b'9A connectivity risk ranking for phosphorus loss alongagricultural drainage ditchesMoloney T1, Fenton O1 and Daly K11Teagasc Environment, Soils and Land-use Department Johnstown Castle, Co. Wexford, IrelandAgricultural drainage systems comprising both in-field pipe drains and surface ditches are typically installed to remove excess water from agricultural land. These drainage networks can provide connectivity between phosphorus (P) sources and surface waters thereby increasing the risk of P loss to rivers and streams. The objective of this study was to derive a farm-scaledrainage ranking that categorises drainage ditches in terms of P loss risk based onconnectivity and physic-chemical characteristics. Ten pilot farms were selected to characterise drainage networks through ground survey and, sediment and water sampling. Five drainage ditch categories were derived based on landscape setting and connectivity. Each category recorded soluble and reactive P concentrations above environmental water quality standards.To assess the risk of surface ditches as a connectivity vector between agricultural P and surface waters ditches were ranked in order of P loss risk by integrating landscape position and sediment P chemistry. Elevated sediment P with high equilibrium P concentration (EPCo) were associated with ditches connected to farm yards, and in sediment sampled at ditch outlets, suggestingP deposition over time indicative of a legacy P source. The greatest risk of P loss was attributed to ditches connecting farm yards to streams, and ditches that connected the drainage network to surface waters, or outlets. The five ditch categories presented provide a connectivity risk ranking for P loss along agricultural drainage ditches and could be included in farm level risk assessment schemes to help target appropriate P loss mitigation measures to the appropriate locations.53'