One of the most productive ecosystems on Cape Cod is an estuary. This transition system contains several distinct habitats that function interdependently and connect freshwater systems (rivers, groundwater) to the ocean. Consequently salinity varies widely depending on the topography of the bay as well as the amount of freshwater influence. An estuary is often encircled by salt marsh habitat and portions that are brackish.
Estuaries are very productive systems and support a large diversity of wildlife. Nutrients that support plants and algae, particularly phytoplankton, are abundant in estuaries. This in turn supports many commercially important shellfish and finfish populations. Unfortunately sometimes these nutrients, notably nitrogen, occur in excess and eutrophication conditions can occur. Algae blooms followed by a reduction in shellfish and crab populations are the result.
Estuaries are important areas for protecting uplands from coastal storm damage, shelter for migratory birds, and preventing the intrusion of contaminants into the water. Sometimes these systems are well mixed between the salt water and the freshwater input. Freshwater has a lower density than salt water and may perch on its surface.
Many animals that survive in estuaries must have the ability to tolerate changes in salinity (euryhaline) species). For example, herring are anadramous species that migrate from the ocean to freshwater. An animal must have the ability to regulate its water and salt balance if it is to survive under these conditions. However most species are stenohaline and are not adapted to widely fluctuating salinities.
Estuaries are popular areas for recreation. Human pressures from activities such as boating can place environmental stress on the system. Because of their popularity the areas surrounding an estuary are often heavily built up so that effluent from septic systems and runoff from roads can create nutrient loading issues.
The Waquoit Bay estuary in Falmouth is an excellent example of a rich and diverse ecosystem that includes salt marsh habitat and is influenced by surrounding development. Fishing and boating are popular activities there and the Waquoit Bay National Estuarine Research Reserve conducts research and provides many educational opportunities for the public.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.