Silicon Biogeochemical Cycle Along The Land To Ocean Continuum

Silicon is the second most abundant element in Earth's crust and one of the key nutrient in aquatic ecosystems. There are strong interactions of Si with carbon cycle and biogeochemical processes. The present thesis focused on variability of silicon (amorphous-ASi, lithogenic-LSi and dissolved-DSi) and Si isotopes along the land to ocean continuum. We investigated the seasonal and spatial variability of ASi, LSi & DSi and Si isotopes in ~20 Indian estuaries. We categorize the estuaries using statistical analysis (PCA and cluster analysis). Diatom uptake seems to be the main process controlling ASi during dry period, especially in the South. Weathering and erosion control the variability of LSi in the remaining estuaries. Similarly lithogenic supply controls Si during wet period in all estuaries and no impact of diatoms was seen because of high suspended load. Si isotopic compositions trace the Si sources and biogeochemical pathways. The isotopic results exhibit clear seasonal difference with high impact of type of weathering during both seasons. They show that southwest watersheds are very special in terms of weathering regime compared to the other watersheds because of topography and climate. The impact of agriculture and forest cover on Si cycle is also clearly evidenced in all the basins during wet period. We show that groundwater Si isotopic variability results from a combination of dissolution and production of minerals. Overall, this study shows the preponderant influence of weathering and type of secondary clays on Si isotopes irrespective to the seasons, rather than the biological uptake or mixing as reported elsewhere.

In the biogeochemical dynamics of marine ecosystems, silicon is a major element whose role has, for a long time, been underestimated. It is however indispensable to the activity of several biomineralizing marine organisms, some of which play an essential role in the biological pump of oceanic carbon. This book presents notions indispensable to the knowledge on the silicon biogeochemical cycle in ocean systems, first of all describing the main quantitative analysis techniques and examination of the major organisms involved in the cycle. The author then moves on to study the most up-to-date processes to control the use of silicon and its regeneration in natural conditions, before mentioning the central role played by this original element in the control of all the biogeochemical cycles in the global ocean. The available information finally enables the global biogeochemical budget of silicon in the marine environment to be quantified.

The biogeochemical cycling of nutrient silicon (Si) through rivers, wetlands, lakes, and artificial reservoirs regulates the magnitude and bioavailability of Si delivered downstream and to the ocean (Frings et al. 2014; Maavara et al. 2014; Laruelle et al. 2009; Struyf & Conley 2012). Lakes are areas of Si retention along the land to ocean continuum due to uptake of dissolved Si (DSi) by silicon-requiring phytoplankton, such as diatoms, and burial of biogenic Si (BSi) as siliceous frustules in sediments (Frings et al. 2014). The nearshore zones of lakes and the coastal ocean directly receive nutrient inputs from the watershed, which may lead to eutrophication (Haffner et al. 1983; Jickells 1998; Mackenzie et al. 2000; Strayer & Findlay 2010). Enrichment with the nutrients phosphorus (P) and nitrogen (N) can enhance DSi uptake, which can ultimately lead to Si depletion and limitation of siliceous phytoplankton growth in the water column (Schelske & Stoermer 1971; Schelske & Stoermer 1972). Sediments can play an important role in water column nutrient dynamics through acting as a source or a sink of Si and P (Orihel et al. 2017; Nriagu 1978; Schelske 1985). Interactions between dissolved Si and P in pore waters and oxygenation at the sediment-water interface may influence the release of Si and P from sediments (Tuominen et al. 1998; Hartikainen et al. 1996; Tallberg & Koski-Vahala 2001; Koski-Vähälä et al. 2001; Tallberg et al. 2008; Siipola et al. 2016; Lehtimäki et al. 2016). Relatively little is known about Si cycling in the sediments and water column of nearshore zones of large lakes, such as the Laurentian Great Lakes, and it's response to eutrophication. This thesis examined the biogeochemical cycling of reactive Si in the Hamilton Harbour Area of Concern, a highly eutrophic and human impacted nearshore area of Lake Ontario. The Hamilton Harbour Area of Concern includes Cootes' Paradise marsh and Hamilton Harbour.

This is the second issue of the Research Topic: Biogeochemistry and Genomics of Silicification and Silicifiers. The first issue article collection can be found here: https://www.frontiersin.org/research-topics/5364/biogeochemistry-and-genomics-of-silicification-and-silicifiers Silicifiers are among the most important living organisms of planet Earth. They are able to take advantage of the abundance of silicon in the Earth crust to build silicified architectures, which in particular can help for protection against predators or for facilitating the penetration of light and nutrients to the cells.

This book is a product of the joint JGOFS (Joint Global Ocean Flux Study)/LOICZ (Land–Ocean Interactions in the Coastal Zone) Continental Margins Task Team which was established to facilitate continental margins research in the two projects. It contains signi cant information on the physical, biogeochemical, and ecosystems of continental margins nationally and regionally and provides a very valuable synthesis of this information and the physical, biogeochemical and ecosystem processes which occur on continental margins. The publication of this book is timely as it provides a very strong foundation for the development of the joint IMBER (Integrated Marine Biogeochemistry and Ecosystems Research)/LOICZ Science Plan and Implemen- tion Strategy for biogeochemical and ecosystems research in the continental margins and the impacts of global change on these systems. This initiative will move forward integrated biogeochemical and ecosystems research in the continental margins. We thank all the contributors to this volume and especially Kon-Kee Liu who has dedicated a great deal of time to ensuring a high-quality book is published. IMBER Scienti c Steering Committee Julie Hall LOICZ Scienti c Steering Committee Jozef Pacyna v 1 Preface In general, interfaces between the Earth’s larger material reservoirs (i. e. , the land, atmosphere, ocean, and sediments) are important in the control of the biogeoche- cal dynamics and cycling of the major bio-essential elements, including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and silicon (Si), found in organic matter and the inorganic skeletons, shells, and tests of benthic and marine organisms.

Silicon is among the most abundant elements on earth. It plays a key but largely unappreciated role in many biogeochemical processes, including those that regulate climate and undergird marine food webs. The Silicon Cycle is the first book in more than 20 years to present a comprehensive overview of the silicon cycle and issues associated with it. The book summarizes the major outcomes of the project Land-Ocean Interactions: Silica Cycle, initiated by the Scientific Community on Problems of the Environment (SCOPE) of the International Council of Scientific Unions (ICSU). It tracks the pathway of silicon from land to sea and discusses its biotic and abiotic modifications in transit as well as its cycling in the coastal seas. Natural geological processes in combination with atmospheric and hydrological processes are discussed, as well as human perturbations of the natural controls of the silicon cycle.

Biological processes in the oceans play a crucial role in regulating the fluxes of many important elements such as carbon, nitrogen, sulfur, oxygen, phosphorus, and silicon. As we come to the end of the 20th century, oceanographers have increasingly focussed on how these elements are cycled within the ocean, the interdependencies of these cycles, and the effect of the cycle on the composition of the earth's atmosphere and climate. Many techniques and tools have been developed or adapted over the past decade to help in this effort. These include satellite sensors of upper ocean phytoplankton distributions, flow cytometry, molecular biological probes, sophisticated moored and shipboard instrumentation, and vastly increased numerical modeling capabilities. This volume is the result of the 37th Brookhaven Symposium in Biology, in which a wide spectrum of oceanographers, chemists, biologists, and modelers discussed the progress in understanding the role of primary producers in biogeochemical cycles. The symposium is dedicated to Dr. Richard W. Eppley, an intellectual giant in biological oceanography, who inspired a generation of scientists to delve into problems of understanding biogeochemical cycles in the sea. We gratefully acknowledge support from the U.S. Department of Energy, the National Aeronautics and Space Administration, the National Science Foundation, the National Oceanic and Atmospheric Administration, the Electric Power Research Institute, and the Environmental Protection Agency. Special thanks to Claire Lamberti for her help in producing this volume.

The Novartis Foundation Series is a popular collection of the proceedings from Novartis Foundation Symposia, in which groups of leading scientists from a range of topics across biology, chemistry and medicine assembled to present papers and discuss results. The Novartis Foundation, originally known as the Ciba Foundation, is well known to scientists and clinicians around the world.

Accessibly written by a team of international authors, the Encyclopedia of Environmental Change provides a gateway to the complex facts, concepts, techniques, methodology and philosophy of environmental change. This three-volume set illustrates and examines topics within this dynamic and rapidly changing interdisciplinary field. The encyclopedia includes all of the following aspects of environmental change: Diverse evidence of environmental change, including climate change and changes on land and in the oceans Underlying natural and anthropogenic causes and mechanisms Wide-ranging local, regional and global impacts from the polar regions to the tropics Responses of geo-ecosystems and human-environmental systems in the face of past, present and future environmental change Approaches, methodologies and techniques used for reconstructing, dating, monitoring, modelling, projecting and predicting change Social, economic and political dimensions of environmental issues, environmental conservation and management and environmental policy Over 4,000 entries explore the following key themes and more: Conservation Demographic change Environmental management Environmental policy Environmental security Food security Glaciation Green Revolution Human impact on environment Industrialization Landuse change Military impacts on environment Mining and mining impacts Nuclear energy Pollution Renewable resources Solar energy Sustainability Tourism Trade Water resources Water security Wildlife conservation The comprehensive coverage of terminology includes layers of entries ranging from one-line definitions to short essays, making this an invaluable companion for any student of physical geography, environmental geography or environmental sciences.