Ultrasonic in situ measurements of density, adiabatic compressibility, and stability frequency

Gräfe, Holger; Boehrer, Bertram; Hoppe, N.; Müller, Stefan; Hauptmann, P.

doi:10.4319/lo.2002.47.4.1255

Cited by 11 publications

(4 citation statements)

References 9 publications

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“…Usually, the reference of normal conditions (atmospheric pressure) is used, and the term potential density may be more correct. Hence density is a magnitude of central importance in limnophysics, but direct measurement in the field is not feasible at the required accuracy [see Gräfe et al , 2002]. As a consequence, the most practical way is to evaluate density from measurements of electrical conductivity and temperature.…”

Section: Quantitative Approximations For Stratification Relevant Quanmentioning

confidence: 99%

Stratification of lakes

Boehrer

Schultze

2008

Reviews of Geophysics

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567

381

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Many lakes show vertical stratification of their water masses, at least for some extended time periods. Density differences in water bodies facilitate an evolution of chemical differences with many consequences for living organisms in lakes. Temperature and dissolved substances contribute to density differences in water. The atmosphere imposes a temperature signal on the lake surface. As a result, thermal stratification can be established during the warm season if a lake is sufficiently deep. On the contrary, during the cold period, surface cooling forces vertical circulation of water masses and removal of gradients of water properties. However, gradients of dissolved substances may be sustained for periods much longer than one annual cycle. Such lakes do not experience full overturns. Gradients may be a consequence of external inflows or groundwater seepage. In addition, photosynthesis at the lake surface and subsequent decomposition of organic material in the deeper layers of a lake can sustain a gradient of dissolved substances. Three more geochemical cycles, namely, calcite precipitation, iron cycle, and manganese cycle, are known for sustaining meromixis. A limited number of lakes do not experience a complete overturn because of pressure dependence of temperature of maximum density. Such lakes must be sufficiently deep and lie in the appropriate climate zone. Although these lakes are permanently stratified, deep waters are well ventilated, and chemical differences are small. Turbulent mixing and convective deep water renewal must be very effective. As a consequence, these lakes usually are not termed meromictic. Permanent stratification may also be created by episodic partial recharging of the deep water layer. This mechanism resembles the cycling of the ocean: horizontal gradients result from gradients at the surface, such as differential cooling or enhanced evaporation in adjacent shallow side bays. Dense water parcels can be formed which intrude the deep water layer. In the final section, stratification relevant physical properties, such as sound speed, hydrostatic pressure, electrical conductivity, and density, are discussed. The assumptions behind salinity, electrical conductance, potential density, and potential temperature are introduced. Finally, empirical and theoretical approaches for quantitative evaluation from easy to measure properties conclude this contribution.

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Section: Quantitative Approximations For Stratification Relevant Quanmentioning

confidence: 99%

Stratification of lakes

Boehrer

Schultze

2008

Reviews of Geophysics

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567

381

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“…The above mentioned methods usually yield an underestimation of the actual densities and density gradients (Gräfe and Boehrer, 2000;Schimmele and Herzsprung, 2000). Therefore, temperature dependence of density in mining lakes needs to be redefined until performance of the direct density measurements is improved to accomplish high enough accuracy (Gräfe et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Physical characteristics of Acidic Mining Lake 111

Karakas

Brookland

Boehrer

2003

Aquatic Sciences - Research Across Boundaries

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Abstract. Measurements of physical properties have been conducted in Mining Lake 111 (ML111), located in Lusatia, Germany over the time period 1996 -2002. In the deepest area of the ML111, a monimolimnion was observed, that persisted for the years 1996 -1999. It disappeared in 2000 and again formed in 2001. The definition of the main physical properties, such as the temperature compensation for electrical conductivity, in acidic mining lakes required a lake specific approach. The relation between conductivity, temperature and density was determined for the acidic ML111. The variation in dissolved Aquat. Sci. 65 (2003) Dübendorf, 2003 Aquatic Sciences substances affected these relationships such that conductivity varied with temperature even in different layers of the water column and the limitations for a lake wide correlation was evident. Variation in the conductivity of the epilimnion could be verified, and agreed with the estimates of evaporation from the lake surface during summer stratification. Calculations, following the gradient flux method, indicated vertical transport coefficients between 10 -7 and 10 -6 m 2 /s throughout the hypolimnion. The heat budget indicated that heat was transferred into the lake bed or the ground during spring.297-307 1015-1621/03/030297-11 DOI 10.1007/s00027-003-0651-z © EAWAG,

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“…Better accuracy can be achieved by measuring density of lake water and correlating the results with electrical conductivity and temperature (e.g., Jellison et al 1999;Karakas et al 2003). Sufficiently precise methods for in situ measurements of density in lakes are not available (Gräfe et al 2002). Dietz et al (2012) showed that density differences can easily be calculated from "specific density fraction" as long as concentrations are in the freshwater range (<3 g/L).…”

Section: Density Approachesmentioning

confidence: 99%