Nitrate

Nitrate (NO₃^-) is one of the dissolved forms of nitrogen. Nitrogen, along with phosphorus, is a limiting nutrient in many biological systems (organic material contains not only carbon but also nitrogen and phosphorus). Excess runoff of nitrogen bearing waters to lakes or estuaries can cause blooms of algae and adversely affect water quality.

Agriculture is the primary source for excess nitrate. Excess nitrate fertilizer from agricultural areas gets into the watersheds through surface runoff. On the other hand, nitrate is also a by-product of septic systems. As such, water quality may also be affected through ground water flowpaths in watersheds that have a high number of septic systems.

As shown in figure 1 below, nitrate is barely present at the eight sampling sites in the Nequasset watershed. In fact, to be accurate, only four (Kohler Road Pond, Wright Lane, Delano Road tributary, and Nequasset Park) of the eight sampling sites demonstrate any readings of nitrate above the 0.1 mg/l dectection limit. Of the four sampling sites that are significant, Kohler Road Pond is the most dominant both quantitative and qualitatively. With three readings above 0.1 mg/l and the highest being 0.2 mg/1, the Pond's comparatively high nitrate level can be explained by its comparitively lack of vegetation cover (figure 2).

Vegetation, such as trees and shrubs, acts as a buffer that intercepts surface run-off. They not only slow down the runoff physically, but also uptake nitrates chemically, thereby decreasing the nitrate level in the water. Based on this analogy, the denser the vegetation cover, the lower the nitrate level should be. This is further reaffirmed when we compare the density of the vegatation at Hedge Bridge Road (figure 3), which recorded no nitrate throughout, with that of Kohler Road Pond's. Moreover, Kohler Pond is also a comparitively smaller watershed - meaning it is more likely to see the impact of nitrate level compared to other larger watersheds.

As for the rest of the sampling sites in general, vegetated wetlands that surround them take up most inorganic forms of nitrogen (including nitrate) and convert them to organic forms. As a result, barely any nitrate is recorded. Figure 4 below provides the wetland distribution in the Nequasset Lake Watershed.

Figure 1. This is a graph of Nitrate at the sampling sites in the Nequasset watershed. 

Figure 2. Kohler Road Pond (Google Earth Image)

Figure 3. Hedge Bridge Road (Google Earth Image)

Figure 4. Nequasset Lake Watershed Wetlands (ArcGIS)