Retention lake water

This section provides a general overview of the properties of lake systems and presents tlie basic tools needed for modeling of lake water quality. The priiiciptil physical features of a lake are length, depth (i.e., water level), area (both of the water surface and of tire drainage area), and volume. The relationship betw een the flow of a lake or reserv oir and the volume is also an important characteristic. The ratio of the volume to the (volumetric) flow represents tlie hydraulic retention time (i.e., the time it would take to empty out the lake or reservoir if all inputs of water to the lake ceased). This retention time is given by the ratio of the water body volume and tire volumetric flow rate. 

Measurements of S cycling in Little Rock Lake, Wisconsin, and Lake Sempach, Switzerland, are used together with literature data to show the major factors regulating S retention and speciation in sediments. Retention of S in sediments is controlled by rates of seston (planktonic S) deposition, sulfate diffusion, and S recycling. Data from 80 lakes suggest that seston deposition is the major source of sedimentary S for approximately 50% of the lakes sulfate diffusion and subsequent reduction dominate in the remainder. Concentrations of sulfate in lake water and carbon deposition rates are important controls on diffusive fluxes. Diffusive fluxes are much lower than rates of sulfate reduction, however. Rates of sulfate reduction in many lakes appear to be limited by rates of sulfide oxidation. Much sulfide oxidation occurs anaerobically, but the pathways and electron acceptors remain unknown. The intrasediment cycle of sulfate reduction and sulfide oxidation is rapid relative to rates of S accumulation in sediments. Concentrations and speciation of sulfur in sediments are shown to be sensitive indicators of paleolimnological conditions of salinity, aeration, and eutrophication. 

Loughnan (22) gives this chemical composition for illite, pointing out that illite is characterized by substitutions in the silica sheet. Potassium collection and retention by silicate skeletons is a phenomenon recognized in lacustrine environments. As pH of the lake water increased, silica became more mobile than alumina. Formation of the relatively silica-poor illite resulted. Dehydration of the dissolved silica in the sediment s water (equation 3) produced quartz. The large amounts of illite from the reactions... 

Other LC-MS/MS methods for the detection of toxins in water include the analysis of lipophihc phyco-toxins in coastal waters [69]. This method has the identification capability of the MS/MS method, which uses collision-induced dissociation (CID)-produced mass spectra to correlate LC retention times from the analytes of interest. Another MS/MS method finds toxins from cyanobacteria in lake water and reinforces the need for quantification of toxins. The total amount of toxins not only exists in the water but also in the cell walls of the algae, and contributes to the overall toxin load in the sample [70]. This method uses the confirmative properties of the LC-MS/MS system and provides the desired nanogram per miUihter detection limits. 

For both Tables 9.1 and 9.2 Area Xvkt area. Dm=mean depth, T= theoretical lake water retention time, ADA=area of drainage area, perch fry that is > 1 year old but < 2 years old... 

Table 93. Dose of lime and theoretical retention time of lake water...

Fig. 9.4. The new mixed model for metals in lakes. Load (or dose) parameters are related to the input of metals to the lake (direct load and load from the catchment), the metal amount in the lake water is distributed into dissolved and particulate phases by the partition coefficient (Kd). Sedimentation is net sedimentation per unit of time (the calculation unit is set to 1 year for Hg and 1 month for Cs). The sensitivity parameters influence biouptake of metals from water to phytoplankton (but they may also be used in other contexts, e.g., to influence the Kd-values, as illustrated by the dotted line, or the rate of sedimentation). The biological or ecosystem variables include pelagic and benthic uptake, bioaccumulation and retention time in the five compartments (lake water, active sediments, phytoplankton, prey and predator fish). The ejfect parameter is the concentration of the metal in predatory fish (used for human consumption). One panel gives the calculation of concentrations, another the driving parameters (model variables should, preferably, not be altered for different lakes, while environmental variables must be altered for each lake). The arrows between these two panels illustrate the phytoplankton biomass submodel...

Lake outflow diss = Retention in lake water Amount dissolved in water... 

Lake outflow part = Amount particulate in water Retention in lake water Sedimentation = Amount particulate in water Sedimentation rate Benthic uptake rate = Pelagic uptake rate DOCUMENT In 1/year. Default value is set equal to the pelagic uptake rate. Bioacc rate plank to prey = 0.16... 

Retention in lake water = lAVater retention time DOCUMENT In 1/years. 

Retention time as used here is not to be confused with turnover times for phosphates in living organisms such as algae or bacteria. In lake waters these turnover times can be of the order of minutes. In this sense turnover time is the time for a phosphate to be ingested by one organism and then transferred to another. Retention times in oceans for a mineral to be completely replaced may be of the order of a few thousands of years to untold billions of years. 

---