User:Gros04/Mille Lacs Lake
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[edit]Biogeochemistry
[edit]Turnover Pattern and Mixing
[edit]Due to the fact that Mille Lacs Lake is fairly shallow, it mixes fairly regularly throughout the ice-free period, making it a cold polymictic lake that is not stratified[1][2]. Constant mixing keeps oxygen and other nutrient levels fairly homogenous, but thermoclines have been known to form in the late summer, which can be associated with decreases in deeper dissolved oxygen levels[3].
Trophic State
[edit]Mille Lacs Lake has an overall trophic state index (TSI) of 43, making it moderately mesotrophic[4]. This trophic state index is within the expected overall TSI range of lakes within its ecoregion[4].
Nutrient Levels
[edit]Compared to other lakes within the ecoregion, the total phosphorus, chlorophyll a, and Secchi depth are all within expected ranges, while chloride, total suspended solids, and conductivity levels are all above their expected ranges[3]. Higher levels of planktivores affect food and nutrient availability needed by other species within the lake.[5]
Low total nitrogen to total phosphorous ratios indicate that the lake is phosphorus limited, which combines with relatively low total Kjeldahl Nitrogen to largely limit algal bloom growths[3].
Mediators of Eutrophication
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Zebra mussels, an aquatic invasive species, became established in Mille Lacs Lake around 2005.[6] The presence of zebra mussels has reduced the trophic state index of the lake, with Secchi depth readings increasing noticeably since their arrival, likely due to their methods of filter feeding on suspended particles.[6] A sharp rise in water transparency of the lake after the year 2010, measured via Secchi depth, coincides with the zebra mussel invasion timeline.[5] As the water clarity is increased within the lake, levels of aquatic vegetation may also increase.[5] This has the potential to alter fish habitats, proving desirable for some species' productivity and undesirable for others'.[5] It is common for increased water clarity to contribute to decreased productivity and abundance of walleye, which is most commonly fished in the lake.[7] Zebra mussels are also known for taking in nutrients from the water column and sequestering it in sediments, thereby reducing the nutrients available to primary producers within the water column.[8] Levels of phosphorus and chlorophyll a, however, are reported to have remained consistent since the invasion, which has been seen before in unstratified lakes.[2][9]
Historical Effects of Human Activity
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Runoff caused by the growth of agriculture in the surrounding area, as well as other anthropogenic factors, caused increasing levels of sediment and phosphorus buildup from the 1960's until at least the early 2000's.[10] This was evident from the analysis of a sediment core drawn from the lake in 2002, which also determined that while few new microbial species had established themselves in the lake since European settlement, microbial communities have still been affected by nutrient and sediment loading.[10] In particular, the sediment core demonstrated the decline of bottom dwelling microbes in favor of microbial taxa that float freely in the water column, likely as a result of increased phosphorus availability within the pelagic zone of the lake.[10] Note that this sediment core was taken before the introduction of zebra mussels, which are known to increase the flux of nutrients from pelagic environments to sediments.[8]
Ground-water can also be an indication of anthropogenic effects. Ground-water in the surrounding areas of Mille Lacs Lake occurs in glacial and bedrock aquifers.[11] Water from these aquifers is released through well withdrawals, escape into nearby aquifers, and flow into bodies of water like Lake Mille Lacs and the Rum River.[11] Upon inspection of this groundwater in the late 1990’s, sodium, manganese, and iron levels repeatedly exceeded acceptable EPA standards for health and drinking water. [11]Multiple common pesticides, trace metals, and volatile organic compounds were also found in samples, but were below detection limits, except for zinc levels.[11] Possible sources of groundwater contamination within lakes due to anthropogenic effects can include but are not limited to land usage and commercial, industrial, and agricultural activities.[11]
References
[edit]- ^ Ahrenstorff, Tyler; Beth, Beth (June 2016). "Mille Lacs Lake Bioenergetics" (PDF). Minnesota Department of Natural Resources. Retrieved 4/19/23.
{{cite web}}: Check date values in:|access-date=(help) - ^ a b Jones, Thomas; Montz, Gary (2020). "Population increase and associated effects of zebra mussels Dreissena polymorpha in Lake Mille Lacs, Minnesota, U.S.A." BioInvasions Records. 9 (4): 772–792. doi:10.3391/bir.2020.9.4.12. ISSN 2242-1300.
- ^ a b c "Mille Lacs Lake Lake Water Quality". Aitkin, Mille Lacs, & Crow Wing County. 2013. Retrieved 4/19/23.
{{cite web}}: Check date values in:|access-date=(help) - ^ a b "Surface Water". webapp.pca.state.mn.us. Retrieved 2023-04-20.
- ^ a b c d Kumar, Rajeev (2015). "Ecosystem based management for Mille Lacs Lake, Minnesota under changing environmental conditions". The University of British Columbia – via The University of British Columbia.
- ^ a b Kumar, Rajeev; Varkey, Divya; Pitcher, Tony (2016-07-10). "Simulation of zebra mussels (Dreissena polymorpha) invasion and evaluation of impacts on Mille Lacs Lake, Minnesota: An ecosystem model". Ecological Modelling. Ecopath 30 years – Modelling ecosystem dynamics: beyond boundaries with EwE. 331: 68–76. doi:10.1016/j.ecolmodel.2016.01.019. ISSN 0304-3800.
- ^ Venturelli, Paul; Bence, James; Brenden, Travis O.; Lester, Nigel P.; Rudstam, Lars G. (December 2014). "Mille Lacs Lake Walleye Blue Ribbon Panel Data Review and Recommendations for Future Data Collection and Management". Minnesota Department of Natural Resources – via Minnesota Department of Natural Resources.
- ^ a b Vanni, Michael J. (2021-02-23). "Invasive mussels regulate nutrient cycling in the largest freshwater ecosystem on Earth". Proceedings of the National Academy of Sciences. 118 (8): e2100275118. doi:10.1073/pnas.2100275118. ISSN 0027-8424. PMC 7923380. PMID 33547254.
{{cite journal}}: CS1 maint: PMC format (link) - ^ Higgins, S. N.; Vander Zanden, M. J.; Joppa, L. N.; Vadeboncoeur, Y. (2011-02). "The effect of dreissenid invasions on chlorophyll and the chlorophyll : total phosphorus ratio in north-temperate lakes". Canadian Journal of Fisheries and Aquatic Sciences. 68 (2): 319–329. doi:10.1139/f10-134. ISSN 0706-652X.
{{cite journal}}: Check date values in:|date=(help) - ^ a b c Kingston, John (2003). "Completion Report Mille Lacs Lake Paleolimnology Project". University of Minnesota Duluth – via University of Minnesota Digital Conservancy.
- ^ a b c d e Trotta, L. C.; Cowdery, T.K. (1998). "Ground water resources of the Mille Lacs Lake area, east-central Minnesota". Mounds View, MN.
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