Intermittent river

Intermittent (or temporary) rivers cease to flow every year or at least twice every five years.[1] Such rivers drain large arid and semi-arid areas, covering approximately a third of the earth’s surface.[2] The extent of temporary rivers is increasing, as many formerly perennial rivers are becoming temporary because of increasing water demand, particularly for irrigation.[3] Despite inconsistent water flow, intermittent rivers are considered land-forming agents in arid regions, as they are agents of significant deposition and erosion during flood events.[4] The combination of dry crusted soils and the highly erosive energy of the rain cause sediment resuspension and transport to the coastal areas.[5] They are among the aquatic habitats most altered by human activities.[6] During the summer even under no flow conditions the point sources are still active such as the wastewater effluents,[7] resulting in nutrients and organic pollutants accumulating in the sediment. Sediment operates as a pollution inventory and pollutants are moved to the next basin with the first flush.[8] Their vulnerability is intensified by the conflict between water use demand and aquatic ecosystem conservation.[9] Advanced modelling tools have been developed to better describe intermittent flow dynamic changes such as the tempQsim model.[10]

Categorization and Distribution

An intermittent river, or intermittent stream, is any river or stream that only flows during certain times of the year, and may not have any flowing surface water during the dry season.[11] Intermittent rivers do not rely on, but may be supplemented by stormwaters or other runoff from upstream sources.[11] Their channels are well-defined,[12] as compared to ephemeral streams, which have no defined channel, and rely mainly on storm runoff.[13] Intermittent rivers are found on every continent, and may even be more common than perennial rivers.[14] More than 30% of the total length and discharge of the global river network is estimated to be intermittent rivers.[4] However, due to some low-order streams being difficult to categorize or track, this total could be over 50% when taking those into account.[14] In the face of global climate change, this total is further increasing, as many of the world’s rivers that were once perennial are now intermittent in regions suffering from severe climatic drying or water appropriation.[15]

Ecology

The inhabitants of intermittent rivers can change with the water level. As a result of contrasting conditions throughout the year, invertebrate assemblages of the same intermittent stream can be notably distinct from one another.[16] How biodiversity of these habitats changes with conditions has been debated in literature. Current findings suggest that while lotic biodiversity generally decreases with increasing flow intermittence, increased lentic and terrestrial biodiversity during those periods can compensate.[15] Thus, when lotic, lentic, and terrestrial communities are considered together, intermittent rivers can account for a high proportion of regional biodiversity.[14] The riparian zone of intermittent rivers can provide habitat and resources for a variety of organisms, and may also be an important source of nutrients for habitats downstream.[12]

References
  1. (Tzoraki and Nikolaidis 2007)
  2. (Thornes, 1977)
  3. (De Girolamo, Calabrese et al. 2012)
  4. Tooth, Stephen (2000). "Process, form and change in dryland rivers: a review of recent research". Earth-Science Reviews. 51 (1–4): 67–107. doi:10.1016/S0012-8252(00)00014-3.
  5. (Tzoraki, Nikolaidis et al. 2009)
  6. (Moyle 2013)
  7. (Perrin and Tournoud 2009; Chahinian, Bancon-Montigny et al. 2013)
  8. (Bernal, von Schiller et al. 2013)
  9. (Webb, Nichols et al. 2012)
  10. (Tzoraki et al., 2009)
  11. "Streams | Rivers & Streams | US EPA". archive.epa.gov. Retrieved 2020-05-18.
  12. "2. EVALUATING THE BIOLOGICAL SIGNIFICANCE OF INTERMITTENT STREAMS". www.fs.fed.us. Retrieved 2020-05-18.
  13. "Identification Methods for the Origins of Intermittent and Perennial streams, Version 3.1. North Carolina Department of Environment and Natural Resources, Division of Water Quality" (PDF).
  14. Datry, Thibault; Larned, Scott T.; Tockner, Klement (2014-03-01). "Intermittent Rivers: A Challenge for Freshwater Ecology". BioScience. 64 (3): 229–235. doi:10.1093/biosci/bit027. ISSN 1525-3244.
  15. Larned, Scott T.; Datry, Thibault; Arscott, David B.; Tockner, Klement (April 2010). "Emerging concepts in temporary-river ecology". Freshwater Biology. 55 (4): 717–738. doi:10.1111/j.1365-2427.2009.02322.x.
  16. Beche, Leah A.; Mcelravy, Eric P.; Resh, Vincent H. (January 2006). "Long-term seasonal variation in the biological traits of benthic-macroinvertebrates in two Mediterranean-climate streams in California, U.S.A.". Freshwater Biology. 51 (1): 56–75. doi:10.1111/j.1365-2427.2005.01473.x. ISSN 0046-5070.
  • Bernal, S., D. von Schiller, et al. (2013). "Hydrological extremes modulate nutrient dynamics in mediterranean climate streams across different spatial scales." Hydrobiologia 719(1): 31-42.
  • Chahinian, N., C. Bancon-Montigny, et al. (2013). "Temporal and spatial variability of organotins in an intermittent Mediterranean river." Journal of Environmental Management 128: 173-181.
  • De Girolamo, A. M., A. Calabrese, et al. (2012). "Impact of anthropogenic activities on a Temporary River." Fresenius Environmental Bulletin 21(11): 3278-3286.
  • Moyle, P. B. (2013). "NOVEL AQUATIC ECOSYSTEMS: THE NEW REALITY FOR STREAMS IN CALIFORNIA AND OTHER MEDITERRANEAN CLIMATE REGIONS." River Research and Applications.
  • Perrin, J. L. and M. G. Tournoud (2009). "Hydrological processes controlling flow generation in a small Mediterranean catchment under karstic influence." Processus hydrologiques contrôlant la génération des débits dans un petit bassin versant Méditerranéen sous influence karstique 54(6): 1125-1140.
  • Tzoraki, O. and N. P. Nikolaidis (2007). "A generalized framework for modeling the hydrologic and biogeochemical response of a Mediterranean temporary river basin." Journal of Hydrology 346(3–4): 112-121.
  • Tzoraki, O., N. P. Nikolaidis, et al. (2009). "A reach-scale biogeochemical model for temporary rivers." Hydrological Processes 23(2): 272-283.
  • Webb, J. A., S. J. Nichols, et al. (2012). "Ecological responses to flow alteration: Assessing causal relationships with eco evidence." Wetlands 32(2): 203-213.
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