**5. Conclusions**

This study evaluated panne/pool development and fluctuations with remote sensing, identifying spatial and temporal patterns of coastal marsh habitat change in a protected National Seashore. Remote sensing methods were essential for understanding how these protected salt marshes changed from 1994 to 2017. This analysis was contingent on the proliferation of remote sensing data which allowed for the synthesis of multiple data types to better understand salt marsh trends and dynamics. Change analysis demonstrated that panne/pool expansion and edge erosion accounted for the majority of salt marsh loss. The losses were partly driven by an increase in edge erosion observed following the breach. Vegetation regrowth occurred with pannes/pools demonstrating increased regrowth when hydrologically connected to a mosquito ditch or channel. The pannes/pools analyzed were not in equilibrium in the two decades analyzed instead demonstrating a long-term trend of expansion.

There is a need for increased salt marsh monitoring for determining where, when, and how salt marshes are changing. This study presents a methodology for salt marsh classification and change analysis of pannes and edge erosion. The aerial imagery classifications achieved satisfactory overall accuracies (> 85%) as suggested by Thomlison et al. [68], however, propagated error when conducting the change analyses was a concern. NAIP imagery is an ideal data source in regards to spatial, temporal and spectral resolution with several caveats. The lack of a NIR band led to a decrease in accuracy due to vegetated and non-vegetated pannes appearing spectrally similar. Additionally, aerial image acquisitions had variable quality and tidal stages at time of acquisition which limited the accuracy of particular years. Finally, the data are only available for the USA. The workflow used in this study allowed for rapid classification and change analysis of salt marsh environments. The biennial collection of NAIP imagery makes it uniquely suited for the low-cost continuation of high-resolution salt marsh monitoring into the future.

**Author Contributions:** Conceptualization, A.C. and Y.W.; Formal Analysis, Y.W.; Funding Acquisition, Y.W.; Investigation, A.C. and Y.W.; Methodology, A.C. and Y.W.; Project administration, Y.W.; Resources, Y.W.; Software, Y.W.; Supervision, Y.W.; Validation, A.C.; Visualization, A.C.; Writing—Original Draft, A.C.; Writing—Review & Editing, A.C. and Y.W.

**Funding:** This research was funded by U.S. National Park Service, gran<sup>t</sup> number: P14AC00230.

**Acknowledgments:** This project was funded by the Northeast Coastal and Barrier Network (NCBN) of the National Park Service (NPS)'s Inventory & Monitoring Program under the Task Agreement Number P14AC00230. We appreciate the guidance and support of Sara Stevens, Dennis Skidds, Bill Thompson, and Charles Roman of the NPS NCBN and North Atlantic Coast CESU. The authors appreciate the assistance by administrators and professionals from Fire Island National Seashore (FIIS), particularly Jordan Raphael for his expertise, insights, field guidance, and logistic support. Additionally, the authors would like to thank the three anonymous reviewers for their comments and constructive criticism.

**Conflicts of Interest:** The authors declare no conflict of interest.
