Water budget of tropical volcanic lakes in center‐north Cameroon: Reconciling the stable isotope and chloride mass balance

Abstract

The Cameroon volcanic line (CVL) hosts numerous volcanic lakes whose internal processes and hydrological functioning remain poorly documented. A detailed understanding of these hydro-systems is however essential, both for the consideration of these lakes as sentinels of the regional hydro-climatic changes and for the calibration of palaeoenvironmental proxies. Here, we present a hydrological and geochemical investigation of five of these lakes (Mbalang, Tabere, Tizon, Gegouba and Baledjam) around Ngaoundere on the Adamawa Plateau, based on repeated sampling of water profiles and monthly monitoring of rain and lake water samples over two seasonal cycles. We show that each of these throughflow lakes bears a distinct geochemical and isotopic signature, despite quite similar morphometric characteristics and a common climatic regime, due to varying contribution of the watersheds to the watermass balance and different partitioning between evaporation (E) and outflow (Inflow minus E). We use these differences as a benchmark for a sensitivity analysis of the classical budget equations of conservative tracers. The results demonstrate that to reconcile chloride and stable isotope data with the standard single-box steady state model would require unusual values of the physical parameters of Craig and Gordon's equation such as the n.θ term that would have to be significantly lower than its usual value (n.θ = 0.5). We also show that the data can be simulated more easily by including the inflow from the watershed while assuming that transpiration exceeds evaporation for this compartment. Using this conceptualization of the throughflow lakes, we were able to constrain the different fluxes. Transpiration from the watershed and evaporation from the lake are on the same order of magnitude, or slightly in favour of † Died October 22, 2022. This work is dedicated to the memory of our colleague and friend, Jean-Luc Michelot, who passed away too early on October 22, 2022.

Preface special issue: “Processes and patterns in tropical hydrology”

“…The authors emphasize the need to specifically assess land cover changes and its role on precipitation regimes in this humid region of the neotropics (anthropogenically modified tropical ecosystems). In another important contribution, Abba et al (2023) use geochemical and water-isotopic tools to assess the hydrological budget of five crater lakes located in northern Cameroon. They show that in this seasonally dry region, transpiration from the upstream catchments is a major flux that is likely to be slightly higher than evaporation from the lakes.…”