Emerging concepts in temporary‐river ecology

Abstract

SUMMARY1. Temporary rivers and streams are among the most common and most hydrologically dynamic freshwater ecosystems. The number of temporary rivers and the severity of flow intermittence may be increasing in regions affected by climatic drying trends or water abstraction. Despite their abundance, temporary rivers have been historically neglected by ecologists. A recent increase in temporary-river research needs to be supported by new models that generate hypotheses and stimulate further research. In this article, we present three conceptual models that address spatial and temporal patterns in temporary-river biodiversity and biogeochemistry. 2. Temporary rivers are characterised by the repeated onset and cessation of flow, and by complex hydrological dynamics in the longitudinal dimension. Longitudinal dynamics, such as advancing and retreating wetted fronts, hydrological connections and disconnections, and gradients in flow permanence, influence biotic communities and nutrient and organic matter processing. 3. The first conceptual model concerns connectivity between habitat patches. Variable connectivity suggests that the metacommunity and metapopulation concepts are applicable in temporary rivers. We predict that aggregations of local communities in the isolated water bodies of temporary rivers function as metacommunities. These metacommunities may become longitudinally nested due to interspecific differences in dispersal and mortality. The metapopulation concept applies to some temporary river species, but not all. In stable metapopulations, rates of local extinction are balanced by recolonisation. However, extinction and recolonisation in many temporary-river species are decoupled by frequent disturbances, and populations of these species are usually expanding or contracting. 4. The second conceptual model predicts that large-scale biodiversity varies as a function of aquatic and terrestrial patch dynamics and water-level fluctuations. Habitat mosaics in temporary rivers change in composition and configuration in response to inundation and drying, and these changes elicit a range of biotic responses. In the model, aquatic biodiversity initially increases directly with water level due to increasing abundance of aquatic patches. When most of the channel is inundated and most aquatic patches are connected, further increases in aquatic habitat and connectivity cause aquatic biodiversity to decline due to community homogenisation and reduced habitat diversity. The predicted responses of terrestrial biodiversity to changes in water level are the inverse of aquatic biodiversity responses. 5. The third conceptual model represents temporary rivers as longitudinal, punctuated biogeochemical reactors. Advancing fronts carry water, solutes and particulate organic matter downstream; subsequent flow recessions and drying result in deposition of transported material in reserves such as pools and bar tops. Material processing is rapid during inundated periods and slower during dry periods. The efficiency of material proc...

Recent perspectives on temporary river ecology

“…Compared to our understanding of perennial stream ecosystems, many important questions remain. Conceptual, empirical, and mechanistic models that may help design and direct future research and test the transferability of results across regions are still lacking (but see Larned et al 2010;Sabater and Tockner 2010). This incomplete understanding of temporary river ecology limits our ability to provide clear management advice for temporary rivers, as the tools needed by water managers (e.g., bioindicators, transferable relationships between flow intermittence and ecosystem processes and patterns) have yet to be developed.…”

Bottom-up effects of streambed drying on consumer performance through changes in resource quality

“…Because effects on microorganisms increase with drying duration (Langhans and Tockner 2006), changes in fungal activity or assemblage composition favouring more resistant or terrestrial species cannot be excluded. Several studies have shown that the consumption rates of shredders vary according to the fungal species in leaf assemblages (Arsuffi and Suberkropp 1984;Chung and Suberkropp 2009;Jabiol and Chauvet 2012), whereas lower microbial activity during the terrestrial phase (Langhans et al 2008;Larned et al 2010;Bruder et al 2011) might have prevented the degradation of repellent secondary metabolites or more recalcitrant C, such as cellulose, lignin or condensed tannins, resulting in increased leaf toughness and thus, less palatable leaves in the INT than PERM treatments (Irons et al 1988;Hladyz et al 2009;Graça and Cressa 2010;Aßmann et al 2011). As expected, the increased consumption of PERM leaves translated into higher growth rates, which is consistent with the bigger size at eclosion found for an insect detritivore reared on continuously submerged resources (Aspbury and Juliano 1998).…”

“…Temporary streams, which exhibit periodical flow interruption, are present in most biomes worldwide (Larned et al 2010). The expected decline in precipitation and higher evapotranspiration rates resulting from increased air temperature will increase drought and likely reduce stream runoff in many regions, including the Mediterranean basin (IPCC 2007) and have already been observed in small catchments in eastern and southern Europe (Stahl et al 2010).…”

Métodos e técnicas de pesquisa em bacias hidrográficas

“…Larned et al (2010) ressaltam que, devido às mudanças climáticas, o número e a extensão de rios temporários podem aumentar em regiões que enfrentam uma tendência à seca e em regiões onde há a captação de água para o uso socioeconômico.…”