Aquatic Health and Turbidity
Excessive turbidity can affect aquatic health. In the case of the Nemadji River system, including Deer Creek, exceedance of the turbidity standard due to high sediment yields has been identified as a living condition that can cause impairment in biota. High sediment yields can cause adverse effects on biota when fine sediments settle into open spaces in the bed of the stream that serve as refuge for invertebrate and young fish. These small spaces are also used as spawning beds for adult fish and the loss of these spaces can ultimately reduce fish fecundity. Algae and other primary food resources can also be buried in the fine sediment disrupting the food web. Turbidity level in the lower portion of Deer Creek run high even during baseflow conditions, when the storm runoff is not affecting the stream.
The Minnesota Pollution Control Agency will monitor for biological health through a recently developed watershed approach. Minnesota’s 81 major watersheds are each placed on a 10-year cycle of condition monitoring. Permanent flow and chemistry stations are set up at the outlets or “pour point” of each watershed. In this case, the Nemadji River Watershed has a ” pour point” station at the mouth of the river in Superior, Wisconsin. Intensive monitoring is then done on a every 10 years.
Historical data review does not reveal any macroinvertebrate sampling done in the Deer Creek watershed, yet there is record of sampling done in other parts of the Greater Nemadji River watershed. These efforts are discussed below and may aid in future biota sampling efforts in Deer Creek.
1980 EPA Report:
In 1980 a EPA report was completed for the Red Clay Project which included the Nemadji River Watershed. Several studies were completed as a part of the final report, including “Effects of Red Clay Turbidity and Sedimentation on Aquatic Life in the Nemadji River System” by P.S. Devore, L.T. Brooke, and W.A. Swenson. The study area included the Nemadji River, Little Balsam Creek, Empire Creek, Skunk Creek, and Elim Creek. Several conclusions were made from the study, including the finding that substrate size had much greater effects on macroinvertebrates than turbidity and sedimentation. Additionally, fish populations were not demonstrated to change as a result of turbid conditions. Water temperature and discharge differences between turbid and clear water sites accounted for species changes.
In 1997 and 1998 the Minnesota Pollution Control Agency gathered biological data at several location in the Nemadji Watershed. The study was done in effort to develop baseline indices of biological integrity. The index of Biological Integrity (IBI) is a multimetric apporach using macroinvertebrates as indicators of pollution. Macroinvertebrates display a large range of living requirements, making them excellent indicators of water quality. The IBI is a scientifically validated tool typpically using 8-12 attributes )metrics) of biological assemblage related to taxa richness, community composition, trophic structure, reproductive function, tolerance to human disturbance, abundance, and condition. Each metric is assigned a rating. When the ratings are summed together and index score is given, representing the biological integrity of the site.