No abstract

We estimated deposition and resuspension rates of natural particulate organic matter (POM) in Bloomington Creek, Idaho, a mountain stream flowing at 225 L s Ϫ1 . POM was collected from the water column, fractionated into two size classes-very fine POM (VFPOM, 15-52 m) and fine POM (FPOM,, and radiolabeled by using 14 C-dimethylsulfate. The labeled particles in each size class and a conservative tracer were released to the stream in metered pulses and then sampled from the water column at six stations extending 1 km downstream for 4 d. Deposition and resuspension rates were estimated by fitting a one-dimensional advection-dispersion model to 14 C-concentrations measured during and after release. Model-estimated deposition velocities were 0.12 (0.09-0.16, 95% confidence interval) and 0.18 (0.10-0.31) mm s Ϫ1 for VFPOM and FPOM, respectively. There was some (ϳ0.05 mm s Ϫ1 ) additional short-term (ϳ20 min) detention of VFPOM and FPOM that may have been related to transient storage. For VFPOM, 34% of deposited particles resuspended after a mean residence time of 13 (6.9-25) h, and the remainder resuspended with a residence time of 7.5 (2.9-19) d. For FPOM, these estimates were 17%, 2.4 (1.0-4.9) h, and 2.6 (1.7-4.0) d, respectively. The weighted mean residence times and downstream velocities of particle migration were 5.1 d and 150 m d Ϫ1 for VFPOM, and 2.2 d and 230 m d Ϫ1 for FPOM. The migration velocities suggest that a significant fraction of particles exported from headwater streams travel long distances and can reach larger riverine or marine environments before mineralization.Headwater streams export typically more than half of the organic matter that they produce or receive from the landscape, and roughly half of this export is in the form of particulate organic matter (POM) (Golladay 1997;Webster and Meyer 1997). It has long been recognized that the exported organic matter can subsidize downstream ecosystems (Fisher and Likens 1973) and influence the structure of downstream consumer communities and food webs (Vannote et al. 1980; Minshall et al. 1983). Yet the strength of such upstream-todownstream linkages and the longitudinal scale over which they occur remain unclear. High rates of CO 2 evasion from large rivers suggest that a substantial fraction of transported 1 Corresponding author (newbold@stroudcenter.org).

Abstract. Net-spinning caddisfly larvae of the family Hydropsychidae are known to prefer microhabitats with large, stable substrate and high water flow velocity. It is often assumed that net spinners in high-velocity microhabitats have higher feeding or growth rates than larvae in less preferred sites, but there is no direct evidence to support this assumption. We hypothesized that net-spinning caddisflies would select microhabitats that offered the greatest feeding rates. This hypothesis was tested by field experiments in which we determined if net-spinning caddisfly larvae preferred high-velocity sites even when substrate size and type were held constant. We then measured feeding rates of net spinners in microhabitats with different flow characteristics. High-flow positions were selected by 96% of hydropsychid larvae colonizing artificial moss substrates. Artemia nauplii released into the water column were captured by individual larvae in high-flow sites at a rate of 0.016%/m, significantly higher than the capture rate in low-flow sites. Combining this rate of prey capture with mean hydropsychid densities of 1125 individuals/m 2 , we estimate that hydropsychid larvae in riffles remove drifting invertebrate prey at a rate of «18%/m. Assuming exponential prey removal, a prey item in the drift would travel an average of only 5.5 m before being consumed. This study is one of the first to show that the distribution of a stream filter feeder is related to the feeding rates obtainable in different microhabitats.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Wiley is collaborating with JSTOR to digitize, preserve and extend access to Ecology Abstract. Temporal partitioning has been found to be a predominant mode of ecological segregation among groups of systematically related stream insects. We extended this concept to a functionally similar but systematically diverse group of species. The life cycles and secondary production of six species of periphyton-grazing insects (scrapers) were studied in a fourth-order unshaded stream reach in the southern Appalachian Mountains.Total annual production (as ash-free dry mass) calculated with the instantaneous-growth rate method was 1195 mg/M2. The size-frequency estimate was 6.4% lower. Annual production (AFDM) by species ranged from 612 mg/M2 for Glossosoma nigrior to 10 mg/M2 for Goera fuscula. The production peaks of the six species occurred at separate points in the year, with very little overlap between species. Comparison with a neutral model indicated that production peaks were significantly more regularly spaced (P < . 1) than would be expected by chance alone. Temporal overlap between species was calculated using density, biomass, and production. Overlaps based on density and biomass were similar (means of .173 and .171, respectively). Mean overlap based on production was significantly lower (. 124).The patterns of temporal organization observed in this group of species were linked with specialized life histories. Five of the six species were univoltine, with periods of larval development (cohort production intervals [CPL]) ranging from 44 to 215 d. The shortest CP~s were associated with species that diapaused in the egg (Agapetus sp.) or larval (Neophylax consimilis) stages. Summer production was dominated by G. nigrior, which had a bivoltine life cycle. Production by the spring-summer cohort of G. nigrior was 4.5x the production of the winter cohort. Glossosoma's bivoltinism apparently provides it with the life history flexibility to utilize the high summer periphyton production permitted by the lack of canopy cover at the study site.Seasonal production by the six species was distributed 18% in winter (January-March), 36% in spring, 38% in summer, and 8% in autumn. The seasonal distribution of grazer secondary production correlates well with previously reported seasonal dynamics of periphyton production.

No abstract