High Water Discharge Research Articles

Gradual diversions of the Rio Pastaza in the Ecuadorian piedmont of the Andes from 1906 to 2008: role of tectonics, alluvial fan aggradation, and ENSO events

The successive courses of the Rio Pastaza in the upper Amazonian Puyo plateau (Ecuador) during the past century have been followed using historical maps, aerial photographs, satellite imagery, topographic and river long profiles, and field studies. The abrupt change in direction of the Rio Pastaza from transverse to longitudinal was a result of two avulsions occurred between 1906 and 1976 at the braided-meandering transition of the former alluvial plain. These avulsions are related to aggradation at the toe of a braided piedmont fan prograding on to a hinterland-dipping topographic slope formed by ongoing tectonic backtilting. The main avulsion proceeded by annexation of a south-dipping depression created in front of the cordillera by backtilting of the plateau. A partial and gradual avulsion having occurred upstream of the former site between 1976 and 2008 is marked by the progressive predominance of a newly formed inner branch. Tectonic backtilting enhanced aggradation upstream of the initial site while it offered the newly avulsed channel a still more favorable way along the cordillera by creating a westward lateral slope. The correlation between ENSO events and the occurrence of the 1976–2008 avulsions strongly suggests that the triggers of the avulsions were the floods caused by the high water and sediment discharges associated with ENSO (La Nina) events contrasting with the regular monthly discharge and the lack of actual ‘normal’ floods during the inter-ENSO periods.

Effects on euthrophication and hydrodynamics of Daning River after impoundment of Three Gorges Reservoir

三峡水库蓄水后支流大宁河水华频发,为了揭示水库蓄水以来,大宁河富营养化变化趋势以及水华暴发期间水动力等环境因子的影响特征,自2005年长期跟踪监测大宁河的水质状况,并于2010年针对东坪坝库湾2次典型水华事件,初步探讨了水华暴发期间的主要影响因素.结果表明:2005年以来,大宁河水体处于中度营养状态,水质尚好,但低估了水华敏感期的富营养化状况.东坪坝3月水华暴发期间,叶绿素a浓度与流速呈显著负相关,与pH、DO也呈显著相关,表明在此次水华期间,流速对藻细胞的增殖或聚集产生直接或间接的影响,pH和DO是引起水华暴发的主要水质因子;5月水华暴发期间,叶绿素a浓度与流速呈显著负相关,与流量呈显著正相关,同时与pH、透明度(SD)呈显著相关,表明在这次水华期间,流速和流量都对藻细胞增殖或聚集产生直接或间接的影响,pH和SD成为水质敏感因子.3月和5月水华暴发时间分别处于水库高水位运行期和泄水期,这可能是导致水华影响因子不同的主要原因,但具体机理还有待于进一步研究.本文结果表明在三峡水库调度运行的不同阶段支流库湾水华暴发的机制不同,需要针对不同时段支流库湾水环境特征分别加以调查研究.;Algal blooms have occurred frequently in the backwater region of the Daning River branch since the impoundment of the Three Gorges Reservoir(TGR). In order to assess the water quality status and the driving factors on algal bloom outbreak, the water quality has been monitored since 2005, and 2 typical algal blooms, occurred in Dongpingba in March and May 2010, were investigated. Results showed that Daning River was mesotrophic and water quality was good, nevertheless the trophic grade was underestimated for the period of algal bloom outbreak. For algal bloom in March, there was a significant negative correlation between Chl. a concentration and velocity, while obvious relationships in Chl. a and pH or DO, indicating that velocity was an important factor for this bloom outbreak and pH, DO were sensitive factors caused by bloom. For algal bloom in May, there was a significant negative correlation between Chl. a concentration and velocity, while a significant positive correlation between Chl. a and flow quantity, and also obvious relationship in Chl. a and pH, SD. It indicated that velocity and flow quantity were important factors for algal bloom outbreak in May, and pH, SD became the sensitive indices. According to the operational schedules of TGR, March and May belong to the period with high water level and discharge, respectively. Schedule times with different hydrodynamics may be responsible for the difference of effect factors on algal bloom, but the mechanism need to be further studied. Results suggested that the algal bloom mechanism in the different operational schedules of TGR is different from each other significantly. Therefore, the study on algal bloom in backwater region of Daning River need to be performed according to the operational schedule of TGR.

Spatial and temporal trends for water-flow velocity and bed-material sediment transport in the lower Mississippi River

Where rivers near the coastline, the receiving basin begins to influence flow, and gradually varied, nonuniform flow conditions arise. The section of the river affected by nonuniform flow is typically referred to as the backwater segment, and for large lowland rivers, this portion of the river can extend many hundreds of kilometers above the outlet. River morphology and kinematics vary in the backwater segment; however, these channel properties have not been explicitly related to properties of the flow and sediment-transport fields. This study examines the influence of spatially and temporally varying flow velocity and sediment transport on channel properties for the lower 800 km of the Mississippi River, a section of the river that includes the backwater segment. Survey transects (n = 2650) were used to constrain the cross-sectional area of water flow every ∼312 m along the Mississippi River channel for eight successive intervals of water discharge. Assuming conservation of water discharge, the local flow velocity was calculated at each transect by dividing water discharge by the local measurement of cross-sectional flow area. Calculated flow velocity was converted to total bed stress using a dimensionless friction coefficient that was determined by optimizing the match between a predicted and a measured water-surface profile. Estimates for the skin-friction component of the total bed stress were produced from the values for total shear stress using a form-drag correction. These skin-friction bed-stress values were then used to model bed-material transport. Results demonstrate that in the lower Mississippi River, cross-sectional flow area increases downstream during low- and moderate-water discharge. This generates a decrease in calculated water-flow velocity and bed-material transport. During high-water discharge, the trend is reversed: Cross-sectional flow area decreases downstream, producing an increase in calculated water-flow velocity and bed-material transport. An important contribution of this work is the identification of a downstream reversal in the trend for channel cross-sectional area due to variable water discharge. By accounting for the spatial divergences in sediment transport predicted over an average annual hydrograph, we demonstrate the tendency for channel-bed aggradation in much of the backwater reach of the Mississippi River (150–600 km above the outlet); however, a region of channel-bed erosion is calculated for the final 150 km. These results help to explain the spatial variability of channel morphology and kinematics for the lower Mississippi River, and they can be extended to other lowland river systems near the coastline.

Punctuated sand transport in the lowermost Mississippi River

[1] Measurements of sand flux and water flow in the Mississippi River are presented for a portion of the system 35–50 km upstream from the head of its subaerial delta. These data are used to provide insight into how nonuniform flow conditions, present in the lower reaches of large alluvial rivers, affect the timing and magnitude of sand transport near the river outlet. Field surveys during both low and high water discharge include (1) sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux, (2) multiple water velocity profiles, and (3) multiple suspended sediment profiles collected using a point-integrated sampler. These data show that total sand transport increases by two orders of magnitude over the measured range in water discharge (11,300 to 38,400 m3 s−1). During low water discharge no sand is measured in suspension, and sand discharge via bed form migration is minimal. During high water discharge 54% of the sand discharge is measured in suspension while 46% of the sand discharge is part of bed form migration. The component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms, and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles. The estimates of boundary shear stress, using measurements of suspended sand transport, bed form transport, and downstream oriented velocity profiles are internally consistent; moreover, the analyses show that boundary shear stress increases by nearly 10-fold over the measured water discharge range. We show how this increase in shear stress is consistent with backwater flow arising where the river approaches its outlet. The hydrodynamic properties of backwater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost Mississippi River. Our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost Mississippi River.

Hydrodynamic response of the Breton Sound estuary to pulsed Mississippi River inputs

Pulsed re-introduction of Mississippi River water into the deltaic plain has been proposed as a wetland restoration strategy for coastal Louisiana. In this study, the hydrodynamic response of the Breton Sound estuary to a two-week pulse of Mississippi River water via the Caernarvon river diversion structure was investigated using a barotropic, three-dimensional, Finite-Volume Coastal Ocean Model (FVCOM). The numerical model was driven by tidal and subtidal forcing at the open Gulf boundary, freshwater discharge from the Caernarvon river diversion structure, as well as wind stress at the water surface. After successfully validating the model with field observations, three numerical experiments were run to assess the response of current, water level, and marsh flooding to different diversion discharge scenarios. The three scenarios considered were: a pulsed scenario of ∼200 m 3 s −1 corresponding to the actual diversion discharge in March 2001, a constant discharge scenario of 40 m 3 s −1 corresponding to the annually averaged discharge of 2001, and a scenario with no discharge. Numerical simulation results indicated that constant 40 m 3 s −1 discharge caused little change in wetland inundation comparing to the no discharge case and, thus, inter-exchange between deep channels and the wetlands was not improved by this rate of diversion discharge. In contrast, the two-week ∼200 m 3 s −1 discharge caused enhanced water exchange between wetlands and adjacent water bodies, substantially increasing water velocity in the bayous and channels of the upper estuary. These effects occurred in the estuary to about 20–25 km from the diversion structure, and caused a noticeable increase in down-estuary residual current with a significant reduction of local estuarine residence times for the whole estuary. Beyond 30 km from the diversion structure, the impact of high water discharge was small and the hydrodynamics was mostly controlled by tides and wind.

Responses of a Maritime Antarctic lake to a catastrophic draining event under a climate change scenario

The limnological features of Lake Boeckella, the main water body of Esperanza/Hope Bay (Antarctic Peninsula), were evaluated over a 16-year period, under a climate change context evidenced by the increasing air temperature trend reported for this region for the last 50 years. We analyzed the physicochemical and phytoplankton data of the lake obtained from 1991 to 2007 during the austral summers. At the beginning of January 2001, a sudden water level drop (~3 m) occurred in Lake Boeckella as a consequence of an extremely high water discharge to the sea. This was triggered by the progressive thawing of the permafrost in the basin of the system. After this disturbance, nutrients, conductivity, chlorophyll a (Chl a) and picoplankton density showed strong peaks. The pre-draining and post-draining periods showed significant differences for most of the limnological variables analyzed. Secchi disk depth significantly decreased throughout the study period, resulting in a thinner euphotic layer. Chrysophyceae and Volvocales dominated the >2 μm phytoplankton fraction in the lake, but from 2004 onwards, other small-sized eukaryotic algae (3–5 μm) also became very abundant. Autotrophic picoplankton showed a significant peak during the summer when the water level decreased. A shift in their composition was observed through the study period: in 1998, picocyanobacteria were numerically dominant; from 2002 onwards, picoeukaryotes increased and became dominant in 2004. This study suggests that climate change may trigger the thawing of the permafrost in the catchments of Maritime Antarctic lakes, leading to catastrophic draining events, which favor natural eutrophication processes.

Seasonal shifts between autochthonous and allochthonous carbon contributions to zooplankton diets in a subarctic lake

We addressed the extent to which autochthonous and allochthonous carbon sources contribute to zooplankton diet throughout the year in oligotrophic subarctic Lake Saanajärvi. Optical measures of dissolved organic matter (DOM) indicated high water discharge and associated terrestrial DOM during winter and low inputs in summer. Bulk particulate organic matter (POM) showed δ13C values consistent with allochthonous inputs of DOM. The most positive POM δ13C values (−27‰) occurred during winter, when heterotrophic bacteria and nanoflagellates peaked in abundance; the isotopically lighter autotrophic phytoplankton shifted the POM δ13C to −29‰ in summer. The δ13C values of zooplankton were up to 4‰ more negative than those of POM, most likely because detritus and other nonliving material with higher δ13C values comprised 45–90% of POM. The δ13C of the cladoceran Daphnia umbra mirrored the trend of POM δ13C, indicating a dietary shift from heavy dependence on autochthonous carbon in summer to allochthonous or heterotrophic food in winter. The δ13C of the most abundant zooplankton in Lake Saanajärvi, Eudiaptomus graciloides and Cyclops abyssorum, remained low and constant in winter, suggestive of little or no food intake during the 8 months of winter. There are significant differences in the zooplankton utilization of nonphytoplankton carbon in different seasons and among species. Although autochthonous carbon seemed to be mainly responsible for the growth of zooplankton, the ability to utilize allochthonous carbon‐fueled microorganisms explains the survival of Daphnia through winter in northern lakes.

The influence of land cover composition and groundwater on thermal habitat availability for brook charr (Salvelinus fontinalis) populations in the United States of America

Abstract – Brook charr (Salvelinus fontinalis) is a sentinel fish species that requires clean, cold water habitats generally resulting from landscapes that allow for surface water flows devoid of sediment and contaminants and high groundwater discharge of cold water. As such, brook charr are impacted by land cover changes that alter stream temperature regimes. We evaluated brook charr populations across their eastern and midwestern range in the United States with reference to thermal habitat availability in relationship to land cover and per cent baseflow. We found that while forest cover does protect brook charr thermal habitat, high levels of groundwater discharge can allow for increased levels of agriculture within a watershed by keeping the water cold in spite of warm ambient summer temperatures. Our study concludes that with enhanced communication among land, water and fisheries managers, society can provide for sustainable stream salmonid populations despite increased threats on cold water resources.

Impact of rainstorm-triggered landslides on high turbidity in a mountain reservoir

Typhoon-triggered landslides deliver huge amounts of sediment to the upstream channel of the Shihmen Reservoir in northern Taiwan. Observation data regarding landsliding, sediment discharge and water turbidity following five major typhoon events from 1985 to 2006 demonstrated that each time water turbidity in the reservoir area rapidly increased up to ten-fold from the river catchment drainage, and the weight of landslide debris exceeded total sediment discharge five-fold. The fact that huge amounts of landslide debris still remained on upstream slopes and water turbidity suddenly increased in the reservoir area but not in upstream channel implied that the increasing water turbidity in the Shihmen Reservoir was indirectly related to the large landslides occurring in the upstream catchment. The main cause of high turbidity in the reservoir area was that, during a typhoon event, high water discharge flowing into the reservoir scoured the fine fraction sediment at the bottom of the reservoir and formed hyperpycanl flow with high turbidity, which then ascended to contaminate the reservoir surface water.

A quantitative assessment of human impacts on decrease in sediment flux from major Chinese rivers entering the western Pacific Ocean

Major rivers with high sediment or water discharge act as natural integrators of surficial processes, including human activities within their drainage basins, and they are also the primary sources of terrestrial materials entering the ocean. The river‐derived materials flux entering the coastal oceans, however, has been strongly affected by anthropogenic activities. Recent studies related to human impacts on river sediment flux have mainly focused on qualitative descriptions. Here we present a quantitative assessment of human impacts on decrease in sediment flux from nine major Chinese rivers entering the western Pacific Ocean, including Changjiang (Yangtze), Huanghe (Yellow), Zhujiang (Pearl), Songhuajiang, Liaohe, Haihe, Huaihe, Qiantangjiang, and Minjiang. During 1959–2007, dams and reservoirs, soil and water conservation programs, water consumption, as well as sand mining decreased the amount of sediment delivered to the ocean by 28, 11.5, 7.5 and 3 gigatons (Gt), respectively. If combined (50 Gt for the period 1959–2007), this reduction was close to the total decreased sediment flux (43 Gt) measured from these nine major rivers over the same period. Besides, the temporal variations in water and sediment fluxes into the ocean from these rivers generally during 1953–2007 were presented. These results are useful for further studies on Chinese and even global river‐derived material flux to the ocean and associated ecological risks.

Temporal and spatial variations of sediment rating curves in the Changjiang (Yangtze River) basin and their implications

The natural hydrologic regime of the Changjiang (Yangtze River) in China has been disturbed considerably by intensified human activities over the past five decades. In this study, sediment rating curves were analyzed based on monthly data of water discharge and suspended-sediment concentration at stations in the upper (Yichang station), middle (Hankou station) and lower (Datong station) reaches of the Changjiang in different periods from 1955 to 2007. Temporal and spatial variations of the sediment rating curves were analyzed with respect to the impact of human activities and watershed characteristics. Results indicate that human disturbances have had a substantial impact on sediment rating parameters, with the magnitude of the impact related to the scale of the river sections. As indicated by the sediment rating parameters, the sediment transport regimes between the upper and the mid-lower reaches differ significantly. In particular, the impoundment of the Three Gorges Dam in 2003 changed the sediment transport regimes in the upper and mid-lower reaches of Changjiang into similar regimes characterized by a decrease in the sediment transport capacity of high water discharge. Furthermore, the sediment rating curve at the Datong station in 1955–1968 was applied to estimate the potential sediment load (1969–2007) in the absence of human influences. The mean annual sediment deficit caused by human activities has increased from 80 Mt/yr (1969–1985) to 250 Mt/yr (2003–2007). This indicates that intensified human activities in the Changjiang basin, especially the construction of the Three Gorges Dam, have altered the natural sediment transport process, and have thus become a dominant force in Changjiang sediment delivery to the sea.

Low retention of nitrogen in a clear-water, shallow, temperate lake

Little Budworth Pool in Cheshire, UK is a small (5 ha), shallow (maximum depth < 1 m) lake with very high total nitrogen (TN) concentration (96 % as NO 3 -N), without any submerged macrophyte beds but with abundance of filamentous green algae. The pool has one inflow surrounded by a reed bed at its entry to the lake, and one outflow. A two-year study revealed high nitrogen loading (mean 15.8 ± SEM 1.1 kg TN ha -1 d -1 ), high annual loss of nitrogen through the outflow (mean 14.2 ± 1.1 kg TN ha -1 d -1 ), and low annual nitrogen retention (mean 1.6 ± 0.3 kg TN ha -1 d -1 ). The small surface area, shallowness, high water discharge (mean 4.3 ± 0.3 x 10 3 m 3 d -1 ), short water residence time (mean 6.5 ± 0.4 day), and a lack of submerged macrophytes for removing nutrients as well as promoting sedimentation by reducing water velocity could explain low nitrogen retention in Little Budworth Pool. The lake, however, acted as an efficient sink for NO 3 -N and TN in summer apparently due to denitrification and uptake of nitrogen by the filamentous green algae (mostly Spirogyra sp.). The reed bed, on the contrary, did not act as a significant source or sink of nutrients probably because of its small area compared with the catchment, and the catchment slope.

Geomorphological evolution of the Tilcara alluvial fan (Jujuy Province, NW Argentina): Tectonic implications and palaeoenvironmental considerations

The development and evolution of the Tilcara alluvial fan, in the Quebrada de Humahuaca (Andean Eastern Cordillera, NW Argentina), has been analysed by using geomorphological mapping techniques, sedimentological characterisation of the deposits and OSL chronological methods. It is a complex segmented alluvial fan made up of five evolutionary stages (units Qf1, Qf2, Qf3, Qf4 and Qf5) developed under arid climatic environments as well as compressive tectonic conditions. Segmentation processes, including aggradation/entrenchment cycles and changes in the location of the depositional lobe, are mainly controlled by climatic and/or tectonic changes as well as channel piracy processes in the drainage system. Alluvial fan deposits include debris flows, sheet flows and braided channel facies associated with high water discharge events in an arid environment. The best mean OSL age estimated for stage Qf2 is 84.5 ± 7 ka BP. In addition, a thrust fault affecting these deposits has been recognized and, as a consequence, the compressive tectonics must date from the Upper Pleistocene in this area of the Andean Eastern Cordillera.

Potential Changes in Extreme Events Under Global Climate Change

Climate-related disasters are a serious problem in Asia. Advances in the understanding of meteorology and in the development of monitoring and forecasting systems have enhanced early warning systems, contributing immensely to reducing fatalities resulting from typhoons, cyclones, and floods. The frequency of extreme events causing water-related disasters has increased, however, over the last decade and may grow in the future due to anthropogenic activity. The sections that follow introduce two recent efforts in hydrologic projection in Asia. Time-slice ensemble experiments using a high-resolution (T106) atmospheric general circulation model (AGCM) on the earth simulator revealed changes in the South Asian summer monsoon resulting from climate change. Model results under global warming conditions suggest increases in mean and extreme precipitation during the Asian summer monsoon. increases generally attributed to greater atmospheric moisture content. a thermodynamic change. Dynamic changes limit the intensification of mean precipitation. Enhanced extreme precipitation over land in South Asia arises from dynamic rather than thermodynamic changes. The impact of global warming on heavy precipitation features and flood risks in the Tama River basin in Japan is addressed using 12 atmosphere-ocean coupled general circulation models (AOGCMs). Multi-model ensemble average 200-year quantiles in Tokyo from 2050 to 2300 under Intergovernmental Panel on Climate Changes (IPCC) Special Reports on Emissions Scenarios (SRES) A1B scenario climate conditions were 1.07-1.20 times greater than that under present climate conditions. A 200-year quantile extreme event in the present occurs in much shorter return periods in the A1B scenario. High-water discharge in the basin rose by 10%-26% and flood volume increased by 46%-131% for precipitation in a 200-year return period. The risk of flooding in the basin is thus, even though the increase of extreme precipitation is not substantial, projected to be much higher than that presently estimated.

Morphological Variations of A Certain Tigris River Reach For Different Periods in Iraq

A morphological variations occurs in the paths of rivers due to many reasons such as the hydraulic changes in the natural flow regime of rivers in-addition to the human activities on rivers such as dams constructions on rivers. Many morphological variations created on Tigris river reach within Mosul city, north Iraq for different periods between 1956 to 2002 had been studied such as the changes on the river width specially near the bridges sites and also the development of the dimensions of the islands and bars within the river reach. The available topographic maps and also an aerial photographs were depended during the data analysis with some field reconnaissance . The research work concluded that one of the main reasons for the development of the islands is the flow regime variation of Tigris river as a result of the Mosul dam operation which in-turn leaded to a reduction in the transported sediment load in the reach due to the released high stream power clear water discharges of sediment from Mosul dam. The second reason was the reduction in the water level which in-turn change the middle and side islands in the river with the growing vegetation cover such as trees and weeds specially in the sites downstream the meander of Al-Rashidia Village and downstream Al-Shuhadaa bridge and upstream Ninevah bridge and finally upstream the fourth bridge in Mosul city.

Rainforest conversion in Central Sulawesi, Indonesia: recent development and consequences for river discharge and water resources

Summary: The present land cover of humid tropical catchment areas mainly regulates the flow of vapour to the atmosphere.Therefore land use decisions play an important role for the water balance of a tropical catchment. Studies that relate land coverchanges with river discharge changes for humid tropical catchment areas at the mesoscale level are rare. This article applies anintegrated remote sensing and hydrological modelling approach to analyse the impact of land cover changes on the water resources of a mesoscale humid tropical catchment. First, a change detection analysis of Landsat/ ETM + satellite images wascarried out to quantify land cover changes of the mesoscale Gumbasa River catchment in Central Sulawesi, Indonesia. There-after the distributed hydrological model WASIM-ETH was calibrated and validated for the current Landsat/ ETM + scene.The historical Landsat/ ETM + scene was integrated for the hydrological model application as a historical land cover scenario.Further hypothetical total-change scenarios were carried out. The results of the hydrological model scenario application clearlydemonstrate a strong relationship between deforestation rates and increasing discharge variability. Especially a significant increase of high water discharges was simulated for the applied scenarios. With regard to the high deforestation rates of the research catchment, one can expect further changes of the water balance.

Factors controlling the seasonal development and distribution of the phytoplankton community in the lowland course of a large river in Northern Italy (River Adige)

The principal environmental factors influencing the seasonal dynamics of phytoplankton were examined from September 1997 to July 1998 in three stations along a 26-km stretch of the lowland course of River Adige (northeast Italy). Nutrient concentrations did not appear to be limiting for the phytoplankton growth. Annual minimum concentrations of reactive and total phosphorus, and dissolved inorganic nitrogen were 22 μg P l−1, 63 μg P l−1 and 0.9 mg N l−1, respectively. The most critical forcing factors were physical variables, mainly water discharge and other variables related to hydrology, i.e. suspended solids and turbidity, which acted negatively and synchronously by diluting phytoplankton cells and decreasing light availability. Higher algal biomass was recorded in early spring, in conditions of lower flow velocity and increasing water temperature. In late spring and summer, higher water discharge caused a decrease in phytoplankton biomass. Conversely, low algal biomass in late autumn and winter, during low discharge, was mainly related to low water temperatures and shorter photoperiod. Physical constraints had a significant and measurable effect not only on the development of total biomass, but also on the temporal dynamics of the phytoplankton community. Abiotic and biotic variables showed a comparable temporal development in the three sampling stations. The small number of instances of spatial differences in phytoplankton abundance during the period of lower flow velocity were related to the increasing importance of biological processes and accumulation of phytoplankton biomass.

Distribution and seasonal changes of lead in an estuarine system affected by agricultural practices: The Penzé estuary, NW France

Over this one-year study, we examined the variations of lead along the salinity gradient of the Penzé estuary (Brittany, Western Channel, France). Concentrations of total dissolved and total particulate lead ranged from 0.04 to 0.62 nM and from 29 to 61 μg g −1, respectively. These values, though being higher than contamination-free systems, remain lower than those found in heavily industrialised systems indicating a limited effect of agricultural practices. Our field data showed, for most seasons (i.e. spring, summer and autumn), a metal removal in the salinity range 0–10, effected mainly by co-precipitation with iron and manganese oxides. On the other hand, after a strong winter ascending flood, an addition of dissolved lead occurred in the estuary following resuspension of particles and desorption mechanisms. This metal addition along with the high water discharge were responsible for the particularly high Pb output flux reported for winter (67 g day −1) compared to the ones estimated for other seasons (1–18 g day −1).

Evolution of Quaternary alluvial fans and terraces in the intramontane Pinjaur Dun, Sub‐Himalaya, NW India: interaction between tectonics and climate change

AbstractQuaternary alluvial fans in the tectonically active Pinjaur Dun, an intramontane valley in the Sub‐Himalaya, were deposited in front of the Nalagarh Thrust and were influenced both by tectonics and glacial climate fluctuations. The surface morphology indicates that an earlier set of first‐order fans (Qf1) became entrenched and onlapped by a series of second‐order fans (Qf2). The younger fan segments were then cut by a pair of terraces (T1 and T2). Quartz optically stimulated luminescence dating establishes that the Qf1 aggradational phase was initiated before 96·5 ± 25·3 ka and terminated after 83·7 ± 16·3 ka. This was followed by a period of incision, before Qf2 fan deposition started at 72·4 ± 13·4 ka and continued until 24·5 ± 4·9 ka. Sediment was deposited on the T1 (upper) and T2 (lower) terraces at 16·3 ± 2·1 and 4·5 ka, respectively, recording a return to overall degradation punctuated by minor deposition on terraces. The period of incision separating the younger and older fan deposits coincided with enhanced SW monsoon precipitation. The subsequent development of the Qf2 fans and their progradation until 20 ka suggest erosional unloading of the thrust hangingwall during a tectonically quiescent phase. Toe cutting, deposition of axial river and lacustrine facies, and retreat of Qf2 around 45 ka, indicate fanward shift of the axial river due to tilting of the valley towards the NE in response to reactivation of the Nalagarh Thrust. The cessation of Qf2 deposition around 20 ka and the onset of through‐fan entrenchment suggest reduced sediment supply but relatively high stream power during the last glacial maxima (LGM). The prolonged stream incision since the cessation of Qf2 deposition, with only minor depositional phases at 16·3 ± 2·1 and 4·5 ka, resulted from high water discharge and low sediment input during intensification of the SW monsoon and vegetation changes in the hinterland.

Seasonal variation of sediment toxicity in the Rivers Dommel and Elbe

Contaminated sediment in the river basin has become a source of pollution with increasing importance to the aquatic ecosystem downstream. To monitor the temporal changes of the sediment bound contaminants in the River Elbe and the River Dommel monthly toxicity tests were applied to layered sediment and river water samples over the course of 10 months. There is an indication that contaminated sediments upstream adversely affected sediments downstream, but this process did not cause a continuous increase of sediment toxicity. A clear decrease of toxic effects in water and upper layer sediment was observed at the River Elbe station in spring related to high water discharge and algal blooms. The less obvious variation of sediment toxicity in the River Dommel could be explained by stable hydrological conditions. Future monitoring programmes should promote a more frequent and intensive sampling regime during these particular events for ecotoxicological evaluation.