Estuarine Water Quality Holds Steady at the Slocum River

 by Lloyd Center Research Associate Jamie Bogart

One of the historical roles of the Lloyd Center’s Research Department has been surveying various parameters indicative of water quality in our local estuaries and salt marshes, both sensitive coastal habitats subject to impacts from human use.

Past projects have included “Turn the Tide” (see summary under research), a complex multi-year effort focused on determining the health status of Dartmouth estuaries (Apponagansett Bay, Slocum River and Little River) known to be in a degraded state due to nutrients and pollutants from human use within the watershed. Parameters surveyed were macroalgae, finfish, shellfish, and birds, all indicators of water quality. Other work occurred at salt marshes (including Nonquitt Marsh) throughout the region which have suffered vegetation dieback due to undersized culverts that have since undergone culvert restoration to improve flow. To assess marsh health we studied water levels and salinity, vegetation, birds, and “nekton” (free swimming aquatics, mainly fish).

All the while, the Buzzards Bay Coalition (CBB), through its renown “Baywatchers” Program (see for details), has monitored water quality throughout Buzzards Bay to assess impacts from human use over time from primarily nitrogen loading, using citizen science to generate long term data. Nitrogen inputs from community uses (e.g. septic systems, road runoff) cause algal growth and reduced oxygen, which harms estuary species. In addition to being an asset to community recreational interests, the Slocum and Little Rivers are vital to the Lloyd Center’s mission of education and research, and where we’ve conducted the monitoring for this program since it started in the early nineties. The CBB sampling sites we’ve monitored most continuously are the mouth of Slocum River off our dock (SR4) and the landing at Gaffney Road (SR1), where we monitor water temperature, clarity, depth, salinity, and most importantly, dissolved oxygen (DO). CBB staff also monitor oxygen more intensively with a probe during the season, kept at our dock due to the importance of the location and convenience of the dock. We also collect the nutrient samples in July and August which identify other inputs to the system such as phosphorus and chlorophyll (algae) content.   

CBB devised a Bay Health Score for systems ranging from 0 (most impaired) to 100 (most pristine), which factors in our sampling and provides insight into estuary health. In addition to posting signage depicting the recent scoring at each site, CBB figures a 5-year average score which is 55 for the Slocum mouth (SR4) and 30 for the Gaffney Road landing (SR1), which depicts a partially degraded system. At SR4, close proximity to Buzzards Bay and mostly forest with minimal housing allows for better water circulation and less oxygen depletion then at the shallow, enclosed embayment near Gaffney Road, where more runoff and poor flow causes oxygen declines. The difference was depicted during past finfish surveys when way more algae appeared in the seine net at the Gaffney section compared to the mouth of the Slocum at Demarest Lloyd State Park.

So, although data reminds us these systems have suffered human impacts, this isn’t to say they are on the verge of collapse, a conclusion supported by what one sees at each location during a DO sampling season. At Gaffney Road, boaters of many kinds come and go, enjoying the river on nice days to paddle and fish, and frequently ask how the work is going. Birds such as Great Blue Herons are never far off, proof that there are fish to be caught. At the Lloyd Center dock, any given morning can be particularly lively, with nesting and fishing osprey always nearby, and perhaps a Belted Kingfisher also perched on the dock and ready to dive for fish. In late summer, egrets and herons gather in numbers at our causeway waiting for fish to come in with the tides. At higher tides in summer, large schools of menhaden swim by, followed sometimes by large splashes of chasing bluefish and striped bass. Gulls and Double-crested Cormorants follow the action. Boaters that launched at Gaffney come and go, passing Demarest Lloyd to and from the open bay.

The overall message is that our Slocum River is an estuary that has suffered more decline than meets the eye, but is surviving and thus has weathered the storm of land uses that have impacted Buzzards Bay and other regions over time. The Slocum River exists in a rural region with a buffer zone consisting of forests, salt marsh, and open fields used for conservation and thus has healthy buffer zones that preserve water quality.  But our collective contribution, including non-destructive recreational uses, and stewardship and research, all help ensure the river continues to thrive.