Influences of Nutrient Outwelling from the Mangrove Swamp on the Distribution of Phytoplankton in the Matang Mangrove Estuary, Malaysia

Distributions of dissolved nutrients and Chl. a were investigated in the Sangga Besar River Estuary in the well-managed Matang Mangrove Forest in West Malaysia. In the estuary, spring tide concentrations of ammonium, silicate and phosphate were higher than those in the neap tide, which suggests that these nutrients are flushed from the mangrove area by the inundation and tidal mixing of the spring tide. Ammonium comprised over 50% of the dissolved inorganic nitrogen in the spring tide, while nitrite tended to dominate in the neap tide, indicating the predominance of nitrification inside the estuary in neap tides. Nutrient concentrations in the creek water were higher than those of estuarine water, indicating the nutrient outwelling from the mangrove swamp and ammonium regeneration from mangrove litter in the creek sediments. The maximum concentration of Chl. a in spring tides reached 80 g/l while it was below 20 g/l in the neap tides. These variations in the phytoplankton biomass and nutrients probably reflect the greater nutrient availability in the spring tide due to outwelling from the mangrove swamp and creek.     

Beneath the surface: Characteristics of oceanic ecosystems under weak mixing conditions – A theoretical investigation

This study considers an important biome in aquatic environments, the subsurface ecosystem that evolves under low mixing conditions, from a theoretical point of view. Employing a conceptual model that involves phytoplankton, a limiting nutrient and sinking detritus, we use a set of key characteristics (thickness, depth, biomass amplitude/productivity) to qualitatively and quantitatively describe subsurface biomass maximum layers (SBMLs) of phytoplankton. These SBMLs are defined by the existence of two community compensation depths in the water column, which confine the layer of net community production; their depth coincides with the upper nutricline. Analysing the results of a large ensemble of simulations with a one-dimensional numerical model, we explore the parameter dependencies to obtain fundamental steady-state relationships that connect primary production, mortality and grazing, remineralization, vertical diffusion and detrital sinking. As a main result, we find that we can distinguish between factors that determine the vertically integrated primary production and others that affect only depth and shape (thickness and biomass amplitude) of this subsurface production layer. A simple relationship is derived analytically, which can be used to estimate the steady-state primary productivity in the subsurface oligotrophic ocean. The fundamental nature of the results provides further insight into the dynamics of these “hidden” ecosystems and their role in marine nutrient cycling.     

Nutrient dynamics and seasonal succession of phytoplankton assemblages in a Southern European Estuary: Ria de Aveiro, Portugal

The spatial and temporal dynamics of dissolved inorganic nitrogen, dissolved phosphate, dissolved silica and chlorophyll a were measured seasonally at eight stations in the Ria de Aveiro. Between December 2000 and September 2001, the seasonal succession of phytoplankton assemblages, inferred after the spatial and seasonal variation of silica and of chlorophyll a concentrations, showed that diatoms (μmol Si L⁻¹) dominated from late autumn until early spring, while chlorophytes (μg Chl a L⁻¹) bloomed during late spring and summer. The Si:N:P ratios and Si concentrations indicated no seasonal depletion in dissolved silica, as in other temperate systems, possibly because of abnormal precipitation and flood events prolonging the supply of dissolved Si to the system. The Si:N:P ratios suggested P limitation at the system level. Despite the relative proportions of available nutrients, the mean phosphorus concentration (5.3 μmol L⁻¹) was above the reported half-saturation constants for P uptake by phytoplankton. Thus, in Ria de Aveiro, the seasonal succession of phytoplankton assemblages may also be dependent on the grazing capacity of the pelagic community through top-down regulation.     

Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang Estuary Ⅰ.Model results

rmIoxThe averag annual dischaIge of the Zhujiang Xiver is 3. 32 x l0ll m3, which ranks theZhujiang River just end to the Changjiang River in China. The dischnye occutring duringthe fltal m between APril and ffepteTnber accounts for 80% of the yearly total. The Zhu-jiang hiver has a yeaIy sediment load of about 1 x l08 tons, which also concentrates in theM arn (Zhao, l990; Chen et al., 1998). The Zhujiang Xiver delta,which has l2 cities ofdifferent sizes and more than 40 towns with a po…     

Microphytobenthos vertical migratory photoresponse as characterised by light-response curves of surface biomass

The migratory response of intertidal microphytobenthos to changes in irradiance was studied on undisturbed estuarine sediments. Two non-destructive optical techniques were used to trace variations in vivo of surface biomass: PAM fluorometry, for measuring the minimum fluorescence level (F_o); and spectral reflectance analysis, for quantifying the normalized difference vegetation index (NDVI). Following the formation of a dense biofilm at the surface, replicated sediment samples were simultaneously exposed to six different irradiance levels, ranging from 50 to 1500 μmol m⁻² s⁻¹, during a period of 120 min. The migratory photoresponse of the biofilms was characterised by constructing biomass vs. light curves (BLC), relating the accumulation of microalgal biomass after that period (estimated by F_o or NDVI) to the irradiance level incident on the surface. BLCs allow characterising the main features of the migratory photoresponse of intact biofilms. Typical BLC showed a clear biphasic pattern, with an increase in microalgal accumulation under irradiances below 100 μmol m⁻² s⁻¹, maximum values under 100–250 μmol m⁻² s⁻¹, and a gradual decrease of surface biomass under higher irradiances, indicating a strong photophobic downward migratory response. Similar BLC patterns were obtained when measuring F_o or NDVI. The construction of BLCs for biofilms from intertidal sites with distinctive sediment characteristics and diatom taxonomic composition allowed to detected significant differences in the migratory photoresponse. Biofilms from a muddy sediment exhibited considerably larger amplitude in the migratory photoresponse than the biofilms from a sandy mud site, especially under high irradiances. The photophobic migratory response to high light was found to vary among diatom species, particularly in the case of the biofilms from the muddy sediments.     

Nutrients, Chlorophyll a and Phytoplankton in the İskenderun Bay (Northeastern Mediterranean)

Abstract. The monthly changes in chlorophyll a , phytoplankton abundance and nutrient concentrations at two stations, one at the inshore and the other at the deep waters of the northern part of İskenderun Bay, were investigated between 1994 – 1995. The vertical distribution of nutrients and phytoplankton biomass were also studied at the deep station. The concentrations of NO₃+NO₂-N, PO₄-P and SiO₄-Si of surface water at both stations were 0.31 – 1.63 µg-at · l^-1, 0.08 – 0.60 µg-at · l^-1 and 0.50 – 2.7 µg-at · l^-1, respectively. The highest concentrations were measured at the inshore station and clear differences were found between the inshore and deep-water stations. Chlorophyll a concentrations ranged from 0.17 to 2.78 µg · l^-1 and the highest value was measured in March. At the inshore station, which was affected by land run-off, phytoplankton abundance reached the highest value (21,308 cells · l^-1) in October 1995, with a marked dominance of Pseudonitzschia pungens (20,200 cells · l^-1). The nutrient and chlorophyll a concentrations at the inshore station were higher than those at the deep station. One reason for this is the land-based nutrient input into the coastal area here. In spite of these effects, the bay is not eutrophicated because of circulation events in the northeastern Mediterranean.     

化合氯对浮游植物对绿素a和光合作用影响的室内研究

化合氯是温排水中主要的化学物质,它的存在会对电厂邻近水域中生活的浮游植物造成一定的影响,运用均匀设计的实验方法研究温度,化合氯浓度,氯处理时间,及这3个因素之间的交互作用,从中筛选出影响叶绿素a含量与光合作用过程的主要因子,结果表明：影响叶绿素a的主要因子是氯处理时间,氯浓度与处理时间之间的交互作用（置信水平为99％）,影响光合作用的主要是氯处理时间,氯浓度,氯处理时间与氯浓度之间的交互作用,以及温度与氯处理时间的交互作用（置换水平为98％）。     

渤海生态动力过程的模型研究 Ⅱ.营养盐以及叶绿素a的季节变化

利用在本系列研究第一部分中所建立的耦合的生物物理模型,模拟了渤海浮游植物生物量和营养盐含量的年度循环特征.模拟结果显示:藻类的春季水华是由经过一冬积累在水体中的营养盐导致,而水华开始的时间在浅水区明显早于深水区,对此深水区水体层化结构的形成可能起着重要作用;另一方面,河载营养盐与悬起的沉积物所释放的营养盐是诱发夏季水华的共同原因.基于模型结果,我们还发现:渤海的浮游植物动力特性就整体而言依然受无机氮限制,但是在莱州湾,磷限制特性表现得非常明显,这主要是由于每年黄河都要携带大量的无机氮进入海水,从而导致莱州湾营养盐的氮磷比已远远超过16.