GIS Analysis of Lake Pontchartrain Water Quality before and After the Bonnet Carré Spillway Opening in 2011

Adebayo Segun (sadebay@tulane.edu), Reda Amer (ramer1@tulane.edu)

Department of Earth & Environmental Sciences, Tulane University 6823 St. Charles Ave, New Orleans, LA 70118

This study focuses on the application of GIS analysis of Lake Pontchartrain’s water quality data through 2011, with emphasis on temporal and spatial changes as well as the impact of the Bonnet Carré spillway opening from May, 9^th to June 20^th. The Lake Pontchartrain Basin Foundation is collecting water samples for analysis of several water quality parameters, including fecal coliform bacteria levels, salinity, turbidity, temperature and dissolved oxygen at 10 sites. Fecal coliform concentrations in Lake Pontchartrain ranged from less than 3 to 576 colonies per 100 milliliters of water (January through December 2011). GIS spatial analysis of a 12-month temporal scale showed that the fecal coliform concentrations were lower during the spillway opening than the months of April and July. Opening of the spillway lowered the fecal coliform levels in the lake. Fecal coliform concentrations were negatively correlated with dissolved oxygen, but there was no significant correlation between fecal coliform and the other parameters. The results of GIS spatial statistical analysis and spatial autocorrelation showed that the p-values are 0.840937 and 0.626242 respectively, which are indicative of random spatial patterns. A spatial trend of periodic increase of fecal coliform concentrations was observed at sampling points located at the outlets of streams and drainage canals. However, fecal coliform levels detected at these locations were between 300 – 500 MPN/100 ml. According to the U.S. Environmental Protection Agency (EPA) and Louisiana Department of Environmental Quality standards, Lake Pontchartrain water quality is poor and might not be safe for fishing and swimming.