I. Habitat Description
The shallow marsh annuals habitat includes portions of lakes, ponds, backwaters, mudflats, or shorelines that are seasonally flooded and more than 10% vegetated with annual (non-persistent) emergent vegetation. Common vegetation types include wild millet (Echinochloa), smartweed/pinkweed (Polygonum), spike-rush (Eleocharis), nutsedge/red-root flatsedge (Cyperus), and beggarticks (Bidens). This habitat may have incursions of submersed, nonrooted-floating aquatics, or persistent emergent vegetation. It is typically found in areas which are seasonally flooded and have soils that are saturated or inundated by water up to 0.2 meters deep. During normal water conditions, there is little flow, though there can be wind-generated currents and stronger flows at inlets and outlets. During flood conditions, these habitats can be connected to rivers or streams, with strong currents and possibly large amounts of debris.
II. Sensitivity to Oil Spills
The shallow marsh annuals habitat is highly sensitive to oil spills. This biologically diverse habitat is critical to many plants and animals. Many animal species, especially waterfowl, rely on annual plants as a food source. Significant loss of this habitat would greatly affect the populations of these animals and consequently, the local ecology. Light refined oils with high amounts of water-soluble fractions can cause acute mortality to animals and plants in these shallow habitats. Heavier oils tend to coat vegetation and animals, though the vegetation may survive if oil coats only the stem. Plant mortality is heightened during the growing season.
III. Sensitivity to Response Methods
The following text describes potential adverse impacts to this habitat resulting from various oil spill response methods and provides recommendations to reduce impact when these methods are implemented. This is not intended to preclude the use of any particular methods, but rather to aid responders in balancing the need to remove oil with the possible adverse effects of removal. More detail about the response methods themselves can be found in the Inland Response Tactics Manual.