Soil: atmosphere fluxes of carbon dioxide, nitrous oxide and methane

Baltimore Ecosystem Study Long-Term Study Plot Soil Metadata Participants Peter Groffman, Cary Institute of Ecosystem Studies Richard V. Pouyat, U.S. Forest Service Introduction The Baltimore Ecosystem Study (BES) has established a network of long-term permanent biogeochemical study plots. These plots will provide long-term data on vegetation, soil and hydrologic processes in the key ecosystem types within the urban ecosystem. The current network of study plots includes eight forest plots, chosen to represent the range of forest conditions in the area, and four grass plots. These plots are complemented by a network of 200 less intensive study plots located across the Baltimore metropolitan area. See Baltimore's Vegetation Structure And Its Ability To Remove Air Pollutants And Sequester Carbon Dioxide, online: http://beslter.org/frame4-page_3b_02.html . Plots are currently instrumented with lysimeters (drainage and tension) to sample soil solution chemistry, time domain reflectometry probes to measure soil moisture, dataloggers to measure and record soil temperature and trace gas flux chambers to measure the flux of carbon dioxide, nitrous oxide and methane from soil to the atmosphere. Measurements of in situ nitrogen mineralization, nitrification and denitrification were made at approximately monthly intervals from Fall 1998 - Fall 2000. Detailed vegetation characterization (all layers) was done in summer 1998. Data from these plots has been published in Groffman et al. (2006, 2009), Groffman and Pouyat (2009) and Savva et al. (2010). Plot Locations and Characterizations In November of 1998 four rural, forested plots were established at Oregon Ridge Park in Baltimore County northeast of the Gwynns Falls Watershed. Oregon Ridge Park contains Pond Branch, the forested reference watershed for BES. Two of these four plots are located on the top of a slope; the other two are located midway up the slope. In June of 2010 measurements at the mid-slope sites on Pond Branch were discontinued. Monuments and equipment remain at the two plots. These plots were replaced with two lowland riparian plots; Oregon upper riparian and Oregon lower riparian. Each riparian sites has four 5 cm by 1-2.5 meter depth slotted wells laid perpendicular to the stream, four tension lysimeters at 10 cm depth, five time domain reflectometry probes, and four trace gas flux chambers in the two dominant microtopographic features of the riparian zones --- high spots (hummocks) and low spots (hollows). Four urban, forested plots were established in November 1998, two at Leakin Park and two adjacent to Hillsdale Park in west Baltimore City in the Gwynns Falls. One of the plots in Hillsdale Park was abandoned in 2004 due to continued vandalism. In May 1999 two grass, lawn plots were established at McDonogh School in Baltimore County west of the city in the Gwynns Falls. One of these plots is an extremely low intensity management area (mowed once or twice a year) and one is in a low intensity management area (frequent mowing, no fertilizer or herbicide use). In 2009, the McDonogh plots were abandoned due to management changes at the school. Two grass lawn plots were established on the campus of the University of Maryland, Baltimore County (UMBC) in fall 2000. One of these plots is in a medium intensity management area (frequent mowing, moderate applications of fertilizer and herbicides) and one is in a high intensity management area (frequent mowing, high applications of fertilizer and herbicides). Plot locations: Hillsdale 1: 39 deg 19'28.14"N, 76 deg 42'16.49"W Hillsdale 2: 39 deg 19'31.24"N, 76 deg 42'28.62"W Leakin 1: 39 deg 18'1.32"N, 76 deg 41'37.08"W Leakin 2: 39 deg 18'5.42"N, 76 deg 41'34.15"W McDonogh 1: 39 deg 23'44.31"N, 76 deg 46'19.26"W McDonogh 2: 39 deg 23'52.26"N, 76 deg 46'23.52"W Oregon top-slope - 1: 39 deg 28'51.11"N, 76 deg 41'22.50"W Oregon mid-slope - 1: 39 deg 28'51.32"N, 76 deg 41'18.24"W Oregon top-slope - 2: 39 deg 29'12.74"N, 76 deg 41'22.88"W Oregon mid-slope - 2: 39 deg 29'12.68"N, 76 deg 41'18.62"W Oregon upper riparian: 39 deg 29'9.03"N, 76 deg 41'15.86"W Oregon lower riparian: 39 deg 28'52.06"N, 76 deg 41'15.54"W McDonogh 1: 39 deg 23'44.31"N, 76 deg 46'19.26"W McDonogh 2: 39 deg 23'52.26"N, 76 deg 46'23.52"W UMBC 1: 39 deg 15'8.82"N, 76 deg 42'10.43"W UMBC 2: 39 deg 14'6.50"N, 76 deg 42'48.71"W Soil atmosphere fluxes of carbon dioxide, nitrous oxide and methane Trace gas (N2O, CO2, and CH4) fluxes from soil to the atmosphere were measured every four to six weeks at each plot using an in situ chamber design. The lawn plots had chambers identical to those used by Bowden et al. (1990) installed flush with the soil surface to allow mowing. These (three per plot, at least 5 m apart and at least 5 m from the plot boundary) consisted of 28.7-cm diameter (ID) by 4.0-cm high polyvinyl chloride (PVC) cylinders which were placed on permanently installed PVC base rings immediately prior to measurement. From 1998 through September 2007, the forest plots had the chambers described by Goldman et al. (1995), constructed from 16.5 cm wide by 20 cm long pieces of PVC pipe fitted with a septum and an air-tight well cap. These chambers were placed 4 cm into the soil and had a total volume of 2 L. Beginning in September 2007, the Bowden et al. (1990) chambers, which are used at many research sites across the world, were installed at the forest sites. A brief period of side by side measurements suggested that the Bowden chambers produce lower gas fluxes than the Goldman chambers. The replacement dates for chambers at different sites are: - Leakin 1 September 2007 - Leakin 2 Septemeber 2007 - Hillsdale 1 Sept 2007 - Oregon Ridge Upper 1 November 2007 - Oregon Ridge Upper 2 November 2007 - Oregon Ridge Middle 1 September 2007 - Oregon Ridge Middle 2 September 2007 At 0, 10, 20 and 30 min following placement of the chamber on the base or installation of the well cap, 9-mL gas samples were collected from gas sampling ports in the center of the chamber top by syringe. Samples were injected into 9 mL evacuated glass vials sealed with septa and aluminum rings. Samples were sent to the Cary Institute of Ecosystem Studies (CIES) for gas chromatography (GC) analysis. Concentrations of CO2 and N2O are measured on a GC equipped with thermal conductivity and electron capture detectors aligned in sequence. Concentrations of CH4 are measured on a GC equipped with a flame ionization detector. Samples and standards are introduced into this GC via syringe and sample loop. Fluxes were calculated from the linear rate of change in gas concentration, the chamber internal volume and soil surface area. Spike standards are processed along with each batch of flux samples. These standards are generated by filling sample vials from a standard tank in the field laboratory in Baltimore and then processing these samples along with samples taken from flux chambers in the field. Percent recoveries of the trip standards are used to correct flux values for leakage or gas absorption that may occur between sampling and analysis. Exceptionally low recoveries for N2O (traced to a change in septa manufacture) led to loss of flux data for this gas for several dates from 2007 - 2009. Literature Cited Bowden R, Steudler P, Melillo J and Aber J. 1990. Annual nitrous oxide fluxes from temperate forest soils in the northeastern United States. J. Geophys. Res.Atmos. 95, 13997 14005. Driscoll CT, Fuller RD and Simone DM (1988) Longitudinal variations in trace metal concentrations in a northern forested ecosystem. J. Environ. Qual. 17: 101-107 Goldman, M. B., P. M. Groffman, R. V. Pouyat, M. J. McDonnell, and S. T. A. Pickett. 1995. CH4 uptake and N availability in forest soils along an urban to rural gradient. Soil Biology and Biochemistry 27:281-286. Groffman PM, Holland E, Myrold DD, Robertson GP and Zou X (1999) Denitrification. In: Robertson GP, Bledsoe CS, Coleman DC and Sollins P (Eds) Standard Soil Methods for Long Term Ecological Research. (pp 272-290). Oxford University Press, New York Groffman PM, Pouyat RV, Cadenasso ML, Zipperer WC, Szlavecz K, Yesilonis IC,. Band LE and Brush GS. 2006. Land use context and natural soil controls on plant community composition and soil nitrogen and carbon dynamics in urban and rural forests. Forest Ecology and Management 236:177-192. Groffman, P.M., C.O. Williams, R.V. Pouyat, L.E. Band and I.C. Yesilonis. 2009. Nitrate leaching and nitrous oxide flux in urban forests and grasslands. Journal of Environmental Quality 38:1848-1860. Groffman, P.M. and R.V. Pouyat. 2009. Methane uptake in urban forests and lawns. Environmental Science and Technology 43:5229-5235. DOI: 10.1021/es803720h. Holland EA, Boone R, Greenberg J, Groffman PM and Robertson GP (1999) Measurement of Soil CO2, N2O and CH4 exchange. In: Robertson GP, Bledsoe CS, Coleman DC and Sollins P (Eds) Standard Soil Methods for Long Term Ecological Research. (pp 258-271). Oxford University Press, New York Robertson GP, Wedin D, Groffman PM, Blair JM, Holland EA, Nadelhoffer KJ and. Harris D. 1999. Soil carbon and nitrogen availability: Nitrogen mineralization, nitrification and carbon turnover. In: Standard Soil Methods for Long Term Ecological Research (Robertson GP, Bledsoe CS, Coleman DC and Sollins P (Eds) Standard Soil Methods for Long Term Ecological Research. (pp 258-271). Oxford University Press, New York Savva, Y., K. Szlavecz, R. V. Pouyat, P. M. Groffman, and G. Heisler. 2010. Effects of land use and vegetation cover on soil temperature in an urban ecosystem. Soil Science Society of America Journal 74:469-480.

巴尔的摩生态系统研究长期样地土壤元数据

参与人员：Peter Groffman，卡内基生态系统研究所（Cary Institute of Ecosystem Studies）；Richard V. Pouyat，美国林务局（U.S. Forest Service）

引言
巴尔的摩生态系统研究（Baltimore Ecosystem Study, BES）已建立一套长期永久生物地球化学样地网络，旨在获取城市生态系统内关键生态类型的植被、土壤及水文过程长期监测数据。当前样地网络包含8个森林样地（覆盖区域内各类森林生境）与4个草地样地，另辅以覆盖巴尔的摩大都市区的200个低密度监测样地。详见《巴尔的摩植被结构及其去除空气污染物与固碳能力》，在线链接：http://beslter.org/frame4-page_3b_02.html。

目前各核心样地已安装渗漏计（lysimeter，包括排水式与张力式）用于采集土壤溶液化学样品，时域反射仪（time domain reflectometry, TDR）探头监测土壤含水量，数据记录仪记录土壤温度，以及痕量气体通量箱用于测定土壤向大气排放的二氧化碳（CO₂）、一氧化二氮（N₂O）与甲烷（CH₄）通量。1998年秋季至2000年秋季，以约每月一次的频率开展原位氮矿化、硝化与反硝化作用监测；1998年夏季完成了全层次植被详细表征。

本样地的相关数据已发表于Groffman等（2006、2009）、Groffman与Pouyat（2009）以及Savva等（2010）的研究中。

样地位置与特征
1998年11月，在巴尔的摩县Gwynns Falls流域东北部的Oregon Ridge公园内建立4个农村森林样地，该公园内的Pond Branch是BES的森林参考流域。其中2个样地位于坡顶，另外2个位于坡中。2010年6月，Pond Branch的坡中样地停止监测，但样地标记与监测设备仍保留，随后以2个河岸低地样地替代：Oregon上游河岸样地与Oregon下游河岸样地。每个河岸样地配置有：4根垂直于溪流布设、尺寸为5cm×1-2.5m的开槽井，4个10cm深度的张力式渗漏计，5台TDR探头，以及针对河岸带2种主要微地形（土丘与洼地）布设的4个痕量气体通量箱。

1998年11月，在巴尔的摩市西部Gwynns Falls流域的Leakin公园建立2个城市森林样地，在Hillsdale公园附近建立2个城市森林样地。其中Hillsdale公园的1个样地因持续遭到人为破坏，于2004年废弃。

1999年5月，在巴尔的摩市西部Gwynns Falls流域的McDonogh学校校园建立2个草地样地：1个为极低管理强度样地（每年修剪1-2次），另1个为低管理强度样地（定期修剪，不施用化肥与除草剂）。2009年因校方管理政策调整，McDonogh样地停止监测。

2000年秋季，在马里兰大学巴尔的摩县分校（University of Maryland, Baltimore County, UMBC）校园建立2个草地样地：1个为中等管理强度样地（定期修剪，适量施用化肥与除草剂），另1个为高管理强度样地（定期修剪，大量施用化肥与除草剂）。

样地坐标：
Hillsdale 1：39°19'28.14"N，76°42'16.49"W
Hillsdale 2：39°19'31.24"N，76°42'28.62"W
Leakin 1：39°18'1.32"N，76°41'37.08"W
Leakin 2：39°18'5.42"N，76°41'34.15"W
McDonogh 1：39°23'44.31"N，76°46'19.26"W
McDonogh 2：39°23'52.26"N，76°46'23.52"W
Oregon坡顶-1：39°28'51.11"N，76°41'22.50"W
Oregon坡中-1：39°28'51.32"N，76°41'18.24"W
Oregon坡顶-2：39°29'12.74"N，76°41'22.88"W
Oregon坡中-2：39°29'12.68"N，76°41'18.62"W
Oregon上游河岸样地：39°29'9.03"N，76°41'15.86"W
Oregon下游河岸样地：39°28'52.06"N，76°41'15.54"W
McDonogh 1：39°23'44.31"N，76°46'19.26"W
McDonogh 2：39°23'52.26"N，76°46'23.52"W
UMBC 1：39°15'8.82"N，76°42'10.43"W
UMBC 2：39°14'6.50"N，76°42'48.71"W

土壤-大气二氧化碳、一氧化二氮与甲烷通量监测
本研究采用原位箱式法，每4-6周对每个样地的土壤向大气排放的痕量气体（N₂O、CO₂、CH₄）通量进行测定。草地样地使用与Bowden等（1990）一致的通量箱，将箱体与土壤表面齐平以方便机械修剪。每个样地布设3个箱体，箱体间距不小于5m，且距离样地边界不小于5m；箱体为内径28.7cm、高4.0cm的聚氯乙烯（polyvinyl chloride, PVC）圆筒，测量前放置于永久安装的PVC底座环上。

1998年至2007年9月，森林样地使用Goldman等（1995）设计的通量箱：由宽16.5cm、长20cm的PVC管制成，配有隔垫与气密井盖，插入土壤4cm，总容积为2L。2007年9月起，改用全球多数研究站点通用的Bowden等（1990）通量箱。前期并行监测结果显示，Bowden通量箱测得的气体通量低于Goldman通量箱。各站点通量箱更换时间如下：
- Leakin 1：2007年9月
- Leakin 2：2007年9月
- Hillsdale 1：2007年9月
- Oregon Ridge坡顶1：2007年11月
- Oregon Ridge坡顶2：2007年11月
- Oregon Ridge坡中1：2007年9月
- Oregon Ridge坡中2：2007年9月

在箱体安装于底座或井盖安装后的0、10、20、30分钟，使用注射器从箱体顶部中央的气体采样口采集9mL气体样品，将样品注入带有隔垫与铝盖的9mL真空玻璃瓶中。样品寄送至卡内基生态系统研究所（Cary Institute of Ecosystem Studies, CIES）进行气相色谱（gas chromatography, GC）分析：CO₂与N₂O浓度使用串联配置热导检测器与电子捕获检测器的GC测定，CH₄浓度使用配备火焰离子化检测器的GC测定。样品与标准品通过注射器与定量环注入色谱系统。通量通过气体浓度的线性变化速率、箱体内体积与土壤表面积计算得到。

每一批通量样品同步分析标准质控样。质控样由巴尔的摩野外实验室的标准气罐灌装至样品瓶中，与野外采集的通量样品一并处理。通过三重标准样的回收率，校正采样至分析过程中可能发生的气体泄漏或吸收导致的偏差。2007年至2009年间，因隔垫生产工艺变更导致N₂O回收率异常偏低，该时段部分日期的N₂O通量数据失效。

参考文献
Bowden R, Steudler P, Melillo J, Aber J. 1990. 美国东北部温带森林土壤的年一氧化二氮通量. 《地球物理研究杂志·大气卷》（Journal of Geophysical Research: Atmospheres）, 95: 13997-14005.
Driscoll CT, Fuller RD, Simone DM. 1988. 北方森林生态系统中痕量金属浓度的纵向变化. 《环境质量杂志》（Journal of Environmental Quality）, 17: 101-107.
Goldman MB, Groffman PM, Pouyat RV, McDonnell MJ, Pickett STA. 1995. 城乡梯度森林土壤的甲烷吸收与氮有效性. 《土壤生物学与生物化学》（Soil Biology and Biochemistry）, 27: 281-286.
Groffman PM, Holland E, Myrold DD, Robertson GP, Zou X. 1999. 反硝化作用. 收录于：Robertson GP, Bledsoe CS, Coleman DC, Sollins P (Eds). 《长期生态研究标准土壤方法》（Standard Soil Methods for Long Term Ecological Research）, 第272-290页. 牛津大学出版社，纽约.
Groffman PM, Pouyat RV, Cadenasso ML, Zipperer WC, Szlavecz K, Yesilonis IC, Band LE, Brush GS. 2006. 土地利用背景与自然土壤因子对城乡森林植物群落组成及土壤氮碳动态的影响. 《森林生态与管理》（Forest Ecology and Management）, 236: 177-192.
Groffman PM, Williams CO, Pouyat RV, Band LE, Yesilonis IC. 2009. 城市森林与草地的硝酸盐淋溶与一氧化二氮通量. 《环境质量杂志》（Journal of Environmental Quality）, 38: 1848-1860.
Groffman PM, Pouyat RV. 2009. 城市森林与草坪的甲烷吸收. 《环境科学与技术》（Environmental Science and Technology）, 43: 5229-5235. DOI: 10.1021/es803720h.
Holland EA, Boone R, Greenberg J, Groffman PM, Robertson GP. 1999. 土壤CO₂、N₂O与CH₄交换的测定. 收录于：Robertson GP, Bledsoe CS, Coleman DC, Sollins P (Eds). 《长期生态研究标准土壤方法》（Standard Soil Methods for Long Term Ecological Research）, 第258-271页. 牛津大学出版社，纽约.
Robertson GP, Wedin D, Groffman PM, Blair JM, Holland EA, Nadelhoffer KJ, Harris D. 1999. 土壤碳氮有效性：氮矿化、硝化与碳周转. 收录于：Robertson GP, Bledsoe CS, Coleman DC, Sollins P (Eds). 《长期生态研究标准土壤方法》（Standard Soil Methods for Long Term Ecological Research）, 第258-271页. 牛津大学出版社，纽约.
Savva Y, Szlavecz K, Pouyat RV, Groffman PM, Heisler G. 2010. 土地利用与植被覆盖对城市生态系统土壤温度的影响. 《美国土壤学会志》（Soil Science Society of America Journal）, 74: 469-480.