Wetlands in the Quaternary Project

Science Center Objects

Wetlands accumulate organic-rich sediment or peat stratigraphically, making them great archives of past environmental change. Wetlands also act as hydrologic buffers on the landscape and are important to global biogeochemical cycling. This project uses wetland archives from a range of environments to better understand how vegetation, hydrology, and hydroclimate has changed on decadal to multi-millennial timescales, and how wetlands have responded to past perturbations, such as fire, sea-level rise, and permafrost degradation. We use a multi-proxy approach that includes pollen, plant macrofossils, stable isotope analysis, and radiometric dating. Study sites range from Florida and the Atlantic Coastal Plain to Alaska.

Sea-level rise 

Wetlands protect coastlines from sea-level rise, but wetland archives can also elucidate past change in rates and the responses of these coastal systems to those changes. By closely examining the layers laid down by wetland sediments and peat, we can use a combination of physical properties and radiometric dating to examine past rates of sea-level rise, while pollen, plant macrofossils, and stable isotopes, can provide insights into the depositional environment at the time of deposition. This project is currently examining Holocene rates of sea-level rise and mechanisms for inundation of formerly terrestrial environments in Florida Bay. We are also examining how tidal freshwater wetlands along the Atlantic Coastal Plain have shifted over the Holocene in response to changing rates of sea-level rise and the resilience of these riparian wetlands in the future. 

 

Permafrost thaw

Permafrost, or permanently frozen ground, underlies vast swaths of the boreal and arctic zones. With thaw accelerating under current warming, wholesale ecological and hydrological changes are occurring, putting wildlife and infrastructure at risk. In permafrost peatlands, ice-rich permafrost thaw causes subsidence that can transform forested peatlands to wet herb and moss peatlands, resulting in large changes not only in the structure and function of these systems, but also in biogeochemical cycling. This project is examining the nature and rate of both permafrost aggradation and degradation on Holocene timescales to better understand trajectories of vegetation change and biogeochemical change upon thaw. Study sites include boreal peatlands in the discontinuous and sporadic permafrost zones of Alaska. 

 

Land-use change 

Miriam Jones, Thomas Sheehan, and Diana Carriker use a Russian Corer to extract samples from The Great Dismal Swamp.

USGS scientists recently collected peat and lake core samples from the Great Dismal Swamp to help reconstruct natural, environmental conditions over the past 12,000 years. Click on the image to learn more.

(Credit: Debra Willard. USGS. Public domain.)

Human evidence of land-use change can be picked up to varying degrees in wetland records. In some cases, modifications are deliberate, such as ditching and draining of wetlands for harvesting of natural resources. In other cases, transformations to the larger landscape result in changes to neighboring wetlands and waterways, such as colonial land clearance that resulted in a large pulse of terrestrial sediment into riparian and coastal wetlands. This study is examining how a range of land-use changes have altered wetlands on decadal to centennial timescales, while also placing these changes into the greater context of natural variability by examining centennial to millennial-scale shifts. This project helps identify markers and impacts of land-use change and can also aid decision-makers and land managers plan for land restoration. Study sites include the Great Dismal Swamp, VA and tidal rivers on the Atlantic Coastal Plain. 

 

Hydroclimate variability

Examining the range of hydroclimate variability from Holocene records can help contextualize recent observations. In some cases, hydroclimate variability is linked to long-term modes of climate variability, which can be linked to precipitation extremes and fisheries productivity. This study is examining Holocene hydroclimate variability using oxygen isotopes derived from peat cellulose across a the northern Gulf of Alaska and the Bering Sea to examine the timing and linkages to Aleutian Low variability and its connection to sea ice extent, ocean and atmosphere circulation, and teleconnections with northern hemisphere climate phenomena, such as El Nino Southern Oscillation, Arctic Oscillation, and the Pacific Decadal Oscillation. 

 

 

Project Lead:

Miriam Jones 

 

Project Team: 

Thomas Sheehan (USGS), Kristen Hoefke (USGS), Diana Carriker (USGS), Bailey Nash (USGS)