Saline variability at ground level after kriging data from Ramalina spp. biomonitors

Abstract

Sea-salt input over the land masses is known to have deleterious effects on man-made structures, plants (crops and natives) and soil/water resources. Recent work has shown the ability of some epiphytic-lichen species to monitor the deposition of airborne salts of marine origin. The atmospheric transport and inland deposition of marine salts can thus be assessed by measuring saline elements in lichens growing over coastal areas. The concentration of Cl − and Na + was determined in lichen thalli collected on three different occasions in south-western Portugal. The extracellular fraction of Na + was obtained by a sequential elution procedure and surface Cl − was recovered after leaching samples with water. The dispersion of element concentration in the area was studied through geostatistical analysis. Numerical values were estimated by two interpolation methods: ordinary kriging and kriging with an external drift. The latter method used the logarithm of the distance to the coast as an auxiliary variable and yielded more reliable results. Every set of data produced a similar spatial pattern, showing a steep gradient in the first 3 km from the coast. However, considerable variation can be observed between surveys. The variability of results is interpreted using the precipitation data obtained for the region under consideration.