Effect of land use and hydrological processes on Escherichia coli concentrations in streams of tropical, humid headwater catchments.

Emma J Rochelle-Newall,Nikom Hmaimum,Christian Valentin,Marion Viguier,Pem Sisouvanh,Keooudone Latsachack,Rinh Pham Dinh,Jean-Louis Janeau,Bounsamay Soulileuth,Chanthamousone Thammahacksa,Laurie Boithias,Olivier Ribolzi,Alain Pierret,Hai Tran Sy,Henri Robain,Piyapong Naporn,Norbert Silvera

doi:10.1038/srep32974

Abstract

Lack of access to clean water and adequate sanitation continues to be a major brake on development. Here we present the results of a 12-month investigation into the dynamics of Escherichia coli, a commonly used indicator of faecal contamination in water supplies, in three small, rural catchments in Laos, Thailand and Vietnam. We show that land use and hydrology are major controlling factors of E. coli concentrations in streamwater and that the relative importance of these two factors varies between the dry and wet seasons. In all three catchments, the highest concentrations were observed during the wet season when storm events and overland flow were highest. However, smaller peaks of E. coli concentration were also observed during the dry season. These latter correspond to periods of intense farming activities and small, episodic rain events. Furthermore, vegetation type, through land use and soil surface crusting, combined with mammalian presence play an important role in determining E. coli loads in the streams. Finally, sampling during stormflow revealed the importance of having appropriate sampling protocols if information on maximum contamination levels is required as grab sampling at a fixed time step may miss important peaks in E. coli numbers.

Highlights

The microbiological quality of rivers is primarily controlled by human and animal density and the management of their waste in the watershed[4,5]
Given the strong relationships between mammalian presence and E. coli loads in streams that have been observed in temperate environments and that the highest overland flows are observed in areas with bare soils and/or crops, we hypothesized that the highest E. coli loads would be observed in catchments with high mammalian presence, highest percentage of annual crop cover and during stormflow
This was noticeable during the wet season (April to October) where the repetition of rain events of sufficient intensity and volume resulted in a peak of discharge of 2.51 L s−1 ha−1 on September 4th, 2015

Summary

Introduction

The microbiological quality of rivers is primarily controlled by human and animal density and the management of their waste in the watershed[4,5]. In developing countries and in rural areas, agriculture is less intensive than in developed countries, wastewater treatment is often lacking and diffuse (non-point) sources of FIB tend to predominate[6] In these rural areas with low human population densities, the primary source of FIB is faecal matter generated by livestock and wild animals. Especially in areas with bare soil and/or annual crops, similar heavy rainfall leads to the erosion of soil and, of any faecal matter on the soil surface[3,13] This elevated overland flow is due, in part, to higher rates of soil surface crusting under bare soils and in annual and perennial crops (e.g. teak trees) that reduce soil infiltrability[14,15,16]. Given the strong relationships between mammalian presence and E. coli loads in streams that have been observed in temperate environments and that the highest overland flows are observed in areas with bare soils and/or crops, we hypothesized that the highest E. coli loads would be observed in catchments with high mammalian presence, highest percentage of annual crop cover and during stormflow

Objectives

Methods

Results

Discussion

Conclusion