Physical, chemical and biological properties of forest and home lawn soils

Abstract: One-meter soil cores were taken to evaluate soil texture, bulk density, carbon and nitrogen pools, microbial biomass carbon and nitrogen content, microbial respiration, potential net nitrogen mineralization, potential net nitrification and inorganic nitrogen pools in 32 residential home lawns that differed by previous land use and age, but had similar soil types. These were compared to soils from 8 forested reference sites. Purpose: Soil cores were obtained from residential and forest sites in the Baltimore, MD USA metropolitan area. The residential sites were mostly within the Gwynns Falls Watershed (-76.012008W, -77.314183E, 39.724847N, 38.708367S and approximately 17 km2) Lawns on residential sites were dominated by a variety of cool season turfgrasses. Forest soil cores were taken from permanent forest plots of the Baltimore Ecosystem Study (BES) LTER (Groffman et al. 2006). These remnant forests are over 100 years old with soils that were comparable in type and texture to those underlying the residential study sites. Soils from all sites were from the Manor series (coarse-loamy, micaceous, mesic Typic Dystrudepts), which are well-drained upland soils with loamy textures and bedrock at 5 to 10 feet below the soil surface. To aid the site selection process we used neighborhoods in the Baltimore City metropolitan area that have been mapped using HERCULES, a high resolution land cover classification system designed to assist in the study of human-ecological systems (Cadenasso et al. 2007). Using HERCULES and additional data sources, we identified residential sites that were similar except for single factors that we hypothesized to be important predictors of ecosystem dynamics. These factors included land use history (agriculture and forest, n = 10 and n = 22), housing density (low and medium/high, n = 9 and n = 23), and housing age (4 to 58 yrs old, n = 32). Housing age was acquired from the Maryland Property View database. Prior land use was determined based on land use change maps developed by integrating aerial photos from 1938, 1957, 1971, and 1999 into a geographic information system. Once a list of residential parcels meeting the predefined criteria were identified, we sent mailings to property owners chosen at random from each of the factor groups with the goal of recruiting 40 property owners for a 3 year study (of which this work is a part). We had recruited 32 property owners at the time that soil cores were obtained. Soil coring took place over a one month period during the summer of 2007. For residential sites, we overlaid a grid onto a map of each property and randomly chose two locations for coring. Locations beneath impervious surfaces (buildings, walkways, driveways) or within close proximity to belowground pipes and power lines were excluded and another random location identified. Undisturbed one-meter soil cores were extracted from each of these locations using a 3.3 cm diameter soil corer. Cores were enclosed in plastic sleeves with end-caps, put into coolers, and transported to the laboratory where they were stored at 4 oC until they could be processed. Coring in the forested reference plots followed a similar procedure, with two cores taken from random locations at each site. In total, 80 intact soil cores were collected from 32 residential properties and 8 forest sites. Digital photos were taken of each soil core followed by a visual inspection to determine horizon depths and Munsell color. Soil cores were also inspected for obvious signs of disturbance such as buried horizons, lithologic discontinuities, or human artifacts of less than 3.3 cm (the diameter of the soil core). Cores were divided into four soil depth intervals (0 to 10 cm, 10 to 30 cm, 30 to 70 cm, and 70 to 100cm) and sorted to remove coarse roots and rocks (> 2 mm). The roots and rocks were dried at 105 oC, weighed and set aside. Rock volume was determined by mass and an assumed density of 2.7 g/cm3. Subsamples of homogenized soil from each depth interval were analyzed for soil dry weight and percent moisture (48 hrs at 105 oC). Bulk density (BD) was calculated as BD = (Total Dry Mass - Rock Mass) / (Total Volume - Rock Volume). Soil texture was obtained by the hydrometer method (Gee and J.W. 1986). Total C and N were obtained by flash-combustion / oxidation using a Thermo Finnigan Flash EA 1112 elemental analyzer (0.06% C and 0.01% N detection limits). For all data, the density of C in a unit area (1 m2) was calculated as C = CfBD(1-d2mm)V, where C is carbon density, d2mm is the fraction of material larger than 2 mm diameter, BD is bulk density, Cf is the fraction by mass of organic C, and V is the volume of the soil core (Post et al., 1982). Subsamples of homogenized soil from each depth interval were set aside to determine 1) initial KCl exchangeable NO3- and NH4+, 2) net nitrification, net mineralization and basal respiration, and 3) microbial biomass C and N. Exchangeable inorganic N (NO3-, NH4+) was extracted from approximately 10 g (dry mass) of soil with 40 ml of 2 M KCl. Samples were agitated for 60 min at 200 rpm on an orbital shaker table and then left undisturbed for 2 hours. The supernatant liquid from each sample was then collected and filtered through Whatman number 42 filter paper into nalgene bottles. Samples were analyzed colorimetrically for NO3- and NH4+ concentration using a Lachat Flow Injection Analyzer (Lachat Instruments, Loveland, CO 80539). Rates of potential net N mineralization, nitrification, and respiration were measured in a 10-day laboratory incubation of soils at room temperature. Soils (25 grams per incubation) were placed in 946-mL glass jars with lids fitted with septa for gas sampling. After 10 days, the headspace of the jars was sampled by syringe, and the gas samples were analyzed for carbon dioxide (CO2) by thermal conductivity gas chromatography. Inorganic N was extracted as described above. Mineralization was calculated as the accumulation of total inorganic N, nitrification was calculated as the accumulation of NO3-, and respiration was calculated as the accumulation of CO2 over the course of the 10-day incubation. Microbial biomass C and N were measured using the chloroform fumigation-incubation method (Jenkinson and Powlson 1976). Field moist soils (25 grams) were fumigated to lyse microbial cells in the samples. The fumigated samples were then inoculated with fresh soil, allowing microorganisms to regrow using the dead cells as substrate. The flushes of CO2 and 2 M KCl-extractable inorganic N (NH4+ and NO3-) released by the cells during the incubation were assumed to be proportional to the C and N in the microbial biomass of the original sample. A proportionality constant (0.45) was used to calculate biomass C from the CO2 ?ush, which was measured by thermal conductivity gas chromatography. Inorganic N flush data were not corrected with a proportionality constant. Column Names: Description 1. Site: House designation or name of Baltimore Ecosystem Study forested reference plot 2. REP#: Used to distinguish between multiple measurements at a single Site 3. Depth: Depth interval from which the soil was collected. Soil in a given depth interval was homogenized prior to analyses. 4. Core_Z_Ht_cm: Height of this subsection of the soil core in cm. For instance, if the depth interval was 0 - 10 cm, this would equal a z-height of 10cm. 5. LU_Current: Current land use (residential or forest) 6. LU_Previous: Land use prior to development (forest or agriculture). Only relevant for sites that are currently residential. Based on historical aerial photos and housing age (see Wehling MA. 2001. Land use/land cover change from 1915 to 1999 in the Gwynns Falls Watershed, Baltimore County, Maryland: creation of a suburban social ecology. [Dissertation]. Athens (OH): Department of Geography, Ohio University.) 7. Yr_Built: Year the house was built (from the Maryland Property View database) 8. CoarseVeg: Coarse vegetation density (i.e. trees) descriptor from the HERCULES land use classification system. See Cadenasso ML, Pickett TA, Schwarz K. 2007. Spatial heterogeneity in urban ecosystems: reconceptualizing land cover and a framework for classification. Front Ecol Environ 5(2):80-8. 9. StructDen: Structure density (i.e. density of buildings/houses) descriptor from the HERCULES land use classification system. See Cadenasso ML, Pickett TA, Schwarz K. 2007. Spatial heterogeneity in urban ecosystems: reconceptualizing land cover and a framework for classification. Front Ecol Environ 5(2):80-8. 10. BD: Bulk Density (g/cm3) 11. N_Perc: Percent nitrogen of the mineral soil 12. C_Perc: Percent carbon of the mineral soil 13. C_N: Carbon to Nitrogen Ratio of the mineral soil 14. N_gm2: Nitrogen content of the mineral soil (g/m2) 15. C_gm2: Carbon content of the mineral soil (g/m2) 16. Sand_Perc: Percent Sand (from soil texture analysis using the hydrometer method; Gee and Bauder 1986) 17. Clay_Perc: Percent Clay (from soil texture analysis using the hydrometer method; Gee and Bauder 1986) 18. Silt_Perc: Percent Silt (from soil texture analysis using the hydrometer method; Gee and Bauder 1986) 19. MB Carbon: Microbial Biomass Carbon; Microbial biomass C and N were measured using the chloroform fumigation-incubation method (Jenkinson and Powlson 1976). 20. Respiration1: Respiration; (ug C/g soil/day) 21. Initial NO3 (+NO2): Initial NO3 (+NO2); (ug N/g soil) 22. Initial NH4: Initial NH4 (ug N/g soil) 23. MBN: Microbial Biomass Nitrogen; (ug N/g soil) 24. Potential Net N Min: Potential Net Nitrogen Mineralization; (ug N/g soil/day) 25. Potential Net Nitrification: Potential Net Nitrogen Mineralization; (ug N/g soil/day) * Ref Plots = Baltimore Ecosystem Study forested reference plot ** House1 to House32 refer to individual addresses, which have been removed to protect anonymity. *** Rates of potential net N mineralization, nitrification, and respiration were measured in a 10-day laboratory incubation of soils at room temperature. (For detailed methods, consult Groffman et al. [1999]). The latitudes and longitudes posted in this record encompass all the plot locations. Individual plot locations are withheld to protect the homeowners' privacy. Data have been published in Raciti et al. (2011a, 2011b) Literature Cited: Cadenasso, M. L., S. T. A. Pickett, and K. Schwarz. 2007. Spatial heterogeneity in urban ecosystems: reconceptualizing land cover and a framework for classification. Frontiers in Ecology and the Environment 5:80-88. Gee, G. W. and B. J.W. 1986. Particle size analysis. Pages 383-411 in A. Klute, editor. Methods of Soil Analysis, part 1. Physical and mineralogical methods, Second Edition. American Society of Agronomy, Madison, WI. Groffman, P. M., R. V. Pouyat, M. L. Cadenasso, W. C. Zipperer, K. Szlavecz, I. D. Yesilonis, L. E. Band, and G. S. Brush. 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. Jenkinson, D. S. and D. S. Powlson. 1976. The effects of biocidal treatments on metabolism in soil V. A method for measuring soil biomass. Soil Biology and Biochemistry 8:209-213. Raciti, S. R., P. M. Groffman, J. C. Jenkins, R. V. Pouyat, and T. J. Fahey. 2011a. Controls on nitrate production and availability in residential soils. Ecological Applications:In press. Raciti, S. R., P. M. Groffman, J. C. Jenkins, R. V. Pouyat, T. J. Fahey, M. L. Cadenasso, and S. T. A. Pickett. 2011b. Accumulation of carbon and nitrogen in residential soils with different land use histories. Ecosystems 14:287-297.