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Take a minute to think about what happens when it rains.

Where does all that water go?

How does it get there?

When water rains down on the earth nearly every drop eventually finds its way into the ocean. The water makes its way into lakes, rivers, and streams which all drain out to sea. Even the snowflakes that fall on the tops of the tallest mountains end up in the marine environment.

As rainwater washes into the sea it carries with it sediment and debris from the land. This water is called runoff. Eventually this runoff ends up in our oceans, along with any soil, debris, or pollutants that it might have picked up along the way. Sometimes rainwater runoff is so rich in sediment that it forms what is called a a sediment plume in the ocean.

Sediment Plumes

Sediment plumes are caused by sediment rich rainwater runoff entering the ocean. The runoff creates a visible pattern of nutrient rich, brown sediment that forms a kind of cloud in the water spreading out from the coastline. From December to March, plumes commonly form at river and stream mouths, near sloughs, and along coasts where a large amount of rain runoff flows directly into the ocean.

On California's central coast most sediment plumes are formed during the winter storm season

This sediment plume formed off the Gaviota coastline after a rain event..

Algal Blooms

Sediment plumes are very rich in nutrients meaning that they have a lot of the things that plants need to survive. Nitrogen and phosphorous are two examples of nutrients. On land plants absorb these nutrients from the soil they grow in. In the ocean, microscopic plant like organisms float freely in the water column and absorb the same nutrients directly from the seawater they live in. Scientists classify these plant-like creatures as phytoplankton, but most people call them microalgae.

Phytoplanton are very important to marine ecosystems because they provide the primary energy source for the entire marine food web.

Just like plants and flowers on land, algae grow and shrink with the seasons. During the winter months algae populations are low. Phytoplankton have difficulty surviving in the wintertime because of the low nutrient inputs.

As spring comes the conditions are perfect for a rebound in the phytoplankton population. Increased nutrient concentrations due to coastal upwelling lead to increased abundance of phytoplankton is called the spring bloom and it continues well into the summer. As winter approaches once again Phytoplankton populations dwindle and the seasonal cycle is completed. This seasonal phenomonon is known as the "plumes and blooms" cycle.

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