Hydrological Controls Research Articles

Evaluation and Improvement Measures of the Runoff Coefficient of Urban Parks for Sustainable Water Balance

As the impermeable sidewalk area increases in urban areas, diverse problems related to water occur. The purposes of this research were to increase the rainwater infiltration rate through water balance analysis and estimate the runoff coefficient according to land cover types in urban parks. The regression equations and runoff coefficients relative to the rainwater infiltration rate were estimated according to the land cover types and applied to eight urban parks. In the results of the experiment, the runoff coefficient was 0.245 for vegetation areas, 0.583 for permeable sidewalks, 0.963 for sidewalk blocks, and 1.000 for impervious sidewalks, which had 100% outflow. The results show that the vegetation area in urban parks is significantly related to rainfall–runoff, infiltration, and evapotranspiration. The average of eight urban parks was 126.52 mm, indicating that 11.80% of the rainfall was recharged into groundwater. Additionally, the average runoff rate was 498.56 mm, indicating that 46.52% was leaked externally. Therefore, it is suggested to decrease the impermeable sidewalk areas in urban parks. Additionally, extending the waterway, swamp, and gravel sidewalk areas is suggested. Urban parks should be developed in order to contribute to hydrological control through the water balance in urban land use.

Tracer-aided identification of hydrological and biogeochemical controls on in-stream water quality in a riparian wetland

In-stream water quality reflects the integrated results of hydrological mixing of different water sources and associated biogeochemical transformations. However, quantifying the relative importance of these controls is often challenging, particularly in riparian wetlands due to complex process interactions and marked spatio-temporal heterogeneity in environmental gradients. Here, we established a two-step method to differentiate the dominance of hydrological and biogeochemical controls on water quality in a riparian peatland in northern Germany. First, an isotope-based mixing model was developed for distributed modelling of in-stream water balance over a two-year period. The simulation showed the predominance of groundwater inflows for most of the time period, while lateral inflows and channel leakage became more influential in mid-summer, as stream-groundwater connectivity weakened due to declining groundwater levels. A moderate downstream shift from groundwater to lateral inflow was also observed due to the changing channel network geometries and inflow from field drains. The mixing model was then further applied to predict the in-stream concentrations of nutrients, major ions and trace elements. The predicted concentrations were assumed to be those resulting from hydrological mixing only, while influence of biogeochemical controls were reflected by the prediction deviation from observation. Accordingly, 15 water quality parameters were grouped based on their simulation performances into hydrologically-controlled (Cl–, Mg, Na, K, and Si), biogeochemically-controlled (DOC, SO42−, Mn, and Zn), or controlled-by-both (SRP, NO3-N, Ca, Fe, Al, and Cu). The mixing modelling not only reproduced the spatiotemporal in-stream water balance with finer process conceptualisation, but also provided a generic method to quantitatively disentangle the relative strength of hydrological and biogeochemical controls. Such a method can be employed as a robust learning tool before extending a hydrological model for water quality simulation, as when, where and how strong biogeochemical controls are exerted provides a strong indicator on which dominant processes need to be conceptualised.

Scientific Evidence behind the Ecosystem Services Provided by Sustainable Urban Drainage Systems

Urban green infrastructure such as sustainable urban drainage systems are potential providers of ecosystem services. This paper reviews the field studies that empirically verify the potential benefits of SUDS. The cultural, provisioning, supporting, and regulating ecosystem services investigated in real cases have been studied and classified according to climatology (except for the control of urban hydrology, which has been widely corroborated). Although successful cases of runoff decontamination are numerous, there is heterogeneity in the results of the systems beyond those associated with climatic differences. The other ecosystem services have not been as widely studied, giving very variable and even negative results in some cases such as climate change control (in some instances, these techniques can emit greenhouse gases). Installations in temperate climates are, by far, the most studied. These services derive from the biological processes developed in green infrastructure and they depend on climate, so it would be advisable to carry out specific studies that could serve as the basis for a design that optimizes potential ecosystem services, avoiding possible disservices.

Hydrological control of river and seawater lithium isotopes

Seawater lithium isotopes (δ7Li) record changes over Earth history, including a ∼9‰ increase during the Cenozoic interpreted as reflecting either a change in continental silicate weathering rate or weathering feedback strength, associated with tectonic uplift. However, mechanisms controlling the dissolved δ7Li remain debated. Here we report time-series δ7Li measurements from Tibetan and Pamir rivers, and combine them with published seasonal data, covering small (<102 km2) to large rivers (>106 km2). We find seasonal changes in δ7Li across all latitudes: dry seasons consistently have higher δ7Li than wet seasons, by −0.3‰ to 16.4‰ (mean 5.0 ± 2.5‰). A globally negative correlation between δ7Li and annual runoff reflects the hydrological intensity operating in catchments, regulating water residence time and δ7Li values. This hydrological control on δ7Li is consistent across climate events back to ~445 Ma. We propose that hydrological changes result in shifts in river δ7Li and urge reconsideration of its use to examine past weathering intensity and flux, opening a new window to reconstruct hydrological conditions.

Hydrologic Controls on Peat Permafrost and Carbon Processes: New Insights From Past and Future Modeling

Soil carbon (C) in permafrost peatlands is vulnerable to decomposition with thaw under a warming climate. The amount and form of C loss likely depends on the site hydrology following permafrost thaw, but antecedent conditions during peat accumulation are also likely important. We test the role of differing hydrologic conditions on rates of peat accumulation, permafrost formation, and response to warming at an Arctic tundra fen using a process-based model of peatland dynamics in wet and dry landscape settings that persist from peat initiation in the mid-Holocene through future simulations to 2100 CE and 2300 CE. Climate conditions for both the wet and dry landscape settings are driven by the same downscaled TraCE-21ka transient paleoclimate simulations and CCSM4 RCP8.5 climate drivers. The landscape setting controlled the rates of peat accumulation, permafrost formation and the response to climatic warming and permafrost thaw. The dry landscape scenario had high rates of initial peat accumulation (11.7 ± 3.4 mm decade−1) and rapid permafrost aggradation but similar total C stocks as the wet landscape scenario. The wet landscape scenario was more resilient to 21st century warming temperatures than the dry landscape scenario and showed 60% smaller C losses and 70% more new net peat C additions by 2100 CE. Differences in the modeled responses indicate the largest effect is related to the landscape setting and basin hydrology due to permafrost controls on decomposition, suggesting an important sensitivity to changing runoff patterns. These subtle hydrological effects will be difficult to capture at circumpolar scales but are important for the carbon balance of permafrost peatlands under future climate warming.

Modeling and predicting rainfall time series using seasonal-trend decomposition and machine learning

This study presents a hybrid approach that integrates seasonal-trend decomposition and machine learning (termed STL-ML) for predicting the rainfall time series one step ahead based on the historical rainfall and other meteorological (e.g., temperature, humidity, etc.) data. The proposed hybrid STL-ML approach mainly consists of three steps: (1) The seasonal-trend decomposition is used to firstly decompose the rainfall time series into the trend, seasonal, and remainder components; (2) Three different machine learning (ML) models, namely Gated Recurrent Unit (GRU) network, multi-time-scale GRU network, and Light Gradient Boosting Machine (LightGBM) model, are developed for modeling and predicting the three components, respectively; (3) The predicted rainfall is eventually acquired by adding up the predicted values of the three components, and several metrics are used to evaluate the model performance. To verify the applicability and validity of the proposed approach, a case study is conducted on the daily meteorology data collected in Cairns, Australia, from 1st Jan 2000 to 31st Dec 2020. The case study results imply that: (1) Through the seasonal-trend decomposition of the rainfall time series, various patterns and information beneath the rainfall time series can be fully extracted and explicitly demonstrated in its three components, which is beneficial to an accurate rainfall prediction. (2) The GRU network, multi-time-scale GRU network, and LightGBM model can well fit and predict the trend, seasonal, and remainder components, respectively. (3) By adding up the predicted values of the three components, the predicted rainfall shows satisfactory agreement with the ground truth, and a reliable one-step-ahead prediction can be achieved even if an sudden extreme rainfall occurs. (4) The comparisons with three baseline methods further justify the rationality and effectiveness of the hybrid STL-ML approach. The novelty of the proposed STL-ML approach lies in its capabilities of (1) fully extracting and utilizing the information in every regard to predict rainfall; (2) providing a good one-step-ahead rainfall estimation for sudden heavy rainfall events. Therefore, it can be used as an essential complement to numerical rainfall prediction and thus can play a crucial role in flood prediction and hydrological disaster control.

Hydrological control of threshold transitions in vegetation over early-period wetland development

Hydrological processes are a fundamental driver of vegetation across Earth’s ecosystems and have been increasingly altered and managed by humanity. Whether vegetation exhibits threshold responses to gradual changes in hydrology is an important but unresolved question. Here, we examined this question by providing the first remote sensing-based investigation of decadal-scale vegetation changes along hydrological gradients over early-period wetland development. We focused on wetlands on three estuarine fluvial islands, where sedimentation was driving wetlands to transition from an initially mudflat state to a vegetated marsh state (dominated by Suaeda salsa). Our results showed that Suaeda marshes decreased in a nonlinear, threshold manner with increasing flooding frequency, a pattern consistently observed in periods when plants were still acquiring their hydrological niches. Further, although the breadth of Suaeda’s hydrological niche (i.e., the range of flooding frequencies with Suaeda presence) expanded linearly or nonlinearly on all three islands, changes in niche position (i.e., lower and upper limits) differed. Both lower and upper limits of their hydrological niche expanded on sheltered islands in the inner part of the estuary, while their upper limits expanded and lower limits retreated on more exposed, outer islands. Our findings provide unique evidence that nonlinear, threshold hydrological controls of vegetation may be pervasive even in early stages of wetland development, although the underlying mechanisms may be specific and depend on other factors (e.g., wave exposure). Incorporating these threshold behaviors are key to predicting and managing transitions between vegetated and unvegetated states of ecosystems in an anthropogenic hydrosphere.

Studies on Hydrological Processes on Karst Slopes for Control of Soil and Water Loss

Soil and water loss in karst areas seriously restricts the sustainable development of karst ecosystems, the economy and society in southwest China, which has been a concern of, and studied by, many scholars in China and abroad. Soil and water loss has a great influence on the evolution of rocky desertification, groundwater quality, drought and flood disasters in karst regions. This paper aimed to provide a review of studies of slope hydrological processes in soil and water loss. In this paper, 322 related articles retrieved from the Web of Science database and CNKI database were systematically reviewed. Firstly, a quantitative study was conducted to analyze the annual number, countries and research progress of the published literature. Secondly, the main progress and achievements of slope hydrology and soil erosion control technology were classified and summarized according to theoretical research, mechanism research, technology research and technical demonstration. Finally, the key problems and future research prospects are put forward, starting with the existing technology, in order to find more suitable soil and water loss control measures in karst regions and achieve economic and ecological benefits.

Resiliency of Silica Export Signatures When Low Order Streams Are Subject to Storm Events

AbstractSilicon stable isotope ratios (30Si) of over 150 stream water samples were measured during seven storm events in six small critical zone observatory (CZO) catchments spanning a wide range in climate (sub‐humid to wet, tropical) and lithology (granite, volcanic, and mixed sedimentary). Here we report a cross‐site analysis of this dataset to gain insight into stream 30Si variability across low‐order catchments and to identify potential climate (i.e., runoff), hydrologic, lithologic, and biogeochemical controls on observed stream Si chemical and isotopic signatures. Event‐based 30Si exhibit variability both within and across sites (−0.22‰ to +2.27‰) on the scale of what is observed globally in both small catchments and large rivers. Notably, each site shows distinct 30Si signatures that are preserved even after normalization for bedrock composition. Successful characterization of observed cross‐site behavior requires the merging of two distinct frameworks in a novel combined model describing both non‐uniform fluid transit time distributions and multiple fractionating pathways in application to low‐order catchments. The combined model reveals that site‐specific architecture (i.e., biogeochemical reaction pathways and hydrologic routing) regulates stream silicon export signatures even when subject to extreme precipitation events.

Hydrogeomorphic advancements in river science for water security in India

Effective management of rivers and the maintenance of the integrity of linked biophysical systems require multidisciplinary approaches. Thus, River Science is a relatively new arena of scientific inquiry that focuses on problems of sustainable management of river systems and it actively integrates multiple scales and various concepts. This paper presents a review of new developments in hydrogeomorphic processes understanding, which are critical to assess water security for Indian river systems.Indian rivers are under the influence of a diverse interplay of climatic, geomorphic, tectonic, and anthropogenic forces, and are broadly classified in terms of Himalayan and Peninsular rivers, which can be further subdivided into 6 major types. The Himalayan rivers have received greater attention in comparison to rivers in peninsular India. Within the backdrop of changing climate, an improved understanding of the interrelationships between hydrological, morphological and ecological processes is the key to quantifying water security for Indian rivers in the near future. Geomorphic threshold, hydrological and sediment connectivity, Groundwater-Surfacewater (GW-SW) interaction and Environmental-flow (E-flow) assessment are the essential elements to understand the hydrology-morphological-ecological processes. Such studies have been initiated in Indian river systems, however, these are still limited in number. Stream power distribution based approaches are frequently employed to understand hydrological controls on morphological processes and form in regulated and unregulated rivers. As a majority of the Himalayan rivers are hydrologically and morphologically disconnected due to large dams or barrages, the result is a discontinuum of channel processes. Peninsular rivers are dominantly bedrock and highly regulated river systems, which show significant short- to long-term flow variability and have tributaries which are not perennial. Disconnectivity due to extensive flow regulation and water withdrawals impose great stress on the flow processes and sediment transport, and result in the progressive decline in channel morphology, habitat, and ecosystem flow needs. A critical research question in highly regulated river systems is regarding how the flow regime at the reach scale and the associated hydrogeomorphic variability can be systematically characterized. Identification of geomorphic thresholds at different scales and quantification of (a) hydrological and sediment connectivity in river systems, (b) surface–groundwater interaction, and (c) E-flow assessment for different reaches in each river basin are the major gaps in River Science studies specific to Indian river systems. Especially, E-flow assessment for different river basins using a holistic approach must be the leading area of River Science research to aid management and policy making with the goal of enhancing water security. Relatively less studied peninsular rivers need more quantitative process-based hydrogeomorphic studies and their application for E-flow assessment.

Evolution and origin of global glaciers and their impacts on the environment

Glacier is one of the most important freshwater resources. However, the situation of glaciers is changed nowadays because of global warming. This study aimed at two types of glaciers, and analyzed their evolution, origin and impacts on the environment. As for typical melting glaciers, the Vatnajokull glacier and Urumqi Glacier No.1, Tianshan Mountains gradually melt over time. Their causes are related to atmospheric River events, black carbon pollutants, ice recycling, global warming, and human activities. The impacts of glacier retreat mainly include sea-level rise and can alleviate global warming and cause surface deformation. However, there are some “weird” glaciers because they are expanded in the past few years rather than shrinking. Those glaciers are highly concentrated in the Karakoram, Pamir Mountains, Svalbard, the Canadian Arctic islands, Alaska, and Iceland, which are called surged-type glaciers. Hydrological control, thermal regime, deformable bed hypothesis, and critical mass are reasons for glacier expansion. There is no clear and unified opinion on the advantages or disadvantages of glacier expansion.

Analysis of watershed parameters controlling turbidity following the West Fork Complex fire

In this work we explore watershed characteristics associated with increased turbidity following the 2013 West Fork Complex Fire (WFC) in southwest Colorado, USA with the goal of understanding the hydrologic and geomorphic controls on turbidity. Turbidity, precipitation, and stream discharge were measured from May to September in 2015 and 2016 in seven watersheds, four burned and three unburned. Slope, slope aspect, soil type, vegetation, and burn severity—as well as precipitation and discharge—were characterized as independent variables for each of the seven watersheds. During snowmelt-driven runoff from May to June, no significant difference in turbidity between burned and unburned watersheds was found. However, in results from July to September of both 2015 and 2016, burned watersheds had larger spikes in turbidity following precipitation events than unburned watersheds. In the watersheds with higher burn severity and poor vegetation recovery, positive correlations between total storm volume and turbidity existed, though short-term trends in Enhanced Vegetation Index (EVI) were not consistently correlated with turbidity changes with precipitation, nor were watershed slope and aspect alone. These results indicate that other drivers of turbidity in these burned watersheds, for example erodible soils, were more susceptible to precipitation than snowmelt due in part to processes like rain splash. Results from this work provide insight on characteristics that influence stream turbidity after a wildfire and can help watershed managers predict future wildfire impacts on water quality, the health of aquatic organisms, and water treatment infrastructure.

The response of the suspended sediment load of the headwaters of the Brahmaputra River to climate change: Quantitative attribution to the effects of hydrological, cryospheric and vegetation controls

The response of suspended sediment load to climate change has important implications for downstream ecosystems and biogeochemical cycles. Glaciers, permafrost, vegetation and hydrological processes are rapidly changing in high-altitude regions. However, there is currently no consensus about how and to what extent these factors will affect interannual changes of fluvial sediment export. Here, we investigate the increasing trend of suspended sediment load in the headwaters of the Brahmaputra River from 1972 to 2008. The key influencing factors, including the hydrodynamic flux and erosivity of glacier runoff, precipitation, vegetation cover, and soil erodibility were quantified, and their changing trends were analyzed. Two methods were used to attribute the variation of sediment load; Partial Least Squares Path Modeling (PLS-PM) based on statistical regression and Sediment Identity (SI) based on algebraic equations. The results obtained by these two relatively independent methods were broadly consistent, and the error of the SI model was less than 8%. The sediment load showed a significant increasing trend at an average changing rate of 18.9%/10a, without any abrupt fluctuations. The increase in fluvial sediment load was primarily due to increases in both the amount (43%) and erosivity (55%) of precipitation, combined with minor influences from increased sediment supply due to earlier thawing (16%) and intensified glacier melting (14%). The increases in fluvial sediment load were partially buffered by a decrease in water yield capacity due to denser vegetation cover (−29%). This study provides valuable insights into the natural response of fluvial sediment loads to climatic and environmental change, and the findings are critical for soil and water conservation planning in cold and high-altitude regions.

A Co‐Spectral Budget Model Links Turbulent Eddies to Suspended Sediment Concentration in Channel Flows

AbstractThe vertical distribution of suspended sediment concentration remains a subject of active research given its relevance to a plethora of problems in hydraulics, hydrology, ecology, and water quality control. Many of the classical theories developed over the course of 90 years represent the effects of turbulence on suspended sediments (SS) using an effective mixing length or eddy diffusivity without explicitly accounting for the energetics of turbulent eddies across scales. To address this gap, the turbulent flux of sediments is derived using a co‐spectral budget (CSB) model that can be imminently used in SS and other fine particle transport models. The CSB closes the pressure‐redistribution effect using a spectral linear Rotta scheme modified to include isotropization of production and interactions between turbulent eddies and sediment grains through a modified scale‐dependent de‐correlation time. The result is a formulation similar in complexity to the widely used Rouse's equation but with all characteristic scales, Reynolds number, and Schmidt number effects derived from well‐established spectral shapes of the vertical velocity and accepted constants from turbulence models. Finally, the proposed CSB model can recover Prandtl's and Rouse's equations under restricted conditions.

Investigating hydrologic controls on 26 Precambrian shield catchments using landscape, isotope tracer and flow metrics

AbstractAlthough many studies focus on catchment classification, hydrologists are challenged to find the most important variables for a meaningful catchment classification, especially in the heterogeneous environment of the Precambrian Shield. This study investigates landscape controls on hydrologic response by conducting a catchment classification of 26 catchments located within two Precambrian Shield watersheds (Sturgeon–French–Nipissing [SNF] and Muskoka) in central and Northeastern Ontario, Canada, using combinations of landscape characteristics (e.g. topography, geology, landcover), hydrometric variables, and stable isotopes of δ18O and δ2H in river flow. Weekly to monthly surveys of δ18O and δ2H in river flow were collected between 2013 and 2019. Flow metrics (e.g. Pardé coefficient and coefficient of variation of streamflow) were generated for 14 of the 26 rivers between 2008 and 2018. Principal component analyses (PCA) and Hierarchical Clustering on Principal Components (HCPC) analyses were used to identify variables controlling catchment clustering according to their similarities for four different scenarios. Despite their similar location along the southern edge of the Precambrian Shield, the 26 catchments generally clustered by watershed (SNF and Muskoka) with some exceptions. Differences in wetland and lake area (%), mean slope, and % area covered by glacialacustrine and glaciofluvial outwash deposits were the most influential variables in catchment classification. A positive correlation between % wetland area and streamflow stable isotope damping ratios suggests greater % wetland area (with shallow and potentially seasonally variable surface areas and/or hydrologic connection) observed in the SNF catchments increases variability in the influence of evaporative enrichment in SNF catchments. The catchment classification analyses in combination with stable isotopes of δ18O and δ2H were functional tools to investigate the combined influences of diverse types of catchment characteristics that lead to differences in hydrometric response. These results could support future studies focusing on generating hydrologic models and representing wetlands connectivity in the region.

Organizational Principles of Hyporheic Exchange Flow and Biogeochemical Cycling in River Networks Across Scales

AbstractHyporheic zones increase freshwater ecosystem resilience to hydrological extremes and global environmental change. However, current conceptualizations of hyporheic exchange, residence time distributions, and the associated biogeochemical cycling in streambed sediments do not always accurately explain the hydrological and biogeochemical complexity observed in streams and rivers. Specifically, existing conceptual models insufficiently represent the coupled transport and reactivity along groundwater and surface water flow paths, the role of autochthonous organic matter in streambed biogeochemical functioning, and the feedbacks between surface‐subsurface ecological processes, both within and across spatial and temporal scales. While simplified approaches to these issues are justifiable and necessary for transferability, the exclusion of important hyporheic processes from our conceptualizations can lead to erroneous conclusions and inadequate understanding and management of interconnected surface water and groundwater environments. This is particularly true at the landscape scale, where the organizational principles of spatio‐temporal dynamics of hyporheic exchange flow (HEF) and biogeochemical processes remain largely uncharacterized. This article seeks to identify the most important drivers and controls of HEF and biogeochemical cycling based on a comprehensive synthesis of findings from a wide range of river systems. We use these observations to test current paradigms and conceptual models, discussing the interactions of local‐to‐regional hydrological, geomorphological, and ecological controls of hyporheic zone functioning. This improved conceptualization of the landscape organizational principles of drivers of HEF and biogeochemical processes from reach to catchment scales will inform future river research directions and watershed management strategies.

Time‐lapse photogrammetry reveals hydrological controls of fine‐scale High‐Arctic glacier surface roughness evolution

AbstractIn a warming Arctic, as glacier snowlines rise, short‐ to medium‐term increases in seasonal bare‐ice extent are forecast for the next few decades. These changes will enhance the importance of turbulent energy fluxes for surface ablation and glacier mass balance. Turbulent energy exchanges at the ice surface are conditioned by its topography, or roughness, which has been hypothesized to be controlled by supraglacial hydrology at the glacier scale. However, current understanding of the dynamics in surface topography, and the role of drainage development, remains incomplete, particularly for the transition between seasonal snow cover and well‐developed, weathered bare‐ice. Using time‐lapse photogrammetry, we report a daily timeseries of fine (millimetre)‐scale supraglacial topography at a 2 m2 plot on the Lower Foxfonna glacier, Svalbard, over two 9‐day periods in 2011. We show traditional kernel‐based morphometric descriptions of roughness were ineffective in describing temporal change, but indicated fine‐scale albedo feedbacks at depths of ~60 mm contributed to conditioning surface topography. We found profile‐based and two‐dimensional estimates of roughness revealed temporal change, and the aerodynamic roughness parameter, z0, showed a 22–32% decrease from ~1 mm following the exposure of bare‐ice, and a subsequent 72–77% increase. Using geostatistical techniques, we identified ‘hole effect’ properties in the surface elevation semivariograms, and demonstrated that hydrological drivers control the plot‐scale topography: degradation of superimposed ice reduces roughness while the inception of braided rills initiates a subsequent development and amplification of topography. Our study presents an analytical framework for future studies that interrogate the coupling between ice surface roughness and hydro‐meteorological variables and seek to improve parameterizations of topographically evolving bare‐ice areas.

Removal of Fecal Indicator Bacteria by River Networks

Fecal contamination is a significant source of water quality impairment globally. Aquatic ecosystems can provide an important ecosystem service of fecal contamination removal. Understanding the processes that regulate the removal of fecal contamination among river networks across flow conditions is critical. We applied a river network model, the Framework for Aquatic Modeling in the Earth System (FrAMES-Ecoli), to quantify removal of fecal indicator bacteria by river networks across flow conditions during summers in a series of New England watersheds of different characteristics. FrAMES-Ecoli simulates sources, transport, and riverine removal of Escherichia coli (E. coli). Aquatic E. coli removal was simulated in both the water column and the hyporheic zone, and is a function of hydraulic conditions, flow exchange rates with the hyporheic zone, and die-off in each compartment. We found that, at the river network scale during summers, removal by river networks can be high (19–99%) with variability controlled by hydrologic conditions, watershed size, and distribution of sources in the watershed. Hydrology controls much of the variability, with 68–99% of network scale inputs removed under base flow conditions and 19–85% removed during storm events. Removal by the water column alone could not explain the observed pattern in E. coli, suggesting that processes such as hyporheic removal must be considered. These results suggest that river network removal of fecal indicator bacteria should be taken into consideration in managing fecal contamination at critical downstream receiving waters.

The Evolution of the Glacier Surges in the Tuanjie Peak, the Qilian Mountains

Glacier surges (GSs) are a manifestation of glacier instability and one of the most striking phenomena in the mountain cryosphere. Here, we utilize optical images acquired between 1973 and 2021 to map changes in glacier surface velocity and morphology and characterize differences in surface elevation using multi-source DEMs in the Tuanjie Peak (TJP), located in the Qilian Mountains (QLMs). These data provide valuable insights into the recent dynamic evolution of glaciers and hint at how they might evolve in the next few years. We identified a confirmed surge-type glacier (STG), three likely STGs, and three possible STGs. Our observations show that TJP GSs are generally long-term, although they are shorter in some cases. During the active phase, all glaciers exhibit thickened reservoir areas and thinned receiving areas, or vice-versa. The ice volume transfer was between 0.11 ± 0.13 × 107 m3 to 5.71 ± 0.69 × 107 m3. Although it was impossible to obtain integrated velocity profiles throughout the glacier surge process due to the limitations of available satellite imagery, our recent observations show that winter velocities were much higher than summer velocities, suggesting an obvious correlation between surge dynamics and glacial hydrology. However, the initiation and termination phase of GSs in this region was slow, which is similar to Svalbard-type STGs. We hypothesize that both thermal and hydrological controls are crucial. Moreover, we suggest that the regional warming trend may potentially increase glacier instability and the possibility of surge occurrence in this region.

Hydrologic processes regulate nutrient retention in stormwater detention ponds

Managed stormwater ponds are abundant in urban landscapes in much of the world, performing vital but under-studied functions for attenuation of urban runoff and nutrient pollution. Water quality improvements are widely assumed to arise from settling of nutrients and other contaminants bound to particulates, with less consideration of hydrological and biogeochemical processes. To inform improved management of ponds for nutrient retention, we studied three mature urban detention ponds in the Twin Cities, MN, USA using continuous monitoring of pond hydrology and concentrations of nitrogen and phosphorus, coupled with periodic measurement of physiochemical conditions in the ponds. Across the three sites, annual nutrient retention was high for both nitrogen (>58%) and phosphorus (>48%) despite expectations of poor performance for phosphorus due to old age and internal loading linked to hypolimnetic anoxia. Both annual and event-scale analyses suggested strong hydrologic controls on nutrient retention, with retention for individual storm events strongly regulated by antecedent pond storage capacity. Events with net nutrient export occurred primarily due to low volume retention rather than relatively high outflow concentrations. Together these results suggest that understanding and improving pond hydrologic function is crucial to improving managed stormwater pond performance for meeting downstream water quality goals.