Catchment litter: a phosphorus source mobilized during seasonal rainfall

Wetlands in south-western Australia are often situated in the interdunal depressions of coastal sand dunes and have catchments with significant areas of native vegetation. While farming and urbanization are two common sources of nutrients, natural processes such as P release from catchment litter and its significance as a P source for these waters have rarely been investigated. We studied litter production in a wooded catchment, and the leaching potential of litter P over the wet season. High concentrations of P, from 1.2-4.6 mg l-¹ (non-flooded conditions) to 1.5-5.7 mg l-¹ (flooded conditions) were leached from litter during the 'first flush' of the wet season. Overall 25.7-84.1% of the total P in litter was released via leachate during rainy months of May to November, mostly during the 'first flush'. This equals a load of 0.91 kg P ha-¹ year-¹ in response to annual leaf litter production on this catchment. The source was relatively small compared with the fertiliser P use in agricultural soils of the region (3.1-9.8 kg P ha-¹ year-¹) but was comparable with P export from agricultural catchments. Catchment litter as a source of P will need to be accounted for in the wetland management.