You are here:
Eutrophication: State of the Gulf of Maine
Citation:
Impact/Purpose:
Report on the status of eutrophication in the Gulf of Maine coastal and estuarine waterbody
Description:
Cultural eutrophication is an ecosystem response to increases in nutrient (primarily nitrogen and phosphorus) inputs from human sources. Estuaries, bays and nearshore coastal waters in the Gulf of Maine receive nutrient inputs from land-based sources via rivers and streams, directly from human activities adjacent to and within marine environments, atmospheric deposition, and oceanic upwelling and circulation. These inputs result in predictable consequences once they enter the waterbody (Cloern 2001; Bricker et al. 2007, Figure 2). First, nutrient loading to the water column increases, which then stimulates growth and production of both phytoplankton and larger algal species such as floating mats of macroalgae, such as Ulva or sea lettuce. Although a certain amount of phytoplankton and macroalgae are needed to support upper trophic levels (i.e., fish), excessive algal growth can lead to other more serious water quality consequences. For example, high concentrations of phytoplankton may cloud the water and cause die-off of seagrasses (submerged aquatic vegetation), which are considered important habitat for juvenile fish. Macroalgal growth can smother seagrasses and bottom-dwelling organisms such as clams, leading to die-offs of both. In addition, episodes of low bottom water dissolved oxygen (i.e., hypoxia or anoxia) may occur if algae sink to the bottom and deplete oxygen levels during decomposition. The phytoplankton community may also shift to favor more toxic and nuisance species, or harmful algal blooms (red tides) that may also result in public health concerns. The eutrophication process, however, is more complex than portrayed here. Estuaries are part of larger systems and the development of eutrophic symptoms is influenced by both “bottom-up” (e.g., nutrient inputs) and “top-down” (e.g., phytoplankton grazers such as shellfish) effects. It is important to stress that eutrophication has potential negative impacts on our coastal habitat and recreational values that are so important to the Gulf of Maine communities.