Chemical Characteristics of Rainwater in Sumatera, Indonesia, during 2001–2010

The chemical composition of acid deposition shows that ammonium and chloride concentrations as the indicators of forest fires were higher than sulfate and nitrate in Sumatera areas such as Medan, Lampung, Palembang, and Kototabang. Chloride had higher concentration than sodium (Na+ sea originated) with the ratio value of Cl−/Na+ > 1.16 found in Medan and Palembang. Ionic compositions from the lowest to the highest concentration in Kototabang were H+ > Cl− > Na+ > NH4+ > nss-Ca2+ > K+ > NO3- > nss-SO42- > Mg2+ > ss-SO42- > ss-Ca2+. Acid rain takes place if the acid compounds such as sulfates, nitrates, and chlorides dominate. If the ratio value of NO3-/(nss-SO42- + NO3-) < 0.5 then it indicates that nss-SO42- is higher than NO3-. Between 2001 and 2010 it was found that the frequency value of NO3-/(nss-SO42- + NO3-) < 0.5 was 97% from annual mean of 34 pieces of data in Medan, Kototabang, Lampung, and Palembang. Forest fires influence was more dominant than anthropogenic activities in Kototabang, Palembang and Lampung, except in Medan. It showed that ammonium was higher than NO3- content if the ratio value of NO3-/(NH4+ + NO3-) < 0.5 was 62%. For the period 2001–2010 the frequency value of NO3-/(NH4+ + NO3-) < 0.5 was 74% from total 34 annual mean pieces of data in four locations, that is, Medan, Kototabang, Palembang, and Lampung.