Water, Energy, and Biogeochemical Budgets in Puerto Rico and Panamá

Robert Stallard: Telephone: +1-303-541-3022; FAX: +1-303-447-2505
e-mail: stallard@colorado.edu

El Yunque Peak from Bisley Ridge in the Luquillo Experimental Forest, Puerto Rico

(2) USGS WEBB-Related Research: Research in Puerto Rico and Panama is part of the USGS WEBB Program. Sites are in eastern Puerto Rico, including the Luquillo Experimental Forest, and in the Panama Canal Watershed. Both regions are excellent metaphors for future development in the tropics. We endeavor to characterize the processes that control the distribution and transport of major, important-minor, and nutrient elements through soils, downslope, and out of the watersheds. Multiple-paired watersheds are used to compare processes among geologically matched, natural and developed environments. Much of the Panama Canal Basin is being deforested, while Puerto Rico is undergoing afforestation as it urbanizes. The Luquillo WEBB Project has operated since 1990, and has accumulated a large body of data and publications. Parallel long-term monitoring in Panama started in 1991; work is on Barro Colorado Island and is funded by the Terrestrial Environmental Studies Program of the Smithsonian Tropical research Institute (STRI TESP). Work was extended to the entire Panama Canal Basin through funding by the US Agency for International Development as the Panama Canal Watershed Monitoring Project (1996-1998). At the present time, we are assembling data sets for mapped data (in Arc/Info), hydrology, sediment studies, and solute chemistry for Puerto Rico and Panama. In addition to using classical approaches to watershed mass balances, we are incorporating new methods, such as in situ-produced cosmogenic beryllium-10, to study long-term rates of erosion and biogeochemical cycling.

Work is now underway to assemble a database for Puerto Rico to prepare a biogeochemical image of the island using both WEBB and non-WEBB sources. Of all US Territory in the tropics, Puerto Rico is the most geologically diverse, and we anticipate that this synthesis will be applicable to many tropical regions. NASA funded an effort to analyze extant atmospheric chemical data, including rain chemistry, stream chemistry, and gas chemistry to determine possible abiotic causes of on-going frog population declines and extinctions in eastern Puerto Rico. The conclusion, published in a special issue of Conservation Biology, is that Puerto Rico is being bathed in a growing suite of human-generated, potentially frog-killing contaminants. A Panama Canal Watershed study was funded by the US Agency for International Development from 4/1997 to 12/1999. In FY 2001, the first summary article was published in Bioscience. The US Army is supporting additional work. We are preparing for publication an implementation of TOPMODEL coupled to a stream-chemistry model that works for the flashy stream catchments that are typical of mountainous areas of the humid tropics. In addition, we are using the hydrologic model in an analysis of the edaphic factors that control the distribution of herbaceous and woody plants in Panama.

Theory: Human-Impact Biogeochemistry: Humans have intercalated themselves into all aspects of the Earth-surface environment and have markedly altered biogeochemical cycles. Some alterations, such as the rapid increase in the concentrations of greenhouse gases, have received particular attention. Others have been at least as spectacular, but are largely ignored by Earth and ecosystem scientists. Regional-scale studies are rare, because of the complexity and the need to examine details such as rare events and intense, but localized, phenomena. Since the early 1800's, approximately 15% of the earth's non-ice-covered land surface has been transformed into cultivated land, mostly in temperate zones, with most future changes forecast for the tropics. We ask: (1) How do human activities, particularly land-use change, affect environments being examined? (2) How do we use rivers to integrate phenomena at local spatial scales up to continental scales? (3) What do rivers deliver to the ocean? The WEBB project work in Puerto Rico and parallel work in Panama and the Mississippi Basin Carbon Project (MBCP) use models of erosion and hydrology in combination with geographic information systems to examine how accelerated erosion, terrestrial sedimentation, and nutrient loading affect carbon and nutrient cycles. Significant carbon may be deposited with terrestrial sediment, perhaps 0.6 to 1.5109 tonnes year-1 globally. This sink is not climatologically significant unless the eroded carbon is replaced photosynthetically. Two hypotheses are being tested: (1) that significant amounts of additional carbon are buried during the deposition of sediments in terrestrial environments, in large part because of human acceleration of erosion and modifications of hydrologic systems and nutrient supplies, and (2) that the carbon being buried is being replaced by newly fixed carbon at the site of erosion or by alluvial and lacustrine production.

Impact (1):: The WEBB Project treats weathering, erosion, biogeochemical cycling, and atmospheric-gas exchange, in small, nested watersheds. Agriculturally developed and natural watersheds are paired for rigorous comparison. It is the only WEBB site, of five, that has this focus. Moreover, this particular approach is now being adopted by the NSF-funded Long-Term Ecological Research (LTER) Program. I supervised the drafting of the original Luquillo WEBB Proposal in the summer of 1990, and I have been very active in coordinating most aspects of the scientific program. At the same time, I endeavored to have Matt Larsen, now the Caribbean District Chief, brought into a Ph.D. Program at the University of Colorado so that well trained local leadership could be developed. In recognition of my work in tropical watersheds, I was made a "Research Associate" at the Smithsonian Tropical Research Institute (STRI) starting January, 1997. The following organizational units are involved: USGS-WRD-NRP, USGS-WRD-Caribbean District Office, US Forest Service-International Institute for Tropical Forestry, LTER-Luquillo Experimental Forest, STRI in Panama-Environmental Studies Program, US Agency for International Development (USAID), and the US Army.

Impact (2): Of particular note is the Panama Canal Watershed Monitoring Project, funded by the USAID through STRI. I was (in my capacity of being a Research Associate at STRI) Consultant and Principal Investigator for one entire component of this $3M program. I trained and supervised a cadre of Panamanians in watershed research. Training took place in Puerto Rico, Boulder, and Panama. Six to eight people were on my team for the four years. In the end, an 8-volume unpublished data report was produced in English and Spanish editions, and data were compiled on 21 CD-ROMs. The project was completed on time (before the handover of the Canal), and all the team obtained jobs in environmental monitoring in Panama, one of the major objectives in leaving a good US legacy behind. I am working now on getting the material into publishable form (Condit et al., 2001).

Recent Research Efforts (to find out more, click on effort):



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