Influence of the Danube River inputs on C and N stable isotope ratios of the Romanian coastal waters and sediment (Black Sea)

The main aim of this study was to estimate the influence of the seasonal variations of the Danube River particulate organic matter (POM) inputs on the Black Sea surface seawater POM and upper layer of sediments along the Romanian coast. Ratios of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) stable isotopes allowed differentiating river and marine organic matter sources. Danube River POM presented significantly lower average values of delta(13)C (-27.52+/-0.88 per thousand) and delta(15)N (4.88+/-1.45 per thousand) than seawater POM (delta(13)C=-24.70+/-2.37 per thousand and delta(15)N=6.75+/-1.96 per thousand), whereas surface sediment presented average values similar to seawater POM (delta(13)C=-24.02+/-2.39 per thousand and delta(15)N=7.29+/-2.16 per thousand). Stable isotope values showed that the Danube River influence on marine ecosystems decreased from the North to the South of the Romanian coast. Strong seasonal variations of C and N isotopic signatures were observed in all compartments studied with generally higher values in spring when the river was flooding.     

Characterization and origin of dissolved organic carbon in Yegua ground water in Brazos County, Texas

Dissolved organic carbon (DOC) concentrations in five shallow (< 20 m) and three deeper wells (27 to 30 m) in the Eocene Yegua Formation (Brazos County in east-central Texas) ranged from 92 to 500 microns. Characterization of high, intermediate, and low molecular weight DOC fractions (HMW > 3000 amu, IMW 1000 to 3000 amu, and LMW 500 to 1000 amu) and combined neutral sugar analyses provide information on organic matter sources in the Yegua aquifers. Combined neutral sugars ranged in concentration from 0.6 to 2.7 mumol/L and comprised 0.8% to 6.7% of DOC in ground water. Glucose was the most abundant neutral sugar, followed by xylose and galactose, arabinose, mannose, rhamnose, and fucose. These combined neutral sugars were more diagenetically altered in shallow, oxic ground water as indicated by high mole % fucose + rhamnose and low neutral sugar yield. The precursors for neutral sugars are most probably angiosperm leaves, which show a similar distribution pattern of neutral sugars. Ground water DOC was depleted in 13C relative to soil-zone organic matter (OM) (-16@1000 to -19@1000). The delta 13C values of bulk DOC and HMW DOC ranged from -24@1000 to -32@1000, whereas LMW and IMW DOC ranged from -32@1000 to -34@1000 and -16@1000 to -28@1000, respectively. This variability in delta 13C values is probably related to microbial processes and selective preservation of OM. Carbon isotope analyses in bulk and different molecular weight DOC fractions imply a predominantly C3 OM source and a low contribution of soil-zone OM to DOC.     

Stable isotope evidence for the environmental impact of a land-based fish farm in the western Mediterranean

Isotopic examination (delta(13)C and delta(15)N) of organic matter sources and consumers was used to assess the impact and trace the dispersal of wastewater from a land-based fish farm in western Mediterranean. The results provide evidence of the non-negligible effect of aquaculture facilities on the natural stable isotopic composition of organisms. Aquaculture waste entered the food web, altering the natural isotopic composition of organic matter sources at the base and the upper trophic levels. Nitrogen-rich fish waste mainly affected delta(15)N values, while delta(13)C showed less alteration. Waste seemed to disperse widely enough to affect the isotopic composition at the study site about 500 m from the outfall, while sites at 1 and 2 km from the outfall showed values that were similar to each other and different from those of the impacted site. The impact was detected at different ecosystem levels, although primary producers were more affected by fish farm waste taking up aquaculture-derived nutrients.     

Distribution and sources of sedimentary organic matter in a tropical estuary,south west coast of India (Cochin estuary): A baseline study

Surface sediments samples were collected from 9 stations of the Cochin estuary during the monsoon, post-monsoon and pre-monsoon seasons and were analyzed for grain size, total organic carbon (OC), total nitrogen (TN) and stable isotopic ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) to identify major sources of organic matter in surface sediments. Sediment grain size is found to be the key factor influencing the organic matter accumulation in surface sediments. The δ¹³C values ranges from ?27.5‰ to ?21.7‰ in surface sediments with a gradual increase from inner part of the estuary to the seaward side that suggest an increasing contribution of marine autogenous organic matter towards the seaward side. The δ¹⁵N value varies between 3.1‰ and 6.7‰ and it exhibits complex spatial and seasonal distributions in the study area. It is found that the dynamic cycling of nitrogen through various biogeochemical and organic matter degradation processes modifies the OC/TN ratios and δ¹⁵N to a considerable degree. The fraction of terrestrial organic matter in the total organic matter pool ranges from 13% to 74% in the surface sediments as estimated by δ¹³C based two end member mixing model.     

Investigating the distribution and sources of organic matter in surface sediment of Coombabah Lake (Australia) using elemental,isotopic and fatty acid biomarkers

Extensive physical and biological measurements were made of the surface sediments within the shallow, semi-urbanised Coombabah Lake in southern Moreton Bay, Australia. Sediment bulk parameters (C/N ratios, δ¹³C and δ¹⁵N) and fatty acid biomarkers were used to determine distributions and sources of organic matter in the intertidal sediments. The determination of organic matter sources within coastal and estuarine settings is important in understanding the roles of organic matter as energy and nutrient sources. Spatial variability of biomarker values within the sediments were interpreted by thematic maps employing the Krigging algorithm. Grain size analysis indicated the lake was dominated by mud (<63 μm) in the southern (landward) and sand (>63 μm) in the northern (seaward) lake regions, respectively. Surface sediment organic C and N values ranged from 0.12% to 1.76% and 0.01% to 0.12% dry weight, respectively, and C/N ratios averaged 16.3±3.19%. Sedimentary δ¹³C values ranged from −26.1‰ to −20.9‰, with an average value of −23.9±1.0‰. Sedimentary δ¹⁵N values ranged from +1.7‰ to +4.8‰, with an average value of +2.8±0.8‰. Bulk sediment parameters suggested that sedimentary organic matter is provided predominantly by allochthonous sources in the form of fringing mangroves. Thirty-nine individual fatty acids were identified using gas chromatography–mass spectrometry. The mean contributions of long chain fatty acids (LCFAs), polyunsaturated fatty acids (PUFAs), saturated fatty acids (SAFAs) and bacterial fatty acids (BAFAs) were, respectively, 13.9±11.4%, 7.6±4.1%, 53.6±8.6% and 18.2±4.6% of the identified fatty acid methyl esters (FAMEs), with BAFAs occurring in all sampled sediments. Fatty acid compositions varied throughout lake sediments, which indicated spatial differences in autochthonous and allochthonous organic matter sources, including terrestrial and planktonic (i.e. zooplankton, diatoms and other algal species) sources. The contribution of organic matter from shoreline mangroves was confirmed by the presence of LCFAs and 18:2ω6 and 18:3ω3, which are markers for mangroves in this ecosystem. BAFAs were identified in increased proportions in sediments adjacent to urban developments and dominated by mud. Grain size was identified as a dominant factor in the fatty acid compositions and contributing values to FAME pool. Spatial patterns of C/N ratios, δ¹³C and δ¹⁵N values, and fatty acid biomarker contributions illustrated that there is a greater contribution of autochthonous and labile organic matter to the sedimentary organic matter pool in the northern (marine entrance) sediments compared to the more allochthonous sourced organic matter of the southern region of the lake. This study details the distribution and sources of organic matter within Coombabah Lake and illustrates the usefulness of a multiple biomarker approach in discriminating organic matter sources within estuarine environments.     

An isotopic model for the origin of autochthonous organic matter contained in the bottom sediments of a reservoir

Geochemical analysis of surface sediment samples collected in 2005 and 2006 was used to evaluate the potential sources of the organic matter present in sediments of southeast Poland's Solina Reservoir.Statistical analysis of sediment variables(carbon to nitrogen ratio, and the carbon 13 and nitrogen 15 isotope ratios) determined for the organic fraction indicated significant spatial variability with respect to sources of organic matter. A binary mixing model was developed from literature sources to predict the relative contributions of allochthonous and autochthonous production to sediment organic matter.Autochthonous production was shown to account for 60-75% of bulk sedimentation in the lacustrine parts of the reservoir, near the dam. In contrast, autochthonous production accounted for only 25% of sedimentation in the riverine zone receiving stream inputs. Statistical analysis identified the δ~(15)N of organic matter as the best predictor of the source of organic matter. Multiple regression analysis indicated that two water-quality variables(nitrate and dissolved silica) were significantly related to the δ~(15)N signature of organic matter. This led to a conclusion that limnetic nitrate and dissolved silica concentrations were regulating organic matter production in the Solina Reservoir.     

Comparative study on CO2 sources in soil developed on carbonate rock and non-carbonate rock in Central Guizhou

In this paper, by using concentration and carbon stable isotope the CO2 sources of soil profiles developed on limestone, dolostone and claystone basements in Central Guizhou, China are comparatively studied. The results show that CO2 concentration of soil profiles developed on different basements is different, having the following sequence: limestone>dolostone>claystone. Below the soil depth of 20 cm from the surface the ? 13C value of CO2 in soil profile developed on limestone ranges from -12.811‰ - -13.492‰(PDB), that in soil profile developed on dolostone varys from -13.212‰ - -14.271‰(PDB) and that in soil profile developed on claystone is about -20.234‰ - -21.485‰(PDB). Taking the carbon isotope of soil organic matter and carbonate rock as two isotopic endmembers, the proportion of soil CO2 generated by dissolution of carbonate rock is calculated, about 21%-25% for soil profile developed on limestone basement, 19%-21% for soil profile developed on dolostone basement. There is almost no influx of CO2 generated by the dissolution of carbonate rock in soil profile developed on claystone basement.     

河库连续体中溶解性无机碳及其同位素的时空分异特征——以澜沧江云南段为例

河流及水库等水生态系统中的溶解性无机碳(DIC)是全球碳循环与大气、陆地和海洋之间碳相互作用的重要组成部分.以澜沧江云南段上游天然河段及下游梯级水库群形成的连续体为研究对象,分析了河库连续体表层水体中水化学特征、溶解性无机碳浓度及其碳同位素时空分布特征.研究结果表明:河库连续体水体中溶解无机碳(DIC)及其同位素(δ13 C DIC)组成特征总体表现为:DIC浓度丰水期较低,枯水期较高,平均值分别为2.59±0.44和3.30±0.37 mmol/L;δ13 C DIC值丰水期偏负、枯水期偏正,平均值分别为-8.52‰±0.38‰和-6.95‰±0.53‰,与自然河流的季节变化特征相似.水体DIC来源主要包括土壤及水体有机质分解生成的CO 2、碳酸盐风化和水气界面CO 2的交换过程.澜沧江河库连续体中DIC浓度及δ13 C DIC组成的时空异质性特征与流域岩性、土壤生物地球化学过程以及微生物活动强度等均有较大关系.当前,澜沧江梯级水库群建库时间短,梯级联合运行下调度复杂,水文条件多变,梯级水库对河流重要生源要素——碳累积影响方面的“水库效应”还不明显.     

Land–ocean distribution of allochthonous organic matter in surface sediments of the Chiloé and Aysén interior seas (Chilean Northern Patagonia)

We investigated the relative distribution of allochthonous (i.e., terrigenous) organic matter in the complex, continuous, river–fjord–sound–channel–gulf system of Chile’s North Patagonia (41.5–46.5°S) in order to establish whether this organic matter can reach the open ocean or whether it is largely retained near its fluvial sources. Grain size distribution, total organic carbon and total nitrogen contents, and carbon stable isotope contents (δ¹³C) were quantified in 53 surface sediment samples collected during the CIMAR Fiordos cruises 1, 4, 8, and 10, as were salinity and silicic acid concentrations in the surface waters. A principal component analysis segregated the Chiloé and Aysén interior seas into two zones: (i) the continental fjords, with sediment enriched in allochthonous organic matter, having higher C:N molar ratios (10–14) and lower δ¹³C composition (?23‰ to ?27‰); and (ii) the channels and gulfs, with a prevalent autochthonous marine source, having lower C:N values (6–10) and higher δ¹³C composition (?20‰ to ?23‰). Estuarine waters with low salinity (2–30) and high silicic acid (10–90 μM) were associated with high C:N ratios and low δ¹³C in surface sediments, meaning that terrestrial organic matter was transported up to the mouth of the continental fjords. A two-source mixing model confirmed that allochthonous (terrestrial) organic matter contents (50–90%) associated with local river discharges were present within the continental fjords. On the contrary, autochthonous (marine) organic matter was prevalent (50–90%) at the sites in the marine influenced channels, sounds, and gulfs.     

鄱阳湖网箱养殖区沉积物有机质来源分析

通过对鱼苗时期鄱阳湖网箱养殖区沉积物、饵料及鱼粪等样品总有机碳(TOC)含量、总氮(TN)含量、碳氮比(C/N)、δ^13 C及δ^15 N的测定,分析探讨了鄱阳湖网箱养殖区沉积物有机质来源,量化了网箱养殖废物对养殖区沉积物有机质的贡献.结果表明,网箱养殖区沉积物的δ^13 C和δ^15 N值分别为-27.67‰~-25.65‰和5.19‰~7.27‰,饵料的δ^13 C和δ^15 N值分别为-24.73‰和10.28‰,鱼粪的δ^13 C和δ^15 N值分别为-26.30‰和15.54‰.网箱养殖区沉积物有机质来源主要有残饵、浮游生物及其他来源,其贡献率分别为48.3%±11.4%、25.6%±11.3%及26.0%±5.8%,而鱼粪的贡献几乎可以忽略不计.在水动力平流引起的扩散及沉积物的再悬浮的影响下,网箱养殖源有机质的扩散距离达1500 m.在鱼苗时期,鱼类网箱养殖的残饵是鄱阳湖网箱养殖区沉积物有机质的主要来源.     

Organic carbon deliveries and their flow related dynamics in the Fitzroy estuary

The Fitzroy estuary (Queensland, Australia) receives large, but highly episodic, river flows from a catchment (144,000 km(2)) which has undergone major land clearing. Large quantities of suspended sediments, and particulate and dissolved organic carbon are delivered. At peak flows, delta(13)C (-21.7+/-0.8 per thousand) and C/N (14.8+/-1.3) of the suspended solids indicate that the particulate organic material entering the estuary is principally soil organic carbon. At the lower beginning flows the particulate organic matter comes from in-stream producers (delta(13)C=-26 per thousand). The DOC load is about 10 times the POC load. Using the inverse method, budgets for POC and DOC were constructed for high and low flows. Under high flows, only a small portion of the POC and DOC load is lost in the estuary. Under dry season (low flow) conditions the estuary is a sink for DOC, but remains a source of POC to the coastal waters.     

Sulfur and carbon isotopic systematics of Guadalupian‐Lopingian (Permian) mid‐Panthalassa: δ34S and δ13C profiles in accreted paleo‐atoll carbonates in Japan

Immediately before the extinction of the end‐Guadalupian (Middle Permian; ca 260 Ma), a significant change to the global carbon cycle occurred in the superocean Panthalassa, as indicated by a prominent positive δ¹³C excursion called the Kamura event. However, the causes of this event and its connection to the major extinction of marine invertebrates remain unclear. To understand the mutual relationships between these changes, we analyzed the sulfur isotope ratio of the carbonate‐associated sulfate (CAS) and HCl‐insoluble residue, as well as the carbon isotope ratio of bulk organic matter, for the Middle‐Upper Permian carbonates of an accreted mid‐oceanic paleo‐atoll complex from Japan, where the Kamura event was first documented. We detected the following unique aspects of the stable carbon and sulfur isotope records. First, the extremely high δ¹³C values of carbonate (δ¹³C_carb) over +5 ‰ during the Capitanian (late Guadalupian) were associated with large isotopic differences between carbonate and organic matter (Δ¹³C = δ¹³C_carb ? δ¹³C_org). We infer that the Capitanian Kamura event reflected an unusually large amount of dissolved organic matter in the expanded oxygen minimum zone at mid‐depth. Second, the δ³⁴S values of CAS (δ³⁴S_CAS) were inversely correlated with the δ¹³C_carb values during the Capitanian to early Wuchiapingian (early Late Permian) interval. The Capitanian trend may have appeared under increased oceanic sulfate conditions, which were accelerated by intense volcanic outgassing. Bacterial sulfate reduction with increased sulfate concentrations in seawater may have stimulated the production of pyrite that may have incorporated iron in pre‐existing iron hydroxide/oxide. This stimulated phosphorus release, which enhanced organic matter production and resulted in high δ¹³C_carb. Low δ³⁴S_CAS values under high sulfate concentrations were maintained and the continuous supply of sulfate cannot by explained only by the volcanic eruption of the Emeishan Trap, which has been proposed as a cause of the extinction. The Wuchiapingian δ³⁴S_CAS–δ¹³C_carb correlation, likely related to low sulfate concentration, may have been caused by the removal of oceanic sulfate through the massive evaporite deposition.     

贵州草海湖泊系统碳循环简单模式

本文分析了贵州草海湖泊系统中的主要含碳物质－湖水DIC、表层沉积物有机质、水生植物的稳定碳同位素组成,其δ^13C值分别为：－3．70‰至－10．60‰,－20．90‰至－21．60％,－16．10‰至－17．40,通过质量平衡计算,建立了草海区域碳循环的简单模式,结果表明：对于草海这样一个水生植物茂盛的浅水富氧湖而言,光合一呼吸作用和有机质的降解对整个湖泊体系的稳定碳同位素组成具有决定性的作用。     

Carbon isotopic compositions of organic matter across continental Cretaceous–Tertiary (K–T) boundary sections: Implications for paleoenvironment after the K–T impact event

To assess the environmental perturbation induced by the impact event that marks the Cretaceous–Tertiary (K–T) boundary, concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial K–T boundary at Dogie Creek, Montana, and Brownie Butte, Wyoming in the Western Interior of the United States. The boundary clays at both sites are not bounded by coals. Although coals consist mainly of organic matter derived from plant tissue, siliceous sedimentary rocks, such as shale and clay, may contain organic matter derived from microbiota as well as plants. Coals record δ¹³C values of plant-derived organic matter, reflecting the δ¹³C value of atmospheric CO₂, whereas siliceous sedimentary rocks record the δ¹³C values of organic matter derived from plants and microbiota. The microbiota δ¹³C value reflects not only the δ¹³C value of atmospheric CO₂, but also biological productivity. Therefore, the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds.Across the freshwater K–T boundary at Brownie Butte, the δ¹³C values decrease by 2.6‰ (from − 26.15‰ below the boundary clay to − 28.78‰ above the boundary clay), similar to the trend in carbonate at marine K–T sites. This means that the organic δ¹³C values reflect the variation of δ¹³C of atmospheric CO₂, which is in equilibrium with carbon isotopes at the ocean surface. Although a decrease in δ¹³C values is observed across the K–T boundary at Dogie Creek (from − 25.32‰ below the boundary clay to − 26.11‰ above the boundary clay), the degree of δ¹³C-decrease at Dogie Creek is smaller than that at Brownie Butte and that for marine carbonate.About 2‰ decrease in δ¹³C of atmospheric CO₂ was expected from the δ¹³C variation of marine carbonate at the K–T boundary. This δ¹³C-decrease of atmospheric CO₂ should affect the δ¹³C values of organic matter derived from plant tissue. As such a decrease in δ¹³C value was not observed at Dogie Creek, a process that compensates the δ¹³C-decrease of atmospheric CO₂ should be involved. For example, the enhanced contribution of ¹³C-enriched organic matter derived from algae in a high-productivity environment could be responsible. The δ¹³C values of algal organic matter become higher than, and thus distinguishable from, those of plant organic matter in situations with high productivity, where dissolved HCO₃⁻ becomes an important carbon source, as well as dissolved CO₂. As the δ¹³C-decrease of atmospheric CO₂ reflected a reduction of marine productivity, the compensation of the δ¹³C decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment.A distinct positive δ¹³C excursion of 2‰ in the K–T boundary clays is superimposed on the overall decreasing trend at Dogie Creek; this coincides with an increase in the content of organic carbon. We conclude that the K–T boundary clays include ¹³C-enriched organic matter derived from highly productive algae. Such a high biological productivity was induced by phenomena resulting from the K–T impact, such as nitrogen fertilization and/or eutrophication induced by enhanced sulfide formation. The high productivity recorded in the K–T boundary clays means that the freshwater environments (in contrast to marine environments) recovered rapidly enough to almost immediately (within 10 yr) respond to the impact-related environmental perturbations.     

Geochemical processes during five years of aquifer storage recovery

A key factor in the long-term viability of aquifer storage recovery (ASR) is the extent of mineral solution interaction between two dissimilar water types and consequent impact on water quality and aquifer stability. We collected geochemical and isotopic data from three observation wells located 25, 65, and 325 m from an injection well at an experimental ASR site located in a karstic, confined carbonate aquifer in South Australia. The experiment involved five major injection cycles of a total of 2.5 x 10(5) m3 of storm water (total dissolved solids [TDS] approximately 150 mg/L) into the brackish (TDS approximately 2400 mg/L) aquifer. Approximately 60% of the mixture was pumped out during the fifth year of the experiment. The major effect on water quality within a 25 m radius of the injection well following injection of storm water was carbonate dissolution (35 +/- 6 g of CaCO3 dissolved/m3 of aquifer) and sulfide mineral oxidation (50 +/- 10 g as FeS2/m3 after one injection). < 0.005% of the total aquifer carbonate matrix was dissolved during each injection event, and approximately 0.2% of the total reduced sulfur. Increasing amounts of ambient ground water was entrained into the injected mixture during each of the storage periods. High 14C(DIC) activities and slightly more negative delta13C(DIC) values measured immediately after injection events show that substantial CO2(aq) is produced by oxidation of organic matter associated with injectant. There were no detectable geochemical reactions while pumping during the recovery phase in the fifth year of the experiment.     

ENVIRONMENTAL RESPONSE OF THE PERMIAN VOLCANISM IN LUCAOGOU FORMATION IN JIMSAR SAG,JUNGGAR BASIN,NORTHWEST CHINA

The lithological features, the types of organic matter and its occurrence and carbon and oxygen isotopic value were clarified by combining core observation, thin slice authentication, X ray diffraction analysis, kerogen type identification and carbon and oxygen isotope analysis. The characteristic of strata, the distribution of volcanoes of Junggar Basin were also taken into consideration. A comprehensive analysis was conducted to evaluate environmental response of volcanism in Lucaogou formation in Jimsar sag. The results show that rocks is a mixed sedimentation of effusive rock and carbonate rocks, volcanic materials is widely developed in Lucaogou formation and origins from the edge of sag or distant source volcano activity. Organic matter is predominantly unstructural algae and asphaltene. The carbon isotopic value of carbonates ranges between 6.8‰ and 9.7‰ with an average of 8.3‰, featured in high positive excursions, while oxygen isotopic value varies from -11.9‰ to -4.3‰ with an average of -6.2‰. During the period of volcanic activity, the volcanic material released high amounts of nutrient to the lake basin, which is beneficial to the algae and other organic organisms. In the poor oxygen and calm water environments, the organic matter is distributed in the laminar algal and the carbon isotope value is high positive drift. During the intermittent period of volcanic activity, the lake level decreased and the lake bottom water changed to the oxygen-enriched environments. The organic matter is locally enriched or dispersed in local layers, and the carbon isotope values decreased slightly. The frequent volcanic activity promoted the organism boom, which lead carbon isotope value to have high positive characteristics and change trends.     

Coral skeletal delta(15)N reveals isotopic traces of an agricultural revolution

This study introduces a new method of tracing the history of nutrient loading in coastal oceans via delta(15)N analysis of organic nitrogen preserved in the skeleton of the massive Porites coral. Four coral cores were collected in Bali, Indonesia, from reefs exposed to high levels of fertilizers in agricultural run-off, from lagoonal corals impacted by sewage, and from a reef located 30 km offshore. Skeletal delta(15)N in the agriculturally exposed coral declined from 10.7+/-0.4 per thousand in 1970-1971, when synthetic fertilizers (-0.8 per thousand+/-0.2 per thousand) were introduced to Bali, to a depleted "anthropogenic" baseline of 3.5 per thousand+/-0.4% in the mid-1990s. delta(15)N values were negatively correlated with rainfall, suggesting that marine delta(15)N lowers during flood-bourn influxes of waste fertilizers. Reef cores exposed to untreated sewage in terrestrial discharge were enriched (7.8 and 7.3+/-0.4 per thousand), while the offshore core reflected background oceanic signals (6.2+/-0.4 per thousand). delta(15)N, N concentration, and C:N systematics indicate that the N isotopic composition of skeletal organic matter was generally well preserved over 30 years. We suggest that skeletal organic delta(15)N can serve as a recorder of past nitrogen sources. In Bali, this tracer suggests that the intensification of Western style agricultural practices since 1970 are contributing to the degradation of coastal coral reefs.     

Allochthonous subsidies of organic matter across a lake–river–fjord landscape in the Chilean Patagonia: Implications for marine zooplankton in inner fjord areas

Ecosystems can act as both sources and sinks of allochthonous nutrients and organic matter. In this sense, fjord ecosystems are a typical interface and buffer zone between freshwater systems, glaciated continents, and the coastal ocean. In order to evaluate the potential sources and composition of organic matter across fjord ecosystems, we characterized particulate organic matter along a lake–river–fjord corridor in the Chilean Patagonia using stable isotope (δ¹³C) and lipid (fatty acid composition) biomarker analyses. Furthermore, estimates of zooplankton carbon ingestion rates and measurements of δ¹³C and δ¹⁵N in zooplankton (copepods) were used to evaluate the implications of allochthonous subsidies for copepods inhabiting inner fjord areas. Our results showed that riverine freshwater flows contributed an important amount of dissolved silicon but, scarce nitrate and phosphate to the brackish surface layer of the fjord ecosystem. Isotopic signatures of particulate organic matter from lakes and rivers were distinct from their counterparts in oceanic influenced stations. Terrestrial allochthonous sources could support around 68–86% of the particulate organic carbon in the river plume and glacier melting areas, whereas fatty acid concentrations were maximal in the surface waters of the Pascua and Baker river plumes. Estimates of carbon ingestion rates and δ¹³C in copepods from the river plume areas indicated that terrestrial carbon could account for a significant percentage of the copepod body carbon (20–50%) during periods of food limitation. Particulate organic matter from the Pascua River showed a greater allochthonous contribution of terrigenous/vascular plant sources. Rivers may provide fjord ecosystems with allochthonous contributions from different sources because of the distinct vegetation coverage and land use along each river’s watershed. These observations have significant implications for the management of local riverine areas in the context of any human project that may modify terrestrial habitats as well as the productivity, food webs, and community structure of rivers, lakes, fjords, and the coastal ocean in the Chilean Patagonia.     

Geochemistry of organic carbon and nitrogen in surface sediments of coastal Bohai Bay inferred from their ratios and stable isotopic signatures

Total organic carbon (TOC), total nitrogen (TN) and their δ(13)C and δ(15)N values were determined for 42 surface sediments from coastal Bohai Bay in order to determine the concentration and identify the source of organic matter. The sampling sites covered both the marine region of coastal Bohai Bay and the major rivers it connects with. More abundant TOC and TN in sediments from rivers than from the marine region reflect the situation that most of the terrestrial organic matter is deposited before it meets the sea. The spatial variation in δ(13)C and δ(15)N signatures implies that the input of organic matter from anthropogenic activities has a more significant influence on its distribution than that from natural processes. Taking the area as a whole, surface sediments in the marine region of coastal Bohai Bay are dominated by marine derived organic carbon, which on average accounts for 62±11% of TOC.