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Format:
Print
Author:
Reusser, Lucas Jonathan
Dept./Program:
Natural Resources
Year:
2014
Degree:
Ph. D.
Abstract:
Human activities such as agriculture, development, mineral extraction, and land clearance, move more material at Earth's surface than any natural process. Quantifying natural, or background rates of landscape erosion is prerequisite to understanding the impact of human landuse practices on natural process rates. Through the clearance of hillslopes, human activities have profoundly altered the source areas of sediment in drainage basins, and the mixing of sediment in river networks around the globe. Traditional approaches used to quantify the mass of sediment moving through fluvial systems (such as contemporary sediment yield data) are typically uncertain and often biased, and thus do not reflect background rates of erosion.
This research utilizes concentrations of both meteoric and in situ ¹⁰Be measured in samples of river sediment to locate source areas of disproportionately high sediment production and to estimate rates of long-term background erosion in order to quantify human-impacts on natural erosion rates in two locations; 1) the east coast of New Zealand's North Island, and 2) the southern Appalachian Piedmont draining the North American Atlantic passive margin. While these two regions represent very different geologic and climate conditions, they share a common history of intensive land clearance for agriculture, peaking in the early 1900's, and the ensuing erosional consequences.
In the Waipaoa River Basin, New Zealand, concentrations of meteoric ¹⁰Be in river sediment trace the mixing of sediment from tributary basins characterized by different erosion styles as they mix downstream. A simple mixing model indicates that the gullied headwater regions of the Waipaoa river system produce sediment at a rate ~20 times that of the eastern and western tributaries. A limited number of in situ ¹⁰Be measurement suggest that the Waipaoa landscape erodes naturally at a rate of ~300 m/My, nearly 10 times slower than the modern, human-induced sediment output from the catchment.
In situ ¹⁰Be data from the southern Appalachian Piedmont suggest that the region naturally erodes more than 100 times more slowly (~9 vs. ~950 m/My) than during the period of peak agricultural use. Further, a carefully designed sampling strategy robustly characterizes background erosion rates at the landscape-scale, and allows for the prediction of background erosion rates at any point across the Piedmont with a simple yet strong (R² = 0.88) average basin slope-based regression model.
Findings from both studies provide valuable information for improving our ability to manage landscapes affected by human activities. Meteoric ¹⁰Be-based mixing models, such as those generated in the Waipaoa Basin, can apportion the relative contribution of sediment from different regions on non-uniformly eroding landscapes, while landscape-based predictive erosion models, such as that produced for the southern Piedmont can inform total maximum daily load values for sediment and associated pollutants.