One of the most consequential impacts of fertilizers is the harm done to our waterways, and the ecosystems which rely on them. When we spread too much fertilizer, the excess enters our streams, lakes, and oceans through groundwater and runoff.
The algae inside waterways feed on this excess nitrogen and phosphorus. It forms toxic algal blooms which can deplete oxygen and interfere with the photosynthesis process. Eutrophication, or the lack of oxygen resulting from this harmful excess nitrogen, will create “dead zones” that kill plants, fish, and other living organisms.
A watershed is considered “fishable, swimmable, and boatable” with a B or above rating from the Environmental Protection Agency. For context in the Boston area, the Charles and Mystic Rivers currently meet these criteria, but they have both been rated below D because of dead zones and pollution in the recent past.
There was quite a stink when thousands of menhaden and striped bass died in the Mystic River during the summer of 2018.
Fertilization is likely the principal cause of these harmful dead zones where the MWRA is managing sewer and septic, and conservation commissions managing runoff from what agriculture is in the watershed.
Algae blooms and subsequent dead zones cause problems on multiple fronts. Economic problems include reduced fish stock and diversity for fisherman.
Ponds and lakes can be closed due to toxic algal blooms. Recreational opportunities are reduced because swallowing cyanobacteria or swimming in blooming algae can cause illness and has killed dogs.
Best not to spread fertilizers, or use one application of 100% slow release fertilizer in the fall or spring when waters are not as warm and daylight is not as long.
