Hongfeng Lake Research Articles

Carbon export and fate in carbonate catchments: A case study in the karst plateau of southwestern China

Abstract The consumption of CO 2 due to carbonate weathering is thought to be an important terrestrial sink for atmospheric CO 2 . However, the reaction and fate of weathering products may significantly affect the magnitude of the sink. Carbon mass balances were determined in Hongfeng Lake, a small artificial lake located in the carbonate plateau of SW China. This was accomplished by measuring the concentrations of DIC (dissolved inorganic C), DOC (dissolved organic C), POC (particulate organic C), and CO 2 partial pressure in lake waters, inflows and outflows, and in surrounding spring waters. Results show that maximum DIC (mainly HCO 3 - derived from carbonate weathering by CO 2 ) to DOC ratios in the catchment export load reach ∼21, implying that as much as ∼80% of the exported primary production is in the form of HCO 3 - , and, therefore, the CO 2 consumed by carbonate weathering and subsequent DIC export is a critical component of the C balance in this ecosystem. This exported HCO 3 - subsidizes C cycling of aquatic ecosystems in the catchment, and 32% (excluding carbonate-derived C) returns to the atmosphere as CO 2 evasion through the fluvial and lacustrine water–air interface and 10% is stored in lake sediment. This lake has a small CO 2 emission rate (13.2 ± 3.9 mmol m −2 d −1 , or 0.097 mol m −2 a −1 relative to catchment area) compared to mean values for many reservoirs found in temperate and tropical climatic zones. This is likely due in part to low organic C loads supplied by the karst-dominated catchment, and low lake water DOC concentrations. The estimate indicates that more C (39%) returns to the atmosphere and much less (13%) is stored in sediments, implying that the C sink of carbonate weathering may not be as significant as once thought.

Application of chemical fractionation and X-ray powder diffraction to study phosphorus speciation in sediments from Lake Hongfeng, China

Based on the techniques of sequential extraction and X-ray powder diffraction (XRD), the distribution characteristics of phosphorus speciation were investigated in 13 sediment samples from Lake Hongfeng, an important drinking water source for Guiyang with a typical karstic limestone environment. The total phosphorus (TP) concentrations in the sediments ranged from 973.36 to 2334.18 mg/kg with a mean concentration of 1635.87 mg/kg (dry weight), and it was evident that the phosphorus level in the sediments was high compared with other eutrophic lakes such as Lake Chaohu and Lake Xihu. The results of the two methods, sequential extraction and XRD, demonstrated the presence of different phosphorus species in the lake sediments. Being compatible with local geophysical characteristics, the results of sequential extraction techniques indicate that the average percentages of dissolved phosphorus (DP), aluminum-bound phosphorus (Al-P), iron-bound phosphorus (Fe-P), calcium-bound phosphorus (Ca-P) and organic phosphorus (OP) in the sediments were 0.40%, 7.06%, 5.07%, 45.48% and 38.49%, respectively. Notably, the concentrations of inorganic phosphorus (IP) were higher than those of OP, and the IP consisted primarily of Ca-P. The high concentrations of Ca-P may temporarily control the release of phosphorus from the sediments because it is a relatively stable, inert and non-bioavailable phosphorus fraction. The results of XRD analysis indicated that, among phosphorus species, AlPO4 was found in all sediment samples at relatively high concentrations. Moreover, the TP concentrations in the sediments were high; thus the release potential and bioavailability of phosphorus in the sediments was important. Further statistical analyses of the results revealed significant correlations between phosphorus species in the sediments with two extractable principal components and four selectable cluster levels allowing interpretation of possible origins of phosphorus loading and transformation mechanisms of phosphorus species. Furthermore, available remediation measures were briefly assessed for the lake while considering its distinct environmental features.

Iron Isotope Compositions of Natural River and Lake Samples in the Karst Area, Guizhou Province, Southwest China

Abstract:To better understand the Fe isotope characteristics of natural samples in the Karst area, the Fe isotope compositions of riverine suspended particulates, lake suspended particulates, lake sediments, porewaters, phytoplanktons, and aerosols in the watersheds of Lake Aha (a mineralized water system) and Lake Hongfeng (a mesotrophic water system), which are located in the Karst area, southwest China, were investigated. The studied samples displayed a variable range between δ56Fe=–2.03‰ and 0.36‰. Aerosols and phytoplanktons have similar or slightly heavier Fe isotope compositions relative to the average of igneous rocks. Fe isotope compositions of riverine Suspended Particulate Matter (SPM) were mainly affected by the types of tributaries. Suspended particulates collected from tributaries seriously contaminated with coal mine drainages displayed negative δ56Fe values (–0.89‰ to –0.31‰) during summer, and there were significant increases of δ56Fe values in winter, except AR2, which was polluted with both coal mine drainage and sewage effluent. Characteristics of lakes have important influences on Fe isotope compositions of suspended particulates, lake sediments, and porewaters. The epilimnetic particulate Fe of Lake Hongfeng had δ56Fe=–0.04‰ to 0.13‰, while lighter Fe isotope compositions were measured for particulate Fe from Lake Aha, ranging from –0.42‰ to –0.09‰. Sediments collected from Hou Wu (HW) station of Lake Hongfeng have an average δ56Fe value of 0.09‰ and their corresponding porewaters have lighter Fe isotope compositions, ranging from –0.57‰ to –0.31‰; no significant variations have been observed. For the Liang Jiang Kou (LJK) station of Lake Aha, the content of reactive Fe and the concentration of sulfate were all high. Due to the reactive Fe recycling, including dissimilatory Fe reduction, adsorption, and Fe–sulfide formation, porewaters sampled near the sediment surface have been found to have a δ56Fe value as low as –2.03‰ and an increase up to 0.12‰, with a burial depth of 10 cm. In contrast, an opposite variation trend was found for LJK sediments. Sediments sampled at 1‐cm depth had a value of δ56Fe=–0.59‰ and decrease as low as –1.75‰ with burial depth. This investigation demonstrated that significant Fe isotope fractionations occur in surface environments. Fe isotope compositions of particulate Fe were seriously affected by Fe sources, and Fe biogeochemical recycling has an important influence on Fe isotope fractionations in lake sediments, especially when there are significant amounts of reactive Fe and sulfate.

Historical lead pollution in the central region of Guizhou province, China: A record of lead stable isotopes of lake sediments

Abstract Economic reform in China since 1978 has accelerated economic development nationwide hugely, but has also brought about some environmental pollution. In order to identify the primary Pb source to the atmosphere in the central Guizhou region, Pb isotopic ratios in the acid soluble fraction of sediment from Hongfeng Lake were investigated. Lead isotopes in the lake sediments record the history of regional atmospheric Pb pollution. Before the economic reform in 1978, the 208Pb/206Pb and 206Pb/207Pb ratios in the leachates of lake sediments were constant, with a range of 2.0060 to 2.0117 and of 1.2314 to 1.2355, respectively. In the early period of economic reform (1978 to 1988), with the rapid industrial growth in Guizhou province, the acid soluble Pb isotope ratios in the lake sediments changed sharply: the 208Pb/206Pb ratios increased from 2.0212 to about 2.05, while the 206Pb/207Pb ratios decreased from 1.2251 to 1.2060. Emissions from Pb-ore-related industries are suggested to be the major pollution source of Pb in this period. Due to output from a local power plant since 1988, the isotope ratios of the acid soluble Pb in sediments in 1990s are characterized by a little higher radiogenic Pb (208Pb/206Pb = 2.0340–2.0400; 206Pb/207Pb = 1.2122–1.2158) than for the 1980s.

Phosphorus speciation in sediments of Lake Hongfeng, China

This study was conducted to evaluate the distribution characteristics of phosphorus and its species in 14 sediments samples collected from Lake Hongfeng based on sequential extraction. Lake Hongfeng, a major drinking-water source for Guiyang City in southwestern China, is one of the largest artificial reservoirs located in a typical karstic area of the Yunnan-Guizhou Plateau. The results of this study indicate that the average percentages of DP, Al-P, Fe-P, Ca-P and OP in the lake sediments were 0.52, 6.59, 6.09, 42.85 and 40.27, respectively. The concentrations of organic phosphorus (OP) were lower than those of inorganic phosphorus (IP), which consisted mainly of calcium-bound phosphorus (Ca-P). The high concentrations of Ca-P may temporarily control the release of phosphorus from the sediments because it is a relatively stable, inert, and non-bioavailable phosphorus fraction. However, a large number of phosphate solubilizing bacteria can transform insoluble phosphate into bioavailable forms. Moreover, the concentrations of total phosphorus (TP) in the lake sediments were high; thus, the potential for the release of phosphorus from the sediments to the water column and phosphorus bioavailability were still significant. Further statistical analyses of the results revealed significant correlations between phosphorus species in sediments from the lake with two extractable principal component species (PCs) and five selectable cluster levels allowing interpretation of possible origins of phosphorus loading and the release of phosphorus. Furthermore, available remediation measures were briefly assessed for the lake with consideration of its distinctive environmental features.

Screening level of PAHs in sediment core from Lake Hongfeng, Southwest China.

Using data from a 25-year retrospective of polycyclic aromatic hydrocarbons (PAHs) in sediment core from Lake Hongfeng, Southwest China, their possible sources and potential toxicologic significance were investigated. The total PAH concentrations (16 priority PAHs as proposed by the United States Environmental Protection Agency) in sediments ranged from 2936.1 to 5282.3 ng/g and gradually increased from the analyzed deeper sediments to surface sediments. PAHs were dominated by low molecular-weight components, especially phenanthrene (PHEN) and fluorene (FLU). However, a significantly increased number of high molecular-weight (HMW) PAHs was found in upper segments. The temporal trends of individual PAH species suggest that there may have been a change in energy use from low- to high-temperature combustion, especially after approximately 2001. PAH input to Lake Hongfeng originated mainly from domestic coal combustion and biomass burning, whereas fuel combustion characteristics have also been found in recent years. Sediment-quality assessment implied that potential adverse biologic impact could be a probability for most low-ring PAHs (including naphthalene, acenaphthylene, acenaphthylene, FLU, PHEN, and anthracene). Nevertheless, more concern should be paid to HMW PAHs in the future due to their rapidly increasing trends in upper sediments. Because only one core was analyzed in this study, more work is needed to confirm the sources and toxicity of PAHs in Lake Hongfeng.Electronic supplementary materialThe online version of this article (doi:10.1007/s00244-010-9568-4) contains supplementary material, which is available to authorized users.

Studies on Activity of Alkaline Phosphatase and Phosphorus Speciation in Sediments from Lake Hongfeng, China

Environmentally significant activity of alkaline phosphatase (APA), phosphorus loading and its species were determined in 14 sediment samples from Lake Hongfeng, one of the key drinking-water sources in Guizhou Province, China. The results of this research indicates that APA presented a high level and notable fluctuations with spatial variations in sediments, ranging from 8.712×10-5 to 25.667×10-5 mol of p-nitrophenol g−1•h-1, and the average value of total phosphorus (TP) in sediments from the lake was 1129.81 mg/kg (dry weight). The content of inorganic phosphorus (IP) was higher than that of organic phosphorus (OP), and the content of the iron/aluminum-bound phosphorus (Fe/Al-P) with phosphorus release risk was also high. In addition, the Pearson’s correlation analysis shows various correlations between APA and Ca-P, Fe/Al-P, OP and IP.

Potential Ecological Risk Assessment of Heavy Metals in Sediments from Hongfeng Lake, China

Hongfeng Lake, a man-made reservoir, is one of the five key drinking-water sources for Guiyang City, the capital of Guizhou Province in southwestern China. In the present research, the distribution and accumulation characteristics of seven heavy metals (Pb, Cd, As, Hg, Cu, Cr and Zn) in the sediment of this lake were analyzed by examining fourteen sediment samples. A method based on toxic-response factor was used to assess the potential ecological risk of these heavy metals to this lake. For comparison, the two sets of reference data representing the pre-industrial and the local baseline pollution levels of interested heavy metals were employed to derive their accumulating coefficients and potential ecological risk indices. The calculated potential ecological risk indices indicate that the lake was polluted by heavy metals, and both mercury and cadmium loadings were critical factors responsible for the ecological hazards posed to Hongfeng Lake among these seven elements.

Excitation-emission matrix characterization of dissolved organic matter sources in two eutrophic lakes (Southwestern China Plateau)

l ‐1 in the epilimnion and 1.4‐41.0 µg l ‐1 in hypolimnion with the maximum level in July when water temperature (WT) was the highest of the year. DOC concentrations were significantly correlated with Chl a and WT. Chl a was well correlated with WT in the epilimnion of Lake Hongfeng, suggesting that biological activities might be a major DOC source in the lake waters. DOC concentrations were weakly correlated or not correlated with fulvic acid-like fluorescence in the epilimnion, but they were significantly correlated with tryptophan-like fluorescence, indicating that the tryptophan-like fluorescent material was from new DOM in the lakes during the summer period. But these correlations were often insignificant or absent in the waters of Lake Baihua except peaks T and TUV, which may be caused by the input of organic contaminants from the industrial activities near Lake Baihua. This study may assist to better understand the sources of lake DOM and the effects of organic matter pollution on the biogeochemical cycling of DOM in lake environments.

Characterization of dissolved organic matter fractions from Lake Hongfeng, Southwestern China Plateau

With XAD-series and ion exchange resins, dissolved organic matter (DOM) from Lake Hongfeng in Southwestern China Plateau was isolated into 6 fractions, i.e., humic acid (HA), fulvic acid (FA), hydrophobic neutrals (HON), hydrophilic acids (HIA), hydrophilic bases (HIB) and hydrophilic neutrals (HIN). Those fractions were characterized by high performance size exclusion chromatography, fluorescence spectroscopy and UV absorbance. Among the 6 fractions, FA was predominant and accounted for 51% of the total DOM. The weight-average ( M w) and number-averaged ( M n) molecular weight of these fractions ranged from 1688 to 2355 Da and from 1338 to 1928 Da, respectively. A strong correlation was observed between specific UV absorbance at 280 nm, E 2/ E 3 (absorbance at 250 nm to 365 nm), and the molecular weight for DOM fractions. UV-Vis fulvic-like fluorescence peaks were found in all fractions. Protein-like fluorescence peaks existed in HON may indicate that microbial activity was severely in Lake Hongfeng. There was a significant relationship between fluorescence intensities and specific UV absorbance at 254 nm for those DOM fractions, suggesting their similar luminescence characteristics. The values of fluorescence index ( f 450/500) indicated that hydrophobic fractions may derive from terrestrial sources, and the hydrophilic fractions from microbial and terrestrial origins. Those results suggest that there were inter-relationships between molecular weight, fluorescence and absorbance characteristics, and also subtle consistencies between the hydrophilic and hydrophobic properties and the sources for these 6 fractions from Lake Hongfeng.

Composition and activity of external carbonic anhydrase of microalgae from karst lakes in China

SUMMARYThe species composition, the net photosynthetic O2 evolution rate and the activity of external carbonic anhydrase (CA) of microalgae from three reservoirs were studied. Carbonic anhydrase activity had a significant positive correlation with the density of Cyanobacteria in Lake Aha. Microalgae's carbonic anhydrase activity in Lakes Baihua and Hongfeng was related to the density of Chlorophyceae. The species abundances of microalgae in Lake Aha, Lake Baihua, and Lake Hongfeng were different. A relationship between carbonic anhydrase activity and net photosynthetic O2 evolution rate had also been established. Algae with external CA influenced the algal productivity. These results demonstrate the role of external CA in facilitating the availability of CO2 that limits the photosynthesis of microalgae in karst lakes in China.

Temporal and spatial distributions of dissolved organic carbon and nitrogen in two small lakes on the Southwestern China Plateau

Temporal and spatial distributions of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chlorophyll-a and inorganic nitrogen were investigated in two small mountainous lakes (Lake Hongfeng and Baihua), on the Southwestern China Plateau, based on almost 2 years’ field observation. DOC concentrations ranged from 163 μM to 248 μM in Lake Hongfeng and from 143 μM to 308 μM in Lake Baihua, respectively, during the study period. DON concentrations ranged from 7 μM to 26 μM in Lake Hongfeng and from 14 μM to 47 μM in Lake Baihua. DOC showed vertical heterogeneity with higher concentrations in the epilimnion than in the hypolimnion during the stratification period. The DON concentration profiles appeared to be more variable than the DOC profiles. Apparent DON maxima occurred in the upper layer of water. In Lake Hongfeng, DOC concentration in the surface water was highest at the end of spring and early summer. DON concentration was 2–5 μM higher in May 2003 and in June 2004 than in adjacent months. DOC and chlorophyll-a concentrations were significantly correlated (r = 0.79, P < 0.05). The period of highest concentrations of DOC in Lake Hongfeng was also the season of concentrated rainfall. Algae activity and allochthonous input might result in an increase of DOC and DON concentrations together. In Lake Baihua, the maximum concentrations of DOC and DON in the surface water occurred simultaneously in May 2003 and February 2004. DOC concentrations were significantly correlated with DON (r = 0.90, P < 0.01), indicating the common sources. Allochthonous input, biological processes, stratification and mixing were the most important factors controlling the distributions and cycling of dissolved organic matter (DOM) and inorganic nitrogen in these two lakes. Inference from the corresponding vertical distributions of DOM and inorganic nitrogen indicated that DOM played potential roles in the internal loading of nitrogen and metabolism in the water body in these small lakes. The carbon/nitrogen (C/N) ratio showed a potential significance for tracing the source and biogeochemical processes of DOM in the lakes. These results are of significance in the further understanding of biogeochemical cycling and environmental effects of DOM and nitrogen in lake ecosystems.

Seasonal variation and vertical characteristics of the δ&lt;sup&gt;15&lt;/sup&gt;N of particulate organic matter in Lake Hongfeng and Lake Baihua, Guizhou Province

The stable nitrogen isotopic ratios of particulate organic matter (δ15NPOM) was used to elucidate the seasonal variation and vertical characteristics of the different dissolved inorganic nitrogen sources and autochthonous biogeochemistry processes in two lakes (Hongfeng and Baihua) in Guizhou Province, China. The δ15N values of surface POM seasonally varied from 3.7‰ to 14.9‰ in Lake Hongfeng and from 1.3‰ to 8.7‰ in Lake Baihua. It indicated that source of POM was greatly varied in these two lakes during study period. In Lake Hongfeng, the higher δ15N POM values appeared in winter (February, 2004) and summer (September, 2003). The highest δ15N POM values in winter were attributted to the input of high contents and 15N-enriched inorganic nitrogen from industry wastes. During spring, the δ15N POM values decreased when phytoplankton uptake 14N-enriched inorganic nitrate generated by nitrification in the interior Lake Hongfeng. The variation of δ15N values in surface POM coincided well with the variation of δ15N values of inorganic nitrogen sources. It suggestted that the variation of δ15NPOM mainly influenced by inorganic nitrogen sources, which might resulted from the impact of allochthonous human activities. In Lake Baihua, the higher values of δ15NPOM appeared in summer (September, 2003) while the values were low during winter season. These high and low values were possibly aroused by the growth of primary production and large 15N-depleted organic particles input from sewage respectively. In addition, the combination of δ15NPOM and C/N values in the vertical profile can be used to trace some special biogeochemistry processes in lacustrine ecosystem.

Magnetic properties of core HF1-2 from Lake Hongfeng in Guizhou Province and its implications for soil erosion

通过对红枫湖沉积物柱芯HF1-2磁性参数测量,总结出不同阶段沉积物磁性参数变化的特征,再结合137Cs、粒度、TOC(%)和C/N的分析结果,解译出红枫湖流域自1960-2003年的土壤侵蚀变化过程.从沉积物的分析得出,流域的土壤侵蚀经历了强弱交替的过程,两个明显土壤侵蚀增强的过程分别是1977-1980年和1987-1997年.初步探讨土壤侵蚀强烈的原因可能与降水量有关,但也明显存在着其它因素的影响.;Lake Hongfeng is a reservoir located in the center of Guizhou Province, which was built in 1960. A 35cm sediment core HF1-2 was sampled from the lake for analysis in 2004. Some mineral magnetism parameters such as SIRM, χ_lf, IRM_20mT, χ _ARM, Hard, χ_fd% are measured, furthermore HIRM, ARM/SIRM, IRM_20mT/SIRM, ARM/χ_lf, SIRM/χ_lf are calculated from them. Based on magnetic measurements of the core, we can find the changes of magnetic properties influenced by soil erosion in the catchments during the past 43 years from 1960 to 2003. Combination with the results of analyses of¹³⁷Cs, grain size, TOC(%)and C/N, we divide the changes of soil erosion in the drainage area into several periods during these 43 years, the most seriously soil-erosion periods are during 1977 to1980 and 1987 to 1997. Compared with the rainfall data, we find the precipitation, especially summer precipitation may be the major reason of soil-erosion during 1977-1980, and there are some other unknown complex factors to affect the serious soil-erosion during period of 1987 to 1997.

Global fallout Pu recorded in lacustrine sediments in Lake Hongfeng, SW China

Studies on the distribution and isotope compositions of fallout Pu are important for source characterization of possible future non-fallout Pu contamination in aquatic environments, and useful for dating of recent sediments to understand the pollution history of environmental contaminants. We present the historical record of atmospheric Pu fallout reconstructed from a sediment core from Lake Hongfeng, China. The Pu activity profile was in agreement with the 137Cs profile. Inventories were 50.7 Bq m −2 for 239+240Pu and 1586 Bq m −2 for 137Cs. The average 240Pu/ 239Pu atom ratio was 0.185 ± 0.009, indicating that Pu originated from global stratospheric fallout rather than from direct tropospheric or close-in fallout from the Chinese nuclear testing conducted in the 1970s. Our data suggested that Lake Hongfeng would be an ideal setting for monitoring atmospheric fallout and environmental changes in this region.

Situation of sewage input reflected by nitrogen isotopic composition in a sediment core of Hongfeng Lake

Nitrogen in Hongfeng South Lake water mainly comes from sewage with high N concentrations from Pingba Chemical Fertilizer Plant (PCFP). Studies on the sediment core HF010427 sampled in the lake showed that the upward increase of nitrogen isotopic composition of sedimentary organic nitrogen (δ15Norg) accorded with the trend of industrial total production (TP) of PCFC. On the contrary, diagenesis will theoretically cause an upward decrease of δ15Norg. Because no treatment of sewage water was carried out, TP corresponds with sewage emission, indicating that sedimentary δ15Norg can reflect well the total trend of sewage input. The very similar profile shape between nitrogen isotopic composition of sedimentary absorbed ammonium (δ15NH4 absorbed +) and TP of PCFP suggests that δ15NH4 absorbed + can be used to reconstruct more detailed situation of sewage input. The study has a reference to history investigation of sewage input.

Relationship between fluorescence characteristics and molecular weight distribution of natural dissolved organic matter in Lake Hongfeng and Lake Baihua, China

Dissolved organic matter (DOM) is one of the most interesting and difficult problems in recent years due to its important functions in the ecological and environmental system and the complexity of its chemical composition and structure. It is well accepted that fluorescence characteristics and molecular weight distribution are two important parameters in the DOM characterization. However, the relationship between them is still unknown. In this study, fluorescence and molecular weight distribution of DOM in Lake Hongfeng, Lake Baihua and their rivers, and their relationship were investigated using the combination of fluorescence spectroscopy and high-performance size exclusion chromatography (HPSEC) with on-line UV absorbance and fluorescence detectors. The results show that there were two obvious humic-like fluorescence peaks (Peaks A and B) in DOM from lake water. But there was another obvious protein-like fluorescence peak (Peak C) in DOM from river water. The humic-like fluorescence material consisted of DOM fraction with smaller molecular weight, ranging from 1.0 to 3.0 kDa, while the protein-like fluorescence material mainly consisted of DOM fraction with MW larger than 2.0 kDa. The calculation of MW using HPSEC was related to the UV absorbance wavelength chosen.

Molecular weight distribution of dissolved organic matter in Lake Hongfeng determined by high performance size exclusion chromatography (HPSEC) with on-line UV-vis absorbance and fluorescence detection

The molecular weight distribution (MWD) of dissolved organic matter (DOM) in lake waters from Lake Hongfeng was examined using high performance size exclusion chromatography (HPSEC) with UV-vis absorbance and fluorescence detection. The elution curves obtained by absorbance and fluorescence techniques expressed similar patterns, with the exception of diminishing of large fraction and the peaks behind several seconds in fluorescence chromatograms. According to its molecular weight (MW), DOM in water samples is divided into several fractions: large (> 3.5 kDa); medium-large (3.5−2.0 kDa); medium (2.0−1.0 kDa) and small (< 1.0 kDa). The average molecular weight was calculated using the elution curve detected by UV-vis absorbance and fluorescence detection techniques. The results showed that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) calculated by UV-vis absorbance techniques range from 1750 to 2050 Dalton and from 1450 to 1850 Dalton, respectively. And theMw andMn obtained by fluorescence detection are lower by 50 to 400 Dalton. As a reference, the molecular weight of Fluka humic acid (FHA) is larger than that of water samples by about 200 Dalton. The average molecular weight of DOM for water samples collected in March and July was compared. The results revealed that the molecular weight is lower for water samples obtained in July than that obtained in March, indicating the ambient environment has an influence on the molecular weight, including photo-degradation and biological activity.

Enzymatic and microbial degradation of organic matter in Lake Hongfeng, Guizhou Province, China

In this work, enzymatic and microbial degradation of organic matter in Lake Hongfeng, Guizhou Province, is described in terms of variations in DNA, α-glucosidase and sulfatereduction bacteria (SRB). Organic matter is degraded by microbes and extracellular enzymes excreted by the former, to a relatively low content below the 11-cm sediment depth. The distribution of DNA indicated that microbes are very active at the 9-cm sediment depth, where organic matter is degraded by microbes intensively. The contents of α-glucosidase are highest in suspend layer (0.75 μmol · min−1· g−1 dry sediments), showing that starch and hepatin in organic matter have been degraded intensively. α-glucosidase activity weakens with sediment depth. At the 11-cm depth where the degradation of organic matter started to slow down, α-glucosidase activity has been reduced to 0.17 μmol · min−1 · g−1 (dry sediment). Molecular biological research indicated that sulfate reduction bacteria (SRB) are distributed mainly at the upper 7-cm sediments in Lake Hongfeng. Combined with the results of research on the variations of organic matter and SO 4 2− , it is indicated that SO 4 2− is unlikely to become an important electron acceptor and sulfate reduction is not limited by the supply of organic matter in Lake Hongfeng.

The Phosphorus Forms and Depositional History in Sediments of Lake Hongfeng, Guizhou Province

采集了云贵高原深水湖泊红枫湖现代沉积物未受扰动的柱状样品,通过分析不同形态沉积磷在沉积剖面上的分布特征,并结合沉积物样品柱的²¹⁰Pb、¹³⁷Cs年代学研究结果,揭示了红枫湖现代沉积过程中不同形态沉积磷的早期成岩改造的时间变化序列,以及沉积磷外源输入负荷的历史变化.采用Ruttenberg法分析沉积磷的地球化学赋存形态,研究表明,红枫湖沉积物中有机磷和铁结合态磷是沉积磷的主要赋存形态,分别占沉积全磷的60%和28%.沉积磷在垂直剖面上的分布特征显示,红枫湖现代沉积过程中,沉积磷在最终埋藏前可能发生非常剧烈的形态转化和再迁移,尤其是有机磷和铁结合态磷的成岩改造可能是湖泊系统磷循环质量平衡的重要方面.年代学数据同时表明,近年的人为活动导致湖泊系统(包括沉积物)磷负荷的显著增加.;Phosphorus is one of the important limited elements to lake eutrophication.The regeneration of phosphorus from sediment may be an important phosphorus resource for lakes.Several undisturbed sediment cores have been sampled at the deepest area of a canyon-reservoir, Lake Hongfeng, on Guizhou Plateau, southwestern China.The concentration and distributions of various phosphorus forms in sediment cores have been studied.The chronology data have been obtained by means of ²¹⁰Pb, 13_Cs for the same sediment cores.The geochemical processes of various forms of sedimental phosphorus were mainly controlled by early diagenesis and anthrogenic disturbances on the phosphorus burial in sediment.In our study, the SEDEX method from Ruttenberg has been used to identify the various forms of phosphorus in sediment samples.The species of phosphorus include: loosely sorbed P, Fe-bound P, Ca-bound P, detrial-P and Organic-P.The results showed that the organic-P and Fe-bound P could been seen as two main sorts phosphorus in sediment of Lake Hongfeng, about 60% and 28% in total sediment phosphorus respectively.The forms and vertical distrubition profiles of sediment phosphorus implied that the sediment phosphorus could have strong ability of regeneration during the terminal burial in the bottom of Lake Hongfeng.Under certain conditions, the sediment of Lake Hongfeng could be regarded as the important resource of phosphorus for lake system rather than a sink.