Ditching effects on salt marsh porewater drainage rates under current and predicted sea levels

Parallel grid ditches installed to reduce mosquito breeding habitats have had the unintended consequence of altering salt marsh ecosystem functioning. Ditches increase landscape drainage but changes in porewater loss rates are rarely quantified. I leveraged the unique landscape of a temperate, mesotidal marsh where there are adjacent ditched and unditched areas (MA, USA). Pressure transducers were deployed in ditched and unditched marshes over two years to quantify soil water levels and loss rates through ditch and creek drainage faces. In the ditched marsh, drainage rates through creek (0.30±0.17 m3 m-1 day-1) and ditch (0.27±0.14 m3 m-1 day-1) faces were similar. The combined drainage through those faces was five times greater than porewater loss rates via the creek face in the unditched marsh. Sea-level rise porewater drainage change is modeled under inundation and sea-level rise scenarios. In the most conservative scenarios, porewater drainage will increase by 2050 but decrease by 2100 with increased flooding frequency.