Use pattern of pesticides and their predicted mobility into shallow groundwater and surface water bodies of paddy lands in Mahaweli river basin in Sri Lanka

Abstract

Pesticides applied on agricultural lands reach groundwater by leaching, and move to offsite water bodies by direct runoff, erosion and spray drift. Therefore, an assessment of the mobility of pesticides in water resources is important to safeguard such resources. Mobility of pesticides on agricultural lands of Mahaweli river basin in Sri Lanka has not been reported to date. In this context, the mobility potential of 32 pesticides on surface water and groundwater was assessed by widely used pesticide risk indicators, such as Attenuation Factor (AF) index and the Pesticide Impact Rating Index (PIRI) with some modifications. Four surface water bodies having greater than 20% land use of the catchment under agriculture, and shallow groundwater table at 3.0 m depth were selected for the risk assessment. According to AF, carbofuran, quinclorac and thiamethoxam are three most leachable pesticides having AF values 1.44 × 10, 1.87 × 10 and 5.70 × 10, respectively. Using PIRI, offsite movement of pesticides by direct runoff was found to be greater than with the erosion of soil particles for the study area. Carbofuran and quinclorac are most mobile pesticides by direct runoff with runoff fractions of 0.01 and 0.08, respectively, at the studied area. Thiamethoxam and novaluron are the most mobile pesticides by erosion with erosion factions of 1.02 × 10 and 1.05 × 10, respectively. Expected pesticide residue levels in both surface and groundwater were predicted to remain below the USEPA health advisory levels, except for carbofuran, indicating that pesticide pollution is unlikely to exceed the available health guidelines in the Mahaweli river basin in Sri Lanka.

The Mahaweli Development Project and the ‘rendering technical’ of agrarian development in Sri Lanka

“…To provide a second example, both the allocation of water and the determining which crops should be cultivated (based on the water intensity of a particular crop) came to be decided vis-à-vis a central committee that preside over MDP's irrigation systems, and such decisions were made based on national-level requirements. Often, the committee decides which crop should be cultivated based on conditions of both local and international markets (Aravinna et al., 2017; Paranage, 2018c; Withanachchi et al., 2014). These changes all signal that the cultivational practices endorsed by the MDP are tinted by impersonal capitalist overtones; quite unlike the subsistence-based irrigation model that Sri Lankan farmers may originally have been used to.…”

Fertilizer usage and cadmium in soils, crops and food

“…[45] also disregard irrigation-water inputs of Cd into farm soils. A study of the translocation and dispersion of pesticides by irrigation waters of the Mahaweli river also showed the effect to be negligible [1]. That this should be so is also easily ascertained by a simple calculation based on mass balance.…”

Streamflow Variability in Mahaweli River Basin of Sri Lanka during 1990–2014 and Its Possible Mechanisms

“…Therefore, studying the hydro-climatic variability and changes in the Mahaweli River Basin (MRB) is important for effective water management and irrigation. According to the previous studies, most of the research related to MRB address water resource management [23], water pollution [24], agriculture, and soil [25]. Up to date, very limited studies have been focused on investigating seasonal streamflow characteristics, the variation of streamflow extremes, and their linkages with the major climatic variables over MRB.…”