Results of Water Quality Measurements in Messer Pond Bob Crane, Messer Pond Protective Association (MPPA) Board

Transcription

1 Results of Water Quality Measurements in Messer Pond Bob Crane, Messer Pond Protective Association (MPPA) Board The collection of water samples for the assessment of water quality in Messer Pond, New London, New Hampshire started back in the early 1980 s. A serious sampling campaign started in 1996 and continues to the present time. Data from the chemical analysis of the water samples has been archived by the New Hampshire Department of Environmental Services (NHDES). Depth profiles and time series of results from the NHDES archives are presented below. Data for 2005 have not been finalized and released to the archives as yet. Data from this year s campaign are presented as submitted to NHDES. Data were collected at the deep spot in the pond, at inlets to the pond from three small brooks, two draining the hillside above I-89 (Brown and Nutter inlets) and one draining Burpee and Knights Hills and flowing in from County Rd., and at the Bog Rd. outlet (see map on next page). Temperature and dissolved oxygen profiles observed over more than a decade show the well mixed upper layer (Epilimnion) and the cool, stratified bottom layer (Hypolimnion) typical of deeper lakes and ponds in New Hampshire. The lower or bottom layer has a summertime temperature more than 5 to 10 C colder than the top layer and often contains very small amounts of dissolved oxygen. Dissolved oxygen levels lower than 2 milligrams / liter (mg/l) will not support fish life. In all but two years, the dissolved oxygen was above 2 mg/l, at depths above 3 meters (m), sufficient to support fish life over much of the pond. Temperature Profiles at the Deep Spot

2 2 Messer Pond

3 3 Dissolved Oxygen Profiles Highly acidic water, with a ph less than 5.5 limits fish growth and reproduction. The ideal ph range for a freshwater fishery is between 6.5 and 7.0. NHDES considers the ph range from 6.1 to 8.0 satisfactory for the survival and reproduction of fish and other aquatic life. The upper layer, above about 2 m, the epilimnion, is generally in the ideal range for aquatic life; the hypolimnion is not. The time series values for the ph in two of the inlet brooks were often too acidic to be satisfactory, but the surface water and the water in Nutter brook and the outlook brook were adequate for aquatic life. The acidic neutralizing capacity (ANC) of the water in the upper layer of the pond was sufficient to neutralize the acidity of the inlet brooks. However, given the recorded values shown below, NHDES considers the pond moderately vulnerable to possible increases in acidity. The conductivity of water in inlet brooks and pond is an indication of the concentration of ionic particles and is used to estimate the amount of total dissolved salts (TDS). NHDES considers conductivity values greater than 100 microsiemens / centimeter (µs/cm) to be indicative of human activity. Typical sources of large amounts of TDS are road salts, agricultural runoff, septic systems, forestry operations, sediments from gravel roads, and decomposition of organic material in the hypolimnion. Increases in the total phosphorous in the lake can contribute to increased algae growth that, in turn produces the organic material that settles to the bottom and decomposes.

4 ph Time Series 4

5 5 ANC Time Series The conductivity values in both the epilimnion and lower layers at the deep spot in the pond are approximately the same. Up until 1998 and this year, the values are below the level indicative of human activities but above the average for lakes and ponds in New Hampshire. The conductivity time series for the inlet brooks show the effects of human activity for both Brown and Nutter inlets. The peak value for Brown inlet is as high as the most affected pond in Manchester, New Hampshire. The residence time for road salt contamination is quite long. The high values obtained in the summer when the samples were taken could be caused by road salt deposited in prior winters. The brooks that feed both Nutter and Brown inlets flow from higher on the hill across I-89 from the pond. Agricultural use of the land, construction, or forestry operations anywhere along the brook could cause the high-observed values. A series of water samples should be collected along the brook both above and below I-89 to ascertain the source of the contamination. The County Rd inlet shows little contamination and, the mixing of water with high conductivity values with the rest of the water in the upper layer of the pond produces a much slower variation in conductivity through the years with a gradual return to acceptable levels. The total phosphorous values for both the epilimnion and hypolimnion layers at the deep spot show periodic spikes that reach high to excessive values (in micrograms / liter, µg/l). These variations illustrate the variability of plant nutrients in the water. The total phosphorous content of water in the brooks feeding the Nutter and Brown inlets are well above average and spend much of their time in the excessive to extreme range. The size of the pond relative to the amount of water input from the two brooks reduced the

6 6 problem. The values in the upper layer at the deep spot and in the outlet brook are in the average range for a New Hampshire lake. Conductivity Time Series

7 Total Phosphorus Time Series 7

8 8 Chlorophyll-a Density and Turbidity Time Series The pond water responds to increases in total phosphorous by producing algae. The resultant concentration is estimated by the chlorophyll-a concentrations. NHDES considers chlorophyll-a concentrations greater than 10 mg/m 3 at a depth of 3 m, i.e. in the metalimnion, an indication of an algae bloom. From the record, the pond experienced a bloom in The algae, when it dies and settles to the bottom can increase the turbidity in the hypolimnion. A spike in the turbidity time series immediately followed some of the increases in the chlorophyll-a concentrations. The median value for turbidity in New Hampshire is 1,0 NTU. Extreme values of turbidity were observed at the Brown inlet in 2004 and again this year. These high values could be caused by construction or forestry operations upstream from the inlet.

9 Turbidity Time Series 9