Research plan for the investigation of water, energy, and biogeochemical budgets in the Luquillo mountains, Puerto Rico

Larsen, M.C., Collar, P.D., and Stallard, R.F., 1993, Research plan for the investigation of water, energy, and biogeochemical budgets in the Luquillo mountains, Puerto Rico: U.S. Geological Survey Open-file Report 92-150, 19 p.

The Luquillo mountains of eastern Puerto Rico are the site of U. S. Geological Survey (USGS) research into biogeochemical and geomorphic processes that control the movement and transformation of water, energy, bedrock weathering products, and nutrients in the earth-surface environment. This study was begun in 1990 and is scheduled to last three years, with the possibility of being extended for further data collection. The study area for this research effort includes the 113 square kilometers Luquillo Experimental Forest (LEF) that is administered by the U. S. Forest Service. The LEF has been the site of ongoing research since 1988 as part of the National Science Foundation's Long Term Ecological Research program. In addition, comparative studies are being conducted in the Río Grande de Loíza basin (Loíza basin), an urban and agriculturally developed 600 square kilometers watershed located immediately to the west of the LEF. The principal elements of the study described in the report are as follows: Determination of biogeochemical budgets: water, energy, carbon, nutrient, ion, sediment, and gas budgets will be calculated in two LEF watersheds instrumented with meteorologic, soil, hydrologic, and ground-water monitoring equipment. A biweekly time series of samples is being collected. In addition, intensive sampling is undertaken during selected storms. Study of weathering, erosion, and mass-wasting processes in undeveloped watersheds of contrasting lithology: chemical-weathering, erosion, and mass-wasting processes in watersheds underlain by the two dominant rock types, volcaniclastic and quartz diorite, are being compared. The effects of mass wasting on biogeochemical cycling in each rock type will be evaluated through a compilation of physical, chemical, and mineralogic properties for a chronosequence of landslides. Water and sediment budgets will be used to develop a conceptual model of hillslope hydrology and landform evolution. Comparison of weathering and gas flux in developed and forested watersheds: paired basins were selected and gaged in the relatively undisturbed LEF and in the agriculturally developed Loíza basin. Budgets of all aqueous constituents will be compared and contrasted in the developed and forested basins of similar lithology. Gas-flux differences (carbon dioxide, nitrogen dioxide, methane) between developed and undeveloped areas will be evaluated using chamber techniques and the results related to land-use differences. Measurement of reservoir and agricultural pond gas fluxes: methane production is being measured in selected reservoirs and agricultural ponds in and near the Loíza basin and LEF. A regional methane budget will be calculated.