It is paramount to recognize that ecosystems are never conservative and stable but instead are subject to the constant pressures of external factors. Such factors can either have a driving effect on the development of biocenoses or inhibit any biological activity. Human economic activity leads to the second scenario in the world’s oceans, resulting in dead zones. Terminologically, such zones should be referred to as the water areas of the world’s oceans with severe oxygen deficits. Hypoxia of the waters may be provoked by eutrophic processes: fertilizer through groundwater and interstitial waters entering the seas catalyzes enhanced algae growth.
The consequence of this effect is a reduction of oxygen levels, as prokaryotes that absorb algae actively consume it. As a result, hydrobionts cannot live in such areas. Examples of dead salt zones are the Baltic Sea, East China Sea, coastal area of Atlantic near east coast US, while freshwater uninhabited (or sparsely habitable) zones may be represented by Lake Erie in the US.
Biological activity can also be inhibited by chemical toxins called biocides. This term combines a combination of herbicides, insecticides, and pesticides that have traditionally been used by humans to improve the economic performance of farmland. However, biocides often have adverse effects that affect both biogeocenosis life and human health in the long run. Rachel Carson, who studied the clinical effects of the popular insecticide DDT, proved that this toxin could accumulate in the human body, leading to the development of pathological conditions: cancer or genetic defects. As a result, the use of DDT was banned in the United States in 1972.
Wetlands are essential parts of the ecosystem. They provide protection and quality of clean water and provide habitat for many hydrobionts. In addition, such wetlands are reserves for preserving natural floodwater surpluses. At the same time, draining such systems is undesirable because they act as an excellent filter for water. Consequently, the preservation of wetlands is a priority for the ecological security of the region.
One of the negative factors of anthropogenic activities on natural ecosystems is irrigation. The diversion of water from freshwater sources to fields and farms depletes natural water reservoirs. In North America, the Ogallala Aquifer was the aquifer that provided municipalities with plenty of freshwaters. The aquifer extends from north Texas to the lower South Dakota border. Accordingly, the climate of these zones is based on the desert and semi-arid types, which are characterized by high summer temperatures throughout the area: as a result, agriculture is in great need of freshwater sources. Therefore, about 50% of all the Ogallala has been used up as a result of irrigation processes.
In the Central Asian region, such a body of water is a former salt lake called the Aral Sea. As in the North American horizon, the Aral Sea was depleted by irrigation processes initiated more than sixty years ago. As a result of the Aral Sea’s water potential, its volume was reduced by twenty percent already ten years after the initiation of irrigation programs. The areas once occupied by the Aral Sea were the borders of Kazakhstan and Uzbekistan (former USSR): accordingly, it was a continental climate with large temperature amplitudes. In addition to the climate, the driving force for the use of the Aral Sea resources was the inadequate policy of the Soviet authorities, who decided to develop the “tselina” land.
Finally, the construction of large dams and levees makes a significant contribution to changes in the landscape and natural areas. In his desire to regulate flow processes, a man rarely understands the seriousness of the consequences of changing the movement and velocity of rivers. Profound transformations occur both in upstream flows and downstream after dams. Upstream artificial structures turn into reservoirs, naturally flooding forests and destroying habitats for terrestrial native animals and plants. At the same time, due to the stagnant state of freshwater, the currents after the dam have a deficit of salts and sediments.
This, in turn, leads to changes in water chemistry and reductions in the biodiversity of the river ecosystem after the dam. In addition, the delta of rivers narrows after the dam, causing localized soil erosion and a reduction in the number of aquifers. Finally, the dam construction has negative consequences for humans as well: downstream villages and farms are deprived of fisheries as a source of food. All this leads to the fact that artificial structures on water deltas have many adverse effects on the local ecosystem in both the short and long term.