The Building of Dams
The earliest remains of dams that archaeologists have unearthed date back to around 5000 A.D.They were constructed as part of a domestic water supply system for the ancient town of Jawa in Jordan. Over the next few millennia, the building of dams for water retention spread throughout the Mediterranean, the Middle East, Southern Asia, China, and Central America. Later, as technologies increased and industrialization took hold in Europe, dam mechanisms advanced to incorporate watermills. With the advent of the water turbine in 1832 and developments in electrical engineering, the first hydropower plant began running in Wisconsin in 1882 (IRN n. pag.). Over the next few decades, while structural engineering techniques improved, dams multiplied in size, strength, and numbers worldwide.
Today, although the construction of new dams is halting ( albeit with less vigor in underdeveloped countries) (de Villiers 146; Pielou 206), they are still being built around the globe for a multitude of social and economical reasons: flood control, hydroelectric power production, river navigation, irrigation, human consumption, industrial use, emergency water reservation, tourism, and flat-water recreation (e.g., NPDP n. pag.; Trout Unlimited 11). For all the benefits that dams provide, however, there are adverse effects and concerns that arise from manipulating the environment in such an unnatural manner.
Impacts of Dams on the Hydrologic Regime
Dams are ultimately created as a water reservoir. This impounding of water impedes the circulation of a river and subsequently changes the hydrology and ecology of the river system and its contiguous environments.
Behind a dam, the rise in water level submerges the landscape; often displacing people and engorging culturally valuable ruins. Furthermore, biodiversity of the region is constrained by the destruction of vegetation and loss or extinction of wildlife (Power et al. 887-895). In essence, both the aquatic and land-based ecosystems are damaged by the advent of a dam (Pielou 209).
Upstream of the barricade, the once flowing water that housed the riverine habitat becomes still, oxygen depleted, deepens into darkness, temperature stratified, and susceptible to enhanced evaporation which adjusts the entire hydrologic cycle (e.g., Pielou 207, 210; Ocean Planet n. pag.; Leopold 157). Moreover, drowned vegetation in the stagnant water is subject to rotting and may thereby pollute the atmosphere and reservoir with methane and carbon dioxide (Leopold 158; Pielou 208).
Another change in the water chemistry that alters many river-based systems is the inclusion of heavy metals (and minerals) such as methyl mercury due to reactions between the reservoir bed and the standing water (Pielou 114, 207). If undetected, these toxins may bioaccumulate by moving through the trophic levels of the food web, eventually reaching humans.
Aside from the changes in the chemical constituencies of...