2009 circulator performance report final

2009 Dudley Pond Circulator Evaluation Report

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March 2010/by Toni Moores, SWQC

Introduction This report summarizes the third year of a testing program to understand the impact of pond circulators on water chemistry associated with milfoil growth in Dudley Pond. This report contains a summary and conclusions, methods, results and a discussion of the results. This water chemistry testing report is part of an evaluation of the use of pond circulators for the management of Eurasian Watermilfoil (milfoil) in Dudley Pond required by the Wayland Conservation Committee and funded by the Community Preservation Committee. Summary and Conclusions The Wayland Surface Water Quality Committee (WSWQC) voted to continue the evaluation of pond circulators during the 2009 growing season even though Dudley Pond was treated with the herbicide Sonar in May of 2008. This report focuses on Dudley Pond water chemistry as it was impacted by the pond circulators and was essentially the same water chemistry evaluation program as executed in 2007 and 2008, except that analysis of nutrients was not done due to the unremarkable results in 2008 and 2009. This section is a summary and conclusion of the impact of the pond circulators on various water chemistry parameters in Dudley Pond for 2009. During the 2009 growing season it does not appear that the pond circulators had a significant impact on the water chemistry of Dudley Pond, as summarized below. History:

Three Eco-Guide SunGo model 001 circulators were placed in Dudley Pond during the third week of May 2007 at the locations shown on Figure 1. The locations of the circulators were selected by the circulator manufacturer, Eco-Guide.

During the summer of 2007 the Pond weeds in the Pond were mechanically harvested.

In May of 2008 the Pond was treated with an herbicide by the trade name of Sonar in an attempt to manage the milfoil in the Pond.

The circulators continued to operate in 2009 and 2008 in the same locations as 2007.

The circulator evaluation program for 2009 was the same as in 2008 and was designed to measure the degree of mixing, the changes in water chemistry and clarity. However, in-situ samples were not analyzed for N and P and milfoil bio-mass was not tracked because of the lack of significant differences during 2007 and 2008.


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Measures

Water Clarity Why is water clarity important to measure as it relates to the performance of the pond circulators? The cloudiness of lake/pond water and how far down you can see is often related to the amount of nutrients in the water. Nutrients promote growth of microscopic plant cells (phytoplankton) that are fed upon by microscopic animals (zooplankton). Nutrients, particularly soluble nitrogen and phosphate compounds, also promote the growth of weeds such as milfoil. The more the nutrients, the more the plants and animals and the cloudier the water becomes. This condition, called eutrophication, is a natural aging process of lakes, which is unnaturally accelerated by excess nutrients. When these plants and animals die and biologically decompose, large amounts of dissolved oxygen in the water are consumed resulting in stress on animals that require dissolved oxygen for respiration. Water clarity is a general indication of the health of a lake/pond. Clear is generally an indication of good water quality. A lack of clarity is generally an indication of poor water clarity.

1. Water clarity, as measured with a Secchi disc during 2009, did not appear to be any better or worse in the circulated areas of the Pond near sample points SA, SB, SC and SD than in the non-circulated area of the Pond near sample point SX.

2. Water transparency data for the past three years is shown in the following table.

Spring Mid-Season Fall

Year Secchi Range (m) Secchi Range (m) Secchi Range (m)

2007 - 1.4 – 2.1 2.4 – 3.8

2008 2 – 2.8 2.3 – 2.8 3.0 – 4.2

2009 3 2.1 – 2.6 3.0 - 4.4

Table 1 - Annual Secchi Disc Ranges

With low Secchi measurements being worse and high Secchi measurements being better, it appears that there has been an improvement in water transparency over the three years of data gathering. The reason for the improvement in transparency is not known.

Temperature Why is an understanding of temperature in Dudley Pond important as it relates to performance of the pond circulators?


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Biological activity in ponds/lakes occurs between 10 – 40 C. For every 10 degree C increase in temperature most biological reaction rates double. The rate of nitrification of ammonia is at a maximum rate between 30 – 35 C and ceases at low temperature of 10 C and a high of 40 C. Knowing if a thermocline (temperature discontinuity) exists within a pond’s water column is helpful assessing the mixing of water in deeper areas of the pond. For more information on thermoclines see the discussion on pages 8 and 24.

1. One would expect there to be less of a temperature gradient from the surface to the bottom in the circulated areas of the Pond than in the non-circulated areas do to mixing – this was not the case. Based on this finding it does not appear that the circulators had an impact on the temperature of the water column.

2. Measured temperature extremes and locations for three years of testing are presented in Table 2.

2007 2008 2009

High Temp C Location Depth ft Date

25.72 Sample Point C

1 July 21


1 August 27

25.58 Sample Point D

1 August 9

Low Temp C Location Depth ft Date

7.13 Sample Point X

9 November 18

10 Sample Point D

Bottom April 25

9.6 Sample Point B

Bottom November 8

Table 2 - Yearly Extremes, Measured Temperatures

3. Temperatures of Dudley Pond were taken at 3 foot intervals near the deepest

area of the Pond as shown in Figure 2 and a thermocline was found at approximately 12 feet, below which no natural mixing of the water column occurs and very little photosynthesis occurs. During cold periods, the coldest water is on top while during warm periods, the coldest water is on the bottom. The thermocline disappears with the spring and fall turnover.

Dissolved Oxygen (DO) Percent Saturation Why was it important to measure dissolved oxygen (DO) during the evaluation of the pond circulators? Since nitrification of ammonia is possible only above a concentration of 2 mg/l DO and denitrification occurs only when the DO is less than 2 mg/l, it is important to know the concentration/percent saturation of DO in order to understand the nitrogen cycle in the water column as it applies to milfoil growth.


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1. The circulators did not appear to have made a difference in the saturation of dissolved oxygen in the Pond.

2. Measured extremes in dissolved oxygen as a percent of saturation at locations and dates for three years of testing are shown in Table 3.

2007 2008 2009

High DO % Location Depth ft Date


1 November 18

167 Sample Point C

9 April 25

125 Sample point C

Bottom April 24

Low DO % Location Depth ft Date

50.6 Sample Point D

Bottom October 14

28.1 Sample Point X

Bottom July 10

85.4 Sample Point B

Bottom August 9

Table 3 - Yearly Extremes, Measured Dissolved Oxygen Percent of Saturation

It is not clear why the extremes in dissolved oxygen as a percent of saturation were greater in 2008 than in 2007 or 2009; however, the low DO % in 2009 was considerably greater than in 2007 and 2008 may be due to better mixing due to the fact that there were fewer weeds present allowing better mixing and more sunlight penetration.

3. On August 9, 2009 the dissolved oxygen as a percent of saturation near the deepest area of the Pond was 101.9 % at three feet and 1.4 % at 25 feet.

pH Values pH is a measure of acidity and alkalinity. Why was it important to measure pH during the evaluation of the pond circulators? Most lakes/ponds have a pH in the range of 5.5 – 9.0., The pH value can indicate that bacterial decomposition and photosynthesis is taking place. pH varies from close to 9 near the surface in bright sun light to slightly less than 6 at the bottom where sunlight does not penetrate and biological decomposition of organic materials is occurring producing carbon dioxide, an acid. The optimum pH for biological oxidation of ammonia to nitrate is 7.5 – 8.5.

1. In 2009 the pH at Sample Point X (non-circulated) was relatively high near the surface and relatively low at the bottom when compared to the more uniform pH ranges, top to bottom, at the other sample points. This difference could have been due to a lack of mixing in the vicinity of Sample Point X.

2. Measured extremes in pH values at sample points and dates for three years of

testing are shown in Table 4.


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2007 2008 2009

High pH Location Depth ft Date

8.42 Sample Point A

1 October 14

9.33 Sample Point X

3 November 18

8.29 Sample Point X

1 April 24

Low pH Location Depth ft Date

7.02 Sample Point X

9 July 21

6.98 Sample Point B

Bottom July 10

6.43 Sample Point X

1 April 24

Table 4 - Yearly Extremes, Measured pH Values

3. The shape of the pH curves were remarkably like the shape of the water clarity

curves, with the highest values recorded during the April and November samplings. It is believed that the cold water temperatures in April and November were responsible for slowing the rate of biological degradation and associated carbon dioxide (an acid responsible for depressing pH) production and sunlight penetration (water clarity) was greatest in April and November increasing the rate of carbon dioxide consumption via photosynthesis.

Oxidation-Reduction Potential Oxidation- Reduction Potential (ORP) is the activity or strength of oxidizing and reducing compounds in relation to their concentration contained in the water column. ORP is measured in millivolts (mv). Why is ORP an important parameter to measure in Dudley Pond? The most popular theory as to why pond circulators can be effective is that milfoil obtains its required nitrogen nutrients from ammonia. Nitrates are apparently not useable by milfoil to satisfy its nutritive needs for nitrogen. At ORP values in the +100 to +350 range oxidation of ammonia to nitrate is possible. At ORP values in the -50 to +50 range, nitrates can be biologically denitrified to gaseous nitrogen and bubble out of the pond water.

1. In 2009 circulation of the Pond did not appear to have an impact on the oxidation-reduction potential.

2. Measured extremes in oxidation-reduction potential values and dates for three years of testing are shown in Table 5.


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2007 2008 2009

High ORP (mv) Location Depth ft Date

217.2 Sample Point A

3 October 14

203.2 Sample Point X

1 October 6

210.5 Sample Point B

1 April 24

Low ORP (mv) Location Depth ft Date

-102.1 Sample Point B

Bottom September 15

-106.1 Sample Point C

Bottom July 10

-152 Sample Point A

Bottom August 9

Table 5 – Yearly Extremes, Oxidation-Reduction Potential

3. If one assumes that in order to minimize milfoil growth, pond circulators must

create conditions where ammonia is biologically converted to nitrate; therefore the ORP in the water column and presumably the root zone must be above +100 mv. Sample Point X was the only sample location where an ORP of greater than +100 mv measured throughout the water column on all three sampling dates. No ORP data was gathered from the root zone. As a point of interest, the ORP was almost constant with depth at Sample Point X for all three sampling dates in 2009. Since the water column at Sample Point X was not close to a pond circulator, one would have expected that the ORP variation with depth at Sample Point X would have had the greatest variation of all the sample points.

Trophic State Index – combining measures for an overall view A trophic state index is a convenient way to quantify the health of a water body with regard to nutrients and based on Secchi depths, total phosphorus (P) and alpha chlorophyll relationship shown in Figure 9 on page 23. One popular index was developed by Dr. Robert Carlson of Kent State University. Trophic states range from oligotrophic on the good end of the scale through mesotrophic, to eutrophic and hypereutrophic on the bad end of the scale. High trophic indexes correspond to poor water quality and low trophic indexes correspond to good water quality.

1. Although Secchi depth was the only parameter used during 2009 to evaluate the Pond’s trophic state, the trophic state of the pond ranged from 42 to 49 with an average of 45.3, which places the Pond solidly within the mesotrophic range.

2. Trophic index states for 2007, 2008 and 2009 based on total P plus Secchi depth and for Secchi depth alone are shown below in Table 6.

http://bioweb.biology.kent.edu/FacultyandStaff/carlson.html


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2007 2008 2009

Based on Tot. P & Secchi Depth Trophic Index Range Average Trophic Index Trophic State

49 – 72 61

Eutrophic

42 – 75

58 Eutrophic

No TP analysis

Based on Secchi Depth only Trophic Index Range Average Trophic Index Trophic State

47 – 53

50 High

Mesotrophic

42 – 52

47 Mesotrophic

42 – 49

45.3 Mesotrophic

Table 6 - Trophic State Indexes – 2007, 2008 & 2009, with & w/o Total P

Analyses

3. Clearly the concentration of total P in the Pond has a significant impact on the trophic state index. Since the total P analyses done by SWQC in 2008 did not agree with the random samples sent to an outside laboratory, the trophic indexes based on Secchi depths plus total P may not be useful.

4. It did not appear that the pond circulators had any effect on the trophic index of the Pond during 2009.


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Methods This section summarizes the methods that were used to evaluate the effectiveness of pond circulators on water chemistry in relation to milfoil in Dudley Pond. Water Clarity – A Secchi disc was used to measure the clarity of the Pond water at the five sample locations; SA, SB, SC, SD and SX as shown in Figure 1. A Secchi disc was lowered into the water via a rope graduated in feet and also meters until the disc could no longer be seen from the boat on the surface. Secchi disc data was gathered on April 24, 2009, August 9, 2009 and November 8, 2009. In-situ Water Quality Parameters – A number of water quality parameters were measured at one foot, three feet, six feet, nine feet intervals and at the Pond bottom at each of the sample locations (SA, SB, SC, SD, SX). The parameters that were measured were conductivity, temperature, pH, dissolved oxygen, percent dissolved oxygen saturation and oxidation reduction potential (ORP). The date, time and barometric pressure were also recorded at the five sample points. The data was gathered by means of an YSI 556 Multimeter with the sensors attached to a 10 meter cable, which was graduated in foot increments. The sensors were lowered into the water and data was gathered at one foot, three feet, six feet, nine feet and at the Pond bottom. A link to information regarding the YSI 556 can be found in the appendix of this report. The YSI meter and sensors were calibrated before each data gathering session per the manufacturer’s instructions. In-situ water quality data was gathered on April 24, 2009, August 9, 2009, and November 8, 2009. Trophic Index - Secchi disc data was gathered at each of the five sampling points SA, SB,

SC, SD and SX on April 24, 2009, August 9, 2009 and November 8, 2009. Alpha chlorophyll and total phosphorus data normally included as a component of the trophic index were not gathered because of the cost and lack of remarkable results in 2007 and 2008. Secchi disc depths were plotted on a trophic index bar graph for each date. Thermocline Depth – On August 9, 2009 water temperature, percent saturation dissolved oxygen and ORP were measured with the YSI Multimeter at 3 foot increments starting at the surface and terminating at the bottom of the Pond (25’). Figure 2 indicates the location that the thermocline data was gathered.


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Figure 1

Dudley Pond Circulators, Sample Points & Weed Squares (CJ Peters)

Circulators – Circles A, B, C Sample Points – Triangles - SX, SA, SB, SC, SD Weed Squares – X1 - X6 & E1 – E6


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Figure 2 – Location of Sample Point for Thermocline Data


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Results This section presents the results obtained via the methods summarized in the previous section. The results of the water clarity (Secchi disc), in-situ analyses and the weed nutrients appear in Tables 7 - 10. The following notes apply to Tables 7 - 9.

MEASURE SYMBOL UNITS DESCRIPTION

Sample Points Sp Pt Lat/lon Locations of sample points A, B, C, D, and X are marked on Figure 1.

Depth D feet Depth is measured from the water surface to the bottom. The Pond bottom is denoted as 99 with the bottom depth from waterline shown in the sample point column. It should be noted that 99 and 10 were used interchangeably when graphing data.

Water Clarity Sec meters The depth at which a Secchi disc is no longer visible

Temperature Temp C Degrees Centigrade

Conductivity Cond Micor Siemans/cm Electrical conductivity

Dissolved Oxygen Pct DO% Percent Oxygen saturation for the temperature and barometric pressure

Dissplved Oxygen DO mg/l Milligrams per litre Absolute amount of dissolved oxygen

pH pH Standardized units Acidity – alkalinity

Oxidation Reduction Potential

ORP Millivolts Tendency to oxidation or reduction chemical reactions

Barometic Pressure Barom Mm of mercury Atmospheric Pressure

Time Time of Day Hours/Minutes 24 hour time

The thermocline data collected on August 9, 2009 is presented in Table 10.


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Table 7

Date 4/24/09 By Ted & Toni Weather: Sunny, 70F, Breeze Circulators moved to summer locations on 4/17 but not operating

File Name Sp Pt D ft Sec m Temp C Cond mS/cm DO % DO mg/l pH ORP mv Barom Time NH3 N ppm NO3 N ppm P ppm

Dudley A 1 3 13.62 0.4 113.7 11.76 6.83 208 770.4 15:03

3 13.45 0.401 113 11.76 6.82 207.4

6 12.95 0.4 113.3 11.95 6.83 206

9 12.88 0.4 115.7 12.2 6.87 201.8

14' 99 12.87 0.4 114.9 12.1 6.92 191.2

Dudley B 1 3 13.68 0.4 115.5 11.97 7.09 210.5 770 15:31

3 13.65 0.4 115 11.74 7.08 208

6 13.33 0.399 116.8 12.19 7.08 206.8

9 13.06 0.399 118.1 12.44 7.12 203

10' 99 13.02 0.399 120.8 12.74 7.44 42.8

Dudley C 1 3 13.81 0.401 114.7 11.84 7.42 115.3 769.9 15:44

3 13.8 0.401 113.9 11.79 7.39 116.6

6 13.78 0.4 113.3 11.74 7.39 117.5

9 13.36 0.399 118.3 12.63 7.46 110.6

10' 99 13.06 0.398 125.8 13.32 7.57 -68.4

Dudley D 1 3 13.65 0.4 114.2 11.84 7.55 85.5 769.7 15:53

3 13.63 0.4 113.7 11.8 7.52 87.3

6 13.59 0.4 113.4 11.78 7.51 87.9

9 13.32 0.4 115 12.15 7.53 84.8

12' 99 13.06 0.399 117 12.2 7.55 54.8

Dudley X 1 3 13.56 0.396 113.6 11.75 6.43 207 770 14:47

3 13.46 0.399 114 11.84 6.48 208

6 12.79 0.399 115.5 12.2 6.56 204.8

9 12.69 0.399 116.7 12.39 6.6 199.7

11' 99 12.59 0.399 115.5 12.21 6.74 182.1

Low High

Dudley Pond In-Situ Water Quality Data Sheet


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Table 8

Date 8/9/09 By Mike amd Toni Weather - Overcast, light wind, 70 - 75 F


Dudley A 1 25.52 0.348 103 8.42 7.95 163.4 769.5 9:33

3 25.52 0.348 102.6 8.39 7.95 160.9

6 25.51 0.347 102.2 8.36 7.95 159.5

9 25.49 0.348 101.8 8.32 7.95 157.5

13' 99 2.5 25.17 0.345 94.2 7.75 7.86 -152

Dudley B 1 25.52 0.348 103.1 8.45 7.94 17 769.3 9:51

3 25.52 0.348 102.7 8.4 7.96 21.9

6 25.42 0.347 102 8.35 7.96 26.6

9 25.16 0.346 99.7 8.2 7.95 28.9

10' 99 2.3 25.22 0.344 85.4 7.22 7.79 -132.5

Dudley C 1 25.5 0.348 102.2 8.36 7.9 3.5 769.3 10:03

3 25.51 0.348 100.1 8.19 7.92 15.5

6 25.47 0.347 98.9 8.09 7.9 22

9 25.31 0.347 98 8.03 7.87 25.3

10' 99 2.1 25.3 0.346 93.5 7.7 7.82 -29

Dudley D 1 25.58 0.349 102.7 8.4 7.94 32.8 769.3 10:18

3 25.57 0.349 103.1 8.41 7.95 31.5

6 25.55 0.348 102.5 8.37 7.96 33.1

9 25.54 0.348 101.7 8.31 7.96 34.7

12' 99 2.1 25.45 0.347 97.5 8.02 7.93 -20

Dudley X 1 25.5 0.347 100.2 8.2 8.29 165 769.2 9:17

3 25.47 0.347 98.4 8.06 8.18 163.2

6 25.45 0.347 98 8.02 8.1 163.1

9 25.36 0.346 97.4 7.99 8.03 161.8

12' 99 2.6 25.36 0.346 91.3 7.67 7.54 138.4

Low High



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Table 9

Date: Nov 8, 2009, By: TM & ML Weather: Sunny w/ Light Breeze


Dudley A 1 9.8 0.342 90.7 10,24 7.55 143.1 771 13:32

3 9.8 0.342 91.6 10.42 7.53 144

6 9.82 0.342 94 10.62 7.53 142.4

9 9.82 0.342 93.3 10.55 7.52 142.2

on bottom 99 4.4 9.68 0.342 93.7 10.66 7.52 141.2

Dudley B 1 10.43 0.342 94.4 10.57 7.5 140 771.2 13:45

3 10.39 0.342 95 10.61 7.49 140.4

6 9.88 0.342 96.8 10.93 7.49 139.4

9 9.58 0.342 101.2 11.53 7.49 138.5

on bottom 99 3 9.6 0.342 103.8 11.81 7.51 138.3

Dudley C 1 10.34 0.342 95.3 10.63 7.44 129.5 771.2 14:11

3 10.24 0.342 94 10.53 7.41 131.3

6 10.15 0.342 93.8 10.55 7.4 132.2

9 9.88 0.342 96.5 10.92 7.46 128.2

on bottom 99 3 9.87 0.342 95.7 10.82 7.42 71.8

Dudley D 1 10.25 0.342 92.2 10.36 7.49 136.5 771.3 13:58

3 10.09 0.342 92.4 10.39 7.47 137.4

6 10.04 0.342 92.3 10.4 7.45 137.5

9 9.94 0.342 92 10.38 7.43 138.3

bottom 4.5 99 3.5 9.78 0.342 93.3 10.56 7.42 123

Dudley X 1 9.94 0.342 91.6 10.34 7.36 111.1 771.6 14:31

3 9.89 0.342 90.9 10.34 7.36 112.2

6 9.78 0.342 91.3 10.36 7.37 112.3

9 9.7 0.342 91.9 10.44 7.37 111.4

on bottom 99 3.3 9.68 0.342 94 10.66 7.37 110.8

Low 248.37

High Avg



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Table 10 Thermocline Data (Aug 9, 2009)

Depth ft Temp C DO % ORP mv

3 25.53 101.9 5.5

6 25.49 101.1 9.5

9 25.45 98.3 14.8

12 25.34 96.4 17.5

15 22.83 64.1 53

18 19.85 21.2 71.5

21 16.87 76 69.4

25 14.18 1.4 -123.4


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Discussion This section contains a discussion of the results found in Tables 7 – 10 in the previous section of this report. Water Clarity - When Secchi disc measurements from Tables 7 – 9 are plotted as in Figure 3 one gets an indication as to how the water clarity of the Pond water varied over the 2009 growing season in the circulated areas and the non-circulated areas of the Pond.

Figure 3 - 2009 Secchi Disc Measurements, Depths vs. Sample Dates

Based on the Secchi disc depth measured during the 2009 season, it does not appear that the circulators had much impact on water clarity – the pattern was not different between the sample points A-D and the control point X.


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For comparison of water clarity Secchi disc depths taken during 2008 are shown in Figure 4 below.

Figure 4 - 2008 Secchi Disc Measurments, Depths vs Sample Dates

A comparison of Figures 3 and 4 suggests that the water clarity in Dudley Pond was marginally better in 2009 than in 2008 at most of the sample points. The reason for this slightly improved water clarity is not apparent. Temperature Figure 5 is a graphical presentation of the temperatures of Dudley Pond at various depths, at the five sample points on three sampling dates during 2009. In general the temperatures in the Pond decreased with depth on all sampling dates. However, there was less than a 1.2 C temperature difference top to bottom on any of the sampling dates. One would have expected that the greatest temperature difference with depth would have been at sample point X (unmixed area) particularly during April and November. This was not the case. The highest temperature measured in 2009 was 28.58 C measured at Sample Point D at a depth of one foot on August 9th. The lowest temperature measured during 2009 was 9.6 C at the bottom at Sample Point B on November 8th. It does not appear that the circulators resulted in a more uniform temperatures in the water column associated with the circulated sample points (Sample Points A, B, C, & D). Temperatures measured during the 2008 sampling season compared to 2009 were unremarkable.


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Figure 5 - 2009 Temperature versus Depth Profiles


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Dissolved Oxygen – The dissolved oxygen (DO) in most ponds is a function of photosynthesis (oxygen produced), bacterial decomposition (oxygen consumed) of organic material, the air-water interface, temperature, depth, and wind velocity. The DO near the surface can be supersaturated during bright sunshine due to potosynthesis. The DO can approach zero at the bottom of a pond in the absence of sunlight, particularly during warm summer months, where organic matter is being decomposed and oxygen is being consumed by decomposing organic material (weeds). These effects are apparent in Figure 6 below. It should be noted that in the Spring or Fall when sunlight penetrates to the bottom of a pond facilitating photosynthesis by benthic algae and when water temperatures are cold impeding biological decomposition and oxygen consumption, it is possible to have oxygen supersaturation throughout the water column. The YSI Multimeter used to gather DO data automatically compensates for temperature and barometric pressure and provides data regarding the DO as a percent of saturation. Percent DO in a pond is usually more useful and easier to understand than the uncompensated DO concentration in milligrams per liter. The current theory put forth by pond ciculator proponents states that pond circulators mix the water column providing DO throughout entire water column and presumably the root zone allowing nitrifying bacteria to oxidize ammonia, a critical nutrient that the milfoil need for growth. With the ammonia oxidized to nitrate, the milfoil is starved for ammonia and growth is limited. However, the DO in mg/l must be above about 2 mg/l in order for nitrification to occur. The lowest DO measured in the circulation test area during 2009 was 7.22 mg/l at the bottom at Sample Point B on August 9th. This means that it was possible for nitrification of ammonia to occur within the water column; however, since no DO data was collected in the root zone, it is not clear whether nitrification of ammonia was possible in the root zone where most of the nutrients are assimilated into the milfoil plants The dissolved oxygen was relatively constant at all sample points throughout 2009, particularly during the August 9th sampling when algal photosynthysis is maximized. The fact that low DOs are not seen at the bottom at Sample Point X (no circulation) during the August 8th indicates that the circulators were having very little impact.


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Figure 6 - 2009 Dissolved Oxygen Percent Saturation versus Depth Profiles


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pH – Technically pH is an inverse logarithmic representation of the hydrogen ion concentration; however, pH is more generally understood as a measure of the acidity or alkalinity of an aqueous solution. High pH values (7- 14) indicate alkaline conditions. Low pH values (1 – 7) indicate acidic conditions. Most biological reactions occur in a pH range of 5 – 9. In a fresh water pond with active photosynthesis, near mid-day on a clear day, the pH can be in the 8 – 9.5 range because photosynthesis is consuming the weak acid carbon dioxide and producing oxygen. At night the pH of a pond can become slightly acidic (pH = 5 – 7) because the concentration of carbon dioxide is increasing due to biological oxidation of organic material producing carbon dioxide and a lack of carbon dioxide consuming photosynthesis. The pH in most bodies of water is a function of the natural buffering chemicals present and the amount of photosynthesis and biodegredation occuring. Given that the highest rate of photosynthesis occurs where the sunlight is the brightest, pH is usually the highest during daylight hours near the surface of the water and lowest at night near the bottom where more carbon dioxide is being produced due to the conversion of organic material to carbon dioxide. As noted before, high pH values can occur at depths early or late in the growing season when the water is cold and sunlight penetrates to the bottom. Figure 7 presents the pH profiles as a function of depth for all sample points for the three 2009 sampling dates. The range of pH values for Dudley Pond in 2009 was unremarkable for a fresh water pond, with a low pH of 6.43 at a depth of one foot depth at Sample Point X on April 24thth and a high pH of 8.29 at a depth of one foot on August 29th at Sample Point X. During 2008 the low pH of 6.98 was found at the bottom of Sample Point B on July 10th and a high pH of 9.33 at a depth of one foot on November 8th at Sample Point X. The reason for generally lower pH values found during 2009 when compared to 2008 is not known, but could be due to the decomposition of larger amount of biomass (milfoil) in the bottom of the Pond, resulting from the 2008 application of herbicide, producing carbon dioxide (a weak acid) and/or the nitrification of ammonia resulting in the consumption ammonia a weak base and the production of a strong acid (nitrate) during 2009. The fact that the pH profile for Sample Point X was the lowest of all the sample points during the April and November samplings seems supports the decomposing weed theory. Additionally, since nitrification does not occur at temperatures less than 10 C, the lower pH values found during April and November were probably not due to nitrification of ammonia. The range of pH values for Sample Points A – D during the August 9th sampling are relatively small compared to the pH range for Sample Point X on the same date. Mixing in the vacinity of Sample Points A - D is thought to indicate more water column homogenaity, whereas the broader pH range in the vicinity of Sample Point X on August 9th is thought to be an indicator of less mixing. This larger pH range for Sample Point X is one of the few indications of the impact of the circulators found during 2009.


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Figure 7 - pH versus Depth Profiles


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ORP - Oxidation Reduction Potential is the activity or strength of oxidizing and reducing compounds in relation to their concentration contained in the water column. ORP is measured in millivolts (mv). Why is ORP an important parameter to measure circulator in Dudley Pond? The most popular theory as to why pond circulators are effective is that milfoil obtains its nitrogen nutrients from ammonia. Nitrates are apparently not useable by milfoil to satisfy its nutritive needs for nitrogen. Therefore if the water in a pond is circulated distributing dissolved oxygen throughout the water column, the ammonia that is present will be biologically oxidized to nitrates and very little ammonia will be available as a nutrient for the milfoil.

Ammonia in Dudley Pond comes primarily from decaying vegetation and algae, rain water runoff containing fertilizers and incompletely treated septic tank leachate. Ammonia can be biologically oxidized to form nitrate, primarily in the upper portions of the water column where dissolved oxygen from photosynthesis is plentiful. Nitrification is the oxidation of ionized ammonia (NH4+) to nitrate (NO3-) and is performed by nitrifying bacteria when the ORP of the water is in the range of +100 to +350 mv. Nitrifying bacteria are not very robust and are relatively sensitive to pH and temperature. Not much nitrification occurs at temperatures below 10 C or at pH values outside the range of 5 to 9. The oxidation of ammonia to nitrate removes alkalinity (ammonia) from the water producing an acid (nitrate) and is accompanied with a decrease in pH, which usually has a small impact on pH because of the buffering present in most pond waters.

De-nitrification is the reduction of nitrate (NO3-) to molecular nitrogen (N2 gas) and is performed by many types of bacteria when the ORP of the water is in the range of +50 to -50 mv. De-nitrifying bacteria are more robust and ubiquitous than nitrifying bacteria and can function in broader ranges of pH and temperature. Most de-nitrification occurs near the bottom of the pond where the ORP is low and there is very little, if any, dissolved oxygen present. Since nitrogen gas bubbles are formed and bubble out of the water, de-nitrification is a way that nitrogenous compounds are removed from the Pond’s nitrogen cycle. ORP versus depth profiles for 2009 are presented in Figure 8 on the following page. During 2009 the highest ORP value of 210 was recorded at Sample Point B at a depth of one foot on April 24th. The lowest 2009 ORP value of – 152 mv was recorded at Sample Point A at the bottom on August 9th. During 2008 the highest ORP value of +203.2 mv was recorded at a depth of one foot at Sample Point X on October 6th and the lowest ORP value of -106.1 mv was recorded at Sample Point C at the bottom of the Pond on July 10th. Since an ORP value of >100 mv and a temperature of > 10 C is required for nitrification, nitrification was possible primarily during April, but not at all sample points. Denitrification can occur at ORPs in the +50 - -50 range and therefor most of the denitrification occued during August. With very little difference between the ORP range versus depth at Sample Pont X as compared the ORP ranges versus depth at the other sample points, it does not appear that the circulators had much impact on the ORP in the Pond.


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Figure 8 - Oxidation-Reduction Potential versus Depth Profiles


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Trophic Index – The cloudiness of lake/pond water and how far down you can see is often related to

the amount of nutrients in the water. Nutrients promote growth of microscopic plant cells

(phytoplankton) that are fed upon by microscopic animals (zooplankton). The more the nutrients, the

more the plants and animals and the cloudier the water is. This condition, called eutrophication, is a

natural aging process of lakes, which is unnaturally accelerated by excess nutrients. The concept of

trophic status is based on the fact that changes in nutrient levels (measured by total phosphorus)

causes changes in algal biomass (measured by chlorophyll a) which in turn causes changes in lake

clarity (measured by Secchi disk transparency). A trophic state index is a convenient way to quantify

this relationship. One popular index was developed by Dr. Robert Carlson of Kent State University.

Data shown in Table 11 was generated using 2009 Secchi disc information and the Carlson Trophic Index

format.

Table 11 - Trophic Indexes for 2009

Date Trophic Index Trophic State

April 24, 2009 45 Mesotrophic

August 9, 2009 49 Mesotrophic

November 8, 2008 42 Mesotrophic

2009 Avg 45.3 Mesotrophic

If average 2009 transparency alone was used to determine the trophic state index, the trophic state

index did not vary much for the three sampling dates. The average trophic state indexes, based on

transparency, for the three sampling dates were 45, 49 and 42, - all in the mesotrophic range as shown

in Figure 9.

Figure 9 - 2009 Carlson Trophic Index Based only on Transparency

http://bioweb.biology.kent.edu/FacultyandStaff/carlson.html


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It is expected that if Total Phosphorus data had been gathered, the trophic state index for 2009 would have been higher; however, the average trophic index (4.3) for 2009 was marginally lower (better) than the average (47.3) in 2008.

If Secchi disc measurements at each of the sample points are averaged for the 2009 season, as

presented in Table 12 below. The average Secchi disc measurements in the circulated area of the Pond

(2.91 m) was almost identical to the average Secchi disc measurement in the non-circulated area of the

Pond (2.93 m). As a result it does not appear that the circulators had any impact on the Secchi disc

measurements.

Table 12 - Average 2009 Secchi Measurements by Location

Location 2009 Average Secchi Depth

Sample Point A 3.3 m

Sample Point B 2.76 m

Sample Point C 2.7 m

Sample Point D 2.87 m

Sample Point X ( non-circulated) 2.93 m

Thermocline – A thermocline in a lake/pond is a discontinuity in temperature and usually related to

seasonal change in temperatures. Above the thermocline the water is relatively well mixed as a result of

wind and solar energy. In the summer the temperature above the thermocline is warmer and relatively

constant due to mixing and sun light. The water below the thermocline is colder. There is very little

mixing between the water above the thermocline and the water below the thermocline. As a result

dissolved oxygen below the thermocline is depleted and nutrients accumulate due to anaerobic

decomposition. There are usually no plants or algae below the thermocline because sunlight does not

usually penetrate to this depth making photosynthesis impossible. With fall the surface water cools until

it reaches 4 C, the temperature at which water is most dense and sinks to the bottom of the lake

replacing the water below the thermocline and the two layers tend to mix bringing nutrients to the

surface. In the spring the ice at the surface melts and the temperature of the water column becomes

homogeneous which again allows mixing of the water. The annual spring and fall mixing is referred to as

turnover. Further information can be obtained at http://www.ourlake.org/html/thermocline.html .

In Dudley Pond no thermocline exists in most of the pond because of the Pond is relatively shallow and

the water column is mixed by sunlight and some wave action; however, in the deepest area of the Pond

a thermocline usually exists. On August 9, 2009 measurements were taken in the deepest area of the

Pond. That data is presented in Figure 10.

http://www.ourlake.org/html/thermocline.html


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Figure 10 - Temperature, DO % Saturation & ORP versus Depth


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The discontinuity in the temperature profile at approximately 12 feet is an indication of the presence of a thermocline. The plot of dissolved oxygen versus depth is relatively typical until a depth of about 18 feet is reached where the dissolved oxygen increases until a depth of about 21 feet is reached, whereupon the dissolved oxygen decreases as the bottom (25’) of the Pond is approached. The relatively high dissolved oxygen percent saturation measured at 21 feet is either an error or there is some unexplained reason for this result, which is not reflected in the temperature profile. The ORP was found to be nearly zero near the surface of the water and the ORP increased with depth until a depth of about 21 feet was reached and then rapidly decreased as the bottom was approached. The increase in the ORP in the upper 12 feet at the point, where the thermocline was measured, was approximately the same compared to the ORP data gathered near the circulator test Sample Points B, C and D on August 9, 2009 (Figure 8). The reasons for the atypical dissolved oxygen profile at the thermocline location are not known. How does the thermocline found in Dudley Pond on August 9th relate to the pond circulators? Indirectly at best.

Most, if not all, of the milfoil plants in Dudley Pond are rooted at depths above the August 9th thermocline depth where there is some natural mixing occurs from sun and to a lesser extent from wind.

The dissolved oxygen (percent saturation) in the upper 12 feet, where the thermocline was measured, was essentially the same as the dissolved oxygen (percent saturation) in the vicinity of all the sample points in the circulator performance tests (on August 9th), including Sample Point X, which is not circulated.

The temperatures in the upper 12 feet, where the thermocline was measured, were essentially the same as the temperatures measured (on August 9th) at all the sample points in the circulator performance test, including Sample Point X, which was not circulated.


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Appendix

A

Analytical Procedures In-situ Chemistry Analyses via YSI 556 www.ysi.com/portal/page/portal/YSI_Environmental/Products/Product_Family/Product?productID=WQS_556

http://www.ysi.com/portal/page/portal/YSI_Environmental/Products/Product_Family/Product?productID=WQS_556

http://www.ysi.com/portal/page/portal/YSI_Environmental/Products/Product_Family/Product?productID=WQS_556

Documents

2009 circulator performance report final