Water Quality Data

Basic water quality parameters have been monitored in the "deep spot" of the waterbody, as well as in its inlet and outlet, typically once a month in June, July, and August, since the year 2000. Monitoring procedures follow the New Hampshire Volunteer Lakes Assessment Program protocols.

View the table and graphs below for the annual average measurement of each water quality parameter for each of the Manchester urban ponds.

Annual water quality reports for each of the ponds can be found by visiting the Urban Ponds Restoration Program publications page or by visiting the New Hampshire Volunteer Lake Assessment Program website.

All Ponds Water Quality Tables 2000-2011

The following is a brief explanation of basic water quality parameters.

Temperature and Dissolved Oxygen

The dissolved oxygen concentration of a water body is directly related to temperature. At colder temperatures, water holds more oxygen than at warmer temperatures. Thus, summer dissolved oxygen concentrations are typically lower than those in cooler months. Dissolved oxygen levels are key to the health of a pond ecosystem. Aquatic organisms cannot survive in extremely low oxygen environments.

A dissolved oxygen (DO) and temperature profile is determined by measuring DO and temperature at each meter of depth from the water’s surface to the pond bottom. Deeper ponds experience pronounced thermal stratification, while in shallower ponds stratification is more subtle, if present at all. Due to biological processes that consume oxygen at the pond bottom, some ponds incur a dissolved oxygen deficit in the hypolimnion (bottom layer).

Pond stratification occurs when different temperatures exist at the top (epilimnion), middle (metalimnion), and bottom (hypolimnion) layers of the water column. Generally, the deeper a body of water, the more pronounced the stratification may become. This is mainly influenced by the amount of solar energy that reaches each water layer. As the sun becomes lower in the sky in the fall, thermal stratification lessens and usually disappears completely by winter.

“Typically, the deeper the reading, the lower the percent saturation of oxygen. Colder waters are able to hold more dissolved oxygen than warmer waters, and generally, the deeper the water, the colder the temperature. As a result, a reading of 9 mg/L of oxygen at the surface will yield a higher percent saturation than a reading of 9 mg/L at 25 meters, because of the difference in water temperature.” (NH Dept. of Env. Services, 1999).

pH

The lower the pH of water, the more acidic the water. The higher the pH of water, the more alkaline the water. Pond pH is crucial to the well being of pond dwelling organisms. A pH of less than 5.5 (acidic) has detrimental effects on fish growth and reproduction. A pH between 6.5 and 7.0 is considered ideal for freshwater ecosystems. The median pH for New Hampshire lakes is 6.7. (NH Dept. of Env. Services, 1999).

Acid Neutralizing Capacity

Acid Neutralizing Capacity (ANC) describes the ability of water to buffer against acidic inputs, like acid rain. This is also known as a lake’s alkalinity. The higher a water body’s ANC, the better it’s ability to buffer acidic inputs. Lakes with low ANC, typical of New Hampshire, are especially vulnerable to the effects of acid precipitation.

A desirable ANC for any lake is greater than 20 mg/L of CaCO. The average ANC for New Hampshire lakes is 6.5 mg/L. (NH Dept. of Env. Services, 1999.)

Conductivity

Conductivity, also known as specific conductance, is a measure of the ability of water to conduct an electric current. This is determined by the number of ionic particles present in the water. High conductivity values may be indicative of non-point source pollution, but at the same time, may be affected even more dramatically by natural geologic features of the watershed.

Conductivity values for New Hampshire lakes that are greater than 100 uMhos are most likely indicative of anthropogenic sources of excess ions in the water, since the average conductivity for New Hampshire lakes is 56.8 uMhos. Anthropogenic sources include urban runoff (metals, sodium), and agricultural runoff (sediment, phosphorus). (NH Dept. of Env. Services, 1999.)

Phosphorus

Phosphorus is the nutrient that generally, or often limits algal production in lakes and ponds. Without excess phosphorus in the system, algal production is hindered and nuisance algal blooms do not occur. As phosphorus amounts increase, so do algae concentrations.

Phosphorus exists as a natural element, but becomes a problem when inputs from such sources as septic systems, erosion, animal wastes, and fertilizer load the water body with excess amounts. The median phosphorus concentration in the epilimnion of New Hampshire lakes is .011 mg/L. (NH Dept. of Env. Services, 1999.)

Chlorophyll a

The concentration of chlorophyll a is an indicator of algal abundance. Because of the presence of chlorophyll a pigment in algae, the relative concentration of chlorophyll a in the water gives an indication of the concentration of algae. As the algae population increases, so does the chlorophyll a concentration.

Chlorophyll a concentrations greater than 10.0 mg/m3 usually indicate an algal bloom. The mean chlorophyll a value for New Hampshire lakes is 7.47 mg/m3. (NH Dept. of Env. Services, 1999.)

Secchi Disk Transparency

Secchi disk sighting measures the depth that one can see into the water. To measure Secchi disk transparency, a black and white patterned disk is lowered into the water, and the depth at which it is no longer visible is recorded. This is indicative of actual water clarity, which is affected by the amount of algae and particulate matter (turbidity) in the water column. Secchi disk readings are somewhat subjective, but generally correlate with chlorophyll a concentrations and turbidity levels.

The mean transparency for New Hampshire lakes is 3.7 meters. (NH Dept. of Env. Services, 1999.)

Turbidity

Turbidity is a measure of suspended matter in the water. The more material (clay, silt, algae) suspended in the water, the higher the turbidity. These materials cause light to be scattered and absorbed, instead of transmitted in straight lines, leading to decreased water clarity. High turbidity readings are often found in water adjacent to construction sites, or waters otherwise polluted. (NH Dept. of Env. Services, 1999.)

The median turbidity for New Hampshire lakes is 1.0 NTU. (NH Dept. of Env. Services, 1999.)