Temperature and freezing effects on phosphorus release from soils to overlying floodwater under flooded‐anaerobic conditions

Abstract

Increased phosphorus (P) availability under flooded, anaerobic conditions may accelerate P loss from soils to water bodies. Existing knowledge on P release to floodwater from flooded soils is limited to summer conditions and/or room temperatures. Spring snowmelt runoff, which occurs under cold temperatures with frequent freeze-thaw events, is the dominant mode of P loss from agricultural lands to water bodies in the Canadian Prairies. This research examined the effects of temperature on P dynamics under flooded conditions in a laboratory study using five agricultural soils from Manitoba, Canada. The treatments were (a) freezing for 1 wk at −20 • C, thawing and flooding at 4 ± 1 • C (frozen, cold); (b) flooding unfrozen soil at 4 ± 1 • C (unfrozen, cold); and (c) flooding unfrozen soil at 20 ± 2 • C (warm). Pore water and surface water were collected weekly over 8 wk and analyzed for dissolved reactive phosphorus (DRP), pH, calcium, magnesium, iron (Fe), and manganese (Mn). Soils under warm flooding showed enhanced P release with significantly higher DRP concentrations in pore and surface floodwater compared with cold flooding of frozen and unfrozen soils.The development of anaerobic conditions was slow under cold flooding with only a slight decrease in Eh, whereas under warm flooding Eh declined sharply, favoring reductive dissolution reactions releasing P, Fe, and Mn. Pore water and floodwater DRP concentrations were similar between frozen and unfrozen soil under cold flooding, suggesting that one freeze-thaw event prior to flooding had minimal effect on P release under simulated snowmelt conditions. Abbreviations: DAF, days after flooding; DRP, dissolved reactive phosphorus.

Phosphorus mobilization from intact soil monoliths flooded under simulated summer versus spring snowmelt with intermittent freeze–thaw conditions

“…When anaerobic conditions develop with flooding, P would initially be released to pore water, which would then transfer to overlying floodwater through the oxidized soil–water interface. The redox reactions releasing P under anerobic conditions and the process of P diffusion from pore water to floodwater are both temperature dependent (Dharmakeerthi, Kumaragamage, Goltz, & Indraratne, 2019; Kumaragamage et al., 2020; Tang et al., 2016). To examine the temperature and freeze–thaw effects on P transfer from pore water to overlying floodwater, we explored the relationships between DRP concentrations in floodwater and pore water under SSF and IFT flooding conditions.…”

“…However, the majority of studies investigating the effects of flooding on P release from soils were conducted under room temperature or summer conditions (Amarawansha et al, 2015;Kumaragamage et al, 2020). A few studies investigating the temperature effect on floodinginduced P release have shown that the rate and magnitude of P mobilization was greater when soils were flooded under warm than under cold temperatures Kumaragamage et al, 2020;Tang et al, 2016), with an average Q 10 (temperature coefficient indicating the rate of change of a biological or a chemi-…”

Phosphorus release from intact soil monoliths of manure‐amended fields under simulated snowmelt flooding

“…by 10°C than under summer flooding, which may reduce P mobilization to floodwater from soils as a result of reductive dissolution reactions because the development of anaerobic conditions is slower under cold than under warm conditions (Kumaragamage et al, 2020).…”

“…Phosphorus transported to water bodies from agricultural lands can negatively affect the environment by stimulating excessive algal growth and eutrophication (Schindler, Hecky, & McCullough, 2012;Sharpley, McDowell, & Kleinman, Goltz, & Indraratne, 2019;Kumaragamage et al, 2020). The enhanced release of P from soils under flooded, anaerobic conditions had been attributed mainly to the reductive dissolution reactions, particularly involving Fe(III) and Mn(IV), releasing P from adsorbed and precipitated forms (Amarawansha et al, 2015;Jayarathne, Kumaragamage, Indraratne, Flaten, & Goltz, 2016).…”

Streambank Legacy Sediments in Surface Waters: Phosphorus Sources or Sinks?

“…Temperature could also be a factor influencing the release of P under anoxic conditions. Soils under warm flooded and anaerobic conditions released more P than similar anoxic soils under cold or unfrozen/frozen conditions [56]. These responses would likely extend to legacy sediments too with some sediments releasing relatively more P than others under varying anoxic conditions.…”