Coastal and Estuarine Research

Salt marshes provide essential ecosystem services for coastal regions around the world. However, their future survival is threatened by changes in coastal land use, water quality, climate, introduction of invasive species, and ongoing sea level rise. The processes that govern marsh integrity and resilience to both natural and anthropogenic stressors remain poorly understood in part because the maintenance of coastal wetlands involves complex biophysical feedbacks between inorganic sediment supply, nutrients, plant growth, and flooding. I am involved in several projects evaluating current marsh integrity, historical trends, causes of marsh change, and modern sedimentary processes.

Linking unvegetated to vegetated marsh ratio (UVVR) to causes of coastal marsh change

The goal of this collaborative research with Jon Woodruff (UMass Geosciences), Kostas Andreasdis (UMass Civil and Environmental Engineering) and Neil Ganju(USGS) is to improve the predictive performance of the remotely sensed unvegetated to vegetated marsh ratio (UVVR) as a marsh vulnerability index and increase our understanding of the causal mechanisms underlying marsh changes for systems characterized by a range of vulnerabilities and UVVRs. We are using geospatial analysis tools to identify links between oceanographic and environmental condition, land use history, and other variables with marsh UVVR. These analyses are paired with targeted field studies and marsh sediment core analyses to provide a long-term perspective on recent trends in marsh integrity and extent.

Sedimentary Controls on Tidal Marsh Integrity and Resilience

The supply of sediment to marshes is a critical factor controlling marsh survival and adaptability to rising sea level. However, the availability sediment varies from site-to-site and the factors that control its delivery to marshes are poorly constrained. This is particularly true for the Northeast where the geology and predominant sediment sources, as well as oceanographic characteristics including tides and waves, are especially variable. With support from the Northeast Climate Adaptation Science Center (NECASC), I am collaborating with Jon Woodruff (UMass) and Brian Yellen (UMass) to study controls on the availability of fine sediment to marshes and the mechanisms responsible for distributing sediment throughout marshes. This work is examining a network of marsh sites across New England and involves instrumental observations of suspended sediment and water level variations, measurements of sediment deposition on marsh surfaces, and evaluation of long-term trends from sediment cores.

Watershed Studies

Response of the New England Landscape to Natural and Human disturbances

This research, in collaboration with Noah Snyder (Boston College) is examining the sensitivity of the intensively lived-in New England landscape to disturbances such as floods, landslides, forest fires, and land clearance. We are studying a network or watersheds across New England, with varying geographic, geologic, and land-use characteristics. Sediment cores collected from lakes within each watershed are used to develop records of spatial and temporal variations in sediment yield from the early Holocene through the present day. These long-term records are combined with analyses of high-resolution digital elevation models, geologic maps, aerial photographs, and historical archives to quantify changes in land use, climate, and hydrology, and evaluate their control on erosion and quantify the impact of various disturbances. This ongoing work has been supported b they Northeast Climate Adaptation Science Center (NECASC) and a Bullard Fellowship from Harvard Forest. Some initial results from this work highlight climatic influences on erosion and quantify the impacts of timber harvest on sediment yields. Ongoing work continues to examine controls on spatial variability in sediment yields and sensitivity to disturbance along with a focus on the cascading impacts of landscape and climate change on water quality and ecosystem integrity.

Climate Change

Paleoclimate reconstructions from lake sediments

Understanding spatial variability and environmental impacts associated with global climate change requires reconstructions of past climatic conditions from natural geologic archives. I have been involved in several projects focused on paleoclimate reconstructions from high-latitude locations where positive feedbacks within in the climate system amplify the climatic changes.  This includes work on Ellesmere Island in the Canadian Arctic and Lake El’gygytgyn, a meteorite impact crater in Siberia preserving a continuous 2.8 million year record of Arctic climate change described in Science in 2012 and 2013.

Sensitivity of High Arctic lake-ice conditions to climate change

The duration of ice cover on lakes is of fundamental importance to physical, chemical and biological processes in lake systems. I used remote sensing data to evaluate recent changes in the ice cover of Upper Murray Lake in the Canadian High Arctic, with the goal of understanding the sensitivity of lake ice cover to past and future changes in climatic conditions. The combination of a long, cold winter and a brief summer melt season leads to the development of 1.5-2.2 m thick ice cover at the start of the melt season and limited open water conditions. Changes in lake-ice conditions were monitored using space-borne synthetic aperture radar (SAR) data from the Canadian Space Agency (CSA) Radarsat-1 satellite. Climatic controls on the rate and timing of ice melt were evaluated using the National Centers for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) reanalysis data. Under current climatic conditions Upper Murray Lake averages several weeks of ice-free conditions in August and early September, although in some years a continuous ice cover persists throughout the year. The relationship between summer temperature and ice melt at Upper Murray Lake indicates that recent warming in the High Arctic has forced the lake across a threshold from a state of perennial ice cover to seasonal melting. Projected future warming will continue to increase the duration of ice-free conditions in High Arctic lakes. At Upper Murray Lake ice out is predicted to occur ~14 days earlier for every 1° C of warming. Results of this study were published in Arctic, Antarctic and Alpine Research.