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Abstract

Sediment and nutrient losses from exotic Pinus plantation management operations under simulated rainfall.

Abstract

Rainfall simulation experiments were carried out to measure runoff and soil water fluxes of suspended solids, total nitrogen, total phosphorus, dissolved organic carbon and total iron from sites in Pinus plantations on the coastal lowlands of south-eastern Queensland, Australia, subjected to various operations (treatments). The operations investigated were cultivated and non-cultivated site preparation, fertilized site preparation, clear fell harvesting and controlled burning these treatments were compared with an 8-year-old established plantation. Flow-weighted mean concentrations of total nitrogen and total phosphorus in surface runoff from the cultivated and non-cultivated site-preparation, clear fell harvest, controlled burning and 8-year-old established plantation treatments were very similar. However, both the soil water and the runoff from the fertilized site preparation treatment contained more nitrogen (N) and phosphorus (P) than the other treatments - with 3.10 mg N litre-1 and 4.32 mg P litre-1 (4 and 20 times more) in the runoff. Dissolved organic carbon concentrations in runoff from the non-cultivated site preparation and prescribed burn treatments were increased. Iron concentrations were highest in runoff from the non-cultivated site preparation and 8-year-old established plantation treatments. Concentrations of suspended solids in runoff were higher from cultivated site preparation and controlled burning treatments, and reflect the great disturbance of surface soil at these sites. The concentrations of all analytes were highest in initial runoff from plots, and generally decreased with time. The total nitrogen (mean 7.28, range 0.11-43.27 mg litre-1) and total phosphorus (mean 11.60, range 0.06-83.99 mg litre-1) concentrations in soil water were between 2 and 10 times higher than in surface runoff, which highlights the potential for nutrient fluxes in interflow (i.e. in the soil above the water table) through the general plantation area. Implications with regard to forest management are discussed, along with results of larger catchment-scale studies.