Year

1995

Degree Name

Master of Environmental Science (Hons.)

Department

Department of Environmental Science

Abstract

In the northern section of the Shoalhaven River floodplain, flood mitigation drains have worsened the impacts of acid sulphate soils. Such impacts include levels of pH and aluminium in the drains and estuary that are potentially fatal to flora and fauna, especially after heavy rains. This study concentrates on four properties to the south of Berry on 251 hectares of improved pastoral land.

Water quality was monitored in wells, drainsites and in Broughton Creek over a 15 week period from June to September 1994 that was drier than average. Soils were also sampled and analysed.

Actual and potential acid sulphate soils, including jarositic clay layers seem to be confined to unripe soil below 0.2 m elevation in low backswamp areas. Water quality was worst in the drains and in backswamp wells with pH as low as 3.1 and aluminium concentration as high as 58 mg/L in the drains. Main drains cut into actual acid sulphate soils and poor quality water from the soils flows into them. Water level dropped in all wells and main drainsites over the monitoring period and had dropped below the top of jarositic clay in some backswamp wells. pH dropped with water level in the main drains but not in wells.

Raising the water level in the drains with stop boards or temporary weirs in order to raise the water table above the top of jarositic clay seems the most promising option that might be trialed. Recommendations for further research include continued and expanded monitoring of water quality and further soil sampling.

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