Nov 14, 2016 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 initiated 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. Summary
On November 14, 2016, 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 and Secchi depths were measured at each of the three sample points. Samples were gathered by SWQC members and analyzed by Nashoba Analytical LLC. Ambient air temperatures during October and November 2016 had been warmer than average and the entire state was continuing to experience drought conditions. Key water quality parameters found on November 14, 2016 are shown in the following table, along with the same parameters from previous years for comparison purposes. Table 1 – Key Dudley Pond Water Quality Parameters Date
TSI
Nov 14, 2016 Nov 16, 2015 Nov 12, 2014 Nov 15, 2013 Nov 11, 2012 Nov 13, 2011 Nov 18, 2007
40 - 45 26 - 43 47 - 48 49 - 51 42 - 46 42 - 44 -
Chlorophyll a ppb ND 0.39 – 3.29 4 – 6.3 4.24 – 9.79 2.2 – 4.6 2.6 – 6.6 -
Secchi Depth meters 4 4.39 2.73 2.12 3.4 3.4 2.85
Total Phosphorus ppm ND – 0.02 ND ND ND ND ND – 0.01 -
The water quality data obtained on November 14, 2016 is the second best of the past six years based on the Secchi depth; however, the lack of Chlorophyll a and the elevated Total Phosphorus concentrations are unusual when compared to previous years. These anomalies may be due to the presence of the herbicide Fluridone in the Pond from April 21, 2016 thru November 14, 2016 used to treat Milfoil. The water quality implications of elevated Total Phosphorus concentrations for next year are not known.
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 Mansion Beach – “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/watersampler-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 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 http://www.molecularhydrogenfoundation.org/core-information/oxidation-reduction-potentialorp-explained/ Dissolved Oxygen Dissolved Oxygen % Saturation Temperature Secchi Depth (http://water.epa.gov/type/rsl/monitoring/155.cfm) Nashoba Analytical, LLC was used to perform analyses of samples from Sample Points 24, 25 and 27. Analyses were performed by Nashoba Analytical, LLC for the following parameters.
Total Phosphorus, ppm (as P) (Soluble + Insoluble) Orthophosphate, ppm (as P) (Soluble) Ammonia, ppm (as N) Nitrate/Nitrite, ppm (as N) Total 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 an average TP concentration for each sample point the three Total Phosphorus concentrations for the sample point were averaged. In order to obtain an average Chlorophyll a concentrations for each sample location, the average of the chlorophyll a concentration at each sample point was calculated using the average of the chlorophyll a concentrations at the three depths. (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 14, 2016 sampling are shown in Table 2. The analytical data was plotted to determine the TSI and is shown in Figure 2.
Table 2 – November 14, 2016 Dudley Pond Water Quality Data
Figure 2 – Carlson Trophic State Index Results for November 14, 2016, 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 5.05 at a depth of one foot at Sample Point 27 to 6.96 at 5 feet at Sample Point 24. With the exception of the pH at one foot at Sample Point 27 there was very little variation in pH readings at each sample point, which may be due to mixing within the water column. The pH readings for November 14, 2016 were lower than previous years. The reason for this is unknown, but may be the result of a minimum of weed and algal photosynthesis occurring. It should be understood that as pH rises various forms of TP such as iron and aluminum salts, which are insoluble and biologically unavailable, become soluble and bio-available. During an algal bloom carbon dioxide in the water column is consumed by the algae resulting in an increase in the pH and the conversion of TP into orthophosphate and more algae. DO Percent Saturation – DO percent saturation measurements ranged from 81.8 % found at a depth of 12 feet at Sample Point 25 to 91.2 % at 5 feet at Sample Point 24. DO Percent Saturation measurements did not vary much throughout the water column indicating good mixing and minimum bacterial decomposition and photosynthesis. Temperature – The temperature ranged from 8.4 C at a depth of 24 feet at Sample Point 25 to 10.7 C at 5 feet at Sample Points 24 and at 3 feet at Sample Point 27. The lack of variation in temperature throughout the water column indicates the presence of mixing. Oxidation Reduction Potential (ORP) – The ORP ranged from 176.1 mv at a depth of 5 feet at Sample Point 24 to 263.6 mv at a depth of 1 foot at Sample Point 27, which are similar to the ORP values that have been measured in the past and are within the values expected for a relatively healthy fresh water pond. ORP values were relatively uniform top to bottom at each of the sample points, but varied from sample point to sample point. The lack of ORP variation at each sample point is thought to be due to mixing, but the reason for ORP variation from sample point to sample point is not known. For more information regarding ORP see the following link. http://www.molecularhydrogenfoundation.org/core-information/oxidation-reduction-potentialorp-explained/ Secchi Depths – Secchi depth (a measure of color, turbidity and suspended solids, such as algae) on November 14, 2016 was 4 m. Accurate Secchi depths at Sample Points 24 and 27 could not be obtained because the bottom was clearly visible implying the Secchi depth was greater than the bottom depth. Therefore it has been assumed that the Secchi depths at Sample Points 24 and 27 were similar to that at Sample Point 25. It should be noted from the above that the pH, DO % saturation and the temperature at 5 feet at sample Point 24 were the highest and the ORP was the lowest for all of the readings taken on November 14, 2016. The reason for this is unknown, but may be due to the fact that data was gathered from 5 feet at Sample Point 24 last during the November 14, 2016 sampling. Samples/data were taken from Sample Point 27 at one foot at approximately 11:00 AM and from Sample Point 24 at 5 feet at approximately 1:00 PM. Phosphorus Concentrations – There was no detectable Ortho-phosphate found at any of the sample points. Total Phosphorus (TP) concentrations ranged from a low of ND at one foot at one and three feet at Sample Point 24 to high of 0.23 mg/l at a depth of 5 feet (bottom) at Sample Point 24. In view of the
relatively similar concentrations of TP at Sample Points 25 and 27 the concentration of 0.23 mg/l at the bottom of Sample Point 24 is thought to be an anomaly and therefore was not used to calculate the trophic index. This is the first time that any phosphorus compounds have been found in the fall samples taken by the SWQC. Ortho-phosphate 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. Because non-reactive TP species can be converted by natural processes into biologically available Ortho-phosphate there is concern that the elevated TP found on November 13, 2016, may portend a worse than usual 2017 weed/algae season. Nitrite/Nitrate – No nitrite was found at any of the sample points. Nitrate concentrations ranging from 0.09 mg/l to 0.1 mg/l were found at all of the sample points and at all depths. This is not unusual. For example, in 2011 the nitrate concentrations ranged from 0.15 mg/l to 0.24 mg/l. The relatively similar concentrations of nitrate found at all sample points and at all depths is most likely the result of mixing in the water column associated with the Fall “turnover” of the Pond. Total Kjeldahl Nitrogen (TKN) – TKN is a measure of the organic nitrogen plus ammonia nitrogen expressed as N. TKN concentrations were fairly similar for all samples points and at all depths, a further indication of water column mixing. These concentrations are within the range expected for relatively healthy fresh water ponds. Alpha Chlorophyll (Chlorophyll a) – On November 14, 2016 Chlorophyll a, an indirect measure of the algae concentration, ranged from ND at various depths at all three sample points to 3.3 ug/l (ppb) at the bottom of Sample Point 25. We have seen elevated Chlorophyll a concentrations at the bottom of Sample Point 25 in the past and believe that gravity may concentrate the Chlorophyll a at the bottom and therefore do not believe that the concentration of Chlorophyll a at the bottom of Sample Point 25 is representative of the water column and should not be included in the determination of the Trophic State Index (TSI). The Chlorophyll a concentrations found on November 14, 2016 were the lowest November concentrations recorded by the SWQC over the past six years. Low pH values, no supersaturation of oxygen, good water charity (Secchi depth of 4 m), the presence of Total Phosphorus and no Chlorophyll a found during the November 14, 2016 sampling suggest minimal photosynthetic activity, which may be due to measurable concentration of Fluridone in the Pond from April through November 2016. Mixing – Within the water column there was relatively little variation in the parameters. This lack of parameter concentration variation is thought to be the result of mixing that is common during the fall and spring turnovers of the Pond. The sample from the bottom of Sample Point 27 may have contained algae resulting in a minimal amount of Chlorophyll a [1.5 ug/l (ppb)]. Getting solids free samples was difficult at the bottom of Sample Points 24 and 27 because of the large amount of diffuse decomposing biomass on the bottom. Carlson Trophic State Index – As Dudley Pond is primarily used for recreational purposes a TSI less than 50 is tolerable and less than 40 would be great. Without including the Chlorophyll a concentration at the bottom of Sample Point 25 or the TP concentration at the bottom of Sample Point 24, the TSI on November 14, 2016 for the three sample points ranged from 40 to 45 indicating that the Dudley Pond trophic state index (TSI) was in the low to mid-mesotrophic range. The relatively high TP concentrations at Sample Points 25 and 27 were responsible for expanding the Trophic index range from 40 to 47. 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