Nutrient spiraling in streams and river networks

Abstract

Over the past 3 decades, nutrient spiraling has become a unifying paradigm for stream biogeochemical research. This paper presents (1) a quantitative synthesis of the nutrient spiraling literature and (2) application of these data to elucidate trends in nutrient spiraling within stream networks. Results are based on 404 individual experiments on ammonium (NH 4 ), nitrate (NO 3 ), and phosphate (PO 4 ) from 52 published studies. Sixty‐nine percent of the experiments were performed in first‐ and second‐order streams, and 31% were performed in third‐ to fifth‐order streams. Uptake lengths, S w , of NH 4 (median = 86 m) and PO 4 (median = 96 m) were significantly different ( α = 0.05) than NO 3 (median = 236 m). Areal uptake rates of NH 4 (median = 28 μ g m −2 min −1 ) were significantly different than NO 3 and PO 4 (median = 15 and 14 μ g m −2 min −1 , respectively). There were significant differences among NH 4 , NO 3 , and PO 4 uptake velocity (median = 5, 1, and 2 mm min −1 , respectively). Correlation analysis results were equivocal on the effect of transient storage on nutrient spiraling. Application of these data to a stream network model showed that recycling (defined here as stream length ÷ S w ) of NH 4 and NO 3 generally increased with stream order, while PO 4 recycling remained constant along a first‐ to fifth‐order stream gradient. Within this hypothetical stream network, cumulative NH 4 uptake decreased slightly with stream order, while cumulative NO 3 and PO 4 uptake increased with stream order. These data suggest the importance of larger rivers to nutrient spiraling and the need to consider how stream networks affect nutrient flux between terrestrial and marine ecosystems.