Natural and Anthropogenic Controls on Wood Loads in River Corridors of the Rocky, Cascade, and Olympic Mountains, USA

Water Resources Research

Wohl

2018

Wood in rivers creates habitat, shapes the morphology of valley bottoms, and acts as a pool of organic carbon (OC). Effective riverine wood management depends on a robust understanding of the spatial distribution of wood throughout river networks. This motivates the analysis of wood load in relation to both reach‐ and basin‐scale processes. We present wood load data coupled with precipitation, forest stand characteristic, land use, and geomorphic data across four basins in the Rocky, Cascade, and Olympic Mountains of the western U.S. We compare basins with differing land use within the same climatic region and basins in differing climates and statistically model intrabasin wood load variability. Wood load is a function of metrics that generally describe river corridor spatial heterogeneity, metrics that describe wood storage patterns, and, at a broader scale, metrics that relate to wood supply. From this, we generate a conceptual model to describe controls on wood load across spatial scales. We use this model to propose that spatial heterogeneity and wood storage pattern together determine reach‐scale wood trapping efficiency. Trapping efficiency in turn regulates how wood supply to valley bottoms determines wood load. We also find that wood in an undisturbed basin stores significant amounts of OC and that wood load restoration has the potential to restore significant amounts of OC to valley bottoms. This conceptual model of wood load controls may serve as a framework to guide wood load modeling and restoration at multiple scales.

Section: Resultsmentioning

confidence: 99%

Natural and Anthropogenic Controls on Wood Loads in River Corridors of the Rocky, Cascade, and Olympic Mountains, USA

Water Resources Research

Wohl

2018

“…This work was done alongside work presented in Scott and Wohl (2018b) and hence shares field sites, study design, GIS, and sampling techniques. We quantified soil organic carbon concentrations to a depth of approximately 1 m in the Big Sandy basin in the Wind River Range of Wyoming and the Middle Fork Snoqualmie basin in the central Cascade Mountains of Washington (Fig.…”

Section: Methodsmentioning

confidence: 99%

Geomorphic regulation of floodplain soil organic carbon concentration in watersheds of the Rocky and Cascade Mountains, USA

Wohl

2018

Earth Surf. Dynam.

Abstract. Mountain rivers have the potential to retain OC-rich soil and store large quantities of organic carbon (OC) in floodplain soils. We characterize valley bottom morphology, floodplain soil, and vegetation in two disparate mountain river basins: the Middle Fork Snoqualmie in the Cascade Mountains and the Big Sandy in the Wind River Range of the Rocky Mountains. We use this dataset to examine variability in OC concentration between these basins as well as within them at multiple spatial scales. We find that although there are some differences between basins, much of the variability in OC concentration is due to local factors, such as soil moisture and valley bottom geometry. From this, we conclude that local factors likely play a dominant role in regulating OC concentration in valley bottoms and that interbasin differences in climate or vegetation characteristics may not translate directly into differences in OC storage. We also use an analysis of OC concentration and soil texture by depth to infer that OC is input to floodplain soils mainly by decaying vegetation, not overbank deposition of fine, OC-bearing sediment. Geomorphology and hydrology play strong roles in determining the spatial distribution of soil OC in mountain river corridors.

“…Net changes in wood and soil retention due to activities such as forest harvest in the wet glaciogenic basin (Scott & Wohl, 2018a) have likely caused substantial redistribution of OC and potential sequestration lower in the network (Wohl, Hall, et al, 2017;Wohl & Scott, 2016). A century-scale turnover (assuming stocks are currently in steady state) of the majority of the substantial floodplain soil OC pool indicates that changes in soil retention and resulting storage of OC (e.g., due to land use change) should be tightly linked to OC respiration rate to the atmosphere over moderate timescales.…”

Section: Discussionmentioning

confidence: 99%

“…This study was conducted alongside work presented in Scott & Wohl (2018a, 2018b, and hence shares many of the same methods with those two works.…”

Section: Methodsmentioning

confidence: 99%

Geomorphology and climate interact to control organic carbon stock and age in mountain river valley bottoms

Earth Surf Processes Landf

Wohl²

2020

Self Cite

Organic carbon (OC) in valley bottom downed wood and soil that cycles over short to moderate timescales (10 to 10 5 yr) represents a large, dynamic, and poorly quantified pool of carbon whose distribution and residence time affects global climate. We compare four disparate mountain river basins to show that mountain river valley bottoms store substantial estimated OC stocks in floodplain soil and downed wood (127.3-37.4 +24.5 MgC/ha, n = 178). Although soil OC is generally young (exhibiting a median radiocarbon fraction modern value of 0.97-0.01 +0.02 , n = 121), geomorphic processes regulate soil burial and processes that limit microbial respiration, preserving aged OC in certain parts of the river network. Statistical modeling of OC stocks suggests that biogeomorphic processes and the legacy of past erosion regulate the modern distribution of OC in river networks. Our results suggest that although mountain rivers may accumulate large OC stocks relatively rapidly, those stocks are highly sensitive to alterations in soil and wood retention, implying both short-and long-term feedbacks between retentiveness and the distribution of OC between the land and atmosphere.