Lay Monitoring Water Clarity Report to Groton Lake Association, 2012

For a number of years (with the exception of 2009) we have been measuring water clarity of the pond during the summer season.  We do this as volunteers to the Department of Environmental Conservation, which collects similar data from all over Vermont.  Since 2005, we have also been taking samples for water quality testing by the State of Vermont.

Using a SECCHI disk, we take clarity readings in designated spots in the southern and northern parts of the pond.  The disk is a heavy steel plate painted in black and white quadrants that we lower into the water.  We measure how deep the disk can be lowered and still be seen.

At the northern location, which is at or near the deepest part of the pond (about 45 feet), we collect samples from twice as deep as SECCHI visibility, usually 6 to 8 meters or so.  We send the samples to Montpelier for testing for phosphorus, and we also send filter samples for chlorophyll content.

We take readings and samples about once a week from June through August, at least 9 times a season.  The following are this year’s readings (in meters [1M = about 3 1/2 ft.]):

Date                              Station 1 (north)                                     Station 2 (south)

6/3                                        2.6         2.8
6/9                                        2.6         3.5
6/18                                      3.2         2.3
6/29                                      2.7         2.6
7/7                                        3.0         3.0
7/16                                      2.8         3.4
7/21                                      3.9         3.4
8/23                                      3.5         4.2
9/3                                        3.7         4.5

Average water clarity in 2012 was 3.21 meters, compared with 2011 (2.66 meters), compared with 2010 (3.38 meters), 2008 (3.19 meters), 2007 (3.46 meters), 2006 (3.17 meters), and 2005 (3.56 meters).  This year’s average clarity is improved from 2011’s, probably due to the high levels of rain and runoff experienced last year.

On the next page is a table showing readings since 1999 (also 1979-1988 for comparison), when sampling began at Groton Pond.  We will update this chart each year as we receive the data from the State of Vermont.  We are also posting these results on the Groton Pond website.

We’re looking forward to continuing this project in the coming year.

 

David & Cathy Donath
September 2012


 

Annual Average Water Quality Results – Groton Pond

 

Year Days                 Secchi       Chloro-a Summer TP        Spring TP
  Sampled                      (m)            (ug/l)      (ug/l)                  (ug/l)

1979      6                                                                                      4.0
1980    10                       3.6                                                           8.0
1981      9                       3.7                                                           7.0
1982    12                       4.0                                                           9.0
1983      4                                                                                    10.0
1984    13                       3.0                 3.6                                      6.0
1985    13                       3.9                 3.9                                      7.0
1986    14                       3.5                 2.6                                      8.0
1987    13                       3.9                 3.2                                    16.0
1988    21                       4.3                 2.5                                         

                                                                                                        

1999    11                       3.7                                                           6.8
2000    10                       3.4
2001    11                       4.3
2002      8                       3.2
2003      8                       3.7
2004      9                       3.6
2005      9                       3.6                 3.4         12.0                       6.5
2006      9                       3.2                 4.1         12.0                       9.8
2007    10                       3.4                 6.7         12.0
2008    10                       3.2                                                              
2009      0
2010      9                       3.5                 5.9         12.0
2011      9                       2.7                 5.1         15.0                          
2012      9                       3.2                                                              

 

Key:     Secchi refers to visible water clarity (depth in meters).
            Cloro-a refers to the sampled amount of chlorophyll.
            Summer TP refers to the level of phosphorus in the summer samples.
            Spring TP refers to the level of phosphorus in the spring samples.

 

[Amy Picotte, 2011 Vermont Lay Monitoring Report (Waterbury: ANR, 2011), p. 67]