On the low-frequency transport processes in a shallow coastal lagoon

The low-frequency transport processes in a small, shallow coastal lagoon (Indian River Bay, Delaware) are examined based on a set of data derived from tide gauges, near-bottom current meter measurements, and drifter releases. The subtidal sea-level fluctuations in the interior of the lagoon are forced primarily by the coastal sea-level fluctuations off the mouth of the inlet, which connects the lagoon with the coastal ocean. The effect of local wind plays a secondary role in modifying the coastally forced sea level inside the lagoon. Given the continuity constraint which links sea-level fluctuations to the depth and laterally integrated barotropic transport, the coastal pumping effect would be expected to be the dominant factor in controlling the subtidal barotropic exchange within the bay. However, the dominance of the coastal pumping effect on the barotropic exchange does not readily translate into the dominance of this effect on the transport and distribution of waterborne material in the bay at subtidal frequencies. The observed nearbottom subtidal current fluctuations are not coherent with the coastal sea-level fluctuations. The observed current is also much stronger than the barotropic current inferred from the continuity constraint. This suggests the presence of a depth-dependent flow field, with current in the upper layer fluctuating in opposite direction to that at depth. Furthermore, the observed near-bottom current also shows significant spatial variability within the bay. As for the mean current, the residual flow field shows distinctly different patterns between the surface and the bottom. The residual current at the surface exhibits a consistent mean flow out of the bay. At the bottom, the residual current shows a mean flow into the estuary in the upper part of the lagoon and a spatially variable flow in the lower part of the lagoon. A competition between gravitational circulation and tidally rectified current may contribute to the observed vertical and horizontal variabilities in the residual flow field.     

The fish community of a shallow tropical lagoon in Belize,Central America

Trawl collections indicate that the fish community of the Belize barrier reef lagoon is dominated numerically and in biomass by grunts (Haemulidae), especiallyHaemulon sciurus andHaemulon flavolineatum. Although the gear selected for small sizes, length frequency analysis indicated seasonality in recruitment of the dominant species of grunts. Apogonids and tetraodontiform fishes were also dominant components of the community. Most fishes collected were juveniles of species that occur as adults on the main reef, or were small species that are resident in the lagoon. Of three habitats sampled, the mangrove creek had the greatest relative abundance and biomass of fishes, followed by the seagrass bed and the sand-rubble zone. There were no significant seasonal differences in fish relative abundance or biomass. Community structure analysis indicated a uniqueness in the mangrove fish community. Diversity (H′) was high, and was due to high species richness and evenness of distribution of individuals among species. The Belize barrier reef lagoon serves as an important nursery habitat for juvenile fishes.     

Microphytobenthos contribution to nutrient-phytoplankton dynamics in a shallow coastal lagoon

Nutrient fluxes and primary production were examined in Lake Illawarra (New South Wales, Australia), a shallow (Z_mean=1.9 m) coastal lagoon with a surface area of 35 km², by intensive measurement of dissolved nutrients and oxygen profiles over a 22-h period. Rates of primary production and nutrient uptake were calculated for the microphytobenthos, seagrass beds, macroalgae, and pelagic phytoplankton. Although gross nutrient release rates to the water column and sediment pore waters were potentially high, primary production by microphytobenthos rapidly sequesters the re-mineralized nutrients so that net releases, averaged over times longer than a day, were low. Production in the water column was closely coupled with the relatively low sediment net nutrient release rates and detrital decomposition in the water column. Dissolved inorganic nitrogen and silica concentrations in the water column are drawn down at the beginning of the day. The system did not appear to be light limited so photosynthesis occurs as fast as the nutrients become available to the phytoplankton and microphytobenthos. We conjecture that microphytobenthos are the dominant primary producers and, as has been shown previously, that the nutrient uptake occurs in phase with the various stages of the diatom growth.     

Wind-driven sediment suspension controls light availability in a shallow coastal lagoon

Light availability is critically important for primary productivity in coastal systems, yet current research approaches may not be adequate in shallow coastal lagoons. Light attenuation in these systems is typically dominated by suspended sediment, while light attenuation in deeper estuaries is often dominated by phytoplankton. This difference in controls on light attenuation suggests that physical processes may exert a greater influence on light availability in coastal lagoons than in deeper estuaries. Light availability in Hog Island Bay, a shallow coastal lagoon on the eastern shore of Virginia, was determined for a summer and late fall time period with different wind conditions. We combined field measurements and a process-based modeling approach that predicts sediment suspension and light availability from waves and currents to examine both the variability and drivers of light attenuation. Total suspended solids was the only significant predictor of light attenuation in Hog Island Bay. Waves and currents in Hog Island Bay responded strongly to wind forcing, with bottom stresses from wind driven waves dominant for 60% of the modeled area for the late fall period and 24% of the modeled area for the summer period. Higher wind speeds in late fall than in summer caused greater sediment suspension (41 and 3 mg l⁻¹ average, respectively) and lower average (spatial and temporal) downwelling light availability (32% and 55%, respectively). Because of the episodic nature of wind events and the spatially variable nature of sediment suspension, conventional methods of examining light availability, such as fair-weather monitoring or single in situ recorders, do not adequately represent light conditions for benthic plants.     

Observations and simulations of water-sediment heat exchange in a shallow coastal lagoon

Water and sediment temperatures from Florida's Indian River Lagoon are used to investigate water-sediment heat energy exchanges and the resulting sub-bottom temperature fluctuations in a shallow-water estuarine environment. A 132-day study documents the response to cold-air outbreaks and spring warming. A one-dimensional, 120-layer numerical model simulates temperatures in the top 24 m of the sediment in response to observed water temperatures. Model simulations supplement sediment temperatures measured 50 and 95 cm below the water-sediment interface approximately weekly. Simulated water-sediment heat fluxes are generally between +0.075 (into the sediment) and −0.050 cal cm⁻² min⁻¹. The average simulated water-sediment heat flux is +0.003 cal cm⁻² min⁻¹. Over the course of an average day, heat entering the sediment reaches a maximum rate of 0.037 cal cm⁻² min⁻¹ at 1700, and fluxes out of the sediments reach −0.021 cal cm⁻² min⁻¹ at 0700. The standard deviations of sediment temperatures simulated for the 0–20, 80–100, and 180–200 cm layers are 85%, 41%, and 14%, respectively, of the standard deviation of the water temperature.     

Diel dissolved oxygen dynamics and eutrophication in a shallow,well-mixed tropical lagoon (Cancun,Mexico)

Bojorquez Lagoon (BL), located on the Mexican Caribbean, has received sewage and dredging impacts as a result of tourism development. The lagoon supports a high diversity of primary producers compared to sheltered adjacent lagoons dominated byThalassia testudinum communities. The Diurnal Curve Method (Odum and Hoskin 1958) was used to measure community metabolism and assess eutrophication in BL by comparing it to the nonimpacted lagoons and to other systems studied with this method. Dissolved oxygen community input to the water column in BL ranged between 8.3 g O₂ m^?2 d^?1 and 41.5 g O₂ m^?2 d^?1 during 1985 and 1986, and averaged 17.1, whereas dissolved oxygen community consumption ranged from 6.4 g O₂ m^?2 d^?1 during 1985 and 1986, and averaged 17.1, whereas dissolved oxygen community consumption ranged from 6.4 g O₂ m^?2 d^?1 to 37.6 g O₂ m^?2 d^?1 and averaged 15.2. These values are higher than those found for the adjacent lagoons and similar coastal lagoons, and are similar to results from other lagoons with sewage or seafood waste discharge. Net flux of oxygen from the community to the water column averaged 1.9 g O₂ m^?2 d^?1 and ranged from ?9.8 g O₂ m^?2 d^?1 to 8.1 g O₂ m^?2 d^?1. These values are low compared to the adjacent lagoons, and close to zero, as in dystrophic environments. Primary productivity, as estimated by oxygen input, increased in BL during the period of study, indicating that eutrophication is proceeding, but the lagoon has not reached yet a level of “critical eutrophication” as defined by Mee (1988).     

A comparative analysis of eutrophication patterns in a temperate coastal lagoon

The coastal bays and lagoons of Maryland extend the full length of the state's Atlantic coast and compose a substantial ecosystem at the land-sea margin that is characterized by shallow depth, a well-mixed water column, slow exchange with the coastal ocean, and minimal freshwater input from the land. For at least 25 years, various types of measurements have been made intermittently in these systems, but almost no effort has been made to determine if water quality or habitat conditions have changed over the years or if distinctive spatial gradients in these features have developed in response to changing land uses. The purpose of this work was to examine this fragmented database and determine if such patterns have emerged and how they may be related to land uses. Turbidity, dissolved inorganic phosphate, algal biomass, and primary production rates in most areas of the coastal bays followed a regular seasonal pattern, which was well correlated with water temperature. Nitrate concentrations were low (<5 μM), and only modestly higher in tributary creeks (<20 μM). Additionally, there was little indication of the spring bloom typical of river-dominated systems. There does appear to be a strong spatial gradient in water quality conditions (more eutrophic in the upper bays, especially in tributary creeks). Comparisons of water quality data collected between 1970 and 1991 indicate little temporal change in most areas and some small improvements in a few areas, probably related to decreases in point-source discharges. Seagrass communities were once extensive in these systems but at present are restricted to the eastern portion of the lower bays where water clarity is sufficient to support plant survival. Even in these areas, seagrass densities have recently decreased. Examination of diel dissolved oxygen data collected in the summer indicates progressively larger diel excursions from lower to upper bays and from open bays to tributary subsystems; however, hypoxic conditions (<2 mg 1^?1) were rarely observed in any location. Nitrogen input data (point, surface runoff, groundwater and atmospheric deposition to surface waters) were assembled for seven regions of the coastal bay system; annual loading rates ranged from 2.4 g N m^?2 yr^?1 to 39.7 g N m^?2 yr^?1. Compared with a sampling of loading rates to other coastal systems, those to the upper and lower bays were low while those to tributaries were moderate to high. Regression analysis indicated significant relationships between annual nitrogen loading rates and average annual total nitrogen and chlorophyll a concentrations in the water column. Similar analyses also indicated significant relationships between chlorophyll a and the magnitude of diel dissolved oxygen changes in the water column. It is concluded that these simple models, which could be improved with a well-designed monitoring program, could be used as quantitative management tools to relate habitat conditions to nutrient loading rates.     

Arsenic in framboidal pyrite from recent sediments of a shallow water lagoon of the Baltic Sea

Arsenic is a redox‐sensitive element of environmental relevance and often enriched in iron sulphides. Because sediments from the Achterwasser lagoon, a part of the estuarine system of the river Oder, south‐west Baltic Sea, show unexpectedly high pyrite concentrations of up to 7·5 wt% they were used to investigate the influence of authigenic pyrite on the mobility and burial of As in the coastal environment. Micro‐X‐ray‐fluorescence measurements of 106 micrometre‐sized pyrite framboids from the anoxic sediments show highly variable As concentrations ranging from 6 to 1142 μg g^?1. Even within a 1 cm thick layer, the As concentration of different framboids varies greatly and no clear depth trend is visible throughout the 50 cm long sediment core. Pyrite can account for 9 to 55% (average 22%) of the total As budget of the sediments and the degree of trace metalloid pyritization for As ranges from 26 to 61%, indicating that authigenic pyrite formation is an important process in the geochemical cycling of As in coastal sediments. High‐resolution micro‐X‐ray fluorescence mapping of single pyrite grains shows that As is distributed inhomogeneously within larger framboids, suggesting changing pore water composition during pyrite growth. X‐ray absorption near edge structure spectra indicate that As is usually present as As(‐I) substituting S in the pyrite lattice. However, in samples close to the sediment/water interface a considerable part of As is in higher valence states (+III/+V). This can be explained by frequent re‐suspension of the surficial sediments to the oxic water column due to wave action and subsequent re‐deposition, leading to the adsorption of As oxyanions onto pyrite. Although reduced As(‐I) becomes more important in the deeper samples, reflecting decreasing redox potential and a longer time since deposition, the occurrence of oxidized As species (AsIII/AsV) in pyrite in the anoxic part of the sediment suggests formation under dysoxic conditions.     

Factors influencing the salinity regime of Lake Pontchartrain,Lousiana, a shallow coastal lagoon: Analysis of a long-term data set

Lake Pontchartrain., Louisiana is a 1,630 km² shallow brackish lagoon with a mean salinity from 1.2‰ in the west to 5.4‰ in the east., The construction of a 120 km long deep-water connection to the Gulf of Mexico in 1963, was expected to cause a 5‰ increase in lagoon salinity. However, the actual increase was everywhere in the lagoon less than 2‰ Analysis of 31 years of daily salinity and discharge records indicates that discharge is the most important factor controlling salinity variations in Lake Pontchartrain., Seventy-four percent of low-frequency salinity variations are explained by freshwater discharge and the completion of the deep-water canal. Lake Pont.-chartrain experiences annual variations of salinity as high as 8‰ This salinity signal has remained constant since the beginning of the salinity records in 1946. It appears that the deep-water canal is not responsible for observed die-back of freshwater swamps and retreat of lagoon shorelines.     

Phosphorus distribution in the sediments of a shallow eutrophic lake,Lake Chaohu,China

In this study, the sediment profiles of total phosphorus (TP), inorganic phosphorus (P_i), organic phosphorus (P_o), C/P and N/P were used to investigate time-dependent P distribution changes in Lake Chaohu. The characteristics of P_i and P_o fractions in the surface sediments were studied and the difference between east and west lake region was also discussed. The P_i and P_o contents displayed a clear gradient from east to west in sediments of Lake Chaohu, and the P_o/P ratios were lower in sediments with industrial and urban pollution sources input in west lake region. The study indicated that different sediments area had diverse concentrations and distributions of P_o fractions due to their different drainage basin and pollution sources. The profile distribution of the C/P and N/P ratios decreased with increasing depths and stayed relatively constant ratios at the depths of 15–30 cm. The C/P and N/P ratios were always below Redfield ratios in sediment profile, indicating P enrichment but likely due to the preferential loss of carbon in respect to phosphorus. The rank order of P_i-fractions extracted was HCl-P_i > NaOH-P_i > NaHCO₃-P_i in surface sediments. The relative distribution of NaHCO₃-P_i and HCl-P_i was in agreement with the trophic conditions of the regions studied. Among the sequentially extracted P_o forms, the rank order of P_o fractions was residual P_o > HCl-P_o > fulvic acid-P > humic acid-P > NaHCO₃-P_o, with mean relative proportion of 5.4:3.4:2.2:1.1:1.0.     

Notes on the occurrence,distribution, and biology of elasmobranch fishes in the Indian River lagoon system,Florida

Fifteen species of elasmobranchs, eight sharks and seven rays, have been recorded with reasonable certainty from the Indian River lagoon system on the central east coast of Florida. We collected four shark and six ray species during a three and one-half year study of the northern portion of the lagoon system. Five of these appear to be year-round residents, and the remainder utilize the area only at restricted times of the year or as a nursery ground. The most abundant resident species areDasyatis sayi, D. sabina, andCarcharhinus leucas. Pristis pectinata, once a common resident species, has been extirpated from the lagoons. The distribution of ocean inlets and salinity appear to be major factors affecting diversity and numbers of elasmobranchs in the Indian River system.     

Urban land-use effects on groundwater phosphate distribution in a shallow aquifer, Nanfei River basin, China

Groundwater, surface water, soil and river sediment samples, and information on land use in the Nanfei River basin (NRB) of China have been analyzed to study the geochemistry, distribution, and mobilization of phosphorus. The distribution of phosphate (PO ₄ ^3??/sup> ) and the relationships between PO ₄ ^3??/sup> and several constituents in groundwater were studied. Partial correlation analysis relating PO ₄ ^3??/sup> to types of land use was conducted using the data analyzing tool SPSS 15.0. The processes controlling the transport of PO ₄ ^3??/sup> are discussed. The conclusions from this study are: (1) urban land use has obvious impact on PO ₄ ^3??/sup> in groundwater, the average concentration of PO ₄ ^3??/sup> being 4.37?mg/L, greater than that resulting from farmland and mixed land use, which have average PO ₄ ^3??/sup> concentrations of 0.10 and 0.18?mg/L, respectively; (2) the partial correlation between PO ₄ ^3??/sup> and types of land use is significant with a coefficient of 0.760; (3) the PO ₄ ^3??/sup> concentrations in surface water are generally higher than those in groundwater, and the total phosphorus (TP) concentrations in river sediments are generally higher than those in soil samples; (4) groundwater is a carrier of PO ₄ ^3??/sup> and is likely responsible for the redistribution of PO ₄ ^3??/sup> in different regions of NRB.     

Distributional patterns of blue crabs (Callinectes sp.) in a tropical estuarine lagoon

A two-year trawl study of Laguna Joyuda, Puerto Rico, a small, polyhaline lagoon with restricted oceanic exchange, yielded 803 crabs belonging to sixCallinectes species.Callinectes danae was the most abundant (35.7%), followed byC. sapidus (21%),C. ornatus (12.6%),C. bocourti (12.1%),C. exasperatus (1.2%), andC. larvatus (0.4%). Abundances of different species differed more spatially than temporally despite very homogeneous salinities.Callinectes bocourti andC. sapidus were most abundant furthest from the lagoon’s inlet, whileC. danae andC. ornatus were most abundant near the inlet and in the center of lagoon. Juveniles were least abundant in the center of the lagoon. Size frequencies of most species showed common trends with high percentages of small crabs furthest from the inlet, and high percentages of larger crabs near the inlet and central parts of the lagoon. Distributional patterns appear to be a result of complex interactions of habitat preferences and intra- and interspecific interactions among the crabs.     

External controls on the distribution,fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon,Cayo Coco (Cuba)

Active, carbonate‐mineralizing microbial mats flourish in a tropical, highly evaporative, marine‐fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea‐level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light–dark shifts in conjunction with microelectrode O₂ and HS^? profiles. High rates of O₂ production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate‐driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water‐level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind‐driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in‐depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings.     

Origin,distribution and hydrogeochemical controls on methane occurrences in shallow aquifers,southwestern Ontario,Canada

Natural gas reservoirs in organic-rich shales in the Appalachian and Michigan basins in the United States are currently being produced via hydraulic fracturing. Stratigraphically-equivalent shales occur in the Canadian portion of the basins in southwestern Ontario with anecdotal evidence of gas shows, yet there has been no commercial shale gas production to date. To provide baseline data in the case of future environmental issues related to hydraulic fracturing and shale gas production, such as leakage of natural gas, saline water, and/or hydraulic fracturing fluids, and to evaluate hydrogeochemical controls on natural gas accumulations in shallow groundwater in general, this study investigates the origin and distribution of natural gas and brine in shallow aquifers across southwestern Ontario. An extensive geochemical database of major ion and trace metal chemistry and methane concentrations of 1010 groundwater samples from shallow, domestic wells in bedrock and overburden aquifers throughout southwestern Ontario was utilized. In addition, select wells (n = 36) were resampled for detailed dissolved gas composition, δ¹³C of CH₄, C₂, C₃, and CO₂, and δD of CH₄. Dissolved gases in groundwater from bedrock and overburden wells were composed primarily of CH₄ (29.7–98.6 mol% of total gas volume), N₂ (0.8–66.2 mol%), Ar + O₂ (0.2–3.4 mol%), and CO₂ (0–1.2 mol%). Ethane was detected, but only in low concentrations (<0.041 mol%), and no other higher chain hydrocarbons were present, except for one well in overburden overlying the Dundee Formation, which contained 0.81 mol% ethane and 0.21 mol% propane. The highest methane concentrations (30 to >100 in situ % saturation) were found in bedrock wells completed in the Upper Devonian Kettle Point Formation, Middle Devonian Hamilton Group and Dundee Formation, and in surficial aquifers overlying these organic-rich shale-bearing formations, indicating that bedrock geology is the primary control on methane occurrences. A few (n = 40) samples showed Na–Cl–Br evidence of brine mixing with dilute groundwater, however only one of these samples contained high (>60 in situ % saturation) CH₄. The relatively low δ¹³C values of CH₄ (−89.9‰ to −57.3‰), covariance of δD values of CH₄ and H₂O, positive correlation between δ¹³C values of CH₄ and CO₂, and lack of higher chain hydrocarbons (C₃₊) in all but one dissolved gas sample indicates that the methane in groundwater throughout the study area is primarily microbial in origin. The presence or absence of alternative electron acceptors (e.g. dissolved oxygen, Fe, NO₃, SO₄), in addition to organic substrates, controls the occurrence of microbial CH₄ in shallow aquifers. Microbial methane has likely been accumulating in the study area, since at least the Late Pleistocene to the present, as indicated by the co-variance and range of δD values of CH₄ (−314‰ to −263‰) and associated groundwater (−19‰ to −6‰ δD-H₂O).     

浅水湖泊三角洲平原分流河道类型与叠置模式

浅水湖泊三角洲在中国许多陆相盆地中广泛发育,其中分流河道是三角洲平原最主要的砂体类型,它们大多呈现河道频繁改道、多级交叉及叠置的特点,往往形成极为复杂的地下储集层相互叠置的分布格局。基于松辽盆地浅水三角洲平原分流河道砂体的测井曲线特征,系统总结了浅水三角洲平原的分流河道河道类型与砂体叠置模式,并且分析了其对三角洲平原储集层砂体对比的约束作用。研究表明,分流河道河型可划分为3种基本类型:非典型辫流河型、非典型曲流河型和过渡型,其共同点是规模小、下切浅、分支快;而分流河道的叠置存在5种基本模式;河型与叠置特点决定了分流河道中泥质夹层分布存在2种基本类型,即平行分布式泥夹层与低角度侧积泥夹层。利用分流河道类型与叠置模式,可以分析河道发生变化的位置及井间砂体的连通情况,对储集层对比及连通关系分析具有约束作用。     

Sedimentation,dredging, and spoil disposal in a subtropical estuarine lagoon

Kaneohe Bay, Hawaii, is an estuary used as a harbor for a military installation and for recreation, fishing, and research purposes. Rapid shoaling of the bay had been reported and attributed to increased stream erosion and sedimentation from the newly suburbanized watershed. Comparison of a 1976 bathymetric survey of Kaneohe Bay with that of a 1927 survey indicates an average shoaling of the lagoonal area of 1.0 m. Average shoaling for the north and middle bay at 0.6m/49 years (1.2 cm yr⁻¹ is lower than for the south bay at 1.5m/49 years (3.1 cm yr⁻¹). The total lagoonal fill in the 49-year period is about 1.95× 10⁷ m³, assigned as follows: 64% carbonate detritus from the reefs as well as growth of living coral and unrecorded dredging spill, 9% recorded dredging spoils, and only 27% terrigenous sediment. Seismic reflection profiles distinguish spoil from natural sediment and show that the infilling sediment is trapped between, burying reef structures built during Quaternary lower stands of the sea. There had been little obvious change between 1882 and 1927 surveys. All information suggests that increased shoaling rates since 1927 are due to reported and unreported disposal of dredge spoil, mainly from 1939 to 1945 for ship and seaplane channels in the south bay, and not from increased runoff and urbanization around the south bay. Hawaii Institute of Geophysics Contribution No. 1257.     

浅层地下水中磺胺嘧啶与胡敏酸相互作用及相态间分布特征

研究抗生素在浅层地下水中不同相态间的分布特征,对于了解抗生素的行为特征及评估其危害具有重要的意义。本文利用三维荧光淬灭法研究了胡敏酸(humic acid, HA)对磺胺嘧啶(sulfadiazine, SD)在地下水中不同相态间分布规律的影响及相互作用,探讨了HA浓度、pH值、温度对SD在不同相态间分布的影响,对淬灭过程进行拟合并计算了分配系数、淬灭参数以及热力学参数。结果表明:地下水中SD浓度(0.5 mg/L)较低时或者HA浓度增加(0~20 mg/L)时,HA可显著促进悬浮相中SD比例的增加;SD对HA的淬灭机理为形成复合物的单一静态淬灭,结合位点数均约为1,荧光淬灭常数K_sv为5.271×10³ L/mol,淬灭速率常数K_q为5.271×10¹¹ L/(mol·s),属于自发的放热过程;体系处于低温(15 ℃)、弱碱性(8~10)pH值环境时,SD对HA的淬灭作用最强,HA对SD进入悬浮相的促进作用最明显。     

Predation impact on the meiobenthic harpacticoidCanuella perplexa in a lagoon of the Po River Delta,Italy

The impact of predation by juvenile marbled gobies,Pomatoschistus marmoratus, on the meiobenthic harpacticoid copepodCanuella perplexa was investigated at a subtidal station located in a shallow-water, brackish embayment of the Po River delta, northern Italy, in summer and fall 1978. In august, predation mainly centered on adults, with a very large number of prey for each predator; the energy supplied by the harpacticoid is high enough to sustain, almost entirely, the gobies’ daily energy requirement. The situation is different in September and October, when the adult copepod population declines dramatically and predation is shifted to less energy-providing copepodites and marbled gobies sensibly widen their prey spectrum.C. perplexa showed alterations of biological parameters, such as clutch size and average brood size, to cope with such a heavy predation pressure.