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Hydrology The Gardiner Report (1974) lamented the “lack of hard, scientific data concerning the actual water resource dynamics of the Pond” and went on to term the hydrologic description that followed as “general conclusions” (Gardiner Report, p. 51). Schofield’s 1989 article, “Walden Woods Ecosystem” in the publication Walden Woods brought more to light: “…the deep water table and highly permeable soils of the Walden Sand Plain supported a distinct biotic community in the Walden Sand Plan – the Northern Pine-Oak Forest – that differed significantly from the surrounding primeval Northern Transition Forest.” While a great deal was known about the ecology of the forest, little was known about the specific hydrology of Walden Pond. It was generally agreed that the water at the Pond was less clear than it used to be, and its immense popularity as a swimming destination, proximity to Route 126, and status as a catch basin for water runoff were likely causes. Twenty-five years after the Gardiner Report, John A. Colman and Paul J. Friesz completed Geohydrology and Limnology of Walden Pond, Concord, Massachusetts (1999) and answered many questions about the water at Walden Pond. Colman and Friesz describe the Pond’s bathymetry, groundwater contributing area, nutrient levels, plant growth, external inputs, dissolvedoxygen levels, and many other aspects of the Pond. Combining their findings with current data and previous studies, a more complete picture of the Pond’s functions and vulnerabilities comes into view.

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Walden Pond State Reservation Stewardship Plan

Well beneath the sandy soil of Walden Pond is the aquifer bounded by the Concord River to the north, and by the Sudbury River to the west. Schofield: “The Walden Pond Unity – i.e., the sand plain, or kame delta complex – is dominated by a hydrological regime centered on or in the vicinity of Walden Pond in all directions except eastward and southeastward [in the direction of Pine Hill and Sandy Pond].” The aquifer flows from northeast to southwest, and is responsible for the groundwater inflow that accounts for 55 percent of the Pond’s Figure 24: Nitrate concentrations from Colman and Friesz, 1999 Exceptional nitrate levels found on Main water volume. Beach downslope from septic system. The remaining 45 percent is from precipitation. The Pond baseline fluctuates with the seasons and, on account of a five-year residency time for water, with multi-year precipitation trends. Accordingly, between 1956 and 1999 the water level varied by about 11.5 feet (Colman and Friesz,

Inventory and Analysis


p. 12). When the water level is high, Red Cross Beach is submerged, and the Main Beach carries the entire burden of beach goers. Aquatic recreation is at the heart of Walden Pond’s popularity. The Pond is well known across the globe on account of Thoreau; it is well attended on account of the availability of freshwater swimming. “With a ground-water contributing area underlain by a thick unsaturated zone devoid of wetlands and humic substances, Walden Pond has unusually clear water.” (Colman and Friesz, p. 37) To that end, the DCR receives extensive water quality reports throughout the summer to ensure that the beach and water are safe for public use. In the past, the water conditions at the Pond sometimes precluded people from using it. Recently, though, the conditions have been highly satisfactory, due to two significant improvements in the last five years. At the time of Colman and Friesz’s 1999 study, the restroom facilities in the Gateway fed into a traditional septic system. Temporary wells were dug along the Pond shoreline by the Main Beach to measure the potential effects of the septic plume. The results (Figure 24, previous page), were striking. Nitrate levels at the shoreline skyrocketed in a 10 meter area almost directly across the street from the septic system. Since then, the restrooms have been fitted with flushless composting toilet systems. While current nitrate-level data is not available at this time, water quality testing from 2006-2008 for enterococci levels at the Main Beach have consistently remained low.

Inventory and Analysis

Recently, the town of Concord agreed to install drains along Route 126 to reduce the amount of oil- and bacteria-laden stormwater washing down the erodible East Bank soils and onto the Main Beach. The DCR also installed drains along the E-Ramp for similar reasons. These drains allow water to filter through the exceptionally sandy soils around the Pond before reaching the Pond itself. At the same time, the Reservation staff made Fig. 24: the macroalga Nitella the decision to put into disuse the previous method of stormwater collection and mitigation at the pond: a catchbasin connected to a large pipe draining to the center of the Pond. Benefitting from the improvements is the macroalga Nitella (Figure 25), one of the Pond’s most important residents. Whether people were interested in harvesting ice or taking a swim, the clear water of Walden Pond has brought it a great deal of human interest, and along with it, opportunities for degradation and nutrient-loading. Nitella, living 20 to 43 feet below the Pond’s surface and spread out along the Pond, depends on clear

Walden Pond State Reservation Stewardship Plan

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Figure 26: Nitella habitat, Colman and Friesz, 1999

water to receive the amount of sunlight it needs to thrive (Figure 26). In order to keep that water clear, Nitella may tieup large amounts of phosphorous, which would otherwise lead to phytoplankton blooms on the surface and reduce the amount of sunlight available below the surface. Compared to other lakes around North America and Europe, “the Nitella biomass of Walden Pond is large on a per-area basis” (Colman and Friesz, p. 37). As much as the clear water matters to swimmers, it may matter even more to the alga below the surface helping to keep it that way. Around the Reservation are several vernal pools and wetlands (see Hydrology GIS map). The green swath is the aquifer, moving from the Concord River to the northeast to the Sudbury River to the southwest. Vernal pools, both certified (yellow) and potential (pink), are found in all zones, with the exception of

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Walden Pond State Reservation Stewardship Plan

the Walden Gateway. Wetlands are found in the Goose Pond Reserve (by Little Goose Pond), the Southern Mosaic (Heywood’s Meadow), and at Wyman’s Meadow, which lies in both the Pond Circuit and the Thoreaufare. Heavily-used trails lead through Wyman’s Meadow, which lies in both the Pond Circuit and the Thoreaufare, but are nearly impassable when the Pond’s water level is high (Figure 27).

Figure 27: The Pond Path at Wyman’s Cove

In 1987, the Massachusetts Wetland Protection Act was revised to include “wetland habitats” in addition to the wetland types specified in the Act. In so doing, the vernal pool-which offers amphibians a protected and fish-free environment for reproduction and upbringing-was recognized as a functional wetland. Mole salamanders and wood frogs, which can be found on the Reservation, depend on these protected areas for survival. Buffering these areas from foot traffic is a useful way to preserve these fragile but functional aquatic ecosystems.

Inventory and Analysis


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Writing Sample  

Hydrology Analysis taken from the Walden Pond Stewardship Plan (2009)

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