scholarly journals Oxygenation of anoxic sediments triggers hatching of zooplankton eggs

2015 ◽  
Vol 282 (1817) ◽  
pp. 20152025 ◽  
Author(s):  
Elias Broman ◽  
Martin Brüsin ◽  
Mark Dopson ◽  
Samuel Hylander

Many coastal marine systems have extensive areas with anoxic sediments and it is not well known how these conditions affect the benthic–pelagic coupling. Zooplankton lay their eggs in the pelagic zone, and some sink and lie dormant in the sediment, before hatched zooplankton return to the water column. In this study, we investigated how oxygenation of long-term anoxic sediments affects the hatching frequency of dormant zooplankton eggs. Anoxic sediments from the brackish Baltic Sea were sampled and incubated for 26 days with constant aeration whereby, the sediment surface and the overlying water were turned oxic. Newly hatched rotifers and copepod nauplii (juveniles) were observed after 5 and 8 days, respectively. Approximately 1.5 × 10 5 nauplii m −2 emerged from sediment turned oxic compared with 0.02 × 10 5 m −2 from controls maintained anoxic. This study demonstrated that re-oxygenation of anoxic sediments activated a large pool of buried zooplankton eggs, strengthening the benthic–pelagic coupling of the system. Modelling of the studied anoxic zone suggested that a substantial part of the pelagic copepod population can derive from hatching of dormant eggs. We suggest that this process should be included in future studies to understand population dynamics and carbon flows in marine pelagic systems.

2004 ◽  
Vol 64 (2) ◽  
pp. 283-288 ◽  
Author(s):  
E. V. Pardo ◽  
A. C. Z. Amaral

Observations of the feeding behavior of Cirriformia filigera (Delle Chiaje, 1825) (Annelida: Polychaeta) from the intertidal zone of São Francisco and Engenho D'água beaches (São Sebastião, State of São Paulo) were made in the laboratory. This species, like other cirratulids, is a deposit feeder, feeding mainly on sediment surface with the aid of its grooved and ciliated palps, which are used to capture food particles. The worm lies just beneath the substrate surface in a J-shaped tube. When feeding, it extends up to 4 palps over the sediment surface, capturing food particles which pass down the groove of each palp directly to the mouth. Only fine sand grains are ingested. The worm frequently extends 4 branchial filaments into the overlying water for aeration. When it moves with the prostomium sideways, it collects and transports sand grains that pass backwards along its ventral region until reaching the middle part of its body. Next, the parapodia and palps move the sand grains to the dorsal posterior end of the animal, covering this area with sand. Some sand grains are also ingested as the worm moves.


1993 ◽  
Vol 50 (8) ◽  
pp. 1794-1800 ◽  
Author(s):  
Charles Gobeil ◽  
Daniel Cossa

The concentration of dissolved mercury in the pore water of Laurentian Trough sediments varies between the detection limit (2.5 pM) and 64 pM, up to an order of magnitude enriched relative to the overlying water. Dissolved mercury is low near the sediment surface, increases with depth to 5 cm, and then decreases with further depth. Redistribution of remobilized mercury within the sediment column is, however, insufficient to explain the observed depth variations in mercury concentration. In the Lower St. Lawrence Estuary, the vertical profiles of mercury in trough sediments tend to be consistent with the chronology of mercury discharges from chlor-alkali plants located in the St. Lawrence drainage basin. The total amount of anthropogenic mercury in sediments deposited below the 200-m isobath in the entire lower St. Lawrence Estuary since the beginning of industrialization is estimated as 170 ± 85 × 103 kg, about six times the amount of natural mercury that has accumulated during the same period. Near the seaward end of the Trough in the Gulf of St. Lawrence, sedimentary mercury concentrations are much lower than in the Estuary, with a significant portion of the anthropogenic mercury deposited in the sediments probably coming from the atmosphere.


1999 ◽  
Vol 50 (6) ◽  
pp. 557 ◽  
Author(s):  
Christopher M. Burke

Port Phillip Bay is a large, shallow, semi-enclosed bay in south-eastern Australia. Micro- electrodes were used to measure profiles of oxygen concentration in sediment cores taken from nine sites in the bay in January and February 1994. The effects of sediment surface topography, flow rate of the overlying water and irradiance on the distribution of oxygen in the sediments, and on the molecular diffusive fluxes of oxygen, were determined. Oxygen typically penetrated ≤3 mm into the sediment. Deeper penetration occurred when oxygen was photosynthetically produced in situ. In most cores the sediments consumed oxygen. Molecular diffusive fluxes of oxygen, determined from the gradient of oxygen in the DBL, were compared with fluxes modelled from the sediment gradient of oxygen. The modelled diffusive fluxes are considered to give better estimates of the diffusive fluxes in situ. Modelled fluxes ranged from 1.5 to 28.5 mmol O2 m–2 day–1, which was 43% (s.d. = 36%, n = 16) of the total flux at each site. Cores from two sites demonstrated efflux of oxygen, up to 71 mmol O2 m–2 day–1, as a result of photosynthesis in situ. The high degree of variability in oxygen fluxes within cores demonstrates the dynamism of oxygen cycling in these sediments.


1995 ◽  
Vol 46 (1) ◽  
pp. 19 ◽  
Author(s):  
W Petersen ◽  
K Wallman ◽  
L Pinglin ◽  
F Schroeder ◽  
HD Knauth

The exchange processes at the sediment-water interface can significantly influence the transport of trace contaminants in a river. In order to investigate the importance of these processes in the tidal part of the River Elbe, a laboratory 'simulation' apparatus (LABOSI) was used that allows the incubation of undisturbed sediment cores with a relatively large area (1700 cm²) in a closed system under defined conditions (temperature, pH, pE, etc.). Together with measured depth profiles of the pore-water and the solids of the incubated cores before and after the experiment, this method allows all relevant processes to be investigated in all three phases (sediment, overlying water, gas) simultaneously. Under oxic conditions, a flux of heavy metals (Cu, Cd , Zn) into the water phase was observed as a result of the mineralization of organic matter in the thin oxic layer of the sediment (thickness about 3 mm) as well as a flux of manganese caused by diffusion from deeper anoxic layers. Up to 40% of Cd, Zn and Ni and 15% of Zn deposited in the sediment by settling of contaminated suspended particulate matter can be remobilized from the sediment surface by the processes of early diagenesis. Within 14 days, an enrichment of arsenic in the sediment surface caused by diffusion from deeper anoxic layers could be detected. Under anoxic conditions and when the other electron acceptors were consumed, Fe(II) was released and accompanied by a strong remobilization of As, Co and Cr and an accelerated release of Mn(II). This release was soon stopped when the water phase became oxic again, and the trace elements were removed from the water phase by co-precipitation andlor adsorption on the freshly formed hydrous ferric oxides.


2016 ◽  
Vol 75 (2) ◽  
pp. 418-426
Author(s):  
Rathnayake M. L. D. Rathnayake ◽  
Shogo Sugahara ◽  
Hideaki Maki ◽  
Gen Kanaya ◽  
Yasushi Seike ◽  
...  

Bottom hypoxia and consequential hydrogen sulfide (H2S) release from sediment in eutrophic estuaries is a major global environmental issue. We investigated dissolved oxygen, pH and H2S concentration profiles with microsensors and by sectioning sediment cores followed by colorimetric analysis. The results of these analyses were then compared with the physicochemical properties of the bottom water and sediment samples to determine their relationships with H2S production in sediment. High organic matter and fine particle composition of the sediment reduced the oxidation-reduction potential, stimulating H2S production. Use of a microsensor enabled measurement of H2S concentration profiles with submillimetre resolution, whereas the conventional sediment-sectioning method gave H2S measurements with a spatial resolution of 10 mm. Furthermore, microsensor measurements revealed H2S consumption occurring at the sediment surface in both the microbial mat and the sediment anoxic layer, which were not observed with sectioning. This H2S consumption prevented H2S release into the overlying water. However, the microsensor measurements had the potential to underestimate H2S concentrations. We propose that a combination of several techniques to measure microbial activity and determine its relationships with physicochemical properties of the sediment is essential to understanding the sulfur cycle under hypoxic conditions in eutrophic sediments.


2020 ◽  
Vol 643 ◽  
pp. 21-31
Author(s):  
N Deldicq ◽  
L Seuront ◽  
D Langlet ◽  
VMP Bouchet

The assessment of behavioural traits of marine organisms is increasingly recognized as a key issue to understanding their role in ecosystem processes such as bioturbation and nutrient cycling. The movement ability of intertidal foraminifera suggest that they may have a role, yet to be quantified, in benthic-pelagic coupling through their movement on the sediment surface, at the sediment-water interface and within the sediment. In this context, we investigated the behavioural traits of 5 benthic foraminiferal species typical of European temperate mudflats under standardized trophic light and temperature conditions. Behavioural traits related to motion of Ammonia tepida, Haynesina germanica, Cribroelphidium williamsoni, Miliammina fusca and Quinqueloculina seminula were assessed through their travelled distance, velocity, tortuosity of the path, position in the sediment and activity index. By analogy with macrofauna bioturbation functional groups, we describe the studied foraminifera as biodiffusor species with 3 sub-groups defined according to their vertical position in the sediment. C. williamsoni belongs to the epifaunal-biodiffusors, A. tepida and H. germanica belong to the surficial-biodiffusors, and Q. seminula and M. fusca are considered gallery-biodiffusors. Our results further suggest that features such as velocity, activity and tortuosity may mediate sediment-mixing intensity. Therefore, Q. seminula, H. germanica and C. williamsoni, which are the most active species, would have a larger effect on particle reworking rates than the less active A. tepida and M. fusca. Our results suggest that benthic foraminifera may play an underestimated role in bioturbation processes.


1984 ◽  
Vol 41 (11) ◽  
pp. 1609-1617 ◽  
Author(s):  
A. J. Twinch ◽  
R. H. Peters

The soluble phosphate equilibrium between aerobic sediment and overlying water was examined in intact cores of marginal sediment and water from Lake Memphremagog. Radiotracer experiments demonstrated a dynamic phosphate exchange between sediments and water under steady-state conditions. Perturbations of this equilibrium in batch and continuous-flow systems show that aerobic sediment can act as a phosphate source or sink, depending on the phosphate concentration of the overlying water. The existence of an oxidized microzone on the sediment surface does not preclude phosphate release when concentrations in the overlying water drop below the equilibrium concentration. Under natural conditions, soluble reactive phosphorus concentrations in the surface waters of Lake Memphremagog are always lower than the equilibrium concentrations measured in this study. This suggests that aerobic marginal sediments may serve as a phosphate source in lakes where algal demand maintains low levels of soluble phosphate in the water.


2017 ◽  
Vol 4 (2) ◽  
pp. 201-226
Author(s):  
Soner Tauscher

Avrupa ülkelerinin alışık olduğu düzenli işçi göçü ve kontrollü sığınmacı alımı Suriye iç savaşının üst düzeye ulaştığı 2013/2014 yılından itibaren önemli bir değişim göstermektedir. Avrupa Birliği, kuruluşundan bu yana en yoğun mülteci göçüyle karşılaşmaktadır. Yaşanan bu kontrolsüz ve zorunlu göçe Avrupa toplumları ve devletleri hazırlıksız yakalanmıştır. Mülteci krizini ekonomik olarak fırsata çevirmek isteyen Almanya ise göçmenler için 2015 yazından itibaren açık kapı politikası uygulamaya başlamıştır. Ancak uygulanan açık kapı politikası Alman toplumunun azımsanmayacak bir kesiminde mültecilere ve Müslümanlara yönelik ağır ve şiddetli bir karşı kampanya ortaya çıkardı. Mülteciler ve Müslümanlar aşırı sağ toplumsal hareketlerin gösterilerinde “tecavüzcü”, “işgalci”, “kriminal dolandırıcılar” vb. sıfatlar ile birlikte anılmakta, medya da bu söylemlerin taşıyıcılığını yaparak kamusallaşmasını sağlamaktadır. Böylece aşırı sağı desteklemeyen, apolitik, ya da sığınmacılara karşı hoşgörülü davranan toplum kesimlerinde kamuoyu oluşturularak sığınmacı ve göçmenlere karşı olumsuz algı gündemde tutulmakta, politik olanın merkezine yerleştirilmektedir. Bu çalışmada öncelikle göçmenlere karşı aşırı sağ toplumsal hareketlerin oluşturduğu olumsuz söylemin McCombs ve Shaw’un Gündem Belirleme Kuramı (Agenda Setting Function) bağlamında medya tarafından siyasetin merkezine nasıl oturtulduğu tartışılacaktır. Ayrıca gündemde tutulan mültecilere yönelik olumsuz söylemin gerçeği yansıtıp yansıtmadığı, göçmenlerin ve sığınmacıların biyolojik Almanlardan daha çok suça meyilli olup olmadığı oluşturulan soyut söylemlerden ziyade Almanya İçişleri Bakanlığı’nın yıllık olarak yayınladığı Emniyet Suç İstatistikleri temel alınarak incelenecektir.ABSTRACT IN ENGLISHFar right movements in Germany and evaluation of media discourse of criminal immigrant in the light of official documentsFlows of regular worker migration and regular asylum seekers, of whom European countries are familiar, have significantly changed since 2013/2014 when the civil war of Syria reached its peak. The European Union face probably the most intensive refugee migration since its establishment. European societies and states have not been prepared for this uncontrolled and compulsory immigration. Germany seem to want to turn the refugee crisis into an economic opportunity as evident in their open door policy since the summer of 2015. However, implementation of open-door policy has led a substantial part of German society to a strong campaign against the refugees and Muslims. Refugees and Muslims are referred to as “rapists”, “invaders”, “criminal fraudsters”, and so on in demonstrations of far right movements and media has helped disseminating these discourses. Hence, this manipulated and hateful discourse tries to gain support from the segment of society wh normally does not support far right and often apolitical, or tolerant towards asylum seekers. In this study, the ways in which the negative discourse of far right social movements against immigrants is brought to the centre of the political agenda by media is analysed using the agenda setting framework by McCombs and Shaw. Then, the claims that immigrants are involved in crime, or they are prone to be criminals are analysed and contrasted with the data obtained from the annual Crime and Safety Reports of the German Ministry of the Interior.


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