Soil biogeochemical processes in hydropedologic units in a northern hardwood forest
Poster Number:
258
Presenter/Primary Author:
Peter Groffman As part of a hydropedologic study of a forested catchment in Hubbard Brook Experimental Forest (New Hampshire, USA), we investigated the connections between hydropedologic units and soil biogeochemical properties. In August 2010, we collected soils from three transects (high, medium, and low elevation) in the catchment, sampling three distinct hillslope positions and associated soils in each transect: typical spodosols, bimodal spodosols, and Bh podzols. We measured nitrogen (N) concentrations, microbial biomass carbon (C) and N, and microbial respiration, as well as potential rates of net N mineralization, net nitrification, and denitrification in the three surface horizons: forest floor (Oie); humic horizon (Oa/A); and mineral, illuvial horizon (B). We hypothesized that Bh podzols would be biogeochemical hotspots along hillslopes, as zones where hydrologic flow paths converge, and that this would hold true for all soil horizons. There was particular interest in the biological potential of Bh horizons which are carbon rich horizons, relatively deep in the profile with high potential for intercepting hydrologic flow paths.
We found robust patterns of higher carbon and N concentrations and cycling rates in Oie and/or Oa horizons, across all metrics (per g of soil). When viewed on an areal basis (accounting for horizon depth), all metrics were higher in Oa/A and B horizons, supporting the idea that deeper soil horizons are biogeochemically active and important in the landscape. We did not find significant differences between hydropedologic units on an areal basis, but we did see a weak trend of increasing biogeochemical process rates from upslope to downslope positions. We found strong correlations between C (or water) content and C and N cycling rates, across soil horizons and hydropedologic units.
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