Threatened wetland ecology: impact of over fertilization and non-point sources

By Vipin Kumar

Wetlands are highly productive, water saturated areas having life adapted under these conditions. Swamps, marshes, estuaries, and bogs are all examples of wetlands. They act as a sponge to control flood, recharge groundwater and filter nutrients. They also offer habitats to different native flora and fauna, and breeding spaces to migratory birds. In addition to being rich in biodiversity, wetlands provide numerous products and services that benefit human beings living around them. Unfortunately, due to lack of space in the urban cities, ‘wetlands’ have been considered as ‘wastelands’, with people deliberately dumping waste into the wetlands for lack of other alternatives. Wetlands are open access regimes everyone wants to access,  but only few are concerned about their sustainable use (Verma, 2001).

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Figure 1. Sewage from Gandhi Vihar residential colony and adjoining agriculture causing massive nutrient overload at Dheerpur Wetlands.

 

 

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Figure 2. A large water body at Dheerpur Wetland Park before the beginning of the project. Here is seen wetland water contamination through agricultural practices and livestock waste.

 

In urban areas, residential and commercial buildings, as well as paved roads increase impervious surface areas. This declines the permeability of land for rain water, causing decrease in groundwater table, and impairment of the purification process of chemicals carried by storm water. Non-point sources such as storm water raise major concerns as their sources of origin are so diffused; it is difficult to identify their sources, and transport mechanisms of pollutants (Carey et al., 2013). People living in the periphery of wetlands are generally engaged in agriculture and livestock keeping. Indiscriminate use of fertilisers, pesticides and herbicides to increase the harvest leads to contamination of nearby water bodies during the rainy season. Recent studies have highlighted the fact that prolonged nutrient loading has an adverse effect on the quality of water, and the biodiversity of wetlands (Verhoeven et al., 2006). In India, fertiliser consumption increased from about 2.8 million tonnes in 1973-1974 to 28.3 million tonnes in 2010-2011 (Data Source: Indiastat). Agricultural nutrients like nitrates and phosphates get washed off through storm water, and find their way into wetlands, causing algal blooms and eutrophication – a series of sequential changes initiated by enrichment of water bodies with plant nutrients. Algal blooms limit the availability of sunlight to submerged plants, leading to cessation of photosynthesis and consequent death. Bacterial degradation of dead plants and algae increases the Biological Oxygen Demand (BOD) of the water body. In the absence of oxygen, entire life forms of aquatic ecosystems are wiped out, and this highly productive system becomes a dead zone (Smith et al., 1999; Heisler et al., 2008).

Figure 3. Degraded Wetland near Dhaula Kuan, adjacent to Central Ridge.

Increase in impervious surfaces in the urban areas, along with intensive agricultural practices increases nutrient load, thereby negatively affecting the nearby wetlands. Identification of sources and mechanisms of nutrients provide information to urban planners to mitigate problems such impervious surface and usage of fertilisers (Yang & Toor, 2017). Impact assessments prior to permission for urban development will be an important strategy for preventing impervious surfaces in the urban areas, and the increased export of nutrients to wetland ecosystems. In addition to this, reduction of fertiliser application, and the use of nitrogen fixing crops in the vicinity of wetlands could be important steps to ensure the proper functioning of the wetlands.

 

References:

Carey, R.O., Hochmuth, G.J., Martinez, C.J., Boyer, T.H., Dukes, M.D., Toor, G.S., Cisar, J.L., 2013. Evaluating nutrient impacts in urban watersheds: challenges and research opportunities. Environ. Pollut. 173, 138e149

Heisler, J., Glibert, P.M., Burkholder, J.M., Anderson, D.M., Cochlan, W., Dennison, W.C., Dortch, Q., Gobler, C.J., Heil, C.A., Humphries, E., Lewitus, A., Magnien, R., Marshall, H.G., Sellner, K., Stockwell, D.A., Stoecker, D.K., Suddleson, M., 2008. Eutrophication and harmful algal blooms: a scientific consensus. Harmful Algae 8, 3e13

Smith, V.H., Tilman, G.D., Nekola, J.C., 1999. Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems. Environmental Pollution 100, 179e196

Verhoeven, J.T.A., Arheimer, B., Yin, C., Hefting, M.M., 2006. Regional and global concerns over wetlands and water quality. Trends Ecol. Evol. 21 (2), 96–103.

Verma, M., 2001. Economic Valuation of Bhoj Wetlands for Sustainable Use. [EERC Working Paper Series: WB-9]. Indian Institute of Forest Management, Bhopal.

Yang, Y.Y., Toor, G.S 2017. Source and mechanism of nitrate and orthophosphate transport in urban stormwater runoff from residential catchments. Water Research. 112, 176-184.

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