Coastal water quality assessment and groundwater transport in a subtropical mangrove swamp in Daya Bay, China

Kai Xiao; Hailong Li; Meghan Shananan; Xiaoying Zhang; Xuejing Wang; Yan Zhang; Xiaolang Zhang; Haiyan Liu

doi:10.1016/j.scitotenv.2018.07.394

Coastal water quality assessment and groundwater transport in a subtropical mangrove swamp in Daya Bay, China

Sci Total Environ. 2019 Jan 1:646:1419-1432. doi: 10.1016/j.scitotenv.2018.07.394. Epub 2018 Jul 30.

Authors

Kai Xiao¹, Hailong Li², Meghan Shananan³, Xiaoying Zhang⁴, Xuejing Wang¹, Yan Zhang⁵, Xiaolang Zhang¹, Haiyan Liu⁵

Affiliations

¹ School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China.
² School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China; State Key Laboratory of Biogeology and Environmental Geology and School of Water Resources and Environmental Science, China University of Geosciences, Beijing 100083, China. Electronic address: lihailong@sustc.edu.cn.
³ School of the Earth, Ocean and Environment, University of South Carolina, Columbia, SC 29208, United States.
⁴ Institute of Groundwater and Earth Science, Jinan University, Guangzhou 510632, China.
⁵ State Key Laboratory of Biogeology and Environmental Geology and School of Water Resources and Environmental Science, China University of Geosciences, Beijing 100083, China.

PMID: 30235627
DOI: 10.1016/j.scitotenv.2018.07.394

Abstract

Coastal water quality assessment is challenging due to the complex hydrological environment in mangrove swamps. Such assessment requires a good understanding of swamp hydrology and potential solute reactions. In this study, we investigated the concentration variations of a suite of major elements (Na⁺, K⁺, Ca²⁺, Mg²⁺, SO₄^2-, HCO₃^- and Cl^-), nutrients such as dissolved inorganic phosphorous (DIP) and silicate (DSi), and heavy metals (Cu, Zn, As, Hg, Cd, Pb and Cr) along a typical mangrove transect in Daya Bay, China. The transect comprises a tidal creek, a mudflat and two mangrove zones. The major elements exhibited various degrees of dilution and loss, such as losses of K⁺ due to uptake by mangrove trees and of SO₄^2- due to microbial sulfate reduction. Numerical simulations of groundwater flow showed that the inland fresh groundwater can continuously discharge through the landward mangrove zone, where high concentrations of DIP and DSi occurred. However, the middle mangrove zone served as a sink of DIP and DSi due to the weak hydrodynamic environment. The spatial distribution of heavy metal concentrations showed that only Cu pollution occurred in the creek zone. The Metal Pollution Index (MPI) was developed to compare the enrichment capability of heavy metals at the different sampling sites. Results showed that the intertidal groundwater has the strongest heavy metal enrichment capability, followed by sea water, inland groundwater and river water. Within the intertidal zone, the creek zone has the highest MPI, followed by the mangrove zone and the mudflat zone. The local water circulation occurred around the creek should contribute the high MPI in the creek zone.

Keywords: Coastal wetlands; Groundwater flow; Heavy metal; Intertidal zone; Numerical simulation; Nutrients.