Pipeline Construction Impact on Coastal Marsh Vegetation and Soils

Vegetation and soils were sampled 1 month prior to and 1 year after a pipeline was constructed in a Texas coastal marsh. Submerged aquatic (SAV) and emergent vegetation (EV) were sampled to detect changes in taxa frequencies and percent cover within 3 pipeline corridor treatments (soil deposit/borrow, pipeline ditch, construction equipment) and a control. Taxon richness was not significantly altered by pipeline construction within EV plots. However, pipeline construction decreased total vegetative coverage of EV plots within all 3 pipeline treatments. A 33% (2.3 ha) decrease in EV coverage was calculated within a 30.4-m strip along the pipeline ditch using pre- and post-construction aerial photographs and Geographic Information System (GIS) technology. Similarly, data from EV quadrats indicated a 49% (2.2 ha) loss within the 19.8-m wide construction corridor. No analyses were performed on SAV data because these plants were only present during pre-construction sampling. Vertical soil profiles significantly decreased within the pipeline ditch and control in SAV regions. Soil losses within the pipeline ditch may have resulted from erosion. However, decreased soil elevations within the control may have resulted from disturbances by equipment traveling outside the construction corridor. Ultimately, vegetation and soil losses within pipeline construction corridors should be expected with current double-ditching techniques.

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