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Browsing by Author "Dean, W.E."

Now showing 1 - 5 of 5
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    The chemical composition of lakes in the north central United States
    (American Society of Limnology and Oceanography, 1983) Gorham, E.; Dean, W.E.; Sanger, J.E.
    Lake waters of the north-central U.S.A. arc classified into five groups, based on increasing specific conductivity and changes in ionic composition from east to west, from Wisconsin through Minnesota to North and South Dakota, The most dilute group of waters has specific conductivities <29 µmhos -cm-’ at 25°C; the most concentrated group has specific conductances that range from 7,000 to 73,000 µmhos. As conductivity increases all major ions increase, but there is a shift in cation dominance from Ca2+ to Mg2’ to Na’, and in anion dominance from HC03- to SOd2-. This shift partly reflects a westward increase in climatic aridity, and partly a westward sequence of glacial drifts from noncalcareous to calcareous and hence to calcareous with abundant sulfur-bearing minerals. Levels of pH, K, Cl, F, B, and SiO, also show a distinct westward increase. Concentrations of NO,- and Mn increase from east to west, but the trend is less distinct. Concentrations of Fe vary widely without any trend over the range of conductivity. Color, mostly from dissolved organic matter, is controlled chiefly by lake depth, except for lakes with extensive peatlands in their drainage basins.
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    The chemical composition of lakes in the north-central United States
    (1982) Gorham, E.; Dean, W.E.; Sanger, J.E.
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    Major chemical and mineral components of profundal surface sediments of Minnesota lakes
    (American Society of Limnology and Oceanography, 1976) Dean, W.E.; Gorham, E.
    Minnesota lakes, characterized primarily on t&e basis of water chemistry, can also be classified according to the proportions of organic matter, CaCOs, and elastic minerals in their profundal sediments. The northeastern (group 1) lakes are characterized by shallow to very deep basins in Precambrian crystalline rocks, active outlets, and dilute surface waters. Profundal sediments of these lakes contain no sedimentary calcium carbonate and can be subdivided on the basis of organic content. Highly organic sediments of group 1 lakes contain more than 30% organic matter (as loss on ignition), but most group 1 lake sediments contain less than this. The central group 2 lakes occupy shallow to moderately deep basins in calcareous glacial till, have inactive outlets as a result of net evaporation, contain more concentrated salts than group 1 lakes, and commonly precipitate CaCOs during the summer. These lakes can be subdivided on the basis of sedimentary CaCOs. Sediments of group 2 lakes with more than 30% organic material contain little or no CaCOs. Southern group 2 lake sediments are characterized by 1030% CaC03 and 10-300/o organic matter. Sediments of western group 2 lakes contain 30-5070 CaCOs and about twice as much elastic as organic materials. Group 3 lakes occupy shallow depressions in calcareous, sulfur-rich glacial drift of the arid southwestern prairie region and contain even more concentrated salts than group 2 lakes. Sediments in these lakes are mainly elastic, averaging about 12% organic matter and 20% CaCOs. Variations in water and sediment chemistry, and in sediment mineralogy of these lakes are clearly related to an increase in climatic aridity and aquatic productivity from northeast to southwest. Differences in nature of the underlying glacial drift and in degree of erosion also affect the composition of the lake sediments.
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    Some relationships between algal standing crop, water chemistry, and sediment chemistry in the English lakes
    (American Society of Limnology and Oceanography, 1974) Gorham, E.; Lund, J.W.G.; Sanger, J.E.; Dean, W.E.
    Estimates of standing crop, derived approximately from algal counts in surface waters, have been used to separate the English Lakes into three groups of low, intermediate, and high fertility. The fertile lakes are proportionally poorer than the infertile lakes in p-algae, but richer in “large algae” and Cyanophyta. The fertile lakes are richer in dissolved ions, especially calcium and bicarbonate, in filter-passing and particulate vitamin Bx, in sedimentary sulfur, and in sedimentary chlorophyll derivatives and carotenoids. The relationship noted by Pearsall between lake fertility and agricultural activity is shown by a strong correlation between algal standing crop and the percentage of the drainage basin under cultivation. Sediment ratios of carbon to sulfur and of chlorophyll derivatives to carotenoids decline with increasing lake fertility, whereas the ratio of carbon to nitrogen shows little change. This study lends support to the use of sedimentary pigments as indicts to lake productivity. The pigment data also indicate that much of the organic matter in sediments of productive lakes comes from autochthonous sources within the lakes.