Isotopes in Environmental and Health Studies Vol. 41, No. 1, March 2005, 31–38 Using natural 15 N abundances to trace the fate of waste-derived nitrogen in forest ecosystems: New Zealand case studies H.WANG*, G. N. MAGESAN, P.W. CLINTON and J. M. LAVERY Forest Research, Private Bag 3020, Rotorua, New Zealand (Received 21 October 2004; in final form 17 January 2005) Treatment of wastewater generally results in elevated natural 15 N abundance (δ 15 N) in the effluent and sludges. For example, high δ 15 N values are found in treated sewage effluent, biosolids, and other wastes that are commonly applied to land. In contrast, N deficient coniferous forest soils usually have a low δ 15 N. When wastes with high δ 15 N values are applied to land, their distinctive δ 15 N signature can potentially be used to trace the fate of waste-derived N in the ecosystem. In this paper, we provide an overview of the use of δ 15 N in land application of wastes, including New Zealand case studies on tracing nitrogen in forest ecosystems. Keywords: Ecosystem; Effluent; Forest; Natural abundances; Nitrogen-15; Sludge; Waste 1. Introduction In recent years, land application of organic wastes has attracted renewed interest because of its potential for managing municipal and industrial residues in an environmentally friendly manner. Many organic wastes contain relatively high nitrogen (N) concentration. When N-rich waste is applied to land, nitrate is often identified as one of the potential ground- water contaminants, although only accepted agronomic rates of total N loadings are applied in most situations [1]. Sometimes waste-derived N may also cause off-site effects, contributing to eutrophication of water bodies [2]. Nitrogen occurs in a variety of chemical forms and is actively involved in many important biological processes in soil ecosystems, where it is difficult to trace the fate of waste derived N by using conventional chemical methods. Recent studies indicate that the stable isotope technique can be used as a tool to trace the fate of waste-derived N in ecosystems [1, 3, 4]. This paper presents potential uses of natural 15 N abundance to trace waste-derived N in the environment, and two case studies conducted in New Zealand forest ecosystems. *Corresponding author. Email: hailong.wang@forestresearch.co.nz Isotopes in Environmental and Health Studies ISSN 1025-6016 print/ISSN 1477-2639 online © 2005 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/10256010500053250