bluuebunny/crossref_metadata_2025 huggingface dataset:
Serum Neutrophil Gelatinase-Associated Lipocalin in Infants and Children with Sepsis-Related Conditions with or without Acute Renal Dysfunction
Authors: Afify Mohammed Farouk M. , Maher Sheren Esam , Ibrahim Nora Mohamed , El-Hamied Waleed Mahamoud Abd
Published: August 2016

Purpose

To validate serum neutrophil gelatinase-associated lipocalin (NGAL) as an early biomarker for acute kidney injury (AKI) in sepsis-related conditions and its predictive and prognostic values.

Patients and Methods

This study included 65 patients, who were clinically evaluated for sepsis, severe sepsis, or septic shock, and 20 apparently healthy served as controls. Patients were divided into two groups: Group I (AKI-sepsis): 65 newly admitted patients diagnosed as sepsis, who were further divided into three subgroups according to the severity: systemic inflammatory response syndrome, severe sepsis, and septic shock, and Group II (control group): 20 apparently healthy subjects matched for age and sex, serum creatinine and serum NGAL concentrations were estimated initially within 24 hours of admission and after 72 hours of admission in all patients and control groups.

Results

Serum NGAL increased significantly with increasing severity of renal impairment. Receiver-operating characteristic analysis suggested that serum NGAL cutoff value of 40 ng/mL within the first 24 hours of admission is highly specific and sensitive for predicting AKI, with sensitivity of 90.9% and specificity of 75.8%.

Conclusion

We concluded that early measurement of serum NGAL level in sepsis can serve as a clinically useful marker for early prediction of AKI and for grading of its severity.
Environmental Health and Safety Hazards of Indigenous Small-Scale Gold Mining Using Cyanidation in the Philippines
Authors: Leung Ana Marie R. , Lu Jinky Leilanie DP.
Published: August 2016

Objectives

This cross-sectional study aimed at the environmental health hazards at work and cyanide exposure of small-scale gold miners engaged in gold extraction from ores in a mining area in the Philippines.

Methods

Methods consisted of structured questionnaire-guided interviews, work process observation tools, physical health assessment by medical doctors, and laboratory examination and blood cyanide determination in the blood samples of 34 indigenous small-scale gold miners from Benguet, Philippines.

Results

The small-scale gold miners worked for a mean of 10.3 years, had a mean age of 36 years, with mean lifetime mining work hours of 18,564. All were involved in tunneling work (100%) while a considerable number were involved in mixing cyanide with the ore (44%). A considerable number were injured (35%) during the mining activity, and an alarming number (35%) had elevated blood cyanide level. The most prevalent hazard was exposure to chemicals, particularly to cyanide and nitric acid, which were usually handled with bare hands.

Conclusion

The small-scale gold miners were exposed to occupational and environmental hazards at work.
PHOSPHATE REGENERATION BY ZOOPLANKTON IN CAYUGA LAKE
Authors: Barlow John P. , Bishop John W.
Published: August 2016

Rates of liberation of phosphate by the zooplankton in Cayuga Lake were measured in late summer when the lake was strongly stratified. About 80% of the phosphorus was liberated in the epilimnion, apparently principally by cladocerans. The regeneration of phosphorus by the zooplankton in the epilimnion appears to be sufficient to supply the requirements of the phytoplankton populations of that period.
VARIATIONS IN PHOTOSYNTHETIC ASSIMILATION RATIOS IN NATURAL, MARINE PHYTOPLANKTON COMMUNITIES1
Authors: Curl Herbert , Small Lawrence F.
Published: August 2016

Thirteen in situ measurements of primary production were made 25 miles (46 km) west of Newport, Oregon between April 1962 and June 1964. Assimilation ratios [mg C hr‐1 (mg Chl a)‐1] at light saturation ranged between 6 and 21. The mean value was 8.6 with a 95% confidence interval of ±1.3. There was no correlation between maximum assimilation ratios and total daily solar radiation. with recently upwelled water. The highest values observed were associated with recently upwelled water. It is suggested on the basis of these experiments and the work of others that assimilation ratios of 0–3 indicate nutrient depletion; ratios between 3 and 5 indicate borderline nutrient deficiency, and ratios between 5 and 10 indicate nutrient‐rich waters. It is concluded that emperically determined Cassimilation ratios, derived from as near‐natural experiments as possible, should be used in production equations.
A SUBMERGED PEAT DEPOSIT OFF THE ATLANTIC COAST OF THE UNITED STATES1
Authors: Emery K. O. , Wigley R. L. , Rubin Meyer
Published: August 2016

A sample of salt‐marsh peat from a depth of 59 m at the northwestern margin of Georges Bank has a radiocarbon age of 11,000 ± 350 years. No greater depth or age of salt‐marsh peat lying exposed on the ocean floor elsewhere in the world are known to the authors. The age corresponds well with the date of ice retreat from the Gulf of Maine and with the ages of oyster and other shells that mark the advance of the ocean across the bank and the adjacent continental shelf.
CARBON DIOXIDE IN THE SURFACE WATERS OF THE NORTH ATLANTIC OCEAN AND THE BARENTS AND KARA SEAS1
Authors: Kelley John J.
Published: August 2016

Measurements of the equilibrium concentration of carbon dioxide with respect to air in the surface waters of the Kara, Barents, and Norwegian Seas during the late summer of 1967 show undersaturation. The North Atlantic Ocean during late summer is slightly undersaturated except for limited areas such as the North Sea, south of Nova Scotia, and within the Gulf Stream, where supersaturation is found. Observations across the North Atlantic Ocean from the North Sea to Massachusetts Bay agree closely with the results of K. Buch from a similar track in 1935. The data indicate that for a 1C increase in surface sea temperature there is a 10 ppm increase in CO2 concentration. An increase in oxygen concentration of 1.0 ml/liter is associated with a decrease of 45 ppm CO2. In the Barents Sea, a linear relationship is found between CO2 and salinity, with a rise of 39 ppm CO2 per part per thousand increase in surface salinity.
The applicability of fish yield indices in freshwater and marine ecosystems
Authors: Kerr S. R. , Ryder R. A.
Published: August 2016

Marine fisheries are subject to external forcing by physical factors over a much larger range of size scales than are freshwater fisheries, but there are many similarities in the way the process of fish production is organized. Fish yield indicators, particularly those based on abiotic environmental factors, have provided useful management tools in both environments. We discuss examples from each, including a separate category for rivers and impoundments because of their particular sensitivity to physical factors. We conclude that the apparent dichotomy between freshwater and marine fisheries science results as much from differing management imperatives as from any scientific distinctions and suggest there would be advantages to fuller communication between the disciplines.
Physical energy inputs and the comparative ecology of lake and marine ecosystems
Authors: Nixon Scott W.
Published: August 2016

Although freshwater and marine systems both receive light and heat energy from the sun and are mixed by the wind, only marine systems receive additional mechanical energy from the tide. This input is very small relative to the flux of solar energy but may exceed that from wind. Some obvious physical consequences of this additional energy input include the development of intertidal habitats, the presence of stronger currents, and more vigorous vertical mixing. It is argued that these (and perhaps other) consequences lead to coastal marine ecosystems which differ in a number of important ways from temperate lakes.

There is some evidence that coastal marine systems generally maintain a larger standing crop of benthic animals and that these fauna are more effective in mixing the bottom sediments. As a result of better sediment mixing (and perhaps warmer and better oxygenated bottom water), organic matter deposited on the bottom of coastal marine areas may be more completely metabolized and less C, N, and P retained than in lake sediments. Materials that are more tightly bound to particles, like many metals, may behave similarly in lake and marine sediments. Although many lakes are strong sinks for nutrients and metals, marine bays and estuaries may be much less effective in retaining nutrients.

A major consequence of the input of tidal energy appears to be a more intensive yield of fish from marine systems compared with temperate lakes. The data suggest that this more intense yield is not due to the size or interconnection of marine areas or to higher primary production. Rather, the efficiency of transfer of primary production to fish appears to be greater. Tropical lakes appear more like marine systems in this regard, and this may be related to lower thermal stability and more efficient wind energy transfer because of a small Coriolis effect at low latitudes.
Mierobial biogeochemistry and heterotrophy in sediments of a marine hydrocarbon seep
Authors: Bauer James E. , Montagna Paul A. , Spies Robert B. , Prieto Maria C. , Hardin Dane
Published: August 2016

Vertical profiles of sediment and pore‐water constituents and rates of microbially mediated geochemical processes were determined in surficial sediments (0–7‐cm depth) of three stations in and around Isla Vista hydrocarbon seep off Santa Barbara, California. Measurements were made of pore‐water alkalinity (total and carbonate), pH, Eh, dissolved oxygen, sulfate, and sulfide, total sedimentary organic carbon (TOC) and nitrogen, ATP, sulfate reduction and dark bicarbonate uptake and incorporation, and oxygen flux across the sediment‐water interface in benthic chambers.

In general, alkalinity, pH, sulfide, TOC, ATP, and all rate processes were greatest in sediments of that station (A) with active seepage and decreased with increasing distance from the seep. Sulfate depletion and extremely low Eh values occurred in station A sediments. At a station (B) with lower seepage rates than station A, sedimentary and pore‐water constituents and rate processes were intermediate to those measured at station A and a station (C) without seepage. Pore‐water and sedimentary constituents as well as oxygen flux were strongly correlated with total extractable sedimentary hydrocarbons (TEH) measured at each station and for each corresponding depth interval. All parameters exhibited seasonal differences that may have been temperature‐dependent.

The greater concentrations of TEH, sulfide, and alkalinity with increasing sedimentary depth indicate that seep sediments are a source of these constituents to the water column and a sink for O2 and SO42‒. The strong heterotrophic, and possibly chemoautotrophic, character of seep sediments resembles that of other organically enriched systems. The diagenesis of petroleum hydrocarbons is a function of the biogeochemical patterns and microbial heterotrophic activities in surficial sediments.
Carbon conversion efficiency for bacterial growth on lignocellulose: Implications for detritus‐based food webs
Authors: Benner Ronald , Lay Jan , K&nees Elizabeth , Hodson Robert E.
Published: August 2016

Carbon conversion efficiencies were determined for the bacterial utilization of lignocellulosic detritus in waters from an estuarine and a freshwater wetland. Conversion efficiencies during bacterial growth on lignocellulose averaged ∼30% in both estuarine (salt marsh) and freshwater (Okefenokee Swamp) samples. Our estimates of bacterial growth efficiencies on refractory particulate detritus are twofold to threefold higher than previous estimates owing, in large part, to the higher biovolume‐to‐carbon conversion factor (0.22 g C cm‒3) used in the present study to convert bacterial biovolumes into units of carbon. Bacterial growth on lignocellulosic detritus was N limited in salt‐marsh water and P limited in Okefenokee water; carbon conversion efficiencies increased to 45% upon addition of ammonium and phosphate to salt‐marsh and Okefenokee incubations, respectively. These results indicate that bacterial biomass produced at the expense of lignocellulosic detritus is likely to be an important nutrient source to food webs in aquatic ecosystems with an abundance of macrophyte detritus and favorable conditions for microbial decomposition.
Twin cosmogenic radiotracer studies of phosphorus recycling and chemical fluxes in the upper ocean
Authors: Lai D. , Chung Y. , Platt T. , Lee T.
Published: August 2016

We determined the feasibility of using two cosmogenic radionuclides, 32P (half life, 14.3 d) and 33P (half‐life, 25.3 d) as tracers for studying nutrient cycling and chemical fluxes in the upper layers of the ocean. Various chemical procedures were tried to extract dissolved inorganic phosphorus (DIP) from several thousand liters of seawater as required to measure the natural activities of 32P and 33P. We developed a simple and convenient procedure for extraction of DIP from about 103 liters of seawater h 1, simultaneously from several depths. The activities of 32P and 33P were measured with a low‐level Q‐gas flow counter. The 32P activities in coastal waters off La Jolla and San Diego range between 0.5 and 0.9 dpm m‒3 of seawater. The 32P‐specific activities in coastal plankton samples range between 20 and 100 [dpm (g P)‒1], zooplankton samples being consistently lower than phytoplankton samples. The phytoplankton samples have 32P activities (dpm m‒3 of seawater) close to those in surface waters.

The observed concentrations and specific activities of these tracers in dissolved and particulate phosphorus pools are in excellent agreement with expectations. Our studies demonstrate their usefulness as suitable tracers for studies of P pathways through the pelagic food chain and P flux through the thermocline, averaged over a time scale of 1–2 months.
Consequences of thymidine catabolism for estimates of bacterial production: An example from a coastal marine sediment
Authors: Carman Kevin R. , Dobbs Fred C. , Guckert James B.
Published: August 2016

Radioactively labeled thymidine (TdR) has been used extensively to measure bacterial production in aquatic environments, but critical assumptions of the TdR technique often have gone untested. In this study of a coastal marine sediment, the metabolic fate of methyl [3H]TdR and methyl [14C]TdR was at variance with the assumptions necessary for determining bacterial production. Only 2% of incorporated radioactivity was recovered in the DNA fraction of TCA‐insoluble material following time‐course incubations of 1–300 min. At least the methyl group of TdR was extensively catabolized, as shown by copious production of 14CO2. The temporal patterns of 3H: 14C ratios in macromolecular fractions indicated that products of catabolism were recycled into the DNA fraction. The accuracy of the TdR technique depends in large part on the degree to which such catabolism occurs.
The biogeochemical cycling of dissolved organic nitrogen in estuarine sediments
Authors: Burdige David J. , Zheng Shilong
Published: August 2016

Benthic fluxes and pore‐water profiles of dissolved organic nitrogen and carbon (DON and DOC, respectively) were determined in seasonal studies at contrasting sites in Chesapeake Bay. Pore‐water dissolved organic matter (DOM) concentrations were elevated over bottom‐water values, generally increased with depth, and ranged from 15 to ~160 µM for DON and ~200–2000 µM for DOC. Pore‐water DOM concentrations and the C:N ratio of this material showed spatial (depth) and temporal changes that varied among the sites studied. These trends appeared to be related to differences in the types of sediment organic matter (SOM) undergoing remineralization, as well as differences in the biogeochemical processes occurring in the sediments (e.g., the presence or absence of bioturbation and bioirrigation). Measured DON fluxes ranged from essentially zero to ~0.4 mmol m−2 d−1, and together with benthic DOC fluxes were coupled to seasonal trends in temperature and SOM remineralization rates. On an annual basis, benthic DON fluxes were a small fraction (~3%) of benthic inorganic nitrogen fluxes. At an anoxic nonbioturbated site measured DON fluxes were essentially identical to calculated diffusive DON fluxes, whereas at a bioturbated and bioirrigated site, measured DON fluxes were much greater than calculated fluxes. The molar ratios of DOC to DON benthic fluxes ranged from ~2 to 6 and were lower than those of pore‐water DOM, which were >~10. This implies that DOM accumulating in these sediment pore waters was carbon‐rich compared with the DOM that was either remineralized or escaped the sediment as a benthic flux. These measured benthic DON fluxes and estimated DON fluxes from continental margin sediments combine to yield a lower limit for the integrated sediment DON flux to the oceans that is similar to a value estimated previously. These net DON inputs to the oceans are small compared with internal oceanic DON cycling rates, although sediment DON fluxes and riverine DON inputs are roughly of the same order. At the same time, our results also suggest that the DON escaping from these sediments may not be inherently refractory because of its observed low C:N ratio. This implies that estuarine sediments (and perhaps marine sediment in general) may not be a major source of “refractory” DON to the oceans.
Greedy algae reduce arsenate
Authors: Hellweger Ferdi L. , Farley Kevin J. , Lall Upmanu , Di Toro Dominic M.
Published: August 2016

Algae reduce and methylate arsenate, producing arsenite (As(III)) when the growth rates are high and dimethylarsinic acid (DMA) when the growth rates are low. In lakes, this leads to high As(III) concentrations in the early stages of spring and fall blooms and high DMA concentrations in the summer. We hypothesize that under phosphorus (P)‐limited conditions, which usually exist in the summer, algae take up phosphate (PO4) and, because of similar chemical characteristics, As(V) as well. Inside the cell, As(V) is reduced to As(III), methylated to monomethylarsonic acid (MMA) and DMA, and then excreted. However, under non—P‐limited conditions, which exist in the early stages of blooms, algae up‐regulate their PO4 transport system to take up excess P, a phenomenon known as luxury uptake. Since As(V) is taken up by the PO4 transport system, As(V) uptake also increases at this time. Within the cell, the reduction of As(V) to As(III) is fast, but methylation is slower, causing As(III) to build up in the cell and be excreted, which, in turn, causes an increase in extracellular As(III). This mechanism permits the synergistic (luxury uptake) and antagonistic (competition) effects of PO4 on As(V) uptake and can therefore explain the seemingly contradictory results found in the literature. A mathematical model is constructed on the basis of existing established algal—nutrient interaction models and is used to simulate As transformation in two laboratory batch experiments. In addition to algal and P responses, the model can reasonably well reproduce the observed As(III) peak during the log growth phase and the more gradual appearance of DMA during the stationary phase.
Genetic and environmental factors influence survival and hatching of diapausing eggs
Authors: Allen Michael R.
Published: August 2016

To test the hypothesis that variation in hatching and survival of Daphnia dormant eggs is fostered by genetic differences among populations, rather than system‐specific availability of environmental cues, I measured hatching and egg survival rates for Daphnia from 22 shallow, fishless ponds in the midwestern U.S.A. Although all eggs were incubated at a water depth of 0.75 m or less in their natal pond, hatching rates varied between 5% and 90% and survival rates of eggs remaining in the egg bank ranged from 7% to 72%. There was no significant relationship between hatching and environmental cues such as light, oxygen content, or conductivity, although a negative relationship with depth was observed. Reciprocal transplant experiments quantified genetic and environmental influences on dormancy and survival, revealing strong population‐by‐host environment interactions. Thus, plasticity to environmental cues and genetic or maternal effects likely interact to determine hatching and survival rates in the field.
Dark production of hydrogen peroxide in the Gulf of Alaska
Authors: Vermilyea Andrew W. , Paul Hansard S. , Voelker Bettina M.
Published: August 2016

Dark H2O2 production rates were measured in samples collected in the Gulf of Alaska. We used a simple, novel method for determining absolute rates of dark production and decay of H2O2, both of which are occurring simultaneously (presumably as a result of biological activity) in unfiltered samples. [H2O2] vs. time was measured in 24‐h dark incubations of both unaltered samples and the same samples spiked with 100–250 nmol L−1 H2O2. Data were modeled with zero‐order H2O2 production rates and first‐order H2O2 decay coefficients as fitting parameters, with the assumption that addition of [H2O2] to a sample does not change either parameter. H2O2 production rates ranged from < 0.5 nmol L−1 h−1 to 8 nmol L−1 h−1, and generally decreased with depth and decreasing chlorophyll. Comparison of dark production with estimates of average photochemical H2O2 production rates in the top 50 m of the water column indicated that dark production is likely to be a significant source of H2O2. Indeed, many of the unaltered incubations indicated that in situ [H2O2] was close to a steady state between dark production and decay, especially in samples from depths of ≥ 10 m.
Simultaneous measurements of nitrate, oxygen, and carbon dioxide on oceanographic moorings: Observing the Redfield Ratio in real time
Authors: Johnson Kenneth S.
Published: August 2016

Autonomous observations of dissolved nitrate, oxygen, and total inorganic carbon (TCO2, which is derived from pCO2 and estimates of alkalinity) from sensors on the M1 and M2 moorings, off Monterey Bay, California, are examined. These observations are used to assess the linkages between nitrogen, oxygen, and carbon cycling with the Redfield ratio as a framework for the analysis. Concentrations of TCO2, oxygen, and nitrate were highpass filtered to remove low‐frequency signals driven by water mass changes. Daily cycles in each property are apparent with maxima or minima at the end of daylight. These daily cycles are consistent with biological production of oxygen or uptake of TCO2 and nitrate. Ratios of the changes in these diel cycles approach values expected from the Redfield ratio early in upwelling cycles. However, periods are frequently seen where the utilization of nitrate N is substantially lower than expected when compared to observed changes in TCO2 or oxygen. During these periods, fixed nitrogen must be supplied from other sources, such as ammonium or urea, or it is obtained from deeper waters by vertically migrating phytoplankton. These migrating phytoplankton must then return to the surface where inorganic carbon is consumed and oxygen is produced.
Hemoglobin concentration in Daphnia (D. galeata‐hyalina) from the epilimnion is related to the state of nutrition and the degree of protein homeostasis
Authors: Schwerin Susanne , Zeis Bettina , Horn Wolfgang , Horn Heidemarie , Paul Rüdiger J.
Published: August 2016

The function of hemoglobin (Hb), which is a key protein of many species, was analyzed in Daphnia from the field. Temperature and oxygen content; abundance and composition of phytoplankton; and abundance, body, and clutch sizes of the Daphnia assemblage were measured in the epilimnion and around the thermocline of a reservoir for 2 yr. In addition, carbohydrate, lactate, and hemoglobin concentrations were determined in whole Daphnia. In Daphnia from the thermocline, hypoxia‐induced Hb expression was responsible for an increase in Hb concentration in parallel with a decrease in oxygen content. In Daphnia from oxygen‐rich water (epilimnion), however, Hb concentration unexpectedly showed a negative relationship to temperature and to the animals’ temperature‐dependent metabolic rate. Furthermore, the seasonal minima of Hb concentration coincided with low food (phytoplankton) availability and maxima of Daphnia’s reproductive activity. These data suggest that Hb serves a dual function as respiratory protein and protein store. Laboratory experiments supported this hypothesis: starvation caused the concentration of Hb and other hemolymph proteins to decrease during normoxia, whereas the hemolymph protein store remained stable during hypoxia. Hemolymph proteins obviously function as a buffer between food (protein) availability and protein demand, with the latter increasing with temperature mainly because of elevated growth and reproduction rates. Accordingly, the size of the hemolymph protein store can indicate the state of nutrition of Daphnia (and possibly other species) from oxygen‐rich water, which can easily be assessed by spectroscopic measurement of Hb in whole animals.
Direct determination of nitrogen cycling rates and pathways in Arctic fjord sediments (Svalbard, Norway)
Authors: Gihring Thomas M. , Lavik Gaute , Kuypers Marcel M. M. , Kostka Joel E.
Published: August 2016

Results from a study of benthic nitrogen cycling in two Arctic fjords are presented. Intact sediment core incubations were used to quantify net fluxes of dissolved inorganic nitrogen, organic nitrogen, organic carbon, and oxygen across the sediment‐water interface. Rates of gross denitrification, anammox, nitrification, dissimilatory nitrate reduction to ammonium, and N2 fixation were quantified using core incubations and slurry experiments. Profiles of dissolved inorganic nitrogen in pore‐water, and organic carbon and nitrogen contents in the solid phase, were also obtained. Net nitrogen losses as N2, measured directly as changes in N2 : Ar, ranged from 152 µmol N m−2 d−1 to 453 µmol N m−2 d−1. Gross denitrification, as determined using 15N‐NO3− tracers, was 34–294 µmol N m−2 d−1. Rates of anammox ranged from 10 µmol N m−2 d−1 to 26 µmol N m−2 d−1 and contributed 5–23% of gross N2 generation. Nitrification rates were as high as 833 µmol N m−2 d−1 and sediments were a substantial source of nitrate to the water column (169–393 µmol N m−2 d−1 efflux). Uptake of ammonium (52–87 µmol N m−2 d−1), dissolved organic nitrogen (291‐486 µmol N m−2 d−1), and dissolved organic carbon (1313–2504 µmol N m−2 d−1) were observed. Nitrogen loss from the seafloor is shown to occur at rates comparable to temperate coastal environments and the sediments provide a substantial source of nitrate to the water column of Arctic fjords. In addition, anammox is confirmed as an important pathway in Arctic marine sediments, although N2 production is dominated by denitrification.
Body size dependence of euphausiid spatial patchiness
Authors: Décima Moira , Ohman Mark D. , Robertis Alex De
Published: August 2016

We analyzed size‐dependent variations in spatial patchiness of the eight numerically dominant euphausiid species in the California Current System (Euphausia pacifica, Nematoscelis difficilis, Nyctiphanes simplex, Thysanoessa gregaria, Euphausia recurva, Euphausia gibboides, Thysanoessa spinifera, and Euphausia eximia). Patchiness was measured by using a count‐based statistic using euphausiid densities and applied to 11 yr of detailed size‐specific enumerations from the California Cooperative Oceanic Fisheries Investigations program. We rejected the hypothesis of size‐independent patchiness for seven of the eight species. The most common pattern observed was a “U‐shaped” curve, showing elevated patchiness in the smallest size classes, a rapid decrease in patchiness of intermediate‐sized euphausiids, and a later increase in patchiness of adults following the onset of reproductive maturity. These size‐dependent changes parallel ontogenetic changes in spatial dispersion observed for some marine fishes. The initial descending limb of the patchiness curve appears to be caused by turbulent diffusion, while the later ascending limb of the curve is consistent with the onset of predator‐induced aggregation behavior. The patterns were surprisingly consistent across years and different reproductive characteristics (egg‐brooding vs. broadcast spawning euphausiids).
Drivers of metabolism and net heterotrophy in contrasting lakes
Authors: Staehr Peter A. , Sand-Jensen Kaj , Raun Ane L. , Nilsson Bertel , Kidmose Jacob
Published: August 2016

We investigated the influence of light, nutrients, and organic matter on gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP = GPP ‐ R) in a dystrophic forest lake and an open eutrophic lake. Forest vegetation reduced incoming irradiance (20%) and wind speed (34%) in dystrophic Gribsø, having thermal stratification 1 month longer than in eutrophic Slotssø. While Gribsø had nutrient‐limited phytoplankton during most of the year, Slotssø only experienced nutrient depletion during algal blooms. Colored dissolved organic matter (CDOM) absorbed most light (average 82%) in dystrophic Gribsø, while phytoplankton and other particles absorbed most light (45%) in eutrophic Slotssø. GPP and NEP were positively related to irradiance in both lakes. However, because of higher CDOM absorbance, three times more light was needed to attain autotrophy in Gribsø, being net heterotrophic (NEP < 0) for 79% of all days, compared to 59% in Slotssø. This difference vanished when NEP was scaled to light absorption by pigments, although the eutrophic lake maintained a higher photon yield. Metabolic rates varied much more in Slotssø, where higher light and nutrient availability facilitated occasional phytoplankton blooms, while low light and nutrient availability in Gribsø dampened temporal variability. Both lakes were annually net heterotrophic with similar annual areal rates (NEP, ‐14 mol C m−2). Net heterotrophy in dystrophic Gribsø derives from high import of organic carbon‐rich water, while heterotrophy in eutrophic Slotssø is fueled by degradation of sediment pools of organic matter accumulated under previous hypereutrophic conditions, emphasizing the importance of lake history on the contemporary metabolic state.
Effects of fetch and dissolved organic carbon on epilimnion depth and light climate in small forest lakes in southern Sweden
Authors: von Einem Jessica , Granéli Wilhelm
Published: August 2016

We sampled small (0.03 to 3.3 km2 surface area) forest lakes in southern Sweden during two summers to investigate how concentration of dissolved organic carbon (DOC) and lake size influence epilimnion depth (ze) and light conditions in the epilimnion. ze increased with increasing fetch (square root of lake area) but did not decrease with increasing DOC concentration. This suggests greater importance of wind mixing in our study area than in areas with more continental climate, i.e., epilimnion‐deepening wind mixing overrides the tendency for epilimnion depth to decrease with increasing DOC concentration. Extinction of photosynthetically active radiation was mainly caused by DOC. The euphotic zone was shallower in the first year than in the second, probably because of higher precipitation and lower solar irradiance in 2007, which together led to higher water color. Mean epilimnetic irradiance was low, especially in 2007, mainly because the increase in DOC did not lead to shallower epilimnia. Browning of lakes in southern Sweden, in combination with a predicted increase in the number of storm events, may lead to more severe light limitation of phytoplankton in small, nutrient‐poor lakes, since it may not be accompanied by a compensatory shallowing of the epilimnion. As a consequence, lake ecosystems will become more heterotrophic, CO2‐evasion to the atmosphere will increase, and fish production decrease.
Variable sediment oxygen uptake in response to dynamic forcing
Authors: Bryant Lee D. , Lorrai Claudia , McGinnis Daniel F. , Brand Andreas , est Alfred Wü , Little John C.
Published: August 2016

Seiche‐induced turbulence and the vertical distribution of dissolved oxygen above and within the sediment were analyzed to evaluate the sediment oxygen uptake rate (JO2), diffusive boundary layer thickness (δDBL), and sediment oxic zone depth (zmax) in situ. High temporal‐resolution microprofiles across the sediment‐water interface and current velocity data within the bottom boundary layer in a medium‐sized mesotrophic lake were obtained during a 12‐h field study. We resolved the dynamic forcing of a full 8‐h seiche cycle and evaluated JO2 from both sides of the sediment‐water interface. Turbulence (characterized by the energy dissipation rate, ε), the vertical distribution of dissolved oxygen across the sediment‐water interface (characterized by δDBL and zmax), JO2, and the sediment oxygen consumption rate (RO2) are all strongly correlated in our freshwater system. Seiche‐induced turbulence shifted from relatively active (ε = 1.2 × 10−8 W kg−1) to inactive (ε = 7.8 × 10−12 W kg−1). In response to this dynamic forcing, δDBL increased from 1.0 mm to the point of becoming undefined, zmax decreased from 2.2 to 0.3 mm as oxygen was depleted from the sediment, and JO2 decreased from 7.0 to 1.1 mmol m−2 d−1 over a time span of hours. JO2 and oxygen consumption were found to be almost equivalent (within ~ 5% and thus close to steady state), with RO2 adjusting rapidly to changes in JO2. Our results reveal the transient nature of sediment oxygen uptake and the importance of accurately characterizing turbulence when estimating JO2.
The isotopic and hydrologic response of small, closed‐basin lakes to climate forcing from predictive models: Application to paleoclimate studies in the upper Columbia River basin
Authors: Steinman Byron A. , Rosenmeier Michael F. , Abbott Mark B. , Bain Daniel J.
Published: August 2016

Simulations conducted using a coupled lake‐catchment, hydrologic and isotope mass‐balance model indicate that small, closed‐basin lakes in north‐central Washington are isotopically sensitive to changes in precipitation, relative humidity, and temperature. Most notably, model simulations predicted inconsistent lake responses to precipitation changes due to differences in lake outseepage rates and surface area to volume (SA :V) ratios. Greater outseepage within model experiments resulted in increased sensitivity to changes in mean precipitation. Moreover, simulations suggest that, in lakes with appreciable outseepage, SA :V ratio changes resulting from lake‐level variations control the direction of changes in lake water oxygen isotope composition (δ18O). Specifically, in lakes with a SA:V ratio that increases at higher lake levels, steady state δ18O values will increase in response to greater long‐term average precipitation. These results suggest that closed‐basin lakes with low outseepage rates will exhibit a transient isotopic response to stochastic variability in hydrologic forcing but will not strongly respond at steady state to variation in mean hydrologic conditions. Conversely, closed‐basin lakes with appreciable outseepage will exhibit strong isotopic responses to both stochastic variability and variation in mean hydrologic conditions (i.e., mean precipitation, relative humidity, and temperature control of catchment hydrologic inputs to the lake). These relationships provide a mechanism for explaining inconsistencies in the isotopic responses of lakes within a given region to hydrologic forcing and demonstrate that semiquantitative models for describing the relationship between lake hydrologic and isotopic responses to climate variability are not appropriate for all closed‐basin lakes.
Diatom sinkings speeds: Improved predictions and insight from a modified Stokes' law
Authors: Miklasz Kevin A. , Denny Mark W.
Published: August 2016

Accurately predicting the size‐dependant sinking rate of diatoms is necessary to fully understand the cycling of oceanic carbon and silicon. Stokes' law predicts that sinking velocity should be proportional to the square of a diatom's radius (a scaling exponent of 2), which does not agree with empirically measured sinking speeds (scaling exponents of 1.2‐1.6). We offer an alternative model for sinking speed that separately accounts for the different densities of a diatom's frustule (its siliceous cell armor) and its cytoplasm. The ratio of frustule to cytoplasm volume changes with size and, thereby, affects the scaling relationship between velocity and radius. The resulting model predicts a scaling exponent between 1 and 2 depending on the size and shape of the diatom, more accurately predicting the upper bound of measured sinking speeds and offering an analytical formula for the prediction of the maximum sinking speed of diatoms.
Characteristics and sources of chromophoric dissolved organic matter in lakes of the Yungui Plateau, China, differing in trophic state and altitude
Authors: Zhang Yunlin , Zhang Enlou , Yin Yan , van Dijk Mark A. , Feng Longqing , Shi Zhiqiang , Liu Mingliang , Qina Boqiang
Published: August 2016

The high‐mountain lakes on the Yungui Plateau in China are exposed to high‐intensity ultraviolet radiation, and contain low concentrations of chromophoric dissolved organic matter (CDOM). We determined CDOM absorption, fluorescence, composition, and source in 38 lakes on the Yungui Plateau at altitudes of 1516 to 4591 m above sea level. Total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chl a) concentrations significantly increased with increasing trophic state, and decreased with altitude. The CDOM absorption coefficient aCDOM(280) significantly increased with increasing trophic state, but not with altitude. There were significant and negative correlations between altitude and TN, TP, Chl a concentrations, and aCDOM(280). Parallel factor analysis identified two humic‐like and two protein‐like fluorescent components. Humic‐like component 1 was terrestrially derived and positively correlated to CDOM absorption. Component 2 was similar to a marine humic‐like substance originating from biological degradation of phytoplankton. Components 3 and 4 were autochthonous tryptophanlike and tyrosine‐like fluorophores. CDOM was, thus, a mixture of material from the catchment and autochthonous material produced by biota in the lake. CDOM fluorescence characteristics of oligotrophic and mesotrophic lakes were dominated by the spectral signatures of protein‐like components, but marine and terrestrial humic‐like components dominated in eutrophic lakes. The fluorescence indices FI255, FI310, and FI370 were useful tools for readily defining and classifying CDOM characteristics in the Yungui Plateau lake waters.
Remote climate forcing of decadal‐scale regime shifts in Northwest Atlantic shelf ecosystems
Authors: Greene Charles H. , Meyer-Gutbrod Erin , Monger Bruce C. , McGarry Louise P. , Pershing Andrew J. , Belkin Igor M. , Fratantoni Paula S. , Mountain David G. , Pickart Robert S. , Proshutinsky Andrey , Ji Rubao , Bisagni James J. , Hakkinen Sirpa M. A. , Haidvogel Dale B. , Wang Jia , Head Erica , Smith Peter , Reid Philip C. , Conversi Alessandra
Published: August 2016

Decadal‐scale regime shifts in Northwest Atlantic shelf ecosystems can be remotely forced by climate‐associated atmosphere‐ocean interactions in the North Atlantic and Arctic Ocean Basins. This remote climate forcing is mediated primarily by basin‐ and hemispheric‐scale changes in ocean circulation. We review and synthesize results from process‐oriented field studies and retrospective analyses of time‐series data to document the linkages between climate, ocean circulation, and ecosystem dynamics. Bottom‐up forcing associated with climate plays a prominent role in the dynamics of these ecosystems, comparable in importance to that of top‐down forcing associated with commercial fishing. A broad perspective, one encompassing the effects of basin‐ and hemispheric‐scale climate processes on marine ecosystems, will be critical to the sustainable management of marine living resources in the Northwest Atlantic.
Ecosystem respiration: Drivers of daily variability and background respiration in lakes around the globe
Authors: Solomon Christopher T. , Bruesewitz Denise A. , Richardson David C. , Rose Kevin C. , Van de Bogert Matthew C. , Hanson Paul C. , Kratz Timothy K. , Larget Bret , Adrian Rita , Babin Brenda Leroux , Chiu Chih-Yu , Hamilton David P. , Gaiser Evelyn E. , Hendricks Susan , Istvànovics Vera , Laas Alo , O'Donnell David M. , Pace Michael L. , Ryder Elizabeth , Staehr Peter A. , Torgersen Thomas , Vanni Michael J. , Weathers Kathleen C. , Zhu Guangwei
Published: August 2016

We assembled data from a global network of automated lake observatories to test hypotheses regarding the drivers of ecosystem metabolism. We estimated daily rates of respiration and gross primary production (GPP) for up to a full year in each lake, via maximum likelihood fits of a free‐water metabolism model to continuous high‐frequency measurements of dissolved oxygen concentrations. Uncertainties were determined by a bootstrap analysis, allowing lake‐days with poorly constrained rate estimates to be down‐weighted in subsequent analyses. GPP and respiration varied considerably among lakes and at seasonal and daily timescales. Mean annual GPP and respiration ranged from 0.1 to 5.0 mg O2 L−1 d−1 and were positively related to total phosphorus but not dissolved organic carbon concentration. Within lakes, significant day‐to‐day differences in respiration were common despite large uncertainties in estimated rates on some lake‐days. Daily variation in GPP explained 5% to 85% of the daily variation in respiration after temperature correction. Respiration was tightly coupled to GPP at a daily scale in oligotrophic and dystrophic lakes, and more weakly coupled in mesotrophic and eutrophic lakes. Background respiration ranged from 0.017 to 2.1 mg O2 L−1 d−1 and was positively related to indicators of recalcitrant allochthonous and autochthonous organic matter loads, but was not clearly related to an indicator of the quality of allochthonous organic matter inputs.
Physical responses of small temperate lakes to variation in dissolved organic carbon concentrations
Authors: Read Jordan S. , Rose Kevin C.
Published: August 2016

We used a mechanistic physical model to examine the effect of variability in dissolved organic carbon (DOC) concentrations on the physical properties of small temperate lakes. The model was validated on eight small (6 × 10−4 to 3.8 × 10−2 km2) lakes in Wisconsin and Michigan, with a standard error < 1°C for seven of eight lakes. Attenuation of photosynthetically active radiation (400–700 nm) in these lakes was regulated by DOC concentrations and was important in the vertical structuring of water temperatures. Heat exchange below the surface mixed layer was near the molecular rate, increasing the importance of water clarity as a control on the heat content of deeper waters. To understand the thermal effects of changing DOC concentrations, we applied scenarios of a 50% increase and 50% decrease in DOC concentrations for one lake (Trout Bog) and found water temperatures to vary in response, with the seasonally averaged temperatures in the increased DOC scenario being > 2°C colder than the reduced scenario. We found a nonlinear relationship between DOC and temperature, with clearer (lower DOC) simulations being more sensitive to climate variability, suggesting that DOC may act as a buffer against a warming climate. Our model showed that DOC also influenced epilimnetic depths, as nocturnal mixing (related to the vertical partitioning of heat) was more important than wind‐driven mixing. Small lakes are globally important regulators of biogeochemical cycles and are structurally different from larger lakes. Important feedbacks to physical processes must be accounted for when understanding the effects of changing DOC and climate on small lakes.
Taxon‐ and vector‐specific variation in species richness and abundance during the transport stage of biological invasions
Authors: Briski Elizabeta , Bailey Sarah A. , Casas-Monroy Oscar , DiBacco Claudio , Kaczmarska Irena , Lawrence Janice E. , Leichsenring Jonas , Levings Colin , MacGillivary Michael L. , McKindsey Christopher W. , Nasmith Leslie E. , Parenteau Marie , Piercey Grace E. , Rivkin Richard B. , Rochon Andre , Roy Suzanne , Simard Nathalie , Sun Bei , Way Candice , Weise Andrea M. , MacIsaac Hugh J.
Published: August 2016

Recent empirical and statistical evidence suggest that propagule pressure (i.e., number of individuals introduced per event, and the number and frequency of events) and colonization pressure (i.e., number of species released per event, and the number and frequency of events) are of vital importance to invasion success. To explore possible changes in propagule and colonization pressure during the transport stage of the invasion process, we examine abundance and species richness of virus‐like particles, bacteria, diatoms, dinoflagellates, and invertebrates transported in commercial ships—a leading vector for global spread of aquatic nonindigenous species. We collected 154 ballast water samples from ships that had performed or were exempt from ballast water exchange (BWE) prior to arrival at Pacific and Atlantic ports in Canada and Laurentian Great Lakes ports. We found that abundance and species richness varied across taxa and regions, with ships arriving to the Atlantic region carrying the highest abundance of taxa. The highest species richness of invertebrates and diatoms was recorded from ships arriving to the Pacific, whereas the richest communities of dinoflagellates occurred in the Atlantic region. We also found that BWE had no effect on abundance or species richness of most taxa (dinoflagellates, diatoms, bacteria, and virus‐like particles), whereas the effect on abundance of invertebrates was not clear. Finally, longer voyages resulted in lower abundance of all taxa except dinoflagellates, and lower species richness of diatoms. Paradoxically, the elevated abundance and species richness of dinoflagellates following BWE suggest that this group could have enhanced invasion potential when ships manage ballast water by exchange.
Summertime observations of ultrafine particles and cloud
condensation nuclei from the boundary layer to the free troposphere
in the Arctic
Authors: Burkart Julia , Willis Megan D. , Bozem Heiko , Thomas Jennie L. , Law Kathy , Hoor Peter , Aliabadi Amir A. , Köllner Franziska , Schneider Johannes , Herber Andreas , Abbatt Jonathan P. D. , Leaitch W. Richard
Published: August 2016

Abstract. The Arctic is extremely sensitive to climate change. Shrinking sea ice extent increases the area covered by open ocean during Arctic summer, which impacts the surface albedo and aerosol and cloud properties among many things. In this context extensive aerosol measurements (aerosol composition, particle number and size, cloud condensation nuclei, and trace gases) were made during 11 flights of the NETCARE July, 2014 airborne campaign conducted from Resolute Bay, Nunavut (74N, 94W). Flights routinely included vertical profiles from about 60 to 3000 m a.g.l. as well as several low-level horizontal transects over open ocean, fast ice, melt ponds, and polynyas. Here we discuss the vertical distribution of ultrafine particles (UFP, particle diameter, dp: 5–20 nm), size distributions of larger particles (dp: 20 nm to 1 μm), and cloud condensation nuclei (CCN, supersaturation = 0.6 %) in relation to meteorological conditions and underlying surfaces. UFPs were observed predominantly within the boundary layer, where concentrations were often several hundreds to a few thousand particles per cubic centimeter. Occasionally, particle concentrations below 10 cm−3 were found. The highest UFP concentrations were observed above open ocean and at the top of low-level clouds, whereas numbers over ice-covered regions were substantially lower. Overall, UFP formation events were frequent in a clean boundary layer with a low condensation sink. In a few cases this ultrafine mode extended to sizes larger than 40 nm, suggesting that these UFP can grow into a size range where they can impact clouds and therefore climate.