Novel methods for managing freshwater refuges against climate change in southern Australia Supporting document 3: Anthropogenic refuges for freshwater biodiversity
South west Western Australia’s mediterranean climate means that life in freshwater is greatly dependent upon seasonal waterbodies; however, climate change is increasingly removing those opportunities through shortened hydroperiods or through complete, indefinite loss of flow or inundation. Groundwater recharge to streams and wetlands has greatly declined; but at the same time, urbanization of the landscape generates increased runoff from hard surfaces, and may increase access to surface water occurring in drainage channels and basins, for colonizing organisms. Some of this water may represent new, previously unknown, habitat. Anthropogenic waterways may have the capacity to support significant biodiversity, perhaps providing life opportunities that have been lost in other parts of the landscape. This research set out to determine how well freshwater invertebrate species assemblages in anthropogenic refuges represent landscape biodiversity, while characterizing some of the qualities that support refuge function through facilitating survival traits. The waterscape — interspersed wetlands, ponds, streams and drains — within the Perth metropolitan area provided an ideal model system to engage with an aspect of climate change adaptation that is likely to be critical for urban (and potentially rural) environments: can waterbodies of human origin replace lost habitat or enhance survival opportunities?
We sampled over 70 urban waterbodies (including both flowing and standing waters) around the Swan-Canning watershed and Swan coastal plain assessing habitat qualities and aquatic invertebrate assemblages, focusing intensively on a subset (the Beeliar group of wetlands and interspersed urban ponds) from spring 2011 through a summer during which many dried completely and into the following winter’s inundation. Two experiments were performed in a controlled condition laboratory set up for the purpose of manipulating conditions experienced by animals subjected to drying: whole communities were taken from some of the urban ponds and the Beeliar wetlands and the response to loss of surface water over up to 20 days, and under degrees of “harshness”, was examined; and, three widely distributed species with different potential survival traits (a snail, a caddisfly and damselflies) were collected from waterbodies across a 50 km range, then subjected to drying regimes to derive specific models for survival rates and to observe behavioural/physical responses.
We recorded a surprising diversity of habitat characters existing within drainage networks in the Perth metropolitan area, and that diversity appears directly linked to landscape-scale biodiversity, yet a large proportion of site-level variance in invertebrate assemblages cannot be explained directly by habitat character, which makes prediction difficult. This uncertainty is mirrored in the results from the experiments, which revealed a resistance to drying in many species, including hereto unknown traits; this suggested that predictions of species survival in potential refuges may not be accurate given the current paucity of knowledge of life histories and survival traits.
An exhaustive review of international literature provided contextual scope for the research. Internationally, there are increasing numbers of studies recording and recognizing the biodiversity supported by anthropogenic waterbodies not created for conservation purposes, such as: irrigation infrastructure, rice fields, drainage ditches, stormwater basins, agricultural ponds, fire dams, urban ponds, golf course lakes, disused industrial ponds, transport canals, livestock watering points, reservoirs, gravel/clay/ quarry ponds, roadside ponds and retaining walls. We reviewed this literature and evaluated the potential of these places to act as refuges from disturbance, especially impacts of climate change. We observed bias towards north America and Europe, with fewer studies from Asia, tropical/equatorial countries and the southern hemisphere (including Australia).
Most anthropogenic waterbodies are lentic rather than lotic, constraining the species supported. Agricultural ponds, rural and urban drainage ditches and transport canals were the most biodiverse for all aquatic taxa, whereas irrigation infrastructure was the least diverse. Some anthropogenic waterbodies provided stepping-stone refuges for vertebrates, but these are hard to identify for invertebrates. The capacity for anthropogenic refuges to contribute to recolonization processes in landscapes is largely unsubstantiated (yet). However, the landscape-level variables associated with high biodiversity were proximity to and connectivity with other waterbodies and to natural terrestrial vegetation, suggesting that linkages do exist. Management actions associated with improved refuge capacity included promoting aquatic plant growth, creating shallow sloping edges and natural beds, maintaining appropriate hydroperiod and connections to other waterbodies. The results of the empirical research in waterbodies on the Swan coastal plain are consistent with those findings.
Please cite this report as:
Chester, ET, Robson, BJ & Chambers, JM 2013, Novel methods for managing freshwater refuges against climate change in southern Australia. Supporting Document 3: Anthropogenic refuges for freshwater biodiversity, National Climate Change Adaptation Research Facility, Gold Coast, 90 pp.
Banner image: Langford Park drain © Edwin T. Chester