Gathering Comprehensive Water Quality Data
Ferries crossing the Neuse River and Pamlico Sound on regular routes have been equipped with a water quality monitoring system for continuous collection of water samples and water quality data as part of the FerryMon program, which began in 2000. Over the past seven years, the program has uncovered water quality problems, such as toxic algal blooms, changes in water clarity and excessive nutrient loadings, that cannot be detected by standard monitoring techniques.
“Ferries fill an important gap between traditional estuarine monitoring, where you go out once a week or once a month in small boats, and mooring-based offshore monitoring programs,” said Hans Paerl, a professor at University of North Carolina at Chapel Hill’s Institute of Marine Sciences (UNC-IMS). “Our nation’s medium- to large-size water bodies are extremely important for fisheries, our economy, recreation and homeland defense. And yet, they are very challenging to monitor with traditional methods.”
North Carolina did not have a routine monitoring program on Pamlico Sound before FerryMon, Paerl said. Because the Neuse River Estuary and Pamlico Sound are essential nurseries for many important fish species, researchers must be able to predict how this ecosystem will respond to water quality changes so state agencies that are responsible for water quality can take quick action.
FerryMon is commissioned by the North Carolina Department of Environment and Natural Resources (NC-DENR) in conjunction with Duke University Marine Laboratory (DUML), UNC-IMS and the North Carolina Department of Transportation Ferry Division (NCDOT).
FerryMon’s water quality monitoring system, which is about the size of a washing machine, is installed on three NCDOT ferries. One ferry makes 40 crossings daily along the Neuse River between Cherry Branch and Minnesott Beach.
The heart of the monitoring system is the YSI 6200 data acquisition system —interfaced with the small, durable YSI 6600 multiparameter monitoring sonde —customized for FerryMon by YSI’s Integrated Systems & Services division. YSI’s sensors, which fit inside a 3.5-in. by 2-ft cylindrical instrument, measure surface water temperature, salinity, dissolved oxygen, pH, turbidity and chlorophyll a fluorescence (algal biomass). Other underway monitoring systems are often created by wiring together stand-alone components from different sources and then integrating them with a data collection and telemetry system.
“YSI was certainly a pioneer in getting multiprobe sensors in a sonde that not only is sensitive but also compact,” Paerl said.
Global Positioning System (GPS) time-stamped data collected by the sensors and stored in the 6200 system is sent nightly from the ferry by cell phone to the UNC-IMS laboratory. The data is then made available to the NC-DENR, U.S. Environmental Protection Agency, National Oceanic & Atmospheric Administration, local water quality and fisheries agencies, researchers and schools.
Other monitoring systems often require ongoing attention and frequent maintenance, but YSI’s sonde operates self-sufficiently. Maintenance is performed every 10 to 14 days by a technician, who replaces the sonde on each ferry with a newly calibrated one.
With the help of the data system, FerryMon has documented variations in estuary and coastal waters.
“Because marine organisms are seldom distributed homogenously, it’s easy for monthly monitoring programs to miss patterns and patches in time and space,” Paerl said. “An algal bloom may only be a few hundred meters across, so we might not catch it with standard monitoring. This can affect regulatory actions and have important ramifications for management.”
In spring 2007, FerryMon helped researchers identify a large dinoflagellate bloom, which can trigger low oxygen (hypoxia), fish kills and toxicity. “The ferries picked up this bloom and raised the red flag,” Paerl said.
The program caught another dinoflagellate bloom in September 2006, on the heels of tropical storm Ernesto. More extensive sampling allowed researchers to delineate the extent of the bloom, which produced small fish kills in the Neuse River’s tributaries. “For regulatory agencies, this provides more evidence that nutrient-input controls are important, and that the TMDLs in place are justifiable,” Paerl said.
Researchers can review data from the program for trends and attempt to link blooms to nutrient-input events. By analyzing trends over multiple years, researchers can learn whether the frequency of blooms is increasing or decreasing, whether blooms are related to climate change and how the Pamlico Sound responds to hurricanes, tropical storms and droughts.
Paerl said FerryMon data has helped researchers learn how different storms affect water quality in Pamlico Sound and how long these impacts last. Shortly after the first ferry was instrumented in November 2000, it documented the lingering effects of Hurricane Floyd, which struck the area in September 1999. “Elevated chlorophyll levels and changes in species of algae were seen 18 months later,” Paerl said.
Researchers used to make assumptions about the effects of hurricanes on water quality. “Now we can reliably document these effects for the state, which maintains a database for looking at issues such as climate change, long-term impacts and increased frequency of hurricanes,” Paerl said. “We have a much better handle on natural perturbations and their effects compared to human effects.”
The future of ferry monitoring
Underway monitoring is capturing more attention from the scientific community as a reliable, inexpensive way to collect water quality data that would otherwise be too impractical and expensive to collect. By installing these systems on more ships on their regular routes, Paerl has been able to create accurate, high-resolution baseline datasets to observe how water quality, water conditions and ocean life change in the same area over long periods of time.
The state has continued to fund FerryMon. If he can obtain additional funding, Paerl hopes to equip additional ferries on Pamlico Sound with automated monitoring devices in the near future.