Change in water quality during the passage through a tropical montane rainforest in Ecuador

We studied five 20-m transects on the lower slope under tropical lower mont ane rain forest at 1900-2200 m above sea level. We collected samples of soi l and of weekly rainfall, throughfall, litter leachate, and stream water be tween 14 March 1998 and 30 April 1999 and determined the concentrations of Al, total organic C (TOC), Ca, Cl-, Cu, K, Mg, Mn, NH4+-N, NO3--N, total N (TN), Na, P, S, and Zn. The soils were shallow Inceptisols; pH ranged 4.4-6 .3 in the O horizons and 3.9-5.3 in the A horizons, total Ca (6.3-19.3 mg k g(-1)) and Mg concentrations (1.4-5.4) in the O horizon were significantly different between the transects. Annual rainfall was 2193 mm; throughfall v aried between 43 and 91% of rainfall, cloud water inputs were less than or equal to 3.3 mm a(-1) except for one transect (203). The volume- weighted m ean pH was 5.3 in rainfall and 6.1-6.7 in throughfall. The median of the pH of litter leachate and stream water was 4.8-6.8 and 6.8, respectively. The concentrations of Ca and Mg in litter leachate and throughfall correlated significantly with those in the soil (r = 0.76-0.95). Element concentration s in throughfall were larger than in rainfall because of leaching from the leaves (Al, TOC, Ca, K, Mg), particulate dry deposition (TOC, Cu, Cl-, NH4-N), and gaseous dry deposition (NO3--N, total N, S). Net throughfall (= th roughfall-rainfall deposition) was positive for most elements except for Mn , Na, and Zn. High-flow events were associated with elevated Al, TOC, Cu, M n, and Zn concentrations.