Abstract
Phosphorus (P) loss from soils poses a threat of eutrophication to downstream waterbodies. Alum (Al2(SO4)3·18H2O) and gypsum (CaSO4·2H2O) are effective in reducing P loss from soils; however, knowledge on their effectiveness under cold temperatures is limited. This study examined the reduction of P loss from soils with alum and gypsum amendment under simulated snowmelt flooding. Intact soil monoliths (15 cm depth) collected from eight agricultural fields in flood-prone areas of Manitoba, Canada, were surface amended with alum or gypsum, pre-incubated for 2 weeks, then flooded and incubated at 4 °C for 8 weeks. Porewater and floodwater samples collected weekly were analyzed for dissolved reactive P (DRP), dominant cations and anions. An enhanced P release with flooding time was observed in all soils whether amended or unamended; however, alum/gypsum amendment reduced DRP concentrations in porewater and floodwater in general, with alum showing a more consistent effect across soils. The reduction in floodwater DRP concentrations (maximum DRP concentration during flooding) with alum and gypsum ranged from 34–90% and 1–66%, respectively. Based on Visual MINTEQ thermodynamic model predictions, precipitation of P and formation of P-sorbing mineral species with alum and gypsum amendment reduced DRP concentrations at latter stages of flooding.
Highlights
Phosphorus (P) is a major, non-point source pollutant of surface water bodies [1,2].Elevated soluble P concentrations in surface water bodies stimulate algae growth, degrading water quality [3,4]
Compared to previous studies with packed soil columns, more recent studies have shown that flooding of intact soil monoliths resulted in a more rapid development of anaerobic conditions resulting in substantial P release from soils to floodwater [13,43]
We noted that the initial lowering of pH with alum amendment was transitory, and the pH increased with the progression of flooding to values similar to those of the unamended counterparts
Summary
Phosphorus (P) is a major, non-point source pollutant of surface water bodies [1,2]. Elevated soluble P concentrations in surface water bodies stimulate algae growth, degrading water quality [3,4]. Agricultural soils can significantly contribute towards P enrichment in water bodies through P losses via different pathways [4,5]. In cold climatic regions, spring snowmelt runoff over frozen soils is a dominant pathway of P losses from soils [6,7,8,9]. During the snowmelt period in the Canadian prairies, agricultural fields remain flooded for periods ranging from a few days to several weeks [10], depending on soil type, and drainage/landscape position.
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