Spatial Variability of Sediment Denitrification Across the Atchafalaya River Basin, Louisiana, USA

Abstract

Ecosystem-wide denitrification estimates generally depend on the degree of spatial variability in the system, but spatial variability is rarely assessed. To model nitrogen removal rates in the Atchafalaya River Basin we first identified trends in background and potential denitrification across this large floodplain. We conducted a laboratory study to quantify background and potential denitrification rates. Background and potential denitrification rates were significantly different. Background rates ranged from ranged from 0-1.35 μgN g −1 d −1 and potential rates ranged from ranged from 26.72-710.47 μgN g −1 d −1 , illustrating the existence of denitrification hotspots across the landscape. Background rates were related to soil characteristics (carbon, nitrogen, nitrate), but potential rates appeared to be related to landscape position (spatial coordinates). Background denitrification showed a strong positive correlation with soil nitrate, and a negative correlation with soil nitrogen and soil carbon. Potential denitrification rates showed no significant correlations with any parameters tested. We observed a significant relationship between location and potential denitrification rates, with greater potential downstream than upstream, but not between location and background rates. This suggests that landscape scale studies should include additional qualifiers, such as habitat type and organic matter quality, for more reliable estimates of denitrification rates.

Topography and land use effects on spatial variability of soil denitrification and related soil properties in riparian wetlands

“…Similarly, our study found a negative correlation between soil denitrification and riparian elevation in the Yangtze River basin (Table 2). Low-elevation areas flood more frequently than high-elevation areas, which can lead to anoxic or anaerobic conditions favorable for denitrifying microbes (Scaroni et al, 2010). In the present study, agricultural riparian areas showed a 2.5-fold greater unamended denitrification than the Table 3 Effects of topographic conditions and land use on the soil properties and denitrification in riparian wetlands analyzed using generalized linear model.…”

“…In this study, we used the acetylene block technique to measure unamended and potential denitrification rates of riparian soils (Scaroni et al, 2010). The unamended denitrification (i.e., background denitrification) rate was a conservative estimate of in situ denitrification without carbon and NO 3 − amendments, while potential denitrification provided an upper-bound estimate.…”

“…For potential denitrification rate assays, 50 g of homogenised fresh soils from each sampling site were weighed into a 250-mL serum bottle with 30 mL of incubation solution (final concentrations: 0.1 g/L KNO 3 , 0.18 g/L glucose and 1 g/L chloramphenicol). We measured the unamended denitrification rate using a similar procedure, but with the addition of 30 mL of deionized water instead of the incubation solution (Scaroni et al, 2010). All serum bottles were then sealed and purged with N 2 gas for 5 min to induce anaerobic conditions.…”

“…Mineralization of organic matter supplies the ammonia for nitrification, which in turn increases nitrate supply for denitrification (Xu and Cai, 2007). Through decomposition, the supply of soil carbon becomes available for denitrifying bacteria and fungi; hence, a positive correlation is often observed between soil organic carbon and the denitrification potential (Scaroni et al, 2010;Hill et al, 2014). Organic carbon amendments (e.g., the addition of cotton gin trash and biochar) can increase the soil denitrification rate and improve the nitrate removal capacity in wetlands (Ullah and Faulkner, 2006b;Pulou et al, 2012).…”

Distributions of organic carbon and related parameters in a Louisiana sugarcane soil

“…Inorganic C was undetectable in all samples tested; therefore all total C measurements were interpreted as SOC. The ranges of SOC in the burn and no-burn areas were somewhat lower than those found in other soils in the region which ranged from 1.0 to 2.4% in South Louisiana sugarcane fields (Johnson and Richard, 2005) and from 1.1 to 22.6% in non-agricultural floodplain soils of the Atchafalaya River Basin, Louisiana (Scaroni et al, 2010). Nevertheless, highest SOC was encountered in the top zone with a decrease with depth, which is typically encountered for most soils (Mishra et al, 2009).…”