Progress in Fishery Sciences (Apr 2023)
Analysis of Influence of Different Sizes of Perinereis aibuhitensis on the Occurrence Form of Nitrogen and Phosphorus in Sediments
Abstract
Aquaculture in China is spread over a total area of 7.108 5×106 hm2. Nowadays, aquaculture is done with a focus on high bait utilization efficiency. Moreover, the proportion of high-density farming organisms and high investment in aquaculture is increasing every year. However, the negative environmental problems associated with high efficiency of aquaculture are often ignored, especially the eutrophication caused by nitrogen and phosphorus pollution. An aquaculture system is a reservoir of nitrogen and phosphorus and sediments play an important role in regulating nitrogen and phosphorus levels in the system. The occurrence forms of nitrogen and phosphorus are closely related to the adsorption and release rates of nitrogen and phosphorus. Benthic animals contribute to the organic composition of sediments, and biological interference is an important factor affecting the release of nitrogen and phosphorus. Perinereis aibuhitensis Grube is a typical benthic animal living in sediments, which feeds on humus and benthic algae, and is one of the main types of organisms that is artificially bred in China. P. aibuhitensis can change the physical structure of sediments by burrowing and through bioturbation; it can also transport dissolved oxygen from the upper water level to the depths of sediments and increase the redox potential of sediments. Studies of Meng et al (2020) have shown that different specifications of P. aibuhitensis have significant differences in the distance covered by the sediments. Significant differences are also present in pump water, pump water rate, axial crawling speed, and nutrient salt dissolution efficiency. The optimum stocking density of P. aibuhitensis is 330–500 g/m2. Investigation of the occurrence pattern and vertical distribution of nitrogen and phosphorus in sediments is essential for assessing the endogenous nitrogen and phosphorus load in sediments, controlling eutrophication of water bodies, and assessing the risk of nitrogen and phosphorus nutrient release in sediments. In this study, the effects and role of P. aibuhitensis on the transformation of nitrogen and phosphorus speciation in sediments were measured, and the feasibility of its application as a bioremediation species in pollution control was evaluated. This study can provide theoretical basis and technical support for green aquaculture and environmental governance. In order to study the effect of biological disturbance of P. aibuhitensis on the occurrence pattern of nitrogen and phosphorus in sediments, experiments involving P. aibuhitensis with different characteristics were performed. The experiments were divided into four groups with 400 g/m2 biomass of P. aibuhitensis: A small size group [(0.7±0.3) g]; a medium size group [(2.5±0.3) g]; and a large size group [(4.3±0.3) g] as the treatment group; and a no-sand silkworm as the control group. The experimental period was 45 days. Sediment samples were collected in PVC tubes (inner diameter: 1.5 cm), and the collected samples were divided into the upper layer, middle layer, and lower layer by partitioning. The contents of nitrogen and phosphorus in each group were determined as per the methods described by Ruttenberg (1992) and Ruban et al (2001). The different occurrence forms of nitrogen include an ion-exchanged form (IEF-N), a weak acid extractable form (WAEF-N), a strong alkali extractable form (SAEF-N) and a strong oxidant extractable form (SOEF-N). Different forms of phosphorus include non-apatite inorganic phosphorus (NAIP), apatite inorganic phosphorus (AP), inorganic phosphorus (IP), organic phosphorus (OP), and total phosphorus (TP). IEF-N is the most easily released nitrogen form in sediments, which is mainly released due to the adsorption of nitrate in overlying water and the ammonia nitrogen generated by the decomposition of organic nitrogen in sediments. WAEF-N mainly includes nitrogen bound to CO32–, which is affected by CO32– concentration in sediments. SAEF-N mainly refers to Fe/Mn bound nitrogen in sediments, and its formation is related to the redox potential in sediments. SOEF-N mainly refers to the organic form of nitrogen in sediments, which is generally the main form of nitrogen. NAIP refers to the phosphorus bound to Fe, Mn, and Al oxides and their hydroxides in sediments, and this form of phosphorus is easily released in the sediments. AP is a form of phosphorus bound to calcium in sediments, which is considered to be relatively inert. IP refers to total inorganic phosphorus in sediments, which mainly includes NAIP and AP. OP refers to organic phosphorus in sediments, and TP refers to all forms of phosphorus in sediments. The results showed that P. aibuhitensis significantly increased the quantity of IEF-N, WAEF-N, and SAEF-N in the upper and middle layers of sediments (P < 0.05), and the medium and small size groups significantly decreased the content of SOEF-N in sediments (P < 0.05). P. aibuhitensis significantly increased the content of NAIP in the upper and middle layers of sediments (P < 0.05), and the medium and small size groups significantly decreased the content of OP in sediments (P < 0.05). This study showed that P. aibuhitensis could increase the bottom redox potential and promote the formation of Fe/Al bound nitrogen and phosphorus. It could also accelerate the mineralization of organic nitrogen and phosphorus in sediments, promoting the upward migration of other forms of nitrogen and phosphorus in sediments, making nitrogen and phosphorus in sediments easier to decompose and release, which could be used by phytoplankton in water. In the early stages of pond culture, P. aibuhitensis disturbance can make water nutrient rich in the late stage of culture, P. aibuhitensis can reduce the accumulation of nitrogen and phosphorus in sediments, so that the ponds can maintain good breeding conditions. P. aibuhitensis has the potential to repair environmental pollution in conjunction with other aquatic plants and algae.
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