Origin of Dissolved Organic Carbon Studied by UV‐vis Spectroscopy

Dissolved organic carbon (DOC) distributions in water from Lake Ipê, MS, Brazil, were investigated. The samplings were performed monthly (surface, 1 m depth, and bottom) from June 1999 to June 2000. Absorbance at 285 nm and DOC concentrations in mg dm^—3, p(DOC), were highly correlated for the three depths. 77% of the surface, 85% for 1 m and bottom samples presented a variation between 20 dm³ g^—1 cm^—1 and 50 dm³ g^—1 cm^—1 of A(285 nm)/p(DOC), that characterizes the dissolved organic matter in lake water as essentially fulvic. The ratio A(254 nm)/p(DOC) was also sensitive for fulvic matter, and an A(250 nm)/A(365 nm) = 4 ratio was characteristic of strongly colored waters. The ratios A(436 nm)/p(DOC) for the three depths also showed a significant correlation. The predominance of fulvic acid is explained by environmental characteristics such as the tropical climate, temperatures above 18 °C, and the lake environment. It was demonstrated that the variation in the water carbon content due to different compartments in the lake can be monitored by UV‐vis spectroscopy ratios.     

Biosilicium (BSi) in Sedimenten Mecklenburger Seen (Deutschland) und das Calciumcarbonat-Biosilicium-Verhältnis als Trophie- und Wasserstandsindikator Biogenic Silica (BSi) in Sediments of the Mecklenburgian Lake District (Germany) and the Calcite-Silica-Relation as Indicator for Trophy and Water Level

The BSi content has been investigated in the surface sediments of lakes of different trophic state in the Mecklenburgian Lake District. The BSi content differs between 1 to 1000 mg BSi/g dry matter. High values were found in deep eutrophic lakes. Litoral sediments and shallow eutrophic lakes have lower contents. BSi content was found to be correlated with lake morphometry, depth, trophic level, sediment composition and especially with calcite. With the CaCO₃/BSi-value, 3 groups of lakes can be characterized:

• CaCO₃/BSi = 0 oligotrophic and dystrophic lakes
• CaCO₃/BSi ≤ 10 mesotrophic and eutrophic deep lakes
• CaCO₃/BSi ≤ 10 eutrophic shallow lakes

The results from the recent sediments have been compared with those from older sediments. Using the CaCO₃/BSi-value, climatic change, trophic state, and sea level can be detected.