SWQC Water Quality Report - April 27, 2021

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April 27, 2021 Report Dudley Pond Water Quality Assessment Program Program Manager – Norm Marowitz This document is part of an ongoing Surface Water Quality Committee (SWQC) water quality program for Dudley Pond. The objectives of the Program are to gather Dudley Pond water quality data that will be used to: • Compare to similar water quality data gathered in the past at Dudley Pond. • Track the trophic state index (TSI), a measure of water quality, for Dudley Pond during the spring, summer and fall of each year. We will be testing twice per year, varying which seasons we will test in any particular year, based on test results or other pertinent factors. This report contains a summary, background, methods, results, and a discussion. Summary Test points #24 and #27 (see Map at Figure 1) again showed minimal variation of results from 1 feet depth testing to bottom testing (only 5-6 feet), which may lead to testing only one depth in the future at those locations. • •

• •

On April 9, 2021, water quality data was gathered at two depths at the three sample points historically utilized, versus three depths in the past. Water quality parameters such as, pH, oxidation – reduction potential (ORP), (although this parameter seems to be used less and less by industry experts for Lake & Pond monitoring), dissolved oxygen (DO), dissolved oxygen % saturation and temperature were measured at two depths at each of the three sample points by Ben Wetherill (ACASAK) using a YSI Multimeter. Water depths and Secchi depths were measured at each of the three sample points. Samples were gathered between 8:15AM & 9:30AM and delivered to Nashoba Analytical LLC. for other testing parameters. Key water quality parameters found on April 9, 2021 are shown in Table1 below along with the same parameters from four previous Spring samplings for comparison purposes. We decided to not test in the spring of 2020 due to consistently good results in prior spring testing as we shifted to twice annual testing versus previous three times per year due to consistently good results and unnecessary additional cost.

Table 1 – Key Dudley Pond Water Quality Parameters Date

TSI Range (See figure 2)

Secchi Depth Feet

37 - 53 -

Chlorophyll a Range ppb 2.01 – 4.58 -

13’ 5” -

Total Phosphorus Range ppm 10 - 54 -

4/9/2021 Not tested in spring 2020 3/27/19 3/29/18 3/26/17 3/23/16

33 - 43 22 - 36 21 -41 30-40

.9 – 2.3 ND – 1.0 .59 – 1.1 .89 - 5.13

11’ 2” 19’ 0” 12’ 0 15’ 0”

ND ND 0 – 10 ND

ND = Non-Detect •

The Dudley Pond trophic state index (TSI) on April 9, 2021 ranged from oligotrophic to high mesotrophic (37 – 53). (see more on this at Figure 2) The Chlorophyll a concentration was at good overall levels, although a little higher on the bottom of Sampling Point 25, traditionally the highest concentration point, but still at a level considered fairly good by traditional standards (see Chlorophyll a discussion in lower section) Transparency was very good at 13.5 feet, and it should be noted that the low angle of the sun in the morning impacted the Secchi disk readings which would most likely have been deeper. The high end of the TSI was attributed to a higher level of phosphate detected at the bottom of test point 25, the deepest section. This number skews the TSI range,


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