Climatic and ecohydrological feedbacks as conditioning factors to peat initiation and accumulation in tropical valley-bottom fens: lessons from East Africa

Tropical peatlands contain substantial carbon stores, but their degradation is increasing. In East African countries, e.g. Burundi, Rwanda and Uganda, more than 50% of the peatland area is drained, predominantly for agriculture. Subsequent peat subsidence rates are estimated to range from 2.66 to 5.12 cm a⁻¹, indicating a significant carbon loss and reduced water regulation capacity. While these systems are rapidly lost their ecohydrological regimes remain understudied.

This study investigated the temporal and spatial patterns of peat formation in the Kagera River Basin of East Africa, a sub-basin of the Nile system. The basin predominantly contains valley-bottom fen peatlands connected by the waterway system, which are fed by rain-, surface- and ground-water flows. Regardless of their interconnectivity, they vary in their hydro-morphological setting – e.g. relief and proximity to water bodies, size and peat depth.

We synthesized  radiocarbon-dated peat records from literature as well as own work. Peat formation processes in these tropical systems appear to not be driven by climatic factors alone but are strongly influenced by regional and local hydromorphological factors. While increased water availability was critical for enabling widespread peat initiation, the timing and pace of peat growth was conditioned by regional and localized ecohydrological feedbacks of their landscapes, e.g. proximity to lake versus river floodplains. Our findings indicate that management, conservation and restoration activities should first aim to understand the peatlands landscape interactions including site-specific understanding of their ecohydrological conditioning factors.