Changes In River Discharge Research Articles

Changes in Species Composition in Alder Swamp Forest Following Forest Dieback

It is generally hypothesized that forest dieback is a characteristic of alder swamp forests (alder carrs, Alnion glutinosae alliance). Different internal and external factors may trigger this process, including human disturbance, changes in river discharge, unusually severe and prolonged flooding, terminal age of an even-aged alder forest (ca. 100–150 years) and others. Although forest dieback in this type of forest may cause major changes in environmental conditions, the influence of this change on the floristic composition has not been well recognized. The study aimed to detect any possible changes in floristic variation in alder swamp forest following forest dieback. Vegetation plots in alder swamp forests affected by forest dieback were resurveyed 20 years after a previous study. PERMANOVA was used to test the significance of the compositional change and nonmetric multidimensional scaling (NMDS) with passively fitted means of the Ellenberg’s Indicator Values were used to interpret its ecological meaning. In addition, different structural and diversity indices were compared, including species richness, percentage cover of vegetation layers, Shannon and Simpson diversity and evenness. Finally, we analyzed changes in the frequency of vascular plant species using Chi square tests. We recorded clear and significant compositional changes following alder swamp forest dieback. This change was most related to the gradient of moisture, followed by the gradients of light and temperature. The analysis of the individual species showed that the species of hummocks declined, while the species of hollows increased. Moreover, the current communities are dominated by some hydrophytes that were not recorded 20 years ago. Forest dieback resulted in profound changes in the hydrological regime. The observed changes are consistent with a model of cyclic succession as proposed for alder swamps. In addition, we conclude that the natural forest dynamics have to be taken into consideration while interpreting the results of re-survey studies.

Climatic control of Mississippi River flood hazard amplified by river engineering.

Over the past century, many of the world's major rivers have been modified for the purposes of flood mitigation, power generation and commercial navigation. Engineering modifications to the Mississippi River system have altered the river's sediment levels and channel morphology, but the influence of these modifications on flood hazard is debated. Detecting and attributing changes in river discharge is challenging because instrumental streamflow records are often too short to evaluate the range of natural hydrological variability before the establishment of flood mitigation infrastructure. Here we show that multi-decadal trends of flood hazard on the lower Mississippi River are strongly modulated by dynamical modes of climate variability, particularly the El Niño-Southern Oscillation and the Atlantic Multidecadal Oscillation, but that the artificial channelization (confinement to a straightened channel) has greatly amplified flood magnitudes over the past century. Our results, based on a multi-proxy reconstruction of flood frequency and magnitude spanning the past 500 years, reveal that the magnitude of the 100-year flood (a flood with a 1 per cent chance of being exceeded in any year) has increased by 20 per cent over those five centuries, with about 75 per cent of this increase attributed to river engineering. We conclude that the interaction of human alterations to the Mississippi River system with dynamical modes of climate variability has elevated the current flood hazard to levels that are unprecedented within the past five centuries.

Adaptation strategies of agriculture and water management to climate change in the Upper Tarim River basin, NW China

The Upper Tarim River basin, contributing about 85% of the total inflow to the mainstream Tarim River, is heavily influenced by climate change and human interferences. This study is the first integrated assessment of agriculture and water management under climate change scenarios for this arid river basin in Central Asia. It aims to analyze changes in river discharge of the Upper Tarim under 28 climate projections for 3 representative concentration pathways (RCP) and the A1B scenario and 30 combinations of changes in land use (agricultural area) and water saving measures considered as adaptation strategies. Headwater discharge simulations of two hydrological models (SWIM-G and WASA) are used to drive a hydrological model of the lowland area (SWIM-oasis), taking account irrigation and river transmission losses. The projections show that the river discharge of the Upper Tarim River is likely to increase in a warmer climate if the agricultural area is reduced to the level as in 1998 even without any water saving measures. If the agricultural area increases to the 2010 level, strong water saving measures must be applied to ensure sufficient water inflow to the mainstream Tarim under all climate scenarios. If agricultural area continues to expand, there is a risk of decreasing river discharge at the end of this century under the RCP2.6 scenario. The uncertainty of the projections is large, especially in the far future, and it is mainly related to the climate and hydrological models.

Hydrological impacts in La Plata basin under 1.5, 2 and 3 °C global warming above the pre‐industrial level

The assessment of regional climate and hydrological impacts at different levels of global‐mean temperature increase became vital to guide decision makers and water management planners after the adoption of the Paris Agreement in 2015. With current emission trends close to a pathway of 3 °C warming by the end of the present century, this study investigates the projected regional hydrology impacts over La Plata basin (LPB) for the warming thresholds of 1.5 and 2 °C established in Paris and for 3 °C above the pre‐industrial level. We also explore the consequences from following a medium or high‐emission representative concentration pathway (RCP) to achieve the different warming targets. In order to determine the possible changes in precipitation, evapotranspiration, runoff and river discharges, we use the variable infiltration capacity (VIC)‐distributed hydrology model in combination of bias‐corrected GCM outputs from the Inter‐Sectorial Impact Model Intercomparison Project phase 2a (ISIMIP). Because the behaviour of the hydrometeorological variables is not homogeneous over LPB, we analysed impacts of the different changes in mean global temperature and RCPs over four sub‐basins: Paraguay, Paraná, Iguazú and Uruguay. Overall, most of the changes over the sub‐basins suggest moister conditions with increasing temperatures. The comparison of the RCPs indicates that increases in precipitation, evapotranspiration and runoff would be larger under the medium‐emission scenario. When the different responses of the various components of the terrestrial water cycle were integrated, results show that variation of annual mean streamflow in all sub‐basins ranges between ±20%. However, in most cases, the sign of the changes highly depends on the RCP chosen to achieve a warming level.

Simulating the responses of a low-trophic ecosystem in the East China Sea to decadal changes in nutrient load from the Changjiang (Yangtze) River

Using a three-dimensional coupled biophysical model, we simulated the responses of a lowtrophic ecosystem in the East China Sea (ECS) to long-term changes in nutrient load from the Changjiang (Yangtze) River over the period of 1960–2005. Two major factors affected changes in nutrient load: changes in river discharge and the concentration of nutrients in the river water. Increasing or decreasing Changjiang discharge induced different responses in the concentrations of nutrients, phytoplankton, and detritus in the ECS. Changes in dissolved inorganic nitrogen (DIN), silicate (SIL), phytoplankton, and detritus could be identified over a large area of the ECS shelf, but changes in dissolved inorganic phosphate (DIP) were limited to a small area close to the river mouth. The high DIN:DIP and SIL:DIP ratios in the river water were likely associated with the different responses in DIN, DIP, and SIL. As DIP is a candidate limiting nutrient, perturbations in DIP resulting from changes in the Changjiang discharge are quickly consumed through primary production. It is interesting that an increase in the Changjiang discharge did not always lead to an increase in phytoplankton levels in the ECS. Phytoplankton decreases could be found in some areas close to the river mouth. A likely cause of the reduction in phytoplankton was a change in the hydrodynamic field associated with the river plume, although the present model is not suitable for examining the possibility in detail. Increases in DIN and DIP concentrations in the river water primarily led to increases in DIN, DIP, phytoplankton, and detritus levels in the ECS, whereas decreases in the SIL concentration in river water led to lower SIL concentrations in the ECS, indicating that SIL is not a limiting nutrient for photosynthesis, based on our model results from 1960 to 2005. In both of the above-mentioned cases, the sediment accumulation rate of detritus exhibited a large spatial variation near the river mouth, suggesting that core sample data should be carefully interpreted.

A model-based assessment of the environmental impact of land-use change across scales in Southern Amazonia

This article describes the design of a new model-based assessment framework to identify and analyse possible future trajectories of agricultural development and their environmental consequences within the states of Mato Grosso and Para in Southern Amazonia, Brazil. The objective is to provide a tool for improving the information basis for scientists and policy makers regarding the effects of global change and national environmental policies on land-use change and the resulting impacts on the loss of natural vegetation, greenhouse gas emissions, hydrological processes, and soil erosion within the region. For this purpose, the framework combines the regional land-use models, LandSHIFT and alucR, the farm-level model, MPMAS, and the MONICA crop model, with a set of environmental impact models that are operating at the regional and watershed levels. As a first application of the framework, four scenarios with the time horizon 2030 were specified and analysed. Future land-use change will strongly depend on the interplay between the production of agricultural commodities, the agricultural intensification in terms of increasing crop yields and pasture biomass productivity, and the enforcement of environmental laws and policies. On the regional level, the scenarios with the highest increase in agricultural production in combination with weak law enforcement (Trend and Illegal Intensification) generated the highest losses in natural vegetation due to the expansion of agricultural area as well as the highest greenhouse gas emissions. Also, at the watershed level, these scenarios are characterised by the highest changes in river discharge and soil erosion that might lead to a further decline in soil fertility in the long term. Moreover, the analysis of the Sustainable Development scenario indicates that a shift in agricultural production patterns from livestock to crop cultivation, together with effective law enforcement, can effectively reduce land-use change and its negative effects on the environment. With the scenario analysis, we could illustrate that our assessment framework is capable to provide a large variety of valuable information to support the development of future land-use strategies in the study region.

Compositional changes and molecular transformations of dissolved organic matter during the arctic spring floods in the lower Churchill watershed (Northern Manitoba, Canada)

The spring flood season in Northern aquatic systems is characterized by rapid changes in river discharge and fluxes of organic and inorganic species, yet remains under sampled. In this study, we examine the molecular characteristics and transformations of dissolved organic matter (DOM) during the Arctic spring season at three locations in the lower Churchill River watershed. Characteristics including dissolved organic carbon concentrations, optical properties (i.e. absorbance and, excitation-emission matrix fluorescence coupled with parallel factor analysis, EEM-PARAFAC) and molecular characterization using high resolution mass spectrometry (HR-MS) were assessed. As spring floods progressed, a significant reduction in DOM spectral slope (S275–295) and an increase in absorbance (a270) were observed suggesting an increase in DOM molecular weight and concentrations at all sampled locations. A maximum in HR-MS lignin-class compounds coincided with peak flow at all sampled locations, further validated with an increase in PARAFAC humic-like components and a minimum in S275–295. Principal component analyses revealed that both protein and aromatic humic-like material measured by HR-MS and EEM-PARAFAC, respectively, were significantly correlated (ANOVA, p < 0.05), demonstrating similarities in both techniques. Based on network analysis of HR-MS assigned formula, the highest peak flow day was characterized by a maximum in homologous DOM of C2H2O and C2H4 additions, suggesting structural similarities in newly deposited lignin and humic material. Overall, the progression of the spring freshet shifted the lower Churchill River watershed from an environment rich in proteins and lipids to an aquatic system more abundant in lignin, aromatic and humic DOM.

Future river flows and flood extent in the Upper Niger and Inner Niger Delta: GCM-related uncertainty using the CMIP5 ensemble

ABSTRACTA semi-distributed hydrological model of the Upper Niger and the Inner Niger Delta is used to investigate the RCP 4.5 scenario for 41 CMIP5 GCMs in the 2050s and 2080s. In percentage terms, the range of change in precipitation is around four times as large as for potential evapotranspiration, which increases for most GCMs over most sub-catchments. Almost equal numbers of sub-catchment–GCM combinations experience positive and negative precipitation change. River discharge changes are equally uncertain. Inter-GCM range in mean discharge exceeds that of precipitation by three times in percentage terms. Declining seasonal flooding within the Inner Delta is dominant; 78 and 68% of GCMs project declines in October and November for the 2050s and 2080s, respectively. The 10- and 90-percentile changes in mean annual peak inundation range from −6136 km2 (−43%) to +987 km2 (+7%) for the 2050s and −6176 km2 (−43%) to +1165 km2 (+8.2%) for the 2080s.

Stratification and salt-wedge in the Seomjin river estuary under the idealized tidal influence

Advection, straining, and vertical mixing play primary roles in the process of estuarine stratification. Estuaries can be classified as salt-wedge, partially-mixed or well-mixed depending on the vertical density structure determined by the balancing of advection, mixing and straining. In particular, straining plays a major role in the stratification of the estuarine water body along the estuarine channel. Also, the behavior of a salt wedge with a halocline shape in a stratified channel can be controlled by the competition between straining and mixing induced by buoyancy from the riverine source and tidal forcing. The present study uses Finite Volume Coastal Ocean Model (FVCOM) to show that straining and vertical mixing play major roles in controlling along-channel flow and stratification structures in the Seomjin river estuary (SRE) under idealized conditions. The Potential Energy Anomaly (PEA) dynamic equation quantifies the governing processes thereby enabling the determination of the stratification type. By comparing terms in the equation, we examined how the relative strengths of straining and mixing alter the stratification types in the SRE due to changes in river discharge and the depth resulting from dredging activities. SRE under idealized tidal forcing tends to be partially-mixed based on an analysis of the balance between terms and the vertical structure of salinity, and the morphological and hydrological change in SRE results in the shift of stratification type. While the depth affects the mixing, the freshwater discharge mainly controls the straining, and the balance between mixing and straining determines the final state of the stratification in an estuarine channel. As a result, the development and location of a salt wedge along the channel in a partially mixed and highly stratified condition is also determined by the ratio of straining to mixing. Finally, our findings confirm that the contributions of mixing and straining can be assessed by using the conventional non-dimensional parameters with respect to salt-wedge behavior.

The impact of changed river discharge on water quality deterioration in a prairie lake revealed by the sedimentary evidence

Abstract In order to investigate the historical water quality state and identify the factors causing modern environmental degradation in a prairie lake, total organic carbon (TOC), total nitrogen (TN), stable carbon isotopes of organic matter and total phosphorus (TP) from lake sedimentary core with high resolution age frame were analyzed. The results show that the values of proxies (TOC, TN, TP, δ13C, C/N) increased significantly after 2000 compared with before, which indicates Lake Hulun has heightened nutrient level and pollution extent, thus induced growth of algal bloom and water quality deteriorated after 2000. Since the event of decreased river discharge and lowered water level began in 2000 corresponds extremely well with our sedimentary records that nutrients pollution and eutrophication occurred in Lake Hulun at the same moment, the change of river discharge can be seen as the primary and direct reason of lake water quality deterioration in this period. In addition, the increased wind and water erosion as a result of serious and widespread destruction of grassland in Lake Hulun basin is the potential factors for changing the nutrients concentration in Lake Hulun.

Bacterial Biogeography across the Amazon River-Ocean Continuum.

Spatial and temporal patterns in microbial biodiversity across the Amazon river-ocean continuum were investigated along ∼675 km of the lower Amazon River mainstem, in the Tapajós River tributary, and in the plume and coastal ocean during low and high river discharge using amplicon sequencing of 16S rRNA genes in whole water and size-fractionated samples (0.2–2.0 μm and >2.0 μm). River communities varied among tributaries, but mainstem communities were spatially homogeneous and tracked seasonal changes in river discharge and co-varying factors. Co-occurrence network analysis identified strongly interconnected river assemblages during high (May) and low (December) discharge periods, and weakly interconnected transitional assemblages in September, suggesting that this system supports two seasonal microbial communities linked to river discharge. In contrast, plume communities showed little seasonal differences and instead varied spatially tracking salinity. However, salinity explained only a small fraction of community variability, and plume communities in blooms of diatom-diazotroph assemblages were strikingly different than those in other high salinity plume samples. This suggests that while salinity physically structures plumes through buoyancy and mixing, the composition of plume-specific communities is controlled by other factors including nutrients, phytoplankton community composition, and dissolved organic matter chemistry. Co-occurrence networks identified interconnected assemblages associated with the highly productive low salinity near-shore region, diatom-diazotroph blooms, and the plume edge region, and weakly interconnected assemblages in high salinity regions. This suggests that the plume supports a transitional community influenced by immigration of ocean bacteria from the plume edge, and by species sorting as these communities adapt to local environmental conditions. Few studies have explored patterns of microbial diversity in tropical rivers and coastal oceans. Comparison of Amazon continuum microbial communities to those from temperate and arctic systems suggest that river discharge and salinity are master variables structuring a range of environmental conditions that control bacterial communities across the river-ocean continuum.

Comparative Analysis of Distribution of Intertidal Fish Assemblages in Different Estuarine Systems on Northern Coast of Brazil

The northern coast of Brazil has more than 30 estuaries distributed along 650 km of coastline. These conditions favor the presence of relatively large fish communities in estuarine environments, but published information on the fish fauna in tidal creeks in northern Brazil is only available for some mangrove systems, and comparative studies between fish estuarine communities in different tidal creeks are less common. The choice of the study area was based on the fact that it has been poorly investigated with regard to estuarine fish fauna in comparison in mangrove tidal creeks using the same fishing gear. The objective of the present study was to compare the composition of the relative biomass of taxonomic, functional and ecological guilds of fish assemblages occurring in estuarine systems along the northern coast of Brazil. The study area of the present comparative analysis extended from the southeastern edge of the Marajoara Gulf to the western edge of the Maranhense Gulf. A comparative analysis among different estuarine systems was performed using data from other studies. The abundance of juveniles was greater in the Caeté, Curuçá and Cururuca estuaries than other estuaries. Cluster analysis separated the estuaries into two distinct groups and significant differences between these groups only exist in relation to geographical proximity. The present investigation indicates that the coastal region between the states of Pará and Maranhão is characterized by high dynamics and environmental heterogeneity, particularly with regard to changes in river discharge and tidal fluctuations. The present results underscore the importance of ecological information on ichthyofauna in tropical estuaries in order to include appropriate descriptors in conservation or restoration processes of marine communities and habitats.

Assessing changes of river discharge under global warming of 1.5 °C and 2 °C in the upper reaches of the Yangtze River Basin: Approach by using multiple- GCMs and hydrological models

Assessment of climate change impacts on regional hydrological processes is vital for effective water resource management and planning. The 2015 Paris Agreement includes a two-headed temperature goal: “holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C”. The current study assesses the potential effect of global warming of 1.5 °C and 2 °C on river discharge, and their differences in the Upper Yangtze River Basin (UYRB) based on three hydrological models (HBV, SWAT and VIC) driven by bias-corrected climate projections from five General Circulation models (GCMs), namely GFDL, HAD, IPSL, MIROC and NOR as abbreviated, and two Representative Concentration Pathways (RCP2.6 and RCP4.5). Results indicate that all discharges (except autumn) especially winter have slight decreasing tendency (−0.3%, −2.3%, −0.8%, −6.4%, −1.2%, −0.3% respectively for annual, spring, summer, winter, 90% percentile and 10% percentile discharges) under RCP2.6 during 2020–2039 (+1.5 °C global warming) comparing to the reference period of 1986–2005. However, all discharges (except autumn and winter) especially summer have an increasing tendency (1.1%, 1.1%, 3.7%, 0.9%, 2.1% respectively for annual, spring, summer, 90% percentile and 10% percentile discharges) under RCP4.5 during 2040–2059 (+2 °C global warming). Moreover, the occurrence frequency and strength of droughts in dry season under global warming of 1.5 °C will increase, while floods in wet season under global warming of 2 °C tend to increase in UYRB. Additionally, the difference of river discharge between global warming of 2 °C and 1.5 °C is positive for almost all the time scales (1.4%, 3.5%, 4.5%, 2.1%, 2.4% respectively for annual, spring, summer, 90% percentile and 10% percentile discharges), which suggests that the increment of 0.5 °C could lead to more flood events in the UYRB.

Regional climate model and model output statistics method uncertainties and the effect of temperature and precipitation on future river discharges in Scandinavia

We analyze the importance of regional climate models (GCM-RCMs) and model output statistics (MOS) methods as uncertainty sources for future changes of various hydrological variables in Scandinavia. The Hydrological Predictions for the Environment (HYPE) model, driven with daily mean temperature and precipitation, is used to simulate changes in river discharges and other hydrological components from the present-day climate (1980–2009) to mid-21st century conditions (2041–2070). The results show that GCM-RCM differences explain most of the spread in the simulated changes in the annual mean cycle of river discharge. At seasonal level, MOS-method uncertainties are most important during the winter and spring, which is likely explained by the sensitivity of snow processes to the representation of daily variability in the MOS methods. To gain physical insights into the physical processes, the relative importance of changes to temperature or precipitation on changes in surface hydrology are also assessed. In most regions of Scandinavia, changes to temperature explain most of the changes in river discharge volumes and spring peaks. Precipitation changes only have a secondary role in modulating these changes. Again, these results are mostly explained by changes in snow processes in winter and increases in evapotranspiration in summer.

English

Climate change has the potential to affect hydropower generation by either increasing or reducing flows (discharge) and the head. This paper assessed the impacts of climate change on hydropower generation with a focus on Lujeri micro-hydropower scheme in Mulanje district, Malawi. The study analyzed trends in weather time series (air temperature and rainfall) data from 1980 to 2011 in connection to changes in river discharge and their associated impacts on hydropower generation profile. The Mann-Kendall (MK) test was used to detect trends in air temperature, precipitation and discharge. Correlation analysis was also used to uncover the relationship between discharge and precipitation as well as between discharge and temperature. The MK results highlighted significant rising rates of air temperature, precipitation and discharge in some months and decreasing trend in some other months, suggesting significant changes have occurred in the area. The relationship between precipitation and discharge was not significant ( p = 0.552), while that between temperature and discharge was significant ( p = 0.0001). Therefore, as temperature showed significant increasing trend, it will be associated with decrease in discharge, consequently a decrease in hydropower generation (power is directly proportion to discharge). Hence, proper adaptation measures such as standby alternative sources of energy and storage mechanisms devices should be exploited to ensure electric power is available throughout the year, especially in the hot and dry season when the discharge is usually very low. Key words: Climate change, discharge rate, hydropower, Malawi, precipitation, temperature

Observed river discharge changes due to hydropower operations in the Upper Mekong Basin

The Upper Mekong Basin is undergoing extensive hydropower development and its largest dams have recently become operational. Hydropower is built to improve the regional energy supply, but at the same time, it has considerable transboundary impacts on downstream discharge regime and further on aquatic ecosystems, riparian livelihoods and food security. Despite the transboundary significance of the impacts, there is no public information on the hydropower operations or on the already observed downstream discharge impacts since the completion of the largest dams. Therefore, in this study we assess the discharge changes using observed river discharge data and a distributed hydrological model over the period of 1960–2014. Our findings indicate that the hydropower operations have considerably modified the river discharges since 2011 and the largest changes were observed in 2014. According to observed and simulated discharges, the most notable changes occurred in northern Thailand (Chiang Saen) in March-May 2014 when the discharge increased by 121–187% and in July-August 2014 when the discharge decreased by 32–46% compared to average discharges. The respective changes in Cambodia (Kratie) were 41–74% increase in March-May 2014 and 0–6% decrease in July-August 2014 discharges. The earlier model-based predictions of the discharge changes are well in line with the observed changes, although observed changes are partly larger. The discharge impacts are expected to vary from year to year depending on hydropower operations. Altogether, the results highlight the need for strong transboundary cooperation for managing the downstream impacts.

Seasonal hyporheic dynamics control coupled microbiology and geochemistry in Colorado River sediments

AbstractRiverbed microbial communities play an oversized role in many watershed ecosystem functions, including the processing of organic carbon, cycling of nitrogen, and alterations to metal mobility. The structure and activity of microbial assemblages depend in part on geochemical conditions set by river‐groundwater exchange or hyporheic exchange. To assess how seasonal changes in river‐groundwater mixing affect these populations in a snowmelt‐dominated fluvial system, vertical sediment and pore water profiles were sampled at three time points at one location in the hyporheic zone of the Colorado River and analyzed by using geochemical measurements, 16S rRNA gene sequencing, and ecological modeling. Oxic river water penetrated deepest into the subsurface during peak river discharge, while under base flow conditions, anoxic groundwater dominated shallower depths. Over a 70 cm thick interval, riverbed sediments were therefore exposed to seasonally fluctuating redox conditions and hosted microbial populations statistically different from those at both shallower and deeper locations. Additionally, microbial populations within this zone were shown to be the most dynamic across sampling time points, underlining the critical role that hyporheic mixing plays in constraining microbial abundances. Given such mixing effects, we anticipate that future changes in river discharge in mountainous, semiarid western U.S. watersheds may affect microbial community structure and function in riverbed environments, with potential implications for biogeochemical processes in riparian regions.

Seasonal predictions of precipitation in the Aksu-Tarim River basin for improved water resources management

Since the 1950s, the population in the arid to hyperarid Tarim River basin has grown rapidly concurrent with an expansion of irrigated agriculture. This threatens the Tarim River basin's natural ecosystems and causes water shortages, even though increased discharges in the headwaters have been observed more recently. These increases have mainly been attributed to receding glaciers and are projected to cease when the glaciers are unable to provide sufficient amounts of meltwater. Under these circumstances water management will face a serious challenge in adapting its strategies to changes in river discharge, which to a greater extent will depend on changes in precipitation. In this paper, we aim to develop accurate seasonal predictions of precipitation to improve water resources management.Possible predictors of precipitation for the Tarim River basin were either downloaded directly or calculated using NCEP/NCAR Reanalysis 1 and NOAA Extended Reconstructed Sea Surface Temperature (SST) V3b data in monthly resolution. To evaluate the significance of the predictors, they were then correlated with the monthly precipitation dataset GPCCv6 extracted for the Tarim River basin for the period 1961 to 2010. Prior to the Spearman rank correlation analyses, the precipitation data were averaged over the subbasins of the Tarim River. The strongest correlations were mainly detected with lead times of four and five months. Finally, an artificial neural network model, namely a multilayer perceptron (MLP), and a multiple linear regression (LR) model were developed each in two different configurations for the Aksu River subbasin, predicting precipitation five months in advance. Overall, the MLP using all predictors shows the best performance. The performance of both models drops only slightly when restricting the model input to the SST of the Black Sea and the Siberian High Intensity (SHI) pointing towards their importance as predictors.

Impacts of river impoundment on dissolved heavy metals in floodplain soils of the Lahn River (Germany)

The effects of changing soil moisture conditions and oxidation–reduction (redox) processes on dissolved fractions of arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), lead (Pb) and zinc (Zn) were studied in floodplain soils in the Lower Lahn Valley (Germany). Multiple weirs and locks affect the groundwater levels in the adjacent river banks by modifying the river’s discharge rate. Redox conditions act as a key factor for sorption and desorption processes and are strongly regulated by groundwater levels. Hence, floodplain soils situated up- and downstream of impounded river segments were characterized by various contents of their mobile heavy metal fraction. To quantify the variations of the dissolved heavy metal concentrations during seasonal and periodic fluctuations of the groundwater levels, a 2-year field study was conducted. The results indicated that higher seasonal changes of river discharge downstream of a weir caused higher amplitudes of groundwater levels, redox changes and variations in dissolved As, Fe and Mn in soil depths (50–60 cm) with a strong groundwater influence. Upstream of a weir, higher dissolved concentrations and more smooth variations of As, Fe and Mn dominated within the same depths. A high rise of capillary waters within the same study site caused significant enrichments of dissolved Cd and Zn in the middle (25–35 cm) of the soil profile. The comparison of floodplain soils along the Lahn River showed how the stream regulations influence heavy metal concentrations of soil pore waters, which may in turn influence the quality of the river water.

Precipitation changes recorded in the sedimentary total organic carbon isotopes from Lake Poyang in the Middle and Lower Yangtze River, southern China over the last 1600 years

Abstract Lake Poyang, the largest freshwater lake of China, is well known for its ecological and hydrological importance as a dynamic wetland and lake system. The climatic change and its effect on ecological and hydrological system of the lake has aroused considerable interest in recent years. So, a sediment core from Lake Poyang was analyzed for δ 13 C total organic matter (δ 13 Corg) to study the hydrological changes in the Lake Poyang catchment. By comparing with modern meteorological data (precipitation and temperature) and hydrological data (volume of runoff), the result showed that the δ 13 Corg values in the sediment are negatively correlated with the total runoff of the 5 main rivers supplying water to Lake Poyang and precipitation in this area over the past 50 years. Therefore, the δ 13 Corg values of the Lake Poyang sediment can serve as reliable proxies for reconstruction of river discharge and regional precipitation, with negative δ 13 Corg values representing increased precipitation in the Lake Poyang area. On this basis, the river discharge and regional precipitation variation in the Lake Poyang catchment over the past 1600 years were discussed. The δ 13 Corg values suggest that the precipitation was highest in the period 340–880 AD, and then decreased with fluctuations to the minimum at approximately 1110 AD. During the period of Medieval Warm Period (1110–1350 AD, MWP), the precipitation was generally in the high level except low amount during period of 1140 AD to 1220AD. The precipitation was in low amount during the Little Ice Age (1350–1620 AD, LIA), except for a sudden increase at approximately 1550–1560 AD. The precipitation continuously increased with little fluctuation from 1610 AD until now. In general, changes in regional precipitation and river discharge were dominated by variations in the Asian Summer Monsoon (ASM) precipitation in the Lake Poyang area, consistent with other records from the ASM-controlled areas of China.