Biogeochemical data from diel cycles in a turbid-water pond and a clear-water pond in Brussels

The dataset comprises one file containing geo-referenced information with corresponding timestamps. The names of the two ponds are written in French according to the official name defined by Brussels Environment (BE) (i.e. Leybeek and Silex). Field sampling Sampling was done every hour from a pontoon by collecting directly surface waters with 60ml polypropylene syringes for gases (CO2, CH4, N2O). Contents of the syringes were transferred with a silicone tube in 60 ml borosilicate serum bottles (Weathon) for CH4 and N2O, poisoned with 200 µl of a saturated solution of HgCl2, and sealed with a butyl stopper and crimped with aluminium cap, without a headspace for further analysis at home laboratory. CO2 measurements were carried out directly on the field with a Li-Cor Li-840 CO2/H2O gas analyser using the headspace technique by equilibrating four syringes with 30 mL of sample water and 30 mL of atmospheric air by vigorous shaking during 5 min (Borges et al., 2019). The Li-Cor Li-840 was calibrated before and after each cruise with ultrapure N2 and a suite of gas standards (Air Liquide Belgium) with CO2 mixing ratios of 388, 813, 3788 and 8300 ppm. The overall precision of pCO2 measurements was ±2.0%. Water temperature, specific conductivity, and %O2 were also measured every hour in-situ with VWR MU 6100H probe. 2L polyethylene containers were filled with water three to four times a day and processed at home laboratory for nutrients (soluble reactive phosphorus (SRP), ammonium (NH4+), nitrate (NO3-), and nitrite (NO2-)), chlorophyll-a (Chl-a) and total suspended matter (TSM). Meteorological data Meteorological data including hourly air temperature, rainfall, wind speed and atmospheric pressure were retrieved online from https://wow.meteo.be/en from the closest meteorological station of the two ponds (Institute of St-Lambert in Brussels, at 50.8408 °N, 4.4234 °E) located from 2.5km of Pêcheries pond and 5km from Silex pond. CH4 and N2O measurements by gas chromatography and δ13C-CH4 by cavity ring-down spectrometry Measurements of N2O and CH4 concentrations dissolved in water and in the gas were made with the headspace technique (20ml of ultra-pure N2, Air Liquid Belgium, Weiss, 1981) and a gas chromatograph (GC) (SRI 8610C) with a flame ionisation detector for CH4 and an electron capture detector for N2O calibrated with CO2:CH4:N2O:N2 gas mixtures (Air Liquide Belgium) with mixing ratios of 1, 10 and 30 ppm for CH4, 404, 1018, 3961 ppm for CO2, and 0.2, 2.0 and 6.0 ppm for N2O. The precision of measurement based on duplicate samples was ±3.9% for CH4 and ±3.2% for N2O. The δ13C-CH4 was measured in the headspace gas (20 ml of synthetic air, Air Liquid Belgium) equilibrated with the water sample (total volume 60 ml). The gas samples were diluted to achieve a final CH4 partial pressure below 10 ppm, aligning with the instrument's recommended operational concentration range. This prepared gas was then injected into a cavity ring-down spectrometer (G2201-I, Isotopic Analyzer, Picarro) equipped with a Small Sample Introduction Module 2 (SSIM, Picarro). The data were corrected using calibration curves of δ13C-CH4 as a function of concentration, based on two gas standards from Airgas Specialty Gases with certified δ13C-CH4 values of -23.9±0.3 ‰ and -69.0±0.3 ‰. Chlorophyll-a, total suspended matter, and dissolved inorganic nutrients Water was filtered through Whatman GF/F glass microfiber filters (porosity 0.7 µm) with a diameter of 47 mm for TSM and Chl-a determination. Chl-a was extracted from filters that were kept frozen before analysis (-20°C) with 90% acetone and concentrations was determined by fluorimetry (Kontron model SFM 25) (Yentsch and Menzel, 1963). Filters used for determination of TSM were pre-weighed before filtration and weighed after filtration of a known volume of water (after oven drying at 50°C). Filtered water was used for the determination of dissolved nutrients. NH4+ was measured by the nitroprusside-hypochlorite-phenol staining method (Grasshoff and Johannsen, 1972), NO2- and NO3- were measured before and after reduction of NO3- to NO2- by a cadmium-copper column, using the Griess acid reagent staining method (Grasshoff and Kremling, 2009), SRP was measured by the ammonium molybdate, ascorbic acid and potassium antimony tartrate staining method (Koroleff, 1983). References Borges AV, F Darchambeau, T Lambert, C Morana, G H Allen, E Tambwe, A Toengaho Sembaito, T Mambo, J Nlandu Wabakhangazi, J-P Descy, CR Teodoru, S Bouillon (2019) Variations in dissolved greenhouse gases (CO2, CH4, N2O) in the Congo River network overwhelmingly driven by fluvial-wetland connectivity, Biogeosciences, 16, 3801-3834. https://doi.org/10.5194/bg-16-3801-2019 Grasshoff, K., and Johannsen, H (1972). A new sensitive and direct method for the automatic determination of ammonia in sea water. ICES J. Mar. Sci. 34 (3), 516–521. https://doi.org/10.1093/icesjms/34.3.516. Grasshoff, K., Kremling, K., and Ehrhardt, M. (2009). Methods of Seawater Analysis: Determination of Nitrite. John Wiley & Sons. Koroleff, J. (1983). Determination of total phosphorus by alkaline persulphate oxidation. Methods of Seawater Analysis. Verlag Chemie, Wienheim, pp. 136–138. Weiss, R. F. (1981). Determinations of carbon dioxide and methane by dual catalyst flame ionization chromatography and nitrous oxide by electron capture chromatography. Journal of Chromatographic Science, 19(12), 611-616. doi.org/10.1093/chromsci/19.12.611 Yentsch, C. S., & Menzel, D. W. (1963). A method for the determination of phytoplankton chlorophyll and phaeophytin by fluorescence. In Deep Sea Research and Oceanographic Abstracts (Vol. 10, No. 3, pp. 221-231). Elsevier. https://doi.org/10.1016/0011-7471(63)90358-9本数据集包含1份文件，其中包含带对应时间戳的地理参考信息。两座池塘的名称采用布鲁塞尔环境署（Brussels Environment, BE）认定的官方法语名称，分别为Leybeek与Silex。 ## 野外采样 采样工作每小时开展一次，由浮筒平台直接采集表层水，以60mL聚丙烯注射器收集气体（CO₂、CH₄、N₂O）。将注射器内的样品通过硅胶管转移至60mL硼硅酸盐血清瓶（Weathon）中，用于CH₄与N₂O分析；向瓶内加入200μL饱和氯化汞（HgCl₂）溶液以抑制微生物活动，随后用丁基橡胶塞密封，并以铝盖压封，瓶内不留顶空，用于后续实验室分析。 CO₂浓度直接在野外采用Li-Cor Li-840型CO₂/H₂O气体分析仪进行测定，采用顶空平衡法：将4支注射器分别装入30mL水样与30mL大气，剧烈振荡5分钟以实现气液平衡（Borges等，2019）。每轮采样前后均使用超纯N₂及一系列CO₂体积分数分别为388、813、3788和8300ppm的气体标准品（Air Liquide Belgium）对Li-Cor Li-840进行校准。pCO₂测定的整体精度为±2.0%。同时每小时采用VWR MU 6100H型探头原位测定水温、比电导率及溶解氧百分比。 每日3~4次使用2L聚乙烯容器采集水样，运回实验室后用于测定营养盐：可溶性活性磷（soluble reactive phosphorus, SRP）、铵根（ammonium, NH₄⁺）、硝酸根（nitrate, NO₃⁻）、亚硝酸根（nitrite, NO₂⁻）、叶绿素a（chlorophyll-a, Chl-a）及总悬浮颗粒物（total suspended matter, TSM）。 ## 气象数据 气象数据包含逐小时气温、降雨量、风速及大气压强，从https://wow.meteo.be/en在线获取，数据来源于两座池塘附近的气象站——布鲁塞尔圣朗贝尔研究所气象站（坐标50.8408°N，4.4234°E），该站距离Pêcheries池塘约2.5km，距离Silex池塘约5km。 ## 气相色谱法测定CH₄与N₂O浓度及腔环降光谱法测定δ¹³C-CH₄ 采用顶空法（通入20mL超纯N₂，Air Liquide Belgium，Weiss，1981）结合气相色谱仪（GC）SRI 8610C测定水体及气相中溶解的N₂O与CH₄浓度：该气相色谱配备火焰离子化检测器用于CH₄检测，电子捕获检测器用于N₂O检测，使用CO₂:CH₄:N₂O:N₂混合气体标准品（Air Liquide Belgium）进行校准，其中CH₄体积分数分别为1、10和30ppm，CO₂为404、1018和3961ppm，N₂O为0.2、2.0和6.0ppm。基于平行样品的测定精度为：CH₄±3.9%，N₂O±3.2%。 δ¹³C-CH₄的测定采用与水样（总体积60mL）平衡后的顶空气体完成，顶空气体为20mL合成空气（Air Liquide Belgium）。将气体样品稀释至CH₄分压低于10ppm，以符合仪器推荐的操作浓度范围。随后将制备好的气体注入配备小体积进样模块2（Small Sample Introduction Module 2, SSIM）的腔环降光谱仪（G2201-I型同位素分析仪，Picarro）中进行分析。基于Airgas Specialty Gases提供的两种标准气体（其认证δ¹³C-CH₄值分别为-23.9±0.3‰和-69.0±0.3‰），建立δ¹³C-CH₄随浓度变化的校准曲线，对测定数据进行校正。 ## 叶绿素a、总悬浮颗粒物及溶解态无机营养盐测定 测定TSM与Chl-a时，将水样通过直径47mm的Whatman GF/F型玻璃微纤维滤膜（孔径0.7μm）过滤。Chl-a从滤膜中提取：滤膜在分析前需保存于-20℃冷冻环境，采用90%丙酮进行萃取，通过荧光光度法（Kontron SFM 25型仪器）测定浓度（Yentsch和Menzel，1963）。用于TSM测定的滤膜需在过滤前预称重，过滤已知体积的水样后，在50℃烘箱中烘干并再次称重。过滤后的水样用于溶解态营养盐的测定：NH₄⁺采用硝普钠-次氯酸钠-苯酚显色法测定（Grasshoff和Johannsen，1972）；NO₂⁻与NO₃⁻采用格里斯试剂显色法测定，其中NO₃⁻需先通过镉铜柱还原为NO₂⁻（Grasshoff和Kremling，2009）；SRP采用钼酸铵-抗坏血酸-酒石酸锑钾显色法测定（Koroleff，1983）。 ## 参考文献 1. Borges AV, F Darchambeau, T Lambert, C Morana, G H Allen, E Tambwe, A Toengaho Sembaito, T Mambo, J Nlandu Wabakhangazi, J-P Descy, CR Teodoru, S Bouillon. 刚果河网络中溶解态温室气体（CO₂、CH₄、N₂O）的变化主要受河流-湿地连通性驱动. 生物地球科学, 2019, 16: 3801-3834. https://doi.org/10.5194/bg-16-3801-2019 2. Grasshoff K, Johannsen H. 一种灵敏直接的海水氨自动测定新方法. ICES海洋科学杂志, 1972, 34(3): 516-521. https://doi.org/10.1093/icesjms/34.3.516 3. Grasshoff K, Kremling K, Ehrhardt M. 海水分析方法：亚硝酸盐的测定. 约翰威立国际出版公司, 2009. 4. Koroleff J. 碱性过硫酸盐氧化法测定总磷. 海水分析方法. 维也纳海姆出版社, 1983: 136-138. 5. Weiss RF. 双催化剂火焰离子化色谱法测定二氧化碳与甲烷，电子捕获色谱法测定一氧化二氮. 色谱科学杂志, 1981, 19(12): 611-616. https://doi.org/10.1093/chromsci/19.12.611 6. Yentsch CS, Menzel DW. 荧光法测定浮游植物叶绿素与脱镁叶绿素. 深海研究与海洋学文摘, 1963, 10(3): 221-231. https://doi.org/10.1016/0011-7471(63)90358-9