Morgane Derrien

Rivers act as dynamic connectors between terrestrial and marine ecosystems, transporting and transforming materials along the aquatic continuum. We investigated longitudinal biogeochemical patterns across the Rapel catchment (central Chile) by integrating dissolved organic matter (DOM) characterization, dissolved metals and nutrients, and microbial community profiling from the Andean headwaters to the Pacific Ocean. Headwaters were characterized by low DOC and nutrient concentrations, high protein-like fluorescence, and diverse microbial assemblages dominated by Flavobacterium, Polaromonas, and Rhodoferax. Downstream, agricultural and mining activities increased nutrient and metal concentrations and altered microbial community composition with an increasing prevalence of hgcI_clade. The Rapel Reservoir emerged as a major biogeochemical discontinuity, promoting DOM transformation, restructuring microbial assemblages, and modifying downstream chemical conditions. Overall, tributary inputs, land use, and hydrological regulation disrupted simple longitudinal patterns and generated distinct biogeochemical processing zones. These findings highlight the interplay between downstream transport and local processing in shaping riverine functioning in Mediterranean Andean catchments and provide a basis for assessing future climate and land-use impacts on riverine biogeochemistry.

Rivers act as dynamic connectors between terrestrial and marine ecosystems, transporting and transforming materials along the aquatic continuum. We investigated longitudinal biogeochemical patterns across the Rapel catchment (central Chile) by integrating dissolved organic matter (DOM) characterization, dissolved metals and nutrients, and microbial community profiling from the Andean headwaters to the Pacific Ocean. Headwaters were characterized by low DOC and nutrient concentrations, high protein-like fluorescence, and diverse microbial assemblages dominated by Flavobacterium, Polaromonas, and Rhodoferax. Downstream, agricultural and mining activities increased nutrient and metal concentrations and altered microbial community composition with an increasing prevalence of hgcI_clade. The Rapel Reservoir emerged as a major biogeochemical discontinuity, promoting DOM transformation, restructuring microbial assemblages, and modifying downstream chemical conditions. Overall, tributary inputs, land use, and hydrological regulation disrupted simple longitudinal patterns and generated distinct biogeochemical processing zones. These findings highlight the interplay between downstream transport and local processing in shaping riverine functioning in Mediterranean Andean catchments and provide a basis for assessing future climate and land-use impacts on riverine biogeochemistry.

Rivers act as dynamic connectors between terrestrial and marine ecosystems, transporting and transforming materials along the aquatic continuum. We investigated longitudinal biogeochemical patterns across the Rapel catchment (central Chile) by integrating dissolved organic matter (DOM) characterization, dissolved metals and nutrients, and microbial community profiling from the Andean headwaters to the Pacific Ocean. Headwaters were characterized by low DOC and nutrient concentrations, high protein-like fluorescence, and diverse microbial assemblages dominated by Flavobacterium, Polaromonas, and Rhodoferax. Downstream, agricultural and mining activities increased nutrient and metal concentrations and altered microbial community composition with an increasing prevalence of hgcI_clade. The Rapel Reservoir emerged as a major biogeochemical discontinuity, promoting DOM transformation, restructuring microbial assemblages, and modifying downstream chemical conditions. Overall, tributary inputs, land use, and hydrological regulation disrupted simple longitudinal patterns and generated distinct biogeochemical processing zones. These findings highlight the interplay between downstream transport and local processing in shaping riverine functioning in Mediterranean Andean catchments and provide a basis for assessing future climate and land-use impacts on riverine biogeochemistry.

Rivers act as dynamic connectors between terrestrial and marine ecosystems, transporting and transforming materials along the aquatic continuum. We investigated longitudinal biogeochemical patterns across the Rapel catchment (central Chile) by integrating dissolved organic matter (DOM) characterization, dissolved metals and nutrients, and microbial community profiling from the Andean headwaters to the Pacific Ocean. Headwaters were characterized by low DOC and nutrient concentrations, high protein-like fluorescence, and diverse microbial assemblages dominated by Flavobacterium, Polaromonas, and Rhodoferax. Downstream, agricultural and mining activities increased nutrient and metal concentrations and altered microbial community composition with an increasing prevalence of hgcI_clade. The Rapel Reservoir emerged as a major biogeochemical discontinuity, promoting DOM transformation, restructuring microbial assemblages, and modifying downstream chemical conditions. Overall, tributary inputs, land use, and hydrological regulation disrupted simple longitudinal patterns and generated distinct biogeochemical processing zones. These findings highlight the interplay between downstream transport and local processing in shaping riverine functioning in Mediterranean Andean catchments and provide a basis for assessing future climate and land-use impacts on riverine biogeochemistry.

Rivers act as dynamic connectors between terrestrial and marine ecosystems, transporting and transforming materials along the aquatic continuum. We investigated longitudinal biogeochemical patterns across the Rapel catchment (central Chile) by integrating dissolved organic matter (DOM) characterization, dissolved metals and nutrients, and microbial community profiling from the Andean headwaters to the Pacific Ocean. Headwaters were characterized by low DOC and nutrient concentrations, high protein-like fluorescence, and diverse microbial assemblages dominated by Flavobacterium, Polaromonas, and Rhodoferax. Downstream, agricultural and mining activities increased nutrient and metal concentrations and altered microbial community composition with an increasing prevalence of hgcI_clade. The Rapel Reservoir emerged as a major biogeochemical discontinuity, promoting DOM transformation, restructuring microbial assemblages, and modifying downstream chemical conditions. Overall, tributary inputs, land use, and hydrological regulation disrupted simple longitudinal patterns and generated distinct biogeochemical processing zones. These findings highlight the interplay between downstream transport and local processing in shaping riverine functioning in Mediterranean Andean catchments and provide a basis for assessing future climate and land-use impacts on riverine biogeochemistry.

Rivers act as dynamic connectors between terrestrial and marine ecosystems, transporting and transforming materials along the aquatic continuum. We investigated longitudinal biogeochemical patterns across the Rapel catchment (central Chile) by integrating dissolved organic matter (DOM) characterization, dissolved metals and nutrients, and microbial community profiling from the Andean headwaters to the Pacific Ocean. Headwaters were characterized by low DOC and nutrient concentrations, high protein-like fluorescence, and diverse microbial assemblages dominated by Flavobacterium, Polaromonas, and Rhodoferax. Downstream, agricultural and mining activities increased nutrient and metal concentrations and altered microbial community composition with an increasing prevalence of hgcI_clade. The Rapel Reservoir emerged as a major biogeochemical discontinuity, promoting DOM transformation, restructuring microbial assemblages, and modifying downstream chemical conditions. Overall, tributary inputs, land use, and hydrological regulation disrupted simple longitudinal patterns and generated distinct biogeochemical processing zones. These findings highlight the interplay between downstream transport and local processing in shaping riverine functioning in Mediterranean Andean catchments and provide a basis for assessing future climate and land-use impacts on riverine biogeochemistry.

Cyanobacterial harmful algal blooms are an increasing concern for wildlife health, particularly in eutrophic wetlands, yet well-documented avian cases supported by environmental, pathological, and toxicological evidence remain scarce. This study describes a sentinel case of probable microcystin toxicosis in a Red-gartered coot (Fulica armillata) from Laguna Petrel, a protected coastal wetland in central Chile, during a broader wildlife mortality event. Surface-water monitoring included nutrient analyses, in situ physicochemical measurements, phytoplankton assessment, and cyanotoxin quantification. The evaluated bird was documented alive with severe motor impairment, euthanized, and examined by gross necropsy, histopathology, and tissue toxicology. Water analyses showed elevated nutrients, persistently alkaline and highly productive conditions, marked dominance of Microcystis aeruginosa, and high concentrations of microcystin-LR, microcystin-RR, microcystin-YR, and nodularin. The bird showed marked hepatic lesions at necropsy, histopathological changes compatible with acute hepatotoxic injury, and detectable microcystin-LR in lyophilized liver tissue. Taken together, these findings support a diagnosis of probable microcystin toxicosis in this individual. This case highlights the value of waterfowl as sentinels of ecosystem health threats and underscores the importance of integrated monitoring in protected coastal wetlands potentially affected by toxic cyanobacterial blooms.

Inland aquatic ecosystems play a crucial role in the carbon cycle, acting as an interface for carbon exchange between the atmosphere, terrestrial ecosystems, and the oceans. Due to their importance, dissolved organic matter (DOM) dynamics in continental water bodies have been widely studied. However, most studies are limited to specific sections of river basins, such as headwaters or estuaries, leaving a significant gap in understanding continuous fluvial systems encompassing the entire watershed, particularly regarding the behavior of DOM at the basin scale. To address this gap, we investigated the DOM dynamics within a watershed of 14,000 km² with diverse geomorphological features, following its entire course from the Andes to its only outlet into the Pacific Ocean. This watershed is highly diverse, combining high mountain areas impacted by mining activities with intensively farmed agricultural zones, livestock production in the central region, residential areas, and various recreational activities. The study aims to analyze variations in DOM characteristics along a fluvial continuum and their relationship with land use in different basin sections. A total of 25 sampling points were selected across the basin, including locations within the three sub-basins and the most significant tributaries. At each station, water physicochemical properties were measured by using a portable multiparametric probe, and water samples were collected for measurements of dissolved organic carbon (DOC) concentration, DOM optical properties (fluorescence and absorbance spectroscopy), isotopic analyses, as well as metalloids. A portable sensor was also used to measure nitrate concentrations directly on site. The results allowed us to (i) identify the sources of DOM, (ii) characterize DOM dynamics along the continuous river, and (iii) establish the relationship between DOM sources and different land use types across the basin's sections. This study provides the first regional-scale investigation of DOM dynamics along a river continuum in Chile and offers valuable insights into DOM responses across such systems, raising questions about existing theories of the river continuum concept. Finally, this study represents the first step of a more comprehensive and multidisciplinary study that will also cover seasonality and interannual variability of DOM dynamics and aquatic microbial community diversity in this region.

Environmental context: Organic matter (OM) biodegradation plays a key role as it is one of the main processes causing changes in the amount, composition and properties of OM in sediment. However, a complete understanding of its processes and mechanisms is still not reached. In this study, we aim to explore the chemical composition changes during biodegradation and identify underlying processes. Rationale: Although the scientific community has widely investigated organic matter biodegradation processes, only a limited number of studies have explored the molecular changes of this material, whereas its structure, composition and origin play a key role in these processes. Methodology: We decided to examine the effects of biodegradation on the chemical composition of sedimentary organic matter and to explore the underlying mechanisms. We conceived a laboratory-based degradation experiment utilising organic-rich sediments artificially composed of two contrasting organic matter end-members (i.e. soil and algae) under two oxygen conditions. The sediment samples before and after incubation were then analysed by laser desorption ionisation–Fourier-transform–ion cyclotron resonance–mass spectrometry for molecular characterisation and by thermally assisted hydrolysis and methylation gas chromatography–mass spectrometry in order to offer insights into the mechanisms driving the biodegradation processes. Results: Our results from molecular characterisation unveiled distinct pathways of biodegradation contingent upon the source material. Moreover, they hinted at a predilection for altering high molecular weight compounds like lignin & carboxylic-rich alicyclic molecules (CRAM) and condensed aromatic structures (CAS), manifesting as a conversion into lower molecular weight counterparts. Furthermore, the complementary findings from biomarker analyses underscored the influence of environmental factors – specifically oxygen conditions and microbial communities – on organic matter decomposition. Discussion: Although this study is a controlled laboratory experiment and more studies are needed, it demonstrates the intricate interplay among chemical, biological and environmental factors that profoundly shape the reactivity of organic matter. This study underscores the critical need for persistent inquiry, aimed at unravelling the factors and conditions governing the diverse pathways of biodegradation.