Characterizing Phosphorus in Agricultural Ditch Sediments to Guide Effective Ditch Management.

Artificial drainage through manmade ditches or channelized streams is a common practice to allow for agricultural production of poorly drained soils on the Delmarva Peninsula. Over time, ditches accumulate sediment and vegetation that impedes drainage of water from adjacent fields. Sediment removal (or “dip out”) is performed to restore ditch function. However, sedimentation of ditches can lead to nutrient sequestration in ditch sediments and aquatic vegetation. We characterized the physical and chemical properties of sediments from eight ditches in Delaware prior to scheduled maintenance.  Ditch core samples were collected approximately every 100 m along the segment scheduled for maintenance and divided into 0-5, 5-15, and 15+ cm depth increments. Routine soil analysis (Mehlich 3), total P (EPA 3050 digest), and water soluble P (WSP) were completed on all 0-5 cm sediment samples and composited 5-15 and 15+ cm sediment samples.  Preliminary results showed WSP and Mehlich 3 P concentrations in 0-5 cm sediment samples were highly variable within the same ditch, which may be affected by erosion from adjacent land uses or stream bank erosion.  Additionally, adjacent field soil and ditch sediment spoil samples were collected and characterized following maintenance.  An incubation study will be performed to determine the potential for solubilization and subsequent loss of dissolved P following dip-out maintenance by simulating the incorporation of spoil into adjacent fields. Knowledge of ditch sediment properties and the risk of nutrient losses due to current maintenance may aid in developing improved ditch management practices to further reduce non point source pollution.