José L. J. Ledesma

Examining how hydrological responses of streams and riparian groundwater interact during rainfall events can help understand runoff generation mechanisms and their links to biogeochemistry. We analysed rainfall–runoff events in four forest headwater catchments spanning semiarid Mediterranean, subhumid Mediterranean, temperate, and boreal ecoregions. Using sub-daily data, we evaluated how hydroclimatic drivers shaped stream and riparian groundwater. We additionally focussed on the slope (slopeLin) and hysteresis (h) of the riparian groundwater–stream relationship, describing coupled responses and connectivity patterns. Rainfall amount and antecedent wetness primarily controlled individual stream and riparian groundwater hydrological response across sites, while the vertical activation of riparian layers, defined by slopeLin, and timing, defined by h, were site-specific. At the Mediterranean sites, deep, low-conductivity layers dominated the lateral connectivity unless sufficient rainfall and wetness allowed activation of shallower flow pathways. At the temperate and boreal sites, shallow, conductive layers were typically active, with temporary disconnection during warm periods at the temperate site and snowmelt-induced activation of upslope sources at the boreal. Clockwise hysteresis, indicating faster riparian than stream responses, prevailed at the temperate and boreal sites. The Mediterranean sites showed weaker or anticlockwise patterns, suggesting activation of other water sources, likely ephemeral tributaries during intense rainfall. Our results show that the activation and hysteresis of riparian–stream connectivity differs across ecoregions, which has implications for solute mobilization. This framework provides a physically grounded perspective for interpreting both rainfall–runoff and concentration–discharge relationships, which can help predict shifts in catchment functioning under changing hydroclimatic regimes.

Examining how hydrological responses of streams and riparian groundwater interact during rainfall events can help understand runoff generation mechanisms and their links to biogeochemistry. We analysed rainfall–runoff events in four forest headwater catchments spanning semiarid Mediterranean, subhumid Mediterranean, temperate, and boreal ecoregions. Using sub-daily data, we evaluated how hydroclimatic drivers shaped stream and riparian groundwater. We additionally focussed on the slope (slopeLin) and hysteresis (h) of the riparian groundwater–stream relationship, describing coupled responses and connectivity patterns. Rainfall amount and antecedent wetness primarily controlled individual stream and riparian groundwater hydrological response across sites, while the vertical activation of riparian layers, defined by slopeLin, and timing, defined by h, were site-specific. At the Mediterranean sites, deep, low-conductivity layers dominated the lateral connectivity unless sufficient rainfall and wetness allowed activation of shallower flow pathways. At the temperate and boreal sites, shallow, conductive layers were typically active, with temporary disconnection during warm periods at the temperate site and snowmelt-induced activation of upslope sources at the boreal. Clockwise hysteresis, indicating faster riparian than stream responses, prevailed at the temperate and boreal sites. The Mediterranean sites showed weaker or anticlockwise patterns, suggesting activation of other water sources, likely ephemeral tributaries during intense rainfall. Our results show that the activation and hysteresis of riparian–stream connectivity differs across ecoregions, which has implications for solute mobilization. This framework provides a physically grounded perspective for interpreting both rainfall–runoff and concentration–discharge relationships, which can help predict shifts in catchment functioning under changing hydroclimatic regimes.

Elevated dissolved organic carbon (DOC) concentrations are a major concern for ecosystems and drinking water supply. Data-driven studies revealed variable functioning of different landscape units (upland, riparian zone, and groundwater) in catchment DOC mobilization and export. However, lumped and landscape-explicit (separating upland and riparian zone) model structures are generally calibrated to stream DOC concentrations, while the internal DOC dynamics often do not receive sufficient attention. Here, we developed a flexible model with a lumped and landscape-explicit structure for four headwater catchments in the Harz Mountains, Germany. We evaluated these models under a baseline calibration (only against stream DOC concentration) and a constrained calibration (using stream DOC and internal DOC concentrations). Under the baseline calibration, both model structures reproduced stream DOC dynamics with acceptable performance in some catchments (Kling–Gupta efficiency of behavioural simulations>0.6), but with unrealistically high groundwater DOC. By contrast, the constrained calibration reduces the KGE for stream DOC concentrations but produces internal DOC dynamics consistent with the imposed observational and process-based constraints. Additionally, the landscape-explicit model structure is more robust than the lumped model structure under changing boundary conditions. Our study thus shows that robust catchment DOC modelling requires not only explicit representation of different landscape units, but also calibration constraints based on DOC concentrations within those units.

Environmental RNA (eRNA) can potentially augment the biological monitoring ability of the established environmental DNA (eDNA) application in conservation. Despite faster degradation, environmental RNA could offer unique advantages: it may help reduce the legacy signal compared to eDNA, provide insights into physiological status through gene transcription and offer higher detection sensitivity due to the inherent amplification of certain genes in response to physiology and the environmental context. This study investigates the practical application and sensitivity of eRNA for detecting fish in the wild: an endangered freshwater fish in a seasonal stream throughout the year and a pelagic fish of commercial interest in the ocean. We developed attainable field sampling and laboratory protocols for eRNA preservation and extraction, addressing the challenges of its natural instability. Then, we compared the detection sensitivity of two mitochondrial genes using species‐specific digital PCR (dPCR) assays: the cytb gene (eDNA)/ cytb transcript (eRNA) and the 12S rRNA gene (eDNA)/12S rRNA product (eRNA), The results showed higher concentrations of 12S rRNA (eRNA), suggesting its superior utility for detecting low‐abundance organisms while providing empirical information regarding the amount of an eRNA transcript from the primary cellular pathway (cytochrome b). Importantly, in the freshwater system, eRNA and eDNA concentrations followed similar patterns reflecting the variation in hydrological conditions that affected the concentration of nucleic acids in the water. These findings highlight the importance of marker choice in eRNA studies, with a ribosomal gene offering enhanced sensitivity compared to its eDNA. This research provides insights into the temporal and spatial dynamics, sampling strategies, and molecular targets for eRNA‐based biomonitoring. It demonstrates the potential of eRNA to improve the detection of endangered species and inform conservation efforts by providing a more accurate snapshot of extant biological communities and paving the road for the full potential of eRNA to study the physiological status of target organisms.

Examining how hydrological responses of streams and riparian groundwater interact during rainfall events can help understand runoff generation mechanisms and their links to biogeochemistry. We analysed rainfall–runoff events in four forest headwater catchments spanning semiarid Mediterranean, subhumid Mediterranean, temperate, and boreal ecoregions. Using sub-daily data, we evaluated how hydroclimatic drivers shaped stream and riparian groundwater. We additionally focussed on the slope (slopeLin) and hysteresis (h) of the riparian groundwater–stream relationship, describing coupled responses and connectivity patterns. Rainfall amount and antecedent wetness primarily controlled individual stream and riparian groundwater hydrological response across sites, while the vertical activation of riparian layers, defined by slopeLin, and timing, defined by h, were site-specific. At the Mediterranean sites, deep, low-conductivity layers dominated the lateral connectivity unless sufficient rainfall and wetness allowed activation of shallower flow pathways. At the temperate and boreal sites, shallow, conductive layers were typically active, with temporary disconnection during warm periods at the temperate site and snowmelt-induced activation of upslope sources at the boreal. Clockwise hysteresis, indicating faster riparian than stream responses, prevailed at the temperate and boreal sites. The Mediterranean sites showed weaker or anticlockwise patterns, suggesting activation of other water sources, likely ephemeral tributaries during intense rainfall. Our results show that the activation and hysteresis of riparian–stream connectivity differs across ecoregions, which has implications for solute mobilization. This framework provides a physically grounded perspective for interpreting both rainfall–runoff and concentration–discharge relationships, which can help predict shifts in catchment functioning under changing hydroclimatic regimes.

Examining how hydrological responses of streams and riparian groundwater interact during rainfall events can help understand runoff generation mechanisms and their links to biogeochemistry. We analysed rainfall–runoff events in four forest headwater catchments spanning semiarid Mediterranean, subhumid Mediterranean, temperate, and boreal ecoregions. Using sub-daily data, we evaluated how hydroclimatic drivers shaped stream and riparian groundwater. We additionally focussed on the slope (slopeLin) and hysteresis (h) of the riparian groundwater–stream relationship, describing coupled responses and connectivity patterns. Rainfall amount and antecedent wetness primarily controlled individual stream and riparian groundwater hydrological response across sites, while the vertical activation of riparian layers, defined by slopeLin, and timing, defined by h, were site-specific. At the Mediterranean sites, deep, low-conductivity layers dominated the lateral connectivity unless sufficient rainfall and wetness allowed activation of shallower flow pathways. At the temperate and boreal sites, shallow, conductive layers were typically active, with temporary disconnection during warm periods at the temperate site and snowmelt-induced activation of upslope sources at the boreal. Clockwise hysteresis, indicating faster riparian than stream responses, prevailed at the temperate and boreal sites. The Mediterranean sites showed weaker or anticlockwise patterns, suggesting activation of other water sources, likely ephemeral tributaries during intense rainfall. Our results show that the activation and hysteresis of riparian–stream connectivity differs across ecoregions, which has implications for solute mobilization. This framework provides a physically grounded perspective for interpreting both rainfall–runoff and concentration–discharge relationships, which can help predict shifts in catchment functioning under changing hydroclimatic regimes.

Examining how hydrological responses of streams and riparian groundwater interact during rainfall events can help understand runoff generation mechanisms and their links to biogeochemistry. We analysed rainfall–runoff events in four forest headwater catchments spanning semiarid Mediterranean, subhumid Mediterranean, temperate, and boreal ecoregions. Using sub-daily data, we evaluated how hydroclimatic drivers shaped stream and riparian groundwater. We additionally focussed on the slope (slopeLin) and hysteresis (h) of the riparian groundwater–stream relationship, describing coupled responses and connectivity patterns. Rainfall amount and antecedent wetness primarily controlled individual stream and riparian groundwater hydrological response across sites, while the vertical activation of riparian layers, defined by slopeLin, and timing, defined by h, were site-specific. At the Mediterranean sites, deep, low-conductivity layers dominated the lateral connectivity unless sufficient rainfall and wetness allowed activation of shallower flow pathways. At the temperate and boreal sites, shallow, conductive layers were typically active, with temporary disconnection during warm periods at the temperate site and snowmelt-induced activation of upslope sources at the boreal. Clockwise hysteresis, indicating faster riparian than stream responses, prevailed at the temperate and boreal sites. The Mediterranean sites showed weaker or anticlockwise patterns, suggesting activation of other water sources, likely ephemeral tributaries during intense rainfall. Our results show that the activation and hysteresis of riparian–stream connectivity differs across ecoregions, which has implications for solute mobilization. This framework provides a physically grounded perspective for interpreting both rainfall–runoff and concentration–discharge relationships, which can help predict shifts in catchment functioning under changing hydroclimatic regimes.

Elevated dissolved organic carbon (DOC) concentrations are a major concern for ecosystems and drinking water supply. Data-driven studies revealed variable functioning of different landscape units (upland, riparian zone, and groundwater) in catchment DOC mobilization and export. However, lumped and landscape-explicit (separating upland and riparian zone) model structures are generally calibrated to stream DOC concentrations, while the internal DOC dynamics often do not receive sufficient attention. Here, we developed a flexible model with a lumped and landscape-explicit structure for four headwater catchments in the Harz Mountains, Germany. We evaluated these models under a baseline calibration (only using stream DOC concentration) and a constrained calibration (using stream DOC and internal DOC concentrations). Under the baseline calibration, both model structures can reasonably represent stream DOC dynamics in some catchments (Kling–Gupta efficiency of some behavioural simulations > 0.6), but with unreasonably high groundwater DOC. By contrast, the constrained calibration reduces the KGE for stream DOC concentrations but ensures a more realistic representation of internal DOC dynamics. Additionally, the landscape-explicit model structure is more robust than the lumped model structure under changing boundary conditions. Our study thus highlights the necessity of representing different landscape units explicitly in combination with constraining the calibration of DOC concentrations in these landscape units.

Elevated dissolved organic carbon (DOC) concentrations are a major concern for ecosystems and drinking water supply. Data-driven studies revealed variable functioning of different landscape units (upland, riparian zone, and groundwater) in catchment DOC mobilization and export. However, lumped and landscape-explicit (separating upland and riparian zone) model structures are generally calibrated to stream DOC concentrations, while the internal DOC dynamics often do not receive sufficient attention. Here, we developed a flexible model with a lumped and landscape-explicit structure for four headwater catchments in the Harz Mountains, Germany. We evaluated these models under a baseline calibration (only using stream DOC concentration) and a constrained calibration (using stream DOC and internal DOC concentrations). Under the baseline calibration, both model structures can reasonably represent stream DOC dynamics in some catchments (Kling–Gupta efficiency of some behavioural simulations > 0.6), but with unreasonably high groundwater DOC. By contrast, the constrained calibration reduces the KGE for stream DOC concentrations but ensures a more realistic representation of internal DOC dynamics. Additionally, the landscape-explicit model structure is more robust than the lumped model structure under changing boundary conditions. Our study thus highlights the necessity of representing different landscape units explicitly in combination with constraining the calibration of DOC concentrations in these landscape units.

Elevated dissolved organic carbon (DOC) concentrations are a major concern for ecosystems and drinking water supply. Data-driven studies revealed variable functioning of different landscape units (upland, riparian zone, and groundwater) in catchment DOC mobilization and export. However, lumped and landscape-explicit (separating upland and riparian zone) model structures are generally calibrated to stream DOC concentrations, while the internal DOC dynamics often do not receive sufficient attention. Here, we developed a flexible model with a lumped and landscape-explicit structure for four headwater catchments in the Harz Mountains, Germany. We evaluated these models under a baseline calibration (only using stream DOC concentration) and a constrained calibration (using stream DOC and internal DOC concentrations). Under the baseline calibration, both model structures can reasonably represent stream DOC dynamics in some catchments (Kling–Gupta efficiency of some behavioural simulations > 0.6), but with unreasonably high groundwater DOC. By contrast, the constrained calibration reduces the KGE for stream DOC concentrations but ensures a more realistic representation of internal DOC dynamics. Additionally, the landscape-explicit model structure is more robust than the lumped model structure under changing boundary conditions. Our study thus highlights the necessity of representing different landscape units explicitly in combination with constraining the calibration of DOC concentrations in these landscape units.