Soil nitrogen cycle variables

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) and Groffman and Pouyat (2009). 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. 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: 39deg 19'28.14"N, 76deg 42'16.49"W Hillsdale 2: 39deg 19'31.24"N, 76deg 42'28.62"W Leakin 1: 39deg 18'1.32"N, 76deg 41'37.08"W Leakin 2: 39deg 18'5.42"N, 76deg 41'34.15"W McDonogh 1: 39deg 23'44.31"N, 76deg 46'19.26"W McDonogh 2: 39deg 23'52.26"N, 76deg 46'23.52"W Oregon top-slope - 1: 39deg 28'51.11"N, 76deg 41'22.50"W Oregon mid-slope - 1: 39deg 28'51.32"N, 76deg 41'18.24"W Oregon top-slope - 2: 39deg 29'12.74"N, 76deg 41'22.88"W Oregon mid-slope - 2: 39deg 29'12.68"N, 76deg 41'18.62"W McDonogh 1: 39deg 23'44.31"N, 76deg 46'19.26"W McDonogh 2: 39deg 23'52.26"N, 76deg 46'23.52"W UMBC 1: 39deg 15'8.82"N, 76deg 42'10.43"W UMBC 2: 39deg 14'6.50"N, 76deg 42'48.71"W Soil Nitrogen Cycle Variables Soil nitrogen variables were measured at all forested plots once every four to six weeks (except during the winter - December through March) from November 1998 through December 2000. In situ rates of nitrogen mineralization and nitrification were measured using an intact core technique (Robertson et al. 1999). At each plot five ~20 cm long by 2 cm diameter intact soil cores in plexiglass tubes were planted below the surface to incubate for four to six weeks. Tubes were stoppered at the bottom and covered snugly with aluminum foil on top to allow for diffusion of gases. Additionally five fresh cores were taken, and the five incubating cores from the previous month's sampling were collected. All cores were shipped by overnight mail to CIES for denitrification and soil N analyses. Inorganic N (ammonium - NH4+ and nitrate - NO3-) was extracted with 2 N KCl and was quantified colorometrically using a flow injection analyzer. Net N mineralization rates were calculated as the accumulation of total inorganic N over the course of the incubation. Net nitrification rates were calculated as the accumulation of NO3- over the course of the incubation. All cores that were collected for in situ N mineralization and nitrification analyses were also assayed for denitrification using an acetylene (C2H2)-based intact core method (Groffman et al. 1999). Cores were brought back to the laboratory, amended with 10 kPa and incubated at laboratory temperature for 6 hr. Gas samples were taken at 2 and 6 hr and stored in evacuated glass tubes until analysis for nitrous oxide (N2O) concentrations by electron capture gas chromatography. 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 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