Nov 6, 2019 Report Dudley Pond Water Quality Assessment Program Program Manager - Toni Moores 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. This report contains a summary, background, methods, results and a discussion. Summary
On November 6, 2019, water quality data was gathered at three depths at three sample points. Water quality parameters such as, pH, oxidation – reduction potential (ORP), dissolved oxygen (DO), dissolved oxygen % saturation and temperature were measured at three depths at each of the three sample points by SWQC members using a YSI Multimeter. Water depths and Secchi depths were measured at each of the three sample points. Samples were gathered by SWQC members and analyzed by Nashoba Analytical LLC. Key water quality parameters found on November 6, 2019 are shown in Table1 below along with the same parameters from previous fall samplings for comparison purposes. Table 1 – Key Dudley Pond Water Quality Parameters Date
Nov 6, 2019 Nov 8, 2018 Nov 9, 2017 Nov 14, 2016 Nov 16, 2015 Nov 12, 2014 Nov 15, 2013 Nov 11, 2012 Nov 13, 2011 Nov 18, 2007 ND = Non-Detect
TSI Range 22 - 57 20 - 44 20 - 42 40 - 45 26 - 43 47 - 48 49 - 51 42 - 46 42 - 44 -
Chlorophyll a Range ppb 11 - 15 ND – 1.0 0.42 – 1.0 ND 0.39 – 3.29 4 – 6.3 4.24 – 9.79 2.2 – 4.6 2.6 – 6.6 -
Secchi Depth meters 2.62 4.75 3.7 4 4.39 2.73 2.12 3.4 3.4 2.85
Total Phosphorus Range ppb 3.3 – 6.6 ND – 30 ND – 20 ND – 20 ND ND ND ND ND – 10 -
The Dudley Pond trophic state index (TSI) on November 6, 2019 ranged from oligotrophic to low eutrophic (22 – 57). The Chlorophyll a concentrations were the worst November results since the SWQC has been gathering data at Dudley Pond. In determining the TSI range, the relatively low (good) Total Phosphorus concentrations were unfortunately offset by the high Chlorophyll a values as well as the relatively poor Secchi reading of 2.62 meters. High Chlorophyll a and Low Secchi depth values indicate the presence of algae and/or weed fragments in the water column. The reason for these results is not known; however, the results may be related to the use of a
new herbicide, ProcelaCOR, for milfoil control during the past summer and/or weed harvesting late in the summer. Background Historically Dudley Pond has been sampled most frequently at the “deep hole” (Sample Point 25) on Dudley Pond. In order 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.
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 Samples were gathered at depths of one foot (Top), at mid depth (Middle) and 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. Samples and data were/are to be gathered during March, August and November each year, in an attempt to understand seasonal variations. Sample Handling - Multiple sample catches at each depth were composited from the sampler into a one-gallon container in order to get the volume of sample needed for the various analyses. The onegallon container was mixed and aliquots were poured into sample bottles provided by the analytical laboratory. The labels on the sample containers were filled out. One of the sample bottles contained sulfuric acid necessary to “fix”(preserve) the sample for total phosphorus (TP) analysis. All of the samples were stored in a cooler containing ice and delivered with chain of custody documents to the analytical laboratory the day of the sampling or the after the samples were gathered. Sample Analyses - A SWQC owned YSI 556 Multimeter was used to measure the following parameters at the same time that the samples are collected. Date Time Weather Barometric Pressure Location Depth pH ORP https://www.ysi.com/File%20Library/Documents/Application%20Notes/A567-ORP-Management-inWastewater-as-an-Indicator-of-Process-Efficiency.pdf Dissolved Oxygen Dissolved Oxygen % Saturation Temperature Secchi Depth https://en.wikipedia.org/wiki/Secchi_disk Analyses were performed by Nashoba Analytical, LLC for the following parameters. Total Phosphorus (TP), parts per billion (ppb) (as P) (Soluble + Insoluble) Orthophosphate, ppb (as P) (Soluble) Ammonia, parts per million (ppm) (as N) Nitrate/Nitrite, ppm (as N) Total Kjeldahl Nitrogen, ppm (as N) (organic nitrogen + ammonia) Chlorophyll a, ug/l (ppb) http://www.ohiowea.org/docs/Wed0900Lab_Chlorophyll_Analysis.pdf 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 Depths for Sample Points 24 and 27 were greater than the depth of the water, it was assumed that the Secchi Depths for all of the sample points were the same as Sample Point 25. In order to obtain a mean TP concentration for each sample point the three Total Phosphorus concentrations for the sample point were added and divided by three. In order to obtain a mean Chlorophyll a concentrations for each sample location, the mean chlorophyll a concentration at each sample point was calculated using the sum of the chlorophyll a concentrations at the three depths divided by three. (see http://www.aslo.org/lo/toc/vol_22/issue_2/0361.pdf for information re Carlson Trophic State index)
Results The results of the November 6, 2019 sampling are shown in Table 2. The analytical data was plotted to determine the Trophic State Index range and is shown in Figure 2.
Table 2 – November 6, 2019 Dudley Pond Water Quality Data
Figure 2 – Carlson Trophic State Index Results for November 6, 2019, Sample Points 24, 25 & 27
Discussion YSI Measurements - Measurements taken with the YSI 556 Multimeter varied from location to location and by depth. pH – The pH for all three sample points ranged from 7.26 at the bottom at Sample Point 25 and 27 to a high of 7.36 at one foot at Sample Point 24. There was very little variation in pH readings versus depth at each sample point, which may be due to mixing within the water column. DO Percent Saturation – The DO Percent Saturation ranged from a low of 96.3 % at 22 feet at Sample Point 25 to a high of 109 % at one foot at Sample Point 24. DO concentration values and DO Percent Saturation values were relatively uniform at each sample point, but varied from sample point to sample point. The vertical uniformity in dissolved oxygen, indicates mixing in the water column, even at 22 feet at Sample Point 25. It should be understood that it is not unusual to have DO Percent Saturation values in excess of 100%, which is usually due to active photosynthesis producing high concentrations of oxygen in the water column. Temperature – The temperature ranged from a low of 10.48 C at a depth of 22 feet at Sample Point 25 to a high of 11.64 C at a depth of one foot at Sample Points 25. The lack of significant variation in temperature throughout the water column indicates the presence of mixing, even at the 22 foot level at Sample Point 25. Oxidation Reduction Potential (ORP) – The ORP ranged from a low of 39 mv at a depth of one foot at Sample Point 27 to a high of 45.3 mv at a depth of 1 foot at Sample Point 25. ORP values were relatively uniform vertically at each of the sample points, but varied somewhat from sample point to sample point. The lack of significant ORP variation is thought to be due to mixing. ORP values on November 6, 2019 were low compared to previous samplings. The reason for this is not known. Secchi Depths – Secchi depth (a measure of color, turbidity and suspended solids, such as algae) on November 6, 2019 was 8’ 7” (2.62 m) at Sample Point 25. Large Secchi depths indicate better quality water and small Secchi depths indicate poorer quality water. This is the second worst Secchi depth measurement in the past nine years. Part of the poor visibility as measured by the Secchi depth may have been due to the high wind causing surface turbulence and poor water column visibility; however, it is believed that there are other factors that may have caused the poor visibility in the water column. Other possible reasons for the poor visibility may be recent rainfall events and/or algae/suspended weed fragments resulting from the ProcellaCOR herbicide treatment of the milfoil or fragments from the harvesting of tape grass both of which were done during late in the summer. Elevated Chlorophyll a concentrations support the theory that the poor water column visibility was certainly due to algae and/or weed fragments. Phosphorus – There was no ortho-phosphate found at any of the sample points, which is typical during a fall sampling. Total Phosphorus (TP) was found at all three sample points and ranged from 10 to 20 ppb. It is worth noting that 10 ppb is the minimum detection limit for the analytical method used. Orthophosphate is the form of phosphorus that is readily available as a nutrient for bacteria, weeds and algae. Total Phosphorus includes the various forms of phosphorus compounds that are not readily available to biota as a nutrient and also includes ortho-phosphorus. Ammonia – Ammonia was not detectable in any of the nine samples. Nitrite/Nitrate – No nitrite or nitrate were found at any of the sample points, which is not unusual for Dudley Pond.
Total Kjeldahl Nitrogen (TKN) – The TKN concentration, if any, was below the minimum dectection limit at all sample points for the analysis used. Alpha Chlorophyll (Chlorophyll a) – On November 6, 2019 Chlorophyll a, an indirect measure of the algae concentration, ranged from 6.1 ug/l at one foot at Sample Point 27 to 21.7 ug/l at five feet at Sample Point 27. With the exception of Sample Point 27 the Chlorophyll a concentrations were all double digits compared to single digit concentrations for November samplings in years past. These elevated Chlorophyll a concentrations correlate with the relatively poor Secchi disc values and therefore seem to indicate higher concentrations of algae and/or weed fragments in the water column. Carlson Trophic State Index – A low Trophic State Index (TSI) indicates better water quality and a high TSI indicates poorer water quality. As Dudley Pond is primarily used for recreational purposes, a trophic state index (TSI) less than 50 is tolerable and less than 40 would be great. The average TSIs on November 6, 2019 for the three sample points ranged from 22 to 57. Therefore the Dudley Pond TSI was primarily in the mesotrophic range, which is an indication of reasonable quality water for recreational purposes. The relatively low (good) TP concentrations were unfortunately offset the high Chlorophyll a values as well as the relatively poor Secchi reading of 2.62 meters. For this report the TSI range is determined graphically using Figure 2; however, if a mathematical solution is desired the mathematical formula can be found by referring to: http://www.aslo.org/lo/toc/vol_22/issue_2/0361.pdf