By Kathleen Curwen
A Watershed Management Plan (WMP) is a prioritized strategy that enables a community to protect and improve water quality. It is developed with the help of a consultant after assessing trends in water quality and land-use practices within a watershed. Updating Eastman’s WMP is both timely and urgent. Timely, because the NH Department of Environmental Services (NHDES) and the Environmental Protection Agency both suggest updating a WMP every 10 years. Eastman’s first WMP was written in 2009 and it did not include many key elements currently required to be eligible for Clean Water Act Funding.
Updating our WMP is urgent because three water quality parameters are deteriorating in Eastman Lake. Members of the Lakes and Streams Committee along with other volunteers have been working with the NHDES since 1987, collecting and analyzing water samples from Mill Pond, our tributaries, and lake. The NHDES has identified significantly worsening (increasing) conductivity and chloride levels in the lake. Eastman’s chloride levels are 10 times the levels found in undisturbed NH waters. Chronically high chloride levels are toxic to plants, amphibians, and fish. Our rising chloride levels are indicative of salt runoff from road deicing agents used on Routes 89 and 10, and on roads, parking lots, and driveways within Eastman. Dust suppressants sprayed on Eastman’s unpaved roads and discharge from water softeners or failing septic systems also increase conductivity/chloride values. While most of the salt enters through our major tributary, Stoney Brook, some also enter during snowmelt when water flows down the hillside bordering Trail 6 on the west side of the lake and through two smaller tributaries on the northeast side of the lake.
Sediment entering the lake from properties and roads bordering the lake and from spillover from Mill Pond is our second concern. When water carries soil into a body of water, it not only fills in the waterbody, it contributes to loss of clarity and adds harmful nutrients that support excessive algae and aquatic weeds. Mill Pond acts as a natural sediment sink for water entering the lake from Stoney Brook. The pond was last dredged in 2007, but erosion along the banks of the Stoney Brook is causing rapid and heavy sediment accumulation within the pond as soil moves downstream. Figure 1 shows an emergent sand bar in Mill Pond. The Eastman Community Association (ECA) commissioned Pike Hydro to conduct the Mill Pond Sedimentation Study, which was completed in May 2018. This summer, based on recommendations in that study, John Larrabee and community mentors worked with our Youth Conservation Corps (YCC) to build a stone “check dam” on Stoney Brook (see Figure 2) below the erosion site. The dam is slowing the movement of soil into Mill Pond, but it does not prevent erosion along the banks of the brook. As Mill Pond fills up, some material spills over the dam and into the lake. Reducing the flow of stormwater runoff elsewhere around the lake will also lower sediment and pollutant buildup. ECA’s ongoing work along Trail 6 and the newly placed YCC check dam on Cherry Lane are aimed at slowing down and spreading outflow and allowing water to soak into the ground rather than rushing into the lake.
Despite these efforts, in 2018 and again this year the turbidity of lake water at the deep spot has been elevated, leading to our third concern. As unfiltered organic matter sinks to the bottom, decomposers digest the materials and deplete dissolved oxygen, forming an anoxic zone that cannot support plant or animal life. High salinity can also lower oxygen levels and create dead zones in lakes. Last summer and again this summer, dissolved oxygen dropped off significantly in the bottom 2-3 meters of the lake.
Thanks to fundraising efforts on the part of Lakes and Streams Committee members working closely with the Eastman Charitable Foundation (ECF), $13,500 has been raised from grants from the ECF, the Byrne Foundation, and the New Hampshire Charitable Foundation. These funds will defray part of the cost of updating our WMP. ECA is contributing the remainder of the funds. A consultant was hired last spring and the process of updating our WMP is well underway. The plan will be completed by August 2020 and will give Eastman a blueprint for watershed remediation efforts for the next decade.
Kathleen Curwen is a biochemist and a retired environmental chemistry teacher. She oversees water testing for Eastman Lake with the help of many dedicated volunteers.