Comparison of denitrification characteristics among three habitat types of a large river floodplain: Atchafalaya River Basin, Louisiana

Abstract

Mobile forms of nitrogen leach from upland environments into aquatic systems, often discharging to coastal zones. Addition of nitrogen to once N-limited systems results in a host of changes ranging from eutrophication to loss of biodiversity. Floodplains can ameliorate these changes by removing and sequestering nitrogen. In many coastal floodplains, sedimentation causes lakes to transition to baldcypress swamps, and ultimately to bottomland hardwood (BLHW) forests. These habitats differ in their contact with floodwater, which directly and indirectly affects their ability to process nutrients, but the effects of habitat change on denitrification at the floodplain scale cannot be predicted because of lack of suitable data. This study compared denitrification characteristics among the aforementioned habitats within the Atchafalaya River Basin (ARB). Microcosms were established in the laboratory, and the acetylene block technique was used to estimate four denitrification characteristics: background denitrification rates, maximum rates, time to reach maximum rates, and the linear response of denitrification to nitrate concentration. There were significant differences in denitrification characteristics among the three habitat types; specifically, all habitats differed in the time required for denitrification to respond to nitrate in the overlying water, and denitrification in lake habitats differed from both BLHWs and baldcypress swamps. Landscape-scale models should account for different linear relationships between denitrification and nitrate concentrations, and different response times to nitrate concentrations for different habitats. Because denitrification characteristics differ across habitats within the ARB, continued habitat change within the floodplain will alter nutrient discharge to coastal waters.

Floodplain biogeochemical processing of floodwaters in the Atchafalaya River Basin during the Mississippi River flood of 2011

“…Because BryantMason et al [2013] and this study used the same flow data, we believe the largest difference pertains to sample collection (our samples and the USGS NASQAN samples were collected in the center of the channel, in contrast to shoreline [2013]). Our conclusion of relatively high NO 3 À removal from our detailed spatial and temporal observations of water quality is consistent with previous studies showing highdenitrification potential within the ARB [e.g., Lindau et al, 2008;Scaroni et al, 2011], suggesting our results are more representative of ARB nitrogen removal.…”

“…[]). Our conclusion of relatively high NO 3 − removal from our detailed spatial and temporal observations of water quality is consistent with previous studies showing high‐denitrification potential within the ARB [e.g., Lindau et al ., ; Scaroni et al ., ], suggesting our results are more representative of ARB nitrogen removal.…”

“…Furthermore, increasing floodplain connectivity may alter the floodplain ecosystem, yielding an unintended response (e.g., increased export of organic matter). Although some work has investigated the effect of ecotype on, for example, denitrification [e.g., Scaroni et al ., ], and other work has investigated effect of hydrologic change on ecosystem structure [e.g., Keim et al ., ], the interaction between the two remains complex and not well understood [ Houser and Richardson , ]. Ultimately, it is clear that management of connectivity between channelized flow and adjacent floodplains is an essential component of any diversion strategy [ Schiemer et al ., ].…”

An Estimate of Basin‐Wide Denitrification Based on Floodplain Inundation in the Atchafalaya River Basin, Louisiana

“…We estimated the area of specific habitat types inundated under the 41 predicted scenarios for each of the three habitat types studied by Scaroni et al . () using ArcMap 10.0 (Esri, Redlands, CA). To match available potential denitrification estimates, we reclassified land cover data from the US Fish and Wildlife Service () National Wetlands Inventory (NWI) from 110 categories into four generalized categories following Faulkner et al .…”

“…Because of their proximity to the GOM and receipt of nutrient‐laden waters from across much of the USA, freshwater and coastal wetlands of the Mississippi River have received much attention for their great potential to remove NO 3 − when exposed to waters with high NO 3 − concentrations (Lindau et al ., , ; Rivera‐Monroy et al ., , ; Perez et al ., ; Scaroni et al ., ; BryantMason et al ., ). This is true even in some river corridor wetlands that have short water residence times (Lane et al ., , ; Lindau et al ., ).…”