Variation between lakes

Variations Between Lakes. Results of a study to evaluate sulfide production variation with water depth is given in Table V. In this experiment, samples were taken from five different sediment depths over a two-day period at each lake in early October. At both lakes sulfate reduction exceeded putrefaction by a factor of approximately 2 with overall mean rates of 0.55 and 0.29 mg S L-kH1 respectively. Sulfate reduction exceeded cysteine decomposition in all samples except one collected from Third Sister Lake at 17 m. Results of this study snow a good correlation at Third Sister Lake between percent hydrogen sulfide production attributable to putrefaction and depth of sampling station (r=0.94) and oxidation-reduction potential (r=0.98). This correlation was not observed at Frains Lake. A possible factor m differences observed may be the physical nature of the sediment at Frains which was less dense and more flocculent than thatofTliird Sister. 

This equation predicts a value of 26.8%ofor the zebra at Turkana assuming an average value of 6%o for Lake Turkana water. This predicted value is l%o less than the actual value of 27.8%o. Given the variation in methods of sample preparation and analysis, variation between bone and tooth enamel (Stuart-Williams and Schwarcz 1997), and uncertainty in surface water oxygen isotopic composition, these values are extraordinarily close. Alternatively, if the equation is solved for using the actual value of the Turkana zebra. 

This chapter discusses the chemical mechanisms influencing the fate of trace elements (arsenic, chromium, and zinc) in a small eutrophic lake with a seasonally anoxic hypolimnion (Lake Greifen). Arsenic and chromium are redox-sensitive trace elements that may be directly involved in redox cycles, whereas zinc is indirectly influenced by the redox conditions. We will illustrate how the seasonal cycles and the variations between oxic and anoxic conditions affect the concentrations and speciation of iron, manganese, arsenic, chromium, and zinc in the water column. The redox processes occurring in the anoxic hypolimnion are discussed in detail. Interactions between major redox species and trace elements are demonstrated. 

There is considerable variation in the sulfide content in these petroleums, ranging from 16% for Peace River, a bitumen, to 0.2% for Pembina, a conventional oil. The sulfide GC-FID chromatograms of some selected samples are shown in Figure 2, which shows considerable variation between the samples. For example, Bellshill Lake contains substantial quantities of monocyclic sulfides possessing a linear (n-alkane) carbon framework and these appear as partially-resolved clusters of peaks on the bottom chromatogram of Figure 2 (1935). 

The close link between lakes and their catchments was evident in a study of spatial variability in surface sediment composition in a small northern Swedish lake (Korsman et al., 1999). In this study, the information in the near-infrared spectra of surface sediment samples was used to determine how sediment composition varied over the lake bottom. The study showed that the NIR spectra per se provide information that can be used to study sediment characteristics as well as sediment focusing in a qualitative way. The variance in the NIR spectra (Fig. 7) was only to a minor extent explained by the variation in water depth or sediment organic content. More importantly, the spatial evaluation of the spectral data suggested that NIR analysis of lake sediments mainly reflects sediment properties that cannot be simply explained by water depth or amount of organic matter. Principal component modelling of NIR spectra from 165 coring sites, established along a 50m x 50m... 

Comprehensive compilations ofiS N variations in nature can be found in Kaplan, (1983), Owens (1987) and Hoefs (1997) Meyers Lallier-Verges, (1999) provide a brief review of variations in lakes. Ligure 1 shows typical (but not unique) S values for the major N pools that may influence an idealised lake. The range of known values is very large, in excess of l(X)%c (Owens, 1987 Wada Hattori, 1991 Kendall, 1998), but generally lies between -5 and +20%o (Owens, 1987). Values outside these limits tend to occur in unusual circumstances or rather extreme environments such as Antarctic or alkaline lakes (e.g., Wada et al., 1991). One reason for the relatively limited range of common values... 

In coastal areas, temperature differences between the land and the water produce air pressure variations, creating sea and lake breezes that are superimposed on the normal winds. These winds vai"y diurnally and as a function of cloudiness. During the daytime, winds blow from the cool sea toward the warm land, while at night the land becomes cooler than the sea surface, and the winds blow from land to sea. 

Figure 24.11 Variation of Trms (left axis) values measured at port 1 x/d = 4) and CO concentration (right axis) of gases sampled from port 4 x/d= 14) with relative phase angle between primary and secondary air driving in the 50-kilowatt forced combustor at China Lake...

For the most part, sediments are also stratigraphically uniform, showing only a few percentage variation in lithologic composition. Cores from Mountain Lake, which consistently show up-core decreases in carbonate content (to about 60% that at depth), are the only exception. A number of shallow-water cores that contain a thin veneer of organic-rich sediments overlying silt and sand were also excluded from analysis. In most locations the spatial boundary between organic-rich profundal-type sediments and littoral deposits of coarse detritus or massive silt was clearly defined. 

The basinwide flux calculations from the seven lakes show that preindustrial Hg accumulation rates in the sediments ranged between 4.5 and 9.0 xg/m2 per year, and the modern rates range between 16 and 32 xg/m2 per year (Figure 9). More striking is the observation that the range in these rates is a function of the relative size of the terrestrial catchment surrounding each lake basin. Over 90% of the variation in modern Hg accumulation can be accounted for by the ratio of a lake s catchment area to its surface area (Ad A0). The correlation between preindustrial Hg accu-... 

Factors Controlling Rates of Sulfate Reduction. Factors typically cited as controlling sulfate reduction include temperature, sulfate concentration, and availability of carbon substrates. Although sulfate-reducing bacteria typically exhibit steep responses to temperature (rates increase 2.4- to 3.7-fold per increase of 10 °C 85, 101, 105), neither differences between deep and shallow lakes (Table I) nor seasonal variation have been observed in rates of sulfate reduction (78, 85, 101). This apparent lack of response of sulfate reduction rates to changes in temperature may indicate that rates are limited by other factors. 

Experimental (simplex and window diagram). The chromatographic system consisted of a Model 501 supercritical fluid chromatograph (Lee Scientific, Salt Lake City, Utah) with the flame ionization detector (FID) set at 375°C. The instrument was controlled with a Zenith AT computer. A pneumatically driven injector with a 200 nL or a 500 nL loop was used in conjunction with a splitter. Split ratios used were between 5 1 and 50 1, depending on sample concentration and the chosen linear velocity, while the timed injection duration ranged from 50 ms to 1 s. We found that the variation of both the split ratio and injection time allowed greater control over the... 

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