Heat and salt flux estimates in the Duplin River

Overview An experimental study of temperature cycles and the heat budget in the Duplin River, a tidal creek bordered by extensive intertidal salt marshes, was carried out in late summer of 2003 and spring of 2004 near Sapelo Island on the central Georgia coast in the southeastern US. Three water masses are identified with differing temperature and salinity regimes, the characteristics of which are dictated by channel morphology, tidal communication with the neighboring sound, ground water hydrology, the extent of local intertidal salt marshes and side channels and the spring-neap tidal cycle (which controls both energetic mixing and, presumably, ground water input). For the first experiment, heat budgets are constructed for the upper (Figure 1a) and lower (figure 1b) areas of the Duplin River showing the diminishing importance of tidal advection away from the mouth of the creek along with the concomitant increase in the importance of both direct atmospheric fluxes and of interactions with the marsh and side creeks. The second experiment, in the spring of 2004, reexamines the heat budget on seasonal and daily averaged scales revealing the decreased importance of advective fluxes relative to direct atmospheric fluxes on this scale but the constant importance of marsh/creek interactions regardless of time scale or season. Short period temperature fluctuations, which affect larval development, are examined and analogies are drawn to use heat to understand the marsh as a source of sediment, carbon and other nutrients. An experimental study of vertical mixing (Az) and along-channel dispersion parameterized in terms of horizontal mixing (Kx) near the mouth of the Duplin River, a tidal creek bordered by extensive intertidal salt marshes on Sapelo Island, Georgia, was carried out over several spring/neap cycles in the fall of 2005 (see Figure 2). Vertical mixing is modulated on both M4 and fortnightly frequencies with maximum turbulent stresses being generated near the bed on periods of maximum flood and ebb and propagating into the water column showing a linear dependence with depth. Values are significantly greater on spring tide than on neap. Horizontal mixing evaluated by salt fluxes is driven and dominated by tidal dispersion, which is also modulated by the fortnightly spring/neap cycle. Net export of salt from the lower Duplin is shown to be due to residual advection modified by upstream tidal pumping. The tidal dispersion coefficient exhibits a pulsating character with greater values on spring tide followed by smaller values on neap tide.