A Seasonally Anoxic Mountain Lake with an Active Fe Cycle in Tropical Taiwan

Variations of temperature and oxygen indicate that the 2150 m high Great Ghost Lake in tropical Taiwan is seasonally stratified and anoxic. Low concentrations of ions and nutrients and the similarity in the distribution of the reduced species in the water column in the early stages of stagnation indicate that the production of the reduced species occurs mainly in the sediments with a subsequent release into the overlying water. In addition, the high organic matter content in the sediments and the short period of water overturn make Fe(II) the most abundant reduced species in the sediments and in the water column. As a result, the annual Fe cycle plays one of the most important roles in regulating the water chemistry and in driving the reduced species from the sediments to the anoxic hypolimnion. The distribution of reduced species during the stagnation is in agreement with the thermodynamic sequence. The accumulation rates of Fe2+, Mn2+, NH4+, sulfide and CH4 in the water column during the early stages of stagnation are about 5.07, 0.059, 1.69, 0.015 and 1.65 mmol m-2 day-1, respectively.