Up the Seekonk River

The purpose of today's MET High School's program was to observe the waterfront of an "Urban River," to look at how the land is used around the water. The students observed the many uses of the Port, looked at waterside restaurants, hotels, parks and marinas. They observed the occupations that would put people outside to work on the water (boat crew, construction workers, people fishing, etc.) but were definitely surprised as we headed up the River at the sight of dead fish floating by the boat.

"They're all dead. That stuff's nasty!"

And indeed, as we left from the Providence Bay Center and headed north, past the Port of Providence, and up the Seekonk River, we saw more and more dead fish. There were seagulls and cormorants at the surface eating them, splashing around, happy for their easy free lunch.

In order to investigate why the fish might have been dying, we used our YSI off the side of the boat to measure the Temperature (which was still about 72 degrees F surface to bottom), the Salinity (21 parts per thousand at surface and 28 ppt at bottom), and the Dissolved Oxygen, which may have been the problem for the animals. Animals that live under water need to breathe oxygen in, just like we need to. Most underwater animals have gills in order to do this, instead of the lungs to breathe air like we have. The air that we breathe in is about 21% (or 21 parts per hundred) oxygen, and that makes terrestrial animals, such as humans, very happy. However, underwater creatures are much more efficient at using their oxygen. They are happy when their water has more than 5 mg/L (or 5 parts per million) of oxygen to breathe. The readings up the Seekonk River were much lower that that- 0.85 mg/L of oxygen. This is a lethal limit for most sea animals, so they either need to find another place to live quickly, or suffocate from not enough oxygen.

There are several combining factors why the oxygen levels could have been low. Most of the oxygen in the water comes from plants, or phytoplankton. Phytoplankton like to live near the water's surface so they have access to plenty of sunlight, so usually the surface of the water contains the most oxygen. When we have sampled recently for plankton, we have come up with next to none, so there may not be very much oxygen being produced right now due to the low levels of plankton. In addition, the water in the Bay is just about at its peak temperature right now (maybe 1-2 weeks past), and warmer water holds less oxygen in it. Lastly, when organisms die and sink to the bottom, bacteria eats away at it for decomposition to occur, but this process uses oxygen as well. This is another reason why the oxygen levels at the bottom are normally lower than the rest of the water column.

It is a strange sight to see, since normally fish kills happen in Narragansett Bay in July or August, when the air temperature and the water temperatures are both very high and the water is not mixing. It was sad for the students to see, but it was an important lesson on how animals rely on clean healthy water to live in, and how drastic it is when the conditions are not right.

For more information on Narragansett Bay oxygen levels, visit http://omp.gso.uri.edu/doee/science/physical/choxy3.htm

For more information on how to book our "urban rivers" program, visit http://www.savebay.org/education_shipboardoutings.asp