The Biogeochemical Response of Nitrate and Potassium to Landscape Disturbance in Watersheds of the Hubbard Brook Experimental Forest, New Hampshire, USA

Abstract

Disturbances to forest ecosystems alter nutrient availability and loss, with potassium and nitrate typically exhibiting the most mobile behavior. However, the sources and ecosystem processing of potassium and nitrate differ in important ways that shape their response to large-scale forest disturbance. In this chapter we compare the mobilization and subsequent recovery of potassium and nitrate following natural and experimental disturbances at the Hubbard Brook Experimental Forest, New Hampshire. The response of soil and stream water chemistry was evaluated for both natural (i.e., ice storm) and anthropogenic (devegetation, whole-tree harvest, strip cut) experiments. The greatest losses of nutrients were evident in a devegetation experiment, followed by a whole-tree harvest, with similar losses occurring from an ice storm and a strip cut. There was remarkable consistency in the stoichiometric behavior in solutions across this wide range of disturbance types, with an approximately 0.1 molar ratio of potassium to nitrate. After large-scale forest harvest, nitrate concentrations increased and subsequently recovered more rapidly than potassium. We highlight the role of canopy and fresh plant litter leaching of potassium, root nitrogen uptake, microbial processing of nitrogen, and retention of potassium by cation exchange in controlling variation in the magnitude, timing, and duration of nutrient losses.