Intra-annual and ecoregional differences in physico-chemical data between blackwater and non-blackwater streams in the coastal plains of South Carolina

In the coastal plains of southeastern United States, blackwater streams are relatively common. In South Carolina, many naturally occurring blackwater streams have been identified over decades of water monitoring, particularly when they fail to meet water chemistry expectations originally set based on non-blackwater streams. The South Carolina Department of Environmental Services has collected extensive, often monthly, water chemistry data from both blackwater and non-blackwater systems throughout the Southeastern Plains (SEP) and Middle Atlantic Coastal Plain (MACP) ecoregions. Using these data, we compared seasonal patterns in water chemistry parameters between blackwater and non-blackwater streams. Examining monthly patterns between ecoregions and between site types (blackwater vs. non-blackwater), we observed that pH, total alkalinity, and total phosphorus often differed by both ecoregion and site type. For many parameters, however, differences between ecoregions were stronger than any differences by site type. This work has identified certain parameters that can distinguish blackwater from non-blackwater streams, but it has also shown that blackwater streams, even within one state, are not a monolith. They vary based on the underlying characteristics of the broader region in which they are located. The results of this research are relevant to the entire SEP and MACP ecoregions which jointly include parts of 11 U.S. states. Results are likely relevant to other blackwater rivers and streams in the contiguous United States and other blackwater systems globally, but the extent of relevance will require additional research. From a management perspective, this research has demonstrated that the Omernik Level III ecoregions offer a scale-appropriate means of grouping relatively similar blackwater systems conducive to management. The framework of ecoregions also supports collaborative exchange of information across political boundaries. This includes the exchange of information globally among entities with homologous ecoregions.