The Impact of Extreme Low Flows on the Water Quality of the Lower Murray River and Lakes (South Australia)

Abstract

The impact of extreme low flows on the water quality of the Lower Murray River and Lower Lakes (Alexandrina and Albert) in South Australia was assessed by comparing water quality from five sites during an extreme low flow period (March 2007-November 2009 and a preceding reference period (March 2003-November 2005. Significant increases in salinity, total nitrogen, total phosphorus, chlorophyll a and turbidity were observed in the Lower Lakes during the low flow period. Consequently, water quality guidelines for the protection of aquatic ecosystems were greatly exceeded. Principal Component Analysis, empirical and mass balance model calculations suggested these changes could be attributed primarily to the lack of flushing resulting in concentration of dissolved and suspended material in the lakes, and increased sediment resuspension as the lakes became shallower. The river sites also showed significant but more minor salinity increases during the extreme low flow period, but nutrient and turbidity concentrations decreased. The most plausible reasons for these changes were decreased catchment inputs and increased influence of saline groundwater inputs. The results highlight the vulnerability of arid and semi-arid lake systems to reduced flow conditions as a result of climatic changes and/or water management decisions.

Have droughts and increased water extraction from the Murray River (Australia) reduced coastal ocean productivity?

“…This means that Milang, a long-term site for measurement of lake water-quality parameters, is used to estimate nutrient loadings because (1) it has the longest water-quality record, (2) it has been found to best represent the mass balance of nutrients in the lake (Mosley et al 2012) and (3) water in Lake Alexandrina has a short residence time and the water quality is generally similar to that in locations nearer the barrages, except during the 2007-2010 extreme lowflow, drought period where there was saline seepage back into the lake from the barrages (Stone et al 2016). These data were collected on an approximately fortnightly to monthly basis and analysed for total nitrogen (TN) and phosphorus (TP) by using methods described previously (Mosley et al 2012). For the purposes of calculating daily loads through the Murray Mouth, daily water-quality concentrations were interpolated using a cubic interpolation in MATLAB (MathWorks Australia, Sydney, NSW, Australia) and multiplied by the estimated daily discharge volume.…”

“…Continuously logged salinity data were collected by a calibrated water-quality sonde (YSI Pro Plus, Yellow Springs, OH, USA). Grab samples were also collected at 10 locations along the transect and analysed for turbidity by standard methods (Mosley et al 2012).…”

“…Outflows from the Murray River between 2001 and 2010 were extremely low in the period now known as the 'Millennium drought' (Geddes et al 2016). From 2007 to 2009, the river flows were so low that the river ceased to discharge to the ocean (Mosley et al 2012). Following the end of the Millennium drought, there was a large flooding event across the MurrayDarling Basin in 2011-2012 that resulted in a high discharge to the coastal ocean.…”

Assessing temporal and spatial variability of phytoplankton composition in a large reservoir in the Brazilian northeastern region under intense drought conditions

“…These changes, in turn, lead to shifts in phytoplankton attributes (Chellappa et al, 2009;Câmara et al, 2015), which reinforce the use of this community to evaluate the environmental status of these aquatic ecosystems. For example, high concentrations of nutrients, high conductivity and increased phytoplankton biomass could be expected in reservoirs and lakes located in semi-arid regions with reduced water volume (Naselli-Flores, 2003;Bouvy et al, 2003;Mosley et al, 2012;Jirsa et al, 2013). On the other hand, since the reduction of water volume occurs along with intensification in sediment resuspension and turbidity, a negative impact on phytoplankton biomass could also be expected (Braga et al, 2015).…”

Cross-cutting Perspective Freshwater

“…The increase in salinity observed in most lakes and reservoirs during droughts has been often attributed to reduced flushing/outflows and evapoconcentration, rising concentrations of components due to evaporation (Mayer et al 2010;Mosley et al 2012;Burt et al 2014). Although the IPCC fourth assessment reports that an increase in average temperatures of several degrees as a result of climate change will lead to an increase in average global precipitation over the course of the twenty-first century, this amount does not necessarily relate to an increase in the amount of drinking water available.…”