Ambient Nutrient Concentrations Research Articles

Nitrogen uptake and regeneration (ammonium regeneration, nitrification and photoproduction) in waters of the West Florida Shelf prone to blooms of Karenia brevis

The West Florida Shelf (WFS) encompasses a range of environments from inshore estuarine to offshore oligotrophic waters, which are frequently the site of large and persistent blooms of the toxic dinoflagellate, Karenia brevis. The goals of this study were to characterize the nitrogen (N) nutrition of plankton across the range of environmental conditions on the WFS, to quantify the percentage of the plankton N demand met through in situ N regeneration, and to determine whether planktonic N nutrition changes when high concentrations of Karenia are present. In the fall of 2007, 2008, and 2009 we measured ambient nutrient concentrations and used stable isotope techniques to measure rates of primary production and uptake rates of inorganic N (ammonium, NH4+, and nitrate, NO3−), and organic N and carbon (C; urea and amino acids, AA) in estuarine, coastal, and offshore waters, as well as coastal sites with Karenia blooms present. In parallel, we also measured rates of in situ N regeneration – NH4+ regeneration, nitrification, and photoproduction of NH4+, nitrite and AA. Based on microscope observations, ancillary measurements, and previous monitoring history, Karenia blooms sampled represented three bloom stages – initiation in 2008, maintenance in 2007, and late maintenance/stationary phase in 2009. Nutrient concentrations were highest at estuarine sampling sites and lowest at offshore sites. Uptake of NH4+ and NO3− provided the largest contribution to N nutrition at all sites. At the non-Karenia sites, in situ rates of NH4+ regeneration and nitrification were generally sufficient to supply these substrates equal to the rates at which they were taken up. At Karenia sites, NO3− was the most important N substrate during the initiation phase, while NH4+ was the most important N form used during bloom maintenance and stationary phases. Rates of NH4+ regeneration were high but insufficient (85±36% of uptake) to support the measured NH4+ uptake at all the Karenia sites although nitrification rates far exceeded uptake rates of NO3−. Taken together our results support the “no smoking gun” nutrient hypothesis that there is no single nutrient source or strategy that can explain Karenia's frequent dominance in the waters where it occurs. Consistent with other papers in this volume, our results indicate that Karenia can utilize an array of inorganic and organic N forms from a number of N sources.

Nitrogen uptake kinetics in field populations and cultured strains of Karenia brevis

This study represents the most comprehensive assessment of kinetic parameters for Karenia brevis to date as it encompasses natural populations sampled during three different bloom years in addition to cultured strains under controlled conditions. Nitrogen (N) uptake kinetics for ammonium (NH4+), nitrate (NO3−), urea, an amino acid mixture, individual amino acids (glutamate and alanine), and humic substrates were examined for the toxic red tide dinoflagellate, K. brevis, during short term incubations (0.5–1h) using 15N tracer techniques. Experiments were conducted using natural populations collected during extensive blooms along the West Florida Shelf in October 2001, 2002, and 2007, and in cultured strains (CCFWC 251 and CCFWC 267) obtained from the Florida Fish and Wildlife Institute culture collection. Kinetic parameters for the maximum uptake velocity (Vmax), half-saturation concentration (Ks), and the affinity constant (α) were determined. The affinity constant is considered a more accurate indicator of substrate affinity at low concentrations. K. brevis took up all organic substrates tested, including N derived from humic substances. Uptake rates of the amino acid mixture and some NO3− incubations did not saturate even at the highest substrate additions (50–200μmolNL−1). Based upon the calculated α values, the greatest substrate preference was for NH4+ followed by NO3−≥urea, humic compounds and amino acids. The ability of K. brevis to utilize a variety of inorganic and organic substrates likely helps it flourish under a wide range of nutrient conditions from bloom initiation in oligotrophic waters offshore to bloom maintenance near shore where ambient nutrient concentrations may be orders of magnitude greater.

Seasonal patterns of nitrogen and phosphorus limitation in four German lakes and the predictability of limitation status from ambient nutrient concentrations.

To identify the seasonal pattern of nitrogen (N) and phosphorus (P) limitation of phytoplankton in four different lakes, biweekly experiments were conducted from the end of March to September 2011. Lake water samples were enriched with N, P or both nutrients and incubated under two different light intensities. Chlorophyll a fluorescence (Chla) was measured and a model selection procedure was used to assign bioassay outcomes to different limitation categories. N and P were both limiting at some point. For the shallow lakes there was a trend from P limitation in spring to N or light limitation later in the year, while the deep lake remained predominantly P limited. To determine the ability of in-lake N:P ratios to predict the relative strength of N vs. P limitation, three separate regression models were fit with the log-transformed ratio of Chla of the P and N treatments (Response ratio = RR) as the response variable and those of ambient total phosphorus:total nitrogen (TN:TP), dissolved inorganic nitrogen:soluble reactive phosphorus (DIN:SRP), TN:SRP and DIN:TP mass ratios as predictors. All four N:P ratios had significant positive relationships with RR, such that high N:P ratios were associated with P limitation and low N:P ratios with N limitation. The TN:TP and DIN:TP ratios performed better than the DIN:SRP and TN:SRP in terms of misclassification rate and the DIN:TP ratio had the highest R2 value. Nitrogen limitation was predictable, frequent and persistent, suggesting that nitrogen reduction could play a role in water quality management. However, there is still uncertainty about the efficacy of N restriction to control populations of N2 fixing cyanobacteria.

Does B12 vitamin limit phytoplankton growth in the new Iberian Peninsula?

Event Abstract Back to Event Does B12 vitamin limit phytoplankton growth in the new Iberian Peninsula? Esther Barber Lluch1*, Marta Hernández Ruiz1, Antero Prieto1, Eva Teira1 and Emilio Fernández1 1 University of Vigo, Animal Ecology and Biology, Spain The effects of increasing nutrient inputs entering to oceanic and coastal environments on primary producers are hardly predictable. Phytoplankton responses to nutrient supply depend on the autotrophic-heterotrophic coupling and a profound understanding of this interaction is required to describe response patterns. A series of microcosm experiments were carried out to assess the response of primary producers to nutrient amendments and to elucidate the role of B-vitamins on phytoplankton growth in coastal waters off the NW Iberian peninsula. Surface autotrophic microbial populations were monthly collected and exposed to known nutrient concentrations and incubated under in situ light and temperature conditions. The experimental addition treatments included: a) inorganic nutrients (nitrate, ammonium and phosphate); b) B12 vitamin (cobalamin) and c) inorganic nutrients and cobalamin. On two occasions, four additional treatments were included: d) organic nutrients (glucose and amino acids); e) a combination of inorganic and organic nutrients; f) organic nutrients and cobalamin; g) inorganic and organic nutrients plus cobalamin. Amendment experiments lasted 4 days. Samples were collected every 24h for Chlorophyll-a concentration, pico- and nanoplankton abundance and heterotrophic bacterial abundance determination. Our results suggest that phytoplankton growth is co-limited by inorganic nutrients and B12-vitamin. This co-limitation varied along the study period likely related to changes in community composition and ambient nutrient and B-vitamins concentrations. Keywords: cobalamin, co-limitation, addition experiments, NW Iberian Peninsula, Microbial Interactions Conference: IMMR | International Meeting on Marine Research 2014, Peniche, Portugal, 10 Jul - 11 Jul, 2014. Presentation Type: Poster Presentation Topic: BIODIVERSITY, CONSERVATION AND COASTAL MANAGEMENT Citation: Barber Lluch E, Hernández Ruiz M, Prieto A, Teira E and Fernández E (2014). Does B12 vitamin limit phytoplankton growth in the new Iberian Peninsula?. Front. Mar. Sci. Conference Abstract: IMMR | International Meeting on Marine Research 2014. doi: 10.3389/conf.fmars.2014.02.00081 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 09 May 2014; Published Online: 18 Jul 2014. * Correspondence: Miss. Esther Barber Lluch, University of Vigo, Animal Ecology and Biology, Vigo, Spain, esther_barber@hotmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Esther Barber Lluch Marta Hernández Ruiz Antero Prieto Eva Teira Emilio Fernández Google Esther Barber Lluch Marta Hernández Ruiz Antero Prieto Eva Teira Emilio Fernández Google Scholar Esther Barber Lluch Marta Hernández Ruiz Antero Prieto Eva Teira Emilio Fernández PubMed Esther Barber Lluch Marta Hernández Ruiz Antero Prieto Eva Teira Emilio Fernández Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Chronic nutrient enrichment increases prevalence and severity of coral disease and bleaching

Nutrient loading is one of the strongest drivers of marine habitat degradation. Yet, the link between nutrients and disease epizootics in marine organisms is often tenuous and supported only by correlative data. Here, we present experimental evidence that chronic nutrient exposure leads to increases in both disease prevalence and severity and coral bleaching in scleractinian corals, the major habitat-forming organisms in tropical reefs. Over 3 years, from June 2009 to June 2012, we continuously exposed areas of a coral reef to elevated levels of nitrogen and phosphorus. At the termination of the enrichment, we surveyed over 1200 scleractinian corals for signs of disease or bleaching. Siderastrea siderea corals within enrichment plots had a twofold increase in both the prevalence and severity of disease compared with corals in unenriched control plots. In addition, elevated nutrient loading increased coral bleaching; Agaricia spp. of corals exposed to nutrients suffered a 3.5-fold increase in bleaching frequency relative to control corals, providing empirical support for a hypothesized link between nutrient loading and bleaching-induced coral declines. However, 1year later, after nutrient enrichment had been terminated for 10months, there were no differences in coral disease or coral bleaching prevalence between the previously enriched and control treatments. Given that our experimental enrichments were well within the ranges of ambient nutrient concentrations found on many degraded reefs worldwide, these data provide strong empirical support to the idea that coastal nutrient loading is one of the major factors contributing to the increasing levels of both coral disease and coral bleaching. Yet, these data also suggest that simple improvements to water quality may be an effective way to mitigate some coral disease epizootics and the corresponding loss of coral cover in the future.

The paradox of the plankton: species competition and nutrient feedback sustain phytoplankton diversity

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 490:107-119 (2013) - DOI: https://doi.org/10.3354/meps10452 The paradox of the plankton: species competition and nutrient feedback sustain phytoplankton diversity Kasia Kenitz1, Richard G. Williams1,*, Jonathan Sharples1,2, Özgür Selsil3 , Vadim N. Biktashev3 1School of Environmental Sciences, University of Liverpool, Liverpool L69 3GP, UK 2National Oceanography Centre, Liverpool, Liverpool L3 5DA, UK 3School of Mathematical Sciences, University of Liverpool, Liverpool L69 7ZL, UK *Corresponding author. Email: ric@liverpool.ac.uk ABSTRACT: The diversity of phytoplankton species and their relationship to nutrient resources are examined using a coupled phytoplankton and nutrient model for a well-mixed box. The phytoplankton community either reaches a competitive exclusion state, where there is an optimal competitor, or the abundance of each phytoplankton species continually varies in the form of repeating oscillations or irregular chaotic changes. Oscillatory and chaotic solutions make up over half of the model solutions based upon sets of 1000 separate model integrations spanning large, moderate or small random changes in the half-saturation coefficient, Kji. The oscillatory or chaotic states allow a greater number of phytoplankton species to be sustained, even for their number to exceed the number of resources after additional species have been injected into the environment. The chaotic response, however, only occurs for particular model choices: when there is an explicit feedback between nutrient supply and ambient nutrient concentration, and when there are physiological differences among species, including cell quota and Kji. In relation to the surface ocean, the nutrient feedback can be viewed as mimicking the diffusive nutrient supply from the nutricline. Inter-species competition might then be important in generating chaos when this diffusive transfer is important, but less likely to be significant when other transport processes sustain surface nutrient concentrations. KEY WORDS: Plankton paradox · Coexistence · Chaos · Competitive exclusion · Phytoplankton communities Full text in pdf format Supplementary material PreviousNextCite this article as: Kenitz K, Williams RG, Sharples J, Selsil Ö, Biktashev VN (2013) The paradox of the plankton: species competition and nutrient feedback sustain phytoplankton diversity. Mar Ecol Prog Ser 490:107-119. https://doi.org/10.3354/meps10452 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 490. Online publication date: September 17, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Cross‐ecosystem differences in lipid composition and growth limitation of a benthic generalist consumer

In a field study, we analyzed the fatty acid (FA) composition of the benthic generalist Asellus aquaticus collected from boreal lakes, ponds, and streams across gradients in ambient nutrient levels. In laboratory feeding experiments, we tested the diet‐quality and seasonal effects on somatic growth and FAs of spring‐ and autumn‐collected Asellus that were fed four different diets containing increasing concentrations of polyunsaturated FAs (PUFA): conditioned leaf litter, algal flakes, mixed litter and algal flakes (Mixed), or Mixed plus fish‐food flakes. Ambient nutrients were strong determinants of FA variation of field Asellus, explaining > 44% in total. The ratios of eicosapentaenoic acid (EPA) to total FAs, EPA : ω3, and ω3 : ω6 of Asellus increased up to four times with increasing trophic state and decreasing humic matter content, likely because dietary ω3 FAs were more prevalent in benthic habitats of eutrophic than of oligotrophic systems. In the feeding trials, growth of Asellus collected in both seasons was markedly lower on leaf litter than on higher PUFA diets. However, autumn‐collected Asellus fed a Mixed or Mixed+fish‐food diet grew 3–10 times faster, but retained < 50% EPA and PUFA than spring counterparts. Asellus optimized PUFA accumulation in spring but somatic growth in autumn. Our field survey suggests ambient nutrient concentrations modify dietary PUFA supply from basal resources, while laboratory studies show that growth response and PUFA accumulation of Asellus differ between seasons, likely due to its season‐specific physiological status and diet quality. An increase in nutrients will release benthic consumers from growth limitation and favor more efficient trophic transfer.

Effects of nutrient enrichment and herbivory on morphology, reproduction and chemical content of Turbinaria conoides (Phaeophyceae)

SummaryThe effects of nutrient enrichment and herbivory on resource allocation patterns among morphology, reproduction, and chemical content of the brown alga, Turbinaria conoides (J. Agardh) Kützing were tested in the shallow subtidal zone of the Gulf of Thailand. The field experimental design comprised 36 plots (50 × 50 cm2) with and without herbivores, and two nutrient levels. Cages (uncaged and fully caged plots) were used to exclude herbivorous fishes and two nutrients levels were achieved by experimental enrichment above ambient nutrient concentrations. For morphology of Turbinaria, the maximum length (holdfast to frond apex), the width of the base of the stipe, number of blades, holdfast and stipe diameter were measured. Biomass, reproductive output, and tissue nutrient (carbon: nitrogen: phosphorus) content of T. conoides were examined. Phlorotannin concentrations were examined using a modified Folin‐Ciocalteu method. The results showed that herbivory had no effect on morphology, reproduction, or phlorotannin concentrations. This could be due to the structural and morphological deterrents of alga, which might minimize grazing effects from herbivorous fishes. Nutrient enrichment had no effect on morphology and reproduction of T. conoides, possibly due to low nutrient demand in Turbinaria. However, nutrient enrichment did affect phlorotannin concentrations, as phlorotannins in the enriched plots were lower than the ambient plots. These results support, in part, the carbon–nutrient balance hypothesis that states algae will allocate fewer resources to production of anti‐herbivore chemical compounds when enriched with potential growth‐limiting nutrients.

Nutrient shielding in clusters of cells

Cellular nutrient consumption is influenced by both the nutrient uptake kinetics of an individual cell and the cells' spatial arrangement. Large cell clusters or colonies have inhibited growth at the cluster's center due to the shielding of nutrients by the cells closer to the surface. We develop an effective medium theory that predicts a thickness ℓ of the outer shell of cells in the cluster that receives enough nutrient to grow. The cells are treated as partially absorbing identical spherical nutrient sinks, and we identify a dimensionless parameter ν that characterizes the absorption strength of each cell. The parameter ν can vary over many orders of magnitude among different cell types, ranging from bacteria and yeast to human tissue. The thickness ℓ decreases with increasing ν, increasing cell volume fraction φ, and decreasing ambient nutrient concentration ψ(∞). The theoretical results are compared with numerical simulations and experiments. In the latter studies, colonies of budding yeast, Saccharomyces cerevisiae, are grown on glucose media and imaged under a confocal microscope. We measure the growth inside the colonies via a fluorescent protein reporter and compare the experimental and theoretical results for the thickness ℓ.

Top-Down Regulation, Climate and Multi-Decadal Changes in Coastal Zoobenthos Communities in Two Baltic Sea Areas

The structure of many marine ecosystems has changed substantially during recent decades, as a result of overexploitation, climate change and eutrophication. Despite of the apparent ecological and economical importance of coastal areas and communities, this aspect has received relatively little attention in coastal systems. Here we assess the temporal development of zoobenthos communities in two areas on the Swedish Baltic Sea coast during 30 years, and relate their development to changes in climate, eutrophication and top-down regulation from fish. Both communities show substantial structural changes, with a decrease in marine polychaetes and species sensitive to increased water temperatures. Concurrently, opportunistic species tolerant to environmental perturbation have increased in abundance. Species composition show a similar temporal development in both communities and significant changes in species composition occurred in both data sets in the late 1980s and early 1990s. The change in species composition was associated with large scale changes in climate (salinity and water temperature) and to the structure of the local fish community, whereas we found no effects of nutrient loading or ambient nutrient concentrations. Our results suggest that these coastal zoobenthos communities have gone through substantial structural changes over the last 30 years, resulting in communities of different species composition with potentially different ecological functions. We hence suggest that the temporal development of coastal zoobenthos communities should be assessed in light of prevailing climatic conditions considering the potential for top-down effects exerted by local fish communities.

The effect of catchment urbanization on nutrient uptake and biofilm enzyme activity in Lake Superior (USA) tributary streams

We compared landscape, habitat, and chemistry variables with nutrient spiraling and biofilm extracellular enzyme activity (EEA), to assess the response of nine Lake Superior tributaries to the level of urbanization in their catchments. We found no significant correlation between uptake metrics for NH4+ and PO43− and the level of catchment urbanization. NH4+ and PO43– uptake velocities (Vf) were, however, positively correlated with biofilm EEA and with biofilm respiration (DHA). In general, biofilm EEA was negatively correlated with indicators of increased urbanization (e.g., % impervious surface cover and Cl− concentration) and positively correlated with % forest cover. Biofilm respiration measured as dehydrogenase activity (DHA) decreased with indicators of increased urbanization (e.g., % ISC, storm sewer length, % of the stream channel shaded by the riparian canopy, and Cl−) and increased with non-urban indicators (e.g., % forest, % wetland, and stream width and depth). Regression of Vf and uptake rate (U) versus ambient nutrient concentrations indicated phosphorus limitation in the study streams, a result supported by regression biofilm peptidase versus phosphatase activity. There was no evidence of NH4+ saturation or limitation. This is the first study to demonstrate correlations between nutrient uptake and biofilm EEA in streams, with linkages to catchment-scale disturbances.

Influence of Amur River discharge on phytoplankton photophysiology in the Sea of Okhotsk during late summer

AbstractWe investigated the photosynthetic parameters of phytoplankton in the Sea of Okhotsk during the late summer of 2006 to characterize their spatiotemporal variability and to test the hypothesis that discharge from the Amur River could influence the algal photophysiology. The highest maximum quantum yield of carbon fixation in photosynthesis (Φcmax; 0.098 mol C mol photons‐1) was found near the Amur River mouth, where nitrate was depleted. However, none of the photosynthetic parameters, including primary productivity (PP) at the surface, were correlated with temperature, daily photosynthetically available radiation (PAR), or ambient nutrient concentrations. Variations in Φcmax depended on the variations in not only the mean chlorophyll a specific absorption coefficient of phytoplankton (ā*ph) but also the slope index of the absorption coefficient of phytoplankton (aph slope), an indicator for the ratio of nonphotosynthetic carotenoids to photosynthetic carotenoids. These results indicated that the phytoplankton assemblages acclimated to the ambient light conditions by regulating their cellular pigments. Additionally, ā*ph and euphotic depth (Zeu) were significantly correlated with salinity, suggesting that photoacclimation of the phytoplankton assemblages observed in this study could be induced by discharge of Amur River. Because spatiotemporal variations in PP were concomitant with Φcmax, ā*ph, and the chlorophyll a concentration, PP models based on inherent optical property (IOP) were suitable for estimating PP in the Sea of Okhotsk. This study is the first to investigate the factors controlling phytoplankton photophysiology in the Sea of Okhotsk, one of the highest primary production areas in the world.

Response of bacterial community structure and function to experimental rainwater additions in a coastal eutrophic embayment

Although recognized as a potentially important source of both inorganic and organic nutrients, the impact of rainwater on microbial populations from marine planktonic systems has been poorly assessed. The effect of rainwater additions on bacterioplankton metabolism and community composition was evaluated in microcosm experiments enclosing natural marine plankton populations from the Ría de Vigo (NW Spain). The experiments were conducted during three different seasons (spring, autumn and winter) using rainwater collected at three different locations: marine, urban and rural sites. Bacterial abundance and production significantly increased up to 1.3 and 1.8-fold, respectively, after urban rainwater additions in spring, when ambient nutrient concentration was very low. Overall, the increments in bacterial production were higher than those in bacterial respiration, which implies that a higher proportion of carbon consumed by bacteria would be available to higher trophic levels. The response of the different bacterial groups to distinct rainwater types differed between seasons. The most responsive bacterial groups were Betaproteobacteria which significantly increased their abundance after urban (in spring and winter) and marine (in spring) rainwater additions, and Bacteroidetes which positively responded to all rainwater treatments in spring and to urban rainwater in autumn. Gammaproteobacteria and Roseobacter responded only to urban (in spring) and marine (in winter) rainwater treatment, respectively. The responses to rainwater additions were moderate and transient, and the resulting bacterial community structure was not importantly altered.

Effects of temperature, algae biomass and ambient nutrient on the absorption of dissolved nitrogen and phosphate by Rhodophyte Gracilaria asiatica

Gracilaria asiatica, being highly efficient in nutrient absorption, is cultivated in sea cucumber ponds to remove nutrients such as nitrogen and phosphate. It was cultured in a laboratory simulating field conditions, and its nutrient absorption was measured to evaluate effects of environmental conditions. Ammonia nitrogen (AN), nitrate nitrogen (NN), total inorganic nitrogen (TIN), and soluble reactive phosphorus (SRP) uptake rate and removal efficiency were determined in a 4×2 factorial design experiment in water temperatures (T) at 15°C and 25°C, algae biomass (AB) at 0.5 g/L and 1.0 g/L, total inorganic nitrogen (TIN) at 30 μmol/L and 60 μmol/L, and soluble reactive phosphorus (SRP) at 3 and 6 μmol/L. AB and ambient TIN or SRP levels significantly affected uptake rate and removal efficiency of AN, NN, TIN, and SRP ( P< 0.001). G. asiatica in AB of 0.5 g/L showed higher uptake rate and lower removal efficiency relative to that with AB of 1.0 g/L. Nitrogen and phosphorus uptake rate rose with increasing ambient nutrient concentrations; nutrient removal efficiency decreased at higher environmental nutrient concentrations. The algae preferred to absorb AN to NN. Uptake rates of AN, NN, and SRP were significantly affected by temperature (P < 0.001); uptake rate was higher for the 25°C group than for the 15°C group at the initial experiment stage. Only the removal efficiency of AN and SRP showed a significant difference between the two temperature groups (P< 0.01). The four factors had significant interactive effects on absorption of N and P, implying that G. asiatica has great bioremedial potential in sea cucumber culture ponds.

Effects of short-term sediment nutrient enrichment and grazer &lt;i&gt;(Neritina reclivata)&lt;/i&gt; removal on sediment microalgae in a shallow eutrophic estuary (Alabama, USA)

The olive snail (Neritina reclivata) is ubiquitous in tropical and sub-tropical systems of the Gulf of Mexico, however its impacts on sediment microalgae have been little studied. Many coastal systems around the world are being eutrophied due to human activities, and seemingly they will continue to be eutrophied to a further extent in the future. Exploring the single and combined impacts of further nutrient enrichment and grazing by the olive snail on sediment microalgae in such eutrophic systems is an important question for our understanding and management of these systems. Here we examine the effects of short-term nutrient enrichment and grazing by the olive snail N. reclivata on sediment microalgal biomass and composition in a shallow eutrophic estuary (Weeks Bay, Alabama, USA) of the Northern Gulf of Mexico. For this, we performed a series of factorial experiments adding or not nutrients and removing or not the snail, for a total of four treatments in each experiment: ambient grazing, ambient nutrients; ambient grazing, increased nutrients; no grazing, ambient nutrients; and no grazing, increased nutrients. We did not find any significant impact of nutrient addition in any of the eight short-term (i.e. four days) experiments carried out. Impacts by the snail were minor; we only found a decrease in biomass due to snail grazing in one of the eight experiments, and no impacts on microalgal (i.e. diatom) composition. High ambient nutrient concentrations in the sediment porewater and low snail abundances on the sediment could explain these findings. Our results suggest that ephemeral, short-term nutrient pulses into eutrophic coastal systems of the Northern Gulf of Mexico, such as Weeks Bay (Alabama, USA), should not greatly affect the abundance of sediment microalgae, even though those pulses occur in well-lit areas. The results further suggest the snail N. reclivata is not a major control of sediment microalgal populations in the subtidal sedimentary areas studied. Our findings contrast with the results of past work in sediments with well-lit and nutrient poor conditions, or sediments with high densities of other snail grazers. In conjunction this and other investigations indicate that the response of sediment microalgae to nutrient enrichment and modified grazer abundance depends to a large extent on the initial levels of nutrient availability and grazing before the system is altered.

The unique biogeochemical signature of the marine diazotroph trichodesmium.

The elemental composition of phytoplankton can depart from canonical Redfield values under conditions of nutrient limitation or production (e.g., N fixation). Similarly, the trace metal metallome of phytoplankton may be expected to vary as a function of both ambient nutrient concentrations and the biochemical processes of the cell. Diazotrophs such as the colonial cyanobacteria Trichodesmium are likely to have unique metal signatures due to their cell physiology. We present metal (Fe, V, Zn, Ni, Mo, Mn, Cu, Cd) quotas for Trichodesmium collected from the Sargasso Sea which highlight the unique metallome of this organism. The element concentrations of bulk colonies and trichomes sections were analyzed by ICP-MS and synchrotron x-ray fluorescence, respectively. The cells were characterized by low P contents but enrichment in V, Fe, Mo, Ni, and Zn in comparison to other phytoplankton. Vanadium was the most abundant metal in Trichodesmium, and the V quota was up to fourfold higher than the corresponding Fe quota. The stoichiometry of 600C:101N:1P (mol mol−1) reflects P-limiting conditions. Iron and V were enriched in contiguous cells of 10 and 50% of Trichodesmium trichomes, respectively. The distribution of Ni differed from other elements, with the highest concentration in the transverse walls between attached cells. We hypothesize that the enrichments of V, Fe, Mo, and Ni are linked to the biochemical requirements for N fixation either directly through enrichment in the N-fixing enzyme nitrogenase or indirectly by the expression of enzymes responsible for the removal of reactive oxygen species. Unintentional uptake of V via P pathways may also be occurring. Overall, the cellular content of trace metals and macronutrients differs significantly from the (extended) Redfield ratio. The Trichodesmium metallome is an example of how physiology and environmental conditions can cause significant deviations from the idealized stoichiometry.

Effect of tile effluent on nutrient concentration and retention efficiency in agricultural drainage ditches

Abstract Tile drainage is a common water management practice in many agricultural landscapes in the Midwestern United States. Drainage ditches regularly receive water from agricultural fields through these tile drains. This field-scale study was conducted to determine the impact of tile discharge on ambient nutrient concentration, nutrient retention and transport in drainage ditches. Grab water samples were collected during three flow regimes for the determination of soluble phosphorus (SP), ammonium nitrogen (NH 4 + -N), nitrate nitrogen (NO 3 -N) concentrations and their retention in three drainage ditches. Measured nutrient concentration indicated lower SP and NH 4 + -N, and greater NO 3 -N concentrations in tile effluents compared to the ditch water. Net uptake lengths were relatively long, especially for NO 3 -N, indicating that nutrients were generally not assimilated efficiently in these drainage systems. Results also indicated that the study reaches were very dynamic showing alternating increases or decreases in nutrient concentration across the flow regimes. The drainage ditches appeared to be nutrient-rich streams that could potentially influence the quality of downstream waters.

Technical Note: A comparison of two empirical approaches to estimate in-stream net nutrient uptake

Abstract. To establish the relevance of in-stream processes on nutrient export at catchment scale it is important to accurately estimate whole-reach net nutrient uptake rates that consider both uptake and release processes. Two empirical approaches have been used in the literature to estimate these rates: (a) the mass balance approach, which considers changes in ambient nutrient loads corrected by groundwater inputs between two stream locations separated by a certain distance, and (b) the spiralling approach, which is based on the patterns of longitudinal variation in ambient nutrient concentrations along a reach following the nutrient spiralling concept. In this study, we compared the estimates of in-stream net nutrient uptake rates of nitrate (NO3) and ammonium (NH4) and the associated uncertainty obtained with these two approaches at different ambient conditions using a data set of monthly samplings in two contrasting stream reaches during two hydrological years. Overall, the rates calculated with the mass balance approach tended to be higher than those calculated with the spiralling approach only at high ambient nitrogen (N) concentrations. Uncertainty associated with these estimates also differed between both approaches, especially for NH4 due to the general lack of significant longitudinal patterns in concentration. The advantages and disadvantages of each of the approaches are discussed.

Cell size variation of Anoplosolenia brasiliensis(calcareous nannoplankton) in the central equatorial Pacific Ocean

A morphometric analysis on Anoplosolenia brasiliensis(calcareous nannoplankton) was conducted employing samples obtained from 0 to 120 m water depths in the central equatorial Pacific Ocean along the equator ranging from 166.3°E to 170.1°W. Measured cell length of A. brasiliensis showed the minimum of 39 μm to the maximum of 165 μm. The cell width ranged from the minimum of 1 μm to the maximum of 10 μm. Measured cell volumes ranged from the minimum of 28.3 μm3 to the maximum of 2,741 μm3. In addition, length/width ratios ranged from the minimum of 6.8 to the maximum of 37.5. The cell size of this taxon is very large compared to that of other calcareous nannoplankton taxa such as Emiliania huxleyi. Related factors for such a large cell size appears to be: (1)population density of the own taxon; (2)ambient temperature; (3)ambient dissolved oxygen concentration; and (4)other phytoplankton population density such as that of E. huxleyi. The life adaptation of A. brasiliensis is interpreted as fundamentally pursuing a K-strategy, but this taxon is also pursuing an r-strategy when appropriate situation arises. The population density of this taxon may be related to ambient nutrient concentrations, intricate balance among several species of nutrients, and competitions with other coccolithophore taxa such as E. huxleyi.

Nutrient and light limitation of periphyton in selected streams in Ireland

This study was undertaken to improve knowledge on the role of both phosphorus and nitrogen in eutrophication of riverine systems. The potential for nutrient limitation of algal biomass was examined during the early growth season in 4 good water quality Irish streams. Four treatments using nutrient diffusing substrata were employed in each river to test algal growth responses to addition of nitrogen (N), phosphorus (P), and a combination of N and P at 3 con-centrations (0.05, 0.1, and 0.5 mol/L) as well as a control (agar only) in open and closed canopy over a 21 d period. The ambient streamwater nutrient concentrations from all streams remained at low levels with high N:P ratios. Results indicated that algal biomass as chlorophyll a (Chl-a) was significantly greater at all sites located in open canopy than at the closed canopy sites, implicating light as the first limiting factor in the studied streams. Periphyton response to the nutrient treatments was varied: one stream responded significantly to N addition, indicating N limitation; 2 streams were co-limited by both N and P; and a fourth stream did not show significant responses to any treatment. Phosphorus did not seem to be the sole limiting nutrient for algal biofilm in 4 examined Irish streams at this time of year (May–Jun). There was no significant difference in Chl-a concentrations in response to the applied nutrient concentrations for most sites in the open canopy; there was some response in the closed-canopy sites.