Water, Energy, and Biogeochemical Budgets (WEBB) Program

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


Matthew C. Larsen1, Paul D. Collar1, and Robert F. Stallard2

1U.S. Geological Survey, GSA Center, Suite 400-15, 651 Federal Drive, Guaynabo, Puerto Rico, 00965-5703, USA

2U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303-1066, USA


Abstract

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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.

INTRODUCTION

Understanding and predicting global environmental change has become a major social and scientific concern of the late 20th century. Scientists from many disciplines and nations around the world have mobilized in this endeavor. During the past three decades, atmospheric scientists have made substantial progress in developing models that account for most of the important components of the climate system. Significant progress is needed, however, in the understanding of the processes associated with the exchanges of water, energy, and carbon between the earth's surface (including vegetation) and the atmosphere. Progress in this latter area requires the knowledge and skills of specialists in fields such as hydrology, biology, geology, and geochemistry, as well as the atmospheric sciences.

To strengthen terrestrial-process research associated with the interactions of water, energy, gases, nutrients, and vegetation, the U.S. Geological Survey (USGS) Global Change Research Program initiated a nationwide program entitled Water, Energy and Biogeochemical Budgets (WEBB). The purpose of WEBB is twofold: to improve understanding of processes controlling terrestrial water, energy and biogeochemical fluxes, process interactions, and process relations to climatic variables; and to improve the capability to predict terrestrial water, energy, and biogeochemical budgets over a range of spatial and temporal scales. This study was begun in 1990 and is scheduled to last three years, with the possibility of being extended for further data collection.

WEBB process studies are being implemented as a systematic program of intensive, long-term field investigations in Colorado, Georgia, Puerto Rico, Vermont and Wisconsin. Study sites were selected on the basis of geographical and environmental diversity. Sites having extant parallel data collection or WEBB-related process investigations were given priority. The sites include such multidisciplinary research locations as the National Science Foundation sponsored Long-Term Ecological Research sites, the U.S. Forest Service Experimental Forests, and the United Nations Educational, Scientific, and Cultural Organization study areas known as International Biosphere Reserves. A major emphasis of WEBB investigations is the development and maintenance of strong collaborative research relationships among scientists in other Federal agencies and the academic community.

Research at the Puerto Rico WEBB site addresses the biogeochemistry of weathering and erosion in the Luquillo mountains. The research will focus on how mass wasting and other hillslope erosive processes control rates of erosion, the composition of solid and dissolved erosion products, and nutrient and carbon dynamics in the soils of the watershed. This research is accomplished by the development of biogeochemical budgets based on regular biweekly and storm sampling, the study of hillslope geomorphic and hydrologic processes, and the study of biogeochemical processes in soils. In addition, the effects of agricultural development on nutrient budgets and gas budgets will be investigated. This research problem involves a comparison between developed and undeveloped watersheds of 1) water, sediment, and nutrient budgets, 2) soil gas fluxes, and 3) gas fluxes from artificial ponds and lakes.


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.

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