Souhegan Watershed Association
Water Testing Results
Souhegan and Merrimack Rivers
The Souhegan Watershed Association monitors the entire length of the Souhegan River and the section of the Merrimack River between Manchester and Tyngsborough for their aquatic health. Water samples are tested for dissolved oxygen, temperature, turbidity, and bacteria. Occasionally also for pH and phosphorus as needed. Weather and streamflow information is also recorded when water samples are collected. Previous results, beginning in 1997, are available in reports that can be found in local libraries. Summaries and original results are available here.
Heavy metal testing and macroinvertibrate testing has also been done on occasion in the past
This monitoring program is conducted by trained volunteers who believe in cleaner rivers. Financial support for the program comes from your memberships and donations. If you would like to help continue this monitoring effort, please contact George May at 883-3409 or "georgemay (at) comcast (dot) net" or send a check to SWA, PO Box 1474, Merrimack, NH 03054.
E-Coli Bacteria Counts
This test shows how healthy the water is for human useOur E-coli samples are prepared and counted by professionals at the local wastewater treatment plants in Greenville, Merrimack, Milford, and Nashua on a volunteer basis. The results are reported as the number of e-coli bacteria colonies observed in 100 ml of water. Bacteria levels below 88 colonies per 100 ml. are considered safe for public swimming areas. Anything above that level may cause ear and eye infections, diarrhea or other gastrointestinal problems in a percentage of swimmers. These bacteria numbers being reported are good for only a few days. They do indicate the general health of the river water at a particular moment in time. The next measurement can be considerably different, depending on water level and temperature, and what has recently washed, flowed, or been poured into the river. The current E-coli results this year are available below.They are generally available the day after the test.
Dissolved Oxygen Measurements
This test shows the general health of the river itselfDissolved oxygen is "breathed" by fish and insects that live in the water. Dissolved Oxygen requirements for different species vary greatly, even if only fish are considered. One of the more sensitive family groups is trout. The lower limit for them is about 5 mg/L (or 5 ppm). The maximum value attainable is called O2 saturation. The concentration of O2 equal to the saturation limit in water increases with DECREASING temperature and INCREASING pressure. At 1 atmosphere pressure and 20 degrees centigrade the concentration of saturated O2 is 9.1 mg/L, while at 1 atmosphere pressure and 25 degrees centigrade O2 is saturated at 8.2 mg/L. The rate of oxygen usage, the rate of oxygenization (turbulence) and the rate of mixing of the different strata of water all contribute to surface oxygen levels.
The simplified conclusion is that adequate oxygen levels indicate a healthy, balanced river habitat.
Web pages by Richard Hart.