HYDROGEOLOGICAL INFLUENCES AND NUTRIENT INPUTS TO A NUTRIENT SENSITIVE COASTAL LAKE, HORRY COUNTY, SC

Long Lake is a chara-dominated, alkaline coastal lake in Horry County, SC., which occupies a formerly estuarine swale. The inland shore is wooded, with a light footprint of cabins and homes dating to the 1940’s and later. All utilize traditional onsite wastewater treatment systems. Until the early 2000’s, this lake remained in a steady oligotrophic state, with inflows dominated by springs. Accelerating changes that began in the early 2000’s included a lower stratum of flocculated detritus composed of decaying remains of the dominant subaquatic vegetation, chara sp.

This study investigates potential causes of the sudden change of character of the lake. The lake is largely groundwater-fed via the surrounding surficial aquifer, though historical accounts indicate that spring flow from an underlying limestone aquifer may have been an important factor contributing to the previous oligotrophic state. Lines of enquiry include investigation of flow and fate of nutrients generated by human activity via groundwater and surface water, particularly with respect to potential inputs into Long Lake. Stratigraphic borings were undertaken; monitoring well, surface water and under-lake water samples were analyzed; hydraulic conductivity was analyzed via slug testing and grain size analysis; and modelling of the surficial aquifer was undertaken. External factors that may have reduced subsurface inflow into the lake were also evaluated. These possible factors include withdrawals from the confined aquifer that would previously have been feeding the springs. Installation of a stormwater drainage system in a nearby residential area may also have contributed to decreased inflow.