Physiography, geology, and land cover of four watersheds in eastern Puerto Rico—Chapter A
Four watersheds with differing geology and land cover in eastern Puerto Rico have been studied by the U.S. Geological Survey to evaluate water, energy, and biogeochemical budgets on a long-term basis. These watersheds are typical of island-arc, tropical settings found in many parts of the world. Two watersheds are located on coarse-grained granitic plutonic rocks, which weather to quartz- and clay-rich, sandy soils, and two are located on fine-grained volcanic and volcaniclastic sedimentary rocks which weather to quartz-poor, fine-grained soils. For each bedrock type, one watershed is covered with mature forest, and the other watershed, like most of Puerto Rico, has undergone a transformation from pre-European conditions of relatively undisturbed forest, to intensive agriculture in the 19th and early 20th century, to ongoing reforestation resulting from a transition by Puerto Rico to an industrial economy since middle of the 20th century. The comparison of water chemistry and hydrology in these watersheds allows an evaluation of the effects of land use history and geology on hydrologic regimes and erosion rates. This chapter presents the physiography, geology, and land cover of the four watersheds and provides background information for the remaining chapters in this report.