Seasonal and sub-seasonal oxygen and nutrient fluctuations in an embayment of an eastern boundary upwelling system: St Helena Bay

Seasonal, sub-seasonal and spatial fluctuations in bottom dissolved oxygen (DO) were examined in St Helena Bay, South Africa’s largest and most productive embayment, between November 2013 and November 2014. Alongshore bay characteristics were assessed through comparison of variables along the 50-m depth contour. A mean coefficient of variation of 0.35 provided a measure of the relative variability of near-bottom DO concentrations along this contour. Consistently lower DO concentrations in the southern region of the bay in summer and autumn are attributed to enhanced retention. Across-shelf transects captured the seasonal development of hypoxia in relation to the distribution of phytoplankton biomass. Exceptional dinoflagellate blooms form extensive subsurface thin layers preceding the autumn DO minima in the south of the bay, prior to winter ventilation of the bottom waters. The seasonal decline in DO concentrations in the bottom waters was marked by sub-seasonal events of hypoxia, and ultimately anoxia linked to episodic deposition of organic matter, as indicated by increases in bottom chlorophyll-a concentrations. Seasonal changes in bottom water macronutrient concentrations followed trends in apparent oxygen utilisation (AOU), both of which mirrored DO concentrations. In the south of the bay, nitrogen loss through denitrification/anammox in suboxic waters was indicated by a dissolved inorganic N deficit in the bottom waters, which was most pronounced in autumn.     

南海北部陆坡ZSQD196PC柱状样末次间冰期以来的古海洋学记录：氧同位素、有孔虫和硅藻

为了解南海北部陆坡末次间冰期以来的古海洋沉积环境演化特征,对研究区ZSQD196PC柱状样有孔虫、硅藻及有孔虫氧同位素资料开展了分析。依据沉积有孔虫、硅藻主要属种的百分含量、丰度及组合特征,将有孔虫划分为3个组合,分别对应于氧同位素MIS1、2、3~4期;将硅藻划分为4个组合,大致对应于MIS1~4期。MIS1期有孔虫以暖水种占优势,Pulleniatina obliquiloculata百分含量显著升高;硅藻丰度低且以热性种占优势,其中冷期出现大量沿岸种,反映相对温暖的气候条件。MIS2~4期有孔虫以冷水种占优势,温跃层种含量相对较高;硅藻丰度高且以广布种占优势,出现沿岸种含量的升高,反映较冷的气候条件。通过对比浮游有孔虫氧同位素,分析讨论了末次盛冰期、Blling—Allerd暖期和新仙女木事件在ZSQD196PC柱状样的沉积响应,揭示了末次冰期中的气候波动。     

Patterns in the abundance of hyperbenthic zooplankton and colonization of marine benthic invertebrates on the seafloor of Saanich Inlet,a seasonally hypoxic fjord

This study describes changes in abundance of hyperbenthic zooplankton (including meroplankton) and benthic colonists at the seasonally hypoxic seabed of Saanich Inlet, British Columbia, Canada. We used the Victoria Experimental Network Under the Sea (VENUS) cabled observatory to measure water properties and to sample hyperbenthos with a sediment trap at 97 m from September 2008 to September 2009. Some faunal groups exhibited seasonal reproduction, and abundance peaked during their reproductive periods. These included larvae of the barnacle Balanus crenatus, and the crabs Petrolisthes eriomerus, Oregonia gracilis, and Lophopanopeus bellus bellus. Other groups were most abundant in spring and summer when food and oxygen levels were highest and temperature was lowest. These included cumaceans, the siphonophore Diphyes sp., the bryozoan Triticella pedicellata, and tintinnids. We also collected benthic colonists, predominantly bryozoans and polychaetes, on colonization plates deployed in spring/summer 2008, fall 2008/winter 2009, and spring/summer 2009. The total abundance of colonists and of bryozoans did not vary seasonally or with substrate complexity, whereas polychaetes were more numerous in spring/summer deployments and on a highly complex substrate. Taxon richness of colonists was higher in spring/summer 2008 than in fall 2008/winter 2009, whereas an anoxic episode in spring/summer 2009 reduced richness to similar values with that of fall 2008/winter 2009 levels. Substrate complexity had no effect on richness. Juvenile squat lobsters, digitally imaged in fall 2008/winter 2009, were most numerous when oxygen levels were lowest and potentially excluding larger predators. Our study illustrates how season, food availability, temperature, and oxygen can interact to shape community structure in a seasonally hypoxic habitat.     

Urban stormwater quality I. Hillcrest,Hamilton, New Zealand

Water quality parameters associated with siltation (non‐volatile and volatile suspended solids), oxygen depletion (chemical and biochemical oxygen demand), nutrient enrichment (N, P), toxicity (Pb, Zn, Cu, Cr, Ni, Cd), and human pathogenic micro‐organisms (coliforms, faecal coliforms, faecal streptococci) were measured in baseflow and stormflow from a residential catchment in Hamilton, New Zealand, from November 1979 to December 1981. A macro‐invertebrate survey was conducted. All parameters, except nitrogen, were predominantly associated with particulate material, and closely followed suspended solids behaviour during storm runoff. The concentrations of these particulate parameters are linearly related to suspended solid concentrations, which implies a reasonable consistency in the particulate source material, probably attributable to the uniform stable land use. The runoff was enriched with nitrate (from septic tank seepage) and the particles by Zn, Pb, and Cu. There was little or no enrichment of the particulates with phosphorus, nitrogen, organic matter, Cr, or Ni relative to catchment soils. Ni, Cr, and Cd were generally below detection limits. Dissolved reactive phosphorus and NH₄ ⁺‐N levels were low and unimportant in total P or N leaving the catchment. Most organic matter was particulate and only slowly degraded, and consequently the biological oxygen demand was only a small fraction (c. 13%) of chemical oxygen demand. Interpretation of the water quality data allows some tentative predictions to be made of potential receiving water impacts. It is doubtful that urban runoff will cause significant oxygen depletion, although the high level of organic‐rich particulate material could lead to a deterioration of receiving water sediments and affect benthic invertebrates. Urban runoff may be an important source of nutrients, but (apart from nitrate) its importance depends on the amount of suspended material in the runoff rather than increased input of nutrients from urban‐related activities. Bacterial counts indicate a poor water quality. The impact of metals will depend largely on the bioavailability of the particulate‐bound fraction. The key to the understanding of transport, treatment, and impact of most potential pollutants in urban runoff is probably their association with particulate materials.     

Water quality in a polluted lowland stream with chronically depressed dissolved oxygen: Causes and effects

Abstract

The Whangamaire Stream (North Island, New Zealand) has high concentrations of nitrate nitrogen (NO^? ₃‐N), biochemical oxygen demand (BOD₅), and Kjeldahl nitrogen (TKN) as a result of catchment land use practices. The lower reaches of the stream drain intensively farmed land and have dissolved oxygen (DO) levels of 10–50% saturation. The dominant riparian vegetation, Apium nodiflorum, provides a large organic loading by intercepting nutrients in run‐off and then decaying in the stream channel. Water quality and reaeration aspects of the stream were studied in order to explain the observed low DO levels. Measurements of the reaeration coefficient at 20°C, K₂ ²⁰, using methyl chloride (CH₃Cl) as a gas tracer, yielded values of 1.1–3.0 d^?1 for the upper part of the study reach and 15.5–16.2 d^?1 for the lower reach (overall average 12.5 ± 2.5 d^?1). These were in agreement with values inferred from single‐station diurnal curve analysis, which also showed that respiration was dominant in the lower reach where photo‐synthetic activity was inhibited by shade. The relatively large reaeration coefficients ensure that parts of the stream do not become anoxic at night time. Better riparian management and reduced nutrient inputs are likely to improve stream water quality.     

Use of an optical oxygen sensor to measure dissolved oxygen in seawater

The use of an optical oxygen sensor to measure dissolved oxygen in seawater was investigated. The sensor is based on the dynamic quenching of an oxygen-sensitive fluorochrome embedded in the tip. Dissolved oxygen in seawater samples collected from eight stations at depths ranging from 3000 to 6000 m was analyzed both with the optical sensor and by the Winkler titration method. The two sets of data did not differ significantly. The stability and simplicity of the method and the good agreement of the results with those of the titration method indicate that the sensor would be useful for fieldwork.     

秋季东海溶解态和颗粒态氨基酸的分布与组成*

本文对2012年秋季中国东海31个站位的海水样品中溶解态氨基酸（THAA）和颗粒态氨基酸（PAA）的分布与组成进行了研究。结果表明：表层海水中溶解游离氨基酸(DFAA)的平均浓度为0.12±0.04 μmol/L (0.06~0.19 μmol/L),溶解结合氨基酸(DCAA)的平均浓度为0.61±0.51 μmol/L (0.15~1.79 μmol/L),PAA的平均浓度为0.11±0.06 μmol/L (0.02~0.27 μmol/L)。THAA的水平分布特点大致为近岸高、远岸低;PAA的水平分布特点是近岸海域向远海海域分布呈现逐渐减小的趋势。THAA的垂直分布特点是由表层向底层逐渐降低。DCAA、PAA与Chl-a有很好的相关性,而DFAA与Chl-a的相关性不明显。东海表层海水中THAA的主要组分是天门冬氨酸、谷氨酸、丝氨酸、甘氨酸、苏氨酸及丙氨酸,PAA的主要组分是天门冬氨酸、谷氨酸、丝氨酸、甘氨酸、丙氨酸及亮氨酸。在表层海水中氨基酸是作为一个整体而对海洋生物地球化学过程产生影响的。     

长江口外浮游植物死亡释放溶解有机质的降解及其溶氧消耗

浮游植物光合作用产生的溶解有机质(dissolved organic matter,DOM)是海洋中溶解有机质的重要来源,浮游植物死亡后释放的新鲜溶解有机质活性高、数量大、生物可利用性高,其降解过程中对溶解氧(dissolved oxygen,DO)的消耗显著。但到目前为止,对此类溶解有机质的降解过程以及其耗氧情况还鲜有研究。本文基于2013年8月东海航次,对浮游植物(硅藻为主)死亡后释放的新鲜有机质进行人工受控培养,研究其降解过程及对DO的消耗,并评估该降解过程对低氧现象形成的贡献。研究发现:培养体系中溶解有机碳(dissolved organic carbon,DOC)和DO浓度皆随时间呈指数下降,总溶解态碳水化合物(total carbohydrate,TCHO)也出现明显降解;体系的初始DOC浓度越高,降解速率常数k(DOC)、k(DO)越大,k(DOC)受DOC浓度、活性以及DO浓度的影响;培养过程中细菌丰度明显增加,添加Hg Cl2的对比实验表明细菌在降解过程中起到重要作用。本文的研究结果表明,浮游植物死亡后释放的溶解有机质的快速降解及其对溶解氧的消耗,对长江口低氧环境的促成具有重要意义。     

CMIP5地球系统模式溶解氧模拟结果分析

本文基于常用的统计方法,通过与WOA09观测的海洋溶解氧浓度数据进行比较,定量地评估了9个CMIP5地球系统模式在历史排放试验中海洋溶解氧气候态特征的模拟能力。在海表,由于地球系统模式均能很好地模拟海表温度（SST）,模式模拟的海表溶解氧浓度分布与观测一致,模拟结果无论是全球平均浓度偏差还是均方根误差均接近0,空间相关系数与标准偏差接近1。在海洋中层以及深层这些重要水团所在的区域,各模式的模拟能力则差异较大,尤其在溶解氧低值区（OMZs）所在的500m到1000m,各模式均出现全球平均偏差、均方根误差的极大值以及空间相关系数的极小值。在海洋内部,模式偏差的原因比较复杂。经向翻转环流和颗粒有机碳通量均对模式的偏差有贡献。分析结果表明物理场偏差对溶解氧偏差的贡献较大。一些重要水团,比如北大西洋深水,南极底层水以及北太平洋中层水在极大程度上影响了溶解氧在这些海区的分布。需要指出的是,虽然在海洋内部各模式模拟的溶解氧浓度偏差较大,但是多模式平均结果却能表现出与观测较好的一致性。     

178Hz正弦波对刺参行为、呼吸及免疫应答的影响

根据山东荣成沿岸风电机组产生的声波范围选取其中178Hz的峰值声音,声压级控制于(85±5)d B,在实验室水槽中,采用实验生态学方法研究了178Hz声波影响下的刺参(Apostichopus japonicus)幼参的行为反应、耗氧率以及体腔液抗氧化酶(CAT、SOD)浓度的变化。通过平均聚集率的变化比较,发现刺参对178Hz的声波胁迫环境的行为反应敏感;利用空瓶法测得幼参耗氧率显著低于对照组(P0.05);通过测定刺参体腔液免疫活性发现在该频率声波干扰下的刺参CAT活性显著高于对照组(P0.05),而SOD活性于对照组差异不明显(P0.05)。研究结果说明声波对刺参幼参的呼吸和免疫会产生明显影响,可为我国近海刺参养殖和风电发展策略提供参考。