Historical record of atmospheric deposition of metals and d15N in an ombrotrophic karst sinkhole fen, South Carolina, USA

Abstract

Radiometric 210 Pb dating, metal concentrations [As, Cd, Cr, Cu, Hg, Pb and Zn] and nitrogen-isotope (δ 15 N) analyses were conducted on a sediment core from an ombrotrophic karst sinkhole fen in South Carolina, USA, to obtain a historical record of nitrogen signatures and atmospherically deposited metals from increased anthropogenic emissions during the last several decades. Sinkhole fens in carbonate karst terrains are excellent environs for sediment core dating and metal analysis due to the low background metal concentrations in carbonates, as well as the alkaline nature of carbonates and the high organic-matter content in fens, both of which reduce mobility of metals in soils. Metal concentrations were found for the top twenty 1 cm intervals of the core and the bottom at 56 cm. Intervals 21-55 cm were analyzed only for Hg and organic-matter content due to financial constraints. The sinkhole fen in the study is ombrotrophic and receives metal inputs primarily through wet and dry atmospheric deposition, and the 20 cm deep sample had a 210 Pb CRS age of 1954. Metals with significant (p , 0.05) negative correlations with core depth were (negative correlation, sample size): Hg (−0.8948, n 5 56), Pb (−0.9308, n 5 21), Zn (−0.6299, n 5 21), Cd (−0.5023, n 5 21), and Cu (−0.5156, n 5 21). In view of the low background concentrations of these five metals from limestone found in the sinkhole, atmospheric deposition from anthropogenic emissions is likely the predominant source for these increasing concentrations. As (+0.4431, n 5 21) had a significant (p , 0.05) positive correlation with core depth, while Cr (+0.2761, n 5 21) was the only metal with no significant correlation with core depth. Although δ 15 N is shown in other studies to deplete upward in sediment cores due to increasing reactive nitrogen emissions, the sinkhole core in this study had no significant correlation (+0.2580, n 5 21) between δ 15 N and depth. Total carbon, total nitrogen, total phosphorus, and organic-matter content were also measured in intervals 1-20 and 56 cm and found to have several significant (p , 0.05) correlations with depth, metals, and δ 15 N. -Historical record of atmospheric deposition of metals and 15 N in an ombrotrophic karst sinkhole fen, South Carolina, USA. Journal of Cave and Karst Studies, v. 78, no. 2,

Investigation of buried karst sinkholes under a bog using ground penetrating radar (GPR) and electrical resistivity tomography (ERT)

“…The more widely used term ‘buried karst sinkholes’ (e.g., Rodriguez et al, 2014) could be used, as their manifestation on the bog surface is generally negligible; however, this term does not stress that these sinkholes are covered by peat sediments. The reviewed studies for the most part deal with sinkholes that are partially filled by a lake, colluvium, soil, fen or other organic sediments; thus, they are unique archives of palaeoenvironmental history and are investigated mainly from the palaeoecological, environmental pollution and archaeological perspectives (Barreiro‐Lostres et al, 2014; Edwards et al, 2016; Mergelov et al, 2020; Meyer‐Heintze et al, 2020). To our knowledge and based on literature analyses, this is the first study in which a detailed mapping of a buried and peat‐filled karst cover‐collapse sinkhole has been performed using geophysical methods.…”