Lake Zurich

In field studies on coagulation and sedimentation in lakes (Weilenmann et al., 1989), the particle size distribution at concentrations at several depths in the water column of Lake Zurich were measured (Fig. 7.15). 

Observed particle volume concentration distributions in the water column of Lake Zurich. Samples obtained on August 8,1984 at the depths indicated. 

The experimental aspects of this study were focussed on two hard-water lakes in Switzerland, namely, the northern basin of Lake Zurich and Lake Sempach. The hydraulic residence time of Lake Zurich is 1.2 years. Most of the particles in the lake are produced directly or indirectly by biological processes within the lake itself (e.g., photosynthesis, CaC03 precipitation). Phosphorus removal has been implemented in recent years at all wastewater treatment plants discharging into the lake at present Lake Zurich can be described as between meso- and eutrophic. Lake Sempach has an average hydraulic residence time of 15.8 years as in Lake Zurich, particles in the lake waters are primarily autochthonous. Phosphorus concentrations have increased substantially and the lake is eutrophic. 

Results of model simulations of effects of coagulation (a = 0.1) and sedimentation at steady state in Lake Zurich during summer are presented in Fig. 7.16. Particle volume concentrations in the epilimnion and hypolimnion are plotted as functions of the particle production flux in the epilimnion. Biological degradation and chemical dissolution of particles are neglected in these calculations. Predicted particle... 

Model simulations of particle volume concentrations in the summer as functions of the particle production flux in the epilimnion of Lake Zurich, adapted from Weilenmann, O Melia and Stumm (1989). Predictions are made for the epilimnion (A) and the hypolimnion (B). Simulations are made for input particle size distributions ranging from 0.3 to 30 pm described by a power law with an exponent of p. For p = 3, the particle size distribution of inputs peaks at the largest size, i.e., 30 pm. For p = 4, an equal mass or volume input of particles is in every logaritmic size interval. Two particle or aggregate densities (pp) are considered, and a colloidal stability factor (a) of 0.1 us used. The broken line in (A) denotes predicted particle concentrations in the epilimnion when particles are removed from the lake only in the river outflow. Shaded areas show input fluxes based on the collections of total suspendet solids in sediment traps and the composition of the collected solids. 

Table 11.5 shows that sedimentation rates of 0.1 - 2 g nr2 d 1 are typically observed in lakes still higher values are found in very eutrophic lakes. The settling material can be collected in sediment traps it can then be characterized in terms of chemical composition, morphology, and size distribution of the particles. The composition is subject to seasonal variations caused primarily by different biological activities in the various seasons. Representative examples for Lakes Zurich and Constance are given in Fig. 11.10. These two lakes are prealpine lakes, located in regions of predominantly calcareous rocks, both are under the influence of eutrophication. 

The ratios of different elements to C are listed in Table 11.5 as an attempt to test this assumption in various systems. For Lake Zurich and Lake Constance the following tentative ratio was calculated ... 

In Lake Zurich and Lake Constance, correlations between the contents of different trace elements in the settling particles and phosphorus, which may be used as an indicator of biological material, indicate that especially copper and zinc were likely... 

Concentrations of Cu and Zn as a function of P in the settling material from Lake Zurich and Lake Constance. P serves as an indicator of biological material. The regression lines for Zn and Cu fall nearly together, indicating that rather constant ratios Cu Zn P are found in this material. 

Table 11.3 illustrates some data. They are mostly from lakes with high sedimentary fluxes and illustrate that very low concentrations are observed in lakes, in spite of large pollutional inputs into these lakes. The residual concentrations are close to those observed in the open ocean (Bruland, 1983). Even in lakes which are located closer to pollution sources, like Lake Zurich, the concentrations in the water column are at a similarly low level as in the Great Lakes. 

Example Pb in Lake Zurich, summer Sedimentation rate of Pb ... 

Sigg, L., M. Sturm, and D. Kistler (1987), "Vertical Transport of Heavy Metals by Settling Particles in Lake Zurich , Limnol. Oceanogr. 32, 112-130. 

Although the data are scarce, the values for lakes are relatively close to the range and average value predicted based on organic C loading. Further, the relatively low HON in Lake Zurich might be expected based on the high primary productivity in this lake and the restricted input of allochthonous material to much of Lake Zurich (Weilenmann et al., 1989). 

Consider para-dichlorobenzene (DCB), which is used as a toilet disinfectant. The following data are available for DCB the molecular weight is 146 g/mol, the liquid vapor pressure is 1.3 Torr, and the saturated water solubility is 5.3 x 10-4 mol/L. In Lake Zurich, the measured concentration of DCB is lOng/L and the average wind speed is 2.3 m/s. What is this compound s flux into or out of Lake Zurich ... 

Assuming that the air concentration of DCB above Lake Zurich is very low such that we can call it zero, the flux out of the lake is simply... 

Let us check this result with some data measured at Lake Zurich. This lake has an area of 68 km2 and average depth of 50 m. There are two sources of DCB to the lake sewage, which delivers 62 kg/ year, and flow from upstream, which delivers 25 kg/year. The downstream flow removes 27 kg/year from the lake. There is no accumulation of DCB in the lake s sediment. What is the evaporative flux of... 

Figure 10.1. Memory records of sediments, (a) Zn loading in sediments of Lake Zurich. Prior to urbanization of the catchment area of the lake, Zn concentrations of the sediments reflect natural levels. After World War II, increased industrial activity is reflected in the large increase in the Zn concentrations of the sediments. In the last years the Zn load has decreased, largely because of more stringent air pollution legislation and because of improved waste treatment. (Adapted from Beer and Sturm, 1992. (b) Depth-concentration profiles in sediment cores of Pb, Cu, and Zn in Lake Erie. (From Nriagu et al., 1979.)...

Figure 15.8. Concentration of nitrate vs phosphate in Lake Zurich. The drawn out line has a slope of AP/AN 15. The deviations in July-September are related to the development of a metalimnetic oxygen minimum at ca. 20 m depth during this period. (Modified from Sigg and Stumm, 1994.)...

Oxidation Kinetics of Mn(II). This section addresses the question of whether the Mn(II) oxidation rates shown in Figure 4 can be explained by microbiological or abiotic pathways. Several incubation studies of Mn(II) with natural water, natural particulate matter, or pure cultures reported evidence for microbial catalysis of Mn(II) oxidation (4, 18, 54-58). In bottom waters of Lake Zurich (58) and in water samples from the marine fjord of Saanich Inlet (18) maximum Mn oxidation occurred at around 33 and 20 °C, respectively. These results strongly suggest microbial catalysis. In the case of abiotic catalysis, a steady increase in the oxidation rate with temperature is to be expected (16). Working with water samples from the bottom of Lake Zurich that were spiked with Mn(II) at 2 or 10 xM, Diem (58) found a Michaelis-Menten-type rate law for Mn(II) oxidation ... 

Zn and Cu contents in these particles are well correlated with each other (r = 0.956 over all samples), with an average Zn Cu ratio = 3.8 in the summer samples this ratio is up to 8. These relationships are similar to previous observations of correlation in settling particles from Lake Zurich (4). However, the correlations of Zn and Cu with organic C and P are less clear for Lake Greifen. 

These Zn P and Cu P ratios (or the corresponding Zn C and Cu C ratios) may be compared to those observed in other systems and in algae (Table III). The composition of the settling particles in Lake Zurich is quite similar to that in Lake Greifen this similarity is reflected in these ratios. 

Hamilton County Farmers Market Courthouse Square McLeansboro, IL s 618-643-3416 Seasonal Lake Zurich Farmers Market Midlothian E. Main Lake Zurich, IL s 847-438-5572 Seasonal... 

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