Beschreibung: N2O production rates from ammonium, nitrite and nitrate and nitrate reduction rates and ammonium oxidation rates from the top 400 m water depth off the coast of Peru sampled from R/V Meteor during M138 in June 2017.

Beschreibung: Simultaneous fluxes of CO2, CH4 and N2O in twelve reservoirs in Southern Spain during the stratification period and the mixing period were measured using a Picarro G2508 gas analyzer connected to a floating chamber. For each reservoir in each sampling period, we took 3-5 measurements for 40 min. We calculated the daily (from 10 am to 4 pm) average (mean) and the standard error (SE) from these measurements. Flux calculations were based on Zhao et al (2015). To obtain the reservoir radiative forcings we summed the corresponding forcing due to CO2 emissions, the warming potential (GWP) of CH4 in terms of CO2 equivalents, and the warming potential of N2O in terms of CO2 equivalents. We used 34 to convert CH4 in CO2 equivalent and 298 to convert N2O in CO2 equivalent in a 100-year time horizon, including the climate-carbon feedbacks (IPCC 2013). We measured ambient temperature, barometric pressure (HANNA HI 9828), and wind speed (MASTECH MS6252A) at the beginning of each flux measurement. We recorded dissolved oxygen concentration and water temperature using a miniDOT (PME) submersible water logger during the stratification period, and calculated the lake metabolism (i.e., gross primary production, net production and respiration rate) according to Staehr et al (2010).

Beschreibung: 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.

Beschreibung: We sampled twice 12 reservoirs between July 2016 and August 2017 in southern Spain during the summer stratification and the winter mixing. We determined reservoir area, perimeter, and capacity using the next 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 volume (m3) divided by its surface area (m2) will yield the mean depth (m). We also calculated the shoreline development ratio (DL) (Aronow, 1982) and the shallowness index (1/m) by dividing the shoreline development index (DL) by the mean depth (m). We performed the vertical geochemical profiles of the reservoirs using a Seabird 19plus CTD profiler and obtained the measurements of temperature and dissolved oxygen. We collected samples at different depths for dissolved CH4 analysis in air-tight Winkler bottles by duplicate, preserved with a solution of HgCl2 (final concentration 1mM) to inhibit biological activity and sealed with Apiezon® grease to prevent gas exchange. We measured dissolved CH4 using headspace equilibration and gas chromatography (2-3 replicates per bottle). We measured DIC, DOC, TN, and TDN by high–temperature catalytic oxidation using a Shimadzu total organic carbon analyzer (Model TOC-V CSH) coupled to nitrogen analyzer (TNM-1). We determined the NO3 concentration using the ultraviolet spectrophotometric method, using a Perkin Elmer UV-Lambda 40 spectrophotometer at wavelengths of 220 nm and correcting for DOC absorbance at 275 nm (APHA, 1992). We measured NH4 and NO2 concentrations by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Dissolved inorganic nitrogen (DIN) is the addition of the NO3, NH4, and NO2 concentrations. We measured total phosphorus (TP) concentration by triplicate using the molybdenum blue method (Murphy and Riley, 1962) after digestion with a mixture of potassium persulphate and boric acid at 120 °C for 30 min (APHA, 1992). We determined chlorophyll-a concentration by extracting the pigments from filters with 95% methanol in the dark at 4 °C for 24 h (APHA, 1992). We measured chlorophyll-a (Chl-a) absorption using a Perkin Elmer UV-Lambda 40 spectrophotometer at the wavelength of 665 nm and for scattering correction at 750 nm. . To obtain the integrated mean of chlorophyll-a (μg Chl-a /l), from the discrete points along the water column, we used the trapezoidal rule (León-Palmero et al., 2019). To obtain the cumulative chlorophyll-a concentration in the whole water column (mg Chl-a/m2), we summed the concentration of chlorophyll-a from each stratum using the trapezoidal rule, as we did for the integrated chlorophyll-a before, but we omitted the division between the maximum depth. We determined the abundances of cyanobacteria and photosynthetic picoeukaryotes using flow cytometry (FACScalibur) using unfiltered water.

Beschreibung: We estimated gross primary production (GPP), net ecosystem production (NEP), and ecosystem respiration (R) by measuring temporal changes in dissolved oxygen concentration and temperature using a miniDOT (PME) submersible water logger during the stratification period. We used the equations proposed by Staehr et al. (2010) to calculate GPP, NEP, and R.

Beschreibung: 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.