The Effects of Flooding Duration and Salinity on Three Common Upper Estuary Plants

Abstract

Although the effects of permanent flooding on biomass of coastal marsh plants has been extensively documented, the effect of duration of flooding has received little attention. Panicum hemitomon, Sagittaria lancifolia, and Spartina patens were exposed to three flooding durations (day, week, month) and two salinity regimes (0 and 6 ppt) for 3 months. All flooding treatments resulted in the plants being flooded 50 % of the 3 month experimental period. Panicum hemitomon experienced 100 % mortality at 6 ppt but was unaffected by flooding duration at 0 ppt. Sagittaria lancifolia growth and biomass were reduced by both increased salinity and flood duration. Spartina patens growth was unaffected by both flooding and salinity. However, a significant interaction term indicated that S. patens belowground biomass increased with flood duration under fresh conditions but decreased with flood duration under brackish conditions. Examination of the growth patterns showed reduced growth of the grasses when the soil was inundated. Growth of S. lancifolia was reduced at times, when leaves were being replaced, but the pattern did not coincide with flooding and may reflect a specific leaf turnover cycle in this species. Restoration of coastal regions involves manipulation of estuarine hydrology, which can be improved using these study results.