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1.
We determined the range of the tidal variations in nutrient flux across the sediment–water interface and elucidated mechanisms of the flux variation in two estuarine intertidal flats (one sand, one mud) in northeastern Japan. Nutrient flux was measured using in situ light and dark chambers, which were incubated for 2 h, 2–6 times per day. Results showed that nutrient concentration in overlying water varied by tide and was also affected by sewage-treated water inflow. The nutrient fluxes responded quickly to the tidal variation in overlying water chemistry and the range of the variation in flux was as large as the seasonal-scale variation reported in previous studies. In the sand flat, salinity increase likely enhanced benthos respiration and led to increases in both O2 consumption and PO43− regeneration under low illumination, while benthic microalgae were likely to actively generate O2, uptake PO43− and suppress PO43− release under high illumination (>900 μmol photons m−2 s−1). Also in the mud flat, PO43− flux was related with O2 flux, although the range of temporal variation in PO43− flux was small. In both the flats, NH4+ flux was always governed by NH4+ concentration in the overlying water; either an increase in NH4+ uptake or a decrease in NH4+ release was observed as the NH4+ concentration rose due to inflow of river water or input of sewage-treated water. Although NO3− tended to be released in both tidal flats when low NO3− concentration seawater dominated, their relationship was likely to be weakened under conditions of low oxygen consumption and suppressed denitrification. It is likely that tidal variation in nutrient flux is governed more by the nutrient concentration than other factors, such as benthic biological processes, particularly in the case where nutrient concentration in the overlying water is relatively high and with wide amplitude.  相似文献   

2.
In-situ measurements of benthic fluxes of oxygen and nutrients were made in the subtidal region of the Mandovi estuary during premonsoon and monsoon seasons to understand the role of sediment–water exchange processes in the estuarine ecosystem. The Mandovi estuary is a shallow, highly dynamic, macrotidal estuary which experiences marine condition in the premonsoon season and nearly fresh water condition in the monsoon season. The benthic flux of nutrients exhibited strong seasonality, being higher in the premonsoon compared to the monsoon season which explains the higher ecosystem productivity in the dry season in spite of negligible riverine nutrient input. NH4+ was the major form of released N comprising 70–100% of DIN flux. The benthic respiration rate varied from −98.91 to −35.13 mmol m−2 d−1, NH4+ flux from 5.15 to 0.836 mmol m−2 d−1, NO3− + NO2− from 0.06 to −1.06 mmol m−2 d−1, DIP from 0.12 to 0.23 mmol m−2 d−1 and SiO44− from 5.78 to 0.41 mmol m−2 d−1 between premonsoon to monsoon period. The estuarine sediment acted as a net source of DIN in the premonsoon season, but changed to a net sink in the monsoon season. Variation in salinity seemed to control NH4+ flux considerably. Macrofaunal activities, especially bioturbation, enhanced the fluxes 2–25 times. The estuarine sediment was observed to be a huge reservoir of NH4+, PO43− and SiO44− and acted as a net sink of combined N because of the high rate of benthic denitrification as it could remove 22% of riverine DIN influx thereby protecting the eco system from eutrophication and consequent degradation. The estuarine sediment was responsible for ∼30–50% of the total community respiration in the estuary. The benthic supply of DIN, PO43− and SiO44− can potentially meet 49%, 25% and 55% of algal N, P and Si demand, respectively, in the estuary. Based on these observations we hypothesize that it is mainly benthic NH4+ efflux that sustains high estuarine productivity in the NO3− depleted dry season.  相似文献   

3.
We studied the seasonal change of the spatial distribution of nitrite (NO-2), nitrate (NO-3), reactive phosphate (PO3-4), and silicate (SiO2) in the Colorado River Delta. We also generated 24-h time series at one location to study their short-period variability. The delta is a negative estuary. During summer, salinity may be as high as 40. Amplitude of spring tides is as large as 9 m, and this causes great water turbidity by sediment resuspension. Nutrient concentrations were high throughout the whole year, with lower values towards the oceanic region. Maximum nutrient values in the river delta were 15, 53, 11·5 and 92 μM, for NO-2, NO-3, PO3-4, and SiO2, respectively. Most values were under 2, 40, 5, and 60 μM, for NO-2, NO-3, PO3-4, and SiO2, respectively. Our nutrient data show no clear seasonal pattern. Possibly, high NO-3 values in the delta are due to groundwater input, mostly at the internal extreme, and high NO-2, PO3-4, and SiO2 values are due to resuspension of sediments and mixing of porewaters with the water column, caused mainly during spring tides. In the case of NO-2, oxidation of NH+4 in the water column would be part of the mechanism. This would explain the high negative correlation between NO-3 and sea-level, and the relatively low correlation between the other nutrients and sea-level, for the time series generated at a single location.  相似文献   

4.
长江水体溶解态无机氮和磷现状及长期变化特点   总被引：2，自引：0，他引：2  
于2006年2、5、8和11月对长江从攀枝花至河口和上游的两条支流雅砻江和嘉陵江的溶解态无机氮(NO-3-N、NO-2-N和NH+4-N)和磷酸盐(PO43--P)进行了取样调查,同时结合长江营养盐的历史数据,分析了长江水体中溶解态无机氮、磷的长期变化特点。结果表明,长江NO-3-N、NH+4-N、DIN(包括NO-3-N、NO-2-N和NH+4-N)和PO3-4-P浓度从上游到下游显示出增加趋势,但存在季节差异;NO2-N浓度总体较低,在长江中下游(武汉—南京)浓度较高。长江从上游到下游DIN通量的变化主要受径流量的影响,从上游到下游单位面积年产N量逐渐升高;PO3-4-P输送通量从上游往下游呈增加趋势,也主要受径流量控制,但从季节变化来讲,PO3-4-P的月输送通量受其浓度的控制更加明显。自20世纪60年代来,长江水体中NO3--N、NO2--N、DIN和PO3-4-P的浓度都处于缓慢上升趋势,但到80年代上升速度明显加快;不同阶段DIN和34PO-P的季节变化特点也不尽相同,反映了其来源的差异。目前,长江水体中溶解态无机氮、磷浓度与国内及国际河流相比处于中等水平。  相似文献   

5.
从上行控制角度,通过野外采样和围隔培养实验,研究了水母的代谢及分解过程对水体环境中pH、溶解氧、营养盐组成的影响,以及该过程中浮游植物的变化。实验结果表明,沙海蜇在代谢过程中短时间内会大量消耗水体中的溶解氧（dissolved oxygen,DO）,使水体出现低氧和轻度酸化。代谢过程释放出大量营养盐,使水体中的溶解无机氮（dissolved inorganic nitrogen,DIN）浓度在24h内增加为原来的12倍,溶解无机磷（dissolved inorganic phosphorus,DIP）浓度增加了40多倍,进而引起水体中叶绿素a（chlorophyll a,chl a）浓度的增加。沙海蜇的分解过程使水体表现出明显的低氧（缺氧）和酸化现象。沙海蜇生物量越大,分解时间越长,对水体的改变程度越明显,此外,还释放出大量的营养盐并改变原有的营养盐结构,可以刺激甲藻和绿藻的生长,甚至可能引发藻华。  相似文献   

6.
长江口及邻近海区营养盐结构与限制   总被引：5，自引：0，他引：5  
通过研究长江口及邻近海域溶解无机氮(DIN=NO3-+NO2-+NH4+)、磷酸盐(PO43-)、硅酸盐(SiO32-)所表征的营养盐区域结构特征及影响因素,在分析营养盐绝对限制情况的基础上,划分了潜在相对营养限制区域。结果表明,123°E以西近岸表层区域DIN/P比值全年均高于16,而Si/DIN除秋季外基本小于1,显示出长江冲淡水影响下"过量氮"的特征。春夏季河口锋面区(31°~32.5°N,122.5°~124°E)硅藻的大量生长可使DIN/P异常升高和Si/DIN异常降低。秋季研究区域北部DIN/P西低东高且Si/DIN西高东低是由于在高DIN、低PO43-的长江冲淡水影响下,近岸受相对低DIN、高SiO32-的苏北沿岸流南下入侵影响而被分割而成。冬季长江口门东北部存在的高DIN/P和低Si/DIN区则主要由于寡营养盐的黑潮水深入陆架,向东北输送的部分长江冲淡水和增强的苏北沿岸流共同作用造成DIN升高所致。利用Redfield比值进行了不同站位表层潜在相对营养限制情况的区分。近岸123°E以西受高DIN、SiO32-长江冲淡水影响,四季多呈现PO43-潜在相对限制,而在春夏季由于浮游植物的大量吸收PO43-,造成局部PO43-绝对限制及潜在相对限制。春夏季氮限(DIN潜在相对限制)一般发生在外海部分站位,但较为零散。秋季除了东南外海大部分站位外,受苏北沿岸流影响在长江口北部近岸也存在氮限。随着低DIN/P的黑潮表层水(KSW)的入侵加强,冬季外海氮限站位增多。硅限(SiO32-潜在相对限制)在夏季发生在赤潮高发区,而冬季南部存在较多硅限站位表明KSW中SiO32-相对较为缺乏。  相似文献   

7.
桑沟湾养殖海域营养盐和沉积物-水界面扩散通量研究   总被引：7，自引：0，他引：7  
利用2006年4,7,11月和2007年1月4个航次对桑沟湾养殖海域的观测资料,分析了该海域营养盐分布、结构特征、主要控制过程以及沉积物-水界面扩散通量,结果表明,该海域的营养盐分布具有明显的季节变化,海水中NO3-,NO2-,PO43-,DOP,TDP和SiO32-浓度皆是秋季最高,而NH4+,DON,TDN浓度则为夏季最高;各种营养盐的最低值除DON外都出现在春季。春季湾内外海水交换不畅,再加上大型藻类海带等生长旺盛期的消耗,使营养盐浓度处于较低水平,在夏秋两季丰水期沿岸河流注入对该海域营养盐的影响较大,冬季无机营养盐浓度分布主要受沿岸流的影响。磷的结构变化较大,其中DOP百分含量在夏季最高,达到81%。从春季到秋季海水中TDN的结构变化从以DON为主转变成以DIN为主。硅和氮的原子比值全年变化不大,硅和氮和氮和磷原子比值春夏两季的高于秋冬季的。分析营养盐化学计量限制标准和浮游植物生长的最低阈值结果表明,磷是春夏两季桑沟湾浮游植物生长的限制性因素;春季硅浓度低于浮游植物生长的最低阀值,也是一个潜在的限制因素。计算结果显示桑沟湾沉积物释放的NH4+,SiO32-和PO43-对初级生产力的贡献较小,与其他浅海环境相比,桑沟湾沉积物-水界面的营养盐通量处于较低或中等水平。  相似文献   

8.
基于河口潮间带底栖微藻群落水平的环境质量状态评价   总被引：1，自引：1，他引：0  
The feasibility of community-based bioassessment of environmental quality status was studied using microphytobenthos(MPB) in estuarine intertidal ecosystems.The sediment samples of MPB were collected monthly during a 1-year cycle(September 2006–August 2007) at four sampling stations in the Nakdong River Estuary,Korea.Environmental variables,such as salinity,radiation,grain size of sediment,Si(OH)_4(Si),nitrate(NO_3~–),nitrite(NO_2~–),ammonium(NH_4~+) and phosphates(PO_4~(3–)),were measured synchronously for comparison with biotic parameters.The statistical analyses were carried out for assessment the relationship between biotic and environmental parameters.The results showed that:(1) the MPB community structures were significant differences among four sampling stations;(2) spatial variation in the MPB communities were significantly correlated with environmental variables,especially the nutrient NH_4+ in combination with salinity and grain size;(3) three species(Navicula lacustris,Pleurosigma anglulatum and Fragilaria sp.1) were significantly correlated with nutrients and/or Si;and(4) the species richness and diversity were significantly correlated with the grain size.It is suggested that MPB communities may be used as a potentially robust bioindicator for assessing environmental quality status in estuarine intertidal ecosystems.  相似文献   

9.
珠江口磨刀门咸潮及其对环境要素变化的影响   总被引：1，自引：0，他引：1  
于2011年1月25 日-1月26日小潮期间对磨刀门进行26 h定点连续观测,研究了咸潮对环境要素变化的影响.结果表明:调查期间溶解氧没有明显的潮周期变化;NO2-、NH4+浓度随着观测时间的延长不断降低,无明显潮周期变化;底层SiO4-,NO3-浓度具有明显的潮周期变化,且与底层盐度呈显著的正相关关系;溶解无机磷(DIP)、重金属(Zn、Cd)的潮周期变化不明显.当河床剪切力大于0.226N/m2时,发生明显的沉积物再悬浮作用,并对营养盐与重金属的变化产生显著的影响.N,P,si比值分析结果表明,磨刀门水域浮游植物生长受到潜在性的P限制,而咸潮上溯的加强将可能使这种营养盐结构发生变化.磨刀门受N、P的污染仍不容乐观,咸潮不利于污染物质的向海排出,在潮流作用下有发生严重的二次污染的风险.  相似文献   

10.
We examined the impact of a 1:3 year return period flood on benthic and pelagic coupling in the river-dominated sub-tropical Brunswick Estuary. The flood had a significant impact on the study site flushing it with freshwater, reducing the flushing time 0.6 days, increasing nutrient concentrations in the water column and scouring the sediment surface. In the three weeks post-flood the benthic and pelagic systems alternated between being coupled and un-coupled via dissolved, particulate and living material pathways. Immediately post-flood benthic and pelagic coupling via the deposition of phyto-detritus and viable algal cells was reduced due to the scouring of the top sediment layers, and benthic respiration and productivity and NH4+ effluxes all decreased correspondingly. In contrast, benthic and pelagic coupling was enhanced via the uptake and denitrification of NO3− due to elevated NO3− concentrations in the water column. Some of the NO3− consumed by the sediments may have also been converted to DON. Two weeks post-flood benthic and pelagic coupling was significantly enhanced via the deposition of phyto-detritus and viable algal cells associated with a phytoplankton bloom in the water column. This increased supply of phyto-detritus and viable algal cells rapidly increased benthic respiration and productivity and NH4+ efflux. The depletion of water column DIN by the phytoplankton bloom resulted in a de-coupling of the benthic and pelagic systems via the uptake and denitrification of NO3−. However, benthic and pelagic coupling was enhanced via the uptake of NH4+ by benthic microalgae. Three weeks post-flood the phytoplankton bloom had collapsed and the coupling between the benthic and pelagic systems via the deposition of phyto-detritus and living algal cells had diminished. Again benthic and pelagic coupling was enhanced via the uptake and denitrification of NO3− due to elevated NO3− concentrations in the water column associated with the recycling of bloom material. Overall the sediments became less heterotrophic (increasing benthic productivity/respiration ratio) following the flood. Floods can cause rapid and complex changes in the coupling between benthic and pelagic systems in sub-tropical estuaries.  相似文献   

11.
A Geographic Information System (GIS)-aided flow-tracking technique was adopted to investigate nutrient exchange rates between specific benthic communities and overlying seawater in a fringing reef of Ishigaki Island, subtropical Northwestern Pacific. Net exchange rates of NO3 −, NO2 −, NH4 +, PO4 3−, Total-N and Total-P were estimated from concentration changes along the drogue trajectories, each of which was tracked by the Global Positioning System and plotted on a benthic map to determine the types of benthic habitat over which the drogue had passed. The observed nutrient exchange rates were compared between 5 typical benthic zones (branched-coral (B) and Heliopora communities (H), seaweed-reefrock zone (W), bare sand area (S), and seagrass meadow (G)). The dependence of nutrient exchange rates on nutrient concentrations, physical conditions and benthic characteristics was analyzed by multiple regression analysis with the aid of GIS. The spatial correlation between nutrient exchange rates and benthic characteristics was confirmed, especially for NO3 − and PO4 3−, which were usually absorbed in hydrographically upstream zones B and W and regenerated in downstream zones H and G. NO3 − uptake in zones B and W was concentration-dependent, and the uptake rate coefficient was estimated to be 0.58 and 0.67 m h−1, respectively. Both nutrient uptake in zone W and regeneration in zone H were enhanced in summer. The net regeneration ratio of NO3 −/PO4 3− in zone H in summer ranged 5.2 to 34 (mean, 17.4), which was somewhat higher than previously measured NO3 −/PO4 3− for sediment pore waters around this zone (1.1–8.5). Nutrient exchanges in zone S were relatively small, indicating semi-closed nutrient cycling at the sediment-water interface of this zone. NH4 + efflux from sediments was suggested in zone G. The data suggest that the spatial pattern of nutrient dynamics over the reef flat community was constrained by zonation of benthic biota, and that abiotic factors such as nutrient concentrations and flow rates, influenced nutrient exchange rates only in absorption-dominated communities such as zones B and W.  相似文献   

12.
浒苔对NH+4-N与NO-3-N吸收的相互作用   总被引：1，自引：0，他引：1  
在国内首次研究了大型海洋绿潮藻浒苔(Ulva prolifera)对NH4+-N与NO 3--N两种氮源的选择吸收作用。结果表明:当两种氮源等浓度比例存在时,随着NH4+-N与NO3--N浓度升高,藻体对NH4+-N的吸收速率逐渐升高,而对NO3--N吸收受到抑制;当NO3--N和NH 4+-N高浓度比存在时,藻体对NH4-N的吸收速率随着NO3--N/NH4+-N比例的升高和NH4-N浓度的下降而降低;当NO3--N和NH4+-N低浓度比存在时,藻体对NH+4-N保持较高的吸收速率,而对NO3--N的吸收效率随着NO3--N浓度的降低而降低;浒苔具有同时利用水体中较高浓度的NH+4-N和NO3--N的能力,只有当NH4+-N或NO3--N浓度较低时,才以吸收相对应的氮源为主。这说明浒苔能够快速、大量地吸收水体中氮源,为爆发性增殖贮备物质条件。同时,即便两种氮源同时存在,浒苔对NH+4-N的吸收速率也远高于对NO3--N的吸收速率,因此,控制NH4+-N的大量输入仍是预防浒苔绿潮爆发的关键。  相似文献   

13.
朱明  刘峰  陈璐  刘兆普 《海洋与湖沼》2018,49(5):975-982
我国黄海出现的绿潮发源于黄海南部苏北辐射沙洲紫菜养殖区,苏北沙洲区濒临的沿岸河网众多,来自沿岸径流的淡水携带大量氮磷等营养盐间歇性入海,导致海水的富营养化并伴随着盐度的周期性波动。本研究通过模拟实验研究低盐度(15和5)对浒苔吸收氮盐(NO_3~–-N和NH_4~+-N)和磷盐(PO_4~(3–)-P)的影响,主要发现:与盐度30相比,在低盐度(15和5)时,浒苔对NO_3~–-N的1h最大吸收速率(V_(max))和亲和力(V_(max)/Ks)分别提高280%和350%左右,半饱和常数(Ks)下降15%左右,并能够维持对NO_3~–-N的高效吸收(24h);盐度15和5时,浒苔对NH_4~+-N的1h最大吸收速率(V_(max))分别提高40%和200%,亲和力(V_(max)/Ks)分别提高20%和180%, Ks分别提高15%和30%,但是盐度降低对NH_4~+-N的长效吸收产生负面影响,甚至在盐度5条件下出现吸收高浓度NH_4~+-N后再释放的现象;与盐度30相似,盐度15条件下浒苔能够快速吸收PO_4~(3–)-P,而盐度5则导致藻细胞内的PO_4~(3–)-P在早期阶段快速流失,并在后期不能有效吸收PO_4~(3–)-P。本实验的结果表明,降低盐度有利于浒苔对氮源的快速吸收,在盐度15下浒苔能够实现对硝酸盐和磷盐的高效吸收。  相似文献   

14.
溶解态无机氮（dissolved inorganic nitrogen, DIN）主要由亚硝酸盐-氮（NO-2-N）、硝酸盐-氮（NO-3-N）和铵氮（NH+4-N）组成,它们在海洋的生物地球化学循环过程中起重要作用。但人类活动向海洋输入了大量无机氮,导致一系列环境问题。为了更好地开展海洋氮循环研究和环境污染管理,需对海水中的DIN进行测定。在众多分析方法中,光谱法因其通用性好、适用范围广、所需设备简单,成为测定海水DIN的首选。本文总结了近10年来基于光谱法测定海水DIN的研究进展,包括紫外分光光度法测定NO-3-N、萘乙二胺分光光度法测定NO-2-N和NO-3-N、次溴酸盐氧化-分光光度法测定NH+4-N、靛酚蓝分光光度法测定NH+4-N、酸碱指示剂-分光光度法测定NH+4-N、荧光法和化学发光法测定DIN等,比较了各分析方法的特点,并展望了光谱法测定海水DIN的发展趋势。总的来说,在分析方法上,新试剂的使用以及一些新合成材料的出现,丰富了DIN的分析手段;在分析仪器上,以流动分析技术为基础的分析仪器在DIN的实验室及现场分析中得到了广泛应用。DIN的分析方法均朝着简单便捷、全自动化、分析速度快、精确度高、可适用范围广的方向发展。  相似文献   

15.
为了阐释鱼、蚌生态混养的可行性,通过建立微型生态系统,探索不同养殖密度和处理时间的背角无齿蚌(Anodonta woodiana)对池塘底泥释放营养盐的净化效果。结果表明:背角无齿蚌对pH、DO和总固溶物的影响总体不明显,但能够显著降低浊度和Chl-a含量(P0.05),最大去除率分别为79.2%和83.4%;背角无齿蚌对营养盐的净化效果受到处理时间、养殖密度的显著影响(P0.05);TN、NO_3~–-N和NO_2~–-N呈现升高的趋势,而能够显著降低NH_4~+-N、TP和PO_4~(3–)的含量(P0.05),最大去除率分别为90.9%、55.6%和52.9%。响应面优化分析显示蚌养殖密度和处理时间的配比分别为27个/m~3和22.63 d、25个/m~3和23.69 d时,对TP和PO_4~(3–)的去除率可进一步提升至68.9%和58.1%。本研究表明背角无齿蚌有潜力用于养殖池塘底泥富营养化的防控。  相似文献   

16.
Measurements of red tide organism cell counting, chlorophyll a, water temperat-ure, salinity, pH, DO, COD, NH_4~ , NO_3, NO_2, active phosphate, dissolvable siliconwere made in a follow-up observation of a red tide event which occurred in the western harbourof Xiamen from 18th June to 3rd July in 1986.  相似文献   

17.
Seasonal and interannual variations in physicochemical properties were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from December 2000 to December 2005. Physicochemical properties (i.e. temperature, salinity, density, dissolved oxygen and dissolved inorganic nutrient concentration) revealed clear seasonal variations, which were similar to each other during all 5 years. Temperature, salinity and dissolved inorganic nutrients showed rapid, drastic variations within a few days and/or weeks. These variations are related to sea levels, principally due to the shifting effects of the Kuroshio Current axis: they were strongly affected by the Kuroshio Water and other waters, when sea level difference was greater than ca. 35 cm and lower than ca. 15 cm, respectively. Temperature difference (DF T ) increased with sea level difference, and the difference of salinity and dissolved inorganic nutrients (NH4 +-N, NO3 −+NO2 −-N, NH4 ++NO3 −+NO2 −-N, PO4 3−-P and SiO2-Si) increased and decreased with DF T , respectively. All these correlations are significant. Total dissolved inorganic nitrogen (N), phosphate (P) and silicate (Si) revealed seasonal variations in the ranges of 0.57–16.08, 0.0070–0.91 and 0.22–46.38 μM, respectively. From the regression equations between these elements allowed the following relation to be obtained; Si:N:P = 14.8:13.4:1. Dissolved inorganic nutrients were characterized by Si and/or P deficiency, especially in the upper layer (0–20 m depth) during summer. Single and/or combined elements are discussed on the basis of potential and stoichiometric nutrient limitations, which could restrict phytoplankton (diatom) growth as a limiting factor.  相似文献   

18.
长江口和杭州湾海域生物生产力锋面及其生态学效应   总被引：49，自引：10，他引：39  
通过分析海洋生态学资料并结合卫星遥感、渔场及赤潮等资料,发现长江口和杭州湾及其毗邻海域生物生产力的锋面,在离长江口门和杭州湾口约100 km的长江冲淡水中部海域出现蓝细菌丰度、浮游植物现存量和初级生产力以及浮游动物的最大值,该锋面的存在和位置被水色遥感所确认.光和营养盐在此呈现最佳的权衡.在该锋区悬浮体浓度小于5 mg/dm3,盐度为25～30.在该锋面的西侧高的悬浮体浓度造成了浮游植物的光限制,其东侧距长江口和杭州湾口较远,陆源营养盐被稀释,加之浮游植物的消耗,造成了营养盐的限制.夏季水体的层化,增强了水体的垂直稳定,使这种分布格局更加显著.由于细菌多附着在悬浮颗粒物的表面,细菌丰度的最大值出现在近口门区的最大浊度带,在向外海方向随着悬浮体的沉降细菌丰度迅速降低.在生物生产力锋面,浮游植物的旺发导致水体跃层之上高溶解氧浓度和低营养盐浓度,尤其是PO4被耗尽,同时浮游动物饵料的丰富,造成浮游动物旺发;由于蓝细菌的快速增殖,其流式细胞测定的细胞粒径变小.生物生产力锋面的出现产生了显著的生态学效应,一方面造成某些经济鱼类产卵和索饵场的形成,例如鲐鲹鱼、马鲛鱼等;另一方面造成赤潮多发区和底层水缺氧区.  相似文献   

19.
Concentrations of nutrients (NO3, NO2, Si(OH)4, PO4 and dissolved inorganic carbon (DIC) were measured in a series of seawater samples collected over approximately 15 months in 2005 and 2006 by an automatic water sampler (Remote Access Sampler, RAS) in the Northwestern North Pacific. Seasonal variability and concentrations of NO3 + NO2 (NOx and Si(OH)4 were comparable to previous shipboard observations, although there were small errors associated with measurements of PO4 and DIC. Concentrations of these nutrients began to decrease in late April. After the end of June, NOx and Si(OH)4 decreased rapidly, with large fluctuations. After October, these nutrients increased again until late spring 2006. The ratio of the decrease of Si(OH)4 to that of NOx suggests that numbers of biogenic opal-producing creatures, such as diatoms, increased after the end of June. This conclusion was supported by a rapid increase in biogenic opal flux recorded in a sediment trap at 150 m. The relationship between NOx concentrations at the RAS depth of 35 m and NOx integrated over the upper 100 m was determined using previous shipboard hydrocast data. This relationship was used to estimate integrated mixed layer NOx concentration from RAS data. Estimated new production based on seasonal drawdown of integrated NOx averaged approximately 156 mg-C m−2day−1 annually, which agrees with previous estimates. Thus, an automatic seawater sampler that documents annual maximum and minimum nutrient concentrations and episodic events such as storms and spring blooms, which might be missed by an ordinary research vessel, will contribute to time-series observations of nutrients and, by extension, biological pump activity.  相似文献   

20.
This study investigates the biogeochemical processes that control the benthic fluxes of dissolved nitrogen (N) species in Boknis Eck – a 28 m deep site in the Eckernförde Bay (southwestern Baltic Sea). Bottom water oxygen concentrations (O2−BW) fluctuate greatly over the year at Boknis Eck, being well-oxygenated in winter and experiencing severe bottom water hypoxia and even anoxia in late summer. The present communication addresses the winter situation (February 2010). Fluxes of ammonium (NH4+), nitrate (NO3−) and nitrite (NO2−) were simulated using a benthic model that accounted for transport and biogeochemical reactions and constrained with ex situ flux measurements and sediment geochemical analysis. The sediments were a net sink for NO3− (−0.35 mmol m−2 d−1 of NO3−), of which 75% was ascribed to dissimilatory reduction of nitrate to ammonium (DNRA) by sulfide oxidizing bacteria, and 25% to NO3− reduction to NO2− by denitrifying microorganisms. NH4+ fluxes were high (1.74 mmol m−2 d−1 of NH4+), mainly due to the degradation of organic nitrogen, and directed out of the sediment. NO2− fluxes were negligible. The sediments in Boknis Eck are, therefore, a net source of dissolved inorganic nitrogen (DIN = NO3− + NO2− + NH4+) during winter. This is in large part due to bioirrigation, which accounts for 76% of the benthic efflux of NH4+, thus reducing the capacity for nitrification of NH4+. The combined rate of fixed N loss by denitrification and anammox was estimated at 0.08 mmol m−2 d−1 of N2, which is at the lower end of previously reported values. A systematic sensitivity analysis revealed that denitrification and anammox respond strongly and positively to the concentration of NO3− in the bottom water (NO3−BW). Higher O2−BW decreases DNRA and denitrification but stimulates both anammox and the contribution of anammox to total N2 production (%Ramx). A complete mechanistic explanation of these findings is provided. Our analysis indicates that nitrification is the geochemical driving force behind the observed correlation between %Ramx and water depth in the seminal study of Dalsgaard et al. (2005). Despite remaining uncertainties, the results provide a general mechanistic framework for interpreting the existing knowledge of N-turnover processes and fluxes in continental margin sediments, as well as predicting the types of environment where these reactions are expected to occur prominently.  相似文献   

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