Water and sediment quality assessment in the mid-Black Sea coast of Turkey using multivariate statistical techniques

The aim of this study was to investigate the water and sediment quality in the mid-Black Sea coast of Turkey. The samples were collected from six stations during 2007. Investigated parameters were total carbon (TC), total inorganic carbon (TIC), total organic carbon (TOC), ammonium-nitrogen (NH₄-N), nitrate-nitrogen (NO₃-N), nitrite-nitrogen (NO₂-N), total phosphorus (TP), sulphate, total hardness, methylene blue active substances (MBAS), phenol, adsorbable organic halogens (AOX), dissolved oxygen (DO), pH and electrical conductivity (EC) in water samples and TC, TIC, TOC, TP, pH, electrical conductivity (EC), redox potential (Eh) and water content (WC) in sediment samples. Different multivariate statistical techniques were used to evaluate variations in surface water and sediment quality. Principal component analysis helped in identifying the factors or sources responsible for water and sediment quality variations. Five factors were found responsible for 87.63% of the total variance in the surface waters. In sediments, three factors explained 84.73% of the observed total variance. Cluster analysis classified the monitoring sites into two groups based on similarities of water and sediment quality characteristics.     

Spatial variations and distributions of phosphorus and nitrogen in bottom sediments from a typical north-temperate lake,China

Concentrations and vertical distributions of total nitrogen (TN), total phosphorus (TP) and their different forms in sediments obtained from nine locations of Lake Dalinouer in September 2008 were analyzed. The results demonstrated that TP in surface sediments ranged from 0.493 to 0.904 g/kg, and inorganic phosphorus was the main fraction of total phosphorus, ranging from 335 to 738 mg/kg. Simultaneously, the autogenetic calcium phosphorus (ACa-P) was the main fraction of inorganic phosphorus, ranging from 145.4 to 543.2 mg/kg. Vertical distribution of different phosphorus forms in different sediment cores was distinguishing, and most of them tended to increase toward the surface sediment, indicated that the phosphorus concentration was related to the humanity with a certain extent. The relationships between TP and occluded phosphorus and ACa-P were significant. Nitrogen in the sediment was composed mainly of organic nitrogen, accounting for grater than 80 % of TN. NO₃ ^?-N was the dominate fraction of inorganic nitrogen in the surface sediment, ranging between 51 and 346 mg/kg (151.1 ± 104.4 mg/kg), and accounting for between 2.2 and 17.7 % of total sediment nitrogen (6.2 ± 5.6 %). The ratio of organic carbon and TN in sediment was in range of 6.0–25.8 and presented a tendency of lake centre >lake sides, indicating that nitrogen accumulated in the sediments from lake sides came mainly from terrestrial source and nitrogen was mainly autogenetic in lake centre. Ratio of N:P in all sampling sites was below 14, indicated that N was the limiting nutrient for algal growth in this lake.     

Source and Biogeochemical Distribution of Organic Matter in Surface Sediment in the Deep Oligotrophic Lake Fuxian,China

The source, quantity and quality of sedimentary organic matter (SOM) were investigated in the surface sediments of Lake Fuxian, a deep oligotrophic lacustrine system in China. Granulometry, biochemical organic composition, bulk organic proxies and their stable isotopes were determined in the surface sediments (0–4 cm). The values of δ¹³C, δ¹⁵N and atomic ratio of total organic carbon to total nitrogen (TOC/TN) indicated that the sediments in the large partial lake were influenced by autochthonous organic matter. The concentrations of TOC, protein (PRT) and total hydrolysable amino acids may be mainly modulated by phytodetritus sinking from euphotic zones since they correlated significantly with chlorins. Otherwise, the lack of correlation between chlorins concentrations and carbohydrate (CHO) and lipid (LIP) indicated that the latter may have an additional terrestrial source. The highest sediment quantity was found in the deepest station NC owing to its fine sediment. Stations near northwestern shore accumulated more SOM than other littoral stations, which was in accordance with sewage discharge strength. Degradation quality indices, such as chlorin index, degradation index, PRT/CHO, and LIP/CHO, were in general agreement in showing the degraded status of SOM in Lake Fuxian. No clear spatial patterns were found in sediment degradation quality, which may be influenced by bottom oxygen concentration in the deep stations.     

Study on Nitrogen Dynamics at the Sediment–Water Interface of Dongting Lake,China

Eutrophication of lakes and reservoirs has become a worldwide environmental problem, and nitrogen (N) has been recognized as one of the key factors responsible for eutrophication. Nitrogen adsorbed on sediments may be released via chemical and biological processes under changing environmental conditions. Spatial distributions of concentrations of ammonia nitrogen (NH₄ ⁺–N), nitrate nitrogen (NO₃ ^?–N) and total nitrogen (TN) were investigated in sediments and overlying water of Dongting Lake, the second largest freshwater lake in China. The concentration of TN in the sediments exhibited strong spatial variation with relatively high values in the eastern part and relatively low values in the southern part of the lake. The TN concentration in the water of different regions of Dongting Lake was affected by the internal load of sediment N. The vertical distribution of TN in sediment cores showed a decreasing trend with an increase in depth. Concentrations of NH₄ ⁺–N in the sediment cores decreased with the depth increase until 6–8 cm and then increased slowly. However, concentrations of NO₃ ^?–N in the sediment cores showed an opposite trend from those of NH₄ ⁺–N. A kinetic release experiment of NH₄ ⁺–N showed that the maximum release rate occurred in the first 5 min and the amount of NH₄ ⁺–N release reached 77.93–86.34 % of the total amount in 0–10 min. The release of NH₄ ⁺–N in the surface sediments of Dongting Lake fits a first-order kinetics function.     

Hydrogen sulfide and organic carbon at the sediment–water interface in coastal brackish Lake Nakaumi, SW Japan

The relationship among H₂S, total organic carbon (TOC), total sulfur (TS) and total nitrogen contents of surface sediments (0–1 cm) was examined to quantify the relationship between H₂S concentrations and TOC content at the sediment water interface in a coastal brackish lake, Nakaumi, southwest Japan. In this lake, bottom water becomes anoxic during summer due to a strong halocline. Lake water has ample dissolved SO₄ ^2? and the surface sediments are rich in planktic organic matter (C/N 7–9), which is highly reactive in terms of sulfate reduction. In this setting the amount of TOC should be a critical factor regulating the activity of sulfate reduction and H₂S production. In portions of the lake where sediment TOC content is less than 3.5 %, H₂S was very low or absent in both bottom and pore waters. However, in areas with TOC >3.5 %, H₂S was correlated with TOC content (pore water H₂S (ppm) = 13.9 × TOC (%) ? 52.1, correlation coefficient: 0.72). H₂S was also present in areas with sediment TS above 1.2 % (present as iron sulfide), which suggests that iron sulfide formation is tied to the amount of TOC. Based on this relationship, H₂S production has progressively increased after the initiation of land reclamation projects in Lake Nakaumi, as the area of sapropel sediments has significantly increased. This TOC–H₂S relationship at sediment–water interface might be used to infer H₂S production in brackish–lagoonal systems similar to Lake Nakaumi, with readily available SO₄ ^2? and reactive organic matter.     

Geochemistry of Manasbal lake sediments,Kashmir: Weathering,provenance and tectonic setting

This paper presents a detailed sediment chemistry investigation of the Manasbal lake, Srinagar, Jammu and Kashmir, India, which is one of the high altitude lakes in the Kashmir valley. 22 lake floor sediment samples covering the entire lake were collected and analyzed for textural characteristics, CaCO₃, organic matter, TOC, TN contents, C/N ratio, major and trace element chemistry. These analyses were conducted to trace the provenance of the sediments. Textural parameters reveal that the lake sediments consist predominantly clay and silt fractions. The C/N ratio of the sediments indicates a mixed source of TOC, both autochthonous and allochthonous in origin. The log (Fe₂O₃/K₂O) Vs. log (SiO₂/ Al₂O₃) graph of the sediments discriminates the rock types of the catchment area that are Fe-shale, Fe-sand, wacke, shale and litharenite. The Chemical Index of Alteration (CIA) falls between 59.11 to 90.16% and Chemical Index of Weathering (CIW) between 63.97 to 99.68% and these values are higher than the Post-Archaean Australian Shale (PAAS), indicating moderate to highly chemically weathered lake floor sediments. Plagioclase Index of Alteration (PIA) values (60.74-99.63%) suggests the occurrence of plagioclase feldspars in the lake floor sediments. Geochemical characteristics signify a mixed-nature of provenance of the lake floor sediments due to the tectonic settings of the lake basin in a complex catchment area.     

太湖东部湖湾水生植物生长区底泥氮磷污染特征

为了解太湖东部湖湾(贡湖湾、光福湾、渔洋湾)表层底泥中氮、磷的污染特征及其与水生植物生长的关系,采集了各湖湾滨岸带水生植物生长区的表层底泥,探讨了水生植物的生长与分布对表层底泥中总氮(TN)、总磷(TP)及总有机碳(TOC)等含量的影响,并对表层底泥进行营养评价.结果表明,水生植物生长密集区底泥中TN、TP、TOC的含量均显著低于水生植物零星生长区,说明水生植物的生长对太湖东部湖湾表层底泥中营养盐与有机碳含量具有较为明显的影响;相关性分析显示,表层底泥中TOC与TN含量呈显著相关性(R2=0.832 8),而与TP的相关性则较弱(R2=0.166 5),反映了TOC在湖泊底泥中的沉积可能成为湖泊氮的重要来源,而对磷的影响较小.利用有机指数与有机氮指数两种方法分别对东部各湖湾底泥进行污染评价,贡湖湾、光福湾、渔洋湾底泥有机指数平均值分别为0.142 7、0.228 6与0.208 6,均属较清洁与尚清洁水平,而各湖湾有机氮指数平均值均为Ⅲ与Ⅳ级,说明底泥已遭受了一定程度的氮污染.因此,对水生植物零星生长区表层底泥中氮含量的控制与削减有利于湖泊富营养化的预防与治理.     

湖光岩玛珥湖全新世时期沉积物碳氮同位素组成的环境指示意义

通过对湖光岩玛珥湖沉积物的TOC,TN,δ13CTOC,δ15N和s-ratio的研究,作者重建了全新世期间湖泊初级生产力的变 化,从而揭示了湖光岩地区全新世气候演变历史。早全新世时期（10 400~6100 yr BP）,高值的TOC,TN,δ13CTOC和低值 的δ15N,s-ratio指示了高水平的湖泊初级生产力,反映温暖湿润的气候条件; 8500~7400 yr BP期间,δ15N出现最低值,同时 TN出现高值,表明可能受了固氮蓝藻的影响,指示该段时间季风减弱,可能为对应着8.2 ka事件;中全新世期间（6100~ 3600 yr BP）,TOC,TN和δ13CTOC下降,s-ratio上升,指示湖泊生产力下降,气候逐渐向冷干转变;晚全新世期间（3600 yr BP至今）,TOC和TN继续下降,δ13CTOC处于最低值,s-ratio达到最大值,代表季风最弱的时期和湖泊生产力持续降低。全新 世湖泊生产力的逐渐下降反映了季风的逐步减弱,而驱动因素则是北纬30°太阳辐射的减少。在~1000 yr BP以后,δ13CTOC与 δ15N表现出不同于全新世演化趋势的异常,可能指示人类活动的加剧,尤其是烧荒开田对沉积物的影响。     

Sources of nutrient inputs to the Patuxent River estuary

We quantified annual nutrient inputs to the Patuxent River estuary from point and nonpoint sources and from direct atmospheric deposition. We also compared nonpoint source (NPS) discharges from Piedmont and Coastal Plain regions and from agricultural and developed lands. Using continuous automated-sampling, we measured discharges of water, nitrogen, phosphorus, organic carbon (C), and suspended solids from a total of 23 watersheds selected to represent various proportions of developed land and cropland in the Patuxent River basin and the neighboring Rhode River basin. The sampling period spanned two years that differed in annual precipitation by a factor of 1.7. Water discharge from the watershed to the Patuxent River estuary was 3.4 times higher in the wet year than in the dry year. Annual water discharges from the study watersheds increased as the proportion of developed land increased. As the proportion of cropland increased, there were increases in the annual flow-weighted mean concentrations of nitrate (NO₃ ^?), total nitrogen (TN), dissolved silicate (Si), total phosphate (TPO₄ ^3?), total organic phosphorus (TOP), total P (TP), and total suspended solids (TSS) in NPS discharges. The effect of cropland on the concentrations of NO₃ ^? and TN was stronger for Piedmont watersheds than for Coastal Plain watersheds. As the proportion of developed land increased, there were increases in annual mean concentrations of NO₃ ^?, total ammonium (TNH₄ ⁺), total organic N (TON), TN, total organic C (TOC), TPO₄ ^3?, TOP, TP, and TSS and decreases in concentrations of Si. Annual mean concentrations of TON, TOC, forms of P, and TSS were highest in the wet year. Annual mean concentrations of NO₃ ^?, TNH₄ ⁺, TN, and Si did not differ significantly between years. We directly measured NPS discharges from about half of the Patuxent River basin and estimated discharges from the other half of the basin using statistical models that related annual water flow and material concentrations to land cover and physiographic province. We compared NPS discharges to public data on point source (PS) discharges. We estimated direct atmospheric deposition of forms of N, P, and organic C to the Patuxent River estuary based on analysis of bulk deposition near the Rhode River. During the wet year, most of the total terrestrial and atmospheric inputs of forms of N and P came from NPS discharges. During the dry year, 53% of the TNH₄ ⁺ input was from atmospheric deposition and 58% of the NO₃ ^? input was from PS discharges; NPS and PS discharges were about equally important in the total inputs of TN and TPO₄ ^3?. During the entire 2-yr period, the Coastal Plain portion of the Patuxent basin delivered about 80% of the NPS water discharges to the estuary and delivered similar proportions of the NPS TNH₄ ⁺, TN, TOP, and TSS. The Coastal Plain delivered greater proportions of the NPS TON, TOC, Si, and TP (89%, 90%, 93%, and 95%, respectively) than of water, and supplied nearly all of the NPS TPO₄ ^3? (99%). The Piedmont delivered 33% of the NPS NO₃ ^? while delivering only 20% of the NPS water to the stuary. We used statistical models to infer the percentages of NPS discharges supplied by croplands, developed lands, and other lands. Although cropland covers only 10% of the Patuxent River basin, it was the most important source of most materials in NPS discharge, supplying about 84% of the total NPS discharge of NO₃ ^?; about three quarters of the TPO₄ ^3?, TOP, TP, and TSS; and about half of the TNH₄ ⁺ and TN. Compared to developed land, cropland supplied a significantly higher percentage of the NPS discharges of NO₃ ^?, TN, TPO₄ ^3?, TOP, TP, and TSS, despite the fact development land covered 12% of the basin.     

Reciprocal influence of Kürtün Dam and wastewaters from the settlements on water quality in the stream Harşit,NE Turkey

This paper aims to reveal the reciprocal influence of Kürtün Dam and wastewaters from the settlements on the water quality in the stream Har?it, NE Turkey. Several key water-quality indicators were measured: water temperature (T), pH, dissolved oxygen (DO), electrical conductivity, water hardness, chemical oxygen demand (COD), ammonium nitrogen (NH₄ ⁺–N), nitrite nitrogen (NO₂ ^?–N), nitrate nitrogen (NO₃ ^?–N), total Kjeldahl nitrogen (TKN), total nitrogen (TN), orthophosphate phosphorus (PO₄ ^3?–P), and methylene blue active substances (MBAS). The monitoring and sampling studies were conducted every 15 days from March 2009 to February 2010 at two stations selected in the upstream and downstream of the Kürtün Dam. It was concluded that the Kürtün Dam Lake had a high-quality water in terms of T, pH, DO, COD, NH₄ ⁺–N, NO₂ ^?–N and NO₃ ^?–N values, but slightly polluted water with respect to TKN, PO₄ ^3?–P, and MBAS according to the Turkish Water Pollution Control Regulation. The dam improved the stream water quality by increasing the DO concentration, and decreasing the NO₂ ^?–N and PO₄ ^3?–P concentrations thanks to its hydraulic residence time despite the wastewater discharge by the nearby settlements. However, the wastewater discharge deteriorated the stream water quality increasing the COD, NH₄ ⁺–N, NO₃ ^––N, and TN concentrations.     

Geochemical record of anthropogenic impacts on Lake Valencia,Venezuela

Bulk geochemical parameters and organic matter biomarkers in a short, high resolution gravity core (Lake Valencia, Venezuela) were examined to reconstruct anthropogenic impacts on the lake’s conditions. During the period of ca. 1840–1990, sedimentary organic matter was characterized by high contents of total organic C (TOC) and total N (TN), low TOC/TN values as well as relatively enriched δ¹³C and δ¹⁵N signals, suggesting a primary autochthonous (algae and macrophytes) organic matter origin. The occurrence of large amounts of C₂₃ and C₂₅ relative to C₂₉ and C₃₁n-alkanes indicated substantial inputs from submerged/floating macrophytes. The variations of C₃₂ 15-keto-ol, tetrahymanol, diploptene, C₃₂ bishomohopanol, 2-methylhopane, dinosterol and isoarborinol concentrations over the investigated period record changes in the planktonic community structure, including Botryococcus braunii, bacteriavore ciliates, cyanobacteria, Eustigmatophytes and dinoflagellates. A principal shift occurred in the 1910s when cyanobacteria and dinoflagellates became more abundant at the expense and decline of B. braunii and Eustigmatophytes, likely related to increasing anthropogenic activity around the lake. A second shift (less obvious) occurred in the 1960s when cyanobacteria became the sole predominant planktonic class, coinciding with further deterioration of lake conditions.     

Composition and origin of organic matter in surface sediments of Lake Sarbsko: A highly eutrophic and shallow coastal lake (northern Poland)

We present an organic geochemical study of surface sediments of Lake Sarbsko, a shallow coastal lake on the middle Polish Baltic coast. The aim was to provide evidence concerning the origin of the organic matter (OM) and its compositional diversity in surface deposits of this very productive, highly dynamic water body. The content and composition of the OM in the bottom sediments were investigated at 11 sampling stations throughout the lake basin. OM sources were assigned on the basis of bulk indicators [total organic carbon (TOC), total nitrogen (TN), δ¹³C_TOC and δ¹⁵N and extractable OM yield], biomarker composition of extractable OM and compound-specific C isotope signatures. The source characterization of autochthonous compounds was verified via phytoplankton analysis. The distribution of gaseous hydrocarbons in the sediments, as well as temporal changes in lake water pH, the concentration of DIC (dissolved inorganic carbon) and δ¹³C_DIC were used to trace OM decomposition.The sedimentary OM is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition. However, the presence of CH₄ and CO₂ in the bottom deposits provides evidence for microbial degradation of sedimentary OM. The transformation of organic compounds in surface, bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of CaCO₃.The data enhance our understanding of the relationships between the composition of sedimentary OM and environmental conditions within coastal ecosystems and shed light on the reliability of OM proxies for environmental reconstruction of coastal lakes.     

Sediment characteristics and water physicochemical parameters of the Lysimachia Lake, Western Greece

In the present paper, we present the sedimentological characteristics and the water physicochemical parameters of Lysimachia Lake, which is one of the most important lakes of Western Greece, as it is protected by international conventions and is listed in the Natura 2000 European Network. Sedimentological analysis involved grain size analyses, moment measures, total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) measurements, as well as determination of the clay minerals content. Water physicochemical parameters such as pH, temperature, conductivity and dissolved oxygen were measured in situ with portable equipment, while nutrients such as nitrates, nitrites, phosphates and ammonium ions, as well as TOC and TN were analyzed in a time period of 1 year seasonal monitoring. Geographical distribution of grain size and geochemical parameters indicated a clear partition in the northern and southern parts of the lake. This phenomenon can related to the discharging of a channel into the lake, the discharging of sewage effluents from Agrinio city during the last years as well as the type of clay minerals distribution. Clay minerals analyses indicated that smectite predominates in the northern part of the lake, whereas chlorite is more abundant in the southern parts. This explain the higher amounts of TOC and TN observed in the northern part of the lake and can be correlated with the higher external surface and adsorption capacity of minerals in the smectite-rich sediments. The four seasons monitoring of water physicochemical parameters indicates a relatively higher values of TOC and TN in the northern part of the lake, while nutrient concentrations indicate a uniform geographical distribution along the lake.     

苏北潮滩湿地不同生态带碳、氮、磷分布特征*

通过对比苏北潮滩湿地不同生态带的表层以及柱状沉积物中总有机碳、总氮、总磷和有机磷含量,并结合不同植被不同植株部位中碳、氮、磷的含量变化,分析了潮滩沉积物中碳、氮、磷的垂向和水平分布特征与规律,探讨了不同生态带以及潮滩植被对碳、氮、磷等生源要素的富集作用。对比分析结果表明:苏北潮滩湿地各生态带对不同的测量指标有着不同的富集作用,互花米草滩的总有机碳、总氮和有机磷含量要远大于其他几个生态带,光滩沉积物中总磷的含量最高; 粒度效应是控制互花米草前缘地带以及互花米草滩沉积物中有机碳和氮分布的一个重要因素,盐蒿和芦苇滩中有机碳和氮的分布更多的是受粒度之外的其他因素影响; 不同生态带表层沉积物中的C/N比值分布,大致可反映其有机物来源的差异,而不同生态带中柱状沉积物中的C/N比值相对接近,很难根据C/N比值大小来对不同生态带中的有机物来源进行判断,这可能是埋藏在柱状沉积物中的有机物更多的受到了早期成岩作用造成的。植被对潮滩湿地中碳、氮、磷的分布有着重要影响,3种物质在互花米草、盐蒿和芦苇中的含量差别不是很大,因此潮滩植被对沉积物中上述3种物质的贡献差别主要是由不同植被的生物量和其所处环境的沉积动力差异造成的。     

Vertical Profiles of Major Organic Geochemical Constituents and Extracellular Enzymatic Activities in Sandy Sediments of Aransas and Copano Bays, TX

Vertical distribution patterns of organic geochemical constituents and the enzymes aminopeptidase and β-glucosidase provide insights about the nature and reactivity of sediment organic matter in the sandy sediments of two shallow “South Texas” estuaries. Sediment total organic carbon (TOC) δ¹³C values indicated that the organic matter (OM) was derived more from a mixture of seagrass and phytoplankton than from terrigenous OM. Down-core amounts of TOC and total nitrogen (TN) were <0.2% of dry weight, respectively. Enzyme activities were highest near surface and ranged from 25 to 1 μM/h for aminopeptidase as compared to 5 to 0.2 μM/h for glucosidase. In Aransas Bay, aminopeptidase activity correlated with sediment TN content (r _s = 0.30) and β-glucosidase with TOC content (r _s = 0.27). In Copano Bay, aminopeptidase correlated with TOC, TN, and carbohydrate content (r _s = 0.89, 0.90, and 0.83, respectively). Variations of glucosidase activity also related positively to TOC, TN, and total carbohydrate content (r _s = 0.68, 0.77, and 0.48, respectively). Overall, enzyme activities in these low OM, sandy sediments resembled those for other benthic marine environments.     

18.5kaB. P.以来东北四海龙湾玛珥湖全岩有机碳同位素记录及其古气候环境意义

结合含水量、TOC含量和TOC/TN比值变化曲线,18·5kaB·P·以来的四海龙湾玛珥湖沉积物全岩有机碳同位素组成（^δ13C_TOC）记录可划分为3个阶段:1)末次冰期晚期（18·5～14·7kaB·P·）,^δ13C_TOC值偏正,变化范围为-29·50‰～-26·18‰,平均值约为-28·10‰;2)末次冰消期（14·7～11·7kaB·P·）,^δ13C_TOC值显著偏负,变化范围为-33·92‰～-28·40‰,平均值约为-31·75‰,在^δ13C_TOC值变化曲线上表现为一个低谷,但在类似YoungerDryas的冷干事件期间（12·7～11·7kaB·P·）,^δ13C_TOC值再次显著偏正,最高可达-28·4‰;3)全新世以来（11·7kaB·P.至今）,^δ13C_TOC值变化幅度不大（-30·85‰～-27·37‰）,基本上都在平均值-29·1‰左右。研究表明,大气CO₂浓度变化是影响18·5kaB·P·以来四海龙湾玛珥湖^δ13C_TOC值变化的主导因素。     

The characteristic and environmental pollution records of phosphorus species in different trophic regions of Taihu Lake, China

Total organic carbon (TOC), Total nitrogen (TN) and the phosphorus species concentrations of sediment cores taken from Zhushan Bay, Meiliang Bay, and East Taihu Lake regions in Taihu Lake, a large shallow lake in China, were determined. Experimental results showed a conspicuous eutrophication trend in the northern area of Taihu Lake. Inorganic P was found to be the main phosphorus form. Fe-bound P accounted for the largest proportion of Inorganic P in Meiliang Bay, an alga-type lake region. In East Taihu Lake, a macrophytic lake region, Ca-bound P was found in higher proportions than in other lake regions, with Organic P present in similarly large proportions. With respect to Taihu Lake sediment cores, the date at approximately 20 cm layer depth was roughly identified as 1950s, while upper 5 cm layers corresponded to the turn of the century. The drastic increase in phosphorus species concentration except for Ca-bound P was indicative of the large quantities of effluent discharge into Zhushan Bay owing to the increased industrial and agricultural production from the 1950s onwards. TN, Inorganic P, Organic P, and total phosphorus (TP) concentrations increased by over 2, 2.5, 2 and 2.5-fold, respectively, over the past five decades. A large proportion of Organic P accounted for TP, and high C/N ratios indicated that East Taihu Lake can be properly classified as an oligotrophic lake.     

Holocene paleoenvironmental reconstruction in the Eastern Amazonian Basin: Comprido Lake

Two sediment cores were studied from Comprido Lake, a black water floodplain lake located near Monte Alegre City, Eastern Amazonian Basin. The total organic carbon (TOC), nitrogen content (TN), δ¹³C_TOC, sedimentary chlorophyll, diatom record and mineralogical composition revealed different hydrological and climatic regimes during the Holocene. Between 10,300 and 7800 cal yr BP, a dry climate was suggested by low values of TOC and chlorophyll derivatives concentrations that are related to the development of a C₄ grasses on unflooded mud banks. A gap in sedimentation due to a complete dryness of the lake occurred between 7800 and 3000 cal years BP corresponding to the Middle Holocene dry phase. From 3000 cal years BP onwards a gradual increase of the TOC, chlorophyll derivatives and Aulacoseira sp. suggest an increase in the productivity and in water lake level due to the high water flow of the Amazon River and the catchment area as well. The Comprido Lake record indicates that the Late Holocene in this region was characterized by a wetter climate, as also observed in other records of the Amazonian Basin.     

Nitrogen and oxygen isotopic compositions of water-soluble nitrate in Taihu Lake water system, China: implication for nitrate sources and biogeochemical process

The stable isotope nitrogen-15 (¹⁵N) is a robust indicator of nitrogen (N) source, and the joint use of δ¹⁵N and δ¹⁸O–NO₃ ^? values can provide more useful information about nitrate source discrimination and N cycle process. The δ¹⁵N and δ¹⁸O–NO₃ ^? values, as well as major ion tracers, from Taihu Lake in east China were investigated to identify the primary nitrate sources and assess nitrate biogeochemical process in the present study. The results show that the nitrate concentration in West Taihu Lake (WTL) was generally higher than those in East Taihu Lake (ETL) and its upstream inflow rivers. The NO₃ ^?/Cl^? value combined with mapping of δ¹⁵N–NO₃ ^? and NO₃ ^? concentration suggest that the mixing process should play a major effect in WTL, and denitrification was the dominant N transformation process in WTL. A linear relationship of close to ~1: 2 was observed between δ¹⁵N–NO₃ ^? and δ¹⁸O–NO₃ ^? values in WTL, confirming the occurrence of denitrification in WTL. The δ¹⁵N–NO₃ ^? data imply that sewage and manure were the principal nitrate sources in WTL and its feeder rivers, while the nitrate in ETL might derive from soil organic nitrogen and atmospheric deposition. The δ¹⁸O–NO₃ ^? data indicate most of nitrate from microbial nitrification of organic nitrogen matter possibly make a significant contribution to the lake.     

Distribution of n-alkanes in lacustrine sediments from subtropical lake in Brazil

The geochemical composition of lake bed sediments of a tropical reservoir in Brazil have been investigated. The C, N, P composition showed almost no variation between the different sampling points. All samples contained inorganic phosphorus (IP) ranging from 52 to 70%. The Redfield ratios show that the lake is without significant anthropogenic inputs. Most of the organic matter is composed by higher plants decomposition revealed in the total organic carbon (TOC):nitrogen (N) ratio ranging from 15.4 to 57.2. Also, TOC:organic phosphorus (OP) ranged from 265.3 to 933.6, suggesting that most of the organic matter has terrestrial origin from wood plants. The ratios suggest that most organic matter is influenced by the terrestrial characteristics of the watershed. Furthermore, the relative abundance of n-alkane homologues in the sediments was investigated. All samples have been analyzed for the n-alkanes C₈ to C₄₀. The sediments were dominated by n-alkanes C₂₅–C₃₈. It is concluded that n-alkane in sediments mainly come from terrestrial plants, however there is a contribution of submerged aquatic plants, especially in those sites in deeper areas of the lake. On the basis of P_aq index the n-alkanes in sediments comes from terrestrial plants, however there is a contribution from emerged/floating plants.The investigated lake seems to be considered as meso to eutrophic. Because of the relatively high primary productivity in the lakes, there is a substantial organic-matter flux to the sediments, which rapidly becomes anoxic. According to the pristine/phytane ratio the sediments represent an anoxic environment with values found between 0.38 and 1.72.