Responses of water chemistry to flow variability in the Gwydir Wetlands ecosystem, 2008-2009: Final Report to the New South Wales Department of Environment, Climate Change and Water

Abstract

Water chemistry monitoring was undertaken across three lower Gwydir channels in May-June and August 2009, in order to establish any spatial and temporal patterns during a low-flow period. This work was funded by the Australian Government's Water for the Future program, through the NSW Rivers and Environmental Restoration Program SPII whose overarching objective is to guide the 'Better use of environmental water for maintenance of the ecological character for stressed wetlands'. The sites and the monitoring and analytical protocols mirrored those utilised in earlier (2006 to 2009) research. Water temperature, electro-conductivity, dissolved organic carbon, total nitrogen, total phosphorous and chlorophyll a all showed a significant shift between sampling periods, although the latter three parameters also displayed a significant time x space interaction at both the site and watercourse levels. In a general sense, as water levels decreased over winter, all variables increased substantially with the exception of dissolved organic carbon which decreased by around 40%. Moreover, spatial variation in numerous parameters became accentuated over time, and sites became more unique in their water chemical characteristics. These findings, and those from other recent descriptions of lower Gwydir flow ecology, allow recommendations for ongoing monitoring of these channels, including the importance of determining longitudinal patterns in water chemistry, and monitoring sites mid-year as well as before/after discrete flow events. Recommendations for environmental flow management in lower Gwydir channels include limiting releases to spring-summer, establishing a greater stage height and variability of environmental flow releases, and taking a cautious approach when making any future adaptive management changes to environmental flow releases given the narrow set of ecological objectives associated with past releases.