A Nutrient Budget For The Bay

When we think about budgets we usually think in terms of dollars and cents. Do I have enough money to pay the bills, go grocery shopping and go out to the movies? But we can’t calculate the health of an individual or an ecosystem using dollars.  One way to think about the health of an ecosystem though is in terms of supply and demand for nutrients. How much nutrients or food does your dog need to eat to stay healthy? And how much is too much?

Everything needs nutrients to stay alive. Animals must eat to survive, and so do plants, algae, fungus and bacteria. Animals soak up necessary nutrients as they digest the fruits, vegetables and meat we eat. Plants and other sedentary (non-moving) life forms take in nutrients such as nitrogen and phosphorus from their environment—water, earth and air.  When an animal takes in too much nutrients, the excess is expelled so it can be recycled in the environment and reused by other organisms.

Instead of using dollars to calculate a nutrient budget, we use increments of phosphorous and nitrogen compounds. We can calculate how much nutrients (or food) is needed for an individual to survive by evaluating how much we take in and how much is lost to the environment, and examining the health of that individual.

We can also come up with a nutrient budget for an ecosystem by evaluating the point and non-point sources of nutrients entering the system, and measuring how it is being used and where the excess is going.

Consider the Narragansett Bay ecosystem for a moment. The rivers that feed the Bay also bring all that washes into them. This includes all the stormwater that is not soaked up by the trees, grass and plants, all the water from washing our cars and watering our lawns, and all the discharge from wastewater treatment plants. When it rains, the trash, sediment, heavy metals and nutrients that collect on roadways, sidewalks and lawns are washed into storm drains that flow into nearby rivers, wastewater treatment plants or just directly into the Bay. In Rhode Island, only a few treatment plants take stormwater, so much of it is not treated at all before it reaches the rivers or Bay. The Bay essentially becomes the dumping ground for all this pollution. So how much nutrients and pollution is too much for the Bay to handle? And how do we know?

Nayatt Point in Barrington, R.I. is already loaded with seaweed.
Conimicut Point has already raked the beach to remove the
seaweed, and the summer has just begun.

In a healthy system, everything lives in balance with each other. Fish kills and shellfish die offs are one type of clue that nutrient levels may be too high. The big stinking mats of seaweed that wash onto our beaches are also evidence of too much nutrients. To figure out just how much is too much, we must first calculate how much is going in.

Graduate student, Jason Krumholz, is calculating the nutrient budget for the Narragansett Bay.  He is testing whether recent reductions to the amount of nutrients going into the Bay –through wastewater treatment plant upgrades and point source restoration (Read our blog on wastewater treatment plant upgrades)- are enough to change the amount of phytoplankton growing in the Bay, which might decrease the amount of organic material being decomposed at the bottom of the Bay, allowing for higher levels of dissolved oxygen throughout the Bay, making the Bay a healthier place for creatures to live. 

Jason Krumholz makes tiny adjustments
on the nutrient analyzer.

Since 2006 Jason has been collecting seasonal monthly water samples at 13 stations around the Bay and analyzing them for concentrations of nitrates, nitrites, ammonia, phosphate, silica and total nitrogen. He also works with other researchers and state agencies to analyze data from the wastewater treatment plants, river loading data, and a number of fixed monitoring stations throughout the bay.  From this data, he can calculate the total amount of nutrients coming into the Bay. The next step is to figure out where all of those nutrients are going. Some of it washes out to the ocean with the tides, some sinks into the sediment to be used later, and some is released back into the atmosphere, but most of it gets used up by the organisms living in the Bay.

Jason Krumholz and his intern Rossi Ennis
working in their lab at the URI Bay Campus in Narragansett.

Jason is already seeing decreases in dissolved inorganic nitrogen, so one might expect to also see decreases in total nitrogen, but this does not seem to be the case. “It is a bit puzzling” Says Jason. “The Bay is doing something else. We are still seeing high levels of phytoplankton” (microscopic algae) which leaves the same possibility for low levels of dissolved oxygen and potential for fish kills. But we can’t expect to see changes over night.  In many similar ecosystems, response to reduction in nutrient loading has taken several years to manifest.  As the Bay adjusts to the lower levels of nutrients coming in, the species of phytoplankton may shift to ones that can live well with lower levels.  But only time will tell.

We can all help make the Bay cleaner though. Jason suggests using diligence and being a mindful consumer. Be conscientious about the fertilizers you use, purchase detergents without phosphates, and pick up after your pet!