Habitat description
Waterbodies receiving small inflows from first order or ephemeral streams or through groundwater that are deep enough to experience stratification of water temperatures, particularly during the summer, with a cold-water layer at greater depths. These waterbodies may be natural in origin, artificial such as in the case of impoundments, or natural features enlarged by dams. Typically, higher watershed position limits drainage area and total upstream nutrient loading and increases water residence time with concomitant increases in water clarity. Stratification and turnover cycles influence water quality seasonally amidst geographic variability in alkalinity, dissolved organic carbon, and pH. Nearshore habitat may be more abundant and typified by light to moderate stands of aquatic vegetation. The persistence of an oxygenated (>5 mg/l) deepwater layer throughout the ice-free period affords habitat for cool and cold-water fish.
Characteristic communities and species
Specific communities will vary by watershed and will consist of warmwater fish species and cool and coldwater species where an oxygenated bottom layer persists. Typical species include brown bullhead, yellow perch, chain pickerel, pumpkinseed, largemouth bass, and golden shiner among others. Waterbodies with connection to the ocean may be temporarily inhabited by diadromous fish species including alewife. Furthermore, waterbodies underlain by karst geologic types (i.e., limestone) with alkaline waters will support unique plant and invertebrate communities adapted to higher pH, and greater concentrations of species such as shell-building organisms. Freshwater mussel assemblages can be abundant and diverse, found at depths <20-25ft where oxygen is not limiting, and often reaching their high densities at shallow depths (<10 ft). Typical species include eastern elliptio and eastern floater in western and central watersheds with the addition of eastern lampmussel, alewife floater, eastern pondmussel, and tidewater mucket in eastern watersheds (e.g., Taunton, Cape Cod, Merrimack). These lakes and associated habitats also host a variety of species seasonally and annually including turtles, amphibians, waterfowl, fish- and insect-eating birds, beaver, and muskrat.
Associated habitats
Riparian and floodplain, coastal plain ponds, perennially flowing streams (e.g., inflows). Hydrologically connected marginal wetlands including shrub swamps, marshes, wet meadows, and bogs.
Ecological processes
Seasonal stratification and turnover along with relatively long residence time for water are the key factors that determine nutrient cycling and water quality in these habitats. In general, smaller upstream drainage areas will limit nutrient inputs and increase water clarity and residence times. Internal phosphorus cycling (resulting from stratification) may play a larger role in nutrient dynamics depending upon legacy land use and the amount of shoreline modification and development. Water level fluctuations will vary with isolated groundwater-fed lakes being more responsive to patterns of precipitation. Due to these characteristics, deep isolated-headwater lakes are more likely to retain an oxygenated bottom layer year-round yielding suitable habitat for cool- and coldwater species.
Threats
Watershed and nearshore land use alterations, shoreline armoring and or homogenization, drawdown, nonnative species introductions, and increased cyanobacteria blooms. Warmer temperatures associated with climate change will prolong summer stratification, increase internal nutrient cycling which may increase the frequency and intensity of algal blooms and decrease or eliminate coldwater habitat. Extreme weather events such as drought will contribute to increased variability in lake water levels.
Restoration & management recommendations
- Water quality restoration: Lake aging or eutrophication is a natural process by which lentic habitats slowly enrich over time, display greater abundances of phytoplankton and aquatic vegetation, increased rates of sedimentation and decreased water clarity. Humans accelerate these processes via land use modifications that directly and indirectly increase nutrient loading to lakes. Deep isolated and headwater lakes may be initially resilient to excessive nutrient loading via storage and assimilation because of their large volume relative to their small nutrient inputs. However, once present, nutrients are difficult and expensive to physically remove and will overtime result in eutrophication. Actions taken to manage or improve water quality should balance short term temporary symptom relief with long-term solutions to nutrient control. Nutrient control strategies include improved stormwater management, modifying watershed and shoreline land use and management practices to reduce nutrient loads, maintaining shoreline vegetative buffers, and addressing septic leaks. Temporary solutions to water quality include in-lake alum treatments, aquatic plant management, or dosing stations at tributary mouths and dredging.
- Buffer and shoreline restoration: Watershed and shoreline actions could focus on restoring vegetative buffers, improving stormwater management, land management modification, and education. Where shorelines have been homogenized, habitat complexity could be created by leaving in place woody material which falls in the water. Restoration and protection of riparian buffers in these waterbodies should be a high priority because of their typically small watershed size.
- Water quantity restoration: Lake water levels are often manipulated (e.g., drawdowns) to meet a variety of management goals (e.g., aquatic plant control, drinking water supply). However, water level management practices may not fall within the range of natural water level fluctuations set by hydromorphological variables (e.g., watershed size, lake size, water residence time) for a given lake. Consequently, shallow-water habitat supporting aquatic plants, invertebrates, and fish can be impaired or reduced. Restoration of lake water levels in deep isolated or headwater lakes should carefully consider the rate, timing, duration, and magnitude of managed water levels within the constraints of their relatively small watershed, inflows, and large waterbody volume.
- Invasive species control: Invasive aquatic plant and mollusk species (e.g., zebra mussel, Asian clam, Eurasian water milfoil) detrimentally impact lake ecosystem biological communities and resources across Massachusetts. Prevention of their spread and managing for their reduction and eradication are critical to maintaining and restoring native lake biological communities (e.g., plants, invertebrates). Invasive species can be prevented from spreading by thoroughly washing and drying water-based gear and equipment between lake visits. Early detection and rapid response is critical for eradication and preventing establishment within a waterbody. Invasive aquatic plants can be managed using a variety of tools including herbicides, pulling, harvesting/cutting, raking, and dredging. Extensive literature on this topic can be found in the practical guide to lake and pond management.
Examples
- Lake Quinsigamond (Shrewsbury/Worcester)
- Lake Cochituate (Wayland/Framingham/Natick)
- Assawompset Pond (Lakeville/Middleborough)
- Stockbridge Bowl (Stockbridge)
- Lake Wyola (Shutesbury)
Additional resources
The Practical Guide to Lake Management in Massachusetts
Stop Aquatic Hitchhikers Handout