Three bubblers were installed as a pilot project to improve oxygen levels.

Transcription

1 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.

2 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 Plankton blooms create extremely high levels of oxygen in Lake Merritt during the day,

3 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

4 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.

5 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.