2005 Results:
In 2005 Laddie Lake had above-average water quality for this region (NCHF Ecoregion), receiving an overall B grade; the same as since 1993. The lake is slightly eutrophic, though much of the plant growth is manifested as marcophytes (large plants), not algae. By the end of July macrophytes were to the surface on 60% of the lake, though they were not matted on the surface and the plants are spaced about 1-2 feet apart. ACD staff’s subjective observations of algae levels were “some algae” or “clear water” for the entire summer.
Trend Analysis:
Twelve years of water quality data have been collected by the Metropolitan Council and the Anoka Conservation District. This lake has vastly improved water quality since 1980, but recently a slow degradation is occurring. To search for trends since 1992, a repeated measures MANOVA with response variables TP and Cl-a was used on those years only. Secchi depth was excluded because measurements were not available in all years. Water quality has a negative trend (F 1,9=10.73, p=0.01). Based on linear regressions, this trend is due to increases in total phosphorus, but not chlorophyll-a. It is likely that additional phosphorus is consumed by macrophytes, and therefore algae are not increasing and water clarity is not suffering. If this trend continues, it can be expected that at some point macrophytes will be overwhelmed by phosphorus and the lake will shift toward algae-domination.
Discussion:
The abundance of macrophytes in this lake is an indication of a healthy system, not an impairment. As a shallow lake, macrophytes should be expected throughout. They are consuming nutrients that would otherwise fuel algae blooms and they provide excellent waterfowl habitat. Curly leaf pondweed, an invassive exotic, has not been documented in Laddie Lake . The trend of nutrient increases in this lake is p rob ably modest enough that it could be successfully counteracted. A review of stormwater management in the lake’s watershed should be conducted to seek out ways to halt the trend. Future monitoring is highly recommended to further understand this lake and predict changes. It is impressive that this lake is in such good condition given its urban watershed and shoreline development. Note: Secchi depth was not considered in 2005 analyses because secchi depth was greater than the lake depth throughout the year, so secchi could not be accurately determined.