Long‐term suspended sediment and particulate organic carbon yields from the Reynolds Creek Experimental Watershed and Critical Zone Observatory

Abstract

Long‐term (>20 y) suspended sediment (SS) and particulate organic carbon (POC) records are relatively rare and yet are necessary for understanding linkages between climate, erosion and carbon export. We estimated long‐term (>23 y) SS and POC yields from four nested catchments that ranged from <1 to 54 km2 in area across the Reynolds Creek Experimental Watershed and Critical Zone Observatory (RCEW‐CZO) in southwestern Idaho, USA. We found strong relationships between log10SS and log10POC (R2 = 0.38–0.86) that varied across catchments but remained robust across years, one dry and one of the wettest water years on record. Mean annual SS yields varied from 18 to 89 g SS m−2 y−1 and POC from 0.6 to 11.0 g C m−2 y−1 across the four catchments. Water yield explained much of the temporal variation (72%–85%) in SS and POC yields except in a small, snow‐dominated headwater catchment where it explained 15%–51%. The largest five water years accounted for 69%–84% of the total SS and POC yields in catchments with 24 y records. All catchments had positive slopes (>0) for SS and POC concentration‐discharge (C‐Q) relationships, with large catchments exhibiting greater slopes (0.66–0.97) than smaller ones (0.14–0.16). In addition, most catchments were dominated (80%) by clockwise hysteretic curves. Lack of seasonal exhaustion in the SS‐POC relationships, positive C‐Q and clockwise relations indicated that these systems were transport‐rather than supply limited, and that sediment and POC appeared to be sourced from channel/bank erosion and remobilization. POC yields represent 1%–10% of mean water year net ecosystem exchange depending on elevation; lower elevation catchments may shift from being carbon sinks to sources after accounting for fluvial POC export associated with changes in climate.

Multiscale responses and recovery of soils to wildfire in a sagebrush steppe ecosystem

“…These losses were an order of magnitude higher than unburned catchments 36 . Vega et al 25 further showed that the fire response was a two-step process with wind erosion loading leeward (north) aspects preferentially in swales, and these swales were emptied to streams by water erosion 36 . These results again underscore the importance of incorporating multi-scale domains into disturbance models in these regions.…”

“…Other loss pathways not considered in this study but documented in other studies such as wind and water erosional losses may also need consideration in dryland disturbance models. In particular, large losses as sediment and associated particular organic carbon were documented in the two years following the fire, a total of 1.17 and 0.0625 kg m −2 sediment and carbon, respectively 36 . These losses were an order of magnitude higher than unburned catchments 36 .…”

“…In particular, large losses as sediment and associated particular organic carbon were documented in the two years following the fire, a total of 1.17 and 0.0625 kg m −2 sediment and carbon, respectively 36 . These losses were an order of magnitude higher than unburned catchments 36 . Vega et al 25 further showed that the fire response was a two-step process with wind erosion loading leeward (north) aspects preferentially in swales, and these swales were emptied to streams by water erosion 36 .…”

Exploring the Complex Effects of Wildfire on Stream Water Chemistry: Insights From Concentration‐Discharge Relationships

“…A few parameters (POC, PON, total dissolved Al, Zn, and Ba) did increase with event flows and, for these, it's unclear if fire played a role in the increase or if event flows more generally led to enrichment trends as is common for many non‐fire impacted watersheds (Knapp et al., 2020). For POC and PON specifically, it is likely that fire played a part in generating some of the differences across flow categories due to the close connection between processes mobilizing larger material, like suspended sediment and suspended particulate organic matter, that often leads to strong positive correlations in other watersheds (Glossner et al., 2022; Richardson et al., 2023). In addition, many trace elements are found in association with suspended solids, like organic matter and minerals (Brown & Parks, 2001).…”

Seasonality and evaporation of water resources in Reynolds Creek Experimental Watershed and Critical Zone Observatory, Southwestern Idaho, USA

“…The main outlet for Reynolds Creek, Outlet, incorporates streams from the 238 km 2 catchment and includes agriculture areas with flood irrigation and reservoirs. More details on these catchments are described in Glossner et al (2022) and Pierson et al (2001). An irrigation pond, sampled by Souza (2022), collects water from Reynolds Creek and returns irrigation flow prior to the main outlet to be used for additional irrigation within the Reynolds Creek watershed, and it was sampled to determine surface contributions to groundwater recharge at nearby wells.…”