Water chemistry at tea plantation in Taiwan

Occult deposition is deposition of pollutants by direct contact with mist or cloud. The total quantity of fog water is in general much less than that of rain water, however, concentrations in cloud water could be very high. This is because the formation of fog is close to the ground where concentration of air pollutants is high and the per unit volume surface of fog is much higher than that of rain. Due to higher concentrations, the contribution of chemical deposition from fog often exceeds its contribution on water input and its effects on ecosystem cannot be neglected. Cloud forest in Taiwan is also important for tea plantation. In addition to precipitation, fog is another important pathway of atmospheric deposition in tea plantations. As global tea consumption is increasing, tea plantations are expanding and more nitrogen fertilizers are used to increase yields, which could directly or indirectly influence ecosystems. Through collection and analyses of rainfall, fog, throughfall, and stream water, this study aims to evaluate the impacts of atmospheric deposition on nutrient input-output of tea plantations in northern Taiwan. The abundance order of all ions was Cl- > Na+ > SO42- > K+ > NO3- >NH4+ >Ca2+ >Mg2+ in rainwater and Na+>Cl- >NO3- >Mg2+ >SO42- > Ca2+ > NH4+ > K+ in fog water. Cl- and Na+ were the most abundant ions in both fog and rain water, indicating strong oceanic influences on water chemistry. The concentrations of all ions were much higher in fog water and the ratio to fog and rain was K+ (2.11) < NH4+ (5.59) < SO42- (6.99) < Ca2+ (9.25) < Cl- (9.26) < NO3- (10.3) < Na+ (14.2) < Mg2+ (22.2) < DON (46.9), which lies between sites with (mostly were larger than 10) and without (less than 5) major emission, possibly because the study site is close to big cities but the surroundings are well covered with forest. Results from principal component analysis indicates that agriculture influence is the main factor for explaining variance of K+ and NH4+ concentrations in fog water but not rain water. The result indicates that fog was more affected by local air pollution.