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

We studied five 20-m transects on the lower slope under tropical lower montane rain forest at 1900-2200 m above sea level. We collected samples of soil and of weekly rainfall, throughfall, litter leachate, and stream water between 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 kg(-1)) and Mg concentrations (1.4-5.4) in the O horizon were significantly different between the transects. Annual rainfall was 2193 mm; throughfall varied 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 mean 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 concentrations 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 (= throughfall-rainfall deposition) was positive for most elements except for Mn, Na, and Zn. High-flow events were associated with elevated Al, TOC, Cu, Mn, and Zn concentrations.