Water balance and nutrient inputs in bulk precipitation in tropical montane cloud forest in Panama

The hydrological balance and nutrient inputs in water were measured in a lower montane rain forest (1200 m) in Panama. Rainfall and throughfall were measured daily between July 1988 and July 1989 using a standard rain gauge and 50 longitudinal PVC collectors, respectively. Stemflow was measured daily between November 1990 and December 1991 in nine trees varying from 16 to 54 cm diameter at breast height (dbh), using tygon collars. Rainfall and throughfall water samples were collected every 15 days between January and October 1989 for chemical analyses (pH, conductivity, NO3-, NO2-, NH4+, PO43-, SO42-, Ca2+, Cl-, Mg2+, K+, Mn, Fe and Si). Bulk precipitation was 3510 mm. Interception was 37.2%, net precipitation was 62.8%, of which, throughfall was 62.4% and stemflow was 0.4%. The probability distribution of throughfall as a proportion of bulk precipitation, showed that 82% of the total variability is lower than a bulk precipitation value of 1.0 and that there are higher values in this mountain forest than in a lowland rain forest in Brazil were this value was also calculated, suggesting that the canopy of this montane forest is more heterogeneous, In only 6 of 140 of the rain events, was net precipitation higher than bulk precipitation, suggesting that direct inputs of cloud water by fog interception, is not an important water source for this forest. Interception at Fortuna is the highest value yet reported for a tropical montane rain forest; it maybe attributed to a very tall canopy (20-30 m) and abundant epiphyte load. Nutrient inputs in water varied from 0.70 kg ha(-1) per year of PO4-P to 34.5 kg ha(-1) per year of Cl. Leaching varied from 1.45 kg ha(-1) per year for PO4-P to 49.71 kg ha(-1) per year of K. Net absorption by the canopy was measured for S (-7.0 kg ha(-1) per year SO4-S) while for N the total annual input was about the same as the annual throughfall. Annual fluxes of calcium, sodium and potassium in bulk precipitation in the Fortuna forest were in the upper range of values reported for other tropical montane sites, perhaps owing to the proximity to the Caribbean Sea, Nutrient inputs of N, P and K in throughfall are consistent with inputs of throughfall relative to other nutrient pathways in tropical and temperate forests. (C) 1997 Elsevier Science B.V.