Award: OCE-1058747

The Plum Island Ecosystems LTER

Scientific Merit: The Plum Island Ecosystems (PIE) LTER is an integrated research, education and outreach program whose goal is to understand the long-term response of watershed and estuarine ecosystems to changes in three key drivers: climate, sea level and human activities.  The PIE-LTER was established in 1998.  Our principal study site is the Plum Island Sound estuary and its watersheds located in eastern Massachusetts north of Boston.  Some key findings are:

 

1)      Suburbanization has altered the timing and magnitude of water flows in PIE watersheds through pumping of groundwater, through water transfers, by storm water management, and by increasing impervious surfaces. By the early 2000s, the average net diversion of water reached 20% of annual river runoff.  However, the impact of this large diversion is not evident in stream flows because there was an increase in water inputs from precipitation and an increase in runoff due to an increase in impervious surfaces.  The result is that average annual runoff has not changed at the whole watershed scale although variability has increased. 

2)      Recently, beaver populations have dramatically increased in PIE watersheds, greatly altering stream channels.  We found that beaver dams resulted in increased native fish biodiversity and may be increasing the rate at which nitrogen is removed.   

3)      We have developed a circulation model of water flow in PIE. The model has yielded new insights on the importance of hydrologic connections between Plum Island Sound and the Merrimack River. 

4)      The majority of nitrogen entering watersheds at PIE come from food/waste and fertilizer.  Although N inputs are relatively high, our watersheds export a lower percentage of N inputs than other urbanized watersheds in the northeastern United States and more closely resemble the highly retentive watersheds in the southeast.  We believe this is partially due to the location of development in our watershed.  The most urbanized areas are located near headwaters which allow abundant riparian and floodplain wetlands downstream to remove more nitrogen than in watersheds where urbanization is closer to the coast.  Suburbanization, however, does cause a decline in N retention.

5)      Nitrogen removal within marshes and estuaries is an important ecosystem service but rates are quite variable in time and space.  In the subtidal areas of PIE, we find that estuarine N dynamics are strongly controlled by water residence time, salinity, and N inputs. 

6)       We have found that marshes have "tipping points" beyond which they cannot keep up with sea-level rise.  Salt marsh primary production is strongly tied to changes in sea level.  When marshes are perched high in the tidal frame, as they are at PIE, the relative marsh elevation is above the optimum for marsh grass growth.  Consequently, in years when sea level is anomalously high, primary production responds positively.  Sea level also varies over an 18.6 year period (lunar nodal cycle) which changes the amplitude of the tides by about 5 cm.  Our research has shown that this change in the flooding duration is sufficient to alter biogeochemistry and primary production in marshes. 

7)      Creek configuration, bottom type and currents within the estuary create ‘hot spots’ where prey accumulate.  These hot spots are used by striped bass to maximize their feeding.

8)      We have developed new methods to analyze maps to gain ...