Hydropedology of Podzols At Hubbard Brook, NH.

Soils are the primary source of solutes to headwaters, yet few researchers have attempted to characterize spatial variability of soils and their effects on head water chemistry. In Watershed 3 (WS3) of Hubbard Brook Experimental Forest, New Hampshire, soils are predominantly well-drained Spodosols with vertical unsaturated flow. However, preliminary evidence shows that certain areas of the catchment may experience lateral unsaturated flow of groundwater, or throughflow, which transports spodic materials downslope rather than down the soil profile. This lateral podzolization results in Spodosol variants, classified here as six soil functional groups called hydropedologic units (HPUs). The objectives of this hydropedologic study of WS3 are: 1) to identify hydrologic controls on soil genesis, and characterize the chemistry of the six HPUs; and 2) to compare morphological, micromorphological, chemical, physical, and mineralogical characteristics of vertically versus laterally developed spodic horizons. Eighty-nine pedons have been analyzed for dithionite-extractable Fe and Mn, and oxalate-extractable Fe and Al. Also, three transects which capture transitions across HPUs will be constructed, and these soils will be characterized for morphology, micromorphology, chemistry, physical properties, and mineralogy. Current results show that HPUs differ in their chemistry, both by horizon and total element pool in the profile. For example, “E-podzols” are found in bedrock-controlled topography, where Al, Fe, Mn, and C have been leached due to lateral podzolization. However, just a few m downslope, “Bhs-podzols” with especially thick spodic horizons develop due to accumulation of Al, Fe, Mn, and C. Vertically developed spodic horizons in typical, well-drained podzols are relatively thinner, with higher concentrations of Fe, Al, and C. The lateral, throughflow-dominated spodic horizons are thicker, but more diffuse, with lower concentrations of Fe, Al, and C. In WS3, manganese is a good indicator of throughflow, since it is mobile and accumulating relative to Fe in laterally developed soils.