Dependence of coastal wetland ecosystem respiration on temperature and tides: a temporal perspective
Variations in temperature are widely invoked to explain fluctuations in ecosystem respiration (ER), but hydrological conditions also influence ER. Many researchers have observed that aperiodic variations in hydrological conditions affect ER and the associated temperature sensitivity. However, little is known about how periodic hydrological dynamics affect ER and its relationship with temperature on different timescales. In the present study, data from two coastal wetland sites were used to compare the variations in thermal and tidal influences on ER at three timescales (monthly, seasonal, and semiannual), and we found that (1) the influences of tides and temperature on ER varied with time. Especially in summer, the ER exhibited periodic dynamics regulated by tides; (2) in the temporal domain, temperature was dominant at the semiannual and seasonal scales, while the tidal effect was dominant at the monthly scale. In the spatial domain, the relative importance of temperature was greater at higher elevation sites, while tides exerted more influence at lower elevation sites; (3) the monthly model with tidal effect performed best, while regression models at semiannual and seasonal scales generated systematic errors in ER. These results demonstrate that, for coastal wetlands, the application of parameters from regression models based on long-term (seasonal or semiannual) data should be avoided in gap filling, and the effects of tides and elevation should be considered in estimating the carbon budget.