Mitta Mitta Monitoring Program: Project Report 2007

"2008".

Project Number: Monitoring of macro invertebrate communities at select sites in the Murray River and the Mitta Mitta River below Dartmouth Dam – M/BUS/101: and Processing, analysis and reporting of 2002-2005 season macroinvertebrate samples collected from the River Murray and Mitta Mitta River – M/BUS/119.

MDFRC item.

The Mitta Mitta Monitoring Project aims to monitor river health in the Mitta Mitta River below Dartmouth Dam. It attempts to detect and assess potential changes in aspects of water quality and the macroinvertebrate communties, resulting from either the operation of Dartmouth Dam or local catchment related impacts. The Mitta Mitta Monitoring Program commenced in 1998 to monitor the macroinvertebrate communities in the Mitta Mitta River below Dartmouth Dam. Initially the project was conducted by Water ECO science Pty Ltd and ran from 1998 to autumn 2005. The Murray Darling Freshwater Research Centre has continued the project from spring 2005 to present. This report, prepared by the MDFRC, presents the findings from the data collected from spring 2002 through to autumn 2007. The study was conducted in the section of the Mitta Mitta River below Dartmouth Dam to Tallandoon. Three unregulated tributaries, Snowy Creek, Mt Wills Creek and Watchingorra Creek (previously called Callaghans Creek) were also sampled to provide a comparison between the regulated Mitta Mitta River and the unregulated streams. Sampling was performed in accordance with the standard procedures outlined in the bioasssessment manual (EPA, 2003a). Water quality was assessed in accordance with the Victorian EPA's State of the Environment Protection Policy document (SEPP) water quality and nutrient objectives (EPA, 203b, c). Macroinvertebrates were assessed using Rapid Bioassessment Methods and analysed using a number of biotic indices (AusRivAs, SIGNAL, number of Families, number of key Families and EPT scores) and assessed in accordance with the Victorian EPA SEPP biological objectives (EPA, 2004). In most cases physicochemical parameters meet the SEPP objectives (EPA, 2003b, c) and are in general of no concern. Instream flow conditions, climate and catchment characteristic and associated landuse appear to be having an influence on some of the physicochemical parameters through its impact on instream processes, transport of solutes and entrainment of sediment. Turbidity was the parameter that was consistently above the SEPP (EPA, 2003b) objective and should be flagged for attention as part of this monitoring project. Nutrient levels were mostly within the SEPP (EPA, 2003c) objectives at all Mitta Mitta sites and at two of the unregulated sites. Landuse and surrounding vegetation appear to be having an influence on instream nutrient levels. Elevated nutrients were present in Watchingorra Creek (Site 507) which has an extensively cleared catchment with a surrounding land use of diary and beef production. The macroinvertebrate community of the Mitta Mitta River immediately below Dartmouth Dam is substantially impaired, with a loss of taxa across a wide range of taxonomic groups. This impairment largely remains until the Mitta Mitta River/Snowy Creek confluence. Below this there is some recovery in the Mitta Mitta River such that by Site 504 the SEPP (EPA, 2004) objectives are mostly met and the AUSRIVAS model rates the site as equivalent to reference, in three of the five years. The Snowy Creek provides a source of macroinvertebrates for recolonisation in the Mitta Mitta River and reinstates, to a small degree, some of the natural flow variability to the system. All of the unregulated streams had much higher biodiversity, and rated much higher with respect to the SEPP objectives than any of the Mitta Mitta sites. Of the unregulated streams Watchingorra Creek had the highest number of taxa. However many of these were from pollution tolerant groups and lacked several taxa from sensitive groups, a probable response to mild organic pollution due to the surrounding landuse. Both Snowy Creek and Mt Wills Creek are from largely undisturbed catchments and rated well above the SEPP objectives for almost all indices. Water quality does not appear to be a major driver of the loss of biological condition in the Miita Mitta River as in most cases the SEPP (EPA, 2003b, c) are met or nearly so. The operation of Dartmouth Dam and subsequent irrigation releases over the summer/autumn period and low winter spring flows are the most likely cause of the reduced biological condition.