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Focus on Bear Brook

September 15th, 2018

Residential neighborhoods dominate the landscape of the Bear Brook watershed. On an aerial map, bright green lawns stand out against the mossy ambers of the natural wetlands and forests. From above, it’s not hard to imagine the scale of lawn fertilizer and pesticide use, along with other types of nonpoint source pollution often associated with suburban living.

Healthy waterways, or those left untouched by developmental pressures, are protected by native vegetation along the river corridor. Plants and soil filter out pollutants and slow down the flow of stormwater runoff to prevent erosion and flooding. Without a wide, vegetated buffer protecting the brook, many of the pollutants from the Bear Brook watershed flow directly into the waterway, degrading its water quality.

When last assessed in a subwatershed report in 2015, the water quality in Bear Brook was considered “good”. In this assessment, however, the overall water quality score for the brook is linked to the amount of pavement and other hardscape in the surrounding area. About 16.7% of the area, which includes portions of West Windsor, East Windsor, and Robbinsville, are covered with roads, parking lots, and buildings. According to research from the Center for Watershed Protection, more than 10% of impervious surfaces in a particular watershed will negatively impact that stream’s water quality. As you can see in the report card below, the score for impervious cover in this watershed receives a fair rating – which also applies to the Bear Brook as a whole.

Rainwater is between 5-6 on the pH scale, however NJ state standards indicate that streams in our area should have a pH between 6.5-8. Bear Brook falls below the mark, perhaps due to the high impact of stormwater on the stream due to a lack of vegetated buffers. This may also explain its high levels of phosphorus, which in turn leads to lower dissolved oxygen concentrations. Each of these indicators is intertwined with the others, causing a chain reaction of degradation that impacts aquatic organisms living in the stream.

Two biological monitoring sites on Bear Brook indicate a moderate-to-high level of impairment. StreamWatch assessments of site BB1, located downstream of Grovers Mill Pond in Princeton Junction, are fair-to-poor, with NJDEP sites upstream being assessed at fair-to-good. This demonstrates the cumulative impact of urbanization on Bear Brook as it flows downstream.

Acknowledgements

Many thanks to the Michaluk family, Ted Chase, and Rona Webster for monitoring Bear Brook. The StreamWatch program is funded by Janssen Pharmaceuticals Inc, Colgate Palmolive Company, and the New Jersey Water Supply Authority.

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