Nutrient spiralling in streams: implications for nutrient limitation and invertebrate activity.

Abstract

Nutrient cycling in streams occurs in conjunction with downstream transport as a spatially distributed process that has been termed spiralling. The intensity of reutilization of nutrients as they pass downstream can be quantified in terms of the length of stream required for a nutrient atom to complete one (abstract) cycle ("spiralling length'). A model for steady-state spiralling of a limiting nutrient predicts that most of the downstream transport of nutrient occurs in particulate or unavailable form when nutrient limitation is severe; transportability of particulates is a major determinant of spiralling length. When nutrient limitation is moderated by density-dependent mechanisms, however, transport in the dissolved phase dominates, and transportability of particles has little influence on spiralling length. Functional processes of invertebrate grazing and filter feeding are most likely to shorten spiralling length when nutrient limitation is severe; shredding is more likely to shorten spiralling length when nutrient limitation is weak. -from Authors