Bacterial diversity in agricultural drainage ditches shifts with increasing urea-N concentrations

This data was collected once per month during May - August 2017 from an agricultural drainage ditch either next to corn fields (site 10) or soybean fields (site 4) and a forest site (site 6) that was used as a reference. The aim of the project was to determine dominant bacterial communities using 16S rRNA NGS sequencing in drainage ditch sediments under high urea-N concentrations from natural sources (ditch next to soybean and forest site) and applied urea ammonium nitrate fertilizer (ditch next to corn fields) during April 2017 (at-plant and side-dressing applications). The forest site was a small ponded area located next to the farm where a tree had fallen along time ago. Waters draining forested soils collects at this site, which made it easy to collect water quality data with sediment samples for 16S rRNA analysis. A mesocosm experiment was paired with the field data using sediments from an agricultural drainage ditch next of field previously planted to corn. Sediments were collected as twelve cores (30 cm x 12 cm) using spade shovels, and then homogenized on a tarp to reduce variation from non-uniformity in vegetation, organic matter content, and sediment textures within the ditch. Homogenized sediments were divided among nine 18-liter, HDPE buckets (30.5cm diam. x 36.8cm height) to obtain a sediment depth of 10 cm in each mesocosm bucket. Mesocosms were flooded with 4-L of DI water and placed into the re-circulating aquaculture tank filled with water for three days so the mesocosm surface waters could reach the experimental temperature of 24C. Samples for bacterial community analysis were taken 24 hours and 96 hours after enrichment solutions were added.The enrichment solutions contained 0 mg N L-1 for the control, 7 mg nitrate-N L-1, 0.5 mg urea-N L-1, and 4 mg DON-N L-1. Composite sediment samples consisting of seven sediment cores using sterile plastic transfer pipettes were collected from each bucket at 24 and 96 hours, placed in 50-mL sterile centrifuge tubes with Lifeguard Soil Preservation Solution (Mo Bio Laboratories Inc.) and stored at -20C.