Spatio-temporal variations of shallow and deep well groundwater nitrate concentrations along the Indus River floodplain aquifer in Pakistan

TY - JOUR

T1 - Spatio-temporal variations of shallow and deep well groundwater nitrate concentrations along the Indus River floodplain aquifer in Pakistan

AU - Khan, Shahrukh Nawaz

AU - Yasmeen, Tahira

AU - Riaz, Muhammad

AU - Arif, Muhammad Saleem

AU - Rizwan, Muhammad

AU - Ali, Shafaqat

AU - Tariq, Azeem

AU - Jessen, Søren

PY - 2019/10

Y1 - 2019/10

N2 - Excessive use of nitrogenous fertilizers and their improper management in agriculture causes nitrate contamination of surface and groundwater resources. This study was conducted along the seasonally flooded alluvial agricultural area of Indus River Basin to determine the spatial and temporal dynamics of nitrate concentrations in the groundwater along the river. Total of 112 samples were collected from shallow (30–40 ft) and deep groundwater (120–150 ft) wells at seven sites, 25 km apart from each other and covered an area of 170 km along the river, during four sampling campaigns between October 2016 to May 2017 i.e. in start, mid and end of dry season. The study period covered the whole agricultural cycle including the wet summer season with no agricultural activities under flooding and the sampling sites were always less than 2 km from the river bank. Nitrate concentrations of shallow wells were 15–54 and 20–45 mg L−1 during the start and middle of dry season, respectively. However, at the end of the dry season, the highest nitrate concentrations of 35–75 mg L−1 were recorded and 70% of these samples contained nitrate concentrations above the permissible limit 50 mg L−1. Similar seasonal patterns of nitrate concentrations were observed in deep wells, however, δ18O data suggested lower recharge in deep well than shallow wells. The results illustrated that high nitrate concentrations in shallow wells were associated with high δ18O values indicating that the quantity of evaporated water infiltrated from the floodplain, possibly from distribution channels, along with the nitrate polluting shallow wells more than the deep wells. At the end of the dry season, nitrate concentrations exceeded the permissible limits in both shallow and deep wells, which possibly happened due to the horizontal movement of groundwater along with the nitrate mixing during vertical seepage of river water to the aquifers.

AB - Excessive use of nitrogenous fertilizers and their improper management in agriculture causes nitrate contamination of surface and groundwater resources. This study was conducted along the seasonally flooded alluvial agricultural area of Indus River Basin to determine the spatial and temporal dynamics of nitrate concentrations in the groundwater along the river. Total of 112 samples were collected from shallow (30–40 ft) and deep groundwater (120–150 ft) wells at seven sites, 25 km apart from each other and covered an area of 170 km along the river, during four sampling campaigns between October 2016 to May 2017 i.e. in start, mid and end of dry season. The study period covered the whole agricultural cycle including the wet summer season with no agricultural activities under flooding and the sampling sites were always less than 2 km from the river bank. Nitrate concentrations of shallow wells were 15–54 and 20–45 mg L−1 during the start and middle of dry season, respectively. However, at the end of the dry season, the highest nitrate concentrations of 35–75 mg L−1 were recorded and 70% of these samples contained nitrate concentrations above the permissible limit 50 mg L−1. Similar seasonal patterns of nitrate concentrations were observed in deep wells, however, δ18O data suggested lower recharge in deep well than shallow wells. The results illustrated that high nitrate concentrations in shallow wells were associated with high δ18O values indicating that the quantity of evaporated water infiltrated from the floodplain, possibly from distribution channels, along with the nitrate polluting shallow wells more than the deep wells. At the end of the dry season, nitrate concentrations exceeded the permissible limits in both shallow and deep wells, which possibly happened due to the horizontal movement of groundwater along with the nitrate mixing during vertical seepage of river water to the aquifers.

KW - Floodplain

KW - Groundwater pollution

KW - Indus River

KW - Nitrate leaching

KW - Semiarid region

UR - http://www.scopus.com/inward/record.url?scp=85068984769&partnerID=8YFLogxK

U2 - 10.1016/j.envpol.2019.07.019

DO - 10.1016/j.envpol.2019.07.019

M3 - Journal article

C2 - 31325883

AN - SCOPUS:85068984769

SN - 0269-7491

VL - 253

SP - 384

EP - 392

JO - Environmental Pollution

JF - Environmental Pollution

ER -