Tidal Influences on Biotic and Abiotic Factors in the Seomjin River Estuary and Gwangyang Bay,Korea

To assess changes in abiotic and biotic factors between flood and ebb tides, we investigated the seasonal phytoplankton dynamics and environmental conditions along a salinity gradient at 14 stations in the Seomjin River estuary (SRE), Korea, and conducted bioassays to investigate the effect of nutrient addition (+N, +P, and +NP) on phytoplankton growth. Saltwater intrusion upstream was greatly dependent on the amount of freshwater discharge resulting from seasonal rainfall. There was a strong negative correlation between salinity and the nitrate+nitrite concentration (p?<?0.001), and between salinity and the silicate concentration (p?<?0.001), but no clear correlation between salinity and the ammonium concentration, or salinity and the phosphate concentration (p?>?0.01). This indicates that the N and Si loading increased as a result of freshwater input. The algal bioassays showed that high phytoplankton growth rates were usually recorded in response to the +NP treatment, but in the saltwater zone, the phytoplankton community also responded rapidly to the +N treatment, and to the +P treatment in the freshwater zone. The range of nutrient limitation depended on freshwater discharge. The seasonal and horizontal distribution of phytoplankton communities changed along the salinity gradient. The significant differences in abiotic factors between flood and ebb tides play important roles in controlling the biotic factors, including the occurrence of aquatic organisms including microalgae.     

Daily Course of CO2 Fluxes in the Atmosphere–Water System and Variable Fluorescence of Phytoplankton during the Open-Water Period for Lake Baikal according to Long-Term Measurements

The process of gas exchange of CO₂ in the atmosphere–water system and its relation to the daily course of variable fluorescence of phytoplankton is studied on the basis of long-term (2004–2014) measurements during the open water period for Lake Baikal. It is found that the decrease in photosynthetic activity of plankton is almost synchronous to the increase in the CO₂ flux from atmosphere to water. It follows from comparison of the spring and summer data with December measurements that the daily decrease in variable fluorescence of phytoplankton is caused by the internal daily rhythm of the photosynthetic activity of plankton.

     

Climatic and Tidal Forcing of Hydrography and Chlorophyll Concentrations in the Columbia River Estuary

Hydrographic patterns and chlorophyll concentrations in the Columbia River estuary were compared for spring and summer periods during 2004 through 2006. Riverine and oceanic sources of chlorophyll were evaluated at stations along a 27-km along-estuary transect in relation to time series of wind stress, river flow, and tidal stage. Patterns of chlorophyll concentration varied between seasons and years. In spring, the chlorophyll distribution was dominated by high concentrations from freshwater sources. Periods of increased stream flow limited riverine chlorophyll production. In summer, conversely, upwelling winds induced input of high-salinity water from the ocean to the estuary, and this water was often associated with relatively high chlorophyll concentrations. The frequency, duration, and intensity of upwelling events varied both seasonally and interannually, and this variation affected the timing and magnitude of coastally derived material imported to the estuary. The main source of chlorophyll thus varied from riverine in spring to coastal in summer. In both spring and summer seasons and among years, modulation of the spring/neap tidal cycle determined stratification, patterns of mixing, and the fate of (especially freshwater) phytoplankton. Spring tides had higher mixing and neap tides greater stratification, which affected the vertical distribution of chlorophyll. The Columbia River differs from the more tidally dominated coastal estuaries in the Pacific Northwest by its large riverine phytoplankton production and transfer of this biogenic material to the estuary and coastal ocean. However, all Pacific Northwest coastal estuaries investigated to date have exhibited advection of coastally derived chlorophyll during the upwelling season. This constitutes a fundamental difference between Pacific Northwest estuaries and systems not bounded by a coastal upwelling zone.     

南海东北部剪切流场对内波影响的研究进展

南海东北部受黑潮入侵、季风等动力因素的影响,背景剪切流场复杂,涡旋众多,水体垂向层结季节性变化明显,同时又因吕宋海峡的复杂底地形和强潮流的影响,内潮、内孤立波现象显著。但是,以往关于内潮、内孤立波的研究很少考虑到背景剪切流场和涡旋对其影响,因而难以揭示内波的生成、传播和演变规律。主要概述了南海东北部的剪切流、涡旋和内波等多种中尺度物理现象及其之间的相互作用的研究进展,进而提出未来关于南海东北部剪切流场对内波生成、传播和演变影响研究中的一些问题和研究思路。     

Nitrogen limitation of phytoplankton in a shallow embayment in northern Puget Sound

The effect of nutrient enrichments on natural phytoplankton assemblages was examined in six experiments conducted from June to October 1992. Short-term (4 d to 7 d) nutrient enrichment bioassays were incubated in situ in Padilla Bay, a slough-fed estuary in northern Puget Sound, Washington. Ammonium additions (15 μM) significantly (p<0.001) stimulated phytoplankton biomass accumulation during all six experiments. In two experiments, nitrate additions (15 μM) significantly stimulated accumulation of phytoplankton biomass during October, but not September. Addition of phosphate (1.0 μM) or silicate (15 μM) alone did not stimulate phytoplankton biomass accumulation during any of the experiments. In most experiments, phytoplankton response was greatest in combination treatments of ammonium and phosphate. Dissolved inorganic nutrient concentrations in the containers decreased during all incubations, but showed the greatest reduction in treatments receiving nitrogen. Dissolved inorganic nitrogen (DIN) to phosphate (PO₄ ^3?) ratios were below 16∶1 during all experiments, suggesting the potential for nitrogen limitation. In three experiments, the response of photosynthetic nanoplankton (<20 μm) to ammonium additions was compared to that of the total phytoplankton assemblages. Accumulation of nanoplankton biomass exceeded that of the total phytoplankton during two experiments in August but showed no significant response to ammonium additions in October. Results from the bioassays, the low DIN∶PO₄ ^3? ratios, and the reduction in nutrient concentrations in the containers provide evidence for potential nitrogen limitation of phytoplankton production during summer in Padilla Bay.     

海洋次表层叶绿素最大值的特征因子及其影响因素

在多数情况下,海水中叶绿素垂直分布是不均匀的。次表层叶绿素最大值是其中较为常见的一种形式,普遍存在于大洋及沿岸海域。次表层叶绿素最大值层(SCML)的深度、厚度与强度是表征海洋次表层叶绿素最大值(SCM)现象的主要特征因子,受海洋水文环境、营养盐分布以及浮游植物种类等因素共同影响,在不同季节不同海区的分布有较大差异。总体上,相对近海,大洋中SCML特征因子的季节变化较小,SCML深度较大,厚度较大,强度较小。寡营养盐海区SCML深度及强度的影响因素研究已有较明确结论,SCML深度主要受物理因素(光照条件及水体混合程度)影响,而强度则受物理、生物因素(光照条件、水体混合程度或浮游动物摄食等)共同影响。近海富营养盐海区,SCML特征因子的影响因素研究较为薄弱。长时间序列、高分辨率观测站在相应海区的建立,对推进海洋SCM,尤其是近海SCM的研究有重要意义。卫星观测、现场观测和数学模型相结合,定量研究SCML特征因子与各物理、生物、化学因子的普适性关系,是进一步研究SCML特征因子的重要方向之一。     

Modeling the effects of environmental variables on short-term spatial changes in phytoplankton biomass in a large shallow lake,Lake Taihu

Understanding the short-term response of phytoplankton biomass on environmental variables is needed for issuing early warnings of harmful algal blooms in aquatic ecosystems. Predicting harmful algal blooms are particularly challenging in large shallow lakes due to their complex mixing patterns. This study used a two-dimensional hydrodynamic–phytoplankton model to evaluate the effects of environmental variables on short-term changes in the horizontal distribution of phytoplankton biomass in a large shallow lake, Lake Taihu, China. Two simulations were performed using daily and hourly average wind condition and water temperature data collected in 2009. Other model inputs were identical for these two simulations. The response of phytoplankton to wind conditions, light intensity, water temperature, and total dissolved phosphorus and nitrogen concentrations were examined based on a sensitivity analysis using the hourly data. Hourly simulation achieved a more realistic distribution of phytoplankton biomass than the daily simulation. This finding implies that data with a higher temporal resolution are more useful for short-term prediction of phytoplankton biomass in this lake. Sensitivity analysis indicated that water temperature and light intensity dominate short-term changes in phytoplankton biomass in this lake. Wind conditions also affect phytoplankton biomass distribution by causing advective water movement.     

Effect of seasonal and cyclonic winds on internal tides over the Bay of Bengal

The influence of seasonal and cyclonic winds is studied on the characteristics of internal waves (IWs) over the western Bay of Bengal (BoB) by using MITgcm model. As the BoB experiences reversal of seasonal winds and also tropical cyclones during pre-monsoon and post-monsoon months, its effect is seen through the computation of spectral estimates of the IWs. It is seen that the peak estimate is associated with the semidiurnal frequency at all the depths and is found higher in May compared to November. This is attributed to the presence of shallow mixed layer depth and deep thermocline due to the upwelling favorable winds. The computation of isopycnal displacement infers that the internal tides are present from 40 to 120 m depth in case of upwelling favorable winds of May, whereas, the presence of internal tides is restricted between 90 and 120 m for the downwelling favorable winds of November. During May, the available potential energy is also seen in a narrow coastal stretch, whilst it is absent in November. During the Hudhud cyclone period of October 7–14, 2014, it is noticed from the spectral estimates that the IWs of tidal frequency are replaced by inertial frequency with a periodicity of about 2 days as a consequence of strong cyclonic winds. The progressive vector diagram shows the mean current is initially westward up to October 17, 2014 and then northeastward with well-defined clockwise circulation. The maximum radius of inertial oscillation of 15 km is observed. After the cyclone ceases, the estimate associated with inertial frequency slowly diminishes and enhances the estimates related to internal tides. The simulations also suggest that the internal tides are absent for about 6 weeks as a response of the cyclonic winds.

     

A particle conveyor belt process in the Columbia River estuary: Evidence from chlorophyll<Emphasis Type="Italic">a</Emphasis> and particulate organic carbon

Using both the photosynthetically active chlorophylla (chla) content of the organic carbon fraction of suspended particulate matter (chla/POC) and the percentage of photosynthetically, active chla in fluorometrically measured chla plus pheophytina (% chla), we determined that under specified hydrodynamic conditions, neap-spring tidal differentiation in particle dynamics could be observed in the Columbia River estuary. During summer time neap tides, when river discharge was moderate, bottom chla/POC remained relatively unchanged from riverine chla/POC over the full 0–30 psu salinity range, suggesting a benign trapping environment. During summertime spring tides, bottom chla/POC decreased at mid range salinities indicating resuspension of chla-poor POC during flood-ebb transitions. Bottom % chla during neap tides tended to average higher than that during spring tides, suggesting that neap particles were more recently hydrodynamically trapped than those on the spring tides. Such differentiation supported the possibility of operation of a particle conveyor belt process, a process in which low-amplitude neap tides favor selective particle trapping in estuarine turbidity maxima (ETM)., while high-amplitude spring tides favor particle resuspension from the ETM. Untrapped river-derived particles at the surface would continue through the estuary to the coastal ocean on the neap tide; during spring tide some particles eroded from the ETM would combine with unsettled riverine particles in transit toward the ocean. Because in tensified biogeochemical activity is associated with ETM, these neap-spring differences may be critical to maintenance and renewal of populations and processes in the estuary. Very high river discharge (15, 000 m³ s⁻¹) tended to overwhelm neap-spring differences, and significant oceanic input during very low river discharge (5,000 m³ s⁻¹) tended to do the same in the estuarine channel most exposed to ocean input. During heavy springtime phytoplankton blooms, development of a thick bottom fluff layer rich in chla also appeared to negate neapspring differentiation because spring tides apparently acted to resuspend the same rich bottom material that was laid down during neap tides. When photosynthetic assimilation numbers [μgC (μgchl,a)⁻¹h⁻¹] were measured across, the full salinity range, no neap-spring differences and no river discharge effects occurred, indicating that within our suite of measurements the compositional distinction of suspended particulate material was mainly a function of chla/POC, and to a lesser extent % chla. Even though these measurements suggest the existence of a conveyor belt process, proof of actual operation of this phenomenon requires scalar flux measurements of chla properties in and out of the ETM on both neap and spring tides.     

The abundance of fish larvae in estuaries: Within-tide variability at inlet and immigration

The larvae of winter spawning fishes immigrating through Beaufort Inlet into the Pamlico Sound estuarine system (North Carolina, United States) were passively sampled during 14 flood tides and nine of the following ebb tides. Five taxa were abundant in the catches. Pelagic species were represented by Atlantic menhaden, Brevoortia tyrannus. Nonpelagic taxa were represented by Atlantic croaker, Micropogonias undulatus, spot, Leiostomus xanthurus, pinfish, Lagodon rhomboides, and flatfishes of the genus Paralichthys. The sampling was continuous and the sample duration varied between 4 min and 32 min. The longest samples furnished the most accurate and precise estimates of the mean tidal abundance. Sampling 10 min each hour of the tide was the most efficient protocol for determining the mean tidal abundance. The abundance patterns was shown to differ according to the pelagic or nonpelagic behavior of the larvae. Analyses suggested the nonpelagic taxa rely on astronomical tides and vertical migrations synchronous with the direction of the tide flow to be transported upstream in the estuary. These larvae were not dependent upon the strength of the tide to penetrate the inlet. In contrast, menhaden larvae seemed to rely primarily on strong food tides to enter the estuarine area, probably because the vertical positioning of the species within the water column is not dependent upon the direction of the tide. However, if larvae were present outside of the inlet, strong flood tides indiscriminately brought pelagic and nonpelagic species into the estuary.     

Phytoplankton Biomass and Production in Subtropical Hong Kong Waters: Influence of the Pearl River Outflow

The size-fractionated phytoplankton biomass and primary production were investigated in four contrasting areas of Hong Kong waters in 2006. Phytoplankton biomass and production varied seasonally in response to the influence of the Pearl River discharge. In the dry season, the phytoplankton biomass and production were low (<42 mg chl m⁻² and <1.8 g C m⁻² day⁻¹) in all four areas, due to low temperatures and dilution and reduced light availability due to strong vertical mixing. In contrast, in the wet season, in the river-impacted western areas, the phytoplankton biomass and production increased greater than five-fold compared to the dry season, especially in summer. In summer, algal biomass was 15-fold higher than in winter, and the mean integrated primary productivity (IPP) was 9 g C m⁻² day⁻¹ in southern waters due to strong stratification, high temperatures, light availability, and nutrient input from the Pearl River estuary. However, in the highly flushed western waters, chl a and IPP were lower (<30 mg m⁻² and 4 g C m⁻² day⁻¹, respectively) due to dilution. The maximal algal biomass and primary production occurred in southern waters with strong stratification and less flushing. Spring blooms (>10 μg chl a L⁻¹) rarely occurred despite the high chl-specific photosynthetic rate (mostly >10 μg C μg chl a ⁻¹ day⁻¹) as the accumulation of algal biomass was restricted by active physical processes (e.g., strong vertical mixing and freshwater dilution). Phytoplankton biomass and production were mostly dominated by the >5-μm size fraction all year except in eastern waters during spring and mostly composed of fast-growing chain-forming diatoms. In the stratified southern waters in summer, the largest algal blooms occurred in part due to high nutrient inputs from the Pearl River estuary.     

Microphytobenthos: The ecological role of the “secret garden” of unvegetated,shallow-water marine habitats. I. Distribution,abundance and primary production

The microphytobenthos consists of unicellular eukaryotic algae and cyanobacteria that grow within the upper several millimeters of illuminated sediments, typically appearing only as a subtle brownish or greenish shading. The surficial layer of the sediment is a zone of intense microbial and geochemical activity and of considerable physical reworking. In many shallow ecosystems, the biomass of benthic microalgae often exceeds that of the phytoplankton in the overlying waters. Direct comparison of the abundance of benthic and suspended microalgae is complicated by the means used to measure biomass and by the vertical and horizontal distribution of the microphytobenthos in the sediment. Where biomass has been estimated as chlorophyll a, there may be negligible to large (40%) error due to interference by degradation products, except where chlorophyll is measured by high-performance liquid chromatography. The vertical distribution of microphytobenthos, aside from mat-forming species, is determined by the opposing effects of their vertical migration, which tends to concentrate them near the surface, and physical mixing by overlying currents, which tends to cause an even vertical distribution through the mixed layer of sediment. Uncertainties in vertical distribution are compounded by frequently patchy horizontal distribution. Under-sampling on small (<1 m) scales can lead to errors in the estimate that are comparable to the ranges of seasonal and geographic variation. These uncertainties are compounded by biases in the techniques used to estimate production by the microphytobenthos. In most environments studied, biomass (as chlorophyll a) and light availability appear to be the principal determinants of benthic primary production. The effect of variable light intensities on integral production can be described by a functional response curve. When normalized to the chlorophyll content of the surficial sediment, the residual variation in the data described by the functional response curve is due to changes in the chlorophyll-specific response to irradiance. Production by the benthos is often a significant fraction of production in the water column and microphytobenthos may contribute directly to water column production when they are resuspended. Thus on both the basis of biomass and biogeochemical reactivity, benthic microalgae play significant roles in system productivity and trophic dynamics, as well as such habitat characteristics as sediment stability. *** DIRECT SUPPORT *** A01BY074 00003     

Seasonal succession and microlamina formation in a meromictic lake displaying varved sediments

In a small meromictic lake near Toronto, Canada, a mass mortality of photosynthetic bacteria followed the ventilation of the chemocline during fall (autumn) and resulted in 3–8 g m^-2 day^-1 of organic matter being deposited as a dark layer in sediment traps which were suspended in the permanently anaerobic zone. This mass mortality of photosynthetic bacteria occurred in late autumn following the annual thermal destratification of the lake's mixolimnion. Wind mixing during this period of homeothermy resulted in the introduction of low levels of dissolved oxygen into the lake's chemocline. The ensuing mass mortality of photosynthetic bacteria resulted in the release of elemental sulphur as the sulphur-rich bacteria decomposed and sank to the bottom of the lake. The ferrous ions in the water below a depth of 15 m in Crawford Lake reacted with this sulphur to form black ferrous sulphides and pyrite which formed a dark microlamina on the lake floor. Each dark microlamina was overlain by a light coloured (calcite-rich) layer which was deposited each spring and summer during the 3 yr period of this study. The mechanism of microlamina formation elucidated here has been based on the examination of bi-weekly sediment trap information. This approach has permitted an explanation of the mechanisms by which specific events such as calcite precipitation and phytoplankton seasonal succession are transcribed into the sediment record.     

Diurnal and Tidal Variability in the Photobiology of the Seagrass Halophila johnsonii in a Riverine Versus Marine Habitat

The threatened seagrass Halophila johnsonii grows intertidally to 3 m deep in river-influenced and marine-influenced habitats. In this study, environmental parameters and photosynthetic characteristics of H. johnsonii were measured hourly for populations from adjacent riverine and marine habitats under opposite tidal regimes (high tide at midday, low tide at midday). The two populations exhibited habitat-specific diurnal responses, which indicate long-term acclimatization to their different environments. During periods with similar bottom irradiances, effective photochemical efficiencies and chlorophyll concentrations were comparatively greater in the riverine population, indicative of low-light acclimation. In addition, ultraviolet pigment absorbance (340–345 nm) was generally greater in the riverine plants and it generally increased following ebb tides and decreasing salinity, suggesting a stress response. Multivariate analyses indicated that photosynthetic characteristics were most dissimilar when environmental conditions were most dissimilar, i.e., riverine plants when low tide occurred at midday compared to marine plants when high tide occurred at midday. Salinity, photosynthetically active radiation, and optical water quality (K _0PAR, S _CDOM, and a ₄₁₂) were most correlated with variability in photosynthetic characteristics. As there is no significant genetic variation among populations of H. johnsonii, the photosynthetic characteristics of the riverine and marine populations we examined reflect acclimation to their respective habitats through a highly phenoplastic physiology.     

Mixing behavior of dissolved organic carbon and its potential biological significance in the Pawcatuck River Estuary

The distributions of dissolved organic carbon (DOC), phytoplankton biomass (as measured by in vivo fluorescence), total nitrogen and phosphorus, and light extinction were observed on 10 cruises during 1989 and 1990 in the Pawcatuck River estuary located in southern Rhode Island. In the lower estuary, the distance of peak phytoplankton biomass from the head of the estuary was positively correlated with river discharge while the magnitude of the peak increased with decreasing discharge. High light-extinction appeared to limit the accumulation of biomass in the upper estuary. Variability in light extinction was largely (50%) explained by variation in the concentration of DOC. Salinity versus constituent plots suggested that DOC behaved nonconservatively in the estuary. These observational data indicate that the mixing behavior of DOC in the estuary influences light extinction and thus may limit accumulation of phytoplankton biomass in the upper estuary. This interpretation of observational data was supported by experimental work that demonstrated the significant contribution of DOC to light extinction, and by measurements, of phytoplankton productivity that showed greater light limitation in the upper estuary.     

A radioisotope tracer investigation to determine the direction of groundwater movement adjacent to a tidal creek during spring and neap tides

A radioisotope tracer (⁸²Br) was injected into a sand aquifer adjacent to a tidal creek at Hat Head, New South Wales, Australia. The injection was timed to coincide with the falling limb of a spring tide in August 2001 and was repeated in July 2002 during a period of neap tides. The tracer movement was detected using gamma logging and fixed gamma detectors in a bore 0.9 m from an injection bore and in a line approximately perpendicular to the creek. Movement of the tracer was detected by comparing measured gamma activity with calibrated activities determined under laboratory conditions. Net movement of the tracer indicated approximately 0.001 m/day laterally towards the creek and 0.07 m/day vertically upward during spring tide conditions. This pattern is reversed during neap tide conditions with little net vertical movement but horizontal movement of 0.15 m/day. The measurements indicated an oscillatory motion coinciding with the tide but lagging the tide by approximately 4.5–6.5 h. The vertical flow during spring tides indicates that vertical movement of the saline interface occurs and results in mixing of different water types beneath the banks of the creek.     

Adapting the CHEMTAX method for assessing phytoplankton taxonomic composition in Southeastern U.S. estuaries

CHEMTAX is a matrix factorization program used to derive taxonomic structure of phytoplankton from photosynthetic pigment vitios. The program was originally developed from and applied to the analysis of oceanic phytoplankton assemblages. We found that application of the original CHEMTAX reference matrix to southeastern United States estuarine systems produced inaccurate results, as verified by microscopy. Modification of the matrix, based primarily on the pigment ratios of 33 estuarine isolates, improved the predictive capabilities of CHEMTAX for our samples. Limitations of the method included an overstimation of diatom biomass (due to the inability to differentiate diatoms from taxa with chloroplasts derived from diatom endosymbionts, notably some dinoflagellates) and a tendency to exclude some raphidophyte species. In complement with microscopic verification, the method was shown to improve assessment of phytoplankton taxonomic composition.     

The influence of phytoplankton community composition on primary productivity along the riverine to freshwater tidal continuum in the San Joaquin River,California

Differences in phytoplankton community composition along a riverine to, freshwater tidal continuum was an important factor affecting the primary productivity and quantity of phytoplankton biomass available to the San Francisco Estuary food web downstream. The relative contribution of riverine and freshwater tidal phytoplankton was determined using measurements of primary productivity, respiration, and phytoplankton species composition along a riverine to freshwater tidal gradient in the San Joaquin River, one of two major rivers that flow into, the San Francisco Estuary. Chla-specific net primary productivity was greater in the freshwater tidal habitat and was correlated with both a higher growth efficiency and maximum growth potential compared with the river upstream. Cluster analysis indicated these differences in growth parameters were associated with differences in species composition, with greater percent diatom and green algal species biomass upstream and flagellate biomass downstream. Correlation between the chla specific net productivity and phytoplankton species composition suggested the downstream shift from riverine diatom and green algal species to flagellate species contributed to the seaward increase in net primary productivity. Environmental conditions, such as specific conductance and water transparency, may have influenced primary productivity along the riverine to freshwater tidal continuum through their effect on both species composition and growth rate. Data suggest light was not the sole controlling factor for primary productivity in this highly turbid estuary; phytoplankton growth rate did not increase when riverine plankton communities from low light conditions upstream were exposed to higher light conditions downstream. This study suggests that the availability of phytoplankton biomass to the estuarine food web may be influenced by management of both phytoplankton growth and community composition along the riverine to freshwater tidal continuum.     

美国阿巴拉契亚山脉芬卡苏地区奥陶纪海底水道中的内潮汐沉积

本文论述了在世界范围内首次鉴别出的新的沉积类型--内潮汐沉积,发现于美国弗吉尼亚州芬卡苏地区奥陶纪深水海底水道充填沉积中。已识别出两种相:①双向交错纹理极细砂岩相,以发育分别向古水道上方和下方倾斜的双向交错纹理为特征,被归因于内潮汐作用沉积的产物。②单向交错层和交错纹理中至细砂岩相,发育向古水道上方倾斜的低角度板状交错层和交错纹理,被解释为叠加有内波的内潮汐沉积物。据沉积相层序分析,内潮汐沉积形成于海平面上升、粗屑重力流受到抑制的时期。     

Suspended-Sediment Impacts on Light-Limited Productivity in the Delaware Estuary

The Delaware Estuary has a history of high anthropogenic nutrient loadings but has been classified as a high-nutrient, low-growth system due to persistent light limitation caused by turbidity. While the biogeochemical implications of light limitation in turbid estuaries have been well-studied, there has been minimal effort focused on the connectivity between hydrodynamics, sediment dynamics, and light limitation. Our understanding of sediment dynamics in the Delaware Estuary has advanced significantly in the last decade, and this study describes the impact of spatiotemporal variability of the estuarine turbidity maximum (ETM) on light-limited productivity. This analysis uses data from eight along-estuary cruises from March, June, September, and December 2010 and 2011 to evaluate the impact of the turbidity maximum on production. Whereas the movement of the ETM is controlled primarily by river discharge, the structure of the ETM is modulated by stratification, which varies with both river discharge and spring-neap conditions. We observe that the ETM’s location and structure control spatial patterns of light availability. To evaluate the relative contributions of river discharge and spring-neap variability to the location of phytoplankton blooms, we develop an idealized two-dimensional Regional Ocean Modeling System (ROMS) numerical model. We conclude that high river flows and neap tides can drive stratification that is strong enough to prevent sediment from being resuspended into the surface layer, thus providing light conditions favorable for primary production. This study sheds light on the role of stratification in controlling sediment resuspension and promoting production, highlighting the potential limitations of biogeochemical models that neglect sediment processes.