HYDE COUNTY — Mike Piehler leans over the side of a boat, lowering a small, flat disc into the water. The disc is divided into four equal sections of alternating black and white color—resembling a pie chart.
“The secchi disc has been used for a long time to measure water clarity,” explains Piehler, a professor of marine sciences, environmental sciences and engineering, at the University of North Carolina Coastal Studies Institute. “And what you do is lower it into the water until you can no longer distinguish white from black, and that happened pretty quickly in this case.”
In fact, the disc disappeared from view when it reached about one quarter meter under water. That’s a little more than one foot deep. It’s not that much, and that murky water is a good indicator of the problems facing what is North Carolina’s largest natural lake, Lake Mattamuskeet. It's beautiful on the surface, but deep down, which is only a few feet in the shallow body of water, the lake is in trouble.
The murky water means that hardly any light is reaching the bottom. And as everyone knows, if there is no light there is no life.
“We’ve become really concerned about declining water quality in the lake, as well as declines in our aquatic grasses, which we call submerged aquatic vegetation," says Michelle Moorman, a fish and wildlife biologist with the Mattamuskeet/Swan Quarter/Cedar Island National Wildlife Refuge—a part of the United States Fish and Wildlife Service.
“Those grasses are important because they are some of the key foods for the waterfowl that come here in the wintertime.”
The grasses began decline on the west side of the lake in the 1990s. The grasses have been dying on the east side of the lake during the past three years. Those crucial grasses are now virtually gone from the lake.
So scientists are scrambling to understand the lake’s water issues. The first step in achieving that goal is to determine what’s in the water. Researchers have set up monitoring stations on either side of the lake; four on each side.
“We take water samples for water quality analysis," explains Piehler, as he dips a bottle into the lake to collect a sample. The water is a light brown, even though the bottle was filled when it was barely under the surface. “In addition, we do light analysis at all of these stations with the goal of providing a comprehensive picture of what the lake looks like in terms of light availability at the bottom, which is important for the aquatic vegetation restoration we talked about.”
The light analysis is also an indicator of water quality in general because it indicates the amount of algae in the lake. It appears that Lake Mattamuskeet’s lost plants are being replaced by algae.
Researchers know the amounts of nutrients and chemicals flowing into the lake have increased and are fueling algae blooms. Those chemicals include fertilizers and pesticides. There has also been an increase in sediments dumped into the lake. Scientists need to understand the total effects of the algae blooms, the growing suspended sediment load and the connection to the poor water quality.
Graduate student Adam Gold is lowering a device into the water that looks like a small torpedo. He first takes readings about one quarter meter under water. He repeats the process when the device reaches the bottom.
"The device is packed with instruments to measure conductivity, which can be converted to salinity," says Piehler. "It also checks temperature and dissolved oxygen as well as flouresence, which can be converted to chlorophyll and is an indicator of how much algae there is in the water column.”
“We know what the lake was in the past and the stable state it was in, versus vegetation and algae," says Gold. “We know there’s a problem and we have a good idea of what is causing the problem, so now we’re trying to figure out more details about water quality and how we can improve it and what the ecological benefits would be in improving the water quality.”
Because the water quality is so poor, sunlight can’t reach the bottom of the lake. That means underwater grasses are dying all around the 18-mile long, seven-mile wide lake. Those grasses feed migrating waterfowl, provide breeding grounds for fish, and filter the water. The lake’s fish and crab populations are dropping.
“We know historically that the eastern half of the lake was doing really well and so the mystery is what has happened in the last few years,” says Suzanne Thompson, a lab manager at the University of North Carolina Coastal Studies Institute.
“If we can figure out what happened and get the lake back to the way it was, that would be a success.”
It’s likely low rainfall and changing flood trends are also contributing to the lake’s poor water quality. Water isn’t flushing through the lake as it did in the past. Climate change may have permanently altered that water cycle.
So, researchers say everything is on the table in terms of what is cost effective and what will be effective in stabilizing Lake Mattamuskeet.
“Not only do we want to understand why this happened, and what the implications of this happening are, but in the end we want to restore or rehabilitate the lake,” explains Piehler as the research boat returns to the dock after another day of visiting the sampling stations. Flocks of birds soar overhead, angling towards one of the small islands in the lake. The sun flickers off the waves in the boat’s wake. It’s difficult to believe a scene so pretty exists above the water, when a growing disaster lurks below the surface.
“Realistically, it’s difficult to understand what natural is for this system but we know what better is in terms of the function of the ecosystem and what it does for the people who live here,” adds Piehler. “This is an international resource because people come here from all over to hunt and to bird watch, so this is a value to the world, but at the most basic level the lake is connected to the community. So we’ve got to get the lake back to a place where it is functional and much more desirable.”
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