Perirheic mixing and biogeochemical processing in flow‐through and backwater floodplain wetlands

Abstract

Inundation hydrology and associated processes control biogeochemical processing in floodplains. To better understand how hydrologic connectivity, residence time, and intrafloodplain mixing vary in floodplain wetlands, we examined how water quality of two contrasting areas in the floodplain of the Atchafalaya River-a flow-through and a backwater wetland-responded to an annual flood pulse. Large, synoptic sampling campaigns occurred in both wetlands during the rising limb, peak, and falling limb of the hydrograph. Using a combination of conservative and reactive tracers, we inferred three dominant processes that occurred over the course of the flood pulse: flushing (rising limb), advective transport (peak), and organic matter accumulation (falling limb). Biogeochemistry of the two wetlands was similar during the peak while the river overflowed into both. However, during the rising and falling limbs, flow in the backwater wetland experienced much greater residence time. This led to the accumulation of dissolved organic matter and dissolved phosphorus. There were also elevated ratios of dissolved organic carbon to nitrate in the backwater wetland, suggesting nitrogen removal was limited by nitrate transported into the floodplain there. Collectively, our results suggest inclusion of a temporal component into the perirheic concept more fully describes inundation hydrology and biogeochemistry in large river floodplain.

Aquatic vegetation mediates the relationship between hydrologic connectivity and water quality in a managed floodplain

“…Portions of the floodplain with more natural and engineered points of connection to source water had better and more uniform water quality (specifically, higher DO and ion concentrations) during a greater portion of the flood pulse than mostly disconnected regions (Sabo et al, 1999a, b;Kaller et al, 2011;Jones et al, 2014). Buffalo Cove WMU, in the southern ARB and with several points of water ingress from the river, exhibited between-site variability in tracer levels only during the latter part of the flood, indicating longduration connection to the river.…”

River corridor science: Hydrologic exchange and ecological consequences from bedforms to basins

“…The increasing capability of researchers to separate the effects of hydrologic exchange zones has led to improvements in understanding the zonation of key biogeochemical reactions. Enhanced biogeochemical reactions have been detected in streambed algal mats [ Gooseff et al ., ], shallow streambed hyporheic zones [ Argerich et al ., ; Harvey et al ., ; Briggs et al ., ], gravel bars [ Pinay et al ., ; Zarnetske et al ., ], bank storage exchange zones in river banks [ Squillace et al ., ; Gu et al ., ], riparian zones [ Ensign et al ., ; Wollheim et al ., ], and floodplains [ Richardson et al ., ; Forshay and Stanley , ; Jones et al ., ; Scott et al ., ], suggesting that sediment interfaces throughout the river corridor are capable of enhancing reactive uptake of nutrients and contaminants.…”

“…[] and Jones et al . [] and Scott et al . [] explored similar concepts controlling N removal in riparian zones and floodplains, respectively, and those studies are beginning to reveal the cumulative effects of reactive transformations where rising waters expand hydrologic exchange and increase contact with the highly reactive sediments along the margins of river corridors.…”

Intermittent flooding of organic‐rich soil promotes the formation of denitrification hot moments and hot spots

“…, Jones et al. ). Therefore, the water‐level fluctuations could potentially change the dynamics of microbial communities (Corstanje and Reddy , Fiedler et al.…”

“…, Jones et al. , Mahl et al. ), this study utilizes a controlled outdoor laboratory setting to investigate the effect of hydrologic connectivity on denitrification rates, microbial communities, and nitrous oxide fluxes.…”