The pH results for December were slightly higher than our findings in November, with the average pH increasing from about 6.0 to 6.63 in December. This indicates slightly less acidic water conditions, as a pH of 7 is neutral.
December’s air and water temperatures decreased at all sites when compared to November’s temperatures. The air temperatures at the Mauldin Road and Falls Park sites did not change much from last month (0.5°C and 3°C decreases, respectively) likely due to overnight temperatures remaining consistently cool from month to month, but the air temperature at the Swamp Rabbit Café site decreased significantly by 6.5°C due to daytime temperatures at the time of monitoring being lower this month than last. The water temperatures also decreased significantly, with temperatures dropping between 5°C and 7°C at each site. The average air temperature was 9.17°C and the average water temperature was 7°C, compared to 12.17°C and 13°C in November. We can see the impacts of cooler water on both our E. coli and DO results this month.
The E. coli bacteria results from December’s sampling events were all well below the SC State Standard 349 CFU/100mL “high” threshold. The Mauldin Road site only registered with 100 CFU/100mL, 100 CFU less than last month. Falls Park produced 233 CFU/100mL, which was a very slight (33 CFU/100mL) increase from November’s results of 200 CFU/100mL, but not cause for concern, and Swamp Rabbit Café produced 200 CFU/100mL which is consistent with last month’s results. E. coli bacteria levels have a direct correlation with water temperatures: as water temperatures increase, E. coli viability and levels typically also increase. Therefore, this month’s low E. coli CFU populations are typical for this time of year due to lower water temperatures.
December’s dissolved oxygen (DO) results were also more characteristic of what we expect to see in cooler temperatures compared to our findings last month. During our December monitoring event, DO results landed within a range of 8.4 mg/L to 9.6 mg/L. The site at Mauldin Road increased 2.15 mg/L and Swamp Rabbit Café increased 2.5 mg/L, with both sites producing results of 9.6 mg/L this month. The Falls Park site’s DO levels returned to a typical level of 8.4 mg/L, a 7.2 mg/L increase from the sample we collected last month. The water level at Falls Park last month was notably low, with heavy invasive plant (ludwigia sp.) and leaf litter coverage likely impacting the DO levels. The rain events between November and December’s sampling dates seemed to improve flow and return it to normal levels, which likely also helped clear out the decaying leaf litter and may have removed some of the ludwigia from this portion of the tributary as well, or at least lessened its impact. Cooler temperatures could also have contributed to some ludwigia die-back, as the plant did not seem to be nearly as prevalent. We can infer that smaller concentrations of the invasive plant helped contribute to the higher DO levels this month. Combined with the significant reduction in decaying plant material, the stream was better equipped to hold higher levels of DO this month. When leaf litter or yard debris decays in water, the bacteria responsible for decomposition tend to lower DO levels. This is one reason why it’s important for homeowners to properly dispose of yard debris (please don’t dump anything into a stream or into storm drains!). Normal water levels and much cooler water temperatures likely caused the biggest improvement in DO levels across all sites. Dissolved oxygen and temperature have an inverse relationship: the warmer the temperature, the lower the water's capacity to hold DO! DO levels this month were typical for this time of year and well within SC State Standards.
December’s turbidity results also returned to normal levels with results of 5 NTUs at all sites. Last month, the turbidity was very high (65 NTUs) at the Falls Park site. This was likely also caused by the decaying matter floating in the tributary and the very low water levels. Because the Falls Park site is located on a small tributary to the Reedy River and not the Reedy itself, the tributary is more sensitive to low water levels and high levels of debris than larger systems that can dilute and move this type of material out of the system even in lower-flow conditions. We can again attribute the return to lower turbidity levels (clearer water) to higher water levels and less leaf coverage, and are pleased to see all three sites returning to normal levels. We are thankful to the City of Greenville Parks Department for their assistance with ensuring leaves do not build up on the Falls Park site’s tributary and for their ongoing support and commitment to improving and monitoring the water quality in the Reedy River. We will continue to monitor to ensure results stay consistent in the coming months.
Falls Park site looking downstream, December 13, 2023.