Award: OCE-1637630

Scientific 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 response of a linked watershed-marsh-estuarine system in northeastern Massachusetts to rapid environmental change. Some major findings were: 1) Over the past 20 years, rivers entering the estuary show a decline in the mean annual concentrations of nitrate, while phosphate is increasing. The decline of nitrate has occurred despite increased human activity in the watersheds, suggesting that beaver ponds, which have increased since the early 2000s, are altering the relative proportions of storage, emissions, and transport of inorganic nutrients to the estuary. Annual fluxes of other constituents show no temporal trends, instead, export is controlled by the large inter-annual variability in discharge. This suggests that climate variability is currently more important than land use change for most constituents. 2) A major effort was building a robust understanding of how the marsh/estuarine system will respond to sea-level rise (SLR). Marshes must keep up with SLR or drown. Currently our marshes are predominantly high elevation marshes vegetated by Spartina patens with low elevation marshes dominated by Spartina alterniflora only making up about 20% of the marsh area. Measurements and models of the estuary revealed that there is a net loss of marsh due to erosion but that some portion of the eroded sediment is being redeposited onto the marsh platform contributing to marsh accretion. Field measurements on the marsh surface found that marsh accretion rates were significantly correlated with marsh elevation, with higher accretion rates in low-elevation marshes. This was driven by not only the higher deposition of eroded sediments but also by changing production of the grasses with elevation. A model of how both sedimentation and grass growth varies with elevation was coupled with a hydrodynamic model to predict how the marsh will change with SLR. If SLR is moderate (Spartina alterniflora) will begin to replace the higher elevation vegetation (S. patens). At high rates of SLR, (1 cm/yr), the marsh is greatly reduced in size and the high marsh is largely lost. 3) Shifts in habitat configuration and productivity in marshes due to SLR may shift the availability of some types of prey, with cascading consequences for trophic dynamics. Although we have not yet seen a loss of high marsh habitat in PIE marshes, an experiment revealed the importance of the high marsh to intermediate consumers. When altered creek geomorphology prevents mummichogs (a killifish Fundulus heteroclitus) from accessing high marsh prey, it results in decreased mummichog abundance. 4) A large amount of carbon is stored in salt marsh sediments. Measurements from cores, dated using radiometric methods, shows marsh burial rates between 70 to 190 gr.C per m2. Annual measurements of C storage using eddy flux towers, also show similarly high rates, with low marshes storing more C than high marsh. However, these measurements show a large interannual variability which we can relate to changes in summer precipitation and/or soil salinity. We have not seen large lateral losses of inorganic carbon from our marshes in contrast to some other areas. 5) Waters in the Gulf of Maine are warming rapidly, which has led to the northward expansion of southern species such as the fiddler crab, Minex pugnax. Adults were first observed in 2014 and since they have continued to expand in number. Studies have shown that crabs in PIE LTER marshes are larger and have fewer parasites than those in marshes to the south. In areas where the burrows are present, they reduce above ground and below ground plant biomass. The effect on aboveground biomass was surprising because in the fiddler crabs historical range (Cape Cod, Massachusetts and south), they facilitate growth. BROADER IMPACTS: PIE-LTER Schoolyard Program: Our Salt Marsh Science program serves grades 5-12. The program brings students and teachers into the marsh to examine changes in salt marsh vegetation due to tidal restrictions and hydrologic restoration. Mass Audubon has added a new climate change focus that will make use of the vegetation transects teachers and students have been measuring for the past 25 years. The program had serves about 500 students a year and is growing. ● Gulf of Maine Institute (GOMI): PIE scientists provide scientific support to GOMI for teachers to develop their in-class programs which emphasizes the importance of the watershed to the coastal zone. ●Graduate and Undergraduates: Each summer, 15-25 undergraduate students and 10-25 graduate students were involved in the PIE LTER. ● Interactions with Policy Makers and Management Agencies: The science carried out at PIE has influenced environmental policy locally, regionally, and nationally. PIE scientists serve on numerous advisory committees for federal and state commissions and nonprofit environmental organizations. For more information see https://pie-lter.ecosystems.mbl.edu/welcome-plum-island-ecosystems-lter Last Modified: 01/28/2024 Submitted by: AnneEGiblin