Influence Of Hydrology Research Articles

Two‐Decadal Variability of Lacustrine Groundwater Discharge: Coupled Controls From Weather and Hydrologic Changes

AbstractLacustrine groundwater discharge (LGD) is a vital water and solute source for lakes. However, the understanding of the long‐term temporal variability of LGD remains limited owing to insufficient insights into driving mechanisms, such as climatic and hydrologic changes. In this study, we examined the oxbow lake group in the central Yangtze River (YR) and assessed the LGD rates from 2000 to 2022 using 222Rn combined with meteorological and hydrological data. The findings revealed that groundwater was recharged during the wet season and discharged to the lakes during the dry season. We established a mathematical model to link the LGD rates to the meteorological and hydrological factors of the lakes, which accounted for 98.70% of the LGD rate variance. Using a predictive model combined with meteorological and hydrological data to assess the LGD rate over the past two decades, it was found that in wet years with higher precipitation and higher average YR water levels, the LGD rate was higher. The gradual increase in precipitation during the rising water and wet seasons, along with a slow rise in the YR water levels, will cause the LGD rate to exhibit a slightly increasing trend with fluctuations in the future. This study proposed an innovative approach to investigate the long‐term temporal variation in LGD and identify the weather and hydrological influences on LGD.

Influence of El Niño southern oscillation on precipitation variability in Northeast Thailand

This study investigates the influence of El Niño Southern Oscillation (ENSO) on monthly precipitation anomaly (PPTA) in Northeast Thailand using 30 years (1993–2022) data obtained from 27 weather stations of the Thai Meteorological Department (TMD). Pearson correlation analysis elucidates the relationship between ENSO indices and PPTA. Results reveal significant correlations between ENSO indices and PPTA, providing insights into their intricate relationship. La Niña events have a stronger relationship with PPTA than El Niño events, with notable correlations observed.•Strong La Niña phases, PPTA tends to increase across Northeast Thailand when Niño 3, 3.4, and 4 are more strongly negative -0.64, -0.50, and -0.65, respectively. These correlations provide valuable insights into the hydrological influence of ENSO in Thailand.•After the ENSO event, there appears to be a 4–5 month lag period from the impact on PPTA that shows a higher correlation.•Wavelet transform coherence (WTC) analysis dissects the temporal and frequency-specific nature of the relationship between ENSO and PPTA found during the frequency of 2–7 years. These findings underscore the importance of studying regional variations in ENSO impacts for PPTA in Northeast Thailand.

Dual impacts of hydrology and damming on eutrophication: Comparison of two Ramsar wetlands in the middle Yangtze floodplain

Dam construction for social-economic benefits has raised substantial biological and ecological concerns. However, contrasting findings have been reported regarding the role of hydrological modification in floodplain lake ecosystems. Here, we evaluated the influence of hydrology and dam construction on the eutrophication of floodplain lakes over the last 200 years by studying Zn/Al (an indicator of industrial activities), nutrient influxes (total phosphorus, TP), cyanobacteria production (canthaxanthin) and aquatic invertebrate dynamics (chironomids) in 210Pb dated sediment cores from two Ramsar Wetlands of International Importance in the middle Yangtze floodplain, one dammed (Wanghu) and the other freely connected (Poyang) with the Yangtze River. The results show that Wanghu Lake transitioned to a macrophyte-dominated clear water state (as indicated by the increases in pigment derived ultraviolet radiation index and dominance of macrophyte-related chironomid taxa) after local dam construction when anthropogenic nutrient loadings were relatively low. With increases in nutrient loadings, phytoplankton increased in both lakes, but water clarity declined and macrophyte-related chironomids decreased only in the lake which was locally dammed. Our study reveals that local damming facilitates the response of floodplain lake ecosystems to eutrophication and decouples it from the effects of hydrological variability. This study highlights the potential influence of hydrology and damming on the eutrophication of floodplain lakes by influencing water clarity and macrophyte coverage, implying that evaluating the role of local dam construction on ecosystem states should be based on knowledge of nutrient conditions in floodplain lakes.

Velocity of Greenland's Helheim Glacier Controlled Both by Terminus Effects and Subglacial Hydrology With Distinct Realms of Influence

AbstractTwo outstanding questions for the future of the Greenland Ice Sheet are (a) how enhanced meltwater draining beneath the ice will impact the behavior of large tidewater glaciers, and (b) to what extent tidewater glacier velocity is driven by changes at the terminus versus changes in sliding velocity due to meltwater. We present a two‐way coupled framework to simulate the nonlinear feedbacks of evolving subglacial hydrology and ice dynamics using the Subglacial Hydrology And Kinetic, Transient Interactions (SHAKTI) model within the Ice‐sheet and Sea‐level System Model (ISSM). Through coupled simulations of Helheim Glacier, we find that terminus effects dominate the seasonal velocity pattern up to 15 km from the terminus, while hydrology drives the velocity response upstream. With increased melt, the hydrology influence yields seasonal acceleration of several hundred meters per year in the interior, suggesting that hydrology will play an important role in future mass balance of tidewater glaciers.

Hydrological influences on landslide dynamics in the three gorges reservoir area: an SBAS-InSAR study in Yunyang county, Chongqing

Hydrological influences on landslide dynamics in the three gorges reservoir area: an SBAS-InSAR study in Yunyang county, Chongqing

Spectroscopic Phenological Characterization of Mangrove Communities

Spaceborne spectroscopic imaging offers the potential to improve our understanding of biodiversity and ecosystem services, particularly for challenging and rich environments like mangroves. Understanding the signals present in large volumes of high-dimensional spectroscopic observations of vegetation communities requires the characterization of seasonal phenology and response to environmental conditions. This analysis leverages both spectroscopic and phenological information to characterize vegetation communities in the Sundarban riverine mangrove forest of the Ganges–Brahmaputra delta. Parallel analyses of surface reflectance spectra from NASA’s EMIT imaging spectrometer and MODIS vegetation abundance time series (2000–2022) reveal the spectroscopic and phenological diversity of the Sundarban mangrove communities. A comparison of spectral and temporal feature spaces rendered with low-order principal components and 3D embeddings from Uniform Manifold Approximation and Projection (UMAP) reveals similar structures with multiple spectral and temporal endmembers and multiple internal amplitude continua for both EMIT reflectance and MODIS Enhanced Vegetation Index (EVI) phenology. The spectral and temporal feature spaces of the Sundarban represent independent observations sharing a common structure that is driven by the physical processes controlling tree canopy spectral properties and their temporal evolution. Spectral and phenological endmembers reside at the peripheries of the mangrove forest with multiple outward gradients in amplitude of reflectance and phenology within the forest. Longitudinal gradients of both phenology and reflectance amplitude coincide with LiDAR-derived gradients in tree canopy height and sub-canopy ground elevation, suggesting the influence of surface hydrology and sediment deposition. RGB composite maps of both linear (PC) and nonlinear (UMAP) 3D feature spaces reveal a strong contrast between the phenological and spectroscopic diversity of the eastern Sundarban and the less diverse western Sundarban.

Different effects of natural siltation, damming and pollution on two adjacent lakes of Dongting Lake Wetland: Evidence from paleolimnology

Evaluating the influences of hydrology on lotic floodplain lakes has been difficult due to concurrent effects of different human activities in the catchment. This study aims to explore the responses of floodplain lakes to natural siltation and damming by studying grain size and geochemical elements in 210Pb-dated sediment cores from two adjacent lakes with different hydrological conditions in the same catchment, including a hydrologically-isolated lake (Donghu Lake) and a hydrologically-connected lake (East Dongting Lake) in the middle Yangtze floodplain. The results showed that the riverine sediment supply declined in Donghu Lake after its isolation from the Yangtze River due to natural siltation in the 1910s. In East Dongting Lake, the riverine sediment supply remained relatively stable before the operation of the Three Gorges Dam (TGD) in 2003 CE, and then declined rapidly in response to a decrease in riverine sediment supply. Total phosphorus and total organic carbon in Donghu Lake increased after the “reform and opening-up” in the late 1970s, whereas they remained at low concentrations in East Dongting Lake before the TGD operation in 2003 CE. Hydrological isolation from the Yangtze River reduced the influxes of riverine sediments, but promoted nutrient enrichment and primary production in East Dongting Lake through extending water residence times. Stable element composition in Donghu Lake after 2003 CE suggested that the TGD operation had minor effects on hydrologically-isolated lakes. The comparison between hydrologically-closed and hydrologically-free lakes within the same catchment provides an effective method to identify different effects of natural siltation, damming and environmental pollution.

The hydrology of the Jezero crater paleolake: Implications for the climate and limnology of the lake system from hydrological modeling

Jezero crater, the landing site of the Perseverance rover, hosts sedimentary fan deposits, aqueously altered sedimentary rock, and an outlet breach of the crater rim, all of which indicates that a long-lived lake (or lakes) once existed within the crater. The deltaic deposits in the crater may preserve evidence of habitable conditions within the past lake system, which would have been influenced by the climate and conditions of the past hydrological system within the watersheds and basin. However, the aqueously altered sedimentary deposits within Jezero are less extensive than those found in other crater lakes on Mars, like Gale with a crater filling mound of cemented sediment. In this work we use hydrological models of the past Jezero lake system to constrain the climatic and hydrological conditions by comparing model predictions to the proposed lake stands and mineralogy in the crater observed from orbit and by the Perseverance rover thus far. We then compare these results to Gale crater to understand the influence of basin hydrology on the depositional setting found within past crater lakes. We show that a lake forming at the outlet breach elevation or higher in Jezero requires a semiarid or wetter-arid climate, consistent with previous estimates. An integrated hydrologic system with seasonal variations similar to arid and semiarid climates on Earth results in a lake system at Jezero characterized by both surface and subsurface outflow from the lake. Outflow to the subsurface and through the outlet breach will remove dissolved solids from the lake system, mitigating large-scale evaporite cementation within the Jezero basin, which is in contrast to Gale crater, where subsurface inflow constituted a larger percentage of the total inflow to the lake and all loss was through evaporation due to the setting in a deeper impact crater. Furthermore, at hyperarid climatic and/or groundwater-driven hydrological conditions, lake formation within Jezero would have ceased while a lacustrine depositional environment would have continued at Gale. This highlights the importance of considering basin hydrology, in addition to climate, when interpreting lacustrine sedimentary deposits in craters on Mars.

Weakened hydrological oscillation period increased the frequency of river algal blooms

The evolution of riverine aquatic ecosystems typically exhibits notable characteristic with cumulative, enduring, and hysteresis. Exploring the non-linear response of riverine ecology to long-term hydrological fluctuations become a major challenge in contemporary interdisciplinary research. In response to the critical issue of frequent river algal blooms in the lower Han River, which is impacted by Asian largest inter-basin water diversion project. We identified the non-linear response of eco-hydrology across various time scales through the integration of Continuous Wavelet Transform (CWT) and Inverse Wavelet Transform (IWT). Our study revealed that: 1) Over the past half century, the hydrological regime in the lower Han river showed a significant downward trend, and existed three significant hydrological oscillation periods (HOPs), including the short-scale Intra-AC (180 days), the medium-scale AC (365 days, the first major period), and the long-scale Inter-AC (2500 days), the variation of Inter-AC changed most dramatically. 2) We further found that the Inter-AC variation of hydrology is more closely related to the formation of river algal blooms in the Han River, and when the hydrological Inter-AC shows steady state or downward trend, the frequency of algal blooms in the lower Han River increases significantly. 3) The river algal blooms in the lower Han River is a cumulative consequence to the long-term hydrological influences. Weakened hydrological Inter-AC is more likely to increase the frequency of river algal blooms, and 10-years Inter-AC cumulation increased the frequency by 60%. Therefore, the weaken of long-scale HOP will significantly increase the frequency of river algal blooms in the future. This study received a critical scientific insight and aimed at provide guidance for the optimization of ecological management within the framework of national large-scale water conservation.

Lessons learned from the spatiotemporal analysis of long‐term and time‐variable young water fractions of large central European river basins

AbstractThe transit time of precipitation entering a catchment and leaving it as streamflow spatiotemporally varies according to the flow paths that precipitation takes. However, investigating influences of hydrometeorological variables and catchment characteristics on time‐variable transit times is challenging due to the complex water flow through heterogeneous landscapes. Recent studies investigated the fraction of streamflow younger than approximately 3 months (Fyw) using multi‐year data (long‐term Fyw) or one‐year calculation windows to investigate its time‐variability (time‐variable Fyw). Nonetheless, it is still unclear if the inter‐annual variability of one‐year Fyw is due to hydrological influences or its uncertainty, and no minimum time series length for the long‐term Fyw was defined yet. Here, we investigated the impact of catchment characteristics and hydrometeorological variables on the long‐term Fyw, the time‐variable Fyw, and the Fyw depending on discharge of nine river basins in Central Europe. All methods of estimating Fyw led to similar results, with Fyw depending on discharge deemed unreliable due to the monthly sampling interval of streamflow isotopes. Danube and Rhine had the lowest Fyw (0.06), medium Fyw (0.20) were found in eastern basins (e.g., Oder), and the western ones (e.g., Mosel) had the highest Fyw (0.33). Spatial analysis indicated a negative relationship between Fyw and altitude. Contradicting or lacking spatiotemporal relationships to other variables pointed to unknown influential factors controlling the runoff process. Using flow duration curves, it was found that basins with a low flow variability had low Fyw, indicating that the old water of their runoff stems from large subsurface storage. With increasing calculation window size, the within‐basin variability of time‐variable Fyw decreased. Long‐term Fyw depended on the method used to define ‘long‐term’ and the time series length and start and end date. We thus recommend future studies to calculate long‐term and time‐variable Fyw to facilitate comparability between different catchments, and to account for this source of uncertainty. Further, more studies are needed in diverse catchments to investigate the hydrometeorological impacts on Fyw and thus on runoff generation processes.

Hydrothermal Seepage of Altered Crustal Formation Water Seaward of the Middle America Trench, Offshore Costa Rica

AbstractChemical compositions of sediment pore waters are presented from 13 piston and gravity cores that were collected on ∼24 Ma crust of the Cocos Plate seaward of the Middle America Trench and near the onset of crustal faulting from subduction. Cores were collected mainly within a 1.75 km2 area overlying a buried basement topographic high that supports an elevated heat flux, consistent with seawater transport within the upper volcanic crust. Systematic variations in pore water chemical profiles indicate upward seepage speeds (up to 1.7 cm yr−1 providing a net flux of 0.1 L s−1), constrain the chemical composition of the formation water within the underlying upper basaltic basement, and elucidate diagenetic reactions in the sediment. Relative to seawater, formation water has an elevated temperature (70–80°C) and concentrations or values of Ca, chlorinity, Sr, Ba, Li, Fe, Mn, Si, Cs, D/H, and Mo, and lower concentrations or values of Mg, Na, sulfate, alkalinity, TCO2, K, B, F, phosphate, 87Sr/86Sr, δ13C, δ18O, U, and Rb. Although this site is located only 30 km from the trench axis, there is no chemical evidence for subduction‐related hydrologic influences. Instead, the data are explained by a combination of seawater‐basalt reactions within the upper basement and diffusive exchange with overlying sediment, as part of a shallow, ridge‐flank hydrothermal system. It is unclear why this site has an elevated heat flux relative to neighboring crust, but this may result from variations in crustal properties or modification related to flexural faulting outboard of the trench.

Distinct dynamics in mountain watersheds: Exploring mercury and microplastic pollution—Unraveling the influence of atmospheric deposition, human activities, and hydrology

The intensification of human activities all around the globe has led to the spread of micropollutants in high-mountain freshwater environments. We therefore aimed to assess the geospatial distribution and determine the potential sources of (total-) mercury (THg) and microplastics (MPs) in mountain freshwater ecosystems. To do so, we analyzed THg and MP concentrations in brown trout, biofilm, and sediments from lotic and lentic ecosystems in the Pyrenees – all subjected to different types of human pressure. Additionally, we assessed the potential impacts of these pollutants on fish, and explored the bioindication capacity of brown trout (Salmo trutta fario) and biofilm regarding THg and MP pollution. For the first time, we measured concentrations of MPs trapped in the matrix of freshwater biofilm. Our results suggest that THg in the Pyrenees might be explained by both legacy (regional) and distant sources, in combination with environmental characteristics such as the presence of peatlands or streamwater physicochemistry, while MPs in fish are linked to recent local pollution sources such as single-use plastics. In contrast, MPs in biofilm matrix and sediments indicate a combination of distant (i.e., atmospheric deposition) and recent local pollution sources. Moreover, hydrodynamics and plastic density likely control MP distribution in rivers. Based on Fulton's condition factor, we also found that higher THg concentrations caused a negative impact on fish health (K < 1), while no impact of MPs could be seen. Therefore, we suggest that brown trout and biofilm can serve as bioindicators of atmospheric deposition of THg in high-altitude lakes and that biofilm is a reliable bioindicator to assess MP pollution in remote environments. Brown trout may also act as a bioindicator of MP pollution, but only efficiently in more polluted areas.

An advanced global soil erodibility (K) assessment including the effects of saturated hydraulic conductivity

USLE-type models are widely used to estimate average annual soil loss at large scales, with the erodibility factor (K) being the sole component that accounts for soil's susceptibility to erosion. The factor includes the information on permeability in the equation, however, most definitions of the K factor consider the soil hydrological influence only very crudely and indirectly. Thus, the direct impact of surface runoff infiltration and drainage on soil erosion is largely neglected. The objective of this study is to incorporate soil hydraulic properties in the K factor map by merging available global-scale measured saturated hydraulic conductivity (Ksat) data with soil texture and organic carbon information into a modified K factor. To achieve this, the Wischmeier and Smith (1978) soil texture- and permeability-based equation (KWischmeier factor) was modified to include Ksat, called Kksat factor. Using the Random Forest machine learning algorithm, the KWischmeier factor and the Kksat factor were each correlated with soil and remote sensing covariates for spatial extrapolation of two independent K factor maps at 1 km spatial resolution. We noted a clear decrease in the mean value of the Kksat factor (0.023 t ha h ha−1 MJ−1 mm−1) compared to the mean value of the KWischmeier factor (0.027 t ha h ha−1 MJ−1 mm−1). The reduction in Kksat factor values was most pronounced in tropical regions reflecting the difference in soil properties (e.g., clay and iron), whereas other climate regions showed relatively minor changes in comparison to the KWischmeier factor as well as to the recent global modeling of Borrelli et al. (2017) (KGloSEM factor maps). As many studies discussed an overall overestimation of (R)USLE based erosion rates compared to measurements, this reduction in the K factor might improve modeled erosion rates in the right direction. The Kksat marks an important initial step in integrating hydraulic properties into the K factor of USLE-type models and can prove their significance in future studies.

Drivers of annual suspended sediment and nutrient yields in tributaries to Lake Erie

Abstract In the early 2000s, harmful algal blooms and hypoxia returned to Lake Erie following a period of ecosystem recovery from the late 1980s through the 1990s. This corresponds to a drastic increase in dissolved reactive phosphorus loads and flow-weighted mean concentrations in the major tributaries to the Western Lake Erie Basin. However, there is substantial variability in suspended sediment and nutrient yields across Lake Erie tributaries. It is well known that agricultural and urban land uses lead to increased watershed sediment and nutrient yields, especially in the absence of proper management practices. Yet attributes such as watershed soil types and slope can also affect yields. We examined the influence of watershed land use, hydrology, soil type, and slope on annual nutrient and sediment yields from tributaries to Lake Erie monitored as part of the Heidelberg Tributary Loading Program. A minimum of one sample and, during storm runoff, up to three samples a day are analyzed for all major nutrients and suspended sediments. The 5-year average annual yields across these watersheds exhibited distinct geographic patterns from west to east, with high suspended sediment but lower nutrient yields from the eastern most tributaries (Cuyahoga, Old Woman Creek, Huron) and the lowest sediment along with lower nutrient yields from the western most tributaries (Raisin, Tiffin, Lost). The Maumee, Portage, Sandusky, along with select subwatersheds tended to have intermediate sediment yields with high nutrient yields. Altogether, the % cultivated crops and poorly drained soil in the watershed increased nutrient yields whereas a higher % slope and lower % pasture increased sediment yields. These patterns highlighted unique regional differences that can help guide management decisions for these watersheds that ultimately would improve the health of Lake Erie.

Phragmites-fire feedbacks: the influence of fire and disturbance-altered hydrology on the abundance of Phragmites australis

Phragmites-fire feedbacks: the influence of fire and disturbance-altered hydrology on the abundance of Phragmites australis

Techniques to embed channels in finite element shallow water equation models

Two new and novel techniques to efficiently represent channels in large-scale finite element shallow water equation models are introduced. The first enables the discontinuous representation of bathymetric depth by allowing nodes along a discontinuity to have two land surface elevations, one representing the bottom of the discontinuity and the other the top of the discontinuity. Elemental integration proceeds using the nodal depth corresponding to whether the element is on the upper or lower side of the discontinuity and enables efficient treatment of steep sided features in a two-dimensional horizontal discretization. The second technique consolidates nodal equations at paired nodes across a channel. Doing this eliminates cross-channel variability and consequently eliminates the across-channel Courant-Friedrichs-Lewy stability constraint on the model time step. Together the two techniques allow channels of various sizes as well as other instances of steep topography to be embedded seamlessly, efficiently and in a fully coupled manner within an otherwise two-dimensional horizontal spatial discretization. This new capability is especially useful in the interface zone subject to both coastal and hydrological influences as it effectively captures bi-directional channelized flow, bi-directional flow between the channel and the floodplain, and coupled flow when the channel and floodplain are fully submerged. This paper describes the methodological development and presents a series of tests that verify the performance of this novel solution approach.

Do highly anthropized hydrological conditions in marshes influence fish communities according to their life‐history strategies?

AbstractAlterations of natural hydrology in aquatic ecosystems are known to strongly impact the community composition of different taxa. Surprisingly, literature on the potential influence of hydrology on fish community composition is still very scarce in agricultural marshes, where canals represent one of the few remaining aquatic habitats. This study is aimed to address this research gap by monitoring fish communities in independent hydrological units differing in hydrology management over a 6 years period. We predicted variable fish responses to the hydrological context according to different life‐history strategies (opportunistic, equilibrium, or periodic species). Periodic and opportunistic species were the most frequently observed. Despite differences in hydrology between canals (but little variation over years), we found that hydrology explained only a very low proportion of variation in the composition of fish communities. In particular, the flooding duration of meadows in early spring did not influence the composition of fish communities, not even the abundance of periodic species expected to rely on such temporary habitats. Instead, fish communities were more influenced by local habitat variables (aquatic vegetation cover, turbidity, tree roots, and refuges under the canal banks). The hydrological management of most hydrological units for agricultural purposes (i.e., severe flood abatement in spring and shallow water depth in canals in summer) was found to be incompatible with conservation goals to promote more diverse fish communities between hydrological units. Therefore, we call for further investigations in similar habitats covering a larger range of hydrological conditions.

An evaluation of the landscape structure and La Niña climatic anomalies associated with Japanese encephalitis virus outbreaks reported in Australian piggeries in 2022

The widespread activity of Japanese encephalitis virus (JEV) reported in previously unaffected regions of eastern and southern Australia in 2022 represents the most significant local arbovirus emergency in almost 50 years. Japanese encephalitis virus is transmitted by mosquitoes and maintained in wild ardeid birds and amplified in pigs, the latter of which suffer significant reproductive losses as a result of infection. The landscape epidemiology of JEV in mainland Australia is almost entirely unknown, particularly in the eastern and southern parts of the country where the virus has not been previously documented. Although other areas with endemic JEV circulation in the Indo-Pacific region have demonstrated the importance of wild waterbird-livestock interface in agricultural-wetland mosaics, no such investigation has yet determined the composition and configuration of pathogenic landscapes for Australia. Moreover, the recent emergence in Australia has followed substantial precipitation and temperature anomalies associated with the La Niña phase of the El Niño Southern Oscillation. This study investigated the landscape epidemiology of JEV outbreaks in Australian piggeries reported between January and April of 2022 to determine the influence of ardeid habitat suitability, hydrogeography, hydrology, land cover and La Niña-associated climate anomalies. Outbreaks of JEV in domestic pigs were associated with intermediate ardeid species richness, cultivated land and grassland fragmentation, waterway proximity, temporary wetlands, and hydrological flow accumulation. This study has identified the composition and configuration of landscape features that were associated with piggery outbreaks reported in 2022 in Australia. Although preliminary, these findings can inform actionable strategies for the development of new One Health JEV surveillance specific to the needs of Australia.

Unraveling the climate control on debris-free glacier evolution in the Everest region (Nepal, central Himalaya) during the Holocene

Current mass balance and meteorological surveys of Mera glacier located about 30 km south of Mount Everest in Nepal show the dominant role of Asian monsoon precipitation on interannual mass balance variability while temperature controls the altitude of snow-rain threshold. As these observations on mass balance variability only explore the recent decades, studies on paleo glacial extents are useful to investigate the long-term climate forcing on glacier evolution. To do so, we investigated the long-term evolution of the debris-free Mera glacier and a neighbouring small debris-free South Khare glacier. Fifty-one 10Be CRE ages were obtained from samples collected on moraine boulders and roches moutonnées. 10Be CRE ages of the boulders span from the end of the Lateglacial (19.0–11.7 ka) to the Little Ice Age (∼0.6–0.1 ka). The oldest dated moraine in this study was observed at the base of South Khare glacier with an age of 13.6 ± 0.5 ka. The two glaciers subsequently experienced their largest Holocene extent in the Early Holocene with moraines dated to 11.0 ± 0.3 ka at the base of Mera glacier and 10.8 ± 0.5 ka at the base of South Khare glacier. We did not observe any moraine from the Mid-Holocene. During the Late Holocene several glacier advances were recorded around 2.3 ± 0.2 ka, 1.5 ka and then during the last centuries at Mera glacier and around 2.8 ± 0.6 ka, and during the Little Ice Age at South Khare glacier. To explore the links between long-term Nepalese glacier changes and climate, we used oceanic and terrestrial Indian Summer monsoon reconstructions and temperature and precipitation output from two transient global climate models TraCE and LOVECLIM. These climate data outputs were corrected by a reconstruction of the Atlantic Meridional Overturning Circulation (AMOC) over the Holocene and its associated climatic impacts. We also used sensitivity experiments from the IPSL (Institut Pierre Simon Laplace) model to discuss the possible influence of horizontal resolution, land hydrology, vegetation and runoff on changes in Asian summer monsoon. Importantly, we show this long-term Nepalese glacier pattern does not perfectly conform neither to the Indian monsoon precipitation that is documented from terrestrial and marine records nor to temperature and precipitation changes simulated by the models. While the maximum glacier extent in the Early Holocene corresponds to enhanced precipitation documented by proxies and models, the Late Holocene glacier advance remains puzzling. We claim that new paleo glacier records and improved climate simulations are necessary to get a better understanding of past glacier changes and the associated climate dynamics, which might be crucial to gain confidence in both glacier and climate future evolutions.

Unraveling seasonal and interannual nutrient variability shows exceptionally high human impact in eutrophic coastal waters

AbstractNutrient import into eutrophic estuarine‐coastal zones is modulated by river discharge and anthropogenic activities (agriculture, industry, sewage, etc.). Comparing anthropogenic vs. hydrological influences on nutrient loading is important for ecosystem managers but has been a long‐standing challenge. As an attempt to fill this gap, a retrospective study was conducted using multiyear (2012–2022) data in one of the most eutrophic coastal seas in China, the Jiangsu coastal waters. Of the two main pollutants on the Jiangsu coast, dissolved inorganic nitrogen (DIN) is extremely overloaded relative to phosphate (PO4). Their spatial distribution shows clear terrestrial sources as concentrations decrease offshore. Although in each survey DIN and PO4 are enriched in low‐salinity waters, their spatially averaged concentrations are out of phase with river discharge on the seasonal and interannual scales. A box model was applied to decompose contributions of river discharge and nutrient import by anthropogenic activities. Results show that the human impacts on the interannual nutrient variability exceed those of hydrological factors on the Jiangsu coast. Anthropogenic nutrient loading decreases during 2012–2020, paralleled with the reduced fertilizer use and other nonpoint sources. Sporadic nutrient fluxes from point sources are likely responsible for the aseasonal nutrient‐rich patches. Our study demonstrates that water quality in the Jiangsu coastal waters is highly affected by anthropogenic activities. Findings in this study have broad implications for local monitoring strategies and restoration efforts and provide insight into assessing human stress from field data in global eutrophic ecosystems.