Water quality and macroinvertebrate response to acidification following intensified summer droughts in a Western Australian wetland

A decline in pH from similar to6-8 to similar to4-5 over a period of 4 year s was detected during routine monitoring of surface waters at Lake Jandabup . This was accompanied by lower water levels, shorter periods of inundation and measurable changes in other attributes of the water: sulfate, iron and ammonium concentrations increased markedly, and filterable reactive phosph orus and colour (gilvin) decreased. Macroinvertebrate family richness did n ot change notably over this period, but there were shifts in community stru cture: ostracods, isopods and oligochaete worms became less abundant; amphi pods, mayflies and gastropods disappeared, while ceratopogonids (Diptera) a nd macrothricid cladocerans increased in abundance. Historical evidence sug gests that at least one other acidification event has occurred in the recen t past. Mechanisms associated with the acidification, and the wetland's cap acity to recover from such events, are discussed.