不同风浪条件下太湖梅梁湾光合有效辐射的衰减

基于2003年7月12～17日在太湖梅梁湾进行的连续6d原位水下光场观测资料,分析了不同风浪条件下光合有效辐射(PAR)的衰减和真光层深度,探讨了影响水下光合有效辐射的主导因子.结果表明,整个观测期间向下PAR衰减系数为2.63～4.71·m^-1(均值为3.63±0.47·m^-1),对应的真光层深度为0.98～1.75m(均值为1.29±0.18m),显示1.5m以下深度浮游植物、沉水植物基本上无法获取足够的太阳光能进行光合作用.从小风浪到中风浪、大风浪向下PAR衰减系数分别是2.63、3.72和4.37·m^-1,衰减系数分别增加了41%、66%.透明度、PAR衰减系数、真光层深度与悬浮物浓度存在显著性线性相关,并且与悬浮物中无机颗粒物相关性最好,而与叶绿素a、脱镁叶绿素及溶解性有机碳相关性很低.多元逐步线性回归表明,叶绿素a和溶解性有机碳最先被剔除方程,说明在梅梁湾由于风浪扰动引起悬浮物浓度的改变是影响水下光场的主导因素.     

基于稳定碳同位素分析宁夏典型林分土壤有机碳分布格局及影响因素

选择宁夏自北向南方向的贺兰山、罗山和六盘山(3座山的降水量呈现逐渐增加的趋势)共有的青海云杉林和油松林土壤作为研究对象,分析两种针叶林土壤有机碳特征[土壤有机碳(SOC)含量、稳定碳同位素组成(δ13C)和有机碳分解速率(β值)]的变化情况,并采用冗余分析法分析土壤化学指标对土壤有机碳特征的影响作用,探究干旱半干旱区土...     

紫外辐射对两种海洋微藻生长及培养体系碳流的影响

以硅藻威氏海链藻(Thalassiosira weissflogii)和甲藻锥状斯氏藻(Scrippsiella trochoidea)为实验材料, 通过室内模拟华南地区秋季晴天紫外辐照强度, 研究两种不同波段的紫外辐射(Ultraviolet radiation, UVR)对两种微藻生长以及培养体系碳流的影响。结果表明: UV-A 对两种微藻的生长有显著的促进作用, 而UV-B 则表现为抑制作用。锥状斯氏藻对UV-B 的耐受性更强。在UV-A 的作用下, 培养体系中溶解无机碳(Dissolved inorganic carbon, DIC)的净消耗量低于对照组, 但释放出更多的溶解有机碳(Dissolved organic carbon, DOC)。对照组的有色溶解有机物(Chromophoric dissolved organic matter, CDOM)含量显著升高, 表明浮游植物生长过程是CDOM的来源之一。然而, 在UV-A的作用下, 两种微藻培养体系的CDOM浓度变化呈现相反趋势, 说明不同藻种的CDOM 产物受光漂白和光腐殖化的影响不同。在UV-B 的作用下, 微藻碎屑的分解使水体DIC 和DOC 浓度轻微升高。总体上, 锥状斯氏藻比威氏海链藻净释放出更多的DOC 和CDOM。     

Chromophoric dissolved organic matter (CDOM) absorption characteristics in relation to fluorescence in Lake Taihu,China, a large shallow subtropical lake

Absorption measurements from chromophoric dissolved organic matter (CDOM) and their relationships with dissolved organic carbon (DOC) and fluorescence were studied in Lake Taihu, a large, shallow, subtropical lake in China. Absorption spectra of lake water samples were measured from 240 nm to 800 nm. Highest values of a(λ), DOC and F _n (355) occurred near the river inflow to Meiliang Bay and decreased towards the central lake basin. A significant spatial difference was found between Meiliang Bay and the central lake basin in absorption coefficient, DOC-specific absorption coefficient, exponential slope coefficient, DOC concentration and fluorescence value. The spatial distribution of CDOM suggested that a major part of CDOM in the lake was from river input. CDOM absorption coefficients were correlated with DOC over the wavelength range 280–500 nm, and a(355) was also correlated with F _n (355), which showed that CDOM absorption could be inferred from DOC and fluorescence measurement. The coefficient of variation between a(λ) and DOC concentration decreased with increase in wavelength from 240 nm to 800 nm. Furthermore, a significant negative linear relationship was recorded between S value and CDOM absorption coefficient, as well as DOC-specific absorption coefficient. S value and DOC-specific absorption coefficient were used as a proxy for CDOM composition and source. Accurate CDOM absorption measurements are very useful in explaining UV attenuation and in developing, validating remote sensing model of water quality in Lake Taihu.     

Spatial, geomorphological, and seasonal variability of CDOM in estuaries of the Florida Coastal Everglades

This paper demonstrates the usefulness of fluorescence techniques for long-term monitoring and assessment of the dynamics (sources, transport and fate) of chromophoric dissolved organic matter (CDOM) in highly compartmentalized estuarine regions with non-point water sources. Water samples were collected monthly from a total of 73 sampling stations in the Florida Coastal Everglades (FCE) estuaries during 2001 and 2002. Spatial and seasonal variability of CDOM characteristics were investigated for geomorphologically distinct sub-regions within Florida Bay (FB), the Ten Thousand Islands (TTI), and Whitewater Bay (WWB). These variations were observed in both quantity and quality of CDOM. TOC concentrations in the FCE estuaries were generally higher during the wet season (June–October), reflecting high freshwater loadings from the Everglades in TTI, and a high primary productivity of marine biomass in FB. Fluorescence parameters suggested that the CDOM in FB is mainly of marine/microbial origin, while for TTI and WWB a terrestrial origin from Everglades marsh plants and mangroves was evident. Variations in CDOM quality seemed mainly controlled by tidal exchange/mixing of Everglades freshwater with Florida Shelf waters, tidally controlled releases of CDOM from fringe mangroves, primary productivity of marine vegetation in FB and diagenetic processes such as photodegradation (particularly for WWB). The source and dynamics of CDOM in these subtropical estuaries is complex and found to be influenced by many factors including hydrology, geomorphology, vegetation cover, landuse and biogeochemical processes. Simple, easy to measure, high sample throughput fluorescence parameters for surface waters can add valuable information on CDOM dynamics to long-term water quality studies which can not be obtained from quantitative determinations alone.     

太湖水色因子空间分布特征及其对水生植物光合作用的影响

利用太湖全湖64个采样点的数据,分析了各水色因子及真光层深度的空间分布和变化特征,并探讨了其对水生植物光合作用的影响.结果表明:叶绿素a浓度在全湖间的差异最大,其变化范围为1.67～159.94μg.L-1,均方差为41.03μg.L-1,在梅梁湾、竺山湖、夹浦港和小梅口附近湖区,叶绿素a浓度较高且空间变化明显,等值线在这些湖区密集分布;悬浮物浓度变化次之,其含量在6.47～143.47mg.L-1之间变化,均方差为31.63mg.L-1,其在大浦港和小梅口入湖口附近湖区的空间变化明显,等值线分布密集;有色可溶性有机物(CDOM)吸收系数在全湖变化较小,没有明显的空间变化特征;真光层深度受悬浮物和叶绿素的共同影响,其空间分布特征与悬浮物相反.     

Variation of chromophoric dissolved organic matter and possible attenuation depth of ultraviolet radiation in Yunnan Plateau lakes

The increase of ultraviolet radiation (UVR, 280–400 nm) caused by stratospheric ozone depletion has profound effects on aquatic ecosystems. High-altitude lakes in the Yunnan Plateau are exposed to high intensities of UVR and contain low concentrations of chromophoric dissolved organic matter (CDOM). Thirty-eight lakes in the Yunnan Plateau with elevations from 1291 to 3809 m above sea level were investigated to study CDOM concentrations and possible effects of UVR on the lake ecosystem. The attenuation of UVR in the Yunnan Plateau lakes was calculated from the absorption coefficient of CDOM based on an empirical relationship from lakes in the Alps and Pyrenees mountains. Absorption coefficients [α(λ)] at 320 nm [α(320)] ranged from 0.52 to 14.05 m⁻¹ (mean ± standard deviation, 4.40 ± 3.85 m⁻¹) and at 380 nm [α(380)] from 0.05 to 4.51 m⁻¹ (1.40 ± 1.30 m⁻¹). The exponential slope coefficient for the relationship of wavelength to α(λ) ranged from 16.2 to 41.4 μm⁻¹ (21.74 ± 4.93 μm⁻¹) over the 280–400 nm interval. Normalized fluorescence emission (NFLU) at 450 nm from an excitation wavelength of 355 nm, F _n(355), averaged 7.93 ± 3.22 NFLU. A significant positive relationship was found between α(355) and F _n(355). The estimated diffuse attenuation coefficients of UV-B (320 nm) and UV-A (380 nm) ranged from 0.55 to 15.77 m⁻¹ and from 0.24 to 6.73 m⁻¹; the corresponding 1% attenuation depths ranged from 0.29 to 8.44 m and from 0.68 to 19.12 m. Twenty-five of 38 lakes had 1% UV-B attenuation depths of 1.5 m or more. The median 1% attenuation depth was 28.8% of the sampling depth for UV-B radiation and 60% for UV-A. In addition to CDOM, chlorophyll α (Chla) and total suspended matter (TSM) also may contribute to attenuation of UVR.     

A study of absorption characteristics of chromophoric dissolved organic matter and particles in Lake Taihu,China

Absorptions by non-phytoplankton particles and phytoplankton, and chromophoric dissolved organic matter (CDOM) were measured at 50 sites in large, shallow, Lake Taihu in winter and summer 2006 to study their seasonal and spatial variations, and their relative contributions to total absorption. The CDOM absorption was significantly higher in winter than in summer, due to degradation and release of fixed carbon in phytoplankton and submerged aquatic vegetation (SAV). The hyperbolic model was used to model the spectral absorption of CDOM, and the mean spectral slope of 6.38 nm⁻¹ was obtained. At most sites, the spectral absorption of non-phytoplankton particles was similar to that of the total particles, demonstrating that the absorption of the total particles is dominated by the absorption of non-phytoplankton particles. In summer, phytoplankton absorption increased markedly, due to frequent algal blooms especially in Meiliang Bay. In winter, the significant increase in non-phytoplankton particle absorption resulted from the increase of inorganic particulate matter caused by sediment resuspension. Strong linear relationships were found between a _d(440) and total suspended matter (TSM), organic suspended matter (OSM), and inorganic suspended matter (ISM). Strong linear relationships were also found between a _ph(440), a _ph(675) and chlorophyll a (Chl-a) concentration. The total relative contributions of non-phytoplankton particles over the range of photosynthetically active radiation (PAR) (400–700 nm) were 48.4 and 79.9% in summer and winter respectively. Non-phytoplankton particle absorption dominated the total absorption, especially in winter, in Lake Taihu, due to frequent sediment resuspension in the large shallow lake as a result of strong windy conditions. The results indicate that strong absorption by CDOM and non-phytoplankton particles at the blue wavelength has an impact on the spectral availability, and acts as a selection factor for the composition of the phytoplankton community, with cyanobacteria being the dominate species in Lake Taihu. Handling editor: L. Naselli-Flores     

吉安地区典型景观湖泊浮游植物群落特征及其与水环境因子的关系

2012年8月至2013年7月,对吉安地区将军湖、龙湖、庐陵湖和挹翠湖4个景观湖泊水体浮游植物群落及其主要水环境因子进行了调查,并利用生物多样性指数法(Shannon指数H、Margalef指数D和Pielou指数J)和主成分分析(PCA)法分别对湖泊水质和水环境因子进行了评价。结果表明:4个湖泊共鉴定浮游植物7门82属163种,主要优势种为硅藻或绿藻;浮游植物细胞丰度呈季节性变化,秋夏居高,冬春季偏低,平均丰度变化范围为25.45×10~6~54.04×10~6cells·L~(-1);将军湖、龙湖、庐陵湖和挹翠湖的H值分别为1.26~2.08、1.82~2.61、2.27~2.62和1.10~2.32;D值分别为2.03~3.51、2.36~3.71、2.48~3.93和3.12~3.96;J值分别为0.45~0.69、0.59~0.80、0.67~0.77和0.50~0.84。综合评价结果显示,4个湖泊处于富营养化状态、中等污染水平。而对污染较重的庐陵湖水环境因子PCA分析结果表明,水温(WT)、溶解氧(DO)和总氮(TN)是影响小型封闭景观水体浮游植物群落变化的主要因素。建议对小型封闭景观水体进行必要的治理和生态修复。     

华南典型树种凋落叶的野外分解和溶解性有机质溶出动态

选用华南亚热带地区常见阔叶树种木荷和针叶树种湿地松的新近凋落叶,在野外分解0、30、60、90、150、210、240、365 d,分析溶出的溶解性有机质(DOM)浓度、组成和性质的变化,以及对土壤可溶性有机碳(DOC)的影响.结果表明: 随着分解的进行,尽管木荷叶片的DOM浓度高于松针,但是2种凋落叶DOM浓度、性质和物质组成变化规律一致;2种凋落叶的DOM浓度均呈下降趋势,芳香化程度和分子量增大,富里酸、腐殖酸类物质逐渐增多,可降解的简单芳烃蛋白(如酪氨酸)逐渐减少.在分解初期,DOM主要由亲水中性和酸性部分组成,易分解、易迁移,对表层土壤DOC影响不显著;在分解后期,DOM主要为腐殖酸和富里酸类物质,吸附性强,表层土壤DOC浓度显著下降.     

Modeled Effects of Dissolved Organic Carbon and Solar Spectra on Photobleaching in Lake Ecosystems

Dissolved organic matter (DOM) contains molecules that absorb light at various wavelengths. This chromophoric DOM (CDOM) influences the transmission of both visible and ultraviolet energy through water. The absorption of light by CDOM often causes structural changes that reduce its capacity to further absorb light, a process termed ‘photobleaching‘. A model was designed to assess photobleaching through the entire water column of lake ecosystems. The model uses lake morphometry and dissolved organic carbon (DOC) concentration in conjunction with a defined solar spectrum and experimentally measured photobleaching rates to compute the total water columm photobleaching. The model was initially applied to a theoretical ‘average‘ lake using solar spectra for both the north (N) and south (S) temperate western hemispheres and variable DOC from 0.3 to 30 mg L⁻¹. The consequences of varying waveband-specific photobleaching coefficients and lake morphometry were explored in a second set of simulations. Finally, the model was also applied to four temperate northern lakes for which we had prior measurements of CDOM photobleaching rates. The model demonstrates that all three wavebands of solar radiation (UVB, UVA, and PAR) contribute significantly to total water column photobleaching, with UVA being most important. The relative contributions of the three wavebands were invariant for DOC more than 3 mg L⁻¹. Total water column photobleaching at 440 nm was three to five times faster under the UV-enriched solar spectrum of the southern hemisphere. Increasing the lake’s mean depth (from 0.37 to 9.39 m) resulted in five- or 15-fold slower rates of total water column photobleaching for DOC concentrations of 1 or 10 mg L⁻¹, respectively. Varying the waveband-specific photobleaching coefficients by 10-fold resulted in a similar change in total water column photobleaching rates. Applying the model to four specific lakes revealed that photobleaching for the entire water column would reduce CDOM light absorption by 50% in 18–44 days under summer conditions. Received 17 November 1998; accepted 27 June 2000.     

The attenuation of ultraviolet and visible radiation in Dutch inland waters

The vertical attenuation coefficients (K _d) of downward ultraviolet (UV) and visible irradiance (PAR) were measured in 19 different inland waters in the Netherlands using a scanning spectroradiometer. Water chemistry variables such as dissolved organic carbon (DOC), absorbance of dissolved matter (a _d), chlorophyll-a, and particulate matter were measured to determine the relative contribution of dissolved and particulate components in explaining the variation in K _d. In addition to the field measurements, laboratory measurements were performed to test the relationships between water properties and light attenuation. The attenuation properties of Dutch inland waters vary. In most systems the penetration of UV-B radiation (280–320 nm) is limited to the upper decimetres. Lake Maarsseveen was the clearest waterbody in this study, with K _dUVB of 9.1 (m^–1). The DOC concentration had limited power in predicting UV attenuation in this study (r ²=0.33), because of the large differences in carbon-specific absorption. A _d300 was a much better predictor of UV attenuation (r ²=0.75). The relationships obtained in the laboratory experiments can be used to give a good prediction of in situ K _d values, based on 3 variables (chlorophyll-a, ash weight, and absorption of dissolved matter).     

Role of dissolved organic carbon in the attenuation of photosynthetically active and ultraviolet radiation in Adirondack lakes

1. We surveyed eighty-five lakes located in the Adirondack Mountain Region of New York State, U.S.A., to characterize the attenuation of photosynthetically active (PAR) and ultraviolet radiation (UVR) in relation to dissolved organic carbon (DOC) concentrations and pH. Attenuation of PAR was quantified in situ . Attenuation was also inferred by measuring the light absorption of filtered lake water samples at wavelengths (300, 340 and 440 nm) representing UV-B, UV-A and PAR.
2. Substantial variation in transparency was observed among lakes in this region. Attenuation depths ( z _1%) for PAR ranged from 0.5 to greater than 20 m, while inferred values for UV-B and UV-A ranged from a few centimetres to > 5 m. Median values of UV-A penetration (0.75 m) and UV-B penetration (0.45 m) corresponded to 11% (UV-A) and 6% (UV-B) of lake maximum depth.
3. Much of the variation in PAR and UVR attenuation was explained by differences in lake DOC. Univariate power models based solely on DOC accounted for 85% (PAR), 90% (UV-A) and 91% (UV-B) of the variation in absorption.
4. Attenuation and absorption coefficients were generally lower for recently acidified lakes compared to acidic and circumneutral lakes which have not undergone recent acidification. However, differences among these three groups of lakes were not statistically significant. Our results suggest that the effects of acidification on the optical properties of a regional population of lakes, even in an area experiencing widespread acidification, are relatively subtle in comparison with other factors contributing to inter-lake variability.
5. The presence of near-shore wetlands is probably a key factor influencing regional variability in DOC and light climate among Adirondack lakes. Temporal variability in climatic factors influencing wetland DOC production and export may mask more subtle influences on lake DOC associated with anthropogenic acidification.