Freshwater habitats are disproportionally diverse compared to other ecosystems, with them only covering 1% of the world surface yet providing habitat for over 25% of described vertebrates (Kipping, 2008). It has been estimated by the ICUN that there are around 27,400 freshwater species including fish, crabs, dragonflies and plants. With such a vast biodiversity, freshwater ecosystems provide many important goods and services not only to ecology but to humans also, including building materials and flood and erosion control. Many of the world's poorest neighbourhoods rely solely on these ecosystems.
Since the industrial revolution, many anthropogenic activities have caused alterations in the structure and functioning of freshwater environments (Millbrook, 2009). By increasing demands of aquatic environments, eutrophication has lead to undesirable changes in freshwater biodiversity (Smith et al. 1999). Changes in land use, including land clearing for agriculture, forestry, animal husbandry and urbanisation has caused an increase in the available limiting nutrients, nitrogen and phosphorous in global biochemical cycles, that have been polluting lakes and streams worldwide (Vitousek et al. 1997). This surplus of nitrogen in terrestrial soils can move easily from land to surface water, migrating into groundwaters, increasing the toxicity (Nolan et al. 1997). With increasing human population densities, the increasing combustion of fossil fuels has been causing additional atmospheric nitrogen to enter water sources, increasing nutrient levels in many water bodies that are located near heavily populated areas. To understand how freshwater biodiversity is severely threatened by nutrient loading, it becomes vital to understand firstly, what is meant by this word 'eutrophication'.
'Eutrophication is the process by which water bodies are made more eutrophic through an increase in their nutrient supply. This can choke rivers, lakes and other waterways by excess algae growth which has been simulated by fertilisers and poor disposal of human sewage' (Smith et al. 1999).
Eutrophication influences the production of blue-green algae (cyanobacteria) and the growth of vascular plants in freshwater ecosystems which can effect light penetration into water bodies. The impacts are much more wide reaching than plant growth alone. Eutrophication also causes degradation of such water bodies resulting in a loss of species. (Postel and Carpenter, 1996).
Blue-green algae (a easily observable green layer covering a fresh water source).
In recent decades, eutrophication has been highlighted as one of the most serious environmental problems facing water managers. In Europe, this is especially seen as a highly destructive problem, hence why the European Water Framework Directive has allocated it as a important issue on their agenda (Sandergaard et al. 2007). Billions has already been invested to curb this issue by improved water treatment, however, despite this, eutrophication still remains a devastating problem in many areas. Saandergaard et al. (2007) portrays how internal mechanisms, both chemical and biological can prevent lake recovery. Such internal mechanisms include, internal loading from lake sediments (Marsden, 1989) and the 'development of zooplanktivorous and bethivorous fish in eutrophic lakes which reduces the top down control of zooplankton and phytoplankton' (Shapiro and Wright, 1984).
Whether there is success or not from eutrophication conservation strategies, it has been certified that permanent effects of restoration can only be achieved if external nutrient loading is reduced sufficiently to low levels. Millbrook (2009) explains how
'historically environmental management strategies of freshwater systems have focused on reducing phosphorus pollution. While this has minimised freshwater algae blooms, it passed a great deal of nitrogen pollution to coastal systems'.
With eutrophication a GLOBAL concern (affecting not only freshwater ecosystems, but coastal and marine systems), it is becoming ever more important to acknowledge reliable management strategies. With the numbers of human population sporadically rising- euthrophication continually poses a greater threat to one of the world's most vulnerable ecosystem!
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