Fresh Water
Maslow's hierarchy of needs categorizes water as a basic and psychological need, and it is a need which must to be met before more complex needs can be addressed.
Figure 1: Maslow's Hierarchy
Fresh water is essential for humans to survive and makes up 2.5% of the water on Earth. Out of this 2.5%, 1% is surface fresh water, 20% is groundwater, and 79% is trapped in ice caps and glaciers. However, our inefficient consumption of large amounts of water as well as our pollution of limited water sources has resulted in a water crisis. According to the Food and Agriculture Organization of the United Nations (FAO), it is estimated that by 2025 two-thirds of the world population will be living in water-stressed countries if no action is taken to change our current consumption patterns. Of the world population, two-thirds experience extreme water scarcity for at least one month out of the year, while half a billion experience it throughout the whole year.
Water pollution
Eutrophication is one result of water pollution. We use fertilizers containing phosphorous and nitrogen to enhance crop growth, but when it rains these chemicals run off into nearby rivers and lakes causing algal blooms (made of cyanobacteria) and increased plant growth. In turn, this growth blocks out sunlight and decreases the oxygen necessary for autotrophs and heterotrophs living in these habitats to thrive. Eutrophication science regarding lakes is not a new topic, but people are still learning more about fertilizer impacts on rivers and streams (Dodds and Smith 2015). Approximately 30 years ago, it was believed that phosphorous mostly had consequences on freshwater, while nitrogen largely had consequences on marine waters. Since then, however, studies regarding lakes have discovered that nitrogen also has a large impact on algal blooms in lakes. These studies are based on bioassays, enrichment experiments, and statistical correlations. Further research is required to confirm these findings and to determine the best techniques to mitigate eutrophication (Dodds and Smith 2015).
Figure 2: Explanation of the eutrophication process
Although both phosphorous and nitrogen are believed to worsen eutrophication, some believe phosphorous is the main culprit.
Schindler et al. found strong evidence showing that reducing phosphorus inputs was successful in mitigating eutrophication, however they did not find any evidence backing the effectiveness of minimizing the introduction of nitrogen. Further, a few case studies demonstrated an improvement of conditions from the addition of nitrogen. This may have had to do with the ratio of phosphorous and nitrogen in the water body allowing other species to displace the cyanobacteria (Schindler et al. 2016).
Additionally, according to a study done by Watson et al. on Lake Erie, reducing phosphorous introduction into the lake was the best way to minimize algal blooms and hypoxic conditions. Nitrogen reduction would still be beneficial, but to a lesser extent. However, the study’s authors still believe that the reduction of nitrogen should be considered as a potential adaptation strategy.
Watson et al. also believe climate change should be considered when discussing eutrophication. Human actions are a major causal factor of warming temperatures and climate change. Over the last 120 years or so, the global temperature has increased roughly 1.01° Celsius. The dangerous levels of carbon dioxide and other greenhouse gases humans have put into the atmosphere results in the greenhouse gas effect and in the warming of our atmosphere. Watson et al. propose that climate change and increasing temperatures may in fact worsen the time span and rate of occurrence of hypoxia. This is due to rising water temperatures as well as higher runoff levels (Watson et al. 2016).
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