Table 1 – Key Dudley Pond Water Quality Parameters Date TSI Range (See figure 2) Chlorophyll a Range ppb Secchi Depth Feet Total Phosphorus Range ppm 30 53 2.10 2.50 7’ 0” 20 30 37 53 2.01 4.58 13’ 5” 10 54 Not tested in spring 2020 33 43 .9 2.3 11’ 2” ND 22 36 ND 1.0 19’ 0” ND 21 41 .59 1.1 12’ 0 0 10 30 40 .89 5.13 15’ 0” ND
3/26/17
• 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.
April 2022 Report
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4/13/2022
• Key water quality parameters found are shown in Table1 below along with the same parameters from previous Spring samplings for comparison purposes.
• Based on advice from Ben Wetherill, aquatic consultant, due to the “spring mixing” that typically occurs after “ice out” on lakes and ponds, on April, 13, 2022, water quality data was gathered at one depth at all three test points In the spring, the water surface warms. This causes the temperature of the top and bottom layers of the lake to equalize. With the help of strong winds, this new equilibrium breaks the thermal stratification, and the lake is able to mix. Due to this, the test results at different depths would likely show statistical indifference.
4/9/2021
Summary
3/23/16
3/29/18
Dudley Pond Water Quality Assessment Program Program Manager Norm Marowitz
• Samples were gathered between 7:40 AM & 8:20 AM and delivered that morning to Nashoba Analytical LLC for other testing parameters.
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:
• 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 each of the three sample points by Ben Wetherill (ACASAK) using a YSI Multim eter. Water depths and Secchi depths were measured at each of the three sample points.
ND = Not Detected
3/27/19
• Compare to similar water quality data gathered in the past at Dudley Pond.
This report contains a summary, background, methods, results, and a discussion. An addendum report from Ben Wetherell of ACASAK should also be considered as part of this report. That report is also available.
To have data sets that are comparable to historical data, samples were gathered at locations 24, 25 and 27 as indicated in Figure 1. Two of these sample locations correspond to the sample locations used in the Larkin (1978) and IEP (1983) reports. Line of site intersections were used to locate sampling points.
The methods of analysis used are described below and the data for the three sampling points shown in Table 2
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Figure 1 – Dudley Pond Sampling Points
Sample Point 24 is located at the intersection of the lines of site between Rocky Point Bayfield Rd and Williams Point “The Chat”. Sample Point 25 is located at the intersection of the lines of site between Mansion Beach Southern point of the Dudley Rd. peninsula and Lowery’s dock Williams Point. Sample Point 27 is located at the intersection of the lines of site between the Dudley Pond outlet 107 Dudley Rd. and the foot of Maiden Lane the 20” outfall adjacent 27 Bayfield Rd.
Methods
Dissolved Oxygen
Analyses were performed by Nashoba Analytical, LLC, Ayer, Massachusetts for the following parameters:
Samples w ere gathered at depths of one foot (Top) and approximately one foot off the bottom (Bottom) at Sample Points 24, 25 and 27. A water sampler as shown at http://pentairaes.com/water sampler 1.html with a sample volume of 1.0 1.5 liters was used to gather samples at various depths.
Total Kjeldahl Nitrogen (TKN) ppm (as N) (organic nitrogen + ammonia)
Date Time Weather Barometric Pressure
Sampling Multiple sample catches at each depth were composited from the sampler into a one gallon container to get the volume of sample needed for the various analyses. The one gallon container was mixed and aliquots were poured into sample bottles provided by the analytical laboratory Bottles were pre labeled by location as Top or Bottom.
Sample Analyses A YSI 556 Multimeter was used by ACASAK (Ben Wetherill) to measure the following parameters at the same time the samples were collected, except the Secchi depth, which was measured using a Secchi disk
Carlson Trophic State Index TP concentrations, Chlorophyll a and Secchi depths were used to plot the Carlson Trophic State Index (TSI) for the three sample points in Dudley Pond. Since the Secchi disk testing for Sample Points 24 and 27 were visible to the very bottom , it was assumed that the Secchi Depths for all the sample points were the same as Sample Point 25, the deepest section of the pond.
One of the sample bottles contained sulfuric acid necessary to “fix” (preserve) the sample for total phosphorus (TP) analysis. All the samples were stored in a cooler containing ice and delivered with chain of custody docume nts to the analytical laboratory the day of the sampling or the after the samples were gathered
Dissolved Oxygen % Saturation
Temperature
Secchi Depth https://en.wikipedia.org/wiki/Secchi_disk
Chlorophyll a, ug/l (ppb) http://www.ohiowea.org/docs/Wed0900Lab_Chlorophyll_Analysis.pdf
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Location Depth pH ORP https://bit.ly/3yV3mwo
Total Phosphorus (TP), parts per billion (ppb) (as P) (Soluble + Insoluble) Nitrate
Barometric pressure 762.7 (mmHg)
See addendum report provided by Ben Wetherell of ACASAK for more complete description of results.
DO% Saturation 108.2 106.2 111.9 79.3 109.2 108.4 Temp C 11.7 8.5 12.1 12.0 12.2 12.1 Secchi Depth >6.0 13' 0" >7.0
Table 2 Testing Results: April 13, 2022 Dudley Pond Water Quality Data Date 4/13/2022
DO (mg/l) 11.60 11.43 12.13 9.26 11.69 11.64
LOCATION # ON POND 24 24 25 25 27 27 TOP BOT TOP BOT TOP BOT
Total Phosphorus (ppm) 30 n/a 20 n/a 20 n/a Nitrate .41 “ .39 “ .39 “ Chlorophyll a ppb (ug/l) 2.1 “ 2.5 “ 2.2 “ TKN (as N) ppm (mg/l) ND “ ND “ ND “
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Testing & sampling began at approx. 7:40 AM, completed appr. 8:20 AM
Depth (Feet) 1 5 1 23 1 5 pH 7.73 7.16 7.57 7.44 7.72 7.60
Note:
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The Dudley Pond trophic state index (TSI) on April 13, 2022 ranged from 20 53 which is in the oligotrophic to high mesotrophic range (Figure 2). A description of these classifications is shown in Table 3. It should be noted that the high end was due to the Total Phosphorous reading at test point 24 near the Chateau where we observed significant Milfoil and other plant growth.
The Chlorophyll a concentration was at good overall levels. Transparency was much more limited than usual at 7.0 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. For a more in depth discussion on this, see the addendum report by ACASAK. The high end of the TSI was attributed to a higher level of phosphate detected at the bottom of test point 24, near the Chateau. This number skews the TSI range, and we believe it is due to the accumulation of dead plant and other matter in that section. We do not believe this gives a fair representation of the pond’s overall water quality, but we will continue to monitor it for any significant changes over time.
Table 3: Trophic state descriptions
Secchi Disc (meters) 2.13 m 2.13 m 2.13 m
Figure 2 – Carlson Trophic State Index Results for April 13, 2022, Sample Points 24, 25 & 27
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Phosphorus Total Phosphorus (TP) was detected at 30 ppb at test point 24 near the Chateau (10 30 ppb is the level found in uncontaminated lakes, plant growth may be stimulated from 30 100 ppb with 100 being the maximum sustainable level to avoid accelerated eutrophication) It is worth noting that 10 ppb is the minimum detection level for the analytical method used . Total Phosphorus is a measure of all forms of phosphorous, dissolved or particulate, that are found in a s ample. It is an essential element for plant life, however, at higher levels, it can speed up eutrophication (reduction in dissolved oxygen). There are many sources of phosphorus in aquatic systems. These sources can be natural, such as waterfowl (Swans, geese, etc.) waste, atmospheric deposition, and plant decomposition; or they can be human induced, such as fertilizer, pet waste, agricultural and urban runoff, industrial and domestic sewage, or faulty or overloaded septic systems. While tested levels have generally been low, we suspect levels “hiding” in the soil in the lake from plant decomposition and other sources may be why we have experienced high levels of plant growth. This a good reason to remove aquatic vegetation at reasonable levels to avoid continued build up at the bottom and decomposition. For information on managing phosphorous levels in lakes and ponds, see https://www.des.nh.gov/organization/commissioner/pip/factsheets/bb/documents/bb 20.pdf
Sample Point 25 (Yellow )
TP (ppb) 30 ppb 20 ppb 20 ppb Chlor a (ppb) 2.1 ppb 2.5 ppb 2.2 ppb
Sample Point 27 (Blue)
Sample Point 24 (Red)
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Total Kjeldahl Nitrogen (TKN) The TKN concentration was below the minimum detection level at all sample points. Acceptable levels are up to 6 mg/L. The TKN method in chemistry is for the quantitative determination of nitrogen contained in organic and inorganic compounds (ammonia (NH3) & ammonium (NH4)). It is usually used to gain knowledge of the total nitrogen content of a sample. Alpha Chlorophyll (Chlorophyll a) On April 13, 2022 Chlorophyll a, an indirect measure of the algae concentration , ranged from 2.1 ug/L at sample point 24 to 2.5 ug/L at test point 25. For reference: < 3 ug/L Excellent
In summary, the water quality testing results from the April 13, 2022 sampling indicate good water quality overall ranging from Oligotrophic to high Mesotrophic as seen in Table 3 above. The higher end of this range was caused by the higher Phosphorous measured at test point 24 near the Chateau All other locations tested indicated water quality in the Oligotrophic to low Mesotrophic range. It is difficult to know exactly what causes these variations at different sections of the pond, however, we know that both growing vegetation and drift of floating vegetation tends to accumulate in the Chateau area of the pond during the summer water temperature stratification period also Swans nest there in Spring. The deepest section of pond, test point 25 tends to accumulate dead plant matter, etc., affecting testing results seasonally.
3 7 ug/L Good
Less than desirable > 15 ug/L Nuisance
Nitrate Levels test at .41, .39 & .39 MG/L at test points 24, 25 & 27 respectively. As a reference point, nitrate below 10 mg/L is considered safe for drinking.
7 15 ug/L
The next testing and report will be for August 2022.