River Loads Research Articles

Sediment Transport and Its Impacts on Lake Kivu, Gihira Water Treatment Plant and Various Hydropower Plants along Sebeya River in Rwanda

Complex processes of sediment transport in a river impact on overall aquatic system and result in the productivity decrease of socio-economic development projects taking the river as a source of water. The present study was designed to estimate Sebeya river sediment load and assess its impacts on Lake Kivu, Gihira water treatment plant and various hydropower plants constructed in Sebeya catchment located in Western Province of Rwanda. Water samples were hand-collected from five different sampling points along Sebeya river during rainy and dry seasons. Laboratory analysis for turbidity, total suspended solids, sieve analysis for bed load materials and NPK content of water samples were conducted. The results revealed that the average turbidity was found to be high during rainy season compared to dry season. The same trend was found in total suspended solids concentrations. At all 5 sampling sites and during rainy season compared to dry season, the average mass flowrates of bed load materials were 7.84 and 2.96 kg/hr respectively. Sieve analysis results showed that all bed load sediments were mainly composed of high proportions of fine sand of more than 70% which adversely causes damages on hydropower turbines and the effect of high soil erosion rates on Gihira water treatment plant was traduced by high turbidity of raw water and excessive costs of reagents. At Sebeya outlet, nutrients load and high turbidity reduce significantly the aesthetic quality of Lake Kivu, having a harmful impact on recreation and tourism, aquatic life and affect the livelihoods of people living in the vicinity. Researchers recommend two options of reducing the amount of sediment load in Sebeya river: either to prevent soil erosion or to trap eroded sediment at the upstream of the hydropower and the water treatment plants. Assessing the sediment load fluctuations in Sebeya river is useful for water managers and planners to adjust operations accordingly at water treatment and hydropower plants.

Improving total sediment load prediction using genetic programming technique (Case Study: Malaysia)

Predicted total sediment load is usually used to identify the intensity of a sedimentation process. Currently, the existing available models to predict total load are mostly developed based on data collected from flumes, channels and rivers located in western countries. These models known as sediment transport model may not be valid to predict total sediment load of rivers in the tropics due to significant differences in the hydrological and sediment characteristics conditions. A new technique called Genetic programming (GP) technique is used to develop a new model to improve the prediction of total sediment load for rivers in tropical Malaysia. The new model named Evolutionary Polynomial Regression (EPR) model is compared with other three available sediment transport models using the different techniques including, Regression Equation, Modified Graf and Multiple Regression. Statistical analyses based on 82 data sets show the sediment transport model using this new technique perform well compare to other models.

Phosphorus, nitrogen and dissolved organic carbon fluxes from sediments in freshwater rivermouths entering Green Bay (Lake Michigan; USA)

Transitional areas between ecosystem types are often active biogeochemically due to resource limitation changes. Lotic-to-lentic transitions in freshwaters appear active biogeochemically, but few studies have directly measured nutrient processing rates to assess whether processing within the rivermouth is important for load estimates or the local communities. We measured oxic fluxes of inorganic nitrogen and phosphorus and dissolved organic carbon (DOC) from sediments in two rivermouths of Green Bay (Lake Michigan, USA). Soluble reactive phosphorus (SRP) flux was positive in most cases (overall mean 1.74 mg SRP m− 2 day− 1), as was ammonium (NH4) flux (40.6 mg NH4 m− 2 day− 1). Partial least square regression (PLSR) indicated a latent variable associated with both sediment [loosely bound phosphorus (P), iron bound P, organic content] and water column properties [temperature, DOC:dissolved inorganic nitrogen (DIN) and DOC:SRP ratios (negatively)] that was moderately associated with variation in SRP flux. PLSR analysis also indicated several sediment characteristics were moderately related to NH4 flux, especially organic content, density (negative), and porosity. Flux of nitrates/nitrites (NOX) and DOC were positively associated with the water column concentrations of NOX and DOC and qualitative estimates of the labile, non-humic types of DOC. In early summer, water column NOX and DOC concentrations were high and labile DOC may have fueled denitrification, resulting in net flux into sediments of both NOX and DOC. By late summer, water column NOX and DOC were very low and both these constituents were fluxing out of sediments into the water column. Based on our estimates for the entire period from April through September, rivermouth sediments were a net source of SRP and DIN, with a DIN:SRP ratio of ~ 44 and a NH4:NOX > 1. We estimated that the sediments in the Fox rivermouth probably contributed a small proportion of the total Fox River load during the growing season 2016 (< 5%), but at times may have contributed as much as 14% of the daily load. Despite the small size of the Fox rivermouth (< 0.5% of the watershed area), these results indicate that at times sediments can contribute substantially to the overall delivery of nitrogen and phosphorus to the nearshore zone.

Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef, Australia

AbstractDissolved inorganic carbon (DIC) transport by rivers is an important control on the pH and carbonate chemistry of the coastal ocean. Here, we combine DIC and total alkalinity (TAlk) concentrations from four tropical rivers of the Great Barrier Reef region in Australia with daily river discharge to quantify annual river loads and export rates. DIC in the four rivers ranged from 284 to 2,639 μmol kg−1 and TAlk ranged from 220 to 2,612 μmol kg−1. DIC:TAlk ratios were mostly greater than one suggesting elevated exports of free [CO2*]. This was pronounced in the Johnstone and Herbert rivers of the tropical wet north. The largest annual loads were transported in the two large river catchments of the southern Great Barrier Reef region, the Fitzroy and Burdekin rivers. The carbon stable isotopic composition of DIC suggests that carbonate weathering was the dominant source of DIC in the southern rivers, and silicate weathering was likely a source of DIC in the northern Wet Tropics rivers. Annual loads and export rates were strongly driven by precipitation and discharge patterns, the occurrence of tropical cyclones, and associated flooding events, as well as distinct seasonal dry and wet periods. As such, short‐lived hydrological events and long‐term (seasonal and inter‐annual) variation of DIC and TAlk that are pronounced in rivers of the tropical and subtropical wet and dry climate zone should be accounted for when assessing inorganic carbon loads to the coastal ocean and the potential to buffer against or accelerate ocean acidification.

Recent Patterns in Lake Erie Phosphorus and Chlorophyll a Concentrations in Response to Changing Loads.

Despite the initial success of extensive efforts to reduce phosphorus (P) loading to Lake Erie as a part of the Great Lakes Water Quality Agreement, Lake Erie appears to be undergoing a re-eutrophication and it is plagued by harmful algal blooms. To offer insights into potential lake responses under differing Maumee River loads and reveal recent changes with time, we explored patterns in phosphorus and chlorophyll a data from 2008 to 2018 collected in western Lake Erie near the mouth of the Maumee River. We found high, but relatively stable Maumee River and lake concentrations of total P (TP) and soluble reactive P (SRP) with no discernable annual or seasonal patterns. Maumee spring TP load was not strongly related to lake TP, and lake SRP concentrations were positively but weakly related to SRP loads. Lake TP was a strong predictor of chlorophyll a, but the relationship was weaker at sites closer to the Maumee. These results highlight spatial differences both in P concentration and the relationship between TP and chlorophyll a, and these indicate that spring phosphorus loads are a weak algal biomass predictor in the portion of the western basin of Lake Erie represented by these sampling stations.

GLOBAL-FATE (version 1.0.0): A geographical information system (GIS)-based model for assessing contaminants fate in the global river network

Abstract. GLOBAL-FATE is the first open-source, multiplatform, user-friendly, and modular contaminant-fate model operating at the global scale linking human consumption of pharmaceutical-like compounds with their concentration in the river network. GLOBAL-FATE simulates human consumption and excretion of pharmaceuticals, the attenuation of the contaminant load in waste water treatment plants as well as the attenuation of the contaminant load in river reaches, lakes, and reservoirs as a first-order decay depending on residence time. We provide a comprehensive description of model equations and the overall structure of the model, with special attention to input–output datasets. GLOBAL-FATE is written in C, can be compiled in any platform, and uses inputs in standard geographical information system (GIS) format. Additionally, the model can be run in the Quantum Geographic Information System (QGIS) as a plug-in. The model has no built-in working resolution, which depends on the intended use and the availability of appropriate model inputs and observed data. We exemplify the application of GLOBAL-FATE solving the global concentration of diclofenac in the river network. A comparison with a dataset of diclofenac concentration observations in rivers suggests that GLOBAL-FATE can be successfully applied in real-case modelling exercises. The model is particularly sensitive to the generation of contaminant loads by human pharmaceutical consumption and to the processes governing contaminant attenuation in the river network. GLOBAL-FATE will be a valuable tool for the scientific community and the policymaking arena and could be used to test the effectiveness of large-scale management strategies related to pharmaceutical consumption control and waste water treatment implementation and upgrading.

Fertilizer, landscape features and climate regulate phosphorus retention and river export in diverse Midwestern watersheds

Non-point source pollution of phosphorus (P) is a primary cause of eutrophication of aquatic ecosystems, and poses a persistent management challenge due to the dynamic and poorly understood processes controlling the transport and transformation of P at the watershed scale. We examined phosphorus inputs, retention, and riverine losses in 62 diverse watersheds that included a wide range of land cover and use (minimally disturbed to human dominated) and human P inputs in Minnesota, USA. Fertilizer inputs from row crop cultivation were the dominant source of P to agricultural watersheds. A large majority of P inputs was retained in watershed soils or removed in agricultural products. However, fertilizer input was the most important factor associated with average annual river transport of total, dissolved, and particulate phosphorus (PP). Mean annual runoff increased total and dissolved P yields and decreased P retention. Dissolved P made up a significant portion of annual river loads at sites with high rates of P inputs and river TP export, with the ratio of dissolved to PP export increasing with crop cover and fertilizer inputs. PP export rose with larger extents of eroding bluffs near channels. Bluffs constitute only a small proportion of watershed area, but make a disproportionately high contribution to sediment loads due to their close proximity to river channels that are increasingly affected by human and climate-driven changes to river hydrology. Together, our results suggest that rising discharge and flow variability due to climate change and agricultural intensification coupled with high rates of P inputs will maintain elevated fluvial P export into the future. Without reductions in P inputs and reductions in both soluble P losses and stream bank erosion, reversal of water quality degradation will be difficult to achieve.

Effect of instream logs on bank erosion potential: a flume study with a single log

It is well established that riparian trees reduce bank erosion. However, fallen trees can increase bank erosion as the flow is deflected and accelerated between the log and its root-plate and the bank face, increasing the boundary shear stress and eroding the bank. This erosion contributes to hydraulic variability but can also be a concern in restoring wood loads in rivers. In this first quantitative study into this phenomenon, we develop a theoretical hydraulic model to estimate the near-bank velocity around a single log using principles of continuity and energy loss for a range of log characteristics (morphology, angle, distance from the bank) and flow characteristics. Flume experiments support the theoretical model and suggest that a single log can almost double the near-bank velocity. The fractional channel area taken up by the log (blockage ratio) and the distance between the log and the bank are key factors governing the near-bank velocity. The smaller the angle of the log with the bank the lower the erosion rate, but also the further downstream the erosion extends. As the morphology of the log changes after falling into the channel, bank erosion potentially develops quickly, but slows over time; and migrates downstream.

Changes in chlorophyll concentration and phenology in the North Sea in relation to de‐eutrophication and sea surface warming

AbstractAt least two major drivers of phytoplankton production have changed in recent decades in the North Sea: sea surface temperature (SST) has increased by ~ 1.6°C between 1988 and 2014, and the nitrogen and phosphorus loads from surrounding rivers have decreased from the mid‐1980s onward, following reduction policies. Long time series spanning four decades (1975–2015) of nutrients, chlorophyll (Chl), and pH measurements in the Southern and Central North Sea were analyzed to assess the impact of both the warming and the de‐eutrophication trends on Chl. The de‐eutrophication process, detectable in the reduction of nutrient river loads to the sea, caused a decrease of nutrient concentrations in coastal waters under riverine influence. A decline in annual mean Chl was observed at 11 out of 18 sampling sites (coastal and offshore) in the period 1988–2016. Also, a shift in Chl phenology was observed around 2000, with spring bloom formation occurring earlier in the year. A long time series of pH in the Southern North Sea showed an increase until the mid‐1980s followed by a rapid decrease, suggesting changes in phytoplankton production that would support the observed changes in Chl. Linear correlations, however, did not reveal significant relationships between Chl variability and winter nutrients or SST at the sampling sites. We propose that the observed changes in Chl (annual or seasonal) around 2000 are a response of phytoplankton dynamics to multiple stressors, directly or indirectly influenced by de‐eutrophication and climate warming.

Rainfall and Streamflow Effects on Estuarine Staphylococcus aureus and Fecal Indicator Bacteria Concentrations

Pathogenic bacteria in nearshore waters are a public health threat, and many have watershed sources. Hence, understanding direct and indirect causes of bacterial loading can improve awareness and watershed management. Rainfall‐driven runoff influences river discharge, affecting pathogen transport to the ocean. This study assessed pathogen loading to nearshore waters under varying weather conditions within Hilo Bay, Hawaii, from 2014 to 2017. Staphylococcus aureus, methicillin‐resistant S. aureus (MRSA), and fecal indicator bacteria (FIB) were quantified in the bay, rivers, and potential watershed sources using culture‐based methods. Relationships between their concentrations with rainfall, river discharge, and water quality data were examined. Staphylococcus aureus, MRSA, and FIB were present within Hilo Bay and its rivers, as well as road runoff, sewage, and soils; MRSA was less prevalent. Staphylococcus aureus and FIB concentrations increased with rainfall and river discharge. Turbidity and salinity were the best water quality parameters for predicting bacteria concentrations, with positive and negative relationships, respectively. Our results suggest that more intense storms, especially after longer dry periods between events, will increase S. aureus and FIB loads to nearshore waters, as storms comprise &gt;80% of annual river loads. Our models can be used to assess recreational water users’ health risks and predict future water quality conditions with changing rainfall patterns.Core Ideas Staphylococcus aureus and FIB were present in the bay, rivers, road runoff, sewage, and soils. MRSA was less prevalent in the environment than S. aureus and FIB. S. aureus and FIB bay concentrations increased with rainfall and river discharge. S. aureus and FIB bay concentrations varied with bay salinity and turbidity. Bay bacteria concentrations can be modeled from hydrologic and water quality data.

GLAM Bio-Lith RT: A Tool for Remote Sensing Reflectance Simulation and Water Components Concentration Retrieval in Glacial Lakes

A new open--source software tool, called GLAM BioLith--RT (Glacier Lakes Assisted Melting Biological Lithological Radiative Transfer), has been developed for modeling of Radiative Transfer (RT) in water bodies containing suspended lithic particles , phytoplankton, dissolved salts, and colored dissolved organic matter. Although our objective is an application to glacial lakes of High Mountain Asia, the model has potential application for the study of seawater, organic-rich lakes, rivers, etc. The tool is built on a solid foundation of an existing published open-source code called WASI, which has been reviewed and augmented with new capabilities, notably the addition of a suspended lithic particle grain size parameterization. GLAM BioLith-RT operates in both a forward modeling and inverse modeling mode. The forward mode is specifically designed to compute the reflectance spectra of glacier lakes from inherent optical water properties. Conversely, in the inverse mode, measured spectral reflectance is employed with other inputs to derive best fitting water component properties (e.g., suspended particles concentration). The inverse modeling includes Bayesian Optimization of the output which is a significant advance over the existing software. We have tested the code for sensitivity to noise, and uncertainties in input parameters. The model succeeds in nearly reproducing the hyperspectral reflectance of some glacial lakes in Nepal as observed by the EO-1 Hyperion hyperspectral imager. The inverse modeling approach, when supported up by validated forward modeling, offers a means for remote sensing characterization of suspended sediment load in glacial lakes and rivers and hence, use of suspended sediment as a proxy for glacial activity; and many other potential applications in other thematic areas.

Effects of Climate Variability and Human Activities on Suspended Sediment Load in the Ganjiang River Basin, China

AbstractClimate variability and human activities have substantially affected the delivery process of suspended sediment load (SSL) in rivers, which is a major driving force of river configuration a...

Large Scale Flood Hazard Analysis by Including Defence Failures on the Dutch River System

To make informed flood risk management (FRM) decisions in large protected river systems, flood risk and hazard analyses should include the potential for dike breaching. ‘Load interdependency’ analyses attempt to include the system-wide effects of dike breaching while accounting for the uncertainty of both river loads and dike fragility. The intensive stochastic computation required for these analyses often precludes the use of complex hydraulic models, but simpler models may miss spatial inundation interactions such as flows that ‘cascade’ between compartmentalised regions and overland flows that ‘shortcut’ between river branches. The potential for these interactions in the Netherlands has previously been identified, and so a schematisation of the Dutch floodplain and protection system is here developed for use in a load interdependency analysis. The approach allows for the spatial distribution of hazard to be quantified under various scenarios and return periods. The results demonstrate the importance of including spatial inundation interactions on hazard estimation at three specific locations, and for the system in general. The modelling approach can be used at a local scale to focus flood-risk analysis and management on the relevant causes of inundation, and at a system-wide scale to estimate the overall impact of large-scale measures.

Seasonal variation of bacterial load in river and lake waters of Dhaka city, Bangladesh

Surface water is often contaminated due to human excreta and urban and industrial pollution. The increased population growth and industrialization are likely to exacerbate the situation. Microbiological analysis of waters from rivers (Turag and Buriganga) and lakes (Banani and Dhanmondi) around Dhaka city were conducted for Spring, Monsoon and Fall seasons of the year, 2016 and 2017. Total Viable Count (TVC), Total Coliform Count (TCC), Total Fecal Coliform Count (TFCC) and Total Salmonella Shigella Count (TSSC) were conducted to obtain bacterial load in both enriched and without enrichment water samples. All the Isolates were identified by microscopy, cultural characteristics and biochemical methods. Most of the water reservoirs have a decline in the bacterial load in monsoon where the microbial load of pathogens is highest during spring. Without enrichment, E. coli, Enterobacter sp., Klebsiella sp. and S. aureus were abundant, where others like Shigella sp., Proteus sp., Serratia sp., Pseudomonas sp., Acinetobacter sp., and Alcaligenes faecalis mostly exhibited growth following enrichment. Results indicate that pathogenic environmental isolates can cause serious health issue if water is left untreated or poorly treated from reservoirs within and around Dhaka city.&#x0D; Bangladesh J Microbiol, Volume 35 Number 2 December 2018, pp 116-121

Persistent contaminants as potential constraints on the recovery of urban river food webs from gross pollution

Urban areas contribute substantially to xenobiotic contaminant loads in rivers, but their effects have been investigated more for individual organisms and sensitive taxa, rather than through the emergent properties of communities. Here, we use replicated, catchment-scale sampling of benthic invertebrates and novel multivariate techniques to assess whether urban wastewater contaminants affected the structure and function of river food webs. We postulated that the continued occurrence of selected contaminants in river systems might explain the incomplete recovery of urban rivers from legacy gross pollution. Benthic invertebrate communities were sampled monthly over a year (2016–2017) at 18 sites across 3 river systems in South Wales (United Kingdom). Contaminant sources were characterised using remote sensing, water quality data from routine monitoring and measured concentrations of selected persistent xenobiotic pollutants (polychlorinated biphenyls and polybrominated diphenyl ethers). Urban wastewater discharges had relatively limited effects on river water quality, with small increases in nitrate, phosphate, temperature, conductivity and total dissolved solids in urban systems. Concentrations of polychlorinated biphenyls and polybrominated diphenyl ethers in invertebrates, however, were significantly higher under greater urban land cover and wastewater discharge. Food webs at the most highly contaminated urban sites were characterised by: (i) reduced taxonomic and functional diversity; (ii) simplified food web structure with reduced network connectance; and (iii) reductions in the abundance of prey important for apex predators such as the Eurasian dipper (Cinclus cinclus). Although correlative and partially confounded by other effects, these data provide support for the hypothesis that impairment to food webs resulting from urban pollutants might explain population, community and ecosystem-level effects in urban river systems, and hence incomplete recovery from past pollution.

Disentangling the relative impacts of climate change and human activities on fluvial sediment supply to the coast by the world\u2019s large rivers: Pearl River Basin, China

The world’s large rivers are under stress and experiencing unprecedented changes in hydrology, ecosystems, and fluvial sediment loads. Many of these rivers terminate at the great deltas of the world (home to 500 million people), which depend on fluvial sediments for their very existence. While fluvial sediment loads of large rivers have already been greatly modified by human activities, climate change is expected to further exacerbate the situation. But how does the effect of climate change on fluvial sediment loads compare with that of human impacts? Here, we address this question by combining historical observations and 21st century projections for one of the world’s largest 25 rivers containing two mega dams; Pearl River, China. Our analysis shows that variations in fluvial sediment supply to the coast from the Pearl river over a ~150 year study period are dominated by human activities. Projected climate change driven 21st century increases in riverflow will only compensate for about 1% of the human induced deficit in sediment load, leading to the coastal zone being starved of about 6000 Mt of sediment over the remainder of this century. A similar dominance of human impacts on fluvial sediment supply is likely at other heavily engineered rivers.

Local and landscape influences on turbidity in urban streams: a global approach using citizen scientists

The ecological degradation of urban rivers and streams has been termed the ‘urban stream syndrome’ and attributed to increased catchment urbanization. Limiting future degradation requires an understanding of the drivers of reduced water quality at both catchment and site scales. The goal of this study was to identify the probable drivers of turbidity in river ecosystems in highly urbanized areas, under the premise that turbidity does not respond consistently to urbanization. Catchment-scale data were compiled from remotely sensed datasets, whereas local-scale data were collected by citizen scientists as part of the global FreshWater Watch (FWW) program. The local-scale data included nearly 2600 coincident measurements of turbidity and observations of other local characteristics taken with a common method between March 2013 and June 2016 across 127 unique locations in 6 major population centers: Vancouver (Canada), São Paulo (Brazil), Curitiba (Brazil), Buenos Aires (Argentina), Hong Kong SAR (China), and Guangzhou-Foshan (China). Catchment- and site-scale information were modeled with Boosted Regression Trees (BRT) to identify likely drivers of increased turbidity both across the entire dataset and within individual cities. Urbanization was not consistently associated with turbidity. The global BRT model explained 60% of the variation in turbidity, and key predictors were catchment area, % of the catchment as grassland, rainfall, Gross Domestic Product, and % of the catchment as artificial surfaces. City-specific BRT models explained 35–67% of the variation in turbidity. Key predictors varied between cities and were often different than those observed at the global scale. Local-scale data collected by citizen scientists were less predictive of turbidity than catchment-scale factors and explained ~12% of the observed global variability in turbidity. Factors such as riverbank vegetation and the presence of point pollution sources explained some of the variation in turbidity, indicating their management could help mitigate elevated turbidity and sediment load in some urban rivers. Through this high-resolution, site-scale information, we highlight how community-sourced data may add value to freshwater monitoring programs.

Long-term erosion rates as a function of climate derived from the impact crater inventory

Abstract. Worldwide erosion rates seem to have increased strongly since the beginning of the Quaternary, but there is still discussion about the role of glaciation as a potential driver and even whether the increase is real at all or an artifact due to losses in the long-term sedimentary record. In this study we derive estimates of average erosion rates on the timescale of some tens of millions of years from the terrestrial impact crater inventory. This approach is completely independent from all other methods to infer erosion rates such as river loads, preserved sediments, cosmogenic nuclides, and thermochronometry. Our approach yields average erosion rates as a function of present-day topography and climate. The results confirm that topography accounts for the main part of the huge variation in erosion on Earth, but also identifies a significant systematic dependence on climate in contrast to several previous studies. We found a 5-fold increase in erosional efficacy from the cold regimes to the tropical zone and that temperate and arid climates are very similar in this context. Combining our results into a worldwide mean erosion rate, we found that erosion rates on the timescale of some tens of millions of years are at least as high as present-day rates and suggest that glaciation has a rather regional effect with a limited impact at the continental scale.

Small river basin and estuarine sediment fluxes: The magnitude necessary for coastal dispersion and siltation effects on a coral reef

Increasing continental suspended sediment influx to coral reefs is an example of land-sea coupling that requires the identification of sources, magnitude of transport, and controlling processes. In Brazil, a small coastal basin (Macaé River) was identified as a source of suspended sediment to a coral reef on the coast of Cape Armação dos Búzios. Biannual suspended sediment loads were measured at the basin as were fluxes within the estuary and towards the coast during eight tidal cycles. Particle load and yield from this basin were typical of small coastal basins, showing high to moderate slopes and transitional land management. However, the magnitude of the river loads was lower than the sediment transport within the estuary, indicating that the estuary amplifies river fluxes and sustains the transference of suspended sediment alongshore to the coral reef. Nonetheless, the estuary displays both suspended particle retention and export capacity and, therefore, fluxes to the coast and the coral reef occur as episodic events.

Changing of the riverine sediment load supply into Lake Baikal: The natural and anthropogenic causes (Russia)

The influences of natural and anthropogenic factors on temporal changes in sediment load of the main Baikal rivers (Upper Angara River and Barguzin River) were analyzed through the relationship between hydro-climatic parameters (air temperature, precipitation, water discharge and sediment load) and their variation tendencies for the periods of 1945–2014, 1945–1975 and 1976–2014. Mann–Kendall test, abrupt change test were employed to analyze the hydro-climatic data. The results indicated that the air temperature increased on 1.0–1.1 °C in the watersheds over the warming period (1976–2014), and the precipitation had an insignificant decreasing trend in this period, and the reduction was −2.6% and −4.9%. The statistically insignificant increasing in water discharge was 4.2% and 1.3% in the Upper Angara and Barguzin over the period 1976–2014, respectively. Meanwhile, there was a strong decrease in sediment load of −66% and −70%. The abrupt decrease the sediment load in the Upper Angara since the mid-1970s was caused by the combination of human activities in river basin and changes of natural processes. In the Barguzin basin, the significant anthropogenic impact against the background the changes of natural processes in the mid-1980s was began. In the Upper Angara, the period of rapid decline of sediment load from 1976 to 1984 continued, in the Barguzin – from 1976 to 1991, after that, the other regime of sediment load had established. In recent decades, the actual sediment load supply from the Upper Angara and Barguzin into Lake Baikal are 92 × 103 t y−1 and 27 × 103 t y−1 or 22% and 18% of the 1945–1975, respectively.