophic State in Voyageurs National Park Lakes before and after Implementation of a Revised Water‐Level Management Plan
Author(s) -
Christensen Victoria G.,
Maki Ryan P.
Publication year - 2015
Publication title -
jawra journal of the american water resources association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.957
H-Index - 105
eISSN - 1752-1688
pISSN - 1093-474X
DOI - 10.1111/jawr.12234
Subject(s) - bay , trophic state index , trophic level , eutrophication , secchi disk , environmental science , hydrology (agriculture) , wet season , chlorophyll a , national park , nutrient , ecology , oceanography , biology , geology , botany , geotechnical engineering
We compiled Secchi depth, total phosphorus, and chlorophyll a (Chl a ) data from Voyageurs National Park lakes and compared datasets before and after a new water‐level management plan was implemented in January 2000. Average Secchi depth transparency improved (from 1.9 to 2.1 m, p = 0.020) between 1977‐1999 and 2000‐2011 in Kabetogama Lake for August samples only and remained unchanged in Rainy, Namakan, and Sand Point Lakes, and Black Bay in Rainy Lake. Average open‐water season Chl a concentration decreased in Black Bay (from an average of 13 to 6.0 μg/l, p = 0.001) and Kabetogama Lake (from 9.9 to 6.2 μg/l, p = 0.006) between 1977‐1999 and 2000‐2011. Trophic state index decreased significantly in Black Bay from 59 to 51 ( p = 0.006) and in Kabetogama Lake from 57 to 50 ( p = 0.006) between 1977‐1999 and 2000‐2011. Trophic state indices based on Chl a indicated that after 2000, Sand Point, Namakan, and Rainy Lakes remained oligotrophic, whereas eutrophication has decreased in Kabetogama Lake and Black Bay. Although nutrient inputs from inflows and internal sources are still sufficient to produce annual cyanobacterial blooms and may inhibit designated water uses, trophic state has decreased for Kabetogama Lake and Black Bay and there has been no decline in lake ecosystem health since the implementation of the revised water‐level management plan.