Distribution of manganese, iron, phosphorus, magnesium, potassium, sodium, and calcium in the surface sediments of Lake Mendota, Wisconsin

Abstract

Analysis of 32 surface sediment samples from different areas of Lake Mendota, Wis., indicated a high positive statistical correlation between Mn, Fe, and P concentration in the sample and the depth of water overlying the point of sample recovery. An inverse correlation was found for Mg and K. No statistical correlation between concentration and depth of sample recovery was found for Ca and Na. urface sediment samples were collected from Lake S Mendota, Wis., during the summer and early fall of 1967.The purpose of the sampling was to assess the chemical composition of the sediments with respect to water depth and location in the lake. Studies conducted during the early 1950's reported by Rohlich (1963) indicate that N, P, and Fe concentrations become greater with increasing depth of water, Later work by Nriagu (1968) showed a correlation between the concentration of total-and sulfide-S and depth of overlying water for seven sediment samples collected from the central area of Lake Mendota, with depths ranging from approximately 11 to 25 meters. Gravity core sediment samples from different areas of Lake Mendota were collected by Murray (1956). The sediments in the deeper areas of the lake were typically black sludge or gyttja, resting on top of buff-colored marl deposits. The average CaC03 content of the black sludge is 32 x (dry weight basis). The sludge in the deeper area of the lake generally showed a higher carbonate content than sludge in shallower areas. Lee (1962) summarized previous studies that found shifting of the bottom muds in University Bay, located in the southcentral part of the lake. This was determined by plotting concentration contours for the summer and winter seasons. The variations in the element distribution contours were attributed to the effects of bottom currents induced by strong winds which prevail during fall and winter. An extensive survey of the circulation of Lake Mendota was conducted by Bryson and Suomi (1952). They found that wind-driven epilimnetic waters resulted in a depression of the thermocline in the downwind portion of the lake. A resultant upward release of this depression created measurable hypolimnetic currents. These hypolimnetic currents would be sufficient to disturb the extremely flocculent surface sediments. Gardner and Lee (1965) reported that scuba divers operating in the waters above the surface sediments created sufficient water currents to agitate the sediments, resulting in highly turbid bottom water conditions. Thus, continuous wind-driven circulation of the epilimnion, followed by hypolimnetic circulation, would account for the displacement and partial alteration of sedimentary element distribution patterns.The study reported here extends the available information Present address, Department of Chemistry (DFC), USAF Academy, Colo. 80840. about the distribution of certain elements in the surface sediments of Lake Mendota. The results show the effect of depth and possibly bottom morphology on the concentration of elements in surface sediments, and thus can ...

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“…However, for Mg the comparable statistics were only 0.5 ± 0.3 mg L™1, or 2% of the epilimnetic mean. On the basis of these results and independent sedimentary evidence (21)(22)(23), Mg acts conservatively (F = F' = 0) in these study lákes. Calcium is also conservative in soft-water lakes of the Northern Highlands.…”

“…In humid regions with abundant dolomite, Mg offers advantages over Ca as a tracer because, once in solution, it does not re-form a carbonate in lakes unless Mg/Ca > 2 (20). This geochemical distinction accounts for the very high CaO/MgO ratios in lake sediments of southeast Wisconsin (21,22) and elsewhere (19,23). Because Mg behaves nearly conservatively within the lake water column, only a few measurements will suffice to estimate C0' and C¿ for individual study lakes.…”

Cycling of manganese and iron in Lake Mendota, Wisconsin

“…On the basis of statistical analysis of 35 sediment samples, Delfino et al (33) concluded that Mn and P were much more closely related in recent Mendota sediments than Fe and P. Because of the long-known association between Fe and P in certain environments undergoing redox shifts (cf. 2,36,50), this Mn-P "association" has been labeled a statistical "artifact" (57).…”

“…This application of "ratio estimation" (cf. 35) depends on the close geochemical association among Fe, Mn, and P in the postcultural sludge sediments (called gytta) in Mendota (33). Annual losses of Mn and Fe at the outlet were computed based on seasonal discharge (cf.…”

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“…Depending on the morphological and hydrophysical characteristics of lakes and marine basins, redox changes may cause a spatial redistribution of particulate Mn in lakes (Delfino et al 1969;Ostendorp and Frevert 1979;Schaller and Wehrli 1996;Dellwig et al 2018) and marine basins (Rajendran et al 1992;Lenz et al 2015a, b;Häusler et al 2018;Schaller and Wehrli 1996) introduced the term ''geochemical focusing'' to address the mobilisation of Mn from shallow sediments, its transportation within the water column, and sedimentation in the deep zones of lakes. In marine geology and sedimentology, the term ''shelf-to-basin shuttle'' is more common for this transport process (Lyons and Severmann 2006;Scholz et al 2013).…”