2005 Results:
In 2005 West Moore Lake had average water quality for this region of the state (NCHF Ecoregion), receiving an overall C grade, similar to other recent years. This grade does not factor-in macrophyte infestations. The lake is eutrophic. Average phosphorus in 2005 was lower than in the last two monitored years, in part due to a lack of mid-summer phosphorus spikes, which occurred in 2002 and 2003. 2005 phosphorus increased only mildly throughout the growing season. Algae (chlorophyll-a) and Secchi depth were similar to other recent years. ACD staff subjectively ranked physical conditions as “some” to “high” algae. Subjective ranking of recreational suitability were that conditions ranged from slightly to completely swimming impaired, in large part due to dense curly leaf pondweed and Elodea infestations. The infestations of these plants in 2005 were not as severe as other recent years. Interestingly, in August 2005 relatively few aquatic plants were present.
Trend Analysis:
Seventeen years of water quality data have been collected by the Minnesota Pollution Control Agency (1977-87) and the Anoka Conservation District (1999-2003, 2005). Water quality has significantly improved from 1977 to 2005 (repeated measures MANOVA with response variables TP, Cl-a, and Secchi depth, F 2,14= 6.07, p=0.01). Total phosphorus and Secchi depth have improved, but not chlorophyll-a. Additional comparisons show that most, if not all, of these improvements occurred between 1987 and 1999 when no monitoring was done. In the late 1980’s the City of Fridley received a grant from the MPCA to divert storm water from the lake. When pre-and post storm water diversion water quality are compared, total phosphorus and Secchi depths, but not chlorophyll-a, are significantly improved after the diversions (repeated measures MANOVA F 2,14= 5.26, p=0.02), though we cannot be certain that is the cause of the improvements.
Discussion:
Factors that are likely affecting water quality include runoff from the highly developed watershed, overly abundant waterfowl, and infestations of certain aquatic vegetation. While healthy populations of aquatic vegetation will improve water quality, current infestations of curly leaf pondweed and Elodea are hampering recreation and can release large amounts of nutrients when they decompose. Curly leaf pondweed die-off likely caused the mid-summer phosphorus spikes seen in several years, such as 2002 and 2003. 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.