Evidence from isotopic geochemistry as an indicator of eutrophication of Meiliang Bay in Lake Taihu,China

In this paper, Lake Taihu, a large shallow freshwater lake in China, is chosen as an example of reconstruction of eutrophication through the comparison between stable isotopes from dissolved nutrients and plants and water column nutrient parameters and integration of multiple proxies in a sediment core from Meiliang Bay including TN, TP, TOC, C/N, δ ¹⁵N, δ ¹³C, etc. Differences in aquatic plant species and trophic status between East Taihu Bay and Meiliang Bay are indicated by their variations in δ ¹³C and δ ¹⁵N of aquatic plants and δ ¹⁵N of NH₄ ⁺. A significant influence of external nutrient inputs on Meiliang Bay is reflected in temporal changes in δ ¹⁵N of NH₄ ⁺ and hydro-environmental parameters. The synchronous change between δ ¹³C and δ ¹⁵N values of sedimented organic matter (OM) has been attributed to elevated primary production at the beginning of eutrophication between 1950 and 1990, then recent inverse correlation between them has been caused by the uptake of ¹⁵N-enriched inorganic nitrogen by phytoplankton grown under eutrophication and subsequent OM decomposition and denitrification in surface sediments, indicating that the lake has suffered from progressive eutrophication since 1990. Based on the use of a combination of stable isotopes and elemental geochemistry, the eutrophication of Meiliang Bay in Lake Taihu could be better traced. These transitions of the lake eutrophication respectively occurring in the 1950s and 1990s have been suggested as a reflection of growing impacts of human activities, which is coincident with the instrumental data.     

Evidence from isotopic geochemistry as an indicator of eutrophication of Meiliang Bay in Lake Taihu, China

In this paper, Lake Taihu, a large shallow freshwater lake in China, is chosen as an example of reconstruction of eutrophication through the comparison between stable isotopes from dissolved nutrients and plants and water column nutrient parameters and integration of multiple proxies in a sediment core from Meiliang Bay including TN, TP, TOC, C/N,δ15N,δ13C, etc. Differences in aquatic plant species and trophic status between East Taihu Bay and Meiliang Bay are indicated by their variations inδ13C andδ15N of aquatic plants andδ15N of NH4 . A significant influence of external nutrient inputs on Meiliang Bay is reflected in temporal changes inδ15N of NH4 and hydro-environmental parameters. The synchronous change betweenδ13C andδ15N values of sedi-mented organic matter (OM) has been attributed to elevated primary production at the beginning of eutrophication between 1950 and 1990, then recent inverse correlation between them has been caused by the uptake of 15N-enriched inorganic nitrogen by phytoplankton grown under eutrophication and subsequent OM decomposition and denitrification in surface sediments, indicating that the lake has suffered from progressive eutrophication since 1990. Based on the use of a combination of stable isotopes and elemental geochemistry, the eutrophication of Meiliang Bay in Lake Taihu could be better traced. These transitions of the lake eutrophication respectively occurring in the 1950s and 1990s have been suggested as a reflection of growing impacts of human activities, which is coincident with the instrumental data.     

太湖不同生态类型湖区浮游甲壳动物群落结构季节变化比较

水体富营养化会对整个水生态系统产生重要影响.为了解太湖富营养化对浮游甲壳动物群落结构的影响,于2012年3月至2013年2月对太湖3个典型湖区——藻型湖区(梅梁湾)、草型湖区(胥口湾)和强扰动湖区(湖心区)开展浮游甲壳动物群落结构季节变化比较研究.3个湖区中,湖心区营养水平最高,胥口湾最低.梅梁湾浮游甲壳动物密度和生物量最高,其次是湖心区,胥口湾最低.梅梁湾、湖心区和胥口湾的浮游甲壳动物年平均密度分别为199、150和91 ind./L,年平均生物量分别为1.950、1.557和0.743 mg/L.在整个研究期间,梅梁湾、胥口湾和湖心区的浮游甲壳动物种类数分别为13、11和11;3个湖区的浮游甲壳动物优势种均为中华窄腹剑水蚤和简弧象鼻溞,其中中华窄腹剑水蚤在梅梁湾、胥口湾和湖心区的年平均密度分别为57、25和36 ind./L,简弧象鼻溞在3个湖区的年平均密度分别为40、22和32 ind./L.胥口湾浮游甲壳动物生物多样性指数显著低于梅梁湾和湖心区.相关分析表明,浮游甲壳动物密度与叶绿素a浓度呈极显著正相关.研究表明,同一湖泊不同生态类型湖区浮游甲壳动物会对水体富营养化产生不同的生态响应.     

太湖富营养化湖区秋季水体和沉积物中硝化微生物分布特征及控制因素

微生物参与下的氮循环是富营养化湖泊十分重要的生物地球化学循环过程.采用基于amoA功能基因和16S rRNA基因的荧光定量PCR、PCR-DGGE与高通量测序等分子生物学技术,调查秋季太湖不同水体和表层沉积物中氨氧化古菌(AOA)、氨氧化细菌(AOB)和亚硝酸盐氧化菌(NOB)群落丰度和组成,探讨影响硝化微生物分布的关键环境因子.结果表明,中度富营养化的梅梁湾湖区水体表层、中层和底层水样和表层底泥中AOA amoA基因的丰度分别低于轻度富营养化的湖心区,而不同层水样中AOB amoA基因的丰度分别高于湖心区.梅梁湾湖区和湖心区水样中AOA群落组成基本相似,2个湖区表层沉积物样品中AOA群落组成亦基本相似,水体中AOA群落组成与表层沉积物中AOA群落组成有差异,AOA群落丰度显著受硝态氮、pH和DO影响;表层沉积物中AOB群落丰度有明显差异且显著受总氮含量影响,表层沉积物中NOB群落丰度也有明显差异且显著受亚硝态氮含量影响.太湖梅梁湾湖区和湖心区水体与表层沉积物AOA群落包括Nitrosopumilium和Nitrosotalea两大属;表层沉积物AOB群落主要包括亚硝化单胞菌(Nitrosomonas)和亚硝化螺菌(Nitrosospira)两大属,NOB群落主要包括硝化刺菌(Nitrospina)和硝化螺菌(Nitrospira)两大属,其中硝化螺菌属是淡水湖泊中比较少见的亚硝酸盐氧化菌.影响太湖水体和沉积物中AOA和AOB丰度的最主要环境因子为总氮、总磷与铵态氮.研究表明典型富营养指标(总氮、总磷、铵态氮、硝态氮和硝态氮等)是影响太湖梅梁湾和湖心区水体和沉积物中AOA或AOB丰度以及硝化微生物群落丰度的重要因素.     

太湖不同湖湾中铜锈环棱螺(Bellamya aeruginosa)的氮稳定同位素特征

进入湖泊中不同氮源氮稳定同位素值(δ15N)的差异和生物对氮稳定同位素的记忆作用,可以反映流域人类活动输入的污染物对生态系统的影响程度.本文调查了太湖4个湖湾(梅梁湾、贡湖湾、竺山湾和东太湖)中铜锈环棱螺(Bel-lamya aeruginosa)的δ15N值,结果表明环棱螺δ15N值的变幅为6.9‰～18.1‰,平均值为11.2‰,不同湖湾中环棱螺δ15N值差异极显著,从高到低依次为梅梁湾(17.7‰)、贡湖湾(13.2‰)、东太湖(10.2‰)和竺山湾(7.8‰).分析认为,梅梁湾和贡湖湾接纳较多的人类活动产生的污染物,其周边城市如无锡、常州等地的污水处理效率有待提高;竺山湾水体氮素主要来自于农业面源污染,需降低农田化肥的使用量.     

CO2浓度升高对浮游藻类元素化学计量值的影响

通过梅梁湾和东太湖的四季原位实验,研究CO_2浓度升高对不同营养水平淡水生态系统中浮游藻类C、N、P元素计量值的影响.实验设置了270、380和750 ppm共3个CO_2浓度,分别代表工业革命前、当前和IPCC预测的21世纪末的CO_2浓度.结果表明梅梁湾水体营养盐浓度在四季均高于东太湖水体营养盐浓度,但梅梁湾原位实验中浮游藻类C、N、P含量却普遍低于东太湖原位实验中浮游藻类营养元素含量,并且前者在季节上变化更大.CO_2浓度升高使梅梁湾原位实验中浮游藻类C∶P比明显增加,N∶P比略有增加,这种增加归因于藻细胞内C、N含量的升高,而东太湖浮游藻类化学计量值对CO_2浓度变化的响应不显著.因此浮游藻类元素化学计量值对CO_2浓度变化的响应程度与水体营养盐的绝对浓度无关,而与浮游藻类的生长是否受营养盐限制有关,只有当藻类生长受到水体营养盐浓度限制时,CO_2浓度升高才会显著改变其元素组成.     

Changes in carbon and nitrogen cycling in a floodplain lake over recent decades linked to littoral expansion,declining riverine influx,and eutrophication

This study aimed to understand changes in the biogeochemical processing of organic matter (OM) in response to multiple stressors (e.g., littoral area expansion, wastewater input, and hydrological regulation) in East Dongting Lake (Central China) over the past 60 years, using analyses of total organic carbon (TOC), total nitrogen (TN), C/N ratios, δ¹³C, δ¹⁵N, and diatoms from 2 sediment cores collected from the littoral and central parts of the lake. OM mainly originated from phytoplankton and C₃ plant‐derived soil OM based on the ranges of C/N ratios (from 7 to 11) and δ¹³C (between ?27‰ and ?23‰). Littoral area expansion due to siltation caused an increasing influx of terrestrial soil OM in the 1980s and the 1990s, subsequently lowering δ¹³C values and rising C/N ratios in both sediment cores. Meanwhile, higher δ¹⁵N was linked to a high influx of isotopically heavy nitrate from urban and agricultural wastewaters. After 2000, slight decreases in TOC and TN in the littoral area were attributable to reducing inputs of external OM, likely linked to declining sediment influx from the upper reaches resulting from the Three Gorges Dam impoundment. Contrasting increases in TOC, TN, and C/N ratios in the central part indicated a high influx of terrestrial soil OM due to the declining distance from the shoreline with littoral area expansion. Declining δ¹⁵N values after 2000 indicated an increase in N₂‐fixing cyanobacteria with eutrophication. Changes in diatom assemblages in both the littoral and central zones reflected nutrient enrichment and hydrological alterations. These results indicate that littoral expansion, declining riverine influx, and anthropogenic nutrient inputs are potential driving forces for the biogeochemical processing of OM in floodplain lakes. This study provides sedimentary biogeochemical clues for tracking past limnological conditions of floodplain lakes that are subjected to increasing disturbances from hydrological regulation and eutrophication.     

太湖春季浮游动物磷释放的初步研究

浮游动物是湖泊生态系统的主要组成之一,于2004年3月至5月间调查了太湖梅梁湾、五里湖浮游动物数量,并在实验室条件下分别测定了浮游动物正磷酸盐(PO4-P)的释放率．结果表明,研究期间梅梁湾的枝角类密度都高于五里湖,五里湖的轮虫数量高于梅梁湾,两水域桡足类密度上的差异不明显;梅梁湾和五里湖浮游动物PO4-p释放率的范围分别为0．20-O．43 mg／(g(DW)·h)和0．19-0．54 mg／(g(DW)·h)．因此浮游动物营养盐释放对湖泊生态系统营养盐循环具有一定的作用．     

太湖冬季有色可溶性有机物吸收荧光特性及遥感算法

基于2006年和2007年1月两次太湖采样,对50个点位的有色可溶性有机物(CDOM)光谱吸收、荧光、溶解性有机碳(DOE)浓度及遥感反射率进行测定与分析,探讨冬季太湖CDOM的吸收荧光特性及空间分布,建立CDOM吸收系数的遥感反演算法.结果表明,太湖冬季CDOM在355nm处吸收系数a(355)变化范围和均值分别为1...     

五里湖富营养化过程中水生生物及生态环境的演变

五里湖是太湖西北部一个小型浅水湖湾,是无锡市的饮用水源和主要风景游览区。50年代时,该湖基本保持着原始状态,全湖以大型水生植物占优势。湖水清澈见底,水质为中营养水平,溶氧接近饱和,对外来的N、P污染冲击具有很强的缓冲能力。底泥的氧化程度较高,磷和有机物含量仅为0.023％和0.75％。浮游藻类受到了大型水生植物的强烈抑制,年均数量为26.7×10~4个/L,以硅藻和隐藻为主;从春季至秋季,随着大型水生植物的增长,浮游藻类数量大幅度减少。浮游动物多达190种,年均数量为5660ind./L。大型底栖动物较多,以日本沼虾和螺、蚌类为主。鱼类资源十分丰富,63种鱼中以凶猛性鱼类占优势,并有较多的底栖性鱼类。 自50年代以来,大约有1/2的湖面被围垦,沿岸带生态条件被破坏,失去了最适合于大型水生植物生长的浅水区。加之60年代后期在全湖放养草鱼,水生植被遭到彻底毁灭。外源污染加剧,引起了水质的严重富营养化。围垦和修建水闸隔断了五里湖与太湖间的通道,限制了两个水体间的水流交换,妨碍了污染物的稀释扩散,使得来自无锡市区的污水成了五里湖的主要补给水源,加速了富营养化的进程。五里湖水质已达重富营养水平,透明度小于0.5m,缺氧较为严重。营养物在底泥中大量积累,TP和TOC含量分别增高了4.17倍和1.87倍。在春末     

太湖高等水生植物稳定碳、氮同位素特征

高等水生植物的稳定碳、氮同位素能够反映其生理生态学信息.从太湖贡湖湾和梅梁湾采集高等水生植物,分析两湖湾高等水生植物的稳定碳、氮同位素值时空变化和种类差异.结果显示:水生植物的稳定碳、氮同位素值因时间、空间和种类而发生变化,总体上时间变化规律不明显,空间变化有一定规律性:梅梁湾中穗花狐尾藻、马来眼子菜、苦草、凤眼莲的δ~(15)N明显高于贡湖湾,挺水植物芦苇的δ~(15)N差异不显著,反映了梅梁湾较贡湖湾有较高的营养水平;贡湖湾中穗花狐尾藻、苦草的δ~(13)C显著高于梅梁湾,其它种类没有显著差异.从种类特征来看,贡湖湾和梅梁湾浮叶植物与挺水植物芦苇、凤眼莲、菱的δ~(13)C偏低,而微齿眼子菜、金鱼藻、马来眼子菜、苦草、伊乐藻、穗花狐尾藻等沉水植物的δ~(13)C值较高,这与它们所处的环境和碳源有关.     

太湖有色可溶性有机物(CDOM)对COD及BOD5的指示意义

化学需氧量(COD)、五日生化需氧量(BOD_5)及溶解性有机碳(DOC)是指示湖泊水质的重要指标,然而上述指标测定通常耗费大量时间、试剂及人力物力且排放大量有害废液.有色可溶性有机物(CDOM)是溶解性有机物(DOM)中可以强烈吸收光谱中的紫外光和可见光的部分,数据测定耗时短、方便快捷,且样品处理过程环境友好,能在很大程度上反映湖泊水质.本研究基于2016年2、5和8月在太湖均匀布设的32个采样点进行样品采集,运用光谱吸收与三维荧光-平行因子分析(EEMs-PARAFAC)探究太湖CDOM的光谱吸收和荧光组分,探讨CDOM光谱指标对湖泊BOD_5、COD及DOC浓度等湖泊环境质量指标的可替代性.结果表明:(1)运用EEMs-PARAFAC方法解析出3种荧光组分:类腐殖酸C1、类酪氨酸C2和类色氨酸C3.(2) COD和BOD_5和DOC在空间上呈现出相似的分布趋势,不同水期的最高值均出现在竺山湾和梅梁湾,由西北湖区至中部敞水区、东南湖湾递减.(3)在不同水期,COD、BOD_5、DOC浓度和C1组分均表现为丰水期极显著大于枯水期和平水期,a_(254)在丰、平、枯水期间无显著性差异,最大值出现在丰水期;C2与C3组分均在枯水期和平水期极显著大于丰水期.(4)在不同水文时期,COD、BOD_5和DOC浓度均与a_(254)、类腐殖酸C1呈显著正相关,丰水期太湖COD、BOD_5和DOC浓度与CDOM光谱指标的线性相关性要优于枯水期和平水期.(5) CDOM光谱指标在不同水文时期均能很好地替代COD、BOD_5和DOC等作为反映太湖水体中有机物污染程度及湖泊水质的指标.     

太湖长孢藻属(Dolichospermum)生物量长期动态变化及驱动因子

针对近年来太湖水体中长孢藻（Dolichospermum,曾用名鱼腥藻Anabaena）比例增加的趋势,本文研究了2005—2019年太湖春季不同湖区长孢藻生物量的长期变化趋势和空间差异,探究了冬、春季气象条件（气温、日照时长、风速、降雨量）和营养盐（总氮、总磷）水平对其的影响.结果表明,2005—2019年太湖监测数据显示春季长孢藻生物量有比较明显的升高现象,主要发生在竺山湖富营养程度较高的区域,其次是湖心区、梅梁湾和南部湖区.偏最小二乘路径建模（PLS-PM）结果表明,不同湖区长孢藻生物量变化的主要驱动因素存在差异.在湖心区,春季长孢藻的生物量主要受冬季气候条件（气温、风速、日照时长）的影响,其次受春季营养盐和春季气候条件的影响.在梅梁湾、竺山湖和南部湖区,春季长孢藻的生物量主要受春季气候条件的影响.在梅梁湾和竺山湖,春季风速、日照时长是春季长孢藻生物量的显著影响因子;在南部湖区,春季长孢藻生物量的主要驱动因素是春季的日照时长和春季气温.本研究从长时间序列角度,对太湖固氮蓝藻的时空分布特征和影响因素开展了研究,为太湖不同湖区开展针对性的藻类水华防控和富营养化治理提供理论基础.     

Spatial distributions of δ13C, δ15N and C/N ratios in suspended particulate organic matter of a bay under serious anthropogenic influences: Daya Bay,China

Stable isotopic signatures (δ¹³C and δ¹⁵N) and C/N ratios of suspended particulate organic matter (POM) were investigated from the surface water of Daya Bay during summer and winter of 2015. The relatively high δ¹³C_POM values suggested the input of ¹³C-depleted terrigenous organic matter was low in Daya Bay. There were significant correlations between δ¹³C_POM values and chlorophyll a concentrations both during summer and winter, suggesting the δ¹³C_POM values were mainly controlled by the phytoplankton biomass in the surface water. The distribution of δ¹⁵N_POM values was more complicated than that of δ¹³C_POM and displayed low values in the outer bay and the Dan'ao River estuary. ¹⁵N-depleted ammonia originating from industrial wastewater might have strongly influenced the water quality and stable isotopic signatures of POM near the Dan'ao River estuary. The δ¹³C_POM and δ¹⁵N_POM values strongly reflect the influences of anthropogenic activity and eutrophication in Daya Bay.     

Elemental and stable isotopic constraints on river influence and patterns of nitrogen cycling and biological productivity in Hudson Bay

Elemental (carbon and nitrogen) ratios and stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) are examined in sediments and suspended particulate matter from Hudson Bay to study the influence of river inputs and autochthonous production on organic matter distribution. River-derived particulate organic matter (POM) is heterogeneous, nitrogen-poor and isotopically depleted, consistent with expectations for OM derived from terrestrial C3 vascular plant sources, and distinct from marine OM sources. Both δ¹³C and C/N source signatures seem to be transmitted to sediments with little or no modification, therefore making good tracers for terrigenous OM in Hudson Bay. They suggest progressively larger contributions from marine sources with distance from shore and secondarily from south to north, which broadly corresponds to the distribution of river inputs to Hudson Bay. Processes other than mixing of marine and terrigenous OM influence sedimentary δ¹⁵N values, including variability in the δ¹⁵N of phytoplankton in the Bay's surface waters due to differences in relative nitrate utilization, and post-production processes, which bring about an apparently constant ¹⁵N-enrichment between surface waters and underlying sediments. Variability in the δ¹⁵N of phytoplankton in the Bay's surface waters, in contrast, seems to be organized spatially with a pattern that suggests an inshore–offshore difference in surface water nitrogen conditions (open- vs. closed-system) and hence the δ¹⁵N value of phytoplankton. The δ¹⁵N patterns, supported by a simple nitrate box-model budget, suggest that in inshore regions of Hudson Bay, upwelling of deep, nutrient-rich waters replenishes surface nitrate, resulting in ‘open system’ conditions which tend to maintain nitrate δ¹⁵N at low and constant values, and these values are reflected in the sinking detritus. River inflow, which is constrained to inshore regions of Hudson Bay, appears to be a relatively minor source of nitrate compared to upwelling of deep waters. However, river inflow may contribute indirectly to enhanced inshore nutrient supply by supporting large-scale estuarine circulation and consequently entrainment and upwelling of deep water in this area. In contrast to previous proposals that Hudson Bay is oligotrophic because it receives too much fresh water (Dunbar, 1993), our results support most of the primary production being organized around the margin of the Bay, where river flow is constrained.     

Stable isotopes of carbon and nitrogen in the study of organochlorine contaminants in albatrosses and petrels

Carbon and nitrogen stable isotopes in albatrosses and petrels collected off southern Brazil were compared with concentrations of organochlorine contaminants (OCs). δ¹³C and δ¹⁵N values, as well as OCs concentrations, exhibited a high degree of variability among individuals and overlap among species. δ¹³C values reflected latitudinal differences among species, with lower values found in Wandering and Tristan Albatrosses and higher values found in Black-browed and Atlantic Yellow-nosed Albatrosses and White-chinned Petrels. Some relationships were found between OCs and stable isotopes, but in general a partial ‘uncoupling’ was observed between OCs concentrations and stable isotopes ratios (especially for δ¹⁵N). δ¹³C and δ¹⁵N values in Procellariiformes tissues during the non-breeding season appear to be a better indicator of foraging habitats than of trophic relationships, which may partially explain the high degree of variability between concentrations of OCs and stable isotopes ratios in birds with a diversified diet and wide foraging range.     

Horizontal distribution and transport processes of bloom-forming Microcystis in a large shallow lake (Taihu, China)

The horizontal distribution of bloom-forming Microcystis in a specific lake area and the transport of Microcystis by wind-driven lake currents between Meiliang Bay and the open water of Taihu Lake were measured during continuous field observations from August 21 to 25, 2006. During the observations, the horizontal distributions of Microcystis, represented by Chlorophyll a, showed a clear concentration toward downwind lake areas. According to the lake currents and the Chl a concentrations on the boundary line between the Meiliang Bay and the open water, the transported Chl a was less than 2% of the total weight of Chl a in Meiliang Bay on August 22, 24 and 25. The results suggest that the horizontal distribution of the bloom-forming Microcystis was strongly affected by the wind conditions, and the wind-driven Microcystis accumulation was mainly determined by surface drift; the transport of Microcystis by lake currents was much less important in this large, shallow lake.     

酸雨对太湖水环境潜在影响的初步研究

测定了1998－2000年冬、春季太源梅梁湾口雨水、地表径流水的PH值和N、P等营养元素化合物离子浓度。因降雨带进太湖的TIN、PO^3-4和COD分别占同期入湖TN、TP和COD总量的9．8％－15．5％、1．9％－2．2％和3．5％－6．0％;依据1999年冬、春季太湖梅梁湾口湖水总硬度和总碱度测定值,结合历史资料分析,指出湖水总硬度对总碱度比值的升高是太湖水体生态系统受持续性酸性降水长期影响的一种反馈形式。     

History of anthropogenic nitrogen input to the German Bight/SE North Sea as reflected by nitrogen isotopes in surface sediments,sediment cores and hindcast models

The German Bight/SE North Sea is considered a hot-spot of river-induced eutrophication, but the scarce observational data of river nitrate loads prior to the 1970s complicate the assessment of target conditions for environmental management and legislation. Stable nitrogen isotope ratios (δ¹⁵N) in sediment records can be used to decipher historical river nitrate contributions. To better constrain pre-1970s conditions, we determined δ¹⁵N in archive sediment samples (1950–1969) and dated cores from the Helgoland depositional area. We also modeled the δ¹⁵N in past situations (1960 and 1860) using an N-isotope-tracking ecosystem model. The modeled spatial distribution of δ¹⁵N in sediments for 1960 conditions and the observed spatial pattern of δ¹⁵N in archive sediment samples (1950–1969) represent a period of moderate eutrophication. The modeled spatial distribution of δ¹⁵N in sediments for 1860 conditions (pre-industrial) showed a moderate δ¹⁵N gradient from the Elbe river mouth (δ¹⁵N<4‰) to the open sea (δ¹⁵N∼5‰). This pattern contrasts with the δ¹⁵N pattern in modern surface sediments, which exhibits a steep and inverted δ¹⁵N gradient from the Elbe river mouth (δ¹⁵N>9‰) to the open sea (δ¹⁵N<7‰). Modeled δ¹⁵N for 1860 conditions are consistent with δ¹⁵N values observed in dated sediment cores that span the last 900 years. Value of δ¹⁵N in sediment cores increased from approximately 1860 to 2000 by 2.5‰. The increasing trend reflects changes in the abundance and isotopic composition of riverine nitrate loads caused by anthropogenic activities. Sensitivity tests suggest that loads and isotopic ratios of nitrogen forms other than nitrate (ammonium and organic nitrogen) have minor impact on the modeled surface sediments, despite their higher abundance in the riverborne loads in the past. Our results suggest that eutrophication of the German Bight predates the 1960 period of documented rapidly increasing river loads. Pre-industrial levels of δ¹⁵N modeled with 28% of the modern annual (1990–1999) atmospheric loads and 10% of the modern annual river loads agree best with levels of δ¹⁵N (∼6‰) observed in sediments of the cores dated to 1860.     

太湖流域降雨和湖水酸根阴离子长期变化及其环境意义

为揭示太湖流域降雨和湖水酸根阴离子长期变化特征及环境意义,通过历史数据收集和采样分析,对太湖流域降雨和湖水中的SO₄^2-、NO₃^-变化特征和来源进行了研究.结果表明：自1990s以来太湖流域降雨中SO₄^2-呈显著下降趋势,年平均下降率为0.28 mg/（L·a）;NO₃^-浓度却呈显著上升趋势,年平均增长率为0.05 mg/（L·a）,降雨中氮污染呈现加重的趋势.与之相反,湖水中SO₄^2-呈显著上升趋势,年平均增长率为1.24 mg/（L·a）;NO₃^-浓度却呈显著下降趋势,年平均下降率为0.02 mg/（L·a）.30年以来,太湖水体SO₄^2-/NO₃^-比值不断升高,远高于降水SO₄^2-/NO₃^-比值.研究认为：流域SO₂排放引起的酸沉降是湖水SO₄^2-浓度增长的最重要原因,但氮氧化物排放并未引起湖水NO₃^-浓度升高,说明太湖流域对大气沉降的氮氧化物有滞留作用,而太湖水体是流域大气沉降硫酸盐的重要汇.综合治理太湖流域酸性物质排放对防止太湖水体酸化和治理富营养化都具有重要意义.