Centuries of strain on river add up
Like most New England rivers, the Assabet River flows through a landscape that bears the imprint of human activity. Roads, houses, and other human uses of the land affect both the river's water quality and its flow. Home to a watershed population of 177,000 (and growing), the river and the aquifers beneath provide both wastewater disposal and water supply for watershed residents.
As the business, industrial and residential
population grows, these demands on the river increase. However,
initial results of the Assabet River TMDL (Total Maximum Daily
Loading) analysis provide strong evidence that the capacity of the
region's water resources to sustainably meet those demands has
already been exceeded.
As the Assabet watershed struggles with the
challenge of continued growth despite the limits of its natural
resources, it is OAR's goal to make sure that the river has a strong
voice in decisions that will affect it.
Eutrophication and water quality
In the summer, parts of the Assabet River are as green as a well-watered lawn. The green is a blanket of floating duckweed and algae, and, beneath that, hides a forest of aquatic plants rooted in the shallow sediments. This condition, termed "eutrophication," is caused by an over-abundance of nutrients (mainly nitrogen and phosphorus) in the river acting as fertilizer for the aquatic plants. During the growing season the over-growth of plants creates problems for fish and other aquatic creatures by affecting dissolved oxygen concentrations and pH in the water column. After the growing season, the plants and algae decay, lowering dissolved oxygen levels and producing that distinctive bad odor you probably associate with late summer along the Assabet if you've walked by the Powdermill dam on Rte 62 near the bait shop in Acton or lived along the Ben Smith impoundment in Maynard.
excess of nutrients and the effects of eutrophication means that the
river fails to meet state water quality standards for "fishable
and swimmable" waters. The bulk of the nutrient loading to the
river comes from the seven wastewater treatment plants that line its
banks and from nonpoint sources (carried by stormwater). Storm water
runoff and the recycling of nutrients trapped in river sediments
also contribute to the river's excess of nutrients. Dams all along
the river create large, slow moving sections (impoundments) where
nutrient-rich sediments have accumulated over many years. Before the
river can meet "fishable and swimmable" standards nutrient
loads from the wastewater treatment plants and nonpoint sources will
need to be dramatically reduced.
For more information about water quality, and what
OAR is doing about it, click over to our WQ
program or our Nutrient Outreach
"Quantity" or "flow" simply
refers to the amount of water in the river. The river needs not only
good-quality water but also enough water to provide habitat for a
healthy population of fish, to support recreational uses (canoeing,
kayaking, fishing) and to dilute pollutants in wastewater discharges
and storm water. The river's problems are exacerbated by low flows.
During the natural low flow periods in the summer and early fall,
upper sections of the river can consist largely of treated
wastewater. Summertime flow in the river depends on "baseflow,"
the cool, clean water coming from aquifers and tributaries in the
watershed. When an aquifer is tapped for water supply and the water
taken is not returned to that aquifer, the water is not available to
the tributary streams or river. If the aquifers are depleted, the
river suffers and water supply in the region is threatened.
For current flow conditions or more information on
baseflow, water use and conservation, or fish habitat and
populations, click over to our StreamWatch
project. As part of OAR's efforts to protect flow in the river, OAR
comments on water withdrawal permits, has advocated for a hydrologic
study of the watershed, holds water conservation workshops, and
participates in an ongoing discussion of minimum flow
recommendations in the state.
To learn about OAR's programs that target the Assabet's issues, check out OAR Programs.