Ocean Matters
Wetlands:
The Importance of Wetlands and the
Impacts of Reservoirs and Dams
Introducing Wetlands
Disappearing wetlands are disrupting nature’s delicate balance on a global scale. Both wetlands and rivers play a major role in the environmental balance of the oceans. Below, we examine how the loss of wetlands caused by reservoir and dam development has affected the oceans.
Wetland Definition
According to the United States Environmental Protection Agency (EPA), wetlands are transitional zones occurring between aquatic and terrestrial areas. The EPA's definition also states that a wetland should be composed of mainly aquatic plants, have undrained hydric soils and, at some point in the year, be saturated or flooded with shallow water. The southern United States is home to several well-known wetlands such as the Louisiana Bayou and Everglades National Park.
Everglades National Park:
At one point there were 600 animal and 900 plant species within Everglades National Park, but sadly that is no longer the case. Faced with large-scale human developments since the 1920's, more than half of the park has dried out and the rest has become polluted. Now animal populations in the park are dropping and wading bird nest sites have decreased by a staggering 90 percent.
Loss of Wetlands in Louisiana:
Wetland losses in Louisiana have been caused by groundwater usage, rising sea levels and levees on the Mississippi River, fundamentally altering the nature of Louisiana’s wetlands. These wetlands may face eventual extinction due to being cut-off from replacement sediments and water once provided by the Mississippi River. Altering the natural river dynamics of the Mississippi and its tributaries with levees and dams may have been the single largest impact on the Louisiana wetlands. Fortunately, not all is lost. In recent years, the Louisiana government has established a Wetlands Restoration and Conservation fund, which helps fund projects to keep the Louisiana wetlands from further degradation.
Human Impacts on Wetlands
Human activities such as urban development, deforestation, farmland conversion and aquaculture contribute significantly to the loss of wetlands. Global warming, another human-driven phenomenon, is also negatively impacting wetlands by way of rising sea levels.
Impact of Reservoirs and Dams on the Oceans
Although reservoirs provide us with many important things such as potable water, energy and water for irrigation and industry, they often produce negative environmental outcomes. Reservoirs decrease natural runoff from watersheds into the oceans and reduce the amount of downstream sediments available to replenish coastal wetlands (e.g. Louisiana Bayou). Often the water released from dams is poorly oxygenated and potentially polluted.
The following three brief case studies will provide us with examples where dams have had harmful environmental consequences.
Impacts on the Columbia River:
The Columbia River system running through British Columbia, Canada and the northwest United States has a total of 56 dams and reservoirs that disrupt annual water flow. Before the establishment of these dams there were an estimated 16 million salmon that spawned in the river, some of which travelled greater than 2000 kilometres upstream to do so! Today, unfortunately, there are only 2.5 million salmon that spawn in the river, most of which are from hatcheries.
Impacts on the San Joaquin River in California from Dams:
Dams on the San Joaquin River in California have diverted upwards of 90 percent of the total water flow for irrigation projects. As a direct result of this diverted water, the San Joaquin delta has become extremely salty and less likely to support life. Due to the increased salinity of the delta, structures have been built to help reduce the amount of incoming salts.
Reservoir Impacts on the Nile River:
The impacts of the Aswan High Dam on the Nile River in Egypt also illustrate problems with dams. The impacts of the Aswan dam include silt holdbacks (these silts acted as fertilizers to downriver farms), increasingly salty agricultural soils because of altered river flow and loss of river nutrients into the Mediterranean Sea. Consequently, because of decreased nutrient flow into the Mediterranean from the dam, sardine and shrimp fisheries have declined.
Solutions
There are many things we can do to reduce the need for large dams and – in doing so – help conserve and restore wetlands. One simple action would be to decommission older dams when they are no longer useful. This would allow rivers to be restored back to their natural courses. We can also make slight modifications to our consumptive behaviours that translate into decreased energy and water demands. For example, by conserving, reusing and recycling water in agricultural, industrial and domestic settings, we can significantly reduce the need for large dams.
Even after a new dam has been constructed, there are measures that may be taken to mitigate its damages such as restoring sediment and nutrient flows to help coastal ecosystems and organisms receive the resources they require to survive or constructing fish ladders to aid spawning salmon overcome dam barriers as they migrate upstream to reproduce. Other solutions include allocating a portion of dam revenues towards compensating the impacts a particular dam might have on a local wetland (such compensation programs are currently in place along the Columbia River in Canada and the United States). In the future, new dam projects should include some mitigation measures as part of the developmental costs.
Despite the numerous threats, by making wise conservation and management actions today we can help reduce the numerous threats facing wetlands.
For more information go to:
Wetlands International
University of Guelph (Canada)
Environmental Protection Agency (US) (PDF)
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