Water-Quality Assessment of the Lower Grand River Basin, Missouri and Iowa, USA, in Support of Integrated Conservation Practices

Abstract

The effectiveness of agricultural conservation programmes to adequately reduce nutrient exports to receiving streams and to help limit downstream hypoxia issues remains a concern. Quantifying programme success can be difficult given that short‐term basin changes may be masked by long‐term water‐quality shifts. We evaluated nutrient export at stream sites in the 44 months that followed a period of increased, integrated conservation implementation within the Lower Grand River Basin. These short‐term responses were then compared with export that occurred in the main stem and adjacent rivers in northern Missouri over a 22‐year period to better contextualize any recent changes. Results indicate that short‐term (October 2010 through May 2014) total nitrogen (TN) concentrations in the Grand River were 20% less than the long‐term average, and total phosphorus (TP) concentrations were 23% less. Nutrient reductions in the short term were primarily the result of the less‐than‐average precipitation and, consequently, streamflow that was 36% below normal. Therefore, nutrient concentrations measured in tributary streams were likely less than normal during the implementation period. Northern Missouri streamflow‐normalized TN concentrations remained relatively flat or declined over the period 1991 through 2013 likely because available sources of nitrogen, determined as the sum of commercial fertilizers, available animal manures and atmospheric inputs, were typically less than crop requirement for much of that time frame. Conversely, flow‐normalized stream TP concentrations increased over the past 22 years in northern Missouri streams, likely in response to many years of phosphorus inputs in excess of crop requirements. Stream nutrient changes were most pronounced during periods that coincided with the major tillage, planting and growth phases of row crops and increased streamflow. Nutrient reduction strategies targeted at the period February through June would likely have the greatest impact on reducing nutrient export from the basin. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Temporal changes in nitrogen and phosphorus concentrations with comparisons to conservation practices and agricultural activities in the Lower Grand River, Missouri and Iowa, and selected watersheds, 1969–2015

“…1; table 1) that were within or near the Lower Grand River and were part of a long-term (having 20 years or (2015) presented TN and TP concentrations from October 2010 through May 2014 for MRBI sites (sites 1-6) and from January 1990 through May 2014 for long-term sites (sites 7-11). This report extends the model periods used by Wilkison and Armstrong (2015) through the end of water year 2015 (September 2015) at all sites and extends the start of the model periods for long-term sites to the beginning of the earliest water year that TN or TP samples were collected during consecutive water years. A water year is the period from October 1 to September 30 and is designated by the year in which it ends.…”

Statistical assessment of nonpoint source pollution in agricultural watersheds in the Lower Grand River watershed, MO, USA

“…These impairments seem to be primarily a result of agricultural activities, although urban activities can also contribute to surface water degradation in the few watersheds with more development. Wilkison and Armstrong ( 2015 ) studied the impact of commercial fertilizers in the Lower Grand River Watershed, finding that the average application rates of agricultural chemicals, such as phosphorus and nitrogen, in this watershed have approximately doubled during the last four decades.…”

Floodplain Trapping and Cycling Compared to Streambank Erosion of Sediment and Nutrients in an Agricultural Watershed

“…In agricultural watersheds, high nutrient application rates from fertilizer and manure associated with crops, pasture, and confined animal operations lead to high downstream loading rates of nitrogen (N) and phosphorus (P) (Longphuirt et al 2015;Wilkison and Armstrong 2016). In addition, row crop agriculture (Blanco-Canqui and Lal 2008) and livestock access to streams (Magner et al 2008) can generate high rates of soil and bank erosion that exports sediment and nutrients downstream (Brakebill et al 2010).…”