Abstract. Differences in stream nutrient concentrations typically reflect upstream differences in land use. In particular, nitrate concentrations are greatly increased by losses from nitrogen (N) fertiliser applied to areas of intensive cropping. In the present study, a relationship between the area of such land use and the nitrate concentrations in the receiving streams was predicted. This relationship was tested using several data sets from the Tully basin, in the wet-tropics bioregion of north Queensland, Australia. The proportions of fertiliser-additive land use (FALU), mostly sugarcane and bananas, were correlated with the concentrations of nutrients in streams that drain these land uses. The data compared included two longterm sampling studies in the Tully River catchment and more recent, broader catchment sampling and plot-scale studies in this region. A strong relationship was shown for nitrate, but weaker relationships were observed for other N-nutrient and P-nutrient forms. Comparisons were made with contemporary and historical land-use changes in the Tully basin. The strong relationship of FALU with nitrate provides evidence that the nitrate exports from this catchment are largely derived from fertiliser use. This relationship can be used to derive nitrate run-off coefficients for fertilised land use in catchment models or to monitor changes following management to reduce fertiliser usage.
Enhanced run-off of nutrients from agricultural development in catchments bordering the Great Barrier Reef (GBR) is regarded as a potential threat to inshore reefs. In an attempt to better understand the impact of river run-off, the Australian Institute of Marine Science (AIMS) initiated a sampling program to measure nutrient concentrations in rivers draining to the GBR shelf. Our longest data set is from the Tully River in the wet tropics, sampled in collaboration with the Bureau of Sugar Experiment Stations (BSES). After thirteen years, we ask whether there has been any change in river nutrient levels. Water samples were collected at monthly intervals, with additional, wet-season samples. In recent years, a trend of increase in nitrate (at low flow) and particulate nitrogen concentrations has been observed. In this period, a significant increase in agricultural activity has occurred within the Tully basin. The area under sugarcane and bananas has doubled and fertiliser nitrogen use has increased by 130%. Increased concentrations of nitrogen in the river system may be a consequence of this increase in agricultural activity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.