Effects of floating Azolla on phosphorus fluxes and recovery from former agricultural lands in wetland microcosms

Abstract

The long-term fertilization results in accumulation of phosphorus especially in the top layer of the soils. Inundation of agricultural lands leads to a switch to anaerobic soil condition, causing reduction of iron and leaching of phosphate simultaneously. From the ecological and environmental perspective, high nutrients flux especially phosphorus will increase the possibility of eutrophication in aquatic system. The fern Azolla had a good potential to adsorb phosphorus, it also has distinctive nitrogen-fixing capacity. We conducted a 10-week aquarium experiment to investigate the phosphorus release capacity from two agricultural soils in the Netherlands with different Fe and P concentrations but comparable Fe/P ratios. Besides, the research questions rose to whether Azolla could use the mobilized phosphate released from the soils for growth. We also tried to find an effective indicator to estimate the actually phosphate mobilization from sediment to water layer. Results showed that the soils with high Fe and P concentrations had higher phosphate release rate compared with the soil with low Fe and P concentrations. Pore water Fe: PO 4 3− ratios were valid to identify P release to surface water, when the Fe: PO 4 3− ratios less than 8 mol mol −1 substantial phosphorus mobilization occurred. The conclusions showed that the actual mobilization of phosphate is more important than the phosphorus retained in the sediments for the internal PO 4 3− fluxes. From 10-week experimental results, we found that Azolla can reuse the phosphate retained in soils thus removed the mobilized phosphate in a moderately low surface water nutrient loading.

CO2 sequestration by propagation of the fast-growing Azolla spp.

“…Sometimes Azolla can be used as a biofertilizer for a variety of crops due to its high biomass productivity (Hanafy et al 2018 ; Kaur and Purewal 2019 ). It can be also used to control high nitrogen and phosphorus levels in contaminated freshwater sources in certain polluted ecosystems (Amare et al 2018 ; Wang et al 2019 ). The capability of Azolla of rapid growth is heavily aided by its tolerance to a variety of stressful environmental conditions.…”

Biochar and Azolla Effects on Soil Chemical Properties, Lead Content and Growth of Paddy

“…The Azolla sp application reduced pH (1-2%), phosphorus (4%), and organic carbon (0,53%) from soilcontaminated Pb. Wang et al (2019) stated that the Azolla had a good potential to adsorb phosphorus. Asghar (2018) and El Husieny et al ( 2020) stated that application of Azolla reduced the soil EC and soil pH.…”

Evaluating growth-dependent enhanced carbon dioxide sequestration potential of Azolla pinnata using cattle wastes (cow dung and cow urine)

“…It has a higher biomass doubling capacity in a short period of time, even in a polluted aquatic environment and is used as a biofertilizer, cattle feed, fish feed, water reclaimer, biofuel feedstock, etc. [ [14] , [15] , [16] , [17] , [18] , [19] ]. Azolla can grow well in a nitrogen-limited environment due to its atmospheric nitrogen fixation ability through the symbiotic association with blue-green alga ( Anabaena azollae ) [ 20 , 21 ].…”