Title: Long-term Estimates of Inland Riverine Sediment and Particulate Organic Carbon (POC) fluxes from Reynolds Creek Experimental Watershed, Idaho USA
Abstract
There are large uncertainties in how inland riverine suspended sediment (SS) and particulate organic carbon (POC) fluxes will respond to climate change as key controls driving fluxes remain uncertain, specifically within semi-arid regions. The objective of this study was to quantify a 25-year sediment export record utilizing four nested watersheds within the Reynolds Creek Experimental Watershed (RCEW) in southwestern Idaho, including Tollgate and Johnston Draw. From historic sediment data, custom models were built in a load estimate model, Loadflex, to calculate loads and transferred to a load trend estimation package, EGRET, to determine flow-normalized fluxes. Three years of POC concentrations were then correlated to sediment concentrations, and POC export was estimated for each nested watershed. Initial results using linear interpolation show that flow-normalized SS fluxes ranged by 3 orders of magnitude across RCEW from 14.80 kg/yr in water year (WY) 2011 at Tollgate to 0.029 kg/yr at Johnston Draw during the WY. Inter-annual variability spanned 1 order of magnitude; for example, at Tollgate, flow-normalized flux varied from 14.80 kg SS/yr in WY2011 to 2.02 kg SS/yr in WY1996. Sediment fluxes are thought to be predominately influenced by quantity and phase of precipitation, with peak concentrations during high WY. At RCEW, flowpaths shift in high WY, leading to distinct SS fluxes. Typically, clockwise hysteresis loops are observed at Tollgate in average WYs (e.g., WY2004), suggesting SS is transported and exhausted from in-stream sources. However, this hysteresis shifts directions in high WYs (e.g., WY2017) and counter-clockwise hysteric loops suggest that sediment is transported from overland sources. These overland sources may vary with elevation, depending on whether rapid snow melt, rain-on-snow, or rain-on-frozen-ground events predominate. POC and SS relationships generated from 2016 data showed unique power-law relationships across watersheds. The model currently underestimates carbon at high flows, perhaps because POC was undersampled at these flows. Findings from our study suggest there is large inter-annual variability in sediment and POC export from streams, and that rain-on-snow events and timing of snowmelt are important drivers of variability in semi-arid regions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H21K1820G
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0438 Diel;
- seasonal;
- and annual cycles;
- BIOGEOSCIENCESDE: 1807 Climate impacts;
- HYDROLOGYDE: 1836 Hydrological cycles and budgets;
- HYDROLOGY