skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: The importance of oxbow lakes in the floodplain storage of pollutants
Abstract Oxbow lakes are important stores for fine-grained sediment, which potentially makes them critical sinks for sediment-associated pollutants. We leverage an exhaustive public archive of coring data, supplemented by our data collection, to provide a quantitative assessment of the role of oxbows as off-channel sinks. We investigated loading trends of sediment-sorbed polychlorinated biphenyls (PCBs) within oxbows of the Housatonic River, an actively meandering river in western Massachusetts, USA. Our results reveal the efficiency of oxbows as sinks, with average PCB concentrations (14.8 ppm) that are nearly twice that of the surrounding floodplain (7.56 ppm). Even though the 5.83 km2 floodplain is the largest sink of PCB-laden material, storing as much as 14.1 t of PCBs or 2.42 g m−2, oxbows store more than 20% of all PCBs (3.63 t of PCBs or 11.2 g m−2) while making up just over 5% of the floodplain surface area. Nearly 85% of the oxbow storage of PCBs occurs within the first 50 m of floodplain, making clear the significance of regular oxbow production to the off-channel storage of sediment-associated pollutants.  more » « less
Award ID(s):
2026789
PAR ID:
10533279
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
Geological Society of America
Date Published:
Journal Name:
Geology
Volume:
50
Issue:
4
ISSN:
0091-7613
Page Range / eLocation ID:
392 to 396
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, Geology)
    Abstract Spatial complexity impacts the resilience of river ecosystems by mediating processes that control the sources and sinks of sediment and organic material. Using four independent geochemical tracers and three morphometric indices, we show that downstream spatial gradients in stream power (Ω) predict storage of material in the channels and margins and/or floodplains. A field test in a 48 km2 watershed demonstrates that reaches with downstream decreases in Ω coincide with wider floodplains and elevated inventories of 137Cs, 210Pbex (ex—excess), and organic matter in locations of the ~3 to 20 yr floodplain. In contrast, reaches with downstream increases in Ω coincide with narrower floodplains and decreased inventories of 137Cs, 210Pbex, and organic matter. The occurrence of in-channel bedrock exposures and the activity of short-lived 7Be in within-channel sediments also correlate with downstream Ω gradients, demonstrating a link, over both short and long time scales, between withinchannel processes and floodplain-forming processes. The combined geochemical and physical characteristics demonstrate the importance of downstream gradients in sediment transport, characterized by downstream changes in stream power rather than at-a-point stream power, in determining spatial complexity in carbon and sediment storage at intermediate scales (102 to 103 m) in river systems. 
    more » « less
  2. ; ; (, Journal of Geophysical Research: Earth Surface)
    Abstract Floodplains provide important ecological, hydrological, and geomorphic functions within river corridors. During overbank flows, complex hydrodynamic conditions occur as water exits and re‐enters the channel and interacts with hydraulically rough floodplain vegetation. However, the extent to which floodplain vegetation influences channel‐altering hydrodynamic forces and thus bedform topography and sediment transport is poorly understood. We address this knowledge gap and present the results of flume experiments where we measured bedform topography under varied floodplain vegetation conditions at two overbank flow relative depths. The experiments were conducted in a 1‐m wide meandering compound channel inset in a 15.4 long, 4.9‐m wide basin. The channel bed was a mobile sand‐and‐gravel mixture with a median sediment size of 3.3 mm, and sediment transport occurred only within the channel. We tested bare and vegetated floodplain conditions with 2.7‐cm diameter rigid emergent vegetation elements at spacings of 3.0 and 12.1 units m−2. We performed a moving‐window analysis of topographic surface metrics including skewness, coefficient of variation, and standard deviation, as well as topographic patch analysis of area and contagion to measure changes in bedform heterogeneity as flow depth and vegetation density were varied. Our results show that both greater density vegetation and larger flows can increase bedform topographic heterogeneity. These findings suggest that floodplain vegetation and natural hydrologic regimes that include overbank flows can enhance stream habitat complexity. Designing for the effects of established vegetation conditions and prioritizing floodplain vegetation planting may be useful for river managers striving to achieve successful biomic river restoration. 
    more » « less
  3. ; ; ; (, Geophysical Research Letters)
    Abstract Source‐to‐sink transfer of sediment and organic carbon (OC) is regulated by river mobility. Quantifying trends in river mobility is, however, challenging due to diverse planform morphologies (e.g., meandering, braided) and measurement methods. Here, we utilize a remote‐sensing method applicable to all planform morphologies to quantify the mobility timescales of 80 rivers worldwide. Results show that, across the continuum from meandering to braided rivers, there is a systematic reduction in the timescales of channel mobility and—to a lesser extent—floodplain reworking. This leads to a decrease in the efficiency with which braided rivers rework old floodplain material compared to their meandering counterparts. Reduced floodplain reworking efficiency of braided rivers leads to smaller channel‐belt areas relative to their size. Results suggest that river‐mobility timescales derived from remote sensing can aid in the characterization of sediment and OC storage and transit times at a global scale. 
    more » « less
  4. ; (, Geology)
    Abstract Channel planform patterns arise from internal dynamics of sediment transport and fluid flow in rivers and are affected by external controls such as valley confinement. Understanding whether these channel patterns are preserved in the rock record has critical implications for our ability to constrain past environmental conditions. Rivers are preserved as channel belts, which are one of the most ubiquitous and accessible parts of the sedimentary record, yet the relationship between river and channel-belt planform patterns remains unquantified. We analyzed planform patterns of rivers and channel belts from 30 systems globally. Channel patterns were classified using a graph theory-based metric, the Entropic Braided Index (eBI), which quantifies the number of river channels by considering the partitioning of water and sediment discharge. We find that, after normalizing by river size, channel-belt width and wavelength, amplitude, and curvature of the belt edges decrease with increasing river channel number (eBI). Active flow in single-channel rivers occupies as little as 1% of the channel belt, while in multichannel rivers it can occupy >50% of the channel belt. Moreover, we find that channel patterns lie along a continuum of channel numbers. Our findings have implications for studies on river and floodplain interaction, storage timescales of floodplain sediment, and paleoenvironmental reconstruction. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Environmental Research Letters)
    Abstract Rapid warming in the Arctic threatens to destabilize mercury (Hg) deposits contained within soils in permafrost regions. Yet current estimates of the amount of Hg in permafrost vary by ∼4 times. Moreover, how Hg will be released to the environment as permafrost thaws remains poorly known, despite threats to water quality, human health, and the environment. Here we present new measurements of total mercury (THg) contents in discontinuous permafrost in the Yukon River Basin in Alaska. We collected riverbank and floodplain sediments from exposed banks and bars near the villages of Huslia and Beaver. Median THg contents were 49+13/−21ng THg g sediment−1and 39+16/−18ng THg g sediment−1for Huslia and Beaver, respectively (uncertainties as 15th and 85th percentiles). Corresponding THg:organic carbon ratios were 5.4+2.0/−2.4Gg THg Pg C−1and 4.2+2.4/−2.9Gg THg Pg C−1. To constrain floodplain THg stocks, we combined measured THg contents with floodplain stratigraphy. Trends of THg increasing with smaller sediment size and calculated stocks in the upper 1 m and 3 m are similar to those suggested for this region by prior pan-Arctic studies. We combined THg stocks and river migration rates derived from remote sensing to estimate particulate THg erosional and depositional fluxes as river channels migrate across the floodplain. Results show similar fluxes within uncertainty into the river from erosion at both sites (95+12/−47kg THg yr−1and 26+154/−13kg THg yr−1at Huslia and Beaver, respectively), but different fluxes out of the river via deposition in aggrading bars (60+40/−29kg THg yr−1and 10+5.3/−1.7kg THg yr−1). Thus, a significant amount of THg is liberated from permafrost during bank erosion, while a variable but generally lesser portion is subsequently redeposited by migrating rivers. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email