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

Abstract

Maximizing the reduction of nitrate to dinitrogen gas (denitrification) has been advocated as a means to decrease nitrate pollution that causes eutrophication and hypoxia in estuaries worldwide. Managing this flux in bottomland forest wetlands of the Mississippi River could potentially reduce the world's second largest hypoxic zone. We used published denitrification rates, geospatial data on habitat area and inundation frequency, water level records , and average monthly temperatures to estimate annual denitrification in the Atchafalaya River Basin, the principal distributary of the Mississippi River. Denitrification rates ranged from 5394 kg N year À1 (3.07 kg N km À2 year À1 ) in 1988 to 17 420 kg N year À1 (9.92 kg N km À2 year À1 ) in 1981, and rates were consistently higher in fall compared with those in spring. Total NO 3 À denitrified in the basin was negligible compared with total NO 3 À entering the Gulf of Mexico. If all N denitrified in the basin instead entered the Gulf, the hypoxic zone was predicted to increase only 5.07 km 2 (0.06%). This negligible effect of the basin on N dynamics in the Gulf agrees with other mass balance and isotopic studies in the region.

Using Flow-Ecology Relationships to Evaluate Ecosystem Service Trade-Offs and Complementarities in the Nation’s Largest River Swamp

“…For instance, denitrification [conversion of nitrate (NO 3 -) to atmospheric nitrogen (N 2 gas)] removes agricultural pollutants from freshwater ecosystems. Although the ARB was found to be a net source of nitrogen to the Gulf of Mexico, exporting 2.3 % more mass of nitrate and nitrite (NO 2 -) than entered the ARB from 1978(Xu 2006, the effects of annual hydrologic variability in the ARB on denitrification have not been fully explored (Bennett et al 2015). Other supporting services include various nutrient cycles, primary production, and soil formation.…”

“…Efforts to increase crawfish production may also promote nutrient loading to the Gulf of Mexico through reduced denitrification (Fig. 4); however the role of denitrification in the ARB may be so limited as to not factor into decisionmaking (Bennett et al 2015;Xu 2006). This analysis identifies individual components of a flow regime that may be ecologically and socioeconomically significant and relevant to water management decisions.…”

“…Maximizing denitrification has been identified as a potential way to decrease the hypoxic zone in the Gulf of Mexico (Mitsch et al 1999;Mitsch and Gosselink 2007). Values from a model estimating annual basin-wide nitrogen removal via respiratory denitrification in the ARB (Bennett et al 2015) were used to examine relationships with flow regime.…”

Integrating Water Observation from Space Product and Time-Series Flow Data for Modeling Spatio-Temporal Flood Inundation Dynamics

“…Although covering only about 4% to 6% of the Earth's ice-free land surface [1,2], wetlands and floodplains play a key role in ecological and hydrological cycles. Their inundation usually exhibits obvious seasonal and inter-annual variations [3], which alters their connectivity to the main stem rivers and thus changes nutrient retention and processing [4]. This also affects the aquatic system productivity [5], as well as spawning and nursery habitat [6,7].…”

Landscape Scale Assessment of Floodplain Inundation Frequency Using Landsat Imagery

“…The hydrologic regime (depth, duration and frequency of flooding) is the primary driver determining species composition and productivity in swamp forests (Hosner, 1957;Conner and Day, 1976;Conner et al, 1981;Megonigal et al, 1997) and adjacent alluvial floodplains (Hodges, 1997;Kellison and Young, 1997). Inundation dynamics on the floodplain affect nutrient retention and processing as increased contact between water and soil or sediment will increase nitrogen retention and processing through increased biological activity (Pinay et al, 2002;Bennett et al, 2014). The spatial extent of floodplain inundation also defines the downstream impact of flooding (Opperman et al, 2009).…”