DOI: 10.7267/w0892j79s
title: Spatiotemporal variation in Oregon salt marsh expansion and contraction

description: The dataset is a layer file created in ArcGIS Pro 2.2. The dataset includes digitized outlines of the seaward edges of five Oregon salt marshes (Nehalem, Netarts, Salmon, Alsea, and Coquille). These are roughly decadal from 1939 to 2018 and were hand-digitized using historical aerial photography (1939 to the late 1990s) scanned at the University of Oregon’s Map & Aerial Photography Library and aerial imagery downloaded from the Oregon Statewide Imagery Program (https://www.oregon.gov/geo/Pages/imagery_data.aspx). Historical aerial imagery were georeferenced using ≥ 10 control points that were placed at stable locations including road and channel intersections, and using a second order polynomial transformation. Salt marsh areas were determined using a stable upslope edge (Pacific Marine & Estuarine Fish Habitat Partnership current extent map https://www.pacificfishhabitat.org/data/). The dataset also includes rates of salt marsh seaward edge change which was calculated using the USGS Digital Shoreline Analysis System (DSAS; https://www.usgs.gov/centers/whcmsc/science/digital-shoreline-analysis-system-dsas?qt-science_center_objects=0#qt-science_center_objects) in ArcMap 10.7.1 over roughly decadal periods from 1939 to 2018 and integrated over the period of record. DSAS automatically placed transects at 5 m intervals perpendicular to digitized marsh edges. When calculating the rate of edge change integrated over all digitized edges, regressions were fit for any transect that passed through ≥ 6 edges. Error estimates associated with the regressions were calculated with 95% confidence intervals. These rates and uncertainties can be found in the attribute tables of each shapefile.
description: These data were collected to assess potential drivers of marsh lateral rates of expansion/contraction over the last ~80 y in five Oregon estuaries: Nehalem Bay, Netarts Bay, Salmon River Estuary, Alsea Bay, and Coquille River Estuary (focusing on marshes relatively unimpacted by dikes). These systems vary in terms of bay morphology, mean annual fluvial sediment supply, and relative sea level changes. These forcings were assessed by comparing net lateral rates of edge change within and across estuaries. Further, to assess the importance of changing land use and hydroclimate on marsh morphodynamics, roughly decadal rates of marsh expansion/contraction were compared for each estuary. These rates were binned into four distinct periods to assess the relative importance of the PDO and history of timber harvest in uplands on marsh expansion/contraction (1939 to 1944, 1944 to 1977, 1977 to 2000, and 2000 to 2018). Results will elucidated both spatiotemporal patterns of marsh lateral change and provided an idea of future trajectories under changing climate and land use scenarios.   
description: Shorelines were roughly decadal from 1939 to 2018 and were hand-digitized using historical aerial photography (1939 to the late 1990s) scanned at the University of Oregon’s Map & Aerial Photography Library and aerial imagery downloaded from the Oregon Statewide Imagery Program (https://www.oregon.gov/geo/Pages/imagery_data.aspx). Historical aerial imagery were georeferenced using ≥ 10 control points that were placed at stable locations including road and channel intersections, and using a second order polynomial transformation. Salt marsh areas were determined using a stable upslope edge (Pacific Marine & Estuarine Fish Habitat Partnership current extent map https://www.pacificfishhabitat.org/data/). The dataset also includes rates of salt marsh seaward edge change which was calculated using the USGS Digital Shoreline Analysis System (DSAS; https://www.usgs.gov/centers/whcmsc/science/digital-shoreline-analysis-system-dsas?qt-science_center_objects=0#qt-science_center_objects) in ArcMap 10.7.1 over roughly decadal periods from 1939 to 2018 and integrated over the period of record. DSAS automatically placed transects at 5 m intervals perpendicular to digitized marsh edges. When calculating the rate of edge change integrated over all digitized edges, regressions were fit for any transect that passed through ≥ 6 edges. Error estimates associated with the regressions were calculated with 95% confidence intervals. These rates and uncertainties can be found in the attribute tables of each shapefile.