Determining Water Quality Parameters

Most of the water quality monitoring of Wolfeboro Waters has been done using ​volunteers​ to collect samples and having the samples analyzed either by the University of New Hampshire’s Extension Service (Lay Lakes Monitoring Program-LLMP) or the NH Department of Environmental Services (Volunteer Lake Assessment Program-VLAP). The two programs have similar objectives. Water samples are collected and processed and stored by volunteers following program guidelines and then the samples are analyzed in the UNH or NHDES lab using standardized methods. In addition, some measurements, such as temperature, pH, clarity, depth, and conductance are made directly in the lakes with the right equipment.

To assess the many different dimensions of water quality, a number of different parameters are measured. Some of these, such as clarity, are measured directly, while others are determined indirectly or by surrogates, such as using the concentration of E. coli ​bacteria as an indication of the level of human pathogens in the water. Most of the types of measures used to assess the quality of Wolfeboro Waters are described below, along with their interpretation.

Salinity/Conductivity​: The salinity of water is an important determinant of the type of life that it can support. Most ocean/marine life require water with higher salinity. Freshwater life generally requires low salinity. Most often measuring conductivity is used as a surrogate for salinity--the lower the conductivity the better.

Specific categories of good and bad levels cannot be constructed for conductivity, because variations in watershed geology can result in natural fluctuations in conductivity. However, values in NH lakes exceeding 100 uMhos/cm generally indicate human disturbance--NHDES/VLAP. ​ Similarly, increasing conductivity over time can also suggest human disturbance. (UNH-LLMP considers less than 50 uMhos/cm to be minimal impact.)

Clarity/Turbidity: Water clarity is measured by determining the depth of water when a standardized black/white patterned disk (Secchi) can no longer be seen from the surface when looking through a tube that limits observation to the water column. Greater than 4.0 meters (~13feet) is excellent, between 2.5 – 4.0 meters is fair, and less than 2.5 meters is poor. (UNH-LLMP)

Color:​ The (dissolved) color of water is determined on filtered water samples. A reading of fewer than 10 color units is uncolored, 10-20 units is slightly colored, 20-40 units is light tea colored, 40-80 units is tea colored, and more than 80 units is highly colored.

pH (Acidity vs. Alkalinity): pH is a measure of acidity or alkalinity. A pH of 7 is neutral. The lower pH is below 7, the more acidic the water. The greater the pH above 7 the more alkaline/basic the water. A pH of 6.5 to 9.0 is optimum for fish growth and reproduction. A pH of less than 5.5 is considered suboptimal. (UNH-LLMP)

Toxic Chemical Concentrations: The lower the concentration of toxic chemicals the better. There are different standards based upon the specific chemical. With few suspected sources of toxic chemicals, few measurements have been done on our lakes, except Upper Beach Pond, which is a reservoir for Wolfeboro’s drinking water. Note: groundwaters in our region have a much greater likelihood of having concentrations of toxic chemical (e.g. arsenic, MTBE, radon, and PFAS).

Pathogen Concentration: Clean water should have low concentrations of human pathogens, of  which there are many. E. coli is a class of bacteria that is associated with the human intestines. Most ​E. coli ​are harmless, but a few are infectious. NHDES measures E. coli levels at public beaches and uses their concentration as an indication of the presence of the full range of human pathogens. NHDES will issue a Beach Closure Advisory if either two or more samples collected at a beach exceed the state standard of 88 counts of ​ E. coli ​ per 100 milliliters (ml) of water or one sample exceeds 158 counts of E. coli ​per 100 ml of water.

Temperature and Temperature/Depth Profiles: The temperature of the water is measured because it is one of the factors that influences the makeup of plant, animal, and microorganisms that live comfortably in the lake, seasonally and over longer time periods.

Temperatures are also measured by depth in the water to provide a profile. If there is a location where the temperature of the water increases or decreases rapidly by depth (e.g. two-degree Fahrenheit/one-degree Centigrade per meter/three feet), the depth of that rapid transition is called a thermocline. Thermoclines represent a place where the water column is stratified into zones that mix very little. Thermoclines typically form in deeper waters during the summer when the waters near the surface become warmer than the waters near the bottom. Conversely, in the winter the surface waters exposed to the cold air may become significantly colder (and, indeed, freeze) compared to the liquid water toward the bottom of the lake.

When waters are stratified, scientists use the term epilimnion to refer to the surface-water region, hypolimnion to refer to the bottom-water region and metalimnion to the region between them around the thermocline. The depth of measurements and sample collection are important because there may be significant and important differences between what is happening in the surface waters versus the bottom waters.

Typically, stratified waters will mix as the temperature of the surface waters cool or warm to close to the temperature of the bottom waters. This mixing is called turnover. The exact time of turnover in the autumn or the spring may also be influenced by major wind events as the temperature differences decrease.

Dissolved Oxygen​: The amount of dissolved oxygen in the water is important. Fish need oxygen to survive. If an area of a waterbody develops stratification (usually deeper waters) and if there is organic matter on the bottom of the lake, bacterial action on that organic matter may consume enough oxygen (that cannot be restored by mixing with the oxygen-rich waters above) to lower or completely deplete the dissolved oxygen on the bottom. Fish need oxygen levels of at least 4-5 ug/L. While warm water fish may be able to adapt by swimming in the warmer oxygenated water closer to the surface, it is a problem for colder water fish.​ If the oxygen level becomes totally depleted, the chemistry of the sediment and water can change​ (e.g., to increase significantly total phosphorous levels). UNH-LLMP classifies oxygen levels of 5 mg/L or more to be excellent, 2.0-5.0 mg/L to be fair (mesotrophic), and below 2.0 mg/L to be poor (eutrophic).

Total Phosphorous​: ​ Phosphorous is one of several nutrients in our waters. Phosphorous is not toxic. Phosphorous is measured because it is believed its concentration controls the amount of biological growth, including plants, algae, and cyanobacteria, because all the other essential nutrients for their growth are already present in higher concentrations than needed. In this case, more phosphorous, more growth. The lower, the better.

The NHDES-VLAP classifies total phosphorous concentrations (TP):

  • 1-10 ug/L   Low (good)
  • 11-20 ug/L  Average
  • 21-40 ug/L  High
  • >40 ug/L     Excessive

The UNH-LLMP classifies total phosphorous concentrations (TP):

  • < 8 ug/L       Excellent (ogliotrophic)
  • 8 -12 ug/L    Fair (mesotrophic)
  • 12-28.0 ug/L Poor (eutrophic)

Algal Growth (Chlorophyll-a)​: A fluorometer that measures the fluorescence of light at one particular wavelength is used to measure the concentration of chlorophyll-a, a protein associated with green algae. The greater the fluorescence the higher the algal concentration.

The UNH-LLMP classifies chlorophyll-a concentrations:

  • < 3.3 ug/L      Excellent
  • 3.3 -5.0 ug/L  Fair
  • >12 ug/L         Poor


 

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