A review of sediment and nutrient concentration data from Australia for use in catchment water quality models

Land use (and land management) change is seen as the primary factor responsible for changes in sediment and nutrient delivery to water bodies. Understanding how sediment and nutrient (or constituent) concentrations vary with land use is critical to understanding the current and future impact of land use change on aquatic ecosystems. Access to appropriate land-use based water quality data is also important for calculating reliable load estimates using water quality models. This study collated published and unpublished runoff, constituent concentration and load data for Australian catchments. Water quality data for total suspended sediments (TSS), total nitrogen (TN) and total phosphorus (TP) were collated from runoff events with a focus on catchment areas that have a single or majority of the contributing area under one land use. Where possible, information on the dissolved forms of nutrients were also collated. For each data point, information was included on the site location, land use type and condition, contributing catchment area, runoff, laboratory analyses, the number of samples collected over the hydrograph and the mean constituent concentration calculation method. A total of similar to 750 entries were recorded from 514 different geographical sites covering 13 different land uses. We found that the nutrient concentrations collected using grab sampling (without a well defined hydrograph) were lower than for sites with gauged auto-samplers although this data set was small and no statistical analysis could be undertaken. There was no statistically significant difference (p <0.05) between data collected at plot and catchment scales for the same land use. This is most likely due to differences in land condition over-shadowing the effects of spatial scale. There was, however, a significant difference in the concentration value for constituent samples collected from sites where >90% of the catchment was represented by a single land use, compared to sites with <90% of the upstream area represented by a single land use. This highlights the need for more single land use water quality data, preferably over a range of spatial scales. Overall, the land uses with the highest median TSS concentrations were mining (similar to 50,000 mg/l), horticulture (similar to 3000 mg/l), dryland cropping (similar to 2000 mg/l), cotton (similar to 600 mg/l) and grazing on native pastures (similar to 300 mg/l). The highest median TN concentrations are from horticulture (similar to 32,000 mu g/l), cotton (similar to 6500 mu g/l), bananas (similar to 2700 mu g/l), grazing on modified pastures (similar to 2200 mu g/l) and sugar (similar to 1700 mu g/l). For TP it is forestry (similar to 5800 mu g/l), horticulture (similar to 1500 mu g/l), bananas (similar to 1400 mu g/l), dryland cropping (similar to 900 mg/l) and grazing on modified pastures (similar to 400 mu g/l). For the dissolved nutrient fractions, the sugarcane land use had the highest concentrations of dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP). Urban land use had the highest concentrations of dissolved inorganic phosphorus (DIP). This study provides modellers and catchment managers with an increased understanding of the processes involved in estimating constituent concentrations, the data available for use in modelling projects, and the conditions under which they should be applied. Areas requiring more data are also discussed. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.