Lotifa Tamanna Toma
Climate change distresses water resources through changes in evaporation, groundwater recharge, temperature, runoff, and rainfall. In freshwater systems, these modifications have an impact on the transportation, distribution, and mobilization of nutrients. Water quality is affected by biological, physical, and chemical changes as a result of both direct and indirect effects of climate change. Pathogenic bacteria in water are one example of biological changes. Physical alterations include warmer water, less ice on rivers and lakes, less water mixing in deep-water lakes, more stable vertical stratification, and adjustments to water outflow that impact retention duration and water level. Increased nutrient concentrations, changed water color, and reduced oxygen content are examples of chemical alterations.
Climate Change and the Water Cycle
Impacts of Climate Change on Physicochemical Properties of Water
Worldwide, present challenges with surface water quality are made worse by climate change. It may lead to notable adjustments in the factors influencing the water’s quality. A surface water body’s water quality is directly related to the chemical inputs it receives from the surrounding environment and the air, as well as the biogeochemical activities that occur inside the water body to change those inputs from both human activity and natural processes. The physicochemical quality of water will be indirectly impacted by changes in the hydrology. Events with high precipitation may exacerbate soil erosion, which will raise the amount of pollutants and nutrients that wash into surface waterways. Water clarity will decline when eutrophication increases in water systems. On the other hand, the physicochemical quality of surface waters is threatened by climate change. Different physicochemical parameters of water quality are changing due to climate change.
Temperature
Water temperature rises with the air temperature. As a result, the temperature of the water will shift in conjunction with the ambient temperature. In deep lakes, high temperatures also lead to less vertical mixing and greater thermal stratification. This will have a major impact on lake water mixing, which in turn influences phytoplankton biomass, nutrient cycling, and deep water oxygen conditions.
Turbidity and Light Conditions
An essential indicator of surface water quality, turbidity can reveal the presence of organic matter, other minute particles, microbes, and scattered suspended solids. Certain bodies of surface water will have less light due to climate change. The greater the dispersed light intensity, the higher the turbidity values observed.
Total suspended solids (TSS) and turbidity are frequently related because high TSS water usually has a more complicated appearance and higher turbidity readings. Increased soil erosion and, as a result, a rise in water column turbidity will result from more severe precipitation.
Therefore, there are two ways that climate change lessens the transparency of water bodies: it increases soil erosion and particulate matter and nutrient loading; and it lowers the critical nutrient threshold value, which is the point at which a system transitions from a clear to a turbid condition.
Nitrification and Denitrification
Along with phosphorus, nitrogen is a crucial component of ecosystems and the principal productivity nutrient. Excess nitrogen can cause eutrophic conditions, which have a negative impact on the quality of the water and the ecosystem. The digestion of nitrate in water is influenced by two biological processes: nitrification and denitrification.
Ammonium (NH4+) is converted to nitrate (NO3-) during the nitrification (aerobic process). Since primary producers employ nitrate (NO3-), this process is referred to as a “nitrate” input process for water. Aquatic environments lose nitrate as a result of the anaerobic process of denitrification, which converts nitrate (NO3-) into nitrous oxide (N2O) or nitrogen (N2). Nitrate is finally expelled from the water column into the atmosphere. One of the main greenhouse gases is nitrous oxide. These activities have the ability to impact ecosystem health and water quality because they either add to or remove nitrate from the water system. Global warming has an impact on these two processes since their rates rise with temperature.
Acidification
The oceans get more acidic due to increased atmospheric CO2 concentrations. Many freshwater environments get significant amounts of carbon from terrestrial ecosystems, in contrast to ocean waters. The primary type of this is organic carbon that has dissolved. The DOC is mineralized into CO2 by bacterial action. Because of this, lakes’ CO2 concentrations are often correlated with dissolved organic carbon concentrations rather than being in equilibrium with the atmosphere, as is the case with oceans.
Acid deposition and acid precipitation are the principal causes of soil and freshwater acidification. Emissions from transportation, agriculture, and industry are the primary sources of SO2, NOx, and NH3 emissions that lead to acid precipitation. Climate variables that could affect acidification include:
Higher temperatures,
Increased summer drought, Wetter winters,
Reduced snow pack, Concomitant changes in hydrological pathways, and Increased occurrence of sea-salt deposition events.
Salinization
Seawater intrusion or a rise in surface water chloride content are the two main ways that freshwater is salinized. River flows will be minimal during the sweltering summers, and the anticipated rise in sea level will make seawater intrusion more likely. Groundwater in coastal locations is most affected by saltwater intrusion, especially in polder environments. Freshwater aquatic life, agriculture irrigation, and drinking water are all under risk from saltwater intrusion.
Nutrient and Contaminant Concentrations
The quantities of pollutants and nutrients in surface water are influenced by extreme weather events including heat waves and torrential rains. Flooding may result from more and more severe precipitation. Soil pollution can result from contaminated water seeping into the soil. Hazardous materials may seep into the water from flooded landfills.
Severe droughts may cause low water releases and episodes of dehydration, which may alter the amount of pollutants and nutrients present. Events involving dehydration will stop microbial activity, which leads to a buildup of nutrients like phosphates and nitrogen.
Conclusion
Climate change will have an impact on water quality through temperature increases as well as hydrological changes in rainfall that will alter runoff and the mobilization of pollutants and nutrients. Any changes to these (physical, chemical, and biological) variables have an effect on all the environmental and socioeconomic products and services that are either directly or indirectly dependent on these systems. The pace of biogeochemical and biological processes that define water quality, as well as the ice cover and circulation patterns in lakes and rivers, will all be impacted by rising water temperatures. Water quality may suffer in regions where groundwater recharge and river flow are expected to decline because of reduced pollutant dilution. Extreme precipitation events and floods with greater severity and frequency are predicted to increase the burden of contaminants (organic matter, Higher intensity and frequency of floods and more recurrent extreme precipitation events are expected to increase the load of pollutants (organic matter, nutrients, and hazardous substances) wash away from soils and overflows of sewage systems to water bodies.
Author is a MS Student at Bangladesh Agricultural University
Email: it.toma08@gmail.com
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