A fast and sensitive method for the continuous in situ determination of dissolved methane and its d13C-isotope ratio in surface waters

A fast and sensitive method for the continuous determination of methane (CH4) and its stable carbon isotopic values (d13C-CH4) in surface waters was developed by applying a vacuum to a gas/liquid exchange membrane and measuring the extracted gases by a portable cavity ring-down spectroscopy analyser (M-CRDS). The M-CRDS was calibrated and characterized for CH4 concentration and d13C-CH4 with synthetic water standards. The detection limit of the M-CRDS for the simultaneous determination of CH4 and d13CCH4 is 3.6 nmol L21 CH4. A measurement precision of CH4 concentrations and d13C-CH4 in the range of 1.1%, respectively, 1.7& (1r) and accuracy (1.3%, respectively, 0.8& [1r]) was achieved for single measurements and averaging times of 10 min. The response time s of 5765 s allow determination of d13C-CH4 values more than twice as fast than other methods. The demonstrated M-CRDS method was applied and tested for Lake Stechlin (Germany) and compared with the headspace-gas chromatography and fast membrane CH4 concentration methods. Maximum CH4 concentrations (577 nmol L21) and lightest d13C-CH4 (235.2&) were found around the thermocline in depth profile measurements. The M-CRDS-method was in good agreement with other methods. Temporal variations in CH4 concentration and d13C-CH4 obtained in 24 h measurements indicate either local methane production/oxidation or physical variations in the thermocline. Therefore, these results illustrate the need of fast and sensitive analyses to achieve a better understanding of different mechanisms and pathways of CH4 formation in aquatic environments

Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer

To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L−1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4°C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature.Additional co-authors: Jolanda Verspagen, Maria van Herk, Maria G. Antoniou, Nikoletta Tsiarta, Valerie McCarthy, Victor C. Perello, Danielle Machado-Vieira, Alinne Gurjao de Oliveira, Dubravka Špoljaric Maronic, Filip Stevic, Tanja Žuna Pfeiffer, Itana Bokan Vucelic, Petar Žutinic, Marija Gligora Udovic, Anđelka Plenkovic-Moraj, Ludek Blaha, Rodan Geriš, Markéta Frankova, Kirsten Seestern Christoffersen, Trine Perlt Warming, Tõnu Feldmann, Alo Laas, Kristel Panksep, Lea Tuvikene, Kersti Kangro, Judita Koreiviene, Jurate Karosiene, Jurate Kasperoviciene, Ksenija Savadova-Ratkus, Irma Vitonyte, Kerstin Häggqvist, Pauliina Salmi, Lauri Arvola, Karl Rothhaupt, Christos Avagianos, Triantafyllos Kaloudis, Spyros Gkelis, Manthos Panou, Theodoros Triantis, Sevasti-Kiriaki Zervou, Anastasia Hiskia, Ulrike Obertegger, Adriano Boscaini, Giovanna Flaim, Nico Salmaso, Leonardo Cerasino, Sigrid Haande, Birger Skjelbred, Magdalena Grabowska, Maciej Karpowicz, Damian Chmura, Lidia Nawrocka, Justyna Kobos, Hanna Mazur-Marzec, Pablo Alcaraz-Parraga, Elżbieta Wilk-Wozniak, Wojciech Krzton, Edward Walusiak, Ilona Gagala-Borowska, Joana Mankiewicz-Boczek, Magdalena Toporowska, Barbara Pawlik-Skowronska, Michał Niedzwiecki, Wojciech Pęczuła, Agnieszka Napiorkowska-Krzebietke, Julita Dunalska, Justyna Sienska, Daniel Szymanski, Marek Kruk, Agnieszka Budzynska, Ryszard Goldyn, Anna Kozak, Joanna Rosinska, Elżbieta Szeląg-Wasielewska, Piotr Domek, Natalia Jakubowska-Krepska, Kinga Kwasizur, Beata Messyasz, Aleksandra Pełechata, Mariusz Pełechaty, Mikolaj Kokocinski, Beata Madrecka-Witkowska, Iwona Kostrzewska-Szlakowska, Magdalena Frąk, Agnieszka Bankowska-Sobczak, Michał Wasilewicz, Agnieszka Ochocka, Agnieszka Pasztaleniec, Iwona Jasser, Ana M. Antao-Geraldes, Manel Leira, Vitor Vasconcelos, Joao Morais, Micaela Vale, Pedro M. Raposeiro, Vítor Gonçalves, Boris Aleksovski, Svetislav Krstic, Hana Nemova, Iveta Drastichova, Lucia Chomova, Spela Remec-Rekar, Tina Elersek, Lars-Anders Hansson, Pablo Urrutia-Cordero, Andrea G. Bravo, Moritz Buck, William Colom-Montero, Kristiina Mustonen, Don Pierson, Yang Yang, Christine Edwards, Hannah Cromie, Jordi Delgado-Martín, David García, Jose Luís Cereijo, Joan Gomà, Mari Carmen Trapote, Teresa Vegas-Vilarrúbia, Biel Obrador, Ana García-Murcia, Monserrat Real, Elvira Romans, Jordi Noguero-Ribes, David Parreño Duque, Elísabeth Fernandez-Moran, Barbara Úbeda, José Angel Galvez, Núria Catalan, Carmen Pérez-Martínez, Eloísa Ramos-Rodríguez, Carmen Cillero-Castro, Enrique Moreno-Ostos, José María Blanco, Valeriano Rodríguez, Jorge Juan Montes-Pérez, Roberto L. Palomino, Estela Rodríguez-Pérez, Armand Hernandez, Rafael Carballeira, Antonio Camacho, Antonio Picazo, Carlos Rochera, Anna C. Santamans, Carmen Ferriol, Susana Romo, Juan Miguel Soria, Arda Özen, Tünay Karan, Nilsun Demir, Meryem Beklioglu, Nur Filiz, Eti Levi, Ugur Iskin, Gizem Bezirci, Ülkü Nihan Tavsanoglu, Kemal Çelik, Koray Ozhan, Nusret Karakaya, Mehmet Ali Turan Koçer, Mete Yilmaz, Faruk Maras¸lıoglu, Özden Fakioglu, Elif Neyran Soylu, Meral Apaydın Yagcı, Sakir Çınar, Kadir Çapkın, Abdulkadir Yagcı, Mehmet Cesur, Fuat Bilgin, Cafer Bulut, Rahmi Uysal, Köker Latife, Reyhan Akçaalan, Meriç Albay, Mehmet Tahir Alp, Korhan Özkan, Tugba Ongun Sevindik, Hatice Tunca, Burçin Önem, Hans Paerl, Cayelan C. Carey, Bastiaan W. Ibeling

The extent and variability of storm-induced temperature changes in lakes measured with long-term and high-frequency data

The intensity and frequency of storms are projected to increase in many regions of the world because of climate change. Storms can alter environmental conditions in many ecosystems. In lakes and reservoirs, storms can reduce epilimnetic temperatures from wind-induced mixing with colder hypolimnetic waters, direct precipitation to the lake's surface, and watershed runoff. We analyzed 18 long-term and high-frequency lake datasets from 11 countries to assess the magnitude of wind- vs. rainstorm-induced changes in epilimnetic temperature. We found small day-to-day epilimnetic temperature decreases in response to strong wind and heavy rain during stratified conditions. Day-to-day epilimnetic temperature decreased, on average, by 0.28 degrees C during the strongest windstorms (storm mean daily wind speed among lakes: 6.7 +/- 2.7 m s(-1), 1 SD) and by 0.15 degrees C after the heaviest rainstorms (storm mean daily rainfall: 21.3 +/- 9.0 mm). The largest decreases in epilimnetic temperature were observed >= 2 d after sustained strong wind or heavy rain (top 5(th) percentile of wind and rain events for each lake) in shallow and medium-depth lakes. The smallest decreases occurred in deep lakes. Epilimnetic temperature change from windstorms, but not rainstorms, was negatively correlated with maximum lake depth. However, even the largest storm-induced mean epilimnetic temperature decreases were typicallyPeer reviewe

Anoxia begets anoxia: a positive feedback to the deoxygenation of temperate lakes

Declining oxygen concentrations in the deep waters of lakes worldwide pose a pressing environmental and societal challenge. Existing theory suggests that low deep-water dissolved oxygen (DO) concentrations could trigger a positive feedback through which anoxia (i.e., very low DO) during a given summer begets increasingly severe occurrences of anoxia in following summers. Specifically, anoxic conditions can promote nutrient release from sediments, thereby stimulating phytoplankton growth, and subsequent phytoplankton decomposition can fuel heterotrophic respiration, resulting in increased spatial extent and duration of anoxia. However, while the individual relationships in this feedback are well established, to our knowledge, there has not been a systematic analysis within or across lakes that simultaneously demonstrates all of the mechanisms necessary to produce a positive feedback that reinforces anoxia. Here, we compiled data from 656 widespread temperate lakes and reservoirs to analyze the proposed anoxia begets anoxia feedback. Lakes in the dataset span a broad range of surface area (1–126,909 ha), maximum depth (6–370 m), and morphometry, with a median time-series duration of 30 years at each lake. Using linear mixed models, we found support for each of the positive feedback relationships between anoxia, phosphorus concentrations, chlorophyll a concentrations, and oxygen demand across the 656-lake dataset. Likewise, we found further support for these relationships by analyzing time-series data from individual lakes. Our results indicate that the strength of these feedback relationships may vary with lake-specific characteristics: For example, we found that surface phosphorus concentrations were more positively associated with chlorophyll a in high-phosphorus lakes, and oxygen demand had a stronger influence on the extent of anoxia in deep lakes. Taken together, these results support the existence of a positive feedback that could magnify the effects of climate change and other anthropogenic pressures driving the development of anoxia in lakes around the world

Global Patterns and Controls of Nutrient Immobilization On Decomposing Cellulose In Riverine Ecosystems

Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature

What makes a cyanobacterial bloom disappear? A review of the abiotic and biotic cyanobacterial bloom loss factors

Cyanobacterial blooms present substantial challenges to managers and threaten ecological and public health. Although the majority of cyanobacterial bloom research and management focuses on factors that control bloom initiation, duration, toxicity, and geographical extent, relatively little research focuses on the role of loss processes in blooms and how these processes are regulated. Here, we define a loss process in terms of population dynamics as any process that removes cells from a population, thereby decelerating or reducing the development and extent of blooms. We review abiotic (e.g., hydraulic flushing and oxidative stress/UV light) and biotic factors (e.g., allelopathic compounds, infections, grazing, and resting cells/programmed cell death) known to govern bloom loss. We found that the dominant loss processes depend on several system specific factors including cyanobacterial genera-specific traits, in situ physicochemical conditions, and the microbial, phytoplankton, and consumer community composition. We also address loss processes in the context of bloom management and discuss perspectives and challenges in predicting how a changing climate may directly and indirectly affect loss processes on blooms. A deeper understanding of bloom loss processes and their underlying mechanisms may help to mitigate the negative consequences of cyanobacterial blooms and improve current management strategies

Widespread deoxygenation of temperate lakes

The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity, nutrient biogeochemistry, greenhouse gas emissions, and the quality of drinking water. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world’s oceans and could threaten essential lake ecosystem services

A communal catalogue reveals Earth's multiscale microbial diversity

Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.Peer reviewe

A communal catalogue reveals Earth’s multiscale microbial diversity

Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth’s microbial diversity