Precipitation as the Primary Driver of Variability in River Nitrogen Loads in the Midwest United States

Abstract

Research Impact Statement: Recent increases in river N-loads in the Midwest United States are primarily caused by wet climate. Under current cropping systems, tile-water remediation will be necessary to reduce river N-loads.ABSTRACT: Nitrogen (N) losses from agricultural lands in the Midwest United States are contributing to the expansion of the hypoxic zone in the Gulf of Mexico. This study evaluated the importance of inter-annual variability in precipitation, land cover, and N fertilizer use on NO 3 + NO 2 -N loads in seven United States Midwestern Rivers using the backward stepwise regression analysis. At the annual scale, fluctuations in the current and previous years' precipitations explained much of the variation in streamflow, baseflow, and N-load. Previous years precipitation effects were associated with fillable soil porosity. In some years, higher residual soil N from previous dry years also contributed to an increase in N-load. Area under soybean production (SOY), a surrogate for replacement of prairies and small grains was generally not a significant explanatory variable. Fertilizer use from 1987 to 2012 was also not a significant explanatory variable in the annual analysis. Precipitation in both the current and previous months and previous year were important in explaining variation in monthly streamflow, baseflow, and N-load. SOY was significant in one or two months from June to August, but had a higher pvalue than precipitation. We conclude recent increases in river N-loads are primarily due to wet climate and minimally due to the changes in land cover or N fertilizer use. Under current cropping systems and agronomic N application rates, tile water remediation will be necessary to reduce river N-loads.(

Long‐term impacts of drain spacing, crop management, and weather on nitrate leaching to subsurface drains

“…These results underscore the importance of such noncontrollable factors as weather in determining nitrate‐N losses from cropped fields. Baeumler and Gupta (2020) also concluded that precipitation variations were the main driver for variations in river N loads in the U.S. Midwest.…”

“…The effects of year‐to‐year variations in precipitation on drainage and nitrate loads have been discussed for decades (e.g., Randall & Goss, 2001; Randall & Mulla, 2001). Recently, however, there is greater attention being paid to long‐term increases in precipitation amounts and variability and the contribution of these trends to increased drain flows and nitrate losses from drained agricultural lands (Baeumler & Gupta, 2020; Nangia et al., 2010b). These climate changes give even more impetus to develop integrated management systems that are resilient under varying conditions.…”

Crop modeling defines opportunities and challenges for drought escape, water capture, and yield increase using chilling-tolerant sorghum

“…The observed annual precipitation, averaged across locations, was used to classify years into three “precipitation level” quantiles: “dry” years (161–428 mm), “moderate” years (428–580 mm), and “wet” years (580–1380 mm). Note, this classification is not intended as a formal envirotyping of water deficit scenarios (Chenu et al, 2013) but to reflect the type of informal classification used by growers and agronomic practitioners in the region (Baeumler and Gupta, 2020). The effects of planting date and the interaction of planting date and precipitation levels on all variables were tested using analysis of variance (ANOVA), considering planting date, precipitation level, and hybrid type as fixed factors, and location and year as random factors.…”

Non-Parametric Analysis of Nitrogen Trends in the form of Nitrate and Nitrite in Rivers and Streams of the Contiguous United States for 1990-2019

“…Nitrogen, in particular, has been the focus of numerous research with different agendas. In particular, in the area of excess nutrients, limiting nutrient [7], sources of excess nitrogen in fertilizers and septic tanks [2], best management practices to control nitrogen from fertilizers and septic tanks [8,9], and impacts of other hydrological parameters such as precipitation on nitrogen concentration [10] have been well documented. These works target mainly groundwater flow as it directly receives nitrogen in different ionic forms such as nitrate-nitrogen (NO3-N) and nitrite-nitrogen (NO2-N) from infiltration [11,12].…”