Figure 4
Remote sensing measured marsh shoreline erosion rates 1956–2018 (m yr−1). Data are means with 90% confidence intervals, n = 5 for Reference, 9 for Oiled-Untreated, 5 for Oiled-Manual, 9 for Oiled-Mechanical, and 5 for Oiled-Mechanical-Planted treatments. Marsh erosion rates differed among oiling/treatment categories (F4,28 = 9.368, p = 0.000); among time-periods (F2.48,69.47 = 62.210, p = 0.000); and for the interaction of oiling/treatment and time-period (F9.92,69.47 = 4.593, p = 0.000). In the post-Katrina/pre-spill period (2005–2010) erosion differences were not observed among any oiling/treatment classes, including Reference (p = 0.868 to 1.000). In the spill impact period (2010–2012) erosion differences were observed between: Reference versus all oiled classes (p = 0.000 to 0.001) except Planted (p = 0.410); between the Manual and Mechanical treatments (p = 0.063); and between Planted versus all other oiled classes (p = 0.000 to 0.065). In the post-spill period (2012–2018) erosion differences were observed between: Planted versus Untreated and Manual treatments (p = 0.066 and 0.072). Between the post-Katrina/pre-spill and spill impact time-periods, erosion differences were not observed within the Reference (p = 0.989) or Planted (p = 0.340) classes; however, differences were observed between these time-periods within each of the other oiled classes (p = 0.000 in all cases). See Supplementary Table S3 for detailed two-way mixed ANOVA results. Tukey’s test was used for all pairwise comparisons after ANOVA.
