Category 1: Fish (channel) This indicator was not evaluated at the local scale (Selected Area). It was designed to provide data for Basin-scale evaluation. Native bony herring and carp gudgeons dominated the large-bodied and fish assemblages, respectively. Other small-bodied species sampled included the invasive Gambusia and native unspecked hardyhead and Murray rainbowfish. Other large-bodied species sampled included the invasive common carp and natives golden perch, Murray cod, freshwater catfish and silver perch. Category 3: Hydrological Regime What did CEW contribute to: Help increase hydraulic diversity within weir pools? Increased median velocity up to 0.07 m s1 over the year compared to without CEW, with some cross sections in the weir pool transforming into moderate-flowing habitat for large-bodied fish. Help increase water levels within weir pools? Increases in water levels in weir pools of up to 0.2 m in the upper reaches. Periodic increases in water levels could improve the condition of riparian vegetation and increase biofilm diversity. The increase in flow (discharge) to SA due to CEW from 5,200–6,700 ML day-1 to 9,000–10,000 ML day-1 from October to November 2014 and again from January to March 2015 resulted in an increase in water level in the order of 0.2 m in the upper reaches of each weir pool. Over the same period, CEW contributed to the increase in median velocity in the weir pool generally from ~0.1 m s-1 to ~0.15 m s-1 depending on the weir pool (lower weir pools tended to have slightly slower velocities). Velocities for some cross sections in the LMR increased into the range representing moderate-flowing habitat for large-bodied fish due to CEW.
Figure E12. Change in weir pool median velocity each day due to Commonwealth environmental water. Colours represent the timing of the change, shaded by season. The height of each bar represents the number of days over the year the change in velocity due to environmental water was within that range. F: Background Flow provides habitat and resources for aquatic organisms by altering the concentrations and transport of dissolved and particulate matter. Here we consider dissolved and particulate matter to include: Salinity, which is a measure of total dissolved salts and is a key parameter governing the distribution and abundance of aquatic biota. Salinity is strongly influenced by flow through the alteration of groundwater inputs, evapoconcentration and intrusions of seawater (Brookes et al. 2009; Aldridge et al. 2011; 2012; Mosley et al. 2012). Dissolved inorganic nutrients, which are essential resources for the growth and survival biota and are readily assimilated (Poff et al. 1997). Nitrogen, phosphorus and silica are particularly important because they often control the productivity of aquatic ecosystems. Flow results in the mobilisation and transport of dissolved nutrients through the leaching of nutrients from dried sediments and dead organic matter. Particulate organic nutrients (phosphorus and nitrogen), which are those nutrients incorporated into the tissue of living and dead organisms. Flow can influence particulate organic nutrient concentrations and transport through a number of mechanisms, including through increased productivity associated with elevated dissolved nutrient concentrations. Chlorophyll a, which is a measure of phytoplankton biomass, with phytoplankton being an important primary producer of riverine ecosystems. Flow can influence chlorophyll a concentrations and transport through increased phytoplankton productivity.