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Thorndike Pond
Conservation Association

Water Report - 2018

2018 Water Report

We work with the State’s Department of Environmental Services on their Volunteer Lake Assessment Program (VLAP). This year the leader of VLAP participated in the June sampling for the first time in about 8 years as we could both remember.  She said the Oxygen level are the highest she has seen this season, and clarity was excellent.  In that sampling we could see the secchi disk down to a depth of almost 16 feet, the clearest water we can either remember on Thorndike Pond.

There have been a number of outside findings this year, that shed light on our water quality.  I will cover them in the order they occurred.

I reported at last year’s annual meeting that some e-coli readings at the Town Beach caused the state to report that beach as impaired.  This is not part of the VLAP testing that I do, but it does show in DES’s annual assessment.  After the meeting, at the request of those present, mostly Steve Epstein, I tracked this down further. The beach assessment evaluates data from a ten-year period and the report was using data from 2004-2013.  This is included in the annual report (even though it’s not looking specifically at one year of data) because it’s looking at the long-term ability of a waterbody or beach area to support swimming and recreation.  During this period the Town Beach had two separate occasions where the bacteria levels exceeded 400 cts/100 mL, once in 2008 and once in 2011.  If there were two exceedances of 88 cts/100 mL in the 10-yr. period, so it is listed as not-supporting the designate use, which is swimming or primary contact recreation.  The person I talked to at DES said, “If you ask me, based on the data collected at the Town Beach, this criterion may be a little over-protective, and once the period of assessment phases out the 2008 data, you will likely see this go back to fully supporting or good.”

The second incident that prompted some research was an article in the Keene Sentinel, on Nov. 27th.  Spofford lake is having a problem with storm water runoff and their lake association has launched a study that was the subject of the article.  But at the end of the article they mentioned other lakes classified by the state as threatened or impaired.  Janet Grant brought this to my attention because of this list.  When I contacted the state, I was told that lakes in NH are categorized into three types depending on the amount of nutrients entering the water.  The best is Oligotrophic which has the least amount of nutrients and is characterized by: “Larger, deeper lakes with clear water, rocky of sandy shorelines, low phosphorus enrichment, limited root plant growth, low algae growth, and adequate dissolved oxygen throughout.”  Thorndike, despite its limited depth is in this category and therefore has more stringent limits on Phosphorus and Chlorophyll.  Thorndike is close to the limits on both measurements and occasionally goes over, earning a potential impairment rating.  If Thorndike was in the middle category of lakes, Mesotrophic, it would be satisfactory on both measurements, so the impairment is dependent on our classification. For those:

  • The Phosphorus limit tor lakes classified as Oligotrophic is <8ug/L.  Our peak observations in the past 28 years of measurements is around 8 with about ½ of the years with readings over 8.  The last 6 years we have been on or under 8 and when I asked DES they said the recent trend has shown we are actually improving.  The general causes of high Phosphorus are groundwater runoff, sewage or septic waste and waterfowl.  Looking at the measurements shows that the worst readings are at the two inlets and the best reading is at the outlet, so this is not something that homes on the pond are generating.  This inlet readings are normally attributed to upstream beaver activity.  When I asked the keynote speaker at this year’s lake congress, about this during lunch, he was not surprised or alarmed.
  • The Chlorophyll-a limits for lakes classified as Oligotrophic is <3.3ug/L.  Again, we are sometimes over and sometimes under this threshold, but DES again said when I asked them that the recent trend has been improving.  By the way, the average for the state is 4.58.
  • pH is also listed as marginal, but this is common in NH lakes, caused by a combination of acid rain and poor Acid Neutralizing Capacity attributed of our granite base.  Again, the readings show the 2 inlets have the worst readings.  By the way, the keynote speaker I mentioned before, thought that a reading of 6.0 is not a problem and the state’s threshold of 6.5 is way too conservative.  He didn’t think we have a problem.

The third incident is that I went to the annual NH Lake Congress meeting in Meredith this year, the first time the TPCA has sent anyone during the 14 years I have been on the board, probably ever.  We chose to send someone because there was a speaker talking about the affect that climate change will have on our lakes, a topic that is relevant and not well documented.  I have a separate report on this meeting. The President of NH Lakes, an organization that we are a member of and who runs the LakeHost program, said in his opening comments, that the three biggest issues facing NH lakes are:

  • Ground water runoff usually associated with new developments.  The Shoreland Protection act, that you should all be aware of if doing work on your lake frontage, deals with this issue.  We on Thorndike don’t have any development and can’t, and also benefit that our houses are generally set back from the pond.  As DES said during their June VLAP visit, we have a lot of vegetation along our waterfront.
  • Invasive Species, what we are trying to avoid with our LakeHost and weedwatcher programs.  Our LakeHost program, which you will hear about shortly from Evie, is pretty good, well above average.
  • Climate change, I will cover as part of the Lake Congress Report.