Prealpine River Research Articles

Development of a mechanistic model (ERIMO-I) for analyzing the temporal dynamics of the benthic community of an intermittent Mediterranean stream

To evaluate the role of the benthic community within headwater stream ecosystems, it is crucial to understand the mechanisms of the processes dominating their turnover rates and temporal dynamics. To analyze the benthic community dynamics of an intermittent Mediterranean stream (Fuirosos, Spain), we developed a mechanistic model that describes the most important ecosystem components (five functional feeding groups of invertebrates, periphyton, and benthic organic matter) under consideration of important transformation processes. The model is an extension of that developed for application to the prealpine River Sihl (Switzerland). A combination of prior knowledge from the literature and information from field observations within a Bayesian framework is used to constrain plausible ranges of the estimated model parameters and to evaluate the uncertainty of the model outcome. The Bayesian inference resulted in a realistic description of most of the main features of the system, offered insights into the degree of information the data contains about model parameters, and also made it possible to quantify the dependence structure of the parameter estimates. Local and global sensitivity analyses revealed that rate parameters for growth and death of invertebrate functional feeding groups are most influential on the model results and additional information on these parameters would be most helpful to reduce output uncertainty. The study clearly points out the importance of organic matter dynamics, as allochthonous organic matter is the main energy source in this Mediterranean headwater stream. Hydrological disturbances of the system such as droughts and floods lead to complex colonization patterns which would require additional data to support a more detailed description by an extended model. Furthermore, the study shows that it is possible to deal with a complex ecological model with eight state variables and more than 60 parameters in a Bayesian framework.

The importance of structural features for spawning habitat of nase Chondrostoma nasus (L.) and barbel Barbus barbus (L.) in a pre-Alpine river

This study develops univariate utilisation- and preference indices and analyses multivariate microhabitat use of spawning nase Chondrostoma nasus (L.) and barbel Barbus barbus (L.) in the Pielach River, a pre-Alpine tributary to the Danube, Austria. During the spawning season we daily surveyed species presence, number of individuals and habitat size. Habitat features, i.e. flow velocity, water depth, shading, cover, flow protection, type of structure, substrate and embeddedness were recorded at ten spawning grounds used by 1900 spawners within one spawning season. Spawning habitat features were compared with available habitat. Nase spawns in fast-flowing water (~1 m/s) that is significantly faster than available habitat. In contrast, barbel constructs redds that differ in water temperature, depth, velocity and cover structure from those of nase. Multivariate analyses (PCA) underlined the importance of shading and, as a consequence, the occurrence of vegetation along river banks for both fish species. This study demonstrates that efficient river restoration requires re-establishing riparian vegetation besides hydromorphological habitat improvements in order to provide adequate spawning grounds for nase and barbel.

Estimation of seepage rates in a losing stream by means of fiber-optic high-resolution vertical temperature profiling

Summary Vertical temperature profiling in the river beds of losing streams has been shown to be useful in obtaining seepage rates. We present a method for high-resolution vertical temperature profiling in surface-water sediments for detailed quantification of seepage flux over depth and time. The method is based on fiber-optic distributed temperature sensing, in which temperature profiles along an optical fiber are obtained by making use of Raman scattering. An optical fiber was wrapped around a 2 in. PVC tube and installed vertically within the streambed sediment. The wrapping transfers the spatial resolution along the fiber of 1 m to a vertical resolution of about 5 mm. The high-resolution temperature profiler was tested at a losing reach of the Swiss prealpine River Thur resulting in a 20-day long temperature time series with a temporal resolution of 10 min. The time series are analyzed by means of dynamic harmonic regression to obtain the diurnal contributions of the measured time series at all depths and time points. The time for the diurnal temperature signal to reach the observation depth and the associated attenuation of the signal are calculated from the phase angles and amplitudes of the diurnal contributions. The time shift results in an apparent celerity of diurnal temperature propagation, which is converted into an apparent seepage rate by fitting the data to the analytical solution for convective–conductive heat transfer in a semi-infinite, uniform, one-dimensional domain with a sinusoidal surface temperature. The high spatial resolution allows the location of discontinuities in the river bed which would have remained undetected if temperature had been measured only at a few individual depths to be identified. This is a particular strength of the fiber-optic high-resolution temperature profiler. The time series also give evidence of sporadic high infiltration rates at times of high water tables.

Immune deficiency causes annual late summer brown trout (Salmo trutta) mortality in Austrian prealpine river systems

For several years, severe brown trout (Salmo trutta) mortality has been observed in different prealpine river systems of Austria, Southern Germany, and Switzerland during late summer and early autumn. Often, the skin of the effected fish shows a medium to intense black pigmentation, and therefore this phenomenon is called “Schwarze Bachforelle Phanomen” or “proliferative darkening syndrom”. The present study was conducted to gain insight about its presence. From middle of May to end of August, brown trout and rainbow trout were kept in experimental tanks supplied with water from an effected river system. In brown trout, samples for blood diagnostics and histological investigations were taken after 0, 47, 62, and 77 days, and in rainbow trout after 0 and 107 days. Brown trout from a wild population were investigated for comparative purposes. Brown trout showed no abnormalities till the end of June. All fish sampled in the second half of July suffered from severe immune deficiency as the numbers of peripheral blood granulocytes and lymphocytes, plasma lysozyme activity, and plasma immunoglobulin levels significantly decreased. During August, the number of erythrocytes decreased and the osmotic fragility of the erythrocytes increased. Senescent erythrocytes became more frequent and the hematopoietic tissue of spleen and kidney enlarged. Also, the cellular composition of the spleen changed as the number of hemoblasts and normal erythroblasts decreased while the number of atypical erythroblasts increased. In the pronephros and hematopoietic tissue of the mesonephros, aggregation of macrophages and tissue disintegration was frequently observed. This was similar for brown trout from the field experiment and from the wild population. High mortality occurred in the end of July and during August. Death of the fishes might have been caused by secondary infections with microorganisms. Almost similar changes were observed in rainbow trout, however, the mortality was lower.

Response of benthic invertebrate assemblages to varying drought conditions in the Po river (NW Italy)

In the rivers of northern Italy, the presence of water is typically continuous all year long, although in the last five decades there has been a conspicuous increase in drought periods, mainly caused by human impacts and climate change. The aim of this study was to assess the impact of the length of the drought periods on macroinvertebrate assemblages. We collected invertebrates in four reaches of the Po river, characterised by different periods of absence of surface water. We found significant differences among the stations in invertebrate abundance and taxa richness, with a decrease in the more drought‐affected stream reaches. Collector‐gatherers significantly increased as the drought period lengthened, while the opposite occurred for scrapers and shredders. The areas with a discontinuous presence of water were mainly colonised by small, fast‐growing, plurivoltine organisms. A main result of our study is that only a few taxa appear to be able to survive in reaches with intermittent flow, underlining the great ecological difference between perennial and naturally intermittent streams. Our results suggest that the recent increase of droughts will likely cause an impoverishment of benthic communities in prealpine rivers.

Intensity of mineralization in the hyporheic zone of the prealpine river Bača (West Slovenia)

Respiratory electron transport system (ETS) activity and oxygen consumption in the interstitial water, and in the fine (i.e. silt) and coarse (sand) sediment fractions from the hyporheic zone of the prealpine river Baca (W Slovenia) have been measured in order to estimate the intensity of potential and actual carbon mineralization through microbial communities. Hyporheic samples from the river bed (RB) and gravel bars (GB) were compared. ETS activity and oxygen consumption of all fractions from the RB did not differ significantly from those from the GB. ETS activity and oxygen consumption of biofilm attached to 1 g of the silt were higher than of that attached to the same mass of the sand. A significant correlation between ETS activity and oxygen consumption indicated that the former should be a good indicator of intensity of bioactivity in hyporheic sediments. The ratio of ETS activity to oxygen consumption (ETS/R ratio) revealed that the oxygen consumption of microorganisms is responsible for approximately 60% of the metabolic potential in the hyporheic sediments. The contributions of different fractions of sediment to the total ETS activity differed between RB and GB. The contribution of microorganisms in the interstitial water and silt was higher in GB than in the RB, but the sand fraction contributed less to potential carbon loss in GB than in the RB. Average total respiratory carbon loss per volume through the hyporheic zone was higher in the RB than in GB. The main reasons suggested are the different intensity of exchange of surface water with the hyporheic zone, and the rate of consolidation of sediments, which is primarily a function of river hydrology and geomorphology.

Changes in summertime soil water patterns in complex terrain due to climatic change

Summary Climate change is expected to have a profound influence on soil moisture. According to that the present study aimed at the investigation of future soil water evolution by considering the relationship between soil moisture changes resulting from climate change projections, soil, and terrain characteristics, with special emphasis on slope and groundwater depth. The distributed hydrological model WaSiM-ETH was used to simulate root zone soil water content at a 1 km grid resolution in the 1700 km2 Thur river basin (NE Switzerland) during the 6-month period from April to September. The model was driven by baseline climate data from national data records for 1981–2000, or by scenario data for 2081–2100. The latter were based on grid point projections of two global climate models (CSIRO [B2] and HadCM3 [A2]). The datasets were completed with observations and simulations for the exceptionally warm and dry summer of 2003. The results suggested that a warmer climate with less summertime precipitation may significantly lower the seasonal mean soil water content in many parts of this basin, leading to frequent water stress conditions. Strongest effects occurred with HadCM3, and to a similar extent with 2003 weather data. The magnitude of soil moisture changes were related to land use, soil texture, and slope. In relative terms, reductions in soil water were largest for sloping soils with low water storage capacity, and also larger for forests than for cropland and grasslands. In absolute (volumetric) units, most pronounced reductions were indicated for flat areas with good water supply (mostly dominated by cropland). Here, the rooting zone was often connected to the groundwater, and capillary rise counteracted soil water depletion under current climate during the first half of the season, but was disconnected much earlier under climate change conditions. In steeper areas, groundwater had no influence and thus soil water content changed mainly in response to decreased precipitation and increased evapotranspiration. It is concluded that soil water contents generally decline in this pre-alpine river basin with climate change, but that the degree of soil water depletion varies with climate scenario, land use, soil texture, and topographic conditions. Thus, realistic soil water projections require reliable predictions of summertime climate, and the use of a full representation of biophysical processes that control evapotranspiration, including vertical and lateral subsurface water flows.

A classification of semi-natural northern prealpine river stretches based on chironomid communities

Using cluster analysis, ecological profiles of the species, and the (Diamesinae + Orthocladiinae) / Chironominae ratios, prealpine rivers were classified by their chironomid communities based on 338 species: (1) summer-cold mountain rivers (Isar, Salzach, Inn/Mühldorf), (2) summer-warm moraine-stretches (Würm, Alz/moraine rupture, Amper, Altmühl), (3) the summerwarm lowland river Upper Alz (lake outlet and the stretch to Altenmarkt village), (4) the lower section of the river Inn regulated by dams, which is dominated by a littoral community. The river Upper Alz is faunistically differentiated along it’s course. Classification of river stretches is predominantly explained by rhithral and eurytope species. Potamal and littoral species had no effect on classification. The results suggest that water temperature is the most important factor of the chironomid-based river classification, which is in harmony with studies by Rossaro (1992) and Lindegaard & Brodersen (1995). Locally, other morphological parameters as reach slope and substrate may be important factors as well. However, further data are needed to clarify their role in species distribution.

Response of the epibenthic and hyporheic invertebrates to stream drying in a prealpine river

Response of the epibenthic and hyporheic invertebrates to stream drying in a prealpine river

Exploring an aquifer system by integrating hydraulic, hydrogeologic and environmental tracer data in a three-dimensional hydrodynamic transport model

This article presents a numerical model of a part of an aquifer that is recharged by infiltration from the Swiss pre-Alpine river Töss in the Linsental (north-eastern Switzerland). The nearby city of Winterthur makes use of this aquifer as a resource of drinking water. The presented model is part of a larger interdisciplinary research program undertaken with the goal to evaluate the possible impacts of a planned revitalization of the severely canalized river Töss. Above all it should show the extent of decrease of the groundwater residence time if the river bed is allowed to move towards the drinking water wells. The flow model was constrained and calibrated by transport modelling of tritiogenic 3He. This tracer reflects both the aging of the water (by accumulation of 3He resulting from tritium-decay) as well as the two different components of the mixture (river water free of tritiogenic 3He due to degassing, and groundwater enriched in 3He due to accumulation). By simulating a Dirac-pulse-shaped input of a conservative tracer at different sources (river cells or upstream flux boundary cells) it is possible to determine the age distributions as well as the mixing ratios of the two types of water at the two pumping stations within the model area. The same calculations for a hypothetical river course passing directly beside the pumping stations indicate a decrease of the mean residence time of the pumped water together with an increase of the amount of the younger river water component.

Resistance and resilience of ecosystem metabolism in a flood‐prone river system

1. Gross primary production (GPP) and ecosystem respiration (ER) were analysed for 18 months in two reaches of the River Thur, a prealpine river in Switzerland. The upper reach at 655 m above sea level (a.s.l.) is bedrock constrained, has a high slope (0.60%) and a catchment area of 126 km2. The lower reach at 370 m a.s.l. has a more extensive hyporheic zone, a lower slope (0.17%) and a catchment of 1696 km2. 2. In both reaches, temporal patterns of stream metabolism reflected the occurrence of bed‐moving spates. Average reductions of GPP and ER by spates were 53 and 24% in the upper reach, and 37 and 14% in the lower reach, respectively. The greater resistance of ER than GPP in both reaches shifted the ecosystem metabolism towards heterotrophy (decrease of the ratio of GPP to ER (P/R)) following spates. 3. Recovery of GPP was significantly faster in the lower reach and exhibited distinct seasonal variation (positive correlation with incident light). The differences in stability (both resistance and resilience) between reaches reflected differences in geomorphic settings and disturbance regime. 4. Stepwise regression analysis was used to explore the potential influence of season, disturbance and prevailing environmental conditions on stream metabolism in each reach. Time since spate plus temperature explained 73 and 86% of variation in ER and GPP, respectively, in the upper reach and 55% of variation in ER in the lower reach. Season plus prevailing environmental conditions explained 67% of variation in GPP in the lower reach. 5. To test how the perception of stability may change with increasing scale of observation, the disturbance regimes of 12 sites were compared with the disturbance regime of the entire Thur catchment. The analysis suggests that stream metabolism at the catchment scale is far more resistant to high flow events than at the reach scale.

Ecosystem Metabolism, Disturbance, and Stability in a Prealpine Gravel Bed River

The extent of temporal variation in ecosystem metabolism was determined in a 6th-order, gravel-bottomed, prealpine river (mean discharge 4.6 m 3 /s), which is subject to disturbance by bed-moving spates. Daily integrals of gross primary production and ecosystem respiration were measured for 447 d between May 1992 and November 1994 based on single station diel oxygen curves. In 1993 gross primary production averaged 2.5 g O 2 m -2 d -1 and ecosystem respiration averaged 3.5 g O 2 m -2 d -1 (maximum daily rates observed in summer were 12.6 and 11.7 g O 2 m -2 d -1 ). During the investigation, 32 bed-moving spates (peak discharge >28 m 3 /s) occurred. Bed-moving spates distinctly depressed primary production and ecosystem respiration. Spates shifted ecosystem metabolism toward heterotrophy (decreased P/R) because gross primary production was more affected than ecosystem respiration. Recovery rates of gross...

A new device to extract sediment cages colonized by microfauna from coarse gravel river sediments

A device was developed in order to extract semi-natural substrata, exposed in the coarse sediments of a prealpine river, the Necker (Switzerland). Cylindrical wire cages filled with pre-sieved sediment were placed in a perforated stainless steel tube, that had previously been buried in the sediment. The chambers were extracted by pushing plexiglass tubes down to their bottom, thus sealing them at their lower ends. This enabled recovery of the porewater and sediment with a minimum of disturbance. We show examples of our results concerning flagellate and ciliate densities in cages from four sampling dates at the sediment surface (0-6cm) and from a deeper layer (28-34 cm). Cell densities ranged from 55 to 403 ciliates and 4400 to 67700 flagellates per ml pore volume. These abundances were markedly higher than in pore water extracted directly from the river bed.

Impacts of Embanking on the Soil-Vegetation Relationships in a Floodplain Ecosystem of a Pre-Alpine River

Impacts of Embanking on the Soil-Vegetation Relationships in a Floodplain Ecosystem of a Pre-Alpine River

Response of benthic invertebrates to natural versus experimental disturbance in a Swiss prealpine river

1. The crucial point of disturbance experiments in streams is the extent to which they can simulate a natural spate. Ideally, disturbance experiments should proceed side by side with a phenomenological study to allow a direct comparison. In the present study conducted in a prealpine Swiss river, the River Necker, fortuitous events made such a comparison possible.2. In summer 1994, we took Surber samples one day before and on several sampling dates after a major flood (recurrence interval ≈ 5 years), which was followed by a long period of uniform discharge in a river characterized by frequent spates. Beginning 19 days after this flood, patches of the stream bed (≈ 9 m2) were physically disturbed by kicking and raking.3. The degrees of reduction in the total number of individuals and the dominant taxa were similar after both types of disturbance, as were the recolonization patterns of Rhithrogena spp., Leuctra spp. and Hydracarina. Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Corynoneura/Thienemanniella spp. showed a distinct lag phase after the flood before recolonization began, whereas there was no such lag phase after the experiment. Therefore, the time needed to recover to pre‐flood densities was longer for these taxa. Nevertheless, recolonization rates and patterns after the lag phase were similar to those after the experimental disturbance.4. Size‐class measurements indicated that recruitment from egg hatching may have been more important after the flood than after the experimental disturbance for Rhithrogena spp., but not for Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Leuctra spp. Invertebrate drift was probably the most important pathway of recolonization after both types of disturbance.5. Our experiment allowed a realistic simulation of several important effects of the large flood on the invertebrate community. Smaller spates that induce substratum movement at a spatial scale similar to our experimental plots are much more common than large floods in the River Necker. For these spates, our experiment should provide an even more realistic simulation of natural disturbance.

Periphyton dynamics in a floodprone prealpine river: evaluation of significant processes by modelling

1. Periphyton chlorophyll a was measured at weekly or 2 weekly intervals from October 1992 to March 1994 at four sites in a Swiss prealpine gravel bed river that was frequently disturbed by unpredictable spates.2. To evaluate the dominant processes that control periphyton biomass, measured data were compared with a set of simulations from an empirical dynamic periphyton model. Different combinations of process hypotheses were systematically activated and deactivated in order to assess their importance.3. The simplest model leading to an acceptable agreement with measured data employs a biomass‐dependent growth rate, a detachment rate directly proportional to discharge and biomass, and a catastrophic loss rate during bed moving spates. Terms describing light or temperature dependence had a minor effect on the model fit.4. The model describes the temporal pattern of the periphyton biomass as a series of growth curves periodically truncated by spates. Within the uncertainties of the measurements, mainly caused by the spatial heterogeneity of periphyton, the biomass recovered along deterministic trajectories.5. Sensitivity analyses with respect to model parameters and model structure showed that site‐specific model parameters could not be unequivocally determined, and that the model yields similar results with slightly different formulations of processes. This indicates that the data base with respect to periphyton biomass was too small for a unique identification of model details but that the main conclusions on the significance of processes did not depend on arbitrary choices of the model formulation.

Ground Penetrating Radar for Assessing Sediment Structures in the Hyporheic Zone of a Prealpine River

Ground penetrating radar (GPR) was used to investigate the structure of the sediments in a floodprone gravel-bed river. Measurements were made on 2 gravel bars and in the adjacent channel. We buried a metallic object to calibrate depth and to visualize changes in GPR-profiles taken before and after digging. In addition, along 2 GPR-profiles the structure of the alluvial sediment of a gravel bar was visually verified by digging a trench down to the groundwater table. The GPR method enables one to distinguish sedimentary units of different texture with a vertical resolution of about 0.25 m. The investigation showed the depth of the alluvial valley fill, and it revealed geomorphological features such as lateral point bar accretion, fills of former pools, or open framework textures. These structures form a complex 3-dimensional mosaic of sediment patches. The GPR method also allowed us to document the changes resulting from bed-moving floods, such as in the formation of homogeneous gravel sheets during high magnitude floods. At some sites we observed intercalations of coarse organic matter between adjacent sedimentary units. Based on GPR data and the analysis of geomorphological structures near the study site, we developed a diagrammatic model of the sediments of this site in the lower Necker Valley.

Recolonization by benthic invertebrates after experimental disturbance in a Swiss prealpine river

1. Although the crucial point of disturbance experiments in streams is the extent to which they can simulate an actual spate, this aspect has been widely neglected in the design of such studies. Similarly, the influence of the specific hydrological disturbance regime of a stream on its benthic community has received much theoretical attention in recent years, but hypotheses have rarely been tested in the field.2. Our field experiment compared the structure of the benthic invertebrate community in the prealpine River Necker in north‐eastern Switzerland with predictions of the patch dynamics concept about the faunal composition of frequently disturbed streams. We also compared the resistance and resilience of the invertebrates between two sites in the River Necker. A similar substratum composition at both sites, but higher shear stress values both at baseflow and bankfull discharge at site 2, implied a higher disturbance frequency at the latter site. Five patches of stream bed of ≈ 9 m2 were disturbed by kicking and raking at each site, while five similar areas served as controls. From each plot, six Surber samples were taken: the first immediately after the disturbance, and the following five 1, 3, 6, 10 and 30 days later.3. Resilience of the total benthic invertebrate fauna was high. The total number of individuals recovered to undisturbed densities within 30 days at site 1 and 6 days at site 2. Taxon richness recovered within 3 days. In accordance with theory, taxa with high recolonization rates made up a major percentage of the total number of individuals, especially in disturbed plots. However, this percentage was lower at site 2 in spite of the higher disturbance frequency at this site. Rhithrogena spp., Leuctra spp. and the Simuliidae recovered faster to undisturbed densities at site 2. In contrast, absolute recolonization rates of these taxa were higher at site 1, where total invertebrate densities were more than twice as high as at site 2.4. Our results suggest that the time since the last disturbance should be considered as an important factor in studies of benthic invertebrate communities in prealpine rivers, because disturbances can alter the community structure. In frequently disturbed streams, very short sampling intervals may be needed to detect differences in taxon‐specific colonization rates. The specific hydrological disturbance regime of such streams is also important, because even within‐stream differences in the resilience of the benthic invertebrate community are possible.

POM-dynamics and community respiration in the sediments of a floodprone prealpine river (Necker, Switzerland)

In a prealpine river particulate organic matter (POM) and sediment community respiration within the uppermost 40 cm of the bed sediment were measured from April to July 1992. Tubes filled with sorted sediment (4-8 mm) were incubated for 6 weeks. Respiration rates were detected using a closed chamber system with internal water circulation. Total POM content decreased from 4.3 kg m -2 to 1.5 kg m -2 during a five week period of low flow and increased to 8.0 kg m -2 after several sediment-moving floods. These variations probably reflect the enhanced mobility of POM particles after such floods. Sediment community respiration showed a similar temporal pattern. It declined from 0.5 g to 0.3 g O 2 m -2 d -1 and reached 0.7 g O 2 m -2 d -1 at the end of the study.

Effects of spates on the benthic macroinvertebrate community of a prealpine river (First results)

Effects of spates on the benthic macroinvertebrate community of a prealpine river (First results)