Seepage and runoff waters from soils forming in sulfide-bearing dredge materials (SBDM) can have dramatic effects on water quality if they are placed adjacent to open water and do not have adequate containment. Soils forming in SBDM can produce large amounts of acidity upon sulfide oxidation and the oxidation and hydrolysis of released ferrous iron when they are drained or otherwise exposed to air. These soils, under certain environmental conditions, can produce low pH seepage and runoff waters containing large amounts of iron and aluminum, especially after heavy rain that follows a prolonged dry period. During the course of the soil survey update of Somerset County, Maryland (MD), USA, 2 areas of soils forming in SBDM of differing age were identified in close proximity to the sites of recent fish kills on the Pocomoke Sound in Somerset County. Both of these soil areas were initially contained by earthen berms. The dredge materials were deposited directly over the natural tidal marsh soil. Soils forming in SBDM that are approximately 60 years of age were classified as fine-silty, mixed mesic Sulfic Endoaquepts, while the second area of SBDM are 8 years of age and classified as fine-silty, mixed, mesic Typic Sulfaquepts, by Soil Taxonomy. The presence of jarosite was confirmed in both soils by X-ray diffraction, and the presence of ironstone (iron oxyhydroxides) was confirmed in both soils at the effluent discharge points. This is an indication that these soils have undergone intensive acid sulfate weathering (sulfuricization) and that they have released a large quantity of iron to waters leaving the sites. Studies have shown that the 2 mechanisms responsible for acid production from soils forming in SBDM are (i) the oxidation and hydrolysis of mobile ferrous iron; and (ii) the oxidation of the sulfur occurring in the form of pyrite. It is suggested that the resultant low pH, Fe- and Al-enriched water from these soils that entered the Pocomoke Sound may have made fish more susceptible to microbial predation by weakening mucous membranes and/or by promoting the growth of harmful cyannobacteria and flagellates. This paper reports the nature and classification of soils that developed in SBDM at 2 sites of differing age and of the possible environmental impacts of seepage and runoff from these sites entering the Pocomoke Sound.
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