Spatial and Seasonal Distribution and Transportation of Different Forms of Phosphorus in the Middle Reaches of the Yarlung Zangbo River

Abstract

The Yarlung Zangbo River basin ecosystem is fragile. The distribution and transportation of phosphorus is of great significance for aquatic environmental protection and ecological security. The sequential extraction method and molybdenum antimony anti-spectrophotometry were used to measure the concentrations of different forms of phosphorus in the surface sediments from 15 sampling sites along the middle reaches of the Yarlung Zangbo River and its tributaries. The results show that the total phosphorus concentration in the surface sediments is 194.0~540.7 mg/kg, which is mainly composed of inorganic phosphorus. The concentrations of various phosphorus forms ranked as calcium-bound phosphorus (355.6 ± 86.0 mg/kg) > soluble phosphorus (15.9 ± 10.0 mg/kg) > iron-bound phosphorus (12.4 ± 12.3 mg/kg) > organic phosphorus (9.6 ± 6.1 mg/kg) > occluded phosphorus (9.2 ± 3.8 mg/kg) > aluminum-bound phosphorus (5.4 ± 2.3 mg/kg). On the whole, phosphorus concentration is greater in wet season than dry season. Regarding the spatial distribution characteristics, there are great disparities in the different forms of phosphorus in the middle reaches of the Yarlung Zangbo River. Comprehensive analysis shows that phosphorus of this area is mainly self-generated, and concentration of bioavailable phosphorus is small, demonstrating there will not be a large release. We also drew a “specific triangle” of the different forms of phosphorus concentrations in the research area and defined the “α” angle to determine the nutrient status of the overlying water quickly and effectively. Finally, phosphorus flux of the mainstream was estimated. This research may provide information on the phosphorus of Plateau Rivers.

Spatial–Temporal Distribution of Phosphorus Fractions and Their Relationship in Water–Sediment Phases in the Tuojiang River, China

“…However, the Fe-P was the dominant fraction in the Tuojiang River. Fe-P is usually used to indicate the extent of phosphorus pollution and reflect the scales of the impact of anthropogenic activities on an environment [5]. This result was similar to that reported in the Minjiang River and was consistent with their environmental settings with both intensive industrial and domestic phosphorus emissions in these areas [25].…”

“…This may be due to the fact that the Yarlung Zangbo River is a typical plateau river. The river flows through the Qinghai-Tibet Plateau, where the vegetation in the basin is mostly grassland and sparsely populated, and the degree of industrialization and urbanization is very low [5]. The SRP was the dominant fraction of phosphorus fractions in the water in the Tuojiang River, which was similar to that in the Minjiang River and Qiuxi River.…”

“…Phosphorus bioavailability is not only related to the concentration of total phosphorus (TP), but also to the phosphorus fraction [3] as soluble reactive phosphorus (SRP), dissolved organic phosphorus (DOP), and total particulate phosphorus (PP) in aqueous environments, and exists as six phosphorus fractions (exchangeable phosphorus (Ex-P), organic phosphorus (Or-P), phosphorus bound by Fe oxides (Fe-P), authigenic phosphorus (Ca-P), detrital phosphorus (De-P), and refractory phosphorus (Res-P)) in sediment. Each fraction has unique bioavailability, chemical reactivity, and environmental fate, which can play different roles in regulating water quality and the biogeochemical cycling of other bioactive elements in aquatic environments [4,5]. Therefore, understanding the distribution of phosphorus fractions is important in evaluating water quality and managing phosphorus pollution in aquatic environments [1].…”

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

“…As SP is soluble in water and the overlying water used in the experiment is distilled water, there is a difference in the phosphorus concentration between the two interfaces, which leads to the migration and release of SP into the overlying water along the concentration gradient. The contents of Ca-P and Oc-P in the sediments are the dominant forms of phosphorus, accounting for 92.8% of the total phosphorus, which confirms that self-generated phosphorus is the main phosphorus form in the middle reaches of the Yarlung Zangbo River on the basis of a report by Cheng et al [24]. However, the contents of these two phosphorus forms do not change with freeze-thaw cycles; that is, Ca-P and Oc-P are stable and insoluble in water and are not easily affected by environmental changes, which is consistent with the prevailing conclusions [36].…”

“…The middle reaches of the Yarlung Zangbo River were selected as the study area (Figure 1). According to the investigation results of Chen et al [24] on the phosphorus background value of sediments in the middle reaches of the Yarlung Zangbo River, the section with a relatively high phosphorus content was selected as the actual sampling section. According to the Yarlung Zangbo River ice satellite image [25] (Figure 1a), the specific location of the freeze-thaw area along the midstream section (S 2 , 29°20′6.49′′ N, 90°42′4.30′′ E) was determined, and samples were collected along the riverbank in September 2018.…”