Relationships between land use and nutrient concentrations in streams draining a 'wet-tropics' catchment in northern Australia

Abstract

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.

Modifications of ecological trophic structures on chemical gradients in lotic ecosystems and their relations to stream ecosystem health

“…This pattern was opposite to the forest cover, which had an inverse relation with percentage of urban cover. These results suggest that land-use pattern in the watershed determined the nutrients, dissolved ionic contents, and organic matters in the stream water, resulting in an influence on primary productivity (Mitchell et al 2009). …”

Target setting for pollutant discharge management of rivers in the Great Barrier Reef catchment area

“…The level of uncertainty in the load estimates for the Tully basin is moderate (Table 2), because (i) modelled and monitored DIN concentrations at six sampling locations were in general agreement (Armour et al 2009); (ii) compared to pre-1850 loads, the current total nitrogen (TN) load appears to have increased by a factor of around 3 (McKergow et al 2005b), which corresponds to the estimated 80% reduction required in DIN concentrations at the end-of-river site for the Tully River (Euramo); (iii) the Tully River has a low level of interannual variation compared with most Australian rivers (Mitchell et al 2009);and (iv) much of the load is missed at Euramo due to the overbank flow components discussed above.…”

“…Chl-a concentrations in the waters off Cape York average 0.2 µg L −1 , whereas in the area of coral reef biodiversity loss (wet tropics coast) concentrations average 0.7 µg L −1 . The difference is ascribed to the increased nutrient discharge from rivers such as the Tully caused by increased erosion and fertiliser loss (Mitchell et al 2001(Mitchell et al , 2009Furnas 2003;McKergow et al 2005a;Brodie et al 2007). Water quality trigger values for the GBRWHA have been set for chl-a at 0.6 µg L −1 for inshore waters (Moss et al 2005) and later to 0.5 µg L −1 (GBRMPA 2008; since then reduced to 0.45 µg L −1 ), and this value (0.5 µg L −1 ) was used as the GBR target for the Tully WQIP.…”

“…Our current estimates of DIN loads are based on modelling using the SedNet/ANNEX model (McKergow et al 2005b;Armour et al 2009) and long-term monitoring data (Mitchell et al 2001(Mitchell et al , 2009Furnas 2003). The most recent estimate from ANNEX modelling for the Tully basin is an average annual load of 1160 t DIN year −1 , which makes the target load 232 t (i.e.…”

“…Loads of pollutants discharging from these basins have increased greatly with the development of the river catchments for agriculture over the past 150 years (Furnas 2003;McKergow et al 2005aMcKergow et al , 2005b. Pollutant loads have increased by up to five times for suspended sediment from some rivers (McKergow et al 2005a), and up to six times for nitrate in others (Hunter and Walton 2008;Mitchell et al 2009). Moreover, considerable quantities of pesticides are now discharged that would have been completely absent before the 1950s (Johnson and Ebert 2000;Mitchell et al 2005).…”