Relationships between the development of acid sulphate soil and landsc
ape characteristics were examined in a fluvial-dominated, estuarine-de
ltaic plain of the South China coast. It was found that the accumulati
on of pyrite (potential acid sulphate material) has been limited gener
ally by rapid sedimentation rates and insufficient supply of sulphate
ion. The occurrence of the pyritic sediments is, however, closely asso
ciated with a particular depositional pattern, i.e. ''surrounding isla
nd deposition''. The acid sulphate soils in the area frequently occur
within narrow zones surrounding present-day's rocky hills (previously
bedrock islands). This provides a guide for predicting the occurrence
of potential acid sulphate soils in the area. Apart from the naturally
large input of fluvial sediment, human activities have also accelerat
ed the delta progradation and limited the vertical accretion of the de
ltaic surface. These effects have had significant impacts on the thick
ness and occurrence depth of the pyritic layer. With a history of more
than 1000 years of land reclamation, the intensive cultivation in the
area has turned most of the potential acid sulphate soils into actual
acid sulphate soils, however, the soil properties vary markedly with
landuse types, The case of the Pearl River Delta is generally in agree
ment with Pons and van Breemen's (1982) conclusion in that the accumul
ation of pyrite is inversely related to the rate of sedimentation. Our
results show that the existence of bedrock islands in the estuary bas
in provided zones of slow sedimentation and therefore enhanced pyrite
accumulation. On the other hand, human intervention over the past 2000
years has acted to reduce pyrite accumulation both through landward c
atchment clearing that increased sediment discharge to the estuary and
through empolderment and associated land management practices.