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Showing 1 - 200 of 2341 Journals sorted alphabetically
3D Research     Hybrid Journal   (Followers: 19, SJR: 0.214, h-index: 10)
4OR: A Quarterly J. of Operations Research     Hybrid Journal   (Followers: 9, SJR: 1.073, h-index: 25)
AAPS J.     Hybrid Journal   (Followers: 17, SJR: 1.192, h-index: 74)
AAPS PharmSciTech     Hybrid Journal   (Followers: 6, SJR: 0.718, h-index: 54)
Abdominal Imaging     Hybrid Journal   (Followers: 16, SJR: 0.723, h-index: 60)
Abhandlungen aus dem Mathematischen Seminar der Universitat Hamburg     Hybrid Journal   (Followers: 2, SJR: 0.447, h-index: 12)
Academic Psychiatry     Full-text available via subscription   (Followers: 22, SJR: 0.492, h-index: 32)
Academic Questions     Hybrid Journal   (Followers: 7, SJR: 0.135, h-index: 6)
Accreditation and Quality Assurance: J. for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 26, SJR: 0.378, h-index: 30)
Acoustical Physics     Hybrid Journal   (Followers: 10, SJR: 0.355, h-index: 20)
Acoustics Australia     Hybrid Journal  
Acta Analytica     Hybrid Journal   (Followers: 7, SJR: 0.387, h-index: 6)
Acta Applicandae Mathematicae     Hybrid Journal   (Followers: 1, SJR: 0.624, h-index: 34)
Acta Biotheoretica     Hybrid Journal   (Followers: 5, SJR: 0.419, h-index: 25)
Acta Diabetologica     Hybrid Journal   (Followers: 12, SJR: 1.318, h-index: 46)
Acta Endoscopica     Hybrid Journal   (Followers: 1, SJR: 0.113, h-index: 8)
acta ethologica     Hybrid Journal   (Followers: 4, SJR: 0.465, h-index: 23)
Acta Geochimica     Hybrid Journal   (Followers: 3)
Acta Geodaetica et Geophysica     Hybrid Journal   (Followers: 1, SJR: 0.294, h-index: 13)
Acta Geotechnica     Hybrid Journal   (Followers: 6, SJR: 1.818, h-index: 22)
Acta Informatica     Hybrid Journal   (Followers: 5, SJR: 0.524, h-index: 32)
Acta Mathematica     Hybrid Journal   (Followers: 10, SJR: 8.021, h-index: 47)
Acta Mathematica Hungarica     Hybrid Journal   (Followers: 2, SJR: 0.53, h-index: 29)
Acta Mathematica Sinica, English Series     Hybrid Journal   (Followers: 5, SJR: 0.406, h-index: 30)
Acta Mathematica Vietnamica     Hybrid Journal   (SJR: 0.451, h-index: 5)
Acta Mathematicae Applicatae Sinica, English Series     Hybrid Journal   (SJR: 0.22, h-index: 20)
Acta Mechanica     Hybrid Journal   (Followers: 18, SJR: 0.898, h-index: 52)
Acta Mechanica Sinica     Hybrid Journal   (Followers: 4, SJR: 0.426, h-index: 29)
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 5, SJR: 0.525, h-index: 18)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3, SJR: 0.524, h-index: 14)
Acta Neurochirurgica     Hybrid Journal   (Followers: 6, SJR: 0.833, h-index: 73)
Acta Neurologica Belgica     Hybrid Journal   (SJR: 0.348, h-index: 27)
Acta Neuropathologica     Hybrid Journal   (Followers: 3, SJR: 6.61, h-index: 117)
Acta Oceanologica Sinica     Hybrid Journal   (Followers: 3, SJR: 0.295, h-index: 17)
Acta Parasitologica     Hybrid Journal   (Followers: 9, SJR: 0.581, h-index: 28)
Acta Physiologiae Plantarum     Hybrid Journal   (Followers: 2, SJR: 0.551, h-index: 39)
Acta Politica     Hybrid Journal   (Followers: 13, SJR: 0.658, h-index: 20)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 5, SJR: 0.103, h-index: 4)
ADHD Attention Deficit and Hyperactivity Disorders     Hybrid Journal   (Followers: 20, SJR: 0.871, h-index: 15)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 7)
Administration and Policy in Mental Health and Mental Health Services Research     Partially Free   (Followers: 14, SJR: 0.795, h-index: 40)
Adsorption     Hybrid Journal   (Followers: 4, SJR: 0.774, h-index: 52)
Advances in Applied Clifford Algebras     Hybrid Journal   (Followers: 3, SJR: 0.319, h-index: 15)
Advances in Atmospheric Sciences     Hybrid Journal   (Followers: 34, SJR: 0.959, h-index: 44)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 15, SJR: 1.255, h-index: 44)
Advances in Contraception     Hybrid Journal   (Followers: 2)
Advances in Data Analysis and Classification     Hybrid Journal   (Followers: 52, SJR: 1.113, h-index: 14)
Advances in Gerontology     Partially Free   (Followers: 8, SJR: 0.141, h-index: 3)
Advances in Health Sciences Education     Hybrid Journal   (Followers: 23, SJR: 1.397, h-index: 42)
Advances in Manufacturing     Hybrid Journal   (Followers: 3, SJR: 0.2, h-index: 4)
Advances in Polymer Science     Hybrid Journal   (Followers: 40, SJR: 0.637, h-index: 89)
Advances in Therapy     Hybrid Journal   (Followers: 5, SJR: 0.79, h-index: 44)
Aegean Review of the Law of the Sea and Maritime Law     Hybrid Journal   (Followers: 7)
Aequationes Mathematicae     Hybrid Journal   (Followers: 2, SJR: 0.882, h-index: 23)
Aerobiologia     Hybrid Journal   (Followers: 1, SJR: 0.511, h-index: 36)
Aesthetic Plastic Surgery     Hybrid Journal   (Followers: 8, SJR: 0.821, h-index: 49)
African Archaeological Review     Hybrid Journal   (Followers: 14, SJR: 0.612, h-index: 24)
Afrika Matematika     Hybrid Journal   (Followers: 1, SJR: 0.248, h-index: 6)
AGE     Hybrid Journal   (Followers: 7, SJR: 1.358, h-index: 33)
Ageing Intl.     Hybrid Journal   (Followers: 7, SJR: 0.337, h-index: 10)
Aggiornamenti CIO     Hybrid Journal   (Followers: 1)
Aging Clinical and Experimental Research     Hybrid Journal   (Followers: 3, SJR: 0.529, h-index: 55)
Agricultural Research     Hybrid Journal   (Followers: 3)
Agriculture and Human Values     Hybrid Journal   (Followers: 12, SJR: 1.197, h-index: 49)
Agroforestry Systems     Hybrid Journal   (Followers: 20, SJR: 0.64, h-index: 56)
Agronomy for Sustainable Development     Hybrid Journal   (Followers: 10, SJR: 1.732, h-index: 59)
AI & Society     Hybrid Journal   (Followers: 7, SJR: 0.171, h-index: 19)
AIDS and Behavior     Hybrid Journal   (Followers: 13, SJR: 2.006, h-index: 71)
Air Quality, Atmosphere & Health     Hybrid Journal   (Followers: 2, SJR: 0.706, h-index: 19)
Akupunktur & Aurikulomedizin     Full-text available via subscription   (Followers: 1)
Algebra and Logic     Hybrid Journal   (Followers: 2, SJR: 0.566, h-index: 18)
Algebra Universalis     Hybrid Journal   (Followers: 2, SJR: 0.388, h-index: 22)
Algebras and Representation Theory     Hybrid Journal   (Followers: 1, SJR: 0.868, h-index: 20)
Algorithmica     Hybrid Journal   (Followers: 7, SJR: 0.898, h-index: 56)
Allergo J.     Full-text available via subscription   (Followers: 1, SJR: 0.183, h-index: 20)
Allergo J. Intl.     Hybrid Journal   (Followers: 2)
Alpine Botany     Hybrid Journal   (Followers: 3, SJR: 0.729, h-index: 20)
ALTEX : Alternatives to Animal Experimentation     Open Access   (Followers: 3, SJR: 1.392, h-index: 32)
AMBIO     Hybrid Journal   (Followers: 14, SJR: 1.094, h-index: 87)
American J. of Cardiovascular Drugs     Hybrid Journal   (Followers: 10, SJR: 0.864, h-index: 39)
American J. of Community Psychology     Hybrid Journal   (Followers: 24, SJR: 1.237, h-index: 83)
American J. of Criminal Justice     Hybrid Journal   (Followers: 5, SJR: 0.634, h-index: 13)
American J. of Cultural Sociology     Hybrid Journal   (Followers: 11, SJR: 0.283, h-index: 3)
American J. of Dance Therapy     Hybrid Journal   (Followers: 4, SJR: 0.175, h-index: 13)
American J. of Potato Research     Hybrid Journal   (Followers: 2, SJR: 0.558, h-index: 35)
American J. of Psychoanalysis     Hybrid Journal   (Followers: 21, SJR: 0.293, h-index: 13)
American Sociologist     Hybrid Journal   (Followers: 11, SJR: 0.18, h-index: 13)
Amino Acids     Hybrid Journal   (Followers: 7, SJR: 1.362, h-index: 83)
AMS Review     Partially Free   (Followers: 4)
Analog Integrated Circuits and Signal Processing     Hybrid Journal   (Followers: 5, SJR: 0.21, h-index: 37)
Analysis and Mathematical Physics     Hybrid Journal   (Followers: 4, SJR: 0.665, h-index: 7)
Analysis in Theory and Applications     Hybrid Journal  
Analysis of Verbal Behavior     Hybrid Journal   (Followers: 4)
Analytical and Bioanalytical Chemistry     Hybrid Journal   (Followers: 28, SJR: 1.096, h-index: 123)
Anatomical Science Intl.     Hybrid Journal   (Followers: 2, SJR: 0.301, h-index: 26)
Angewandte Schmerztherapie und Palliativmedizin     Hybrid Journal  
Angiogenesis     Hybrid Journal   (Followers: 3, SJR: 2.212, h-index: 69)
Animal Cognition     Hybrid Journal   (Followers: 14, SJR: 1.122, h-index: 55)
Annales françaises de médecine d'urgence     Hybrid Journal   (Followers: 1, SJR: 0.156, h-index: 4)
Annales Henri Poincaré     Hybrid Journal   (Followers: 3, SJR: 1.377, h-index: 32)
Annales mathématiques du Québec     Hybrid Journal   (Followers: 4)
Annali dell'Universita di Ferrara     Hybrid Journal   (SJR: 0.504, h-index: 14)
Annali di Matematica Pura ed Applicata     Hybrid Journal   (Followers: 1, SJR: 1.167, h-index: 26)
Annals of Behavioral Medicine     Hybrid Journal   (Followers: 11, SJR: 2.112, h-index: 98)
Annals of Biomedical Engineering     Hybrid Journal   (Followers: 18, SJR: 1.182, h-index: 94)
Annals of Combinatorics     Hybrid Journal   (Followers: 3, SJR: 0.849, h-index: 15)
Annals of Data Science     Hybrid Journal   (Followers: 8)
Annals of Dyslexia     Hybrid Journal   (Followers: 9, SJR: 0.857, h-index: 40)
Annals of Finance     Hybrid Journal   (Followers: 27, SJR: 0.686, h-index: 14)
Annals of Forest Science     Hybrid Journal   (Followers: 4, SJR: 0.929, h-index: 57)
Annals of Global Analysis and Geometry     Hybrid Journal   (Followers: 1, SJR: 1.136, h-index: 23)
Annals of Hematology     Hybrid Journal   (Followers: 13, SJR: 1.117, h-index: 62)
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 6, SJR: 0.593, h-index: 42)
Annals of Microbiology     Hybrid Journal   (Followers: 9, SJR: 0.402, h-index: 26)
Annals of Nuclear Medicine     Hybrid Journal   (Followers: 5, SJR: 0.68, h-index: 45)
Annals of Operations Research     Hybrid Journal   (Followers: 8, SJR: 1.186, h-index: 78)
Annals of Regional Science     Hybrid Journal   (Followers: 7, SJR: 0.405, h-index: 42)
Annals of Software Engineering     Hybrid Journal   (Followers: 12)
Annals of Solid and Structural Mechanics     Hybrid Journal   (Followers: 9, SJR: 0.553, h-index: 8)
Annals of Surgical Oncology     Hybrid Journal   (Followers: 11, SJR: 1.902, h-index: 127)
Annals of Telecommunications     Hybrid Journal   (Followers: 7, SJR: 0.315, h-index: 25)
Annals of the Institute of Statistical Mathematics     Hybrid Journal   (Followers: 1, SJR: 0.931, h-index: 31)
Antonie van Leeuwenhoek     Hybrid Journal   (Followers: 5, SJR: 0.992, h-index: 87)
Apidologie     Hybrid Journal   (Followers: 4, SJR: 1.14, h-index: 57)
APOPTOSIS     Hybrid Journal   (Followers: 7, SJR: 1.554, h-index: 87)
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2, SJR: 0.354, h-index: 27)
Applications of Mathematics     Hybrid Journal   (Followers: 1, SJR: 0.274, h-index: 20)
Applied Biochemistry and Biotechnology     Hybrid Journal   (Followers: 44, SJR: 0.575, h-index: 80)
Applied Biochemistry and Microbiology     Hybrid Journal   (Followers: 17, SJR: 0.267, h-index: 26)
Applied Categorical Structures     Hybrid Journal   (Followers: 2, SJR: 0.361, h-index: 21)
Applied Composite Materials     Hybrid Journal   (Followers: 45, SJR: 0.705, h-index: 35)
Applied Entomology and Zoology     Partially Free   (Followers: 2, SJR: 0.554, h-index: 34)
Applied Geomatics     Hybrid Journal   (Followers: 3, SJR: 0.323, h-index: 9)
Applied Geophysics     Hybrid Journal   (Followers: 7, SJR: 0.541, h-index: 13)
Applied Intelligence     Hybrid Journal   (Followers: 14, SJR: 0.777, h-index: 43)
Applied Magnetic Resonance     Hybrid Journal   (Followers: 3, SJR: 0.358, h-index: 34)
Applied Mathematics & Optimization     Hybrid Journal   (Followers: 4, SJR: 0.955, h-index: 33)
Applied Mathematics - A J. of Chinese Universities     Hybrid Journal   (SJR: 0.275, h-index: 8)
Applied Mathematics and Mechanics     Hybrid Journal   (Followers: 4, SJR: 0.37, h-index: 26)
Applied Microbiology and Biotechnology     Hybrid Journal   (Followers: 61, SJR: 1.262, h-index: 161)
Applied Physics A     Hybrid Journal   (Followers: 7, SJR: 0.535, h-index: 121)
Applied Physics B: Lasers and Optics     Hybrid Journal   (Followers: 23, SJR: 0.983, h-index: 104)
Applied Psychophysiology and Biofeedback     Hybrid Journal   (Followers: 6, SJR: 0.677, h-index: 47)
Applied Research in Quality of Life     Hybrid Journal   (Followers: 10, SJR: 0.288, h-index: 15)
Applied Solar Energy     Hybrid Journal   (Followers: 15, SJR: 0.251, h-index: 6)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4, SJR: 0.351, h-index: 9)
Aquaculture Intl.     Hybrid Journal   (Followers: 21, SJR: 0.613, h-index: 40)
Aquarium Sciences and Conservation     Hybrid Journal   (Followers: 1)
Aquatic Ecology     Hybrid Journal   (Followers: 30, SJR: 0.646, h-index: 44)
Aquatic Geochemistry     Hybrid Journal   (Followers: 3, SJR: 0.764, h-index: 39)
Aquatic Sciences     Hybrid Journal   (Followers: 12, SJR: 1.172, h-index: 53)
Arabian J. for Science and Engineering     Hybrid Journal   (Followers: 5, SJR: 0.345, h-index: 20)
Arabian J. of Geosciences     Hybrid Journal   (Followers: 1, SJR: 0.417, h-index: 16)
Archaeological and Anthropological Sciences     Hybrid Journal   (Followers: 21, SJR: 1.056, h-index: 15)
Archaeologies     Hybrid Journal   (Followers: 12, SJR: 0.397, h-index: 13)
Archiv der Mathematik     Hybrid Journal   (Followers: 1, SJR: 0.597, h-index: 29)
Archival Science     Hybrid Journal   (Followers: 51, SJR: 0.804, h-index: 22)
Archive for History of Exact Sciences     Hybrid Journal   (Followers: 7, SJR: 0.28, h-index: 15)
Archive for Mathematical Logic     Hybrid Journal   (Followers: 1, SJR: 0.946, h-index: 23)
Archive for Rational Mechanics and Analysis     Hybrid Journal   (SJR: 4.091, h-index: 66)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 4, SJR: 0.865, h-index: 40)
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 4, SJR: 2.841, h-index: 40)
Archives of Dermatological Research     Hybrid Journal   (Followers: 6, SJR: 0.9, h-index: 65)
Archives of Environmental Contamination and Toxicology     Hybrid Journal   (Followers: 10, SJR: 0.846, h-index: 84)
Archives of Gynecology and Obstetrics     Hybrid Journal   (Followers: 16, SJR: 0.695, h-index: 47)
Archives of Microbiology     Hybrid Journal   (Followers: 8, SJR: 0.702, h-index: 85)
Archives of Orthopaedic and Trauma Surgery     Hybrid Journal   (Followers: 8, SJR: 1.039, h-index: 56)
Archives of Osteoporosis     Hybrid Journal   (Followers: 2, SJR: 1.092, h-index: 13)
Archives of Sexual Behavior     Hybrid Journal   (Followers: 9, SJR: 1.198, h-index: 74)
Archives of Toxicology     Hybrid Journal   (Followers: 15, SJR: 1.595, h-index: 76)
Archives of Virology     Hybrid Journal   (Followers: 5, SJR: 1.086, h-index: 90)
Archives of Women's Mental Health     Hybrid Journal   (Followers: 13, SJR: 1.264, h-index: 50)
Archivio di Ortopedia e Reumatologia     Hybrid Journal  
Archivum Immunologiae et Therapiae Experimentalis     Hybrid Journal   (Followers: 2, SJR: 1.2, h-index: 42)
ArgoSpine News & J.     Hybrid Journal   (SJR: 0.102, h-index: 3)
Argumentation     Hybrid Journal   (Followers: 4, SJR: 0.295, h-index: 18)
Arid Ecosystems     Hybrid Journal   (Followers: 3)
Arkiv för Matematik     Hybrid Journal   (Followers: 1, SJR: 0.948, h-index: 22)
Arnold Mathematical J.     Hybrid Journal   (Followers: 1)
Arthropod-Plant Interactions     Hybrid Journal   (Followers: 2, SJR: 0.797, h-index: 17)
Arthroskopie     Hybrid Journal   (Followers: 1, SJR: 0.145, h-index: 8)
Artificial Intelligence and Law     Hybrid Journal   (Followers: 10, SJR: 0.288, h-index: 25)
Artificial Intelligence Review     Hybrid Journal   (Followers: 15, SJR: 0.948, h-index: 48)
Artificial Life and Robotics     Hybrid Journal   (Followers: 8, SJR: 0.231, h-index: 14)
Asia Europe J.     Hybrid Journal   (Followers: 4, SJR: 0.247, h-index: 9)
Asia Pacific Education Review     Hybrid Journal   (Followers: 9, SJR: 0.371, h-index: 17)
Asia Pacific J. of Management     Hybrid Journal   (Followers: 11, SJR: 1.676, h-index: 50)
Asia-Pacific Education Researcher     Hybrid Journal   (Followers: 11, SJR: 0.353, h-index: 13)
Asia-Pacific Financial Markets     Hybrid Journal   (Followers: 2, SJR: 0.19, h-index: 15)
Asia-Pacific J. of Atmospheric Sciences     Hybrid Journal   (Followers: 20, SJR: 1.006, h-index: 14)
Asian Business & Management     Hybrid Journal   (Followers: 7, SJR: 0.41, h-index: 10)
Asian J. of Business Ethics     Hybrid Journal   (Followers: 7)
Asian J. of Criminology     Hybrid Journal   (Followers: 5, SJR: 0.263, h-index: 8)
AStA Advances in Statistical Analysis     Hybrid Journal   (Followers: 2, SJR: 0.681, h-index: 15)
AStA Wirtschafts- und Sozialstatistisches Archiv     Hybrid Journal   (Followers: 5, SJR: 0.195, h-index: 5)
ästhetische dermatologie & kosmetologie     Full-text available via subscription  
Astronomy and Astrophysics Review     Hybrid Journal   (Followers: 21, SJR: 4.511, h-index: 44)
Astronomy Letters     Hybrid Journal   (Followers: 19, SJR: 0.58, h-index: 30)
Astronomy Reports     Hybrid Journal   (Followers: 12, SJR: 0.473, h-index: 23)
Astrophysical Bulletin     Hybrid Journal   (Followers: 2, SJR: 0.469, h-index: 11)

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Journal Cover Aquatic Geochemistry
  [SJR: 0.764]   [H-I: 39]   [3 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1573-1421 - ISSN (Online) 1380-6165
   Published by Springer-Verlag Homepage  [2341 journals]
  • The Speciation of Metals in Natural Waters
    • Authors: Denis Pierrot; Frank J. Millero
      Pages: 1 - 20
      Abstract: Abstract The equilibria and rates of reactions of trace metals in natural waters are affected by their speciation or the form of the metal in the solution phase. Many workers have shown, for example, that biological uptake (Anderson and Morel in Limnol Oceanogr 27:789–813, 1982), the toxicity (Sunda and Ferguson in Trace metals in seawater, Plenum Press, New York, 1983) as well as the solubility (Millero et al. in Mar Chem 50:21–39, 1995; Liu and Millero in Geochim Cosmochim Acta 63:3487–3497, 1999) are affected by the speciation. For example, Fe(II) and Mn(II) are biologically available for marine organisms, while Fe(III) and Mn(IV) are normally not available. The speciation of metals also affects the rates of oxidation (Millero in Geochim Cosmochim Acta 49:547–553, 1985, Res Trends Curr Top Sol Chem 1:141–169, 1994; Sharma and Millero in Geochim Cosmochim Acta 53:2269–2276, 1989; Vazquez et al. in Geophys Res Lett 16:1363–1366, 1989) and reduction (Res Trends Curr Top Sol Chem 1:141–169, 1994; Millero et al. in Mar Chem 36:71–83, 1991) of metals in natural waters. The ionic interactions of metals are controlled by interactions with inorganic (Cl−, OH−, CO3 2−, etc.) and organic ligands (e.g., Fulvic and Humic acids). The speciation of metals is also affected by the oxidation potential (Eh) and the pH in the solution. In this paper we have developed a Pitzer Model (Pitzer in J Phys Chem 77:268–277, 1973, Activity coefficients in electrolyte solutions, 2nd edn, CRC Press, Boca Raton, 1991) that can be used to determine the speciation of trace metals in seawater and other natural waters. It is based upon the Miami Pitzer Model (Millero and Pierrot in Aquatic Geochem 4:153–199, 1998) that has been shown to predict reliable activity coefficients for the major components of seawater. The computer code (Pierrot in Ph.D. Thesis, University of Miami, Miami, Florida, 2002) for these calculations is described in detail, in this paper. It has been used in an earlier paper (Millero and Pierrot in Chemistry of marine water and sediments, Springer, Berlin, 2002) and more recently used to examine the effect of pH on the speciation of metals in seawater (Millero et al. in Oceanography 22(4):72–85, 2009).
      PubDate: 2017-02-01
      DOI: 10.1007/s10498-016-9292-4
      Issue No: Vol. 23, No. 1 (2017)
  • Assessment of the Hydrogeochemical Processes Affecting Groundwater Quality
           in the Eocene Limestone Aquifer at the Desert Fringes of El Minia
           Governorate, Egypt
    • Authors: Reda G. M. Ibrahim; W. Berry Lyons
      Pages: 33 - 52
      Abstract: Abstract El Minia Governorate is within the Nile Valley and is surrounded by the Eocene limestone plateaus from the east and west. The present study focuses on the hydrogeochemistry of the Eocene limestone aquifer in both the eastern and western desert fringes of El Minia. Thirty groundwater samples from the Eocene aquifer (east and west of the Nile) and seven samples from post-Eocene aquifers in this area were analyzed to assess the groundwater geochemistry, isotopic compositions and the subsurface hydrology. Samples obtained from depths of 24–120 m were measured for major components, nutrients, oxygen-18, deuterium and carbon-13. The groundwater TDS (total dissolved solids) concentrations ranged from 530 to 2788 and 453 to 1903 mg/l at the western and eastern desert fringes, respectively. Values of Eocene aquifer water δ18O ranged from −8.31 to −0.44 and −2.07 to 0.55 ‰, and those of water δD ranged from −63.6 to −2.32 and −9.03 to 5.03 ‰ for the Eocene aquifer at the western and eastern side, respectively. Chemical analysis shows that the main chemical facies of the Eocene water are Ca–Mg–HCO3 and Ca–SO4. The chemical and isotopic data show that water–rock interaction (calcite dissolution and silicate weathering) and mixing between different water types control the major ion chemistry of Eocene aquifer water. The chemical composition of Eocene water has also evolved by evaporation and ion exchange. The present study indicates the need for regional chemical and isotopic study for the Eocene aquifer along the Nile Valley region to delineate the sources of recharge to this important aquifer.
      PubDate: 2017-02-01
      DOI: 10.1007/s10498-016-9298-y
      Issue No: Vol. 23, No. 1 (2017)
  • Sediment Biogeochemistry of Mesophotic Meadows of Calcifying Macroalgae
    • Authors: Francis J. Sansone; Heather L. Spalding; Celia M. Smith
      Abstract: Abstract Mesophotic (low light) sands were studied in Hawaiian coastal waters (39–204 m water depth) from O‘ahu to Kaho‘olawe by sampling inside and outside of extensive macroalgal meadows of chlorophytes Halimeda kanaloana and Udotea sp. during September 2004, December 2004, and November 2006. Porewater nutrient concentrations in these permeable sediments were comparable to those in nearshore sands and were highly elevated at sediment depths available to holdfasts of some algae (5–10 cm); maximum levels were 3.0 µM reactive phosphorus, 33 µM nitrate, 0.70 µM nitrite, 38 µM ammonium, and 130 µM silicic acid. Benthic material is calculated to be the major source of organic matter driving diagenesis in these sediments. Vegetated sediments appeared more oxidizing than unvegetated sediments, and the presence of macroalgae, particularly Halimeda, was generally associated with higher sediment dissolved inorganic carbon levels. Halimeda-vegetated sediments generally had low dissolved inorganic nitrogen (DIN) levels compared to the Udotea-vegetated and non-vegetated sediments, consistent with the net N loss indicated by sediment stoichiometric relationships. In contrast, Udotea-vegetated sediments showed minimal apparent algal DIN uptake.
      PubDate: 2017-03-30
      DOI: 10.1007/s10498-017-9315-9
  • Chemical Analysis of Gaet’ale, a Hypersaline Pond in Danakil Depression
           (Ethiopia): New Record for the Most Saline Water Body on Earth
    • Authors: Eduardo Pérez; Yonas Chebude
      Abstract: Abstract The chemical analysis of the water of Gaet’ale Pond, a small water body located in Danakil Depression, Ethiopia, resulted to be the most saline water body on earth with total dissolved solids (TDS) of 433 g kg−1. The composition of the water indicates the predominance of two main salts: CaCl2 and MgCl2 at a proportion of Ca:Mg = 3.1 (w/w). Traces of K+, Na+ and NO3 − are also detected, as well as Fe(III) complexes that give the water a characteristic yellow color. Density measurements, elemental analysis, thermogravimetrical analysis (TGA) and powder X-ray diffraction data are consistent with the composition and salinity determined. The water of this pond has a similar composition to Don Juan Pond, Antarctica, but a higher salinity, which can be explained in terms of temperature and solubility of the main components.
      PubDate: 2017-03-23
      DOI: 10.1007/s10498-017-9312-z
  • Evolution of Mg/Ca Ratios During Limestone Dissolution Under Epikarstic
    • Authors: Pavel Pracný; Jiří Faimon; Dalibor Všianský; Ludvík Kabelka
      Abstract: Abstract The Mg/Ca ratios in karst water are generally believed to comprise information on climate, and, being encoded in speleothems, they are utilized as paleoenvironmental proxy. However, the mechanism and dynamic of Mg release from limestone during dissolution is not well understood. A theoretical evolution of the Mg/Ca ratios during limestone dissolution under epikarstic conditions (T = 10 °C, \(\log P_{{{\text{CO}}_{2} }}\)  = −1.5) was studied via a dynamic model. The results were compared with (1) the dripwater data set collected in Punkva Caves (Moravian Karst, Czech Republic) during one-year period and (2) the published data from various locations worldwide. The modeling showed that the Mg/Ca ratios are governed by composition of Mg-calcite present in limestone. Two distinct stages in the dissolution dynamics were recognized: (1) an initial congruent dissolution with stoichiometric release of Ca and Mg and, subsequently, (2) an incongruent dissolution demonstrated by the gradual release of Mg with simultaneous Ca decrease via calcite precipitation. Additional identified factors influencing the reaction path and Mg/Ca ratio evolution were the dolomitic component of limestone and the ratio of limestone/solution boundary area to water volume. Finally, the water–rock interaction time controls the resulting Mg/Ca ratio in dripwater determining how far the dissolution proceeds along the reaction path. Thus, the study results indicate that Mg/Ca ratio depends on many factors in addition to climatic variables.
      PubDate: 2017-03-04
      DOI: 10.1007/s10498-017-9313-y
  • Lipid Biomarker Analysis of Suspended Particulate Matter from the Great
           Kwa River, SE Nigeria: Origins and Environmental Implications of Biogenic
           and Anthropogenic Organic Compounds
    • Authors: Bernd R. T. Simoneit; Oliva Pisani; Bassey O. Ekpo; Ebirien P. Fubara; Prince J. Nna; Okon D. Ekpa
      Abstract: Abstract Biomarkers found in natural waters, sediments, soils, fossils, crude oil, and coal can be unambiguously linked to specific precursors biosynthesized by biota. Petroleum and its refinery products carry their biomarker information into the environment when they are released by pollution. Lipid biomarkers can be used to assess the environmental status of an ecosystem and the degree to which it has been influenced by biogenic and anthropogenic inputs. The marine ecosystem of the southeastern Niger Delta of Nigeria is receiving new attention due to increased human and industrial development and the consequent potential health effects. Suspended particulate matter (SPM) from the Great Kwa River was characterized using biomarkers to assess such pollution. The total organic carbon contents of SPM from the river at low and high tide was 12–50% (avg 34.75%) and 16–28% (avg 24.25%), respectively. The lipid biomarkers identified using gas chromatography–mass spectrometry were mainly n-alkanes, n-alkan-2-ones, triterpenoids and minor amounts of aromatic compounds. The n-alkanes ranged from C 17 to C 35, with an odd/even predominance and C max > 27, indicating a mixed origin from higher plant wax, biodegraded detritus, and petroleum. The n-alkan-2-ones in most samples ranged from C 16 to C 33, with C max = 31, also supporting an input from vascular plants dominating the riparian zone along the river. The triterpenoids, mainly taraxerone, taraxerol, α- and β-amyrins, and friedelin, also derived from higher plants (angiosperms). Minor amounts of aromatic hydrocarbon derivatives from α- and β-amyrins were present and are likely the result of different diagenetic processes. The presence of trace fossil fuel-derived hopanes with an unresolved complex mixture of branched and cyclic hydrocarbons supported a minor petroleum product input to the SPM of the Great Kwa River.
      PubDate: 2017-02-04
      DOI: 10.1007/s10498-017-9311-0
  • Spatiotemporal Assessment of CO 2 –Carbonic Acid System Dynamics in a
           Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern
           Hawaiian Islands
    • Authors: Andrea K. Kealoha; Fred T. Mackenzie; Samuel E. Kahng; Randall K. Kosaki; Simone R. Alin; Christopher D. Winn
      Abstract: Abstract Observations of surface seawater fugacity of carbon dioxide (fCO2) and pH were collected over a period of several days at French Frigate Shoals (FFS) in the Northwestern Hawaiian Islands (NWHI) in order to gain an understanding of the natural spatiotemporal variability of the marine inorganic carbon system in a pristine coral reef ecosystem. These data show clear island-to-open ocean gradients in fCO2 and total alkalinity that can be measured 10–20 km offshore, indicating that metabolic processes influence the CO2–carbonic acid system over large areas of ocean surrounding FFS and by implication the islands and atolls of the NWHI. The magnitude and extent of this spatial gradient may be driven by a combination of physical and biogeochemical processes including reef water residence time, hydrodynamic forcing of currents and tidal flow, and metabolic processes that occur both on the reef and within the lagoon.
      PubDate: 2017-01-27
      DOI: 10.1007/s10498-017-9310-1
  • Decadal Change in Sediment Community Oxygen Consumption in the Abyssal
           Northeast Pacific
    • Authors: K. L. Smith; C. L. Huffard; A. D. Sherman; H. A. Ruhl
      Pages: 401 - 417
      Abstract: Abstract Long time-series studies are critical to assessing impacts of climate change on the marine carbon cycle. A 27-year time-series study in the abyssal northeast Pacific (Sta. M, 4000 m depth) has provided the first concurrent measurements of sinking particulate organic carbon supply (POC flux) and remineralization by the benthic community. Sediment community oxygen consumption (SCOC), an estimate of organic carbon remineralization, was measured in situ over daily to interannual periods with four different instruments. Daily averages of SCOC ranged from a low of 5.0 mg C m−2 day−1 in February 1991 to a high of 31.0 mg C m−2 day−1 in June 2012. POC flux estimated from sediment trap collections at 600 and 50 m above bottom ranged from 0.3 mg C m−2 day−1 in October 2013 to 32.0 mg C m−2 day−1 in June 2011. Monthly averages of SCOC and POC flux correlated significantly with no time lag. Over the long time series, yearly average POC flux accounted for 63 % of the estimated carbon demand of the benthic community. Long time-series studies of sediment community processes, particularly SCOC, have shown similar fluctuations with the flux of POC reaching the abyssal seafloor. SCOC quickly responds to changes in food supply and tracks POC flux. Yet, SCOC consistently exceeds POC flux as measured by sediment traps alone. The shortfall of ~37 % could be explained by sediment trap sampling artifacts over decadal scales including undersampling of large sinking particles. High-resolution measurements of SCOC are critical to developing a realistic carbon cycle model for the open ocean. Such input is essential to evaluate the impact of climate change on the oceanic carbon cycle, and the long-term influences on the sedimentation record.
      PubDate: 2016-12-01
      DOI: 10.1007/s10498-016-9293-3
      Issue No: Vol. 22, No. 5-6 (2016)
  • Using a Thermal Proxy to Examine Sediment–Water Exchange in
           Mid-Continental Shelf Sandy Sediments
    • Authors: William B. Savidge; Alicia Wilson; Gwendolyn Woodward
      Pages: 419 - 441
      Abstract: Abstract Fluid exchange across the sediment–water interface in a sandy open continental shelf setting was studied using heat as a tracer. Summertime tidal oscillation of cross-shelf thermal fronts on the South Atlantic Bight provided a sufficient signal at the sediment–water interface to trace the advective and conductive transport of heat into and out of the seabed, indicating rapid flushing of ocean water through the upper 10–40 cm of the sandy seafloor. A newly developed transport model was applied to the in situ temperature data set to estimate the extent to which heat was transported by advection rather than conduction. Heat transported by shallow 3-D porewater flow processes was accounted for in the model by using a dispersion term, the depth and intensity of which reflected the depth and intensity of shallow flushing. Similar to the results of past studies in shallower and more energetic nearshore settings, transport of heat was greater when higher near-bed velocities and shear stresses occurred over a rippled bed. However, boundary layer processes by themselves were insufficient to promote non-conductive heat transport. Advective heat transport only occurred when both larger boundary layer stresses and thermal instabilities within the porespace were present. The latter process is dependent on shelf-scale heating and cooling of bottom water associated with upwelling events that are not coupled to local-scale boundary layer processes.
      PubDate: 2016-12-01
      DOI: 10.1007/s10498-016-9295-1
      Issue No: Vol. 22, No. 5-6 (2016)
  • A Tribute to Rick and Debbie Jahnke: From Deep Sea Pore Water to Coastal
           Permeable Sediments-Contributions that Cover the Oceans
    • Authors: Timothy J. Shaw; Steve Emerson; Herbert L. Windom
      PubDate: 2016-12-09
      DOI: 10.1007/s10498-016-9309-z
  • CO 2 Outgassing from Spring Waters
    • Authors: Benjamin J. Maas; Carol M. Wicks
      Abstract: Abstract CO2 released from lakes, rivers, and estuaries has been included in estimates of the global CO2 budget; however, CO2 released from carbonate springs has not been routinely included in the estimate of the global CO2 budget. The omission of carbonate spring water as a source of CO2 might result in an underestimation of the overall flux of CO2 from surface waters to the atmosphere. In this study, the flux of CO2 from carbonate springs was calculated and compared to the rate of outgassing of CO2 reported in the literature for other surface water bodies. The calculated fluxes of CO2 from carbonate springs ranged 280–380,000 mmol m−2 d−1. A range that is larger than the range of CO2 fluxes reported for estuaries (100–1900 mmol m−2 d−1), headwater streams and rivers (100–1600 mmol m−2 d−1), freshwater lakes (−300 to 3200 mmol m−2 d−1), and saline lakes (−300 to 9900 mmol m−2 d−1). This work demonstrates that the outgassing of CO2 from springs should be included in the global CO2 budget.
      PubDate: 2016-11-30
      DOI: 10.1007/s10498-016-9302-6
  • Production of Reactive Oxygen Species in the Rhizosphere of a Spartina-
           Dominated Salt Marsh Systems
    • Authors: Dewamunnage Muditha C. Dias; Justin M. Copeland; Carrie L. Milliken; Xiangming Shi; John L. Ferry; Timothy J. Shaw
      Abstract: Abstract This paper reports the presence of a metastable mixture of Fe(II), O2, superoxide and hydrogen peroxide in sediment pore water in organic carbon-rich sediments in Spartina alterniflora-dominated salt marsh systems. Field measurements at two different estuarine sites in South Carolina (one heavily urbanized and a protected research reserve) showed a broad region of reactive oxygen species (ROS) production more than 15 cm below the sediment surface within and immediately adjacent to the rhizospheres of S. alterniflora. Dissolved Fe(II) was positively correlated with hydrogen peroxide indicating a possible abiotic pathway to ROS production (r 2 = 0.94). The null hypothesis was tested that Fe(II) inventories were maintained by protective ligands and thus unreactive with respect to O2 consumption and ROS production. The addition of an Fe-binding ligand, DTPA, resulted in rapid decline of ROS in pore water, indicating that Fe(II) was labile. The half-life of superoxide under the measured solution conditions was calculated and found to be less than a second. The combination of high lability and persistent ROS was interpreted to indicate a high rate of Fe(II) and O2 supply to the pore water. The 224Ra/228Th disequilibrium was measured to determine the potential for advective mass transfer of dissolved oxygen via pore water exchange. The estimated pore water exchange of 54 L m−2 day−1 was significant but could not support the measured production of ROS alone, the direct exchange of O2 from the S. alterniflora root system may have contributed significantly to ROS production in the sediments.
      PubDate: 2016-11-30
      DOI: 10.1007/s10498-016-9307-1
  • Recycling of Organic Matter in the Sediments of Santa Monica Basin,
           California Borderland
    • Authors: Tomoko Komada; David J. Burdige; Cédric Magen; Huan-Lei Li; Jeffrey Chanton
      Abstract: Abstract Geochemical and isotopic data for the uppermost 1.2 m of the sediments of the central Santa Monica Basin plain were examined to better understand organic matter deposition and recycling at this site. Isotopic signatures (Δ14C and δ13C) of methane (CH4) and dissolved inorganic carbon (DIC) indicate the occurrence of anaerobic oxidation of CH4 that is fueled by CH4 supplied from a relict reservoir that is decoupled from local organic carbon (Corg) degradation and methanogenesis. This finding was corroborated by a flux budget of pore-water solutes across the basal horizon of the profile. Together these results provide a plausible explanation for the anomalously low ratio between alkalinity production and sulfate consumption reported for these sediments over two decades ago. Shifts in Δ14C and δ13C signatures of Corg have previously been reported across the 20-cm depth horizon for this site and attributed to a transition from oxic to anoxic bottom water that occurred ~350 years BP. However, we show that this horizon also coincides with a boundary between the base of a hemipelagic mud section and the top of a turbidite interval, complicating the interpretation of organic geochemical data across this boundary. Radiocarbon signatures of DIC diffusing upward into surface sediments indicate that remineralization at depth is supported by relatively 14C-enriched Corg within the sedimentary matrix. While the exact nature of this Corg is unclear, possible sources are hemipelagic mud sections that were buried rapidly under thick turbidites, and 14C-rich moieties dispersed within Corg-poor turbidite sections.
      PubDate: 2016-11-29
      DOI: 10.1007/s10498-016-9308-0
  • Enhanced Dissolved Organic Matter Recovery from Saltwater Samples with
    • Authors: Luke R. Chambers; Ellery D. Ingall; Emily M. Saad; Amelia F. Longo; Masayuki Takeuchi; Yuanzhi Tang; Claudia Benitez-Nelson; Sheean T. Haley; Sonya T. Dyhrman; Jay Brandes; Aron Stubbins
      Abstract: Abstract Complexities associated with dissolved organic matter (DOM) isolation from seawater have hampered compositional characterization of this key component of global carbon and nutrient cycles. DOM isolation efficiency by electrodialysis (ED) from salt-containing waters was optimized and evaluated on samples including coastal ocean seawater, open ocean seawater, artificial seawater from axenic cultures of marine phytoplankton, and artificial seawater samples containing standard compounds of different molecular sizes and charge. ED was performed with a system optimized for processing 2–10 L sample volumes. Additionally, the combination of ED and solid-phase extraction, using Bond Elut PPL exchange resin, was evaluated. Using only ED, the following DOC recoveries were achieved: coastal seawater, 71.3 ± 6.5 %; open ocean, 50.5 ± 3.1 %; phytoplankton cultures, 70.3 ± 12.5 %; glucose, 90.2 ± 2.1 %; EDTA, 67.5 ± 9.9 %; and vitamin B12, 98.3 ± 1.6 %. With the combination of PPL and ED techniques, an average DOC recovery of 76.7 ± 2.6 % was obtained for coastal seawater, but this recovery was not statistically different from seawater recoveries using only ED. Comparison of C/N ratios and fluorescence excitation emission matrices taken at the beginning and end of the recovery process for coastal samples processed using only ED indicated that the final recovered material was representative of the DOM present in the original samples. Typical recoveries using combined PPL and ED exceed those of previous isolation methods.
      PubDate: 2016-10-24
      DOI: 10.1007/s10498-016-9306-2
  • Benthic Oxygen Fluxes Measured by Eddy Covariance in Permeable Gulf of
           Mexico Shallow-Water Sands
    • Authors: Lindsay Chipman; Peter Berg; Markus Huettel
      Abstract: Abstract Oxygen fluxes across the sediment–water interface reflect primary production and organic matter degradation in coastal sediments and thus provide data that can be used for assessing ecosystem function, carbon cycling and the response to coastal eutrophication. In this study, the aquatic eddy covariance technique was used to measure seafloor–water column oxygen fluxes at shallow coastal sites with highly permeable sandy sediment in the northeastern Gulf of Mexico for which oxygen flux data currently are lacking. Oxygen fluxes at wave-exposed Gulf sites were compared to those at protected Bay sites over a period of 4 years and covering the four seasons. A total of 17 daytime and 14 nighttime deployments, producing 408 flux measurements (14.5 min each), were conducted. Average annual oxygen release and uptake (mean ± standard error) were 191 ± 66 and −191 ± 45 mmol m−2 day−1 for the Gulf sites and 130 ± 57 and −152 ± 64 mmol m−2 day−1 for the Bay sites. Seasonal variation in oxygen flux was observed, with high rates typically occurring during spring and lower rates during summer. The ratio of average oxygen release to uptake at both sites was close to 1 (Bay: 0.9, Gulf: 1.0). Close responses of the flux to changes in light, temperature, bottom current velocity, and wave action (significant wave height) documented tight physical–biological, benthic–pelagic coupling. The increase of the sedimentary oxygen uptake with increasing temperature corresponded to a Q10 temperature coefficient of 1.4 ± 0.3. An increase in flow velocity resulted in increased oxygen uptake (by a factor of 1–6 for a doubling in flow), which is explained by the enhanced transport of organic matter and electron acceptors into the permeable sediment. Benthic photosynthetic production and oxygen release from the sediment was modulated by light intensity at the temporal scale (minutes) of the flux measurements. The fluxes measured in this study contribute to baseline data in a region with rapid coastal development and can be used in large-scale assessments and estimates of carbon transformations.
      PubDate: 2016-10-21
      DOI: 10.1007/s10498-016-9305-3
  • Dissolution of Al-Substituted Goethite in the Presence of Ferrichrome and
           Enterobactin at pH 6.5
    • Authors: William E. Dubbin; Florence Bullough
      Abstract: Abstract Naturally occurring goethites often show Al for Fe substitution approaching 33 mol% Al. This substitution has potential to influence the rate of goethite dissolution and therefore the supply of bioavailable Fe. Siderophores such as ferrichrome and enterobactin have considerable potential to dissolve Fe from Fe3+ rich minerals, including Al-substituted goethites. Here, we show that Al substitution in synthetic goethites (0.021 ≥ x ≥ 0.098) gives rise to a significant increase in both ferrichrome- and enterobactin-mediated dissolution rates. In the presence of ferrichrome, Al-goethite (x = 0.033) yields a dissolution rate of 19.0 × 10−3 µmol m−2 h−1, nearly twice that of pure goethite, whereas dissolution of the most highly substituted Al-goethite (x = 0.098) is 36.9 × 10−3 µmol m−2 h−1, more than threefold greater than the pure mineral. Similarly, in the presence of enterobactin, the dissolution rate of Al-goethite increases with increasing Al substitution. Ferrichrome is a less effective ligand than enterobactin in its dissolution of both pure goethite and the range of Al-goethites, an observation we ascribe to the lower affinity of the hydroxamate functional groups of ferrichrome for both Fe3+ and Al3+. Despite greater affinity of both ferrichrome and enterobactin for Fe3+ over Al3+, we observe a broadly congruent dissolution of all our Al-goethites.
      PubDate: 2016-10-12
      DOI: 10.1007/s10498-016-9304-4
  • The Dynamics of Benthic Respiration at a Mid-Shelf Station Off Oregon
    • Abstract: Abstract Mid-shelf sediments off the Oregon coast are characterized as fine sands that trap and remineralize phytodetritus leading to the consumption of significant quantities of dissolved oxygen. Sediment oxygen consumption (SOC) can be delayed from seasonal organic matter inputs because of a transient buildup of reduced constituents during periods of quiescent physical processes. Between 2009 and 2013, benthic oxygen exchange rates were measured using the noninvasive eddy covariance (EC) method five separate times at a single 80-m station. Ancillary measurements included in situ microprofiles of oxygen at the sediment–water interface, and concentration profiles of pore water nutrients and trace metals, and solid-phase organic C and sulfide minerals from cores. Sediment cores were also incubated to derive anaerobic respiration rates. The EC measurements were made during spring, summer, and fall conditions, and they produced average benthic oxygen flux estimates that varied between −2 and −15 mmol m−2 d−1. The EC oxygen fluxes were most highly correlated with bottom-sensed, significant wave heights (H s). The relationship with H s was used with an annual record of deepwater swell heights to predict an integrated oxygen consumption rate for the mid-shelf of 1.5 mol m−2 for the upwelling season (May–September) and 6.8 mol m−2 y−1. The annual prediction requires that SOC rates are enhanced in the winter because of sand filtering and pore water advection under large waves, and it counters budgets that assume a dominance of organic matter export from the shelf. Refined budgets will require winter flux measurements and observations from cross-shelf transects over multiple years.
      PubDate: 2016-09-27
      DOI: 10.1007/s10498-016-9303-5
  • The Influence of Bioturbation on Iron and Sulphur Cycling in Marine
           Sediments: A Model Analysis
    • Authors: Sebastiaan van de Velde; Filip J. R. Meysman
      Abstract: Abstract The geochemical cycles of iron and sulphur in marine sediments are strongly intertwined and give rise to a complex network of redox and precipitation reactions. Bioturbation refers to all modes of transport of particles and solutes induced by larger organisms, and in the present-day seafloor, bioturbation is one of the most important factors controlling the biogeochemical cycling of iron and sulphur. To better understand how bioturbation controls Fe and S cycling, we developed reactive transport model of a coastal sediment impacted by faunal activity. Subsequently, we performed a model sensitivity analysis, separately investigating the two different transport modes of bioturbation, i.e. bio-mixing (solid particle transport) and bio-irrigation (enhanced solute transport). This analysis reveals that bio-mixing and bio-irrigation have distinct—and largely opposing effects on both the iron and sulphur cycles. Bio-mixing enhances transport between the oxic and suboxic zones, thus promoting the reduction of oxidised species (e.g. iron oxyhydroxides) and the oxidation of reduced species (e.g. iron sulphides). Through the re-oxidation of iron sulphides, bio-mixing strongly enhances the recycling of Fe and S between their reduced and oxidised states. Bio-irrigation on the other hand removes reduced solutes, i.e. ferrous iron and free sulphide, from the sediment pore water. These reduced species are then reoxidised in the overlying water and not recycled within the sediment column, which leads to a decrease in Fe and S recycling. Overall, our results demonstrate that the ecology of the macrofauna (inducing bio-mixing or bio-irrigation, or both) matters when assessing their impact on sediment geochemistry. This finding seems particularly relevant for sedimentary cycling across Cambrian transition, when benthic fauna started colonizing and reworking the seafloor.
      PubDate: 2016-09-10
      DOI: 10.1007/s10498-016-9301-7
  • Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea
           Loch: An Integrative In Situ Study
    • Authors: Ronnie N. Glud; Peter Berg; Henrik Stahl; Andrew Hume; Morten Larsen; Bradley D. Eyre; Perran L. M. Cook
      Abstract: Abstract Based on in situ microprofiles, chamber incubations and eddy covariance measurements, we investigated the benthic carbon mineralization and nutrient regeneration in a ~65-m-deep sedimentation basin of Loch Etive, UK. The sediment hosted a considerable amount of infauna that was dominated by the brittle star A. filiformis. The numerous burrows were intensively irrigated enhancing the benthic in situ O2 uptake by ~50 %, and inducing highly variable redox conditions and O2 distribution in the surface sediment as also documented by complementary laboratory-based planar optode measurements. The average benthic O2 exchange as derived by chamber incubations and the eddy covariance approach were similar (14.9 ± 2.5 and 13.1 ± 9.0 mmol m−2 day−1) providing confidence in the two measuring approaches. Moreover, the non-invasive eddy approach revealed a flow-dependent benthic O2 flux that was partly ascribed to enhanced ventilation of infauna burrows during periods of elevated flow rates. The ratio in exchange rates of ΣCO2 and O2 was close to unity, confirming that the O2 uptake was a good proxy for the benthic carbon mineralization in this setting. The infauna activity resulted in highly dynamic redox conditions that presumably facilitated an efficient degradation of both terrestrial and marine-derived organic material. The complex O2 dynamics of the burrow environment also concurrently stimulated nitrification and coupled denitrification rates making the sediment an efficient sink for bioavailable nitrogen. Furthermore, bioturbation mediated a high efflux of dissolved phosphorus and silicate. The study documents a high spatial and temporal variation in benthic solute exchange with important implications for benthic turnover of organic carbon and nutrients. However, more long-term in situ investigations with like approaches are required to fully understand how environmental events and spatio-temporal variations interrelate to the overall biogeochemical functioning of coastal sediments.
      PubDate: 2016-09-08
      DOI: 10.1007/s10498-016-9300-8
  • The Application of Raman Spectroscopy to Probe the Association of H 4 SiO
           4 with Iron Oxides
    • Authors: Yohan Ferras; John Robertson; Peter J. Swedlund
      Abstract: Abstract The aquatic geochemistry of many trace elements is influenced by two important products from the weathering of minerals: iron oxide solid phases and silicic acid (H4SiO4) in the aqueous phase. The chemistry of H4SiO4 on iron oxide surfaces is an interesting mix of sorption and polymerization, and this has been shown to affect the sorption, coprecipitation and transport of many trace elements. Infrared spectroscopy is a valuable probe of H4SiO4 chemistry on iron oxide surfaces, and in this study, we assess the utility of Raman spectroscopy for studying H4SiO4 chemistry on the poorly ordered iron oxide ferrihydrite. This was undertaken because Raman spectroscopy provides complimentary information to IR, in addition to often having narrower bands than IR spectra and less interference from water during in situ measurements. The IR spectra of H4SiO4 adsorbed on ferrihydrite showed the expected strong Si–O stretching feature, termed ν(Si–O), which had a central band and shoulders on either side. As the surface concentration of H4SiO4 increased, there was a clear shift in the position of the central band of the ν(Si–O) feature from ~950 to 1060 cm−1 reflecting the degree of silicate polymerization. The Raman spectra of the same samples had a very broad and weak ν(Si–O) feature which had a poor signal-to-noise ratio even after accumulating spectra over 1 h. The ν(Si–O) in the Raman spectra did not have discernable shoulders, as observed in the IR spectra, and there was only a fairly subtle shift in the position of this feature from 950 to 970 cm−1 as the degree of silicate polymerization increased. Overall, the results indicate that Raman spectroscopy can be used to study H4SiO4 adsorption and polymerization on iron oxides, but its utility is constrained by a weak signal combined with a subtle shift in peak position with H4SiO4 polymerization.
      PubDate: 2016-08-17
      DOI: 10.1007/s10498-016-9294-2
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