world. It is caused by the rising of the water table due to the evaporation of water from the soil. In drylands, the water loss is reduced due to the removal of vegetation and change in land use patterns that allows accumulation of more salts into the soil and groundwater, which have adverse effects on plant growth and lead to low crop yield (Zaman et al. 2018). The other causes that induce water table rise are restricted drainage systems, excessive recharge of groundwater due to heavy rains and floods, and replacement of deep‐rooted perennial plants with shallow‐rooted annual plants.
3.4.3 Tertiary Salinity
Tertiary salinity is also called irrigated salinity. It is characterised by the rise in the local groundwater level due to repetitive irrigation with large quantities of water over many cycles. This process can add some salts to the soil profile, which may also be mobilised into the groundwater. Each successive irrigation or reuse of saline groundwater keeps adding more salts to the groundwater, which progressively becomes more saline, resulting in higher levels of salinity over several cycles (Zaman et al. 2018). It gets even worse when irrigating from poor quality water or saltwater.
3.4.4 Urban Salinity
Urban salinity is a combination of both dryland salinity and irrigation salinity that has the potential to affect valuable assets. It is characterized by the rise in groundwater level that is possibly due to blocking or changing natural drainage patterns due to urban developmental activities like laying roads, constructing buildings and other infrastructures, and leakage of pipes and drains. The most common sources of urban salinity are untreated urban effluents/industrial wastewater, building materials, fertilizers, and chemicals (Brindha and Schneider 2019).
3.5 Effects on Agriculture
3.5.1 Soil Structure
The bivalent cations such as Ca2+ and Mg2+ tend to flocculate, which facilitates penetration of water into roots, whereas the monovalent cations such as Na+ and K+ disperse the clay particles, which reduces the porosity of the soil. Hence the excess amount of Na+ and K+ has a profound impact on the relationship between soil and water, resulting in soil erosion and crop failure (Chibowski 2011).
3.5.2 Oxidative and Alkaline Stress
In general, the osmotic gradient helps in taking water from the soil by roots. Salinity in soil diminishes the osmotic gradient, which reduces the intake of water by roots and hinders cellular activities. This leads to the loss of vacuole fluid and the plant starts to wilt (Litalien and Zeeb 2019). The alkaline soils, usually saline/saline‐sodic with pH above 8, tend to reduce the absorption of nutrients that due to the redox potential of major nutrients (Husson 2013).
3.5.3 Ion Toxicity
Long‐term saline stress in terms of excess Cl− and Na+ ions in soils induces the accumulation of ions into the plant that leads to ion toxicity. A high concentration of Cl− ions in the soils affect the plant; further, it can affect photosynthesis, which leads to leaf burn and necrosis. Whereas the excess amount of Na+ ions in soil reduces the intake of K+ ions, which is highly desirable (White and Broadley 2001; Barhoumie et al. 2007; Machado and Serralheiro 2017). Boron toxicity is a common issue in the soils of the arid and semi‐arid regions. It affects various aspects of the plant growth, such as metabolism alteration, lowering chlorophyll content in leaves, and decreasing root growth (Nable et al. 1990, 1997).
3.5.4 Nutrient Deficiencies
Continuous salt accumulation in soils over a period of time can cause an ionic imbalance in plant cells that inhibits the absorption of core elements like Ca2+, K+, and NO32−. Accumulation of Na+ and Cl− ions in soil induces nutritional deficiencies in plant tissues, which results in Na+ induced Ca2+ and K+, Ca2+ induced Mg2+ and Cl− induced NO32− deficiencies (Grattan and Grieve 1992). Excess boron in soils results in deficiencies of Ca2 + in plants that cause necrosis of the leaf (Abdulnour et al. 2000).
3.6 Effects on Non‐Agricultural Lands and Other Natural Resources
3.6.1 Subsidence of Land
Salinity has a profound effect on land subsidence, especially in clay‐dominated coastal soils. Higher salinity in water reduces the interconnectivity of the pores by converting clay fabrics into parallel alignments that induce the fast dissipation of pore water. Hence, consolidation is more pronounced (Sarah et al. 2018).
3.6.2 Corrosive Risk
In general, the corrosive risk of freshwater is lower than that of saline water. The water containing a high percentage of dissolved oxygen and sodium and other chlorides makes metals like steel and low‐alloy steels more susceptible to metal corrosion. In fact, these are not only the causes but are also affected by the other dependant factors such as pH, temperature, amount of soluble gases, and pollutants (Zakowski et al. 2014).
3.6.3 Deterioration of Water Quality
Salinity is one of the major issues that affect water resources in various forms. It is possibly due to both natural and anthropogenic activities. Seawater intrusion, rise 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).
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