Browsing by Subject "gis"
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Item A geographic information system (GIS) based determination of estuarine and marine wetland and shoreline changes in the Galveston Bay estuary from 1995 to 2002(Texas A&M University, 2008-10-10) Taylor, Christina ClaudetteThe purpose of this study was to identify and quantify estuarine and marine wetland and shore changes circa Galveston Bay Estuary (GBE) from 1995 to 2002 by using aerial photography and GIS mapping techniques. Aerial photographs in digital format were acquired from Texas Natural Resource Information System (TNRIS) and the Houston Galveston Area Council (HGAC); these photographs were selected because the images were taken at the time period desired, existed in digital formats at resolutions of 1 m or greater, and were in coordinate systems that were already in or could be properly aligned and georeferenced. Maps for each of thirty quadrangles that include estuarine and/or marine habitats around the GBE were created, depicting wetlands and shorelines for the years 1995 and 2002 as well as changes between the two time periods. Polygons representing different habitats in 1995 were drawn while working at a scale of 1:4,000 or greater. Maps of habitats in 2002 and maps showing changes from 1995 to 2002 were produced by modifying individual 1995 polygons to document boundary shifts or habitat changes from 1995 to 2002. All resulting maps were constructed at 1:24,000 scale in UTM NAD 83 coordinate system to match USGS quad maps. Areas of each habitat in 1995 and 2002 and changes between the two years were calculated in acres and comparisons were made. There were four objectives developed to be examined by the creation of the new set of maps for GBE. They were to determine habitat changes during the time period in question, effectiveness of mapping technique, where differences in change occurred, and what type (i.e. erosion, development, accretion, etc.) of change occurred. My analyses of these maps indicated that there were 117,670 acres of estuarine wetlands and 21,983 acres of unconsolidated estuarine and marine shores present in 1995. In 2002, these values changed to 116,534 acres of estuarine wetlands and 21,630 acres of estuarine and marine shores. The rate of wetland loss was estimated as 162 acres per year or 0.1% of all wetlands annually from 1995 to 2002. This rate has slowed from the previous rate of 405 acres per year or 0.4% in 1979 and remained the same as the 161 acres per year or 0.1% reported in 1993 for the GBE. Further, the results of my analyses indicated that losses from direct human influences (e.g. development, dredging, and filling) were less than losses associated with natural processes like erosion and subsidence.Item Evolutionary dynamics of Pinus taeda L. in the Late Quaternary: An interdisciplinary approach(Texas A&M University, 2004-11-15) Al-Rabab'ah, Moh'd AliPinus taeda L. dynamics, migration patterns and genetic structure were investigated over geological time scale (the past 21,000 years), historical time scale (the past 500 years) and recent time scale (the past 50 years ago) using multi-source data and an interdisciplinary approach. Population genetics, microsatellite markers, DNA fingerprinting, fossil records, geological history, historical records, aerial photographs, soil maps, weather data, remote sensing and geographic information systems (GIS) were used to assess the dynamics of P. taeda populations especially for the Lost Pines (LP), a disjunct population at the westernmost edge of the species range. Pinus taeda populations east and west of the Mississippi River Valley are genetically differentiated. Eastern populations had higher allelic diversity and diagnostic alleles than western populations. Gene flow estimates are high. Allelic diversity and diagnostic alleles patterns are attributed to the prevailing wind direction. Differentiation east and west of the MRV was attributed to separation to two refugia during the Pleistocene. The Lost Pines population is believed to have undergone one or more bottleneck events with loss of rare alleles. Despite the bottleneck, allelic richness was similar for the LP and the control population from the Western Gulf (WG) population. Population size contraction of the LP was attributed to climate change in central Texas over geological time scale. The natural origin of the Lost Pines was investigated. Multivariate and clustering techniques and assignment and exclusion methods using DNA markers show that the LP population shared ancestry with the WG populations with no evidence for admixture from other sources. Historical records parallel this conclusion. With the absence of logging within Bastrop and Buescher State Parks, P. taeda area and patch size increased from 1949 to 1995. Thirty six percent of the pine patches observed in 1949 had disappeared by 1995 by merging. Landscape pattern analysis shows significant dynamics. The distribution of P. taeda in Bastrop County was associated with sandy light topsoils, clayey heavy sub-soils and high permeable soils. Pinus taeda grow on various soil types as well. Growing on these soils under current climatic conditions may compensate for the precipitation regime in this area.Item Extending the utility of machine based height sensors to spatially monitor cotton growth(Texas A&M University, 2004-09-30) Geiger, David WilliamThe recommended procedures for implementing COTMAN; a cotton management expert system; suggest frequent crop scouting at numerous locations for each field. Machine based height sensors coupled with the ability to spatially record height values make it possible to locate regions of a field that are height representative of the entire field. A machine based height measurement system called HMAP was used to assess plant height in various fields in the 2003 growing season while the same fields were monitored with COTMAN. The plant height data was used to determine an optimal COTMAN sampling scheme for each field consisting of significantly fewer sampling locations than recommended by COTMAN. It was possible to ascertain equivalent information from COTMAN using two sites selected from height data in place of six sites selected per COTMAN recommendations. The HMAP system was extended to monitor rate of growth in real time in addition to plant height by comparing historical plant height data recorded on previous field passes to current height values. The rate of growth capable HMAP system will make it possible to track cotton growth and development with an automated system.