Effects of Freeze-Thaw Cycles on Phosphorus from Sediments in the Middle Reaches of the Yarlung Zangbo River

Abstract

The effect of the freeze-thaw process is an important factor in soil nutrient changes and erosion enhancement. Sediments in the middle reaches of the Yarlung Zangbo River are likely affected by the daily freeze-thaw cycles in winter. Examining the freeze-thaw effects of phosphorus from sediments in this area is of great significance for protecting the structure and safety of the ecosystem. The freeze-thaw process of sediments in the middle reaches of the Yarlung Zangbo River was simulated through laboratory experiments, and different phosphorus contents and particle states were synchronously detected and analyzed. The results show that freeze-thaw cycles can accelerate phosphorus migration and release in the sediments, and the total amount of phosphorus release increases by 12%. After being subjected to freeze-thaw cycles, the sediment particles were broken, and the competition between ions for adsorption sites reduced phosphorus adsorption onto the sediments from the middle reaches of the Yarlung Zangbo River. The organic matter on the sediment surface was also broken down, and the energy dispersive spectroscopy (EDS) results showed that the combined ions that were released competed for the adsorption sites on the particle surfaces, thereby promoting phosphorus release. Among the different forms of phosphorus, aluminum-bound phosphorus (Al-P) and iron-bound phosphorus (Fe-P) are the two most released phosphorus forms by the freeze-thaw process. Although the contents of Al-P and Fe-P only account for 2.41% of the total phosphorus content, both phosphorus forms are biologically available, and freeze-thaw cycles may increase the risk of nutrient loss. This research may provide information for the study of phosphorus in river ecosystems in areas subjected to freeze-thaw cycles.

Spatial distribution of soil nutrients and evaluation of cultivated land in Xuwen county

“…The study area belongs to acidic red soil in southern China, which is rich in iron and aluminum ions. It is easy to chemically react with phosphate fertilizers applied to the soil and form sediments and accumulate in the soil, which cannot be used by plants, resulting in generally high soil available phosphorus content ( Liao et al, 2019 ). However, different types of organic fertilizers and soil parent materials have different capacity to fix soil phosphorus, resulting in differences in soil available phosphorus content ( Mehmood et al, 2015 ; Shu, Qi & Wang, 2021 ).…”

Cold spots and cold moments: The potential for sediment freezing to depress denitrification in wetland sediments

“…For example, soil water content may affect the amplitude and duration of freezing (Jiang et al., 2020), suggesting the potential for differences between agricultural soil and saturated wetland sediment. Gradients of soil moisture content both seasonally and spatially can have an important influence on FTC effects (Hung & Whalen, 2020), and the number of FTCs can yield important but variable effects (e.g., Liao et al., 2019; Lui et al., 2021; Sang et al., 2021). Ultimately, to better understand how FTCs affect N cycling in wetlands, work across a broader range of wetlands in human‐impacted and more pristine environments is required and across multiple processes and pools, for example, assessing effects on nitrification, NO 3 – assimilation via dissimilatory NO 3 – reduction to ammonia (Ribas et al., 2013), and pools of N and C. A key next step is to better understand the spatial extent of sediment freezing both within wetlands and at the scale of large landscapes under a range of winter conditions (Duguay & Lafleur, 2003).…”

“…For example, research has shown that following FTCs microbial biomass may either remain stable (Kopenen et al., 2006), decrease (Feng et al., 2007; Yanai et al., 2004, 2007), or increase (Liu et al., 2021; Sang et al., 2021) and that functional changes can also occur, including increased respiration, increased activity (Pesaro et al., 2003; Sharma et al., 2006), and increased expression of denitrifying genes (shown following freeze–thaw treatments in grassland soils; Sharma et al., 2006). Freeze–thaw cycles can also increase the availability of DOC and N in soil (Herrmann & Witter, 2002; Matzner & Borken, 2008; Schimel & Clein, 1996), affecting C mineralization, organic matter availability, and DOC concentration, with potential for the magnitude of effects to be mediated by the number of FTCs (Feng et al., 2007; Herrmann & Witter, 2002; Liao et al., 2019; Liu et al., 2021; Sang et al., 2021; Yu et al., 2011). Dissolved N may also change.…”

“…Dissolved inorganic N can increase with FTCs in wetlands (Yu et al., 2011) and upland soils (Ruan & Robertson, 2017), although complex changes can also be mediated by multiple FTCs (Sang et al., 2021), including physical changes. Although the first FTC may have the greatest impact on soil/sediment porosity (Congreves et al., 2018), multiple FTCs can be important in breaking up soil/sediment aggregates and increasing sediment surface area (Boswell et al., 2020; Liao et al., 2019; Ruan & Roberston, 2017).…”

“…Studies cited include results from diverse ecosystems (1: Henry, 2008; 2: Brin et al., 2019; 3: Lim et al., 2020; 4: Schimel & Clein, 1996; 5: Herrmann & Witter, 2002; 6: Mørkved et al., 2006; 7: Matzner & Borken, 2008; 8: Risk et al., 2013; 9: Libby et al., 2020; 10: Song et al., 2006; 11: Yanai et al., 2004; 12: Yu et al., 2011; 13: Koponen et al., 2006; 14: Feng et al., 2007; 15: Yanai et al., 2007; 16: Juan et al., 2020; 17: Sharma et al., 2006; 18: Pesaro et al., 2003; 19: Wagner‐Riddle et al., 2017). Other impacts of FTCs include the breakup of sediment particles and organic matter (Liao et al., 2019), release of nutrients from aboveground plant tissue (Whitfield et al., 2019) and the induction of pulses of nitrous oxide emission (Lu et al., 2015; Wagner‐Riddle et al., 2017). DNRA, dissimilatory NO 3 – reduction to NH 4 + ; DOC, dissolved organic C…”