Contrasting Flow Regimes Research Articles

Macroinvertebrate assemblages downstream of dams show no sign of impairment despite flow regulation and thermal alteration

Flow regulation by dams produced downstream effects, including geomorphological, hydrological and thermal alterations. We aimed to analyse the alterations of the thermal regime caused by hypolimnetic releases of regulated flow compared to the unregulated thermal regime, and the effects of both thermal and flow regime alterations on macroinvertebrate communities. Stream temperature was monitored over three-years in three rivers with contrasting flow regimes, all located in the Mediterranean ecoregion. Results show that regulated rivers present an inverted flow regime with high discharges in summer, colder water from February to September arising maximum differences of 7.4 °C in July and presenting a delayed thermal maximum of 2 to 2.5 months compared with the unregulated river. Given the relevant hydrological and thermal alterations found in both regulated rivers, unexpectedly no differences were found between regulated and unregulated rivers when analysing macroinvertebrate richness and diversity indexes. The taxonomic response is significantly different among the three rivers in summer and was mostly explained by summer indicators, with the maximum water temperature of July being present in all models. An indirect driver that exacerbates the thermal differences found between regulated and unregulated rivers would be the geomorphological configuration of the rivers reciprocally interacting with the riparian vegetation. The monitoring of stream temperature is a crucial activity needed to implement since this parameter together with water flow shapes the distribution of aquatic biota in river ecosystems.

Cold-water coral framework architecture is selectively shaped by bottom current flow

The three-dimensional (3D) structure of habitat-forming corals has profound impacts on reef ecosystem processes. Elucidating coral structural responses to the environment is therefore crucial to understand changes in these ecosystems. However, little is known of how environmental factors shape coral structure in deep and dark waters, where cold-water coral (CWC) reefs thrive. Here, we attempt to infer the influence of current flow on CWC framework architecture, using 3D scanning to quantify colony shape traits (volume compactness and surface complexity) in the reef-building CWC Desmophyllum pertusum from adjacent fjord and offshore habitats with contrasting flow regimes. We find substantial architectural variability both between and within habitats. We show that corals are generally more compact in the fjord habitat, reflecting the prevailing higher current speeds, although differences in volume compactness between fjord and offshore corals are more subtle when comparing the fjord with the more exposed side of the offshore setting, probably due to locally intensified currents. Conversely, we observe no clear disparity in coral surface complexity between habitats (despite its positive correlation with volume compactness), suggesting it is not affected by current speed. Unlike volume compactness, surface complexity is similarly variable within a single colony as it is between colonies within the same habitat or between habitats and is therefore perhaps more dependent than volume compactness on microenvironmental conditions. These findings suggest a highly plastic, trait-specific and functionally relevant structural response of CWCs to current flow and underscore the importance of multiple concurrent sources of hydrodynamic forcing on CWC growth.

A Bayesian hierarchical spatially explicit modelling framework to examine phosphorus export between contrasting flow regimes

We examine the ability of a SPARROW-based model (SPAtially Referenced Regression On Watershed attributes) to assess regional P export coefficients that can assist with evaluation of nutrient mitigation projects and support adaptive watershed management. Limitations in number of tributary monitoring stations were overcome by assembling multi-agency water quality data from provincial, municipal, citizen science, and academic programs. We introduced a Bayesian hierarchical framework designed to guide parameter estimation from tributary nutrient loading in southern Georgian Bay drainage basin during contrasting flow regimes, such as dry and wet years. Agriculture was identified as a major non-point P source representing between 30 and 48% of delivered P loading. Our source apportionment predicted TP loss rates from croplands that exceeded those from forested areas by 320% during dry years and by 360% during wet years, while low intensity agricultural areas (hay and pasture) exceeded P export from forests by a mere 20% and 30%, respectively. Our study identified urban runoff as another significant non-point nutrient source displaying the highest variability between dry and wet years. In particular, owing to the extensive urbanization in the Lake Simcoe watershed, urban runoff contributed nearly half of delivered P loading from tributaries into the lake. The nutrient loading management plan for Lake Simcoe calls for a reduction in P loading by ∼40% from a long-term average of 72 t P y−1 in 2002–2007 to 44 t P y−1 by 2045. Our analysis emphasizes the importance of mitigating urban non-point sources together with efforts to control agricultural runoff.

Polarimetric radar reveals the spatial distribution of ice fabric at domes and divides in East Antarctica

Abstract. Ice crystals are mechanically and dielectrically anisotropic. They progressively align under cumulative deformation, forming an ice-crystal-orientation fabric that, in turn, impacts ice deformation. However, almost all the observations of ice fabric are from ice core analysis, and its influence on the ice flow is unclear. Here, we present a non-linear inverse approach to process co- and cross-polarized phase-sensitive radar data. We estimate the continuous depth profile of georeferenced ice fabric orientation along with the reflection ratio and horizontal anisotropy of the ice column. Our method approximates the complete second-order orientation tensor and all the ice fabric eigenvalues. As a result, we infer the vertical ice fabric anisotropy, which is an essential factor to better understand ice deformation using anisotropic ice flow models. The approach is validated at two Antarctic ice core sites (EPICA (European Project for Ice Coring in Antarctica) Dome C and EPICA Dronning Maud Land) in contrasting flow regimes. Spatial variability in ice fabric characteristics in the dome-to-flank transition near Dome C is quantified with 20 more sites located along with a 36 km long cross-section. Local horizontal anisotropy increases under the dome summit and decreases away from the dome summit. We suggest that this is a consequence of the non-linear rheology of ice, also known as the Raymond effect. On larger spatial scales, horizontal anisotropy increases with increasing distance from the dome. At most of the sites, the main driver of ice fabric evolution is vertical compression, yet our data show that the horizontal distribution of the ice fabric is consistent with the present horizontal flow. This method uses polarimetric-radar data, which are suitable for profiling radar applications and are able to constrain ice fabric distribution on a spatial scale comparable to ice flow observations and models.

Hydrological responses to rainfall events including the extratropical cyclone Gloria in two contrasting Mediterranean headwaters in Spain; the perennial font del Regàs and the intermittent Fuirosos

AbstractCatchment hydrological responses to precipitation inputs, particularly during exceptionally large storms, are complex and variable, and our understanding of the associated runoff generation processes during those events is limited. Hydrological monitoring of climatically and hydrologically distinct catchments can help to improve this understanding by shedding light on the interplay between antecedent soil moisture conditions, hydrological connectivity, and rainfall event characteristics. This knowledge is urgently needed considering that both the frequency and magnitude of extreme precipitation events are increasing worldwide as a consequence of climate change. In autumn 2018, we installed water level sensors to monitor stream water and near‐stream groundwater levels at two Mediterranean forest headwater catchments with contrasting hydrological regimes: Font del Regàs (sub‐humid climate, perennial flow regime) and Fuirosos (semi‐arid climate, intermittent flow regime). Both catchments are located in northeastern Spain, where the extratropical cyclone Gloria hit in January 2020 and left in ca. 65 h outstanding accumulated rainfalls of 424 mm in Font del Regàs and 230 mm in Fuirosos. During rainfall events of low mean intensity, hydrological responses to precipitation inputs at the semi‐arid Fuirosos were more delayed and more variable than at the sub‐humid Font del Regàs. We explain these divergences by differences in antecedent soil moisture conditions and associated differences in catchment hydrological connectivity between the two catchments, which in this case are likely driven by differences in local climate rather than by differences in local topography. In contrast, during events of moderate and high mean rainfall intensities, including the storm Gloria, precipitation inputs and hydrological responses correlated similarly in the two catchments. We explain this convergence by rapid development of hydrological connectivity independently of antecedent soil moisture conditions. The data set presented here is unique and contributes to our mechanistic understanding on how streams respond to rainfall events and exceptionally large storms in catchments with contrasting flow regimes.

Long-term acoustic telemetry reveals limited movement of fish in an unregulated, perennial river

Anthropogenic changes to river flows can alter hydrological connectivity and cues necessary for the movement of fish to complete their life cycles. Quantifying flow-related movement ecology of fish and understanding how this varies between species and river systems is important for effective environmental flow management. This study aimed to determine hydroecological factors that influence fish movements in an unregulated, perennial river and to compare these findings to fish from regulated river systems. Broad-scale movements of the endangered Maccullochella ikei and Tandanus tandanus were recorded over 3 years in the unregulated, perennial Nymboida River, Australia. The limited movements both species exhibited were infrequent and over short distances. Although M. ikei movements appeared mostly unrelated to environmental changes, T. tandanus moved on flow pulse peaks and were more likely to move during the breeding season. These findings contrast with previous studies of the same or similar species in differing flow regimes, suggesting that fish in perennial, highly connected rivers may not need to move as frequently as those in more regulated or intermittent systems. Should these disparate behaviours be present in other species occurring among contrasting flow regimes, it will be challenging to define generalisable environmental flow rules to inform river management.

Stable Boundary Layer Regimes in Single-Column Models

Abstract Two contrasting flow regimes exist in the stable boundary layer (SBL), as evidenced from both observational and modeling studies. In general, numerical schemes such as those used in numerical weather prediction and climate models (NWPCs) reproduce a transition between SBL regimes. However, the characteristics of such a transition depend on the turbulence parameterizations and stability functions used to represent the eddy diffusivity in the models. The main goal of the present study is to detail how the two SBL regimes occur in single-column models (SCMs) by analyzing the SBL structure and its dependence on external parameters. Two different turbulence closure orders (first order and an E–l model) and two types of stability functions (short and long tail) are considered. The control exerted by the geostrophic wind and the surface cooling rate on the model SBL regimes is addressed. The model flow presents a three-layer structure: a fully turbulent, weakly stable layer (WSL) next to the surface; a very stable layer (VSL) above that; and a laminar layer above the other two and toward the domain top. It is shown that the WSL and VSL are related to both SBL regimes, respectively. Furthermore, the numerically simulated SBL presents the two-layer structure regardless of the turbulence parameterization order and stability function used. The models also reproduce other features reported in recent observational studies: an S-shaped dependence of the thermal gradient on the mean wind speed and an independence of the vertical gradient of friction velocity δu* on the mean wind speed.

Temporal hydrochemical dynamics of the River Wensum, UK: Observations from long-term high-resolution monitoring (2011–2018)

In 2010, the UK government established the Demonstration Test Catchment (DTC) initiative to evaluate the extent to which on-farm mitigation measures can cost-effectively reduce the impacts of agricultural water pollution on river ecology whilst maintaining food production capacity. A central component of the DTC platform was the establishment of a comprehensive network of automated, web-based sensor technologies to generate high-temporal resolution (30 min) empirical datasets of surface water, groundwater and meteorological parameters over a long period (2011–2018). Utilising 8.9 million water quality measurements generated for the River Wensum, this paper demonstrates how long-term, high-resolution monitoring of hydrochemistry can improve our understanding of the complex temporal dynamics of riverine processes from 30 min to annual timescales. This paper explores the impact of groundwater-surface water interactions on instream pollutant concentrations (principally nitrogen, phosphorus and turbidity) and reveals how varying hydrochemical associations under contrasting flow regimes can elicit important information on the dominant pollution pathways. Furthermore, this paper examines the relationships between agricultural pollutants and precipitation events of varying magnitude, whilst demonstrating how high-resolution data can be utilised to develop conceptual models of hydrochemical processes for contrasting winter and summer seasons. Finally, this paper considers how high-resolution hydrochemical data can be used to increase land manager awareness of environmentally damaging farming operations and encourage the adoption of more water sensitive land management practices.

Technical note: An improved discharge sensitivity metric for young water fractions

Abstract. Recent virtual and experimental investigations have shown that the young water fraction Fyw (i.e. the proportion of catchment outflow younger than circa 2–3 months) increases with discharge in most catchments. The discharge sensitivity of Fyw has been defined as the rate of increase in Fyw with increasing discharge (Q) and has been estimated by the linear regression slope between Fyw and Q, hereafter called DS(Q). The combined use of both metrics, Fyw and DS(Q), provides a promising method for catchment inter-comparison studies that seek to understand streamflow generation processes. Here we explore the discharge sensitivity of Fyw in the intensively sampled small Mediterranean research catchment Can Vila. Intensive sampling of high flows at Can Vila allows young water fractions to be estimated for the far upper tail of the flow frequency distribution. These young water fractions converge toward 1 at the highest flows, illustrating a conceptual limitation in the linear regression method for estimating DS(Q) as a metric of discharge sensitivity: Fyw cannot grow with discharge indefinitely, since the fraction of young water in discharge can never be larger than 1. Here we propose to quantify discharge sensitivity by the parameter of an exponential-type equation that expresses how Fyw varies with discharge. The exponential parameter (Sd) approximates DS(Q) at moderate discharges where Fyw is well below 1; however, the exponential equation and its discharge sensitivity metric better capture the non-linear relationship between Fyw and Q and are robust with respect to changes in the range of sampled discharges, allowing comparisons between catchments with strongly contrasting flow regimes.

Evolutionary responses of aquatic macroinvertebrates to two contrasting flow regimes

Natural disturbances are agents of natural selection that drive multiple biological adaptations along evolutionary time. Frequent, high magnitude disturbances are expected to select for morphological and behavioral traits to resist or to avoid them. In contrast, predictable and seasonal disturbances are expected to select for synchronized life cycles to avoid unfavorable periods. We assessed the effect of flood disturbances on aquatic macroinvertebrates in two rivers with contrasting flow regimes: the Gila (USA) with seasonal floods and droughts, and the Thur (Switzerland) with a high frequency of aseasonal floods. Macroinvertebrates were analyzed based on 46 biological trait categories classified into morphological, life-cycle synchronization, and behavioral strategies. Flood effects on diversity and composition were much clearer for the Gila than for the Thur. Overall, biological adaptations were related to the flood regime of each river. Morphological adaptations to resist or avoid floods prevailed under frequent and aseasonal disturbances (the Thur), whereas life-cycle synchronization and behavioral adaptations were associated with highly seasonal, predictable, and low-frequency disturbances (the Gila). Given that forecasted future flow regimes differ between regions, our results suggest that the effects of future flow regime alterations will ultimately depend on the adaptation strategies to current flow regimes.

Spatio-temporal effects of river regulation on habitat quality for Atlantic salmon fry

Many upland rivers in the Northern Hemisphere contain important habitat for Atlantic salmon (Salmo salar L.). Owing to their sensitivity to environmental change, salmon are often used as bio-indicators. In Scotland, rivers containing potentially suitable habitat for salmon fry are often also regulated for hydropower. Regulated flow regimes can differ substantially spatially and temporally. Thus, where river management may be needed to maintain, restore, and protect their ecological functioning, this needs to be based on evidence of such spatio-temporal effects. This study investigated the effects of different types of river regulation on the hydraulic characteristics of downstream river reaches and the inferred consequences for salmon fry using hydraulic habitat quality models. The study focussed on the River Lyon (390km2), a tributary of the Tay (4587km2), Scotland, UK. Hydraulic habitat variability was assessed for three reach-scale sites with contrasting flow regimes characterised by (a) releases from hydropower generation, (b) compensation flow and (c) partly re-naturalised flow conditions. For each site, high resolution Digital Terrain Models (DTMs) were developed from bathymetric surveys and 2D hydraulic models were used to assess hydraulic characteristics. Discharge time series were used to simulate hydraulic conditions for regulated and simulated natural flows. Depth and velocity data were extracted from the hydraulic models and used to infer habitat quality using a habitat model developed for Atlantic salmon fry in similar-sized Scottish rivers. Results showed the effects of regulation can vary substantially within reaches and between seasons. Comparison to natural flow regimes suggested that flow alteration has a variable influence on habitat quality depending on the type of regulation and time of year. This work has improved understanding of the effects of regulation on biophysical processes and may also be useful for managing trade-offs between management, restoration, and societal benefits.

Morphological differentiation in northern pike (Esoxlucius): the influence of environmental conditions and sex on body shape

Morphological differentiation may allow individuals to cope with prevailing environmental conditions. Morphological differentiation in fish characterized by sagittiform shape and ambush predator behaviour, such as northern pike (Esox lucius L., 1758), has rarely been addressed. Morphological differentiation was assessed in two rivers exhibiting contrasting flow regimes: a hydropeaking river characterized by large and frequent fluctuations in flow rates and an unregulated river. An increase in northern pike movement rate was observed in the hydropeaking river. Therefore, morphological features enhancing sustained and burst swimming, as well as manoeuvrability, were expected. Our objectives are to (i) compare morphology between the two rivers and (ii) assess morphological differentiation between sexes. Using geometric morphometrics, shape significantly diverged between rivers irrespective of sex and between sexes in the hydropeaking river. Individuals from the hydropeaking river had more elongated heads, deeper bodies and caudal peduncles, and longer dorsal fin insertions than individuals from the unregulated river. Caudal fin differences between rivers were not consistent between sexes. Morphological differentiation suggested a trade-off among adaptations for sustained and burst swimming, as well as manoeuvrability, to cope with variable flows in a hydropeaking river. Morphological differentiation may allow the exploitation of spatially and temporally variable environmental conditions, including those stemming from river flow regulation.

Temporal variability in taxonomic and trait compositions of invertebrate assemblages in two climatic regions with contrasting flow regimes

ContextUnderstanding natural temporal changes in Mediterranean rivers with contrasting flow regimes in relation to those of temperate rivers may prove helpful in predicting effects of climate change on aquatic biodiversity. GoalWe aimed to compare temporal variability in taxonomic and trait compositions of nearly natural rivers in two climatic regions with varying flow regimes to address the effects of future climate changes on aquatic biodiversity in reference conditions. MethodsWe analysed taxonomic and biological trait compositions using the Foucard multivariate method to compare within-site temporal variability levels and the evolution of within-date spatial variability patterns. In addition, we assessed the effects of temporal variability levels on taxonomic and functional diversity and on community specialization. ResultsOur results reveal (i) highly fluctuating environments of the Mediterranean region, particularly in intermittent rivers, which lead to higher levels of temporal variability in both taxonomic and trait compositions of benthic invertebrate assemblages, with marked synchrony in Mediterranean streams linked to contrasting flow characteristics; (ii) higher degrees of taxonomic richness associated with higher levels of functional diversity in Mediterranean rivers relative to temperate rivers, (iii) higher temporal stability for functional diversity and trait compositions of benthic invertebrate assemblages than for taxonomic richness and compositions; and (iv) a recovery of all diversity metrics following drying events in intermittent sites. ConclusionThis study offers insight into a rarely addressed question concerning the temporal variability of trait compositions in benthic invertebrate assemblages among rivers differing in terms of flow regimes. It suggests that temperate rivers will experience higher levels of temporal variability in terms of taxonomic and trait compositions under future climatic change scenarios, even in sites that will remain perennial, resulting in higher levels of taxonomic and functional diversity. This lack of temporal stability in least-disturbed situations should be taken into account when developing bioassessment tools based on reference conditions.

Valley-scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes

High-resolution topographic surveys using LiDAR and multibeam sonar can be used to characterize and quantify fluvial change. This study used repeat surveys to explore how topographic change, fluvial processes, sediment budgets, and aggradation and incision rates vary across spatial scales and across two contrasting decadal flow regimes in a regulated gravel/cobble river. A novel method for quantifying digital elevation model uncertainty was developed and applied to a topographic change detection analysis from 2006/2008 to 2014. During this period, which had four modest ~3–5year floods, most sediment was laterally redistributed through bank erosion and channel migration. Erosion primarily occurred in the floodplain (97,000m3), terraces (80,000m3), and lateral bars (58,000m3); while deposition occurred in the adjacent pools (73,000m3), fast glides (48,000m3), and runs (36,000m3). In contrast, significantly higher magnitude and longer duration floods from 1999 to 2006/2008 caused sediment to be displaced longitudinally, with the upstream reaches exporting sediment and the downstream reaches aggrading. The river maintained floodplain connectivity during both periods, despite different processes dominating the type of connectivity. Larger floods promoted overbank scour and avulsion, while smaller floods promoted bank erosion and lateral migration. This study explores and illustrates how the geomorphic response to contrasting flood regimes in a nonuniform river is highly dependent on which landforms are controlling hydraulics.

Unravelling the joint effects of flow regime, climatic variability and dispersal mode on beta diversity of riverine communities

Summary Differences in the composition of ecological communities among rivers with contrasting flow regimes have been detected in many regions worldwide. However, we know little of how climatic variation alters these spatial patterns for constituent species with varying dispersal modes and strengths. We predicted that beta diversity (spatial variation in composition) of macroinvertebrate and fish assemblages among streams with near‐perennial, mildly intermittent and highly intermittent flow regimes would be greater during prolonged drought than under wetter climate conditions. We hypothesised that changes in beta diversity between these climate phases would be greater for taxa with stronger dispersal ability. We tested these predictions with biomonitoring data from Australian subtropical rivers. Differences in average community composition among flow regimes were statistically significant for six groups of macroinvertebrates with differing dispersal (non‐swimmers, weak swimmers, strong swimmers, non‐fliers, weak fliers and strong fliers) and two groups of fish (potamodromous and diadromous), but not for locally dispersing fish. For each of these biotic groups, shifts in assemblage composition between supra‐seasonal drought and a subsequent non‐drought period were either statistically non‐significant or of similar magnitude among flow regimes. Therefore, beta diversity among flow regimes did not change significantly with climate phase. Beta diversity within flow‐regime classes was greater during the drought than afterwards or not significantly different between climate phases, depending on the flow regime and biotic group. Stronger powers of flight were associated with greater change in beta diversity between climate phases in near‐perennial streams, but stronger powers of swimming were not. Within‐regime beta diversity was driven more by replacement of taxa among samples than by nestedness, except for diadromous fish in near‐perennial streams. Our findings are consistent with the hypothesis that decreasing hydrological connectivity and greater environmental heterogeneity during prolonged drought increase beta diversity of stream communities. However, changes in beta diversity between climate phases were not as pronounced as we expected. The communities may have been somewhat drought resistant because the magnitude and duration of the drought were within the range of historical variability and because surface water persisted at study sites during drought‐imposed flow cessations. Our findings suggest that maintenance of refuge pools will be critical to lessening drought impacts on river biodiversity at landscape scales, particularly if drought duration and intensity increase in the future.

Main potential drivers of trout population dynamics in bypassed stream sections

AbstractThe key role of hydrological variability in structuring brown trout populations is well established. However, the influence of additional drivers is more difficult to identify. The implementation of long‐term monitoring and the development of reliable tools can help to reveal fine local drivers structuring fish populations in contrasted flow regimes. This study used data series for nine reaches monitored for nine to nineteen years in four French salmonid streams. Study reaches were within five bypassed sections influenced by instream flow. A deterministic trout population dynamics model was applied on each reach, with calibration and validation procedures. Results revealed that biological drivers structured all reaches similarly. In addition, seven other drivers were identified. Among these additional drivers, hydrology mainly explained temporal fluctuations in trout density, regardless of reach. Three drivers independent of hydrology were also revealed: poor water quality, limited spawning area and the effect of power plant operations (overtopping, flushing or plant shutdown). All drivers influenced the whole bypassed section and were never limited to the scale of the reach (sampling area). Further analyses of each driver are now needed, to regionalise and quantify their respective impact precisely. Thus, assessment of trout population status would be simplified, enabling implementation of efficient management rules.

Differences in movements of northern pike inhabiting rivers with contrasting flow regimes

AbstractLittle is known about the effect of short‐term flow changes on the movement of northern pike (Esox lucius L.). We conducted a comparative study in two rivers with different flow regimes (i.e. one regulated and one unregulated) to evaluate the extent to which adult northern pike movement is influenced by short‐term river flow conditions. Data on northern pike hourly movement were collected in northeastern Ontario on 40 individuals in the Mississagi River, a river subjected to extreme daily flow variations associated with hydro‐electric operations (i.e. hydropeaking), and the Aubinadong River, an unregulated river. Using manual tracking by radio‐telemetry, we found that northern pike moved at a higher rate in the river subjected to short‐term changes in river flow than in the unregulated river. Results also show that the relationship between movement of northern pike and flow can vary among rivers. In the Mississagi River, flow had a significant positive effect on northern pike activity, while the effect of flow in the Aubinadong River depended on water temperature. Moreover, fish in the Mississagi River utilized a restricted river section and travelled more laterally in comparison to fish inhabiting the Aubinadong River, where longer upstream‐downstream movements were more common. The present study contributes to our understanding of the effects of short‐term changes in flow on fish movement. This constitutes the first step towards assessing the effect of flow on fish habitat use, and eventually developing flow management strategies to mitigate impacts on fish. Copyright © 2016 John Wiley & Sons, Ltd.

Temporal variation in benthic primary production in streams of the Australian wet–dry tropics

In the Australian wet–dry tropics, seasonal changes in hydrology can influence abiotic conditions and consequently influence standing stocks of benthic biomass and production. While there is some understanding of these processes at riverscape scales, effects of seasonal hydrology on benthic biomass and production in low-order streams remain largely unquantified. We observed changes in water quality, algal and macroinvertebrate biomass, and stream benthic primary productivity over a 15-month period in three low-order streams with contrasting flow regimes in the wet–dry tropics of northern Australia. Water quantity and quality showed a distinct seasonal signature reflected in seasonal peaks in algal (maximum 1.29 µg cm−2) and macroinvertebrate biomass (maximum 0.24 g m−2), and productivity (maximum 0.41 g C m−2 days−1). In particular, transitional periods between dry and wet seasons were key times of elevated production and algal biomass. Overall, variation in biomass and benthic primary production was greater between seasons than among streams indicating that extrapolation between seasons may not be appropriate.

Megacrystals track magma convection between reservoir and surface

Active volcanoes are typically fed by magmatic reservoirs situated within the upper crust. The development of thermal and/or compositional gradients in such magma chambers may lead to vigorous convection as inferred from theoretical models and evidence for magma mixing recorded in volcanic rocks. Bi-directional flow is also inferred to prevail in the conduits of numerous persistently-active volcanoes based on observed gas and thermal emissions at the surface, as well as experiments with analogue models. However, more direct evidence for such exchange flows has hitherto been lacking. Here, we analyse the remarkable oscillatory zoning of anorthoclase feldspar megacrystals erupted from the lava lake of Erebus volcano, Antarctica. A comprehensive approach, combining phase equilibria, solubility experiments and melt inclusion and textural analyses shows that the chemical profiles are best explained as a result of multiple episodes of magma transport between a deeper reservoir and the lava lake at the surface. Individual crystals have repeatedly travelled up-and-down the plumbing system, over distances of up to several kilometers, presumably as a consequence of entrainment in the bulk magma flow. Our findings thus corroborate the model of bi-directional flow in magmatic conduits. They also imply contrasting flow regimes in reservoir and conduit, with vigorous convection in the former (regular convective cycles of ∼150 days at a speed of ∼0.5 mm s−1) and more complex cycles of exchange flow and re-entrainment in the latter. We estimate that typical, 1-cm-wide crystals should be at least 14 years old, and can record several (from 1 to 3) complete cycles between the reservoir and the lava lake via the conduit. This persistent recycling of phonolitic magma is likely sustained by CO2 fluxing, suggesting that accumulation of mafic magma in the lower crust is volumetrically more significant than that of evolved magma within the edifice.

Modeling the evolution of riparian woodlands facing climate change in three European rivers with contrasting flow regimes.

Global circulation models forecasts indicate a future temperature and rainfall pattern modification worldwide. Such phenomena will become particularly evident in Europe where climate modifications could be more severe than the average change at the global level. As such, river flow regimes are expected to change, with resultant impacts on aquatic and riparian ecosystems. Riparian woodlands are among the most endangered ecosystems on earth and provide vital services to interconnected ecosystems and human societies. However, they have not been the object of many studies designed to spatially and temporally quantify how these ecosystems will react to climate change-induced flow regimes. Our goal was to assess the effects of climate-changed flow regimes on the existing riparian vegetation of three different European flow regimes. Cases studies were selected in the light of the most common watershed alimentation modes occurring across European regions, with the objective of appraising expected alterations in the riparian elements of fluvial systems due to climate change. Riparian vegetation modeling was performed using the CASiMiR-vegetation model, which bases its computation on the fluvial disturbance of the riparian patch mosaic. Modeling results show that riparian woodlands may undergo not only at least moderate changes for all flow regimes, but also some dramatic adjustments in specific areas of particular vegetation development stages. There are circumstances in which complete annihilation is feasible. Pluvial flow regimes, like the ones in southern European rivers, are those likely to experience more pronounced changes. Furthermore, regardless of the flow regime, younger and more water-dependent individuals are expected to be the most affected by climate change.