birds, and spread of non-indigenous species. Impacts on benthic fauna, harbor seals, birds, and spread of non-indigenous species are discussed elsewhere in this chapter.
Boat generated waves may erode the edge of marsh vegetated areas and mudflats. Impacts on turbidity by motor boat traffic are also likely to be pulsed and rapidly dissipated, especially given tidal mixing and advection in Drakes Estero. Over time the wetlands will recover under alternative A, but it is unlikely that the wetlands will return to historic conditions, in contrast to the statement in the DEIS that removal of DBOC structures “would increase the potential that the project area could be converted back to historic wetland habitat.”8 It is more likely that the wetlands will reach a new equilibrium depending on sediment dynamics and species colonizing the area (e.g., Villnas et al., 2011).
Shifting sediments following the removal of culture bag is a potential threat to benthic fauna (and eelgrass beds). Upon removal of the bags, which occurs under alternative A once and at the end of each crop cycle under alternatives B, C, and D, sediment surfaces will be exposed to currents and waves allowing for sediment reworking until a new equilibrium is reached. Although this is expected to be a short-term effect, management of sediment redistribution as described in the DEIS may be necessary to avoid burial of benthic invertebrates and eelgrass. Once sediment dynamics stabilize, risks of burial should be negligible. Some additional references on research on shellfish culture impacts on these types of benthic communities, such as the Bouchet and Sauriau (2008) paper on oyster culture on intertidal mudflats in France and reviews such as Forrest et al. (2009) would provide more context for this section of the DEIS.
II. REASONABLENESS OF THE CONCLUSIONS, ASSESSMENT OF LEVEL OF UNCERTAINTY, ALTERNATE CONCLUSIONS
The committee finds that the impact definitions, review of scientific information, and conclusions on wetland impacts are reasonable. The DEIS concludes that the impact of DBOC activities including physical buildings and structures, boating operations, and mariculture practices, on wetlands will be moderate adverse, a conclusion that the committee finds to be reasonable and is associated with a moderate level of uncertainty. It is likely that alternatives B, C, and D would continue to have an adverse impact on wetlands over the next 10 years, and these impacts would continue to be localized.
The committee identified a few issues that could be clarified or expanded in the wetland section as follows. According to the DEIS, sediment erosion occurs along the edges of culture bags, but it is uncertain whether this is a short-term process that stabilizes once a new equilibrium between currents and sediments is reached or whether this is an ongoing, long-term process. If this point cannot be clarified, the committee would assign a moderate level of uncertainty to the conclusion that the bag culture has a moderately adverse impact.
Since potential impacts of DBOC operations are not necessarily confined to the project area per se, a more ecologically sound definition of the project area would be the Estero from the head of tide in Barries, Creamery, Schooner, and Home Bay to the mouth of the Estero with lateral boundaries determined by the landward extent of tidal wetlands. This would include the tidal freshwater wetlands at the heads of Schooner and Home Bays.
III. WAYS TO REDUCE THE LEVEL OF UNCERTAINTY
Observations on the effects of oyster bags and clam culture operations on the conformation of the mud and sand flats would reduce uncertainty with regard to impact intensity and duration. The DEIS9 assumes that wetland disturbance will not be a long term impact: “After bags or clusters are removed for oyster harvest or transfer, natural processes would be expected to resume in E2US3 and E2US1/2 wetlands until new culture is placed there. The length of time required for natural processes to resume would vary depending on the level of disturbance (Wisehart et al., 2007; Zieman, 1976).” However, no details are provided on the approaches, methods, and evaluation that would be used for restoration of wetlands.
To achieve long-term recovery, adaptive management would be essential given uncertainties associated with restoration of many of these ecosystems (e.g., mudflats). This would require monitoring of sediment dynamics such as accretion and erosion rates in the marsh using SET-tables (Cahoon et al., 1995) and sediment grain size and organic content in the marshes as well as the mudflats.
8 DEIS, p. 252.
9 DEIS, p. 253.