The scientific method in it’s most cyclical form. Image from here.

One of the very first things anybody learns about science is the scientific method. Observation, hypothesis, experiment, conclusion. It’s the scientific creed. The motto scientists live by. But, despite the seemingly simple 4-steps, in reality, the scientific method is a tortuous path that can be slow, complicated, winding, and at times, incredibly frustrating. To really dive deep into what the scientific method means in ‘real-world’ terms, let’s take a look at the story of the Neuse River Estuary located in eastern North Carolina.

Background: The Neuse River Estuary (or NRE for short) is a familiar system to many of us living and working on the coast of North Carolina. The watershed of the estuary starts just northwest of the rapidly growing Raleigh-Durham area, flows through the agriculturally developed coastal NC region from Goldsboro to New Bern and then flows into the estuary itself. Along the way, the water picks up all kinds of things. Stuff such as street run-off from Durham, wastewater treatment plant effluent from Raleigh, fertilizer from fields outside of Goldsboro, and animal waste from chicken and pig operations near Kinston. All of this stuff ends up in the NRE where it becomes food for phytoplankton. This is the point where the scientific method really gets going…

The Neuse River Estuary watershed which stretches from the Raleigh-Durham area through coastal North Carolina. Image from LNBA.

Observation: Back in the 1970’s, people in the upper part of the NRE started noticing very

The large, green, smelly phytoplankton blooms of the upper NRE in the 1980’s. From Paerl et al., 2004.

large, green, and smelly phytoplankton blooms. These phytoplankton blooms were composed of specific phytoplankton called cyanobacteria. Not only were these blooms smelly and gross, they also led to fish kills. Clearly these phytoplankton blooms were not a good thing and something needed to be done to control them, but what?

Hypothesis: Remember when I was talking about all the ‘stuff’ that is flushed down to the NRE from human activities in the watershed? In the 1980’s, scientists started thinking about all this stuff and how it might contribute to the issue of phytoplankton blooms. They hypothesized that the blooms were due to too much phosphorus in the water. Phosphorus comes from lots of different sources, but mainly from human waste and phosphorus containing soaps and detergents and is an important nutrient phytoplankton need to grow. By reducing the amount of phosphorus in the water, scientists hypothesized there would be a reduction in large phytoplankton blooms.

Experiment: Based on this hypothesis (and on experiments conducted in the laboratory) the North Carolina government enacted a ban on all phosphorus containing soaps and mandated better wastewater treatment to remove phosphorus.

Conclusion: With the ban and better wastewater treatment, concentrations of phosphorus in the NRE decreased AND the occurrence of large phytoplankton blooms in the upper NRE deceased (yay!). But….

Observation #2: While there was a reduction in phytoplankton blooms in the upper NRE, there were now large phytoplankton blooms (and associated fish kills) in the mid-NRE.

Hypothesis #2: So, scientists came up with another hypothesis. Phosphorus isn’t the only thing that phytoplankton need to grow. They also need nitrogen and it turns out, there’s a lot of nitrogen in the NRE. Scientists hypothesized that by reducing nitrogen to the NRE there would be a reduction in phytoplankton blooms in the mid-NRE as well.

Experiment #2: And again, based on this second hypothesis (and even more experiments conducted in the laboratory) the North Carolina government enacted legislation to reduce nitrogen to the NRE. Specifically, they mandated there must be a 30% reduction in total nitrogen to the system by removing nitrogen from wastewater treatment plant effluent, from run-off from agricultural operations, and from urban run-off and fertilizer use.

Conclusion #2: The 30% reduction in total nitrogen was enacted in 1999, but there has yet to be a conclusive reduction in phytoplankton blooms in the mid-NRE or fewer fish kills. And there have been studies that have shown there has been a some reduction in some forms of nitrogen, but not all. So it’s back to the drawing board…

A good visual for what happened in the Neuse River Estuary. From Paerl et al., 2004.

Observation #3: Despite successful reductions of phosphorus and some success in reducing nitrogen, there are still large phytoplankton blooms in the NRE. And there are a few guesses for why this is the case…

Hypothesis #3:

a. It may be the form of nitrogen that is still causing these phytoplankton blooms. As mentioned above, there has been decreases in the simple forms of nitrogen, called inorganic nitrogen, but there have been increases in more complicated forms of nitrogen, called organic nitrogen. It’s possible phytoplankton are still using this more complicated form of nitrogen for growth, meaning we need to reduce both the simple and complicated forms of this vital nutrient.

b. Another hypothesis revolves around the sediment of the NRE. Sediments can act as storage for nutrients, including both nitrogen and phosphorus. In the past when there was so much phosphorus and nitrogen loading to the NRE, it’s possible some of this excess phosphorus and nitrogen made it’s way to the sediment and was essentially stored there. Now that there has been reductions in these nutrients to the NRE, it’s thought that the nutrients stored in the sediment are being released and used for phytoplankton growth.

And so, the scientific method continues. Scientists are actively testing these (and many more) hypotheses to understand why these phytoplankton blooms are still occurring and looking for more ways to limit these blooms (and the negative impacts that are associated with them, like fish kills). As you can see, the scientific method, while superficially straight forward, is a complicated path that often leads to more questions than answers. But, the scientific method provides a great framework for which to begin to understand the world around us.

For a good scientific paper on the story of the NRE, see ‘Solving problems resulting from solutions: evolution of a dual nutrient management strategy for the eutrophying Neuse River Estuary, North Carolina’