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State releases plan to cut phosphorus in Lake Memphremagog

Submitted by tim on

Newport City harbor, Lake Memphremagog. VBM file photo.

Vermont Business Magazine Most of thephosphorus load inLake Memphremagog is from agricultural activities and the state has developed a plan to reduce such pollution by a third. The Department of Environmental Conservation (DEC) is holding two public meetings to present theLake Memphremagog, Coaticook and Tomifobia Rivers Tactical Basin Plan, which outlines how the state will achieve new phosphorus pollution targets for the Memphremagog Watershed in Vermont.​The USEnvironmental Protection Agency recently approved the Lake Memphremagog phosphorus TMDL or Total Maximum Daily Load, which calls for a 29 percent reduction in phosphorus flowing off the land into the lake. Too much phosphorus causesnuisance plant and algae growth and occasional cyanobacteria blooms that limit recreational use of the lake.

DECcollaborated with local and regional experts to develop thetactical basin plan, with public input throughout the process. The plan outlines watershed-specific actions and projects that reduce phosphorus pollution from farms, roads, developed lands, and forests necessary to achieve the target.

“Whether you are a landowner, farmer, municipal official, developer, or logger, as Vermonters, we all have a responsibility to ensure a legacy of clean water for this and future generations,” says DEC Commissioner Emily Boedecker. “We are eager to begin implementing this plan, in close coordination with our local and regional partners that have been integral to its development.”

Basin 17 includes the Vermont portions of the StFrancis River Watershed encompassing a total of 589 square miles between the Lake Memphremagog drainage and the Tomifobia and Coaticook River watersheds. The Vermont portion of this basin includes the Black, Barton and Clyde Rivers and many lakes and ponds, including Great and Little Hosmer Lakes, Lake Parker, Crystal Lake, Lake Willoughby, Island Pond, Great and Little Averill Ponds, Norton Pond, Holland Pond and Seymour Lake.

According to the EPA, the largest source of phosphorus from the Vermont watershed is from the agricultural sector, estimated at 46% of the loading to Lake Memphremagog, followed by loading from developed land at 22%, stream channel erosion at 21% and finally forest and water/wetland at 12%. Modeling for the Lake Memphremagog TMDL further breaks down loading across several land uses for each of these major land use sectors as shown in Table 4 and Figure 3. For developed lands the largest sources of loading are buildings/parking lots/lawn areas (developed in the pie chart) at 9% as well as dirt roads with loading of 8% with lesser amounts of loading from paved roads, septic and WWTF loading.

For agricultural lands, loading is most significant from hay land due to the large percentage of the watershed comprised by these lands, 11% of the watershed in Vermont, resulting in an estimated loading of 19%. This is followed by cropland, agricultural production areas and pasture lands. As noted above there is a loading of 21% from stream channel erosion, and 12% from forest/wetland/water due to the large percentage of the watershed these land uses make up at 78% of the watershed in Vermont.

LOAD ALLOCATION

The TMDL load allocations apply to nonpoint sources in the categories of agriculture, forest land, and stream channel erosion, as well as to any non-NPDES regulated point sources to the extent they exist (VTDEC is not specifically aware of such sources). The approach to setting the load allocation was the same across the entire Vermont portion of the Lake Memphremagog watershed and was similar in many ways to the approach that was followed for the Lake Champlain TMDL.

Only a modest reduction of 5% from the forest sector was applied due to limited phosphorus reduction opportunities for this sector. These load reductions will be achieved through updates to the Acceptable Management Practices (AMP’s) that include practices to improve erosion control for forest roads and water crossings to avoid water quality impacts as well as outreach to loggers and forest lands owners about these practices and through the support of a skidder bridge rental program.

Loading reductions achievable thorough the restoration of stream equilibrium condition were estimated based on the BMP treatment efficiency that was developed for the Lake Champlain TMDL using phosphorus loading derived from SWAT modeling in relation to the dominant channel evolution stage at the HUC12 level. The Lake Champlain TMDL applied the restoration of stream equilibrium condition to streams above the 25th or 50th phosphorus loading percentiles for all lake segments except for Missisquoi where this BMP was applied to all streams. Since a SWAT model was not used in the development of the Lake Memphremagog TMDL an identical calculation could not be made for this watershed.

As an alternative approach, an estimate of loading from unstable stream channels was made for reaches where phase 2 stream geomorphic assessments were completed. Based on this assessment, the restoration of stream equilibrium conditions BMP was applied to the 42% of the loading that was estimated to come from reaches that had lost access to their floodplain. In addition to this, several reaches on the Black River and a few on the Barton River had elevated levels of estimated streambank erosion and loading based on high rates of planform adjustment likely driven by a loss of riparian vegetation and not stream incision. For these streams, increasing riparian vegetation will increase boundary conditions and will reduce erosion and loading rates from stream channels in the Lake Memphremagog basin.

The restoration of equilibrium conditions for unstable streams in the Lake Memphremagog watershed will be achieved through improved floodplain and river corridor protection, river corridor easements, and the regulation of stream alterations. This will also be supported though the restoration of buffers along streams which will be supported through new Required Agricultural Practices (RAPs), as well as voluntary buffer planting programs for both agricultural and developed lands in the basin.

The approach to setting load reductions achievable from agricultural lands was to approximate the BMP’s that would be installed based on new Required Agricultural Practices (RAPs) adopted in the fall of 2016 as well as technical and financial assistance provided through a RCPP (Regional Conservation Partnership Program) grant and other funding sources which are being targeted based on water quality sampling results. Specific BMP’s that were applied included:

1. Ditch and Riparian buffers or manure spreading setbacks on 40% and 30% of hay lands respectively along with grassed waterways to stabilize gully erosion on 3% of hay land.

2. Applying fencing on pasture lands with and without buffers (25% each) and managed intensive grazing for 25% of pasture lands. The latter BMP was based on load reduction estimates developed for the Chesapeake Bay watershed (Chesapeake Bay Program 2013).

Meetings

For information on theMemphremagog TMDL and theLake Memphremagog, Coaticook and Tomifobia Rivers Tactical BasinPlan, visit:http://dec.vermont.gov/watershed/map/basin-planning/basin17.

Source:MONTPELIER —The Department of Environmental Conservation 1.8.2017