Ion Fluxes with Bulk and Throughfall Deposition along an Urban-Suburban-Rural Gradient

摘要

Fluxes of principal anions and cations with bulk and throughfall deposition during the growing period (April-September) were investigated for three years (2001-2003) at three sites differently exposed to the second biggest Lithuanian city - Kaunas. Fluxes of all investigated anions (SO_4~(2-), NO_3~- and Cl_3~-) and most cations were found to be the highest in suburban area to compare with both - Rural and urban sites. The highest seasonal variability of monthly ion fluxes and the highest differences between throughfall and bulk fluxes (net throughfall) were recorded in suburban area. The highest throughfall enrichment by sulphur was detected in spring and the beginning of summer (April, May) in urban and especially in suburban sites. For nitrogen compounds (NO_3~-, NH_4~+) positive net throughfall values were characteristic for urban and suburban sites and negative for rural site almost during the entire growing period. Uptake of NH4 ions was detected to be much higher of that for nitrates in rural area (46% vs. 22%). The most intensive enrichment of throughfall fluxes by K~+ ions took place during the summer time (May, June, July), however, intensity of potassium leaching at the same amount of precipitation was the highest in suburban area.