Biogenic Fenton process - A possible mechanism for the mineralization of organic carbon in fresh waters

To explore the mechanisms that mineralize poorly bioavailable natural organic carbon (OC), we measured the mineralization of OC in two lake waters over long-term experiments (up to 623 days) at different pH and iron (Fe) levels. Both the microbial and photochemical mineralization of OC was higher at pH acidified to 4 than at the ambient pH 5 or an elevated pH 6. During 244 days, microbes mineralized up to 60% of OC in the 10-mu m filtrates of lake water and more than 27% in the 1-mu m filtrates indicating that large-sized microbes/grazers enhance the mineralization of OC. A reactivity continuum model indicated that the acidification stimulated the microbial mineralization of OC especially in the later (> weeks) phases of experiment when the bioavailability of OC was poor. The reactive oxygen species produced by light or microbial metabolism could have contributed to the mineralization of poorly bioavailable OC through photochemical and biogenic Fenton processes catalyzed by the indigenous Fe in lake water. When Fe was introduced to artificial lake water to the concentration found in the study lakes, it increased the densities of bacteria growing on solid phase extracted dissolved organic matter and in a larger extent at low pH 4 than at pH 5. Our results suggest that in addition to the photochemical Fenton process (photo-Fenton), microbes can transfer poorly bioavailable OC into labile forms and CO2 through extracellular Fe-catalyzed reactions (i.e., biogenic Fenton process). (C) 2020 Elsevier Ltd. All rights reserved.Peer reviewe

Photochemical Mineralization of Terrigenous DOC to Dissolved Inorganic Carbon in Ocean

When terrigenous dissolved organic carbon (tDOC) rich in chromophoric dissolved organic matter (tCDOM) enters the ocean, solar radiation mineralizes it partially into dissolved inorganic carbon (DIC). This study addresses the amount and the rates of DIC photoproduction from tDOC and the area of ocean required to photomineralize tDOC. We collected water samples from 10 major rivers, mixed them with artificial seawater, and irradiated them with simulated solar radiation to measure DIC photoproduction and the photobleaching of tCDOM. The linear relationship between DIC photoproduction and tCDOM photobleaching was used to estimate the amount of photoproduced DIC from the tCDOM fluxes of the study rivers. Solar radiation was estimated to mineralize 12.5 +/- 3.7 Tg C yr(-1) (10 rivers)(-1) or 18 +/- 8% of tDOC flux. The irradiation experiments also approximated typical apparent spectral quantum yields for DIC photoproduction (phi(lambda)) over the entire lifetime of the tCDOM. Based on phi(lambda)s and the local solar irradiances in river plumes, the annual areal DIC photoproduction rates from tDOC were calculated to range from 52 +/- 4 (Lena River) to 157 +/- 2 mmol C m(-2) yr(-1) (Mississippi River). When the amount of photoproduced DIC was divided by the areal rate, 9.6 +/- 2.5 x 10(6) km(2) of ocean was required for the photomineralization of tDOC from the study rivers. Extrapolation to the global tDOC flux yields 45 (31-58) Tg of photoproduced DIC per year in the river plumes that cover 34 (25-43) x 10(6) km(2) of the ocean.Peer reviewe

Selective incorporation of dissolved organic matter (DOM) during sea ice formation

This study investigated the incorporation of DOM from seawater into >2 day-old sea ice in tanks filled with seawater alone or amended with DOM extracted from the microalga, Chlorella vulgaris. Optical properties, including chromophoric DOM (CDOM) absorption and fluorescence, as well as concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved carbohydrates (dCHOs) and dissolved uronic acids (dUAs) were measured. Enrichment factors (EFs), calculated from salinity-normalized concentrations of DOM in bulk ice, brine and frost flowers relative to under-ice water, were generally >1. The enrichment factors varied for different DOM fractions: EFs were the lowest for humic-like DOM (1.0–1.39) and highest for amino acid-like DOM (1.10–3.94). Enrichment was generally highest in frost flowers with there being less enrichment in bulk ice and brine. Size exclusion chromatography indicated that there was a shift towards smaller molecules in the molecular size distribution of DOM in the samples collected from newly formed ice compared to seawater. Spectral slope coefficients did not reveal any consistent differences between seawater and ice samples. We conclude that DOM is incorporated to sea ice relatively more than inorganic solutes during initial formation of sea ice and the degree of the enrichment depends on the chemical composition of DO

Identifying sites with high biodiversity value using filtered species records from a biodiversity information facility

Aim Efficient mitigation of the biodiversity crisis requires targeted conservation actions in locations with high species richness, the presence of endangered species and unique species communities. However, prioritising sites remains challenging because of sparse knowledge on biodiversity, limiting the possibility of communicating efficiently with local decision makers. We examine easy-to-replicate, yet robust, methods to identify areas with high conservation values on large spatial scales using data filtering and complementary biodiversity indicators based on species records from a biodiversity information facility. Location Finland, Europe. Methods We illustrate the protocol by focusing on Lepidoptera in Finnish municipal districts. We mobilised over 3 million species records on 878 native Lepidoptera (2001–2020) from the Finnish Biodiversity Information Facility. We estimated the richness of overall and endangered species using species accumulation curves, as well as the uniqueness of species communities, using measures of local contribution to beta diversity (LCBD). After testing for multiple thresholds and their effect on indicator accuracy, 97 districts with >5000 records were included in the analyses. Results Estimated overall species richness was highest on the southern coast and significantly decreased in the North, following a known pattern with Lepidoptera in Finland. Species richness was not the highest in the districts with the greatest number of records and the ranking differed from the raw data, demonstrating the importance of correcting for sampling intensity. The estimated number of endangered species correlated with overall species richness, except in northernmost districts, where the proportion of endangered species was exceptionally high. High LCBD replacement (i.e. unique species communities) was concentrated in the Southwest (hemi-boreal) and North (northern boreal) of the country. Main Conclusions We provided an example and interpretations of how scalable biodiversity indicators based on accumulation curves and LCBD analyses, and careful data filtering (thresholds) can be used to identify sites with conservation priorities from multi-sourced species records.peerReviewe

Superoxide-driven autocatalytic dark production of hydroxyl radicals in the presence of complexes of natural dissolved organic matter and iron

We introduced superoxide as potassium superoxide (KO2) to artificial lake water containing dissolved organic matter (DOM) without or with introduced ferric iron complexes (DOM-Fe), and monitored the production rate of hydroxyl radicals as well as changes in the absorption and fluorescence properties of DOM. The introduction of KO2 decreased the absorption by DOM but increased the spectral slope coefficient of DOM more with complexed ferric Fe than without it. The introduction of KO2 increased the fluorescence of humic-like components in DOM without introduced ferric Fe but resulted in the loss of fluorescence in DOM with introduced ferric Fe. A single introduction of 13 μmol L−1 KO2 produced 10 μmol L−1 and 104 μmol L−1 hydroxyl radicals during a week-long experiment without and with the introduced DOM-Fe complexes, respectively. The production rate of hydroxyl radicals decreased exponentially with time but levelled off and continued several days in DOM with introduced ferric Fe. These findings suggest that in the presence of DOM-Fe complexes, superoxide can trigger an autocatalytic Fenton reaction that produces hydroxyl radicals and breaks down DOM.peerReviewe

Molecular composition of dissolved organic matter from a wetland plant (Juncus effusus) after photochemical and microbial decomposition (1.25 yr): Common features with deep sea dissolved organic matter

We hypothesized that microbial and photochemical processing of dissolved organic matter (DOM) determines its molecular formula composition in aquatic systems to a greater degree than does the original source of the DOM. To test this hypothesis, we exposed DOM from a leachate of a wetland plant (Juncus effusus) to solar radiation or incubated it in the dark for 1.25 yr. Analysis of the extracted DOM of the leachates via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) identified 2800 molecular formulae. Of the formulae in the initial DOM, 11% were lost during microbial decomposition in the dark and 54% under solar radiation. Solar radiation also produced a large number of formulae containing N, that were preferentially degraded by microorganisms (47% loss). We compared the “recalcitrant formulae”, i.e. those not degraded in the experiment, with those of DOM from the deep North Pacific Ocean. Of the deep sea DOM formulae, 18% were present in the recalcitrant fraction of the initial DOM. An additional 18% of the formulae in marine DOM were photoproduced and recalcitrant, and 8% were produced by microbes in the experiment. Consequently, 44% of the deep sea DOM shares identical molecular formulae with the recalcitrant DOM from the experiment, most of which were produced by the combined action of sunlight and microbes. This indicates that processes in the water column may be more important than the original source in determining the composition of bulk DOM

Urbanization related changes in lepidopteran community

Urbanization displaces natural habitats with impervious surfaces and managed ornamental green infrastructure. This study compared the structure of lepidopteran community in an office campus cleared from forest to that in the remaining forest. For the comparison, we trapped 2,233 lepidopteran specimens of 56 species from an office campus and adjacent forest. The species richness of lepidopteran assemblage in the office campus was half of that in the forest and consisted primarily of the same species found in the forest. The abundance and biomass of Lepidoptera in the office campus was a quarter of that in the forest. The biomass and abundance of Lepidoptera decreased along with the impervious area within 100-meter radius around the traps and approached zero when impervious surfaces covered the area entirely. The specimens in the trapped lepidopteran assembly from the office campus were on average larger, indicating elevated mobility, than those caught from the forest. Our results support earlier studies concluding that fragmented urban landscape selects for large mobile species, which can feed on ornamental plants or can disperse between high-quality habitats within urban landscape. Green infrastructure with native plants, high-quality native habitats and their connectivity can maintain species-rich lepidopteran communities in urban landscapes.Peer reviewe

Urbanization related changes in lepidopteran community

Urbanization displaces natural habitats with impervious surfaces and managed ornamental green infrastructure. This study compared the structure of lepidopteran community in an office campus cleared from forest to that in the remaining forest. For the comparison, we trapped 2,233 lepidopteran specimens of 56 species from an office campus and adjacent forest. The species richness of lepidopteran assemblage in the office campus was half of that in the forest and consisted primarily of the same species found in the forest. The abundance and biomass of Lepidoptera in the office campus was a quarter of that in the forest. The biomass and abundance of Lepidoptera decreased along with the impervious area within 100-meter radius around the traps and approached zero when impervious surfaces covered the area entirely. The specimens in the trapped lepidopteran assembly from the office campus were on average larger, indicating elevated mobility, than those caught from the forest. Our results support earlier studies concluding that fragmented urban landscape selects for large mobile species, which can feed on ornamental plants or can disperse between high-quality habitats within urban landscape. Green infrastructure with native plants, high-quality native habitats and their connectivity can maintain species-rich lepidopteran communities in urban landscapes.peerReviewe

Interannual variation and long-term trends in proportions of resident individuals in partially migratory birds

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