Surface water contamination by pathogen bacteria remains a threat to public health in the rural areas of developing countries. Fecal indicator bacteria (FIB) like Escherichia coli (E. coli) are widely used to assess water contamination, but their behavior in tropical ecosystems is poorly documented. Our study focused on headwater wetlands which are likely to play a key role in stream water purification of fecal pollutants. Our main objectives were to: (i) evaluate decay rates (k) of the total, particle-attached and free-living E. coli; (ii) quantify the relative importance of solar radiation exposition and suspended particles deposition on k; and (iii) investigate E. coli survival in the deposited sediment. We installed and monitored 12 mesocosms, 4500 mL each, across the main headwater wetland of the Houay Pano catchment, northern Lao People’s Democratic Republic (Lao PDR), for 8 days. The four treatments with triplicates were: sediment deposition-light (DL); sediment deposition-dark (DD); sediment resuspension-light (RL); and sediment resuspension-dark (RD). Particle-attached bacteria predominated in all mesocosms (97 ± 6%). Decay rates ranged from 1.43 ± 0.15 to 1.17 ± 0.13 day⁻¹ for DL and DD treatments, and from 0.50 ± 0.15 to −0.14 ± 0.37 day⁻¹ for RL and RD treatments. Deposition processes accounted for an average of 92% of E. coli stock reduction, while solar radiation accounted for around 2% over the experiment duration. The sampling of E. coli by temporary resuspension of the deposited sediment showed k values close to zero, suggesting potential survival or even growth of bacteria in the sediment. The present findings may help parameterizing hydrological and water quality models in a tropical context.

This dataset has been collected thanks to the long-term partnership with Department of Agricultural Land Management (DALaM), Lao PDR, which granted the permission for field access, and to the financial, scientific, technical, and/or logistical support of the Multiscale TROPIcal CatchmentS (SNO M-TROPICS; https://mtropics.obs-mip.fr/) critical zone observatory (previously MSEC). The tabular data provided include water quality and environmental variables measured within and outside a set of 15 mesocosms installed from August 9 to August 16, 2019, across the main headwater wetland of the Houay Pano catchment, northern Lao PDR. Water quality variables are Escherichia coli concentrations (MPN 100 mL-1) for both total and free-living bacteria with upper and lower limits of the confidence interval, total suspended sediment concentration (g L-1), turbidity (NTU), and dissolved organic carbon concentration (µM C). Environmental variables are Rainfall (mm mn-1), temperature (°C) in the air, the water, and the sediment, and solar radiation (W m-2) in the surrounding vegetation at 380, 100, and 3 cm height above swamp bottom sediment, and inside mesocosms. Water volumes include initial and final water volumes (mL) in each one of the mesocosms. In the mesocosms, a control and four treatments were tested: resuspension-dark (RD), resuspension-light (RL), deposition-dark (DD), and deposition-light (DL). The authors acknowledge the financial support of the Institut de Recherche pour le Développement (IRD) and the French national grant EC2CO-Biohefect/Ecodyn//Dril/MicrobiEn (NARIBACT).