Influence Of Hydrology Research Articles

Assessment of the Effects of Climate Change on Evapotranspiration with an Improved Elasticity Method in a Nonhumid Area

Climatic elasticity is a crucial metric to assess the hydrological influence of climate change. Based on the Budyko equation, this study performed an analytical derivation of the climatic elasticity of evapotranspiration (ET). With this derived elasticity, it is possible to quantitatively separate the impacts of precipitation, air temperature, net radiation, relative humidity, and wind speed on ET in a watershed. This method was applied in the Wuding River Watershed (WRW), located in the center of the Yellow River Watershed of China. The estimated rate of change in ET caused by climatic variables is −10.69 mm/decade, which is close to the rate of change in ET (−8.06 mm/decade) derived from observable data. The accurate estimation with the elasticity method demonstrates its reliability. Our analysis shows that ET in the WRW had a significant downward trend, but the ET ratio in the WRW has increased continually over the past 52 years. Decreasing precipitation is the first-order cause for the reduction of ET, and decreasing net radiation is the secondary cause. Weakening wind speed also contributed to this reduction. In contrast, regional warming led to an increase in ET that partly offset the negative contributions from other climatic variables. Moreover, reforestation can affect the energy budget of a watershed by decreasing albedo, compensating for the negative influence of global dimming. The integrated effect from precipitation and temperature can affect the energy budget of a watershed by causing a large fluctuation in winter albedo.

Mapping landscape-level hydrological connectivity of headwater wetlands to downstream waters: A catchment modeling approach - Part 2

In Part 1 of this two-part manuscript series, we presented an effective assessment method for mapping inundation of geographically isolated wetlands (GIWs) and quantifying their cumulative landscape-scale hydrological connectivity with downstream waters using time series remotely sensed data (Yeo et al., 2018). This study suggested strong hydrological coupling between GIWs and downstream waters at the seasonal timescale via groundwater. This follow-on paper investigates the hydrological connectivity of GIWs with downstream waters and cumulative watershed-scale hydrological impacts over multiple time scales. Modifications were made to the representation of wetland processes within the Soil and Water Assessment Tool (SWAT). A version of SWAT with improved wetland function, SWAT-WET, was applied to Greensboro Watershed, which is located in the Mid-Atlantic Region of USA, to simulate hydrological processes over 1985–2015 under two contrasting land use scenarios (i.e., presence and absence of GIWs). Comparative analysis of simulation outputs elucidated how GIWs could influence partitioning of precipitation between evapotranspiration (ET) and terrestrial water storage, and affect water transport mechanisms and routing processes that generate streamflow. Model results showed that GIWs influenced the watershed water budget and stream flow generation processes over the long-term (30 year), inter-annual, and monthly time scales. GIWs in the study watershed increased terrestrial water storage during the wet season, and buffered the dynamics of shallow groundwater during the dry season. The inter-annual modeling analysis illustrated that densely distributed GIWs can exert strong hydrological influence on downstream waters by regulating surface water runoff, while maintaining groundwater recharge and ET under changing (wetter) climate conditions. The study findings highlight the hydrological connectivity of GIWs with downstream waters and the cumulative hydrological influence of GIWs as hydrologic sources to downstream ecosystems through different runoff processes over multiple time scales.

Glacial Erosion Driven by Variations in Meltwater Drainage

AbstractThe subglacial processes of abrasion and quarrying are thought to be primarily responsible for bedrock erosion by glaciers. While theory points to sliding speed as the dominant control on abrasion, rates of quarrying are likely scaled by a more complex combination of sliding speed, effective pressure, bed roughness, and short‐term water‐pressure fluctuations. Here we pair a model for quarrying based on statistical characterization of bedrock strength with a model for subglacial hydrology that describes the temporal evolution of cavities under the influence of variations in sliding speed and effective pressure. Using a finite element model, we simulate the evolution of the hydrological system at the base of a glacier and compute rates of abrasion and quarrying. Cavity lengths and channel cross sections evolve through time, causing temporal shifts in ice‐bed contact area, which in turn govern the differential stress that influences erosion over the course of a year. Our results demonstrate how variations in meltwater production amplify rates of subglacial erosion relative to the case of steady meltwater generation. The level of amplification depends on how the variations control the ice‐bed contact area. Seasonal variations are most effective in boosting mean rates of basal sliding and hence subglacial abrasion, whereas shorter‐term variations (monthly‐weekly) most strongly influence rates of subglacial quarrying through temporal amplification of differential bedrock stress around cavities. This influence of transient hydrology on subglacial erosion processes may explain why glaciers in temperate climates with strong variations in temperature and precipitation erode faster than similar‐type glaciers in polar environments.

Hydrological influences on aquatic communities at the mesohabitat scale in high Andean streams of southern Ecuador

AbstractThis study assessed the effects of hydrological events on aquatic communities at the mesohabitat scale (pool, run, and riffle) in the high Andean region. Four headwater sites located in the Zhurucay microcatchment (southern Ecuador), with elevations higher than 3,500 m, were selected and monitored considering in each site a 50‐m‐long reach and within each reach five cross sections. In each of these reaches, 19 sampling campaigns were conducted in the period December 2011–October 2013, collecting macroinvertebrates and physical characteristics. A total of 27 hydrological indices were calculated using the daily flow rate as input. Large peak flow, small peak flow, and low flow (LF) events were defined based on discharge thresholds. Multivariate statistics showed that 14 hydrological indices were significantly related to the aquatic community. Further, the study revealed that (a) peak events produced stronger effects on communities than LF events, (b) the observed effects of LF events were weaker than those encountered in other latitudes, and (c) local benthic communities have more resilience than similar communities studied in other latitudes.

Hydrological influences on aquatic communities at the mesohabitat scale in high Andean streams of southern Ecuador

This study assessed the effects of hydrological events on aquatic communities at the mesohabitat scale (pool, run, and riffle) in the high Andean region. Four headwater sites located in the Zhurucay microcatchment (southern Ecuador), with elevations higher than 3,500 m, were selected and monitored considering in each site a 50 ]m ]long reach and within each reach five cross sections. In each of these reaches, 19 sampling campaigns were conducted in the period December 2011.October 2013, collecting macroinvertebrates and physical characteristics. A total of 27 hydrological indices were calculated using the daily flow rate as input. Large peak flow, small peak flow, and low flow (LF) events were defined based on discharge thresholds. Multivariate statistics showed that 14 hydrological indices were significantly related to the aquatic community. Further, the study revealed that (a) peak events produced stronger effects on communities than LF events, (b) the observed effects of LF events were weaker than those encountered in other latitudes, and (c) local benthic communities have more resilience than similar communities studied in other latitudes.

Human exposure to trace elements in central Cambodia: Influence of seasonal hydrology and food-chain bioaccumulation behaviour

Exposure to mercury and other trace elements remains an important public health concern, worldwide. The present study involved a comprehensive field study to determine concentrations of fourteen trace elements (Al, As, Cr, Co, Cd, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn) in surface water and different fish species from Tonlé Sap Lake in central Cambodia, during both the dry and wet seasons. Total arsenic (tAs) and Mn in surface water during the dry season exceeded WHO drinking water guidelines. Total mercury (tHg) concentrations (µg/g wet wt.) in fish during the wet season (GM = 0.055; CI95 = 0.01–0.26) were approximately 15 times higher (P < 0.05) compared to those during the dry season (GM = 0.0035; CI95 = 0.0004–0.033). Mean target hazard quotients (THQs) for inorganic arsenic (iAs), methyl mercury (MeHg), Mn and Pb were > 1, with estimated maximum values greatly exceeding 1. Mean THQs of Zn, Cd, Ni and Se were very near 1, with estimated maximum values exceeding 1. The MeHg THQ (min-max range: 0.16–9.09) during the wet season was 7 times higher than in the dry season (min-max range: 0.05–1.35). Concentrations of Hg and other trace elements varied widely between fish species. The findings suggest that exposure of some trace elements via water and food is of concern in this region. High consumption rates of fish and rice key factors related to trace element exposure. Seasonal hydrology and species-specific bioaccumulation behaviour in the Tonlé Sap Lake watershed also play an important role. The generated information will be useful to better mitigate trace element exposure in this region.

A Small Temperate Lake in the 21st Century: Dynamics of Water Temperature, Ice Phenology, Dissolved Oxygen, and Chlorophyll a

AbstractIt is unclear how small temperate lakes will evolve physically and biologically in the whole water column under future climate because previous modeling studies usually focused on only one or two physical or biological state variables in the surface waters. Here we used a well‐validated lake biogeochemistry model driven by different climate scenarios of the 21st century to predict the dynamics of ice phenology, water temperature, dissolved oxygen (DO), and chlorophyll a in a small Canadian temperate lake (0.714 km2) that is oligotrophic and strongly stratified in summer, considering the influence of catchment hydrology. The ice season and thickness of the lake are projected to shrink substantially under warming, resulting in a positive energy feedback between climate and the lake. Due to the reduced heat diffusion and water mixing, the dynamics of water temperature in surface and deep waters of the lake are considerably different, with surface waters warmed dramatically but deep waters muted to warming. DO depletion is predicted to occur in the whole water column of the lake under warming, but the controlling processes are depth dependent. Unexpectedly, the predicted growth of the lake's chlorophyll a is small under warming, due to the weakened convection and the mismatch of the timings of favorable solar radiation, thermal, and nutrient conditions. For the examined state variables, our prediction shows that only the dynamics of DO is significantly impacted by the changing catchment hydrology. This study suggests that similar temperate lakes will have diverse physical and biological responses to climate change.

Deltaic and Coastal Sediments as Recorders of Mediterranean Regional Climate and Human Impact Over the Past Three Millennia

AbstractDeltaic and shallow marine sediments represent unique natural archives to study the evolution of surface coastal ocean water properties as compared to environmental changes in adjacent continents. Sea surface temperatures (SSTs) and higher plant biomarker records were generated from the Rhone and Var River deltaic sediments (NW Mediterranean Sea), and three sites in the South Adriatic Sea (Central/Eastern Mediterranean Sea), spanning all or part of the past three millennia. Because of the high sediment accumulation rates at all core sites, we were able to produce time series at decadal time scale. SSTs in the Gulf of Lion and the convection area of the South Adriatic Sea indicate similar cold mean values (around 17 °C) and pronounced cold spells, reflecting strong wind‐driven surface water heat loss. However, they differ in the rate of postindustrial warming, which is steeper in the Gulf of Lion. The three Adriatic Sea SST records are notably different reflecting different hydrological influence from nearshore to open sea sites. The compositional features of higher plant n‐alkanes in the Rhone and Var delta sediments and inferred vegetation types show differences consistent with the latitudinal extension of the drainage basins of both river streams. In the Adriatic Sea, both coastal and open sea sediments indicate enhanced land‐derived material over the past 500 years, which is not seen in the NW Mediterranean record. We suggest that increased erosion as the result of changes in land use practices is the most likely cause for this trend.

A two-year analysis of the iOSG-24 superconducting gravimeter at the low noise underground laboratory (LSBB URL) of Rustrel, France: Environmental noise estimate

Since July 2015 a Superconducting Gravimeter (SG) of the latest generation, the iOSG-24, has been recording continuously the time-varying gravity field at the low noise underground laboratory (LSBB URL) of Rustrel, France. This instrument designed for observatory purpose has a levitated Niobium sphere weighting 17.7 g instead of 4.3 g. The advantage of increasing the mass of the sphere is to reduce the thermal noise due to Brownian motion inside the sensor. A comparison of the noise levels shows that the combination of this iOSG-24 with the environmental condition at the LSBB makes this site one of the quietest worldwide SG sites. Parallel measurements with an absolute FG5 gravimeter give a calibration factor of −451 ± 3 nm/s2/V and a negligible linear drift is observed 3 months after the installation. Tidal analyses are consistent with theoretical predictions and have shown a strong S1 thermal wave. Influence of the hydrological water content, mostly related to the Fontaine de Vaucluse catchment, is clearly visible on the SG residuals after tides removal. However the hydrological influence modelled using the MERRA2 products does not fully explain the observed noise level at periods between 1 and 10 days. Longer gravimetric time-series are necessary to further study the seasonal hydrological effects.

The Ensemble Kalman Filter for Groundwater Plume Characterization: A Case Study

The Kalman filter is an efficient data assimilation tool to refine an estimate of a state variable using measured data and the variable's correlations in space and/or time. The ensemble Kalman filter (EnKF) (Evensen 2004, 2009) is a Kalman filter variant that employs Monte Carlo analysis to define the correlations that help to refine the updated state. While use of EnKF in hydrology is somewhat limited, it has been successfully applied in other fields of engineering (e.g., oil reservoir modeling, weather forecasting). Here, EnKF is used to refine a simulated groundwater tetrachloroethylene (TCE) plume that underlies the Tooele Army Depot-North (TEAD-N) in Utah, based on observations of TCE in the aquifer. The resulting EnKF-based assimilated plume is simulated forward in time to predict future plume migration. The correlations that underpin EnKF updating implicitly contain information about how the plume developed over time under the influence of complex site hydrology and variable source history, as they are predicated on multiple realizations of a well-calibrated numerical groundwater flow and transport model. The EnKF methodology is compared to an ordinary kriging-based assimilation method with respect to the accurate representation of plume concentrations in order to determine the relative efficacy of EnKF for water quality data assimilation.

The Ensemble Kalman Filter for Groundwater Plume Characterization: A Case Study

ABSTRACTThe Kalman filter is an efficient data assimilation tool to refine an estimate of a state variable using measured data and the variable's correlations in space and/or time. The ensemble Kalman filter (EnKF) (Evensen, 2004, 2009) is a Kalman filter variant that employs Monte Carlo analysis to define the correlations that help to refine the updated state. While use of EnKF in hydrology is somewhat limited, it has been successfully applied in other fields of engineering (e.g. oil reservoir modeling, weather forecasting). Here, EnKF is used to refine a simulated groundwater TCE plume that underlies the Tooele Army Depot‐North (TEAD‐N) in Utah, based on observations of TCE in the aquifer. The resulting EnKF‐based assimilated plume is simulated forward in time to predict future plume migration. The correlations that underpin EnKF updating implicitly contain information about how the plume developed over time under the influence of complex site hydrology and variable source history, as they are predicated on multiple realizations of a well‐calibrated numerical groundwater flow and transport model. The EnKF methodology is compared to an ordinary kriging‐based assimilation method with respect to the accurate representation of plume concentrations in order to determine the relative efficacy of EnKF for water quality data assimilation.

Understanding the Role of Rainfall and Hydrology in Determining Fluvial Erosion Efficiency

Due to the challenges in upscaling daily climatic forcing to geological time, physically realistic models describing how rainfall drives fluvial erosion are lacking. To bridge this gap between short‐term hydrology and long‐term geomorphology, we derive a theoretical framework for long‐term fluvial erosion rates driven by realistic climate by integrating an established stochastic‐mechanistic model of hydrology into a threshold‐stochastic formulation of stream power. The hydrological theory provides equations for the daily streamflow probability distribution as a function of climatic boundary conditions. The new parameters introduced are rooted firmly in established climatic and hydrological theory. This allows us to account for how fluvial erosion rates respond to changes in rainfall intensity, frequency, evapotranspiration rates, and soil moisture dynamics in a way that is consistent with existing theories. We use this framework to demonstrate how hydroclimatic conditions and erosion threshold magnitude control the degree of nonlinearity between steepness index and erosion rate. We find that hydrological processes can have a significant influence on how erosive a particular climatic forcing will be. By accounting for the influence of hydrology on fluvial erosion, we conclude that climate is an important control on erosion rates and long‐term landscape evolution.

Geodiversity Mapping and Relationship with Vegetation: A Regional-Scale Application in SE Brazil

The natural variability of geological, geomorphological, pedological, and hydrological elements can be described and assessed in terms of geodiversity. This geodiversity is intrinsically linked to biodiversity, since the physical environment provides the conditions in which biological elements develop. The use of geodiversity as a tool for environmental studies is of growing importance, describing and highlighting the importance of the physical environment and strengthening the idea of holistic approach of the nature. This work consisted of a qualitative mapping of the geodiversity in Armacao dos Buzios municipality, in Rio de Janeiro State, southeastern Brazil. Based on integration of the physical environment elements, geodiversity units were defined, in which the geological substrate, relief forms, and soil types are similar. The hydrological influence was also taken into account in specific units. Subsequently, each geodiversity unit was analyzed in terms of its regional type of vegetation, in order to investigate the correlation between spatial distributions of the physical and biological environments. As a result, a Geodiversity Map of Armacao dos Buzios was created, describing the physical environment of the area. The inclusion of data on vegetation types showed direct correspondence of the Geodiversity Map and the biological environment, since each geodiversity unit is occupied by specific vegetation types. This result shows that the use of geodiversity as a tool to understand vegetation distribution patterns is valid and should be explored further within the contexts of land management and nature conservation. It is expected that this product becomes a tool for territorial management and an incentive for the development of furthermore research focused on holistic approaches to nature.

Testing the response of macroinvertebrate communities and biomonitoring indices under multiple stressors in a lowland regulated river

River systems and their communities are exposed to diverse and multiple threats. Understanding how these threats affect the behaviour of biomonitoring indices is essential in order to provide reliable tools for the management and conservation of watercourses. To this purpose we tested the relationship of the STAR_ICMi index and its metrics, LIFE index and macroinvertebrate community with hydrology, water chemistry and land use in 8 sites located along the Oglio River course (Northern Italy), a watercourse originating from a large and deep lake. Macroinvertebrates and water samples were collected seasonally from summer 2013 to summer 2015 and daily discharge data were used to calculate several indices of hydrological alteration. A subset of these variables was selected by principal component analysis for using in the data analysis. The influence of hydrology, water chemistry and land use on macroinvertebrate community structure was explored with the variance partitioning method, while their influence on biomonitoring indices was analysed in a linear mixed effect model framework. Temporal and spatial constraints were explicitly considered in both analyses. Macroinvertebrate community structure was mainly related to these last two factors and to their joint effects with water chemistry and hydrology. STAR_ICMi, its metrics (with the exception of the Shannon index) and LIFE were related to the distance from the lake outlet, a proxy of mean annual discharge, groundwater input and artificial land use. STAR_ICMi, ASPT and EPT richness were also inversely related to the flow variability in the 3 months preceding sample collection. Surprisingly LIFE index was not related to any of the hydrological variables. The results of this study highlight weakness in the current biomonitoring tools and support the need for further investigations on macroinvertebrate interrelations with environmental drivers and their spatial and temporal structure. This is essential to overcome the limitations that may affect the reliability of macroinvertebrate-based indices in aquatic biomonitoring.

One Person's Drain Is another's Water Supply: Why Property Rights, Scope, Measurement and Hydrology Matter when it Comes to Integrated Water Resources Management

The expansion of Integrated Water Resource Management (IWRM) philosophies has given rise to some improvements in decision-making with greater attention being given to the relationship between upstream choices and downstream consequences. However, the limits of IWRM also need to be recognised, especially the demands on water planners seeking to balance multiple objectives across multiple sites. This paper scrutinises the need for superordinate integrated decisions when property rights are already well-defined and tradeable. By using simplified examples derived from the Australian milieu, we also consider cases where the property rights are less-well defined and trade is not an easy option. The examples demonstrate that efficient decisions can arise without a superordinate water utility making integrated plans but the scale of decisions does matter, as does the measurement of the attributes of water in question. The paper also shows the necessity for understanding and linking institutional scope, hydrological influences and ecological responses whenever IWRM is purportedly seeking to simultaneously bring about ecological gains. Vesting integrated decisions in water utilities on the basis of their revenue-raising capacity is also briefly scrutinised.

Short-Term Effects of Drying-Rewetting and Long-Term Effects of Nutrient Loading on Periphyton N:P Stoichiometry

Nitrogen (N) and phosphorus (P) concentrations and N:P ratios critically influence periphyton productivity and nutrient cycling in aquatic ecosystems. In coastal wetlands, variations in hydrology and water source (fresh or marine) influence nutrient availability, but short-term effects of drying and rewetting and long-term effects of nutrient exposure on periphyton nutrient retention are uncertain. An outdoor microcosm experiment simulated short-term exposure to variation in drying-rewetting frequency on periphyton mat nutrient retention. A 13-year dataset from freshwater marshes of the Florida Everglades was examined for the effect of long-term proximity to different N and P sources on mat-forming periphyton nutrient standing stocks and stoichiometry. Field sites were selected from one drainage with shorter hydroperiod and higher connectivity to freshwater anthropogenic nutrient supplies (Taylor Slough/Panhandle, TS/Ph) and another drainage with longer hydroperiod and higher connectivity to marine nutrient supplies (Shark River Slough, SRS). Total P, but not total N, increased in periphyton mats exposed to both low and high drying-rewetting frequency with respect to the control mats in our experimental microcosm. In SRS, N:P ratios slightly decreased downstream due to marine nutrient supplies, while TS/Ph increased. Mats exposed to short-term drying-rewetting had higher nutrient retention, similar to nutrient standing stocks from long-term field data. Periphyton mat microbial communities may undergo community shifts upon drying-rewetting and chronic exposure to nutrient loads. Additional work on microbial species composition may further explain how periphyton communities interact with drying-rewetting dynamics to influence nutrient cycling and retention in wetlands.

Influence of hydrology, sediment supply and sediment gradation on river bar morphodynamics: application to the Loire River at Bréhémont (France)

Rivers inherently show heterogeneous sediment sizes and can also show a strong sediment supply variability in time because of natural episodic events or as a consequence of human activities, which alter the characteristics and dynamics of alluvial bars at the macro-scale. The impact of the combination between sediment size heterogeneity and sediment supply variation, or even with other forcings (i.e. hydrology, channel geometry) remains poorly documented. In this work, a physics-based numerical model is applied on a trained reach of a sandy-gravel bed river to investigate the combination of these parameters on bar morphodynamics. The morphodynamic computations are performed with a two-dimensional depth-averaged hydrodynamic solver, internally coupled to a sediment transport and bed evolution module, which estimate the transport of graded sediment and model bed stratigraphy, respectively. A 1 km long reach of the Loire River at Bréhémont (France) is selected to conduct the numerical investigations. The interaction between several forcing mechanisms induces highly complex bar morphodynamic processes in this area.A comprehensive set of high-definition data is available, which allows to study the river morphodynamics for a succession of three flooding events and a period of low flows. Based on this model, a variety of scenarios is presented with the aim of exploring the implications of sediment gradation, geometrical and boundary forcing effects on in situ bars morphodynamics.

Assessment of Water Quality in Slum Area Ibadan

The quantity of water is as important as the quality, since these affect the quantity and the quality of available water, water quality is used to express the suitability of water and sustainable to various uses or processes. It is affected by a wide range of natural and human influences, the most important of the natural influences is hydrological influence. The water qualities study was carried out in Ibadan using three landuse (urban, peri urban and rural) in slum areas of Ibadan were evaluated for these physicochemical parameters: temperature, total dissolved solid (TDS), pH, and dissolved oxygen (DO), from well, borehole, water from vendor or pipeborne, from 8 localities and 3 LGA in Ibadan. The results showed variations in the water quality parameters the slum areas. Water pH is lowest in Awotan and Apete of Ido LGA water source which makeup rural slums landuse. with water pH of 5.7 well and 5.8 borehole which is acidic, there is highest value of conc of Lead in these areas of (0.259 mg/l) compared to other landuse and locality, water is of best quality among water from vendors. Using the sig value of 0.05, that is no sig difference between the water quality in slum areas and WHO standards. Using Anova with physico-chemical parameters of water temperature, pH, dissolved oxygen, total dissolved solids, conc of zinc, and iron also having no significant. But a significant spatial variation of water quality of Lead concentration with the sig value of 0.033 and F value of 2.983. There is significant variation in different water source of water pH, total dissolved solid and dissolved oxygen. a sig value of 0.028, 0.031, and 0.000 respectively.

Connectivity, migration and recruitment in a catadromous fish

Understanding the influence of river hydrology and connectivity on the migration and recruitment of diadromous fishes is fundamental for species management and conservation. We investigated the downstream catadromous spawning migration of adult female congolli (Pseudaphritis urvillii) using acoustic telemetry, and subsequent juvenile recruitment, in the lower reaches of the River Murray, Australia, in 2009–2011. The years 2009 and 2010 were characterised by diminished freshwater flow, closure of tidal barrages, and disconnection of freshwater and estuarine habitats; however, a navigation lock was operated to facilitate downstream fish passage in 2010. In both years, &gt;70% of individuals tagged upstream undertook downstream migrations, in association with day-of-the-year (June–July) and moonphase (full), and accumulated upstream of the tidal barrages. In 2009, fish were unable to pass the barrages and remained upstream, but in 2010, an estimated &gt;15000 individuals passed through the navigation lock, including 40% of individuals tagged upstream. These transitioned rapidly (&lt;24h) through the estuary and into the ocean. In association, abundances of upstream migrant juveniles in spring–summer 2010–2011 were up to 180 times greater than in spring–summer 2009–2010. Our study illustrates the potential impact of tidal barriers on migrations and population dynamics of catadromous fish, and the importance of understanding species-specific migration ecology.

Re‐assessment of the age and depositional origin of the Paviland Moraine, Gower, south Wales, UK

The Bristol Channel, including onshore areas, is critical for reconstructing Pleistocene glacial limits in southwest Britain. Debate about the precise regional southern limits of Devensian (Oxygen Isotope Stage (OIS) 2) and Anglian (OIS 12) glaciations has recently been rekindled. The Paviland Moraine (Llanddewi Formation), Gower, south Wales is conventionally regarded as Anglian in age. Its ‘old’ age has been based on reported highly weathered clasts, a subdued morphology and ‘field relationships’ to fossil beach sediments of now disputed age(s). Relatively little about its sedimentary characteristics has been previously published. This paper: (i) presents new sedimentological evidence including lithofacies analysis, XRF analysis and electrical resistivity tomography (ERT) of sediment cores and electrical resistivity of a tied 3D field grid; (ii) re‐assesses the proposed ‘old’ age; (iii) suggests a likely depositional origin; and (iv) discusses implications for regional glacial dynamics and future research priorities. The sediments comprise mostly dipping glacigenic diamict units containing mainly Welsh Coalfield erratics. The location and subdued moraine morphology are attributed to the hydrological influence of the underlying limestone, the local topography and ice‐sheet behaviour rather than to long‐term degradation. Moraine formation is attributed mainly to sediment gravity flows that coalesced to produce an ice‐frontal apron. Neither geochemical data nor clasts indicate prolonged subaerial weathering and in‐situ moraine sediments are restricted to a limestone plateau above and inland of fossil beach sediments. We recommend rejecting the view that the moraine represents the only recognized OIS 12 deposit in Wales and conclude that instead it marks the limit of relatively thin Last Glacial Maximum (LGM) ice in west Gower. This requires revision of the accepted view of a more restricted LGM limit in the area. We suggest that substrate hydrological conditions may be a more influential factor in moraine location and form than is currently acknowledged.