LOESS ECOSYSTEMS OF NORTHERN ALASKA - REGIONAL GRADIENT AND TOPOSEQUENCE AT PRUDHOE BAY

Loess-dominated ecosystems cover almost-equal-to 14% (11 000 km2) of the Arctic Coastal Plain and much of the northern portion of the Arctic Foothills. Knowledge of this poorly known ecosystem is important for sound land-use planning of the expanding developments in the region and for understanding the paleoecological dynamics of eolian systems that once dominated much of northern Alaska. A conceptual alkaline-tundra toposequence includes eight common vegetation types and associated soils that occur near the arctic coast. A model of the regional loess gradient describes soils and vegetation downwind of the Sagavanirktok River. The addition of calcareous loess affects numerous soil properties, including bulk density, pH, water retention properties, concentrations of soil nutrients, and seasonal thaw depths. Many plant taxa, particularly cryptogams, increase in abundance downwind of the river, apparently in response to higher amounts of nutrients and moisture associated with finer soil-particle sizes and greater organic content. For example, the highest extractable P values (8-12-mu-g/g) occur in areas with circumneutral pH and finer grained soils, and low P values (< 2-mu-g/g) occur in acidic soils north of the loess region. Early, minerotrophic stages of tundra succession are maintained by loess blown from the Sagavanirktok, Canning, and other large braided-river floodplains. Areas downwind of these rivers provide analogues for vegetation that existed in unstable areas of the Alaskan Coastal Plain during and following full glacial conditions. Total aboveground phytomass in wet acidic sites at Prudhoe Bay (163 +/- 21 g/m2) is close to values from similar sites at Barrow and Devon Island. Only a small amount of data is available for alkaline areas, but there is indication of lower biomass near the major rivers, suggesting a response to lower nutrient regimes. Properties of loess tundra important for land-use planning include: (1) its high ice content, which contributes to its susceptibility to thermokarst; (2) high salinities, which hamper revegetation efforts; and (3) presence of certain plant species such as Dryas intergrifolia, which are particularly sensitive to disturbance. The loess gradient provides a natural analogue for road dust, an extensive disturbance associated with oil-field development.