Lake Monitoring

Reprinted from the Dead Lake Association Newsletter August 2012

 

Lake Monitoring by Sue Hansen

The water sample results for the first 3 summer months are now posted on-line at www.rmbel.info (http://www.mapfeeder.net/rmb.php/guest)and so far the results are looking pretty good. Listed below is data for the 5 Dead Lake test sites for May, June and July:

                           North Bay (205)      West Bay (211)     Narrows (207)      East Bay (202)      South Bay (212)

May Secchi Depth      17.0 ft.                      11.5 ft.                15.0 ft.                   18.0 ft                     15.5 ft.

June Secchi Depth     10.5 ft.                        8.0 ft.                  9.0 ft.                   13.5ft.                       7.0 ft.

July Secchi Depth        7.5 ft.                        6.0 ft.                10.5 ft.                   14.5 ft.                         -- ft.

Phosphorus Avg.        24 ug/l                      28 ug/l               22 ug/l                   28 ug/l                    23 ug/l

Chlorophyll-a Avg.       7 ug/l                         4 ug/l                  5 ug/l                     6 ug/l                       5 ug/l

TSI Index Average         47                              47                       47                           45                              46

 

For our new lake residents and also for the rest of us, here’s a reminder of what all of these numbers mean:  Phosphorus, Chlorophyll-a (algae concentration) and Secchi depth are related. When phosphorus increases,  this means there is more food available for algae, so algae concentrations increase. When algae concentrations increase, the water becomes less transparent and the Secchi depth decreases. The resulting numbers from these three measurements are converted to a trophic state index using an equation. The TSI ranges from 0-100. 0-30 is Oligotrophic, where water is very clear, phosphorus is low and algae is sparce. 30-50 is an in-between stage where the number of aquatic plants algae increase due to more available phosphorus. A TSI of over 50 describes a lake that is eutrophic, with a high density of plants and algae that could be unpleasant for swimming at certain times in the summer.

The good news is that we are still holding our own with a TSI average under 50 (our average to date is 46 TSI). Parts of the lake did show higher phosphorus levels than last year; however, we are staying within the DLA’s goal for phosphorus levels of 20-30 in all the bays. The chlorophyll levels in comparison to last year were considerably lower which is also good news. The secchi depth for the entire lake for these 3 months averages 11.7 feet compared to 11 feet last year and 10 feet the year before.

Thanks to our volunteer water samplers: Roger Cullen, Jim Hatlevig, Dennis Loecken and Tim Sullivan.