BY STAFF REPORTER
Freshwater ecosystems such as lakes, ponds, rivers, streams and wetlands are estimated to cover 15 per cent of the world’s continental surface area. These inland bodies of water are bastions of biodiversity, hosting about 10 per cent of the world’s animals and one-third of all vertebrate species.
Demand for freshwater is outstripping supply. Many water systems around the world are currently overtaxed, and some are already very close to running dry: The city of Cape Town, South Africa barely averted “Day Zero,” when the city’s taps were expected to be turned off. According to one estimate, by 2030 our need for water will be 40 per cent greater than our reliable water supplies.
Freshwater ecosystems worldwide are subjected to a variety of anthropogenic threats (Malmqvist and Rundle 2002). However, this biodiversity is being threatened by human population growth, unsustainable development, land use and water management as well as climate change.
Inappropriate land-use practices, pollutants, overexploitation, and overpopulation have simplified/fragmented aquatic habitats and degraded biodiversity and water quality. Thus, conserving and reviving freshwater health and biodiversity are increasingly becoming global aims to ensure ecosystem integrity and freshwater ecosystem sustainability.
Agriculture, industrial processes, untreated waste and degraded lands are leading causes of pollution in freshwater systems. Poor water quality threatens freshwater species, affects fisheries to coasts, increases water treatment costs and poses risks to human health.
Around the world, climate change is already affecting freshwater systems, as droughts and floods occur with greater frequency and intensity. Degraded ecosystems — and the species that live in them — are less resilient to these climate impacts, and communities that depend on the services provided by healthy freshwater ecosystems are becoming increasingly vulnerable.
In pursuit of development, societies across the globe have negatively impacted water-related ecosystems. A shocking example of this is that the rate of loss of global wetlands between 1900 and 2000 is estimated to be around 69-75% (Davidson 2014, see Figure 1). 40% of the loss occurred between 1970-2008, according to the 2015 Ramsar Convention on Wetlands.
Increased water abstraction for growing urban populations was partly to blame, as was the transformation of wetlands – lands saturated by water, such as marshes or river deltas – into arable agricultural land.
Freshwater ecosystems are polluted by a variety of human activities, from large-scale agriculture and industry to everyday behaviours, such as driving cars and fertilizing lawns. Large quantities of pollution often enter freshwater systems from point sources, such as industrial or municipal sewage outflows; for example, 23.4 billion tons of sewage and industrial waste was dumped into the Yangtze River in 2001, threatening
human health and the survival of the endangered Yangtze River dolphin (Young, 2002). Thus, the focus on protecting water quality in many countries has been on preventing point source pollution (i.e. U.S. Clean Water Act of 1972). However, nonpoint source pollution is far more significant in many cases. Airborne pollutants can enter the atmosphere and travel long distances, entering lakes and waterways in otherwise pristine locations.
Pollutants dissolved in runoff from the surrounding landscape may account for the greatest source of pollution in many freshwater ecosystems—for example, it has been estimated that 80% of the nutrients (nitrogen and phosphorus) that pollute U.S. waterways derive from nonpoint sources such as agricultural and urban runoff
Runoff from fertilizers used in commercial agriculture or private yards adds large amounts of nitrogen and phosphorus to freshwater ecosystems. This can be especially problematic in lowland areas and lakes or rivers with developed shores.
The added nutrients lead to excess growth of algae (which is sometimes toxic), resulting in reduced water clarity and light penetration. Because of this increased primary productivity, the the activity of decomposing, oxygen-consuming bacteria increases and oxygen levels decline.
Shifts in the food web and alterations in bottom-water habitat can lead to changes in species composition and distribution. For example, the density, distribution and relative abundance of aquatic plants can change after eutrophication (Schmieder, 1997), and valuable fish species are often replaced by less desirable fauna that can tolerate low oxygen levels (Egerton, 1987). Natural eutrophication is a normal state in the succession of lakes as they age, but polluted runoff has led to early eutrophication and changes in the community structure of many naturally oligotrophic (nutrient-poor) lakes.
Toxic pollution in freshwater ecosystems can devastate local biota and endanger human food sources. Most toxic pollution derives from industry (i.e. dioxin, PCBs) or agriculture (pesticides such as DDT and toxaphene). Heavy metals, such as arsenic, zinc, selenium, and mercury are also released from mining and other industrial activities.
Destructive land-use practices that result in vegetation loss anywhere within the drainage basin of a river can have negative impacts on freshwater ecosystems. The forests and native plant communities surrounding lakes, rivers, and wetlands help protect water quality and quantity by filtering and storing runoff. Changes in land use brought about by agriculture and urbanization (such as deforestation, chemical fertilization, and paving) lead to increased runoff with higher levels of nutrients and other pollutants.
Wetlands are one of the most productive ecosystems that provide many of the services that society depends on, ranging from the provision of food and water, regulation of flows of water, recycling of nutrients and waste, and cultural benefits, such as spiritual, recreational or educational uses.
Water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers, and lakes, are vital to providing social and economic benefits for people. The declining condition of the ecosystems directly impacts water availability as well as other essential services such as biodiversity, food production and flood control.
For that reason, Target 6.6 – By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes – is set to contribute to the achievement of Goal 6. In service of that, indicator 6.6.1 – Change in the extent of water-related ecosystems over time – and its component sub-indicators, will be used to monitor management performance about the target.
Those who control how water is valued control how it is used. Values are a central aspect of power and equity in water resources governance. The failure to fully value water in all its different uses is considered a root cause, or a symptom, of the political neglect of water and its mismanagement. All too often, the value of water, or its full suite of multiple values, is not prominent in decision-making at all.
The Ethiopian Herald March 28/2021
