Figure 1.
Evolution of temperature profiles in Lake Kivu.
Figure 2.
Epilimnion temperatures between January 2011 and March 2013.
Temperatures were recoded by a string of moored Onset temperature loggers. A. Records from individual thermistors. B. Same data as a contour plot against depth. Thermistors were recovered and redeployed in November 2011 and October 2012, at which times several loggers were replaced and additional ones added.
Figure 3.
Deep-water temperatures between October 2012 and March 2013.
Temperatures were recorded using moored Seabird temperature loggers. A,B: Temperature time series (deviations from the mean) at the depths of 68 m (T1) and 355 m (T2). The green line is pressure recorded at T1. C,D: The same but in more detail for two anomalous events in October and December 2012.
Figure 4.
18O and 2H isotopic signals in Lake Kivu's main basin (black) and Kabuno Bay (grey).
Also shown are data for a surface hot spring in Gisenyi (triangles), surface stream in Gisenyi (open circle), and a single rain event (square in panel B). The dashed line in panel A is an inverted and scaled profile of water conductivity, shown here for illustration as an indicator of water column stratification.
Figure 5.
Changes in water column temperature.
A) At selected depths against time, relative to 1975 measurements [32]. B) As a function of depth, based on comparison of our January 2011 profile with [32]. The exponential fit line is drawn through points (marked by symbols) between major thermoclines where temperature gradients are minimal and also least affected by the vertical movement of thermoclines.
Figure 6.
Simulated vs. observed change in water temperature in response to decreased epilimnetic heat removal.
The change in water temperatures between 1973 and 2011 is simulated for a decrease in heat removal at the base of the mixolimnion of 0.5 W m−2. The solid black line is the same as the exponential fit line in Fig. 5. Dashed lines illustrate the simulation results for different values of the mixing coefficient Kz: selected constant values, values obtained from the correlation of Kz with the stability frequency N2 as suggested in [19], and tabulated values suggested for Lake Kivu in [8]. For comparison, the molecular thermal diffusivity in water (at 25°C) is 0.143⋅10−6 m2 s−1.