Estimating critical loads by accounting for local variability in wet and dry deposition

Wet and dry depositions were collected in Agra, India, using a polypropylene bottle and funnel collector. All the wet and dry deposition samples were analysed for major anions and cations (Cl-, NO3-, SO42-, Ca2+, Mg2+, Na+, K+ and NH4+). Deposition data (wet and dry) showed very high pH and Ca2+ concentration indicated the direct influence of crustal sources. In both wet and dry deposition concentrations of SO42-, NO3-, Cl- indicated exclusive neutralization of acidity by alkaline constitutes which originate from both local soil and adjacent Thar desert. Further, acid neutralization capacity of soil has also been quantified and found to be positive (33 µeq g-1) which indicates that at this site soil is not vulnerable to acidification due to its alkaline pH with value ranging between 7.5 and 8.2. Critical load for acidity (S and N) of soil with respect to vegetation was also evaluated using the local variable data of deposition. The present level of deposition of S and N (483 eq ha-1 yr-1 and 1520 eq ha-1 yr-1) was found to be much lower than critical load calculated for S and N (2192 eq ha-1 yr-1 and 4512 eq ha-1 yr-1). In addition to this, present critical load exceedance was also calculated for soil and it was found to be negative indicates that the ecosystem which is enriched with these species is still protected.