Geology topics

Jonathan L Pitchford

Publications and source records attributed to Jonathan L Pitchford.

3 recordsLinked to original sources

USGS2025

Shifts in marsh erosion, migration, and wave exposure over nearly two centuries of sea-level rise in the Gulf of Mexico

Coastal wetlands are economically important ecosystems, but are at risk to erosion from waves, storms, and sea level rise. However, marshes can persist under rising sea level through vertical accretion and migration into adjacent higher-elevation habitats. We measured rates of marsh shoreline change and migration and compared the results for historical and modern periods in a largely undeveloped and marine-dominated estuary within the Mississippi-Alabama coast of the Northern Gulf of Mexico. Mean shoreline change rate for the modern (post-1957) period was higher than historical rates (pre-1957) at −1.55 ± 0.11 m yr −1 and -0.84 ± 0.07 m yr −1 , respectively. Shoreline change rates were highest in regions where exposure to wind-driven waves increased due to barrier island migration and land loss. Marsh migration (modern 1.25 ± 0.37 m yr −1 and historical 1.01 ± 0.13 m yr −1 ) occurred at similar rates as shoreline erosion except for the highest erosive shorelines, leading to an overall 15% marsh loss. Upland-to-marsh conversion occurred in forested areas and may have been encouraged by changes in management practices. In the Grand Bay estuary, our data show that marsh migration is not occurring at sufficient rates to compensate for marsh loss, resulting in overall loss in marsh habitat. Overall, migration may allow marsh to persist under rising sea levels but can lead to an overall reduction in forested or freshwater habitats if steep slopes or other barriers prevent their migration.

Alabama, Mississippi↗

USGS2021

Coastal wetland shoreline change monitoring: A comparison of shorelines from high-resolution WorldView satellite imagery, aerial imagery, and field surveys

Shoreline change analysis is an important environmental monitoring tool for evaluating coastal exposure to erosion hazards, particularly for vulnerable habitats such as coastal wetlands where habitat loss is problematic world-wide. The increasing availability of high-resolution satellite imagery and emerging developments in analysis techniques support the implementation of these data into shoreline monitoring. Geospatial shoreline data created from a semi-automated methodology using WorldView (WV) satellite data between 2013 and 2020 were compared to contemporaneous field-surveyed Global Position System (GPS) data. WV-derived shorelines were found to have a mean difference of 2 ± 0.08 m of GPS data, but accuracy decreased at high-wave energy shorelines that were unvegetated, bordered by sandy beach or semi-submergent sand bars. Shoreline change rates calculated from WV imagery were comparable to those calculated from GPS surveys and geospatial data derived from aerial remote sensing but tended to overestimate shoreline erosion at highly erosive locations (greater than 2 m yr −1 ). High-resolution satellite imagery can increase the spatial scale-range of shoreline change monitoring, provide rapid response to estimate impacts of coastal erosion, and reduce cost of labor-intensive practices.

Remote Sensing↗

USGS2021

Lateral shoreline erosion and shore-proximal sediment deposition on a coastal marsh from seasonal, storm and decadal measurements

The persistence of coastal marsh is dependent on its ability to maintain elevation relative to sea level, particularly for marshes experiencing high rates of shoreline erosion due to wave-attack, storms, and sea level rise. Sediments eroded at the marsh edge are either delivered onto the marsh platform or into the estuary, the latter resulting in a net loss of marsh sediments and soil carbon. Knowledge on the timing, pattern, and quantity of sediment deposition versus shoreline erosion along the marsh-estuary interface is critical for evaluating the overall health and vulnerability of coastal marshes to future scenarios of sea level rise and for estimating sediment budgets . Here we examined marsh shoreline erosion and sediment deposition for marsh sites experiencing a range of shoreline erosion rates and different levels of wind-wave exposure within the Grand Bay National Estuarine Research Reserve and Wildlife Refuge in Mississippi. We developed a method for calculating an erosion-deposition sediment budget using marsh elevation profiles, shoreline erosion rate, and sediment deposition measurements. Sediment budgets were calculated at four sites with varying shoreline erosion rates. Much of the sediment eroded at the marsh edge can be accounted for as marsh platform deposition, except at the most erosive site, suggesting a possible erosion threshold where eroded sediment mass is greater than platform deposition. Consistent with other studies of marsh creeks, sediment delivery to the marsh platform appears to be largely driven by wave climate. These data suggest that for erosive bay-estuarine shorelines, sediment delivered into the marsh is largely concentrated near the marsh shoreline, although shoreline erosion does not always result in a net loss of sediments from the marsh system in either decadal or annual assessments.

Mississippi↗