Isotopic Composition as a Tool for Assessment of Origin and Dynamic of Organic Matter in Tropical Freshwater

The isotopic composition (¹³C and ¹⁵N) and C:N ratio of sediment and particulate were investigated to assess the origin and dynamic of the organic matter in two river basins located in the Parana State, Brazil. The main sources of organic matter, plants, litter and soil, were analyzed in the study. This study was carried out during the dry and wet seasons. Although organic matter contribution for the particulate material has been mixed, the main contribution in the two seasons for both rivers was autochthonous characterized by δ¹³C and C:N ratio values ranging from −31.0 to −21.8‰ and from 5.1 to 11.4, respectively. The soil with δ¹³C values ranging from −25.9 to −20.6‰, and C:N ratio from 10.2 to 15.8, was the main carbon source for the river sediment for the two tributaries in the wet and dry seasons. The sediment δ¹⁵N values for both the rivers in the wet season showed an ¹⁵N enrichment trend in most of studied sites when compared to the dry season values, suggesting major input of nutrients as dissolved organic nitrogen and sewage nitrate. In the dry season, ¹⁴N enriched compounds, could have been used by phytoplankton, causing ¹⁵N enrichment. The isotope and C:N ratio data clearly showed that the agricultural activity has been influencing the origin and dynamic of organic matter in the two rivers, with potential biochemical consequences for the lower basin of the major Tibagi river.     

The UN climate change negotiations and the role of the United States: assessing American leadership from Copenhagen to Paris

The role of American leadership in the UN climate negotiations that produced the 2015 Paris Agreement is examined. First, United States (US) climate goals are identified. Then, utilizing unique survey data collected at eight UN climate summits between 2008 and 2015, the extent to which the US was recognized as a leader by potential followers is investigated. Finally, the extent to which US goals are reflected in negotiation outcomes is evaluated. Recognition of the US as a leader varied over time, peaking at the UN climate meetings in Copenhagen and Paris, reflecting US leadership in shaping the outcomes of both meetings. Although the results reveal a divided leadership landscape in which the US must compete for leadership with other actors, such as the European Union and China, US leadership was crucial to the successful adoption of the Paris Agreement.     

Nitrogen Subsidies from Hillslope Alder Stands to Streamside Wetlands and Headwater Streams,Kenai Peninsula,Alaska

We examined nitrogen transport and wetland primary production along hydrologic flow paths that link nitrogen‐fixing alder (Alnus spp.) stands to downslope wetlands and streams in the Kenai Lowlands, Alaska. We expected that nitrate concentrations in surface water and groundwater would be higher on flow paths below alder. We further expected that nitrate concentrations would be higher in surface water and groundwater at the base of short flow paths with alder and that streamside wetlands at the base of alder‐near flow paths would be less nitrogen limited than wetlands at the base of long flow paths with alder. Our results showed that groundwater nitrate‐N concentrations were significantly higher at alder‐near sites than at no‐alder sites, but did not differ significantly between alder‐far sites and no‐alder sites or between alder‐far sites and alder‐near sites. A survey of ¹⁵N stable isotope signatures in soils and foliage in alder‐near and no‐alder flow paths indicated the alder‐derived nitrogen evident in soils below alder is quickly integrated downslope. Additionally, there was a significant difference in the relative increase in plant biomass after nitrogen fertilization, with the greatest increase occurring in the no‐alder sites. This study demonstrates that streamside wetlands and streams are connected to the surrounding landscapes through hydrologic flow paths, and flow paths with alder stands are potential “hot spots” for nitrogen subsidies at the hillslope scale.     

Genotoxicity evaluation of the insecticide endosulfan in the wetland macrophyte Bidens laevis L

The frequency of micronuclei (MN) and chromosome aberrations in anaphase-telophase (CAAT) was determined in root tips of the wetland macrophyte Bidens laevis exposed to environmentally relevant concentrations of endosulfan (0.01, 0.02, 0.5 and 5microg/L) for 48h. MN frequency varied from 0 in negative controls and plants exposed to 0.01microg/L endosulfan to 0-3 in plants exposed to 5microg/L. Moreover, a significant concentration-dependent increase of CAAT was observed. The higher proportion of laggards and vagrand chromosomes observed at 5microg/L would indicate that endosulfan interacts with the spindle interrupting normal chromosome migration. Endosulfan resulted genotoxic to B. laevis, a species of potential value for bioassays and in situ monitoring of environmental contamination by pesticides.     

MnOx／Al-SBA-15催化剂低温NH3选择性催化还原NO的原位红外研究

用原位红外分别进行了MnOx／Al-SBA-15催化剂上NH3和NO＋O2的吸附态和瞬态实验以及NH3＋NO＋02反应的稳态实验。结果表明,催化剂上存在着L酸位和B酸位,NH3吸附在催化剂上形成配位态的NH3和NH4＋,配位态的NH3能脱氢形成-NH2活性中间态。NO＋O2在催化剂上吸附形成硝酸盐类、硝基类和亚硝酸盐类。将NO＋O2通入预吸附NH3的催化剂中时,表面的配位态的NH3、NH4＋和-NH2都会减少直至消失,SCR反应显著。而将NH3通人预吸附NO＋O2的催化剂中时,只有硝基类和亚硝酸盐类减少,硝酸盐类基本不发生变化,SCR反应微弱。NH3＋NO＋O2稳态反应中,催化剂表面稳定存在着NH4＋和硝酸盐类,SCR反应显著。     

Biomonitoring of traffic-related nitrogen oxides in the Maurienne valley (Savoie, France), using purple moor grass growth parameters and leaf N/N ratio

Effects of traffic-related nitrogenous emissions on purple moor grass (Molinia caerulea (L.) Moench) transplants, used here as a new biomonitoring species, were assessed along 500 m long transects orthogonal to roads located in two open areas in the Maurienne valley (French Alps). Leaves were sampled during summer 2004 and 2005 for total N-content and ¹⁵N-abundance determination while nitrogen oxides (NO and NO₂) concentrations were determined using passive diffusion samplers. A significant and negative correlation was observed between plant total N-content, and ¹⁵N-abundance and the logarithm of the distance to the road axis. The strongest decreases in plant N parameters were observed between 15 and 100 m from road axis. They were equivalent to background levels at a distance of about 800 m from the roads. In addition, motor vehicle pollution significantly affected vegetation at road edge, as was established from the relationship between leaf ¹⁵N-abundance, total N-content and road traffic densities.     

Nitrogen isotope variations in camphor (Cinnamomum Camphora) leaves of different ages in upper and lower canopies as an indicator of atmospheric nitrogen sources

Nitrogen isotopic composition of new, middle-aged and old camphor leaves in upper and lower canopies has been determined in a living area, near a motorway and near an industrial area (Jiangan Chemical Fertilizer Plant). We found that at sites near roads, more positive δ¹⁵N values were observed in the camphor leaves, especially in old leaves of upper canopies, and ?δ¹⁵N = δ¹⁵N_upper − δ¹⁵N_lower > 0, while those near the industrial area had more negative δ¹⁵N values and ?δ¹⁵N < 0. These could be explained by two isotopically different atmospheric N sources: greater uptake from isotopically heavy pools of atmospheric NO_x by old leaves in upper canopies at sites adjacent to roads, and greater uptake of ¹⁵N-depleted NH_y in atmospheric deposition by leaves at sites near the industrial area. This study presents novel evidence that ¹⁵N natural abundance of camphor leaves can be used as a robust indicator of atmospheric N sources.     

Use of Stable Nitrogen Isotopes and Permeable Membrane Devices to Study what Factors Influence Freshwater Mollusk Survival in the Conasauaga River

Recent biological inventory data shows severe declines in freshwater mussel abundance and biodiversity in the Conasauga River Basin in Northwest Georgia, USA. Based on assessments of habitat conditions, mussel populations should be sustainable. We conducted a study of sediment and water quality to evaluate the impact of anthropogenic contamination on mussel populations. Permeable membrane devices (PMD), polar organic chemical integrative samplers (POCIS™), conventional water and sediment quality analyses, and stable nitrogen isotope ratio analyses (δ¹⁵N) of snails and sediments were used to assess sediment and water quality at target sites throughout the basin. Ambient concentrations of organic contaminants in water were well below any aquatic life criteria; concentrations of some nutrients were detected above aquatic life criteria levels. Most mussel species in the river are endangered or threatened; therefore, snails were collected for δ¹⁵N analyses. Mean δ¹⁵N values for snails collected at forested upper watershed sites (national forest areas) were significantly lower than δ¹⁵N values from snails in agricultural areas. δ¹⁵N values for raw cow manure and manure-treated soil were similar to δ¹⁵N values for snails collected in agricultural areas. Dissolved nitrate from water samples had elevated δ¹⁵N values similar to the upper range of δ¹⁵N values for snails in agricultural areas. Data, particularly stable nitrogen isotope data, indicates that a land use change from national forest land to agriculture alters nitrogen sources to the basin and snails. Implications of nutrient release on freshwater molluscan reproduction, growth, and survival are discussed.     

^15N isotope fractionation in an aquatic food chain： Bellamya aeruginosa （Reeve） as an algal control agent

15N isotope tracer techniques and ecological modeling were adopted to investigate the fractionation of nitrogen,its uptake and transformation in algae and snail(Bellamya aeruginosa Reeve).Different algal species were found to differ in their uptake of nitrogen isotopes.Microcystis aeruginisa Ktz.demonstrated the greatest 15N accumulation capacity,with the natural variation in isotopic ratio(δ 15N) and the isotope fractionation factor(ε,‰) being the highest among the species investigated.The transformation and utilization of 15N by snails differed depending on the specific algae consumed(highest for Chlorella pyrenoidosa Chick.,lowest for M.aeruginisa).When snails was seeded in the experimental pond,the algae population structure changed significantly,and total algal biomass as well as the concentration of all nitrogen species decreased,causing an increase in water transparency.A model,incorporating several chemical and biological parameters,was developed to predict algal biomass in an aquatic system when snails was present.The data collected during this investigation indicated that the gastropods such as snails could significantly impact biological community and water quality of small water bodies,suggesting a role for biological control of noxious algal blooms associated with eutrophication.     

An improved ion-exchange/diffusion method for ～(15)N isotope tracing analysis of nitrate in surface waters from watersheds

An improved method,suitable for collecting nitrate from surface waters in the watershed for 15 N isotope tracing analysis,was developed on the basis of the anion exchange coupled with diffusion through systematic simulation and comparison experiments.The results showed that the nitrate could be separated and enriched from the waters efficiently by using the improved method.Being simple and practical in operation principle and procedures,cost-economic,and highly efficient in nitrate separation/enrichment,the method met the requirements of δ 15 N mass spectrum analysis and would lay a foundation for the application of 15 N isotope tracing approach to the research on non-point source pollution in watershed.