Influences of Woody Debris on Flow Patterns and Channel Morphology in a Low Energy,Sand‐Bed Stream Reach

In lowland areas, such as the glacial landscapes of eastern Germany, sand‐bed streams are the most common stream type. They have low gradients and their hydrological regime is often subdued due to the frequent interruption by lakes. Very few is known about the influence of woody debris in these streams, since nearly all previous studies are from high‐gradient conditions, where streams have coarse bed sediments and harsh hydrological regimes. The research objectives of this study were first to assess the quasi‐natural quantity and quality of wood in a lowland sand‐bed stream and second to understand the influence of wood on the channel morphology and the flow patterns at base‐flow. The three‐dimensional stream bed relief was surveyed by electronic distance measurement. The position and the size of large woody debris was assessed by close‐up photography. An acoustic Doppler velocimeter was used to record the patterns of flow velocity and turbulence. Overlay and analysis of the spatial data was done using a Geographic Information System. The standing stock of wood was 1.9 m³ and 39 woody elements per 100 m² of stream bed. The flow pattern was clearly controlled by the wood. Woody elements elevated above the stream bed deflected flow and locally caused strong secondary current, high turbulence, and scour of the stream bed at baseflow. Wood resting directly on the stream bed, which contributed the majority of the wood inside the bank‐full channel, determined the roughness of the stream bed. Near‐bed flow patterns observed were isolated roughness flow and wake interference flow, which was registered inside the accumulations of wood. 68% of the stream bed had shear stress above critical. Hence, the secondary morphological structures of the sand‐bed were controlled at base‐flow by the flow which was determined by the woody debris distribution.     

Egg development and hatching success in alpine chironomids

1. Climate change affects both alpine freshwater ecosystems and their benthic communities, dominated by Chironomidae (Diptera). Previous studies assigned each chironomid species a narrow thermal niche and a correspondingly high sensitivity towards global warming. Nevertheless, to date no study has examined egg development although the potential effect of changing temperatures on this initial phase of life might be crucial to existence and/or survival in harsh environments.
2. Adaption towards low temperatures might result in the most efficient egg development (lowest degree‐day demand) at the species’ temperature optimum close to the freezing point, theoretically allowing for bivoltinism. Similar to the eggs of other benthic insects, chironomid eggs could be the most temperature resistant life stage, not limiting the species distribution and persistence with regard to climate change effects.
3. Here, we show the effect of water temperature on the egg development in five Diamesa (Diptera, Chironomidae) and five Orthocladiinae (Diptera, Chironomidae) species from a spring‐fed and a glacier‐fed alpine stream in the Stubai Alps (Austria). Laboratory breeding experiments were carried out at four different temperatures (2, 4, 8, and 12°C).
4. Hatching success of all tested species proved to be consistently high throughout all experimental treatments, suggesting a high plasticity against a wide range of rearing temperatures. With increasing temperatures, the development rates increased. The degree‐day demands, however, also increased, indicating a special physiological adaption of cold‐stenotherm chironomids towards low temperatures.
5. The knowledge presented herein regarding the temperature dependency of chironomid egg development was used to predict the potential date of hatching for each tested species in their natural environment, taking into account thermal profiles of their habitat and theoretically allowing for bivoltinism in cold‐streams. As this is only a first contribution towards the modelling of alpine chironomid life cycle dynamics under climate change scenarios, further experiments of this kind are urgently needed to determine the threshold temperatures for successful egg development, to include other abiotic parameters (e.g. photoperiod), and to expand the number of species.

     

Wood addition in the hatchery and river environments affects post‐release performance of overwintering brown trout

1. Habitat structural complexity affects the behaviour and physiology of individuals, and responses to the environment can be immediate or influence performance later in life through delayed effects.
2. Here, we investigated how structural enrichment, both pre‐release in the hatchery rearing environment and post‐release in the wild, influenced winter growth and site fidelity of brown trout stocked into side channels of a regulated river.
3. Experiencing structural enrichment in the rearing environment during 3 months in autumn had no pre‐release effect on growth, but a delayed positive effect after release during the subsequent winter. Moreover, trout recaptured in wood‐treated sections of the side channels had grown more than trout recaptured in control sections. Wood enrichment in the side channels also increased overwinter site fidelity.
4. These results show that adding structure during a relatively short period may alter growth trajectories, and adding wood to side channels is a cost‐effective method to enhance winter habitat carrying capacity for juvenile salmonids in regulated rivers.

     

A mutation in the pericentrin gene causes abnormal interneuron migration to the olfactory bulb in mice

Precise control of neuronal migration is essential for proper function of the brain. Taking a forward genetic screen, we isolated a mutant mouse with defects in interneuron migration. By genetic mapping, we identified a frame shift mutation in the pericentrin (Pcnt) gene. The Pcnt gene encodes a large centrosomal coiled-coil protein that has been implicated in schizophrenia. Recently, frame shift and premature termination mutations in the pericentrin (PCNT) gene were identified in individuals with Seckel syndrome and microcephalic osteodysplastic primordial dwarfism (MOPD II), both of which are characterized by greatly reduced body and brain sizes. The mouse Pcnt mutant shares features with the human syndromes in its overall growth retardation and reduced brain size. We found that dorsal lateral ganglionic eminence (dLGE)-derived olfactory bulb interneurons are severely affected and distributed abnormally in the rostral forebrain in the mutant. Furthermore, mutant interneurons exhibit abnormal migration behavior and RNA interference knockdown of Pcnt impairs cell migration along the rostal migratory stream (RMS) into the olfactory bulb. These findings indicate that pericentrin is required for proper migration of olfactory bulb interneurons and provide a developmental basis for association of pericentrin function with interneuron defects in human schizophrenia.     

Thrombospondin-1 binds to ApoER2 and VLDL receptor and functions in postnatal neuronal migration

Apolipoprotein E receptor 2 (ApoER2), very low-density lipoprotein receptor (VLDLR), and Dab1 are the main components of the Reelin signalling cascade. Reelin is the sole ligand defined so far in signalling through this pathway. Postnatal migration of neuronal precursors from the subventricular zone (SVZ) to the olfactory bulb (OB), however, depends on ApoER2 and Dab1, but functions independently of Reelin. Here, we show that thrombospondin-1 (THBS-1) is a novel physiological ligand for ApoER2 and VLDLR. THBS-1 is present in the SVZ and along the entire rostral migratory stream (RMS). It binds to ApoER2 and VLDLR and induces phosphorylation of Dab1. In contrast to Reelin, it does not induce Dab1 degradation or Akt phosphorylation, but stabilizes neuronal precursor chains derived from subventricular explants. Lack of THBS-1 results in anatomical abnormalities of the RMS and leads to a reduction of postnatal neuronal precursors entering the OB.     

Invertebrate drift along a longitudinal gradient in a Neotropical stream in Serra do Cipó National Park,Brazil

The diversity and composition of drift invertebrate assemblages were evaluated along a longitudinal gradient of an altitudinal stream in southeastern Brazil. The main goal of this study was to evaluate the influence of seasonality, stream order, and some abiotic factors on invertebrate drift and the use of drifting invertebrate assemblages to assess aquatic invertebrate diversity. Drift samples were collected over a 24 h period using nets (open area of 0.08 m²; mesh 0.250 mm), partially submerged (60%) in the water column. Taxonomic richness, Pielou evenness (J), Shannon–Wiener diversity (H), and total density of drift invertebrate assemblages were used in unpaired t-tests, Kruskal–Wallis and stepwise multiple regression analysis. The results showed a high taxonomic richness of aquatic invertebrates, with 91 taxa found. Chironomidae and Ephemeroptera represented together c. 80% of the total density of drift organisms. The drift approach allowed the collection of new and rare taxa, besides the knowledge of pupae stage of several chironomid genera. Significant differences in the taxonomic richness and diversity of drift invertebrate assemblages were found between the rainy and dry periods, indicating a significant influence of seasonality. An increase in water flow and electrical conductivity were associated with the increase in the taxonomic richness and diversity in the rainy period. No significant differences were found among the other abiotic variables among the stream orders.     

A comparison of natural and human determinants of phytoplankton communities in the Kentucky River basin,USA

Physical, chemical, and biological characteristics of the Kentucky River and its tributaries were assessed for one year to compare effects of seasonal, spatial, and human environmental factors on phytoplankton. Phytoplankton cell densities were highest in the fall and summer and lowest in the winter. Cell densities averaged 1162 (± 289 SE) cells m1^–1. Cell densities were positively correlated to water temperature and negatively correlated to dissolved oxygen concentration and to factors associated with high-flow conditions (such as, suspended sediment concentrations). Chrysophytes, diatoms, and blue-green algae dominated winter, spring, and summer assemblages, respectively. Ordination analyses (DCCA) indicated that variation in taxonomic composition of assemblages was associated with stream size as well as season.Spatial variation in phytoplankton assemblages and effects of humans was investigated by sampling 55 sites in low flow conditions during August. Phytoplankton density increased with stream size. Assemblages shifted in composition from those dominated by benthic diatoms upstream to downstream communities dominated by blue-green algae and small flagellates. Human impacts were assumed to cause higher algal densities in stream basins with high proportions of agricultural or urban land use than in basins with forested/mined land use. While density and composition of phytoplankton were positively correlated to agricultural land use, they were poorly correlated to nutrient concentrations. Phytoplankton diversity changed with water quality: decreasing with nutrient enrichment and increasing with conditions that probably changed species composition or inhibited algal growth. Human impacts on phytoplankton in running water ecosystems were as great or greater than effects by natural seasonal and spatial factors. Our results indicated that phytoplankton could be useful indicators of water quality and ecosystem integrity in large river systems.     

Effect of high external NaCl concentrations on ion transport within the shoot of Lupinus albus. I. Ions in xylem sap

Abstract. Xylem sap was collected from individual leaves of intact transpiring lupin plants exposed to increasing concentrations of NaCl by applying pneumatic pressure to the roots. Concentrations of Na⁺ and Cl⁻ in the xylem sap increased linearly with increases in the external NaCl concentration, averaging about 10% of the external concentration. Concentrations of K⁺ and NO₃⁻, the other major inorganic ions in the sap, were constant at about 2.5 and 1.5 mol m⁻³, respectively. There was no preferential direction of Na ⁺ or Cl⁻ to either young or old leaves: leaves of all ages received xylem sap having similar concentrations of Na⁺ and Cl⁻, and transpiration rates (per unit leaf area) were also similar for all leaves. Plants exposed to 120–160 mol m⁻³ NaCl rapidly developed injury of oldest leaves; when this occurred, the Na⁺ concentration in the leaflet midrib sap had increased to about 40 mol m⁻³ and the total solute concentration to 130 osmol m⁻³. This suggests that uptake of salts from the transpiration stream had fallen behind the rate of delivery to the leaf and that salts were building up in the apoplast.     

Microhabitat and morphometric variation of two Chaetophoracean (Chaetophorales, Chlorophyta) species in tropical streams of southeastern Brazil

Two populations of Chaetophora elegans (Roth) C. Agardh and two of Stigeoclonium helveticum Vischer were investigated for microhabitat characteristics and morphological variation in streams of São Paulo State, southeastern Brazil. Different patterns of microhabitat distribution were found between species investigated. Populations of C, elegans were distributed under relatively narrow microhabitat conditions (high irradiance, low depth, moderate to high current velocity, rocky substrata and lower values of niche width) and showing little morphometric variation (colony diameter, main axis cell size, and apical branch number), Stigeoclonium helveticum occurred under more diverse microhabitat conditions, revealed by lack of significant difference between sampling units with and without the alga and wider niche width, but also exhibited relatively narrow morphometric variation (plant length, main axis cell and ateral branch cell sizes). The narrow microhabitat conditions and smaller niche width of C. elegans can explain its low abundance (percentage cover) in streams from the area studied as well as in other regions of São Paulo State, In contrast, the wider variation of microhabitat conditions and the higher niche widths of S. helveticum suggest that this green alga is able to grow in a high number of stream ecosystems in the region investigated, ranging from undisturbed to highly disturbed habitats. Thus. the results suggest that S. helveticum is a generalist species.