bluuebunny/crossref_metadata_2025_split huggingface dataset:
A hydrogeography of unregulated streams in the United States and an examination of scale‐dependence in some hydrological descriptors
Authors: POFF N. 
Published: November 2003

1. Relatively undisturbed streams in continental U.S.A. were classified according to variation in ten ecologically relevant hydrological characteristics. Measures of flow variability and predictability for average conditions, as well as for low‐ and high‐flow extremes, were extracted from long‐term (15–58‐year) daily streamflow data for 806 streams.2. Two groups of sites were analysed: all 806 sites and a subset of 420 ‘best’ sites. For each group, cluster analysis identified ten distinctive stream types, seven permanent and three intermittent. The geographical clustering exhibited by the stream types indicated regional differences in climatic and geological features. A bootstrapping technique applied to the permanent stream classes showed the majority of them were statistically robust.3. The derived classification of U.S. streams based on ecologically relevant hydrological characteristics provides a comprehensive catalogue of small to mid‐size streams that, according to ecological theory, may differ in major aspects of their ecological organization. The classification provides a basis for hypothesis generation and affords an objective framework for matching streams for purposes of comparative ecological investigations.4. A subset of 118 streams from the ten classification groups was selected to determine whether certain hydrological variables often used by ecologists to make cross‐system comparisons are sensitive to the temporal coarseness of the hydrological time series used to derive the variables. The three hydrological variables considered were streamflow predictability, streamflow variability and flood timing.5. Streamflow predictability (using Colwell’s Index) was calculated at daily, weekly, monthly and seasonal time scales. Estimates of predictability showed either no change across time scales, a gradual and consistent increase across time scales, or a maximum value at the monthly time scale. Coefficient of variation of streamflow was calculated at daily, weekly, monthly, seasonal, and annual time steps. Daily values were always greatest for all streams. Some groups showed minimum variability at the monthly scale, others at the seasonal. Timing of daily peak flows could be detected with 50–90% accuracy across stream groups using coarser grain monthly and annual hydrographic data.6. Inferences about hydrological similarity among streams across broad geographical scales can be sensitive to choice of time scale used in the hydrological characterization.
The U.K. Acid Waters Monitoring Network: an assessment of chemistry data, 1988–93
Authors: JENKINS ALAN , BOORMAN DAVID , RENSHAW MIKE 
Published: November 2003

1. The current extent and distribution of acidified surface waters in the U.K. is assessed using data collected between 1988 and 1993 as part of the U.K. Acid Waters Monitoring Network (AWMN). The data have been collected against a background of constant S deposition across the U.K. throughout the monitoring period.2. Surface waters with mean pH < 5.0 occur in south‐west Scotland, south‐east Northern Ireland, the Lake District and south‐east England. In addition, sites with mean pH < 5.5 are found in central and north‐east Scotland, the Pennines and north Wales. These areas receive, and have historically received, high levels of S deposition and xSO4 is identified as the main contribution to non‐marine acid anion concentrations.3. Mean total oxidized nitrogen (TON) concentrations are > 10 μeq l–1 at ten of the twenty‐two sites which are found in areas broadly corresponding to areas of high N deposition. The mean contribution of TON to total non‐marine acid anion concentration is > 10% at sixteen sites and > 20% at six sites. Most sites, except for those with TON < 10 μeq l–1 and mainly located in north‐west Scotland and Northern Ireland, demonstrate strong seasonality in TON concentrations and during autumn and winter instantaneous contributions of TON to total non‐marine acid anions is up to 60%. This confirms the importance of N with respect to surface water acidification and strengthens the case for implementation of controls on future N emissions.4. The data period is currently too short for rigorous trend analysis given the monthly/quarterly sampling frequency in streams/lakes, respectively. Nevertheless, increased SO4 and xSO4 can be observed in the time series at sites in south‐west Scotland and north Wales despite constant deposition to these areas. Similar trends are evident in longer‐term more frequent data at two sites and may reflect hydrometeorological influences, especially the duration and intensity of hot and dry weather in summer which promotes mineralization of organic S.
Palaeolimnological evidence for recent chemical and biological changes in U.K. Acid Waters Monitoring Network sites
Authors: JUGGINS S. , FLOWER R.J. , BATTARBEE R.W. 
Published: November 2003

1. Palaeolimnological evidence is presented for the long‐term (post‐1850) and recent (post‐1970) trends in acidity of eleven sites in the U.K. Acid Waters Monitoring Network.2. Sites are located throughout the U.K. in areas sensitive to acidification, and results show that all have been acidified since pre‐industrial times. Although there is considerable variation in the timing and magnitude of these changes the results are consistent with other evidence of the widespread and severe acidification of sensitive U.K. freshwaters as a result of acidic deposition.3. The most severely acidified sites generally have the highest critical load exceedance, although there is a only a poor relationship between exceedance and post‐1850 pH change (r = 0.58, P = 0.06) or diatom floristic change (r = 0.52, P = 0.1). These results highlight the difficulty of inferring biological change or ‘damage’ in freshwater ecosystems from current national maps of critical load exceedances.4. Evidence of chemical and biological response to the post‐1970 reduction in U.K. S emissions is variable: seven lakes show continued acidification in the 1970s and early 1980s while four appear to have been in steady state. One afforested site shows continued acidification until at least 1990, the year of coring, suggesting that at this site increased scavenging of acid anions following canopy closure and/or increased nitrate leaching have offset the benefits of reduced S deposition.5. Five sites appear to have been in steady state since the early to mid‐1980s, and two show unambiguous evidence for a recent increase in pH and a reversal in the diatom assemblages to that of earlier levels. The results support and extend the findings of other studies and show that biological recovery is occurring in at least two chronically acidified areas of the U.K. (Galloway, SW Scotland, and north Wales), and that natural recovery can lead to the re‐establishment of biota previously present at the site.
Size‐dependent changes in phytoplankton C and N uptake in the dynamic mixed layer of Lake Biwa
Authors: FRENETTE JEAN‐JACQUES , VINCENT WARWICK , LEGENDRE LOUIS , NAGATA TOSHI 
Published: November 2003

1. Short‐term (days) hydrodynamic effects of wind‐induced mixing on phytoplankton size structure, and C and N uptake characteristics, were studied in the surface mixed layer (epilimnion) of Lake Biwa (North Basin), before and during a period of high winds (typhoons).2. The latter period was characterized by two major typhoon events associated with deepening of the seasonal thermocline, reduced water column stability, decreased underwater irradiance and increased dissolved reactive N and particulate P.3. Nutrient concentrations, seston C/N ratios, and uptake rates indicated that phytoplankton biomass and production were limited by P and not N throughout the study. Higher C‐ and N‐based productivity during the typhoon period than before reflected the increased phytoplankton biomass and higher specific uptake rates due to increased nutrient supply.4. Changes in the size‐structure of phytoplankton (< 2 and > 2 μm) were associated with variations in the stratification and mixing regime. When vertical stability was high (before the typhoons) concentrations of > 2 μm biomass (chlorophyll a, particulate organic C and N) were higher at the bottom of the mixed layer than at the surface whereas, when stability of the mixed layer was low (the typhoon period), the contribution of picoplankton (< 2 μm) to total Chl a increased at the surface and decreased at the bottom following the first high winds.5. Photoadaptive adjustments of the phytoplankton provided further evidence of hydrodynamic control. The lower intracellular Chl a concentrations and C and N uptake efficiencies in the < 2 μm fraction suggest that they experienced, on average, higher irradiance than the larger cells because of their lower sinking rates. During the stability period, picoplankton exhibited higher photosynthetic efficiencies at the bottom of the mixed layer than at the surface. Such differences disappeared during the typhoon period indicating that the mixing rate was then probably higher than the photoacclimation rate in the small size fraction.6. The present results stress the highly transient nature of biological homogeneity in the surface mixed layer of the lake.
Colonization dynamics of river benthos in response to local changes in bed characteristics
Authors: WILLIAMS D. , SMITH MARILYN 
Published: November 2003

1. The effects of small‐scale variation in the nature of a river bed upon the colonization dynamics of benthic invertebrates were explored through a series of microhabitat implants placed in a small river in southern Ontario. The implants presented variations in the levels of four microhabitat features: substrate particle size, current regime, added food and light. The sixteen possible combinations of these variables were replicated five times, for a total of eighty implants.2. After 14 days of exposure, some of the controlled variables had been modified and a number of other variables (sand, fine (FPOM) and coarse (CPOM) particulate organic matter) had been added by the river.3. Benthic diversity differed among the implants, with sand and CPOM accounting for 15.5% of the variation. Benthic density was more uniform and was weakly related only to added food. Application of the CANOCO program to the data set suggested that, in general, the environmental variables manipulated in this study were not the key factors influencing colonization, although they may have been important in non‐linear combination.4. A number of important positive associations were evident among colonizing species, some of which are thought to reflect those of predator and prey.5. Control of colonization appears to be through multiple factors (abiotic, biotic, autochthonous, allochthonous) that differ in nature according to species, and which underline the complexity of selection responses of individual taxa to local variations in bed structure. Researchers must acknowledge this multifactorial organization and dynamic nature if workable models of lotic community structure and development are to be forthcoming.
Comparison of leaf processing rates under different temperature regimes in three headwater streams
Authors: ROWE JACQUELYN , MEEGAN SEAN , ENGSTROM S. , PERRY SUE , PERRY WILLIAM 
Published: November 2003

1. We studied the effects of different temperature regimes on leaf litter processing in three forested Appalachian headwater streams of different pH (mean pH = 4.2, 6.5, 7.5).2. We compared leaf breakdown rates, microbial biomass and macroinvertebrate shredder density and biomass between two 12‐week processing periods (October–January and November–February) in each stream. Leaf processing rates were calculated both as k (day–1) and kd (degree day–1).3. There were no significant differences in processing rates (k day–1) between the two study periods for any leaf species in any stream. The average difference in temperature between the two study periods was 175 degree days. Shredder density was significantly higher during the earlier study period on 40% of the sample dates, but shredder biomass was not significantly different between the two study periods. ATP concentration was significantly higher during the early study period for 60% of the sample dates.4. More significant differences in these variables (shredder density and biomass, ATP concentration) were seen among the three study streams than between the two study periods. This indicates that in this study other factors, particularly stream pH, contributed more to processing rate variation than did differences in thermal regime.
Inland dispersal of adult aquatic insects
Authors: KOVATS ZSOLT , CIBOROWSKI JAN , CORKUM LYNDA 
Published: November 2003

1. Adult caddisflies (Trichoptera) and mayflies (Ephemeroptera) were light‐trapped on summer evenings along the Detroit River and Lake St. Clair, near Windsor, Ontario, Canada. Light traps were located at the shore and at increasing distances inland up to 5 km, and were operated simultaneously for 2 h following sunset. Catches of five species of caddisflies of the family Hydropsychidae (Cheumatopsychecampyla, Cheumatopsychespeciosa, Hydropsychehageni, Hydropsychephalerata, Macrostemumzebratum) and the mayfly Hexagenia (Ephemeridae) were used to examine inland distribution.2. Inland dispersal was limited: catches of caddisflies declined at a greater than exponential rate with increasing distance from shore. Mean dispersal distance from the shoreline ranged from 650 to 1845 m. Smaller caddisfly species dispersed shorter distances than larger caddisflies and Hexagenia.3. Inland distribution of adult caddisflies exhibited considerable interspecific variation: distribution was inconsistent among trials for Hexagenia, possibly owing to timing of collections in relation to periods of peak emergence.4. Sex ratios of caddisflies were female biased at most sites. No consistent bias was observed for Hexagenia. Different inland distribution patterns were observed for males and females. The differences appeared to reflect species‐specific reproductive strategies.
The effect of habitat‐specific sampling on biological assessment of water quality using a predictive model
Authors: PARSONS MELISSA , NORRIS RICHARD 
Published: November 2003

1. Detection of impairment in macroinvertebrate communities using rapid biological assessment depends on the ability to compare sites, with confidence that differences obtained result from water quality. However, collections from more than one habitat type may introduce variation that can potentially mask water quality differences among sites. Data were collected from the riffle, edge, pool‐rock and macrophyte habitats at reference (minimally disturbed) and test (disturbed) stream sites throughout the Australian Capital Territory. The effect of habitat‐specific sampling on predictive models for detecting impairment in macroinvertebrate communities was determined. Four models were used: riffle only, edge only, each habitat as an individual object, and all habitats sampled at a site considered as a composite sample.2. Macroinvertebrates from individual habitats generally clustered into separate groups because collections from the same habitat at different sites were more similar than collections from different habitats within a site. Thus, in the habitats as individual objects model, the taxa predicted to occur at a test site may be an indication of habitat type rather than water quality. The outputs of the composite habitats and riffle and edge models were similar. However, the variable number of habitats included at each site in the composite model may confound the detection of biological impairment because of unequal sampling effort. The riffle and edge models were the most robust because they were less confounded by inter‐habitat variation and were based on comparisons made between equivalent environmental units.3. Comparison of observed/expected taxa ratios for test sites showed that each model could detect biological impairment, indicating considerable data redundancy was introduced by sampling several habitats. In particular, the pool‐rock and macrophyte habitats contributed no information with regard to macroinvertebrate taxon occurrence or detection of biological impairment that could not be obtained from either the riffle or edge habitats within the study area.
Artificial mixing prevents nuisance blooms of the cyanobacterium Microcystis in Lake Nieuwe Meer, the Netherlands
Authors: VISSER PETRA , IBELINGS BAS , VAN DER VEER BART , KOEDOOD JAN , MUR R. 
Published: November 2003

1. Artificial mixing in the hypertrophic Lake Nieuwe Meer was successful in preventing blooms of the cyanobacterium Microcystis. During the 2 years of artificial, deep mixing the number of colonies of Microcystis per litre and also per m2 was lower than in the two preceding control years. Hardly any nuisance scums of Microcystis occurred in the lake.2. The phytoplankton shifted from a cyanobacteria‐dominated community in summer to a mixed community of flagellates, green algae and diatoms. Reduced sedimentation losses in the mixed lake, probably in combination with a lower pH, favoured non‐buoyant algae, while the entrainment of cyanobacteria in the turbulent flow nullified their advantage of buoyancy.3. The chlorophyll concentrations were much lower in the mixed lake, but the euphotic depth did not show clear differences between the years. The chlorophyll content integrated through depth (m–2) increased in the artificially mixed lake.4. The deep lake normally stratified in summer, but artificial mixing of the lake in 1993 resulted in a homogeneous temperature and oxygen distribution with depth. In spring 1994, the mixing was applied intermittently with a reduction of 75% of the energy costs, while the mixing was still sufficient to prevent stratification.5. Determination of the buoyancy state of the colonies on a sunny and calm day showed that the buoyancy loss was low close to the bubble plumes, and high at some distance from these plumes. This suggests that Microcystis could escape the mixing at some distance from the plumes, and could synthesize more carbohydrates during its stay in the upper illuminated layer of the lake than the deep mixed colonies close to the bubble plumes. Determination of the buoyancy state appeared to be a good and simple method to investigate the extent of entrainment of colonies in the turbulent flow.
Endemism and ecological islands: the ostracods from Jamaican bromeliads
Authors: LITTLE TOM , HEBERT PAUL 
Published: November 2003

1. The inhabitants of ecological islands, such as the phytolemata of bromeliad plants, provide an opportunity to examine the genetic patterns resulting from island radiations and draw inferences about modes of speciation.2. Allozyme electrophoresis, as well as mitochondrial DNA and morphological analyses, were employed to delimit species boundaries and assess the population genetic structure of the ostracods from bromeliads on the island of Jamaica.3. Nine species from the genus Elpidium were both sexually reproducing and endemic to the island. The other commonly encountered ostracod genus, Candonopsis, was represented by at least two sexually reproducing species.4. Most Elpidium species showed very restricted distributions, low heterozygosity, and marked gene pool fragmentation, suggesting that population bottlenecks have occurred frequently. Whether founder events played a causal role in the diversification of these ostracods remains uncertain, but bromeliad habitats seem to be a source of high biodiversity, and may represent an ideal setting for extensive allopatric speciation.
Spatial and temporal variation of microbial respiration rates in a blackwater stream
Authors: FUSS CAROLYN , SMOCK LEONARD 
Published: November 2003

1. The extent of spatial and temporal variation of microbial respiration was determined in a first‐order, sand‐bottomed, blackwater stream on the coastal plain of south‐eastern Virginia, U.S.A.2. Annual mean respiration rates (as g O2 m–3 h–1) differed significantly among substrata: leaf litter, 12.9; woody debris, 2.4; surface sediment, 0.8; hyporheic sediment, 0.4; water column, 0.003. Rates associated with wood were higher than those with leaves when expressed per unit surface area.3. Highest respiration rates on leaves, wood and in the water column occurred during the summer, whereas rates in the sediments were greatest during the late autumn and winter. Water temperature, as well as particulate organic matter and nitrogen content of the substrata, was correlated positively with respiration rates.4. A stepwise multiple regression showed that temperature and nitrogen content together explained 88% of the variation in respiration rates of leaves and wood. In contrast, particulate organic matter content and nitrogen content explained 89–90% of the variation in respiration in the sediments. Although water temperature was a significant factor in the sediment multiple regressions, its addition as an independent variable improved the regression models only slightly.5. Annual mean respiration in the stream channel, based on the proportional amount of respiration occurring associated with each type of substratum during each month, was 1.1 kg O2 m–2 yr–1. Seventy per cent of respiration in the stream occurred in the hyporheic zone, 8–13% occurred in the surface sediment, leaf litter or woody debris, and < 1% occurred in the water column. Approximately 16% of total detritus, or 40% of non‐woody detritus, stored in the stream during the year was lost to microbial respiration.
Temperature‐dependent growth and life cycle of Deleatidium (Ephemeroptera: Leptophlebiidae) in two high‐country streams in New Zealand
Authors: HURYN D. 
Published: November 2003

1. Measurements of larval growth rates were used to produce an empirical model for examining factors influencing patterns of size structure and emergence period for populations of the leptophlebiid mayfly Deleatidium (lillii group) in two high‐country streams (South Island, New Zealand). Growth rates were measured in situ by enclosing groups of larvae and natural stream substrata in growth chambers.2. Multiple regression analysis showed that temperature explained most variation among growth rates in both streams. Growth rates were also significantly related to larval size, although the effect was minor compared with temperature. A significant relationship between larval biomass per chamber and growth rate was shown at only one site.3. Growth models based on multiple regression equations (R2 = 0.70–0.84) simulated the extended emergence period and complex size structure observed for populations of Deleatidium in the field. Larvae hatching from eggs deposited before mid‐February (austral summer) probably emerge as adults before May (minimum cohort duration ≈ 3 months). Larvae hatching after mid‐February probably do not emerge as adults until the following summer because of low growth rates during winter (maximum cohort duration ≈ 11 months).4. On average, there are probably two generations of Deleatidium per year (bivoltine) at the study sites. The presence of numerous overlapping cohorts throughout summer, however, results in an extended emergence period and complex size structure.