Sources of particulate organic matter at the ecosystem scale: a stable isotope and trace element study in a tropical coral reef

ABSTRACT: Spatial and seasonal variability of sources of particulate organic matter (POM) were evaluated in a coral reef ecosystem. Reef water POM was sampled monthly along a south-north gradient. The passage of tropical cyclone Gamede, which crossed Reunion Island in February 2007, provided an ideal opportunity to examine the impact of high river discharge. Stable isotope composition (δ13C, δ15N) was determined in oceanic, riverine and reef water POM, sedimentary organic matter (SOM), benthic primary producers and detritus. Trace elements (Ti, Fe, Cr, Ni, Cu, Zn) measured in SOM were used as additional terrestrial tracers. Stable isotope analysis of reef water showed that POM was affected by anthropogenic non-point nutrient sources, water circulation patterns and residence time. During the cold and dry season, the southern end of the reef received organic matter input derived from ocean primary production, while the middle and northern reef water POM originated primarily from SOM, reflecting an important bentho-pelagic coupling process. During the hot and wet season, reef water was enriched in benthic detritus due to higher autochthonous production. We found important spatial variability in POM sources, highlighting the importance of small-scale (hundreds of meters) studies when investigating ecosystem functioning. Although coastal tidal currents transported some river discharge material to the south of the reef, riverine POM input was limited, even after cyclone passage. We hypothesized that the major effect of the cyclone was the export of SOM and benthic detritus out of the system and that persistent disturbances such as groundwater discharges can be of greater importance than a cyclone in long-term degradation of ecosystems

Evidence of soil pollution by nitrates derived from pig effluent using 18O and 15N isotope analyses

International audienceIn Réunion Island, expanding human populations, urbanization and agriculture during the last 50 years have all contributed to a steady increase in the level of nitrates in drinking water. Various nitrate point sources are responsible for the nitrate contamination around the island including chemical fertilizers, animal effluent applied to pasture and crops, and urban waste such as sewage and domestic waste water. In terms of agricultural fertilizers, pig effluent is the most widely used, but the cumulative effects of slurry applications on soil water and groundwater are unknown. Our objectives were (1) to characterize and follow in situ the fate of nitrogen through the subsurface after application of pig effluent onto a cultivated soil using stable nitrate isotopes, δ15N and δ18O, and (2) to compare the isotopic signatures of Réunion Island's principal aquifers with results from the experimental site to infer potential contamination sources. The study was conducted on an experimental field site planted with maize in the western part of Réunion Island during the rainy season. A control site with no fertilizer application to the maize was compared with the investigation site which had pig effluent applied once a year. The site which had pig effluent applied over one year had an average maximum surface soil water 15N-${\rm NO}_{3}^{-}$ value of +9.0‰ at 0.45 m depth. This signature was significantly more enriched in 15N than the corresponding subsurface soil water 15N-${\rm NO}_{3}^{-}$ value of +3.8‰ at 10 m depth. The control site average maximum surface soil water 15N-${\rm NO}_{3}^{-}$ value of +3.6‰ at 0.45 m is similar to the subsurface pig effluent application plot. This indicates that nitrates derived from pig effluent have not reached 10 m depth in the subsurface, even though over the last 18 months this site was subjected to two effluent applications, each around 200 kg N ha−1, and more than 1900 mm of rain, more than half of which drains directly into the root zone. This slow migration shows that mobilization of nitrates through cultivated soil can take many tens of years before infiltrating and contaminating the saturated zone situated at several tens, and in places, hundreds of meters depth. On an island-wide scale, an isotopic assessment of nitrates from the experimental site's soil water and other drinking water wells highlights a nitrogenous contamination derived primarily from urban and/or agriculture via effluent application

Augustus Hamilton’s fossil collection at the Museum of New Zealand Te Papa Tongarewa

Augustus Hamilton (1853–1913) was a New Zealand ethnologist and naturalist who amassed a significant collection of fossils, mostly of birds, during his career. Today, those fossils are housed in the Museum of New Zealand Te Papa Tongarewa (NMNZ). While some fossils have been catalogued and integrated into the collection of the NMNZ, a large part remained unsorted and uncatalogued. The present study brings an integrated view of Hamilton’s collection at the NMNZ, highlighting the most significant fossils. In total, there are 3692 specimen lots collected by Hamilton in the NMNZ representing a large sample of taxa and a wide range of locations around Aotearoa New Zealand. Most fossils are of Holocene age and belong to birds. The collection includes type specimens, circa 250 specimen lots belonging to extinct species, and specimens belonging to otherwise poorly represented species in natural history collections. We hope that our study makes Hamilton’s fossils visible and more readily available for future research

(13)C/(12)C composition, a novel parameter to study the downward migration of paper sludge in soils†

δ(13)C values of crop and forest soils were measured 8 years after disposal of paper sewage sludge. The carbon transfer from paper sludge downward to the first humic layer is evidenced by a (13)C-enrichnient of up to + 5.6‰ due to the input of (13)C-enriched sludge carbonates. (13)C/(12)C composition is thus a novel, sensitive parameter to follow the downward transfer of paper sludge carbon

Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)

Stable hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS) isotope compositions expressed as isotope-delta values are typically reported relative to international standards such as Vienna Standard Mean Ocean Water (VSMOW), Vienna Peedee belemnite (VPDB) or Vienna Cañon Diablo Troilite (VCDT). These international standards are chosen by convention and the calibration methods used to realise them in practice undergo occasional changes. To ensure longevity and reusability of published data, a comprehensive description of (1) analytical procedure, (2) traceability, (3) data processing, and (4) uncertainty evaluation is required. Following earlier International Union of Pure and Applied Chemistry documents on terminology and notations, this paper proposes minimum requirements for publishing HCNOS stable-isotope delta results. Each of the requirements are presented with illustrative example

Baseline geochemical characterisation of a vulnerable tropical karstic aquifer; Lifou, New Caledonia

Study region: Lifou Island, near the main island of New Caledonia. Study focus: Stable oxygen and hydrogen isotopes of groundwater and rainfall were used to characterise baseline values for the main fresh water aquifer of Lifou Island and describe its recharge. Other stable isotope parameters (nitrates and DIC) were used to investigate the interaction between surface water (rainfall) and groundwater, including anthropogenic effects from human activities. New hydrological insights for the region: This study represents the first baseline isotopic characterisation of Lifou Island’s groundwater aquifer composition and provides a reference for future investigative studies on groundwater quality and security. Groundwater sampled in June and October 2012 had nearly identical isotopic composition. Tap water sampled monthly between February 2012 and January 2014 also had a constant isotopic composition similar to the groundwater. Groundwater recharge was found to occur when monthly precipitation exceeded 140 mm, with the recharge cycle representing 20–30% of the annual rainfall. Relationships between HCO32− content, pH, soil δ13C DIC and satellite photo interpretation suggests a variance of soil pCO2, which is explained by different vegetation cover and higher water use efficiencies in forested areas (high pCO2, more negative δ13C isotope values). The δ15NNO3 values for most groundwater indicate they are uncontaminated with anthropogenic nitrates, although some samples taken in October (dry season) showed a slight denitrification, possibly of natural origin. Keywords: Reef islands, Precipitation, Karstic aquifer, Hydrogeology, Stable isotopes, Nitrate

A Review of Critical Element Concentrations in High Enthalpy Geothermal Fluids in New Zealand

This review compiles publicly available datasets describing the chemical composition of geothermal fluids from eight wells in the Taupo Volcanic Zone (TVZ) and Ngāwhā, New Zealand. Our review allows previously reported geothermal reservoir water compositions at various locations around the TVZ (and Ngāwhā) to be assessed and compared for the first time. The combined data present a new perspective on potential critical elements of geothermal resources and will be a valuable tool for future research projects and investment opportunities. Composition data were used to estimate the annual flux of different elements in New Zealand geothermal systems. Several elements found in New Zealand geothermal fluids are currently considered ‘critical’ for the transition to a carbon-neutral economy and are present in economically extractable quantities. We estimate that each year, approximately 1100 tons of lithium pass as heat exchange fluids through Wairakei geothermal power station. An overview of the critical elemental capture and extractive potential from New Zealand’s geothermal fields is provided

Ecology of foraminifera during the middle Eocene climatic optimum in Kutch, India

The shallow marine carbonates of Kutch temporally correspond to the globally recognised warming period called Middle Eocene Climatic Optimum (MECO) that extended from later part of planktic foraminiferal zone E11 to E12 and Shallow Benthic Zone (SBZ) 17. The present study aims to investigate how foraminifera responded ecologically to the warming event. It involves identification and distribution of foraminifera, and cluster and detrended correspondence analyses of the species distribution data. Selected samples across E11 and E12 were analysed for carbon isotopes. The major conclusions are: (i) bloom of Jenkinsina columbiana in zone E11, possibly marking the initiation of warming in a shallow, eutrophic sea, (ii) increased foraminiferal diversity, appearance of Orbulinoides beckmanni and Acarinina and a sharp rise in the sea level in the early part of E12 (iii) significant jump in diversity and abundance of larger benthic foraminifera in E12, signifying warm, clear-water oligotrophic seas, promoting the formation of platform carbonates, (iv) MECO does not seem to have adversely impacted the foraminifera in shallow seas, and larger benthic foraminifera were rather ultimately superior in their diversity, abundance, size and latitudinal distribution and (v) δ13C excursions up to 1.5 ‰ are noted in the upper parts of E11 and lower parts of E12

Feeding patterns of two sympatric shark predators in coastal ecosystems of an oceanic island

International audienceStomach contents and stable carbon and nitrogen isotope analyses (13 C and 15 N) were used to investigate the trophic ecology of two apex predators, tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas), from Reunion Island to describe their dietary habits at both the population and individual levels. In this oceanic island, the tiger and bull sharks were more piscivorous and teutophagous than noted in previous research from other localities. The 13 C values suggested that bull sharks depended on more neritic organic matter sources than tiger sharks, confirming a coastal habitat preference for bull sharks. Moreover, the total length of the bull shark influenced 13 C values, with smaller individuals being more coastal than larger individuals. All indicators suggest that there is a higher degree of similarity between individual tiger sharks compared with the more heterogeneous bull shark population, which is composed of individuals who specialize on different prey. These results suggest that the two species have different functions in these coastal habitats, and thus, they must be considered independently in terms of conservation and management