Phosphorus Dynamics in a Woodland Stream Ecosystem: A Study of Nutrient Spiralling

Abstract

The term spiralling refers to the interdependent processes of cycling and downstream transport of nutrients in a stream ecosystem. To describe spiralling in Walker Branch, a first—order woodland stream in Tennessee, we released 32PO4 to the stream water and measured its uptake from the water and then followed its dynamics in coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), aufwuchs, grazers, shredders, collectors, net—spinning filter feeders, and predators over a 6—wk period. Rates of transfer among compartments and rates of downstream transport were estimated by fitting a partial differential equation model of the ecosystem to the data. With the resulting coefficients, the model was run to steady state to estimate standing stocks and fluxes of exchangeable phosphorus. Phosphorus moved downstream at an average velocity of 10.4 m/d, cycling once every 18.4 d. The average downstream distance associated with one cycle, defined as the spiralling length, was therefore 190 m (10.4 m/d ° d). Spiralling length, at steady state, is approximately the ratio of the total downstream flux of phosphorus per unit width of stream (720 mg°d—1°m—1) to the rate of P uptake from the water (3.90 mg°m—2.d—1). CPOM accounted for 60% of the uptake, FPOM for 35%, and aufwuchs for 5%. Turnover times of P in particulates ranged from 5.6 to 6.7, except for FPOM, which showed a second, slower turnover time of 99 d. Of the P uptake from water by particulates, 2.8% was transferred to consumers, while the remainder returned directly to the water. About 30% of the consumer uptake, in turn, was transferred to predators. The spiralling length was partitioned into: (1) an uptake length associated with transport in the water column (165 m), (2) a particulate turnover length associated with transport in FPOM and CPOM (25 m), and (3) a consumer turnover length associated with animal drift (0.05 m). FPOM transport accounted for 99% of the particulate turnover length. The small consumer turnover length reflected low consumer uptake of P from particulates and slow downstream drift velocity (0.013 m/d). In spite of the low rate of phosphorus uptake, the combined consumer—and—predator community accounted for 25% of the standing stock of exchangeable P in the stream. The retentiveness of this community is attributable both to the low drift rate and to a long turnover time (152 d) for P within the community.

The upside-down river: Reservoirs, algal blooms, and tributaries affect temporal and spatial patterns in nitrogen and phosphorus in the Klamath River, USA

“…Actively moving, or lotic, waters exhibit longitudinal gradients that influence aquatic ecosystem structure and function, and therefore also affect nutrient fate and transport (Vannote et al, 1980;Newbold et al, 1983). River impoundments alter longitudinal gradients by causing upstream-downstream shifts in physical, chemical, and biological processes (Ward and Stanford, 1983).…”

A round-trip ticket: the importance of release processes for in-stream nutrient spiraling

“…However, direct fluxes of in-stream R can be measured only by using solute additions of radioactive or stable-isotope tracers (Newbold et al 1983, Peterson et al 2001. These isotopic techniques can be difficult to apply, are expensive, and have low utility for studying the temporal dynamics of spiraling metrics because isotopic signals persist within the ecosystem for different lengths of time because of differences in turnover among ecosystem compartments (Newbold et al 1983, Dodds et al 2004). These methodological constraints limit our ability to develop a complete understanding of stream nutrient spiraling.…”

Nutrient Uptake and Mineralization during Leaf Decay in Streams – a Model Simulation

“…Investigations of nutrient dynamics in streams have almost exclusively focused on uptake processes, while quantitative information on mineralization has been limited to whole-stream tracer studies (e.g., NEWBOLD et al, 1983;PETERSON et al, 2001) or estimates of nutrient regeneration rates by animal excretion (e.g. WANNI, 2002;HOOD et al, 2005;MCINTYRE et al, 2008).…”