The ecosystems of the densely populated coastal regions are especially susceptible to the effects of human activities. Development in the upland basins that drain into the sea has a direct impact on the health and functioning of coastal ecosystems. These regions are also particularly vulnerable to potential effects of global climate change such as sea-level rise. In an effort to address these issues, Ecosystems Center scientists have developed a broadly integrated research program that focuses on change in coastal ecosystems. Our major research site is the Plum Island Sound LTER site (Fig. 1). This is a salt marsh dominated estuary found just north of Boston. (See
Plum Island LTER web site).The basic premise of the coastal research program is that activities in the upland portion of coastal drainage basins are strongly linked to processes and conditions downstream in the wetlands, open waters and sediment systems of estuaries as well as in the open ocean (Fig. 2). They are linked through the water, nutrients, organic matter and sediments that flow downstream.
The runoff of organic matter and nutrients from forested lands differs immensely from that of agricultural lands or settled areas. Thus human activity changes the quantity and quality of the materials that flow downstream into the estuaries. Over the long term, changes in climate and the regular addition of airborne contaminants will also influence the nature of upland runoff into the estuary.
The increased flow of nutrients and organic matter from the uplands into the estuaries leads to increased algal production and noxious blooms, shifts in habitats, altered fish communities and decreases in estuarine fisheries. Extreme overloading can deplete the oxygen dissolved in the water and produce vast fish kills.
At the broadest level, our research efforts are focused on understanding cause-and-effect relationships between human activities, quality of habitats and the structure and productivity of the food web in coastal ecosystems. We are focusing our research on three areas: 1) the amount of runoff of water, nutrients and organic matter from agricultural, residential and forested uplands; 2) the effect of these upland inputs on the trophic structure, production and efficiency of estuarine systems; and 3) the effect of upland inputs on the distribution and quality of estuarine habitats and the production of fish and shellfish.
Two general questions guide our research program:
1) What is the relative importance to estuarine ecosystems of organic carbon and nitrogen inputs from watersheds with differing uses?
2) Does the interaction of inorganic nutrients with the quantity and quality of organic carbon and nitrogen play an important role in determining the trophic structure, production and efficiency of estuaries?
My part in this program is to understand the role of higher trophic level, such as zooplankton, benthic invertebrates, fish and shellfish, in coastal ecosystems. How do these organisms respond to changes in inputs from land? How do changes in the base of the food web, marshes and algae, affect species composition and productivity? What role do animals play in regulating the productivity of estuarine systems?
To answer some of these questions, we are planning a series of field manipulation experiments in small salt marsh tidal creeks. We plan to add nutrients to some tidal creeks to simulate eutrophication. We anticipate this will stimulate algal productivity and alter food webs. In other tidal creeks, we will remove the detritus formed by salt marshes which has been suggested to be the base of the food web. We anticipate declines in fish production as a result of less food at the base of the food web. In another set of creeks, we will remove top-predators to determine if they are exerting top-down control on the smaller fish. As a result of these experiments, we should have a better understanding of the controls on fish production in estuarine areas.