As we have previously advised, the SLA continues to participate in the Michigan Clean Water Corps. (“MiCorps”) Cooperative Lakes Monitoring Program (“CLMP”) wherein we voluntarily provide monitoring data on phosphorous levels (sampled twice a year, spring and late summer) as well as Secchi disk readings (measures a lake’s transparency/clarity—how deep you can see into the water column, sampling is done weekly May-September). SLA Director Scott Scarpelli headed up the monitoring last year and will serve in that capacity again this year and we are seeking additional volunteers around the lake. CLMP has released its 2013 Annual Report which provides the monitoring data on all of the lakes that participate in the CLMP program including our Sanford Lake. The CLMP’s 2013 Annual Report can be found at www.micorps.net/lakereports.
Secchi disk (Transparency): A total of 19 samples were taken with the minimum reading being 1.5 feet and the maximum reading being 5 feet. The mean was 3.5 feet, the median was 3 feet and the standard deviation was 1.1 feet. Finally, Sanford Lake was ranked as a 59 on Carlson’s Trophic State Index or Lake Productivity Index (“TSI”). TSI is used to categorize a lake’s productivity into four classifications: oligotrophic (the clearest of the lake types), mesotrophic, eutrophic and hypereutrophic (the most turbid of the lake types). The gradual increase of lake productivity (the amount of plant and animal/fish life that can be sustained in a lake system) from oligotrophy to eutrophy is called lake aging or eutrophication. Lake eutrophication is a natural process resulting from gradual accumulation of nutrients, increased productivity, slow filling in of the lake basin with accumulated sediments, silt, and muck. Sanford Lake is categorized as the high side of eutrophic bordering on a hypereutrophic lake which is characteristically generally shallow, turbid lakes that support abundant aquatic plant growth.
Phosphorous: Last year only the late summer testing was performed. The reported phosphorous measurement in the late summer sampling was 80 (ug/l). Phosphorous is one of several essential nutrients that algae need to grow and reproduce. The total amount of phosphorous in the water is also typically used to predict the productivity of a lake. An increase in phosphorous over time is a measure of nutrient enrichment in the lake. Sanford Lake’s 67 TSI score for phosphorous categorizes the lake on the low side of hypereutrophic.
Summary of 2012 v. 2013 Results for Sanford Lake: Last year 14 Secchi disk samples were taken verses the 19 taken in 2013. In 2013 the sampling would suggest that Sanford was a bit more turbid (less transparent) than in 2012. In 2012, the minimum reading was 4 feet and the maximum was 9 feet with the mean being 6.2 feet and the median being 6 feet with a standard deviation of 1.8 feet and a TSI score of 51. In 2012 the spring phosphorous reading was 22 (ug/l) and the late summer was 66 (ug/l) resulting in a TSI score of 66. The bottom line is that while the lake’s TSI for both transparency and phosphorous are up, the lake’s categorization as a late eutrophic/early hypereutrophic lake remains consistent. In addition, inconsistencies in the number of samples taken and the location of the sampling can influence the results. For example, prior year’s sampling was done in the deep basin adjacent to the dam where last year’s sampling was taken in the deep basin by the no wake buoy just north of the US 10 bridge. Typically we sampled phosphorous in both the spring and late summer where last year only late summer sampling was conducted. In hindsight the change in sampling locations and frequency was an inadvertent mistake and we will go back to a protocol of diligently sampling the lake in the deep basin adjacent to the dam and submitting phosphorous samples in both the spring and late summer.
Conclusions: It is important to note that water quality in a lake is a continuum and there is no broad agreement among scientists as to the precise point of change between lake classification types. Likewise, lakes can often have highly variable Secchi disk and phosphorous readings from one year to the next which may be exacerbated by inconsistencies in the number, types and the location that sampling that is done from year to year. Additionally, water clarity over time is influenced and/or altered by numerous factors that are inconsistent from one year to the next such as temperature (last summer was among the hottest of recent years), rainfall, aquatic animals present (and the volume of waste they generate) and the state of decay of weeds over the year. While the moderate increase in the turbidity of Sanford from 2012 to 2013 might seem alarming at first, many years (not just a comparison of two succeeding years) are required to separate true long-term changes in a lake’s productivity from seasonal and annual fluctuations which are perfectly normal. Notwithstanding, human activities (what is known as cultural eutrophication) can dramatically increase the amount of nutrients (such as lawn fertilization and agricultural runoff), soil (bank erosion) and organic matter (such as the impact of decaying weeds caused by the weed treatment programs on Sanford Lake) that accumulates in the lake. The SLA’s Water Quality Goals are meant to identity and address some of the cultural eutrophication that is impacting Sanford Lake over time. We cannot do this alone, so if you are interested in volunteering to help with the SLA’s Water Quality initiatives, please contact a SLA Board member.