Elemental cycling in recently deglaciated landscapes, Glacier Bay National Park, Alaska

We collected soil samples and leaves from the dominant vegetation types within each catchment. For each vegetation type we collected composite soil samples from three locations. At each location we combined three soil samples taken from within 1 m2 to account for small-scale heterogeneity. We collected soil to a depth of 10 cm using a hand trowel and soil corer. Soils were kept shaded and cool and were processed within four days of collection at the Glacier Bay field laboratory station. Field moist soils were sieved through a 2 mm mesh screen to remove stones and large detritus. We analysed this 2 mm fraction for gravimetric soil moisture, organic matter content (loss on ignition), and pH following standard methods. We used a separate sample, collected with a hand-corer, to estimate bulk density after drying. Soil texture was analysed using laser diffraction. We determined potential nitrite oxidation by nitrite consumption during a 30-hour incubation as a proxy of nitrification. Potential denitrification was analysed using the acetylene block technique. We extracted〖 NH〗_4^+, NO_2^-, and NO_3^- from slurries of 10 g (equivalent dry weight) of field-moist soil and 80 ml of 2M KCl. Soil slurries were agitated on a continuous wheel shaker for 1 h in 100ml high-density polyethylene bottles. Extracts were filtered to 0.2 μm with nylon filters (Millipore), frozen, and transported to the University of Birmingham, UK. 〖 NH〗_4^(+ ) was determined using the buffered hypochlorite method and NO_3^- using cadmium column reduction to NO_2^- followed by a Griess diazotization reaction. NO_2^- was also determined by Griess diazotization reaction. Colorimetric analyses were accomplished on a Jenway 6800 UV/Vis spectrophotometer. The limit of detection was 0.05 μg ml-1 for all N species, accuracy was equal to or better than 90 percent, and coefficient of variation was lower than 1 percent. We measured total N, total C, δ13C, and δ15N of soil and leaves with an elemental analyzer (Vario PYRO cube, Elementar, Hanau, Germany) coupled to an isotope-ratio mass spectrometer (Isoprime, micromass, Manchester, UK) at the Pierre and Marie Curie University, Paris, France. The coefficient of variation was 0.2‰ for δ 13C and 0.3‰ for 15N.