Fate of Contaminants of Emerging Concern in a Sinkhole Lake, Florida, USA

Highly karstified carbonate platforms such as Florida are characterized by rapid infiltration rates, highly permeable bedrock and the direct connection to the below aquifer through the high density of sinkholes. This combination of physical features makes the groundwater and aquifers highly vulnerable to contamination from synthetic chemicals commonly referred to as contaminants of emerging concern (CECs). The use of septic tanks, otherwise referred to as onsite water treatment systems (OWTS), promotes the introduction of CECs into the environment. In order to study the impacts of CECs from OWTS on a karst landscape, water, sediment, and vegetation samples were collected in a sinkhole lake surrounded by residential housing using this waste disposal method. The main question of this research project is what is the fate of CECs from OWTSs effluent within the catchment of a sinkhole lake? Liquid chromatograph mass spectrometry was used to analyze the samples for the presence of CECs. It was found that the relative quantity of CECs in the individual constituents is dependent upon 1) the hydrophobicity and polarity of the individual compound, 2) the specific sampling site, 3) the topography gradient, and 4) for vegetation, the connectedness of the sample type to the sediment. Hydrogeological studies have found that the sinkholes of the area are all connected to the below aquifer. Consequently, these CECs pose a risk of the contamination of the groundwater. This study is a temporal snapshot, that being the dry season of Florida which is most likely the time of lowest CEC contamination. It is imperative that sampling extend into the wet season when flushing of CECs from the OWTS may increase their concentrations in both the lake but also the aquifers especially since residents use well water as their source of potable water. While this study is based in Florida, we strongly suspect that our findings and recommendations are applicable more generally as OWTS are used throughout the many karst regions of the world.

Association of postfire peat accumulation and microtopography in boreal bogs

Peatlands accumulate organic matter as peat because of disproportionate rates of production and decomposition. However, peat accumulation heterogeneity has not been well studied along the microtopographic gradient (hummocks vs. hollows), particularly with respect to fire. Fire affects peatland species composition by differentially removing vegetation and resetting succession, resulting in peat accumulation changes. We examined peat accumulation and microtopography in two historically burned bogs in Alberta, Canada. Measurements of current and historic microtopography were made, and cores were collected along the gradient to identify depth of peat accumulated since fire, as well as to assess properties of the accumulated peat. Current microtopography is significant and correlated with the immediate postfire surface relief. However, differences in the magnitude of variability between sites suggests that differential rates of growth between features are exacerbated between sites and reflected in bog microtopography. Rates of organic matter accumulation, ranging from 156 to 257 g·m–2·year–1, were elevated but comparable to published rates of recent accumulation. Organic matter content and accumulation rate were greater for hummocks than hollows at Athabasca bog, but the difference between features diminished at Sinkhole Lake, suggesting that the pattern and properties of peat accumulation and microtopography postfire may be attributable to differences in site conditions.