Ferries crossing the Neuse River and Pamlico Sound in North Carolina have been equipped with a water quality monitoring system for continuously collecting water samples and water quality data as part of the state-funded FerryMon program. The Neuse River Estuary and surrounding waters are nurseries for a variety of important fish species so researchers need to be able to predict how this ecosystem will respond to water quality changes so the state agencies responsible for water quality and fisheries habitat can take quick action as necessary.
North Carolina followed Finland’s ferry-monitoring Baltic Sea Algaline Project and installed systems on three ferries that travel in the Neuse River vicinity. The heart of the monitoring system is the YSI 6200 Data Acquisition System, interfaced with the simple, small and durable YSI 6600 Multiparameter Monitoring Sonde, which was customized for FerryMon.
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YSI’s sensors measure surface water temperature, salinity, dissolved oxygen, pH, turbidity and chlorophyll a fluorescence (algal biomass). “YSI was certainly a pioneer in getting multi-probe sensors in a sonde that not only is sensitive but also compact,” Hans Paerl of the University of North Carolina explains. Global Positioning System (GPS) time-stamps the data collected by the sensors and stores it in the 6200 system. It is then sent nightly from the ferry by mobile phone to a laboratory where it is processed and made available to the NC-DENR, U.S. EPA, NOAA, local water quality and fisheries agencies, researchers and schools.
During the ferry’s journey, the system also collects surface water samples, documenting where and when they were taken. “A refrigerated automatic water sampler stores samples for later study in the lab. A technician then travels onboard the ferry once every few days to collect samples and program the sampling unit,” Paerl explains. |
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Underway monitoring is capturing more attention from the scientific community as a reliable, inexpensive way to collect a wealth of water quality data that otherwise would be too impractical and expensive to collect. Unlike other underway monitoring systems, which often need researchers’ ongoing attention and frequent maintenance, YSI’s sonde operates self-sufficiently. Maintenance is performed every 10 to 14 days by a technician, who simply swaps the sonde on each ferry with a newly calibrated one.
By installing these systems on ships of opportunity it is possible 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.
During this programme, FerryMon has documented variations in estuary and coastal waters and detected certain water quality issues that otherwise would not have been captured. In spring 2007, FerryMon helped reseachers identify a large dinoflagellate bloom, which can trigger low oxygen, toxicity and kill fish. “The ferries picked up this bloom and raised the red flag,” Paerl said. “An algal bloom may only be a few hundred meters across, so we might not catch it with standard monitoring. Ferry monitoring is proving to be an incredibly good tool for monitoring and assessing long-term decadal changes, or changes due to hurricanes, sea level rise and global warming.”
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 a levels and changes in species of algae were seen 18 months later,” Paerl said.
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Since then, several ‘wet’ and ‘dry’ storms have hit the North Carolina coast such as Hurricane Isabel in 2003 which was a large, windy, ‘dry’ storm that churned the waters but delivered little rainfall, therefore, little runoff. “FerryMon saw elevated chlorophyll a and turbidity right after this hurricane, but the system recovered quickly,” Paerl noted. However, FerryMon found that tropical storm Ernesto and other ‘wet’ coastal storms that brought significant rainfall, produced longer lasting effects. “We saw more freshwater and more nutrients carried downstream to the open sound system,” 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 explains. |
Since 2000, FerryMon has uncovered many water quality problems, such as toxic algal blooms, changes in water clarity and excessive nutrient loadings, that could not have been detected by standard water quality monitoring techniques. They have eliminated the need for monitoring groups to charter research vessels for expensive sampling cruises, and minimized the need to set up numerous automatic monitoring stations on buoys, both of which can collect data only in limited areas. The programme has shown that an automated, continuous water quality monitoring program can be implemented on ships of opportunity for a relatively modest investment.