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11/8/2011 - Barnegat Bay mapping to begin

NEPTUNE — Barnegat Bay will get its first complete charting and depth-sounding in decades, starting this week, a critical step that paves the way for more investigations into the bay’s complex currents and pollution levels that are choking the state’s largest coastal estuary. Called a bathymetry survey, the effort by the U.S. Geological Survey is starting with side-scan sonar on the research vessel Rafael in deep water. It will continue early next year when an aircraft carrying laser-powered imaging equipment scans the bay’s extensive shallows. “The last bathymetry that was done in Barnegat Bay was in the 1930s,” said Jill Lipoti, director of water monitoring and standards at the state Department of Environmental Protection. “It’s like a topographical map of the bottom of the bay. We really need accurate (depth) numbers for input into the hydrodynamic model.” Also called a circulation model, that future study will look to update earlier attempts to define how long it takes for tidal exchange to happen between the bay and ocean — a process that previous estimates say may take as long as 30 days in summer for a complete turnover, a poor flushing process that is a big factor in the bay’s problems. “We’ll be looking at the nutrient loading that’s coming in from the tributaries,” Lipoti said, referring to the mostly nitrogen compounds, like lawn fertilizer that washes off lawns, which feed excessive algae blooms in the bay. “How much of it doesn’t leave through the inlets, but just sloshes back and forth with the tide?” Barnegat Bay has just three widely separated connections to the sea: the Point Pleasant Canal that ties the bay to the ocean via the Manasquan River; Barnegat Inlet near the bay’s center; and Little Egg Inlet to the south. Little Egg could soon revert to its old binary system of two inlets, with a breakthrough expected at the southern tip of Long Beach Island. So few outlets along its 42-mile length is probably one reason for nutrient hotspots in the bay, said Michael Kennish, a research professor with the Institute of Marine and Coastal Sciences at Rutgers University. (Page 2 of 2) “This plays a big role in determining how long nitrogen may be trapped within different areas of the estuary, where plants have the opportunity to assimilate it over a protracted period of time,” Kennish said. “We see elevated readings of nitrogen in both the northern and southern parts of the estuary. The peak levels in Manahawkin Bay and upper Little Egg Harbor are probably linked to the higher water residence time there.” Having that topographic map of the bay bottom — a three-dimensional picture that shows what the bay would look like if it was somehow drained — will clue scientists to how currents move in the bay. The DEP is paying for most of the project’s $600,000 cost as part of its ongoing Barnegat Bay restoration program. The three-member USGS survey team also will collect data about the composition of bottom sediments and particle sizes in the sand and silt. “That gets to what kinds of plants can grow there,” such as the eelgrass and widgeon grass that are critical habitat for crabs and fish, Lipoti said. “We see this as a fundamental piece of information that will be used for a lot of other studies,” said Anthony Navoy of the geological survey’s New Jersey Water Science Center. The work this week will be in deeper water where Rafael can maneuver with its acoustic depth-sounding equipment and side-scan sonar, Navoy said. The boat and crew comes from the USGS mapping program based at the Woods Hole Oceanographic Institute in Massachusetts. The local operation will be based at Dillon’s Creek Marina in Island Heights. Two 10-day expeditions on the boat, this week and again in March, will chart deeper parts of the bay. In late winter or early spring, when bay waters tend to be clearest, surveyors will use an aircraft carrying Lidar laser-imaging technology to map out the bay’s shallow flats. “Green-frequency lasers have more chance of penetrating water” and returning signals to show the bottom contours, Navoy said. Preliminary data should be available to other researchers in summer 2012, with a full report peer-reviewed by independent scientists within another six to 12 months, he said. The resolution from the imagery will be accurate down to scales of a few feet, and present an unprecedented picture of the bay, Lipoti said, adding, “This data is going to be used for years to come.” “This plays a big role in determining how long nitrogen may be trapped within different areas of the estuary, where plants have the opportunity to assimilate it over a protracted period of time,” Kennish said. “We see elevated readings of nitrogen in both the northern and southern parts of the estuary. The peak levels in Manahawkin Bay and upper Little Egg Harbor are probably linked to the higher water residence time there.” Having that topographic map of the bay bottom — a three-dimensional picture that shows what the bay would look like if it was somehow drained — will clue scientists to how currents move in the bay. The DEP is paying for most of the project’s $600,000 cost as part of its ongoing Barnegat Bay restoration program. The three-member USGS survey team also will collect data about the composition of bottom sediments and particle sizes in the sand and silt. “That gets to what kinds of plants can grow there,” such as the eelgrass and widgeon grass that are critical habitat for crabs and fish, Lipoti said. Kirk Moore, NJ Press Media



 

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