TROPICAL GEOGRAPHY ›› 2016, Vol. 36 ›› Issue (5): 878-886.

### Water Quality Fluctuations in Coastal Shallow Groundwater under Tidal Influence

LU Jianfei1，GAN Huayang1，PANG Yuan2

1. （1．Guangzhou Marine Geological Survey，Guangzhou 510760，China；2．Guangzhou Hydraulic Research Institute，Guangzhou 510220，China）
• Received:2015-01-20 Online:2016-09-05 Published:2016-09-05

Abstract:

Based on hourly sampling data in coastal shallow groundwater at eastern part of Leizhou Peninsula, water quality fluctuations under tidal influence are analyzed. The results prove that: 1) Na+ and Cl- are the chief ions in the groundwater of the research zone, while K+ and CO3 2- are ignorable. Groundwater quality in Donghai Island is stabilized, and no obvious correlations can be found among ions in the water. Quasi-synchronization variations of ions in the groundwater do exist in Nandu River basin and Xinliao Island. 2) The damage of alkalization of groundwater to soil in Nandu River area is the lowest, while that in Xinliao Island the highest, especially during spring tide. Changes of alkalization degree in Donghai Island are within very limited boundaries that are barely affected by tidal power. On the contrary, higher alkalization damage comes about during spring tide in both Nandu River area and Xinliao Island, derived from stronger seawater intrusion caused by strengthened tidal power, which aggravates the damage of alkalization of groundwater to soil. 3) As for the intensity of seawater intrusion to the groundwater, Donghai Island suffers the worst hit on average regardless of tidal power, which indicates an ordinary phenomenon. The maximal intensity during spring tide in Xinliao Island is higher than that in Donghai Island, while mean damage in Xinliao Island is lower than that in Donghai Island. Intensity of seawater intrusion is the lowest in Nandu River area and even down to zero at some time. 4) Na+ and Cl- in the groundwater of each monitoring well are closely correlated and are the major constituents in TDS, which also lead to main changes in TDS. TDS fluctuation is the most obvious in Nandu River area, and then in Xinliao Island. TDS in Donghai Island barely changes. 5) Conductivity monitoring in groundwater can be a way to monitor mineralization of water, as well as Na+ and Cl- in Nandu River and Xinliao Island, while interval instead of precise monitoring can be carried out for Donghai Island.