Sephadex columns have been used to fractionate organic matter in natural water into apparent molecular weight groups. Moderately colored creek water was fractionated into 10 fractions. The ratios of dichromate-oxidizable organic matter, color, and organic nitrogen were different for each fraction. Various lakes, streams, and leachable organic matter from lake sediments showed different organic carbon elution patterns. Gel permeation chromatography shows promise as a

4 The significance of denitrification as a sink in the nitrogen budget has been determined for Lake Mendota, Wis. About 28,100 kg. of nitrogen were lost from the lake hypolimnion during the summer of 1966. However, this relatively large amount represented only about 11% of the estimated total annual nitrogen input. Denitrification rates ranged from 8 to 26 pg. of N per liter per day, while rates of nitrate reduction (to ammonia and organic nitrogen) were found by 15N tracer techniques to range from 1.4 to 13.4 pg. of N per liter per day in the hypolimnion of the lake. Nitrate depletion is more than an order of magnitude slower than oxygen depletion in the hypolimnion of Lake Mendota, and denitrification is probably not significant with respect to respiration and catabolic processes in the lake hypolimnion. There is some evidence to indicate that dissolved nitrogen gas concentrations increase above those expected on the basis of solubility as the result of denitrification. Evaluation of various nitrogen sinks for Lake Mendota has revealed that only about one third of the estimated annual nitrogen input can be accounted for by currently evaluated sinks. Sediment deposition probably accounts for most of the remaining two thirds. enitrification probably occurs in stratified lakes which D lose their hypolimnetic oxygen, but the significance of this has not been properly assessed. Hutchinson (1957) has reviewed many examples of lakes in which the late summer nitrate distribution is dichotomic as the result of depletion by nitrate assimilation in the surface waters and by denitrification and nitrate reduction in the anoxic bottom waters. Only recently Dugdale, 1966a, 1966b) have estimates been made of in situ denitrification rates in natural waters. However, these rates do not necessarily define the quantitative significance of denitrification as a sink in the nitrogen budget of a water body. A recent investigation of nitrogen cycle dynamics in natural waters (Brezonik, 1967) permits an estimate of this sort for Lake Mendota, Wis.Lake Mendota has been one of the most frequently studied lakes in the world, and descriptions of its characteristics are numerous in the limnological literature. A few facts germane to the following study should be mentioned. The lake covers 3938 hectares and has a maximum depth of about 24 meters. The lake is moderately eutrophic and loses its dissolved oxygen below about 10 meters during summer stratification. A heavy influx of nutrient compounds results from the lake's Present address, Department of Bioenvironmental Engineering, University of Florida, Gainesville, Fla. 32601 location in a basin of fertile crop and pasture land and partially from the urban influence of the city of Madison, which now nearly surrounds the lake. Lee et al. (1966) have recently estimated nitrogen and phosphorus sources for the lake which show an annual input of nitrogen equivalent to 0.50 mg. of N per liter of lake water and an annual phosphorus input equivalent to 0.047 mg. of P per liter of the lake. This ra...

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 ...

Solutions of 14C-labeled glycine, glucose, citric acid, and phenylalanine in distilled water and lake water, and distilled water solutions of lindane, were freeze-concentrated by freezing them in stainless steel buckets with constant agitation. Samples of various volumes (800 ml. to 16 liters) with initial solute concentrations ranging from 0.01 to 1.0 mg. per liter were concentrated by factors of 3 to 22. Recoveries of the organic compounds approached 100%. Solute losses in freeze concentration seem to be due, at least in part, to nonspecific entrapment that can be controlled by careful choice of operating parameters for the freeze concentration process used.

The role of lake sediments in the detoxification of lakes which were treated with toxaphene was evaluated under environmental and laboratory conditions. The extent of toxaphene accumulation in sediments of three Wisconsin lakes was determined by electron capture gas chromatographic