Submarine Groundwater Discharge And Associated Fluxes Of Nutrients And Carbon Into The Pearl River Estuary

Submarine groundwater discharge(SGD) has been recognized as an important component of the land-ocean interactions in fields from hydrology to oceanography. In this thesis, using naturally occurring radioactive tracers(223Ra,224Ra,226Ra,228Ra), we estimated residence time, submarine groundwater discharge, and nutrients and carbon fluxes from the subterranean estuary into the estuary of Lingdingyang in different seasons in the Pearl River estuary.Based on a tidal prism model, we estimated the flushing time of Lingdingyang in the Pearl River estuary and our results indicated that there was no difference in flushing time estimated using different radium isotopes. The flushing time was2.19d in summer and4.00d in winter.We used radium mass-balance to estimate SGD into Lingdingyang. Radium sources include river (carrying dissolved and what desorbs from suspended particles), diffusion from sediments, and SGD. The loss terms include mixing with the ocean and radioactive decay. The average flux of SGD in summer was(0.84±0.31)×108m3d-1and (1.35±0.57)×108m3d-1in winter, equivalent to10%and73%of the concomitant Pearl river water discharge, respectively.The net export DIN, DSi, SRP, DIC and DOC fluxes from the STE in the winter was (0.34±0.29)×108mol d-1,(0.29±0.26)×108mol d-1,(0.34±2.39)×105mol d-1,(1.38±2.75)×108mol d-1, and (0.16±0.24)×108mol d-1, equivalent to71%,121%,8%,46%,48%of the riverine fluxes; The net export DIN, DSi, SRP and DIC flux from STE in the summer was (0.21±0.17)×108mol d-1,(0.13±0.13)×108mol d-1,(0.09±1.49)×105mol d-1,(1.33±1.71)×108mol d-1,equivalent to19%,12%,0.6%,12%of the riverine fluxes. The ratio between the net export material fluxes from the STE and river is winter>summer. The net material additions from the STE occurred throughout the estuary, so the concentration of materials versus salinity almost follows conservative lines.