水产养殖池塘沉积物有机质富集的环境效应与修复策略

沉积物有机质富集是养殖池塘的重要特征,有机质的分解将驱动营养物质的释放,其主要机制在于自身的矿化与底层厌氧状态的形成,后者将进一步促进有毒有害物质的产生和累积,进而影响水产品的产量与质量。因此,必须针对沉积物有机质富集的特征开展及时而准确的监测,同时采用选择性去除、原位氧化和生态修复相结合的方法对其实施有效地处置,以调节养殖池塘生态系统的结构与功能,最大限度地利用可再生资源和天然饵料,进而实现渔业生产与水环境的可持续发展。     

广州市郊养殖池塘表层沉积物中氮磷的初步研究

2006年2、3月对广州市郊养殖池塘表层沉积物中的氮磷含量及分布特征进行了调查.结果表明:池塘表层沉积物中的TN和TP、含水率、TOM(总有机质)均明显高于珠江参照点,TN、TP、含水率和TOM分别为2.358 mg/g、1.643 mg/g、62%和9.9%;养殖池塘表层沉积物磷形态主要是以HCl-P为主,占TP的45.8%,而珠江参照点则主要是以NaOH-P为主,占TP的66.1%.池塘表层沉积物中TN/TP与水体中TN/TP有近一个数量级之差,前者为6.27～16.37,而后者则仅为0.82～1.97,这可能与表层沉积物氮磷的循环特点有重要关系.     

不同季节刺参养殖池塘沉积物菌群结构及其影响因素

本研究以辽宁省营口地区刺参(Apostichopus japonicus)养殖池塘为研究对象,利用高通量测序技术,构建不同季节刺参养殖池塘沉积物菌群16S rRNA基因测序文库,解析刺参养殖池塘沉积物菌群的季节性差异和共性,查明影响沉积物菌群构成的主导环境因子。结果显示,营口地区刺参养殖池塘沉积物菌群的丰度和多样性以夏季最高,春秋次之,冬季最低。不同季节刺参养殖池塘沉积物差异菌群呈显著性季节演替特征(P<0.05)。其中,春季差异菌群主要隶属于拟杆菌门(Bacteroides),夏季差异菌群主要隶属于酸杆菌门(Acidobacteria)、疣微菌门(Verrucomicrobia)和浮霉菌门(Planctomycetes),秋季差异菌群主要隶属于厚壁菌门(Firmicutes),冬季差异菌群主要隶属于放线菌门(Actinobacteria)。尽管不同季节沉积物细菌组分比例不同,但第一优势菌门均隶属于变形菌门(Proteobacteria)(相对丰度>43.19%)。环境因子中,影响刺参养殖池塘沉积物菌群的主导环境因子为温度、总有机碳、总氮和pH。本研究将为刺参养殖池塘微生态调控提供理论参考。     

基于脂肪酸探究青虾扰动作用对沉积物中有机质降解的影响

为了探索池塘沉积物中有机质过度积累导致养殖环境污染问题,以青虾(Macrobrachium nipponense)为养殖对象,探究其扰动作用对沉积物中有机质降解的影响。实验设置青虾实验组和空白对照组,分别测定沉积物理化性质、脂肪酸及碳氮含量,并以脂肪酸为生物标记物指征沉积物中有机质降解状态。结果显示:青虾扰动作用显著提高了沉积物的含水率(MC)和氧化还原电位(ORP),并显著降低了pH值;沉积物中定量分析出18种脂肪酸,其中以C16∶0和低碳偶碳链脂肪酸为主,实验组平均碳链长度(average carbon length,ACL)较空白组显著增大,ACL与ORP、MC分别呈显著正相关;青虾扰动作用对沉积物碳氮含量影响不显著,但能显著降低沉积物的碳氮比,并改善沉积物的有机污染状况。结果表明:青虾扰动作用能降低沉积物pH值、提高沉积物MC及ORP。同时,ACL指征青虾扰动作用可以促进沉积物中有机质的降解。     

斑节对虾混养池塘微生物群落生态功能初探

利用宏基因组技术比较斑节对虾单独养殖、斑节对虾与海蜇混养、斑节对虾与海蜇和菲律宾蛤仔混养3种养殖模式池塘沉积物的微生物群落。试验结果显示,皮氏罗尔斯通氏菌为最主要的致病菌,斑节对虾养殖池塘沉积物中致病菌的丰度相比于对照组沉积物均明显下降。与非海水养殖池塘对照沉积物相比,斑节对虾养殖池塘沉积物的微生物群落中硝酸盐还原生成氨氮的相关基因以及硫酸盐还原产生硫化氢的相关基因含量更高,而亚硝酸盐和氨氮利用基因含量较低。3种斑节对虾养殖模式中,斑节对虾单独养殖和斑节对虾与海蜇和菲律宾蛤仔混养池塘沉积物中硝酸盐和硫酸盐还原基因丰度均高于斑节对虾与海蜇混养模式。此外,斑节对虾养殖池塘沉积物中,一些特定的生物地球化学循环过程由包括交替单胞菌、拟杆菌、着色菌、黄杆菌、脱硫杆菌和脱硫弧菌等多种微生物共同完成。探明不同斑节对虾养殖池塘微生物群落中潜在的人类致病菌情况以及氮、硫等基本元素的生物地球化学循环,对于优化养殖技术、控制疾病暴发同时提高养殖产量具有重要意义。     

吉富罗非鱼温棚池塘上覆水−沉积物间隙水营养盐垂直分布特征及其界面交换通量

利用Peeper(pore water equilibriums)技术采集上覆水-沉积物间隙水整个垂直剖面的原位水样,然后使用微量分光光度法测定样品中主要营养盐NH4+-N、NO3--N、NO2--N、PO43--P和SO42--S的浓度,从而分析吉富罗非鱼(GIFT,Oreochromis niloticus)温棚养殖池塘各营养盐的垂直分布特征,并估算其在上覆水-沉积物界面处的交换通量。结果表明:(1)两罗非鱼温棚养殖池塘,4个Peeper实验组在上覆水-沉积物间隙水中各营养盐组间重复性都较好,且各营养盐都有较强的垂直分布规律。NH4+-N主要存在于沉积物间隙水中,从其表面深度0至6 cm间隙水中NH4+-N浓度迅速增高,8 cm后趋于相对稳定;NO3--N主要存在于上覆水中,沉积物0至4 cm间隙水中3NO--N浓度迅速降低;NO2--N浓度在沉积物表层2 cm处出现峰值;PO43--P浓度在沉积物0至4 cm间隙水中浓度迅速增加至最大值,深度超过4 cm浓度有降低趋势;SO42--S主要存在于上覆水中,沉积物0至8 cm间隙水中SO42--S浓度迅速降低。(2)不同深度的水样根据营养盐浓度,各实验组都可聚类为3组差异显著的类群:上覆水组、表层沉积物组(上覆水-沉积物交界面组)和深层沉积物组。(3)通过Fick第一定律估算营养盐在上覆水-沉积物界面的扩散通量得出:NH4+-N和PO43--P为从沉积物间隙水扩散至上覆水中;NO3--N和SO42--S为从上覆水扩散至沉积物中。4个Peeper实验组NH4+-N的扩散通量分别为22.44 mg/(m2·d)、22.93 mg/(m2·d)、50.84 mg/(m2·d)和16.74 mg/(m2·d),为两罗非鱼温棚养殖池塘主要的沉积物内源释放营养盐。与类似研究比较,本研究通量相对较高,表明养殖池塘沉积物有机质含量相对较高。SO42--S的扩散通量分别为–87.05 mg/(m2·d)、–164.87 mg/(m2·d)、–77.37 mg/(m2·d)和–91.30 mg/(m2·d),为两养殖池塘沉积物最大的吸收营养盐,表明SO42--S还原可能为罗非鱼养殖池塘沉积物中有机质降解的主要途径之一。     

主养草鱼与主养黄颡鱼池塘沉积物—水界面氮磷营养盐通量变化及与环境因子的关系

为了探讨不同主养模式池塘养殖期间沉积物—水界面氮磷营养盐通量变化特征以及与环境因子之间的相互关系,利用沉积物—水界面营养盐扩散通量的原位观测装置,分析了2013年4—10月主养草鱼和主养黄颡鱼池塘沉积物—水界面营养盐交换通量,并探讨了影响营养盐交换通量的因素。结果发现:(1)在养殖初期,各种形态氮磷在养殖池塘沉积物—水界面主要表现为从上覆水向沉积物的沉积,养殖中后期,由于温度升高以及池塘沉积物中营养物质的大量累积,各种形态氮磷表现为以沉积物向上覆水扩散为主,表明池塘沉积物是氮磷营养盐的源与汇;(2)两种不同主养模式池塘氮磷通量的统计结果表明,沉积物—水界面-N、-N和-P通量变化无显著差异,而-N、TN和TP通量有显著差异;(3)上覆水中DO含量的升高显著促进界面间-N和-N释放通量,而-N和-P释放通量与上覆水DO浓度成显著负相关;温度的升高对各种无机形态的氮磷通量有显著的促进作用。     

刺参-中国对虾复合养殖系统重金属分布特征

比较了刺参-中国对虾混养和刺参单养两种养殖模式下养殖池塘中底泥表层沉积物和水体悬浮颗粒物以及养殖刺参体组织中Mn、Cr、Hg、Zn、Cu、Pb、Cd、As等重金属的含量,并调查分析了两种养殖池塘水体中总悬浮颗粒物和颗粒有机物的变化,研究刺参-中国对虾混养模式对刺参生长环境及刺参体内重金属含量的影响。研究结果表明,刺参体组织中重金属Cu、As和Mn的含量在单养池塘和混养池塘变化趋势一致,且刺参体内Cu和As在混养池塘的含量要低于单养池塘。相比于单养模式,养殖池塘内悬浮颗粒物(TPM)和悬浮颗粒有机物(POM)的含量在混养模式下显著减少,这一结果表明刺参-中国对虾混养模式可显著改善刺参养殖水体的水环境状况。此外,在两种养殖模式下,悬浮颗粒物中不同重金属元素的含量均不相同且呈现出不同的变化趋势,悬浮颗粒物内Cr、Mn、Hg的含量在刺参-中国对虾混养模式下呈显著下降趋势,且含量低于单养池塘。表层沉积物中有机质含量具有一定的波动性,表现出先下降后升高的趋势,且混养池塘有机质含量比同期的单养池塘更高。表层沉积物的重金属含量与强热失量(LOI)的相关性分析结果表明,两种混养模式下,表层沉积物的Cd、Zn、Pb、Mn等重金属水平均与LOI呈正相关关系。     

菲律宾蛤仔对养殖池塘沉积物/水界面反硝化和厌氧氨氧化反应速率的影响

养殖尾水氮含量过高等富营养化问题是影响当前我国池塘养殖产业健康可持续发展的重要因素，反硝化和厌氧氨氧化是自然水生态系统中重要的氮循环过程，是沉积物氮素营养迁出的主要途径，埋栖型贝类通过滤水和蠕动等生命活动不仅能净化水质，还可以使沉积物颗粒混合并改变沉积物/水界面的物质交换。本研究于2020年9、10、11、12月采集菲律宾蛤仔(Ruditapes philippinarum)养殖池塘贝类区域(有贝区)和对照区域(无贝区)的沉积物表层样品，进行泥浆培养实验，利用氮稳定同位素示踪技术检测其反硝化和厌氧氨氧化反应速率，并分析了其与间隙水理化参数的相关性。结果显示，菲律宾蛤仔养殖池塘有贝区10月和11月样品检测到厌氧氨氧化反应，并有反硝化—厌氧氨氧化耦合反应；有贝区9—12月沉积物反硝化反应速率均高于无贝区，有贝区9月的反硝化反应速率最高(0.005 8 μmol/kg·h)；水体温度与沉积物反硝化反应速率呈极显著正相关(P<0.01)，氨氮(NH4+-N)浓度与厌氧氨氧化反应速率呈极显著正相关(P<0.01)。研究表明，海水池塘养殖生态系统中也存在厌氧氨氧化过程，养殖菲律宾蛤仔等埋栖型贝类有利于池塘沉积物/水界面的反硝化和厌氧氨氧化反应，有效地促进池塘沉积物脱氮过程，研究结果不仅丰富了海水养殖生态系统氮循环理论，也为开展尾水生物净化工作提供了新思路。     

崇明岛草鱼池塘沉积物中多环芳烃的分布状况及生态风险

为探究崇明岛池塘养殖持久性污染状况，采用气相色谱-质谱联用法对崇明岛不同区域草鱼池塘沉积物中16种优先控制多环芳烃(PAHs)的含量及分布情况进行了研究，同时运用主成分分析法、特征比值法和质量标准法等对草鱼池塘中PAHs的来源及生态风险进行了分析。结果显示，崇明岛草鱼池塘养殖沉积物中的PAHs总含量为未检出(ND)~1 654.09 μg/kg，平均含量为95.13 μg/kg，其中4~5环PAHs对总浓度的贡献率最高；崇明岛不同区域草鱼池塘沉积物中的PAHs含量差异较大，表现为岛中部池塘含量低，沿岛四周池塘含量较高，尤其是岛西部沿岸区池塘含量最高且种类多；分析发现，崇明岛草鱼养殖池塘中的PAHs主要来源于岛内生物燃烧和石油燃烧，总体处于中等偏下污染水平，生态风险较低，但在西北部池塘存在潜在生态风险，应予以重视。     

上海地区池塘沉积物中氮、磷、有机碳及重金属风险评价

为综合评估上海地区池塘沉积物环境质量状况，2016-2019年对上海地区36个养殖场池塘采集沉积物样品360个，检测和分析沉积物中总氮（TN）、总磷（TP）、总有机碳（TOC）及重金属Cu、Zn、Pb、Cd、Cr、Hg和As含量。研究结果表明，池塘0~10 cm层和10~20 cm层沉积物中TN、TP、TOC及各重金属均值分布无显著差异（P>0.05），0~20 cm层沉积物（干重）中TN、TP和TOC平均含量分别为（873.37±352.45）mg/kg、（685.66±199.66）mg/kg和（6.62±3.05）mg/g，三者相关性显著。综合污染指数法和有机指数法评价结果表明，池塘沉积物中氮和有机物质的累积量较低，磷累积量相对较高，均低于其他地区高产池塘。池塘沉积物中Cr、Cd、Cu和Hg样品超标率分别为6.42%、3.21%、4.13%和1.38%，Zn、Pb和As无超标现象。地质累积指数、潜在生态危害指数法和一致性沉积物质量基准评价结果表明，上海地区池塘沉积物中重金属整体上处于清洁等级、低潜在生态危害状态，预测不会引发生物毒性效应。     

Sediment Quality in Arkansas Bait Minnow Ponds

Sediment cores were collected from 7-yr-old, 20- to 25-yr-old, and 30- to 35-yr-old ponds at a bait minnow farm at Lonoke, Arkansas, USA. Average depths of soft sediment (S and M horizons) were 8 cm in young ponds, 12 em in intermediate-age ponds, and 26 cm in old ponds. Organic carbon concentrations in sediment were low to moderate (1–2%) and carbon to nitrogen ratios were wide (20–50). Phosphorus and sulfur concentrations increased as ponds aged. Most of the phosphorus (78.9%) was in organic form, but sulfur was primarily inorganic in form (presumably iron sulfide). There appears to be two major problems associated with sediment accumulation over time. Deep, soft sediment interferes with pond management and especially with harvest. High phosphorus concentration in old sediment may contribute to dense phytoplankton blooms by supplying phosphorus to the water. Sodium nitrate treatment did not increase the rate of sediment organic matter decomposition in laboratory trials and would not be expected to enhance the degradation of sediment organic matter in ponds. The best method for improving the condition of bottoms in older bait minnow ponds probably is to remove the sediment.     

Accumulation, organic carbon and dry matter concentration of sediment in commercial channel catfish ponds

Sediment depth and organic carbon (OC) concentration were measured in sediment cores (n=675) collected from 45 commercial channel catfish ponds in northwest Mississippi from April to September in 1998 and 1999. Ponds had been in continuous catfish production from 14 days to 21 years. Sediment depth ranged from 1 to 95 cm and was heterogeneously distributed within ponds: least in the shallow end (26.3 cm) and greatest in deeper areas (33.7 cm). Mean sediment depth increased with pond age, although the rate of sediment accumulation was greatest in the first year (12.5 cm per year). Organic carbon concentration varied slightly within ponds ranging from 0.76 to 3.43% of dry matter (DM). Mean organic carbon concentration in the upper 2 cm of sediment (1.77%) was significantly greater than in the deeper sediment layer (1.55%). Mean dry matter content in the upper 2 cm of sediment averaged 24.2% of total wet weight. Mean dry matter for the lower sediment fraction was 37.8% of total wet weight. Despite large inputs of organic matter from feed and primary production, sediment organic carbon concentrations did not increase with pond age.     

Using pigment level as a primary production indicator to assess organic matter variability in two linked wetland systems with different disturbance levels and its effect on secondary communities

In a mesocosm experiment, pigment levels, organic matter and the structure of macroinvertebrate community were compared in two linked wetland systems encompassing fish-farm pond and natural reservoir. A stratified sampling design was applied, and treated experimental azoic sediment was placed in suspended boxes. The set of box was used to follow cumulative colonization period and single-month colonization approach for the study of macrofauna and biochemical parameters (organic matter, chlorophyll a and phaeopigments). There were significant differences between systems for the abiotic and community variables and polychaete diversity. Regarding the structure of macroinvertebrate community, the pond system appears to have higher abundance than the natural system. Monthly fluctuation was observed for abiotic variable and community variables in both systems, but polychaete diversity indices did not vary monthly in the pond system, which suggests that diversity indices in disturbed systems do not follow the organic matter variation. The correlation coefficient was also tested within abiotic and community variables for both systems. In the pond system, the organic matter was strongly related with chlorophyll a, carotenoid and phaeopigments. Due to the fact that the source of OM in the pond system is allochthonous, phaeopigments level is likely not to be directly affected by organic matter enrichment, but organic matter inputs create the high primary production and consequently affect the phaeopigments level. Polychaete abundance was positively correlated with the load in organic matter for both reservoir and pond systems, but the correlation coefficient between organic matter and polychaete diversity indices was higher in reservoir than in the pond system. The Moss index was used to indicate the production and degradation state of the systems, and it represented the natural reservoir in a higher production phase than the fish pond, and later on, the monthly variation of the percentage of degradation confirms the pond system in a more decayed state than the natural reservoir system. This study shows that although the organic matter and phaeopigments level tend to be higher in disturbed system, this does not necessarily favor all species, and more sensitive species are endangered of getting displaced by opportunistic species in systems with anthropogenic impact.     

Pond Bottom Management at Commercial Shrimp Farms in Chantaburi Province,Thailand

Most shrimp farmers in Chantaburi Province, Thailand, use water jets to dislodge sediment from empty pond bottoms, and wastewater is held for sedimentation before discharge into natural waters. Other pond bottom management practices used by a few farmers are sediment excavation, leave sediment but till entire pond bottom, and no mechanical treatment. All four methods of pond bottom treatment are followed by sun drying for 30 d. Soil organic carbon concentration in ponds following dry‐out seldom exceeded 2%. Although shrimp production in 24 ponds supplied by the same source of water was negatively correlated with increasing soil organic carbon concentration (r = ?0.582), this observation does not confirm a causative relationship. Moreover, in trials conducted at Burapha University, Chantaburi Campus, bottom soil organic matter concentration following dry‐out differed little irrespective of treatment method. Lower soil moisture concentration revealed that dry‐out was more complete with sediment removal than without, but better dry‐out resulted in lower soil pH. Removal of sediment by excavation or flushing is expensive, and natural dry‐out combined with liming and occasional sediment removal should be investigated as a less expensive and more environment‐friendly alternative to removing sediment after each crop.     

Bacteria in shrimp pond sediments: their role in mineralizing nutrients and some suggested sampling strategies

Strategies for sampling sediment bacteria were examined in intensive shrimp. Penaeus monodon (Fabririus), ponds in tropical Australia. Stratified sampling of bacteria at the end of the production season showed that the pond centre, containing flocculated sludge, had significantly higher bacterial counts (15.5 × 10⁹ g-¹ dw) than the pond periphery (8.1 × 10⁹g^?1 dw), where the action of aerators had swept the pond floor. The variation in bacterial counts between these two zones within a pond was higher than that between sites within each zone or between ponds. Therefore, sampling effort should be focused within these zones; for example, sampling two ponds at six locations within each of the two zones resulted in a coefficient of variation of ± 5%. Bacterial numbers in the sediment were highly correlated with sediment grain size, probably because eroded soil particles and organic waste both accumulated in the centre of the pond. Despite high inputs of organic matter added to the ponds, principally as pelleted feeds, the mean bacterial numbers and nutrient concentrations (i.e. organic carbon, nitrogen and phosphorus) in the sediment were similar to those found in mangrove sediments. This suggests that bacteria are rapidly remineralizing particulates into soluble compounds. Bacterial numbers were highly correlated with organic carbon and total kjeldahl nitrogen in the sediment, suggesting that these were limiting factors to bacterial growth.     

Shrimp and fish pond soils: processes and management

The pond bottom soil and the accumulated sediments are integral parts of ponds. Concentrations of nutrients, organic matter and microorganism density in the pond bottom are several orders of magnitude greater than in the water. The accumulation of organic sediments may limit pond intensification. The intensive organic matter degradation at the pond bottom and high sediment oxygen demand exceeds the oxygen renewal rate. This leads to the development of anoxic conditions in the sediments and at the sediment–water interface. A series of anaerobic processes, affected by the redox potential of the system, are taking place. A large number of potentially toxic materials are generated. Among those are organic acids, reduced organic sulfur compounds, reduced manganese and sulfides.

Shrimp, as animals that normally live on or near the bottom, are exposed to conditions on the pond bottom. Exposure to toxic materials endanger the well being of the cultured shrimp. Reduced feeding, slower growth, mortality and possibly higher sensitivity to disease are reported.

The rational use of aerators to minimize the area of sludge accumulation, construction of ponds to trap sludge, stirring sediments, chemical poising of the redox system and environmentally accepted treatment and reuse of drained sediments are means to control the conditions at the pond bottom.     

Physical and chemical characteristics of sediments in catfish, freshwater prawn and carp ponds in Thailand

Sediment samples were collected from 42 catfish (Clarias hybrid) ponds, 40 freshwater prawn (Macrobrachium rosenbergii) ponds and 18 carp (Puntius spp.) ponds in Thailand. Regression analysis revealed that pond age (1–30 years) was not a major factor influencing the physical and chemical composition of pond sediments. Sediment depth, F+S horizon thickness and bulk density of S horizon were greater (P<0.05) in carp ponds than in catfish and prawn ponds. This occurred because sediment was removed from catfish and prawn ponds more frequently than from carp ponds. Total carbon, organic carbon and total nitrogen concentrations were greater (P<0.05) in carp ponds than prawn and catfish ponds. Few ponds had sediment organic carbon concentrations above 3%, and carbon:nitrogen ratio values did not differ (P>0.05) among ponds for the three species. Total phosphorus and other sediment phosphorus fractions increased in the order prawn ponds, carp ponds and catfish ponds. Sediment sulphur concentrations also increased in the same order. There were no differences in major or minor nutrient concentrations in sediment that would influence aquacultural production. Although there were significant correlations (P<0.05) between various sediment quality variables, no single variable or group of variables would be useful in estimating sediment quality. Pond bottom management practices used by producers in Thailand included drying of pond bottoms between crops, liming, tilling and periodic sediment removal. These practices have maintained relatively good bottom quality. They should be continued in Thailand and adopted in other places.     

Carbon and nitrogen budgets in shrimp ponds of extensive mixed shrimp–mangrove forestry farms in the Mekong delta,Vietnam

Mass balance estimates of carbon and nitrogen flux through two extensive shrimp ponds in the Mekong delta, Vietnam, were constructed to identify major sources and sinks of organic matter potentially available for shrimp production. Nutrient transformations in the sediments were measured to further assess rates of decomposition and burial and quality of organic matter. Tidal exchange was the major pathway for inputs and outputs of carbon and nitrogen in both ponds, with net primary production, nitrogen fixation and precipitation being minor inputs. No fertilizers or artificial feeds were added to either pond. The nutrient budgets identified burial and respiration as the next most important outputs after tidal exchange losses of particulate and dissolved carbon and nitrogen. There was no measurable denitrification in either pond, and volatilization was negligible. Mineralization efficiency of carbon in the water column was high (> 100%) in pond 23 reflecting rapid respiration rates; efficiency was lower (36%) in pond 12 waters. Mineralization efficiency of sediment nutrients averaged 34% for C and 41% for N in the pond with a higher annual shrimp yield (pond 12); lower mineralization efficiencies (11% for C, 10% for N) were calculated for the lower yield pond (pond 23). High burial efficiencies for both C (66–89%) and N (59–90%) in the sediments of both ponds suggest that little organic matter was shunted into biological production. Conversion efficiency for shrimp averaged 16% for C and 24% for N from pond 12, and 6% for C and 18% for N from pond 23. The high quantity but low quality of organic matter entering the ponds coupled with other factors, such as poor water quality, limits shrimp productivity. On average, nutrient outputs were greater than inputs in both ponds. This imbalance partly explains why shrimp yields are declining in these ponds.     

Effect of in situ sediment remediation combining oyster shells and bottom microporous aeration on nitrogen removal and microbiota

The present intensive aquaculture results in an excessive accumulation of nutrient and organic residues in sediment. Then, pollutants accumulated in sediment would strongly affect water quality and increase the occurrence of pathogenic microorganisms. Thus, remediation of sediment is needed for removing excess nutrient and preventing aquatic animal diseases. In the present research, sediment in cement tanks was remediated with a combined method: crushed oyster shells (OS) and bottom microporous aeration (MA) treatment. The experiment included the control group (CK), treatment 1 (bottom MA), treatment 2 (crushed OS), and treatment 3 (bottom MA and crushed OS, MA+OS). The experimental results showed that from the second week after the experiment began, the organic matter (OM) content in the sediment from MA+OS was lower than that of the CK. From the eighth week, the total nitrogen (TN) and ammonia nitrogen (NH₄‐N) levels in the sediment from MA+OS were lower than those of CK, and the remediation experiments on sediment had little effect on the water quality in the experimental groups. Functional bacteria in the water column, including the families Erythrobacteraceae and Microbacteriaceae and the genera Phenylobacterium and Beggiatoa, were elevated in MA+OS. Thus, crushed OS and bottom aeration could promote nitrification in water, reducing the levels of OM, (NH₄‐N), and TN in sediment, through affecting the microbiota in the water column and promoting nutrient circulation, and could improve the overall benthic environment. The method has been demonstrated to be easy and effective for nitrogen removal from sediment.