Natural Drought and Flood Histories from Lacustrine Archives Project

Holocene Synthesis Project

Holocene Synthesis Project

The Holocene Synthesis Project integrates a variety of information about past climate variability across the North American continent for the past ~12,000 years. 

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Land Change Science Program

Land Change Science Program

Learn more about this project and it's role in the Land Change Science Program.

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Heavy rainfall, flooding, and drought frequently devastate North American populations and are predicted to continue posing serious threats over the next century. The nature of these phenomena at centennial and millennial timescales is not well constrained. Clarifying the spatial patterns of drought and moisture trends is fundamental for comparison with other datasets for the purposes of understanding the mechanisms that drive natural, low-frequency variability and for improving computer models that predict future changes. This project aims to augment existing data with additional paleorecords, which are needed to disentangle the complex patterns of and controls on interior continental hydrologic variability during the Holocene. Data produced for this project is directly useful for local, state, and federal governments for mitigation planning, disaster relief, wildlife conservation, and resource management. Climate model researchers will benefit from data produced during this project, which provides an independent dataset to test model performance and improve prediction of future patterns and trends.

Project Lead: Jessica Rodysill

Project Team: Andrew Everett, Karlee PrinceKristen Steele

 

Paleorecords capture the low-frequency variability that instrumental records are too short to capture, yet the hydrology of the central U.S. is highly complex and paleorecords from the region are exceedingly sparse.  Previous work performed as part of the USGS Holocene Synthesis project illuminated complex centennial-scale patterns of drought and wetter-than-average conditions across the North American continent interior during the past two millennia, where paleorecord data coverage is sparse.  In order to elucidate the patterns of naturally-occurring drought, floods, and storms for the past, this project develops new well-dated, high-resolution reconstructions from lacustrine archives from the continent interior.  Using a combination of new and existing sediment cores, this project utilizes geophysical, geochemical, and biological proxy data in concert with novel 14C, 210Pb, and 137Cs-based statistical approaches for quantifying age-depth relationships to expand paleoflood and drought data coverage across the Upper Midwest and central U.S. during the Holocene.

Scientists are collecting core samples from the Great Dismal Swamp in Virginia

Scientists collect core samples from the Great Dismal Swamp, VA in order to understand natural conditions before centuries of ditching, draining and harvesting. (Credit: Debra Willard, USGS. Public domain.)

Study site reconnaissance will include searching the literature for previous work performed in the region, searching online databases for site information and data from previous studies, using historic maps and imagery to characterize the quality of proposed sites for flood and lake level reconstructions, and performing site visits to obtain basic water depth and geophysical (e.g. GPR/CHIRP) data and water and surface sediment samples.  Sites determined to have high potential for archiving a continuous, high-resolution record of environmental changes with known historical flooding/drought will be prioritized to improve proxy validation. Sediment cores will be scanned and imaged on the GeoTek MSCL, split, described, sub-sampled, and analyzed for bulk mineralogy (smear slides, magnetic susceptibility), grain size (sieving or laser particle analysis), and organic content (loss-on-ignition).  Smear slide analyses will be used to direct more specialized lab measurements for each site based on the presence and variability in abundance/types of sediment components downcore (e.g. total inorganic carbon coulometry, XRD, abundances and stable isotopes of C, N, and/or O, diatom assemblages).  Sediment-based records will be dated using 210Pb, 137Cs, and 14C dating techniques, and age modeling will be performed using the Bacon software package or a similar technique to produce age-depth relationships with an approximation of uncertainty statistics.

Interpretations of flood histories will be based upon multi-proxy evidence for high energy event deposition (e.g. coarse grain abundance, stratigraphic evidence for event deposition and/or slumping, geochemical evidence of sediment delivery from terrigenous sources during periods of higher runoff) paired with elevation-based flood modeling, where possible. Where the sediment record overlaps with instrumental data, proxy validation will be performed to strengthen downcore proxy interpretations. Interpretations of drought histories will be based upon multiproxy evidence, mainly proxies for lake salinity, runoff, stratigraphic evidence for desiccation, and lake water elevation changes. Supporting information from vegetation proxies, diatom assemblages, evidence of fires, and isotopes of precipitation will be included when possible, depending on collaborator availability.  Where the sediment record overlaps with instrumental data, proxy validation will be performed to strengthen downcore proxy interpretations.