Water Quality Monitoring
What is a healthy pond?
Healthy ponds have eelgrass, clean water, clean sediment, and a high diversity of animals large and small. This is what a healthy Pond looks like according to the Massachusetts Estuaries Project (MEP) and EPA Guidelines:
℘Dissolved O2 ≥ 6.0 mg/L
℘Temperature ≤ 85°F
℘Transparency 1.5 – 3.0 m (or bottom, if <3 m)
℘Total nitrogen 0.28 – 0.61 mg N/L
℘Chlorophyll-a pigments 3-10 μg/L
Increasing nutrient pollution or “eutrophication” is the greatest threat to Martha’s Vineyard’s estuaries. Our Vineyard ponds are much healthier than most of the East Coast estuaries and they are just slightly above the suggested limit. Fortunately, this degree of pollution can be reversed with timely management and restoration efforts going forward. The MEP set a benchmark of Total Nitrogen ≤ 0.5 mg N/L averaged across all Edgartown Great Pond sites in order to restore the estuary.
How and Why is the GPF monitoring EGP?
In the spring of 2016 Foundation purchased state of the art equipment so that we can assess Pond health and collect an abundance of quality data this year and all years going forward. We have begun sampling 12 sites around the Pond every week during the summer in order to record trends and be the first to identify any potential anomalies before they become detrimental. We are working in conjunction with the MVC to ensure that our methods and results are readily comparable and can be used for future studies. By having the scientific grade equipment in house, the Foundation now has the ability to answer site-specific and time-dependent questions. We are interested in how the quality of the Pond varies throughout the coves, throughout the season, and in response to Pond openings.
We use a handheld probe called a CTD (Conductivity Temperature Depth) from YSI called the ProDSS Multiparameter Sampling Instrument. This device measures Dissolved Oxygen, Turbidity, pH, ORP/Redox, Conductivity, Specific Conductance, Salinity, Total Dissolved Solids, Resistivity, Seawater Density, Total Suspended Solids, Depth, and Temperature. We also have a 9500 Photometer from YSI to measure nutrients. We are currently measuring Ammonia, Nitrate, Phosphate, and Silica, but have the ability to measure many other nutrients with this device, should they be of interest.
Frequently asked questions:
What is eutrophication?
Eutrophication is the build up of excess of nutrients in a pond or lake. The presence of these nutrients can stimulate a rapid and extensive growth of phytoplankton. This rapid growth or “bloom” can in turn deplete the oxygen from the water causing local hypoxia (oxygen poor ) or even anoxic (oxygen free) regions. Most plants and animals in a pond need oxygen to live, so this depletion of oxygen can be devastating to the ecosystem. Some nutrients of interest are phosphate, nitrate, and ammonia. This can happen from runoff or wastewater discharge. Phosphate is present in fertilizers. Nitrate and Ammonia occur naturally through decomposition and animal waste.
Where do these “nutrients” come from?
Nitrogen and Phosphorus are the most commonly measured nutrients because of their role in phytoplankton growth. Nitrogen enters a pond system through rainwater, decomposition of biological mater, animal waste, septic sources, or fertilizer. Phosphorus is a component of both fertilizer and detergents. In systems where Nitrogen and Phosphorus are not limiting factors, Silicates can be the limiting nutrient for phytoplankton growth. Most Silica comes from the weathering of rocks.
What is a Photometer and how does it work?
A Photometer works by passing light of a specific wavelength through a solution to measure the intensity of color. This color develops as a result of a chemical reaction. We add reagents to Pond water and these reagents react with the nutrient in question and produce a color. It is important to measure a clear solution to prevent a falsely elevated reading due to precipitates in the solution.