Update – April, 2010
Three bubblers were installed as a pilot project to improve oxygen levels.
Based on a proposal by Dr. Alex Horne (professor emeritus of engineering at UC
Berkeley) and Dr. Ken O’Hara (AMEC-Geomatrix) installation of 140 aeration
bubblers was considered by the City of Oakland. The proposed, patented system
would mix the bottom layer of the Lake (parts of which are sometimes a dead zone
due to low oxygen) with the adequately oxygenated surface layer. The system would
have cost about $500,000 and funds were available from Measure DD.
Three pilot project bubblers were installed in April, 2005 and operated for six
months. The bubblers were still functioning quite well after six months, but the City
of Oakland did not follow up on the proposal and dead zones still appear in the Lake.
BACKGROUND
In May of 1999 the US Environmental Protection Agency listed Lake Merritt as a body
of water whose beneficial uses were impaired by low levels of dissolved oxygen. This
white paper provides information on:
Why oxygen is important to the Lake;
Why the Lake was listed; and
What can be done to improve the situation.
What is the Source of Oxygen in the Lake?
Oxygen comes from plants and from air. It is created by plants during photosynthesis,
which occurs only in the presence of light. At night, or in places where there is no light,
photosynthesis does not occur, and oxygen is not produced. In Lake Merritt, oxygen
comes from the vast populations of plant life (especially plankton) and from contact with
the air, which contains vast quantities of oxygen.
What Causes Low Oxygen?
Oxygen is used up by respiration (breathing) and by chemical reactions. In Lake Merritt
oxygen is used up by the respiration of plants and animals, and especially by biological
and chemical reactions in the mud at the bottom where leaves and other organic matter
are decomposed. Because of this, oxygen levels at the bottom of Lake Merritt are lower
that at the surface.
WHY OXYGEN IS IMPORTANT
Oxygen is necessary for most forms of life. Because of its low solubility, oxygen in
water is only a tiny fraction of the amount in air. Air is 20% oxygen, but when oxygen is
dissolved in water, it typically exists at levels from 0 to 20 milligrams per liter, which is
equal to 20 parts per million ( 20 ppm). When oxygen levels in water are too low,
animals that live there will move away or they will die.
What Are The Standards For Oxygen?
State water quality standards recommend that oxygen be at least 5 ppm in natural water
bodies. Estuaries (such as Lake Merritt) often have levels below 5 ppm, but when levels
are below 3 ppm, problems can occur. These can include the death of fish and other
aquatic life, and the production of smelly gases, such as hydrogen sulfide.
WHY LAKE MERRITT WAS LISTED AS IMPAIRED
Oxygen Levels in Lake Merritt
Most of Lake Merritt is not impaired by low oxygen during most of the time. Levels are
typically above 5 ppm. However, under certain conditions, some areas of the Lake
become impaired.
From 1990 to 1995 the Alameda County Flood Control District published annual reports
on water quality in Lake Merritt. These reports, and other data, are on file at the Institute
office. Included in the reports were the results of weekly or monthly oxygen testing of
surface, and bottom waters. Briefly summarized, these reports verified that:
Surface waters contain medium to high levels of oxygen. Typical readings at the Lake
center are between 7 and 13 ppm. At the ends of Lake arms, surface levels are typically
above 5 ppm. Higher levels are sometimes recorded during plankton blooms. Oxygen
levels at the petrobarriers (the black and yellow floating barriers) occasionally drop
below 4 ppm.
Bottom waters are what have caused Lake Merritt to be listed as impaired by EPA.
Typical readings at the Lake center are from 5 to 10 ppm (but fell below 3 ppm four
times in 1991, and once in 1992). At the ends of Lake arms, bottom levels have typically
been below 5 ppm and fell below 3 ppm 14 times in 1991, 9 times in 1992 and 7 times in
1993.
Plankton blooms create extremely high levels of oxygen in Lake Merritt during the day,
but at night, their respiration can significantly reduce oxygen levels. Also, when the
plankton die off, oxygen is used up by their decomposition and low levels can occur.
They thus promote both high and low levels.
Conditions near major storm drain outfalls are the worst of any area tested in the Lake.
These outfalls bring in leaves and other materials which use up oxygen in the water
through chemical and biological reactions. The aeration fountains are located in these
areas to transfer oxygen from the air to the water.
Recent Studies
The County Flood Control District stopped taking water quality samples at Lake Merritt
in 1996 or 1997 except for bacterial testing. But for the past two years, students from the
Environmental Academy at Oakland High School have been taking water quality samples
weekly during the school year. A request for copies of the data has been made to the
Academy.
WHAT CAN BE DONE TO IMPROVE THE SITUATION
The report by the City Public Works Agency - Environmental Studies Division has listed
several important actions which can improve oxygen levels at Lake Merritt. These
include: Further planning to eliminate sanitary sewer overflows; a review of the
discharges from animal stables at Children's Fairyland and the Police stables;
Modification of operation of the County's tide gates at 7th Street; Reduction of sediment
transported to creeks; Construction of wetland habitats; A reduction of leaf /organic
matter inflow, especially from Piedmont; Regular harvesting of widgeon grass and algae;
Minimize pesticide and especially fertilizer input into the Lake; Reduce the level of bird
waste around the Lake; and Conduct regular water quality testing.
Following are additional details on some of the aforementioned topics, and other
suggestions:
Tide Gate Closure was the topic of a study done in March of 1991 and described in the
1990 annual water quality report. During closure, tidal circulation is cut off, and water
mixing is minimal. The test was done to see if gate closure lowered oxygen levels due to
minimal tidal mixing. Oxygen levels were not seen to be significantly degraded during
the 5 day test, in part because stratification already existed before the gates were closed,
and due to the input of oxygen from rainfall and plankton blooms. This report concluded
that tidal mixing may not always sufficiently increase surface layer salinity to the point
where the top and bottom layers mix. A further conclusion is that: "Winter storm
conditions at the Lake reduce bottom dissolved oxygen concentrations to levels that may
endanger benthic organisms. However, a gate closure for a winter storm that is moderate
in length (less than five or six days) does not seem to adversely affect lake water
quality..."
However, in warmer and dryer weather, a lack of tidal circulation is more likely to create
low oxygen conditions. This is because biological activity is higher under these
conditions and rainfall does not add oxygen to the water. The gate closure test was
repeated in September of 1991 when the gates were closed for four days. Although
oxygen levels increased somewhat after gate closure due to plankton blooms, bottom
levels almost uniformly increased even more after the gates were opened on September
16th (based on a comparison of levels on September 15th and 17th). This indicates that
tidal flushing does increase oxygen levels at the bottom in the absence of rainfall.
During some periods of gate closure, putrid water and dead fish have been observed in
the channel. Many years ago when the tide gates were always kept closed, fish kills from
a lack of oxygen would sometimes occur. Gate closure and the subsequent lack of
circulation can be significant factors in reducing oxygen levels at Lake Merritt during
closures when there is no rainfall or plankton blooms.
Recommendation:
To provide for tidal flushing, promote the health of wetlands that are expected to be built
in 2000, and provide for the passage of migratory fish, tide gate closure should be
avoided except during imminent flood threat and for occasional 12 hour boating events or
maintenance efforts.
Alameda county should make personnel available on an as-needed basis 7 days a week,
24 hours a day to open and close the gates. The damage to Lake Merritt marine life,
future wetlands and potentially to oxygen levels from keeping tide gates closed more than
absolutely necessary far outweighs the cost of overtime for 1-2 employees several weeks
per year. For example, if a boat race ends on Saturday or Sunday afternoon, the gates
should be opened that night, not Monday morning. In like manner, when rain is not
expected within 12 hours, the gates should remain open. A twelve hour window should
be adequate to drain the Lake on a low tide and close the gates to keep out a high tide.
Optimal operation of this very expensive capital improvement should not be hampered by
the cost of labor needed to run it.
Aeration Fountains provide both oxygen and aesthetic benefits at the Lake. The Institute
installed two new units one year ago, and one older unit was upgraded. They increase
oxygen levels in a localized area and improve stratification problems to a certain extent.
Oxygen levels measured at bottom waters near the bandstand fountain contained above 4
ppm oxygen at a time when levels 20 to 60 or more feet away were 2 ppm or less. This
improvement is expected to be much more significant at the Embarcadero fountain,
which is designed more for aeration. In their first year of operation, the Lake Merritt
fountains have operated about 80% of the time, a figure that should increase next year
due to improvements that have been made in maintenance procedures. More than $3,900
was recently donated for these popular devices.
Aeration Bubblers have not yet been tried at Lake Merritt. Operating on 110 volts, they
provide a more economical (but less aesthetic) means of adding oxygen directly to the
water. They are commonly used at residential lagoons and in Lakes to break up
stratification. Small compressors are installed in boxes along the shoreline, and feed air to
underwater dispersion devices near the bottom. Capital costs are about half that of
fountains and there are no intake screens to clog. Due to their location on the bottom,
encrustation with barnacle, mussels and tube worms would not be expected to be a
problem, but this should be tested in a year long demonstration project.
Because of their ability to prevent stratification, aeration bubblers can play a significant
role in improving oxygen conditions at Lake Merritt. Their installation and use does not
depend upon long term educational and enforcement measures, which are likely to be
only partially successful. The 18th Street cove would be an ideal location for a
demonstration project, which could be accomplished in the $5-10,000 range.
Eliminate Sanitary Sewer Overflows:
There have been 2 - 3 very noticeable such events in the last three years. The program to
eliminate these should continue, with the goal of minimizing them from all areas of the
watershed, including the City of Piedmont.
Reduce Sediment and Organic Material Transport to Lake: This concept will be very
useful in reducing transport of oxygen demanding materials. Results will be long term,
but may be difficult to measure in terms of Lake oxygen levels.
Harvest Widgeon Grass:
This will remove organic material before it decomposes and uses up oxygen. However,
the area where it grows increases each year as the plant spreads, and long term control
(reducing the total area where it grows) will require rotavation or dredging.
Integrated Pest Management Programs:
Cemeteries and golf courses typically contribute very large quantities of nutrients to
downstream areas. A reduction in the flow of these nutrients to Lake Merritt should
reduce plankton blooms and result in less oxygen demand.
Bird Waste:
Excessive bird feeding (we have seen 10 loaves of bread at one time) and excessive bird
waste contribute to both bacteria and low dissolved oxygen problems at Lake Merritt.
Recreational districts in Hayward and Fremont actively discourage the build up of large
concentrations of birds. We concur that a reduction in bird feeding should be considered
as a means of improving oxygen (and bacterial) conditions in the Lake.
Water Quality Analysis:
The Environmental Academy of Oakland High School is currently analyzing water
quality weekly during the school year. However, we also need data during the summer
when school is not in session. Testing must conform to set protocols and be conducted in
a very controlled manner if the data are to be useful. Elementary school students may not
be old enough to perform such tasks, and the City may want to consider an outside
contract for summer testing.
Funding:
The Institute concurs in the list of possible funding sources. Alameda County should be
added to this list when considering capital improvement, flood control projects, which are
funded by a tax assessment.