Nutrient Budget Studies for Forests Along an Elevational Gradient in New Mexico

Abstract

Element budgets are presented for watersheds which differ markedly in vegetation biomass, structure, productivity, soil development and hydrology. The net organic matter increment of one of the watersheds has been estimated to be negative. The patterns in the output and net change of Ca, Mg, K and Na among watersheds are related to soil chemistry and stream discharge rates. These factors may not be related to the net organic matter increment of the ecosystem. Actual atmospheric inputs of these elements to some of the ecosystems may be an order of magnitude greater than those measured in bulk precipitation. Nitrogen outputs in stream water are strongly regulated by all of the watershed ecosystems including the one which appears to have a negative net organic increment. Low losses of nitrogen in stream water, however, do not mean a system will minimize other types of N losses (e.g., denitrification). Nutrient budgets generated from bulk precipitation and stream water discharge in the Southwest cannot prove or disprove hypotheses about nutrient regulation by net organic matter increment. Additional inputs (aerosol impaction, weathering, N fixation, NH3 absorption) and outputs (denitrification, aerosols) must be quantified before a valid test can be made of these hypotheses.