Sources of Cultural Eutrophication |
Research: Impacts of Cultural Eutrophication on Lakes
|
As seen in Figure 2, cultural eutrophication is caused by human land use, including agriculture and residential or industrial developments. As land is developed, the natural habitat is altered and phosphorus is no longer held in the soil but is washed into lakes. More importantly, the artificial input of nutrients from run-off, along with the discharge of effluent from sources such as sewage works, agriculture, and factories, result in a eutrophic lake high in nutrient levels. Although sewage, agriculture, and factories all increase nutrient input in watersheds, the amount of input varies according to the types and amounts of human activity occurring in each watershed (Smith and Schindler 2009). The combination of these effects causes a rapid growth of algae and other biomass as well as a significant de crease in the concentration of dissolved oxygen, harming marine organisms and making compliance with local and federal regulations more difficult to achieve (WHO 2003).
Additionally, lowered oxygen results in the death of fish that need high levels of dissolved oxygen to survive. The consequent decrease in populations of fish, such as trout, salmon, and other desirable sport fish, harms the fishing industry and alters the ecosystem of the lake (Mandeville 2000).
Industrial wastes and domestic sewage are the major urban sources of nutrient overload, responsible for 50% of the total amount of phosphorus unloaded into lakes from human settlements (Smith et al. 2006). Approximately 15% of the US population contributes phosphorus- containing wastewater effluents to lakes, resulting in eutrophication (Hammer 1986). By 1970, nearly 10,000 public lakes had been affected by excessive human-influenced nutrient enrichment (Knud-Hansen 1994).
Other sources that contribute to cultural eutrophication include the use of fertilizers, faulty septic systems, and erosion into the lake. Industrial agriculture, with its reliance on phosphate-rich fertilizers, is the primary source of excess phosphorus responsible for degrading lakes (Carpenter 2008). The routine application of chemical fertilizers and phosphorus-laden manure has resulted in the gradual accumulation of phosphorus in soil, which washes into lakes of the watershed where it is applied. While many states have implemented bans on chemical phosphorus, farmers still apply phosphorus fertilizers, even when soils already have a reservoir of the nutrient. This significantly intensifies the amount of phosphorus runoff to lakes (Ben net et al. 2001). Moreover, studies predict that fertilizer demand and use will continue to increase to 208 million tons by 2020, with greater increases in developing countries, further aggravating a trend of freshwater eutrophication worldwide (Bumb and Baanante 1996).
On a global basis, researchers have demonstrated a strong correlation between total phosphorus inputs and algal biomass in lakes (Anderson et al. 2002). Since 1950, phosphorus inputs to the environment have been increasing as the use of phosphate-containing fertilizer, manure, and laundry detergent has become more common (Litke 1999). Consequently, humans re lease 75% more phosphorus to the soil than would be naturally deposited by weathering of rock (Bennet et al. 2001). Even increases in minute amounts of the nutrient can stimulate tremendous growth and productivity (Addy and Green 1996). According to an estimate, 400 grams of phosphates could potentially induce an algal bloom to the extent of 350 tons (Sharma 1999).
Industrial wastes and domestic sewage are the major urban sources of nutrient overload, responsible for 50% of the total amount of phosphorus unloaded into lakes from human settlements (Smith et al. 2006). Approximately 15% of the US population contributes phosphorus- containing wastewater effluents to lakes, resulting in eutrophication (Hammer 1986). By 1970, nearly 10,000 public lakes had been affected by excessive human-influenced nutrient enrichment (Knud-Hansen 1994).
Other sources that contribute to cultural eutrophication include the use of fertilizers, faulty septic systems, and erosion into the lake. Industrial agriculture, with its reliance on phosphate-rich fertilizers, is the primary source of excess phosphorus responsible for degrading lakes (Carpenter 2008). The routine application of chemical fertilizers and phosphorus-laden manure has resulted in the gradual accumulation of phosphorus in soil, which washes into lakes of the watershed where it is applied. While many states have implemented bans on chemical phosphorus, farmers still apply phosphorus fertilizers, even when soils already have a reservoir of the nutrient. This significantly intensifies the amount of phosphorus runoff to lakes (Ben net et al. 2001). Moreover, studies predict that fertilizer demand and use will continue to increase to 208 million tons by 2020, with greater increases in developing countries, further aggravating a trend of freshwater eutrophication worldwide (Bumb and Baanante 1996).
On a global basis, researchers have demonstrated a strong correlation between total phosphorus inputs and algal biomass in lakes (Anderson et al. 2002). Since 1950, phosphorus inputs to the environment have been increasing as the use of phosphate-containing fertilizer, manure, and laundry detergent has become more common (Litke 1999). Consequently, humans re lease 75% more phosphorus to the soil than would be naturally deposited by weathering of rock (Bennet et al. 2001). Even increases in minute amounts of the nutrient can stimulate tremendous growth and productivity (Addy and Green 1996). According to an estimate, 400 grams of phosphates could potentially induce an algal bloom to the extent of 350 tons (Sharma 1999).
Algal blooms threaten ecosystems by choking off oxygen and thereby causing the deaths of plants and animals throughout that ecosystem. An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Freshwater algal blooms are the result of an excess of nutrients, particularly phosphorus (Diersing 2009). The excess nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes. These nutrients can then enter watersheds through water runoff (Lathrop et al. 1998).
When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. As the nutrient sources’ higher levels persist and conditions remain favourable, algal blooms can become long-term events that have an impact on the ecosystem. Algae tend to grow very quickly under high nutrient availability, but each algae is short-lived, and the result is a high concentration of dead organic matter that starts to decay. The decay pro cess consumes dissolved oxygen in the water, resulting in hypoxic (low oxygen) conditions. Without sufficient dissolved oxygen in the water, animals, and plants die off in large numbers.
Additionally, sustained blooms can reduce or block out sunlight penetrating the water, stressing or killing aquatic plants. In severe eutrophic conditions, harmful algal blooms (HAB) have been known to occur. HABs are algal blooms that can have negative impacts on other organisms due to the production of natural toxins, the infliction of mechanical damage, or by other means. These algae are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisoning (Diersing 2009).
When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. As the nutrient sources’ higher levels persist and conditions remain favourable, algal blooms can become long-term events that have an impact on the ecosystem. Algae tend to grow very quickly under high nutrient availability, but each algae is short-lived, and the result is a high concentration of dead organic matter that starts to decay. The decay pro cess consumes dissolved oxygen in the water, resulting in hypoxic (low oxygen) conditions. Without sufficient dissolved oxygen in the water, animals, and plants die off in large numbers.
Additionally, sustained blooms can reduce or block out sunlight penetrating the water, stressing or killing aquatic plants. In severe eutrophic conditions, harmful algal blooms (HAB) have been known to occur. HABs are algal blooms that can have negative impacts on other organisms due to the production of natural toxins, the infliction of mechanical damage, or by other means. These algae are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisoning (Diersing 2009).