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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. This content downloaded from 141.210.2.78 on Mon, Abstract. Laboratory-determined larval growth rates of the detritivore (collector-gatherer) Paratendipes albimanus (Chironomidae) responded proportionally to the microbial densities of 4 food sources. Substrates with higher microbial activities and biomasses produced greater growth rates in the order: pignut hickory (Carya glabra) leaves > white oak (Quercus alba) > insect feces > natural stream detritus. Laboratory growth rates of P. albimanus were linearly related to quantitative estimates of food quality based on substrate adenosine triphosphate (ATP) and respiration rates but were not statistically related to total N or C. Although P. albimanus is univoltine in Augusta Creek, Michigan, an experimental laboratory population of first-instar larvae completed a 2nd generation during the summer when fed detritus generated from hickory leaves. A second experimental population failed to develop past the first instar when fed natural detritus. The natural growth pattern of P. albimanus involves the interaction of temperature and food quality.

1. Species-discharge relationships (SDR) are aquatic analogues of species-area relationships, and are increasingly used in both basic research and conservation planning. SDR studies are often limited, however, by two shortcomings. First, they do not determine whether reported SDRs, which normally use complete drainage basins as sampling units, are scale dependent. Second, they do not account for the effects of habitat diversity within or among samples. 2. We addressed both problems by using discrete fish zones as sampling units in a SDR analysis. To do so, we first tested for longitudinal zonation in three rivers in the southeastern U.S.A. In each river, we detected successive 'lower', 'middle', and 'upper' fish zones, which were characterized by distinct fish assemblages with predictable habitat requirements. Because our analyses combined fish data from multiple sources, we also used rarefaction and Monte Carlo simulation to ensure that our zonation results were robust to spurious sampling effects. 3. Next, we estimated the average discharge within each zone, and plotted these estimates against the respective species richness within each zone (log 10 data). This revealed a significant, linear SDR (r 2 = 0.83; P < 0.01). Notably, this zonal SDR fit the empirical data better than a comparable SDR that did not discriminate among longitudinal zones. We therefore conclude that the southeastern fish SDR is scale dependent, and that accounting for within-basin habitat diversity is an important step in explaining the high diversity of southeastern fishes. 4. We then discuss how our zonal SDR can be used to improve conservation planning. Specifically, we show how the slope of the SDR can be used to forecast potential extinction rates, and how the zonal data can be used to identify species of greatest concern.

A comparison between stream community processing rates of naturally entrained leaf litter and leaves in packs or 1‐mm‐mesh bags demonstrated that packs served as a suitable analogue of processing in exposed sites (riffles) whereas bags did not. In riffles, leaves in bags were processed at rates characteristic of litter in depositional zones (pools and alcoves). A length‐weight regression method for evaluating the range of microhabitat‐related processing rates in stream communities appears suitable. Leaf litter nitrogen levels and increased processing rates by shredders reflected microbial conditioning. Shredders responded to high quality bass‐wood (Tilia americana) leaves by increasing their density rather than growth per individual.

The detritus standing crop, microbial respiration, and macroinvertebrate biomass were examined in monthly samples from the riffle sections of a first-order woodland stream. Total detritus was remarkably constant; the average (with 95% cL) ash-free dry mass standing crop was 426.4 ± 85.9 glm 2 over the 14 mo of the study. Throughout the year benthic detritus was dominated by fine particulate detritus ( < 1 mm), which made up 68.9% of the total ash-free dry mass. Woody debris made up 8%, whole leaves 3.5%, and leaffragments and other coarse particulate detritus accounted for 19.7% ofthe total standing crop. Decreases in standing crop were attributable to microbial respiration, macroinvertebrate assimilation, and downstream export. Microbial respiration annually removed 150% of the average standing crop, with the major effect on the smallest particle size category. Macroinvertebrate assimilation, defined as the sum of respiration and growth, removed 11.6% of the detritus standing crop annually. Shredders accounted for 20% of total animal assimilation, with the remaining 80% attributable to collectors and grazers. Based on monthly changes, it appears that total detritus standing crop is the result of the past discharge regime, which determines the overall amount of detritus present, and the rate of biological (microbial and invertebrate) processes, which determine the size and quality ofthe detritus particles. This suggests that detritus in streams, while strongly affected by both biotic and abiotic factors, may be in equilibrium within physical and biological constraints such that an annual steady-state system exists, similar to that for soil systems.

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.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract.Annual flooding in low-gradient rivers is recognized as an important subsidy between the river and its broad adjoining floodplains. Unfortunately, relatively few lowgradient rivers are unregulated and retain their natural "flood pulse" behavior in most developed regions of the world. Furthermore, attempts to quantify flood inundation dynamics of any river floodplain are scarce. We used aerial photography to delineate the degree of floodplain inundation and GIS to quantify flooded areas on the forested floodplain of a 6.3-km reach of the Ogeechee River, an unregulated sixth-order river in the southeastern USA. A regression was used to quantify the relationship between discharge and percentage floodplain inundation. Using 58 years of daily discharge data obtained from a U.S. Geological Survey gaging station, we converted daily discharge into daily percentage inundation and produced an inundation-duration curve, which describes the percentage of time that a particular inundation level is exceeded. This showed, for example, that >50% of the floodplain was inundated 15% of the time (54 d/yr) and that 100% was inundated 3.6% of the time (13 d/yr) for the average year. At 50% inundation, system width exceeded channel width by 19 times. In a relatively wet year, we showed that 50-100% of the floodplain was inundated for several months during the winter-spring. Even in a relatively dry year, >20% of the floodplain (seven times the river width) was inundated for several months. The longterm pattern over a period of 58 years showed considerable fluctuation in inundation and recession occurring throughout most years, with the highest peaks found during winter and spring. The floodplain failed to reach 50% inundation in only four of 58 years. However, in six years, >50% of the floodplain was inundated for at least 30% of the time (i.e., four months of the year). Floods of 50% inundation typically had a duration of at least 30 d. Thus, although inundation may fluctuate considerably within a year, much of the floodplain can be inundated for a relatively long duration. Description of such longterm patterns is essential for understanding natural hydrodynamics of unregulated rivers, particularly as attempts are made to restore previously altered systems. The flood pulse for this forested floodplain river is less predictable and floods are of shorter duration than the large tropical rivers for which the flood pulse concept was originally conceived. Unlike tropical rivers where seasonal patterns of flooding are driven by precipitation, flooding in the Ogeechee River is primarily co...

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The potential contribution of woody debris to fine particulate organic matter pools (0.45 μm ≤ FROM < 1 mm) was investigated in a coniferous forest stream ecosystem in western Oregon. The amount of wetted surface area of both large (>10 cm) and fine woody debris (1–10 cm) was 0.018 and 0.069 m2∙m−2 stream bed, respectively, during summer base flow. These values increase to 0.062 and 0.195 m2∙m−2 stream bed during winter flows. Studies of vertical distribution indicated that most fine wood is concentrated within 0.3 m of the stream bottom, while large wood is more evenly distributed up to 0.7 m. Lignin concentrations of large wood, soil, and FROM were very similar. Examination of FPOM samples with scanning electron microscopy revealed an abundance of wood-derived particles. Erosion rates of wood surfaces ranged between 0.5 and 11 mm∙yr−1 depending on decay state of the log. Using conservative estimates of processing rates, woody debris could be a source for approximately 90 g∙m−2∙yr−1 of FPOM, but with slightly a less conservative estimate, wood processing could easily generate several times the FPOM that is contributed by leaf and needle litter.