Natural disasters and long-term recovery: A baseline study of historical change and habitat structure of Juncus roemerianus marsh at Grand Bay, Mississippi.

摘要

Ecosystem structure and function in a Juncus roemerianus dominated marsh in coastal Mississippi was investigated using remote sensing techniques. Rate of change in land cover types were computed from historical aerial photography (1940 to 2006) of the study area located in Kreole, MS. Baseline biodiversity and vegetation coverage were determined from in situ line intercept vegetation analyses. Post-classification difference maps for intervals between image time periods and baseline parameters were compared using 2006 vegetation transects and a 1 m resolution Digital Ortho Quarter Quadrangle (DOQQ) image as ground-reference. The ancillary photographs and digital imagery were rectified, digitized and interpreted from both analog and digital file formats using a combination of geospatial techniques. A Gaussian normalization technique provided a minimum standard deviation in pixel brightness among 1940, 1985 and 2006 images as compared to other image normalization techniques. Additional investigations were made from images with dates significant to Hurricane Elena (1985) and Hurricane Katrina (2005) storm events in coastal Mississippi. Data collected from Mahalanobis distance supervised image classification and simple value difference maps demonstrated that change in marsh structure did occur between pre and post-storms at the study area in Mississippi. A classification error matrix showed accuracies ranging from 46.80% in the 1940 classification to 91.96% in the 2006 ground reference. The supervised post classification percent change of natural marsh for the Hurricane Elena (1985) imagery was +5.25% Juncus roemerianus marsh, +2.47% pine hummock, +0.91% open-water, -7.14% salt panne, and +0.34% unclassified. The Hurricane Katrina (January 2004-March 2006) supervised post classification percent change was +13.62% Juncus roemerianus marsh, -13.3230% pine hummock, -2.90% open-water, +2.61% salt panne, and 0.0% unclassified. The percent change difference map for Hurricane Elena (natural) was 0%, 10.81%, 88.85%, and 0.34% respectfully with a mean of 2.8952% and standard deviation of 1.0683% across all classes. The Hurricane Katrina percent change difference was 0%, 11.68%, 88.32%, and 0% respectively with a mean of 2.8832% and standard deviation of 0.3212%. The overall pixel change in pre and post storm images from Hurricane Elena were 10.34% of the pixels (2811 m2) and 11.68% (3175 m2) for Hurricane Katrina.