Do dams and levees impact nitrogen cycling? Simulating the effects of flood alterations on floodplain denitrification

Abstract

A fundamental challenge in understanding the global nitrogen cycle is the quantification of denitrification on large heterogeneous landscapes. Because floodplains are important sites for denitrification and nitrogen retention, we developed a generalized floodplain biogeochemical model to determine whether dams and flood-control levees affect floodplain denitrification by altering floodplain inundation. We combined a statistical model of floodplain topography with a model of hydrology and nitrogen biogeochemistry to simulate floods of different magnitude. The model predicted substantial decreases in NO 3 -N processing on floodplains whose overbank floods have been altered by levees and upstream dams. Our simulations suggest that dams may reduce nitrate processing more than setback levees. Levees increased areal floodplain denitrification rates, but this effect was offset by a reduction in the area inundated. Scenarios that involved a levee also resulted in more variability in N processing among replicate floodplains.Nitrate loss occurred rapidly and completely in our model floodplains. As a consequence, total flood volume and the initial mass of nitrate reaching a floodplain may provide reasonable estimates of total N processing on floodplains during floods. This finding suggests that quantifying the impact of dams and levees on floodplain denitrification may be possible using recent advances in remote sensing of floodplain topography and flood stage. Furthermore, when considering flooding over the long-term, the cumulative N processed by frequent smaller floods was estimated to be quite large relative to that processed by larger, less frequent floods. Our results suggest that floodplain denitrification may be greatly influenced by the pervasive anthropogenic flood-control measures that currently exist on most majors river floodplains throughout the world, and may have the potential to be impacted by future changes in flood probabilities that will likely occur as a result of climate shifts.

The Role of Buffer Zones for Agricultural Runoff

“…However, neither of these approaches considers buffer zone shape, which can be important for increasing buffer zone effectiveness (e.g. Gergel et al 2005).…”

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

“…Floodplains are frequently identified as important sites for nutrient retention and removal (Brinson et al 1984;Craft and Casey 2000;Gergel et al 2005;Forshay and Stanley 2005;Noe and Hupp 2009). Denitrification in particular has the potential to remove significant amounts of nitrogen (N) from floodplains, as seasonal river inundation establishes anaerobic soil conditions, delivers nitrate, and preserves carbon (C).…”

Sediment and nutrient trapping as a result of a temporary Mississippi River floodplain restoration: The Morganza Spillway during the 2011 Mississippi River Flood

“…Models of the effects on nutrient reduction to the Gulf of Mexico were created (Galat et al, 1998;Lane et al, 2003;Mitsch et al, 2009;Opperman et al, 2009). Gergel et al (2005) modeled different hydrologic scenarios including lakes and leveed rivers as well as natural floodplains. They found that short, frequent floods processed more NO 3 than long infrequent floods.…”