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Allochthonous and autochthonous dissolved organic matter (DOM) and nutrient availability (nitrogen [N], phosphorus [P]) are expected to increase in lakes as a consequence of climate change. These increases can alter the planktonic food web, especially in oligotrophic systems.This study addresses the consequences of DOM and nutrient increase on heterotrophic bacterioplankton (Hbact) and phytoplankton in high‐altitude lakes. A planktonic community from a high‐altitude lake was incubated for 10 days and laboratory microcosms were subjected to a full factorial design 4 × 2 × 2 of three factors: carbon (C‐control, glucose, algal lysate, soil extract), inorganic nutrients (no added nutrients, addition of N and P) and light (light:dark cycle, dark).Hbact was co‐limited by organic C and inorganic nutrients, resulting in lower biomass and production with glucose or inorganic nutrients added alone than with the two sources added in combination. Algal‐derived DOM was more labile, more consumed, and resulted in higher bacterial production, while soil‐derived DOM was less labile and less consumed. Phytoplankton was strongly limited by inorganic nutrients. DOM additions, via the interactions with Hbact, increased phytoplankton biomass and modified the community composition. Mixotrophs increased with C under light or nutrient limitation, pointing them as major factors in controlling mixotrophy in high‐altitude lakes. Soil‐derived DOM led to higher algal biomass, higher proportion of mixotrophs, and more taxa adapted to nutrient‐enriched conditions.This study reveals a shift in planktonic interactions with changes in DOM quality and quantity. Under the projected climate change, we expect an increase in heterotrophy and a modification of trophic interactions with important repercussions on the C cycle in high‐altitude lakes. [ABSTRACT FROM AUTHOR]

This work aimed to investigate, in detail, the elemental and molecular composition of soil samples collected from the various horizons of an Amazon spodosol profile by combining the atomic technique laser-induced breakdown spectroscopy (LIBS) with two molecular techniques, i.e., Raman and fluorescence spectroscopies. The emission lines of the elements Fe, C, Si, Mg, Al, Ti, Ca, and K with various relative intensities were detected by using LIBS. In particular, C appeared to accumulate in the transition horizon and was proven to be mostly humified by fluorescence analysis. The Raman peaks detected at 465 cm−1 and 800 cm−1 corresponded with the symmetric stretching and bending modes of O-Si-O and Si-OH, respectively. Small shifts toward higher frequencies and slight increases in the width and full width at half maximum (FWHM) of the quartz band at 465 cm−1 appeared in the Tr to K2 horizons, which could be ascribed to a local distortion caused by the high contents of Al of kaolinite mineral phases, as also shown by the LIBS data. Thus, a small amount of kaolinite mineral phase and K measured by LIBS would be present also in the A1 to E2 horizons. The lifetime fluorescence was almost constant in the surface and middle horizons, whereas it increased sharply in the transition horizon and then decreased slightly in the kaolin horizons, which confirmed the presence of more humified recalcitrant organic matter in deeper soil horizons. In conclusion, the combined use of the three spectroscopic techniques appeared to be a very promising approach for studying Amazon soils. [ABSTRACT FROM AUTHOR]

Climate change is altering both dissolved organic matter (DOM) properties and phytoplankton dynamics in lakes. High‐altitude lakes are good sentinels of global change. However, their value as sentinels depends on how well we understand their functioning. This study analysed physical, chemical and biological data during three pre‐defined periods running from complete ice‐cover right to the end of the ice‐free season, in a high‐altitude oligotrophic lake. A functional approach was used to assess how relationships between DOM and the planktonic community vary over time.Phytoplankton functional change was found to occur with shifts in DOM. During the ice‐influenced period, from February to the end of the thaw, the phytoplankton community was dominated by small autotrophs and mixotrophic flagellates and DOM from sediment and terrestrial origin dominated the DOM pool of the lake. Phytoplankton diversity and richness increased during the post‐snowmelt overturn period, when terrestrial DOM dominated the DOM pool. Finally, large siliceous autotrophs, competitive under low nitrogen concentrations and high temperature, dominated almost exclusively during the late summer period (LSP). Increased phytoplankton biomass meant that phytoplankton‐derived DOM was dominant during the LSP.These phenological changes in the phytoplankton community resulted in functional shifts at the base of the food web. Based on the relationships between the variables in the study, it can be deduced that the nature of the relationship between phytoplankton and bacteria progressively shifted from strong top‐down control exerted by phytoplankton over bacteria towards predominantly bottom‐up control at the end of the ice‐free season.Synthesis. Using a field survey starting from complete ice‐cover and lasting right to the end of the ice‐free season in a sentinel lake, we show seasonal shifts in the link between DOM properties and plankton community traits. Differences in environmental conditions and DOM origin explained variation in phytoplankton community structure and function, pointing to seasonal shifts in microbial food web interactions. Our research suggests that, under climate change, the balance between mixotrophy and autotrophy and the control exerted by phytoplankton over bacterioplankton will change in oligotrophic high‐altitude lakes with large, vegetated catchments. [ABSTRACT FROM AUTHOR]

Worldwide, peatlands are important sources of dissolved organic matter (DOM) and trace metals (TMs) to surface waters, and these fluxes may increase with peatland degradation. In Southeast Asia, tropical peatlands are being rapidly deforested and drained. The blackwater rivers draining these peatland areas have high concentrations of DOM and the potential to be hotspots for CO2 release. However, the fate of this fluvial carbon export is uncertain, and its role as a trace metal carrier has never been investigated. This work aims to address these gaps in our understanding of tropical peatland DOM and associated elements in the context of degraded tropical peatlands in Indonesian Borneo. We quantified dissolved organic carbon and trace metal concentrations in the dissolved and fine colloidal (<0.22 µ m) and coarse colloidal (0.22–2.7 µ m) fractions and determined the characteristics (δ13 C, absorbance, fluorescence: excitation-emission matrix and parallel factor – PARAFAC – analysis) of the peatland-derived DOM as it drains from peatland canals, flows along the Ambawang River (blackwater river) and eventually mixes with the Kapuas Kecil River (whitewater river) before meeting the ocean near the city of Pontianak in West Kalimantan, Indonesia. We observe downstream shifts in indicators of in-stream processing. An increase in the δ13 C of dissolved organic carbon (DOC), along with an increase in the C1/C2 ratio of PARAFAC fluorophores, and a decrease in SUVA (specific UV absorbance) along the continuum suggest the predominance of photo-oxidation. However, very low dissolved oxygen concentrations also suggest that oxygen is quickly consumed by microbial degradation of DOM in the shallow layers of water. Blackwater rivers draining degraded peatlands show significantly higher concentrations of Al, Fe, Pb, As, Ni and Cd compared to the whitewater river. A strong association is observed between DOM, Fe, As, Cd and Zn in the dissolved and fine colloid fraction, while Al is associated with Pb and Ni and present in a higher proportion in the coarse colloidal fraction. We additionally measured the isotopic composition of lead released from degraded tropical peatlands for the first time and show that Pb originates from anthropogenic atmospheric deposition. Degraded tropical peatlands are important sources of DOM and trace metals to rivers and a secondary source of atmospherically deposited contaminants. [ABSTRACT FROM AUTHOR]

Worldwide, peatlands are important sources of dissolved organic matter (DOM) and trace metals (TM) to surface waters and these fluxes may increase with peatland degradation. In Southeast Asia, tropical peatlands are being rapidly deforested and drained. The black rivers draining these peatland areas have high concentrations of DOM, and the potential to be hotspots for CO2 release. However, the fate of this fluvial carbon export is uncertain, and its role as a trace metal carrier has never been investigated. This work aims to address these gaps in our understanding of tropical peatland DOM and associated elements in the context of degraded tropical peatlands of Indonesian Borneo. We quantified dissolved organic carbon and trace metals concentrations in the dissolved and fine colloidal (< 0.22 μm) and coarse colloidal (0.22-2.7 μm) fractions and characterized the characteristics (δ13C, Absorbance, Fluorescence: excitation-emission matrix and PARAFAC analysis) of the peatland-derived DOM as it drains from peatland canals, flows along the blackwater Ambawang River, and eventually mixes with Kapuas Kecil River before meeting the ocean near the city of Pontianak in West Kalimantan, Indonesia. We observe downstream shifts in indicators of in-stream processing. The increase in the δ13C of DOC, along with an increase in the C1/C2 ratio of PARAFAC fluorophores, and decrease in SUVA (Specific UV Absorbance) along the continuum suggest the predominance pf photo-oxidation. However, we also observe very low dissolved oxygen concentrations, suggesting that oxygen is quickly consumed by microbial degradation of DOM in the shallow layers of water. Black rivers draining degraded peatlands show significantly higher concentrations of Al, Fe, Pb, As, Ni, and Cd. A strong association is observed between DOM, Fe, As, Cd and Zn in the dissolved and fine colloid fraction, while Al is associated to Pb and Ni and present in a higher proportion in the coarse colloidal fraction. We additionally measure the isotopic composition of lead released from degraded tropical peatlands for the first time and show that Pb originates from anthropogenic atmospheric deposition. Degraded tropical peatlands are important sources of DOM and trace metals to rivers and a secondary source of atmospherically deposited contaminants. [ABSTRACT FROM AUTHOR]

The spatio-temporal variability of fluorescent dissolved organic matter (FDOM) and its relationships with physical (temperature, salinity) and chemical (nutrients, chlorophyll a, dissolved and particulate organic carbon, nitrogen and phosphorus) parameters were investigated in inland waters of the Rhône River delta and the Fos-Marseille marine area (northwestern Mediterranean, France). Samples were taken approximately twice per month in two inland sites and three marine sites from February 2011 to January 2012. FDOM was analysed using fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC). In inland waters, humic-like components C1 (λ/λ: 250 (330)/394 nm) and C3 (λ/λ: 250 (350)/454 nm) dominated over one tryptophan-like component C2 (λ/λ: 230 (280)/340 nm), reflecting a background contribution of terrigenous material (~67% of total fluorescence intensity, in quinine sulphate unit (QSU)) throughout the year. In marine waters, protein-like material, with tyrosine-like C4 (λ/λ: <220 (275)/<300 nm) and tryptophan-like C5 (λ/λ: 230 (280)/342 nm), dominated (~71% of total fluorescence intensity, in QSU) over a single humic-like component C6 (λ/λ: 245 (300)/450 nm). In inland waters of the Rhône River delta, humic-like components C1 and C3 were more abundant in autumn-winter, very likely due to inputs of terrestrial organic matter from rainfalls, runoffs and wind-induced sediment resuspension. In marine sites, intrusions of the Berre Lagoon and Rhône River waters had a significant impact on the local biogeochemistry, leading to higher fluorescence intensities of humic- and protein-like components in spring-summer. On average, the fluorescence intensities of FDOM components C4, C5 and C6 increased by 33-81% under lower salinity. This work highlights the complex dynamics of FDOM in coastal waters and confirms the link between marine FDOM and the Rhône River freshwater intrusions on larger spatial and temporal scales in the Fos-Marseille marine area. [ABSTRACT FROM AUTHOR]