January 13, 2018
What happens to the products you use in your garden when you spray or broadcast fertilizers, herbicides and pesticides? They could end up impacting surface water or flowing into the watershed.
The watersheds of Marin County, more than 3,000 miles of creeks, flow to our beloved San Francisco Bay and on to the ocean. If you go to marinwatersheds.org you can look up your watershed. For instance, half of the Tiburon peninsula, Marin City, Sausalito and parts of Mill Valley and Corte Madera flow to Richardson Bay, connected to the greater San Francisco Bay. The Ross Valley watershed — made up of Fairfax, San Anselmo, Kentfield, Ross, Larkspur, parts of Mill Valley and Corte Madera — flows to San Pablo Bay, primarily through Corte Madera Creek.
It is important to note that, while the impact of pesticides on groundwater quality is mainly a human health concern (because of its effect on well water’s suitability for drinking) the effect on surface water quality is often a concern for the bay’s aquatic organisms and for other wildlife.
Interestingly, there are commonly used things we might not associate with pesticides. Treated wood is laced with toxins to keep insects at bay and shouldn’t be used in raised vegetable beds or children’s jungle gyms. If you opt to use treated wood wear gloves when handling, a mask if sawing and never burn it. There are specialized sealants that will help minimize the risk of chemical transfer or you could consider using rot-resistant woods such as redwood and cedar. As treated wood naturally decays some of the chemicals could leach into the watershed.
The University of California has a technical, but informative, article on the impact of pesticides on water quality at anrcatalog.ucanr.edu/pdf/8119.pdf. There are many factors that affect how pesticides travel. Soil properties such as texture and organic matter, how a pesticide goes into the soil and how long it lasts, known as its half-life, rainfall and application techniques. All of this, in turn, affects how it gets into the watershed or surface water. The article also has tables that rate most pesticides for toxicity to fish, birds and other wildlife so you could look up what you use and get an idea of its impact. The National Pesticide Information Center, npic.orst.edu, has a good website to sort out definitions of pesticides, offer alternatives and general information on a very user-friendly platform.
Because they don’t know what else to do, people have been known to pour paint thinner, paint, oil, gasoline and other toxins into gutters and storm drains, which flow unfiltered directly to the bay. Take them to the transfer station at 535 Jacoby St. in San Rafael, which will take them free to be properly disposed of or recycled.
As we consider the big world around us, what we use in our little gardens wouldn’t seem to make much difference. But we all want to live in the cleanest possible world and so it matters what we do on our little plot of the blue marble. None of us want to be responsible for poisoning fish or birds, never mind the amazing coordinated web of beneficial insect life that each of our gardens represents.
Some simple steps to lessen our impact:
• Use less fertilizer and you’ll need to mow less often
• Take your car to the car wash where runoff will be recycled
• Use rainwater in the garden by collecting into rain barrels
• Consider using permeable paving
• Reconfigure areas of your garden to allow water to soak into the ground rather than create run-off
• Limit or eliminate pesticide use
Enjoy your garden while keeping it as pristine as possible.