Micronutrient, toxic, and other trace elements in the soil-plant-water system in the PECOS study area: implications for natural and anthropogenic fluxes to agricultural land
This thesis study is an integrated part of an interdisciplinary research program, the Prairie Ecosystem Study (PECOS). Element compositions in the soil - plant - water systems are important aspects in evaluating the sustainability of the Prairie ecosystem. However, only a limited number of elements have been comprehensively studied. Objectives of this study were: to establish chemical compositions in the soil - plant - water system in the PECOS study area; to assess possible anthropogenic influences through agricultural activities, by the comparison of chemical composition in samples from natural unbroken land and farmed land; and to address the health of soils, quality of crops and quality of surface waters for the sustainable agricultural practice in the prairie area. The study area is in the "Region 3BN" of southwestern Saskatchewan, Canada. Sampling sites were selected at both natural unbroken land in the Matador area, and farmed land in the Lucky Lake area. Collected samples included soils, wild plants, crop grains, surface water, precipitation, fertilizers, and pesticides. Fifty eight elements, which were grouped into macronutrient, micronutrient, potential toxic, uncharacterized, and rare earth elements, were analysed using inductively coupled plasma mass spectrometry (ICP-MS) and inductivity coupled plasma atomic emission spectrometry (ICP-AES). Element concentrations in soils indicate that regional soils contain high Ca, Na, and Mg relative to average world soils. Their concentrations in soils from farmed land were depleted compared with those from unbroken land. In contrast, concentrations of micronutrients (i.e., Zn, Cu, Co, Fe) and toxic elements (Cd and U) are enriched in soils from farmed land relative to unbroken land. Depletion and enrichment of element concentrations in soils from farmed land are attributed to soil erosion and intensive application of P fertilizers, respectively. Element concentrations in wild plants from unbroken land suggest that most elements are in the normal range as compared with World Land Plants. In crop grains, most element concentrations are uniform except Cd, which varies among crop species. Compared with available values in Durum wheat, relatively high P, Zn and Cd concentrations were observed in samples from the study area. Surface waters in the study area are highly alkaline. Most elements are enriched in the Jarae proportion of dugouts and sloughs relative to the South Saskatchewan River and the World River Averap. These emidments suggest that element concentrations in surface waters are controlled by soil weathering. evaporation, and agrochemical runoff. However, all surveyed surface waters ftom the study area are generally below the "Water Quality Standards" set for drinking water and livestock water, except Mn and Fe. Tested precipitation and agrochemicals collected from the study area show that there are not significant amounts of most elements in precipitation, nitrogen and potash fertilizers, and pesticides. However, P fertilizers contain relatively high levels of many elements, especially Cd, Zn, and U, which may cause increasing concentrations of these elements in soils from farmed land and some crop grains. This study provides basic database on element compositions in soil - plant - water system in the PECOS study area. The implications for the health of prairie ecosystem, policy of sustainable agriculture practice and future directions are discussed.