Groundwater salinization challenges in agriculturally valuable low-lying North Sea region: A review

Groundwater is an essential freshwater source in the North Sea region (NSR) used in agricultural irrigation, for trade, transport, and tourism in addition to regulating environmental flows. Historical palaeogeographical transformations and human land- and water-use modifications have put the aquifers in the NSR at high risk to groundwater salinization. This review assesses current knowledge on the vulnerability to groundwater salinization in the NSR, threats and mechanisms involved in the process and relates them to the agricultural value of the region, which has not been done previously. Connate salinity, overextraction via groundwater pumping and sea level rise/ climate change driven processes were the main threats to groundwater salinization in the region. Flooding, saline intrusion, irrigation using brackish water and airborne transfer of saline droplets were the main mechanisms propagating salinization. Forty-one studies evaluating on the phenomenon were identified and sixteen of those were from the Netherlands. Numerical modelling using SEAWAT was the commonest method to simulate groundwater salinity. The review highlights the negative influence of groundwater salinization in the NSR agricultural economy and the complexity of the phenomenon, which is controlled by historical landscape changes, human interference through land-use and water-use changes and climate modifications. These complexities were best represented using numerical models and hence, their preference compared to other methods. Numerical modelling is vulnerable to uncertainties in groundwater salinization studies, which can be alleviated through intensified research in underassessed areas using advanced technology and integrated numerical modelling, which incorporates calibration and validation analysis and links subsurface and surface hydrological processes.