Candace E. Martin

Nd-Sr isotopic and trace element geochemistry of river sediments and soils in a fertilized catchment, New South Wales, Australia

Abstract Neodymium and strontium isotopes and a suite of trace elements have been used to distinguish between the various sources of particulate loads and soils in a major catchment of the Murray-Darling drainage system, the largest river in Australia. One of the goals was to estimate additions of Sr and rare earth elements of anthropogenic (fertilizer) origin to the natural catchment sources to the soils and streams. Among possible sediment sources, Tertiary basalts and Paleozoic metagraywackes have the lowest 87 Sr/ 86 Sr and highest ϵ Nd , whereas Paleozoic metapelitic rocks have negative ϵ Nd and the highest 87 Sr/ 86 Sr. Phosphate fertilizers have strongly negative ϵ Nd and 87 Sr/ 86 Sr similar to Tertiary seawater. Soils formed on basalt and metagraywacke have compositions that are shifted toward higher 87 Sr/ 86 Sr and lower ϵ Nd than their parent rocks. REE patterns and elemental ratios such as Nd/P are also distinctive between fertilizer and natural catchment sources. Reservoir sediment from the upper catchment have isotopic and trace element compositions that confirm that the dominant source of stream particulates is from basalt soils in the steep upland part of the catchment. Mixing calculations based on isotopic and elemental compositions for reservoir sediment in the upper catchment are consistent with less than 0.2% bulk addition by mass of fertilizer to the natural sediment source. The isotopic compositions of soils in less easily eroded portions of the upper catchment reflect the addition of a component to the soil which is interpreted to be wind-blown dust, derived either from Paleozoic granitoids that dominate the lower regions of the catchment or from more distal westerly sources. Sediment from the lower catchment requires that the dominant source below the reservoir is derived from Paleozoic granitoid and metapelitic rocks of the New England fold belt. The lower catchment sediments show no definitive evidence of either basalt or fertilizer input. Natural sources dominate the particulate loads in these streams.

Sources and sinks of unradiogenic osmium runoff from Papua New Guinea

The Fly and Sepik are two of the largest rivers draining the island of New Guinea and among the world’s large rivers in discharge and sediment yield. Sediment from the upper Fly River and its delta have low 187Os/188Os of 0.511–0.560, and sediments from the upper and lower Sepik River have even lower ratios of 0.294–0.418. Filtered waters ( 1.2). Burial of Os of both seawater and riverine derivation occurs in conjunction with organic carbon burial in the Gulf of Papua. There is a negative correlation between the Os isotopic composition of the bulk sediment and the fraction of organic matter of terrestrial origin based on C isotopes. The systematic relationship between C and Os isotopic compositions in these samples indicates that organic matter is the major host of Os in tropical estuarine sediments. The Os/Corg of Gulf of Papua surface sediments is intermediate between that of other modern and ancient sediments. Approximately 1011 mol/yr of Corg and 20–57 mol/yr of Os are buried in the inner shelf (<50 m depth) of the Gulf of Papua over an area of only 21 000 km2, corresponding to 1–3% of the global marine Os burial flux in 0.006% of the total sea surface area. These results suggest that a large proportion of the global burial flux of Os may take place in conjunction with the deposition of low-Corg sediments. Lowering of the Os isotopic composition of ambient seawater due to a large flux of unradiogenic riverine Os may be indicated by the Os isotopic composition of water from the Coral Sea (187Os/188Os=0.844) and marine sediments within the Gulf of Papua. The island of New Guinea is estimated to provide 4–5% of the global riverine Os flux. Given the very large particulate and dissolved flux to the oceans from rivers in the wet tropics, the effect of the weathering of young arc-related crust in the SW Pacific is an important source of unradiogenic Os to modern seawater.

Tracing the source of sediment and phosphorus into the Great Barrier Reef lagoon

Neodymium and strontium isotopic systematics show that terrestrial phosphorus (P) entering the inner Great Barrier Reef (GBR) is dominated by the transport and dispersal of fine-grained basaltic soils. Soils derived from alkali basalts have high total P (3000^4000 mg/kg) and distinctive 143 Nd/ 144 Nd isotopic signatures (ONdV+3 to +5), while the more common Palaeozoic granitic/metamorphic soils have much lower total P (300^600 mg/kg) and 143 Nd isotopic signatures (ONdV38). The nearshore environment (6 5 km from the coast) is dominated by coarse-grained, graniticderived fluvial detritus, while s 20 km from the coast, carbonate-rich sediments with increasing contributions from basaltic components become more important. In the offshore sites adjacent to coral reefs, it is shown that basaltderived sediments can account for s 90% of the terrestrial P, although making up less than half of the total terrigenous detritus. Equilibrium phosphorus concentration measurements on the marine sediments indicate that P enters the GBR lagoon via a two-stage process. Firstly, during episodic flood events, P is transported into the GBR lagoon on P-retentive fine-grained suspended sediments, with only minor desorption of P occurring in the low-salinity flood plumes. Desorption of P mainly occurs over longer timescales, predominantly in regions of sediment anoxia, with release of PO 33 4 directly into marine pore waters probably via reduction of ferric phosphates, and subsequent release into the water column by re-suspension. This process causes P depletion of the re-deposited sediments. = 2003 Elsevier Science B.V. All rights reserved.

Osmium isotope geochemistry of a tropical estuary

Abstract Fundamental aspects of the estuarine geochemistry of Os were investigated by analysis of the Os isotope composition and concentration variations in filtered water samples from a salinity transect taken in the estuary of the tropical Fly River of New Guinea. 187Os/188Os of the waters in the salinity transect increase with salinity from 0.6165 in the river endmember (0.1‰ salinity) to a maximum of 0.913 in the most saline water (33‰). These values are distinctly lower than the 187Os/188Os of 1.06 reported for open ocean waters from the Indian and Pacific Oceans Sharma et al 1997 , Levasseur et al 1998 , Woodhouse et al 1999 . The Os concentrations in the waters range from a minimum of 4.59 pg Os/g in the river to a maximum of 5.66 pg Os/kg at 12‰ salinity. These concentrations are all significantly lower than the open ocean range of 6.6 to 10.86 pg Os/kg Levasseur et al 1998 , Woodhouse et al 1999 . The isotopic results indicate that the rivers draining the New Guinea landmass provide unradiogenic dissolved Os to the oceans and led to a lowering of the 187Os/188Os of the local seawater. The Os concentration-salinity relationship indicates that the mixing process is not conservative and that removal of Os from the dissolved state has taken place. The proportion of Os lost from solution increases with salinity, resulting in removal of a large proportion of seawater Os in the estuary. High concentrations of Os in marine sediments within the Gulf of Papua were previously interpreted to be due to incorporation of seawater-derived Os into organic matter ( Martin et al., 2000 , Earth Planet. Sci. Lett.183, 261–274) and are the likely complement to the processes observed in the dissolved state. Enhanced removal of seawater Os in estuaries could help to resolve the differences in estimates of Os residence time made on the basis of oceanic deposits versus those based on measured river water concentrations.

Linking a late Miocene–Pliocene hiatus in the deep-sea Bounty Fan off South Island, New Zealand, to onshore tectonism and lacustrine sediment storage

The cored record at Ocean Drilling Program Site 1122, located on the levee of the Bounty Fan off southeastern New Zealand, shows a major late Miocene to Pliocene (11.0–3.5 Ma) hiatus in sedimentation. This hiatus straddles a period of major uplift in the Southern Alps where the rivers that feed sediment to the Bounty Fan are ultimately sourced. There are no significant changes in sediment provenance across this interval. We link this hiatus to a combination of decreased sediment supply owing to tectonic disruption of fluvial drainage and a roughly simultaneous increase in bottom-current strength. Evidence for this scenario includes the distribution of current-generated structures in the core, the relative timing of an onshore transition from fluvial to lacustrine sedimentation, and a potential post-hiatus pulse of more weathered sediment into the Bounty Fan. This sediment pulse was possibly associated with the reestablishment of throughgoing drainage and the erosion and flushing of stored alluvial to lacustrine sediments through the system. Thus the Bounty Fan provides an excellent example of how the complex interplay between tectonic and paleoceanographic forces can affect the sedimentary record in deep-marine systems.

Temporal and spatial variability of acid rock drainage in a rehabilitated coal mine, Wangaloa, South Otago, New Zealand.

Abstract The Wangaloa open cast coal mine ceased operations in 1989, with no restoration of the 252 ha site, and moderate acid rock drainage developed. A major rehabilitation programme was initiated in 2002 with removal of exotic vegetation, and extensive planting (>60 000) of native seedlings was begun in 2003. By 2006, most seedlings were thriving, and, combined with adventive exotic weeds, a 70% vegetation cover had been achieved. The site substrates were highly variable on the 10–100 m2 scale, and have been characterised by paste pH (>700 measurements). In 2003, substrates had moderate acidity (pH = 4.5 ± 0.9) with distinctly acid patches (pH down to <2). By 2006, the average substrate pH was essentially unchanged. Some distinctly acid patches had higher pH, and one patch had apparently become more acid. Water compositions (>100 samples from 15 sites) were also highly variable spatially and temporally. Incoming stream and rainwater (pH 5–6) chemically interacted with acid substrates, especially waste rock piles that contain pyrite‐bearing material, and evolved to lower pH (pH down to 3.4), sulfate‐rich waters. A pit lake on the site receives most surface and groundwater runoff, and this lake, with a water residence time of 1–2 yr, controls the site discharge water quality. The lake pH varies on a monthly time‐scale from 4.5 to 6.5, synchronised with pH variations in groundwater boreholes in waste rock. In addition, there has been a general increase in pH of the lake during rehabilitation from consistent pH 4.6–4.8 before rehabilitation to near pH 6 during rehabilitation. The sulfate/chloride ratio of lake water has decreased from 20 to <10 during rehabilitation as well. These changes in lake water composition from year to year may be a result of increased input of rainwater that has had less interaction with substrate than runoff water had before rehabilitation began.

Investigation of nutrient limitation status and nutrient pathways in Lake Hayes, Otago, New Zealand: A case study for integrated lake assessment

Abstract We present a case study illustrating an integrated approach to lake water quality assessment, for Lake Hayes, Otago, New Zealand. This approach improved understanding of the biological importance of several macro‐ and micronutrients and their major pathways (including groundwater), and, coupled with trophic state monitoring, could be the basis for more effective management of lakes exhibiting algal blooms. A nutrient enrichment bioassay experiment found that additions of zinc and nitrogen stimulated productivity, indicating that phytoplankton growth in the lake may have been limited by these nutrients. Nutrient data confirmed the potential for nitrogen limitation at times. The main source of nutrients to the lake was the surface inflow, but almost 30% of the nitrate input entered the lake via a groundwater‐fed spring, highlighting the importance of nutrients in groundwater as a potential driver of algal proliferation. A recent shift in phytoplankton community structure from dominance of cyanobacteria and desmids to dominance of mobile, mixotrophic dinoflagellates indicates that the dominant phytoplankter may no longer be restricted to using only epilimnetic and inorganic forms of nutrients. This integrated assessment of Lake Hayes also suggested strong internal phosphorus cycling, which could explain why phytoplankton blooms continue despite improved catchment nutrient management.

The evolution of hydrous magmas in the Tongariro Volcanic Centre: the 10 ka Pahoka-Mangamate eruptions

The majority of arc-type andesites in the Tongariro Volcanic Centre are highly porphyritic, hornblende-free, two-pyroxene andesites. An exception is tephras from the c. 10,000 ka Pahoka-Mangamate event. Magmas of these Plinian eruptions bypassed the extensive crustal mush columns under the central volcanoes and sequentially derived a series of almost aphyric rocks spanning a compositional range from dacite to basaltic andesite. Mineral composition, trace element and isotopic data suggest that this eruptive series tapped a mid-crustal magma reservoir, resulting in the initial eruption of an hydrous dacitic magma and several following eruptions characterised by less-evolved and less-hydrous compositions at progressively higher temperatures and substantially lower 87Sr/86Sr ratios. Systematic changes in magma chemistry are also reflected in a sequential change in phenocryst content starting with an early hornblende–plagioclase-dominated assemblage to a late olivine–plagioclase-dominated assemblage.

Sources and downstream variation of surface water chemistry in the dammed Waitaki catchment, South Island, New Zealand

ABSTRACT This article presents the results of a pilot study exploring downstream changes in water chemistry in the Waitaki catchment, which drains the eastern slopes of the Southern Alps. The headwaters of this catchment are glaciated, and both natural glacial lakes and hydroelectric reservoirs occur in the catchment. The dominant lithology is calcite-poor quartzo-feldspathic metasedimentary rock. We sampled surface waters from streams and the inflow and outflow of lakes in the catchment on four occasions over the course of 1year, at c. 3-monthly intervals between summer 2013 and spring 2014. We also sampled ice released from the terminus of the Tasman Glacier. Small but measurable variations were observed in the major element (Ca, Mg, K, Na, Si), trace element (Al, Fe, Rb, Sr) and Sr isotopic composition of the surface waters in the catchment. The composition of the waters is interpreted to reflect the change from calcite-dominated weathering near the top of the catchment toward more silicate weathering down the catchment that has been observed in other studies. The composition of samples collected from the uppermost part of the catchment displays more temporal variability than those samples collected from dammed lakes, suggesting that seasonality is dampened by anthropogenic modification of the catchment.