Seasonal variations of size-fractionated phytoplankton along the salinity gradient in the York River estuary, Virginia (USA)

The dynamics of phytoplankton size structure were investigatedin the freshwater, transitional and estuarine zones of the YorkRiver over an annual cycle. The contribution of large cells(microplankton, >20 µm) to total concentrations ofchlorophyll a increased downstream during winter, whereas thatof small cells (nanoplankton, 3–20 µm; picoplankton,<3 µm) increased downstream during summer. In the freshwaterregion, the contribution of micro phytoplankton to total concentrationsof chlorophyll a was significant during warm seasons (springand summer) but not during colder seasons (winter), whereasthe contribution of small-sized cells (especially picoplankton)increased during cold seasons. Temperature, light and high flushingrate appear to control phytoplankton community structure inthe freshwater region. In the transitional region, nano-sizedcells dominated the phytoplankton population throughout allseasons except during the spring bloom (April) when the chlorophylla concentration of micro phytoplankton increased. Size structurein the transitional region is most likely regulated by lightavailability. In the mesohaline region, nano- and pico-sizedcells dominated the phytoplankton population during the summerbloom, whereas micro-sized cells dominated during the winterbloom. Factors controlling phytoplankton community size structurein the mesohaline zone may be riverine nitrogen input, temperatureand/or advective transport from up-river. Based on these results,the spatial and seasonal variations in size structure of phytoplanktonobserved on the estuarine scale may be determined both by thedifferent preferences for nutrients and by different light requirementsof micro-, nano- and picoplankton. The results suggest thatanalyses of phytoplankton size structure are necessary to betterunderstand controls on phytoplankton dynamics and to bettermanage water quality in river-dominated, estuarine systems.     

Aerobic and anaerobic degradation and mineralization of 14C-chitin by water column and sediment inocula of the York River estuary, Virginia.

Potential rates of chitin degradation (Cd) and mineralization (Cm) by estuarine water and sediment bacteria were measured as a function of inoculum source, temperature, and oxygen condition. In the water column inoculum, 88 to 93% of the particulate chitin was mineralized to CO2 with no apparent lag between degradation and mineralization. No measurable dissolved pool of radiolabel was found in the water column. For the sediment inocula, 70 to 90% of the chitin was degraded while only 55 to 65% was mineralized to CO2. 14C label recoveries in the dissolved pool were 19 to 21% for sand, 17 to 24% in aerobic mud, and 12 to 21% for the anaerobic mud. This uncoupling between degradation and mineralization occurred in all sediment inocula. More than 98% of the initial 14C-chitin was recovered in the three measured fractions. The highest Cd and Cm values, 30 and 27% day-1, occurred in the water column inoculum at 25 degrees C. The lowest Cd and Cm values were found in the aerobic and anaerobic mud inocula incubated at 15 degrees C. Significant differences in Cd and Cm values among water column and sediment inocula as well as between temperature treatments were evident. An increased incubation temperature resulted in shorter lag times before the onset of chitinoclastic bacterial growth, degradation, and mineralization and resulted in apparent Q10 values of 1.1 for water and 1.3 to 2.1 for sediment inocula. It is clear that chitin degradation and mineralization occur rapidly in the estuary and that water column bacteria may be more important in this process than previously acknowledged.     

Trophic ecology of two congeneric pipefishes (Syngnathidae) of the lower York River,Virginia

Synopsis The northern pipefish, Syngnathus fuscus, and the dusky pipefish, S. floridae, co-exist in eelgrass beds in the lower York River. To compare the trophic ecology of both pipefishes, gut contents of 3488 northern pipefish, and 1422 dusky pipefish were examined and quantified by dry weight. Samples were taken with a dip net from May through November 1992. Syngnathus fuscus fed mainly on amphipods (Gammarus mucronatus, Amphithoe longimana, and Caprella penantis), and to a lesser degree on copepods, and isopods (Edotea spp. and Erichsonella attenuata). Syngnathus floridae fed mainly on grass shrimps (Palaemonetes pugio, P. vulgaris, and Palaemonetes eggs), and to a lesser degree on copepods, isopods, and mysids (Mysidopsis bigelowi). No seasonal trends were observed in the feeding habits of these pipefishes. Specimens of both species smaller than 100 mm TL fed mainly on copepods. Larger S. fuscus fed on amphipods, while larger S. floridae fed on grass shrimps. Schoener's diet overlap index revealed high consumption of the same prey type by both pipefish species only in July, but only for those specimens smaller than 110 mm TL. Food partitioning between both pipefish was associated with different snout sizes and shapes.     

Feeding chronology and habits of Alosa spp. (Clupeidae) juveniles from the lower Hudson River estuary, New York

Synopsis Feeding habits of juvenile alewife, A. pseudoharengus, blueback herring, A. aestivalis, and American shad, Alosa sapidissima, were examined over a 24 h period at an inshore location on the lower Hudson River. Feeding periodicity differed by species: alewives showed no diel differences, whereas shad fed least intensively near dawn and herring least intensively at night. Alewives fed primarily on chironomids and the amphipod Corophium lacustre, shad on Formicidae and larval chironomids, and herring on chironomids and copepods. Diel variation in prey selection was evident. Dietary overlap was generally greatest between alewife and herring and least between shad and herring.     

Integrative ecosystem analyses of phytoplankton dynamics in the York River estuary (USA)

The relative importance of biotic (top-down) vs. abiotic (bottom-up) controls on phytoplankton dynamics was investigated in the York River estuary, Virginia (USA) by a combination of extensive analyses of long-term data sets collected by the U.S. Environmental Protection Agency (EPA) monitoring program over 17 years (1984–2001), field studies (1996–1997) and ecosystem modeling analyses. Results from the analysis of long-term data records collected at three stations along the salinity gradient suggested that phytoplankton are more likely controlled by abiotic mechanisms such as resource limitation than biotic mechanisms such as grazing since annual cycles of primary production and phytoplankton biomass were similar and no grazing effects were evident based on the observed relationship between phytoplankton and zooplankton biomass (R ² < 0.2, p > 0.1). This scenario was supported by short-term field observations made over an annual cycle at three stations in the mid-channel of the estuary where both chlorophyll a and primary production demonstrated similar patterns of seasonal variation. Ratios of fluorescence before and after acidification at all study sites were relatively high suggesting low grazing pressure in the estuary. A tidally-averaged, size-structured plankton ecosystem model was previously developed and verified for the lower York River estuary. The validated ecosystem model was also used to examine this issue and simulation results supported the importance of bottom-up control in the York River estuary.     

Ecology of the Ogun River estuary,Nigeria

The distribution of benthonic communities (particularly Foraminifera) were studied from fourteen samples obtained from the Ogun River estuary and environs. Ten species of benthonic Foraminifera were identified; two of these constitute over 90% of the total foraminiferal population.Two broad biofacies are recognisable, namely the upper estuarine facies of Ammobaculites and the lower estuarine facies comprising arenaceous and calcereous forms with a preponderance of Ammonia beccarii (Linnaeus).Large populations of few species occur in the lower estuary, an area of weakly saline water with marked salinity fluctuations. The upper estuary on the other hand is sparsely populated and contains tests mainly of arenaeous Foraminifera. A few species are distinctive of particular facies but some are distributed throughout the estuary. Substrate is not a causal ecological factor, because sediments are similar in physical attributes throughout the estuary. Salinity and rate of sedimentation are among the more important factors affecting the distribution of all species. The low-energy nature of the environment is established by the abundance of faecal pellets and the fragility of the tests of the arenaceous Foraminifera.     

Comparative digestive biology between the ponyfishes from the Pranburi River estuary,Thailand

We investigated the digestive biology of two prevalent leiognathid species in Pranburi River estuary, Thailand: the decorated ponyfish (Nuchequula gerreoides) and the splendid polyfish (Eubleekeria splendens). A total of 632 samples collected from February to April and September to November 2017 were analysed using morphological and histological approaches. The overall structures were similar between the species: a short mucous-cell-rich oesophagus region, a well-developed gastric gland uniformly present across the stomach's mucosal layer, and three finger-like pyloric caeca between the stomach and intestine. However, there were marked differences in the mouth, gill raker, and intestinal coefficient (IC). N. gerreoides had a relatively longer mouth, smoother gill rakers, and an IC of 1.08 ± 0.01, similar to those of other carnivorous fish. In contrast, the gill raker of E. splendens had more villiform teeth that can filter-feed better, and their IC was 2.16 ± 0.02 (i.e., longer intestine). Although digestive structures were generally similar between the ponyfishes, these differences suggest that N. gerreoides is relatively carnivorous with stronger suction, whereas E. splendens may be an omnivorous or herbivorous filter-feeder.     

Hydro-sedimentology of the Johnstone River estuary

This paper examines the physical consequences of increased catchment sediment yields on the sediment budget and the hydrodynamic setting of the South Johnstone River estuary in North Queensland. A combined study involving hydrological monitoring, assessment of sediment sources, estimation of riverine sediment budget and hydro-sedimentological numerical modelling for estuarine sediment transport is currently underway. Initial field and laboratory observations indicate that the sediment delivery from highly erosion-prone sugar cane cultivations in the tropical catchment has increased dramatically during the last 10 years. This has subsequently given rise to elevated flood levels in both the lower and upper catchment areas, as well as significant modifications to the river bed morphology.     

Distribution of shorebirds at the Berg River estuary, South Africa, in relation to foraging mode, food supply and environmental features

Foraging densities of Curlew Sandpipers Calidris ferruginea and Grey Plovers Pluvialis squa-tarola at the Berg River estuary, South Africa, are examined in relation to prey and habitat attributes.
There is a substantial overlap in the prey species eaten by Curlew Sandpipers and Grey Plovers, but the distribution patterns of the two species within the estuary could not be explained by the same prey attributes.
The distribution of tactilely foraging Curlew Sandpipers was determined largely by the numerical abundance of nereid worms. They foraged preferentialiy on muddy rather than sandy substrata, but their distribution could not be explained on the basis of substratum penetrability. The density of visually foraging Grey Plovers was correlated with the biomass, rather than abundance, of the larger of the two common nereids on the estuary. The favoured foraging area of Grey Plovers had a high vegetation cover, but their foraging dispersion was not influenced by substratum type.
The energy intake rates of Curlew Sandpipers were broadly inversely related to their foraging density, although the rate of prey capture was maximal at high prey density. These birds may use neighbour success rates in selecting foraging sites. Energy intake rates of Grey Plovers were very consistent across the estuary, suggesting that individuals occupy or defend areas which provide access to comparable food resources.     

Bacterial polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenases in the sediments from the Pearl River estuary, China

Bacterial community compositions were characterized using denaturing gradient gel electrophoresis analysis of bacterial 16S rRNA gene in the sediments of the Pearl River estuary. Sequencing analyses of the excised bands indicated that Gram-negative bacteria, especially Gammaproteobacteria, were dominant in the Pearl River estuary. The diversity of polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenase (PAH-RHD) gene in this estuary was then assessed by clone library analysis. The phylogenetic analyses showed that all PAH-RHD gene sequences of Gram-negative bacteria (PAH-RHD_[GN]) were closely related to the nagAc gene described for Ralstonia sp. U2 or nahAc gene for Pseudomonas sp. 9816–4, while the PAH-RHD gene sequences of Gram-positive bacteria (PAH-RHD_[GP]) at sampling site A1 showed high sequence similarity to the nidA gene from Mycobacterium species. Meanwhile, molecular diversity of the two functional genes was higher at the upstream of this region, while lower at the downstream. Redundancy analysis indicated that environmental factors, such as NH₄-N, ∑PAHs, pH, SiO₃-Si, and water depth, affected the distribution of the PAH-RHD_[GN] gene in the Pearl River estuary.     

Pollution and tidal benthic communities of the James River Estuary,Virginia

Distribution of benthic communities in the estuarine portion of the James River was controlled mainly by salinity. Pollution effects were localized and difficult to assess because of a rigorous physical environment. Mesohaline and oligohaline communities were very similar to those in other estuaries of the eastern United States. Macrobenthic densities were most severely depressed in tidal freshwater habitats near Richmond & Hopewell, where the major portion of the pollution load enters the river. Cluster analysis of species distributional patterns and ordination of pollution and physical parameters produced similar results, dividing the river into mesohaline, oligohaline, and upper and lower tidal freshwater zones. Further analysis of only the tidal freshwater portion indicated the distribution of benthic communities reflected the location and concentration of pollution sources along the river. Tidal freshwater communities were dominated by the Asiatic clam, Corbicula fluminea, tubificid oligochaetes of the genus Limnodrilus and the chironomid insect larva Coelotanypus scapularis. The fauna of the freshwater zones was very eurytopic with respect to sediment type and has a great resemblance to the fauna of eutrophic lakes. The classical concept of a sharp increase in number of species occurring from oligohaline to freshwater zones was found to be misleading. This increase does not occur until free flowing (or lotic) freshwater areas of greater habitat diversity are reached.     

The nutrient status of the Kromme River estuary,South Africa

The Kromme is a small estuary in rural eastern Cape, South Africa with a relatively unpopulated and undisturbed catchment. Physical and chemical variables including the major nutrients and E. coli were examined. It was found to be a well oxygenated, well mixed estuary with some stratification in its upper reaches. Nutrient levels were generally low with nitrate values higher in winter than during summer. While no overt seasonality was detected for phosphorus, levels were comparatively high. Faecal E. coli levels were low with a mean count of 26 per 100 ml for the estuary. Along the Kromme, nutrients were highest at the confluence of the Geelhoutboom tributary suggesting it was a major nutrient contributor. At the head of the Kromme, silicate and E. coli were significantly linked to riverflow, while nitrate was correlated with rainfall. In the Geelhoutboom, only nitrate was correlated with riverflow and rainfall. When nutrient gradients (total inorganic nitrogen, total phosphorus and silicate) were correlated against salinity, significant relationships were observed for nitrogen and silicate (Kromme and Geelhoutboom) and for phosphorus along the Geelhoutboom, but not the Kromme, reflecting differences in sub-catchments. An overall N:P atomic ratio of 0.89:1 was found for the system, with more nitrogen relative to phosphorus at the head of the Kromme and vice versa for the Geelhoutboom and mouth. The Kromme is low in nitrogen, conservative in silicate and low in phosphorus while the Geelhoutboom supplies nitrogen, phosphorus and silicate to the system. Although there may be nutrient absorption by sediments in the upper estuary, and by macrophytes in the lower estuary, the Kromme may be classified as a non-conservative mesotrophic marine-dominated estuary which probably exhibits some nutrient recycling.     

Observations of an ash lagoon spill on the new River,Virginia

An estimated 7 million liters of slightly alkaline water (pH = 7.7) and ash entered New River on 23 July 1973 near Pearisburg, Virginia. The rate of dispersion, 1.4 km/hr, allowed qualitative collections of fishes and macroinvertebrates to be made immediately before and after the biological impact of the spill. Diversity and relative abundance indicated that fishes and macroinvertebrates were little affected. Physicochemical parameters from the flyash lagoon, as projected from 1971–1972 data, were within the known tolerance ranges of aquatic biota common to New River.     

Site-Specific Derivation of the Acute Copper Criteria for the Clinch River,Virginia

Previous studies indicated that inputs from the Clinch River Plant (CRP), a coal-burning, power-generating facility in Carbo, Virginia, caused impairment to transplanted freshwater mussels. These findings necessitated the examination of instream biological responses to CRP effluents. Therefore, our objective was to derive a site-specific Criterion Maximum Concentration (CMC) for copper (Cu), the toxic constituent of the effluent. This was accomplished by conducting acute toxicity tests with Cu using 17 different genera native to or currently residing in the Clinch River watershed. Four native unionids and a mayfly (Isonychia bicolor) had genus mean acute values of 60?µJ.g/L or lower (ranging from 37 to 60?µJ,g/L). With a GMAV of 88?µJ,g/L, Ceriodaphnia dubia ranked sixth among the 17 genera tested, and the fathead minnow, Pimephales promelas, ranked fourteenth with a GMAV of 310?µJ.g/L. Despite the sensitivity of the indigenous mussels tested, the site-specific CMC of 18?µJg/L was not substantially lower than the national CMC for Cu (20?µJ,g/L, hardness = 150?mg/L as CaCO3). While we conducted acute exposure tests, future investigations should incorporate both biomarker and population or community-level studies to determine low-level contaminant impacts on freshwater mussels.     

Radium in the Suwannee River and estuary

A two-year study of radium in the Suwannee River has shown that groundwater discharge, via springs, is a very important source of radium both to the river and to offshore Gulf of Mexico waters. Dissolved radium is maintained within relatively narrow limits in the river by uptake into suspended particles. In the estuary, dissolved radium versus salinity profiles show distinctive nonconservative behavior with radium in significant excess of its linear mixing value at mid-salinities. Unlike the situation in many other estuaries, however, desorption of radium from particles cannot account for most of the observed excess. Thus, the anomalously high radium characteristic of much of the west Florida shelf apparently does not have a riverine source. Direct effusion of high-radium groundwater into these coastal waters is thought to be the major supplier of radium, and perhaps other elements as well.     

Radium in the Suwannee River and estuary

A two-year study of radium in the Suwannee River has shown that groundwater discharge, via springs, is a very important source of radium both to the river and to offshore Gulf of Mexico waters. Dissolved radium is maintained within relatively narrow limits in the river by uptake into suspended particles. In the estuary, dissolved radium versus salinity profiles show distinctive nonconservative behavior with radium in significant excess of its linear mixing value at mid-salinities. Unlike the situation in many other estuaries, however, desorption of radium from particles cannot account for most of the observed excess. Thus, the anomalously high radium characteristic of much of the west Florida shelf apparently does not have a riverine source. Direct effusion of high-radium groundwater into these coastal waters is thought to be the major supplier of radium, and perhaps other elements as well.     

Behavior of mercury in the Patuxent River estuary

An overview of a comprehensive study of the behavior and fate of mercury in the estuarine Patuxent River is presented. Total Hg (Hg_T) and methylmercury (MeHg) exhibited weakly non-conservative behavior in the estuary. Total Hg concentrations ranged from 6 ng L^-1 in the upper reaches of the sub-urbanized tidal freshwater river to <0.5 ng L^-1 in the mesohaline lower estuary. Filterable (0.2 µm) Hg_T ranged from 0.2 to 1.5 ng L^-1. On average, MeHg accounted for <5% of unfiltered Hg_T and <2% of filterable Hg_T. Dissolved gaseous section Hg (DGHg) concentrations were highest (up to 150 pg L^-1) in the summer in the mesohaline, but were not well correlated with primary production or chlorophyll a, demonstrating the complex nature of Hg⁰ formation and cycling in an estuarine environment. Organic matter content appeared to control the Hg_T content of sediments, while MeHg in sediments was positively correlated with Hg_T and organic matter, and negatively correlated with sulfide. MeHg in sediments was low (0.1 to 0.5% of Hg_T). Preliminary findings suggest that net MeHg production within sediments exceeds net accumulation. Although Hg_T in pore waters increased with increasing sulfide, bulk MeHg concentrations decreased. The concentration of MeHg in sediments was not related to the concentration of Hg_T in pore waters. These observations support the hypothesis that sulfide affects the speciation and therefore bioavailability of dissolved and/or solid-phase Hg for methylation. Comparison with other ecosystems, and the negative correlation between pore water sulfide and sediment MeHg, suggest that sulfide limits production and accumulation of MeHg in this system.     

甲藻孢囊在长江口海域表层沉积物中的分布

为了了解长江口海域赤潮爆发潜势,于2002年4月至5月用采泥器采集了位于122°～123．5°E、29°～32°N之间12个站位的表层沉积物,分析沉积物中甲藻孢囊的分布．共分析鉴定出孢囊类型29种,其中自养型11种,异养型18种．每个站位的孢囊种类在10～21之间,孢囊密度为11．7～587孢囊·g-1干泥之间．远岸海域孢囊种类较为丰富,密度也较高．在调查区域内,孢囊密度及种类自西向东、自北向南逐渐增加．亚历山大藻孢囊分布广泛,最高密度为40．4孢囊·g-1干泥,其他赤潮种类的孢囊如链状裸甲藻、多边舌甲藻、锥状斯氏藻、科夫多沟藻和无纹多沟藻等都在长江口海域有分布．     

Selective effects of phytoplankton entrainment at the Surry Power Plant,James River,Virginia

Loss of cryptophyte cells entrained in the Surry Power Plant cooling water was significantly correlated with discharge water temperature in the range 27.2–37.5 °C. Entrained Skeletonema costatum and benthic diatom populations experienced losses of 25–80% in the summer, but correlations between % loss and discharge temperature were insignificant. Cropping by benthic filter feeders in the intake and discharge canals could account for the summer removal of diatoms. Shortening of entrained S. costatum chains was detected in both winter and summer, indicating a mechanical effect of turbulence.Benthic diatoms were vulnerable to entrainment only during daylight hours, when they migrated to the sediment surface at low tide. Skeletonema costatum was most vulnerable in the summer, when elevated salinities permitted it to range upstream to the intake area. Cryptophyte populations peaked in the summer when entrainment loss was greatest.The composition of the entrained phytoplankton community was altered by the species specific interactions of factors affecting vulnerability and entrainment loss. At Surry the discharged cooling water mixes rapidly with the main stem James River, and the selective effects of entrainment are not detectable in phytoplankton samples taken beyond the immediate discharge zone. More persistent modifications of the phytoplankton could be expected at sites where power plants discharge into creeks or embayments.Contribution No. 1106, Virginia Institute of Marine Science.Contribution No. 1106, Virginia Institute of Marine Science.