bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of dissolved organic carbon quality on microbial decomposition and nitrification rates in stream sediments
Authors: Strauss Eric A. , Lamberti Gary A. 
Published: March 2003

1. Microbial decomposition of dissolved organic carbon (DOC) contributes to overall stream metabolism and can influence many processes in the nitrogen cycle, including nitrification. Little is known, however, about the relative decomposition rates of different DOC sources and their subsequent effect on nitrification.2. In this study, labile fraction and overall microbial decomposition of DOC were measured for leaf leachates from 18 temperate forest tree species. Between 61 and 82% (mean, 75%) of the DOC was metabolized in 24 days. Significant differences among leachates were found for labile fraction rates (P < 0.0001) but not for overall rates (P=0.088).3. Nitrification rates in stream sediments were determined after addition of 10 mg C L–1of each leachate. Nitrification rates ranged from below detection to 0.49 μg N mL  sediment–1 day–1and were significantly correlated with two independent measures of leachate DOC quality, overall microbial decomposition rate (r=–0.594,P=0.0093) and specific ultraviolet absorbance (r=0.469,P=0.0497). Both correlations suggest that nitrification rates were lower in the presence of higher quality carbon.4. Nitrification rates in sediments also were measured after additions of four leachates and glucose at three carbon concentrations (10, 30, and 50 mg C L–1). For all carbon sources, nitrification rates decreased as carbon concentration increased. Glucose and white pine leachate most strongly depressed nitrification. Glucose likely increased the metabolism of heterotrophic bacteria, which then out‐competed nitrifying bacteria for NH4+. White pine leachate probably increased heterotrophic metabolism and directly inhibited nitrification by allelopathy.
Persistence and stability of lotic invertebrate communities in New Zealand
Authors: SCARSBROOK M.R. 
Published: March 2003

1. Persistence and stability of lotic invertebrate communities were determined at an annual time scale over a 9‐year period (1990–98) at 26 river sites over the northern half of New Zealand. In addition, a number of water quality variables were measured monthly and flow information collected continuously over the same period at each site.2. The aim of the study was to describe the levels of interannual variability in invertebrate communities, and relate community changes to variability in environmental conditions. The consequences of this temporal variability for the sensitivity of predictive models were also investigated.3. Levels of change in environmental conditions varied significantly between years, but were relatively similar across sites. In contrast, community persistence (similarity between years in species assemblage composition), and stability (similarity between years with respect to relative abundance of species in the community) both varied significantly between sites, but changes between years were similar. Community stability was highest at sites with relatively harsh flow conditions (high coefficient of variation, high relative size of floods), and was also greater in communities dominated by Ephemeroptera.4. Relationships between change in environmental conditions and changes in community composition and structure were relatively weak for most individual sites. However, when average levels of change for each of the 26 sites were used, communities showed greater persistence under conditions where flow conditions remained relatively constant. Water quality changes had no significant effect on community persistence when assessed for all 26 sites combined.5. Results from this study suggest that lotic invertebrate communities fluctuate around a relatively stable state, at least over a 9‐year period. However, the extent of interannual variation in community composition and structure observed, along with the relatively low degree of cluster fidelity observed within a single region, suggests that predictive models based on reference site conditions extrapolated over several years should be applied with caution in New Zealand streams.
Catchment land‐use, macroinvertebrates and detritus processing in headwater streams: taxonomic richness versus function
Authors: HURYN ALEXANDER D. , BUTZ HURYN VIVIAN M. , ARBUCKLE CHRIS J. , TSOMIDES LEONIDAS 
Published: March 2003

1. We used a litter bag technique to assess the effect of catchment land‐use (forest, wetland, agriculture, urban) on the processing of red maple (Acer rubrum L.) litter in 17 streams in Maine, U.S.A. Litter processing by fungi was predicted to increase with nutrient concentrations along a gradient of land use, from relatively unmodified to highly modified. Litter processing by litter‐shredding macroinvertebrates was predicted to decline along this gradient because of a decline in their taxonomic richness and biomass.2. Land use was associated with the anticipated gradient in nutrient and macroinvertebrate attributes, and a significant relationship was found between land use and nitrate concentration. There was, however, no significant relationship between land use and soluble reactive phosphorus (SRP) concentration. Similarly, shredder taxonomic richness was significantly related to land use type, whereas shredder biomass showed no significant relationship to land use.3. Attributes of the shredder assemblage structure and nutrient concentrations were both strong determinants of litter processing. Increasing biomass and taxonomic richness of shredders was significantly related to increasing rates of litter mass loss. Increasing concentrations of nitrate and SRP were significantly related to increasing rates of litter softening below threshold concentrations (approximately 0.20 mg NO3‐N L–1 and 5 μg SRP L–1).4. The potentially additive effects of nitrate and SRP concentrations or shredder richness and biomass on litter processing rates were confounded by the lack of significant correlation between these pairs of variables. Consequently, rates of litter processing (as rates of softening or mass loss) did not vary systematically among different land use regimes.
Dispersal in drift‐prone macroinvertebrates: a case for density‐independence
Authors: HUMPHRIES S. 
Published: March 2003

1. Studies of dispersal of macroinvertebrates in streams and rivers tend to be focused on drift, whilst benthic movements are usually considered to be less important.2. Field‐enclosure experiments with the mayflyBaetis rhodaniindicate that net dispersal in this species is simply a proportional loss of individuals from the benthos.3. Neither net upstream or downstream movements exhibited evidence of density‐dependence in the form of curvilinear relationships between initial and final densities.4. The net number of animals moving upstream did not differ significantly from the net number moving downstream.5. The probable mechanisms behind density‐independent dispersal are discussed, as are the implications for our understanding of population dynamics in relation to invertebrate drift.
Correlations between nutrient concentrations and zooplankton populations in a mesotrophic reservoir
Authors: CONDE‐PORCUNA J. M. , RAMOS‐RODRÍGUEZ E. , PÉREZ‐MARTÍNEZ C. 
Published: March 2003

1. A year‐round study was conducted in a mesotrophic reservoir to determine the dynamics of zooplankton populations as a function of food availability (edible phytoplankton), nutrient concentration, temperature and hydraulic regime.2. Rotifer biomass was correlated with soluble reactive phosphorus (SRP) concentration. The abundance of the rotifers Keratella cochlearis and Anuraeopsis fissa were not correlated with food availability (measured by chlorophyll and cell counts) but showed a strong dependence on P availability. Another rotifer, Synchaeta oblonga, and crustacean species were not related to nutrient availability but seemed to be dependent on food concentrations, especially of some phytoplankton taxa.3. In this field study, rotifers seemed more susceptible than Daphnia or copepods to P‐limitation. Among rotifer species, Keratella seemed to be more susceptible than Anuraeopsis to P limitation. Different susceptibilities of zooplankton species to nutrient limitation may be important in explaining the dynamics of these organisms in natural situations. Further analyses are warranted to clarify the interactions between nutrient limitation and energy limitation among zooplankton.
Food web structure in riverine landscapes
Authors: WOODWARD GUY , HILDREW ALAN G. 
Published: March 2003

1. Most research on freshwater (and other) food webs has focused on apparently discrete communities, in well‐defined habitats at small spatial and temporal scales, whereas in reality food webs are embedded in complex landscapes, such as river corridors. Food web linkages across such landscapes may be crucial for ecological pattern and process, however. Here, we consider the importance of large scale influences upon lotic food webs across the three spatial dimensions and through time.2. We assess the roles of biotic factors (e.g. predation, competition) and physical habitat features (e.g. geology, land‐use, habitat fragmentation) in moulding food web structure at the landscape scale. As examples, external subsidies to lotic communities of nutrients, detritus and prey vary along the river corridor, and food web links are made and broken across the land–water interface with the rise and fall of the flood.3. We identify several avenues of potentially fruitful research, particularly the need to quantify energy flow and population dynamics. Stoichiometric analysis of changes in C : N : P nutrient ratios over large spatial gradients (e.g. from river source to mouth, in forested versus agricultural catchments), offers a novel method of uniting energy flow and population dynamics to provide a more holistic view of riverine food webs from a landscape perspective. Macroecological approaches can be used to examine large‐scale patterns in riverine food webs (e.g. trophic rank and species–area relationships). New multivariate statistical techniques can be used to examine community responses to environmental gradients and to assign traits to individual species (e.g. body‐size, functional feeding group), to unravel the organisation and trophic structure of riverine food webs.
Remote sensing of riverine landscapes
Authors: MERTES LEAL A. K. 
Published: March 2003

1. The fashion for examining riverine landscapes is changing as our technical instruments, from microprobes to satellites, expands to be able to examine the spatial and temporal relationships among biota, hydrology and geomorphology across scales from microhabitats to channel units to valleys to catchments.2. The range of successful applications from remote sensing analyses of riverine landscapes has especially increased with the launch of many new instruments that record data across the electromagnetic spectrum. Engineering of the instruments has also improved such that knowledge of the radiometric properties of the digital data is more complete as a result of better instrumentation and installation of on‐board calibrations systems for many instruments.3. With the development of faster processing on cheaper computers, it is now common for comprehensive data sets to be processed through algorithms that previously could only be applied to relatively small (<1 Mbyte) rasters of data. This technical advance is especially important for the statistical algorithms such as principal components and spectral mixture analysis that can decompose gradients in the spectral data. The combined effect is the production of regional views of riverine landscapes separated into components of water, vegetation and soil.4. The landscape properties of riverine landscapes that have been most successfully measured with remote sensing data include community and habitat level classification and connectivity of waterbodies with optical and radar data. Laser and radar altimetric data measured from aircraft provide land elevations at resolutions as fine as decimetres. A remaining challenge is to achieve an exact match between the categories of landscape classification from the remote sensing analysis and data from field surveys or model outputs.5. In contrast to many landscape properties, several water properties are now routinely measured as absolute values (water surface elevation, temperature, surface sediment concentration and algal concentration) with remote sensing. New analyses of both passive and active radar data in addition have led to measurements of inundation and wetness that are providing valuable insight into the dynamics of flooding and its effect on riverine landscapes.6. Finally, an effective examination of the variability in landscape cover includes additional analyses of remote sensing products using pattern metrics that measure the scale of patchiness and distribution of the landscape properties. These types of variability measures at the regional scale contribute to an increased understanding of the way in which spatial heterogeneity of riverine landscapes varies across scales and how landscape filters (sensu Poff, 1997) influence the evolution of these diversity patterns.
Re‐establishing and assessing ecological integrity in riverine landscapes
Authors: JUNGWIRTH M. , MUHAR S. , SCHMUTZ S. 
Published: March 2003

1. River–floodplain systems are among the most diverse and complex ecosystems. The lack of detailed information about functional relationships and processes at the landscape and catchment scale currently hampers assessment of their ecological status.2. Intensive use and alteration of riverine landscapes by humans have led to severe degradation of river–floodplain systems, especially in highly industrialised countries. Recent water‐related regulations and legislation focussing on high standards of ecological integrity back efforts to restore or rehabilitate these systems.3. Most restoration projects in the past have suffered from a range of deficits, which pertain to project design, the planning process, the integration of associated disciplines, scaling issues and monitoring.4. The so‐called `Leitbild' (i.e. a target vision) assumes a key role in river restoration and the assessment of ecological integrity in general. The development of such a Leitbild requires a multistep approach. Including explicitly the first step that defines the natural, type‐specific reference condition (i.e. a visionary as opposed to an operational Leitbild), has great practical advantages for restoration efforts, primarily because it provides an objective benchmark, as is required by the European Water Framework Directive and other legal documents.5. Clearly defined assessment criteria are crucial for evaluating ecological integrity, especially in the pre‐ and postrestoration monitoring phases. Criteria that reflect processes and functions should play a primary role in future assessments, so as to preserve and restore functional integrity as a fundamental component of ecological integrity.6. Case studies on the Kissimmee River (U.S.A.), the Rhine River (Netherlands and Germany), and the Drau River (Austria) are used to illustrate the fundamental principles underlying successful restoration projects of river–floodplain systems.
Colonisation of freshwater habitats by the European eel Anguilla anguilla
Authors: Ibbotson Anton , Smith Jim , Scarlett Peter , Aprhamian Miran 
Published: March 2003

SUMMARY1. The spatial distribution of European eels in 18 U.K. rivers was related to distance from tidal limit using a negative exponential model. This function accounted for between 19 and 90% of the variation in eel density where quantitative data was available. For semiquantitative data the negative exponential function was a significant predictor of eel densities in only six out of 10 cases, although all rivers showed a consistent decline in abundance with distance upstream from the tidal limit.2. The spatial distribution of different age groups of European eel in River Severn showed an initial rapid dispersion into freshwater followed by a much slower dispersion rate. Movement of the population upstream by a wave‐form migration process does not occur in this system. Instead colonisation of freshwaters can be seen as a two‐phase dispersion. Phase‐1 is a rapid dispersion upstream driven by density at the point source. Phase‐2 commences once the eels become yellow eels and is equivalent to random diffusion of particles.3. These processes have important implications for the penetration of freshwaters with reduced numbers of eel larvae arriving on the coast of Europe and North America. Eel abundance will decrease more in freshwaters in an upstream direction whilst it may remain stable or decrease to a lesser extent in estuaries. They are also able to explain the demography of eels migrating upstream over weirs and the observations of varying sex ratios within catchments. We conclude that a dispersion model dependent on age, temperature, difficulty of migration, habitat quality and density of eels should be an important part of freshwater eel management.
Short‐term and long‐term effects of zooplanktivorous fish removal in a shallow lake: a synthesis of 15 years of data from Lake Zwemlust
Authors: Van De Bund Wouter J. , Van Donk Ellen 
Published: March 2003

SUMMARY 1. Removal of zooplanktivorous fish (mainly bream) in 1987 from a shallow eutrophic lake in the Netherlands, Lake Zwemlust, resulted in a quick switch from a turbid state with cyanobacteria blooms to a clear state dominated by macrophytes.2. The clear state was not stable in the long term, however, because of high nutrient loadings.3. In 1999, another removal of zooplanktivorous fish (mainly rudd) had similar effects as in 1987, although macrophytes returned more slowly.4. In the years directly following both interventions there was a ‘transition period’ of very clear water with high densities of zooplanktonic grazers in the absence of macrophytes; low oxygen concentrations indicate that during those years primary production was low relative to heterotrophic activity.5. The transition period appears to provide the light climate necessary for the return of macrophytes.6. Reduction of nutrient loading is necessary to improve water quality in Lake Zwemlust in the long term. In the short term, repeated fish stock reduction is a reasonable management strategy to keep Lake Zwemlust clear.
Differences in the exploitation of bream in three shallow lake systems and their relation to water quality
Authors: Lammens E. H. R. R. , Van Nes E. H. , Mooij W. M. 
Published: March 2003

SUMMARY 1. The development of bream populations, water transparency, chlorophyll‐a concentration, extent of submerged vegetation and densities of the zebra mussel, Dreissena polymorpha, were analysed in three shallow eutrophic lake systems subject to different fish management.2. In Lake Veluwemeer, the bream population was reduced from c. 100 to 20 kg ha−1 after 5 years of fishing. The mortality caused by the fishery was estimated at 38% of bream >15 cm in addition to a 13% natural mortality of bream >17 cm. The decline was followed by an expansion of the Chara beds present in the shallow parts, an increase in water transparency in the open‐water zone, an increase in the density of zebra mussels and a decrease in chlorophyll‐a concentrations.3. The newly created Lake Volkerak showed trends opposite to those in Lake Veluwemeer. Bream colonised the lake in 1988 and reached a biomass of c. 140 kg ha−1 in 1998. The water transparency decreased from a maximum of 3 m to c. 1 m and the chlorophyll‐a concentration increased from 5 to 45 μg L−1. Submerged vegetation colonised up to 20% of the total lake area in the first 5 years after creation of the lake in 1987 but decreased to 10% as turbidity increased.4. Seine fishery in the Frisian lake system did not appear to affect the bream population despite annual catches as high as 40–50 kg ha−1. The estimated natural mortality of fish >15 cm was 15% and mortality by fishery was 26%. The high loss was apparently compensated by good recruitment and high growth rates resulting from a c. 1 °C higher water temperature during the years when bream were removed by fishing. There was only a slight decrease in chlorophyll‐a concentrations and a slight increase in water transparency.5. The results of this study suggest that the effects of bream exploitation in eutrophic lakes can vary depending on the efficiency of the fishery, recruitment success and temperature regime. In the absence of fishery, bream dominated the fish community in the study lakes and apparently prevented D. polymorpha and submerged vegetation from establishing because of physical disturbance, enhanced internal P‐loading and resettling of resuspended sediments.
Phytoplankton–zooplankton seasonal timing and the ‘clear‐water phase’ in some English lakes
Authors: Talling J. F. 
Published: March 2003

SUMMARY 1. An examination is made of the relative seasonal timing of the postwinter increase of phytoplankton and zooplankton populations in four English lake basins. It centres upon weekly sampling over 20 years and rough counts of larger Crustacea, as copepods and cladocerans, from filtered samples that were used for chlorophyll a (Chl) estimation.2. Typically, a spring maximum of phytoplankton, dominated by diatoms and earlier in the shallower lakes, is accompanied or followed by a maximum of copepods and then one of cladocerans dominated by the Daphnia hyalina–galeata complex. Regarding timing, the maximum of copepods has no apparent relation with phytoplankton abundance (Chl). The maximum of cladocerans appears to be largely independent of variation in the phytoplankton maximum, but is generally associated with a minimum in Chl. Evidence for some direct causality in this inverse correlation after the spring phytoplankton maximum is best displayed by the shallow Esthwaite Water in which the peaks of Chl and cladocerans are separated further than in the deep Windermere basins where phytoplankton growth is delayed. In Esthwaite Water, and possibly often in Windermere, a principal minimum in Chl is ascribable to grazing by Daphnia.3. The typical inverse relationship of Chl and cladocerans is lost in some years when relatively inedible large phytoplankters (e.g. colonial chrysomonads, filamentous cyanophytes) are abundant and Chl minima are less pronounced, although maxima of cladocerans still occur. Conversely, available edible phytoplankters include various small forms grouped as μ‐algae and Cryptomonas spp.; their probable depletions by Daphnia appear to be sequential and may limit the latter's maxima, whose inception is temperature‐dependent.4. The spring–summer maxima of cladocerans and minima of Chl are generally coincident with a main seasonal maximum of Secchi disc transparency and light penetration – to which removal of non‐phytoplankton particles by filtering cladocerans may contribute.