Location: Water Quality and Ecology ResearchTitle: Phosphorus dynamics in agricultural drainage ditches: an influence of landscape properties Author
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2018
Publication Date: N/A
Citation: N/A Interpretive Summary: Excess nutrients have been blamed for water quality problems resulting in the hypoxic zone in the Gulf of Mexico and elsewhere. Vegetated drainage ditches are conduits between production agriculture and receiving water bodies. To possibly enhance nutrient mitigation in these ditches, water holding structures such as weirs have been proposed for installation. Measurements of bioavailable phosphorus in ditch sediments during the summer were significantly lower in ditches with weirs than in those without weirs. This indicates vegetated drainage ditches with weirs can sorb excess phosphorus from water into ditch sediments during the growing season, thereby reducing the transport of nutrients downstream and eventually into the Gulf of Mexico.
Technical Abstract: Excessive loading of phosphorus (P) into aquatic systems from adjacent terrestrial ecosystems often results in eutrophication and subsequent degradation of aquatic resources. This study investigated the dynamics of P within replicated experimental conventional and controlled (with weirs) agricultural drainage systems during simulated storm runoff events (summer and winter). The objective of the study was to examine the capacity of experimental agricultural drainage ditches to sorb and act as a P sink. In the summer runoff event, ditches with weirs had significantly lower (0.01) bioavailable P (Pw) (0.018 mg/g) compared with conventional ditches with no weirs (0.021 mg/g), suggesting inundation enhanced by weirs could play a vital role in increasing P sorption capacity of agricultural drainage ditches during the growing season via an apparent decrease in soil pH, which facilitates P adsorption to sediment and also reduces P solubility. Mean P sorption maxima (Smax) (139- 671.8 mg/kg in summer vs 525- 1288 mg/kg in winter,) and P binding energy (K) (0.63- 1.34 L/mg in summer; 0.09-0.30 L/mg in winter) were high for all drainage ditch sediments, indicating experimental drainage ditches were capable of sorbing P and could therefore be described as a P sink. These results will assist farm managers in making informed decisions on effective P management in relation to agricultural runoff directed through drainage ditches.