ABSTRACT

Hydrologic variability poses significant challenges to society. However, the potential for hydrologic change remains poorly understood. Sedimentary patterns within small lake basins record past changes in water levels and can be used to track shifts in moisture availability over time. This study assesses hydrologic variability at the scale of millennia and centuries over the past 11,000 years in Massachusetts, where existing lake sedimentary data appear to indicate significant changes in the frequency of past droughts. The creation, analysis, and synthesis of new, well-resolved sedimentary data, in combination with detailed fossil pollen data, is used to evaluate sub-millennial hydrologic variability, its controls, and its effects.

Intellectual Merit
Past hydroclimatic variation is poorly understood, especially in humid temperate regions. Little is known about the frequency, magnitude, and cause of variations. Stratigraphic records of lakelevel change in the northeastern U.S. can provide new insight into important regional to global climatic processes. High-resolution geophysical surveys and sediment cores of lakes in the northeastern U.S. have documented climatically meaningful patterns in the sedimentary record - and indicate possible changes in high-frequency hydrologic variability. Existing data appear to indicate a series of low lake stands of millennial and sub-millennial duration between 6000 and 2000 years ago in contrast to little variability on these time scales during earlier and later portions of the Holocene. This grant studies four lakes to produce detailed lake-level histories. Similarities and differences among the histories are used to evaluate past hydroclimatic changes and to better understand the causes of the apparent high frequency variation. Temperature reconstructions also indicate warmer than modern winters in the northeastern U. S. in the mid-Holocene. Given the potential to understand the effects of future climate warming through analogy, this project evaluates possible linkages between past warmth and hydroclimatic variation. By comparing sediment and pollen data, the group also investigates biotic responses to past climatic changes.

Broader Impacts
Water is a vital resource and risk of drought is a major societal concern. Questions exist about the potential for dramatic hydrologic change in humid, heavily populated regions like the eastern U.S. Expectations of future climate warming increase the need to understand the mechanisms that drive changes in water resources. This study offers important baseline data regarding the range of regional hydrologic variability and its ecological impacts. This data provides insight into water resource responses to climatic conditions like those predicted for the future. The results of this study are useful to a wide variety of stakeholders from agricultural businesses to habitat conservation groups and municipalities concerned with managing water supplies and mitigating drought risk. Resource managers and policy makers have access to the results to make informed decisions. This project also advances the development of young researchers while promoting innovative science.

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