Abstract
Riverine sediment can reconstruct the history of organic pollution loads and can provide reliable temporal information for pesticide metabolite dynamics in watershed. Sediment core samples were collected from two riverine sections of a cold watershed base in the presence land use change under agricultural development, and the vertical concentrations of four pesticides (atrazine, prometryn, isoprothiolane, and oxadiazon) and two atrazine metabolites (deisopropyl-atrazine and deethyl-atrazine) were determined by gas chromatography–mass spectrometry. The presence of pesticides and metabolites was detected at different depths (11–17 cm) at 1-cm intervals along the two sediment cores, and the flux was calculated with a constant rate of supply model based on the observed concentrations and 210Pb isotope radioactivity chronology. By comparing the concentrations and fluxes of pesticides between the two sediment sections, significant differences in accumulation under different land-use patterns were found. Redundancy analysis further indicated that temporal watershed farmland variance was the dominant factor for pesticide loading. The lower concentration of atrazine and the higher concentration of the other pesticides in the estuarine sediment was closely related to the decreasing upland in the upstream area and the increase in paddy fields in the downstream area. The analysis of atrazine and the metabolites indicated that atrazine is more likely degraded to deethyl-atrazine and the metabolites have similar migration processes in the sediments, which can easily migrate downward. Moreover, the ratio of metabolites to atrazine showed that atrazine degradation was intensive during the transport process, but the metabolites efficiency was lower in this area due to the cold temperature. The results provide insights for the management of pesticide pollution control in watersheds and the potential effects of low temperature on the degradation of pesticides.
Highlights
The use of pesticides is of great significance in ensuring food security, but with agricultural expansion and the excessive use of pesticides, the impact of pesticide on ecosystem security has become an important issue of global concern (Anderson et al, 2002; Tilman et al, 2002)
Each pesticide has unique effects based on the crop type; the vertical pesticides concentrations analysis in the two sediment sections highlights the impacts of the watershed land-use distribution (Fairbairn et al, 2015)
The sediment geochemical analysis of two sediment sections further illustrates the influence of land use distribution on pesticide pollution types and the characteristics of pesticide transport in river channels
Summary
The use of pesticides is of great significance in ensuring food security, but with agricultural expansion and the excessive use of pesticides, the impact of pesticide on ecosystem security has become an important issue of global concern (Anderson et al, 2002; Tilman et al, 2002). The transport and degradation fate of pesticides in agricultural watersheds comprise complex processes, which involve hydrolysis, photolysis, adsorption, oxidation, volatilization, photodegradation, and microbial degradation (Ghattas et al, 2017; Qu et al, 2017). Most of these pesticides are hydrophobic contaminants; they can be transported from farmland into the aquatic environment by adsorbing onto soil particles, and they accumulate in surface water and sediment, which can lead to a lasting potential threat to the aquatic environment (Grung et al, 2015; Kaonga et al, 2015, Lapworth et al, 2015).
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