Hyporheic zones (HZs)zones of groundwater–surface water mixingare hotspots for dissolved organic matter (DOM) and nutrient cycling that can disproportionately impact aquatic ecosystem functions. ...However, the mechanisms affecting DOM metabolism through space and time in HZs remain poorly understood. To resolve this gap, we investigate a recently proposed theory describing trade-offs between carbon (C) and nitrogen (N) limitations as a key regulator of HZ metabolism. We propose that throughout the extent of the HZ, a single process like aerobic respiration (AR) can be limited by both DOM thermodynamics and N content due to highly variable C/N ratios over short distances (centimeter scale). To investigate this theory, we used a large flume, continuous optode measurements of dissolved oxygen (DO), and spatially and temporally resolved molecular analysis of DOM. Carbon and N limitations were inferred from changes in the elemental stoichiometric ratio. We show sequential, depth-stratified relationships of DO with DOM thermodynamics and organic N that change across centimeter scales. In the shallow HZ with low C/N, DO was associated with the thermodynamics of DOM, while deeper in the HZ with higher C/N, DO was associated with inferred biochemical reactions involving organic N. Collectively, our results suggest that there are multiple competing processes that limit AR in the HZ. Resolving this spatiotemporal variation could improve predictions from mechanistic models, either via more highly resolved grid cells or by representing AR colimitation by DOM thermodynamics and organic N.
In mountain environments, the coupling of hillslopes processes with the channel network during extreme events is of great importance for rivers dynamics, as debris flows and landslides are among the ...most important sources of sediments. The Stolla Creek (40 km2 drainage area, South Tyrol, Italy) is a confined and partly confined mountain channel that was affected by an extreme flood in August 2017, followed by a smaller event in August 2020. The geomorphic effects of the two floods were investigated both in the main channel and over the entire basin with the aim to assess the impacts of the lateral sediment connectivity to the channel response and to the event-scale sediment export.
An integrated approach was applied, including radar rainfall estimation, hydrologic-hydraulic analysis, analysis of morphological changes and sediment delivery to the stream network. Hillslope and channel processes were mapped and characterized by using geomorphological analysis of multitemporal orthophotos and Digital Terrain Models. Debris-flow connectivity to the main channel was derived by combining field evidence and GIS-based analysis.
The 2017 flood was caused by rainfall with a short duration (6 h) and a rainfall intensity exceeding 45 mm/h. More than 600 debris flows were triggered in the Stolla basin, and the main channel experienced widening (width ratio between 1.3 and 4.9) through bank erosion and overbank deposition. Widening was accompanied by aggradation in the river corridor up to 1.2 m or incision down to −2.2 m. The 2020 flood was characterized by lower rainfall intensity (max 17 mm/h) and a longer duration (48 h), and debris flows were not triggered. The moderate magnitude of the 2020 flood peak did not lead to channel widening, but marked bed incision (up to −1.4 m) occurred in the reaches where aggradation took place during the 2017 event. In both flood events, limited volumes of sediments were exported from the catchment outlet.
Overall, our results highlight how structural connectivity at the basin scale determines the potential sediment cascades linking hillslopes to channels but time-varying functional connectivity – driven by hydrological drivers as rainfall intensities and durations – eventually control the actual sediment transport effectiveness both on hillslopes and along the channel.
•An integrated geomorphological and hydrological approach is applied to two floods•Basin structural connectivity well describes potential sediment delivery to the main channel•Functional connectivity determined by rainfall characteristics controlled actual sediment supply and transport
The analysis of changes in planform geometry of the Biała River during the last 130 years is used to diagnose hydromorphological river degradation and thus to verify the need of river restoration ...through establishing an erodible river corridor. Outcomes from the analysis are then used for delimiting the erodible corridor and predicting the potential for future river widening in the corridor. The study analyses presentations of the active river zone and the structure of river geomorphic units on topographic maps from 1878, 1935 and 1962, aerial photos from 1967, 1977 and 1987, and orthophotos from 1998 and 2009. As a result of river channelization followed by channel incision, during the study period the width of the Biała was reduced to 16%–57% of its width in 1878. The river narrowing was associated with a reduction in the proportion of channel bars in the total river width and nearly complete elimination of islands. All these changes demonstrated the degradation of hydromorphological integrity of the river and the need for its restoration by allowing free channel development in an erodible corridor. The belt of the river migration during the last 130 years identified on the basis of overlays of the river position from all dates was ⁓5 times wider than the contemporary river. This justified delimiting the erodible river corridor on a substantially larger area of the valley floor than the area of the river in 2009. In 2009 the river was narrower than the largest river width recorded between 1878 and 1998 along nearly the whole length of the study river sections. This indicates that the concentration of flood flows in the narrow channel, increasing their unit stream power, is a factor increasing the potential for future bank retreat and channel widening in the erodible corridor of the river.
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•Historical changes in planform geometry of a mountain river were analysed to design appropriate restoration measures.•Hydromorphological river degradation was determined, to delimit an erodible corridor and to diagnose future river widening.•Considerable river narrowing and the simplification of flow pattern justified establishment of erodible river corridor.•Reconstructed belt of historical river migration was an important criterion of delimiting the erodible river corridor.•The analysis of past changes in planform river geometry was useful for the design of erodible river corridor.
•A framework was proposed to assess the effectiveness of ECRL.•Grazing is the main cause of habitat degradation in the river corridor.•ECRL mitigates anthropogenic habitat degradation and improves ...habitat quality.•Ecological restoration policies were proposed to promote river corridor biodiversity.
The ecological conservation red line (ECRL) framework plays an increasingly important role in biodiversity conservation practices in China. Following the implementation of ECRL, it is essential to systematically assess the effectiveness of this national policy in mitigating the negative impacts of human disturbances on habitat quality at the landscape and regional levels. Combined with remote sensing and ground survey data, the Integrated Valuation of Ecosystem Services and Trade-off (InVEST) habitat quality model was used to evaluate the impact of six major anthropogenic activities, including built-up land, roads, mining land, crop land, water pollution, and grazing, on habitat degradation in two grassland river corridors (Kherlen River corridor and Wuerxun River corridor) in Northeastern China. Then, the effectiveness of different management scenarios was assessed based on the ECRL framework. The results indicated that over 80% of the habitat degradation was attributed to grazing activities, followed by water pollution. Built-up land, roads, mining land, and crop land played minor roles in causing habitat degradation. Comparing the implementation of ECRL management scenario with no ECRL management scenario, habitat degradation in the Kherlen River corridor reduced by 17.86%, and habitat quality improved by 11.11%. Similarly, in the Wuerxun River corridor, compared with the priority ECRL management scenario, habitat degradation reduced by 69.23%, and habitat quality improved by 2.38% in the implementation of ECRL management scenario. Moreover, an optimized ECRL management scenario, including grazing prohibition, grassland enclosure, and ecological restoration of river habitats, further improved the habitat quality of both river corridors, resulting in a 12.70% improvement for the Kherlen River corridor and a 3.57% improvement for the Wuerxun River corridor. Our work provides a quantitative framework for optimizing conservation and restoration measures for river corridors based on the ECRL.
•Sediment burial is an important mortality agent in riparian vegetation communities.•Complete burial kills cottonwood and tamarisk, but not box elder seedlings.•Cottonwoods survived partial burial ...when >20cm of their stems remain exposed.•Partial burial induces compensatory height and canopy growth in surviving plants.
Flooding and sediment deposition provide many benefits to riparian plants, including dispersal of propagules, new seedbeds for germination, and transient pulses of water and nutrients during early growth. Though many riparian species are adapted to flood disturbance, sediment deposition can also be a stressor to existing plants, limiting their survival and growth. Though many field studies document short-term changes in plant density immediately following floods, an outstanding question remains to what degree plants can survive and re-emerge following fluvial deposition events. We conducted two year-long studies to quantify the response of riparian trees to sediment deposition, testing a range of species, sizes and burial depths. One experiment focused on long-term survival following complete burial for seedlings and saplings of cottonwood (Populus fremontii), tamarisk (Tamarix ramosissima), and box elder (Acer negundo). A second experiment focused on cottonwood seedling response to more moderate deposition events, comparing survival and vigor (height, diameter growth, and leaf production) across a range of treatments from 10 to 50cm sediment depth. Complete burial killed all tamarisk and cottonwood plants; however all box elder survived and resprouted from the sediment surface in the following growing season. In the partial burial experiment, cottonwood survival was higher in the shallower deposition treatments and for larger plants across all treatments. Cottonwood seedlings with exposed stem length longer than ∼20cm were highly likely to survive (>90%), whereas plant survival was severely reduced for stems with greater portions of their stems buried. Seedlings that survived partial burial experienced a positive, compensatory response in the following growing season, with height increment and canopy expansion proportional to the depth of sediment added. These results suggest that flood-borne sediment deposition events, either under natural or river management conditions, may have non-linear effects on the survival of existing riparian tree cohorts. The severity of the disturbance effects will depend on the magnitude of the event and the initial size of the plants. Together with field studies on riparian plant demography and experiments that test plants’ vulnerability to flood disturbance, our study extends understanding of the drivers of plant mortality in fluvial corridors.
•Heterogeneous riverbed mapping is essential in modeling HEFs in large corridors.•Wavelet analysis reveals multiscale interaction between HEFs and controlling factors.•Transit time was strongly ...correlated with the downwelling ratio of exchange flux.
Hydrological exchange flows (HEFs) across the river-aquifer interface and the associated transit time of river water in the aquifer have important implications for contaminant plume migration and biogeochemical processes in the river corridor. HEFs and transit time are influenced by both subsurface physical features and hydrologic forcing related to the transport process, which can exhibit complex spatial and temporal variations. In this study, we used a massively parallel subsurface flow model and a particle-tracking model to study the influences of different control factors on spatial variability of HEFs and transit time distributions in the Hanford Reach of the Columbia River in Washington State. 100 million particles were randomly injected in time and space and then tracked in a model domain that covers a 51-km2 area (15.1million model cells). We used hourly river stages and groundwater levels to drive the model to provide dynamic velocity fields for the particle tracking in the two + -year simulation period. The groundwater flow simulation and particle-tracking results provide a comprehensive assessment of the spatial distribution of HEFs and transit time in a large, complex river corridor. Our results show that the aquifer hydrogeological structure has strong correlations with the extent and magnitude of exchange flux. The transit time exhibits complex patterns that are affected by all the river geomorphologic, hydrodynamic, and hydrogeologic factors and are strongly correlated with the downwelling ratio of exchange flux. The new insights gained through this study can be used to support the development of reduced-order models of HEFs and transit time distributions for large complex river systems.
The hyporheic zone is a hotspot for biogeochemical cycling where interactions with mineral metals preserve the release and biodegradation of organic matter (OM). A small fraction of OM can still be ...exchanged between localized sediments and the overlying water column, and recent evidence suggests there exists a longitudinal structuring in sediment dissolved OM (DOM) chemistry across the continental United States (CONUS). In this study, we tested a hypothesis that water extractable sediment DOM chemistry could be explained by sediment metal contents and integrative watershed scale features at the CONUS scale. Crowdsourced samples were characterized for high resolution mass spectrometry and coupled with sediment metals determined via x‐ray fluorescence as well as with land cover and soil elemental information obtained from national databases. Our results highlight weak relationships between DOM chemistry and elemental composition at the CONUS scale indicating limited transferability of organo‐metal linkages into multi‐scale hydrobiogeochemical models.
Plain Language Summary
The hyporheic zone is a vital area for chemical cycling that influences the breakdown of organic matter due to interactions with minerals and metals. Some organic matter moves between sediment and water. Recent findings show that sediment organic matter chemistry displays unique east‐west patterns across the continental United States. We tested whether crowdsourced sample sediment organic matter composition could be explained by its mineral metal composition and surrounding environmental features (land cover and soil metal composition). Results revealed weak connections between dissolved organic matter chemistry and elements, indicating limits in applying these connections to continental scale models.
Key Points
Sediment dissolved organic matter chemistry is longitudinally structured across the continental United States
Sediment and soil mineral elemental compositions were weakly correlated with sediment dissolved organic matter composition
Localized metal‐organic matter linkages likely have limited capacity to inform continental‐scale hydrobiogeochemical models
The overall purpose of this paper is to integrate the geomorphic evolution of Glen Canyon and Upper Colorado River Corridor with that of Grand Canyon in order to address two key enigmas: why did the ...Colorado River not arrive at the mouth of Grand Canyon until 5.5 Ma, and how did the Colorado River cross the Kaibab arch high? This evolution was approached from three different perspectives: (1) by reviewing geologic investigations in the Glen Canyon area from the late 1800s to the present; (2) by explaining how a paleo-Colorado River constrained within a lake or a chain of lakes on the Colorado Plateau is necessary for the Colorado River to have arrived at the mouth of Grand Canyon ca. 5.5 Ma; and (3) by proposing how the incision rates in Marble Canyon, Glen Canyon, and central Colorado Plateau may be related to a prolonged base-level fall at the Confluence of the Colorado-Little Colorado rivers starting at ~5.5 Ma, to a karst-connection model of a Colorado River crossing under the Kaibab arch, or to a lake-overflow model. An attempt was made to find field and analytic evidence for a pre-5.5 Ma Miocene lake along the north to west sides of Navajo Mountain, Utah, where high pediment surfaces still remain along the Colorado River, but from field investigations, 26Al10Be cosmogenic dating, and SEM analysis, no direct evidence for a past lake was substantiated. However, a number of lines of indirect evidence are discussed supporting the possible existence of a Miocene lake or chain of lakes along Glen Canyon and Upper Colorado River Corridor. A lake-overflow model is compared with a karst-connection model as to how the Colorado River might have crossed the Kaibab arch.
•Cenozoic geomorphic evolution of the Colorado River, Colorado Plateau•Geology of central Colorado Plateau as it relates to the origin of Grand Canyon•Why the Colorado River reached the mouth of Grand Canyon at 5.5 Ma•How the Colorado River turned west and crossed the Kaibab arch high•A karst-connection model vs. a lake-overflow model for crossing the Kaibab arch
Various physical environmental factors influence the recreational experience of urban river corridors, and understanding visitors' perceptions of these factors holds significant implications for ...promoting the health and well-being of urban residents. This study specifically focuses on the Hutuo River corridor in Shijiazhuang, China, and conducted a semi-structured questionnaire survey with 620 participants. The findings reveal that visitors mainly come here to socialize with family and friends in a natural environment and escape the city's hustle and bustle. Safety, management and maintenance, and overall conditions are the primary features visitors are concerned about in their experience. When addressing usage constraints, visitors highlight accessibility issues, including traffic congestion and overcrowding. Additional limitations encompass deficiencies in physical facilities, such as shortages of shared bicycles, convenience amenities, fitness facilities, and services catering to vulnerable groups. Moreover,challenges include unavailable toilet services and insufficient shaded areas along the riverbanks. Sociodemographic attributes such as gender, age, marital status,education level, monthly income, and residential distance significantly influence the recreational experience of urban river corridors, emphasizing the importance of considering diversity in urban planning and design. By comprehensively exploring the dynamics of urban river corridor utilization from a social-ecological perspective, our study's findings offer insights relevant to future design and maintenance endeavors.
Stream solute tracers are commonly injected to assess transport and transformation in study reaches, but results are biased toward the shortest and fastest storage locations. While this bias has been ...understood for decades, the impact of an experimental constraint on our understanding has yet to be considered. Here, we ask how different our understanding of reach‐ and segment‐scale transport would be if our empirical limits were extended. We demonstrate a novel approach to manipulate experimental conditions and observe mass that is stored at timescales beyond the traditional reach‐scale window of detection. We are able to explain the fate of an average of 26% of solute tracer mass that would have been considered as “lost” in a traditional study design across our 14 replicates, extending our detection limits to characterize flowpaths that would have been previously unmeasured. We demonstrate how this formerly lost mass leads to predicting lower magnitudes of gross gains and losses in individual reaches, and ultimately show that the network turnover we infer from solute tracers represents an upper limit on actual, expected behavior. Finally, we review the evolution of tracer studies and their interpretation including this approach and provide a proposed future direction to extend empirical studies to not‐before‐seen timescales.
Key Points
With careful design, solute tracer studies can be used to assess the fate of solute mass along flowpaths that would not normally be detected
Extended mass recovery allows us to understand the formerly unknown fate of more than 26% of all lost tracer mass
Accounting for mass recovery beyond the typical window of detection reduced inferred channel water turnover, changing interpreted spatial sources of gains
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