Intellectual Merit: The Plum Island Ecosystems (PIE) LTER is an integrated research, education and outreach program whose goal is to develop a predictive understanding of the long-term response of watershed and estuarine ecosystems at the land-sea interface to changes in climate, land use, and sea level. The principal study site is the Plum Island Sound estuary located in the Acadian biogeographic province in eastern New England. The study sites include the coupled Parker, Rowley, and Ipswich River watersheds, their tidal marshes, and the surrounding ocean of the Gulf of Maine. Land use change and urbanization of coastal watersheds are altering both the magnitude and timing of the flow of materials and water to coastal ecosystems. These changes in flows from land, coupled with climate change and sea level rise, will have important, but still poorly understood consequences for the ways in which materials and energy are transformed in the coastal zone. It will also have important consequences for the people who value these ecosystems for food, recreation, and storm protection. The overarching question of this project addresses the ecological consequences of global change in the coastal zone: How do external drivers, ecosystem dynamics, and human activities interact to shape organic matter and nutrient transformations in linked watershed and coastal ecosystems?

This project follows from prior LTER studies of biogeochemistry, food webs, and population biology in the Plum Island watersheds, estuary, and intertidal marshes. In this next phase of PIE LTER research there will be more emphasis on linkages and feedbacks between the component ecosystems, including the human dimension. LTER Researchers will also place a greater emphasis on the role of geomorphology and geomorphic change in ecosystem dynamics. To organize this research the investigators have divided the study into four programmatic areas, each of which addresses an issue critical to answering our overarching question: Q1 Watersheds - How do human alterations of inter-basin material transfers, within-basin ecosystem connectivity, and geomorphology interact with climate to impact ecosystem regulation of water, organic matter, and nutrient fluxes through the watershed to the estuary, and how do these changes feed back to human behaviors that further alter watershed function? Q2 Marsh - Are the relative elevations of salt marshes at PIE in equilibrium with sea level, and if not, what are the consequences for primary production, biogeochemical cycling, and material exchanges between the marsh and estuary? Q3 Estuary - How do human activities and variations in climate that affect the coupling with watersheds, intertidal marshes, and the ocean shape organic matter and nutrient transformations in estuarine tidal creeks and bays? Q4 Higher Trophic Levels - What are the consequences of changes in ecosystem spatial configuration and dynamics for the structure and transfer of productivity in food webs, and for the function of higher trophic levels in estuarine ecosystems?

To address these questions LTER Researchers will use a combination of approaches: 1) the collection of long-term data on key ecosystem drivers and ecosystem responses, 2) short and long-term experiments, 3) comparative ecosystems studies, and 4) modeling. All data collected by the PIE LTER will be centralized and easily accessible to PIE-LTER scientists, local, regional and state partners, and the broader scientific community.

Broader Impacts: The educational and outreach program at PIE LTER is greatly strengthened through partnerships with local educators and NGOs. LTER personnel will continue to collaborate with Massachusetts Audubon and the Governor's Academy for the LTER schoolyard program, which has brought hands-on science training to students in grades 5-12. "Salt marsh Science" currently serves more than 1000 students and 50 teachers a year. Over the next six years the LTER plans to expand teacher training, and include a focus on environmental stewardship. Undergraduates will be served by intensive research experiences focusing on individual projects under the mentorship of PIE scientists. Both undergraduate and graduate student involvement will increase with the addition of new PIs. PIE will maintain an active outreach program through collaboration with many local and regional NGOs including the Gulf of Maine Institute, Essex County Greenbelt, the Ipswich River Association, and the Parker Clean Water Association. PIE scientists help bring scientific information into policy by serving as advisors to policy makers at the local, state, and national level, a role that continues to grow.

Project Report

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 insight into land change processes (Pontius & Connors 2009). We have shown how a common measurement of map comparison, kappa, is flawed, and have proposed a better method that mathematically separates the assessment of the quantity of each category versus the spatial allocation of each category. 9) Haying has been practiced on salt marshes since colonial times. We examined sites which had been hayed for very long periods of time and found that the removal of large amounts of aboveground biomass had no effect on the abundances of small invertebrates, fish or breeding birds, and only minor effects on the food web. Vascular plant diversity did not change. Broader Impacts: Our K-12 schoolyard program, "Salt Marsh Science", is directed by Elizabeth Duff of the Massachusetts Audubon Society who won the "Massachusetts Marine Education of the Year" award in 2010. The program serves over 1,000 students in grades 5-12 in ten schools. College undergraduates are served through internships, research projects and field trips. Both graduate students and post-doctoral investigators work at the PIE site and in addition to their own work, they are exposed to a broad array of research topics at the site. As part of the MBL-Brown IGERT Program, graduate students learn to apply next generation sequencing techniques to approach ecosystem questions. Outreach is an important part of our mission and includes inter-LTER efforts and participation in the MBL’s science journalism program. We have close connections with nearly all of the management agencies and NGOs in the region and serve on many advisory boards.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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David Garrison
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Marine Biological Laboratory
Woods Hole
United States
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