Lake Tahoe geochemical study. I. Lake chemistry and tritium mixing study
The study of vertical mixing in Lake Tahoe by temperature and oxygen measurements is limited to the top layer of the lake, since vertical gradients are extremely small at greater depth. Below 200 m the temperature gradient is about -1.6 ✕ 10<sup>-4</sup> °C m<sup>-1</sup>, with little or no seasonal variation. A tritium profile was taken at a midlake station in 1973 together with samples for measurements on lake chemistry. Oxygen, nitrate, total inorganic carbon, and pH showed the effects of photosynthetic activity to a depth of about 80 m, well below the thermocline; average planktonic composition was calculated from these data. Silicate and carbonate alkalinity profiles were essentially uniform, showing that biological removal is negligible in comparison to the rate of vertical mixing.<br/>
Essentially no variation in tritium concentration with depth was observed. Tritium measurements and input estimates in Crater Lake were used to calculate tritium concentration in Lake Tahoe between 1954 and 1973 and to estimate a ratio in tritium input of 32% precipitation to 68% vapor exchange. The tritium profile gives strong evidence for at least occasional complete mixing of Lake Tahoe. The last complete mixing may have occurred in March 1973 and at least one other such event took place between 1964 and 1968.
Natural radon and phosphorus as limnologic tracers: horizontal and vertical eddy diffusion in Greifensee
Two-dimensional interpretation of monthly measurements of natural radon-222 at different stations in Greifensee, Switzerland, results in hypolimnetic vertical and horizontal eddy diffusion coefficients (<em>K<sub>z</sub></em> and <em>K<sub>x</sub></em>) of 0.2–0.05 and 1,000–100 cm<sup>2</sup> s<sup>-1</sup> during the stagnation period in 1975. Application of the one-dimensional and three-dimensional horizontally well mixed models to the data from the midlake station produces errors of about a factor of two in the vertical eddy diffusion coefficient. With the hypolimnion mixing information, <em>K</em><sub><em>z</em></sub> in the thermocline is estimated to be 0.025 ± 0.015 cm<sup>2</sup> s<sup>-1</sup> by using dissolved phosphorus as a quasi-conservative tracer.<br/>
The eddy diffusion coefficients calculated are in good agreement with those which would be predicted by empirical methods. The results when applied to phosphorus cycling indicate that P reflux from the hypolimnion and thermocline in eutrophic Greifensee is of the same magnitude as external inputs during the months of maximum photosynthesis.
Primary production per unit lake area, Σ<I>P</I>, is selected as a measure of the trophic state of a lake. The relationship between phosphorus loading and Σ<I>P</I> is simulated by means of a dynamic, one-dimensional vertical diffusion model for phosphate [OP] and particulate phosphorus [PP]. Σ<I>P</I> is described by a non-linear function of [OP] and [PP] which takes into account Michaelis Menten saturation and self shadowing by algae. Included in the model are lake morphometry, hydraulic loading, respiration rate, sedimentation, vertical eddy diffusion, depth of thermocline, and exchange of phosphorus at the sediment-water interface. Application of the model to two Swiss lakes, Alpnachersee and Greifensee, as well as to Lake Washington (U.S.A.) shows a good agreement between observation and calculation of the phosphorus variation as a function of time and depth. The calibrated model is used to predict the effectiveness of different eutrophication control measures, such as reduction of phosphorus loading, discharge of hypolimnic water, aeration of the hypolimnion, and destratification. For Greifensee (mean residence time of water 1.2 years) it is shown that a reduction in P-loading to 20% of its present value is needed to achieve permanent aerobic conditions throughout the lake. Other measures result only in minor improvements. For Lake Washington, the model simulates well the observed recovery of the lake after sewage diversion between 1963 and 1967.
Primary production, mineralization, and sedimentation in the euphotic zone of two Swiss lakes
Phosphorus and nitrogen concentrations, phytoplankton, bacteria, detritus, primary production, and sedimentation have been investigated over a year in two Swiss lakes of different trophic state. Inflow and outflow of the lakes were calculated, as well as the eddy diffusion of P and N from the metalimnion into the epilimnion, and from these data a balance of the epilimnetic phosphorus and nitrogen cycle was drawn up. Different methods of calculation all suggested a high intensity of the internal nutrient cycle in the epilimnion. By means of autolysis, destruction, and excretion, about 35–75% of the nitrogen and 55–85% of the phosphorus needed for the measured primary production can thus be regenerated.
Beeinflussung der Oxidationswirkung von Ozon und OH<B><SUP>·</SUP></B>-Radikalen durch Carbonat
In the ozonation of water, ozone may decompose and form hydroxyl radicals (OH<B><SUP>·</SUP></B>). These very reactive intermediates are the most important oxidants for many solutes, but they are even scavenged by carbonate- and bicarbonate ions. Thus, many types of organic trace-impurities in waters are protected by the carbonate species from the oxidation by OH<B><SUP>·</SUP></B>. Studies on solutions of benzene, tetrachloroethylene, methanol and ammonia (0,1-4 mg/l) as model solutes give results in fair agreement with those expected from known reaction-rate constants. Furthermore the effect of CO<sub>3</sub><sup>-</sup> is about 12 times greater than that of HCO<sub>3</sub><sup>-</sup>. The scavenging reaction of carbonate also inhibits a radical chain reaction by which the O<sub>3</sub>-decomposition is accelerated by many organic trace solutes. Thus, carbonate stabilizes O<sub>3</sub> and thereby intensifies the direct reactions of O<sub>3</sub>-molecules with solutes. Measurements on drinking water from different sources (raw water) demonstrate the stabilizing effect of bicarbonate on O<sub>3</sub> and its inhibition on the oxidation of trace impurities. Parallel studies on the scavenging of radiolytically initiated OH<B><SUP>·</SUP></B> by carbonate were used for comparisons with results obtained with ozone.
Nitrifikation in Fliessgewässern - Fallstudie Glatt
Cumulative frequency distributions of ammonium concentrations in Swiss rivers demonstrate that today ammonium standards are exceeded in relatively small rivers only. A predictive, mechanistic nitrification model for rivers is developed and discussed. The model is applicable in rivers with small hydraulic radii (<1 m) and reasonable flow velocities (∼1 m/sec). In a case study for the river Glatt the model is applied (verified) and used as a predictive tool.
Untersuchungen über den Schwermetallhaushalt in Seen
In the mesotrophic Lake of Lucerne (Bay of Horw) and in the eutrophic Lake of Alpnach concentration and sedimentation of iron, copper, zinc, cadmium and lead were investigated as a function of time and depth, and compared with a series of physical and chemical parameters. A metal balance was made for the Lake of Alpnach. A model for the distribution of the metals between biomass, allochthonous material and dissolved phase was employed. Phenomenology and model lead to the following conclusions: the sedimentation of the metals is dominated by allochthonous particles, the biogenic particularization is partially reversed by lake internal decomposition processes and the trace metals reaching the sediment are partially redissolved.
Untersuchungen über die Beeinflussung der planktischen Photosynthese durch anorganische Metallsalze im eutrophen Alpnachersee und in der mesotrophen Horwer Bucht
The effects on phytoplankton photosynthesis of inorganic metal salts HgCl<sub>2</sub>, CuSO<sub>4</sub>, Cd(NO<sub>3</sub>)<sub>2</sub>, ZnCl<sub>2</sub> and Pb(NO<sub>3</sub>)<sub>2</sub> were studied over monthly intervals.<br />
In experiments with individual metals, phytoplankton photosynthesis was not adversely affected if the concentration increase above background levels did not exceed 10<sup>-9</sup> mole Hg/l, 5·10<sup>-9</sup> mole Cu/l, 2·10<sup>-8</sup> mole Cd/l, 5·10<sup>-8</sup> mole Zn/l and 2·10<sup>-7</sup> mole Pb/l, respectively. However when the concentration was increased by 5·10<sup>-10</sup> mole Hg/l + 5·10<sup>-9</sup> mole Cu/l + 5·10<sup>-9</sup> mole Cd/l + 5·10<sup>-8</sup> mole Zn/l + 5·10<sup>-8</sup> mole Pb/l photosynthesis was significantly reduced, due to a synergetic effect of the combined metals.<br />
The influence of phytoplankton density, pH-value concentration of calcium, dissolved organic nitrogen and allochthonous debris on heavy metal toxicity was investigated. Changes in phytoplankton composition are believed to the main reason for the seasonal variation in the toxic effects of heavy metals.
Dissolved loads in streams and rivers - discharge and seasonally related variations
Basins of various sizes have been compared to examine behaviour patterns of chemical and hydrological parameters under different geological and climatic conditions. Data from small forested basins up to 1 km2, middle sized river systems up to 10 000 km2, and several stations on the River Rhine below Lake Constance were used. Basins were investigated with varying degrees of sampling intensity, depending on size and the immediate aims of the particular study. In general the major physical parameters were recorded continuously, and chemical parameters were determined for continuous composite samples from large basins. Frequent grab samples were taken in smaller basins. The basic sampling regime permitted the examination of annual periodicity in fluctuations. The variance of dissolved loads in streams and rivers is markedly reduced when data evaluation includes consideration of the annual cyclic pattern. In the present study this behaviour has been identified for a number of parameters, and annual patterns are similar for small and large basins. The recognition of basin-independent patterns aids comparison of data from basins varying in size and other characteristics.
Ermittlung der Reinigungsleistung einer Schlammbelebungsanlage mit Sauerstoffbegasung von kommunalem Abwasser in der Region Basel
Evalution of the data collected can answer the questions on utilization of the technical oxygen and energy consumption. A comparision of the pollution loads of the waste water in the influent and effluent of the clarifying plant over a period of 10x24 hours with varying loads gave reliable data on clarification performance and process stability.