Effects of Hurricane Matthew on the May River researched

Beth Lewis, stormwater technician for the Town of Bluffton, collects water samples from the May River. The Town regularly conducts microbial source tracking (MST) sampling in the river and many of the stormwater drainages that lead to the river. The goal

Hurricane Matthew hit Bluffton and the surrounding areas in October 2016, leaving a path of highly visible destruction to homes, businesses and the landscape.

Matthew dumped 11-14 inches of rain from Hilton Head to Beaufort, according to the National Weather Service charts.

The impact that storm had on the May River and other area water bodies is still a mystery.

"This is a challenging question to answer because you need to know baseline data before a hurricane occurs. Much of this baseline data is lacking," said Eric W. Montie, an associate professor at the University of South Carolina Beaufort. He runs the Marine Sensory and Neurobiology Lab in the Department of Natural Sciences. "For example, we do not know the total area of oyster reefs in the May River, and we do not know the health of these reefs. But, oyster reefs are tough structures and increased flow from the surge of a hurricane will not dislodge an oyster from the reef."

In the event of a future hurricane, the data Montie is collecting now will be more helpful. The USCB lab has been eavesdropping on the river with acoustic monitoring, which helps indicate whether there will continue to be plenty of food for dolphins and other wildlife.

"Since 2013, our lab has had instruments deployed in the May River that have been keeping tabs on fish spawning by listening to their 'courtship' sounds," Montie said.

The information collected gives important data about feeding, mating and reproducation behaviors of various marine species.

Montie's staff has analyzed the sound data for 2013, 2014, 2015 and 2016. They know that fish use the May River for spawning purposes. He said the finished 2017 analysis will help clarify how Hurricane Matthew might have affected fish spawning.

The Town of Bluffton also oversees monitoring of the May River in a partnership with USCB.

Kim Jones, Watershed Management Division Manager for Bluffton, said the town uses Stormwater Utility Fees to pay $120,000 annually to the university to analyze weekly fecal coliform bacteria and quarterly required Municipal Separate Storm Sewer System (MS4) water quality samples.

Bluffton also has a $38,400 budget for bacterial microbial source tracking (MST) in FY18. MST techniques determine if the source of the bacteria is human, wildlife or domestic animal.

One of the instances that trigger bacterial sampling includes rainfall of more than 0.15 inches. The samples are then taken within 24 hours of the rain event on an outgoing tide, nearing low tide. A rain event that drops more than 0.1 inches over a 72-hour period triggers wet weather MS4 sampling.

Following Matthew, the state Department of Health and Environmental Control (DHEC) took a precautionary step and closed all the state's shellfish beds.

The first four shellfish beds from the headwaters of the May River, including Rose Dhu and Stoney creeks and associated tributaries and marshlands, down to Crane Island are restricted from harvesting. They have failed repeated testing since 2014 due to high counts of fecal coliform colonies during systematic random samplings.

There are several parameters but, simply stated, to be an approved shellfish harvesting bed, there must not be more than 14 colonies per 100 milliliters of fecal coliform Most Probably Number (MPN) per sample.

The 2017 annual geometric mean reading up to September for station 19-19 at the head of the May River is 49.7. In March, the sample read 350 MPN.

Salinity levels are another important indicator of a waterway's health.

Readings taken before and after Matthew at 4M, the first monitoring station at the headwaters, were dramatic. On Oct. 4 the salinity at 4M was at 31.25 parts per thousand (ppt), and on Oct. 18, 10 days after Matthew, salinity was at 13.13 ppt - an 18.12 ppt drop.

"This salinity drop was most likely a stressful event for organisms occupying the headwaters of the May River but less of a salinity issue for marine organisms farther down river," said Montie.

The research goal is to continue developing a program of investigating water quality in the May River with on-scene and continuous long-term monitoring of the different features such as depth (sea level rise), rainfall, salinity, dissolved oxygen and acidity.

"Many of these endpoints are important in understanding how climate change may impact the health of estuaries. In fact, we have shown that the May River has warmed by 1.2° C from 2013 to 2016," said Monte. "This warming is changing the patterns of fish spawning in the May River. There is also some evidence that the May River is becoming fresher ... less salty."

That evidence is in readings taken from February 2010 to as recently as September 2017 clearly showing that all six monitoring stations are showing a drop in salinity levels. The effect on aquatic life has yet to be determined.

Gwyneth J. Saunders is a veteran journalist and freelance writer living in Bluffton.

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