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Contributions of systematic tile drainage to watershed scale phophorus transport

King, Kevin W., Williams, Mark R., Fausey, Norman R.
Journal of environmental quality 2015 v.44 no.2 pp. 486-494
Algae, algal blooms, application rate, best management practices, ecosystem services, fields, freshwater, losses from soil, phosphorus, spring, streams, summer, surface water, tile drainage, water pollution, watersheds, winter, Ohio
Phosphorus (P) transport from agricultural fields continues be a focal point for addressing harmful algal blooms (HABs) and nuisance algae in freshwater systems throughout the world. In humid, poorly drained regions, attention has turned to P delivery through subsurface tile drainage. Research on the contributions of tile drainage to watershed scale P losses, however, is limited. The objective of this study was to evaluate P movement through tile drainage and its manifestation at the watershed outlet. Hydrology, along with associated P concentrations were collected for 8 years (2005-2012) from 6 tile drains and the watershed outlet of a headwater watershed within the Upper Big Walnut Creek watershed in central Ohio, USA. Results showed that tile drainage accounted for 51% of the discharge, 47% of the dissolved P, and 43% of the total P exported from the watershed. Average annual total P loss from the watershed was 0.98 kg/ha and annual total P loss from the 6 tile drains equaled 0.48 kg/ha. Phosphorus loads in tile and watershed discharge tended to be greater in the winter and spring, while P concentrations were greatest in the summer. Over the 8 year study, P transported in tile drains represented less than 2% of application rates and greater than 90% of all measured concentrations exceeded recommended levels (0.03 mg/L) for minimizing HABs and nuisance algae. Thus, the results of this study show that in systematically tile drained headwater watersheds, the amount of P delivered to surface waters via tile drains cannot be dismissed. Given the amount of P loss relative to application rates, development and implementation of best management practices must jointly consider both economic and environmental benefits.