WATERSHED AND ESTUARY CHARACTERISTICS
Management of coastal systems requires not only an understanding of both present conditions, but also of the history of physical and environmental alteration. In addition, within degraded or partially degraded systems, an evaluation of the system's "maximum level of sustainable environmental health" is also needed. Although some of these evaluations are not complete at present, it is clear that there has been significant alteration of the Three Bays hydrologic and biological systems over the past several centuries since the early days of the mills along Goodspeeds River. What follows is a brief description of the Three Bays system focusing on major upland or embayment alterations relating to present system health.
While the nutrient related health of today's Three Bays System is very much linked to changes wrought by human activities, it is the physical structure of the system laid down by the retreat of the Laurentide Ice Sheet about 15,000 years ago that still controls much of the Bays' tolerance to nutrient inputs. The physical structure, shape and depth of a coastal embayment plays a major role in its susceptibility to ecological impacts from nutrient loading. Physical structure (geomorphology), which includes embayment bathymetry, inlet configuration and saltwater reaches, when coupled with the tidal range of the adjacent open waters, determines the system's rate of flushing. System flushing rate is generally the primary factor for removing nutrients from active cycling within coastal bays and harbors like Three Bays. As a result maximizing system flushing is one of the standard approaches for controlling the nutrient related health of coastal embayments.
As the Cape Cod Bay and Buzzards Bay Lobes of the Ice Sheet retreated, the sandy outwash plain that now holds the Three Bays watershed was formed. This sandy outwash produced the highly permeable soils found throughout upper Cape Cod. It is the permeability of the soils which has resulted in the importance of groundwater flow as a major pathway for nutrient transfers from watersheds to adjacent coastal waters in this region. The presence of both groundwater and surface water pathways for input of nutrients into the present estuary has significant impact on its response to changing nutrient loadings with the surrounding watershed from changing land-uses.
As sea level rose and flooded the present basins of the Three Bays, salt marshes began to form and an estuarine ecosystem began to function. At present it is not clear to what extent the embayments basins were formed from flooding kettle ponds versus merely flooding erosional valleys. However, given the shape and depth of the basins compared to other non-kettle systems on the southern shore of the upper Cape, it seems likely that kettle ponds with freshwater stream inflows and outflow were incorporated. With further sea-level rise the present marine beach deposits of Dead Neck, Sampson's Island, Bluff Point, northern tip of Grand Island and near the bridge to Little Island began to develop. The result was a complex estuarine system with a single inlet to Nantucket Sound through Cotuit Bay and major freshwater inputs through the Marstons Mills River and to a lesser extent, Little River.
Based upon studies from other regions of Cape Cod, it is likely that Native Americans utilized the resources of the Three Bays System for several thousand years before ceding the region to Captain Miles Standish in 1648. Native Americans likely used both the upland and estuarine resources. The marine food sources of the system would provide both shellfish (scallops, oysters and quahogs) and fish, particularly herring. According to James Otis, the name Mystic was the Native American term for small streams and ponds, particularly where herring and trout abounded. The largest lake within the watershed is still called Mystic Lake reputedly from this early term.
When Roger Goodspeed, the first European to settle within the Three Bay watershed, settled by the Marstons Mills River (for awhile named Goodspeeds River) in 1653, Three Bays was different from the present system in both its circulation and water quality. The upland was largely forested with some open lands, the Marstons Mills River was free flowing (no dams) and had more extensive freshwater marshes within its lower reaches and the embayment was connected to Nantucket Sound via a single inlet. While this single inlet almost certainly reduced the tidal exchange with high quality Nantucket Sound waters, the very much lower terrestrial input of nutrients suggests a high quality estuarine system. However, it is also likely that, similar to today, within the region of the mouth of the Marstons Mills River and associated salt marshes the sediments and bay waters were among the most nutrient and organic matter rich within the Three Bays System.
However, the aquatic and upland components of this System began to change rapidly. By 1689 a fulling mill was constructed on the Marstons Mills River. In 1704-5 the dam was constructed thus altering the pathway of surface water nutrient transport to the estuary. Town records indicating the leasing of herring rights and the requirement that all mills maintain fish ways is testament to the magnitude of the herring population supported by the system.
During the 1800's utilization of the estuary and its watershed continued to increase. Regions of the watershed were cleared for agricultural land and the Grist Mill at Marstons Mills continued operations past 1842. Land clearing was accelerated by the development of salt works on the shores of the Bay which used fire to fuel evaporation for salt production. This activity peaked in 1812 and then declined. Direct use of marine resources focused on oyster production, where oysters were initially pickled and shipped in barrels to market. In these earlier centuries, as today, oysters were cultured on the Bays' bottom. One of the first growers, Captain George Fisher who was granted a large section of Cotuit Bay, shipped oysters to widespread U.S. markets. With the demand for oysters, the natural beds surrounding Grand Island became depleted and spat were imported from Long Island for grow out. However, at least for awhile, seed could be collected at the mouth of nearby Popponesset Bay on deployed scallop shells to supply the grow out needs. During this period, scallops were harvested within Three Bays in quantity and even at the turn of the century scallops represented a major economic resource. This record of substantial scallop harvest indicates that eelgrass beds were likely prevalent throughout the Bays. This suggests that the water was clearer (greater transparency due to less phytoplankton), hence less nutrient loading from the watershed was occurring. During this period the population was still small, for example there were only 36 homes in Santuit, Little River and Cotuit combined. Throughout the 1800's the residents relied heavily on their coastal resources as salt making, oyster production, fishing, farming, ship-building and coastal trading were the dominant activities.
By far the greatest changes to the Three Bays watershed and estuary have occurred during the 1900's. The most obvious change has been the dramatic shift in land-use to residential housing during the last half of the 1900's. With this shift and the advent of fertilized lawns, has been a dramatic increase in the amount of plant nutrients (primarily nitrogen) which enter the Bays. It is this recent nutrient load which is responsible for incipient declines in environmental health of portions of the estuary. However, there were likely pulses of nutrients to the system during the 1940's associated with the military training areas within the Bays. The barracks, warehouses and storage tanks would result in a "new" source of nitrogen loading and the paving of the beach from Baxter's Neck to Point Isabella may have also increased bacterial contamination in the adjacent waters.
In the early 1900's there was another major change to the Three Bays Estuarine System. Until this time, tidal exchange with Nantucket Sound was restricted to a single inlet to Cotuit Bay. However, a second inlet was opened which likely increased the flushing of West Bay, which previously had exchanged via the Seapuit River and through North Bay. Regardless of the extent to which this second inlet increased the flushing out of nutrient rich estuarine waters, it will have helped to buffer the Bays against the coming nutrient increases in the latter part of the century. Recent efforts to maintain the Bays for navigation may have also helped to maintain tidal exchanges, but the extent that this may have helped lessen the effects of increased watershed loadings has not been determined. Dredging of the Narrows from Prince Cove to North Bay in 1957 and the inlet to Cotuit Bay (most recently in the late 1990's) are two of the more notable examples of recent efforts. Unfortunately while declines in environmental health of the Three Bays System will be reduced by maximizing tidal exchange with the high quality waters of Nantucket Sound, the growing watershed nutrient loading and the structure of the system will require watershed management to restore the Bays to their former level of environmental quality. Watershed management will almost certainly involve reduction of nitrogen inputs at their various sources and possibly the removal of large loads (e.g. wastewater) from the watershed. Watershed management targeted at embayment restoration will usher in a new phase in the ever changing Three Bays System. While it is unlikely that we can restore the Bays to allow a single scalloper to dredge 80 bushels a week as was the case in 1899, a partial restoration of estuarine habitat should be achievable. Since Three Bays is not highly nutrient overloaded and since the habitat decline is relatively recent, partial restoration should be achievable over decadal time-scales and on a level that should benefit both present and future generations.
