Off-site transport of nutrients and sediment from three main land-uses in the Mt Lofty Ranges, South Australia

Abstract

► Generally the highest TSS concentrations were found in surface drainage from a vineyard rather than the apple or cherry orchard. ► TSS was found generally to only be high in the first few flow events but TN did not show any consistent trend with flow volumes. ► TN concentration exceeded the Australian environmental trigger value in >50% of the samples from the apple orchard and >90% of the samples from the cherry orchard and vineyard. ► The TP concentrations exceeded the Australian environmental trigger value in <10% of the samples from the apple and the cherry orchard but in >90% of the samples from the vineyard. ► Current remedial strategies may not be very effective in this environment. This paper reports on the edge-of-field loads of sediment, nitrogen, phosphorus and organic carbon transported from three main land uses, namely an apple and a cherry orchard and a vineyard, in the Mt Lofty Ranges (MLR), South Australia over a three year period. There is a plethora of data in Australia on nutrient losses from dairy but prior to this study there was limited data from horticultural activities which are predominant in the MLR. Generally the highest total suspended solids (TSS) were found in surface drainage from the vineyard. At all three sites the highest TSS load was found in the first runoff event of the year but large flow events were accompanied by spikes in TSS concentration. Generally, within an event, the highest TSS concentration was found at the peak of flow and decreased on the receding limb of the hydrograph. The total nitrogen (TN) concentration exceeded the Australian environmental trigger value of 1 mg/L in >50% of the samples from the apple orchard and >90% of the samples from the cherry orchard and vineyard. The total phosphorus (TP) concentrations exceeded the Australian environmental trigger value of 0.1 mg/L in <10% of the samples from the apple and the cherry orchard but in >90% of the samples from the vineyard. Trends in the timing of the transport of TN, TP and TOC were only clearly observed when flow was large. After the initial seasonal flush of contaminants, generally only a very large runoff volume was sufficient to generate large loads of TN, TP and TOC during the season. Generally, the concentration of TP and TOC but not TN during a flow event was high at the start and declined with flow rate. In low flow situations, these trends were not clear. The transport of TN during an event was variable and unpredictable.