The ‘wet-dry’ in the wet-dry tropics drives river ecosystem structure and processes in northern Australia

Abstract

SUMMARY1. Northern Australia is characterised by a tropical wet-dry climate that regulates the distinctive character of river flow regimes across the region. There is marked hydrological seasonality, with most flow occurring over only a few months of the year during the wet season. Flow is also characterised by high variability between years, and in the degree of flow cessation, or intermittency, over the dry season. 2. At present, the relatively low human population density and demand for water in the region means that most rivers have largely unmodified flow regimes. These rivers therefore provide a good opportunity to understand the role of natural flow variability in river ecosystem structure and processes. 3. This review describes the major flow regime classes characterising northern Australian rivers, from perennial to seasonally intermittent to extremely intermittent, and how these regimes give rise to marked differences in the ecological character of these tropical rivers, particularly their floodplains. 4. We describe the key features of these flow regimes, namely the wet and dry seasons and the transitions between these seasons, and how they regulate the biophysical heterogeneity, primary productivity and movement of biota in Australia's wet-dry tropical rivers. 5. We develop a conceptual model that predicts the likely hydrological and ecological consequences of future increases in water abstraction (e.g. for agriculture), and suggest how such impacts can be managed so that the distinctive ecological character of these rivers is maintained.

Leaf litter chemistry, decomposition and assimilation by macroinvertebrates in two tropical streams

“…Variability in stream discharge can also affect litter breakdown rates where high stream flows increase physical fragmentation of leaves as well as increasing the downstream fluxes of carbon and nutrients to microbes and other biota, thereby increasing mass loss of leaf litter (Glazebrook & Robertson, 1999;Gonçalves et al, 2006). In northern Australia, the strong climatic seasonal cycle of wet and dry seasons influences river hydrology (Boulton et al, 2008, Warfe et al, 2011, which in turn affect the dynamics of the aquatic food web (Douglas et al, 2005;Jardine et al, 2011). However, an understanding of how riverine physical conditions (e.g.…”

Environmental DNA detects Critically Endangered largetooth sawfish in the wild

“…1) lies in the Northern Territory of Australia with an area of 53 000 km 2 , including an extensive area of seasonally inundated floodplain. The hydrology of the river is driven by a highly seasonal monsoonal pattern of flow, with > 90% of annual rainfall occurring in the wet monsoonal period (approximately November to April) (Webster et al 2005, Warfe et al 2011. During the wet season monsoon, inundation allows for the movement of fish from the main river channel onto the floodplain (Warfe et al 2011).…”

“…The hydrology of the river is driven by a highly seasonal monsoonal pattern of flow, with > 90% of annual rainfall occurring in the wet monsoonal period (approximately November to April) (Webster et al 2005, Warfe et al 2011. During the wet season monsoon, inundation allows for the movement of fish from the main river channel onto the floodplain (Warfe et al 2011). As water recedes in the dry monsoonal period (approximately May to October), fish, including P. pristis, retreat to isolated waterhole refugia, which may remain isolated for several months, until the system is reconnected in the following wet season (although interannual variability in rainfall can limit connectivity in some years).…”

Dinámica estacional de la vegetación litoral en el complejo lagunar inundable Zapatosa, Colombia

“…For example, in the middle Amazon it occupies approximately 0.5% of the basin but contributes 5% of the total organic matter to the downstream transport (Hedges et al, 1986). Plant communities in tropical seasonally flooded wetlands and floodplain lakes have been thoroughly studied for Northern Australia (Casanova & Brock, 2000;Finlayson, 2005;Warfe et al, 2011), india (Unni, 1971;Middleton, 1999;van der Valk, Middleton, Williams, Mason, & Davis, 1993), and Africa (Rees, 1978;Müller & Deil, 2005). in tropical and subtropical South America studies on the different aspects of the flooding cycles and their effect on aquatic vegetation were carried out in the Orinoco floodplains of Venezuelan (Castroviejo & López, 1985;Rial, 2000;2006), the Amazon (Junk, 1970;1986;Junk & Piedade, 1993;Ferreira, Piedade, Wittmann, & Franco, 2010;Piedade et al, 2010), the Pantanal (Do Prado, Heckman, & Martins, 1994;Frey, 1995;Fortney et al, 2004;Pott & Pott, 2004;Kufner, Scremin-Dias, & GuglieriCaporal, 2011;Pott, Pott, Lima, Moreira, & Oliveira, 2011), coastal Brazil (Rolon, Lacerda, Maltchik, & Guadagnin, 2008), and particularly the Paraná due to increasing river impoundments (e.g., Franceschi, Torres, Prado, & Lewis, 2000;Murphy et al, 2003;Thomaz, Souza, & Bini, 2003;Santos & Thomaz, 2007;Sabattini & Lallana, 2008;Santos & Thomaz, 2008;Padial et al, 2009;…”

“…The dynamic character of these systems gives rise to complex primary and secondary production processes that are difficult to predict in detail, but nutrient input from rivers and streams are important in general, as a significant contribution can be expected following rainfall from the surrounding watershed. Nutrient cycling proceeds mainly through heterotrophic processes via bacteria, fungi, micro-zooplankton and shreddinginvertebrates (Melack & Fisher, 1990;Wantzen, Yule, Mathooko, & Pringle, 2008;Warfe et al, 2011). The interactions between rivers and their surrounding floodplain motivated Junk, Bayley, and Sparks (1989) to propose the 'flood pulse concept' as a main force controlling the biota of tropical floodplains.…”