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1.
The effects of exposure to UV-B radiation,280-315 nm,and dark or dark repair conditions on the early development of Chondrus ocellatus Holm collected from Qingdao coast were studied under the laboratory condition.After being exposed to different doses [0,36,72,108,144 and 180 J/(m 2 · d)] of UV-B radiation,one treatment of tetraspores were put back to normal culture condition (PAR),the other treatment were put into dark condition to repair for 2 h.During the cultivation,the diameter of the tetraspores were recorded every 4 d till the 50th day when vertical branches formed in all treatments.Then at the 50th day,CPDs,phycoerythrin,chlorophyll a and MAAs (Palythine and asterina-330) were measured.The results showed that low doses UV-B radiation could significantly accelerate the growth rate of the tetraspores of C.ocellatus and the growth rate reduced gradually with UV-B radiation keep on increasing.The variation trend of both the phycoerythrin and chlorophyll a concentration reduced significantly ( P < 0.05) once given the UV-B radiation. Under UV-B stress,the CPDs were induced,and the concentrations of CPDs were significant low in dark repair groups.The data of MAAs analyzed by LC/MS in the tetraspores of C. ocellatus suggested that there were two MAAs formed (palythine and asterina-330) after UV-B radiation induced, and low dose of UV-B irradiation could significantly induced the concentration of MAAs.From the growth and development state of the tetraspores,negative effects of UV-B radiation on the dark repair groups were more serious than PAR.  相似文献   

2.
The effect of UV-B radiation enhancement at experimental doses of 0.00,0.24,0.48,0.72,0.96,and 1.20 kJ/m 2 on the population dynamics of the rotifer Brachionus urceus feeding on the alga Chlorella sp.was studied under controlled laboratory conditions using clonal culture and life-table techniques.The results show that UV-B radiation treatment significantly shortened the survival time of the rotifer (P <0.05): The longest survival time (336 h) occurred in the control (0.00 kJ/m 2 ) while the shortest (222 h) occurred when exposed to the highest UV-B radiation treatment (1.20 kJ/m 2 ).The fecundity of the rotifer B.urceus was enhanced by the lower UV-B radiation treatment (0.24 and 0.48 kJ/m 2 ) but inhibited by the higher treatments (0.96 and 1.20 kJ/m 2 ).Life expectancy also was obviously affected by UV-B radiation (P <0.05).The highest life expectancy occurred in the control (0.00 kJ/m 2 ),and it became shorter with increasing doses of UV-B radiation.The resutls in the present study indicate that the life expectancy of the rotifer B.urceus can be used as an indicator for UV-B radiation enhancement.  相似文献   

3.
南极上空臭氧层的破坏导致了紫外辐射日益增强,高强度的UV-B辐射会造成细胞中DNA的损伤,影响蛋白质、脂类和色素的代谢过程。生长在南极的绿藻具有一系列防御机制以应对增强的UV-B辐射,其中类菌胞素氨基酸(Mycosporine-like amino acids, MAAs)是一类重要的紫外防御物质。为探究类菌胞素氨基酸对UV-B辐射的响应,本文以南极冰藻(Chlamydomonassp.ICE-L)、针丝藻(Raphidonema nivale Lagerheim, NIES-2290)和胶球藻(Coccomyxa subellipsoidea E.Acton, NIES-2166)三种生活在南极的绿藻为材料,采用UV-B辐射胁迫(强度0.35 W/m~2,短时处理3 h),并通过液相色谱-质谱联用法检测类菌胞素氨基酸的种类和含量的变化。Mycosporine-glycine为三种南极绿藻中共有的MAAs,在UV-B辐射胁迫下三种南极绿藻中Mycosporine-glycine含量变化不尽相同,表明不同的南极绿藻中MAAs对UV-B辐射的响应各有其特性。首次在绿藻(南极冰藻和胶球藻)中检测到Gadusol。Gadusol作为MAAs的合成前体,它的合成积累使得生活在海冰环境的南极冰藻和胶球藻具有良好的抗UV-B辐射能力。其中南极冰藻抗紫外能力最强,这可能得益于不同MAAs间的动态转化,含量升高的Palythine及Usujirene/Palythene可能对南极冰藻的紫外屏蔽起着至关重要的作用。  相似文献   

4.
吴亚平  高坤山 《海洋学报》2011,33(5):146-151
阳光紫外(UV)辐射影响浮游植物光合固碳,且不同波长UV辐射的生理效应不一.本文以夏季南海近岸海域浮游植物为研究对象,采用生物加权函数(Biological weighting function,BWF,亦被称为UV辐射作用光谱)的研究方法,探讨了不同波长UV辐射对浮游植物群落光合固碳的作用.结果表明,在只有可见光情况...  相似文献   

5.
We investigated the effects of ultraviolet-B (UV-B) radiation on the natural phytoplankton assemblage in Marine Cove on King George Island, Antarctica, in December 2005. The amount of newly synthesized phytoplankton polyunsaturated fatty acids (PUFAs) was lower with exposure to full irradiation (PAR+UV-A+UV-B) than without such exposure (exposed instead to PAR+UV-A radiation) in an in situ incubation under the light conditions in two different types of incubation bottles: quartz bottles transmitting all light wavelengths including UV-B and polycarbonate bottles with no UV-B transmission and 20 % reduced PAR compared to the quartz bottle. However, the amount of newly synthesized saturated fatty acids was greater with than without UV-B radiation. Thus, UV-B radiation may have a significant influence on fatty acid synthesis in phytoplankton. In particular, the production of eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic acid [22:6(n-3)] was reduced during incubation under the natural solar radiation including UV-B. To understand the indirect influence of UV-B on herbivores (the secondary producer), we conducted feeding experiments with amphipods fed in situ on the natural phytoplankton assemblage. The amphipods fed on the phytoplankton with the low PUFA values also exhibited a low PUFA accumulation rate, which could negatively affect their growth, development, and reproduction. Consequently, the diminished rate of essential fatty acid synthesis [especially 20:5(n-3) and 22:6(n-3)] in primary producers caused by UV-B exposure could affect the structure and function of the Antarctic marine ecosystem.  相似文献   

6.
本研究以海洋微藻——赤潮藻海洋卡盾藻(Chattonella marina)与饵料藻青岛大扁藻(Platymonas helgolandica var.tsingtaoensis)为研究对象,采用单培养和共培养的方法,研究二者间的竞争关系,并在此基础上研究海洋卡盾藻去藻过滤液和藻细胞裂解液对青岛大扁藻的化感作用,同时进一步探讨两种海洋微藻间的化感作用对UV-B辐射增强的响应。结果显示:共培养条件下,海洋卡盾藻在2个高浓度下对青岛大扁藻的生长产生显著抑制(P0.05);海洋卡盾藻去藻过滤液和藻细胞裂解液对青岛大扁藻的生长也具有显著抑制作用(P0.05),且藻细胞裂解液的抑制作用更强,说明海洋卡盾藻对青岛大扁藻产生化感作用,且通过细胞间直接接触传递的化感物质多于通过介质传递的。不同密度比例的2种藻共培养组用UV-B辐射(2.16J/m2)处理后,海洋卡盾藻对青岛大扁藻生长的化感作用有所减弱。  相似文献   

7.
A simple, yet efficient and fairly accurate algorithm is presented to estimate photosynthetically available radiation (PAR) at the ocean surface from Global Imager (GLI) data. The algorithm utilizes plane-parallel radiation-transfer theory and separates the effects of the clear atmosphere and clouds, i.e., the planetary atmosphere is modeled as a clear atmosphere positioned above a cloud layer. PAR is computed as the difference between the incident 400–700 nm solar flux at the top of the atmosphere (known) and the solar flux reflected back to space by the atmosphere and surface (derived from GLI radiance), taking atmospheric absorption into account. Knowledge of pixel composition is not required, eliminating the need for cloud screening and arbitrary assumptions about sub-pixel cloudiness. For each GLI pixel, clear or cloudy, a daily PAR estimate is obtained. Diurnal changes in cloudiness are taken into account statistically, using a regional diurnal albedo climatology based on 5 years of Earth Radiation Budget Satellite (ERBS) data. The algorithm results are verified against other satellite estimates of PAR, the National Centers for Environmental Prediction (NCEP) reanalysis product, and in-situ measurements from fixed buoys. Agreement is generally good between GLI and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) estimates, with root-mean-squared (rms) differences of 7.9 (22%), 4.6 (13%), and 2.7 (8%) Einstein/m2/day on daily, weekly, and monthly time scales, and a bias of only 0.8–0.9 (about 2%) Einstein/m2/day. The rms differences between GLI and Visible and Infrared Spin Scan Radiometer (VISSR) estimates and between GLI and NCEP estimates are smaller and larger, respectively, on monthly time scales, i.e., 3.0 (7%) and 5.0 (14%) Einstein/m2/day, and biases are 1.1 (2%) and −0.2 (−1%) Einstein/m2/day. The comparison with buoy data also shows good agreement, with rms inaccuracies of 10.2 (23%), 6.3 (14%), and 4.5 (10%) Einstein/m2/day on daily, weekly, and monthly time scales, and slightly higher GLI values by about 1.0 (2%) Einstein/m2/day. The good statistical performance makes the algorithm suitable for large-scale studies of aquatic photosynthesis.  相似文献   

8.
紫外光对有毒甲藻塔玛亚历山大藻的生态学效应   总被引：21，自引：1，他引：21  
对1991年分离自南海大鹏湾海域的塔玛亚历山大藻单克隆培养林在不同光照条件、辐射强度（9.5，5．9W／m2）（辐射剂量为：95，190，380,760,1520J/m2）和营养盐（N，P）浓度下，进行紫外辐射敏感性的研究。结果表明，紫外辐射可以导致细胞变形、增大和死亡。不论在什么条件下，低剂量的紫外辐射（95J／m2）就能使该藻的存活率和生长率大幅下降。此后，随着辐射剂量的增加，虽然存活率和生长率继续下降，但下降幅度渐缓。充足的营养盐和辐射处理后的连续光照对藻群的恢复有益，但在缺氮和缺磷条件下培养的藻群，可能由于生理活性减弱而导致对紫外辐射敏感性的迟钝。辐射强度对该藻的紫外辐射敏感性的影响十分显著，而且与辐射剂量具有明显的双重效应。  相似文献   

9.
The effects of wavelength-specific visible light, white light, and ultraviolet-B (UV-B, 280- 315 nm) on selected behaviors, grazing rate, spawning rate, and hatching rate of the marine copepod Calanus sinicus collected from the Yellow Sea were studied. Calanus sinicus placed in a partitioned experimental system responded positively phototaxis to blue-cyan and yellow light but negatively to orange light and UVB. No obvious dodge activity was found among C. sinicus irradiated with <0.005 mW/cm^2 UV-B. Under 0.20, 0.30 and 0.50 mW/cm^2 UV-B radiation, the lethal half times of individuals were 30.47, 2.86, and 1.96 h, respectively. Grazing of C. sinicus was restrained at >0.10 mW/cm^2 UV-B, whereas yellow-red light stimulated grazing. Egg production rate was highest at a white-light intensity of 1.58 mW/cm^2, with an average rate of 10.04 eggs/(female·d). These results are consistent with the observed phenomenon that C. sinicus in the Yellow Sea mostly spawn near dawn. Our results indicate that light intensity and spectrum are important factors affecting the diel vertical migration of C. sinicus under natural conditions in the Yellow Sea.  相似文献   

10.
The role of copepod grazing on the ecosystem dynamics in the Oyashio region, western subarctic Pacific was investigated during six cruises from June 2001 to June 2002. In situ grazing rates of the copepod community (CGR) were measured by the gut fluorescence method in respect to developmental stages of dominant species. In terms of biomass, more than 80% of the copepod community was dominated by six large calanoid species (Neocalanus cristatus, Neocalanus flemingeri, Neocalanus plumchrus, Eucalanus bungii, Metridia pacifica and Metridia okhotensis) throughout the year. Resulting from the observed pattern of the interzonal migrating copepods, the CGR in the Oyashio region was divided into three phases, i.e. spring (bloom), summer (post-bloom) and autumn-winter phase. During the spring bloom, late copepodites of the interzonal migrating species, N. cristatus, N. flemingeri and E. bungii appeared in the surface layer (0-50 m) to consume the production of the bloom, resulting in a high grazing rate of the copepod community (7.9 mg Chl m−2 d−1), though its impact on phytoplankton community was low due to the high primary productivity. During the post-bloom period, although the copepod community which was dominated by N. cristatus, N. plumchrus, M. pacifica and newly recruited E. bungii still maintained a high biomass, the CGR was generally lower (1.8-2.6 mg Chl m−2 d−1 for June and August 2001), probably due to the lower availability of phytoplankton. Nevertheless, the highest CGR was also observed during this period (10.5 mg Chl m−2 d−1 in June 2002). The high CGR on autotrophic carbon accounted for 69% of the primary production, suggesting that the copepod community in the Oyashio region potentially terminates the phytoplankton bloom. Abundant occurrence of young E. bungii, which is a characteristic phenomenon in the Oyashio region, was largely responsible for the high grazing pressure in June 2002 suggesting that success of reproduction, growth, and survival in E. bungii during the spring bloom is an important factor in controlling phytoplankton abundance during the post-bloom season. During autumn and winter, CGR was the lowest in the year (0.29-0.38 mg Chl. m−2 d−1) due to the disappearance of the interzonal migrating copepods from the surface layer. Diel migrant M. pacifica was the most important grazer during this period. The annual ingestion of the copepod community is estimated as 37.7 gC m−2 on autotrophic carbon (converted using C:Chl ratio of 30) or 137.9 gC m−2 on suspended particles (using C:Chl ratio of in situ value, 58-191), accounting for 13% and 46% of annual primary production, respectively. This study confirms that copepod grazing is an important pathway in carbon flow in the Oyashio region and in particular their role in the phytoplankton dynamics is significant for the termination of the spring bloom.  相似文献   

11.
为探讨经济褐藻羊栖菜人工幼苗对阳光紫外辐射变化的响应,在全波段阳光辐射省(PAB,280～700nm)、去除UV-B辐射(PA,320～700nm)和光合有效辐射PAR(P,400～700nm)三种辐射处理及不同辐射水平下培养羊栖菜幼苗,并测定了其生长与光合作用的变化。结果表明,无论在紫外辐射(UVR)存在情况下(PA,PAB)还是滤除UVR(PAR)时,高辐射水平条件下(55%),羊栖菜幼苗都具有较高的生长速率,而低辐射水平下羊栖菜的生长速率较低。在不同辐射处理之间,随着辐射水平的增高,UVR的抑制效应逐渐突显。UVR降低羊栖菜幼苗的光合电子传递速率。  相似文献   

12.
粉叶马尾藻(Sargassum glaucescens)是台湾地区潮间带的重要大型藻类,其对紫外线增强的生理响应特征尚不清楚。本研究关注粉叶马尾藻在急性紫外线辐射(Ultraviolet radiation B,UVB)下的生理指标变化,探索了粉叶马尾藻在急性UVB辐照下抗氧化系统的瞬时反应过程。结果表明:低强度组[0.5W/(m2·s)]藻体在24h内未出现显著氧化损伤和蛋白质含量变化,但是细胞活力在辐照12h后显著降低,藻体超氧化物歧化酶(SOD)酶活性随辐照时间延长而降低,过氧化氢酶(CAT)酶活性呈现升高后下降的趋势,抗坏血酸过氧化物酶(APX)酶活性没有出现显著降低;高强度组[2W/(m2·s)]藻体在辐照3h后藻体出现明显氧化损伤,6h后细胞活力和蛋白质含量显著降低,藻体SOD酶活性随辐照时间延长而降低,CAT和APX酶活性呈现升高后降低的趋势,辐射12h后即显著降低。低强度UVB辐射对粉叶马尾藻的影响相对较小,表明粉叶马尾藻对UVB辐射具有一定耐受性;而高强度UVB辐射的影响较为显著,意味着UVB辐射的持续增强将超出粉叶马尾藻的耐受限度,进而造成不利影响。本研究结果初步揭示了粉叶马尾藻对于急性UVB辐射的增强的生理响应特征,为进一步研究UVB辐射增强的生态学效应提供参考依据。  相似文献   

13.
Abstract

The ultraviolet (UV) sensitivity of five species of freshwater zooplankton (three Cladocera, two Copepoda) were investigated. The animals were exposed to varying levels of UV‐radiation in a sunshine‐simulator and the UV doses for 10 and 50% mortality (LD10, LD50) were estimated using a dose‐response model. To place these doses in context they were compared with modelled clear‐sky surface UV irradiances in New Zealand. The cladocerans Daphnia carinata and Ceriodaphnia dubia were sensitive to levels of UVB irradiance of LD10 = 18–25 kJ m?2 and LD50 = 35–37 kJ m?2. These sensitivities are consistent with published values for other cladocera. In contrast a third cladoceran, Bosmina meridionalis, exhibited no higher mortality over the full range of the cumulative UVB‐doses used (3–40 kJ m?2) than controls receiving no UV exposure. The copepod Boeckella delicata showed the highest UV‐sensitivity of all organisms tested (LD10 = 7 kJ m?2, LD50 = 33 kJ m?2) whereas for Boeckella triarticulata, which was more heavily pigmented than B. delicata, no UV‐induced mortality was observed. Under natural conditions UV irradiances of up to 100 kJ m?2 day?1 can fall on the surface of New Zealand lakes. Although this is attenuated in natural waters, these data suggest that UVB irradiance may be a significant ecological variable to some zooplankton species.  相似文献   

14.
《Journal of Oceanography》2007,63(6):983-994
A mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (∼18 mg chl m−3) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m−3, with no prominent diatom bloom. Photosynthetic competence in terms of F v/F m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (<2 μm) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 μM in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.  相似文献   

15.
The quantity of chromophoric or coloured dissolved organic matter (CDOM) released by eleven species of intertidal and sub-tidal macroalgae commonly found on UK shores was investigated. The subsequent breakdown of CDOM was also measured by exposing collected CDOM samples to light and dark conditions for over two weeks. CDOM absorption properties were compared at a fixed wavelength of 440 nm and across two integrated wave - bands; UV-A (400–315 nm) and UV-B (315–280 nm). Absorption spectra of macroalgal CDOM samples were typically characterized by peaks and shoulders in the UV bands, features which were species specific. The spectral slope, derived using the log-linear method, proved to be very specific to the species and to the effect of light. Slope measurements ranged from 0.010 to 0.027 nm−1, in the range of normal seawater values. Significantly more CDOM was produced by algae which were illuminated, providing evidence for a light driven exudation mechanism. Averaged across all species, exudation in the dark accounted for 63.7% of that in the light in the UV-B band. Interspecific differences in exudation rate encompassed an order of magnitude, with the highest absorption measurements attributable to brown algae. However, some brown algae produced considerably less CDOM (e.g. Pelvetia canaliculata), which were more comparable to the green and red species. Over an exposure time of 16 days, significant photochemical degradation of CDOM was observed using a natural summer sunlight regime, showing that natural solar radiation could be an important removal mechanism for newly produced algal CDOM. Though the most obvious effect was a decrease in absorption, photo-bleaching also caused a significant increase in the spectral slope parameter of 0.004 nm−1.  相似文献   

16.
为探讨太阳紫外辐射(UVR,280~400 nm)和CO2浓度变化对大型海藻的复合效应,选择了常见的经济海藻龙须菜(Gracilaria lemaneiformis)为实验材料,研究了UVR(阳光紫外辐射)和CO2对其生长、光合作用、色素以及紫外吸收物质含量变化的复合作用。实验设置两个CO2梯度(380×10-6和800×10-6)和三种太阳辐射处理(PAB处理——全波长辐射处理, PA辐射处理——滤掉紫外线B和P处理——滤掉全部紫外线)。结果表明,CO2加富(800×10-6)显著地促进了龙须菜的生长,而UVR则产生抑制作用,但两者之间复合作用不显著。UVR促进了藻体的紫外吸收物质的合成,而且在高浓度CO2下经PAB辐射处理的含量要显著高于正常CO2浓度水平下的,这表明高浓度CO2促进了紫外吸收物质的合成。在光合作用受限制的低PAR条件下,紫外线A(UV-A)促进其光合作用,但高浓度CO2却抑制了藻体的光合作用速率。在正常浓度CO2水平下生长的藻体,UVR显著降低其光合作用能力,但是在高浓度CO2下生长的藻体,UVR这种负面效应不显著。UVR显著降低藻红蛋白的含量,高浓度CO2 在P和PA辐射处理下也显著降低藻红蛋白的含量,但在PAB辐射处理下却呈现相反的结果。高浓度CO2下生长的藻体通过增加体内紫外吸收物质的含量来维持较高浓度的藻红蛋白含量,增强了其抵御UVR的能力。  相似文献   

17.
Surface solar radiation over the Pacific Ocean off the Sanriku coast has been estimated using Visible and Infrared Spin Scan Radiometer data supplied by the Geostationary Meteorological Satellite 5 for September, 1996 to June, 1997, when the Ocean Color and Temperature Scanner was functioning. The hourly and daily insolation is estimated with a spatial resolution of 0.01-degree grid. Thein situ surface short wave radiation obtained by the research vessel,Kofu-Maru belonging to the Japan Meteorological Agency is used for validation of the estimated insolation. It is shown that the estimated hourly and daily insolation has an rms (root mean square) error of 17.05% and 8.13%, respectively, which are the ratios between the rms error (W/m2) and the mean insolation (W/m2).  相似文献   

18.
Measurement results of downward longwave radiation (DLR) in a wavelength range of 3.5?C50 ??m are considered which have been obtained with the use of a precision IR radiometer (Eppley pyrgeometer) of the PIR model at the Meteorological Observatory of Moscow State University in 2008?C2010. The influence of air temperature and atmospheric moisture content on the DLR values has been analyzed; correlations between DLR and the above parameters have been found. The effect of clouds on DLR has been estimated: DLR increases by about 30% in daytime and by 25% in nighttime under overcast low clouds. The annual average DLR in Moscow is 305 W/m2, with a minimum in December?CMarch and a maximum in July?CAugust. Variations in DLR throughout a year can exceed 250 W/m2. The daily average amplitude is 18?C33 W/m2 in summer and 6?C13 W/m2 in winter. An increase in DLR by about 40 W/m2 is noted under conditions of haze from forest and peat-bog fires and an aerosol optical depth of about 4 at a wavelength of 500 nm.  相似文献   

19.
人类活动导致臭氧层变薄和混合层变浅,迫使混合层的浮游植物暴露在更高的紫外辐射下。实验以中肋骨条藻（Skeletonema costatum）为研究对象,在自然光照条件下,通过在暗盒上方覆盖不同的截止型滤光板,获得不同波段紫外辐射,探讨不同紫外波段对其生理特性的影响。本实验通过在室外培养,模拟赤潮爆发状态,对中肋骨条藻进行7种不同紫外波段的处理（分别使用280、300、320、340、360、380、400 nm截止型滤光板）。实验结果表明：紫外辐射会显著抑制中肋骨条藻的光合固碳速率,随着紫外波段逐步被滤除,光合固碳速率越来越高;>280 nm和>300 nm波段下的比生长率显著低于>400 nm波段处理;280 nm~300 nm波段紫外对叶绿素a有显著的漂白效应,同时也会显著减少类胡萝卜素的含量;这表明紫外辐射对中肋骨条藻的抑制效应主要是紫外辐射B导致的,而紫外辐射A的作用不显著。在估测浮游植物海洋初级生产力的过程中,紫外辐射的作用往往被忽视。  相似文献   

20.
Factors controlling the timing of major (>10 mg chlorophyll a m−3) spring bloom events in the estuarine waters of the Solent, on the south coast of the UK, have been investigated. Winter to summer variations in chlorophyll a concentration together with relevant meteorological and hydrographical data have been analysed for 5 years (1988, 1992, 2001, 2002 and 2003). Mean water column irradiance is demonstrated to be the main factor controlling the timing of the first major spring bloom event, usually dominated by large chain-forming diatoms. When chlorophyll a concentration first exceeds 10 mg m−3 in spring (usually in May) the mean water column photosynthetic active radiation (PAR) averaged for one week prior to the sampling date was always >380 W h m−2 d−1. Prior to the main spring bloom event surface incident radiation and water turbidity combine to limit chlorophyll a concentration to levels <10 mg m−3. Chlorophyll a concentrations >10 mg m−3 do not occur in the Solent until almost the entire 10 m water column is within the euphotic zone (i.e. above 1% light level) and light extinction coefficient (k) is ca. ≤0.5 m−1. Statistically, river flow explains the largest percentage of the variations in k and the delayed bloom in June 2002 is due to increased cloud cover and high levels of rainfall in May, which caused a reduction in surface incident irradiance and increased turbidity. Chlorophyll a peaks during these major bloom events generally occur on spring tides when increased mixing rates favour net growth of diatoms.  相似文献   

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