|Saporito, Louis - Lou|
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/2007
Publication Date: 7/1/2007
Citation: Kleinman, P.J., Allen, A.L., Needelman, B.A., Sharpley, A.N., Vadas, P.A., Saporito, L.S., Folmar, G.J., Bryant, R.B. 2007. Dynamics of phosphorus transfers from heavily manured coastal plain soils to drainage ditches. Journal of Soil and Water Conservation. 62(4):225-234. Interpretive Summary: Land drainage for agricultural, construction, and public health purposes has been a prominent landscape feature in the United States and Europe for over four centuries. As ditches typically intercept or border agricultural fields, they are a key link between farm land and surface waters. Increasingly, there is recognition of the critical role that drainage ditches play in water quality protection. This study quantifies the role of drainage ditches as conduits of phosphorus from agricultural fields and barns to identify opportunities for the improved management of ditches to protect water quality. In the study, it was found that ditches receiving runoff from point sources (e.g., barns) exported 4.3 to 25.3 kilograms of phosphorus per hectare over the course of one year, while ditches draining areas with only non-point source contributions exported 2.6 to 4.8 kilograms of phosphorus per hectare. Results point to the need for new ditch management practices that can sequester dissolved forms of phosphorus and trap floating sources of phosphorus, to be implemented in combination with traditional methods that primarily address sediment-bound phosphorus.
Technical Abstract: Understanding the dynamics of phosphorus (P) transport in agricultural drainage ditches is essential to their improved management for water quality protection. Seven ditches draining soils with a 20+ yr history of receiving poultry litter and Mehlich-3 P averaging 441 mg/kg (parts per million) were monitored: two for five years, the remainder for one year. Ditches receiving runoff from point sources (e.g., barns) exported 4.3 to 25.3 kg total P per ha (4.9 to 28.8 lbs/acre) from 2005 to 2006, while ditches draining areas with only non-point source contributions exported 2.6 to 4.8 kg total P per ha (2.9 to 5.5 lbs/acre) during that period. Over five years, annual total P losses from two ditches with only non-point source P contributions were 1.4 to 26.2 kg/ha (1.6 to 29.8 lbs/acre). Overland flow from the fields to the two ditches accounted for less than 8% of annual ditch P export, pointing to groundwater and sources within ditches as major controls of P loss. Periodic sampling of groundwater at depths up to 133 cm (4.4 ft) and sampling shortly after storms provided limited insight into groundwater contributions to ditch flow probably because most P is transported during storm events. Floating algae may play an important role in sediment-bound P transport. Results point to the need for new ditch management practices that can sequester dissolved forms of P and trap floating sources of P, in combination with traditional methods that primarily address sediment-bound P.