[Effects of Spartina alterniflora Invasion on Soil Phosphorus Forms in the Jiaozhou Bay Wetland].

To investigate the effects of Spartina alterniflora invasion on soil phosphorus(P) cycling in coastal wetlands, we selected a S. alterniflora zone(SA zone) and mudflat zone(MF zone) in the Jiaozhou Bay as the target areas for the study. The variability of total phosphorus(TP), inorganic phosphorus(IP), and their component contents in wetland soils after S. alterniflora invasion and their influencing factors was evaluated. The results showed that the average contents of TP(472.70 mg·kg-1) and IP(239.00 mg·kg-1) in the soils were significantly higher than those of TP(386.19 mg·kg-1) and IP(212.68 mg·kg-1) in the pre-invasion area, with an increase of 22.40% and 12.38%, respectively. The IP fractions in the study area were dominated by calcium-phosphorus(Ca-P) and iron-phosphorus(Fe-P), accounting for 45%-61% and 31%-49% of IP, respectively. The Ca-P content of the soil in the 10-30 cm layer decreased significantly(P<0.05) after S. alterniflora invasion, which was especially significant in July. The Fe-P content increased significantly(P<0.05); in the 0-40 cm soil layer, Fe-P was higher than that in the 40-60 cm layer(P<0.05), and showed significant enrichment in the 10-40 cm soil in July. The structural equation model showed that organic matter(OM) had a significant positive effect on TP and Fe-P after S. alterniflora invasion(P<0.01), and the normalized path coefficients were 0.775 and 0.724, respectively. Fe-P had a significant negative effect on Ca-P after invasion(P<0.01) with a normalised throughput coefficient of -0.435. The study found that S. alterniflora invasion generally increased wetland soil P content, while promoting the conversion of Ca-P to Fe-P, improving wetland P bioavailability.

Recovery of phosphorus from eutrophic water using nano zero-valent iron-modified biochar and its utilization.

Effective removal and recovery of phosphorus (P) from the aquatic environment was of great significance for eutrophication control and P recovery. This study investigated the effects of different environmental conditions on P adsorption by biochar (BC) and the feasibility of applying the P-laden BC as a fertilizer for plant growth. The nano zero-valent iron (nZVI) modified reeds BC prepared at 700 °C (Fe-700-BC) had the maximum P adsorption capacity of 95.2 mg g-1, which was higher than those prepared at 300, 500, and 900 °C. The addition of Fe-700-BC reduced the concentration of total phosphorus (TP) in the overlying water, in which the soluble reactive phosphorus (SRP) almost completely removed, as well as had a certain inhibitory effect on the growth of algae. Simultaneously, Fe-700-BC reduced the contents of different fractions of P (weakly adsorbed inorganic phosphorus (WA-Pi), potential active inorganic phosphorus (PA-Pi), and Fe/Al-bound inorganic phosphorus (Fe/Al-Pi)) by adsorbing the soluble P released from the sediments, especially in the case of disturbance. Fe-700-BC had no significant effect on the diversity and richness of the microbial community in the sediment. Moreover, P-laden BC was safe and environmentally friendly for application in the soil and tended to increase stem and root length, fresh and dry weight at low doses (0.5 wt%) in wheat planting experiments. The present work could provide a reference for solving the problems related to eutrophication and P deficiency.