Submitted to: Water: A Multidiscplinary Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2010
Publication Date: 8/12/2010
Citation: Ahiablame, L.M., Chaubey, I., Smith, D.R. 2010. Nutrient content at the sediment-water interface of tile-fed agricultural drainage ditches. Water: A Multidiscplinary Research Journal. 2:411-428. DOI:10.2290/w2030411. Interpretive Summary: A substantial number of studies have discussed nutrient transport and dynamics in natural streams, however, fewer studies have given consideration to nutrient transport processes in artificial ditch environments. The study was conducted in three drainage ditches in northern Indiana to: (1) assess equilibrium between sediments and water column P (2) evaluate spatial and seasonal variations in readily available nutrients and phosphorus buffering capacity; (3) determine if differences existed in nutrient retention capacity between sediments collected upstream and downstream of tile drains. Equilibrium phosphorus concentrations ranged from 0.05 to 6.2 mg/L. Ditch sediments acted as both a source and a sink for phosphorus in the water column, but there was no pattern in the behavior of sediments at all sites. Loosely bound phosphorus in sediments ranged from 1.39 to 5.98 mg kg-1 sediment and the ability of sediments to buffer water column P as indicated by the phosphorus sorption index values ranging from 6.5 to 15.2. These data were consistent with reported values by previous studies in drainage ditches of the area. Sampling location respective to tile drains did not have any effect on sediment behavior during the study. The results of this study indicated that these artificial ecosystems behaved as natural systems by acting as sink or source of nutrients they receive. The study suggested that nutrient uptake by agricultural drainage ditch sediments is not always efficient, therefore proper management should be implemented to optimize for nutrient removal from the water column while maintaining adequate drainage.
Technical Abstract: Extensive network of tile drains present in the Midwest USA accelerate losses of nutrients to receiving ditches, rivers and eventually to the Gulf of Mexico. Nutrient inputs from agricultural watersheds and their role in affecting water quality have received increased attention recently; however, benthic sediment nutrient interactions in tile-fed drainage ditches is still a matter of active research in consideration to nutrient discharge from tile drains. In this study, phosphorus (P) and nitrogen (N) contents and variability of nutrient retention ability of benthic sediments upstream and downstream from tile drain outlets were evaluated in managed agricultural drainage ditches in Indiana. Sediment samples were collected every three months upstream and downstream from selected tile drains in three ditches in northwest Indiana. Sediment equilibrium P concentrations (EPC0) were measured to examine P adsorption-desorption and equilibrium characteristics of benthic sediments in the ditches. P sorption index (PSI), exchangeable P (ExP), and exchangeable NH4+-N (ExN) were measured to evaluate nutrient retention ability and readily available nutrient content of benthic sediments. Results indicated a dynamic interaction between benthic sediment and overlying water column where sediments were acting as a sink or a source of P. There were no differences in nutrient retention ability between sediments collected upstream and sediments collected downstream from the selected tile drains. While the data, except for ExN, was comparable to reported values by previous studies in Indiana’s drainage ditches, there was no particular seasonal pattern in the content of exchangeable nutrient content in sediments at all three sites. This study also suggested that nutrient uptake by benthic sediments in these drainage ditches is not always efficient; therefore watershed management should focus on minimizing the delivery of nutrients into ditches while maintaining their drainage functionality.