Overview of Cultural Eutrophication |
Research: Impacts of Cultural Eutrophication on Lakes
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Natural eutrophication is a slow and gradual process, typically occurring over a period of many centuries as nutrient-rich soil washes into lakes. In contrast, human-induced eutrophication can occur over time frames as short as a decade (Addy and Green 1996). Although it has taken only 60 years for humans to turn many freshwater lakes eutrophic, studies suggest their recovery may take 1000 years under the best of circumstances (Carpenter and Lathrop 2008). At present, nearly 38% of US lakes are experiencing eutrophic conditions affecting aquatic life and watershed ecosystems (SAMAB 1996). Runoff, especially from urban and agricultural areas, carries fertilizers, pesticides, sediment, and/or industrial effluent that accelerate eutrophication when discharged into a water body (Smith et al. 1999). With severe eutrophication, hypoxic conditions often result, disrupting normal food web and ecosystem processes by creating a “dead zone” where no animal life can be sustained (Smaya 2008). In the 1960s, Lake Washington (Seattle, USA) was one of the most publicized examples of anthropogenic eutrophication. At the maximum of eutrophication, Lake Washington received 20 million gallons of wastewater effluent each day (Edmondson 1991). More than 37,000 kg of phosphates added in 1955 from developed agricultural and urban lands swamped the lake, stimulating plant and algae growth that choked out most other species (Edmondson 1970).
Eutrophication also jeopardizes the re - source value of lakes as recreation, fishing, and aesthetic enjoyment diminish, causing annual value losses of $2.2 billion in the US (Dodds et al 2009). As such, the impact of eutrophication on recreation and tourism is probably the most sensitive area for the public. Lakes and reservoirs deteriorate through excessive addition of plant nutrients, organic matter, and silt, which combine to produce increased algae and rooted plant biomass, reduced water clarity, and usually decreased water volumes (Harper 1992). In this condition water bodies lose much of their attractiveness for recreation, as well as their usefulness and safety as industrial and domestic water supplies. If the lake serves as a drinking water source, excessive algal growth clogs intakes, increases corrosion of pipes, makes filtration more ex - pensive and often causes taste and odour problems (Vollenweider 1968). Algae removal also increases filtration costs for industries using eutrophic waters. Furthermore, swimming in eutrophic waters causes “swimmer’s itch” (Vol - lenweider 1968) and people generally find clear waters more aesthetically pleasing than turbid (cloudy) waters. Both social impacts and economic losses are important and make eutrophication control necessary.