**6. Conclusion**

344 International Perspectives on Global Environmental Change

exposure of sulpher contained sediments following the river regulations and prolong drought. The processes controlling the FeS pollution in the Murray Darling Basin floodplain lakes is unknown. Establishing a macrophyte colony tolerant to sulphur-induced acidification can be useful. Engelhardt & Ritchie (2001) examined the role of aquatic macrophytes diversity in ecosystem functioning. Greater species richness and biomass of macrophytes tend to lower the chemical activities by filtering the particulate elements from the water and assisting ecosystem functioning and enhancing the wetland management practices. Phytophylous zooplankton such as *Eurycercus* and *Graptoleberis* (Quade, 1969) are proven to be useful for reconstructing past macrophyte cover in some billabongs in Australia (Ogden, 2000). Information regarding macrophyte cover in the past can help elucidating organometallic toxicity in lakes over time. Earliest records of POPs in lake sediments are generally limited, but the PAHs are produced from the combustion of organic matter, and generally have a long term record of past events (e.g. forest fires) in sediment. Sedimentary ratio of 1,7-dimethylphenanthrene and 2,6-dimethylpheanthrene has been used as indicator of wood combustion (Fermàndez et al. 2000). Recently Kattel and Sirocko (2011) have used cladocerans subfossils to identify the range of past anthropogenic regimes

The endemic floodplain lake ecosystems of the North America were invaded by exotic flora and fauna soon after their introduction (e.g., Mooney & Cleland, 2001). The invading microcruastaceans, *Daphnia lumholtzi* also colonised the Upper Paraná River floodplain lakes of South America soon after their introduction. Favourable temperature, water transparency and decreased nutrient concentrations supported the expansion of *D. lumholtzi* in South American wetland system (Simões et al., 2009). The actual effects of alien species on microcrustacean assemblages are not known, but micro-crustacean assemblages are useful for understanding the impacts and timing of invasion on endemic ecosystems. Less *Daphnia* ephippia are deposited in sediments derived from introduced plants such as *Plantago* and *Pinus* in the Murray Darling River floodplain wetlands in Australia (Reid et al., 2007). Caudal remains of exotic zooplankton *Bythotrephes* sp. in sediment of a Canadian lake were useful to track the energy flow toward the higher trophic level as *Bythotrephes* sp. consistently reduced endemic crustacean populations that were important diet of fish (Hall & Yan, 1997). The timing of geographic distribution pattern of exotic *Daphnia* in North America such as *D. galeata* is unnoticed as a result of extensive hybridization with native *Daphnia.* Allozyme analysis of *Daphnia* ephippia in Europe and North America have become useful for reconstructing timing of invasion (Taylor & Hebert, 1993) and a genetic analysis of cladoceran fossil ephippia have advanced further the knowledge of global distribution

patterns and impacts of exotic species on endemic ecosystems (Hairston et al., 1999).

Climate change exacerbates the ecological effects of large river floodplain lakes by altering the dynamics of nutrients, pH, salinity and organic toxics compounds such as PAHs and POPs. Mitigation is an action to reduce the risk and hazards of climate associated impacts on ecosystems (IPCC, 2007). Micro-crustacean assemblages are useful for understanding these impacts on large river floodplain lakes ecosystems and help configuring appropriate mitigation strategies. Cladocerans show variation in temperature optima and tolerance

including the alteration of forest catchments in a European maar lake.

**5.3 Management of invasive species** 

**5.4 Mitigation of climate change** 

Management of large river floodplains lake ecosystems have become increasingly challenging in recent decades as a result of coupled human-climate disturbances. A range of theoretical models being developed in large river systems, have become useful to understand floodplain lake ecosystems processes and develop effective management strategies for restoration of these lakes. However, unprecedented impacts such as river regulation, land use activity, introduction of exotic species and rapid climate warming in recent decades on floodplains lake ecosystems together have intensified the effects and made the ecosystem processes complex to understand. The use of micro-crustaceans particularly the cladocerans are increasingly useful indicator to infer the changes occurring in large river floodplain lakes. Cladocerans play an invaluable role in food web structure and dynamics and they have a wide range of optima and tolerances to temperature as well as other environmental perturbations in floodplains systems. The use of cladoceran subfossils and their ephippia has further reformed our understanding of ecological processes of floodplains lakes of large river system. A long term investigation of the changes in a range of abiotic and biotic assemblages including micro-crustaceans is important to achieve conservation and management goals of large river floodplain lakes ecosystems effectively. Appropriate quantitative and qualitative assessments of these ecosystems can help understanding the past changes and developing future prediction models that provide appropriate information of risks of environmental vulnerabilities and enhances mitigation measures. However, such effort can only be achieved through wider collaborations amongst scientific communities, governments and international organisations.
