Ocean urea fertilization for carbon credits poses high ecological risks

The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.     

Interactive effects of hypoxia and polybrominated diphenyl ethers (PBDEs) on microbial community assembly in surface marine sediments

Hypoxia alters the oxidation–reduction balance and the biogeochemical processes in sediments, but little is known about its impacts on the microbial community that is responsible for such processes. In this study, we investigated the effects of hypoxia and the ubiquitously dispersed flame-retardant BDE47 on the bacterial communities in marine surface sediments during a 28-days microcosm experiment. Both hypoxia and BDE47 alone significantly altered the bacterial community and reduced the species and genetic diversity. UniFrac analysis revealed that BDE47 selected certain bacterial species and resulted in major community shifts, whereas hypoxia changed the relative abundances of taxa, suggesting slower but nonetheless significant community shifts. These two stressors targeted mostly different taxa, but they both favored Bacteroidetes and suppressed Gammaproteobacteria. Importantly, the impacts of BDE47 on bacterial communities were different under hypoxic and normoxic conditions, highlighting the need to consider risk assessments for BDE47 in a broader context of interaction with hypoxia.     

Spatiotemporal variability of hypoxia and eutrophication in Manila Bay,Philippines during the northeast and southwest monsoons

Hypoxia in Manila Bay, Philippines was previously reported during the northeast monsoon (dry season) in February 2010. In this study, four more field surveys of the same 31 stations were conducted in July 2010, August 2011 and 2012 (wet season, southwest monsoon), and February 2011 (dry season, northeast monsoon). During the wet season, bottom hypoxia spread northward towards the coast with dissolved oxygen (DO) ranging from 0.12 to 9.22 mg/L and the bay-wide average reaching 2.10 mg/L. Nutrient levels were elevated, especially near the bottom where dissolved inorganic nitrogen reached 22.3 μM (July 2010) and phosphorus reached 5.61 μM (August 2011). High nutrient concentrations often coincided with low near-bottom DO content. Our work builds on the preliminary assessment of hypoxia in Manila Bay, the importance of repeated temporal studies, and shows hypoxia to prevail significantly during the southwest monsoon (wet season) when increased freshwater discharge caused strong water column stratification.     

A study of anthropogenic and climatic disturbance of the New River Estuary using a Bayesian belief network

The present paper utilizes a Bayesian Belief Network (BBN) approach to intuitively present and quantify our current understanding of the complex physical, chemical, and biological processes that lead to eutrophication in an estuarine ecosystem (New River Estuary, North Carolina, USA). The model is further used to explore the effects of plausible future climatic and nutrient pollution management scenarios on water quality indicators. The BBN, through visualizing the structure of the network, facilitates knowledge communication with managers/stakeholders who might not be experts in the underlying scientific disciplines. Moreover, the developed structure of the BBN is transferable to other comparable estuaries. The BBN nodes are discretized exploring a new approach called moment matching method. The conditional probability tables of the variables are driven by a large dataset (four years). Our results show interaction among various predictors and their impact on water quality indicators. The synergistic effects caution future management actions.     

浅水湖泊湖泛(黑水团)中的微生物生态学研究进展

"湖泛"是指湖泊水体中(包括沉积物)富含大量藻源性(或草源性)的生物质,在微生物的分解作用下,大量消耗氧气,出现厌氧分解,微生物在还原条件下,促进许多"黑臭"物质的形成,进而影响水质和湖泊生态系统结构与功能乃至造成环境灾难.与湖泛发生时的环境特征(如低溶解氧,低p H,高有机质,高总磷、总氮)相对应的是其简化的食物网结构和特殊的微生物类群.本文将主要针对湖泛中的微生物群落及其在物质循环中的作用展开综述.研究显示湖泛水体中主要微生物类群,如真菌、细菌厚壁菌门的梭菌以及产甲烷古菌等,在有机质的快速分解和厌氧矿化过程中发挥着重要作用;沉积物中主要的微生物功能群,如硫酸盐还原细菌、铁还原细菌、甲烷厌氧氧化菌和反硝化细菌等,是湖泛致黑物质形成的关键.缺氧及厌氧条件下碳、硫和铁等元素生物地球化学过程的相互关联以及多种微生物之间形成的互营共生可能是湖泛过程中功能微生物的重要特征.湖泛中微生物功能的进一步研究,亟需借鉴海洋低氧区及深海沉积物的经验,引用先进研究手段,提出可靠的生物地球化学证据.浅水湖泊湖泛(黑水团)中的微生物生态学探索将有助于从机理上揭示湖泛黑臭的成因.     

Effect of parental hypoxic exposure on embryonic development of the offspring of two serpulid polychaetes: Implication for transgenerational epigenetic effect

Sperm production and motility, fecundity, and egg size, complexity and viability of serpulid polychaetes Hydroides elegans and Hydroides diramphus after 2-week treatment to hypoxia (2 mg O₂ l⁻¹) was compared with those under normoxia (6 mg O₂ l⁻¹). Despite reduced fecundity, the effect of parental hypoxic exposure on gamete quality was not discernible for both species. However, regardless of their subsequent dissolved oxygen environment, eggs spawned by H. elegans after hypoxic exposure were found to have lower fertilization success, slower embryonic development and a significantly higher yield of malformed embryos than those with a parental normoxic treatment. In contrast, neither fertilization success nor rate of embryonic development was affected for H. diramphus. The results implied that hypoxia was a potential stress reducing the recruitment of H. elegans through non-adaptive epigenetic effect, whereas H. diramphus was a more tolerant species to survive hypoxic events.     

南极冰穹A低氧复合寒冷环境对考察队员儿茶酚胺含量和心肌酶的影响

南极冰穹A地区气候条件极为恶劣,通过探讨冰穹A低氧复合寒冷环境对考察队员儿茶酚胺激素和心肌酶水平的影响,为冰穹A考察队员医学防治提供依据。分别在上海出发、冰穹A考察和返回上海时,采集第29次中国南极考察昆仑站冰盖队25名男队员外周静脉血样,检测血中去甲肾上腺素(NE)、肾上腺素(E)、多巴胺(DA)、高敏感性C反应蛋白(hs CRP)、肌酸激酶MB(CK-MB)和肌钙蛋白I(c Tn I)水平。队员E和CK-MB水平在冰穹A虽增高但与出发时没有显著性差异,E水平在返回上海后显著降低(P0.01);DA水平在冰穹A和返回上海后均显著增高(P0.05)。与出发(P0.01)和冰穹A(P0.01)数据相比,CK-MB水平在返回上海后均显著降低。肌钙蛋白I(c Tn I)水平在冰穹A和返回上海后均没有发生显著变化,均在正常范围内(0.04 ng·m L-1),hs CRP和NE水平也没有显著性改变。Pearson相关性分析表明,CK-MB水平与E水平呈显著正相关(r=0.285*,P0.05)。结果表明,在冰穹A低氧复合高寒环境下冰盖队员心肌出现了适应性代偿,返回上海后没有出现病理性损伤,心肌酶水平变化与儿茶酚胺类激素水平存在相关性,今后仍需积累多次昆仑站考察队的数据资料,深入探讨潜在的调节机制。     

Research Advances in Sedimentary Records of Coastal Bottom-water Hypoxia

Sedimentary records are potential to provide long-term evidence for better understanding the development mechanism of coastal hypoxia, shedding some light on the forecast, prediction and controlling-measure development to mitigate hypoxia. Therefore, recent research advances in the formation mechanism and evolution history of coastal hypoxia were briefly reviewed, specially with focus on sedimentary records and proxy methods. First, marine environments with hypoxia were classified into semi-enclosed marginal sea/gulf and open shelf sea based on the degree of bottom-water circulation and ventilation, and main characteristics for the hypoxic development were discussed respectively. Secondly, the methodology was reviewed in the efficiency by using different proxies to reconstruct hypoxia development history from sediment cores, including redox indicators of sedimentology, biology, mineralogy and geochemistry. Ultimately, recent research advance in hypoxic development mechanism and evolution history off the Changjiang Estuary were summarized. It is worth noting that long-term evolution history has been less studied from long cores. It is therefore suggested that a synthetic methodology involving multi-core comparison with different-proxy interpretation should be employed to study the development history of seasonal hypoxia off the Changjiang Estuary.     

Behavioural responses of estuarine mysids to hypoxia and disruption by cadmium

Neomysis integer (Peracarida: Mysidacea) occupies the upper, low-salinity regions of estuaries in Europe, where it can experience periods of reduced oxygen concentration associated with the maximum turbidity zone. The present study reports the distribution of N. integer in response to gradients of dissolved oxygen in combination with environmentally realistic cadmium concentrations (0.1, 0.5 and 1.0 microg Cd2+ l(-1). Control and 0.1 microg Cd2+ l(-1) mysids were distributed evenly along a flume containing an oxygen gradient, and demonstrated no avoidance to hypoxia (down to 30% air saturation). In contrast, mysids exposed to 1.0 microg Cd2+ l(-1) migrated away from areas of low dissolved oxygen and, after 90 min, no mysids were found in regions of <75% air saturation. These results indicate that cadmium poses an increased risk to estuarine organisms inhabiting upper estuarine areas subjected to reduced dissolved oxygen concentrations.