REVIEW: Perspectives on wastewater treatment wetlands and waterbird conservation

Abstract

Summary 1.With the global loss of natural wetlands, waterbirds have become increasingly dependent on alternative and artificial habitats, but the use of such wetlands by waterbirds is typically opportunistic and little consideration has been given to the potential implications for water treatment or waterbird conservation objectives. 2. Wastewater treatment wetlands are currently of critical importance for certain waterbird species in some parts of the world, and we illustrate this with an example from south-eastern Australia. Furthermore, we argue that their significance is likely to increase as they offer the most realistic means of treating wastewater in developing countries, where the demand for improved sanitation to lift people out of poverty is intense. 3. There is little scientific evidence to guide the construction of wastewater treatment wetlands with waterbird conservation in mind. 4. The use of wastewater by waterbirds poses health risks for both birds and humans and these risks must be better understood. 5. Synthesis and applications. Wastewater treatment wetlands are not a substitute for natural wetlands and reliance upon them should not compromise wetland conservation efforts. Nonetheless, they are a potentially valuable resource for waterbirds, and research should be directed towards deepening our understanding of their global distribution; food-web dynamics; methods of deterring or excluding birds when bird or human health may be compromised; the effects of wastewater contaminants and pathogens on birds; and the role of waterbirds in human disease transmission.

Eutrophication and Bacterial Pathogens as Risk Factors for Avian Botulism Outbreaks in Wetlands Receiving Effluents from Urban Wastewater Treatment Plants

“…There are seven confirmed types of BoNTs (types A to G); the most frequent in Europe is mosaic type C/D (14,15). High water temperatures and increases in the invertebrate biomass, which frequently occur in wastewater ponds, may attract water birds for feeding and provide optimal conditions for the occurrence of botulism outbreaks, although there is still not enough evidence to support this hypothesis (16). Other factors such as pH between 7.5 and 9, low redox potential (Eh), decreasing turbidity, and low salinity also contribute to botulism risk in wetlands (11,16,17).…”

“…Moreover, the wetlands receiving treated wastewater showed higher prevalences of avian pathogenic bacteria (i.e., APEC and C. perfringens type A) that can kill a small number of birds and therefore provide carcasses which are an optimum substrate for the initial growth of C. botulinum prior to an outbreak. In addition, these eutrophic wetlands have high phytoplankton and zooplankton productivity from spring to autumn that attracts a great amount of water birds, which increases spatial aggregation and the risk of epidemics (16,31). The result of this has been a higher frequency of botulism outbreaks in Navaseca (4 summer outbreaks in the last 5 years) and Veguilla (5 recorded outbreaks since 1978) than in TDNP (only 1 large outbreak in 1999 and another smaller outbreak in an exhibition pond in 2007) (11,32).…”

“…High water temperatures and increases in the invertebrate biomass, which frequently occur in wastewater ponds, may attract water birds for feeding and provide optimal conditions for the occurrence of botulism outbreaks, although there is still not enough evidence to support this hypothesis (16). Other factors such as pH between 7.5 and 9, low redox potential (Eh), decreasing turbidity, and low salinity also contribute to botulism risk in wetlands (11,16,17). Avian mortalities due to any cause have the potential to be a major initiating factor of botulism outbreaks because they provide carcasses for the initial multiplication and toxinogenesis of C. botulinum (18).…”

Waterbird use of farm dams in south-eastern Australia: abundance and influence of biophysical and landscape characteristics

“…Wastewater treatment wetlands (sewage ponds and stormwater treatment ponds) have been the subject of much study in terms of waterbird conservation, particularly in south-eastern Australia (e.g., Hamilton et al 2002Taylor 2004, 2005;Murray and Hamilton 2010), but next to nothing is known about the role of farm dams in this context. There have been a few investigations of other taxa-invertebrates (Geddes 1986;Burgin 2006, 2009;Lake et al 2010) and frogs (Hazell et al 2001)-but even these are highly localised in their geographical coverage, involving surveys of merely a handful of dams; and there are no published studies of waterbird abundance, richness, or community structure.…”

“…For example, while emergent vegetation might provide useful habitat for some species, it may deter others by decreasing visibility and thus ability to maintain predator vigilance (Murray et al 2013), and the sudden death of large swards of macrophytes can increase the risk of a deadly botulism outbreak (Blaker 1967;. Thirdly, in some instances it may be desirable to deter birds from dams (Murray and Hamilton 2010).…”