单环刺螠生物扰动对沉积物-水界面氮磷扩散通量的影响

Effect of bioturbation of Urechis unicinctus on the diffusion flux of nitrogen and phosphorus at the sediment-water interface

为了解单环刺螠生物扰动作用对沉积物-水界面氮磷扩散通量的影响及其持续性,于2020年11—12月,采用室内实验生态学的方法,设置低密度(LD,500尾/m^(2))、中密度(MD,2500尾/m^(2))、高密度(HD,8300尾/m^(2))处理组和1个对照组(CO,0尾/m^(2)),进行了2 d为一个实验时段,为期20 d的模拟实验。结果显示,处理组溶解无机氮(DIN)扩散通量变化范围为10.6~765.3μmol/(m^(2)·d),与对照组相比,低、中、高处理组的DIN通量分别提高了57%、76%、88%。NH_(4)^(+)是DIN的主要贡献者,对DIN的贡献在低、中、高处理组中分别占55%、65%和80%。与对照组相比,低、中、高密度组的平均NH_(4)^(+)通量分别提高了39%、111%和257%,与低、中密度处理组平均NH_(4)^(+)通量相比,高密度处理组分别提高了43.7%和23.6%。在第2~10天,NH_(4)^(+)通量处于持续增加的趋势。处理组PO_(4)^(3-)通量变化范围为-7.85~6.42μmol/(m^(2)·d),第2~6天,处理组PO_(4)^(3-)通量持续增加。研究表明,单环刺螠的生物扰动能够持续地促进DIN由沉积物向水体中扩散,且存在明显的密度效应。研究结果将为深入认识单环刺螠在水层-底栖系统耦合过程中的生态作用提供基础数据。

Bioturbation refers to the biological reworking of soils and sediments by benthic animals,especially macrobenthos(e.g Venerupis philippinarum,Nutaliaolivacea,and Echinocardium cordatum,etc.).Previous studies have shown that bioturbation activity could enhance the migration and transformation of inorganic nitrogen with different forms at the sediments-water interface on the tidal flat,and increase the benthic nitrogen release rate,thus affecting the chemical characteristics of the sediment.In this study,Urechis unicinctus was selected as the research object to explore their effect of bioturbation on the diffusion flux of nitrogen and phosphorus at the sediment-water interface.Chinese Penis Fish,U.unicinctus,is an echiuran species with solid environmental adaptability,and is widely distributed in North Korea,Japan,and northern China,especially near intertidal and subtidal zones along the Bohai Sea coast of China.Usually,U.unicinctus inhabit in U-shaped burrows in sediments in intertidal areas and feed on filtering organic particles in the water.Furthermore,it has high economic value and nutritional value as aquatic products.Currently,the research of U.unicinctus mainly focuses on Reproductive biology,tolerating mechanism for sulfide,extract the active component,ecological health cultivation,etc.However,very few studies can be found about the impact of U.unicinctus bioturbation on the biogeochemical process of biogenic elements.To understand the ecological role of U.unicinctus in the sedimental environment,the effect of biological disturbance of U.unicinctus on the diffusion of nitrogen and phosphorus at the sediment-water interface was studied with indoor experiment.The U.unicinctus were divided according to four areal densities:low density(LD,500 ind/m^(2)),medium density(MD,2500 ind/m^(2)),high density(HD,8300 ind/m^(2))and control group(CO,no worms),respectively.Each of this treatment group has five replicates.The 20-day indoor experiment were carried out in tanks during November-December 2020.The results showed that the release rate of NH_(4)^(+)contents from sediment to water ranged from 10.6 to 765.3μmol/(m^(2)·d),and it increased to the maximum and then decreased gradually with time elapsed.Compared to the control group,the average nutrient release rate increased by 39%,111%,and 257%in the LD,MD,and HD treatment groups,respectively.Significant differences were found for NH_(4)^(+)flux between the LD,MD,HD groups and the CO group(P<0.05).The values of NO_(3)^(−)+NO_(2)^(−)flux ranged from−172.05 to 208.63μmol/(m^(2).d)for all the experiment,but the average flux values were reduced by 8%and 32%,and 81%,respectively,in the LD,MD,and HD treatment groups.Further,the values of PO_(4)^(3-)flux ranged from−7.85 to 6.42μmol/(m^(2).d)in the treatment groups during the entire period.There was a significant difference in PO_(4)^(3-)-P flux between the MD and HD groups and the CO group from day 2 to day 14 during the experiment(P<0.05).It turned out that NH_(4)^(+)is the main dissolved inorganic nitrogen(DIN)that affected by the biological disturbance of U.unicinctus.Taking into account the influence of U.unicinctus's metabolism and ammonia excretion,the NH_(4)^(+)diffusion flux is calculated by subtracting the ammonia excretion.Although the NH_(4)^(+)diffusion flux has a slight decrease,the trend of change over time remains unchanged.The results indicated that although the ammonia excretion effect of U.unicinctus has a certain contribution to the diffusion of NH_(4)^(+)from the sediment to the water body,the dominant factor still comes from the bioturbation effect of U.unicinctus.In addition,the U.unicinctus promoted the diffusion of DIN from sediments to bottom water,with an obvious density effect.This work provides support to evaluate the potential ecological role of the U.unicinctus in the integrated multi-trophic aquaculture(IMTA)system.