Thomas A. Tremblay

Regional controls on geomorphology, hydrology, and ecosystem integrity in the Orinoco Delta, Venezuela

Interacting river discharge, tidal oscillation, and tropical rainfall across the 22,000 km2 Orinoco delta plain support diverse fresh and brackish water ecosystems. To develop environmental baseline information for this largely unpopulated region, we evaluate major coastal plain, shallow marine, and river systems of northeastern South America, which serves to identify principal sources and controls of water and sediment flow into, through, and out of the Orinoco Delta. The regional analysis includes a summary of the geology, hydrodynamics, sediment dynamics, and geomorphic characteristics of the Orinoco drainage basin, river, and delta system. Because the Amazon River is a major source of sediment deposited along the Orinoco coast, we summarize Amazon water and sediment input to the northeastern South American littoral zone. We investigate sediment dynamics and geomorphology of the Guiana coast, where marine processes and Holocene history are similar to the Orinoco coast. Major factors controlling Orinoco Delta water and sediment dynamics include the pronounced annual flood discharge; the uneven distribution of water and sediment discharge across the delta plain; discharge of large volumes of water with low sediment concentrations through the Rio Grande and Araguao distributaries; water and sediment dynamics associated with the Guayana littoral current along the northeastern South American coast; inflow of large volumes of Amazon sediment to the Orinoco coast; development of a fresh water plume seaward of Boca Grande; disruption of the Guayana Current by Trinidad, Boca de Serpientes, and Gulf of Paria; and the constriction at Boca de Serpientes.

Native woodland loss during the mid 1900s in Cameron county, Texas

Abstract Large-scale native woodland loss in the Lower Rio Grande Valley of Texas during the 20th century has been reported in the literature. However, no detailed, quantitative study of landscape change in the area has been conducted. This paper presents an example of quantified native woodland loss within this area. Using historical topographic maps and aerial photographs, we were able to map the extent of native woodland areas in Cameron County in the 1930s. The historical native woodland areas were then compared with the 1983 extent of native woodlands as mapped on modern topographic quadrangles. Our results for Cameron County corroborate previous estimates of native woodlands loss in the Lower Rio Grande Valley, though at a slightly lower percentage (91%). Comparisons with recent land-use and land-cover mapping show that much of the loss was a result of agricultural expansion.

Analysis of EO-1 ALI data to determine local impacts of Hurricane Iris on broadleaf forests in Belize, Central America

Hurricane Iris, a Category Four hurricane on the Saffir-Simpson hurricane scale with winds exceeding 200 kph, made landfall in southern Belize, Central America, on October 8, 2001. Extensive wind damage occurred, including toppled and defoliated trees, and major losses to the local banana industry. Among the regions impacted by the storm was the Monkey River area located approximately 130 km south of Belize City. Imagery acquired on December 4, 2001, from NASAs Earth Observing-1 (EO-1) Advanced Land Imager (ALI) was used to analyze impacts on land cover/land use with emphasis on broadleaf forests. Comparisons were made with pre-hurricane Landsat TM data, in which 14 land cover/land use classes, including 6 classes of forests and savannah, 5 classes of wetlands and coastal lands, and 3 classes of developed land were classified.

Preliminary evaluation of NASA EO-1 imagery through an analysis of land cover/land use in Belize, Central America

This project, funded through NASAs Earth Observing-1 (EO-1) program, is a 2-year investigation to evaluate EO-1 ALI and Hyperion in Belize, Central America. The Bureau of Economic Geology and Center for Space Research are evaluating the newly acquired data in cooperation with the Government of Belize.