River Loads Research Articles

Vegetal Undercurrents-Obscured Riverine Dynamics of Plant Debris.

Much attention has been focused on fine‐grained sediments carried as suspended load in rivers due to their potential to transport, disperse, and preserve organic carbon (OC), while the transfer and fate of OC associated with coarser‐grained sediments in fluvial systems have been less extensively studied. Here, sedimentological, geochemical, and biomolecular characteristics of sediments from river depth profiles reveal distinct hydrodynamic behavior for different pools of OC within the Mackenzie River system. Higher radiocarbon (14C) contents, low N/OC ratios, and elevated plant‐derived biomarker loadings suggest a systematic transport of submerged vascular plant debris above the active riverbed in large channels both upstream of and within the delta. Subzero temperatures hinder OC degradation promoting the accumulation and waterlogging of plant detritus within the watershed. Once entrained into a channel, sustained flow strength and buoyancy prevent plant debris from settling and keep it suspended in the water column above the riverbed. Helical flow motions within meandering river segments concentrate lithogenic and organic debris near the inner river bends forming a sediment‐laden plume. Moving offshore, we observe a lack of discrete, particulate OC in continental shelf sediments, suggesting preferential trapping of coarse debris within deltaic and neritic environments. The delivery of waterlogged plant detritus transport and high sediment loads during the spring flood may reduce oxygen exposure times and microbial decomposition, leading to enhanced sequestration of biospheric OC. Undercurrents enriched in coarse, relatively fresh plant fragments appear to be reoccurring features, highlighting a poorly understood yet significant mechanism operating within the terrestrial carbon cycle.

Short-Term Effects of the EU Nitrate Directive Reintroduction: Reduced N Loads to River from an Alluvial Aquifer in Northern Italy

The Po Plain (northern Italy) is one of the largest aquifers in Europe, and 67% of the utilized agricultural land in this area is classified as a nitrate vulnerable zone (NVZ). However, it hosts intensive agriculture and livestock farming. In a stretch of the Mincio River (a tributary of the Po River), hydraulic heads and physico-chemical parameters of river and groundwater were monitored for a hydrologic year (2020–2021), to evaluate the effects of manure fertilization and flooding irrigation on surface- and groundwater chemistry. From 2020 the Nitrate Directive’s fertilization limit was reintroduced and a comparison has been performed comparing surface- and groundwater data from the 2019 fertilization period (before limit reintroduction) and 2020 (after). Results suggest that in 2021 the phreatic aquifer displayed elevated nitrate (NO3−) concentrations, exceeding 50 mg L−1, although average values were lower than those of 2019. Nitrate loads in the Mincio River reached 6670 kg NO3− d−1 and resulted from the overfertilization in the surrounding area and the quick transfer of nitrogen from groundwater to the river. As compared to 2019, the river loads decreased by 59%, suggesting that the introduction of fertilization limits can produce measurable, short-term responses in alluvial aquifers.

An Efficient Data Driven-Based Model for Prediction of the Total Sediment Load in Rivers

Sediment load in fluvial systems is one of the critical factors shaping the river geomorphological and hydraulic characteristics. A detailed understanding of the total sediment load (TSL) is required for the protection of physical, environmental, and ecological functions of rivers. This study develops a robust methodological approach based on multiple linear regression (MLR) and support vector regression (SVR) models modified by principal component analysis (PCA) to predict the TSL in rivers. A database of sediment measurement from large-scale physical modelling tests with 4759 datapoints were used to develop the predictive model. A dimensional analysis was performed based on the literature, and ten dimensionless parameters were identified as the key drivers of the TSL in rivers. These drivers were converted to uncorrelated principal components to feed the MLR and SVR models (PCA-based MLR and PCA-based SVR models) developed within this study. A stepwise PCA-based MLR and a 10-fold PCA-based SVR model with different kernel-type functions were tuned to derive an accurate TSL predictive model. Our findings suggest that the PCA-based SVR model with the kernel-type radial basis function has the best predictive performance in terms of statistical error measures including the root-mean-square error normalized with the standard deviation (RMSE/StD) and the Nash–Sutcliffe coefficient of efficiency (NSE), for the estimation of the TSL in rivers. The PCA-based MLR and PCA-based SVR models, with an overall RMSE/StD of 0.45 and 0.35, respectively, outperform the existing well-established empirical formulae for TSL estimation. The analysis of the results confirms the robustness of the proposed PCA-based SVR model for prediction of the cases with high concentration of sediments (NSE = 0.68), where the existing sediment estimation models usually have poor performance.

Impact assessment of on-site swine wastewater treatment facilities on spatiotemporal variations of nitrogen loading in an intensive livestock farming watershed.

Excess nitrogen (N) resulting from human activity causes environmental issues, including eutrophication in agricultural watersheds with intensive livestock farming. Among the N sources in Korea, on-site swine wastewater treatment facilities (OSWTFs) tend to be densely distributed in watersheds with intensive livestock farming. Therefore, it is critical to sustainably manage livestock excreta. This study used the Soil and Water Assessment Tool (SWAT) to investigate the effects of various pollution sources, including OSWTFs, on N loads in rivers in the Cheongmi watershed, which is an intensive livestock farming and agricultural area in Korea. The simulated hydrological and water quality outputs were calibrated and validated for 2012-2019 using Sequential Uncertainty Fitting ver. 2 in the SWAT-Calibration and Uncertainty Program. The hydrological simulations agreed with the observations, with a correlation coefficient (R2) of ≥ 0.8 and Nash-Sutcliffe coefficient of 0.67-0.86. The simulated total N (TN) was also strongly correlated with the observed monthly average loading (R2, 0.36-0.73) and annual average concentration (R2 ≥ 0.5), demonstrating the reliability of the model constructed herein. A simulation of management scenarios indicates that, if the permissible N concentration in effluent from OSWTFs was reduced to 60mgN/L, the TN concentrations in rivers would decrease by up to 50%. The findings of this study indicate that more stringent effluent water quality standards are required for OSWTFs to protect water quality and aquatic ecosystems in intensive swine farming watersheds.

The temperature and flow dependence of nitrate concentration and load estimates based on diffusive gradients in thin films.

Concentrations determined using diffusive gradients in thin films (DGT) have been used to derive time-averaged loads in streams and rivers. However, DGT provide time-weighted average concentrations that assume the independence of concentration and flow. Additionally, dynamic and coordinated changes in temperature, flow, and concentration are potential sources of bias in concentration and load calculations. We modeled scenarios in which temperature and flow were correlated to varying degrees with concentration and evaluated the consequences for DGT concentration and load calculations. As the correlation between solution flow and concentration moved toward 1 and -1, the load determined by DGT either overestimated or underestimated the actual load by as much as 30%. In DGT-based load estimates, the degree of potential bias should be assessed, and the concentration-flow relation should be characterized. As the correlation of analyte concentration and temperature approached 1 and -1, the deviation of the concentration determined by DGT from the actual concentration increased. In most cases, this bias was < 2%; however, if the changes in concentration and temperature were large (∼10mg L-1 and ∼10°C), the bias exceeded 5%. Concentration and temperature are unlikely to be perfectly or strongly correlated or anti-correlated in natural systems and thus should not affect the accuracy of DGT concentration calculations in most circumstances. The more solution temperature, flow, and concentration were uncorrelated, the closer DGT-derived concentration and load were to the actual solution concentration and load.

Population transcriptomics reveals the effect of gene flow on the evolution of range limits

One of the most important questions in evolutionary biology is how the spatial distribution of species is limited. Asymmetric gene flow from core populations is suggested to increase the number of poorly adapted immigrants in the populations at the range edge. Genetic load due to migration, i.e., migration load, should prevent adaptation to the local habitat, leading to decreases in distribution range via local extinction or the limiting range expansion. However, few experimental studies have examined the effects of immigration on fitness and natural selection within recipient populations. To investigate the influence of migration load on the evolution of distribution range, we performed field and laboratory observations as well as population transcriptomics for the common river snail, Semisulcospira reiniana. This species meets the conditions that migration from source populations can prevent local adaptation in a sink population because they inhabit the broader range of environments, including middle/upper reaches of a river and estuaries within a single river and they may be more vulnerable to being swept away by water currents due to lowered spontaneous (upward) locomotion activity. We found that river steepness was related to the lower distribution limit of S. reiniana, with a narrower distribution range in the steeper river. Population transcriptomic analysis showed that gene flow was heavily asymmetric from the upstream populations to downstream ones in the steep river, suggesting a greater migration load in the steep river. The number of genes putatively involved in adaptation to the local habitat was lower in the steep river than in the gentle river. Gene expression profiles suggested that individuals achieve better local adaptation in the gentle river. Laboratory experiments suggested that evolutionary differences in salinity tolerance among local populations were only found in the gentle river. Our results consistent with the hypothesis that migration load owing to asymmetric gene flow disturbs local adaptation and restricts the distribution range of river snails.

Four Years of Sediment and Phosphorus Monitoring in the Kraichbach River Using Large-Volume Samplers

Various sampling strategies come into operation to monitor water quality in rivers. Most frequently, grab samples are taken, but they are not suitable for recording the highly dynamic transport of solids and solid-bound pollutants. Composite samples reduce the influence of input and transport dynamics and are better suited to determine the annual river loads. Large-volume samplers (LVSs) produce both a composite sample over a long period of time and an amount of solids which allows for further analyses. In the small sub-catchment area of the Kraichbach river in Baden-Wuerttemberg (Germany) two LVSs have been installed to sample the river flow. The concentration of solids and phosphorus in the supernatant water and the settled sediment in the sampler have been determined and mean concentrations have been derived. Annual river loads were calculated in combination with discharge data from the nearby gauging station. Two sampling strategies of the LVS were tested and compared. For the first strategy, the LVS was used to collect quasi-continuous composite samples throughout the year, whereas, with the second strategy, samples were taken specifically for different flow conditions (low, mean and high flow). This study compares the advantages and constraints of both strategies. Results indicate that the first strategy is better suited to determine annual river loads. Quasi-continuous large-volume composite sampling is recommended for further monitoring campaigns.

Changes in water quality and related environmental conditions of Osaka Bay in summers from 2004 to 2018, focusing on river loads and COD concentrations

Changes in water quality and related environmental conditions of Osaka Bay in summers from 2004 to 2018, focusing on river loads and COD concentrations

Analysis on the variation of total phosphorus concentrations and loads of inflow and outflow rivers from different water resources zones around Lake Taihu

入出湖总磷负荷变化是影响太湖湖体磷收支平衡的关键因素.基于2012-2018年水质水量监测资料，计算全湖及各水资源分区河流入出湖总磷负荷，并以水量加权计算其总磷年平均浓度，探明其时空变化规律；运用双累积曲线法分析不同分区水污关系的变化规律；以月为时间尺度，利用Pearson相关系数，揭示入湖总磷负荷分别与入湖水量、入湖总磷浓度的相关关系；通过讨论分析，明确适用于太湖的入湖总磷平均浓度计算方法、总磷负荷影响因素及控制途径.研究结果表明：（1）水量加权法比算术平均法更加适用于太湖入湖总磷平均浓度的削减管理；环太湖河流入湖总磷浓度多年平均值为0.189 mg/L，明显高于出湖的0.079 mg/L，入湖总磷负荷多年平均值为2206.51 t，也高于出湖的873.73 t；2016年丰水年入、出湖及净入湖总磷负荷均最高，分别为2993.9、1341.1、1652.8 t.（2）湖西区河流入湖总磷浓度多年平均高于所有其他分区，其值为0.226 mg/L，浙西区、武澄锡虞区河流出湖总磷浓度多年平均分别为0.114和0.109 mg/L，均高于其他分区.不同水资源分区的水污关系呈现不同的年际变化规律，但除杭嘉湖区外，其他分区均未表现出入湖总磷得到有效控制的迹象.（3）湖西区和浙西区入湖总磷年负荷多年平均值分别为1748.71和278.61 t，两区各年入湖总磷负荷占总入湖负荷的比重位居前二，湖西区的都在67.88%以上；而浙西区在7%~19%之间变化；太浦河出湖总磷年负荷多年平均值为272.27 t，自2014年起其占出湖总磷年负荷的比重均在30%以上.（4）不同水资源分区月入湖总磷负荷均与入湖水量存在较好的相关关系，且除阳澄淀泖区外，其他分区月尺度入湖总磷负荷变化主要受入湖水量控制.（5）2016年丰水年湖西区入湖河流总磷浓度较高、入湖水量大的共同作用导致了其入湖总磷负荷的显著增加.研究成果可为太湖的磷外源负荷控制提供科学依据.;The variation in inflow and outflow total phosphorus (TP) loads is a key factor affecting the balance of the phosphorus budget for Lake Taihu. Based on the monitoring data of water quality and quantity from 2012 to 2018, the TP load of the rivers in each water resources zone around Lake Taihu were calculated, the flow-weighted mean annual concentrations of TP were attained, and their spatio-temporal variations were analyzed; the double accumulation curve method was adopted to analyze the relationships between water quantity and TP load in different zones; the Pearson correlation coefficient was utilized to reveal the correlation between the TP load and water quantity as well as TP concentrations of the inflow at the monthly time scale; through discussion and analysis, the calculation method of the average TP concentration of inflow applicable to Lake Taihu, the influencing factors of TP loads and measures of controlling the TP load were investigated. The results showed that:(1) The flow-weighted mean concentration of TP is the preferred approach for calculating average concentrations of tributaries with variable flows for Lake Taihu; The average annual TP concentration of inflow rivers of Lake Taihu was 0.189 mg/L, significantly higher than that of outflow rivers (0.079 mg/L). The average annual TP load of the inflow was 2206.51 t, which was also much higher than that of the outflow (873.73 t); in the high flow year of 2016, the TP loads of the inflow, outflow and net inflow of the lake were the largest among 2012-2018, and their values were 2993.9, 1341.1 and 1652.8 t, respectively. (2) The average annual TP concentration of inflow rivers in the Huxi zone was 0.226 mg/L, which was higher than that in other zones; the average annual TP concentrations of outflow rivers in the Zhexi and Wuchengxiyu zones were 0.114 and 0.109 mg/L, which were higher than those in other zones. The interannual variation of the relationships between water quantity and TP load in different water resources zones behaved differently, suggesting that TP pollution was not effectively controlled on the whole except in the Hangjiahu zone. (3) The average annual TP load of the inflow rivers in the Huxi zone and Zhexi zone were 1748.71 and 278.61 t, respectively. The Huxi zone accounted for above 67.88% of the annual total inflow TP load, and the percentage for the Zhexi zone was between 7% and 19%; the average annual outflow TP load of Taipu River was 272.27 t and accounted for more than 30% of the total outflow TP load since 2014. (4) There were good correlations between the monthly TP load and water quantity of the inflow in different water resources zones. Moreover, except in the Yangchengdianmao zone, the variation of monthly TP load of the inflow in other zones was mainly controlled by the water quantity of the inflow. (5) In the high flow year of 2016, the combined effect of high concentration of TP and large water quantity of inflow rivers in the Huxi zone led to a significant increase in the TP load of the inflow. The research results can provide a scientific basis for external phosphorus load control for Lake Taihu.

A Mass Balance Approach in Sediment Budgeting of Large Alluvial Rivers with special emphasis on the Brahmaputra in Assam

Morphology of an alluvial river channel is the consequence of erosion, sediment transport and sedimentation in a river. Sediment budget accounts for the sources, sinks and redistribution pathways of sediments, solutes and nutrients in a unit region over unit time. Human activities are the most important factors that affect the variation in the pattern of river sediment load. This paper discusses sediment budget of a few large rivers by review of literature and estimation of sediment budget of Brahmaputra River in Assam using mass balance approach. An attempt has also been made to discuss human and climatic impact on sediment load of major rivers of the world. Total sediment load in the Brahmaputra River at downstream location (India-Bangladesh border) was estimated to be 814×106 t/year. Considering 10% of sediment load of the Brahmaputra as bed load, suspended sediment load at downstream was estimated to be 733×106 t/year. Tributaries, bank erosion and scouring of river bed were found to contribute 52%, 27% and 21% respectively to sediment load of Brahmaputra at downstream locations. In spite of limitations of the dependable data, future complexity due to climate change impact and hydropower dam initiative in upstream of the River, the study is a simplified approach in sediment budgeting of the Brahmaputra.

Mass balance of saline lakes considering inflow loads of rivers and groundwater: the case of Lake Issyk-Kul, Central Asia

Mass balance of saline lakes considering inflow loads of rivers and groundwater: the case of Lake Issyk-Kul, Central Asia

Mechanisms and Countermeasures on Sediment and Wood Damage in Sediment Retarding Basins

Improvements in sediment retarding basin design are required to mitigate flood damage caused by bed load and wood debris outflow in lower river reaches. We used a scaled sediment retarding basin model to optimize our basin design, with the goal of improving sediment and wood debris transport and capture. Changes to the structural dimensions and elements of the sediment retarding basin were assessed under experimental debris flow conditions. The results obtained from the experiments and simulations were in good agreement regarding sediment flow and containment. The proposed one-dimensional model is useful for showing the effects of flow conditions within a sediment retarding basin on sediment transport.

Combining GRACE and satellite altimetry data to detect change in sediment load to the Bohai Sea

The Gravity Recovery and Climate Experiment (GRACE) satellites provide a powerful tool for monitoring sediment mass change. However, signal leakage from nearby groundwater storage depletion in the North China Plain limits the potential capacity of GRACE to estimate sediment input from the Yellow River flows into the Bohai Sea. In the present work, we developed an improved approach based on forward modeling to reduce signal leakage from GRACE data and combined it with satellite altimetry to recover sediment load changes from 2003 to 2013 to the Bohai Sea. The total sediment input averaged 1.7 ± 0.8 Gt/yr, which agrees well with the estimate based on in-situ sediment data measured from the sediment cores (1.1 Gt/yr). Our method is also capable to describe sediment seasonal variations, with higher inputs in winter and spring, which confirm the output simulated by the sediment transportation model. We make presently tentative connections of seasonal variations to sediment resuspension driven by climatic monsoons contributed rough seas: although sediment load in rivers peaks in summer, low water discharge of the Yellow River leads to most of the sediment being deposited in a narrow area near the river mouth and not transported into the Bohai Sea; in winter and spring, huge waves provide favorable conditions for resuspension resulting in large amounts of sediment near the estuary being transported to the ocean along with northward waves. Moreover, our results indicate coastal erosion is also a nonnegligible resource of the sediment in the Bohai Sea. Comparing to the traditional approach, our study provides a new technological way to derive sediment in the Bohai Sea, which is capable of providing continuous measurements with improved timeliness at a lower cost.

Properties of ammonia‐oxidising bacteria and archaea in a hypereutrophic urban river network

Abstract Ammonia oxidation by ammonia‐oxidising archaea (AOA) and bacteria (AOB) is the first and rate‐limiting step of nitrification. By providing substrate to the nitrogen–removing denitrification processes, nitrification is an important process for attenuation of allochthonous nitrogen loads in urban rivers, thereby mitigating eutrophication of downstream ecosystems. However, the relative importance of AOA and AOB communities in ammonia oxidation, the distribution and varied patterns of these groups and the underlying mechanisms have received limited study in hypereutrophic urban river networks. To investigate spatial and temporal patterns of particle‐attached and free‐living ammonia‐oxidising microbial communities, we conducted a 2‐year study of four different water quality/habitat conditions within a hypereutrophic urban river network of eastern China. The structure and dynamics of ammonia‐oxidising microbial communities were determined by high‐throughput sequencing based on the AOA and AOB amoA gene. We found significant spatial and temporal heterogeneity of ammonia‐oxidising microbial communities, but no significant differences between particle‐attached and free‐living fractions. Analysis revealed that changes in the diversity and composition of ammonia‐oxidising microbial communities were mainly related to substrate availability (e.g., ammonia, nitrite, dissolved oxygen). AOB communities were more complex and had a higher species richness and diversity compared with AOA communities. Our findings indicate that high anthropogenic nitrogen loadings appear to promote higher ammonia‐oxidising microbial richness and diversity, and AOB are more adaptable to the hypereutrophic conditions, thereby playing a more important role than AOA in nitrogen transformations in hypereutrophic urban river networks. This study highlights the importance of ammonia‐oxidising microorganisms in nutrient‐rich river systems and provides valuable insights into ammonia transport and transformations in urban river networks.

Long-Term Mississippi River Trends Expose Shifts in the River Load Response to Watershed Nutrient Balances Between 1975 and 2017.

Excess nutrients transported by the Mississippi River (MR) contribute to hypoxia in the Gulf of Mexico. Nutrient balances are key drivers to river nutrient loads and represent inputs (fertilizer, manure, deposition, wastewater, N-fixation, and weathering) minus outputs (nutrient uptake and removal in harvest, and N emissions). Here, we quantified annual changes in nitrogen (N) and phosphorus (P) river loads and nutrient balances at the MR Outlet and documented that the river load response to watershed nutrient balances shifted between 1975 and 2017. Annual nutrient balances and river loads were positively correlated between 1975 and 1985, but after, a disconnect between both the N and P balances and river loads emerged, and the subsequent river load patterns were different for N versus P. We evaluated the relative impacts of legacy nutrients and other latent factors, for which data were not available, on river nutrient load trends. Our analysis showed that in the case of N, latent factors were potentially just as important in explaining changes in river nutrient loads over time as N balances, and in the case of P, they were even more important. We hypothesized that these factors included implementation of best management practices, changes in watershed buffering capacity, the effects of tile drainage, or increased precipitation. Our analytical approach shows promise for the investigation of drivers of water quality trends that are not well-represented in typical national scale geospatial datasets.

The contrasting estuarine geochemistry of rare earth elements between ice-covered and ice-free conditions

Rare Earth Elements, including the lanthanide series and Y (REYs), are important tracers and paleo-proxies of biogeochemical processes, water mass transport and oceanic mixing. At the interface between the continents and oceans, the geochemical behaviour of REYs in estuarine environments is generally described as being non-conservative, with large-scale removal by particle scavenging. This conventional interpretation stems from observations carried out in tropical or sub-tropical estuaries. However, major river systems in the mid- and high latitude regions are subjected to winter conditions when a frozen watershed and an ice cover may affect the continental input of particles and the REY geochemistry. Here, we investigate the geochemical behaviour of REYs in the Estuary and Gulf of St. Lawrence (EGSL) in spring 2003 as well as winter and summer 2020. In contrast to the ice-free seasons, REYs and Fe behave conservatively in the estuary during the winter. In addition, we observed a higher REY affinity toward particle surfaces and fractionation in REE patterns in the hypoxic deep waters of the estuary. The latter observation may reflect enhanced REY sorption to mineral-carrier surfaces exposed upon the remineralization of organic coatings on settling particles and to manganese oxides of benthic origin. Computed partition coefficient (Kd) values and strong correlations between Y/Ho, Er/Nd and Ce anomalies with dissolved oxygen concentrations support this hypothesis. The estimated annual dissolved load of REYs from the EGSL to the ocean ranges from 0.4 to 75 tons per year, thus contributing significantly to the global marine budget. The global river loading of dissolved Nd to the ocean was also revised to 4000 tons per year based on data available for 21 river systems.

Investigations on River Sediments in Chak Sedimentary Basin, Wardak Province, Afghanistan

This sedimentary is from a largest basin of Afghanistan, which covers an area of 9772 km2. It is located about 80 km, at west side of Kabul. In this research, we studied different types of heavy and light minerals, gravel analysis in river sediments. Logar River is core stream flowing over basin,it carries diverse masses of sediments from dissimilar parts of surroding montians. Further, in the months of summer while snowmelting is started,transfer diverse materials and cause different traces to be made. Area of basin is enclosed by mountain range and separated into two sections,majore part is Khawat Olya and second one is Khawat Sufla. The main aim of study is to characterize different sizes and types of minerals in river load for the previous geological periods. This research is therefore essential to explain different sizes and type of minerals in river sediments, which is no any study has been conducted in the study area. This study found out that the category of sediments is related to the parental materials that are placed in the close mountains such as; gneiss, limestone, and granite, dissimilar varities of conglomerate, slate, schist, reefs, conglomerate and sandston.

Rock weathering and nutrient cycling along an erodosequence

How flowing water and organisms can shape Earth9s surface, the Critical Zone, depends on how fast this layer is turned over by erosion. To quantify the dependence of rock weathering and the cycling of elements through ecosystems on erosion we have used existing and new metrics that quantify the partitioning and cycling of elements between rock, saprolite, soil, plants, and river dissolved and solid loads. We demonstrate their utility at three sites along a global transect of mountain landscapes that differ in erosion rates – an “erodosequence”. These sites are the Swiss Central Alps, a rapidly-eroding, post-glacial mountain belt; the Southern Sierra Nevada, USA, eroding at moderate rates; and the slowly-eroding tropical Highlands of Sri Lanka. The backbone of this analysis is an extensive data set of rock, saprolite, soil, water, and plant geochemical and isotopic data. This set of material properties is converted into process rates by using regolith production and weathering rates from cosmogenic nuclides and river loads, and estimates of biomass growth. Combined, these metrics allow us to derive elemental fluxes through regolith and vegetation. The main findings are: 1) the rates of weathering are set locally in regolith, and not by the rate at which entire landscapes erode; 2) the degree of weathering is mainly controlled by regolith residence time. This results in supply-limited weathering in Sri Lanka where weathering runs to completion in the regolith, and kinetically-limited weathering in the Alps and Sierra Nevada where soluble primary minerals persist; 3) these weathering characteristics are reflected in the sites9 ecosystem processes, namely in that nutritive elements are intensely recycled in the supply-limited setting, and directly taken up from soil and rock in the kinetically settings; 4) the weathering rates are not controlled by biomass growth; 5) at all sites we find a deficit in river solute export when compared to solute production in regolith, the extent of which differs between elements. Plant uptake followed by litter export might explain this deficit for biologically utilized elements of high solubility, and rare, high-discharge flushing events for colloidal-bound elements of low solubility. Our data and new metrics have begun to serve for calibrating metal isotope systems in the weathering zone, the isotope ratios of which depend on the flux partitioning between the compartments of the Critical Zone. We demonstrate this application in several isotope geochemical companion papers.

Future impacts of climate change on sediment influx rate in hydropower reservoir using SWAT

Climate change causes more frequent and intense rainfall events, leading to severe erosion in the catchment and sediment transferred into rivers and reservoirs. This study focus on long term sediment load in major rivers in Cameron Highlands and prediction of annual sediment inflow into Ringlet Reservoir from 2000 to 2030. Soil Water Assessment Tool (SWAT) is used as the simulation tool, utilising future gridded rainfall 2017 to 2030 under CCSM and future land use 2030. Future annual rainfall is minimum at 1551 mm (in 2030) and maximum at 3150 mm (in 2029). The future projected annual sediment load into Ringlet Reservoir from 2017 to 2030 is averaged at 354,013 m3/year, ranging from 216,981 to 461,886 m3/year. Comparing between the historical period of 2000 to 2016 and future projection (2017–2030), annual sediment load shows an increase of 12 %. To combat the increase sediment yield, catchment management such as erosion control plan, drainage and runoff control must be developed to minimise sediment yield and subsequent effect of high sediment load transport via rivers and drainage network.

Estimating urban air pollution contribution to South Platte River nitrogen loads with National Atmospheric Deposition Program data and SPARROW model

Air pollution is commonly disregarded as a source of nutrient loading to impaired surface waters managed under the Clean Water Act per states’ 303(d) list programs. The contribution of air pollution to 2017–2018 South Platte River nitrogen (N) loads was estimated from the headwaters to the gage at Weldona, Colorado, USA (100 km downstream of Denver), using data from the National Atmospheric Deposition Program (NADP) and the SPAtially Referenced Regressions On Watershed attributes (SPARROW) model. The NADP offers wet-deposition raster created by spatial interpolation of data collected from regionally representative monitoring sites, excluding the influences from urban site data. For this study, NADP wet-deposition data obtained from sites within the Denver-Boulder, Colorado, urban corridor were included and excluded in new spatial interpolations of wet-deposition raster, which were used as input for SPARROW to model the influence of urban air pollution sources on South Platte River loads. Because urban air pollution is already incorporated into the NADP Total Deposition modeling methodology, dry N deposition was held constant for each SPARROW modeling scenario when dry deposition was included. By including the urban wet-deposition data in the model, estimated N loading to the South Platte River at Denver increased by 9–11 percent. Factoring in dry deposition at a 1:1.8 dry:wet ratio obtained from the results, urban air pollution was estimated to contribute as much as 20 percent of the nitrate Total Maximum Daily Load for Segment 14 of the South Platte River.