Small Upland Stream Research Articles

An Examination of Stream Water Quality Data from Monitoring of Forest Harvesting in the Eastern Highlands of Victoria

A large data set measuring surface stream turbidity, dissolved oxygen levels, and water temperature was developed by sampling 32 rivers and streams with forested catchments at weekly intervals for between two and three years. This was in response to allegations of possible water quality impairment by forest harvesting (“logging”). Additionally, nine rivers or streams external to the forests were sampled to form a “reference set”; concern was expressed that the water quality of these may be impaired by upstream forest harvesting. An unlogged forested control catchment was selected from the data set and used as a comparator to help reduce seasonal variation. Division of the data into “logged forested catchments” and “unlogged forested catchments” allowed for us to test the null hypothesis. The null hypothesis was that there was no difference between the means of the logged and unlogged sets by a “Student’s t test of difference between means”. The null hypothesis was supported for the three parameters. There was no discernible deterioration in water quality associated with the presence of logging in the stream catchments. It was concluded that logging in this environment was not a determinant of water quality, and that the presence or absence of logging in these catchments did not affect the measured water quality. Spearman rank correlation analysis was unable to detect any statistically significant correlations between the water quality parameters, suggesting they are substantially independent measures of water quality. The monitoring showed that the small upland streams had generally good-to-excellent water quality. The water quality in these was generally better than the “reference set”—this probably reflected agriculture and cultivation in the proximity of their sampling points.

Late Glacial and Holocene evolution of the estuarine section of the Nida River

Based on the results of detailed geological-geomorphological studies, old maps from the past 200 years, and historical data, the paper is the first to present the structure of the valley floor in the estuary of the Nida River, an upland tributary of the Vistula, and discuss changes in the development and course of their channels. The aim of the study was to grasp the importance of local factors, both natural (palaeogeographical, lithological and tectonic) and anthropogenic, in the morphogenesis of this section, where a relatively small upland stream crossed in the medieval and modern periods by important overland and water routes of the Polish-Lithuanian Commonwealth flows into the Vistula River, which is ten times larger. The discussed section is not deltaic in character. The branching of the Nida into several simultaneously functioning outlet arms may have been caused by the blocking of outflow from the valley during floods and the drainage of the flood waters at the valley mouth in several directions, via channels both permanent and periodic. Changes in the numbers and locations of the Nida estuaries in recent centuries have both natural and anthropogenic causes. The interaction between the main stream and its many-times smaller tributary in the studied section has resulted in a complex mosaic of forms and cut-and-fills of both streams, but with the Vistula playing the dominant role. The cut-and-fills of the Vistula “enclose” the Nida alluvium inside its valley on the Winiary-Nowy Korczyn line, while the cut-and-fills of the Nida only occur in a very narrow strip under the edge of the terrace. The Nida followed abandoned channels of the Vistula on Holocene cut-and-fill IIA, flowing parallel to the Vistula for 9 km. The floor of the Nida Valley lacks Holocene mineral-organic and mineral sediments, characteristic of other upland tributaries from loess areas. The regulation of the Vistula in the mid-19th century and the Nida in the first half of the 20th century fixed the courses of the rivers, completely changing the sedi­mentation regime in the estuarine section of the Nida, where backflow and associated sedimentation of fine-grained deposits occurred.

Hydromorphological Inventory and Evaluation of the Upland Stream: Case Study of a Small Ungauged Catchment in Western Carpathians, Poland

The hydromorphological conditions of watercourses depend on numerous natural and anthropogenic factors such as buffer zones or human infrastructure near their banks. We hypothesised that, even in a small stream, there can be substantial differences in the hydromorphological forms associated with naturalness and human impact. The paper aims at the field inventory and evaluation of the hydromorphological conditions of a small upland stream in the conditions of contemporary human activity, against the background of meteorological and hydrological conditions. The study concerned a left-bank tributary of the Stradomka River located in the Wiśnicz Foothills (Western Carpathians). The analyses were conducted with the use of the Polish method, the Hydromorphological Index for Rivers (HIR), which conforms to the EU Water Framework Directive (WFD). The hydromorphological condition and quality of habitats were evaluated based on the Hydromorphological Diversity Score (HDS) and Habitat Modification Score (HMS). The study shows that the largest changes in stream hydomorphology and habitat conditions took place in the downstream, urbanised stream catchment area with an intensive development of construction and technical infrastructure. The hydromorphological condition of the examined stream sections was evaluated as good or poor. The best hydromorphological conditions were found in the section located in the semi-natural area, and the worst in the urbanised area. As our research shows, the strong influence of human activity, including weather extremes, and the risks and hydrological hazards of the hydromorphological conditions of the small, ungauged catchment, highlight the necessity to search for other research methods to support the decision-making cycle in the transformation of riverbeds and catchments.

An evaluation of a low-cost pole aerial photography (PAP) and structure from motion (SfM) approach for topographic surveying of small rivers

ABSTRACTTo better understand fluvial forms and processes, geomorphologists have a need for high-resolution fluvial topographic surveys. Continuous data collection approaches such as airborne laser scanning (ALS), terrestrial laser scanning (TLS), and structure from motion (SfM) photogrammetry provide methods to collect such data sets. Comparisons of SfM and laser-based approaches for topographic surveys have demonstrated site-specific benefits and drawbacks. Survey preference is largely dependent on specific project requirements, indicating a need for examples of best practice for different applications. This study demonstrates how pole aerial photography (PAP) provides specific advantages for SfM data collection when mapping the topography of small river corridors. Digital elevation models (DEMs) were created using three different surveying approaches for a 100-m reach of Coledale Beck, a small upland stream in Cumbria, United Kingdom. This included (a) imagery collected from a 5-m telescopic pole processed using SfM photogrammetry, (b) imagery collected using an unmanned aircraft system (UAS), also processed using SfM photogrammetry, and (c) point cloud data collected using a TLS. All three approaches produce DEMs of sufficient quality to enhance our understanding of fluvial forms and processes, with DEM/point cloud resolutions of 0.01 m for the close-range methods (TLS and PAP) and c. 0.02 m for the longer-range UAS method. Overall, TLS mean errors (0.123–0.135 m) are almost twice as large as the UAS and PAP (0.037–0.103 m) errors, and the standard deviation is approximately 25% higher. However, results vary significantly for different surface cover types (i.e. vegetated, exposed and submerged surfaces), with TLS outperforming the other approaches for exposed gravel surfaces. Data acquisition rates for the PAP approach are approximately half those of the two other methods (430 m2/hour versus 845 and 730 m2/hour for PAP, TLS, and UAS, respectively). When equipment costs and ease of use are taken into consideration, the PAP approach provides an effective way of collecting topographic data from small rivers.

An assessment of carcass counting surveys with increasing time lapse following a simulated fish kill on a small upland stream

AbstractA simulated fish kill was conducted on a small upland stream in Northern Ireland by planting out hatchery‐produced brown trout Salmo trutta L. carcasses of various size categories. Standard, post‐fish kill, assessment walkover surveys were conducted over time intervals to determine the number of carcasses visible. The sample variance between individual surveyors was generally low, with good agreement between the observed counts for the three, discrete, size fractions of fish up to 72 hr after the simulated fish kill. Despite low discharge rates, shallow water and good accessibility to the experimental stream, only 52% of the small category fish (<8 cm LF) were recorded 4 hr after the start of the simulated fish kill. Larger carcasses (>17 cm LF) were more visible, and >90% were detected 48 hr after the start of the simulated fish kill. After 96 hr, all size fractions of carcasses had reduced significantly, and the variability between replicate surveys increased markedly.

Biodiversity and rarity distributions of native freshwater fish in an agricultural landscape: the importance of β diversity between and within water‐body types

Abstract Farmland expansion is a growing threat to aquatic biodiversity. Identifying conservation priority areas in agricultural landscapes is a key issue in freshwater ecology and information on the spatial variability of aquatic biodiversity is vital for prioritization. This study examined patterns of farmland fish assemblages across various water‐body types in northern Japan to develop an effective management plan for freshwater fishes. Water bodies were classified into five types: small lowland streams, small upland streams, large rivers, man‐made ditches, and wetland ponds, and native fishes were collected from each type. The contribution of fish diversity between water‐body types (β2) to the regional fish diversity (γ) was investigated through additive diversity partitioning. Within each water‐body type, the contributions of between‐site diversity (β1) and within‐site diversity (α1) were also examined. The assemblage composition, species richness, and rarity were compared among the water‐body types. The assemblage composition differed significantly among most of the water‐body types, which indicated that the landscape classification was appropriate for representing spatial variations in fish diversity. Additive diversity partitioning revealed that the contributions of β1 and β2 to γ fish diversity were relatively high at 38.2% and 37.3%, respectively, followed by a 24.5% contribution of α1 diversity. This finding demonstrates that the best strategy for conserving regional farmland fish diversity is to preferentially select areas containing various water‐body types as a conservation unit. Among the water‐body types, ditches and streams exhibited the higher contribution ratio for β1 diversity, whereas the contribution of β1 diversity was lower in wetland ponds. The differences in the contribution of β1 diversity might be attributed to human‐induced factors, such as habitat fragmentation or shrinking. These results emphasize that further studies are needed to clarify the factors influencing the β1 diversity of farmland fish to develop better management strategies for each water‐body type. Copyright © 2015 John Wiley & Sons, Ltd.

A review of the Nearctic genus Prostoia (Ricker) (Plecoptera, Nemouridae), with the description of a new species and a surprising range extension for P. hallasi Kondratieff & Kirchner.

The Nearctic genus Prostoia (Plecoptera: Nemouridae) is reviewed. Prostoia ozarkensis sp. n. is described from the male and female adult stages mainly from the Interior Highland region encompassing portions of Arkansas, Missouri, and Oklahoma. Prostoia ozarkensis sp. n. appears most closely related to two species, one distributed broadly across the western Nearctic region, P. besametsa (Ricker), and one found widely throughout the central and eastern Nearctic regions, P. completa (Walker). A surprising range extension is noted for P. hallasi Kondratieff & Kirchner, a species once known only from the Great Dismal Swamp, from small upland streams in southern Illinois. Additional new state records are documented for P. besametsa, P. completa, P. hallasi and P. similis (Hagen). Taxonomic keys to Prostoia males and females are provided, and scanning electron micrographs of adult genitalia of all species are given.

Diel habitat use of two sympatric galaxiid fishes (Galaxias brevipinnis and G. postvectis) at two spatial scales in a small upland stream in Manawatu, New Zealand

Two native New Zealand galaxiid fishes [the kōaro (Galaxias brevipinnis) and the shortjaw kōkopu (Galaxias postvectis)] are declining throughout the country. More knowledge regarding aspects of their ecology is needed in order for conservation actions to be optimally designed. A 100-m reach of small upland stream in Manawatu, New Zealand was mapped to scale and inventoried for microhabitat variables. Flow velocity, depth, surface turbulence, substrate size and interstitial refuge space availability were measured in 0.25-m2 quadrats throughout the reach. Twenty-nine kōaro and 22 shortjaw kōkopu were PIT-tagged within the reach and monitored during the day (N = 26) and night (N = 15) in 2008 with a portable PIT monitoring system. Of these, 72 % of kōaro and 68 % of shortjaw kōkopu were detected at least once and 62 % of kōaro and 46 % of shortjaw kōkopu were detected five times or more within the study reach. During both the day and night kōaro used microhabitats that were faster-flowing, deeper, more turbulent, with larger substrate particles and more interstitial refuge spaces when compared with all microhabitats available in the reach. Shortjaw kōkopu used microhabitats with larger substrate particles and more interstitial refuge spaces when compared to all microhabitats available within the reach. During the day, shortjaw kōkopu were found in areas with larger substrates and higher surface turbulence than areas where they were found at night. Four mesohabitat types were identified in the study area using cluster analyses. Kōaro used the same flow channel-type habitats during the day and at night. Shortjaw kōkopu used flow channel and pool habitats during the day, and used pool habitats at night. These results suggest that biotic factors such as competition from shortjaw kōkopu may have been influencing kōaro habitat use patterns. In addition, these findings have implications for river managers attempting to implement conservation measures to protect these species because increasing anthropogenic impacts such as sedimentation and water abstraction can have negative impacts on instream habitat.

Habitat use of redfin bullies (Gobiomorphus huttoni) in a small upland stream in Manawatu, New Zealand

This study uses Passive Integrated Transponder (PIT) technology to describe the habitat use patterns of the small, benthic redfin bully (Gobiomorphus huttoni). A 100-m reach of small upland stream in Manawatu, New Zealand was mapped to scale and inventoried for microhabitat variables. Flow velocity, depth, surface turbulence, substrate size and interstitial refuge space availability were measured in 0.25-m2 quadrats throughout the reach. A total of 67 redfin bullies were PIT tagged within the reach and monitored during day and night surveys in 2008 with a portable PIT monitoring system. Of these, 72 % were detected at least once and 64 % were detected 5 times or more within the study reach. Univariate analyses showed that redfin bullies utilized microhabitats that had larger substrate particles and more interstitial refuge spaces compared with all microhabitats available in the reach. During the day, redfin bullies were found in areas with larger substrates than areas where they were found at night. No differences in microhabitat use were found regarding gender, body size or season. Multivariate analysis revealed four macrohabitat types and showed that redfin bullies used deeper, complex macrohabitats during the day, then spread out to occupy all available macrohabitats at night. These findings have implications for river managers trying to cope with increasing anthropogenic impacts such as sedimentation.

Physicochemical assessment of Unio crassus habitat quality in a small upland stream and implications for conservation

The abundance of Unio crassus (Philipsson 1788) has declined over the last decades. Despite the high conservation status of this species, knowledge on its ecological requirements is scarce. The objective of this study was to identify key habitat characteristics in areas with recent recruitment of U. crassus in a small upland stream. Furthermore, we investigated stretches where the species is presently absent. Sediment deposition, redox potential, flow velocity, water depth, nitrogen and phosphorus load were investigated. Fine sediment deposition was high with 19.4 kg m−2 month−1 at colonized and 13.3 kg m−2 month−1 at non-colonized stretches of the Sallingbach. At all study stretches, redox potentials in the interstitial zone varied around 300 mV which constitutes the boundary value between oxic and anoxic conditions. Results of chemical water analyses indicated high nitrogen loads. Nitrate nitrogen concentrations averaged between 4.1 and 6.5 mg NO3–N/l at all study stretches, significantly exceeding the currently proposed threshold value of 2.0 mg/l for functional U. crassus streams. The results in this study suggest that U. crassus is more tolerant to eutrophic habitat conditions than previously expected. Our findings show that currently considered physicochemical parameters and high fine sediment deposition cannot mechanistically explain the occurrence of U. crassus in the stream.

Thermal regimes in a large upland salmon river: a simple model to identify the influence of landscape controls and climate change on maximum temperatures

AbstractTemperature observations at 25 sites in the 2000 km2 Dee catchment in NE Scotland were used, in conjunction with geographic information system (GIS) analysis, to identify dominant landscape controls on mean monthly maximum stream temperatures. Maximum winter stream temperatures are mainly controlled by elevation, catchment area and hill shading, whereas the maximum temperatures in summer are driven by more complex interactions, which include the influence of riparian forest cover and distance to coast. Multiple linear regression was used to estimate the catchment‐wide distribution of mean weekly maximum stream temperatures for the hottest week of the 2‐year observation period. The results suggested the streams most sensitive to high temperatures are small upland streams at exposed locations without any forest cover and relatively far inland, while lowland streams with riparian forest cover at locations closer to the coast exhibit a moderated thermal regime. Under current conditions, all streams provide a suitable thermal habitat for both, Atlantic salmon and brown trout. Using two climate change scenarios assuming 2·5 and 4 °C air temperature increases, respectively, temperature‐sensitive zones of the stream network were identified, which could potentially have an adverse effect on the thermal habitat of Atlantic salmon and brown trout. Analysis showed that the extension of riparian forests into headwater streams has the potential to moderate changes in temperature under climate change. Copyright © 2010 John Wiley & Sons, Ltd.

Diel variation in chironomid (Diptera: Insecta) exuviae abundance and taxonomic richness in near-pristine upland streams of the Greater Blue Mountains World Heritage Area, South-Eastern Australia

We assessed diurnal variation of Chironomidae exuviae in two small upland streams in temperate Australia, during summer. Understanding the diel periodicity of exuviae can be an important consideration for biomonitoring purposes or to investigate adult emergence patterns. We collected 1,813 floating exuviae, comprising 54 taxa from four subfamilies, from flowing water using a drift net. Unlike many northern hemisphere temperate studies, we observed that peak exuviae abundance (7.3 exuviae per m³) and taxon richness (1.7 taxa per m³) occurred in the dusk and night hours, with the lowest numbers (0.9 exuviae per m³) and taxon richness (0.6 taxa per m³) recorded in the late morning to early afternoon. We suggest that this could be an adaptation to avoid stressful weather during the heat of summer days, or it could be to avoid visual predators. The numerically dominant taxa exhibited peak abundance in the dusk/night samples which indicates predominant crepuscular/nocturnal patterns of adult emergence. This pattern was consistent across both streams surveyed. Our taxon inventory rose steeply during the first 24-h occasion, then at a reduced rate during the second and third days of sampling. For flowing water collections of exuviae that utilise drift-netting, we suggest that sampling at all sites includes at least three 24-h cycles and avoids periods of heavy rainfall and increased stream flow.

Headwater Influences on Downstream Water Quality

We investigated the influence of riparian and whole watershed land use as a function of stream size on surface water chemistry and assessed regional variation in these relationships. Sixty-eight watersheds in four level III U.S. EPA ecoregions in eastern Kansas were selected as study sites. Riparian land cover and watershed land use were quantified for the entire watershed, and by Strahler order. Multiple regression analyses using riparian land cover classifications as independent variables explained among-site variation in water chemistry parameters, particularly total nitrogen (41%), nitrate (61%), and total phosphorus (63%) concentrations. Whole watershed land use explained slightly less variance, but riparian and whole watershed land use were so tightly correlated that it was difficult to separate their effects. Water chemistry parameters sampled in downstream reaches were most closely correlated with riparian land cover adjacent to the smallest (first-order) streams of watersheds or land use in the entire watershed, with riparian zones immediately upstream of sampling sites offering less explanatory power as stream size increased. Interestingly, headwater effects were evident even at times when these small streams were unlikely to be flowing. Relationships were similar among ecoregions, indicating that land use characteristics were most responsible for water quality variation among watersheds. These findings suggest that nonpoint pollution control strategies should consider the influence of small upland streams and protection of downstream riparian zones alone is not sufficient to protect water quality.

Indirect Effects of Forest Management on Riparian Zone Characteristics in the Adirondack Uplands of New York

Abstract Riparian zones are transitional areas between streams and adjacent terrestrial habitats, and they typically have vegetation communities distinct from both. To identify possible effects of forest management within a watershed on riparian plant community structure and riparian zone width,understory vegetation was sampled in three managed and three unmanaged (Forest Preserve) watersheds (250ߝ550 ha) in the Adirondack Park, New York, at three lateral distances (2, 7, and 12 m) from the stream (n = 6). Abundance of herbs was greater at Preserve sites, althoughrichness was not affected by land use. Abundance and richness both decreased with distance from the stream within each land use type, and this decrease was less steep at Forest Preserve sites. Abundance of saplings was greater under management, and saplings did not respond to distance fromthe channel. Binary discriminant analysis demonstrated differences in herb community composition between land uses, although this difference decreased with increasing proximity to the channel. Although none of the riparian areas in this study have been directly logged, this study shows thatindirect effects of management in a watershed (e.g., increased light and evapotranspiration) can alter the riparian herbaceous community, increase the density of saplings, and narrow the riparian zone of small upland streams. North. J. Appl. For. 23(4):273–279.

Potential ecological effects of water extraction in small, unregulated streams

River regulation can have various effects on the natural flow regime, however the most obvious and perhaps pronounced hydrological effect is the reduction of total water discharge. Whilst there has been an increasing number of studies investigating the impacts of river regulation on lowland rivers, few studies have specifically investigated the effects of water extractions on small upland streams. In this study, we experimentally examined the effects of short-term, summer water extractions from small, unregulated streams. Five 30 m reaches were experimentally manipulated to divert a proportion of the total stream flow, and another five 30 m reaches were designated as controls, in the Yea River catchment, Victoria, Australia. The percentage of total discharge diverted from each experimental reach varied through time and between creeks (28–97%), with discharge always significantly reduced compared to control locations. All sites were monitored for available habitat, biofilm, water quality and macroinvertebrate diversity and density, fortnightly during February and March 2004. Despite the range of total stream volumes being extracted, the manipulation altered important ecological components of these unregulated creeks, including changes in physical habitat features (reduced stream wetted area and maximum stream depth) and reduced dissolved oxygen concentrations. Biofilm parameters showed a slight increase in diverted reaches, but were not statistically different from the controls. There was no statistical difference in total density of macroinvertebrates or EPT taxa; however, the density of Austrocercella mariannae (Notonemouridae) was significantly reduced in diverted reaches. Macroinvertebrate family level diversity, and the family diversity of grazers and shredders was reduced in diverted reaches. This study demonstrates that there are likely to be significant ecological impacts of extracting water in unregulated creeks. Whilst this study has demonstrated the need to consider environmental water requirements in unregulated streams, further studies are required to inform the debate about the volume, timing and predicted ecological response with improved environmental water. Copyright © 2006 John Wiley & Sons, Ltd.

The impacts of road runoff on periphyton in a small upland stream during summer

Motorway runoff transports mineral and organic materials to aquatic ecosystems which may provoke changes in the latter's chemical, physical and biological characteristics. We measured the water quality of a road runoff discharge and its effect on the periphyton communities in a small upland stream. The study was carried out during a summer low flow period (June to September 1998). We did not record notable, or lasting, effects of road runoff on physical and chemical parameters. Similarly, road runoff discharges did not change the mass (biomass, chlorophyll a) or the functioning (net primary production, respiration) of periphyton. The development of this community was most sensitive to rainfall and river flow conditions. The absence of impact possibly results from the fact that our monitoring was not carried out at times of more extreme road runoff. In fact, traffic and pollution, brought to the stream, were quite low and discharge dilutions were generally high during the study period. Thus this study should be continued to determine effects when discharges have potentially a high impact on the receiving water quality.

Spatial variation in fine sediment transport in small upland streams: the effects of flow regulation and catchment geology

AbstractIn cobble‐ and gravel‐bed streams, fine sediments (<4 mm diameter) are an important component of the bed material that can move at a full range of flows, not just during floods and spates. It has been hypothesized that the constant movement of this fine material, as it passes over the coarse bed, is an important ecological disturbance to plants and animals. In this study, I measured baseflow sediment transport rates across a number of regulated and unregulated sites in an upland catchment comprising isolated regions of granite/sandstone and acid volcanics in southern Victoria, southeastern Australia, as a precursor to a study examining the effects of sediment on aquatic biota. Examined on three separate occasions, transport rates for fine sediments were up to 100 times greater in the granite/sandstone streams, but diversion weirs, which greatly reduced downstream sediment loads in the granite/sandstone areas, moderated these differences. Measured transport rates within unregulated sections of the granite/sandstone streams were roughly equivalent to sediment loads found to disturb benthic communities in other experimental studies. On this basis, abrasion by sediment transport in these streams may be sufficient to influence the structure of benthic communities even at baseflow. This hypothesis forms the basis of other research examining the biota at these sites. Copyright © 2004 John Wiley & Sons, Ltd.

Short term dynamics of diatoms in an upland stream and implications for monitoring eutrophication

A study designed to examine the effect of intermittent diffuse nutrient inputs on diatom assemblages in a small upland stream in northern England was confounded by other changes that occurred in the stream just before fertilisation started. A flora dominated by attached diatoms changed, over a period of about 3 weeks to one dominated by motile Nitzschia spp. In the absence of any likely human causes, the most likely reason for this change was undercutting of a meander upstream, releasing fine silts which favoured motile diatoms. Changes due to fertilisation by phosphorus were also recorded, with an increase in the proportion of Epithemia in samples, possibly favoured by the lower N:P ratio caused by the increased P concentration. The implication of these changes for monitoring eutrophication and ecological status in upland streams is discussed.

The independent and interactive effects of fine sediment and flow on benthic invertebrate communities characteristic of small upland streams

SUMMARY 1. Floods are an important mechanism of disturbance operating in streams that can markedly influence the abundance and diversity of benthic fauna. In upland streams many studies cite the scouring effects of fine transported sediments as a potential source of disturbance to the biota during spates, but few studies have sought to test this hypothesis critically.2. Here we used a series of eight artificial streams to test whether high suspended‐sediment concentrations influenced the short‐term response of benthic invertebrate fauna to increases in flow. In an experiment designed to simulate a small spate, flow and sediment loads were each manipulated to examine their independent and interactive effects. Benthic invertebrates were sampled before and after the manipulation, and drift samples were taken at regular intervals during the experiment. The experiment was repeated twice, once at the end of winter (June, 1998), and once in summer (February, 1999).3. Flow increases caused large increases in the number and diversity of drifting animals, and significant declines in the numbers and diversity of organisms found in benthic samples, but these declines were apparently not affected by the addition of fine sediment. The addition of sediment alone had little effect on the fauna. These results were consistent across both experiments.4. The results suggest that flow increases alone can disturb benthic fauna, and that neither substrate movement nor suspended sediment increases are necessary for floods and spates to disturb the benthic assemblage. However, as argued elsewhere, the effects of flow increases are likely to be contingent upon the presence or absence of local flow refugia, which can allow animals to escape the shear forces that would otherwise remove them from the surface or interstitial areas of the streambed.

A quantitative investigation into the temporal and spatial variations in the emergence of adult blackflies (Diptera: Simuliidae) from the Breitenbach, a small upland stream in Germany

As a contribution to the long-term emergence studies carried out as part of the “Breitenbach ecosystem project”, this paper presents the results obtained on emergence patterns and population dynamics of blackflies from 1984 to 1988. The Breitenbach is a small first order stream near Schlitz/Hesse, running into the Fulda river. Adult blackflies were caught in 4 greenhouse emergence traps, each spanning the whole width of the stream for a length of 6 m. A manual and then a partly automated method for collecting trapped insects was applied for three years and one year, respectively. Sixteen blackfly-species of different origin were found in the traps: a) autochthonous species: Prosimulium tomosvaryi, Simulium vernum s.l., S. cryophilum s.l., S. ornatum s.l. (common); S. costatum, S. trifasciatum, S. monticola, S. argyreatum (rare); b) species of doubtful origin: S. lundstromi, S. angustitarse, S. angustipes, S. aureum (very rare); c) allochthonous species: S. lineatum, S. equinum, S. erythrocephalum, S. noelleri. It was shown that the last 4 species had not emerged from the Breitenbach but had flown into the traps as adults. In addition, females of autochthonous species with blood or with mature eggs were trapped, which were also considered to have flown in. Besides revealing a limitation of the trap construction, they supported the detailed interpretation of some intricated patterns of appearance. Variations in emergence patterns and specimen numbers between years and traps were pronounced, but only in a few cases could they be attributed to changes in abiotic factors such as water temperature or discharge. P. tomosvaryi had the most simple and regular life cycle, with one well synchronised emergence peak annually from April to May (or even to June). No gradient of specimen numbers along the stream was evident. The two closely related species S. vernum and S. cryophilum had quite similar emergence patterns: There were two broad peaks per year, extending mainly from March to June and from July to October or November. In some cases the number and separation of consecutive generations was not clear. The abundance of both species clearly decreased downstream, more so for S. cryophilum than for S. vernum. In a trap closest to a tributary spring, S. cryophilum was the dominant species during three of the four years examined. The adults of S. ornatum displayed an intricate pattern of appearance, with very low specimen numbers in spring and medium to very high numbers in July/August and September/October. S. ornatum is the only blackfly species that inhabits both the Breitenbach and the adjacent section of the Fulda river. It was shown that females emerging from the Fulda river regularly invade the Breitenbach valley in greatly varying numbers and oviposit there. This leads to overlapping larval cohorts with corresponding emergence peaks. Although S. ornatum was the most abundant species in one year in the lower traps (60 to 80% of all individuals), it remains uncertain whether it is a long-term, permanent member of the autochthonous blackfly fauna of the Breitenbach. Estimates of total numbers of flown-in adults, actual emergence, dry weight biomass, the ecological separation of the species and their life cycle strategies are discussed.