River Loads Research Articles

Multi-decadal erosion rates from glacierized watersheds on Mount Baker, Washington, USA, reveal topographic, climatic, and lithologic controls on sediment yields

Understanding land surface change in and sediment export out of proglacial landscapes is critical for understanding geohazard and flood risks over engineering timescales and characterizing landscape evolution over geomorphic timescales. We used automated Structure from Motion software to process historical aerial photographs and, with modern lidar data, generated a high-resolution DEM time series with coverage over 10 glacierized watersheds on Mount Baker, Washington, USA for the time period between 1947 and 2015. We measured basin-wide sediment yields and sediment redistribution on hillslopes and in stream channels. Slopes within most measured erosion sites are above theoretical and observed debris-flow thresholds. We observed significant erosion of hillslopes and limited deposition on hillslopes and in stream channels. Sediment delivery ratios during time periods with net erosion averaged 0.73. We determined, consistent with previous field observations, that debris flows originating from moraines are a primary erosion mechanism in proglacial zones on Mount Baker. Time series measurements indicate that temporal variability in erosion rates is associated with climate oscillations, with higher erosion rates during cooler-wetter periods. Basin-wide sediment yield is positively correlated with lithology (r2 = 0.54), hillslope angle (r2 = 0.52), drainage area (r2 = 0.82), and negatively correlated with stream channel slope (r2 = 0.67). Topographic differences between high and low yielding basins indicate that spatial variability in erosion on Mount Baker is sensitive to Pleistocene and Holocene glacial and volcanic activity. Specific sediment yields in six basins averaged 4600 ton/km2/yr, consistent with global measurements in glacierized catchments. Specific sediment yield decreased with increasing basin area, with total loads in the downstream main stem Nooksack River estimated between 480 and 820 ton/km2/yr. Proglacial sediment yields account for between 18 and 32 % of total sediment load in the main stem Nooksack River and exceed contributions by bluff and terrace erosion, which account for between 8 and 13 % of total load. Our findings indicate that erosion in glacierized basins is sensitive to decadal climate oscillations and that high proglacial sediment yields provide an important contribution to river systems downstream, particularly in catchments where upland topography and lithology is favorable.

Nickel mass balance and isotopic records in a serpentinic weathering profile: Implications on the continental Ni budget

During serpentinite rock weathering, Ni is concentrated in the regolith owing to residual and secondary enrichment, forming a Ni-rich deposit under tropical conditions. This study presents geochemical, isotopic, and mineralogical data for Ni from the Serra do Puma Complex (SPC) weathering profile in Carajas (Brazil). The Ni fluxes, redistribution, and Ni isotopic fractionation magnitudes were quantified along the entire weathering profile: rock, saprock, lower and upper saprolite, and limonite. The results show that chlorite and serpentine are the primary Ni-scavenging phases in saprolite, whereas Fe oxyhydroxides are the main Ni-hosting minerals in the limonite unit. The mass balance model confirmed a global Ni gain at the weathered profile scale, with larger Ni enrichment in the upper saprolite. The isotopic dataset obtained in this study contributes greatly to the knowledge of the current Ni cycle on regional and global scales. The detailed insights into Ni isotopes in the SPC, coupled with chemical and mineralogical composition, allow for the first time a Ni mass balance and Ni isotopic values for an entire weathering profile in an Amazonian context. The Ni isotopic profile agrees with the preferential retention of light Ni isotopes in the residual material relative to the parent rock during weathering processes, with the Δ60Ni limonite-saprock of −0.72‰. In the SPC, major isotopic fractionation was notably recorded during saprolitization, while limonitization was accompanied by an overall Ni loss without significant Ni isotopic fractionation. As already observed in previous studies, heavier Ni isotopes, preferentially leached during weathering processes, can be further mobilized downward and lost from the profile or incorporated in secondary minerals in the saprolite and limonite sections. The Ni isotopic mass balance model indicated that the Ni loss from the weathered serpentinite profile was isotopically heavy, in agreement with the isotopically heavier composition of the dissolved load of Amazonian rivers. The isotopically light Ni pool, associated with the significant Ni gain encountered in the upper saprolite, is notable in the SPC weathering profile and confirms the existence of a light Ni isotope reservoir in the continent.

Detroit River load estimation; the need for a new monitoring approach

The Great Lakes Water Quality Agreement (GLWQA) established new Lake Erie phosphorus loading targets, including a 40% total phosphorus load reduction to its western and central basins. The Detroit and Maumee rivers’ loads are roughly equal and contribute about 90% of the load to the western basin and 54% to the whole lake. They are key drivers of central basin hypoxia and western basin algal production. So, accurate estimates of the Detroit River load are important. Direct measurement of that load near its mouth is difficult due to requiring real-time knowledge of flows around islands and the influence of Lake Erie’s seiches. Consequently, most estimates sum the loads to the St. Clair/Detroit River system. But this approach is complicated by uncertainties in the Lake Huron load and load retention in Lake St. Clair. Routine GLWQA reassessments will confirm or adjust over time the goals, loading targets, and approaches based on evolving information. So, there is a need to improve monitoring approaches that ensure accurate Detroit River loads. New approaches should take into account both the characteristics of this dynamic connecting channel and the uses of monitoring results: 1) determining the Detroit River loads to drive models, develop mass balances, set load reduction targets, and track progress; and 2) assessing the sources and processing of the loads to help guide reduction strategies. Herein, we review temporal and spatial variability in the St. Clair/Detroit River system, and suggest adjustments to monitoring that address those variabilities and both uses.

Spatial and seasonal variations in nutrient load and trophic status of Ganga and Yamuna rivers in Uttar Pradesh, India

Abstract Nutrient loading in aquatic systems from anthropogenic sources is a worldwide concern. The Ganga is the most important river in India, but pollution is currently severely threatening its biodiversity and long-term environmental viability. Water samples were taken from 36 locations along the length of the Ganga and Yamuna rivers in Uttar Pradesh and analysed for nutrient concentration to evaluate the nutrient load, eutrophication danger, and river trophic status. The average concentration of NO3-N, PO4-P, NH4-N, and SiO2-Si exceeded the values in unpolluted rivers, indicating the contribution of anthropogenic sources. The concentration of NO3-N and NH4-N showed significant spatial variation, and PO4-P showed significant seasonal variation in the study area. The DIN/DIP ratio in the study area exceeded 16:1, indicating a phosphate-limiting condition for phytoplankton development. The DSi/DIN value showed a declining trend in the downstream region of both rivers with average values <1, indicating nitrate pollution leading to eutrophic conditions. The Indicator for Coastal Eutrophication Potential (ICEP) showed a positive value, indicating that the Ganga and Yamuna rivers in Uttar Pradesh were eutrophic due to nitrogen pollution. Trophic State Index (TSI) values indicated that super-eutrophic conditions existed in the Ganga River (65.62) and hypereutrophic conditions existed in the Yamuna River (75.55) in Uttar Pradesh.

Basin-Scale Geochemical Assessment of Water Quality in the Ganges River during the Dry Season

Identification of sources and transport pathways of heavy metals and major ions is crucial for effective water quality monitoring, particularly in large river systems. The Ganges river basin, the largest and the most populous river basin in India, remains poorly studied in this regard. We conducted a basin-level analysis of major ions, heavy metals, and stable isotopes of nitrate in the Ganges during the pre-monsoon season to constrain the sources and quantify the inorganic chemical composition of the river during its lean flow. Bedrock weathering, anthropogenic interferences, water contribution through tributaries, and surface water-groundwater interaction were identified as the major driver of metal and ion variability in the river. Heavy metals showed the highest concentrations in the upper section of the river, whereas ionic loads were the most variable in the middle. We find a significant impact of tributaries on the metal and ion concentrations of the Ganges in its lower reaches. Isotopic analysis of dissolved nitrate suggested synthetic fertilizers and industrial wastes as the main sources. We find that the otherwise clean waters of the Ganges can show high ionic/metallic concentrations at isolated stretches (As: up to 36 µg/L), suggesting frequent monitoring in the source region to maintain water quality. Except for water collected from the Yamuna and Kannauj in the middle stretch and the Alaknanda and Rishikesh in the upper stretch, the WQI showed acceptable water quality for the sampled stations. These findings provide an insight into the modifications of dissolved inorganic chemical loads and their sources in different sections of the basin, needed for mitigating site-specific pollution in the river, and a roadmap for evaluating chemical loads in other rivers of the world.

Implication of dissolved nitrogen dynamics of urban rivers using multivariate regression and structural equation modeling

AbstractThe river's functional balance varies according to flow regimes and nutrient distribution. Watercourses can receive water from different point and nonpoint sources, which discharge high nitrogen load in rivers generated from domestic and industrial effluents and agricultural runoff. The excessive concentration of nitrogen load affects the riverine ecosystem by attenuating dissolved oxygen balance and disturbing the water quality. A study has been conducted to determine the nitrogen dynamics and their impact on the water quality of the Delhi stretch of Yamuna River, India, which is highly influenced by anthropogenic activities. Multivariate linear regression (MLR) was performed to gain insight into nitrogen dynamics, and structural equation modeling was applied to determine the direct (primary) and indirect (secondary) relation between the water quality parameters and the subsequent impact on water quality. Dissolved inorganic nitrogen (DIN) was measured using ammonia, nitrate, and nitrite, and total Kjeldahl nitrogen was estimated to reflect the dissolved organic nitrogen (DON). The variation in dissolved nitrogen (organic and inorganic) signifies high negative flux on the river's organic content, causing further degradation of river water quality. MLR predicted a high correlation between predicted and observed DIN at the Income Tax Office (ITO) (92.5%) and Nizamuddin (94.37%) and DON at ITO (93.49%) and Nizamuddin (95.28%). The high concentration during the lean period deteriorates the water quality tremendously and suggests that the variation in dissolved nitrogen content should be monitored carefully to maintain the river's water quality dominated by the organic load.

Projection of Sediment Loading from Pearl River Basin, Mississippi into Gulf of Mexico under a Future Climate with Afforestation.

Sediment load in rivers is recognized as both a carrier and a potential source of contaminants. Sediment deposition significantly changes river flow and morphology, thereby affecting stream hydrology and aquatic life. We projected sediment load from the Pearl River basin (PRB), Mississippi into the northern Gulf of Mexico under a future climate with afforestation using the SWAT (Soil and Water Assessment Tool)-based HAWQS (Hydrologic and Water Quality System) model. Three simulation scenarios were developed in this study: (1) the past scenario for estimating the 40-year sediment load from 1981 to 2020; (2) the future scenario for projecting the 40-year sediment load from 2025 to 2064, and (3) the future afforestation scenario that was the same as the future scenario, except for converting the rangeland located in the middle section of the Pearl River watershed of the PRB into the mixed forest land cover. Simulations showed a 16% decrease in sediment load for the future scenario in comparison to the past scenario due to the decrease in future surface runoff. Over both the past and future 40 years, the monthly maximum and minimum sediment loads occurred, respectively, in April and August; whereas the seasonal sediment load followed the order: spring > winter > summer > fall. Among the four seasons, winter and spring accounted for about 86% of sediment load for both scenarios. Under the future 40-year climate conditions, a 10% reduction in annual average sediment load with afforestation was observed in comparison to without afforestation. This study provides new insights into how a future climate with afforestation would affect sediment load into the northern Gulf of Mexico.

Morphoscopic changes in Iraqi territorial waters and their border repercussions

Abstract
 The present study includes the analysis of the morphological change in the Iraqi coastline in Khor Abdullah and the entrance to the Shatt Al-Arab (Al-Ruka Channel), as the northwestern region of the Arabian Gulf is exposed to different erosion and depositions due to the suspended sedimentary load, The comparison between the periods studied showed severe erosion in some coastal areas and depositions in other parts, which led to changes in the shape and extension of the barriers or the sedimentary tongues and made them prominent, especially in the shallow sites (shoals) areas at the entrance to Khor Abdullah and Khor Shaitanah, and those changed parts appear in the maps of the British Admiralty, which draw detailed curves surrounding the varying depths. The extension of the suspended sedimentary load at the head of the Arabian Gulf amounted to 11,014 km2 in the year 2003, which expanded in 2011 to 12,680 km2, by adding suspended sediments of about 1,676 km2 to 6,452,600 tons over 8 years, at a rate of 806.575 tons annually, or 8.5% of the volume of suspended sediments in 1996 due to the decrease of the river flows from the Tigris, Euphrates, and Karun. The line of the lowest tide (zero line) showed a change in the cross-section of the Iraqi waterway lines that it shares with Iran and Kuwait, affecting the location of the approved border line between Iraq and Kuwait, and the largest change was in the width of the entrance to the Shatt Al-Arab (Al-Ruka Channel), and this was influenced by the erosion, sedimentation patterns, and deflection of tidal currents, as well as the temporary effect of port activities in Khor Abdullah. The extension of Abdullah’s Marqat at Ras Al-Bishah reached 15.5 km in 2003, its extension became 17.2 km in 2019 with a varying range of 1.7 km in 16 years, which has increased at lower rates in recent years due to the decrease in the sedimentary load of rivers to legalize water releases. The maximum change in Khor Abdullah in the middle part was 453 meters, which is a contraction in favor of Kuwait at a rate of 453 meters, and in the middle of the Al-Ruka Channel with an average width of 403 meters in favor of Iran, expansion in favor of Iraq was at a rate of 152 and 42 meters at the entrance and middle of Khor Shaitana.

The aquatic environment of Parry Sound, a deep-water embayment complex of Georgian Bay protected from Dreissena

The coastline of eastern Georgian Bay in the Parry Sound region is a distinctive nearshore environment consisting of a large deep-water embayment partially isolated from the open lake and connected with other embayments of diverse morphometric features. The underlying geology of the embayments and their watersheds contrasts with the larger lake basin, resulting in heterogenous water quality stemming from mixing of the high-alkalinity, low phosphorus waters of Georgian Bay with the low-alkalinity and higher phosphorus waters draining watersheds of the Canadian Shield. In 2016, water quality was examined in the deep basin of Parry Sound known as the Big Sound, and six connected embayments to examine the influences of watershed loading and anthropogenic development to enable better detection of changes related to human activity. Inter-basin mixing and river loading accounted for much of the variability in major ions, water clarity and nutrients except for Deep Bay, an embayment exhibiting signs of nutrient enrichment. The oligotrophic conditions in Parry Sound have changed little since 1990 unlike Lake Huron where the dreissenid invasion has correlated with falling phosphorus levels. Low calcium levels may limit dreissenid mussel numbers in Parry Sound and are hypothesized to have pre-empted mussel-related changes in water quality. Apparent productivity, light regime and water column stratification of the Big Sound and connected embayments contrast with the adjacent nearshore of Georgian Bay indicating an aquatic environment distinct from the exposed nearshore of Georgian Bay.

The impact of sewage treatment plant loading to river basin during Movement Control Order

Environment quality is essential aspects of life on earth, any changes in the quality have a significant impact on human beings. The implementation unprecedented Movement Control Order (MCO), which halted social, economic, and other activities except essential services contributed to opportunities for the earth to rejuvenate itself and build a better blue sky, peaceful wildlife, controlled noise pollution, and improved environmental features. Although the unprecedented Movement Control Order (MCO) due to COVID-19 pandemic posed some adverse effects on the environment, but there are also some benefits on the environment. One of the significant positive effects by the MCO is that the environment had rejuvenated during this period, especially significant water quality improvement. Many reports worldwide, including Malaysia, had reported that the environment including water quality had shown signification improvement. With controlled activities, MCO recognized contributed to river water quality rejuvenation amidst one of the main essential service sewage treatment plant operating at its fullest capacity. Amidst of various river pollution sources, Sewage Treatment Plant (STP) effluent discharge loading was identified as one of the main water resource polluters, and the MCO phenomenon turn raises the question of whether the STP effluent discharge loading onto river resources is the main culprit to the river pollution. This is a new challenge for water resources management to examine the impact of sewage treatment effluent discharge loading on water resource pollution loading in Malaysia. This study investigates the influence of sewerage treatment plant effluent loading from the Kuala Lumpur sewerage catchment to the Klang River basin within the Kuala Lumpur City Centre. The river’s natural self-carrying loading was investigated to evaluate the influence of sewerage effluent loading on the selected river basin. The STPs within the study area were identified and segregated based on its tributary river basin. The individual STP’s Biological Oxygen Demand (BOD) and Suspended Solid (SS) average effluent discharge loading of the year 2020 analyzed against the study River’s BOD and SS average self-loading of the year 2020. The STP and River loading were analyzed to investigate the fraction of STP effluent discharge loading against River loading in the study river basin during MCO.

Changes in suspended‐sediment yields under divergent land‐cover disturbance histories: A comparison of two large watersheds, Olympic Mountains, USA

AbstractImprovements in timber harvest practices and reductions in harvest volumes over the past half century are commonly presumed to have reduced sediment loads in many western US rivers. However, direct assessments in larger watersheds are relatively sparse. Here, we compare 2019–21 sediment concentrations against those of the late 1970s in the Bogachiel and Calawah River watersheds, adjacent and similarly sized (~300 km2) basins in the western Olympic Mountains of Washington State. The Calawah River watershed has experienced significant land‐cover disturbance, including a large 1951 fire, extensive post‐fire salvage logging, and relatively high rates of timber harvest through the 1990s. In contrast, the Bogachiel River watershed did not burn, and experienced only modest timber harvest that largely post‐dated 1970s sediment monitoring. Channel‐width trends suggest the Calawah River was still recovering from 1950s disturbances in the late 1970s. We found that 2019–21 suspended‐sediment loads in the Calawah River were 2.3–2.6 times lower than would have been expected based on 1970s sediment rating curves, while recent loads in the Bogachiel River were a factor of 1.4 ± 1.0 lower. We consider the plausibility and possible explanations of declining concentrations in the less‐disturbed Bogachiel River. Suspended‐sediment yields in the Bogachiel River were two times higher than yields in the Calawah River, which is attributed to a combination of modestly higher precipitation, more efficient runoff generation, and more extensive and erodible Quaternary valley fills in the Bogachiel River. Regional shifts in flood hydrology have also influenced suspended‐sediment loads in both watersheds. Our results then document a significant decline in suspended‐sediment concentrations in the Calawah River over the past half century. Reduced land‐cover disturbance provides the simplest and most likely explanation for this decline, though the wide range of possible concentration changes in the Bogachiel River leaves open possibilities that other processes (human, natural, or methodologic) could be a factor.

Updated phosphorus loads from Lake Huron and the Detroit River: Implications

The binational Great Lakes Water Quality Agreement (GLWQA) revised Lake Erie’s phosphorus (P) loading targets, including a 40% western and central basin total P (TP) load reduction from 2008 levels. Because the Detroit and Maumee River loads are roughly equal and contribute almost 90% of the TP load to the western basin and 54% to the whole lake, they have drawn significant policy attention. The Maumee is the primary driver of western basin harmful algal blooms, and the Detroit and Maumee rivers are key drivers of central basin hypoxia and overall western and central basin eutrophication. So, accurate estimates of those loads are particularly important. While daily measurements constrain Maumee load estimates, complex flows near the Detroit River mouth, along with varying Lake Erie water levels and corresponding back flows, make measurements there a questionable representation of loading conditions. Because of this, the Detroit River load is generally estimated by adding loads from Lake Huron to those from the watersheds of the St. Clair and Detroit rivers and Lake St. Clair. However, recent research showed the load from Lake Huron has been significantly underestimated. Herein, I compare different load estimates from Lake Huron and the Detroit River, justify revised higher loads from Lake Huron with a historical reconstruction, and discuss the implications for Lake Erie models and loading targets.

Impact of past steel-making activities on lanthanides and Y (REY) fractionation and potential mobility in riverbank sediments

New technologies significantly disturb the natural riverine cycle of some Rare Earth Elements and Yttrium (REY). Whereas large evidence exists on the anthropogenic impact on REY dissolved and colloidal loads in rivers, there is still a knowledge gap on how suspended load could be impacted. As the river suspended matter is a key driver for the quantity of trace metal transport and mobility toward the other river compartments, it is of importance to evaluate how anthropogenic activity could affect its REY composition. Here, we report how past steel-making processes impacted the REY composition and potential mobility in riverbank sediments collected from a French River basin heavily disturbed by this industrial activity. In comparison to sediment originated from the local soil erosion, the industrial waste released in the river presented very unusual REY patterns. We observed specific LaN/GdN, LaN/LuN and Y/Ho ratios that indicate a strong heritage in the industrial waste of the iron ore used to produce steel. REY enrichments were also highlighted and can be classified as follow: Eu>Yb>Sm>Ce>Tm. The different enrichments might illustrate various fractionation processes that occurred separately on the different lanthanides inside the blast furnace according to temperature, pressure and oxygen fugacity changes. Sequential extractions performed on natural and industrial waste samples showed that REY enrichments in the industrial waste are included in one main fraction, which is strongly labile, whereas REYs contained in the sediment originating from the soil erosion are related to different mineralogical fractions having lower and more specific lability. Finally, REY composition showed that the sediment deposited on the riverbank is composed of two types of materials, which progressively evolved, after the ending of the industrial activity in this region, from a pure industrial waste in depth to a pure natural suspended sediment originated from local soil erosion at the surface.

Heavy Metal and Microbial Assessment of Rivers in the Niger Delta Basin, Nigeria

The present study assessed the heavy metal and microbial loads of Rivers in the Niger Delta basin. Mixed research design was adopted in this study. Nun River, Sagbama River, Andoni River, New Calabar River and Forcados River were purposively selected for the study. Grab method was used to collect the water samples. In each selected rivers selected, three water samples were collected at three different sampling points. The sampling points were about 500 meters apart from each other. Samples were collected against the flow of the water, where any flow was discernible. Water samples were collected at about 10-20cm depth. Determination of water quality was conducted in the laboratory. Descriptive statistics was used to analyze the assembled data. Laboratory results of water quality analyses indicate that most heavy metals and microbial parameters measured were above the acceptable water quality standard which implies that the sampled Rivers are polluted. Seasonal variations were observed in the concentrations of heavy metals and microbial loads. Based on the results, it becomes expedient for aggressive public enlightenment to discontinue the practice where rivers are used as a receptacle for the dumping of all sorts of waste and also as pier toilet for defecation. There is therefore need for regular surveillance of rivers within the Niger Delta basin.

Relationship between sediment load and climate extremes in the major Chinese rivers

Global warming has led to increase in climate extremes, which altered both hydrological cycles and soil erosion processes. However, the responses of river sediment load to climate change, especially climate extremes have not been well understood due to a lack of comprehensive assessment. This study investigated the temporal trends and spatial patterns of sediment load at 70 hydrological stations during the period of 1956–2019 in ten major river basins in China. Both the partial linear square regression model and the double mass curve method were used to quantify the contribution of key climatic indices and anthropogenic driving forces. Overall, the annual total sediment load exhibited a significant negative trend (P < 0.01), decreasing from 1842.18 Mt/yr in 1960 s to 322.72 Mt/yr in 2010 s (82.48 %). The significant decline of sediment load was particularly obvious in the Yangtze River basin and the Yellow River basin. The abrupt changes of sediment load mostly occurred in 1985–2000. Human activities were primarily response for sediment load changes in most basins. The sediment load in mainstream was mainly regulated by reservoirs, while the tributaries were largely affected by soil and water conservation measures. Intensive human activities have led to substantial changes in land surface and resulted in weakened correlation between sediment load and climate extremes. Generally, precipitation, erosive rainfall and precipitation amount in flood period were closely related to sediment load. In the Southwest River basin and Northwest River basin, the sediment load had a relatively good relationship with extreme temperature, which was related to alpine snowmelt and permafrost degradation due to climate warming. This study provides good insights for a better understanding of the interaction between river sediment load and climate extremes variables, which will be valuable for decision-making in river basin management.

River Islands of Khazir River A Geomorphological Study Along the Area from Nedoush Valley to the Upper Zap

The study tackled the phenomenon of river islands in the Al-Kazir river, along the Nedoush valley to the Upper Zab river, which is part of the administrative borders of Mosul and Erbil governorates in northern Iraq. It addresses the main natural and human factors that facilitate the formation of the river islands, including the impact of geological factors and climate, the slope of the stream, and meanders, in addition to delineating the direct fundamental role of the river load on the islands’ formation. It also shows the impact of human factors such as agriculture, grazing, and most importantly, quarries. Then shows the difference in the islands’ numbers and sizes along the study area.

Carbonate weathering, phosphate fertilizer, and hydrologic controls on dissolved uranium in rivers in the US Corn Belt: Disentangling seasonal geogenic- and fertilizer-derived sources

Soil and bedrock weathering and phosphate (P) fertilizers may both contribute to the uranium (U) load of rivers in agricultural regions, but controls over their relative influence are not well known. This study investigates the U sources to rivers in Ohio, United States, part of the Eastern Corn Belt in the Mississippi River watershed. We present a regional picture of seasonal U sources to rivers based on four analyses: 1) a spatial analysis of legacy soil and water data, 2) new measurements of U and carbonate weathering products from rivers at 50 locations across the state collected seasonally over two years, 3) a weekly time series with additional 234U/238U (n = 5) and 87Sr/86Sr (n = 5) measurements from an agricultural river, and 4) a mass-balance approach to U addition to the landscape based on reported P fertilizer use. Uranium concentrations in surface waters collected statewide ranged 0.1–21 nM (n = 132), with significantly higher concentrations in the glaciated agricultural portion of the state (mean = 7.3 nM; n = 105) than the non-glaciated portion (mean = 2.0 nM; n = 24). Concentrations in the glaciated region were highest during the spring and summer and decreased during baseflow. In the time-series, concentrations were ~7 nM during baseflow and ~14 nM during intermediate seasonal discharge conditions, indicating a second more surficial endmember source of U in addition to bedrock weathering that is well correlated with other carbonate weathering products. Systematic increases in 87Sr/86Sr and decreases in 234U/238U with increasing discharge confirm a changing source of carbonate and U weathering and a third surficial endmember during high discharge events. Our mass balance approach and geochemical analysis suggest that elevated U concentrations are the result of carbonate weathering deep in the soil column during elevated seasonal flow. Further work on U dynamics in agricultural rivers is required to understand mechanism controlling seasonal changes in U concentrations and 234U/238U in downstream rivers and U flux.

Mapping the Changjiang Diluted Water in the East China Sea during summer over a 10-year period using GOCI satellite sensor data

The Changjiang River loads freshwater into the East China Sea (ECS) and the Yellow Sea (YS). A low-salinity plume known as Changjiang Diluted Water (CDW) is formed by mixing with saline ambient waters; it disperses toward Jeju Island and the East/Japan Sea due to the dominant southerly wind and tide during summer. To map the offshore surface CDW in the ECS, a proxy was developed using surface water beam attenuation (c) and salinity from 18 annual summer cruises matched with synchronous Geostationary Ocean Color Imager (GOCI) satellite data. We followed a two-step empirical approach. First, a relationship between in situ salinity and c was obtained from hydrographic cruises (1998, 2003–2018, and 2021). Second, in situ c was matched with GOCI remote-sensing reflectance (Rrs) band ratios of all available blue-to-green wavelengths (2011–2018). Finally, satellite-derived surface salinity was determined directly by combining the two empirical relationships, providing a robust estimate over a range of salinities (22–34 psu). Our algorithm was then compared and validated with five previous satellite-derived salinity algorithms based on colored dissolved organic matter and particle concentrations. In the first step, surface salinity was matched and well correlated with c using an 18-year full conductivity–temperature–depth (CTD) dataset (N = 1,345, R2 = 0.93). In the second step, c was synchronously matched and well correlated with GOCI Rrs band ratios using an 8-year summer CTD dataset (N = 391, R2 = 0.93). The satellite-derived surface salinity based on the GOCI was compared with five other approaches and validated using an 8-year summer CTD dataset (2011–2018, N = 707, RMSE = 0.43, bias = 0.053, mean ratio = 1.002). We mapped satellite-derived surface salinity using monthly GOCI images during the summer from 2011 to 2020. The spatial patterns of the CDW were connected to the Changjiang River mouth and extended to the east–northeast during summer. Saline water was confined to the warm current and the upper slope in the eastern part of the study area. Anomalous dispersion of the CDW occurred in August 2016, 2017, and 2020, and limited dispersion occurred in August 2014 and 2019.

Large deltas, small deltas: Toward a more rigorous understanding of coastal marine deltas

Deltas are subaerial landforms that cap underlying deposits with subaqueous extensions that result from a river feeding sediment directly into a standing body of water at a rate that overwhelms any effective dispersal processes derived from the ambient basin. This definition encapsulates both the terrestrial surface expression and the geological focus on the entire sediment mass. Environmental studies also focus on the ecology of deltaic wetlands, their drowning history, and related sustainability issues including societal considerations, history, and culture. A mean 76 ± 16% drop in hydraulic energy occurs in all subaerial deltas regardless of size, given the break in gradients separating fluvial and deltaic surfaces, driving an ever-decreasing bed-material transport, shallowing of distributary channels and concomitant overbank flooding. A delta's sediment mass grows from the addition of new river loads but can also include aeolian and marine sediment derived from outside the delta domain, growth of peat and other biomass, and inputs from human action. Removal of sediment is via river plumes interacting with marine currents, wave-induced transport, sediment failures and gravity flows, high-tide inundation onto the delta plain, tidal channel widening and deepening, and human action (peat, clay, sand and gravel mining). A delta's trapping efficiency ranges from 0 for small-load rivers that discharge directly into an energetic ocean, to 80% for large deltas, and up to 100% for some semi-enclosed bayhead deltas, including fjords. The global (ensemble) subaerial delta aggradation rate is ∼1.6 mm/y if 70% of the global sediment load exits the river mouth(s), a reminder of how much sediment can be expected to be delivered to the surfaces of global deltas at a time when the 2022 CE sea level rise is ∼4 mm/y. At the planetary scale, deltas are environmentally complex given Earth's range in climate, hydrodynamics, tectonic settings, relative sea-level provinces, sediment input, redistribution processes, and human actions. Under natural conditions, the subaerial portion of deltas adapt to change by advancing, retreating, switching, aggrading, and/or drowning, whereas many modern deltas are structurally constrained by societal needs. The 89 large and mud-rich coastal marine deltas (i.e. subaerial area > 1000 km2) account for 84.3% of Earth's total deltaic area that hosts >89% of all humans occupying deltas, many living within megacities. The 885 medium-size deltas (i.e. subaerial areas 10–1000 km2) account for 15.5% of the global delta area and 10.5% of humans living on deltas, with characteristics that fall between the small and large delta categories. The 1460 small and essentially sandy deltas (1–10 km2), including all fjord deltas, are impacted less from human action (with exceptions) and most are better able to withstand climate change. Recognizing the limits of big data in capturing delta complexity, field data remains a necessary gold standard for site investigators.

Re-assessing the effect of differential weathering of minerals on strontium stable isotope behavior during granodiorite weathering

The shift in Sr stable isotope ratios (88Sr/86Sr, reported as δ88/86Sr values) in weathering systems provides insights into the transformation of the binding form of Sr between the dissolved and solid phases. However, the mechanism behind the fractionation of Sr stable isotopes during chemical weathering remains poorly constrained. We present mineral and elemental compositions along with the radiogenic Sr isotope ratios (87Sr/86Sr) and δ88/86Sr values from a ∼ 1 m deep horizontal spheroidal weathering profile of granodiorite in southeast China. Strontium was markedly lost during granodiorite weathering and a large amount of plagioclase and hornblende was decomposed in saprolite relative to the parent rock. The 87Sr/86Sr ratios substantially increased from 0.708704 to 0.712532 and δ88/86Sr values sharply decreased from 0.29‰ to −0.12‰ in the corestone-near saprolite as the weathering intensity increased. However, these values were rather constant in the corestone-distant saprolite, albeit with a large increase in the abundance of kaolinite. The Sr in the different chemical fractions indicates that the silicate components dominate the Sr isotopic composition in bulk rock and saprolite samples. Differential weathering of minerals is mainly responsible for the Sr stable isotopic composition of the corestone-near saprolite, while the lower δ88/86Sr values of the corestone-distant saprolite point to the possibility of preferential incorporation of lighter Sr isotopes into the structural sites of secondary clay minerals. In contrast, δ88/86Sr values of the exchangeable and reducible fractions (0.11‰–0.48‰) were more positive than those of the corresponding bulk samples because they were able to inherit the isotopic signatures of the weathered minerals. Further, an acid leaching experiment on the granodioritic parent rock reveals that mineral weathering reactions dominated the Sr isotope composition of the dissolved phase. The substantially higher δ88/86Sr values in the leachates relative to those in the residual solids (Δ88/86Srleachate-residue = 0.14‰–0.42‰) are consistent with the fact that isotopically heavier Sr in the dissolved load of rivers is mostly set by differential weathering of minerals (such as biotite and plagioclase). Combined with classic indices of chemical weathering (such as the chemical depletion fraction (CDF) and chemical index of alteration (CIA)), we suggest that Sr stable isotopes offer a promising proxy of the intensity of silicate weathering in saprolite studies in which isotope fractionation caused by biological cycling is negligible.