Analysis of Water Quality

In 2006, we resumed periodic monitoring of the water quality in the FLCA. Twice a year, we take samples from the Broad Brook at North Farms Road, from Fitzgerald Lake at the canoe launch and the dam, from the vernal pool adjacent to the Fishing Place Trail (spring only), and from two locations in the marsh adjoining Cooke’s Pasture to the east of the dam. We then analyze the samples for pH, alkalinity, and the concentrations of dissolved oxygen, phosphate and nitrate using simple chemical test kits. The data for 2006-2019 are available here.

The pH, alkalinity and levels of dissolved oxygen, nitrates and phosphates in the lake and the marsh signal a generally healthy aquatic environment. However, we have consistently found that the nitrate concentration in the Broad Brook at North Farms Road exceeds that considered favorable for fish and other aquatic life. Subsequent sampling indicated elevated nitrate concentrations further upstream as well. High nitrate levels can lead to eutrophication, a process in which the nitrates stimulate the growth of plants and algae that eventually settle to the lake floor and are decomposed by bacteria. The heightened bacterial activity in turn consumes oxygen, reducing the dissolved oxygen available to fish and aquatic invertebrates. Our measurements indicated nitrate concentrations of 0.5-4 parts per million (mg/L) in the Broad Brook, depending on the season. This is a red flag given that the desirable level for healthy fresh-water aquatic life is less than 0.1 parts per million. So far, the concentration of dissolved oxygen in the lake has remained at normal levels, but continued monitoring will be necessary to make sure that it does not decline.

The presence of nitrate in the Broad Brook likely stems, at least in part, from a storm drain system that serves a large portion of Florence, extending well into the neighborhoods along Bridge Street, North Maple Street and Country Way. Further inspection revealed high nitrate levels in some of the Broad Brook’s tributaries that drain the Spring Grove Cemetery and the JFK Middle School. Nitrates can come from any one of a number of sources, including fertilizer runoff, leaky septic systems, springs and groundwater flows. We have urged landowners in the Broad Brook drainage basin to limit their fertilizer use and have their septic systems checked on a regular basis.