Nutrient and Fine Sediment Transport Driven by Perturbations in River Bed Movement

In mountainous watersheds,

watershed

An area of land that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually flows to the lowest point in a basin.

Source: USGS Source

riverbeds are commonly composed of gravel sized sediment that undergoes episodic transport during higher magnitude flow events. Gravel-bedded rivers typically have a coarse surface layer (‘armor layer’) that is relatively difficult to move and protects a finer subsurface layer that is often enriched in Phosphorus (P), fine sediment, and Particulate Organic Carbon (POC). When high flow events occur, armor layer motion can release large quantities of nutrients and fines that could explain the large observed temporal variations in POC, suspended sediment (SS), and various forms of P exported from many watersheds. The relative importance of armor layer movement in controlling POC, P, and SS concentrations in rivers will vary with the streambed concentrations of these constituents. These streambed concentrations may also depend on the influence of groundwater

groundwater

Water that occurs below Earth's surface. When rain falls to the ground, a portion percolates (sinks) into the ground and collects in spaces in the underground rocks.

Source: A student's guide to Global Climate Change Source

inputs to the river reach. We test three hypotheses about armor layer motion and river concentrations of POC, P, and SS using detailed field measurements in two river reaches in the upper Jemez River basin, New Mexico. We will take high resolution measurements of armor layer movement and streambed concentrations as well as P, POC, and SS in the water column during flow events over two years. The proposed research will bring a mechanistic understanding of the linkages between geomorphology and nutrient storage, release, and transport. The study also addresses how perturbations, such as the sequence and magnitude of droughts and floods, constrain biogeochemical nutrient cycling

nutrient cycle

The nutrient cycle describes how nutrients move from the physical environment into living organisms and are recycled back to the physical environment.

Source: Sustainable Sanitation and Water Management Toolbox Source

and impact subsequent temporal variations in nutrient and fine sediment export from mountainous watersheds.