Effects of hurricane disturbance on stream water concentrations and fluxesin eight tropical forest watersheds of the Luquillo Experimental Forest, Puerto Rico

Stream water chemistry responds substantially to watershed disturbances, bu t hurricane effects have not been extensively investigated in tropical regi ons. This study presents a long-term (2.5-11 y) weekly record of stream wat er chemistry on eight forested watersheds (catchment basins) in the Luquill o Mountains of Puerto Rico. This includes a period before and at least 2 y after the disturbance caused by the 1989 Hurricane Hugo. Nitrate, potassium and ammonium concentrations increased after the hurricane and remained ele vated for up to 2 y. Sulphate, chloride, sodium, magnesium and calcium show ed smaller relative significant changes. Average stream water exports of po tassium, nitrate and ammonium increased by 13.1, 3.6 and 0.54 kg ha(-1) y(- 1) in the first post-hurricane year across all watersheds. These represent increases of 119, 182 and 102% respectively, compared to the other years of record. The increased stream outputs of potassium and nitrogen in the firs t 2 y post-hurricane are equivalent to 3% (potassium) and 1% (nitrogen) of the hurricane-derived plant litter. Effects of hurricanes on tropical strea m water potassium and nitrogen can be greater than those caused by canopy g aps or limited forest cutting, but less than those following large-scale de forestation or fire.