利用岩体和 n 2o 微传感器估计沉积物脱氮率
Summary
该方法利用乙炔抑制技术和累积的 n-o 的微传感器测量, 估计沉积物岩心中的沉积物反硝化率。该协议描述了收集核心、校准传感器、抑制乙炔、测量 n 2o 积累和计算反硝化率的程序。
Abstract
脱氮是从生物圈中去除活性氮的主要生物地球化学过程。对这一过程的定量评价对于评估人类年龄改变的全球氮循环和温室气体 (即n2o) 的排放尤其重要。有几种方法可用于测量反硝化, 但都不能完全令人满意。现有方法的问题包括灵敏度不足, 以及需要使用扰动样品修改基板水平或改变工艺的物理配置。本工作介绍了一种估算沉积物反硝化率的方法, 该方法结合了取心、乙炔抑制和累积的 n-o 的微传感器测量。该方法的主要优点是对沉积物结构的干扰较小, 并收集了 n2o积累的连续记录;这些使可靠的反硝化率的估计, 最小值高达 0.4μmoln 2o-2-1. 操纵关键因素的能力是获得实验洞察的另一个优势。该协议描述了收集核心、校准传感器、抑制乙炔、测量 n 2o 积累和计算反硝化率的程序。该方法适用于估算任何具有可回收沉积物岩心的水生系统的反硝化率。如果 n2o浓度高于传感器的检测极限, 则可以省略乙炔抑制步骤来估计 n2o排放量, 而不是反硝化。我们展示了如何通过增加硝酸盐的可用性以及过程的温度依赖性来估计实际和潜在的反硝化率。阐述了利用山湖沉积物的工艺, 并讨论了该技术与其他方法相比的优缺点。此方法可以为特定目的进行修改;例如, 它可以与15个n 个示踪剂结合起来, 以评估硝化和反硝化或现场的反硝化率测量。
Introduction
氮循环的人为改变是地球系统1最具挑战性的问题之一。人类活动使生物圈2的活性氮水平至少增加了一倍。然而, 在如何评价全球 n 周期方面仍然存在很大的不确定性。一些通量估计已被量化, 误差小于±20%, 许多具有±50% 和更大的 3倍的不确定性。这些不确定因素表明, 需要准确估计整个生态系统的反硝化率, 并了解潜在的变化机制。脱氮是一种微生物活性, 通过这种活性, 氧化氮, 主要是硝酸盐和亚硝酸盐, 还原为二氮、n2o 和 n24.该途径与活性氮的生物圈供应高度相关, 因为它是去除5的主要过程.n2o 是一种温室气体, 其升温潜能值是100年来二氧化碳的近 300倍, 是目前平流层臭氧消耗的主要原因, 其排放量为6,7.
在下面, 我们提出了一个协议, 用于估计沉积物反硝化率使用岩心和n 2o 微传感器实验 (图 1)。反硝化率是使用乙炔抑制方法8、9和测量在规定时间段内积累的氮2o(图 2和图 3)。我们通过将其应用于山湖沉积物来证明该方法。本案例研究突出了在对沉积物物理结构干扰最小的情况下检测相对较低速率的方法的性能。
反硝化特别难以测量10。有几种替代方法和方法, 每种方法都有优点和缺点。对现有方法的缺点包括使用昂贵的资源、灵敏度不足以及需要使用受干扰的样本修改基板水平或改变过程的物理配置10.测量n2 的一个更根本的挑战是它在环境中的背景水平升高10。乙炔 (c2h2)8、9抑制了 n2o至n2 的还原.因此, 反硝化可以通过测量在 c2h2 存在下的累积 n2o来量化, 这是可行的, 因为环境氮2o 水平较低。
大约40年前 11年, 利用 c2h2 测量沉积物中的反硝化率, 12年后大约12年后, 氮-2o传感器的加入发生. 应用最广泛的乙炔方法是 “静态核心”。在将 c2h2 添加到密封沉积物岩心10的头部空间后, 在长达 24小时的潜伏期内测量累积的氮2o.此处描述的方法遵循此过程和一些创新。我们通过在核心的水相中冒泡气体几分钟来加入 c2h2, 然后用微传感器测量 n2o的积累, 然后用样品水填充所有的头部空间.我们还包括一个搅拌系统, 防止在不重新悬浮沉积物的情况下对水进行分层。该程序量化了每个沉积物表面积的反硝化率 (例如, μmoln 2o-2 h-1 ).
反硝化的高时空变化给反硝化的准确量化带来了另一个困难10。通常情况下, 在孵化过程中采集的前空间样品的气相色谱法可按顺序测量 n 2o 积累。所述方法改进了对 n2o积累的时间变化的监测, 因为微传感器提供了一个连续的信号。微传感器万用表是一种数字微传感器放大器 (皮安计), 与传感器和计算机接口 (图 1a)。万用表允许同时使用多个n2o 微传感器。例如, 可以同时测量同一研究地点最多四个沉积物岩心, 以考虑到空间的变异性。
与其他一些方法 (如泥浆) 相比, 岩心方法几乎不会干扰沉积物结构。如果改变沉积物的完整性, 这将导致不现实的反硝化率 13,这只足以进行相对比较。与岩心方法14相比, 浆料法总是得到较高的速率, 因为后者保留了基板扩散15反硝化的局限性。泥浆措施不能被视为就地率16的代表;它们为与完全相同的程序进行比较提供了相对的措施。
所述方法适用于估算任何可以被岩心的沉积物类型的反硝化速率。我们特别推荐一些驱动因素的实验操作方法。例如, 根据估计反硝化17的能量活化 (e a) 所需的需要修改硝酸盐的可用性和温度的实验 (图 2).
图 1: 实验设置.(a) 利用岩心和 n2o 微传感器估计沉积物反硝化率的一般实验设置。孵化器可确保黑暗和控制温度 (±0.3°c) 的条件。五个完整的沉积物岩心可以使用各自的 n2o传感器同时处理。(b)n2o传感器校准室。我们用橡胶塞子和注射器将其与 n2o水混合 (参见协议步骤 3.4.3)。有一个温度计来控制水温。(c) 将沉积物芯样品特写, 将传感器插入 pvc 盖的中央孔, 用胶带密封接头。搅拌器悬挂在水中, 电磁铁靠近它, 并固定在丙烯酸管的外部部分。(d) 由金属片保护的 n2o微传感器尖端的特写镜头。(e) 刚刚回收的沉积物岩心。它是从深湖中的一条船上取样的;核心的丙烯酸管仍然固定在送声机适应的重力取样器19上。有关执行此方法所需的所有项, 请参阅材料表。请点击这里查看此图的较大版本.
Protocol
Representative Results
Discussion
该方法的主要优点是使用了最小扰动沉积岩心样品和连续记录 n2o积累。这样就可以估计相对较低的反硝化率, 这可能与就地发生的反硝化率相似。尽管如此, 还是讨论了有关取心、传感器性能和潜在改进的一些方面。
该方法的一个明显简单但关键的步骤是良好的核心恢复。沉积物/水界面必须满足三个标准: (一) 不改变其化学或组成成分, (二) 不改变含水量或孔?…
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
西班牙政府通过教育部长司向 c. p-l. (FPU12-00644) 提供资金, 并向经济和竞争事务部长提供研究赠款: nitropir (cglap-19737)、lacus (cgl2013-45提48-p), 调动 (cglp2016-80121-c2-p)。reptim 项目 (inre-interreg 方案)。欧盟-欧盟。efa05615) 支持协议的最终编写。
Materials
| Messenger-adapted gravity corer | – | – | Reference in the manuscript. Made by Glew, J. |
| Sampling tube | – | – | Acrylic. Dimensions: 100 cm (h) × 6.35 cm (d) × 6.50 cm (D). Sharpen the edge of the sampling tube that penetrates into the sediment to minimize the disturbance in the recovered sediment core sample. |
| Handheld sounder | Plastimo | 38074 | Echotest II Depth Sounder. |
| Rubber stopper | VWR | DENE1012114 | With two holes, used to mix the N2O-water in the calibration chamber. Dimensions: 20 mm (h) × 14 mm (d) × 18 mm (D) (3 mm hole (D)). |
| Rubber stopper | VWR | 217-0125 | To seal the bottom part of the methacrylate tube and to sample in shallow water bodies. Dimensions: 45 mm (h) × 56 mm (d) × 65 mm (D). |
| PVC cover | – | – | To seal the top side part of the acrylic tube. Dimensions: 45 mm (h) × 56 mm (d) × 65 mm (D). Dimensions: 65 mm (D). |
| Adhesive tape | – | – | Waterproof. To ensure all joints (PVC cover sampling tube and PVC cover sensor) and to avoid water leaks. |
| Thermometer | – | – | Portable and waterproof, to measure the temperature in the water overlying the sediment just after sampling the cores. |
| GPS | – | – | To save the location of a new sampling site or to arrive at a previous site. |
| Wader | – | – | For littoral or shallow site samplings. |
| Boat | – | – | An inflatable boat is the best option for its lightness if the sampling site is not accessible by car. |
| Rope | – | – | Rope with marks showing its length (e.g., marked with a color code to distinguish each meter). |
| N2O gas bottle and pressure reducer | Abelló Linde | 32768-100 | Gas bottle reference. |
| C2H2 gas bottle and pressure reducer | Abelló Linde | 32468-100 | Gas bottle reference. |
| Tube used to evacuate the excess of water | – | – | Consists of a solid part (e.g., a 5 ml pipette tip without its narrowest end) inserted in a silicone tube. |
| Nitrous Oxide Minisensor w/ Cap | Unisense | N2O-R | We use 4 sensors at a time. |
| Microsensor multimeter 4 Ch. 4 pA channels | Unisense | Multimeter | Picoammeter logged to a laptop. The standard device allows for 2 sensor picoammeter connections (e.g., N2O sensor), one pH/mV and a thermometer. We ordered a device with four picoammeter connections, allowing the use of 4 N2O sensors simultaneously. |
| SensorTrace Basic 3.0 Windows software | Unisense | Sensor data acquisition software. | |
| Calibration Chamber incl. pump | Unisense | CAL300 | Calibration chamber. We tuned it with rubber stoppers and syringes to mix the N2O-water without making bubbles. |
| Incubation chamber | Ibercex | E-600-BV | Indispensable equipment for working at a constant temperature (±0.3 °C). It also allows control of the photoperiod. |
| Electric stirrer | – | – | Part of the stirring system. It hangs in the water, overlying the sediment subject, by a fishing line that is hooked to the PVC cover. |
| Electromagnet | – | – | Part of the stirring system. It is fixed to the outside of the acrylic tube, approximately at the same level as the stirrer. It is activated episodically (ca. 1 on-off per s) by a circuit, attracting the stirrer when it is on and releasing it when it is off, thereby generating the movement that agitates the water. |
| Electromagnetic pulse circuit | – | – | Part of the stirring system. It is connected by wires to the electromagnet and sends pulses of current that turn the electromagnet on and off. |
| Uninterruptible power supply (UPS) | – | – | It improves the quality of the electrical energy that reaches the measurement device, filtering the highs and low of the voltage, thereby ensuring a more constant and stable N2O sensor signal. |
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