A severe drought from 2007 to 2010 resulted in the lowest river levels (1.75 m decline from average) in over 90 years of records at the end of the Murray-Darling Basin in South Australia. Due to the low river level and inability to apply irrigation, the groundwater depth on the adjacent agricultural flood plain also declined substantially (1-1.5 m) and the alluvial clay subsoils dried and cracked. Sulfidic material (pH>4, predominantly in the form of pyrite, FeS2) in these subsoils oxidised to form sulfuric material (pH<4) over an estimated 3300 ha on 13 floodplains. Much of the acidity in the deeply cracked contaminated soil layers was in available form (in pore water and on cation exchange sites), with some layers having retained acidity (iron oxyhydroxysulfate mineral jarosite). Post drought, the rapid raising of surface and ground water levels mobilised acidity in acid sulfate soil profiles to the floodplain drainage channels and this was transported back to the river via pumping. The drainage water exhibited low pH (2-5) with high soluble metal (Al, Co, Mn, Fe, Mn, Ni, and Zn) concentrations, in exceedance of guidelines for ecosystem protection. Irrigation increased the short-term transport of acidity, however loads were generally greater in the non-irrigation (winter) season when rainfall is highest (0.0026 tonnes acidity/ha/day) than in the irrigation (spring-summer) season (0.0013 tonnes acidity/ha/day). Measured reductions in groundwater acidity and increases in pH have been observed over time but severe acidification persisted in floodplain sediments and waters for over two years post-drought. Results from 2-dimensional modelling of the river-floodplain hydrological processes were consistent with field measurements during the drying phase and illustrated how the declining river levels led to floodplain acidification. A modelled management scenario demonstrated how river level stabilisation and limited irrigation could have prevented, or greatly lessened the severity of the acidification.
Large-scale exposure of acid sulfate soils during a hydrological drought in the Lower Lakes of South Australia resulted in acidification of surface water in several locations. Our aim was to describe the techniques used to monitor, assess and manage these acidification events using a field and laboratory dataset (n?=?1,208) of acidic to circum-neutral pH water samples. The median pH of the acidified (pH?6.5) samples was 3.8. Significant (p?0.05) increases in soluble metals (Al, Co, Mn, Ni and Zn above guidelines for ecosystem protection), SO4 (from pyrite oxidation), Si (from aluminosilicate dissolution) and Ca (from carbonate dissolution and limestone addition), were observed under the acidic conditions. The log of the soluble metal concentrations, acidity and SO4/Cl ratio increased linearly with pH. The pH, alkalinity and acidity measurements were used to inform aerial limestone dosing events to neutralise acidic water. Field measurements correlated strongly with laboratory measurements for pH, alkalinity and conductivity (r (2)???0.97) but only moderately with acidity (r (2)?=?0.54), which could be due to difficulties in determining the indicator-based field titration endpoint. Laboratory measured acidity correlated well with calculated acidity (r (2)?=?0.87, acidity present as Al(III)?>?H(+)???Mn(II)?>?Fe(II/III)) but was about 20 % higher on average. Geochemical speciation calculations and XRD measurements indicated that solid phase minerals (schwertmannite and jarosite for Fe and jurbanite for Al) were likely controlling dissolved metal concentrations and influencing measured acidity between pH 2 and 5.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.