太湖西北湖区浮游植物和无机、有机氮的时空分布特征

以太湖重度蓝藻水华发生的西北湖区为研究对象,从河口至湖心区设置5个采样点,于2012年10月至2013年10月逐月采集表层水体样品,测定了水温、溶解氧和浮游细菌丰度,并分析了浮游植物群落结构的组成、溶解性无机氮(DIN)和有机氮(DON)浓度以及氮磷比.研究结果表明,太湖西北湖区浮游植物主要由蓝藻、硅藻、绿藻和隐藻组成.可能由于风、浪等混合作用使太湖西北湖区不同采样点之间蓝藻细胞密度没有显著差异.蓝藻生物量在浮游植物中所占比例最高为34%±15%,春季部分点位隐藻生物量高于50%,表明隐藻与蓝藻的相互竞争趋势显著.CCA排序图结果表明,DIN、DON浓度以及总氮∶总磷比(TN∶TP比)是影响西北湖区浮游植物优势属分布的重要环境因子.5个采样点铵态氮(NH_4~+-N)与DIN浓度具有显著差异,与DON浓度没有显著差异.夏季蓝藻水华暴发期间,可能由于蓝藻的吸收利用引起NH_4~+-N和硝态氮(NO_3~--N)浓度迅速降低.此外,由于NH_4~+-N浓度还可能受到沉积物NH_4~+-N释放的影响,因此,蓝藻细胞密度与NO_3~--N的相关系数和显著水平均高于NH_4~+-N.夏季TN∶TP比和DIN∶TP比降至最低,表明该湖区浮游植物,尤其是蓝藻的生长可能受到氮限制.蓝藻细胞密度与DON浓度呈显著负相关,表明在氮限制条件下,DON可能是蓝藻氮素利用的重要补充.     

Seasonal study of uptake and regeneration of nitrogen on the Scotian Shelf

Nitrate and ammonium uptake and regeneration rates were measured in the euphotic zone of the Scotian Shelf during three cruises (spring, summer and late winter). Nitrate, as a portion of the total nitrogen assimilated (NO₃⁻ uptake/total (NO₃⁻ + NH₄⁻) uptake), decreased with increasing ambient NH₄⁺ concentration and depth. Values integrated through the euphotic zone averaged 30% in the summer, and 27% in the spring, indicating that a large portion of phytoplankton growth was supported by ‘regenerated’ production (NH₄⁺) during those periods. In winter, growth was supported primarily by ‘new’ production since NO₃⁻ uptake represented 67% of the total nitrogen uptake during that period. In all seasons the phytoplankton showed a consistent preference for NH₄⁺ utilization relative to NO₃, despite the abundance of NO₃ at times. In 21 of 23 measurements, NH₄⁺ remineralization exceeded uptake, suggesting that phytoplankton nitrogen requirements were met or exceeded by in situ NH₄⁺ regeneration. Remineralization rates covaried with both productivity (¹⁴C) and NH₄⁺ uptake rates within the euphotic zone. These relationships were most apparent during the summer when nitrogen and carbon fluxes and algal biomass (Chl a) were greatest. The experimental approach used in this study demonstrates a seasonal pattern of NH₄⁺ and NO₃⁻ utilization previously unreported for Scotian Shelf waters.     

Nutrient inputs from submarine groundwater discharge on the Santiago reef flat,Bolinao, Northwestern Philippines

Submarine groundwater discharge (SGD) on the reef flat of Bolinao, Pangasinan (Philippines) was mapped using electrical resistivity, ²²²Rn, and nutrient concentration measurements. Nitrate levels as high as 126 μM, or 1–2 orders of magnitude higher than ambient concentrations, were measured in some areas of the reef flat. Nutrient fluxes were higher during the wet season (May–October) than the dry season (November–April). Dissolved inorganic nitrogen (DIN = NO₃ + NO₂ + NH₄) and soluble reactive phosphorus (SRP) fluxes during the wet season were 4.4 and 0.2 mmoles m⁻² d⁻¹, respectively. With the increase population size and anthropogenic activities in Bolinao, an enhancement of SGD-derived nitrogen levels is likely. This could lead to eutrophic conditions in the otherwise oligotrophic waters surrounding the Santiago reef flat.     

太湖草源性"湖泛"水域沉积物营养盐释放估算

于太湖草源性"湖泛"暴发期,采集柱状沉积物并应用peeper被动采样装置获得"湖泛"区原位沉积物间隙水.泥水样品分析表明:"湖泛"发生水域表层(0~7 cm)沉积物的含水率、孔隙度和有机质含量均明显高于对照区,其中有机质含量更是对照区样品的4倍左右,沉水植物残体促使表层沉积物物化性质改变的作用明显;"湖泛"发生水域表层沉积物间隙水中铵态氮(NH+4-N)、溶解性反应磷(SRP)及Fe2+含量远高于未发生区,植物残体降解对沉积物厌氧环境的营造显著.运用分子扩散模型对沉积物释放通量估算:"湖泛"发生区沉积物NH+4-N、SRP和Fe2+的释放速率分别是对照区的49.8、15.3和123.1倍.研究认为,草源性"湖泛"水体氮、磷等营养物含量升高的主要原因是沉积物的释放,而"湖泛"所营造的厌氧环境是氮、磷释放急剧增加的主要驱动因素.     

中国太湖物理—生物工程实验中菱对水质影响的模式

A model on a physico-biological engineering experiment for purifying water in Wulihu Bay of Lake Taihu by using Trapa natans var. bispinosa was constructed. The state variables in water in the physico-biological engineering were ammonium nitrogen (NH₄⁺-N); nitrate nitrogen (NO₃^--N); nitrite nitrogen (NO₂^--N); phosphate phosphorus (PO₄^3--P); dissolved oxygen (DO); nitrogen (N) and phosphorus (P) in detritus; biomass density, N and P in phytoplankton and in Trapa natans var. bispinosa, N and P in the substance adsorbed by the membrane of the engineering and the rootstocks of Trapa natans var. bispinosa. The state variables in bottom mud layer were PO₄^3--P in the core water,exchangeable P and N. The external forcing functions were solar radiation, water temperature, NH₄⁺-N; NO₃^--N; NO₂^--N; PO₄^3--P; N and P in detritus; DO; phytoplankton concentrations in inflow water and the retention time of the water in physico-biological engineering channel. The main physical, chemical and biological processes considered in the model were:growth of Trapa natans var. bispinosa and phytoplankton; oxidation of NH₄⁺-N and NO₂^--N, of detritus break down; N and P sorption by the enclosure cloth of the experimental engineering and by the rootstocks of Trapa natans var. bispinosa in water; reaeration of water; uptake of P, NH₄⁺-N, NO₃^--N by phytoplankton and Trapa natans var. bispinosa:mortality of the phytoplankton and Trapa natans var. bispinosa:settling of detritus; and nutrient release from sediment. Comparison of calculated results and observed results showed that the model was constructed reasonably for the experiment. The mechanism of purifying lake water in the experiment engineering was discussed by the use of the model.     

Dynamics of a Prorocentrum minimum bloom along the northern coast of Sinaloa,Mexico

To investigate the relative importance of mesoscale physical events, such as upwellings and physical and chemical variables during an algae bloom of Prorocentrum minimum, 25 sampling sites were established offshore of the Navachiste Lagoon Complex on the east side of the Gulf of California. Samples were analyzed for phytoplankton concentration, water chemistry, and temperature during November 1999, January, March, April, May, and August 2000. Satellite imagery of sea surface temperature (SST) for April 2000 was processed to obtain a synoptic view of the area during the extraordinary bloom of P. minimum in the open waters of the Gulf of California. The bloom was associated with change of oceanographic conditions from moderate winds to calm period, temperature increase and high nitrate (NO₃⁻-N) and ammonia (NH₄⁺-N) content in the offshore waters. Depletion of these nutrients during the bloom suggests that this species uses both types of nitrogen substrates. Cysts in the northernmost sampling stations in January and March indicate that upwelling water, rich in nitrates, also carried a seed stock population of P. minimum. SST patterns in the satellite imagery suggest wind-forcing as the responsible mechanisms triggering the algal bloom offshore of the Navachiste Lagoon Complex.     

垂向归纳模型下鄱阳湖丰、枯水期初级生产力特征及与环境因子相关性分析

于2014年1月(枯水期)、7月(丰水期)对鄱阳湖湖水进行采集,测定相应的理化参数、叶绿素a浓度和光合有效辐射,结合初级生产力垂向归纳模型估算浮游植物初级生产力,分析湖区初级生产力特征及与环境因子的相关性.结果表明,鄱阳湖枯水期浮游植物初级生产力波动范围为83.50~355.43 mg C/(m~3·d),平均值为193.33 mg C/(m~3·d),初级生产力空间分布特征主要受水体类型的影响,枯水期初级生产力与氮、磷营养盐浓度呈负相关,其中与铵态氮浓度呈显著负相关,枯水期不会出现营养盐限制现象;丰水期浮游植物初级生产力波动范围为113.80~1134.06 mg C/(m~3·d),平均值为412.12 mg C/(m~3·d),初级生产力空间分布主要受河流注入的影响,丰水期浮游植物初级生产力与总磷及悬浮物浓度呈显著正相关,由于悬浮物对浮游植物生长的促进作用大于抑制作用,鄱阳湖丰水期会出现磷营养盐的限制;鄱阳湖整体平均流速约为0.28 m/s,易于浮游植物的生长,南鄱阳湖平均流速约为0.21 m/s,而北鄱阳湖平均流速约为0.35 m/s,所以南鄱阳湖比北鄱阳湖更容易发生水体富营养化并暴发水华.     

Size-dependent uptake of nitrate and ammonium as a function of light in well-mixed temperate coastal waters

The effect of light on nitrate (NO₃⁻) and ammonium (NH₄⁺) uptake by natural communities was investigated in relation to cell size (<10 and >10 μm) in the well-mixed coastal waters of the English Channel. Nitrogen (N) uptake kinetics as a function of irradiance were assessed using ¹⁵N tracer techniques, for a seasonal cycle of populations collected at 50% and 1% light penetration depth. The nitrogen uptake responses to irradiance can be represented by the formulation used to describe the photosynthesis versus irradiance relationships and modified by the addition of a dark uptake parameter. The response curves of two size fractions of phytoplankton collected at 50% and 1% of incident light did not differ significantly, which suggested that the physiological characteristics of N uptake were not affected by the light intensity at which the phytoplankton assemblages were sampled. The kinetics parameters indicated that the NO₃⁻ uptake system was more strongly dependent on light than the NH₄⁺ uptake system. They also showed that N uptake was less limited by the light intensity in the small size fraction than it was in the large size fraction. At the mean light intensity in the water column, kinetics analysis predicted a NH₄⁺ uptake that was on average 1.8 (±0.6) and 2.4 (±1.0) times greater than the NO₃⁻ uptake, for <10 and >10 μm size fractions, respectively. The kinetics also predicted, at the in situ mean light intensity, that the mean ability to take up nitrogen was twice as high (1.8±0.5) for the small than for the large cells when the N substrate was NH₄⁺ and more than twice as high (2.6±1.5) when the substrate was NO₃⁻. These results added to our understanding of the light effect on N uptake processes in well-mixed waters, and can largely explain the phytoplankton production, mainly regenerated and dominated by small cells, that has been observed in these waters.     

Seasonal and spatial dynamics of nutrients and phytoplankton biomass in Victoria Harbour and its vicinity before and after sewage abatement

This study investigated the seasonal and spatial dynamics of nutrients and phytoplankton biomass at 12 stations in Hong Kong (HK) waters during a three year period from 2004 to 2006 after upgraded sewage treatment and compared these results to observations before sewage treatment. Pearl River estuary (PRE) discharge significantly increased NO₃ and SiO₄ concentrations, particularly in western and southern waters when rainfall and river discharge was maximal in summer. Continuous year round discharge of sewage effluent resulted in high NH₄ and PO₄ in Victoria Harbour (VH) and its vicinity. In winter, spring and fall, the water column at all stations was moderately mixed by winds and tidal currents, and phytoplankton biomass was relatively low compared to summer. In summer, the mean surface phytoplankton chl biomass was generally >9 μg L⁻¹ in most areas as a result of thermohaline stratification, and high nutrients, light, and water temperature. In summer, the potential limiting nutrient is PO₄ in the most productive southern waters and it seldom decreased to limiting levels (∼0.1 μM), suggesting that phytoplankton growth may be only episodically limiting. The mean bottom dissolved oxygen (DO) remained >3.5 mg L⁻¹ at most stations, indicating that the eutrophication impact in HK waters was not as severe as expected for such a eutrophic area. After the implementation of chemically enhanced primary sewage treatment in 2001, water quality in VH improved as indicated by a significant decrease in NH₄ and PO₄ and an increase in bottom DO. In contrast, there were an increase in chl a and NO₃, and a significant decrease in bottom DO in southern waters in summer, suggesting that hypoxic events are most likely to occur in this region if phytoplankton biomass and oxygen consumption keep increasing and exceed the buffering capacity of HK waters maintained by monsoon winds, tidal mixing and zooplankton grazing. Therefore, future studies on the long-term changes in nutrient loading from PRE and HK sewage discharge will be crucial for developing future strategies of sewage management in HK waters.     

Results of Hydrochemical Studies of Lake Azabach'e (Kamchatka)

The nutrient basis of Lake Azabach'e is studied. The distribution of pH and the concentrations of O₂, P_min, Fe, N–NH⁺ ₄, N–NO^– ₃, Si, and organic forms of N and P are considered. The chemical basis of biological production of Lake Azabach'e is assessed. It is found that the amount of Si is excessive everywhere and that phytoplankton production is limited by phosphate and mineral nitrogen deficiency in virtually equal degrees.     

湖光岩玛珥湖水体中营养盐的时空分布特征及其影响因素

湖光岩玛珥湖是世界上最大的玛珥湖,它几乎是封闭的,受外界的干扰小.目前有关玛珥湖的研究主要集中在古气候及生态环境研究方面,而有关玛珥湖营养盐在一年中的生物地球化学循环的研究较少,因此研究湖光岩玛珥湖营养盐的生物地球化学过程具有重要意义.于2015年10月-2016年9月对湖光岩玛珥湖全水柱的营养盐及其他相关参数进行逐月调查,分析营养盐的结构特征、垂直分布特征和时间变化情况,并讨论营养盐时空变化的影响因素.结果表明,湖光岩玛珥湖水中的无机氮（DIN）以铵态氮（NH₄⁺-N）为主（>60%）,其次是硝态氧（NO₃^--N）,亚硝态氮（NO₂^--N）所占比利最低.湖光岩玛珥湖水中的硅酸盐（SiO₃^2--Si）浓度较高,水体浮游植物生长受磷限制.冬季风期间,水体垂直混合较均匀,导致营养盐的垂直分布比较均匀;夏季风期间,水体层化,营养盐浓度在浅层水体较低,在深层水体较高.湖光岩玛珥湖表层水中的NO₃^--N、NH₄⁺-N和SiO₃^2--Si具有明显的时间变化规律：NO₃^--N浓度从10月-次年3月升高,从3-9月降低;NH₄⁺-N浓度从10月-次年5月降低;SiO₃^2--Si浓度从11月-次年5月降低,从5-9月持续升高.营养盐浓度的时间变化受有机质的矿化分解、水体的季节性混合、浮游植物的吸收、降雨的输入等多种因素的综合影响.     

曝气充氧对城市污染河道内源铵态氮释放的控制

以城市污染河道沉积物和上覆水为研究对象,利用模拟实验方法,探讨不同曝气充氧方式(水曝气EW、底泥曝气ES)对污染河道內源铵态氮(NH4+-N)释放的影响.研究结果发现:从间隙水和沉积物中NH4+-N的削减效果来看,底泥曝气均要优于水曝气;实验结束后,底泥曝气组沉积物与间隙水中NH4+-N含量分别减少63.39%和43.33%,水曝气组分别减少了7.54%和13.98%;从沉积物-水界面NH4+-N的扩散通量变化来看,水曝气组界面通量高于对照组,其变化规律与对照组相似;底泥曝气组沉积物-水界面NH4+-N扩散通量变化过程完全不同于其它两组,在整个试验周期内(除第5 d以外),底泥曝气组的通量低于水曝气组,在第15 d最低,为13.73 mg/(m2.d),仅为水曝气组和对照组的14.68%和19.93%,表明底泥曝气组沉积物NH4+-N的释放潜力低于水曝气组沉积物.     

Harmful algal blooms (HABs) in Daya Bay, China: An in situ study of primary production and environmental impacts

A month-long investigation of phytoplankton biomass and primary production (PP) was carried out during a harmful algal bloom (HAB) in Daya Bay, China, in 2003. During the bloom, the phytoplankton community was dominated by Scrippsiella trochoidea and Chattonella marina. The phytoplankton biomass (Chl a) and PP reached peak levels of 519.21 mg m⁻³ and 734.0 mgC m⁻³ h⁻¹, respectively. Micro-phytoplankton was the key contributor to Chl a and PP in a cage-culture area and in the adjacent HAB-affected waters, with percentages of up to 82.91% and 84.94%, respectively. The HAB had complicated relationships with hydrological and meteorological factors in Daya Bay. However, the water around the cage-culture area always showed statistically greater phytoplankton biomass and nutrient loadings than in adjacent waters, suggesting that this was the “trigger area” of the bloom. The spatial and temporal distribution of diverse HABs in Daya Bay, their ecological characteristics, and their environmental impacts are also discussed in this paper.     

Impact of overlying water velocity on ammonium uptake by benthic biofilms

The effect of the overlying water velocity on ammonium (NH₄⁺) uptake by benthic biofilms was studied in a recirculating laboratory flume (260 cm long, 29 cm wide), packed with 5 cm of silica sand arranged into bedforms. NH₄⁺ uptake was determined as the reduction in NH₄⁺ concentration in the water at average overlying water velocities of 0.8, 2, 4 and 8 cm s^?1. NH₄⁺ uptake was relatively constant under laminar flow conditions but increased when the flow regime became turbulent (>4 cm s^?1). This pattern was observed for two biofilms differing in their total biomass and in the abundance of the ammonia‐oxidizing bacteria, thus indicating that NH₄⁺ uptake was strongly controlled by mass‐transfer processes. The near stoichiometric relationship between the rates of NH₄⁺ uptake and nitrate (NO₃^?) accumulation suggests that aerobic nitrification was the main route for NH₄⁺ uptake. Microelectrode measurements showed a sharp decline of oxygen concentrations and pH values within the biofilms, thus supporting strong nitrification activity within the surficial section of the benthic biofilms. The results of this study highlight the key role of hydrodynamic conditions in regulating NH₄⁺ uptake in the transition from laminar to turbulent flow conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Spring and summer blooms of phytoplankton (SeaWiFS/MODIS) along a ferry line in the Bay of Biscay and western English Channel

The seasonal cycle of chlorophyll concentration in the Bay of Biscay and western English Channel has been examined using satellite data (chlorophyll, sea surface temperature (SST), photosynthetically available radiation (PAR) and wind) along the line of the ferry Pride of Bilbao (Bilbao to Portsmouth). The spring phytoplankton bloom develops regularly in the oceanic region of the Bay of Biscay from mid March to the beginning of May with peak chlorophyll concentrations ranging 2–4 mg m^?3. Low wind turbulence is a major factor allowing the development of productivity pulses in the Bay of Biscay during spring. Exceptional blooms of phytoplankton take place in summer (July–August) in the western English Channel with chlorophyll concentrations as high as 40 mg m^?3. Some environmental factors (SST, wind, pressure and tide) are examined. Autumn blooms of phytoplankton (1–2 mg m^?3) are also detected in the northern Bay of Biscay, shelf-break and Celtic Sea in October. A 11 years pluri-annual synthesis of SeaWiFS satellite measurements is presented.     

Low boundary layer response and temperature dependence of nitrogen and phosphorus releases from oxic sediments of an oligotrophic lake

The effects of temperature, diffusive boundary-layer thickness, and sediment composition on fluxes of inorganic N and P were estimated for sediment cores with oxidized surfaces from nearshore waters (2?C10?m) of a montane oligotrophic lake. Fluxes of N and P were not affected by diffusive boundary-layer thickness but were strongly affected by temperature. Below 16?°C, sediments sequestered small amounts of P and released small amounts of N. Above 16?°C, the seasonal maximum water temperature, sediments were substantial sources of N (NH₄ ⁺?CN?=?2?C24?mg?m^?2 d^?1; NO₃ ^??+?NO₂ ^??CN?=?2?C5?mg?m^?2 d^?1) and P (0.1?C0.4?mg?m^?2 d^?1), indicating potential responsiveness of sediment?Cwater nutrient exchange, and of corresponding phytoplankton growth, to synoptic warming.     

改性当地土壤技术修复富营养化水体综合效果研究:Ⅰ.水质改善的应急与长期效果与机制

2010年10月-2011年9月在太湖梅梁湾围隔内研究了改性当地土壤絮凝除藻及其对水质改善的应急和长期效果,并结合室内实验研究了该技术防控底泥再悬浮和减少底泥二次污染的长效机制.现场围隔实验结果表明,改性当地土壤除藻30 min后,TN、NO3--N、NH4+-N、TP、PO34--P和Chl.a的去除率分别为66%、57%、60%、93%、92%和98%;长期监测结果表明,与对照区域相比,围隔内的TN、NH4+-N、NO3--N、TP和PO34--P在处理后11个月内的平均值分别降低了39.83%、52.30%、48.53%、18.75%和60.00%.室内再悬浮实验结果表明,改性土壤和沙子抗再悬浮能力较未改性土壤分别提高了3和5倍.室内柱培养结果表明改性土壤絮凝除藻和沙土覆盖相结合可有效提高表层沉积物-水界面的氧化还原电位和溶解氧,使沉积物向水体的TP和TN通量从源逆转成汇,PO34--P和NH4+-N通量大幅度降低.改性土壤技术在利用絮凝除藻快速改善水质后,可通过改性沙/土分层底泥调控分别达到对藻絮体再悬浮的物理控制和营养盐再释放的化学控制,通过将亚表层底泥中的藻细胞分解并被沉水植物根系吸收,可实现对底泥中水华蓝藻复苏和水体富营养化的长效生态控制.     

Variations in light absorption properties during a phytoplankton bloom in the Pearl River estuary

From 15 to 28 August in 2007, a Chaetoceros socialis bloom was detected in the Pearl River Estuary water with chlorophyll a concentration (Chl a) up to 30 mg m⁻³ and cell density up to 10⁶ cells L⁻¹. Time series of bio-optical measurements was obtained at a single site (114.29°E, 22.06°N) with the mooring of marine optical buoy. Light absorption properties of seawater experienced large variability throughout the algal bloom. Absorption by colored dissolved organic matter (CDOM) was one of the dominant optical components of the light absorption (30–70%) especially for pre- and post-bloom waters, and it tended to decrease with Chl a during the algal bloom. Absorption by phytoplankton was another dominant optical component (18–50%) and increased rapidly with Chl a. Phytoplankton and accompanying material played dominant roles in light absorption as indicated by the relationship between absorption coefficient and Chl a. At high pigment concentrations, water samples showed significantly lower specific phytoplankton absorption, compared with pre- and post-bloom conditions, with the specific phytoplankton concentration at 443 nm varied between 0.011 and 0.022 m² mg⁻¹ and that at 676 nm between 0.007 and 0.018 m² mg⁻¹; small values of blue-to-red ratio of phytoplankton were also observed. These lower values were associated with variations in phytoplankton size structure. Spectral variability of phytoplankton absorption and total absorption (not including the fixed background absorption by pure water itself) could be expressed as simple linear functions linking absorption at one wavelength to the absorption at the other wavelengths, with the slope of the relationship changing with wavelength. The absorption coefficients by non-algal particles and CDOM follow the general exponential functions with remarkably limited variability in the exponent with means of 0.0105 and 0.0166 nm⁻¹, respectively. These spectral dependencies of absorption coefficients provide useful information for retrieving inherent optical properties from reflectance data in a remote-sensing context.     

Net, actual, and potential sediment-water interface NH4 fluxes in the northern Gulf of Mexico (NGOMEX): Evidence for NH4 limitation of microbial dynamics

A new approach, combining ¹⁵NH₄⁺ isotope dilution and continuous-flow techniques, provided estimates of “actual” and “net” NH₄⁺ flux and sediment NH₄⁺ demand (SAD) at the sediment-water interface (SWI) of sites in the northern Gulf of Mexico (NGOMEX). The sites included a hypoxic site (C6), two sites with intermediate oxygen levels (B7 and F5), and a normoxic site (CT). Control cores without isotope addition and other cores from the same site treated with ¹⁵NH₄⁺ labeled overflowing water differentiated between net and actual regeneration flux and actual vs. potential uptake flux of NH₄⁺. Experiments were conducted in 2008 before (July) and after (September) two successive hurricanes (Gustav and Ike) and in January and August, 2009. Actual regeneration was significantly higher than net flux at most sites. Net flux did not differ significantly in most sites/dates, but the actual regeneration, and the actual and potential uptake, showed temporal and spatial variation; the flux at the hypoxic site was more active than non-hypoxic sites. SAD, the difference between potential and actual NH₄⁺ uptake flux, was higher at the hypoxic site than at non-hypoxic sites before and after the hurricanes in 2008 and during the hypoxia season in 2009. SAD related negatively to bottom water DO values. Conclusions: (1) net flux often underestimated actual regeneration, (2) hurricane activity decreased N dynamics, and (3) microbial N limitation status at the hypoxic site related to NH₄⁺ removal processes that were independent of oxygen (e.g., anaerobic heterotrophic uptake or anammox). These results indicate a rather consistent NH₄⁺ demand at the SWI during the hypoxic season and suggest that reduced nitrogen may limit microbial dynamics in the region.