Assessing environmental change through chemical‐sediment chronologies from inland lakes

Abstract

This paper examines the hypothesis that the spatial pattern of metal accumulation rates in inland lake sediments provides insight into the causes of the historical and continued loadings of contaminants to the environment. To address this, copper and lead accumulation rates in the Great Lakes' watershed were studied. A multi‐element approach was used, in which many non‐toxic chemicals were measured along with the toxic chemicals of interest, rather than a target‐specific approach. The multi‐element approach also allowed for assessing the environmental state of the lake with respect to its surrounding watershed. Sediment cores were collected from the deepest portion of five Michigan inland lakes, sectioned, metals extracted by nitric acid, microwave digestion and leachates analysed for 26 metals using an inductively coupled, plasma, mass spectrometer with hexapole technology. Sedimentation rates, ages and focusing factors were calculated via 210Pb. Dasymetric mapping was used to estimate population distributions in lake watersheds. Watershed area was estimated from digital elevation data using Arc/INFO (ESRI, Redlands, California). The data show that as loadings from dominant (regional) sources decrease (e.g. atmospheric deposition in the case of lead), new patterns provide insight into causes for continued contaminant loadings (e.g. population density). The data also show the universal response of the watersheds to the onset of the anthropogenic loadings of lead but not that of copper. Individual watersheds had different onset times for anthropogenic copper loadings. Recent lead loadings to the environment can be related to population density, and those of copper reflect, in part, a spatial pattern that is similar to the regional pattern for lead during the mid‐1970s. As this pattern for lead could be related to a regional gradient of lead concentrations in atmospheric deposition, the same relation cannot be made for copper. The cause for this spatial pattern for copper is not clear.

Spatial and Temporal Distribution of Polycyclic Aromatic Hydrocarbons in Sediments from Michigan Inland Lakes

“…Even as point sources for several known environmental contaminants are regulated and emissions from these sources decline, humans continue to alter the environment in significant ways (e.g., urban sprawl) that will have undetermined impacts on the input of contaminants to the environment ( , ). Therefore, it is essential to understand the contaminant loadings, both that we may assess the effects of environmental legislation and that we may identify emerging sources of pollution.…”

Lake‐specific responses in sedimentary sulphur, after additions of copper sulphate to lakes in Michigan, USA

“…2007a). Copper was analysed in nitric acid‐digested sediment by inductively‐coupled plasma‐mass spectrometry (Yohn et al. 2002).…”

“…Details on 210 Pb analysis and modelling for these cores are available elsewhere Parsons et al 2007a). Copper was analysed in nitric acid-digested sediment by inductivelycoupled plasma-mass spectrometry (Yohn et al 2002). Total sulphur (TS), chromium-reducible sulphur (CRS; reduced forms of sulphur that are decomposed in hot, acidic CrCl 2 to H 2 S) and stable sulphur isotopic compositions (d 34 S) were analysed with the methods of Canfield et al (1998).…”

Study of particle movement in the nearshore region of Lake Superior with radioisotope tracers

“…Unlike in many small lakes where the deepest spots are net depositional sites and the final destination of sediment focusing [Yohn et al, 2002], in large lakes more than one deposition zone is expected. Lake Michigan has two major depositional basins, and the site to which sediments are focused does not coincide with the deepest location in the southern basin [Edgington and Robbins, 1990].…”

“…Isotope inventories (both Pb and 137 Cs) are used to calculate FF. Most commonly, the FF is calculated from the 210 Pb inventory of sediment cores Yohn et al, 2002] according to the following equation: The theoretical 210 Pb inventory is defined as the steady-state inventory that would result if all atmospherically deposited 210 Pb remained at a site. In other words, the theoretical inventory is the rate of atmospheric deposition (F A , dpm/cm 2 yr) divided by the decay constant (k, yr -1 ) for 210 Pb.…”