On processes controlling the distribution and fluxes of boron in natural waters and air along transects across the South Island of New Zealand

The concentrations of boron were measured in rain, air and soil water along transects across the Southern Alps, New Zealand, during southern autumn an d early winter 1999. Estimates of wet deposition, dry deposition, and flux of boron leaving the soil in soil water are presented. At the Main Divide o f the Southern Alps, strong and constant orographic effects: on rain-bearin g fronts resulted in low concentrations and little variation of boron in ra in. Areas with less orographic influence received varying boron concentrati ons in the rain depending on the origin and character of the fronts. Concen trations of boron in air were greater near the sea than in the intramontane basin. High mean concentrations in air go together with large variations c aused by changes of wind direction and speed during frontal passages. Air r eaching the intramontane basin was depleted of boron because of washout ove r the eastern and western ranges and by dry deposition. After a long dry su mmer spell, the first autumn flush of soil water contained high concentrati ons: of boron at low soil water flow. Later, as the soil wetted up, the soi l water concentration approached that of rain water at all sites. Wet depos ition was least at sites away from the coast where there was little rain an d less boron in it. High rainfall with low boron concentrations or mean rai nfall with high boron concentrations occurred near the eastern and western divides. Dry deposition varied over shorter time intervals and distances th an wet deposition. It was high near the coastlines during onshore winds and low in the intramontane basin, especially with weak convective turbulence. The concentrations of boron in springs resembled those in rain and soil wa ter, increasing from the western coastal plain eastwards across the Souther n Alps. (C) 2001 Elsevier Science B.V. All rights reserved.