Measures of Nutrient Processes as Indicators of Stream Ecosystem Health

Abstract

Abstract15 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 d 15 N 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 d 15 N of aquatic plants 26 demonstrating the best regression. However, the d 15 N 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. 29

Dams and Flow in the Cotter River, Australia: Effects on Instream Trophic Structure and Benthic Metabolism

“…Samples were dried for 24 h at 40°C, then ground to a fine powder and analysed for stable isotopes of carbon and nitrogen. Samples were oxidised at high temperature and the resultant CO 2 and N were analysed with a continuous-flow ratio mass spectrometer (Udy et al, 2001;McCutchan & Lewis, 2002). Ratios of 13 C/ 12 C and 14 N/ 15 N were expressed in d notation as the relative per mil (&) difference between the sample and conventional standard (sucrose for carbon and ammonium sulphate for nitrogen), i.e.…”

“…This changed structure of the algal community is likely to have a flow-on effect to the communities of consumer organisms because, as is being increasingly recognised, benthic algae are an important food resource in upland forest streams (Mulholland et al, 2000;Rainer et al, 2001;Salas & Dudgeon, 2001;Woodward & Hildrew, 2002). For an overall perspective, it is probable that stream metabolism can provide an integrative measure of stream ecosystem functioning (Bunn et al, 1999;Udy et al, 2001); it may also indicate the biological response of a stream to a specific flow-based event (Osborne, 1983). As such it may provide a method for observing a direct biological response to manipulations of flows from dams.…”

A significant nexus: Geographically isolated wetlands influence landscape hydrology

“…other contaminants to downstream water bodies [Udy et al, 2006;Mitsch and Gosselink, 2007;Kadlec and Wallace, 2009]. These services are among the many reasons that wetlands have been conferred protected status (e.g., under Section 404 of the U.S. Federal Clean Water Act and Guidance Document 12 of the European Commission's Water Framework Directive).…”

Effects of dilution stress on the functioning of a saline Mediterranean stream

“…Recently, functional indicators of ecosystem processes (metabolic rates, organic matter decomposition, nutrient processes, etc.) have received more attention and are now considered fundamental to determine the health of stream and river ecosystems (Bunn et al, 1999;Bunn & Davies, 2000;Gessner & Chauvet, 2002;Young et al, 2004;Udy et al, 2006) Ecosystem metabolism, the combination of primary production (gross primary production, GPP) and ecosystem respiration (ER), provides a measure of the amount of organic carbon produced and consumed within the system, respectively. Both rates often show seasonal patterns as a consequence of their dependence on environmental factors (light, temperature, nutrients) but are also highly sensitive to many human-induced environmental stressors making them good stream health indicators (Gessner & Chauvet, 2002;Young et al, 2004).…”