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

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 monit or the deposition of airborne salts of marine origin. The atmospheric trans port and inland deposition of marine salts can thus be assessed by measurin g 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 a fter leaching samples with water. The dispersion of element concentration i n the area was studied through geostatistical analysis. Numerical values we re estimated by two interpolation methods: ordinary kriging and kriging wit h an external drift. The latter method used the logarithm of the distance t o the coast as an auxiliary variable and yielded more reliable results. Eve ry 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 o bserved between surveys. The variability of results is interpreted using th e precipitation data obtained for the region under consideration. (C) 1999 Elsevier Science B.V. All rights reserved.