Integrating environmental and social aspects for managing ephemeral wetlands: Case study of Lake Cowal, Australia

Ephemeral wetlands are common throughout inland semi-arid and arid, south-eastern Australia and are characterised by highly variable hydrological regimes with periodical drying and rewetting cycles. They are easily affected by extended droughts and are vulnerable to human activities, such as cropping, grazing and mining, in the immediate vicinity and further afield in the catchment, resulting in excessive loadings of nutrients, in particular phosphorus, with severe ecological effects as a consequence of nutrient enriched sediment and reduced water quality. In addition, the vegetation distribution and dominance in many ephemeral wetlands seems to have changed in response to changes in nutrient loadings, sedimentation and hydrology. This study is to explore the effects of projected land use change and climate change on the biogeochemistry and ecology of inland ephemeral wetlands integrating environmental and social perspectives using Lake Cowal, the largest inland ephemeral wetland in New South Wales, Australia as case study site.
A comprehensive investigation of the physico-chemical characteristics of the water and sediment quality, accounting for the variation in hydrology in different parts of the wetland was conducted and the findings show that the lake was under nutrient enrichment condition. Then a field survey of the vegetation community composition and distribution and an experiment of seedling emergence from the lake sediment to examine the plant abundance and species richness accounting for the seasonal changes were conducted. The findings indicate that the lake had a few emergent plants but no submerged plants with high turbidity and there was low diversity and low abundance of plants emerging from the lake sediments. An investigation of sediment and phosphorus dynamics in the ephemeral wetland was done to improve the understanding of the P adsorption behaviour of ephemeral wetland sediments during drought periods and how the dried sediments P release respond after re-wetting events. As implied from this study, Lake Cowal is a complex system and the lake sediments act either as a source of phosphorus when the lake is receiving low phosphorus concentration runoffs or function as a sink for P. In addition to environmental perspective, a social study was also applied to explore the local ecological knowledge of environmental condition of the lake, information about land-use history, perceptions for management actions on the lake environment. Local people in the Lake Cowal area have a rich and deep knowledge of local ecosystem stemming from ongoing and extensive interactions with the system.
The study indicates that local ecological knowledge complementing with scientific evidences gives a more comprehensive understanding of the ecosystem. The comprehensive understanding obtained by the multidisciplinary approach contributes to build pictorial conceptual models and development of implications for future management in relation to projected climate and land-use changes taking account of local residents’ actual needs and concerns.