TY - JOUR
T1 - A coupled field study of subsurface fracture flow and colloid transport
AU - Zhang, Wei
AU - Tang, Xiang Yu
AU - Weisbrod, Noam
AU - Zhao, Pei
AU - Reid, Brian J.
N1 - Funding Information:
This work was supported by the CAS-SAFEA International Partnership Program for Creative Research Team (No. KZZD-EW-TZ-06), the National Basic Research Program of the Ministry of Science and Technology of China (No. 2012CB417101), the Chinese Academy of Sciences Visiting Professorship for Senior International Scientists (No. 2011T1Z27), the National Natural Science Foundation of China (Nos. 41171372 and 41471268 ) and the Hundred Talents Program of the Chinese Academy of Sciences and Sichuan Province. The authors thank the two anonymous reviewers for their pertinent comments and constructive suggestions.
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/5/1
Y1 - 2015/5/1
N2 - Field studies of subsurface transport of colloids, which may act as carriers of contaminants, are still rare. This is particularly true for heterogeneous and fractured matrices. To address this knowledge gap, a 30-m long monitoring trench was constructed at the lower end of sloping farmland in central Sichuan, southwest China. During the summer of 2013, high resolution dynamic and temporal fracture flow discharging from the interface between fractured mudrock and impermeable sandstone was obtained at intervals of 5min (for fast rising stages), 30-60min (for slow falling stages) or 15min (at all other times). This discharge was analyzed to elucidate fracture flow and colloid transport in response to rainfall events. Colloid concentrations were observed to increase quickly once rainfall started (~15-90min) and reached peak values of up to 188mg/L. Interestingly, maximum colloid concentration occurred prior to the arrival of flow discharge peak (i.e. maximum colloid concentration was observed before saturation of the soil layer). Rainfall intensity (rather than its duration) was noted to be the main factor controlling colloid response and transport. Dissolved organic carbon concentration and δ18O dynamics in combination with soil water potential were used to apportion water sources of fracture flow at different stages. These approaches suggested the main source of the colloids discharged to be associated with the flushing of colloids from the soil mesopores and macropores. Beyond the scientific interest of colloid mobilization and transport at the field scale, these results have important implications for a region of about 160,000km2 in southwest China that featured similar hydrogeologic settings as the experimental site. In this agriculture-dominated area, application of pesticides and fertilizers to farmland is prevalent. These results highlight the need to avoid such applications immediately before rainfall events in order to reduce rapid migration to groundwater via fracture flow in either dissolved form or in association with colloids.
AB - Field studies of subsurface transport of colloids, which may act as carriers of contaminants, are still rare. This is particularly true for heterogeneous and fractured matrices. To address this knowledge gap, a 30-m long monitoring trench was constructed at the lower end of sloping farmland in central Sichuan, southwest China. During the summer of 2013, high resolution dynamic and temporal fracture flow discharging from the interface between fractured mudrock and impermeable sandstone was obtained at intervals of 5min (for fast rising stages), 30-60min (for slow falling stages) or 15min (at all other times). This discharge was analyzed to elucidate fracture flow and colloid transport in response to rainfall events. Colloid concentrations were observed to increase quickly once rainfall started (~15-90min) and reached peak values of up to 188mg/L. Interestingly, maximum colloid concentration occurred prior to the arrival of flow discharge peak (i.e. maximum colloid concentration was observed before saturation of the soil layer). Rainfall intensity (rather than its duration) was noted to be the main factor controlling colloid response and transport. Dissolved organic carbon concentration and δ18O dynamics in combination with soil water potential were used to apportion water sources of fracture flow at different stages. These approaches suggested the main source of the colloids discharged to be associated with the flushing of colloids from the soil mesopores and macropores. Beyond the scientific interest of colloid mobilization and transport at the field scale, these results have important implications for a region of about 160,000km2 in southwest China that featured similar hydrogeologic settings as the experimental site. In this agriculture-dominated area, application of pesticides and fertilizers to farmland is prevalent. These results highlight the need to avoid such applications immediately before rainfall events in order to reduce rapid migration to groundwater via fracture flow in either dissolved form or in association with colloids.
KW - Colloid response
KW - Colloid transport
KW - Fracture flow
KW - Natural rainfall
UR - http://www.scopus.com/inward/record.url?scp=84925128497&partnerID=8YFLogxK
U2 - 10.1016/j.jhydrol.2015.03.001
DO - 10.1016/j.jhydrol.2015.03.001
M3 - Article
AN - SCOPUS:84925128497
SN - 0022-1694
VL - 524
SP - 476
EP - 488
JO - Journal of Hydrology
JF - Journal of Hydrology
ER -