in the water table due to poor irrigation and drainage, disturbance in existing groundwater salinity stratification by digging bore wells, and industrial effluents are the notable natural and human‐induced groundwater salinity sources that can deteriorate the water quality by acidification and release of toxic ions into it. (Greene et al. 2016).
3.7 Effects of Saline Water on Human Health
Salinity is a serious environmental issue worldwide, especially in drylands and coastal regions. Dryland salinity is a major environmental degradation problem observed in Australia (Lambers 2003). Seawater intrusion is a major concern in coastal areas of Bangladesh, Brazil, California, China, India, Indonesia, Netherlands, and Vietnam (Chakraborty et al. 2019; Rahaman et al. 2020). The sea‐level rise is a major issue for coastal cities such as Chennai, Cochin, Kolkata, and Mumbai. The major fertile river deltas in India such as Cauvery, Indus, and Krishna are vulnerable to floods and seawater intrusion (Rahaman et al. 2020). The salinity issues in terms of seawater intrusion and sea‐level rise may increase in the future due to climate change, and human activities like an increase in groundwater overdrafts and shrimp culture along the seacoasts, which may affect the coastal ecosystem to a greater extent (Akib Jabed et al. 2018).
Drinking saline water is a global health issue notably in coastal areas. Earlier, a number of studies reported that the people drinking large quantities of saline water may suffer from cardiovascular disease, diarrhoea, rise in blood pressure, hypertension, infant mortality, and skin and respiratory diseases (Dasgupta et al. 2016; Akib Jabed et al. 2018; Chakraborty et al. 2019). Though the salinity is a global issue, its health effects are often seen in low‐income countries where water is poorly treated or totally untreated (Vineis et al. 2011). Health issues such as chronic malnutrition, low‐calorie intake and hypertension were reported in coastal peoples of Bangladesh (Nahian et al. 2017; Rahaman et al. 2020). Mental and respiratory diseases were reported in Australia due to the inland salinity issue (Jardine et al. 2007). Studies in Arizona, Illinois, and Massachusetts, USA, suggested that high intake of salts would lead to raising blood pressure (Tuthill and Calabrese 1981; Welty et al. 1986; Rahaman et al. 2020). A study from Vietnam reported that high salt intake is highly associated with a rise in blood pressure that increases the risk of cardiovascular disease (Do et al. 2016). Moreover, the salinity shows some considerable impacts on soil microbial species which lowers the crop productivity (Dasgupta et al. 2017).
3.8 Management Strategies
Proper management strategies have to be followed to reduce the salinity effects, especially in arid and semi‐arid areas. They are given in the following sections.
3.8.1 Lowering of the Groundwater Table
Extensive withdrawal of groundwater in the upstream side of the river may reduce the groundwater level in the coastal areas that allows the intrusion of seawater. Hence, crop cultivation is quite difficult in coastal areas due to the presence of saltwater. In order to reduce the salinity effects in coastal areas, leaching of salts has to be reduced. Hence, it is necessary to maintain a proper drainage system to lower the water table at least 1.5 m from the surface of the soil to prevent salt accumulation (Alam et al. 2017).
3.8.2 Construction of Water Harvesting Structures
In order to reduce the effect of salinity, groundwater consumption has to be substituted with freshwater (rainfall) for irrigation. Proper rainwater harvesting structures have to be constructed to cope with salinity for sustaining agricultural livelihood in drylands. Floodwater harvesting such as spat irrigation and runoff farming, macro‐catchments such as highlands, and micro‐catchment structures such as bunds, pits holes, and basins are the rainwater harvesting structures that can reduce the groundwater consumption for irrigation especially in drylands (Gebreyess and Abayineh 2019).
3.8.3 Reclamation of Saline Soils
Soil reclamation is one of the best ways to reduce the impact of salinity. In general, it refers to the strategies to extract soluble salts from the roots of the crops. Some of the best practices to reduce the impact of salinity are leaching, enhanced water management techniques, establishing surface (through ditches) and subsurface drainages (through open ditches, mole drains, crop rotations), use of organic or chemical fertilizers and use of salt‐tolerant cultivars (Esenov and Redjepbaev 1999; Shrivastava and Kumar 2015; Kaledhonkar et al. 2019).
3.8.4 Leaching
Soil salinity is one of the important factors that influence plant physical and biological activities thereby reducing the crop yields. Hence, it is necessary to remove the excess salts from the root zone of the soil for improving crop production. Leaching is one of the important processes to remove salts from the root zone by applying a large amount of freshwater into the field and allowing the water to infiltrate. During infiltration, the excess salts from the root zone are washed away into deep soil layers. This process is effective when it is to be done in soils with low moisture and deep groundwater water tables (Zaman et al. 2018).
3.8.5 Surface and Subsurface Drainage Systems
Drainage refers to the removal of surface or subsurface water by natural or by installing artificial drainage systems. Drainage helps in lowering the water table and reducing the risk of rising groundwater table and accumulation of salts through the capillary rise. Hence, it is necessary to have a proper drainage system in order to reduce the negative impacts of rising water table and accumulation of salts. It can be accomplished by establishing surface (through ditches) and subsurface drainages (through open ditches, mole drains) (Shahid et al. 2018).
3.8.6 Possible Strategies and Practices to Reduce Salinity‐Related Health Issues
Generally, the people from drylands and coastal areas are more vulnerable to salinity‐related health issues to a large extent. Hence, it is necessary to create awareness among the communities to find alternative freshwater supplies to cope with salinity related health issues. Though there are several desalination processes which are of high cost, some low‐cost techniques such as rainwater harvesting structures and ponds should be constructed. Optimal use and reutilisation of rainwater for various purposes is needed to reduce the risk of salinity to some extent.
3.8.7 Organic or Chemical Fertilizers
Organic fertilizers help in releasing various elements like Ca2+ and Mg2+ into the soil through decomposition and help in increasing soil water holding capacity. It also helps in reducing Na+ toxicity through cation exchange capacity (Machado and Serralheiro 2017). Application of potash fertilizers can reduce the salinity effect of soils on crops. It reduces the uptake of Na+, which helps in increasing crop production. It also helps in the uptake of elements such as Ca2+, Mg2+, K+, and P. The boron toxicity can be overcome by adding nitrogen fertilizers (Koohkan and Maftoun 2016). The effects of Cl− toxicity in soils can be ameliorated by adding nitrogen fertilizers (Bar et al. 1997; Karaivazoglou et al. 2005). The toxic effects of sodic soils on crops can be rectified by adding gypsum to the soil (Zaman et al. 2018).
3.8.8 Salt‐Tolerant Cultivars
Salt accumulation in soils is one of the major issues worldwide. An uptaking of a large amount of soluble salts through roots has a significant impact on plant physiological and metabolic processes, which reduces crop yields. Usage of salt‐tolerant cultivars is one of the major mitigation processes to cope with salinity
