Research On Groundwater Discharge Into Jiulongjiang Estuary

This paper,supported by the project of submarine groundwater discharge and its eco-environmental effects in the coastal area(40672166),which belongs to the National Natural Science Foundation of China,calculates flux of SGD in Jiulongjiang estuary via using naturally-occurring radium isotopes(Ra,Ra) tracer technique and estimates flux of nutrients,which lead to the discussion of their potential influence on eco-environmental.Obviously,excess Ra enrichment in Jiulongjiang estuary relative to conservative mixing between river endmember and ocean endmember,speculating have extra Ra from the other way.By identifying the total Ra(²²⁴Ra,²²⁶Ra) input and output of the Jiulongjiang estuary,we found that the Ra inputs contain river transport,ion exchange from suspended particle, diffusion from sediments,desorption from resuspended sediments particles,runoff and rising tide;while outputs consist of radioactive decay,runoff and ebb.Through constructing the ²²⁴Ra mass balance model of Jiulongjiang estuary,quantizing all kinds of source and sink terms,estimated that the SGD flux is 2.13×10⁸m³ d^-1;Through constructing the ²²⁶Ra mass balance model of Jiulongjiang estuary,quantizing all kinds of source and sink terms,estimated that SGD flux is 1.89×10⁸m³ d^-1,and the average SGD flux is 2.01×10⁸m³ d^-1.Based on the previous research of SGD,the re-circulated seawater could account for 60%～90%of the total SGD.The analysis results about nutrients of coastal groundwater samples and inter-tidal groundwater samples show that:the average consistency of total dissolved inorganic nitrogen is about 3.79μg/ml,reactive phosphate is about 0.45μg/ml,reactive silicate is about 11.44μg/ml.Supposing that if the fresh groundwater discharge account for 10%of total SGD,and have conservative chemical process between nearshore aquifer and subterranean estuary, the total dissolved inorganic nitrogen flux of fresh groundwater imput into estuary is about 2.78×10⁴ t/a,reactive phosphate is about 3.37×10³ t/a,reactive silicate is about 8.39×10⁴ t/a.Compared with nutrients flux that river transports into the estuary,the nitrogen flux of fresh groundwater imput into estuary is accounting for 27%of river transport into the estuary,reactive silicate is accounting for 92%,however,reactive phosphate is 34%higher than river transport into the estuary.