Plum rain enhances porewater greenhouse gas fluxes and weakens the acidification buffering potential in saltmarshes

Abstract

Seasonal rainfall, locally known as plum rain, is a potentially important driver of greenhouse gas dynamics in saltmarshes, but no studies of its effects have been reported. We quantified porewater exchange and related greenhouse gas fluxes in a saltmarsh over a spring-neap-spring tidal cycle (30 tidal cycles) during the plum rain season. Radon-traced porewater exchange rates were found to be 15.5 (pre-rain) and 24.8 (plum rain) cm day−1, which released CO2 and CH4 to surface waters with the fluxes (mmol m−2 day−1) of 77.7 and 0.28 during the pre-rain period and 132.3 and 0.63 over the plum rain period, respectively. The large amounts of soil CO2 export through porewater exchange during the plum rain significantly increased the CO2 inventory and reduced the pH from 8.06 to 7.86 (median) in saltmarsh surface water. The result suggests that plum rain-derived porewater exchange with lower pH values may contribute to coastal acidification.