Pelagic-benthic coupling of the microbial food web modifies nutrient cycles along a cascade-dammed river

• Structure of multi-trophic microbial groups were analyzed using DNA metabarcoding. • Discontinuity and trophic interactions were observed along the dam-fragmented river. • C, N and P cycles are driven by top-down and bottom-up forces of microbial food web. • Pelagic-benthic coupling may intensify nutrient accumulation in the river system. Cascade dams disrupt the river continuum, altering hydrology, biodiversity and nutrient flux. Describing the diversity of multi-trophic microbiota and assessing microbial contributions to the ecosystem processes are prerequisites for the restoration of these aquatic systems. This study investigated the microbial food web structure along a cascade-dammed river, paying special attention to the multi-trophic relationships and the potential role of pelagic-benthic coupling in nutrient cycles. Our results revealed the discontinuity in bacterial and eukaryotic community composition, functional group proportion, as well as α-diversity due to fragmentation by damming. The high microbial dissimilarity along the river, with the total multi-trophic β-diversity was 0.84, was almost completely caused by species replacement. Synchronization among trophic levels suggests potential interactions of the pelagic and the benthic groups, of which the β-diversities were primarily influenced by geographic and environmental factors, respectively. Dam-induced environmental variations, especially hydrological and nutrient variables, potentially influence the microbial food web via both top-down and bottom-up forces. We proposed that the cycles of carbon, nitrogen and phosphorus are influenced by multi-trophic groups through autotrophic and heterotrophic processes, predator–prey relationships, as well as the release of nutrients mainly by microfauna. Our results advance the notion that pelagic-benthic trophic coupling may intensify the accumulation of organic carbon, ammonium and inorganic phosphorus, thereby changing the biogeochemical patterns along river systems. As a consequence, researchers should pay more attention to the multi-trophic studies when assessing the environmental impacts, and to provide the necessary guidance for the ecological conservation and restoration of the dam-regulated systems.     

Unveiling the interaction mechanisms of key functional microorganisms in the partial denitrification-anammox process induced by COD

● The availability of PD-anammox was investigated with higher NO₃^––N concentration. ● NO₃^––N concentration affects NO₃^––N accumulation during denitrification. ● COD concentration is determinant for N removal pathways in PD-anammox process. ● The synergy/competition mechanisms between denitrifiers and anammox was explored. Partial denitrification-anammox (PD-anammox) is an innovative process to remove nitrate (NO₃^––N) and ammonia (NH₄⁺–N) simultaneously from wastewater. Stable operation of the PD-anammox process relies on the synergy and competition between anammox bacteria and denitrifiers. However, the mechanism of metabolic between the functional bacteria in the PD-anammox system remains unclear, especially in the treatment of high-strength wastewater. The kinetics of nitrite (NO₂^––N) accumulation during denitrification was investigated using the Michaelis-Menten equation, and it was found that low concentrations of NO₃^––N had a more significant effect on the accumulation of NO₂^––N during denitrification. Organic matter was a key factor to regulate the synergy of anammox and denitrification, and altered the nitrogen removal pathways. The competition for NO₂^––N caused by high COD concentration was a crucial factor that affecting the system stability. Illumina sequencing techniques demonstrated that excess organic matter promoted the relative abundance of the Denitratesoma genus and the nitrite reductase gene nirS, causing the denitrifying bacteria Denitratisoma to compete with Cadidatus Kuenenia for NO₂^––N, thereby affecting the stability of the system. Synergistic carbon and nitrogen removal between partial denitrifiers and anammox bacteria can be effectively achieved by controlling the COD and COD/NO₃^––N.     

陕西省泾惠渠灌区土壤重金属污染累积趋势预测

在对泾惠渠灌区农业生态环境污染现状调查的基础上,以灌区土壤中Cd、Hg、Pb、Cr、As、Cu、Zn为评价因子,通过建立模型,预测和分析了施肥、灌溉等农事活动对土壤中重金属环境容量及累积趋势的影响。结果表明,从2007年到2050年,泾惠渠灌区耕层土壤中Cr增加了4.87%,As7.61%,Pb11.7%,Hg26.4%,Zn30.3%,Cd68.1%,Cu83.2%;各重金属元素的总静环境容量由大到小依次为Zn〉Pb〉Cu〉Cr〉As〉Hg〉Cd,其中Zn的环境容量高出Cd的270倍;灌区土壤用完现存容量所需要的时间Zn最短,只有52a,其次是Cu,为54a,Hg最长,可达572a,但就现存容量所占的比例来看,灌区土壤中As和Zn的现存容量所占比例最小。     

三江平原湿地典型植物群落氮的积累与分配

采用野外采样和室内分析结合的方法,研究了三江平原湿地典型植物群落氮的积累与分配特征。结果表明,小叶章（Calamagrostics angustifolia）、乌拉苔草（Carex meyeriana）和毛苔草（Carex lasiocarpa）群落地上器官氮含量不存在显著差异,根的氮含量存在显著差异,枯落物的氮含量表现为乌拉苔草群落〉小叶章群落〉毛苔草群落（p〈0.01）。小叶章、乌拉苔草和毛苔草群落不同部分的氮积累量和积累速率（VN）季节变化明显,三者地上器官、枯落物的氮积累量和VN表现为乌拉苔草群落〉小叶章群落〉毛苔草群落;三者根的氮积累量表现为小叶章群落〉毛苔草群落〉乌拉苔草群落,VN表现为毛苔草群落〉小叶章群落〉乌拉苔草群落。小叶章、乌拉苔草和毛苔草群落不同部分的氮分配比在各时期差异明显,根是重要的氮储库,其分配比高达（87.76±2.55）%、（79.84±7.53）%和（89.25±5.49）%;地上部分的氮分配比均以叶最高,茎较低;地上与地下的氮分配比呈相反变化规律,反映了其在氮供给方面的密切联系。     

长期施肥条件下水稻土磷素分布特征及对水环境的污染风险

对太湖地区稻麦轮作黄泥土进行23 a长期施肥试验,设14种处理:不施肥(C0)、氮肥(CN)、氮钾肥(CNK)、氮磷肥(CNP)、磷钾肥(CPK)、氮磷钾肥(CNPK)、稻草加氮肥(CRN)、有机肥(M0)、有机肥加氮(MN)、有机肥加氮钾(MNK)、有机肥加氮磷(MNP)、有机肥加磷钾(MPK)、有机肥加氮磷钾(MNPK)、有机肥加稻草加氮(MRN)。结果表明:(1)与无磷处理比较,耕层(0—15 cm)全磷(TP)、有效磷(O lsen-P)和无机磷(I-P)含量均显著增加,有机磷(O-P)含量仅在MNP、MPK、MNPK和CPK处理中显著增加;耕层以下O-P无显著增加,MNPK、MNP、MRN和MN处理中I-P下移可达25 cm,而MNPK处理中TP及MNPK、CNP处理中O lsen-P下移可达30 cm;耕层磷素积累量及磷素下移深度与施磷量、施肥模式(化肥磷、有机肥磷;单施、混施)和磷素形态有关。(2)有机肥I-P下移深度比化肥I-P深。(3)不同施肥处理对水体环境存在不同的污染风险,其中以MNPK处理下土壤磷素对水体环境的污染风险最大;地表水的污染风险大于地下水,稻季的污染风险大于麦季,丰水年的污染风险大于平水年。     

Virtual landscape-scale restoration of altered channels helps us understand the extent of impacts to guide future ecosystem management

Human modification of hydrological connectivity of landscapes has had significant consequences on ecosystem functioning. Artificial drainage practices have fundamentally altered northern landscapes, yet these man made channels are rarely considered in ecosystem management. To better understand the effects of drainage ditches, we conducted a landscape-scale analysis across eleven selected study regions in Sweden. We implemented a unique approach by backfilling ditches in the current digital elevation model to recreate the prehistoric landscape, thus quantifying and characterizing the channel networks of prehistoric (natural) and current (drained) landscapes. Our analysis detected that 58% of the prehistoric natural channels had been converted to ditches. Even more striking was that the average channel density increased from 1.33 km km⁻² in the prehistoric landscape to 4.66 km km⁻² in the current landscape, indicating the extent of ditching activities in the northern regions. These results highlight that man-made ditches should be accurately mapped across northern landscapes to enable more informed decisions in ecosystem management.     

人工湿地宽叶香蒲对重金属的累积与机理

宽叶香蒲(Typha latifolia L.)对环境胁迫具有较强的耐性。为了解宽叶香蒲对重金属的富集能力与耐性机理,通过野外调研,采集韶关凡口铅锌矿废水处理人工湿地中的宽叶香蒲与相应土壤样品,测定了土壤、植物的重金属总量与叶片亚细胞中重金属含量,分析了植物重金属含量与土壤重金属含量的相关性,并估算了宽叶香蒲地上部对重金属的提取量。土壤pH值在6.83~7.70之间,宽叶香蒲能有效降低土壤中的Cd、Pb、Zn、Cu和Mn的含量,对重金属的吸收主要受土壤重金属含量的影响,Pb和Cd的富集系数平均在0.5以上;除Fe外,叶片重金属主要分布在细胞壁和胞基质中。结果表明,宽叶香蒲是多种重金属的耐性植物,根系对重金属的富集与选择性向上运输、叶片细胞壁和胞基质对过量重金属的阻隔与结合作用是宽叶香蒲耐受重金属的重要机理。     

我国东部沿海地区蔬菜中重金属累积分布特征及居民膳食暴露评估

采用电感耦合等离子体质谱仪(ICP-MS)分析了我国东部北方和南方沿海地区市售叶类、根茎类、瓜果类、豆类及食用菌5类蔬菜样品中6种有害金属元素(Cr、Ni、As、Cd、Hg和Pb)及5种人体必需金属元素(Mn、Fe、Cu、Zn和Se)的累积水平,并研究了其在不同蔬菜样品中的分布特征.结果表明,所有蔬菜样品中的6种有害金属水平均远低于国家食品安全标准规定的最高限量,居民食用这些蔬菜不存在明显的非致癌风险,但因食用蔬菜导致的无机砷暴露有10^-5水平的潜在致癌风险.蔬菜对有害金属和必需金属的累积呈现出明显的同步趋势(P <0.01).相比其他蔬菜,食用菌表现出对有害金属及必需金属更高的累积水平,提醒人们需加强对食用菌中重金属污染的监测工作.     

贵州开阳磷矿开采对洋水河水体重金属污染与评价

开阳磷矿大规模采选矿活动对洋水河造成一定程度的重金属污染,为了解其污染状况,分析了洋水河水体中重金属Cd、U、Cu、Pb、Cr、Zn和类金属As等7种元素的含量,探讨其分布特征,并用地累积指数法和潜在生态危害指数法对沉积物中重金属污染程度及潜在生态危害进行了综合评价。结果表明,洋水河河水中重金属的浓度均低于中国地表水环境质量V类水质标准,沉积物中Cd、As和Zn的平均含量为1.27、50.28、151μg/g,分别高于贵州省土壤背景值6.05、3.14、2.26倍,高于中国水系沉积物背景值约9.07、5.53、2.89倍,其余元素均低于或接近贵州省土壤背景值和中国水系沉积物背景值,洋水河沉积物已不同程度受到Cd、As和Zn的污染;地累积指数评价结果表明,沉积物中Cd为中度污染,As属于轻度污染,其余元素均为无污染或轻度污染;潜在生态危害指数评价结果表明,单个重金属元素Cd的生态危害指数最大,其次是As,其余4种重金属均属于轻微生态风险,危害性小,综合潜在生态风险指数表明沉积物中重金属达到中等以上风险水平。     

低C/N比条件下曝气生物滤池深度脱氮

为实现低C/N比条件下曝气生物滤池的深度脱氮目的,同时为低碳源、低能耗、高效率的污水氮素去除提供技术理论参考,实验研究了低C/N比人工模拟污水曝气生物滤池中各种形式氮素的动态变化和去除效果。结果表明,在整个运行期间当曝气量调节为2 mL/min时,此时系统中溶解氧变化范围为0.49~1.02 mg/L,亚硝酸浓度在2.89~7.48 mg/L之间,该C/N比污水中亚硝酸盐的积累率可达50%以上。并且在该运行条件下氮素去除率保持在60%以上,可以实现较低C/N比条件下污染水体中氮素的去除。因此,该研究可为低C/N比污水短程深度脱氮创造条件,为C/N比较低的城市尾水深度脱氮提供依据。