Monitoring locations in the Coorong
What is alkalinity?
Alkalinity is a measure of the buffering capacity of water, or the capacity of the water to neutralise acids and resist pH change. It is expressed in milligrams per litre as calcium carbonate (mg/L as CaCO3) and is present in the water predominantly due to the weathering of carbonate minerals in the catchment.
Alkalinity tends to increase in the main Lower Lakes water body when inflows to the River Murray are low. Alkalinity decreases in the Lower Lakes during flood inflows from the River Murray and tributaries which are dominated by rainwater with low alkalinity levels. Alkalinity can be reduced or completely consumed as acid is released from acid sulfate soils which have become exposed and then been rewet. When water acidification occurred in some areas of the Lower Lakes during the 2007-2009 hydrological drought, limestone was added to restore the alkalinity in Boggy Lake.
Past alkalinity levels
Historically, alkalinity levels within this region have been between 80 and 250 mg/L as CaCO3. During the 2007-2009 hydrological drought, alkalinity was high in the main lake water body but was very low or completely disappeared at some locations on the lake margins.
What is pH?
pH is an indicator of acidity or alkalinity. pH is a logarithmic scale and an increase or decrease of one pH unit is a 10 fold change. Neutral water has a pH of 7, acidic solutions have values between 0-6 and alkaline solutions have values between 8-14.
pH can increase when there are low inflows in the River Murray, and consequently minimal flushing of the Lower Lakes. pH can decrease during River Murray and tributary flood inflows as rainwater has a lower pH. pH can also decrease if exposed acid sulfate soils become rewet by rainfall or rising lake levels.
Past pH levels
The pH in the Lower Lakes is typically between 8 and 9. During the 2007-2009 hydrological drought, the pH remained relatively stable within the main body of Lake Alexandrina. However, acidic water (pH 2 - 4) was identified in several fringing areaas (e.g. Boggy Lake, Loveday Bay) following the exposure and rewetting of acid sulfate soils.
What is salinity?
Salinity is a measure of the amount of dissolved salts in the water. Saline water conducts electricity more readily than freshwater, so electrical conductivity (EC), measured in micro siemens per centimeters (µS/cm) is routinely used to measure salinity.
As salinity increases, it may become harmful to native freshwater organisms. Salinity increases occur as water evaporates from the Lower Lakes (highest in summer) and also during times when inflows to the River Murray are too low to flush the salt out over the barrages and through the Murray Mouth. Salinity decreases occur when rain falls directly onto the Lower Lakes, and during times of high inflows in the River Murray and other tributaries which flush salt from the lakes.
Past salinity levels
Prior to the 2007-2009 hydrological drought, salinity was on average less than 700 EC in Lake Alexandrina (at Milang). During the 2007-2009 drought, levels reached as high as 9000 EC in Lake Alexandrina. Seawater has a salinity of approximately 55,000 EC.