九龙江河口区养虾塘沉积物-水界面营养盐交换通量特征

通过对九龙江河口区陆基养虾塘水样和沉积物样品采集分析及结合室内模拟实验,探讨了虾塘在不同养殖阶段沉积物-水界面营养盐通量时间变化特征及其主要影响因素。虾塘沉积物向上覆水体释放NO_x~--N(NO_2~--N和NO_3~--N)、NH_4~+-N和PO_4~(3-)-P能力均呈现随养殖时间推移而降低的特征。沉积物在养殖中期和后期分别呈现对上覆水体NO_x~--N和PO_4~(3-)-P的吸收现象,但总体表现为释放(平均通量分别为(1.87±1.15)、(1.58±0.52)mg m~(-2)h~(-1)和(1.22±0.62)mg m~(-2)h~(-1))。沉积物-水界面溶解无机氮交换以NH_4~+-N为主(沉积物平均释放通量为(46.18±13.82)mg m~(-2)h~(-1))。沉积物间隙水与上覆水间的营养盐浓度差(梯度)及温度对上述交换通量的时间动态特征具有重要调控作用。研究结果表明养殖初期或中期沉积物较高的无机氮(尤其是NO_2~--N和NH_4~+-N)释放是养殖塘水质恶化的一个极具潜力的污染内源,可能会对虾的健康生长产生负面效应,控制沉积物无机氮释放是养虾塘养殖初期和中期重要的日常管理活动之一。

Temporal variation of nutrients fluxes across the sediment-water interface of shrimp ponds and influencing factors in the Jiulong River Estuary

Eutrophication is increasingly challenging the sustainability and healthy development of aquaculture. The effects of variations in nutrient dynamics remain unclear, including porewater nutrient concentrations and nutrient fluxes at the sediment-water interface (SWI), from aquaculture ponds globally, and particularly in China. In this study, temporal variation of the concentrations of nitrogen and phosphorus in porewater and their fluxes across the interface of sediment-water was investigated in the Jiulong River estuary, a subtropic estuary on the southeast coast of China. Overlying water, intact sediments, and sediment porewater were collected using sediment samplers from three shrimp ponds in June, August, and October 2015. Overlying water and sediment porewater nutrient analyses were performed using an automatic continuous flow analyzer. SONE (sediment oxygen and nutrient exchanges) incubation techniques were used to measure rates of nutrient fluxes (NO₂^--N, NO₃^--N, NH₄⁺-N, and PO₄^3--P). NO₂^--N, NO₃^--N, NH₄⁺-N, and PO₄^3--P concentrations in porewater ranged from 0.01 to 0.06, 0.06 to 0.22, 10.31 to 14.13, and 0.05 to 0.35 mg/L, respectively, with mean values of 0.04, 0.15, 11.83, and 0.17 mg/L. Higher NO₂^--N and NO₃^--N concentrations in porewater occurred during June and higher NH₄⁺-N and PO₄^3--P concentrations occurred during August. The NO₂^--N, NO₃^--N, NH₄⁺-N, and PO₄^3--P fluxes across the interface of sediment-water ranged from -2.96 to 7.60, -1.00 to 3.15, -0.79 to 4.95, and 19.23 to 91.73 mg m^-2 h^-1, respectively. The fluxes of nitrogen and phosphorus nutrients across the interface of sedimentwater showed significant temporal variation, with higher nutrient release fluxes during June and lower fluxes during October. The mean fluxes of NO₂^--N, NO₃N, and PO₄^3--P from the sediment to overlying water were (1.87±1.15), (1.58±0.52), and (1.22±0.62) mg m^-2 h^-1, respectively, indicating that the shrimp pond sediment acted as a nitrogen and phosphorus release source. Dissolved inorganic nitrogen (DIN) release dominated by excess NH₄⁺-N, and the NH₄⁺-N flux from sediment was (46.18±13.82) mg m^-2 h^-1. Pearson''s correlation analysis showed that the temporal variation of nitrogen and phosphorus fluxes were significantly positively correlated with sediment temperature (P < 0.05), but significantly negatively correlated with shrimp biomass (P < 0.05). The results suggest that the temporal variation of nutrients fluxes across the sediment-water interface in shrimp ponds was controlled by the nutrient concentration gradient, sediment temperature, and the foraging and metabolic activity of shrimp. This study highlighted that the relatively high DIN (NO₂^--N and NH₄⁺-N) release from sediment during the initial and middle stages of aquaculture could be a potential pollution source in shrimp ponds, which might increase the risk of shrimp mortality.