WHY FRESHWATER

From excessive use of inorganic fertilizers and pesticides to domestic sewage and industrial effluents, an ever-growing list of pollutants are reducing the quality of wetlands across the country. Water pollution can affect both the quantity and quality of water available in freshwater habitats, while significantly impacting human health and freshwater biodiversity or aquatic ecosystems. 

Untreated industrial effluents, domestic sewage, untreated storm water, agricultural runoff, and solid waste are the primary causes of pollution in the rivers and wetlands. These pollutants have irreversible effects on all wetland inhabitants—from crocodiles to fish to bottom dwellers such as macro-invertebrates. There has been a 50% decline in fish diversity in Ghodaghodi lake alone over the last 20 years (27 fish species were recorded in 1998, but only 13 species were found in 2017).

Overtime, population growth, expanding human settlements, agricultural lands, and unplanned development/industrialization have zeroed in on wetlands, cutting into their boundaries at alarming rates—ultimately resulting in freshwater and wetland shrinkage. These are also some of the underlying causes behind increasing riverbed sand and gravel mining in Nepal, with alarming results such as destruction of fish spawning sites and nursery grounds and habitat destruction of freshwater species such as the critically endangered gharial and the river dolphin among others, in addition to seriously affecting the flow of ecosystem services from rivers. 

Estimates indicate that wetlands across the country have shrunk by 5.41% over the past 25 years. The impacts are especially evident through a bird’s eye-perspective; habitat shrinkage has jeopardized Nepal’s status as a harbor for more than 50,000 migratory birds. 

Another big threat in freshwater habitats is the increase in illegal and destructive fishing practices. With the commercial value of fish in nearby markets, and inadequate regulations and enforcement freshwater habitats are often exploited by illegal or commercial fishermen. Consequently, practices like illegal or over fishing not only depresses local fish populations and species, but can also result in accidental entrapment of other freshwater mega species like the river dolphin and gharial. Likewise, government regulations and enforcement on fishing are limited, which are often exploited by illegal and commercial fishermen.

Excessive nutrients in wetlands can often lead to widespread growth of invasive aquatic plants and species. Invasive species can have wide ranging impacts on freshwater systems, considerably degrading water quality by blocking the air water interface. Left uncontrolled their quick proliferation stifles underwater ecosystems—blocking sunlight, reducing oxygen levels, breeding bacteria and other microorganisms—resulting in elimination of wetland flora and fauna.

The thick and extensive mats block both sunlight and air from reaching the water surface, providing breeding grounds for disease vectors with known cases of contact dermatitis among people and cattle kills. Meanwhile, invasive freshwater species such as the tilapia fish—introduced for economic and nutrition benefits—have a broader environmental tolerance and high reproductive rate which can harm native fish species via competition over available food and space.

Soil erosion and subsequently landslides are one of the primary reason for sediment build up in rivers, lakes, and wetlands. Land use and land cover change, unsustainable agricultural practices upstream often lead to soil erosion, whereas haphazard road construction or infrastructure development can trigger landslides which results in increased sediment aggradation or sediment deposits in wetlands.

Sediment aggradation in river and lake beds reduces the volume of water that wetlands can hold, increasing chances of flooding and water turbidity affecting both freshwater species and human health.

Climate change affects freshwater species through changes in precipitation patterns and hydrological regimes which become less predictable and characterized by frequent extreme events such as droughts and floods. Meanwhile, loss of glaciers and reduced snowpack in mountains further reduces flow in Nepal's snow-fed rivers during the dry seasons. Such flow modifications have negative impacts on ecological diversity and function of river systems. Moreover, climate warming also has direct influence on the survival and distributions of some freshwater species, as increases in water temperatures cause shift in fish distributions.