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Maintaining Water Quality while Restoring
South Bay Salt Ponds to Wetlands
Robert Schlipf [[email protected]], Andree Greenberg, Brian Wines, Shin-Roei Lee, Wil Bruhns
Post Phase I
3.0
10,000
2.0
1.0
5,000
0.0
5/5
6/4
7/4
8/3
9/2
10/2
11/1
Tidal Marsh
4.0
2007
0
Problem
The operation of former salt ponds as managed ponds (i.e.,
circulating Bay waters through water quality control structures)
has threatened water quality especially by decreasing
dissolved oxygen (DO). This is because former salt ponds
have large surface areas, shallow water depths, and long
residence times which makes them extremely conducive to
excessive algal growth, which can lead to a severe depletion in
DO levels when algae suffer die-off or respire during nighttime
hours.
Shallow open water habitat creates excellent foraging
opportunities for shorebirds
The DO levels in former salt ponds are not protective of water
quality since they are often below those considered safe for fish
survival as shown in the graph below from the U.S. EPA’s
Ambient Water Quality Criteria for Dissolved Oxygen*, which
indicates that most fish will survive exposure above 3 mg/L, but
continuous exposure below this threshold will result in mortality in
many species (*EPA Publication Number 440/5-86-003).
Dead topsmelt in Pond A7 from low dissolved oxygen levels
Methods
To improve water quality in former salt ponds, the following
methods have been used to address low DO levels:
1. Switch pond circulation patterns from directional to muted tidal
2. Implement discharge timing
3. Install baffles
4. Install solar powered aerators
All of the above corrective measures have had marginal impacts on
improving DO levels. This is because these corrective measures
do not address the root of the problem, which is pond design.
1,880
9,674
3,317
1,40
0
709
Habitat Type
Restoring salt ponds to tidal marsh will provide the most
improvement to water quality because marsh systems that are
tidally connected to the estuary provide:
● improved water quality by filtering and fixing pollutants
● nursery habitat and protection from predation for juvenile fish
● significant biological productivity to the estuarine system
● habitat for rare, endangered, and other species
Mature tidal marsh
Large surface areas and shallow water make former salt
ponds extremely conducive to excessive algal growth
Dead leopard shark in Pond A7 from low dissolved oxygen levels
13,220
Reversible Muted Tidal
15,000
5.0
Reconfigured Managed
Ponds
Phase I - Habitat Modifications
Alviso Ponds, Weekly 10th Percentile of All Ponds
6.0
Salt Ponds
* From 1978 to 1996, the Aquatic Species Program evaluated the potential to develop
renewable transportation fuels from algae. The main focus of this program was to
develop biodiesel from algae grown in ponds.
Implications
Water quality is severely impacted when former salt ponds are
operated as managed ponds because excessive algae growth
leads to low DO levels. To protect water quality, ponds managed
for bird habitat should be reconfigured to improve water circulation
patterns. Reconfiguration of two ponds systems will occur in
Phase I of the SBSPRP. The graph below shows Phase I actions
that will begin within the next five years.
Tidal Marsh
One of the challenges with this restoration project is that former
salt ponds provide excellent habitat for birds. Unfortunately, the
conditions that make ponds suitable for birds (i.e., shallow open
water habitat over large surface areas) are the same as those
that are conducive to excessive algal growth. In fact, in order to
grow algae, the U.S. Department of Energy’s Aquatic Species
Program* recommends constructing ponds with large surface
areas and shallow water depths because of the need to keep
algae exposed to sunlight. In other words, former salt ponds
greatly resemble the U.S. Department of Energy’s
recommendations for designing an algae farm.
Data/Results
To measure the effect of pond discharges on receiving waters,
DO is measured continuously at pond discharge points. These
data show that DO levels are depleted especially in the late
summer months when algae proliferate in former salt ponds and
the days get longer and hotter. The graph below shows the
average of weekly 10th percentiles in the Alviso Ponds for 2007.
As expected, DO levels trend lower in the later summer months
(August and September) before recovering in the fall.
Salt Ponds
Bird Habitat vs Algae Farms
Acres
The purpose of the South Bay Salt Pond Restoration Project
(SBSPRP) is to restore about 13,000 acres of salt ponds to a
mix of habitats, in particular, tidal marsh, while providing flood
protection and recreational opportunities. The project area is
shown below:
Dissolved Oxygen (mg/L)
Project Purpose
San Francisco Bay Regional Water Quality Control Board, Oakland, CA
The effect of low DO in former salt ponds is not limited to fish
mortality. Diurnal shifts in DO levels caused by excessive algal
growth will also have sub-lethal effects on fish. These effects are
documented in U.S. EPA’s DO Report, which cites a study where
DO levels were kept at 3 mg/L for 8 hours, and 8.3 mg/L for the
remaining hours over 9 days. This diurnal shift in DO levels
produced significant stress on 2 of the 3 fish species tested.
During periods of low DO, fish lost their natural color, increased
their ventilation rate, ignored food, and often vomited food that had
been consumed under the higher oxygen environment. This study
suggests that values around 3 mg/L over a sizable period of the
day will harm aquatic life.
Conclusions
•The design of former salt ponds makes them conducive to
excessive algal growth. If former salt ponds are operated as
managed ponds to provide bird habitat, the configuration of these
ponds should be altered.
•To maximize water quality, former salt ponds should be restored to
tidal marsh within the constraints of meeting habitat goals for birds
and protecting human life and property in the South Bay.
•This very large restoration project has the potential to benefit
humans, water quality, and biological species and should be
phased over the next decades to assure that problems are
minimized and benefits are maximized.