Acidification of lakes and reservoirs in Taiwan

One hundred forty three lakes, ponds and reservoirs in Taiwan and the offshore islands Penghu (Pescadores), Kinmen (Quemoy), Matsu, Hsioliuchiu, Lutao and Lanyu have been investigated in the past few years. Hereafter, the term lake is generally used for the three bodies of water discussed. According to the rock and soil compositions, the authors divided Taiwan into three regions. Zone I consists mainly of igneous rocks with lakes generally of low buffering capacity and low pH. Zone LI consists mainly of noncalcareous sedimentary and metamorphic rocks with lakes of varying buffering capacity and pH. Those at high elevations generally have low buffering capacity and pH but many at low elevations have high alkalinity and pH. Zone III consists mostly of gravel, sand, clay, limestone and the alluvium zone with lakes of high buffering capacity and pH. About 27% of the lakes have low alkalinity and are mostly located in Zones I and II. These lakes are more threatened by acid rain and many indeed are acidic. They are mostly alpine and subalpine lakes or are located near the Tatun and Keelung volcano groups. The NTA (normalized total alkalinity) is used as an acidification index. The decrease of the NTA for Lovers Lake, Yuen-Yang Lake, Carp Lake (Hualien County) and Little Ghost Lake suggested acidification. The other Lakes' NTA mostly remained constant. We also measured the concentrations of 53 chemical species: Ag, Al, Au, B, Ba, Be, Bi, Ca, Cd, C2H5COO-, Cl-, Co, Cr, Cu, Dy, Er, Eu, Fe, Gd, Ge, HCO3-, Hg, In, K, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, NO3-, NO2-, Pb, Pd, PO4-3, Pr, Sc, Si, Sm, Sr, SO4-2, Ta, Tb, Te, Ti, Tm, V, Y, Yb, Zn and Zr in lake water samples. These concentrations were mostly within the limits set by the Environmental Protection Agency. Lovers Lake has lower pH but higher heavy metal concentrations than other lakes.