Estimating Submarine Groundwater Discharge(SGD) And Associated Nutrient Fluxes Into Jiaozhou Bay Using Radium Isotopes

Submarine groundwater discharge(SGD)is defined as any and all flow of water on continental margins from the seabed to the coastal ocean,regardless of fluid composition or driving force.Seawater infiltrating coastal aquifers will change some of its original chemical components.Thus SGD is a good indication of the coastal ecological environment.Jiaozhou Bay is a semi closed Bay with a narrow mouth,and the seawater exchange ability is relatively weak.With the rapid development of economy and human activities,the environment of Jiaozhou Bay is deteriorating.Therefore,it is of great significance to study the submarine groundwater discharge and its nutrient fluxes into the bay.This study evaluated the flushing time and SGD of Jiaozhou Bay using radium isotope mass balance model.On the basis of the above results,we evaluated the submarine fresh groundwater discharge(SFGD)using the water and salt mass balance models.At the same time the result of flushing time of radium isotopes method is verified with the apparent water age model and the tidal prism method,and the SFGD estimation is verified by regional water balance method.According to the physical model,we calculated the flushing time of Jiaozhou Bay,the flushing times in summer and winter are 6.06~13.32 days,9.32~23.08 days,respectively.SGD ranges from 1.16 m3/d×10~7 to 1.81×10~7 m3/d in summer,and ranges from 0.72×10~7 m3/d to 1.11×10~7 m3/d in winter.SFGD is 0.76×106 m3/d~5.69×106 m3/d in summer and 1.34×106 m3/d~2.84×106 m3/d in winter.The ratio of SFGD to SGD in summer and winter are 6.53%~31.40%,18.46%~25.63%,respectively.We also analyzed the fluxes of nutrients into Jiaozhou Bay on the basis of the above results of SGD.In coastal groundwater,dissolved inorganic nitrogen(DIN)concentration is 714.47 mol/L,dissolved inorganic phosphorus(DIP)concentration is 0.31 mol/L,the ratio of nitrogen and phosphorus is 2304 in summer;the concentration of DIN is 69.40 mol/L,the concentration of DIP is 0.66 mol/L,the ratio of nitrogen and phosphorus is 105 in winter.In summer,Jiaozhou Bay's dissolved inorganic nitrogen(DIN)flux is 1.04×10~7 mol/d,dissolved inorganic phosphorus(DIP)flux is 4.49×10~3 mol/d,while in winter the dissolved inorganic nitrogen(DIN)flux is 6.21×105 mol/d,the dissolved inorganic phosphorus(DIP)flux is 5.91×10~3 mol/d.