| |
| |
|
|
|
|
| |
 |
Biogeochemical processes in land-ocean interfaces, surface estuaries, subterranean estuaries and sediment-water interface
|
| |
|
|
Using 224Ra/228Th disequilibrium to illuminate the seasonal and tidal variations of solute transfer across mangrove sediment-water interface and internal cycles
P-C2-07-S
Xueying Shi* , Xiamen University, China
Pinghe Cai, Xiamen University, China
Presenter Email: shixueying@stu.xmu.edu.cn |
| Mangroves are gradually being regard as an important player in coastal biogeochemical and hydrological cycles with their complex belowground structures (i.e., crab burrows) and various biota species in sediments. The former facilitate pore water exchange and submarine groundwater discharge, meanwhile the latter make biochemical properties of mangrove sediments different from other coasts. Spatial and seasonal variability of sedimentary salinity, DIC, nutrients and trace metals concentration were investigated in a tidal cross section of mangrove sediments with four seasons. Exchange and circulation of solute transfer across the sediment-water interface has been recognized as a significant process, the 224Ra/228Th disequilibrium was recently observed in coastal muddy sediments which has been proven to be an excellent proxy for tracing the benthic processes that regulate these solute and calculating their fluxes when they transfer across the interface. Fluxes of dissolved inorganic carbon (DIC) gradually increase from autumn(1.58¡À162.81 mmol/m2/d), winter(328.77¡À774.46 mmol/m2/d) to spring(1707.68¡À773.70 mmol/m2/d) and then decrease in summer(85.14¡À263.88 mmol/m2/d). But if upscale to the whole area of the Zhangjiangkou mangrove in a whole year, mangrove sediments still provide DIC to surroundings(4.57x109¡À2.45x109 mol/y)as a source. Irrigation is a major process that controls solute transfer across the sediment-water interface as we have known, whereas bioturbation is also a significant factor while solute cross the interface in mangrove sediments. However, we not only observe the deficit of 224Ra from 228Th, but also discover the balance even excess between 224Ra and 228Th in this study and these phenomena vary with season and tide that illustrate there is an internal exchange and circulation in mangrove sediments. Our data indicate an obvious water cycle that exits in a tidal cross section of sediments with a two or three layers' loop mode. |
|
|
|
|
|
|
|
|