Journal of Limnology https://www.jlimnol.it/index.php/jlimnol <p>The <strong>Journal of Limnology</strong> publishes peer-reviewed original papers, review papers and notes about all aspects of limnology. The scope of the Journal of Limnology comprises the ecology, biology, microbiology, physics, and chemistry of freshwaters, including the impact of human activities, management and conservation. Coverage includes molecular-, organism-, community-, and ecosystem-level studies both applied and theoretical. Proceedings of workshops, specialized symposia, conferences, may also be accepted for publication. The <strong>Journal of Limnology</strong> is published in three issues per year, open access online and each article is available for downloading for free. A printed version is also available at the annual subscription rate of € 160. For further information on subscription terms, rates, modes of payment and shipping, etc. please contact the Publisher at <a href="mailto:info@pagepress.org">info@pagepress.org</a></p> <h3 style="color: #194480;">The Special Issue <strong><a href="/index.php/jlimnol/issue/view/66">Recent advances in the study of Chironomidae: An overview</a></strong> is now available</h3> en-US <p><strong>PAGEPress</strong> has chosen to apply the&nbsp;<a href="http://creativecommons.org/licenses/by-nc/4.0/" target="_blank" rel="noopener"><strong>Creative Commons Attribution NonCommercial 4.0 International License</strong></a>&nbsp;(CC BY-NC 4.0) to all manuscripts to be published.<br><br> An Open Access Publication is one that meets the following two conditions:</p> <ol> <li>the author(s) and copyright holder(s) grant(s) to all users a free, irrevocable, worldwide, perpetual right of access to, and a license to copy, use, distribute, transmit and display the work publicly and to make and distribute derivative works, in any digital medium for any responsible purpose, subject to proper attribution of authorship, as well as the right to make small numbers of printed copies for their personal use.</li> <li>a complete version of the work and all supplemental materials, including a copy of the permission as stated above, in a suitable standard electronic format is deposited immediately upon initial publication in at least one online repository that is supported by an academic institution, scholarly society, government agency, or other well-established organization that seeks to enable open access, unrestricted distribution, interoperability, and long-term archiving.</li> </ol> <p>Authors who publish with this journal agree to the following terms:</p> <ol> <li>Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under a Creative Commons Attribution License that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.</li> <li>Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.</li> <li>Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as it can lead to productive exchanges, as well as earlier and greater citation of published work.</li> </ol> nadia.moscato@pagepress.org (Nadia Moscato) tiziano.taccini@pagepress.org (Tiziano Taccini) Wed, 21 Nov 2018 10:16:36 +0100 OJS 3.1.1.4 http://blogs.law.harvard.edu/tech/rss 60 Leaf traits of Brazilian semiarid species as regulatory factors for associated aquatic invertebrates https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1743 <p>The input of leaf litter is an important energy source for the riparian vegetation of aquatic ecosystems, and the chemical composition of leaf litter is decisive for colonization by invertebrates in streams. Plant species of the semiarid regions present different morphophysiological characteristics to combat the effects of drought, including tough leaves that have less nutritional quality. However, although concern regarding the decomposition of organic matter in aquatic ecosystems in semiarid regions is increasing, no information exists on the influence of leaf traits (<em>e.g</em>., N, C:N ratio and toughness) before the colonization of invertebrates and the decomposition of leaf litter. We hypothesized that: i) leaves with greater toughness, higher C:N ratio and lower amount of N present low density and biomass of associated invertebrates; ii) greater density and biomass of associated invertebrates results in increased decomposition rates; and iii) leaf traits influences the structure and composition of functional feeding groups of associated invertebrates. We incubated senescent leaves of <em>Tabebuia aurea</em> and <em>Aspidosperma pyrifolium</em> in a Brazilian semiarid stream using litter bags, and after 3, 7, 15 and 30 days, four litter bags were withdrawn for laboratory washing of the remaining leaf sediment and for collection of associated invertebrates. <em>A. pyrifolium</em> leaves presented higher nutritional quality (low C:N ratio, lower toughness), and the decomposition rate was higher than <em>T. aurea</em> leaves. Invertebrate density and biomass varied among litter, being higher in <em>T. aurea </em>and <em>A. pyrifolium</em>, respectively. The leaf litter quality also altered the composition of functional feeding groups. We observed a higher density of filters on <em>T. aurea</em> and collectors on <em>A. pyrifolium</em>. Both <em>T. aurea</em> and <em>A. pyrifolium</em> presented higher biomass of collectors, however <em>T. aurea</em> showed higher biomass of filters than <em>A. pyrifolium</em>. In the absence of shredders, leaf litter may have been used by invertebrates as a substrate, for shelter against predators and current, and sporadically as a food resource. Thus, differences in the leaf traits were important structures of the streams invertebrate. These are the first results of the influence of leaf traits on invertebrate colonization in the streams of semiarid regions, and reinforce the need for studies to verify the contribution of organic matter as well as the feeding preferences of invertebrates.<strong><br clear="all"> </strong></p> Marcos Medeiros Cavalcanti Júnior, Luiz U. Hepp, Joseline Molozzi, Dilma M. de Brito Melo Trovão ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1743 Thu, 03 May 2018 00:00:00 +0200 Variation of stream metabolism along a tropical environmental gradient https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1717 <p>Stream metabolism is affected by both natural and human-induced processes. While metabolism has multiple implications for ecological processes, relatively little is known about how metabolic rates are influenced by land use in tropical streams. In this study, we assessed the metabolic characteristics and related environmental factors of six streams located in a transition area from Cerrado to Atlantic Forest (São Carlos/Brazil). Three streams were relatively preserved, while three were flowing through more agriculturally and/or urban impacted watersheds. Surface water samples were analyzed for biological and physico-chemical parameters as well as discharge and percentage of canopy cover. Metabolism was determined through the single-station method to estimate gross primary production (GPP), ecosystem respiration (ER) and net ecosystem production (NEP) with BAyesian Single-station Estimation (BASE). Nutrient concentrations tended to be higher in impacted <em>versus</em> preserved streams (<em>e.g</em>., average total phosphorus between 0.028-0.042 mg L<sup>-1</sup> and 0.009-0.038 mg L<sup>-1</sup>, respectively). Average canopy cover varied between 58 and 77%, with no significant spatial or seasonal variation. All streams were net heterotrophic (ER exceeded GPP) in all sampling periods. GPP rates were always lower than 0.7 gO<sub>2</sub> m<sup>-2</sup> d<sup>-1 </sup>in all streams and ER varied from 0.6 to 42.1 gO<sub>2</sub> m<sup>-2 </sup>d<sup>-1</sup>.&nbsp; Linear Mixed-Effect models showed that depth, discharge, velocity and total phosphorus are the most important predictors for GPP. For ER, depth, velocity and canopy cover are significant potential predictors. Canopy cover was the main light limiting factor and influenced stream metabolism. Our findings reinforced the concepts that shifts in the shading effect provided by vegetation (<em>e.g</em>., through deforestation) or changes in discharge (<em>e.g</em>., through land use conversion or water abstractions) can impact freshwater metabolism. Our study suggests that human activities in low latitude areas can alter tropical streams’ water quality, ecosystem function, and the degree of riparian influence. Our data showed that tropical streams can be especially responsive to increases of organic matter inputs leading to high respiration rates and net heterotrophy, and this should be considered to support management and restoration efforts.</p> Wesley A. Saltarelli, Walter K. Dodds, Flavia Tromboni, Maria do Carmo Calijuri, Vinicius Neres-Lima, Carlos E. Jordão, Julio C.P. Palhares, Davi G.F. Cunha ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1717 Tue, 22 May 2018 00:00:00 +0200 Climate change dominates recent sedimentation and organic carbon burial in Lake Chenghai, southwest China https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1762 <p>Lacustrine ecosystems are directly influenced by terrestrial soil erosion, and excessive sediment loading constitutes a significant and widespread environmental issue. In order to investigate the response of catchment soil erosion and organic carbon burial to climate change and human activity, a sediment core spanning the last 160 years was retrieved from Lake Chenghai in southwest China. Multi-proxy analysis including grain-size composition and geochemical indicators were undertaken in this study. The result of grain-size <em>vs</em> standard deviation method shows that the sensitive component with a modal size of 13.2 μm is related to fluvial processes and sensitive to the catchment soil erosion. The increasing intensity of soil erosion was mainly determined by the weakening of Indian summer monsoon and global warming, as well as intensive human activities during the middle of 20<sup>th</sup> century, which resulted in decreasing vegetation cover in Lake Chenghai catchment. The organic carbon burial rate was also attributed to the catchment disturbance, indicating that increased catchment soil erosion may impact the terrestrial carbon recycling.</p> Weiwei Sun, Qingfeng Jiang, Enfeng Liu, Jie Chang, Enlou Zhang ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1762 Fri, 11 May 2018 00:00:00 +0200 Ecological drivers of testate amoeba diversity in tropical water bodies of central Mexico https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1699 <p>Testate amoebae are unicellular organisms characterized by a shell-like test. Due to their potential use as bioindicators (and paleoindicators), these organisms have been increasingly studied in the last decade, particularly in temperate latitudes. This study’s objective was two-fold: to identify the testate amoeba communities sampled from 29 water bodies in Mexico and to determine if their presence and distribution also made them suitable bioindicators for tropical latitudes. A total of 40 taxa were recorded within 12 genera, and six significant variables -oxygen, pH, depth, temperature, conductivity, and total alkalinity - that explained testate amoeba distribution within and among the water bodies were identified through a canonical correspondence analysis. The Q-mode clusters rendered five assemblages, each named after their respective dominant species: 1) <em>Centropyxis aculeata</em> strain “aculeata” assemblage, 2) <em>Difflugia oblonga</em> strain “bryophila” assemblage, 3) diverse assemblage, 4) <em>Cucurbitella tricuspis</em> assemblage, and 5) <em>Difflugia protaeiformis</em> strain “acuminata” assemblage. We found that <em>Cucurbitella tricuspis</em> and the <em>Difflugia protaeiformis</em> strain “acuminata” have similar ecological preferences to those reported previously for temperate lakes, with the former identified as an indicator of eutrophic environments and the latter as an indicator of low oxygen levels. On the other hand, <em>Centropyxis aculeata</em> strain “aculeata” and <em>Arcella vulgaris </em>seem to indicate adverse conditions, but the source of this environmental stress apparently differs from that reported in temperate latitudes. Although this stress source could not be identified in all cases, our study nonetheless demonstrates that testate amoebae in the water bodies of central Mexico could reveal the presence of environmental stress.</p> Itzel Sigala Regalado, Socorro Lozano García, Liseth Pérez Alvarado, Margarita Caballero, Alfonso Lugo Vázquez ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1699 Thu, 21 Jun 2018 00:00:00 +0200 Comparison of different solid phase extraction sorbents for the qualitative assessment of dissolved organic nitrogen in freshwater samples using FT-ICR-MS https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1791 <p>Fate and reactivity of dissolved organic matter (DOM) is directly linked to its chemical composition. Therefore, molecular characterisation, for example using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), is used for a better understanding of those factors. To study organic compounds in the water column, an efficient extraction method is important. The commonly used extraction method for FT-ICR-MS is solid phase extraction (SPE) using a reversed-phase sorbent (BondElut PPL). But this method, to the best of our knowledge, was not evaluated for its ability to extract organic nitrogen compounds which are important building blocks of life and therefore an important fraction of DOM. In this study, several solid phase sorbents were tested for their ability to extract organic nitrogen compounds from water samples of natural aqueous environments. Different cartridges concerning their retention mechanism and pore size were tested. Three cartridges with different extraction mechanism (reversed phase, cation exchange or a mixture of both) or different pore size were tested. Except for one sorbent type, which heavily contaminated the samples with organic molecules, the tested cartridges leached neither a significant amount of dissolved organic carbon (DOC) nor dissolved organic nitrogen (DON). The sorbents were tested with lake water to be able to investigate their functionality in real conditions. It could be shown, that the molecular composition of the sample should be considered for the choice of the sorbent material. Additionally, it was shown that a mixed-bed sorbent is a valuable complementary SPE sorbent for the molecular characterisation of lacustrine samples using FT-ICR-MS and it might also be useful for a quantitative extraction. Furthermore, it could be shown that HyperSep Retain CX sorbent allows to extract a broader range of organic nitrogen compounds leading to a more comprehensive data set for investigating organic nitrogen compounds in lakes using FT-ICR-MS.</p> Patrick E. Stücheli, Jutta Niggemann, Carsten J. Schubert ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1791 Wed, 06 Jun 2018 00:00:00 +0200 Environmental drivers influencing stonefly assemblages along a longitudinal gradient in karst lotic habitats https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1816 <p>Stoneflies are among the most sensitive aquatic insect taxa and therefore arguably the best indicator of the excellent, i.e. pristine, ecological status of surface streams. Karst habitats are one of the most exciting freshwater habitats in terms of biological-geological interplay. They, in turn, support a biodiversity far superior to surrounding freshwater habitats and hence these habitats are designated as biodiversity hotspots. Our study deals with both of these crucial ecological players. We studied stonefly assemblages, their microhabitat preferences and emergence patterns along a karst oligotrophic hydrosystem. The sampling was conducted monthly from March 2007 to December 2008 using pyramid-type emergence traps set in various habitats and associated microhabitats (e.g. springs, rivers, streams, tufa barriers × moss, angiosperm, cobble, sand, silt substrates). Favorable environmental conditions, such as a wide range of karst habitat types with low water temperature and high oxygen concentration, resulted in high stonefly species richness (31 recorded species). Water temperature and pH had the highest influence on stonefly assemblages. Species richness and diversity decreased in a downstream direction. We recorded a longitudinal shift from crenal-epirhithral to epirhithral-metarhithral assemblages with some hyporhithral and potamal elements. Upstream sites were dominated by shredders, while downstream sites had a higher proportion of gatherers-collectors. Several species showed a significant preference for a specific microhabitat type in accordance with their feeding strategies and food availability. The majority of recorded species exhibited univoltine life cycles slow or fast. &nbsp;</p> Anamarija Ridl, Marina Vilenica, Marija Ivković, Aleksandar Popijač, Ignac Sivec, Marko Miliša, Zlatko Mihaljević ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1816 Wed, 11 Jul 2018 00:00:00 +0200 Faunistic survey of the zooplankton community in an oligotrophic sinkhole, Cenote Azul (Quintana Roo, Mexico), using different sampling methods, and documented with DNA barcodes https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1746 <p>This study is the first faunistic inventory of a zooplankton community from an open, karstic and oligotrophic aquatic sinkhole in the south of the Yucatan Peninsula (Mexico), we describe the richness of the zooplankton collected with the combination of plankton nets and light traps of our own design, using morphological and molecular characters to identify the species and demonstrate the effectiveness of only one set of primers to sequence all taxa. Recently, it has been demonstrated that different sampling methods can increase the number of zooplankton species from tropical and temperate systems dramatically. These more effective methods together with DNA barcoding can give a new and more realistic picture of the species dwelling in a freshwater system. In total, we sequenced 268 specimens, and the list of species known in this sinkhole increased from 13 to 77 taxa, with a projection of 87 in total, including cladocerans, copepods, ostracods, fish larvae, tadpoles, rotifers, chironomids, water mites, among others. From the 77 taxa identified by us, 72 BINS (Barcode Index Numbers, equivalent to putative species) were assigned by the BOLD Database (boldsystems.org), and 30 of them are new records for both, BOLD and GenBank (<a href="http://www.ncbi.nlm.nih.gov">www.ncbi.nlm.nih.gov</a>). There was an essential difference in the number of taxa collected with the plankton nets and the light traps. Only 23 taxa were registered in the nets, representing between 28 and 29% of the total richness, while 67 were present in the light traps representing 87% of the species found. From these, 46 taxa were exclusive to this sampling method. Light traps are an effective method for rapid evaluation of zooplankton. In the future, combining DNA barcoding and high-throughput sequencing methods with more &nbsp;efficient collecting will enable us to perform quick and precise biomonitoring of any aquatic ecosystem, enabling the detection of changes in zooplankton composition resulting from climate change and anthropogenic disturbances. Nevertheless, as a first step it is fundamental to establish a baseline of DNA barcodes for the species in these ecosystems.</p> Lucia Montes-Ortiz, Manuel Elias-Gutierrez ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1746 Thu, 21 Jun 2018 00:00:00 +0200 Population growth potential of rotifers from a high altitude eutrophic waterbody, Madín reservoir (State of Mexico, Mexico): The importance of seasonal sampling https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1823 <p>To understand the population growth potential of different species of rotifers in nature, field collections through seasons are essential. We sampled zooplankton (and measured selected physicochemical variables) from the Madín reservoir, a high altitude eutrophic urban waterbody from Mexico, every month for a year. Qualitative analysis of zooplankton revealed 28 rotifer species and four cladoceran crustaceans plus one unidentified copepod. <em>Cephalodella catellina</em> (1400 ind L<sup>-1</sup>), <em>Horaella thomassoni</em> (550 ind L<sup>-1</sup>), <em>Conochilus dossuarius </em>(380 ind L<sup>-1</sup>) and <em>Filinia</em> <em>longiseta</em> (25 ind L<sup>-1</sup>) had higher peak density than other rotifers. Based on the concentrations of nitrates and phosphates, chlorophyll a levels or different diversity indices (<em>e.g</em>., Carlson, Shannon-Wiener, Pantle and Buck, Ejsmont-Karabin’s TSI<sub>Rot</sub>), the waterbody is eutrophic to hypertrophic, depending on the season. In this waterbody we observed high densities of <em>Aphanothece</em> sp. which is a toxic picocyanobacterium. During the blooms of <em>Aphanothece</em>, we also recorded higher densities of <em>H. thomassoni</em> and <em>C. catellina</em>. Based on the gut contents we found that both these rotifer species feed on <em>Aphanothece</em> in this waterbody. This study thus suggests the potential growth of <em>Horaella</em>, <em>Cephalodella</em>, <em>Conochilus</em> and <em>Filinia</em> in this eutrophic reservoir containing blooms of <em>Aphanothece</em>.</p> Rosa Martha Moreno-Gutiérrez, S.S.S. Sarma, Alma Socorro Sobrino-Figueroa, S. Nandini ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1823 Wed, 27 Jun 2018 00:00:00 +0200 Application of QUAL2Kw to the Oglio River (Northern Italy) to assess diffuse N pollution via river-groundwater interaction https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1761 <p>Water quality modeling is increasingly recognized as a useful tool for obtaining valuable information for optimal water quality management. In this study, the free software QUAL2Kw was used to evaluate the impacts of agricultural nitrogen (N) excess on river nitrate (NO<sub>3</sub>-N) concentrations. We explored the possibility to use QUAL2Kw in order to back calculate the exchange of water and N from the groundwater to the Oglio River, northern Italy, which drains a heavily irrigated and fertilized agricultural land. Along the river course water monitoring activities carried out in the dry, summer period revealed steep increases of NO<sub>3</sub>-N in different sectors, by up to 2 orders of magnitude, not explained by any significant point inputs. Such increases suggest the occurrence of large water exchange with nitrate-polluted groundwater and diffuse inputs. In turn, groundwater pollution is due to high N excess in the watershed (~200 kg N ha<sup>-1 </sup>yr<sup>-1</sup>), flood-based irrigation techniques and soil permeability. The QUAL2Kw model was calibrated using the average of 2 years' data collected in winter 2010 and 2011 and validated using the data of winter 2012. To minimize the error between simulation results and measured data, the constants of inorganic suspended solid (ISS), ammonium (NH<sub>4</sub>-N), nitrate and organic N were calibrated. The calibration and validation results showed a good correspondence between the calculated and measured values for most of water-quality variables. QUAL2Kw was then run separately with three years' summer data (2009, 2010 and 2011), and large gaps were found between the measured and predicted values of discharge, electrical conductivity, NO<sub>3</sub>-N and total N. Such gaps are discussed in terms of river-groundwater interactions, limited to the summer period and following irrigation by flooding, rise of the groundwater table and vertical transport of N. The gaps allowed to back calculate the volumes of water and the amount of N exchanged. The total load of NO<sub>3</sub>-N entering into the river from groundwater was estimated in 25.17, 25.63 and 29.89 ton per day for NO<sub>3</sub>-N in 2009, 2010 and 2011, respectively. Similar results were obtained in another study based on mass balance of N isotopes. The combination of experimental and QUAL2Kw modelled data proved to be a simple, low cost but effective tool in the estimation of NO<sub>3</sub>-N exchange between the surface and groundwater.</p> Hajar Taherisoudejani, Erica Racchetti, Fulvio Celico, Marco Bartoli ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1761 Wed, 11 Jul 2018 00:00:00 +0200 Drainage ditches as important habitat for species diversity and rare species of aquatic beetles in agricultural landscapes (Insecta: Coleoptera) https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1819 <p>Agricultural drainage ditches are common structures in cultivated lowland areas across Europe. These artificial linear water bodies are interconnected to form networks that can offer valuable habitats for many water associated organisms. The current study contributes to the knowledge of aquatic Coleoptera biodiversity associated with artificial drainage ditches. Fundamental ecological and faunistical findings were combined with aspects relevant for applied nature conservation. Adult beetles were sampled at 124 sampling locations belonging to seven study sites in the federal state of Brandenburg, Germany. With 108 taxa out of 10 families the studied ditches showed a high species richness. Taxa associated with eutrophic conditions dominated with the dytiscid <em>Hydroporus palustris</em> as the most abundant species. In terms of β-diversity, a moderate turnover between the study sites could be observed. Although the sampling locations showed some degree of variability concerning habitat characteristics, measured environmental parameters only weakly explained observed differences in community composition. Beside taxonomical characterization of beetle diversity, aspects of functional diversity were analyzed. Interestingly, individuals with reduced flight ability were dominant. Because the predaceous family Dytiscidae dominated, beetles were mainly integrated as carnivores in the food web of ditches. Throughout the study, 13.0% threatened as well as 18.4% rare taxa could be recorded, referring to the German fauna of aquatic beetles. This may underpin the need to include agricultural drainage ditches into conservation management.</p> Daniel Rolke, Birgit Jaenicke, Jobst Pfaender, Udo Rothe ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1819 Tue, 07 Aug 2018 00:00:00 +0200 Mechanisms regulating CO2 and CH4 dynamics in the Azorean volcanic lakes (São Miguel Island, Portugal) https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1821 <p>Chemical and isotopic vertical profiles from the volcanic lakes of Sete Cidades, Santiago, Fogo, Congro and Furnas (Island of São Miguel, Azores Archipelago, Portugal) were studied to investigate the biogeochemical processes acting at different depths, with a focus on the CO<sub>2</sub> and CH<sub>4</sub> dynamics. These lakes are fed by meteoric water affected by seawater spray and interacting with volcanic rocks at a relatively low extent. In addition to volcanogenic gas inputs, the biogeochemical processes are influenced by microbial activities since the lakes offer specialized ecological niches for oxic and anoxic metabolism. The lakes were sampled in two extreme conditions of (partial) mixing (winter) and stratification (summer), respectively. The seasonal thermal stratification favored the development of anaerobic hypolimnia, showing relatively high concentrations of NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>-</sup>, P and other minor species (Fe, Mn, Zn, As) controlled by microbial activity and minerogenetic processes occurring within the lake sediments. The strongly negative d<sup>13</sup>C-TDIC values measured in almost all the studied lakes suggest dominant contribution of organic carbon. Dissolved gases were mostly consisting of atmospheric compounds with significant concentrations of CO<sub>2</sub> and CH<sub>4</sub>. The d<sup>13</sup>C-CO<sub>2</sub> values were intermediate between those measured in the hydrothermal fluids and those typical of biogenic CO<sub>2</sub>. Dissolved CH<sub>4</sub>, which was the most abundant extra-atmospheric gas in the anoxic waters, was measured at significant concentrations even in the aerobic layers, especially in the winter season. This unexpected feature may tentatively be explained by admitting i) convective mixing of shallow and deep waters, and/or ii) aerobic CH<sub>4</sub> production. Further investigations, focusing on the recognition of microbial populations able to produce CH<sub>4</sub> at different redox conditions, may be useful to corroborate these intriguing hypotheses.</p> Franco Tassi, Jacopo Cabassi, Cesar Andrade, Cristiana Callieri, Catarina Silva, Fatima Viveiros, Gianluca Corno, Orlando Vaselli, Enrico Selmo, Andrea Gallorini, Andrea Ricci, Luciano Giannini, Josè V. Cruz ##submission.copyrightStatement## http://creativecommons.org/licenses/by-nc/4.0 https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1821 Tue, 24 Jul 2018 00:00:00 +0200