| 论文摘要： |
Massive accumulation of nitrogen (N) and phosphorus (P) is the serious problem for development of pond aquaculture. Several efforts have been paid to reduce negative effects of nutrient accumulation. However, little is known about the internal cycling process of N and P in traditional aquaculture ponds. In this study, we determined the kinetic parameters of critical extracellular enzymes (including alkaline phosphatase (AP) and leucine aminopeptidase (LAP)) involved in N and P cycling and variations of trophic states in three kinds of ponds with typical cultured species (fish, crab, and crayfish) around Lake Honghu in four months of different seasons from 2019 to 2020. Additionally, sediment P release potential was assessed meanwhile. Results indicated that trophic state in the ponds was cultural species specific. In fish ponds, soluble reactive phosphorus (SRP) was the major component of the total phosphorus (TP). Accumulation of P and imbalance of N and P ratio occurred due to exogenous inputs. Meanwhile, the concentrations of ammonium and nitrite were also the highest in the fish ponds, reaching 4.14 mg L-1 and 0.29 mg L-1 respectively. Enzymatic kinetic parameters were used to assess trophic state and regeneration rate of N and P in the ponds. The turnover time of organic P mediated by AP (T-AP) and its Michaelis constant (K-m) were found to be significantly positively correlated to SRP concentrations (P < 0.05) and negatively related to N and P ratios (P < 0.05). With increasing TP concentrations, the maximum velocity (V-max) of LAP increased linearly (P < 0.05), accelerating the efficiency of N regeneration. These results suggested excessive P limited the hydrolysis of organic P but promoted the production of harmful NH4+-N from organic N, implying that extracellular enzyme balanced regenerations of N and P in the ponds. Analysis of sediment suggested that there existed higher risks of benthic P release in fish ponds, while the equilibrium P concentrations (EPC0) were significantly positively related to proportion of Fe (OOH) similar to P, contents of TP and organic carbon (OC) (P < 0.05). Even so, the sediment tended to adsorb phosphate rather than release P in most farming months. Overall, harmful ammonium and nitrite accumulated massively in fish ponds due to high P loads, while massive P might derive from exogenous inputs or endogenous sources such as sediment. This study uncovered the coupling interactions between N and P cycles in traditional aquaculture ponds, implicating that a balanced N and P management measures were recommended in aquaculture ponds during farming period. |
