CAN NUTRIENT SPIRALLING BE USED TO DETECT SEASONAL NUTRIENT UPTAKE IN A FORESTED STREAM? SULFIKAR HANAFI, MICHAEL R. GRACE * and BARRY T. HART Water Studies Centre, School of Chemistry, Monash University, Wellington Road PO Box 23, Clayton, Victoria 3800, Australia ( * author for correspondence, e-mail: mike.grace@sci.monash.edu.au; phone: +61-3-99054078; fax: +61-3-99054196) (Received 23 September 2005; accepted 21 February 2006) Abstract. Nutrient spiralling measurements were conducted in Lyrebird Creek, a forested stream in the Dandenong Ranges, Victoria, Australia. Spiralling indices from several nutrient (NH þ 4 , PO 3À 4 ) enrichment experiments were correlated with seasonal variation in factors thought to control nutrient uptake, i.e., temperature, light and algal biomass. It was hypothesized that nutrient uptake would be higher in summer as increased temperatures would promote both biotic and abiotic processes and higher light levels in summer would stimulate photosynthesis. However, results did not support this hypothesis. Uptake length for NH þ 4 À N and PO 3À 4 À P and uptake velocity were not correlated with chlorophyll-a, light or temperature (r 2 <0.30, P >0.1) despite the seasonality of these biophysical factors (r 2 >0.42, P <0.02). Lyrebird Creek might had no seasonal trend in nutrient uptake and/or nutrient spiraling measurements only appears suitable for contrasting streams with large differences in biophysical factors that supports biotic and abiotic nutrient processing. In addition, small errors in measuring a nutrient concentration can result in a large range in the estimated S w and increased difficulty in determining significant differences in nutrient spiralling indices. Keywords: nutrient spiralling, forested stream, seasonal variation, biophysical factors, ecosystem processes 1. Introduction Stream processes modify nutrient concentrations during downstream transport (Meyer & Likens, 1979). Thus, an understanding of in-stream processes is vital in managing nutrient movement from the catchment to the receiving waters (e.g., estuaries, wetlands, lakes). Webster and Patten (1979) introduced the concept of ‘nutrient spiralling’ to explain nutrient movement in lotic ecosystems. As a nutrient atom enters a stream, it is cycled through biotic and abiotic compartments while being transported downstream. The combination of these uptake and longitudinal transport processes, thus resemble a spiral. The distance a nutrient molecule travels while completing a cycle through the biotic and abiotic compartments is called the ‘spiralling length’ (S) (Newbold, Elwood, O’Neill, & Winkle, 1981) and is commonly measured as the uptake length (S w ) (Stream Solute Workshop, 1990). Streams with short spiralling lengths retain more nutrient with less transported downstream. Water, Air, and Soil Pollution: Focus (2006) 6: 403–411 DOI: 10.1007/s11267-006-9054-1 © Springer Science + Business Media B.V. 2006