What is Eutrophication And What Causes It?

Eutrophication refers to the harmful effects of excess nutrients on an aquatic ecosystem resulting in increased growth of phytoplankton (microscopic algae) and depletion of oxygen. This process occurs naturally over centuries as ponds and lakes age and are filled with sediment. However, human activities have accelerated the rate and extent of eutrophication through discharges and loadings of limiting nutrients such as nitrogen and phosphorus into aquatic ecosystems with disastrous consequences for drinking water sources, fisheries and recreational water bodies.

The major contributor to eutrophication of our ponds and lakes on the Cape is largely from human sources and activities. Excess nitrogen comes from poorly treated wastewater (Title V septic systems) as well as fertilizers used on lawns, gardens, golf courses and farms. Excess phosphorus comes from the above sources plus storm water runoff. Harmful algal blooms which block light and oxygen from getting into the water, dead zones, and fish kills are the results of eutrophication. This increase in phosphorus and nitrogen stimulates excess plant growth which then results in the depletion of dissolved oxygen (DO), perhaps the most well-established indicator of water quality.

Oxygen levels can be reduced by many factors including by over fertilization of water plants, by runoff from lawns containing phosphates and nitrates, by too many bacteria or aquatic animals in the area, and by an increase in water temperature. Cutting shade trees on the shores of ponds decreases oxygen level because trees shade streams and ponds, cooling the water. Warm water holds less oxygen. Using a combination of indices for assessing water quality data, APCC's analysis of the acceptability of ponds on Cape Cod noted the percentage (42%) of unacceptable ponds in 2020 increased from 39% in 2019. The Association to Preserve Cape Cod (APCC) notes that of the 996 ponds on the Cape, many ponds continue to show the impacts of nutrient loading

The Red Lily Pond Project has joined with APCC in supporting the PALS program to test our pond. What will help? Alternative septic systems have been identified as potentially useful at Barnstable County's alternative septic system testing center where various methods are being tested, including permeable reactive barriers in Falmouth and Orleans and shellfish aquaculture projects in several towns. Sewers are being installed and are planned to be installed in a number of towns.

Kathleen Brady, M.D.

Former President and Ex Officio Board Member

Red Lily Pond Project Association

Summer 2021