By Andy Bale
Warm weather is coming and algae mats have begun to grow on Northstar Pond again. Parks management and experienced staff know that the industrial-style aerators in place the pond do nothing to improve the pond’s overall water quality or control algae. They have told me so.
However, the Parks Department will be under pressure to run the aerators in the pond all day long as they have in summers past. They should resist this pressure and, instead, look for an effective solution to the pond’s water quality problems and neighborhood concerns.
It likely costs the city about $10,000 a year to run the aerators and, over the years, total costs are likely more than $100,000 — a huge waste of money and resources. Unfortunately, a small group of citizens insists that the aerators control algae in the pond, and they are very vocal. So, Parks continue to run the aerators because, as one manager told me, it is cheaper and easier than dealing with the many calls of complaint that these citizens generate. Rewarding this kind of harassment doesn’t seem like either a fiscally or socially responsible approach.
While aerators have a place in water quality management, they are inappropriate and ineffective in Northstar Pond. In deeper ponds, aerators can provide oxygen to bottom water that is cut off from the atmosphere. They can create circulation, and they can break up algae mats.
But Northstar Pond is very shallow and broad, with no horizontal circulation. Here, the aerators simply churn water and do nothing to control algae or odors in the greater pond. As shown in photos accompanying this column, algae cover the pond right up to the edge of the aerators despite their continuous operation. The photos were taken in September, after a summer of running the aerators all day, seven days a week.
More than 90 percent of the pond is unaffected by the aerators. Besides, being very shallow and full of aquatic plants, it’s unlikely that the pond suffers much from lack of oxygen.
Nearly seven years ago, I was asked by a neighbor to help her negotiate with the Parks Department about the aerator schedule. She lived right on the pond and, for her, the sound of the aerators all day long was unbearable.
As anyone knows who has been near them when they start or stop, the aerators really are loud. Over these many years of talking, she and I have come to agreements with Parks and seen them broken without explanation. Nothing’s been resolved for long, but I have come to understand the issues well.
There are two: the aesthetics of “fountains,” and seasonal warm-weather growth of algae mats (or, pond scum). As a start, Parks should clearly separate these two issues because fountains in this pond have nothing to do with algae growth.
Some people, not everyone by any means, want to see a water feature in the pond. Personally, I prefer the pond natural and quiet. But if there is a strong desire for a water feature, and there are funds to purchase and run it, I’d support a pleasant well-designed fountain.
Controlling algae is a more complicated problem to resolve. And, it’s not clear that everyone would want seasonal growth of algae controlled. Many people may be fine with a naturally eutrophic pond that grows algae in the summer and is clear in the winter. Any effective approach to managing algae in the pond is likely to be costly and will require significant commitment of time and funds.
Basically, to control algae in the pond, Parks needs either to kill them, remove them or inhibit their growth. There are many approaches. Based on discussions with neighbors and colleagues, here is a list of ideas that Parks might consider:
* Rake and remove surface algae regularly;
* Drain the pond, dry its sediments and scrape the bottom to remove nutrients that have built up over the past 20 years;
* Treat the pond to increase color and reduce light penetration;
* Treat the pond to kill algae;
* Create an outlet and periodically fill and drain the pond to remove suspended nutrients. This outlet also could be used to skim off and break up surface algae as studies in UC Davis Arboretum have shown;
* Create an attractive waterfall with a natural rock filter on the island in the pond;
* Install a sprinkler system or moving fountain that could break up surface algae throughout the pond; and
* Design habitat to filter pond water. Originally, the pond was designed so that pond water was used to irrigate surrounding vegetation. Reinstate this design and create habitat on the pond perimeter as a natural filter system to remove organic matter.
Parks officials would be well served to focus their limited resources on establishing a long-term plan for the pond. With community involvement, Parks should determine what kind of pond the city wants, and can afford, to maintain.
A good management plan will require work, and its effectiveness will depend on the Parks Department’s commitment. But I believe that Parks can find an approach that will resolve every reasonable concern about water quality, aesthetics and noise in Northstar Pond. Parks should take serious steps in that direction.
— Andy Bale has lived in the Northstar neighborhood for the past seven years. He holds a Ph.D. in civil and environmental engineering from UC Davis and has specialized in surface water quality and numerical simulation for more than 25 years.