2 Measures of nutrient processes as indicators of stream ecosystem health

15 To better understand how freshwater ecosystems respond to changes in catchment land-use, it is important 16 to develop measures of ecological health that include aspects of both ecosystem structure and function. This 17 study investigated measures of nutrient processes as potential indicators of stream ecosystem health across 18 a land-use gradient from relatively undisturbed to highly modified. A total of seven indicators (potential 19 denitrification; an index of denitrification potential relative to sediment organic matter; benthic algal 20 growth on artificial substrates amended with (a) N only, (b) P only, and (c) N and P; and d15N of aquatic 21 plants and benthic sediment) were measured at 53 streams in southeast Queensland, Australia. The indi-22 cators were evaluated by their response to a defined gradient of agricultural land-use disturbance as well as 23 practical aspects of using the indicators as part of a monitoring program. Regression models based on 24 descriptors of the disturbance gradient explained a large proportion of the variation in six of the seven 25 indicators. With denitrification index, algal growth in N amended substrate, and d15N of aquatic plants 26 demonstrating the best regression. However, the d15N value of benthic sediment was found to be the best 27 indicator overall for incorporation into a monitoring program, as samples were relatively easy to collect 28 and process, and were successfully collected at more than 90 % of the study sites