Temporal and spatial variations in watershed connectivity dictate suspended sediment source and fate
Abstract
Sediment transport by rivers exerts a primary control on the fate of contaminants and nutrients, which are often closely associated with suspended sediment. Despite their importance, downstream transport efficiency and connectivity remain difficult to constrain, due to temporal and spatial variability in suspended sediment fate and the logistical challenge of constructing sediment budgets. Motivated by our ongoing projects studying suspended sediment and contaminant fate on rivers ranging in scale from headwater streams to the Amazon River, we investigate the relative importance of channel and basin morphology, hydrology, and sediment characteristics on transport efficiency. We develop detailed, time-varying suspended sediment budgets for rivers in New England, quantifying sediment inputs using terrestrial and airborne lidar, and fate using cosmogenic radionuclides, direct suspended sediment sampling, and continuous monitoring of turbidity and discharge. We address scale-dependent processes in watersheds between 101-104 km2 and intra-river variability by investigating seasonal fluctuations in connectivity. In watersheds affected by Tropical Storm Irene, prolonged lateral connectivity between disturbed hillslopes and rivers continues to elevate sediment yields 2-20 times above background rates. However, this lateral connectivity is unidirectional (hillslope to channel), and subsequent downstream transport efficiency (>80%) is much higher than in unaffected watersheds (20%), where suspended sediment erosion is approximately balanced by deposition on channel margins and floodplains. Longitudinal connectivity in suspended sediment is not meaningfully limited by run-of-river dams on small rivers, and is only reduced ~50% by low-aspect-ratio dams on larger rivers. These results demonstrate the need for a more nuanced understanding of how the interplay between varied sediment sources and watershed hydrodynamics controls the magnitudes of lateral, longitudinal, and vertical transport.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP51C2103D
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 1804 Catchment;
- HYDROLOGY;
- 1815 Erosion;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY