Resource Spiralling: An Operational Paradigm for Analyzing Lotic Ecosystems

摘要

Spiralling is defined as the spatially dependent cycling of nutrients and the processing (i.e., oxidation, conditioning) of organic matter in lotic ecosystems. It provides a conceptual framework for describing the temporal and spatial dynamics of nutrients and organic carbon in streams and rivers. In addition, structural and functional aspects of stream populations and communities which enhance the retention and utilization (i.e., spiralling) of nutrients and carbon can be interpreted in terms of ecosystem productivity and stability. Spiralling length, defined for a nutrient as the distance required for one complete cycle or for carbon as the distance between its entry into the system and its oxidation, is an index of the utilization of these resources supplied from the surrounding watershed. Unlike processing efficiency, however, both spiralling length and turnover length are independent of the length of stream over which they are measured, and thus, they can be legitimately compared among streams and stream reaches of different size. We suggest that nutrient spiralling in most undisturbed streams is predominantly a biotic process, involving the sorption, retention, and turnover of nutrients by microbes associated with inorganic sediments and detritus on the stream bottom. By shortening the spiralling length, the productivity of lotic ecosystems can increase. The nutrient supply can be stabilized by storing nutrients, thereby damping variations resulting from temporal and spatial variations in lateral inputs. The concept provides a useful operational and analytical paradigm for dealing with the linkages between metabolic processes involved in resource retention, utilization, and turnover and between transport processes, both of which affect resource supply in stream ecosystems. (ERA citation 07:008580)