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Lake Ada (11-0250)
The 2009 water monitoring season began April 24th with the installation of the Lake Ada rain gauge. From the opening date through May 31st we received only 2.1 inches of rainfall and the month was ultimately declared the third driest May in Minnesota recorded weather history. The skies opened up in June and rainfall was plentiful until August. October turned out to be the fifth wettest in Minnesota history.
2009 Cumulative Monthly Precipitation
4/26 0.5”
5/1 0.75”
5/15 1.75”
6/1 2.1”
6/15 3.45”
7/1 6.7”
7/15 8.8"
8/1 11.15”
8/15 12.05”
9/1 12.9”
9/15 13.25”
10/1 14.45”
10/15 15.9”
11/1 19.6"
2009 Monthly Precipitation Totals; May through October
May 2.1”
June 4.6”
July 4.15”
August 2.05”
September 0.55”
October 6.15”
Total 19.6"
Normal Lake Ada precipitation for May through September is 20.7 inches.
Lake level monitoring began May 10th with an initial reading of 1325.03 ft msl, quite typical compared to the same date over the past five years. Lake Ada is normally above the outlet dam in spring, at or slightly below dam level in summer, and below the dam by fall. This year, however, the lake remained at or above the dam for most of the summer. Lake level on Sept 1st was recorded at 1324.6 ft msl, exactly outlet dam level.
The 2009 lake level monitoring season ended November 1st, with a reading of 1324.53. Lake Ada water level data is forwarded to Lake Level Minnesota, a program of the Minnesota Department of Natural resources.
People occasionally ask if water level can be adjusted at the outlet dam. The dam was originally constructed in 1936 with adjustable gates, but by 1947 the DNR had decided Lake Ada’s optimum water level should be 1324.6 feet. The dam was altered at that time to a fixed-gate structure.
Water clarity during 2009 was fairly good, but not outstanding. Our best reading was 17 ft and our poorest 9 ft. To date, the 2009 main lake average is 14 ft, compared to our long-term average of 13.3. It’s long been realized that Lake Ada responds to rainfall with cloudy water, and to dry weather with clear water. A possible reason is the lake is receiving excess storm water runoff. A quick walk along the shore following almost any rain will reveal many small channels where water has washed from the surface of a lawn, down the bank and across the beach. Channels can be small or, as in the case of the public access, very large. Storm water runoff carries pollutants, such as gasoline, oil, pesticides, suspended solids, pet waste, phosphorus and other and nutrients directly to the lake.
The main lake traditionally begins the year clearer than the north bay, but as summer progresses, the bay catches up and usually ends the season clearer.
Lake Ada transparency readings are forwarded to the Citizen’s Lake Monitoring Program, Minnesota Pollution Control Agency.
During the summer of 2009 Lake Ada again joined a chemical water testing program sponsored by the Minnesota Pollution Control Agency, Cass County and the Association of Cass County Lakes. Both the main lake and north bay were sampled five times for Secchi depth, phosphorus and chlorophyll-a. Water samples were sent to RMB Environmental Testing Laboratories, Detroit Lakes, for analysis.
Since Secchi depth, total phosphorus (TP) and chlorophyll-a (Chl-a) are measurements of different types of data, measured in different ways and on different scales, a common denominator is needed so they can be compared. Carlson’s Trophic State Index (TSI) is a means for characterizing fertility, biological productivity and general clarity. The following chart, prepared by RMB Environmental Testing Labs, shows the results of our three-year testing program. The chart depicts mean Secchi depth, TP and Chl-a as TSI’s and compares them with Lake Ada’s mean TSI. Note that as Chl-a raises, Secchi depth drops. Also note how Chl-a TSI is almost always higher than would be expected. The hypothetical dividing line between mesotrophic and oligotrophic waterbodies is generally accepted to be TSI 40.
During the fall of 2009 the Minnesota Pollution Control Agency and RMB Environmental Testing Labs completed transparency trend analyses of Lake Ada based on Secchi disk readings submitted over past years. RMB requires a minimum of eight to ten years of data, with four or more readings per season. MPCA requires minimum ten years of data with eight to ten readings per season.
RMB Environmental Testing Labs reported:
“The probability that a true significant trend exists is 99.9%. Secchi Disk is increasing, which indicates improving water quality.”
MPCA reported:
“Water clarity in this lake (Lake Ada) is almost certainly improving, with an estimated increase of 0.8 feet per decade. This estimated change could potentially range from an increase of 0.3 feet per decade to an increase of 1.2 feet per decade.”
The MPCA analysis also indicated Lake Ada exceeded expectations for both low chlorophyll-a and total phosphorus. Secchi depth readings were at the maximum end of the expectation scale and Trophic State Index was reported at 41.
The trend analyses confirm Lake Ada water quality is improving, and projects untaken by the Association, especially the lake-wide septic survey, are working.