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.