2005 Results:
In 2005 East Moore Lake had average water quality for this region of the state (NCHF Ecoregion), receiving a C grade, similar to recent years. The lake is eutrophic. Conditions deteriorated through early summer. The worst conditions were from mid-June through mid-August, when algae was highest and transparency (Secchi depth) was 2-3 feet. Algae levels fell from mid-July through September, though transparency showed little change. Phosphorus trended similar to algae, except that it was nearly 2 times higher on September 9 than any other time in 2005. This may have been due to storm water flushing into the lake after a 1.5-2inch rainfall a couple of days earlier, or perhaps was due to decomposition of algae from earlier in the year. ACD staff subjectively ranked physical conditions as “some algae” in spring and fall to “high algae” in mid-summer. Subjective ranking of recreational suitability was of minimal swimming p roblems until late June, and swimming impaired thereafter.
Trend Analysis:
Nineteen years of water quality data have been collected by the Minnesota Pollution Control Agency (1977-87 and 1994) and the Anoka Conservation District (1998-2005). There is no significant long-term water quality trend from 1977 to 2005 (repeated measures MANOVA with response variables TP, Cl-a, and Secchi depth, F 2,16= 2.674, p=0.10). However, a comparison of lake water quality before and after storm water diversions from the lake were installed in the late 1980’s shows significant differences (repeated measures MANOVA, F 2,16= 3.63, p=0.05). After storm water was diverted away from the lake total phosphorus and Secchi depth improved, but chlorophyll-a got worse (examined via one-way ANOVAs).
Discussion:
Factors affecting water quality in this lake include runoff from its highly developed watershed, waterfowl and aquatic vegetation. Waterfowl are abundant year round, contributing nutrients that feed algae blooms and feces that increase coliform bacteria counts and may contribute to beach closings. Aquatic vegetation is having negative and positive impacts. Invasive species such as curly leaf pondweed and Elodea hamper recreation and release large amounts of nutrients when they decompose, but also compete with algae for the nutrients. Though connected, East and West Moore have different water quality. East Moore has much higher summertime algae but only slightly higher average total phosphorus. This may be because infestation of Elodea and curly leaf pondweed in the western basin compete with algae for the nutrients.