Inorganic Nutrient Concentrations Research Articles

Complex, Dynamic Combination of Physical, Chemical and Nutritional Variables Controls Spatio-Temporal Variation of Sandy Beach Community Structure

Sandy beach ecological theory states that physical features of the beach control macrobenthic community structure on all but the most dissipative beaches. However, few studies have simultaneously evaluated the relative importance of physical, chemical and biological factors as potential explanatory variables for meso-scale spatio-temporal patterns of intertidal community structure in these systems. Here, we investigate macroinfaunal community structure of a micro-tidal sandy beach that is located on an oligotrophic subtropical coast and is influenced by seasonal estuarine input. We repeatedly sampled biological and environmental variables at a series of beach transects arranged at increasing distances from the estuary mouth. Sampling took place over a period of five months, corresponding with the transition between the dry and wet season. This allowed assessment of biological-physical relationships across chemical and nutritional gradients associated with a range of estuarine inputs. Physical, chemical, and biological response variables, as well as measures of community structure, showed significant spatio-temporal patterns. In general, bivariate relationships between biological and environmental variables were rare and weak. However, multivariate correlation approaches identified a variety of environmental variables (i.e., sampling session, the C∶N ratio of particulate organic matter, dissolved inorganic nutrient concentrations, various size fractions of photopigment concentrations, salinity and, to a lesser extent, beach width and sediment kurtosis) that either alone or combined provided significant explanatory power for spatio-temporal patterns of macroinfaunal community structure. Overall, these results showed that the macrobenthic community on Mtunzini Beach was not structured primarily by physical factors, but instead by a complex and dynamic blend of nutritional, chemical and physical drivers. This emphasises the need to recognise ocean-exposed sandy beaches as functional ecosystems in their own right.

Nitrogen uptake and growth by the opportunistic macroalga Ulva lactuca (Linnaeus) during the internal tide

To determine if an opportunistic macroalga could increase its tissue nitrogen content in response to nutrient pulses forced by the internal tide, independent samples of the green alga Ulva lactuca (Linnaeus), previously cultured in nutrient-poor tanks, were outplanted in the nearshore ocean for 12 h deployment periods (8 daylight periods, 7 night periods), at three different depths (1, 5, and 10 m), during stratified water column conditions and spring tides. Algal tissue nitrogen and growth weight (before and after each deployment), water-column temperature (continuous), and inorganic water-column nutrient concentrations (taken on 3 days during the experiment) were measured. Abrupt drops in temperature (up to 3 °C in an hour) occurred twice daily, at 10 m and occasionally at 5 m depth, associated with the internal tide. Date and deployment depth had significant effects on U. lactuca tissue nitrogen, showing a significant increase for deeper deployments and a positive correlation with the duration of cool water (< 15.8 °C, > 1 μM NO 3 −) at the deployment depth. On days when temperature remained above 15.8 °C at all depths (15.8 °C was established as the temperature below which nitrate was above 1 μM), no significant increase in tissue nitrogen was detected at any depth. Growth and tissue nitrogen were significantly and inversely correlated for mid-water (5 m) and bottom (10 m) deployments, but not at the surface. The data support the hypothesis that U. lactuca can increase tissue nitrogen in response to the cold phase of the semidiurnal internal tide.

Influence of land use patterns on some limnological characteristics in the south-eastern part of Lake Victoria, Tanzania

To investigate the influence of human activities on limnological characteristics of Lake Victoria, we analyzed inorganic nutrient concentrations, phytoplankton diversity and biomass at three locations with different land use patterns: Mwanza (urban/industrial), Magu (agricultural) and Kayenze (sparsely populated). Mwanza had significantly higher ammonia concentration compared to Kayenze and Magu. At the shoreline stations, significantly higher nitrate concentration was observed at Mwanza compared to Kayenze and Magu. Similarly, Mwanza had significantly higher concentrations of soluble reactive phosphorous in the shoreline stations compared to Magu and Kayenze, but not in the open waters stations. Shoreline stations also showed significant differences in phytoplankton diversity among sites. The shoreline station at Mwanza also showed significantly higher levels of Chl. a compared to those at Magu and Kayenze. However, in the open water stations Chl. a concentrations did not differ significantly among sites. The results suggested that urban pollution in Mwanza and agricultural activities in River Simiyu catchment strongly influence the limnology of Lake Victoria and that the nearshore waters, which are the receiving points, were highly impacted compared to the waters outside bays. Thus, proper urban waste management and sustainable land management practices are critical for reducing point and non-point sources of pollution into Lake Victoria.

Development of associations between microalgae and denitrifying bacteria in streams of contrasting anthropogenic influence

We compared the development of microalgal and bacterial-denitrifier communities within biofilms over 28 days in a restored-prairie stream (RP) and a stream receiving treated wastewater effluent (DER). Inorganic nutrient concentrations were an order of magnitude greater in DER, and stream waters differed in the quality of dissolved organics (characterized via pyrolysis-GC/MS). Biofilm biomass and the densities of algae and bacteria increased over time in both systems; however, algal and denitrifier community composition and the patterns of development differed between systems. Specifically, algal and denitrifier taxonomic composition stabilized more quickly in DER than RP, whereas the rates of algal and denitrifier succession were more closely coupled in RP than DER. We hypothesize that, under unenriched conditions, successional changes in algal assemblages influence bacterial denitrifiers due to their dependence on algal exudates, while under enriched conditions, this relationship is decoupled. Between-system differences in organic signatures supported this, as RP biofilms contained more labile, aliphatic compounds than DER. In addition, potential denitrification rates (DNP) were negatively correlated with the percentage of aromatic compounds within the biofilm organic signatures, suggesting a significant relationship between algal exudate composition and denitrification. These results are significant because anthropogenic factors that affect biofilm community composition may alter their capacity to perform critical ecosystem services.

Variation of bacteria biomass and its possible controlling factors in the East China Sea

Two surveys were performed for determining bacteria biomass (BB), temperature, salinity, chlorophyll a (chl-a) and nutrient concentrations at 11 stations with three sampling depths in the high-incidence regions of red tide in the East China Sea (ECS) in the spring of 2006. Temperature and salinity increased from nearshore to offshore region and from high latitude to low latitude in the two cruises of 2006. BB were between 0.35.2 mgC m^(-3) (about 2.1 mgC m^(-3) on average) and 0.26.0 mgC m^(-3) (about 2.7 mgC m^(-3) on average) respectively in the two cruises. BB in the surface layer decreased from the Changjiang River estuary to high sea and from low latitude to high latitude. The results showed that bacterial growth was regulated by temperature, primary production and inorganic nutrient concentrations depending on different hydrographic conditions. In the surface and middle layers where the primary production can supply enough organic substrate, temperature was the main factor to control bacteria biomass. BB showed a good correlation between the surface and middle layers in both cruises. The distribution of nutrients during both cruises showed a similar decreasing trend from nearshore region and high latitude to offshore region and low latitude. High BB values were mainly recorded from samples in the middle layer where chl-a concentrations were also high, indicating primary production being strongly correlated with temperature over the ECS shelf. In the offshore area, phosphate and silicate became limiting factors for phytoplankton growth with indirect influence on BB. Bacteria played an important role in nitrogen regeneration process turning organic nitrogen to inorganic forms such as NH4(superscript +). The increasing ratio of NH4(superscript +)/DIN could be a proof of that.

Influence of fish cage farming on water quality and plankton in fish ponds: A case study in the Rift Valley and North Shoa reservoirs, Ethiopia

The potential impact of Nile Tilapia ( Oreochromis niloticus) cage culture on water quality and pelagic community composition was investigated in two Ethiopian small water bodies, one located in the highlands (Yemlo) and the other in the Great Rift Valley (Allage). This study was designed to assess the difference between the cages and open water in relation to those water quality changes attributable to intensive inputs of fish waste and left-over fish feed. All physico-chemical water quality parameters including inorganic nutrients varied temporally, coupled with dry and wet periods. The reservoir's trophic state ranged from eutrophic to hypereutrophic, with a strong correlation between chlorophyll- a and total phosphorus. The phytoplankton community was dominated by Cyanobacteria (84% of total phytoplankton abundance), in particular by Anabaenopsis sp. in Allage reservoir, whereas Chlorophyta (70%), with Pediastrum simplex as the dominant taxon, prevailed in Yemlo reservoir. A total of 23 zooplankton taxa were recorded during our sampling; rotifers were the richest group with 14 taxa distributed in 6 genera, followed by cladocerans represented by 6 taxa (5 genera) and copepods by 3 taxa (1 genus). Dissolved inorganic nutrient concentrations and other physical parameters showed no significant differences between the cages and open water. The exceptions were dissolved oxygen and ammonium nitrogen, which were lower and higher in the cages, respectively. For the whole study period of 240 days, the mean net weight and daily growth rate per fish were 183.3 g and 1.1 g d − 1 , respectively.

Combined effects of temperature, inorganic nutrients and organic matter on ecosystem processes in intertidal sediments

Multiple anthropogenic stressors can interact, making it difficult to predict their combined impacts on ecosystem processes. Interactions between localised stressors can be further modified by variations in environmental conditions, such as those arising through climate change. This study investigated the individual and combined effects of increased temperature and nutrients and organic enrichment on ecosystem processes in intertidal sedimentary systems. Three levels of nutrient addition (0, 100 and 200 g m − 2 ) were crossed with two levels of organic matter (0 and 200 g m − 2 ) under two temperature regimes (10.0 and 16.5 °C) in laboratory tanks. The influence of organic matter on ecosystem processes moderated by macrofauna did not vary with concentration of inorganic nutrients or temperature. Oxygen consumption, which has repeatedly been shown to increase with increased temperature, was in this case significantly increased by organic matter across all levels of temperature and nutrient enrichment. In addition, temperature affected nutrient cycling regardless of the addition of nutrients or organic matter. Understanding how the combined impacts of multiple stressors may vary depending on environmental conditions is essential for the development of strategies to sustainably manage ecosystems and conserve the delivery of ecosystem services.

Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 62:1-12 (2011) - DOI: https://doi.org/10.3354/ame01451 FEATURE ARTICLE Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean Donn A. Viviani, Karin M. Björkman, David M. Karl, Matthew J. Church* Department of Oceanography, University of Hawaii, Honolulu, Hawaii 96822, USA *Corresponding author. Email: mjchurch@hawaii.edu ABSTRACT: We measured plankton metabolism and evaluated changes in plankton community structure within the central Pacific Ocean during a trans-equatorial cruise from the South Pacific Subtropical Gyre (SPSG) to the North Pacific Subtropical Gyre (NPSG). Rates of net community production (NCP) and respiration (R) were determined in near-surface ocean waters, based on light–dark bottle measurements of oxygen production and consumption. Gross primary production (GPP) was computed, where GPP = NCP + R. Rates of GPP and R in the oligotrophic SPSG and NPSG were tightly coupled, resulting in NCP that was either zero or slightly negative. These subtropical waters were characterized by very low concentrations of inorganic nutrients (e.g. nitrate+nitrite range: 0.004 to 0.033 µmol l–1). Within the relatively nutrient-enriched equatorial waters (e.g. nitrate+nitrite concentrations range: 0.67 to 5.7 µmol l–1), GPP exceeded R by up to 5-fold, resulting in positive NCP. GPP varied ~16-fold (0.25 to 4.05 µmol O2 produced l–1 d–1) while R varied ~5-fold (0.31 to 1.56 µmol O2 consumed l–1 d–1). Picoplankton cell abundances and diagnostic pigment biomarkers were used to determine regional differences in phytoplankton community structure. In the near-equatorial waters, abundances of Synechococcus and photosynthetic picoeukaryotes increased up to 100- and 10-fold, respectively, and diagnostic pigment biomarkers for eukaryotic phytoplankton (including diatoms, pelagophytes, and haptophytes) also increased. These results indicate that variability in nutrient availability constitutes an important regulator of net productivity and plankton community structure in large regions of the open ocean. KEY WORDS: Gross primary production · Respiration · Net community production · Equatorial Pacific · Subtropical gyres Full text in pdf format Information about this Feature Article NextCite this article as: Viviani DA, Björkman KM, Karl DM, Church MJ (2011) Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean. Aquat Microb Ecol 62:1-12. https://doi.org/10.3354/ame01451 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 62, No. 1. Online publication date: January 04, 2011 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2011 Inter-Research.

Non-Random Assembly of Bacterioplankton Communities in the Subtropical North Pacific Ocean

The exploration of bacterial diversity in the global ocean has revealed new taxa and previously unrecognized metabolic potential; however, our understanding of what regulates this diversity is limited. Using terminal restriction fragment length polymorphism (T-RFLP) data from bacterial small-subunit ribosomal RNA genes we show that, independent of depth and time, a large fraction of bacterioplankton co-occurrence patterns are non-random in the oligotrophic North Pacific subtropical gyre (NPSG). Pair-wise correlations of all identified operational taxonomic units (OTUs) revealed a high degree of significance, with 6.6% of the pair-wise co-occurrences being negatively correlated and 20.7% of them being positive. The most abundant OTUs, putatively identified as Prochlorococcus, SAR11, and SAR116 bacteria, were among the most correlated OTUs. As expected, bacterial community composition lacked statistically significant patterns of seasonality in the mostly stratified water column except in a few depth horizons of the sunlit surface waters, with higher frequency variations in community structure apparently related to populations associated with the deep chlorophyll maximum. Communities were structured vertically into epipelagic, mesopelagic, and bathypelagic populations. Permutation-based statistical analyses of T-RFLP data and their corresponding metadata revealed a broad range of putative environmental drivers controlling bacterioplankton community composition in the NPSG, including concentrations of inorganic nutrients and phytoplankton pigments. Together, our results suggest that deterministic forces such as environmental filtering and interactions among taxa determine bacterioplankton community patterns, and consequently affect ecosystem functions in the NPSG.

Effects of Acidification and Alkalinization on a Periphytic Algal Community in an Alaskan Wetland

Experimental research examining how algal communities respond to changes in pH is sparse in the wetland literature. In this study, we used a mesocosm experiment to examine the response of a periphytic algal community to a wide range of pH levels, both decreased to pH 5 (acid treatment) and increased to pH 9 (alkaline treatment) from ambient conditions (pH 7) in an Alaskan marsh. We examined algal communities growing on stems of Equisetum fluviatile (L.) after 24 days of colonization at experimental pH levels. Alkalinization resulted in a two-fold increase in concentrations of inorganic nutrients (dissolved inorganic N, soluble reactive P, SiO2) and a significant increase in algal accrual relative to the control. There were distinct shifts in euglenoid taxa in the alkaline treatment, including a significant increase of Trachelomonas and a significant decrease of Euglena relative to the control. Acidification resulted in an increase of Mougeotia (Chlorophyta, Zygnemataceae) and a decrease in overall taxa richness, which coincided with a significant reduction in concentrations of dissolved inorganic carbon. Trends observed in our study indicate that alkalization may significantly alter algal community structure and loosen nutrient restraints on algal productivity, while acidification may reduce algal diversity in boreal wetlands.

Physico-ecobiogeochemistry of East Antarctic pack ice during the winter-spring transition

Our study provides information on the relationships between physical, chemical, and biological properties of East Antarctic sea ice sampled as part of the Sea Ice Physics and Ecosystem eXperiment (SIPEX) during the winter-spring transition in 2007. The sampled sea ice showed a high contribution of granular ice, indicating the turbulent conditions during sea ice formation off East Antarctica. The sea ice was cold, with brine volumes often below or very close to the theoretical percolation threshold of sea ice. Dissolved inorganic nutrient concentrations showed both positive and negative deviations from theoretical dilution lines, indicating both nutrient uptake as well as nutrient remineralisation in sea ice brines. Cold temperatures, high brine salinities, and low brine volumes limited high ice algal biomass to the warmer and more porous sea ice layers at the ice–water interface. We hypothesise that East Antarctic sea ice shows generally low ice algal biomass accumulation due to a combination of relatively low snow–loading, relatively cold ice temperatures, and short persistence of sea ice into the warm forcing regime, all of which prevent the development of significant internal and surface communities.

Exoenzyme activities as indicators of dissolved organic matter composition in the hyporheic zone of a floodplain river

Summary1. We measured the hyporheic microbial exoenzyme activities in a floodplain river to determine whether dissolved organic matter (DOM) bioavailability varied with overlying riparian vegetation patch structure or position along flowpaths.2. Particulate organic matter (POM), dissolved organic carbon (DOC), dissolved oxygen (DO), electrical conductivity and temperature were sampled from wells in a riparian terrace on the Queets River, Washington, U.S.A. on 25 March, 15 May, 20 July and 09 October 1999. Dissolved nitrate, ammonium and soluble reactive phosphorus were also collected on 20 July and 09 October 1999. Wells were characterised by their associated overlying vegetation: bare cobble/young alder, mid‐aged alder (8–20 years) and old alder/old‐growth conifer (25 to &gt;100 years). POM was analysed for the ash‐free dry mass and the activities of eight exoenzymes (α‐glucosidase, β‐glucosidase, β ‐N‐acetylglucosaminidase, xylosidase, phosphatase, leucine aminopeptidase, esterase and endopeptidase) using fluorogenic substrates.3. Exoenzyme activities in the Queets River hyporheic zone indicated the presence of an active microbial community metabolising a diverse array of organic molecules. Individual exoenzyme activity (mean ± standard error) ranged from 0.507 ± 0.1547 to 22.8 ± 5.69 μmol MUF (g AFDM)−1 h−1, was highly variable among wells and varied seasonally, with the lowest rates occurring in March. Exoenzyme activities were weakly correlated with DO, DOC and inorganic nutrient concentrations.4. Ratios of leucine aminopeptidase : β‐glucosidase were low in March, May and October and high in July, potentially indicating a switch from polysaccharides to proteins as the dominant component of microbial metabolism.5. Principal components analysis indicated that there were patch effects and that these effects were strongest in the summer.6. DOM degradation patterns did not change systematically along hyporheic flowpaths but varied with overlying forest patch type in the Queets River hyporheic zone, suggesting that additional carbon inputs exist. We hypothesise that the most likely input is the downward movement of DOM from overlying riparian soils. Understanding this movement of DOM from soils to subsurface water is essential for understanding both the hyporheic metabolism and the carbon budget of streams and rivers.

Diatom derived dissolved organic matter as a driver of bacterial productivity: The role of nutrient limitation

Variable inorganic nutrient concentrations were used to generate silicate (Si) or nitrogen (N) limited conditions in cultures of the marine diatom Skeletonema costatum. Dissolved organic matter (DOM) harvested in the nutrient limited phase of these cultures was added to a natural bacterial community. Enhanced bacterial abundance and bacterial production were observed, in comparison to un-supplemented controls, when Si-limited (Si-DOM) rather than N-limited (N-DOM) diatom derived DOM or inorganic nutrients was added. This indicates that the bacterial population was limited by organic rather than inorganic resources but only Si-DOM had sufficient lability to alleviate this. Within the bacterial assemblage, a notable increase in the proportion of γ-Proteobacteria was evident on receipt of only Si-DOM. Assessment of the composition of the added DOM suggested that the observed dynamics were related to organic matter composition rather than molecular size as, within the Si- and N-DOM, the proportions of low and high molecular weight compounds were similar, but the polysaccharide and protein signatures were different.

Temporal and spatial variations in phytoplankton productivity in surface waters of a warm-temperate, monomictic lake in New Zealand

Surface phytoplankton productivity measurements were carried out in morphologically complex Lake Rotoiti with the objective of defining variations between sites and seasons, and the dominant environmental drivers of these variations. Measurements were carried out monthly at two depths at each of three morphologically diverse stations for 1 year throughout the lake. Productivity at the surface of the shallow embayment was significantly higher in most months of the year compared with the surface of the other two stations but there were no significant differences from September to December 2004. There were no relationships between measured environmental variables and primary productivity or specific production. Inorganic nutrient concentrations at the surface of the shallow station were low throughout the whole year but at the other two stations they showed a typical pattern for monomictic lakes of higher levels during winter mixing and declining concentrations during thermal stratification. The high variability between sites found in this study indicates that it is important to account for local differences in productivity in morphologically diverse lakes, and that whole lake productivity estimates may vary greatly depending on the location and depth of productivity measurements.

Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 42:65-78 (2010) - DOI: https://doi.org/10.3354/cr00863 Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures M. P. Perring1,4,*, B. R. Cullen2, I. R. Johnson3, M. J. Hovenden1 1School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia 2Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria 3010, Australia 3IMJ Consultants, Armidale, New South Wales 2350, Australia 4Present address: Ecosystem Restoration Lab, School of Plant Biology (M090), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia *Email: michael.perring@uwa.edu.au ABSTRACT: Native perennial grass and sown grass-legume pastures are an important agricultural and environmental resource. We investigated the impact of rising carbon dioxide concentration ([CO2]) and projected climate changes on these pasture ecosystems in southeastern Tasmania, Australia, using a biophysical simulation model, EcoMod. The model consists of interdependent modules that describe soil physicochemical and hydrological characteristics, and pasture growth and senescence, with fluxes described by empirical and mechanistic equations. Our simulations showed that in native pastures, projected climate change increased the biomass of C4 grasses, with limited impact upon C3 grasses, a trend reversed by rising [CO2]. In sown pastures, projected climate change decreased the biomass of perennial rye grass Lolium perenne and total biomass markedly by 2070, whilst subterranean clover Trifolium subterraneum biomass increased. Subterranean clover biomass changed little with increased [CO2] alone, whereas perennial rye grass biomass increased. Responses across pastures reflected species’ tolerances to environmental factors, with projected climate change generally having more of an impact on biomass than rising [CO2]. Changes in both [CO2] and climate led to a reduction in protein content and digestibility. Soil inorganic nutrient concentrations decreased with increasing [CO2] and increased with projected climate change. Further simulations should investigate whether these patterns are robust for different sites and alternative environmental futures. Our results reinforce the need to pursue adaptation strategies in response to environmental change in order to maintain productive pasture ecosystems. KEY WORDS: Lolium perenne · Ecosystem model · Simulation · Nutrient availability · Productivity · Tasmania Full text in pdf format PreviousNextCite this article as: Perring MP, Cullen BR, Johnson IR, Hovenden MJ (2010) Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures. Clim Res 42:65-78. https://doi.org/10.3354/cr00863Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 42, No. 1. Online publication date: June 03, 2010 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2010 Inter-Research.

MINERAL CONCENTRATIONS IN LEAF DRY MATTER AND LEAF AND PETIOLE SAP IN STRAWBERRY DEPEND ON LEAF AGE AND PLANT DEVELOPMENTAL STAGE

Analysis of leaf dry matter is valuable when assessing the plants nutritional status, and for fertilizer evaluations in perennial crops. Methods for analyses of strawberry leaf and petiole sap have now become available, aiming to measure the concentration of inorganic nutrients in sap rather than the concentration of all nutrients accumulated in leaf dry matter. The use of fertigation systems and the possibilities to change fertilizer application rates at any time during the season, suggest that leaf sap analysis may become a useful tool in precision fertilization in strawberry. The present field trial aimed to provide information on variation in leaf and sap nutrient concentration during the season in the strawberry cultivar Korona. Young and unexpanded leaves, youngest fully expanded leaves and old leaves were sampled at defined plant developmental stages in the first and second harvest year. Both leaves and petioles were used for sap analyses, while only the leaf lamina was used for dry matter analysis. A constant fertilizer rate was applied through the drip irrigation system from May to August, but the results demonstrated a large variation in the concentration of mineral elements in both dry matter and sap due to differences between leaf ages, time in the season or plant developmental stage. Leaf sap analyses may offer an improved description of the actual nutrient uptake for some of the minerals during the season, if further developed and standardized. Nutrient remobilisation in the plant, dry matter accumulation and plant part analysed should be considered.

2003년 하계 장목만 단일정점에서 종속영양 와편모류와 광합성 와편모류 현존량의 시간적 변화

Abstract We investigated the temporal variations of heterotrophic dinoflagellates (hereafter HDNF) and photosynthetic dinoflagellates (hereafter PDNF) from 14 June to 4 September 2003 at a single station in Jangmok Bay. We took water samples 47 times from 2 depths (surface and bottom layers) at hide tide. A total of 63 species were encountered and in general the most abundant genera were Prorocentrum and Protoperidinium. The abundance of PDNF and HDNF was in the range of 0.04~55.8x10 4 cells/L and in the range of 0.01~4.35x10 4 cells/L, respectively. The mean abundance of PDNF was approximately 7 times higher than that of HDNF, and was higher in the surface layer where has enough irradiance for photosynthesis than in the bottom layer. The total dinoflagellate abundance was higher in the NLP (nitrogen limitation period) than in the SLP (silicate limitation period), and the abundance in the hypoxic conditions was similar to that in the normal conditions. The Shannon-Weaver species diversity index were slightly higher in the bottom layer, the SLP and the hypoxic conditions. The PDNF abundance were correlated with temperature, DO, total inorganic nitrogen and phosphate in the whole water column, and the HDNF abundance was significantly correlated with temperature, salinity and DO. This study shows that the dinoflagellate abundance might be affected by abiotic factors such as irradiance, temperature, salinity, DO and the concentrations of inorganic nutrients, and provides baseline information for further studies on plankton dynamics in Jangmok Bay. Key Words :Jangmok Bay, Heterotrophic dinoflagellates, Photosynthetic dinoflagellates, Inorganic nutrients, Hypoxia

Comparison of bottom sea-ice algal characteristics from coastal and offshore regions in the Arctic Ocean

Ice-core observations were conducted at three arctic sites in early April 2003: one clean sediment-free site (Chukchi), one sediment-rich site (Beaufort) on landfast sea ice offshore Barrow, and one oceanic Ice Exercise (ICEX) site. Concentrations of inorganic nutrients at coastal sites were similar to but higher than those at the oceanic site. Chlorophyll-a (Chl-a) concentration was much higher in the Chukchi bottom ice than at the other two sites. However, large size Chl-a (>20 μm) dominated (>70%) the bottom-ice algal Chl-a at both the Chukchi and Beaufort sites, whereas the oceanic ICEX site was evenly occupied by large (>20 μm), medium (5–20 μm), and small Chl-a (0.7–5 μm). These in situ data were incorporated into an ocean-ecosystem model. The model results revealed that: (1) strong light attenuation by trapped sediments controlled ice-algal production at the Beaufort site; (2) the peak in ice algae occurred later at the oceanic site than at the Chukchi site because of thicker ice and the consequently reduced amount of light reaching the ice algae at the ice bottom; and (3) maximum production at the oceanic site reached only 10% the level at the Chukchi site because of nutrient limitation.

Organic matter release by coral reef associated benthic algae in the Northern Red Sea

Recent research indicates that coral reef associated benthic algae may control important metabolic processes in reef ecosystems via organic matter release. Yet little information is available about quantity and chemical composition of these algae-derived exudates. Therefore first comprehensive studies on algal organic matter release were conducted at a fringing reef ecosystem in the Northern Red Sea. Dissolved organic carbon (DOC), particulate organic carbon (POC) and nitrogen (PN) release by dominant reef associated benthic algae ( Caulerpa serrulata, Peyssonnelia capensis, turf algae assemblages) were quantified during 4 seasonally resolved expeditions. Additionally, 4 seasonal blooming ( Ulva lactuca, Enteromorpha flexuosa, Liagora turneri, Hydroclathrus clathratus) and 2 patchy growing algae species ( Lobophora variegata, Saragassum dentifolium) were included in these investigations. To complement the dataset organic matter release by Caulerpa was studied under different light conditions, simulating water depths of 1, 5, 10 and 20 m. Environmental parameters (temperature, light availability, inorganic nutrient concentrations) were monitored simultaneously to assess potential effects on algal organic matter release. All 9 investigated genera of benthic algae exuded DOC and POC in amounts of 12.2 ± 2.1 and 4.2 ± 0.3 mg organic C m −² algae surface area h − 1 , respectively. Resident algae, primarily turf algae assemblages, displayed highest and seasonal blooming algae lowest organic matter release rates. Results therefore indicate that organic matter release rates are rather influenced by functional properties (growth form, life strategy) of algae than by taxonomic affiliation. Quantities of organic matter release showed seasonal and depth-mediated variations and were positively correlated with temperature and light availability within photosynthetically active radiation intensities of 0 to 300 µmol quanta m − 2 s − 1 , suggesting photoinhibition as limiting factor for productivity and subsequent organic matter release. Stable isotope signatures of algae-derived organic carbon were within a common range and likewise subjected to seasonal variations ( δ 13C summer: − 11.2‰ ± 0.2‰; δ 13 winter: − 16.7‰ ± 0.4‰). These data provide first comprehensive information about a) the potential contribution of different benthic reef algae to cycles of matter and b) environmental key factors influencing organic matter release by benthic algae in the investigated fringing reef ecosystem.

Natural background concentrations of nutrients in the German Bight area (North Sea)

Natural background concentrations of nutrients are needed for the assessments of eutrophication processes and their status. Natural background concentrations of total nitrogen (TN) and total phosphorus (TP) were modelled for the rivers discharging into the German Bight and the Rhine considering individual catchment sizes, freshwater flows and soil types. These data were validated by comparison with data from unpolluted rivers. The consistency of modelled and some compiled nutrient concentrations was confirmed by their area-specific load dependency on freshwater discharges. Pristine inorganic nutrient concentrations were deduced from modelled relations to TN and TP in unpolluted rivers. Pristine nutrient gradients between rivers and offshore waters were estimated by linear mixing until a salinity of 32, continued by hyperbolic fits towards recent mean offshore values (salinity 34.5-35). Based on these gradients and recent mean salinities, maps of pristine surface gradients were plotted for the whole German Bight. Variability was transferred from recent conditions as percentage of standard deviation. Reported historical nutrient data and concentrations from unpolluted rivers, coastal and offshore North Sea waters are discussed concerning their relations to natural background conditions.