Understanding the fluxes of greenhouse gases in reservoirs under the inspiration of Margalef

Reservoirs are significant sources of greenhouse gases (GHG), such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), to the atmosphere. These systems receive and metabolize a larger amount of organic and inorganic carbon and nitrogen from their watersheds than lakes, resulting in the production of CO2, CH4 and N2O. Despite their global relevance, there are still important uncertainties regarding the magnitude, variability and drivers of their emissions that undermine global estimates. Therefore, a comprehensive understanding of the origin of these emissions is required. Here, I investigate the fluxes of CO2, CH4 and N2O and their concentrations in the water column of twelve Mediterranean reservoirs during the stratification and mixing periods to discern the main pathways involved in their production and the spatial and seasonal variability among these gases and their emissions and radiative forcing. Finally, I provide a theorical framework to understand GHG emissions as a response of reservoirs to eutrophication and external forcing. I integrate Margalef’s ideas about how eutrophication perturbs the biogeochemistry of inland waters with the main findings of my previous work to analyze how the C, N and P inputs from reservoir watersheds modify the biogeochemical cycling of C, N, P and O, and determine the production and emission of CO2, CH4, and N2O. This perturbation effect is especially notable for CH4, and N2O emissions, which increase significantly in eutrophic waters, even exceeding the climate forcing of CO2. Therefore, emission of GHG should be seen as part of the reservoir response to the external forcing that displaces a fraction of the materials to the atmospheric boundaryMinisterio de Economía y Competitividad (HERA project, grant no. CGL2014-52362-R)The Ministerio de Ciencia, Innovación y Universidades (CRONOS project, RTI2018- 098849-B-I00) of SpainPhD fellowship from the Ministerio de Educación, Cultura y Deporte of Spain (grant nos. FPU014/02917)CRONOS project at the University of Granada, and later from Danmarks Frie Forskningsfond (DFF, 1026-00428B) at the University of Southern DenmarkIberian Association of Limnology (AIL) for the award to the best Iberian thesis in the field of limnology 2021SIBECOL-AIL congres

P inputs determine denitrifier abundance explaining dissolved nitrous oxide in reservoirs

This research was supported by the Ministerio de Economía y Competitividad (HERA project, grant no. CGL2014‐52362‐R), and the Ministerio de Ciencia, Innovación y Universidades (CRONOS project, RTI2018‐098849‐B‐I00) of Spain to IR and RM‐B. Elizabeth León‐Palmero was supported by a PhD fellowship from the Ministerio de Educación, Cultura y Deporte of Spain (grant nos. FPU014/02917), and a postdoctoral contract from CRONOS project, and later from Danmarks Frie Forskningsfond (DFF, 1026‐00428B) at SDU. This manuscript was improved through feedback from an anonymous reviewer, and Dr. Van Meter. Universidad de Granada/CBUA funded the open access of this article.Reservoirs are important sites for nitrogen processing, especially those located in agricultural and urban watersheds. Nitrogen inputs promote N2O production and emission, but the microbial pathways controlling N2O have been seldom studied in reservoir water columns. We determined N2O concentration in the water column of 12 reservoirs during the summer stratification and winter mixing. We explored the potential microbial sources and sinks of N2O by quantifying key genes involved in ammonia oxidation (bacterial and archaeal amoA) and denitrification (nirS and nosZ). Dissolved N2O varied up to three orders of magnitude (4.7–2441.2 nmol L−1) across systems, from undersaturated to supersaturated values (37%–24,174%) depending on reservoirs and depths. N2O concentration depended on nitrogen and oxygen availabilities, with the lowest and highest N2O values at suboxic conditions. Ammonia-oxidizing archaea dominated over ammonia-oxidizing bacteria but were not related to the dissolved N2O. In contrast, the abundance of the nirS gene was significantly related to N2O concentration, and three orders of magnitude higher than amoA abundance. Denitrifying bacteria appeared consistently in the water column of all reservoirs. The nirS and nosZ genes appeared in oxic and suboxic waters, but they were more abundant in suboxic waters. The nitrate concentration, and nirS and nosZ relative abundances explained the dissolved N2O. Besides, nirS abundance was related positively with total phosphorus and cumulative chlorophyll a, a proxy for fresh organic matter. Therefore, P inputs, not just N inputs, promoted N2O production by denitrification in the water column of reservoirs.Danmarks Frie Forskningsfond 1026‐00428BMinisterio de Ciencia, Innovación y Universidades RTI2018‐098849‐B‐I00Ministerio de Economía y Competitividad CGL2014‐52362‐RMinisterio de Educación, Cultura y Deporte of Spain FPU014/02917SDUUniversidad de Granada/CBU

Greenhouse gas fluxes from reservoirs determined by watershed lithology, morphometry, and anthropogenic pressure

EL-P was supported by a PhD fellowship FPU (Formación del Profesorado Universitario: 014/02917) from the Ministry of Education, Culture y Sports. This research was also funded by the Consejería de Economía, Conocimiento, Empresas y Universidad and European Regional Development Fund (ERDF), ref. SOMM17/6109/UGR. We specially thank to Jesús Forja, Teodora Ortega and Ana Sierra for helping with gas chromatography analysis and Eulogio Corral Arredondo for sampling support.Human population growth has increased the demand for water and clean energy, leading to the massive construction of reservoirs. Reservoirs can emit greenhouse gases (GHG) affecting the atmospheric radiative budget. The radiative forcing due to CO2, CH4, and N2O emissions and the relative contribution of each GHG in terms of CO2 equivalents to the total forcing is practically unknown. We determined simultaneously the CO2, CH4, and N2O fluxes in reservoirs from diverse watersheds and under variable human pressure to cover the vast idiosyncrasy of temperate Mediterranean reservoirs. We obtained that GHG fluxes ranged more than three orders of magnitude. The reservoirs were sources of CO2 and N2O when the watershed lithology was mostly calcareous, and the crops and the urban areas dominated the landscape. By contrast, reservoirs were sinks of CO2 and N2O when the watershed lithology was predominantly siliceous, and the landscape had more than 40% of forestal coverage. All reservoirs were sources of CH4, and emissions were determined mostly by reservoir mean depth and water temperature. The radiative forcing was substantially higher during the stratification than during the mixing. During the stratification the radiative forcings ranged from 125 mg CO2 equivalents m−2 d−1 to 31 884 mg CO2 equivalents m−2 d−1 and were dominated by the CH4 emissions; whereas during the mixing the radiative forcings ranged from 29 mg CO2 equivalents m−2 d−1 to 722 mg CO2 equivalents m−2 d−1 and were dominated by CO2 emissions. The N2O contribution to the radiative forcing was minor except in one reservoir with a landscape dominated by crops and urban areas. Future construction of reservoirs should consider that siliceous bedrocks, forestal landscapes, and deep canyons could minimize their radiative forcings.This research was funded by the project HERA (CGL2014-52362-R) and CRONOS (RTI2018-098849-B-I00) to IR and RM-B of the Spanish Ministry of Economy and Competitiveness and Spanish Ministry of Science, Innovation, and Universities, and the Modeling Nature Scientific Unit (UCE.PP2017.03) to IR co-financed with FEDER funds

Dissolved CH4 coupled to photosynthetic picoeukaryotes in oxic waters and to cumulative chlorophyll a in anoxic waters of reservoirs

Methane (CH4) emissions from reservoirs are responsible for most of the atmospheric climatic forcing of these aquatic ecosystems, comparable to emissions from paddies or biomass burning. Primarily, CH4 is produced during the anaerobic mineralization of organic carbon in anoxic sediments by methanogenic archaea. However, the origin of the recurrent and ubiquitous CH4 supersaturation in oxic waters (i.e., the methane paradox) is still controversial. Here, we determined the dissolved CH4 concentration in the water column of 12 reservoirs during summer stratification and winter mixing to explore CH4 sources in oxic waters. Reservoir sizes ranged from 1.18 to 26.13 km(2). We found that dissolved CH4 in the water column varied by up to 4 orders of magnitude (0.02-213.64 mu mol L-1), and all oxic depths were consistently supersaturated in both periods. Phytoplanktonic sources appear to determine the concentration of CH4 in these reservoirs primarily. In anoxic waters, the depth-cumulative chlorophyll a concentration, a proxy for the phytoplanktonic biomass exported to sediments, was correlated to CH4 concentration. In oxic waters, the photosynthetic picoeukaryotes' abundance was significantly correlated to the dissolved CH4 concentration during both the stratification and the mixing. The mean depth of the reservoirs, as a surrogate of the vertical CH4 transport from sediment to the oxic waters, also contributed notably to the CH4 concentration in oxic waters. Our findings suggest that photosynthetic picoeukaryotes can play a significant role in determining CH4 concentration in oxic waters, although their role as CH4 sources to explain the methane paradox has been poorly explored

Diversity and antimicrobial potential in sea anemone and holothurian microbiomes

Marine invertebrates, as holobionts, contain symbiotic bacteria that coevolve and develop antimicrobial substances. These symbiotic bacteria are an underexplored source of new bioactive molecules to face the emerging antibiotic resistance in pathogens. Here, we explored the antimicrobial activity of bacteria retrieved from the microbiota of two sea anemones (Anemonia sulcata, Actinia equina) and two holothurians (Holothuria tubulosa, Holothuria forskali). We tested the antimicrobial activity of the isolated bacteria against pathogens with interest for human health, agriculture and aquaculture. We isolated 27 strains with antibacterial activity and 12 of these isolates also showed antifungal activity. We taxonomically identified these strains being Bacillus and Vibrio species the most representative producers of antimicrobial substances. Microbiome species composition of the two sea anemones was similar between them but differed substantially of seawater bacteria. In contrast, microbiome species composition of the two holothurian species was different between them and in comparison with the bacteria in holothurian feces and seawater. In all the holobiont microbiomes Bacteroidetes was the predominant phylum. For each microbiome, we determined diversity and the rank-abundance dominance using five fitted models (null, preemption, log-Normal, Zipf and Zipf-Mandelbrot). The models with less evenness (i.e. Zipf and Zipf-Mandelblot) showed the best fits in all the microbiomes. Finally, we tracked (using the V4 hypervariable region of 16S rRNA gene) the relative abundance of these 27 isolates with antibacterial activity in the total pool of sequences obtained for the microbiome of each holobiont. Coincidences, although with extremely low frequencies, were detected only in the microbiome of H. forskali. This fact suggests that these isolated bacteria belong to the long tail of rare symbiotic bacteria. Therefore, more and more sophisticated culture techniques are necessary to explore this apparently vast pool of rare symbiontic bacteria and to determine their biotechnological potentiality.This work was supported by Campus de Excelencia Internacional BIOTIC (CEI Biotic) Universidad de Granada, http://biotic.ugr.es, Grant PBS46. iMare Natural S.L. provided support in the form of salaries for author PAA, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the `author contributions' section

Warming and CO2 effects under oligotrophication on temperate phytoplankton 2 communities

Eutrophication, global warming, and rising carbon dioxide (CO2) levels are the three most prevalent pressures impacting the biosphere. Despite their individual effects are well-known, it remains untested how oligotrophication (i.e. nutrients reduction) can alter the planktonic community responses to warming and elevated CO2 levels. Here, we performed an indoor mesocosm experiment to investigate the warming×CO2 interaction under a nutrient reduction scenario (40%) mediated by an in-lake management strategy (i.e. addition of a commercial solid-phase phosphorus sorbent - Phoslock®) on a natural freshwater plankton community. Biomass production increased under warming×CO2 relative to present-day conditions; however, a Phoslock® -mediated oligotrophication reduced such values by 30-70%. Conversely, the warming×CO2×oligotrophication interaction stimulated the photosynthesis by 20% compared to ambient nutrient conditions, and matched with higher resource use efficiency (RUE) and nutrient demand. Surprisingly, at a group level, we found that the multi-stressors scenario increased the photosynthesis in eukaryotes by 25%, but greatly impaired in cyanobacteria (ca. -25%). This higher cyanobacterial sensitivity was coupled with a reduced light harvesting efficiency and compensation point. Since Phoslock® -induced oligotrophication unmasked a strong negative warming×CO2 effect on cyanobacteria, it becomes crucial to understand how the interplay between climate change and nutrient abatement actions may alter the, ecosystems functioning. With an integrative understanding of these processes, policy makers will design more appropriate management strategies to improve the ecological status of aquatic ecosystems without compromising their ecological attributes and functioning

Warming and CO2 effects under oligotrophication on temperate phytoplankton 2 communities

Eutrophication, global warming, and rising carbon dioxide (CO2) levels are the three most prevalent pressures impacting the biosphere. Despite their individual effects are well-known, it remains untested how oligotrophication (i.e. nutrients reduction) can alter the planktonic community responses to warming and elevated CO2 levels. Here, we performed an indoor mesocosm experiment to investigate the warming×CO2 interaction under a nutrient reduction scenario (40%) mediated by an in-lake management strategy (i.e. addition of a commercial solid-phase phosphorus sorbent - Phoslock®) on a natural freshwater plankton community. Biomass production increased under warming×CO2 relative to present-day conditions; however, a Phoslock® -mediated oligotrophication reduced such values by 30-70%. Conversely, the warming×CO2×oligotrophication interaction stimulated the photosynthesis by 20% compared to ambient nutrient conditions, and matched with higher resource use efficiency (RUE) and nutrient demand. Surprisingly, at a group level, we found that the multi-stressors scenario increased the photosynthesis in eukaryotes by 25%, but greatly impaired in cyanobacteria (ca. -25%). This higher cyanobacterial sensitivity was coupled with a reduced light harvesting efficiency and compensation point. Since Phoslock® -induced oligotrophication unmasked a strong negative warming×CO2 effect on cyanobacteria, it becomes crucial to understand how the interplay between climate change and nutrient abatement actions may alter the, ecosystems functioning. With an integrative understanding of these processes, policy makers will design more appropriate management strategies to improve the ecological status of aquatic ecosystems without compromising their ecological attributes and functioning

Greenhouse gases in reservoirs: from watersheds to functional genes

En general, esta tesis doctoral ha contribuido al inventario global de los flujos de GEI de los embalses del bioma mediterráneo, mostrando la gran variabilidad entre sistemas, entre estaciones y diaria de los flujos, que debe considerarse en las estimaciones de GEI a escala global. Nuestros resultados también indican que la futura construcción de embalses puede reducir su forzamiento radiativo mediante la selección de ubicaciones óptimas en cuencas de roca silícea, en paisajes forestales y cañones profundos. Demostramos que la eutrofización promueve la producción de metano y óxido nitroso y, por lo tanto, aumenta el forzamiento radiativo de los embalses. Por lo tanto, la reducción de la entrada de N y P a las aguas continentales podría prevenir la degradación de los recursos hídricos y reducir las emisiones de GEI de los embalses ya construidos.Overall, this dissertation contributed to the global inventory of GHG fluxes from reservoirs in the Mediterranean biome, and we showed the great variability at inter-system, inter-season, and daily scales of the fluxes, which must be considered in GHG estimates at global scale. Our results also indicate that future construction of reservoirs may reduce their radiative forcing by selecting optimal locations with siliceous bedrock, in forestal landscapes, and deep canyons. We demonstrated that eutrophication promotes the production of methane and nitrous oxide, and, therefore, increases the radiative forcing of the reservoirs. Thus, the reduction of N and P loading into inland waters may prevent water resources degradation, and reduce the GHG emissions from the already constructed reservoirs.Tesis Univ. Granada.Project HERA (CGL2014-52362-R) to I.Reche and R. Morales-Baquero of the Spanish Ministry of Economy and Competitiveness, the Modeling Nature Scientific Unit (UCE.PP2017.03) of the Universidad de Granada – Unidades de Excelencia to I. RecheEuropean Regional Development Fund (ERDF; grant no. SOMM17/6109/UGR). E. León Palmero was supported by a PhD fellowship FPU (Formación del Profesorado Universitario: 014/02917) from the Ministry of Education, Culture y Sport

Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru

Data availability. The microarray data presented here are available via GEO (Gene Expression Omnibus; http://www.ncbi.nlm.nih.gov/ geo/, NCBI, 2020) at NCBI (National Center for Biotechnology Information) under GEO accession no GSE142806. The N2O production rates were archived in the PANGAEA data archive (https: //doi.pangaea.de/10.1594/PANGAEA.914948, Frey et al., 2020). The N2O data are available from the Marine Methane and Nitrous Oxide (MEMENTO) database (https://memento.geomar.de/de/n2o, last access: 16 April 2020; Kock and Bange, 2015).Supplement. The supplement related to this article is available online at: https://doi.org/10.5194/bg-17-2263-2020-supplement.Oxygen-deficient zones (ODZs) are major sites of net natural nitrous oxide (N2O) production and emissions. In order to understand changes in the magnitude of N2O production in response to global change, knowledge on the individual contributions of the major microbial pathways (nitrification and denitrification) to N2O production and their regulation is needed. In the ODZ in the coastal area off Peru, the sensitivity of N2O production to oxygen and organic matter was investigated using 15N tracer experiments in combination with quantitative PCR (qPCR) and microarray analysis of total and active functional genes targeting archaeal amoA and nirS as marker genes for nitrification and denitrification, respectively. Denitrification was responsible for the highest N2O production with a mean of 8.7 nmol L−1 d−1 but up to 118±27.8 nmol L−1 d−1 just below the oxic–anoxic interface. The highest N2O production from ammonium oxidation (AO) of 0.16±0.003 nmol L−1 d−1 occurred in the upper oxycline at O2 concentrations of 10–30 µmol L−1 which coincided with the highest archaeal amoA transcripts/genes. Hybrid N2O formation (i.e., N2O with one N atom from NH+4 and the other from other substrates such as NO−2) was the dominant species, comprising 70 %–85 % of total produced N2O from NH+4, regardless of the ammonium oxidation rate or O2 concentrations. Oxygen responses of N2O production varied with substrate, but production and yields were generally highest below 10 µmol L−1 O2. Particulate organic matter additions increased N2O production by denitrification up to 5-fold, suggesting increased N2O production during times of high particulate organic matter export. High N2O yields of 2.1 % from AO were measured, but the overall contribution by AO to N2O production was still an order of magnitude lower than that of denitrification. Hence, these findings show that denitrification is the most important N2O production process in low-oxygen conditions fueled by organic carbon supply, which implies a positive feedback of the total oceanic N2O sources in response to increasing oceanic deoxygenation.German Research Foundation (DFG) SFB754Deutscher Akademischer Austausch Dienst (DAAD) 57350888China Scholarship Council 201406330054Universidad de GranadaEuropean Union (EU) 704272Villum Foundation 16518National Science Foundation (NSF) OCE-1657663Spanish Government 014/0291

Location, morphometry, lithology and land-use in the watersheds of reservoirs in Southern Spain

We collected data of reservoir area, capacity, age, and location from open databases: Infraestructura de Datos Espaciales de Andalucía (IDEAndalucia; http://www.ideandalucia.es/portal/web/ideandalucia/) and the Ministerio para la Transición Ecológica (https://www.embalses.net/). The reservoir capacity (m3) divided by its surface area (m2) will yield the mean depth (m). We obtained the lithology and land-use maps using ArcGIS® 10.2 software (ESRI 2012) under the Universidad de Granada license. First, we delimited the watershed of each reservoir using the rivers and hydrographical demarcations, and, second, we calculated the area for each different type of lithology and land-use within watersheds. We used the databases: Infraestructura de Datos Espaciales (IDE) from the Ministerio de Agricultura, Pesca y Alimentación (MAPA; https://www.mapa.gob.es/es/cartografia-y-sig/ide/default.aspx); the Infraestructura de Datos Espaciales de Andalucía(IDEAndalucia; http://www.ideandalucia.es/portal/web/ideandalucia/); the Instituto Geológico y Minero de España (IGME; http://www.igme.es/default.asp); the Confederación Hidrográfica del Segura (CHSEGURA; https://www.chsegura.es/chs/); and The Junta de Comunidades de Castilla-La Mancha (IDE-JCCM; https://castillalamancha.maps.arcgis.com/home/index.html). We defined the next categories: water-covered area; carbonate-rich rocks; limestones, marls, and dolomites; gravels, conglomerates, sands and silts; and non-calcareous rocks. The soils with high capacity to solubilize dissolved inorganic carbon are carbonate-rich rocks and limestones, marls, and dolomites. In contrast, non-calcareous rocks include igneous rocks like basalt and metamorphic rocks like marble, schist, quartzite, phyllite, gneiss, and slate have less capacity to leach dissolved inorganic carbon. The land-use categories were: crops, forest, urban, treeless area, and water covered area. The forestry area includes trees, plantation trees, sparse trees, and dispersed trees