The distribution and fluxes of trichloroacetic acid in a Sitka spruce forest

• Main Author: Reeves, Nicholas Martin
• Published: University of Edinburgh 2000
• Subjects: 634.9
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.661003

Detailed TCAA data are presented from an 18 month period of intensive field sampling at two elevations (602 m and 325 m a.s.l.) in a remote upland Sitka spruce (<i>Picea</i> <i>sitchensis</i>) forest in southern Scotland. Concentrations of TCAA in different year classes of spruce needles and in air, rain water, cloud water, and forest soil were measured concurrently at sites with a wet deposition gradient to investigate the route of atmospheric input to forest. The observations of greater concentrations of TCAA in the needles at higher elevation (1998 year class mean concentration: 38 and 28 ng g^-1 dry weight to the upper and lower elevations, respectively, a trend towards accumulation of TCAA in older needles, and seasonal variations are all consistent with the hypothesis that the TCAA concentration may be controlled by metabolic processes in the needles. Higher concentrations of TCAA in cloud water (median: 0.94 ppb) than rain water (median: 0.87 ppb) with ratios as high as 7:1 at some times have been measured. No seasonal variation of TCAA in wet input to the forest has been observed. The sum of gaseous and particle-bound concentrations of TCAA in air is low (<100 pg m^-3). Concentrations of TCAA in forest soil are extremely variable (5 to 400 ng g^-1 fresh weight) with location and time, and the origin of some very high, but repeatable, measurements (>200 ng g^-1 fresh weight), which cannot be explained by atmospheric input only, has not been identified. The percentage of TCAA which can be extracted from the soil with water is shown to be <10%, suggesting that TCAA is adsorbed or bound to the soil matrix. No significant relationship between soil TCAA concentrations and total organic matter content, water content or pH has been observed. A zero-dimensional mass balance calculation based on measurements at the upper forested site has identified a net source of TCAA in the catchment, suggesting that a natural formation of TCAA in the soil is occurring. However, the nature of the formation process is not, at this stage, identified.