Environmental Impact Statement - Sonoma Land Trust

California Department of Fish and Game
U.S. Fish and Wildlife Service
Section 3.3. Water Quality
Wetland Water Quality
Wetland water quality is influenced by wetland depth and morphology and the
relationship of the wetland to the upstream watershed. The hydrologic regime
determines the frequency, depth, and duration of the water’s influence on
vegetation and the aquatic functions that the wetland provides. Wetlands with
little flushing and high nutrient and contaminant loading rates can become
stagnant, resulting in low dissolved-oxygen content, decreased aquatic habitat
quality, and adverse effects on fish and wildlife. These conditions can also
promote excess algal growth and increase mosquito-breeding potential. An
adequate supply of fresh water to the wetland improves the capacity for removal
of nutrients and contaminants. In a salt marsh environment, adequate tidal
flushing maintains good water quality by reducing the potential for development
of these conditions.
Wetlands can improve the quality of source waters by decreasing water velocity,
inducing sediment deposition, and removing excess nutrients and contaminants.
Nutrients and contaminants can adsorb (attach themselves) to sediments in a
wetland and be removed by deposition, chemical breakdown, and assimilation
into plant and animal tissues.
During winter months, Tolay Creek tends to have freshwater flows due to high
runoff conditions in the upstream drainage basin. During summer months,
freshwater flows are low or negligible, and most of the water in the creek is from
the San Pablo Bay. Turbidity can be high because of the relatively shallow depths
of water and the substantial tidal currents that re-suspend bottom sediments.
Tidal flows, however, nourish and sustain the salt marsh habitat along the levee
at the east end of the proposed wetland restoration site.
Environmental Consequences and Mitigation
Measures
Approach and Methods
Water quality effects were evaluated qualitatively based on professional
judgment because detailed pollutant transport and fate numerical models are not
available. As described in the Environmental Setting section above, all sediments
in the Bay are contaminated to some degree by anthropologic activities.
Restoration, by natural sedimentation or dredged material placement methods,
would result in redistribution of Bay sediments and associated pollutants and
would result in release of a portion of these pollutants into the overlying water
column.
The level of significance for potential water quality impacts was identified by
comparing the water quality effects of the proposed wetland restoration
alternatives to the applicable laws and regulations for water quality in California.
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
3.3-10
April 2012