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

View Article: PubMed Central - PubMed

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.

No MeSH data available.


E. coli loads and rainfall for each of the three studied catchments (E. coli, MPN s−1 ha−1).
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f6: E. coli loads and rainfall for each of the three studied catchments (E. coli, MPN s−1 ha−1).

Mentions: In contrast to Houay Pano and Dong Cao, annual rainfall over the study period in the Huay Ma Nai catchment in Thailand was over 30% lower than the annual average (921 mm versus 1,385 mm; Table 1). Nevertheless, as for the Houay Pano and Dong Cao catchments, episodes of heavy rainfall resulted in an increase in stream discharge (Fig. 5). Indeed, discharges of up to almost 0.25 L s−1 ha−1 were observed on the August 14th, 2015. Large decreases in EC were also observed during the periods of high discharge. Indeed, EC decreased from 320 μS cm−1 during the periods of low discharge to 70 μS cm−1 during the period of high discharge (3rd August–12th September 2015). E. coli concentrations also varied over the year and were of the same order of magnitude as for Houay Pano (78 and 14,000 MPN 100 mL−1; p > 0.05). They were however, significantly higher than the concentrations observed in the Vietnamese catchment (p < 0.05). As in the other catchments, the highest values were observed during the summer months when rainfall and discharge were highest. The loads of E. coli for each catchment over the sample year are shown in Fig. 6. As for the concentrations, loads were lowest during the dry season when rainfall and discharge was lowest. A significant difference was observed between catchments for E. coli loads during dry season (from October 2014 to mid May 2015).


Effect of land use and hydrological processes on Escherichia coli concentrations in streams of tropical, humid headwater catchments
E. coli loads and rainfall for each of the three studied catchments (E. coli, MPN s−1 ha−1).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015105&req=5

f6: E. coli loads and rainfall for each of the three studied catchments (E. coli, MPN s−1 ha−1).
Mentions: In contrast to Houay Pano and Dong Cao, annual rainfall over the study period in the Huay Ma Nai catchment in Thailand was over 30% lower than the annual average (921 mm versus 1,385 mm; Table 1). Nevertheless, as for the Houay Pano and Dong Cao catchments, episodes of heavy rainfall resulted in an increase in stream discharge (Fig. 5). Indeed, discharges of up to almost 0.25 L s−1 ha−1 were observed on the August 14th, 2015. Large decreases in EC were also observed during the periods of high discharge. Indeed, EC decreased from 320 μS cm−1 during the periods of low discharge to 70 μS cm−1 during the period of high discharge (3rd August–12th September 2015). E. coli concentrations also varied over the year and were of the same order of magnitude as for Houay Pano (78 and 14,000 MPN 100 mL−1; p > 0.05). They were however, significantly higher than the concentrations observed in the Vietnamese catchment (p < 0.05). As in the other catchments, the highest values were observed during the summer months when rainfall and discharge were highest. The loads of E. coli for each catchment over the sample year are shown in Fig. 6. As for the concentrations, loads were lowest during the dry season when rainfall and discharge was lowest. A significant difference was observed between catchments for E. coli loads during dry season (from October 2014 to mid May 2015).

View Article: PubMed Central - PubMed

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.

No MeSH data available.