Nitrates are an important nutrient for aquatic plants and algae, but too many nutrients can lead to unchecked growth and eutrophication. It works like this: algae will grow and grow until the water is visibly green, preventing light from penetrating very far. The increased solids in the water increases the water temperature. When the nitrates have been used up or when the sun goes down, the algae stop growing and become a major source of food for bacteria. Bacteria then grow and grow, eating algae and using up oxygen. This creates such a low-oxygen environment that many invertebrates and fish can’t survive. Bacterial metabolism also releases ions into the water that increase conductivity and reduce pH.
Sources of nitrates include fertilizer, animal waste, human waste (typically from leaking septic systems), and industrial pollution. Nitrate levels in San Pablo Creek tend to be below 1mg/L, considered healthy, except occasionally during and after storm when we see peaks of up to 30mg/L.
What can you do? Try not to over-fertilize plants, especially before a rain storm