SGD studies in Laizhou Bay

SGD investigation in the eastern coast

In the eastern part of Laizhou Bay, (Xing et al. , 2016) detects potential SGD by analyzing the seawater surface temperature anomaly obtained from the maximum temperature difference between seawater and groundwater in the thermal image. The results show that when the tide fluctuates between 0.5-1.8m, the temperature changes from 13.8 ℃ to 23.3℃, and the salinity from 17.91 to 33.27‰. In addition, they found the anomaly of sea surface temperature is not related to long coastal circulation or river flow, so it may be related to local SGD.
Recently, (Zhang et al. , 2016) used 222Rn to evaluate SGD on the east coast of Laizhou Bay. Based on the222Rn mass balance model and continuous monitoring, the flux of SGD was 6.64cm3/d to 7.21cm3/d, with an average of 6.93cm3/d, which was consistent with the results of other scholars and numerical simulation. Subsequently, this paper estimated the impact of SGD on local environment. The estimated DIN, TDN and TDP were 7.79*106mol/d, 8.92*106mol/d and 1.41*104mol/d, respectively, which were equal to or even higher than the Yellow River. In addition, this study shows that tides play an important role in SGD variation. The concentration of 222Rn is greatly affected by tides and fluctuates at high tide and low tide, respectively. Moreover, flux and sediment diffusion of226Ra are independent of the total SGD supply.
Although there are few studies on the east coast of Laizhou Bay and the data are severely limited, the results have theoretical and practical significance for the effective management of vulnerable water resources in Laizhou Bay. Based on an understanding of hydrogeological processes, more work and knowledge on the cycle between groundwater and seawater in coastal areas is required to achieve sustainable development and management.

SGD investigation in the northwest coast

On the northwest coast of Laizhou Bay, (Ma et al. , 2015)studied the SGD exchange rate of a tidal flat with a large-scale seepage surface. Under Darcy’s law and taking full account of the density variation, the SGD quantity and inflow quantity here are respectively 8.8 m3• d−1• m−1and 15.3 m3 • d−1• m−1. Due to the large seepage surface area, low sediment permeability and very gentle slope, the outflow showed a trend of first decreasing and then increasing, while the inflow first increased and then decreased, which is obviously different from the sandy or gravel beach.

SGD investigation in the southern coast

On the southern bank of Laizhou Bay, (Hou et al. , 2016) found the silty tidal flat. They found that the salinity here was 25 to 56 g/L. The value of SGD and inflows are 164.0m2/d and 6.5m2/d. Later, more and more scholars have carried out a lot of researches in the south coast of Laizhou Bay, as SGD here is typical and it has a great impact on the coastal environment. Considering the process of groundwater discharge in the intertidal zone, this area is further studied using numerical simulation, field monitoring, electrical conductivity and other methods. (Han et al. , 2014)also studied the hydrochemistry and hydrogeology of the area.
In general, the study results on the southern shore of Laizhou bay can be sumariezed as follows :(1) groundwater farther from the sea is more resupplied from inland sources. (2) Salinity is mainly affected by two factors. On one hand, intense evaporation leads to a continuous accumulation of salt on the beach surface. On the other hand, the brine is extracted and seeped during inland salt leaching, which will also increase the salinity of groundwater. (3) SGD was caused by the existence of seepage surface in intertidal section due to the low permeability coefficient and gentle slope of the intertidal zone. In the intertidal zone from the inland to the ocean, relatively high water heads allow groundwater to drain to the surface. (4) The dynamics of the submarine groundwater in Laizhou Bay is affected by precipitation and tide, and has a periodic variation pattern. (5) The seabed groundwater in Laizhou Bay is stratified, which can be divided into five layers, roughly the same as the sedimentary strata, and is mainly affected by the distribution of brine aquifers formed in three transgression periods since the late Pleistocene. (6) Large amount of water flow is the effect of large amount of underground water flow driven by density. The gradual lowering of salinity to the sea may be due to evaporation, human activities such as the extraction of subsurface brines and the construction of many projects, and the discharge of inland freshwater near low-tide zones.