Date of Award

5-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Laurie J. Osher

Second Committee Member

David B. Dail

Third Committee Member

Mark H. Stolt

Abstract

The coastal zone, specifically estuarine systems, has been largely overlooked in carbon sequestration studies. To gain an understanding of organic matter storage potential in the sub aqueous soils of Taunton Bay estuary (Hancock County, Maine), this study ( I ) quantified soil carbon pools (C pools) in the top 100 cm of the estuarine subaqueous soils (Chapter I), and (2) identified organic carbon sources using stable isotope biogeochemistry (Chapter 2). This study built upon previous research that documented soil/landform relationships in the estuary. Quantification of soil organic carbon revealed that the mean C pool in the top meter of the estuarine soils of Taunton Bay is similar to values reported for Maine's upland forest soils. However, while forest soils store the majority of their organic carbon in surface horizons, the organic carbon content in Taunton Bay estuary soils is relatively constant with depth and in some landforms there is an irregular decrease in organic carbon with depth. The soil organic carbon content in Taunton Bay soils is similar to other near-shore marine sediments, and the C pool (136 Mg C ha-1) is greater than values reported globally for Entisols. Yet this value is low compared with C pools reported in a range of other ecosystems known for there high C sequestration rates, including terrestrial wetlands. The lower bulk density (0.67 g cn-1) of these estuarine soils likely contributes to a C pool that is much less than those of other ecosystems. The large-diurnal flux of tidal water and comparatively small volume of fresh water from the upland watershed results in a well-mixed estuary. The stable isotope analysis of the soils identify that the majority of the organic carbon stored in these estuary soils was fixed by estuarine or marine biota. The terrestrial organic matter present is located primarily in soils at the edges of the estuary which have experienced inundation and burial as a result of rising sea level. With increasing distance toward the estuary channel, the relative content of terrestrial organic matter decreases. These results illustrate the need to quantify organic carbon in coastal ecosystems, and challenges the widely held belief that the organic carbon stored in estuarine systems is primarily transported from in the surrounding watershed via surface water. A more comprehensive quantification of estuarine organic carbon stored in the fine soils of these coastal systems may reduce the quantity of carbon 'missing' from global carbon storage estimates.

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