Submitted to: Society of Wetland Scientists
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2005
Publication Date: 11/30/2005
Citation: Kroger, R., M.M. Holland, M.T. Moore, and C.M. Cooper. Nutrient through flow, deposition and assimilation in agricultural drainage ditches: When and how do nutrients move? Southeastern Chapter Meeting of the Society of Wetland Scientists, San Marcos, TX. CD ROM. 2005. Interpretive Summary:
Technical Abstract: Agricultural activities play a major role as non-point sources of nutrients such as nitrogen and phosphorus. Drainage ditches are integral parts of the agricultural landscape, and act as major conduits for nutrients such as N and P from agricultural lands to receiving waters. Very little research has gone into investigating the utilization of agricultural landscape features for mitigation of nutrients associated with drainage and storm water runoff. The reason is primarily a lack of data on nutrient flux within the drainage ditch, i.e. what are baseline nutrient concentrations? Are ditch sediments assimilating nutrients over time? What is the concentration of through flow under variable hydrological regimes? When do nutrient concentrations reach a maximum? We undertook a two year study of two drainage ditches to monitor nutrient flux on both spatial and temporal gradients. Water samples were collected monthly to establish baseline ditch nutrient concentrations, and collected with every storm event that generated surface runoff and elevated water levels within the ditch. Sediment samples were collected monthly to determine assimilation rates of nutrients. Preliminary results for nitrogen species suggest that nitrate levels spike post fertilization (6.28 mg N/L), but reach maximum levels in winter (18.7 mg N/L), when vegetative senescence provides a large input of inorganic nitrogen into the system. Similar patterns emerge with the runoff and storm data. When nitrate was lowest (February - June; August - September) ammonia levels are highest. This also was concomitant with no water occurring in the ditch. Phosphorus concentrations were highest with storm (4.35 mg P/L) and runoff events (3.75 mg P/L) post fertilizer application, which was expected as the majority of TOP is particulate bound. Ditch drying at this juncture does not have any effect on phosphorus discharge concentrations. Ultimately, quantified results of nutrient concentrations combined with stage/discharge data will provide a nutrient balance of through flow and assimilation at different times of the year.