The Geochemistry and Ecotoxicity of Offshore New Zealand Phosphorites

<p>The New Zealand offshore seabed hosts diverse resources including phosphate rich rocks. Phosphate rock deposits on the Chatham Rise have been the focus of previous investigations into their composition and mining potential; however, the diversity of the geochemistry of phosphate deposits, including their wider distribution beyond the Chatham Rise, their trace metal budget, and potential for ecotoxicity, remain poorly characterised. This study addresses some of these gaps by presenting a geochemical investigation, including trace metals, for a range of phosphate nodules from across the Chatham Rise, Bollons Seamount and offshore southeastern South Island. Elutriate and reconnaissance bioaccumulation experiments provide insights into the potential for ecotoxic trace metal release and effects on biota should sediment disturbance through mining activities occur. The bulk chemistry of Bollons Seamount phosphorite nodules have been characterised for the first time, and show significant enrichment in first row transition metals; Co, Ni, Cu, Zn, in addition to Sr, Y, Mo, U, MnO, CaO and P2O5, and depletion in TiO2, Al2O3, MgO, K2O, FeO, SiO2, Sc, Cr, Ga, Rb, Cs, Hf, and Th relative to average upper continental crust. The cores of these nodules are dominated by apatite, quartz and anorthoclase phases, which are cross cut by Mn rich dendrites. The abundant presence of these minerals results in the significant differences in chemistry observed relative to Chatham Rise phosphorite nodules. The nodules also contain a secondary authigenic apatite phase, with a Mn crust rim. Significant rare earth element enrichment (REE) is most likely due to efficient scavenging by the Mn crust, resulting in seawater REE patterns characterised by negative Ce and Eu anomalies and heavy rare earth element enrichment. The bulk geochemistry of the Chatham Rise and offshore South Island phosphorite nodules is characterised by enrichment in CaO, P2O5, Sr, U, Y, Mo and depletion in TiO2, Al2O3, MnO, MgO, FeO, K2O, Sc, Cr, Cu, Ga, Rb, Cs, Ba, Hf, Ta, Pb and Th relative to average upper continental crust. The low concentrations of Cd in Chatham Rise, offshore South Island, and Bollons Seamount phosphorites make them potentially suitable sources for direct application fertilizers. The New Zealand marine phosphorite nodule deposits formed by repeated cycles of erosive bottom currents and phosphogenesis, resulting in the winnowing and concentration of the deposits. The iron pump model is proposed as a mechanism for the formation of apatite and associated mineral phases, giving the nodules their characteristic concentric zoning. The migration of the nodules through the oxic, suboxic, and anoxic zones of the sediment profile led to the formation of glaucony, apatite (suboxic zone), goethite (oxic zone), and pyrite with associated U enriched (anoxic zone) minerals. Rare earth elements (REE) in the Chatham Rise phosphorite nodules are associated with the glaucony rim minerals, and indicate that since the formation of the rims, very little diagenesis has occurred, preserving seawater REE patterns characterised by negative Ce and Eu anomalies and heavy REE enrichment. Site specific enrichments in trace elements Ba, V, Co, Ni, Cu, Zn, Y, Cd and Pb are attributed to either differences in incorporation of material into precursor carbonate e.g. volcanic materials, or higher fluxes of organic matter, delivering high concentrations of essential metals from biota, especially Cu and Zn. Direct pore water measurements from surficial sediment of the Chatham Rise show high concentrations of dissolved Fe and Mn, along with Cu, indicating suboxic conditions. High Cu concentrations measured in sediment pore water suggest that Cu release requires monitoring should seafloor surficial sediments on the Chatham Rise be disturbed. However, the elutriate experiments were not able to resolve if Cu release by sediment disturbance would exceed Australian and New Zealand Environment Conservation Council (2000) environmental guideline trigger values. The surrogate amphipod species Chaetocorophium c.f. lucasi shows promise as a biomonitor for disturbed marine sediments. Elements enriched in surficial sediments and phosphorite nodules, Hg, Pb, Fe, U and V, were not observed to bioaccumulate. Site specific differences in chemistry were observed, specifically in the different total relative bioaccumulation of Mo between amphipods exposed to sediments from two different sites. This suggests that future monitoring of chemical release during marine sediment disturbance requires the full geochemical characterisation of the substrate. Furthermore, fresh sediment and deep water should be used for future elutriate experiments, as storage of material by freeze-thawing and/or refrigeration causes mobilisation of some key trace metals such as U, V, Mo, Mn.</p>

The Geochemistry and Ecotoxicity of Offshore New Zealand Phosphorites

<p>The New Zealand offshore seabed hosts diverse resources including phosphate rich rocks. Phosphate rock deposits on the Chatham Rise have been the focus of previous investigations into their composition and mining potential; however, the diversity of the geochemistry of phosphate deposits, including their wider distribution beyond the Chatham Rise, their trace metal budget, and potential for ecotoxicity, remain poorly characterised. This study addresses some of these gaps by presenting a geochemical investigation, including trace metals, for a range of phosphate nodules from across the Chatham Rise, Bollons Seamount and offshore southeastern South Island. Elutriate and reconnaissance bioaccumulation experiments provide insights into the potential for ecotoxic trace metal release and effects on biota should sediment disturbance through mining activities occur. The bulk chemistry of Bollons Seamount phosphorite nodules have been characterised for the first time, and show significant enrichment in first row transition metals; Co, Ni, Cu, Zn, in addition to Sr, Y, Mo, U, MnO, CaO and P2O5, and depletion in TiO2, Al2O3, MgO, K2O, FeO, SiO2, Sc, Cr, Ga, Rb, Cs, Hf, and Th relative to average upper continental crust. The cores of these nodules are dominated by apatite, quartz and anorthoclase phases, which are cross cut by Mn rich dendrites. The abundant presence of these minerals results in the significant differences in chemistry observed relative to Chatham Rise phosphorite nodules. The nodules also contain a secondary authigenic apatite phase, with a Mn crust rim. Significant rare earth element enrichment (REE) is most likely due to efficient scavenging by the Mn crust, resulting in seawater REE patterns characterised by negative Ce and Eu anomalies and heavy rare earth element enrichment. The bulk geochemistry of the Chatham Rise and offshore South Island phosphorite nodules is characterised by enrichment in CaO, P2O5, Sr, U, Y, Mo and depletion in TiO2, Al2O3, MnO, MgO, FeO, K2O, Sc, Cr, Cu, Ga, Rb, Cs, Ba, Hf, Ta, Pb and Th relative to average upper continental crust. The low concentrations of Cd in Chatham Rise, offshore South Island, and Bollons Seamount phosphorites make them potentially suitable sources for direct application fertilizers. The New Zealand marine phosphorite nodule deposits formed by repeated cycles of erosive bottom currents and phosphogenesis, resulting in the winnowing and concentration of the deposits. The iron pump model is proposed as a mechanism for the formation of apatite and associated mineral phases, giving the nodules their characteristic concentric zoning. The migration of the nodules through the oxic, suboxic, and anoxic zones of the sediment profile led to the formation of glaucony, apatite (suboxic zone), goethite (oxic zone), and pyrite with associated U enriched (anoxic zone) minerals. Rare earth elements (REE) in the Chatham Rise phosphorite nodules are associated with the glaucony rim minerals, and indicate that since the formation of the rims, very little diagenesis has occurred, preserving seawater REE patterns characterised by negative Ce and Eu anomalies and heavy REE enrichment. Site specific enrichments in trace elements Ba, V, Co, Ni, Cu, Zn, Y, Cd and Pb are attributed to either differences in incorporation of material into precursor carbonate e.g. volcanic materials, or higher fluxes of organic matter, delivering high concentrations of essential metals from biota, especially Cu and Zn. Direct pore water measurements from surficial sediment of the Chatham Rise show high concentrations of dissolved Fe and Mn, along with Cu, indicating suboxic conditions. High Cu concentrations measured in sediment pore water suggest that Cu release requires monitoring should seafloor surficial sediments on the Chatham Rise be disturbed. However, the elutriate experiments were not able to resolve if Cu release by sediment disturbance would exceed Australian and New Zealand Environment Conservation Council (2000) environmental guideline trigger values. The surrogate amphipod species Chaetocorophium c.f. lucasi shows promise as a biomonitor for disturbed marine sediments. Elements enriched in surficial sediments and phosphorite nodules, Hg, Pb, Fe, U and V, were not observed to bioaccumulate. Site specific differences in chemistry were observed, specifically in the different total relative bioaccumulation of Mo between amphipods exposed to sediments from two different sites. This suggests that future monitoring of chemical release during marine sediment disturbance requires the full geochemical characterisation of the substrate. Furthermore, fresh sediment and deep water should be used for future elutriate experiments, as storage of material by freeze-thawing and/or refrigeration causes mobilisation of some key trace metals such as U, V, Mo, Mn.</p>

Sediment Coarsening in Tidal Flats and Stable Coastline of the Abandoned Southern Yellow River Sub-Delta in Response to Fluvial Sediment Flux Decrease During the Past Decades

Due to remarkable reduction of sediment supply, the vulnerability of Yellow River deltaic system increased and ecological impacts occurred to some extent. To have a comprehensive and quantitative understanding of the morphological evolution of deltas, surficial sediments of tidal flat along the abandoned southern Yellow River sub-delta and two adjacent coastal units were systematically collected and evaluated by grain-size analysis in the study. The results reveal that surficial sediments of the abandoned southern Yellow River sub-delta have been coarsening significantly since the 1980s, as characterized by a decrease in both the mud content and the clay/mud ratio. In particular, the transition from cohesive to non-cohesive sediment was completed between 2007 and 2013. With a sharp decrease in sediment flux from the Yellow River estuary, the flood currents from the submarine coastal slope carry few fine particles into the tidal zone, whereas the ebb currents with reverse direction remove some fine particles from the tidal flat. This is a major cause of sediment coarsening in the tidal flat. As sediment coarsening, the coastline of the abandoned southern Yellow River sub-delta has remained stable. The significant change in the grain size of the tidal flat surficial sediments may have a profound impact on the future coastal geomorphic evolution.

Seismic microzonation of a region with complex surficial geology based on different site classification approaches

A seismic microzonation study was conducted to refine the seismic hazard model for the city of Saguenay, Canada. The Quaternary geology underlying Saguenay shows complex glacial and post-glacial stratigraphy with a number of buried valleys filled with fluvioglacial and glaciomarine sediments. High impedance contrast between rock formations and surficial sediments is prone to seismic amplification. To evaluate their applicability, advantages and limitations in capturing the geological specificity of the study area, four site classification methods were applied: the current National Building Code of Canada (NBCC) and Eurocode 8, both mainly based on the average shear-wave velocity for the surficial sediments (VS,avg) and for the top 30 m (VS,30); a method based on the fundamental site period (T0); and a hybrid method based on the combination of VS,30, T0 and VS,avg. The study specifically aimed to evaluate the importance of the site classification parameters on the resulting microzonation maps. VS,30 is capable to present the geological and geotechnical site conditions, however, the results may be further improved by considering Vs,avg in shallow and T0 in thick layers of soil sediments as secondary parameters. The T0 method gives also satisfactory results with T0 showing a better correlation to Vs,30 than to Vs,avg. The versatile hybrid method may be challenging to apply in certain cases with its nine different site categories and parameters.

A Hydrostratigraphic Framework for the Paleozoic Bedrock of Southern Ontario

Groundwater systems in the intermediate to deep subsurface of southern Ontario are poorly understood, despite their value for a number of societal uses. A regional hydrostratigraphic framework is a necessary precursor for improving our understanding of groundwater systems and enabling development of a 3-D hydrostratigraphic model to visualize these groundwater systems. This study is a compilation and integration of published and unpublished geological, hydrogeological, hydrochemical and isotopic data collected over the past 10 years to develop that framework.Bedrock is covered by a thin veneer of surficial sediments that comprise an aquifer/aquitard system of considerable local variability and complexity. Aquifers in the bedrock are thin and regionally extensive, separated by thick aquitards, within a well-defined lithostratigraphic framework and a well-developed hydrochemical depth zonation comprising a shallow fresh water regime, an intermediate brackish to saline sulphur water regime, and a deep brine regime of ancient, evaporated seawater. Occurrence and movement of groundwater in shallow bedrock is principally controlled by modern (Quaternary) karstic dissolution of subcropping carbonate and evaporite rocks, and in the intermediate to deep subsurface by paleokarst horizons developed during the Paleozoic. Flow directions in the surficial sediments of the shallow groundwater regime are down-gradient from topographic highs and down the regional dip of bedrock formations in the intermediate regime. Shallow karst is the entry point for groundwater penetration into the intermediate regime, with paleo-recharge by glacial meltwater and limited recent recharge by meteoric water at subcrop edges, and down-dip hydraulic gradients in confined aquifers. Hydraulic gradient is up-dip in the deep brine regime, at least for the Guelph Aquifer and the Cambrian Aquifer, with no isotopic or hydrochemical evidence of infiltration of meteoric water and no discharge to the surface.Fourteen bedrock hydrostratigraphic units are proposed, and one unit comprising all the surficial sediments. Assignment of lithostratigraphic units as hydrostratigraphic units is based principally on hydrogeological characteristics of Paleozoic bedrock formations in the intermediate to deep groundwater regimes, below the influence of modern meteoric water. Carbonate and evaporite rocks which form aquitards in the subsurface may form aquifers at or near the surface, due to karstic dissolution by acidic meteoric water, necessitating compromises in assignment of hydrostratigraphic units.