Researchers have begun looking into the societal and ecological values of dry riverbeds. Although found on every continent, dry riverbeds have often been ignored by both aquatic and terrestrial ecologists, as they don’t appear to directly fall under either respective category. Griffith University researchers Alisha L Steward, Daniel von Schiller, Klement Tockner, Jonathan C Marshall and Stuart E Bunn, have recently discussed their findings in the journal Frontiers in Ecology and the Environment, published in May 2012.
To define these habitats, dry riverbeds are the channels of temporary rivers that can be exposed during periods of drought. The time period between the dry and water phases of each dry riverbed can vary greatly. Dry riverbeds can occur naturally or be caused anthropologically. Some human-based causes include the interception of river flow caused by dams and weirs, as well as the extraction of water from these sources.
Researchers outlined many important values of dry riverbeds to humans within this study. One such use is that dry riverbeds can be fertile substrates for agricultural purposes. Instances of fruit and vegetable cultivation can be seen within the dry riverbeds of the Indian Ganges River, as well as the production citrus orchids in Mediterranean Spain. Dry riverbeds are also often used as vehicle and walking trails, as well as animal transportation routes and car parks.
More environmental contributions have been identified through this study as well. It is postulated that dry riverbeds have made significant contributions to biodiversity. Because of the presence of both wet and dry phases of a dry riverbed, it is believed that strong selective pressure for the evolution of traits that allow an organism to survive both stages occurred within these features. This has lead to the theory that the drying of pools in temporary river networks may have led to the evolution of the traits that first allowed aquatic organisms to migrate to land.
Other important identified ecological values of dry riverbeds include their roles as egg and seed banks for aquatic invertebrates. Some aquatic crustaceans that live exclusively in temporary waters require the dry phase of the riverbed in order for their eggs to properly hatch. Dry riverbeds also act as sites of organic matter accumulation. This allows for the fueling of the river metabolism upon the recommencement of river flow.
Because of these contributions to the environment, researchers believe that dry riverbeds should become more highly valued among society. The main way researchers argue that this could be achieved would be through inclusion in river management policies. Currently, dry riverbeds are not included in the draft guidelines for the US Environmental Protection Agency Clear Water Act, (an act that regulates the discharge of pollutants into waters) and are also ignored in various instances of European water legislation, including the European Water Framework Directive (a commitment of European Union members to achieve good quantitative and qualitative status of water bodies).
Hopefully the realization of the contributions and importance of dry riverbeds will lead to their inclusion in future management policies, leading to the future protection of these key and vital habitats.
Alisha L Steward, Daniel von Schiller, Klement Tockner, Jonathan C Marshall, and Stuart E Bunn. 2012. When the river runs dry: human and ecological values of dry riverbeds. Frontiers in Ecology and the Environment 10: 202–209. http://dx.doi.org/10.1890/110136
Article Review by Danielle Gardner