A GIS-BASED MODEL FOR URBAN CHANGE AND WATER QUALITY IN THE PONTCHARTRAIN BASIN

The combination of remote sensing techniques and Geographic Information Systems (GIS) to measure water quality allows researchers to monitor changes in various water quality parameters over temporal and spatial scales that are not always readily apparent from in situ measurements. Water has a distinct spectral behavior in comparison to soil, vegetation and impervious cover, and therefore can be distinguished from surrounding environments. This study involves using remote sensing and GIS methods to map urban expansion and its resulting influences on water quality in the Pontchartrain Basin over the last three decades. A Landsat Thematic Mapper (TM) image from 1985 and a Landsat Operational Land Imager (OLI) image from 2015 were processed using the Spectral Angle Mapper (SAM) algorithm to map urban expansion. In order to estimate how water quality has changed in the Pontchartrain Basin between 1985 and 2015, in situ water quality data from the Louisiana Department of Environmental Quality was interpolated over the entire extent of the basin using Empirical Bayesian Kriging (EBK). A GIS model was constructed using Python Scripting that allows for the data in each data attribute to be auto-interpolated using EBK and produce a separate prediction map for the dataset. The water quality parameters of interest for this study included fecal coliform, nitrogen, phosphorous, and dissolved oxygen. The results of this study demonstrated that high levels of fecal coliform were consistent with increased urbanization in water bodies in the Pontchartrain Basin. Nitrogen levels were much lower in 2015 than in 1985. Phosphorous levels were higher in 2015 compared to 1985 and were at levels high enough to lead to eutrophic conditions. Dissolved oxygen levels were generally reflective of changes in temperature, however, low dissolved oxygen levels were present near the mouth of the Mississippi river in 2015 and not in 1985. The results indicated that urban expansion increased and resulted in impaired water quality in the Pontchartrain Basin.