Inorganic and Organic Nitrogen Uptake by Phytoplankton and Bacteria in Hong Kong Waters

Measurements of uptake rates of inorganic (NO₃⁻ and NH₄⁺) and organic (urea, glycine, and glutamic acid) N, and indirect estimates of total N uptake by bacteria, were made in four contrasting environments in sub-tropical Hong Kong waters in summer of 2008. In addition, the effects of several days of rain on N uptake rates were studied in eastern waters. Although ambient NO₃⁻ was the dominant form of N in Hong Kong waters, the dominant N form taken up by phytoplankton was usually NH₄⁺ and organic N, including urea and amino acids, rather than NO₃⁻. Hence, because of the low NO₃⁻ uptake, there was a long turnover time for NO₃⁻ (100 days), and most of the NO₃⁻ was apparently transported offshore into deeper shelf waters. In eastern waters where NH₄⁺ was undetectable, NO₃⁻ uptake rates were positively correlated with phytoplankton cell size. In contrast, potential rates of glutamic acid uptake were negatively correlated with phytoplankton size. N uptake rates in the smaller size fraction (0.7–2.8 μm) were less affected by the rain event, and smaller phytoplankton appeared to outcompete larger cells after several days of rain. The surface (PN)-specific N uptake rates in the >8-μm fraction decreased from 0.02 to 0.0001 h⁻¹, while the smaller fraction only exhibited a one- to threefold decrease after the rainfall. In contrast, bacterial production and N uptake were not affected by the rain event, and bacteria N uptake accounted for 10–60% of the total N uptake by phytoplankton.     

Blooms of Dinoflagellate Mixotrophs in a Lower Chesapeake Bay Tributary: Carbon and Nitrogen Uptake over Diurnal,Seasonal, and Interannual Timescales

A multi-year study was conducted in the eutrophic Lafayette River, a sub-tributary of the lower Chesapeake Bay during which uptake of inorganic and organic nitrogen (N) and C compounds was measured during multiple seasons and years when different dinoflagellate species were dominant. Seasonal dinoflagellate blooms included a variety of mixotrophic dinoflagellates including Heterocapsa triquetra in the late winter, Prorocentrum minimum in the spring, Akashiwo sanguinea in the early summer, and Scrippsiella trochoidea and Cochlodinium polykrikoides in late summer and fall. Results showed that no single N source fueled algal growth, rather rates of N and C uptake varied on seasonal and diurnal timescales, and within blooms as they initiated and developed. Rates of photosynthetic C uptake were low yielding low assimilation numbers during much of the study period and the ability to assimilate dissolved organic carbon augmented photosynthetic C uptake during bloom and non-bloom periods. The ability to use dissolved organic C during the day and night may allow mixotrophic bloom organisms a competitive advantage over co-occurring phytoplankton that are restricted to photoautotrophic growth, obtaining N and C during the day and in well-lit surface waters.     

Phosphorus Burial in Sediments Along the Salinity Gradient of the Patuxent River,a Subestuary of the Chesapeake Bay (USA)

We used a sequential extraction technique and ²¹⁰Pb dating to determine the chemical form and amount of particulate phosphorus (PP) that is retained during burial in 1-m-long sediment cores collected along a salinity gradient from tidal freshwater to the mesohaline waters of the Patuxent River, a subestuary of the Chesapeake Bay. PP buried in the study sites with salinity values ≤3 was similar in concentration and form to PP entering the Patuxent from the watershed, suggesting efficient sequestration by the sediments at these low-salinity sites. PP extracted with citrate–dithionite–bicarbonate was the dominant form of PP at all salinities and all depths, and organic-P was the second most abundant fraction. We estimated that 81% of PP entering from the watershed is trapped in the sediments of the upper Patuxent subestuary and that the subtidal sediments retain three times as much PP as the marshes adjacent to the study sites.     

Comparison of the Salinity Structure of the Chesapeake Bay,the Delaware Bay and Long Island Sound Using a Linearly Tapered Advection-Dispersion Model

Long records of monthly salinity observations along the axis of Chesapeake Bay, Delaware Bay, and Long Island Sound are used to test a simple advection–dispersion model of the salt distribution in linearly tapered estuaries developed in a previous paper. We subdivide each estuary into three to five segments, each with linear taper allowing a distributed input of fresh water, and evaluate the dispersion in each segment. While Delaware Bay has weak dispersion and a classical sigmoidal salinity structure, Long Island Sound and Chesapeake Bay are more dispersive and have relatively small gradients in the central stretches. Long Island Sound is distinguished by having a net volume and salt flux out of its low-salinity end resulting in a smaller range of salinity and increasing axial gradients at its head rather than the usual asymptotic approach to zero salinity. Estimates of residence times based on model transport coefficients show that Long Island Sound has the most rapid response to fresh-water flux variations. It also has the largest amplitude cycle in river discharge fluctuation. In combination, these cause the large seasonal variation in the salinity structure relative to interannual variability in Long Island Sound as compared with Chesapeake Bay and Delaware Bay.     

Potential Salinity and Temperature Futures for the Chesapeake Bay Using a Statistical Downscaling Spatial Disaggregation Framework

Estuaries are productive and ecologically important ecosystems, incorporating environmental drivers from watersheds, rivers, and the coastal ocean. Climate change has potential to modify the physical properties of estuaries, with impacts on resident organisms. However, projections from general circulation models (GCMs) are generally too coarse to resolve important estuarine processes. Here, we statistically downscaled near-surface air temperature and precipitation projections to the scale of the Chesapeake Bay watershed and estuary. These variables were linked to Susquehanna River streamflow using a water balance model and finally to spatially resolved Chesapeake Bay surface temperature and salinity using statistical model trees. The low computational cost of this approach allowed rapid assessment of projected changes from four GCMs spanning a range of potential futures under a high CO₂ emission scenario, for four different downscaling methods. Choice of GCM contributed strongly to the spread in projections, but choice of downscaling method was also influential in the warmest models. Models projected a ~2–5.5 °C increase in surface water temperatures in the Chesapeake Bay by the end of the century. Projections of salinity were more uncertain and spatially complex. Models showing increases in winter-spring streamflow generated freshening in the Upper Bay and tributaries, while models with decreased streamflow produced salinity increases. Changes to the Chesapeake Bay environment have implications for fish and invertebrate habitats, as well as migration, spawning phenology, recruitment, and occurrence of pathogens. Our results underline a potentially expanded role of statistical downscaling to complement dynamical approaches in assessing climate change impacts in dynamically challenging estuaries.     

Responses of Estuarine Bacterioplankton,Phytoplankton and Zooplankton to Dissolved Organic Carbon (DOC) and Inorganic Nutrient Additions

The response of planktonic bacteria and phytoplankton to various additions of dissolved organic carbon (DOC) as glucose, with and without inorganic nutrients (nitrogen and phosphorus), was tested in the upper to mid Hunter Estuary, Australia. In situ microcosms (1.25 L) were performed at two sites with varying salinities over three seasons. Analysis of variance showed a significant difference among control and treatments for all seasons for the bacterial, dissolved oxygen and chlorophyll a responses (P < 0.05). A significant interaction between treatment and site was found in autumn for dissolved oxygen, autumn and spring for bacterial and spring for chlorophyll a responses. At both sites for each season, and on nearly all occasions, bacterial surface area was enhanced by DOC addition as indicated by both increased bacterial abundance and dissolved oxygen utilisation. DOC in combination with inorganic nutrients sometimes further enhanced the bacterial response compared to DOC alone. Inorganic nutrients alone did not enhance growth of the heterotrophic bacterioplankton. Addition of DOC alone led to decreased chlorophyll a relative to the control, probably due to competition for limited inorganic nutrients with the bacterioplankton DOC non-limiting conditions. Results suggest that the heterotrophic community was limited by DOC at both sites and across seasons. An experiment with a larger volume (70 L), performed over a longer time, compared a control with DOC addition. Increased bacterial biomass as a result of DOC addition occurred at day 2. Chlorophyll a did not significantly differ between treatments. An increase in zooplankton density was recorded in the DOC treatment relative to the control at day 10. This study supports the contention that increased DOC delivery with river inflows through environmental flow allocations will stimulate heterotrophic bacterioplankton production in the upper Hunter Estuary.     

Anthropogenic Nutrient Sources Supplied to a Chesapeake Bay Tributary Support Algal Growth: A Bioassay and High-Resolution Mass Spectrometry Approach

Three anthropogenic sources (urban, soil, and industrial runoff) were characterized for bulk nutrient and dissolved organic matter (DOM) composition using wet chemistry and Fourier transform ion cyclotron resonance mass spectrometry. Each source was unique based on its chemical composition. Dissolved inorganic nitrogen (N) comprised 91, 60, and 20 % of the total N pool in the soil, urban, and industrial sources, respectively. The DOM composition was dominated by terrestrial compounds in the soil, condensed hydrocarbons, lipids and proteins in the urban, and lipid-like compounds in the industrial source. A York River (VA) phytoplankton assemblage, dominated by Cochlodinium polykrikoides, was amended with the sources during a 7-day bioassay. There was a doubling of chlorophyll a and/or cell concentrations within 2 days, in the +Urban and +Soil treatments. The + Industrial treatment supported algal growth, but increases in cell abundances were only statistically significant at the end of the experiment (days 5–7), suggesting that this material was less labile to the original York River community than the other anthropogenic nutrient sources, on the relatively short timescale of the study.     

Sources, input pathways, and distributions of Fe, Cu, and Zn in a Chesapeake Bay tidal freshwater marsh

Tidal freshwater marshes exist at the interface between watersheds and estuaries, and thus may serve as critical buffers protecting estuaries from anthropogenic metal pollution. Bi-weekly samples of newly deposited marsh sediments were collected and analyzed for Cu, Zn, and Fe concentrations over 21 months from July 1995 to March 1997 in five distinct habitats at the head of Bush River, Maryland. Bi-weekly anthropogenic metal enrichments ranged from 0.9–4.7. Anthropogenic excess metal loadings averaged over 1996 ranged from 6–306 and 25–1302 μg cm⁻² year⁻¹ between sites for Cu and Zn, respectively. Based on Fe-normalized trace metal signatures, Susquehanna River sediment does not significantly contribute to upper Bush River. Organic matter was found to dilute total metal concentrations, whereas past studies suggested organics enhance labile metal content. Analysis of metal input pathways shows that marsh metals are primarily imported from nearby subtidal accumulations of historic watershed material by tidal flushing. Received: 29 April 1999 / Accepted: 7 December 1999     

Spectral Irradiance and Phytoplankton Community Composition in a Blackwater-Dominated Estuary,Winyah Bay,South Carolina,USA

We investigated spatial and temporal relationships between spectral irradiance and phytoplankton community composition in the blackwater-influenced estuary Winyah Bay, South Carolina. Upstream, high concentrations of chromophoric dissolved organic matter (CDOM) absorbed blue wavelengths, resulting in a predominantly red light field. Green light prevailed downstream near the lower-CDOM coastal ocean, and phytoplankton community composition was distinct from upstream and mid-estuarine communities. Diatoms were abundant throughout the estuary in January, August, and October, cryptophytes dominated in July, and chlorophytes were abundant in December 2006. Only diatoms and chlorophytes showed significant covariation with the spectral attenuation coefficient (k(λ)): Chlorophytes showed positive relationships with k(442) (blue light) while diatoms were negatively correlated with k(442) and k(490) (violet to blue). Phytoplankton community composition in Winyah Bay appears to be driven by strong horizontal flow rather than gradients in spectral irradiance, but results indicate that water color is likely to play a greater role in blackwater-influenced estuaries with longer residence times.     

Nutrient Inputs, Phytoplankton Response, and CO2 Variations in a Semi-Enclosed Subtropical Embayment, Kaneohe Bay, Hawaii

The marine shelf areas in subtropical and tropical regions represent only 35% of the total shelf areas globally, but receive a disproportionately large amount of water (65%) and sediment (58%) discharges that enter such environments. Small rivers and/or streams that drain the mountainous areas in these climatic zones deliver the majority of the sediment and nutrient inputs to these narrow shelf environments; such inputs often occur as discrete, episodic introductions associated with storm events. To gain insight into the linked biogeochemical behavior of subtropical/tropical mountainous watershed-coastal ocean ecosystems, this work describes the use of a buoy system to monitor autonomously water quality responses to land-derived nutrient inputs and physical forcing associated with local storm events in the coastal ocean of southern Kaneohe Bay, Oahu, Hawaii, USA. The data represent 2.5 years of near-real time observations at a fixed station, collected concurrently with spatially distributed synoptic sampling over larger sections of Kaneohe Bay. Storm events cause most of the fluvial nutrient, particulate, and dissolved organic carbon inputs to Kaneohe Bay. Nutrient loadings from direct rainfall and/or terrestrial runoff produce an immediate increase in the N:P ratio of bay waters up to values of 48 and drive phytoplankton biomass growth. Rapid uptake of such nutrient subsidies by phytoplankton causes rapid declines of N levels, return to N-limited conditions, and subsequent decline of phytoplankton biomass over timescales ranging from a few days to several weeks, depending on conditions and proximity to the sources of runoff. The enhanced productivity may promote the drawing down of pCO₂ and lowering of surface water column carbonate saturation states, and in some events, a temporary shift from N to P limitation. The productivity-driven CO₂ drawdown may temporarily lead to air-to-sea transfer of atmospheric CO₂ in a system that is on an annual basis a source of CO₂ to the atmosphere due to calcification and perhaps heterotrophy. Storms may also strongly affect proximal coastal zone pCO₂ and hence carbonate saturation state due to river runoff flushing out high pCO₂ soil and ground waters. Mixing of the CO₂-charged water with seawater causes a salting out effect that releases CO₂ to the atmosphere. Many subtropical and tropical systems throughout the Pacific region are similar to Kaneohe Bay, and our work provides an important indication of the variability and range of CO₂ dynamics that are likely to exist elsewhere. Such variability must be taken into account in any analysis of the direction and magnitude of the air?Csea CO₂ exchange for the integrated coastal ocean, proximal and distal. It cannot be overemphasized that this research illustrates several examples of how high frequency sampling by a moored autonomous system can provide details about ecosystem responses to stochastic atmospheric forcing that are commonly missed by traditional synoptic observational approaches. Finally, the work exemplifies the utility of combining synoptic sampling and real-time autonomous observations to elucidate the biogeochemical and physical responses of coastal subtropical/tropical coral reef ecosystems to climatic perturbations.     

Climate Regime Shift and Phytoplankton Phenology in a Macrotidal Estuary: Long-Term Surveys in Gyeonggi Bay,Korea

Phytoplankton are finely tuned to the seasonality of their environment, and shifts in the timing of phytoplankton phenology provide some of the most compelling evidence that species and ecosystems are being influenced by global climate change. Evaluation of a 50-year dataset of climatic parameters, a 12-year dataset of nutrients, and a 15-year dataset of phytoplankton biomass and composition in Gyeonggi Bay of the Yellow Sea revealed that the climate has shifted from a cold to a warm phase in the last few decades and that recent warm climatic and eutrophication trends are affecting phytoplankton biomass, phenology, and structure. In Gyeonggi Bay, climatic and ecological regime shifts were detected during the 1990s and 2000s, respectively. The asymmetric relationship between climate and ecological regime shift probably depends on macrotidal system configurations that are more resistant to environmental perturbation. The spring diatom blooms observed in the 1990s have moved forward to winter blooms in the 2000s because early winter warming has been induced by higher light and precipitation, which has removed prior light limitation and control of diatom blooms. Summer blooms are triggered by enhanced nutrients, which leads to frequent and recurring dominance of dinoflagellates and diatoms, supporting the hypothesis that summer phenology might be brought about by local processes such as eutrophication, as well as by climate change. Overall, differences in phenological trends can be brought about by differences in the underlying drivers of seasonality. Based on the results of this study, perspectives are drawn regarding the utility of phenology as an organizing principle for analysis of pelagic ecosystems.     

Temporal patterns of feeding by blue crabs (Callinectes sapidus) in a tidal-marsh creek and adjacent seagrass meadow in the lower Chesapeake Bay

A 24-h study of blue crab feeding periodicity was conducted concurrently in a tidal marsh creek and adjacent seagrass meadow in the lower Chesapeake Bay. Crabs from the grassbed tended to have fuller guts than crabs from the marsh creek. In the grassbed, a weak trend toward nocturnal feeding was observed, with an apparent peak at dusk. During the day, crabs were not easily observed and were assumed to be feeding beneath the eelgrass canopy; at night crabs fed in the canopy. In the marsh creek, feeding was related to the tidal cycle, with guts being fullest at high tide and decreasing to lows just prior to the next high tide. This study suggests the potential importance of habitat on blue crab feeding patterns.     

A rapid procedure for the determination of thorium,uranium, cadmium and molybdenum in small sediment samples by inductively coupled plasma-mass spectrometry: application in Chesapeake Bay

This paper describes a rapid procedure that allows precise analysis of Mo, Cd, U and Th in sediment samples as small as 10 mg by using a novel approach that utilizes a “pseudo” isotope dilution for Th and conventional isotope dilution for Mo, Cd and U by ICP-MS. Long-term reproducibility of the method is between 2.5 and 5% with an advantage of rapid analysis on a single digestion of sediment sample and the potential of adding other elements of interest if so desired. Application of this method to two piston cores collected near the mouth of the Patuxent River in Chesapeake Bay showed that the accumulation of authigenic Mo and Cd varied in response to the changing bottom water redox conditions, with anoxia showing consistent oscillations throughout both pre-industrial and industrial times. Accumulation of authigenic U shows consistent oscillations as well, without any apparent increase in productivity related to anoxic trends. Degrees of Mo and Cd enrichment also inversely correlate to halophilic microfaunal assemblages already established as paleoclimate proxies within the bay indicating that bottom water anoxia is driven in part by the amount of freshwater discharge that the area receives.     

SAV Communities of Western Biscayne Bay,Miami, Florida,USA: Human and Natural Drivers of Seagrass and Macroalgae Abundance and Distribution Along a Continuous Shoreline

Nearshore benthic habitats of Biscayne Bay fit the prediction of communities at risk due to their location adjacent to a large metropolitan center (Miami) and being influenced by changes in hydrology through the activities of the Comprehensive Everglades Restoration Plan (CERP). We examine whether the proposed programmatic expansion of mesohaline salinities through the introduction of additional fresh water would result in: (1) increases in seagrass cover; (2) expansion in the distribution and cover of Halodule; and (3) a reduction in the dominance of Thalassia, as hypothesized by CERP. Seagrasses were present at 98 % of sites where they covered 23 % of the bottom. Salinity was the only physical variable with a significant relationship to the occurrence of all SAV taxa. Occurrence of Thalassia, Halimeda, and Penicillus increased significantly with increasing salinity, but Halodule, Syringodium, Laurencia, Udotea, Batophora, Caulerpa, and Acetabularia showed a significant negative relationship with salinity. Mesohaline habitats had higher cover of seagrass and Halodule, and reduced dominance by Thalassia. Thus, we expect increases in the extent of mesohaline habitats to achieve the established CERP goals. We also examined the nutrient content of seagrass blades to evaluate whether: (1) nutrient availability is higher in areas close to canal discharges; and (2) tissue nutrient levels are related to seagrass abundance. The low abundance of Thalassia along the shoreline is not only due to its exclusion from low-salinity environments but also by higher nutrient availability that favors Halodule. Percent N and P, and N:P ratios in seagrass tissue suggest that Biscayne Bay receives high N inputs and is P-limited. Thus, increased P availability may facilitate an expansion of Halodule. The data presented suggest that increased mesohaline salinities will increase seagrass abundance and support co-dominance by Halodule and Thalassia as hypothesized, but raise concerns that current high N availability and increases in P may prompt a shift away from seagrass-dominated to algal-dominated communities under scenarios of enhanced fresh water inputs.     

中国南极长城湾及附近海区1993/1994年度夏季表层水样无机氮、磷酸盐的浓度及其分布状况(英)

The concentrations and distributions of four species of inorganic nutrient salts in surface sea water of Chinese Great Wall Bay and its adjacent sea area, Antarctica were surveyed during austral summers of 1993～1994.The results obtained are as follows:The general concentrations of NH4-N, NO3-N, NO2-N and PO4-P are 2. 13, 7. 07, 0. 74 and 1. 12 μg. din-3, respectively. Generally speaking, the concentrations are higher inside the Bay than those　 outside and the higher values of those inorganic salts often appear in December. The time for the station　where their higher and lower concentrations appear are not completely the same. The descending order　of the magnitudes of ΣN/P value according to the arrangement monthly is: Dec. Feb. Jan.. The　 variations of water temperature are mostly consist with the concentrations of NH4-N, PO4-P and ΣN/P, but not often with NO2-N. The low concentrations of nutrient salts as shown in some stations may be related with absorption by phytoplankton, perhaps including autotrophic bacteria.The results suggest that the area surveyed has a typical characteristic of an inner shallow water bay, sub-Antarctica. The nutrients needed for phytoplankton are sufficient, and the Bay surveyed is still in a normal condition.     

Flow and nutrient dynamics in a subterranean estuary (Waquoit Bay, MA, USA): Field data and reactive transport modeling

A two-dimensional (2D) reactive transport model is used to investigate the controls on nutrient (, , PO₄) dynamics in a coastal aquifer. The model couples density-dependent flow to a reaction network which includes oxic degradation of organic matter, denitrification, iron oxide reduction, nitrification, Fe²⁺ oxidation and sorption of PO₄ onto iron oxides. Porewater measurements from a well transect at Waquoit Bay, MA, USA indicate the presence of a reducing plume with high Fe²⁺, , DOC (dissolved organic carbon) and PO₄ concentrations overlying a more oxidizing -rich plume. These two plumes travel nearly conservatively until they start to overlap in the intertidal coastal sediments prior to discharge into the bay. In this zone, the aeration of the surface beach sediments drives nitrification and allows the precipitation of iron oxide, which leads to the removal of PO₄ through sorption. Model simulations suggest that removal of through denitrification is inhibited by the limited overlap between the two freshwater plumes, as well as by the refractory nature of terrestrial DOC. Submarine groundwater discharge is a significant source of to the bay.     

Effects of Increased Salinity and Inundation on Inorganic Nitrogen Exchange and Phosphorus Sorption by Tidal Freshwater Floodplain Forest Soils, Georgia (USA)

We investigated the effects of increasing salinity and inundation on inorganic N exchange and P sorption/precipitation in soils of tidal freshwater floodplain forests (TFFF) of coastal Georgia, USA. Our objectives were to better understand how sea level rise, increasing inundation, and saltwater intrusion will affect the ability of TFFFs to retain nitrogen (N) and phosphorus (P). We collected soil cores (0–5 cm) from three TFFFs that do not currently experience saltwater intrusion and from one TFFF currently experiencing saltwater intrusion and measured NH₄-N exchange and PO₄-P removal over five simulated 6-h tidal cycles using nutrient-enriched freshwater (30 μM NH₄-N and 5 μM PO₄-P). In a second experiment, we exposed soil cores to three salinities (0, 2, and 5) and two inundation depths (5 and 10 cm) using the same nutrient enrichment. When flooded with nutrient-enriched freshwater, soils from the three TFFFs that do not experience saltwater intrusion removed inorganic N and P in amounts ranging from 5.2 to 10.7 and 2.3 to 4.4 mg/m², respectively, and the TFFF soils experiencing saltwater intrusion removed 2.1 to 3.8 mg P/m². However, TFFF soils experiencing saltwater intrusion released inorganic N to the water column in amounts ranging from 7.1 to 67.5 mg/m². In the second experiment, soils from TFFFs not experiencing saltwater intrusion released NH₄-N to the water column when exposed to 2 and 5 salinity, and the amount of N released increased with salinity and number of tidal cycles. In contrast, the same TFFF soils sorbed two and three times more PO₄-P when exposed to 2 and 5 salinity than when exposed to 0 salinity. P removal on a mass basis was greater under 10 cm of inundation, but the efficiency of removal was greater under the 5 cm flooding depth. Our findings suggest that saltwater intrusion caused by sea level rise will promote N release into the water column through organic matter mineralization and/or ion exchange and may promote P sorption, or precipitation of P with metal cations. In addition, release of N and resulting increased N/P could exacerbate eutrophication of estuaries in the future.     

渤海湾西岸现代岸线钻孔记录的全新世沉积环境与相对海面变化

以渤海湾西岸现代岸线附近的NP3、CH110和BT113三个钻孔全新世岩心为研究对象,采用沉积岩石学、AMS ¹⁴C(accelerator mass spectrometry ¹⁴C,加速器质谱¹⁴C)测年、微体生物聚类分析等方法精细判别沉积相,重建渤海湾西岸全新世沉积演化历史,并利用微体生物组合分带对水深变化的指示,定量讨论全新世相对海面变化。结果表明:渤海湾西岸全新世受海陆交互作用影响,经历了沼泽-潮滩-浅海-前三角洲-三角洲前缘-三角洲平原环境的演化过程。全新世初始阶段,研究区中部和北部发育沼泽环境,南部未见沉积,与上更新统河流相沉积呈不整合接触。全新世早期,研究区潮滩环境发育。潮滩层厚度约1 m,历时数百至1千余年。至7000 cal BP前后水深增大,研究区进入浅海环境。约6000 cal BP,沿岸南北两端先后进入三角洲过渡环境,中部三角洲环境约开始于1500 cal BP。渤海湾西岸地区全新世的环境演化同时记录了该地区的相对海面变化:约10000 cal BP前后,渤海湾相对海平面已接近21.3~20.4 m。约8000 cal BP,相对海平面介于18.6~17.0 m。约6000 cal BP时相对海平面低于6.8 m,5000~1000 cal BP,相对海平面高于-2.5 m,1000~800 cal BP,相对海平面介于-1.3~-0.4 m。8000~5000 cal BP时,相对海面上升约15.0 m,上升速率达5 m/1 ka。     

液氮冷凝吸收热解-电感耦合等离子体质谱法测定岩石土壤沉积物中的溴碘

分析地质样品中的溴碘,目前常用的提取方法有半熔法、稀氨水密封溶样法和热解法,但由于元素含量低、易损失,样品分解和溴碘的提取过程是主要的误差来源。本文改进了传统热解法的吸收装置,用液氮冷凝吸收代替常规的碱溶液吸收,提取地质样品中的溴碘,用电感耦合等离子体质谱法测定其含量。以标准偏差的10倍计算,稀释倍数为50,溴碘的检出限分别为0.06μg/g、0.01μg/g,低于传统热解法和半熔法,略高于稀氨水密封溶样法;精密度(RSD)为6.4%~21.0%。本方法相对于传统的碱溶液吸收热解法,减少了碱试剂的引入,降低了基体空白和稀释倍数,提高了精密度,操作较半熔法简便,可作为稀氨水密封溶样法的一种补充方法。因此,对于土壤和水系沉积物,宜采用稀氨水密封溶样法;对于岩石以及采用稀氨水密封溶样法难以完全提取的样品,可采用本方法。     

Determining Spatial and Temporal Inputs of Freshwater,Including Submarine Groundwater Discharge,to a Subtropical Estuary Using Geochemical Tracers,Biscayne Bay,South Florida

Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr²⁺/Ca²⁺ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ ¹⁸O = −2.66‰, δD −7.60‰) similar to rainfall (δ ¹⁸O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ ¹⁸O = −0.46‰, δD = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr²⁺/Ca²⁺ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr²⁺/Ca²⁺ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the total fresh and saline water input.