The Chemistry of Human Impacts on the Sea

Humans can have a significant impact of the biology of the ocean where we alter its chemical composition. Some of the ways human activities influence ocean chemistry are explained below, including sewage and trash, storm drain and river run-off, and oil spills.

Sewage and trash- All over the world (including the USA), sewage and trash are dumped into the sea. This ranges from raw, untreated sewage, to partially treated sewage. Chemically, sewage acts like fertilizer and can be responsible for toxic plankton blooms. Another possible effect is deoxification which kills marine life because there is not enough oxygen in the water to breathe.

CHEM WINDOW - Deoxification


Sewage may also introduce diseases and unhealthy chemicals like heavy metals and carcinogens into coastal waters. Although the ocean is good at ridding itself of pollutants by chemical processes and dilution, as coastal populations grow, so do the human impacts on the marine environment.

Storm Drain and River Run-off- These sources of marine pollution may begin far away from the coast. The term for this is non-point source pollution.

What goes down the gutter in your neighborhood? Looking out my window, I see a styrofoam coffee cup, oil and gasoline, soap from washing cars, a candy wrapper, water from fertilized lawns, cigarette butts, and some dog poo (bleh!).


Now, whether I'm hours from the ocean in Grapevine, TX or minutes away in La Jolla, CA, everything I just mentioned is going to flow down into a storm drain or ditch, into a creek which flows into a river, which (assuming it gets over a couple dams) will eventually flow into the ocean--maybe right onto my favorite beach or yours.

Fertilizers, soap, and organic wastes will increase plankton and bacteria levels in the ocean the same way sewage does. Oil and gasoline are toxic in both freshwater and saltwater. Debris like trash can entangle or be eaten by birds, fish and mammals which can be very harmful (and it looks ugly!).

Oil spills- Yuck! Pictures of birds and seals covered with oil speak for themselves for this human impact. Oil floats on the surface of sea water, so when oil spills occur, the oil tends to end up on the shore where it negatively impacts coastal wildlife and humans. It can hurt wildlife by matting down bird feathers, sticking to fish gills, disrupting breeding, and by poisoning animals and plants. Humans are affected when beaches are closed and seafood cannot be harvested.

Once an oil spill occurs, chemicals can be used to disperse the oil, but these chemicals may also be toxic to marine life. To clean up a spill with minimum impact to the environment, bioremediation may be used. In this process, nitrogen and phosphorous-rich fertilizers are added to contaminated beaches to promote the growth of bacteria that essentially "eat" the oil.

CHEM WINDOW - Bioremediation


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This completes The Chemistry of Human Impacts on the Sea


Return to the beginning of the Ocean Chemistry unit.