How the Distribution of Anthropogenic Nitrogen Has Changed in Narragansett Bay (RI,USA) Following Major Reductions in Nutrient Loads

Over the past decade, nitrogen (N) loads to Narragansett Bay have decreased by more than 50%. These reductions were, in large part, the direct result of multiple wastewater treatment facility upgrades to tertiary treatment, a process which employs N removal. Here, we document ecosystem response to the N reductions and assess how the distribution of sewage N in Narragansett Bay has changed from before, during, and shortly after the upgrades. While others have observed clear responses when data were considered annually, our seasonal and regional comparisons of pre- and post-tertiary treatment dissolved inorganic nitrogen (DIN) concentrations and Secchi depth data, from bay-wide surveys conducted periodically from the early 1970s through 2016, resulted in only a few subtle differences. Thus, we sought to use stable isotope data to assess how sewage N is incorporated into the ecology of the Bay and how its distribution may have changed after the upgrades. The nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope measurements of particulate matter served as a proxy for phytoplankton, while macroalgae served as short-term integrators of water column bio-available N, and hard clams (Mercenaria mercenaria) as integrators of water column production. In contrast to other estuarine stable isotope studies that have observed an increased influence of isotopically lower marine N when sewage N is reduced, the opposite has occurred in Narragansett Bay. The tertiary treatment upgrades have increased the effluent δ¹⁵N values by at least 2‰. The plants and animals throughout Narragansett Bay have similarly increased by 1–2‰, on average. In contrast, the δ¹³C values measured in particulate matter and hard clams have declined by about the same amount. The δ¹⁵N results indicated that, even after the N reductions, sewage N still plays an important role in supporting primary and secondary production throughout the bay. However, the δ¹³C suggests that overall net production in Narragansett Bay has decreased. In the 5 years after the major wastewater treatment facilities came on-line for nutrient removal, oligotrophication has begun but sewage remains the dominant source of N to Narragansett Bay.     

Modeled Nitrogen Loading to Narragansett Bay: 1850 to 2015

Nutrient loading to estuaries with heavily populated watersheds can have profound ecological consequences. In evaluating policy options for managing nitrogen (N), it is helpful to understand current and historic spatial loading patterns to the system. We modeled N inputs to Narragansett Bay from 1850 to 2000, using data on population, human waste disposal, livestock, fertilizer, and atmospheric deposition. We found that total N loading to the bay increased 250% from 1850 to 2000, and 80% from 1900 to 2000. Loading to the upper bay increased far more than that to the lower bay, and the most important source shifted from non-point animal waste to human waste concentrated at sewage treatment facilities. We also modeled future N loads in 2015 under four management scenarios. Planned improvements in sewage treatment would reduce N loads 9% below business-as-usual, to the 1990 loading rate. Greater reductions, to circa 1900 rates of loading, may be possible.     

Deciphering the Seasonal Cycle of Copepod Trophic Dynamics in the Strait of Georgia,Canada, Using Stable Isotopes and Fatty Acids

Characterizing trophic flows is central to our understanding of energy transfer in marine ecosystems. The food webs of coastal systems are difficult to study because the proportion of autochthonous to allochthonous sources often varies seasonally and is often overlaid on a seasonal cycle of zooplankton composition. Here, we use a combination of fatty acids and stable isotopes to disentangle the trophic pathways in a productive coastal system (the Strait of Georgia (SoG), Canada). Over the span of a year, Metridia pacifica, a ubiquitous omnivorous copepod, can utilize a wide range of dietary items including diatoms, flagellates, bacteria, detritus, and microzooplankton. M. pacifica can switch from herbivory to carnivory in response to declining chlorophyll concentrations after the spring bloom and can occasionally utilize detrital sources. These findings are discussed in the context of previous knowledge of the SoG ecosystem, the current state of ecosystem modeling in the region, and the use of stable isotopes and fatty acids to assess trophic dynamics.     

Nitrogen Stable Isotopes of Macrophytes Assess Stormwater Nitrogen Inputs to an Urbanized Estuary

The ¹⁵N composition of seagrass and benthic macroalgae from shallow waters of Sarasota Bay was measured to determine if stable N isotopes can be used to trace stormwater N into macrophyte production within an urbanized estuary. Results show isotopically enriched macroalgae at the landward stations near creeks and bayous in the central Bay and in the southern portion of the Bay. A known sewage outfall at Whitaker Bayou resulted in δ ¹⁵NO₃ values from 0 to +9‰. Isotopically enriched NH₄ values in Phillippi Creek (+10 to +17‰) were similar to the stormwater ¹⁵NH₄ values from the watershed (+7 to +18‰). Enriched N sources supported a significant portion of macroalgae N demands in the southern reaches of the Bay while isotopically depleted N sources (i.e., atmospheric deposition and/or fertilizers) appear to be more important for macroalgae in the northern portion of the Bay. Macroalgae were typically more enriched than seagrass and appear to be better indicators of anthropogenic loadings near creeks and bayous that receive large volumes of stormwater and other anthropogenic N sources. Historically, studies have used enriched ¹⁵N in macrophytes to infer wastewater influences. This study shows that stormwater N inputs need to be considered in nitrogen budgets for aquatic systems that show anthropogenic ¹⁵N enrichment.     

Stable Isotopes Reveal Complex Changes in Trophic Relationships Following Nutrient Addition in a Coastal Marine Ecosystem

Complex links between the top-down and bottom-up forces that structure communities can be disrupted by anthropogenic alterations of natural habitats. We used relative abundance and stable isotopes to examine changes in epifaunal food webs in seagrass (Thalassia testudinum) beds following 6 months of experimental nutrient addition at two sites in Florida Bay (USA) with different ambient fertility. At a eutrophic site, nutrient addition did not strongly affect food web structure, but at a nutrient-poor site, enrichment increased the abundances of crustacean epiphyte grazers, and the diets of these grazers became more varied. Benthic grazers did not change in abundance but shifted their diet away from green macroalgae + associated epiphytes and towards an opportunistic seagrass (Halodule wrightii) that occurred only in nutrient addition treatments. Benthic predators did not change in abundance, but their diets were more varied in enriched plots. Food chain length was short and unaffected by site or nutrient treatment, but increased food web complexity in enriched plots was suggested by increasingly mixed diets. Strong bottom-up modifications of food web structure in the nutrient-limited site and the limited top-down influences of grazers on seagrass epiphyte biomass suggest that, in this system, the bottom-up role of nutrient enrichment can have substantial impacts on community structure, trophic relationships, and, ultimately, the productivity values of the ecosystem.     

Suspended material in Narragansett Bay: fatty acid and hydrocarbon composition

Suspended material collected at various stations in Narragansett Bay was analyzed for fatty acids and hydrocarbons. The qualitative and quantitative distributions of these compounds indicated that the influence of sewage and other pollutants was greatest in the river areas. Based on concentrations of polyunsaturated fatty acids, the highest densities of phytoplankton were interpreted to occur at the mid and lower Bay stations, and the percentage of phytoplankton in suspended material was estimated from the concentration of heneicosahexaene. The concentrations of fatty acids and hydrocarbons in the suspended material decreased from the river stations to the mid and lower Bay stations, closely following a similar trend observed in the sediment. Possible sources of the suspended material and the influence of these sources on this material in various areas of the Bay are discussed, and attempts are made to interrelate the suspended material, resuspended sediment, phytoplankton, and sewage effluent with chemical and biochemical diagenetic changes.     

Linking juvenile fish and their habitats: An example from Narragansett Bay, Rhode Island

We used two methods and existing field survey data to link juvenile fish and their habitats. The first method used seine survey data collected monthly from July to October 1988–1996 at fixed stations in Narragansett Bay, Rhode Island. Thirteen fish species making up 1% or more of the catch were analyzed by principal components analysis for two time periods: July–August and September–October. The stations were then plotted by their principal component scores to identify station groupings and habitat types. The second method used environmental data collected in July and August 1996 at the established survey stations in a principal components analysis. The stations and 13 most abundant species were plotted by principal components scores resulting from the environmental data. For the environmental data, the first two principal components explained 59% of the variance. The first principal component described the amount of energy shaping the habitat and was positively correlated with salinity, dissolved oxygen, current flow, and slope, and negatively correlated with silt. The second component was positively correlated with depth and silt, and negatively correlated with dissolved oxygen. The environmental data grouped the stations according to their distance from the ocean and three habitat types emerged. The uppermost station was a silty barren having low salinities and dissolved oxygen. Three other stations grouped together as low energy, protected habitats with sandy substrates. Lower bay stations had higher salinities, higher dissolved oxygen, higher flow rates, greater slopes, and larger size substrates, mostly cobble and gravel. Results from the fish data grouped the stations similarly. Combining results from both datasets revealed the uppermost station had the highest catches, most species, and greatest number of winter flounder (Pseudopleuronectes americanus) juveniles. Plots of winter flounder catches with principal component scores from the environmental data indicated the winter flounder distribution in the bay has shrunk from baywide to mostly the upper estuary near their primary spawning grounds. Results illustrate the value of coupling historic fish survey data with environmental measurements for identifying previously undervalued habitats important to fish.     

渤海东海海洋沉积物中碳氮稳定同位素标准物质研制

海洋沉积物中碳氮稳定同位素因其能够确定有机质的来源,有助于了解碳循环、气候变化、有机质迁移转化而备受关注,但其分析测试过程中尚缺乏海洋沉积物碳氮稳定同位素标准物质进行质量监控。本文依据ISO导则35和国家《一级标准物质技术规范》(JJG1006—1994),研制了三个海洋沉积物碳氮稳定同位素标准物质(MSCNI-1、MSCNI-2和MSCNI-3),候选物样品分别采自我国渤海锦州湾湿地、东海闽浙近岸和东海冲绳海槽,定值组分为总碳氮同位素(δ~(13)C-TC、δ~(15)N-TN)和有机碳氮同位素(δ~(13)C-C~(org)、δ~(15)N-N~(org)),定值方法采用元素分析-同位素比值质谱法(EA-IRMS)多家实验室协同定值。经检验,三个标准物质候选物均匀性良好,一年内定值组分均无显著变化,具有良好的稳定性;δ~(13)C和δ~(15)N的标准不确定度分别小于0.15%和0.24%,标准值和标准不确定度合理。该套标准物质是我国以海底沉积物为介质的基体型碳氮稳定同位素标准物质,定值方法准确可靠,可供海洋、地质及环境等相关领域实验室用于仪器校准、方法评价和质量监控等。     

Prehistoric nutrient inputs and productivity in Narragansett Bay

Calculations by others of the preindustrial deposition of inorganic nitrogen from the atmosphere in the area of Narragansett Bay compared with recent measurements suggest that this flux has increased almost 15 times over natural background. On the basis of modern studies of the export of nitrogen and phosphorus from temperate forests, the prehistoric watershed also probably contributed very little reactive N or P to the bay. New information from undisturbed old-growth forests suggests that most of the N that was exported from the watershed was probably associated with refractory dissolved organic matter and thus contributed little to the fertility of the bay. The largest source of reactive dissolved inorganic nitrogen (DIN) and phosphorus (DIP) for Narragansett Bay under prehistoric conditions was the coastal ocean water entrained in the bay in estuarine circulation. The total input of DIN to this estuary has increased about five-fold and the input of total DIP has approximately doubled as a result of human activities. Recent ecosystem-level experiments using large (13 m³, 5 m deep) mesocosms designed as living models of Narragansett Bay showed that the primary production of phytoplankton in the bay is limited by the supply of DIN and that annual phytoplankton production is strongly correlated with the rate of input of DIN. The relationship between DIN input and annual phytoplankton production in the mesocosms is consistent with observations published by others working in 10 different natural marine systems, and a functional regression of the field and experimental data provides a tool to calculate the rate of prehistoric phytoplankton production that would have been associated with the prehistoric DIN input estimates. The result of this calculation suggests that phytoplankton production in the bay has approximately doubled (from about 130 g C m^?2 yr^?1 to 290 g C m^?2 yr^?1 for a baywide average) since the time of European contact. It also seems likely that seagrasses and macroalgae once made a much larger contribution to total system production than they do today.     

Habitat Use by Coastal Birds Inferred from Stable Carbon and Nitrogen Isotopes

Conservationists need to know the degree of habitat fidelity for species of conservation concern. Stable Isotope Analysis in R quantified the contribution of terrestrial vs. saltmarsh primary production sources to terrestrial passerine food webs from four habitats of Sapelo Island, Georgia (USA), saltmarsh, maritime scrub–shrub, maritime broadleaf (oak), and maritime narrowleaf (pine) forests, using δ ¹³C and δ ¹⁵N. Models suggested Northern Parula (Parula americana) in oak forests, White-eyed Vireos (Vireo griseus) in shrub, and Brown-headed Nuthatches (Sitta pusilla) in pine forests derived most of their food from habitats they occupied (53–100%). Saltmarsh provided 47–94% of Painted Bunting (Passerina ciris) food sources, supporting previous findings by Springborn and Meyers (2005). Thus, Painted Bunting conservation in the Southeastern USA should focus on Springborn and Meyers’ suggestion of maritime scrub–shrub habitat and forests with <75% canopy, >50% ground cover, and patches of shrubs that are within 700 m of saltmarsh.     

海洋沉积物有机碳和稳定氮同位素分析的前处理影响

海洋沉积物中的有机碳和稳定氮同位素为海洋古环境和碳氮循环提供了大量信息,然而不同的前处理方法对有机碳和稳定氮同位素测定结果的准确性产生不同程度的影响.笔者通过大量条件实验,分析了前处理过程中影响结果准确性的可能因素.①器皿材质:使用聚丙烯和玻璃离心管进行酸处理所得样品的δ13C和δ15N基本无差别.②干燥方式:样品经热烘干燥会导致样品中轻碳组分和易挥发组分的逸散,引起样品中δ13C的分馏.鲜样和酸处理后样均采用热烘干燥会引起样品中δ15N发生明显分馏.③驱酸方式和洗酸程度:水洗造成溶解性有机碳和氮的损失,致使δ13C和δ15N值较真实值偏正,但酸蒸法不能保证氯离子的有效驱除.洗至中性后的洗酸次数对δ13C影响甚小,但会导致δ15N继续偏正.全程采用冷冻干燥,选用PP离心管作为主要酸处理水洗和干燥的器皿,具有很好的重复性,可获得较理想、准确的δ13C和δ15N测试数值.     

Review of the Study on the Stable Isotopes of Nitrogen and Oxygen in Atmospheric Nitrate

Due to the emissions from intensive human activities and rapid development of industry and agriculture, atmospheric nitrate (NO {}_3^{-} ) contamination is becoming more serious and now is a worldwide environmental problem. The isotopic compositions of NO {}_3^{-} (δ¹⁵N, δ¹⁸O and Δ¹⁷O) can deliver more information than the concentration alone, i.e., the nitrogen and oxygen isotopes can suggest the sources of NO {}_3^{-} and oxidation capability of the atmosphere, providing a powerful tool for investigating atmospheric nitrogen cycling and atmospheric NO {}_3^{-} pollution control. The δ¹⁵N of different sourced NO {}_3^{-} in the atmosphere, as well as the seasonal variation of δ¹⁵N (NO {}_3^{-} ) and the associated mechanisms were reviewed. In addition, the oxygen isotopes of various oxidants and NO {}_3^{-} (δ¹⁸O and Δ¹⁷O) in the atmosphere were summarized, and the global distribution patterns of the oxygen isotopes of NO {}_3^{-} were discussed. Lastly, the available analysis techniques of isotopic compositions of NO {}_3^{-} were reviewed. Based on the research progress of NO {}_3^{-} isotopes in the atmosphere, it was suggested that further investigations should focus on measuring the isotopic compositions of oxidants and NOx from different sources, characterizing the production mechanisms of NO {}_3^{-} , as well as investigating chemical recycling between NOx and NO {}_3^{-} with the aid of atmospheric chemical models.     

大气硝酸盐中氮氧稳定同位素研究进展

受人类活动和工农业快速发展的影响,大气硝酸盐(NO_3^-)污染越来越严重且已成为世界范围内的环境问题之一。探究大气NO_3^-的稳定同位素组成(δ15N,δ18O和Δ17O),可以为深入理解大气氮循环、有效控制大气NO_3^-污染提供有力依据。综述了目前大气NO_3^-不同来源NOx的δ15N值、NO_3^-的δ15N季节变化特征及主要影响因素,总结了大气中不同氧化剂的δ18O值和Δ17O值,归纳了全球范围内部分大气NO_3^-中δ18O值和Δ17O值的时空分布特征及可能影响因素,回顾了NO_3^-同位素分析测试技术的主要进展,在前期工作基础上提出未来大气NO_3^-稳定同位素研究应更多关注NO_3^-的氧化生成机制(不同类型氧化剂同位素组成时空差异)、不同NOx来源的δ15N组成、借助化学模型开展大气NO_3^-循环过程等方面的研究。     

On the residence time of water in Narragansett Bay

For Narragansett Bay, Rhode Island, newly calculated and archival data for the area, mean depth, total volume, mean salinity and fresh water input are presented. Estimates of the residence time of the water, derived from 22 sets of monthly mean values, were related to estimates of the fresh water input according to the empirical relationship T=41.8 e^?0.00435(FW), where T is the flushing time in days, and FW is the fresh water input in m³ per s; the r² value is 0.841. Adding estimates of the mean wind speed into a multiple regression increased the correlation coefficient only to 0.864. At the long-term mean rate of fresh water input (105 m³ per s) the flushing time is 26 days. At the lowest mean monthly input rate observed the flushing time was nearly 40 days, while at the highest mean monthly input rate in the data set (325 m³ per s) the flushing time was about 10 days. Known sources of random error appear sufficient to account for most of the deviations from the relationship. The evidence suggests that variation in the flushing time is largely determined by variation in the fresh water input.     

A chlorophyll time series for Narragansett Bay: Assessment of the potential effect of tidal phase on measurement

An 18-yr chlorophyll time series for Narragansett Bay based on weekly samples collected without regard to tidal phase revealed a long-term decrease in mean annual levels. The potential influence of neglecting tidal phase in the sampling strategy on measured chlorophyll and its apparent long-term decrease is evaluated. A two year data set (1995–1996) is used as a proxy for the 1973–1990 time series together with an observed relationship between continuous measurements of in situ chlorophyll fluorescence and accompanying tidal phase. The deviations in chlorophyll from long-term means relative to deviations from mean low water at the time of sample collection are also analyzed, as is the potential influence of tidally-induced advective increases or dilution on measured chlorophyll levels. The analyses, which compare the magnitude and trends in tidally adjusted and directly measured chlorophyll, indicate that semi-diurnal intratidal variations in chlorophyll had little apparent effect on the long-term and seasonal patterns and trends deduced from the chlorophyll measurements. Neither tidal advection of the chlorophyll gradient, nor bloom magnitude appear to compromise application of the model. The 18-yr decline in annual mean chlorophyll observed between 1973–1990 in narragansett Bay is considered to be a bonafide portrayal of actual events, and not an artifact of failure to consider tidal phase in the weekly sampling strategy. The results also suggest that intratidal variability in chlorophyll does not seriously confound its meaningful measurement and usefulness as a representative index of phytoplankton abundance at the permanent monitoring station established for Narragansett Bay. Nonetheless, there is need to refine and to incorporate temporal sampling strategies more closely attuned to the tempo of growth, grazing, and nutrient recycling which accompany estuarine phytoplankton dynamics.     

Rates of nitrification along an estuarine gradient in Narragansett Bay

Rates of pelagic nitrification, measured using N-Serve-sensitive [¹⁴C]bicarbonate uptake, varied by as much as an order-of-magnitude among three sites along the salinity gradient of Narragansett Bay (Rhode Island, United States). Rates were always higher at the Providence River estuary site (0.04–11.2 μmol N I^?1 d^?1) than at either the lower Narragansett Bay site (0.02–0.98 μmol N I^?1d^?1) or the freshwater Blackstone River site (0.04–1.7 μmol N I^?1d^?1). Although temperature was the most important variable regulating the annual cycle of nitrification, ammonium concentrations were most likely responsible for the large differences in rates among the three sites in summer. At the levels found in this estuarine system, salinity and concentrations of oxygen or total suspended matter did not appear to have a direct measurable effect on nitrification and pH did only occasionally. Nitrification played an important role in the nitrogen cycle at all three sites. In Narragansett Bay, nitrification contributed 55% of the NO₂ ^? and NO₃ ^? entering annually, and was the major source during spring and summer. Water from offshore was the only other large source of NO₂ ^? and NO₃ ^?, contributing 34%. High summer rates of nitrification could support much of the phytoplankton uptake of NO₂ ^? and NO₃ ^?. In the Providence River estuary, the largest annual input of NO₂ ^? and NO₃ ^? was from rivers (54%), although nitrification (28%) and water from lower portions of the bay (11%) also made large contributions. Again, nitrification was most important in the summer. The high rates of nitrification in the Providence River estuary during summer were also likely to be important in terms of oxygen demand, and the production of nitric and nitrous oxides. In the Blackstone River, NO₂ ^? and NO₃ ^? concentrations increased as the river flowed through Rhode Island, and nitrification was a possible source.     

沉积有机质中稳定碳同位素逆转现象初探

本文研究了沉积有机质的可溶部分（抽提物）和不溶部分（干酪根）及抽提物的族组分（饱和烃、芳烃、非烃、沥青质）的碳同位素组成特征。通过其δ13C的分布为:干酪根>抽提物;沥青质 >非烃 >芳烃 >饱和烃。研究表明由于生源物质的不同,沉积环境的差异可构沉积有机质碳同位素组成异常。如非烃 >沥青质 >芳烃 >非烃、本文称为沉积有机质碳同位素局部逆转。当沉积有机质可溶部分>干酪根时,称之为总体逆转。湖沼相或河间湖相高等植物来源常为正常组或型;经细菌强烈改造生源以高等植物为主有低等生物为类脂组分加入常形成局部逆转的碳同位素组成。总体逆转则常现于有机质演化程度很高的海相沉积岩中。     

陆面过程中稳定水同位素逐日变化的数学模拟——引入稳定同位素效应的CLM实例分析

将稳定同位素效应引入CLM(Community Land Model),并对巴西马瑙斯站在平衡年的稳定水同位素的逐日变化进行模拟和分析.结果表明: 降水、水汽和地表径流中δ18O存在明显的季节变化,并与相应的水量存在显著的负相关关系,但凝结物中δ18O与地面凝结量存在显著的正相关关系,蒸发水汽中δ18O与蒸发量之间无显著的相关关系.受土壤贮水削峰功能的影响,表层土壤和根区水中δ18O的季节变化全无.植被层蒸发水汽中稳定同位素的丰度与大气的干湿程度存在密切联系: 当降水量少时,大气干燥,植被层的蒸发较少,植被蒸发中δ18O较高;当降水量较大时,空气湿润,植被层的蒸发量较大,蒸发中δ18O则较低.植被蒸腾中δ18O的变化与源区水体中δ18O的变化保持一致,尤其是与根区水中的δ18O.由于地下径流直接源自根区水的补充,因此,地下径流中δ18O等于根区水中的δ18O.模拟结果还显示,降水MWL (大气水线)的梯度项和常数项均比全球平均MWL略偏小.尽管主要来自降水的贡献,但地表径流和植被层水体的MWLs与降水MWL存在较大的差异,这一方面与两类水体在蒸发过程中的稳定同位素的富集作用有关,另一方面与CLM模拟的水量有关.大气水汽线与降水的MWL的梯度值相近,说明大气水汽与降水近似处于稳定同位素平衡状态.另外,模拟的地面的凝结线与植被层的凝结线均与全球大气水线相近,且具有非常高相关程度,说明CLM的模拟是合理的.     

Mapping of benthic enrichment patterns in Narragansett Bay,Rhode Island

A synoptic reconnaissance survey was performed over a five-day period in August 1988 to assess benthic habitat quality throughout Narragansett Bay, Rhode Island, using REMOTS^® sediment-profile photography and analysis in combination with measurements of the levels ofClostridium perfringens spores (a fecal indicator) in sediments. Three main areas of degraded benthic habitat quality related to either excessive organic enrichment or physical disturbance were identified based solely on the REMOTS^® analysis: the Providence River Reach, Greenwich Bay and its associated coves and harbors, and an area located along the southwest side of Prudence Island. Sediments at many stations in these areas exhibited shallow apparent redox-potential discontinuity (RPD) depths, high apparent oxygen demand, and low-order benthic successional stages. ElevatedClostridium perfringens spore counts in surface sediments were attributed to inputs from wastewater treatment facilities. The highest spore counts occurred at the head of the bay, where wastewater treatment discharges and associated combined sewer overflows are numerous. Using data from the REMOTS^® analysis and the sediment inventory ofC. perfringens spores, a distinction was made between organic enrichment of the bottom from sewage, versus nonsewage enrichment or physical disturbance. The combination of techniques employed in this investigation could be used to design more efficient monitoring programs to assess eutrophication effects in estuaries and determine the effectiveness of regulatory or management initiatives to reduce organic overenrichment of benthic habitats.     

北美洲降水中稳定同位素的时空分布以及与ENSO的关系

分析了北美洲降水中δ¹⁸O的时空分布特征以及与温度、降水量、ENSO的关系.结果表明:无论是在陆地还是在海洋,北美降水中平均δ¹⁸O的纬向分布是非常显著的.随着纬度的升高,降水中δ¹⁸O迅速减小.整个北美大陆均存在温度效应,并随纬度的增加而加强.不同季节温度效应分布的差异仅表现在其范围和强度的变化上.降水量效应主要出现在低纬度海洋、中低纬度太平洋的东海岸和湾流的西北海岸.在内陆区,降水量效应不存在.不同季节降水量效应分布的差异也仅表现在其范围和强度的变化上.在大陆内部和高纬度地区,对应显著的温度效应,δ¹⁸O的季节差异Δδ¹⁸O具有较大的正值;在低纬度海洋,对应显著的降水量效应,Δδ¹⁸O较小或为负值;在相同的纬度,陆地上的Δδ¹⁸O明显大于海洋.代表大陆性特征的渥太华站和代表海洋性特征的中途岛站降水中δ¹⁸O与Ni o-4的SST具有显著的正相关关系,其中,尤以5月的δ¹⁸O与Ni o-4的SST的连续相关关系最显著,表明ENSO事件的强信号对该时期陆地和海洋降水中稳定同位素的变化具有重要影响.