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David Heckman

Publications and source records attributed to David Heckman.

2 recordsLinked to original sources
USGS2011

Shoreline surveys of oil-impacted marsh in southern Louisiana, July to August 2010

This report describes shoreline surveys conducted in the marshes of Louisiana in areas impacted by oil spilled from the Deepwater Horizon offshore oil drilling platform in the Gulf of Mexico. Three field expeditions were conducted on July 7-10, August 12-14, and August 24-26, 2010, in central Barataria Bay and the Bird's Foot area at the terminus of the Mississippi River delta. This preliminary report includes locations of survey points, a photographic record of each site, field observations of vegetation cover and descriptions of oil coverage in the water and on plants, including measurements of the distance of oil penetration from the shoreline. Oiling in Barataria Bay marshes ranged from lightly oiled sections of stems of the predominant species Spartina alterniflora and Juncus roemerianus to wide zones of oil-damaged canopies and broken stems penetrating as far as 19 m into the marsh. For the 34 survey points in Barataria Bay where dimensions of oil damaged zones were measured, the depth of the oil-damaged zone extended, on average, 6.7 m into the marsh, with a standard deviation of 4.5 m. The median depth of penetration was 5.5 m. The extent to which the oil-damaged zone stretched along the shore varied with location but often extended more than 100 m parallel to the shoreline. Oil was observed on the marsh sediment at some sites in Barataria Bay. This oiled sediment was observed both above and a few centimeters below the water surface depending on the level of the tide. Phragmites australis was the dominant vegetation in oil-impacted zones in the Bird's Foot area of the Mississippi River delta. Oiling of the leaves and portions of the thick stems of P. australis was observed during field surveys. In contrast to the marshes of Barataria Bay, fewer areas of oil-damaged canopy were documented in the Bird's Foot area. In both areas, oil was observed to be persistent on the marsh plants from the earliest (July 7) to the latest (August 24) surveys. At sites repeatedly visited in Barataria Bay over this time period, oiled plant stems and leaves, laid over by the weight of the oil, broke and were removed from the vegetation canopy, likely due to tidal action. In these areas, a zone of 2-5 cm high plant stubble remained at the edge of the marsh. Signs of both further degradation and recovery were observed and varied with site. Oil damage to the marsh at some sites resulted in complete reduction of live vegetation cover and erosion of exposed sediments, while other damaged zones had signs of regrowth of vegetation in up to 10 percent of the areal coverage.

Open-File Report↗
USGS2011

Land area change in coastal Louisiana from 1932 to 2010

Coastal Louisiana wetlands make up the seventh largest delta on Earth, contain about 37 percent of the estuarine herbaceous marshes in the conterminous United States, and support the largest commercial fishery in the lower 48 States. These wetlands are in peril because Louisiana currently undergoes about 90 percent of the total coastal wetland loss in the continental United States. Documenting and understanding the occurrence and rates of wetland loss are necessary for effective planning, protection, and restoration activities. The analyses of landscape change presented in this report use historical surveys, aerial data, and satellite data to track landscape changes. Summary data are presented for 1932-2010; trend data are presented for 1985-2010. These later data were calculated separately because of concerns over the comparability of the 1932 and 1956 datasets (which are based on survey and aerial data, respectively) with the later datasets (which are all based on satellite imagery). These analyses show that coastal Louisiana has undergone a net change in land area of about -1,883 square miles (mi 2 ) from 1932 to 2010. This net change in land area amounts to a decrease of about 25 percent of the 1932 land area. Persistent losses account for 95 percent of this land area decrease; the remainder are areas that have converted to water but have not yet exhibited the persistence necessary to be classified as "loss." Trend analyses from 1985 to 2010 show a wetland loss rate of 16.57 mi 2 per year. If this loss were to occur at a constant rate, it would equate to Louisiana losing an area the size of one football field per hour. The use of 17 datasets plus the application of consistent change criteria in this study provide opportunities to better understand the timing and causal mechanisms of wetland loss that are critical for forecasting landscape changes in the future.

Louisiana↗