- Lake Forest Association (LFA) - Caretakers of Eastwood Lake in Chapel Hill, NC.
Our fourth, “Labor Day” 2015 water samples were taken Thurs , Aug 20, 2015 around 9:30am
#1 Dock 45 cfu
#2 Cedar Fork Creek 12 cfu
#3 Booker Creek 3 cfu
Caution level is individual reading above 400 cfu, or average above 200 cfu.
Lake water temp ranged from 28.5C/84F to 29C/85F, a bit cooler than our last test . The SECCI clarity reading was 26 inches, normal turbidity (cloudiness) for mid summer. The rain gauge had 1.0 inch of water in it.
The CFU readings are well within the safe limits, with the values from sample sites 1 & 2 reversed from our last test. The lab noted that there were other coliforms present in the #2 sample (non-fecal meaning from something other than the intestines of a warm-blooded animal). Not being a bacteriologist, I have no idea what to make of that other than the lab analyst’s comment that it was a limitation of the AGAR they use for their cultures, there weren’t many, and it is of no concern to the health department.
It rained lightly on each of the two days preceding the test. Normally I would have waited another day to take samples but I am getting ready to go on vacation and would not be able to report the results or retest if necessary if I had waited. The guideline for our sampling protocol is to not take samples immediately after a heavy rain, because the water near the surface at that time is not representative of most of the water in the lake. In the past when we were taking frequent samples from more sites to assist OWASA while they were improving the sewer system upstream, we learned about the rates at which surface water moves through the lake. If we had taken the samples 1 day earlier, the values for sites 1 and 2 would have been reversed as they were on June 29.
Last week there was 4.5 inches of water in the rain gauge. When we have low rainfall at this time of year, the clarity increases a lot. We have had August SECCI disk readings around 50 inches. In this case, clarity, which is aesthetically appealing, is not an indication of ecosystem health, just low water flow. Our lake becomes a “settling bed” when the rains stop. Not the case this year. There was a fair amount of debris on the surface everywhere in the lake, most of it looks like goose down but I’m not at all sure if that is what it actually is.
I did NOT see any bright plumes of fresh silt in the water, that is something we need to become vigilant about as all sorts of new development is going on at the far northwestern edge of our watershed, near the intersection of Weaver Dairy Road and MLK Jr. Drive. Unusually high turbidity (smaller SECCI disk numbers) would be another early warning. Readings of 16 inches or less would definitely be out of the normal range for our lake.
Since I’m seeing some new development and home sales near the lake, I need to repeat the warnings about fall lawn and garden maintenance. Use “lake margin” fertilizer formulations (no phosphorous) unless you have added new soil….Phosphates remain bound in the soil so the main way they are lost and need to be replenished is from erosion. Erosion also causes silting-in (eutrophication). That is a natural process in this area, but we need to limit it if we want to keep our lake as a lake. There is only one natural lake in North Carolina, White Lake. Eutrophication is the main reason why this is so.
Phosphates dissolved from the soil in the lake nourish algae, creating algae blooms that rob the lake water of oxygen when the algae die. That, in turn, messes up the lake ecosystem and stunts the growth of fish. So fertilize lightly, not before a rain (since most of the rain we get comes in the form of “gulley-washers”), and water-in any newly applied fertilizer or lawn chemicals. . Please make sure your yard maintenance people are aware of this, it is not always common knowledge.
Finally, we do have normally occurring algae blooms in late spring. These usually do not have lasting negative consequences, and are mostly just unpleasantly junky water for about 10 days.
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