Acidification of an estuarine tributary in eastern Australia due to drainage of acid sulfate soils

Abstract

Episodic acidification (pH <5) of estuarine tributaries caused by the oxidation of sulfidic floodplain sediments is widespread in eastern Australia. Drainage and flood mitigation works promote oxidation and the export of sulfuric acid and dissolved aluminium and iron into streams. This paper examines the acidification of a tidal reach on the Richmond River, New South Wales. Acid discharge is controlled by the floodplain water balance, drainage of shallow acid groundwater, and tidal floodgate operation. Floodgates store acid waters for more than six months. Acid discharges ranged from short pulses during light rains to ~950 t of sulfuric acid in a major flood that acidified the reach for over seven weeks. Extensive iron flocs accompanied acidification and coated the benthos. The chemistry of the reach reflected mixing of acid groundwater with upland waters and showed pH-dependent enhancement or depletion of species relative to chloride. Concentrations of monomeric aluminium were over 300 times larger than local (ANZECC) guidelines and 90 km of the river were acidified after floods. The estimated rate of sulfuric acid production from the floodplain is ~300 kg ha-1 year-1 and discharge may occur for over 1000 years. Management options are considered; however, the long-term consequences of acidification of tidal reaches are unknown.

Alteration of groundwater and sediment geochemistry in a sulfidic backswamp due to Melaleuca quinquenervia encroachment

“…Acid groundwater is often brackish to moderately saline (Walker 1972) with high concentrations of SO 4 2-and acidic metal cations, principally Fe and Al. Large amounts of acidity, Fe and Al are exported from sulfidic backswamps into adjacent estuaries via artificial drainage systems (Sammut et al 1996;Wilson et al 1999;Blunden and Indraratna 2000). The consequences of this export for estuarine biota and ecological function are widely recognised as a major issue and significant resources are currently focused on developing and implementing management strategies to reduce acid outflows.…”

Treatment of Acidic Groundwater in Acid Sulfate Soil Terrain Using Recycled Concrete: Column Experiments

“…The oxidation of residual sulphide minerals such as pyrite in the vadose zone of ASS terrains can produce acidic pore waters which can mobilise potentially toxic metals such as aluminium (Al) and iron (Fe) from the soil (Indraratna et al 2005). Infiltration of such acidic and metal-rich water into aquifers and discharge to nearby surface water bodies can lead to adverse environmental and social impacts such as incompatibility of land and groundwater for agriculture and aquaculture, and ecological disturbance in surface water ecosystems (Sammut et al 1996). Therefore, discharge from acid sulphate soil can be an intractable environmental issue in many coastal regions around the world.…”

Micromorphological evidence for mineral weathering pathways in a coastal acid sulfate soil sequence with Mediterranean-type climate, South Australia

“…The present study involves a natural and a drained mangrove environment that was until recently under marine-dominated tidal conditions, the only similar study being from East Trinity (Hicks et al 1999). Most studies are of brackish estuary floodplain and backswamp environments that were under mangrove vegetation at some time during the Holocene with only minor tidal influences and minimal flushing with sea water (Sammut et al 1996). Micromorphological studies of ASS in Australia have been conducted by Willett et al (1992), Fitzpatrick et al (1993Fitzpatrick et al ( , 1996, Bush and Sullivan (1996, 1998, and Poch et al (2004).…”

“…Willett and Walker 1982;Lin and Melville 1992;White et al , 1997Sammut et al 1994Sammut et al , 1995Sammut et al , 1996Ahern et al 1998Ahern et al , 2000. Few published studies have involved coastal ASS from southern Australia, with a Mediterranean climate (e.g.…”