Hierarchy, spatial configuration, and nutrient cycling in a desert stream

Abstract

Recent studies of nutrient cycling in Sycamore Creek in Arizona, USA, suggest that a thorough understanding requires a spatially explicit, hierarchical approach. Physical configuration determines the path that water follows as it moves downstream. Water follows flowpaths through surface stream components, the hyporheic zone beneath the surface stream, and the parafluvial (sand bar) zone. Characteristic biogeochemical processes in these subsystems alter nitrogen (N) species in transport, in part as a function of available concentrations of N species. At several hierarchical levels, substrate materials are an important determinant of nitrogen dynamics in desert streams. Sand is present in bars of variable size and shape, each of which can be considered a unit, interacting with the surface stream. Groups of these stream-sandbar units form a higher level, the reach. At the next higher scale, sandy reaches (runs) alternate with riffles. Where flowpaths converge, rates of N transformation are high and, as a result, change in concentration is a non-linear function of fiowpath length. Disturbance by flash floods alters sandbar configuration. Between floods, the interaction of subsurface and surface flowpaths shapes configuration in each, thus a self-organizing element of spatial structure exists. Sandy runs are dominated by subsurface processes and are likely to be net nitrifiers while riffles are dominated by surface flow and are nitrogen fixers. Whether a stream ecosystem retains nitrogen, or transports it to downstream recipient systems, or is a net emitter of gaseous forms of N, depends upon the dynamics of a spatial mosaic of interacting elements. An understanding of the net effect of this mosaic requires a spatially e.xplicit, hierarchical, multi-scale approach.

Spatial Distribution of Zooplankton Diversity across Temporary Pools in a Semiarid Intermittent River

“…During the wet season, the mechanical force of the water flow changes the physical habitat and modifies water chemical characteristics and nutrient dynamics [5,7], whereas during the dry season, discontinuation of flow and water volume reduction influence community structure and diversity by concentrating nutrients and affecting physical and chemical characteristics of the water [5,8]. Furthermore, during this phase, the water retention in semipermanent and temporary pools represents refugia for the maintenance of aquatic species [9].…”

Disruptions of stream sediment size and stability by lakes in mountain watersheds: potential effects on periphyton biomass

“…Flowpath divergence and convergence.-Improved descriptions of changes in ecological processes along hydrologic flow paths (e.g., Sobczak andFindlay 2002, Lewis et al 2007) have yielded a view of stream ecosystems as collections of individual flow paths (Fisher et al 1998a, Fisher et al 2004 [ Fig. 1], Lewis et al 2007).…”

Nitrogen retention in natural Mediterranean wetland-streams affected by agricultural runoff

“…On the other hand, NH + 4 -N is more sensitive than NO − 3 -N to slight changes of local conditions (chemical, physical and biological variables) (Hill, 1996;Butturini and Sabater, 1998;Gücker and Boëchat, 2004), which also change as flow discharge does (Fisher et al, 1998;Von Schiller et al, 2008). Furthermore, NH + 4 -N reacts abiotically via adsorption/desorption reactions, and displays processing lengths that reflect the nature of the sediments and the chemical environment (Triska et al, 1994).…”