Sampling Location Updates

On September 9, October 6, and October 12, our team sampled at the following 13 sites across the Black and Sampit Rivers:

Black River Sites:

Sampit River Sites:

You might have noticed that two new sites have been added to our Black River sampling program! In June, Erin and I partnered up with the folks over at the North Inlet-Winyah Bay National Estuarine Research Reserve. With their collaboration, we began a nutrient monitoring project building on the data Erin and I have been collecting along the Black River. We added two monitoring sites, JUN and POC, to our monthly sampling regimen this June. While our nutrient and YSI data is not publicly available on our website yet, the results from our YSI data collection are visualized in the graphs below.

Dissolved Oxygen and pH

After some low dissolved oxygen conditions this summer, CAC on the Sampit saw a boost in DO levels in September. However, September and October also yielded some of our lowest dissolved oxygen concentrations along the Black River to date. JUN, MCL, and SIX all demonstrated hypoxic conditions in October’s sampling. The Black River at June Burn Road near Manning has maintained hypoxic conditions since August, which is most likely due to the lack of rainfall this summer and the site’s observed low flow conditions. MED, PHL, and RPF continue to maintain the highest dissolved oxygen levels across our sampling sites into the fall.

Unsurprisingly, JUN also maintained low pH conditions in September and October and seems to follow water quality trends similar to those present at Mingo Creek, Peters Creek, and Six Mile Creek. I suspect this is because the water within these ecosystems may receive the most tannic organic material from the surrounding swamps and wetlands. Our mid to upriver sampling sites (MED and PHL) continue to maintain the highest pH levels; in October, their pH levels measured between 7.30 to 7.72.

It is important to note that our two sampling sites on the Sampit are located within different ecosystem conditions. While CAC is fairly close to Winyah Bay and experiences lots of tidal mixing across its wide stretch, BOG is located near the headwaters of the Sampit and runs intimately between narrow channels of swamp. This difference seems most pronounced in their pH charts, which highlight how seawater and tannic material are constantly influencing the chemical makeup of the river at these locations.

Black River Salinity Increases

Starting in late summer Erin and I began to notice salinity increasing upriver in places where we have historically documented freshwater conditions. In the chart below, you can see all of our salinity data from February to October along the Black River, with the sites organized from the highest upriver site (JUN) to the lowest downriver site (PFL). Please note the tidal stage legend in the bottom of the chart, which indicates when each sample was collected during the tidal cycle. In these charts we have marked Pumphouse Landing as the end of tidal influence as changes to salinity and water level from Winyah Bay seem to end between here and Browns Ferry Landing. Because the Black River is a river dominated estuary, we suspect that a combination of less rainfall this summer and the ecosystem’s seasonal mixing conditions are the driving forces behind the salinity increases. Interestingly, although Mingo Creek is a tidally influenced tributary to the Black River, we have not seen major salinity increases at this location.

So, why does this matter? We primarily track salinity within our water quality programs to determine which fecal indicator bacteria to test for in our water samples. Currently, Winyah Rivers Alliance follows SCDES guidance that water samples above 0.48 ppt should test for Enterococcus and samples below 0.48 ppt should test for E.coli. The blue dotted line on these charts visualize SCDES’ salinity threshold of 0.48 ppt. As you can see from these charts, we have measured salinity values increasing towards Pumphouse Landing and Browns Ferry Landing. While these sites are tidally influenced, they typically maintain more freshwater conditions due to dominating freshwater flows. To analyze whether these salinity values are “normal” for this stretch of the Black River, I am working to convert conductivity values from SCDES’ freshwater monitoring on the Black River into salinity values. More to come on that analysis in the future!

Fecal Indicator Bacteria

This October, PFL and PCL were the only two sites along the Black River with fecal indicator bacteria concentrations above the EPA’s Beach Action Values (235 MPN/100 mL of E.coli and 104 MPN/100 mL of Enterococcus). As you may have noticed, Erin and I had to switch between testing for E.coli and Enterococcus at these sites as they experience frequent changes in salinity. JUN and POC are not a part of our bacteria sampling program and thus are not found in the graphs below. Additionally, the October bacteria samples for the Sampit River were rejected for quality assurance reasons and their concentrations are not shown in the charts below either.