Coastal Resource Guide Pleasant Bay and ... - Town to Chatham

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Coastal Resource Guide for Pleasant Bay and Chatham HarborSection 7Natural Resources237.1 PurposeThe purposes of this section are to briefly describe the region’sglacial history and sediment regime, and to illustrate the breadth ofnatural resources in the Pleasant Bay system, including the currentstatus of water quality in the Bay.7.2 MethodologyNarratives describing the Bay’s diverse natural resources are basedon previous scientific studies and resource management plansfor the Bay, as well as information from local town officials. GISdata depicting wildlife habitats was supplemented by informationfrom Mass Audubon staff familiar with the Bay. Water qualityinformation was derived from studies determining critical nitrogenloading thresholds. Robert Oldale’s 2001 publication describing thegeology of Cape Cod and the Islands provided useful informationabout the glacial history and geology of the bay area.The location and distribution of natural resources in the Bay is basedon existing maps, Geographic Information System (GIS) data layers(including MORIS and ESI data layers), and local knowledge.Coastal wetland resource areas (e.g., dune, salt marsh, etc.),eelgrass, fish and wildlife, and priority natural community typesare delineated by MORIS and ESI data mapping. MORIS, theMassachusetts Ocean Resource Information System, is an onlinemapping tool created by Massachusetts Office of Coastal ZoneManagement (CZM) and the Massachusetts Office of GeographicInformation (MassGIS). MORIS can be used to search anddisplay spatial data related to the Massachusetts coastal zone(e.g., eelgrass beds, coastal wetlands, shore access points, etc.)on a backdrop of aerial photographs. Environmental SensitivityIndex (ESI) maps delineate coastal resources that are at risk,including biological resources, in a geodatabase format. TheMassachusetts Environmental Sensitivity Index Metadata (April2000) provides attribute definition and source information.7.3 Surficial GeologyThe type and distribution of natural resources in and aroundPleasant Bay and Chatham Harbor are largely influenced bythe area’s Pleistocene glacial history and the diverse types anddistribution of sediments deposited during this time. The surficialgeology of Cape Cod, including the Pleasant Bay area, owes itsorigin to the last continental glacier (Laurentide ice sheet) andthe subsequent rise in sea-level. The dynamics and timing ofglaciation as well as the variety of deposits left by the glacier asit advanced and retreated over the landscape of Cape Cod isdescribed in detail by Robert Oldale in his book Cape Cod, Martha’sVineyard & Nantucket: The Geologic Story (Oldale, 2001). Threebroad categories of glacial sediments were deposited during thePleistocene epoch (10,000 years or older) on the Cape: glacialtill, glacial moraine deposits, and glacial stratified deposits (Stone& DiGiacomo-Cohen, 2009). Glacial till consists of unsorted andunstratified sediments of various grain sizes (boulders, gravel,sand, silt, clay) deposited directly on bedrock by the glacier. GlacialSection HighlightsPleasant Bay supports a wide variety of inland andcoastal wetland resources, fish and wildlife, and manyrare species and natural community types.Coastal and inland wetlands serve important publicinterests such as flood control, storm damageprevention, pollution prevention, and marine andterrestrial wildlife habitat.Approximately 1,400 acres of salt marsh and 225 acresof intertidal flats exist in the Bay. Several areas of saltmarsh and tidal flat in the Bay are identified as “Areasof Critical Marine Habitat” based on their habitat valuesfor coastal waterbirds, horseshoe crabs, and the rarediamondback terrapin.Over 1,800 acres of eelgrass beds occur in the Bay. Thesehighly productive subtidal communities provide feedingand nursery habitat for many marine species, includingmany commercially valuable finfish and shellfish species.Seven rare wildlife species have been documented usingbay habitats, including Piping Plover, Northern Harrier,and Diamondback terrapin. Many other rare speciesoccur within the study area.Nutrient impacts on Bay water quality have beenmonitored since 2000, and data were used to identifythreshold limits for Total Nitrogen. Reductions in currentwatershed nitrogen load will be needed to maintain orrestore healthy water quality. Increased flushing fromthe 2007 inlet did not result in changes sufficient tomitigate the effects of watershed nitrogen loading.moraine deposits are similarly unsorted and unstratified, sandysediments with coarser materials including boulders. Morainedeposits accumulated in ice-walled lakes and streams and onstagnant, buried ice in front of the receding edge of the ice sheet.Glacial stratified deposits are layered, well-sorted to poorlysortedgravel, sand, silt and clay laid down by flowing meltwaterin glacial streams and lakes in front of the retreating ice margin(identified as “coarse” in Map 9). The glacial stratified depositson Cape Cod (e.g., Harwich outwash plain deposits) are the mostextensive in Massachusetts. These broad, gently sloping plainsare sometimes pitted, forming dry depressions or kettle pondswhere the depressions intersect groundwater. Less common areglacial lake sediments composed of gravelly sand, silt and claythat were deposited in lakes impounded by glacial ice (identifiedas “glaciolacustrine fine” in Map 9). The diverse sedimenttypes deposited by the Laurentide ice sheet comprise the parentmaterials of the Cape’s modern sedimentary environments. Risingsea-levels reworked the glacial sediments forming beaches, dunesPleasant Bay Alliance 2011
Coastal Resource Guide for Pleasant Bay and Chatham Harborand marshes during the Holocene epoch (post-glacial, less than10,000 years old). Bedrock is not exposed on the Cape due to thethick layer of glacial sediments.The distribution and types of surficial geologic deposits aroundPleasant Bay is shown on the U.S. Geological Survey’s Chathamand Orleans geologic quadrangle maps (Map 9) (Stone &DiGiacomo-Cohen, 2009). Glacial stratified deposits (“coarse”)comprise almost all of the uplands (not including Nauset Beach)surrounding the Pleasant Bay and Chatham Harbor. This map unitconsists of stratified sand and gravel deposits laid down in variousdepositional environments in front of the retreating ice margin(e.g., meltwater stream, lake deltas, etc.). The sediment layersmay be poorly sorted in gravel deposits to well-sorted in sand andgravel deposits, with faulted bedding due to post-depositionalcollapse.Post-glacial deposits in the region surrounding Pleasant Bay andChatham Harbor include beaches, dunes, salt marshes, freshwaterswamp and marsh deposits, as well as artificial fill. Beaches aretypically linear, narrow deposits of sand and fine gravel reworkedby waves and currents. The texture of beach deposits varies locallyand is generally controlled by the sediment composition of nearbyglacial materials eroded by wave action. Dunes are wind-depositedsands and granules derived from beaches, which may consist ofcross-bedded deposits up to 100 feet thick. Nauset Beach andNorth Beach Island are composed of beaches and extensive dunes,with localized areas of storm beach deposits (e.g., overwash fans,channels) consisting of sand and gravel deposited by high energystorm waves. Beach and dune deposits may also include artificialsand deposits from locally-replenished beaches. Swamp and marshdeposits are composed of decaying marine grasses and vegetationwith varying amounts of fine marine sediments. These olderpeat deposits are overlain by live marine and brackish wetlandvegetation. Swamp and marsh deposits occur locally on barrierbeaches where depressions intersect groundwater. Cranberry bogsexist locally in low-lying upland areas. Artificial fill occurs alongthe shoreline (e.g., beneficial re-use of dredged materials on townbeaches).7.4 Coastal Wetland ResourcesSeveral coastal wetland resource areas, as defined by theMassachusetts Wetlands Protection Act (MWPA) (M.G.L. c. 131,s. 40) and its Regulations (310 CMR 10.00), occur in Pleasant Bayincluding: Salt Marsh, Barrier Beach, Coastal Beach, Coastal Dune, 7.4.2 Marine and Estuarine WetlandsCoastal Bank, and other lands subject to tidal flow (Map 10 and Marine and estuarine wetlands include non-vegetated flats (tidalTable 3). The MWPA protects wetlands and the public interests flats) and vegetated, tidal wetlands. Non-vegetated flats arethey serve, including flood control, prevention of pollution composed of various combinations of sand, silt and clay (Tiner,and storm damage, and protection of public and private 2010). Some flats are colonized by algae, while shallow estuarinewater supplies, groundwater supply, fisheries, land containing waters in the Bay support extensive beds of eelgrass. Tidal wetlandsshellfish, and wildlife habitat. For example, Coastal Beach is include salt marshes and brackish marshes, which are salinitysignificant to the interests of storm damage prevention, flood dependent. Salt marshes develop closest to the ocean wherecontrol, and the protection of wildlife. Salt Marshes are also salinities are highest, while brackish marshes form along tidal riverssignificant to the protection of storm damage prevention and and streams where salt water is significantly diluted by fresh water.wildlife habitat, but also to the protection of marine fisheries,shellfish, the prevention of pollution, and groundwater supply.These public interests are protected by requiring a carefulreview of proposed work that may alter these wetlands. The 24Pleasant Bay Alliance 2011law protects not only wetlands, but other coastal resourceareas, such as Land Subject to Coastal Storm Flowage (100-yearcoastal floodplain), the Riverfront Area (Rivers Protection Act),and Land Under Salt Ponds, Land Under the Ocean, and fishruns. Several tidal or salt ponds exist in the study area, includingRound Cove in Harwich, Crows Pond in Chatham, and QuansetPond, Arey’s Pond, and Kescayogansett (Lonnie’s) Pond in Orleans.Freshwater wetlands and water bodies that outflow into PleasantBay, as well as isolated wetlands located on coastal landforms(Nauset Beach), also occur within the study area. These includehydrologically-connected lakes and ponds and their borderingfreshwater wetlands, vernal pools, bogs, shrub swamps, woodedswamps, and freshwater seeps. These wetlands are similarlyprotected by the MWPA and its regulations under several wetlandresource area types: Bordering Vegetated Wetlands, Bank, LandUnder Water Bodies and Waterways, Land Subject to Flooding, andRiverfront Area.Activities within the above wetland resource areas are also strictlyregulated by local and federal wetland protection laws andregulations. Activities undertaken within 100 feet of wetlandslocated within the state-designated ACEC are subject to the higherstandard of “no adverse effect.” Local wetland bylaws for townsbordering the Bay may extend wetland protections further thanstate or federal regulations.7.4.1 Beaches, Dunes and Coastal BanksNauset Beach, the most prominent coastal landform in the PleasantBay area, is a barrier beach consisting of coastal beach and extensivecoastal dune resource areas. Smaller barrier beaches exist elsewherearound the Bay, extending downdrift of headlands (e.g., StrongIsland) and protecting small coves and marshes. Coastal beachesbacked by coastal banks composed of glacial sediments (andsometimes associated with small, linear dunes or fringing salt marsh)form much of the shoreline on the western side of the Bay. Wherecoastal banks are actively eroding, they provide sediment to thecoastal system, allowing beaches, marshes and flats to accrete andkeep pace with ongoing sea-level rise. Eroding banks also providenesting sites for some bird species (e.g., bank swallow, beltedkingfisher). Where coastal structures such as seawalls or revetmentsexist, beach and dune environments are typically narrower unlessthe shore has been re-nourished.
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