bluuebunny/crossref_metadata_2025_split huggingface dataset:
Particle transport in lakes: Models and measurements
Authors: Weilenmann Ulrich , O'Melia Charles R. , Stumm Werner 
Published: April 2010

Results of experimental measurements and mathematical modeling demonstrate that coagulation in lakes can be sufficiently rapid and extensive to affect suspended particle concentrations and sedimenting fluxes significantly. The process dominates particle removal in Lake Zürich and substantially influences particle concentrations in the water column of Lake Sempach.Natural coagulation in lakes is a process that is strongly influenced by solution chemistry. Calcium ions act as destabilizing agents and enhance natural coagulation while dissolved natural organic matter stabilizes particles and retards coagulation. Since solution chemistry varies widely among lakes, natural coagulation rates are expected to differ among lacustrine systems. Field observations of Lakes Zürich and Sempach support this view. Although primary productivity in Lake Zürich is considerably lower than in Lake Sempach, higher sedimenting fluxes are observed in Lake Zürich. The waters of Lake Zürich are low in dissolved organic carbon, permitting rapid coagulation in the epilimnion of the lake and producing correspondingly rapid sedimentation rates. Colloidal stability can be a factor in eutrophication.
Optimal foraging theory as a predictor of chemically mediated food selection by suspension‐feeding copepods
Authors: DeMott William R. 
Published: April 2010

Chemically mediated food selection was studied by offering copepods pairs of particles which differed in nutritional quality or size. Eudiaptomus spp. fed in varying concentrations of algae and polystyrene spheres, high#x2010;quality algae of different sizes, toxic and nontoxic algae, digestible and digestion#x2010;resistant algae, live and dead algae, and dead algae with and without attached bacteria.Experiments with polystyrene spheres showed that the rejection of nonfood particles did not interfere with feeding on relatively scarce algae. Particle selection in mixtures of algae exhibited good agreement with predictions of optimal foraging theory. Selectivity did not change with food concentration for mixtures of high#x2010;quality algae or mixtures of toxic and nontoxic algae. Copepods showed a weak but consistent preference for the larger of a pair of high#x2010;quality algae, whereas a toxic blue#x2010;green bacterium was eaten at a very low rate whether offered alone or in combination with an edible alga. Selection against low#x2010;quality nontoxic particles (e.g. digestion#x2010;resistant algae), however, was sensitive to food concentration. Discrimination against low#x2010;quality particles was strong when high#x2010;quality food was abundant and weak when high#x2010;quality food was scarce. In agreement with theory, diet selection by Eudiaptomus spp. is strongly influenced by both particle quality and the abundance of alternative foods.
A detailed organic carbon budget as an ecosystem‐level calibration of bacterial respiration in an oligotrophic lake during midsummer
Authors: Cole Jonathan J. , Caraco Nina F. , Strayer David L. , Ochs Clifford , Nolan Scott 
Published: April 2010

During a 1‐month period at the peak of summer stratification, we made intensive measurements of the major inputs and outputs of organic carbon to and from the epilimnetic water column of oligotrophic Mirror Lake, New Hampshire. These measurements included allochthonous and autochthonous components, as well as changes in storage, and were designed to construct a complete carbon budget. Bacterial respiration was compared directly to our budget in an effort to use ecosystem‐level constraints to test the major assumptions used to estimate bacterial production and respiration. On the basis of the difference between all other inputs and outputs, bacterial respiration must lie between 0.4 and 6 nmol C m−2 d−1. With measured rates of thymidine incorporation and measured bacterial cell sizes, this organic‐C budget constrains the thymidine conversion factor (cell nM−1 thymidine) to be between 1 and 6 × 109 cells nM−1 thymidine for growth yields between 10 and 80%. If the thymidine conversion factor were > 10 × 109 cells nmol−1, bacterial respiration alone would exceed the total input of C to the system, even at assumed growth yields of 80%. The same analysis indicates that the carbon conversion factor cannot exceed 3 × 10−7 µg µm−3 for any reasonable values of growth yield and thymidine conversion factor.On the basis of our best estimates for all parameters, bacterial production was equal to 16% of primary production and bacterial respiration was about 40% as large as the respiration of macrozooplankton. The respiration of nanoflagellate microzooplankton was <10% as large as the respiration of macrozooplankton and could account for the remineralization of only 25% of bacterial production.
Effects of predator‐induced spines on individual fitness in Daphnia pulex
Authors: Walls Mari , Ketola Matti 
Published: April 2010

We studied both the cues for spine induction and costs of spine production in Daphnia pulex (Cladocera). A significant number of D. pulex cultured individually in water treated with Chaoborus crystallinus larvae that were fed carried spines to the end of the fourth instar. Water treated with Chaoborus that were starved induced only minor morphological changes in D. pulex. Treatments with crushed D. pulex did not affect neck spine induction.Spine production carries a cost evident in the timing of first reproduction of D. pulex. Over half (58%) of D. pulex grown in culture conditions with a high density of Chaoborus postponed first reproduction from the fifth to the sixth instar. A decrease in growth of the spined morphs was attributable to an increase in duration of instars. Fitness effects persisted through the third reproductive instar. The intrinsic rate of increase was lowest in D. pulex populations cultured in Chaoborus‐treated water. Treatments with crushed D. pulex did not affect growth but did significantly increase clutch size of D. pulex.
Bacterial uptake of dissolved free and combined amino acids in estuarine waters
Authors: Coffin Richard B. 
Published: April 2010

The Delaware estuary was sampled at 10–14 stations along the main salinity axis from February to August 1985. Dissolved free and combined amino acid concentrations ranged from 50 nM to 1.4 µM and 0.1 to 8.0 µM, respectively. Combined amino acid concentrations were generally higher than dissolved free amino acids. Highest amino acid concentrations were measured in the lower estuary in early spring. Molecular weight analysis of the dissolved combined amino acids revealed that a high percentage of the pool contained peptides of <1,000 daltons.Uptake of 14C‐labeled amino acids and an algal protein were used to estimate the relative importance of these potential bacterial substrates. Laboratory experiments verified that peptide and protein uptake was nonspecific and that labeled algal protein was a good model substrate. Combined and free amino acid uptake rates ranged spatially and temporally from 15 to 600 nM h−1. Combined amino acid uptake averaged 51% of the bacterial amino nitrogen demand.
Sulfate reduction and other sedimentary biogeochemistry in a northern New England salt marsh
Authors: Hines Mark E. , Knollmeyer Stephen L. , Tugel Joyce B. 
Published: April 2010

Sulfate reduction rates, dissolved iron and sulfide concentrations, and titration alkalinity were measured in salt marsh soils along a transect that included areas inhabited by both the tall and short forms of Spartina alterniflora and by Spartina patens. Pore waters were collected with in situ “sippers” to acquire temporal data from the same location without disturbing plant roots. During 1984, data collected at weekly intervals showed rapid temporal changes in belowground biogeochemical processes that coincided with changes in S. alterniflora physiology. Rates of SO42 reduction increased fivefold (to >2.5 µmol ml−1 d−1) when plants began elongating aboveground yet decreased fourfold upon plant flowering. This rapid increase in rates of SO42 reduction must have been fueled by dissolved organic matter released from roots only during active growth. Once plants flowered, the supply of oxidants to the soil decreased and sulfide and alkalinity concentrations increased despite decreases in SO42− reduction and increases in SO42−: Cl− ratios. Sulfide concentrations were highest in soils inhabited by tallest plants.During 1985, S. alterniflora became infested with fly larvae (Chaetopsis apicalis John) and aboveground growth ceased in late June. This cessation was accompanied by decreased rates of SO42− reduction similar to those noted during the previous year when flowering occurred. After the fly infestation, the pore‐water chemical profiles of these soils resembled profiles of soils inhabited by the short form of S. alterniflora.The SO42− reduction rates in S. patens soils are the first reported. Rates were similar to those in S. alterniflora except that they did not increase greatly when S. patens was elongating. Tidal and rainfall events produced desiccation‐saturation cycles that altered redox conditions in the S. patens soils, resulting in rapid changes in the dissolution and precipitation of iron and in the magnitude and spatial distribution of SO42 reduction.
Seasonal patterns of bacterivory by flagellates, ciliates, rotifers, and cladocerans in a freshwater planktonic community
Authors: Sanders Robert W. , Porter Karen G. , Bennett Susan J. , DeBiase Adrienne E. 
Published: April 2010

Bacterivory in eutrophic Lake Oglethorpe, Georgia, was determined by direct observation of tracer particle uptake by all members of the planktonic community. Heterotrophic flagellates dominated grazing at all times, accounting for 49–81% of grazing on an areal basis and up to 98% of grazing at some depths. Pigmented (mixotrophic) flagellates were major grazers during winter and spring blooms, when they contributed up to 45% of community grazing on an areal basis and 79% at depths of maximum abundance. In late spring to early summer, rotifers and ciliates were responsible for as much as 25 and 30% of bacterivory at some depths, but averaged 3 and 11% over the year, respectively. Grazing impact of cladoceran crustaceans was generally <1% of the total. Bacterivory by copepods was not detected. Total bacterial mortality due to grazing ranged from 11 to 162% of bacterial cell production estimated from the incorporation of [3H]thymidine.Use of 0.57‐µm microspheres as tracers gave similar estimates of ingestion to fluorescently labeled bacteria in this system. The use of 4% ice‐cold glutaraldehyde mixed 1 : 1 with the water sample was found to be equally effective to an acrolein‐tannic acid mixture for reducing egestion of particles by protists. We therefore consider our findings to be representative of bacterivory by the planktonic community in this eutrophic system.
Cycling of organic carbon in the photic zone of a eutrophic lake with special reference to the heterotrophic bacteria
Authors: Vadstein Olav , Harkjerr Bjørn Ola , Jensen Arne , Olsen Yngvar , Reinertsen Helge 
Published: April 2010

Cycling of organic carbon in the photic zone was investigated in a eutrophic Norwegian lake during the ice‐free period. Special attention was paid to heterotrophic bacteria and the factors influencing their production and biomass development.The average proportions of the biomass of phytoplankton, zooplankton, and bacteria were 17 : : 1 on a carbon basis. Phytoplankton primary production averaged 580 mg C m−2 d−1, and 22% of the fixed carbon was exuded. Bacterial production, estimated by frequency of dividing cells, averaged 160 mg C m−2 d−1 and equaled 25% of the gross primary production on a seasonal basis. Increased bacterial activity was either correlated with increased exudation or followed a collapse in the phytoplankton community. Grazing was estimated to amount to 35–180% and 41–84% of the total losses of phytoplankton and bacteria. Cladocerans were the main grazers on phytoplankton, and heterotrophic flagellates were the main grazers on bacteria.Because of high death rates of zooplankton and cycling of carbon within the microbial loop, the available substrate for bacteria equaled the primary production on a seasonal basis. Exudates, egestion products from grazers, and dead zooplankton constituted two‐thirds of the available substrate, and these sources were of equal magnitude.
Natural fluorescence of chlorophyll a: Relationship to photosynthesis and chlorophyll concentration in the western South Pacific gyre
Authors: Kiefer D. A. , Chamberlin W. S. , Booth C. R. 
Published: April 2010

A new optical instrument, designed specifically to measure the natural or solar‐induced fluorescence of chlorophyll a, was deployed in the tropical and temperate waters of the western South Pacific gyre. During the 12 days of transit from Papeete, Tahiti, to Auckland, New Zealand, measurements were made of the vertical distribution of temperature, salinity, upwelling radiance and downwelling irradiance at selected wavelengths, the beam attenuation coefficient at 683 nm, the scalar irradiance of photosynthetically available radiation (PAR), and the nadir radiance at 683 nm, which is the wavelength of peak emission by Chl a. In addition, water samples were collected at regular depth intervals and analyzed for the concentration of Chl a and for the spectral absorption coefficient of cells and associated detrital particles.To examine the relationship between natural fluorescence and the size and photosynthetic rate of the phytoplankton crop, we derived several simple equations and applied them to the analysis of the data. One relates the nadir radiance at 683 nm to the total fluorescence emitted by the phytoplankton crop within the field ofview, another relates natural fluorescence to the concentration of Chl a, and a third relates natural fluorescence to the gross rate of photosynthesis of the crop. We found that even in the extremely oligotrophic waters of the central South Pacific gyre, natural fluorescence was easily measured throughout the euphotic zone at depths >6 m. As found in previous studies, the value of natural fluorescence varied spatially and temporally with ambient scalar irradiance of PAR and the concentration of Chl a. The quantum yield of fluorescence, which varied fivefold, averaged about 0.035 photons emitted to photons absorbed and generally decreased with increasing levels of exciting irradiance. Most importantly, we found natural fluorescence covaried closely with calculated rates of photosynthesis. A linear regression of calculated photosynthetic rate on fluorescence yielded a correlation coefficient of 0.84 and a slope of 2.0 atoms of carbon fixed per photon emitted as fluorescence.
Feeding depths and organic absorption for the deposit feeding benthic amphipods Pontoporera affinis and Pontoporeia femorata
Authors: Lopez Glenn , Elmgren Ragnar 
Published: April 2010

Using fluorescent particles as sediment markers, we show that the congeneric, deposit‐feeding amphipods Pontoporeia affinis and Pontoporeia femorata feed almost exclusively on the surface layer (upper centimeter) of sediment, even though they may spend much of their time deeper. Pontoporeia affinis feeds more rapidly than P. femorata. There was some evidence that food intake decreased at night for P. affinis, but not for P. femorata.The two species were equally good at absorbing sedimentary organic carbon, both absorbing ~ 40% from surficial and 28% from deeper sediment. Neither species was very selective in ingesting the organic fraction of sediment.Pontoporeia femorata resides deeper in the sediment than its morphologically similar congener P. affinis, and this difference is enhanced in sympatric populations. Yet, there is no evidence of food partitioning between the two species. An innate tendency of P. affinis to move up, and P. femorata down, upon disturbance from burrowing activities of neighbors may be the primary cause of the enhanced vertical stratification in sympatric populations. It may result in differential susceptibility to predation. In addition, P. affinis swims more actively than P. femorata and should more easily find new patches of high‐quality, surficial sediment. Thus predation and microhabitat partitioning may contribute to the coexistence commonly observed in the two species, in spite of suspected exploitative food competition.
Copepod diel migration, feeding, and the vertical flux of pheopigments.
Authors: Dagg M. J. , Frost B. W. , Walser W. E. 
Published: April 2010

Feeding and diel vertical migration in the copepods Calanus pacificus Brodsky and Metridia lucens Boeck were examined during dusk and dawn in Dabob Bay, Washington. Both species migrated from below 75 m during the day into the upper 25 m at night. Feeding on phytoplankton was confined to periods spent in the surface layer.Metridia lucens arrived in the surface 0.5 h after sunset, fed at high rates throughout the night until 1.0 h before sunrise, and then returned to depth. In contrast, C. pacificus appeared in the surface layer 0.5–1.5 h before sunset but fed at low rates until ~1 h after sunset, then increased its feeding rate. Feeding decreased before sunrise, although migratory descent was not completed until after sunrise. These patterns are not in agreement with models of diel migration that predict the onset of feeding 1–2 h before sunset.During the night in surface waters, these copepods defecated 2.3–2.9 mg pigment m−2. In comparison, active transport of pigment to deep waters via migratory descent was only 0.01–0.02 mg pigment m−2 d−1.
Internal sources and sinks of water, P, N, Ca, and Cl in Lake Kinneret, Israel
Authors: Smith S. V. , Serruya S. , Geifman Y. , Berman T. 
Published: April 2010

Mass‐balance budgets linked among several materials are used to infer rates of processes affecting Lake Kinneret. Comparisons among budgets reveal the magnitudes of “internal” sources and sinks that cannot be directly inferred from individual budgets.A water budget indicates that ~180 × 106 m3 of sublacustrine spring water plus ungauged surface flow enters the lake annually‐about a fifth the total inflow and two‐thirds as much water as is lost to evaporation. This total ungauged inflow delivers about 90,000 t of Cl yr−1, nine times the stream input. Ca input from total ungauged flow is about a third the stream input, and the net internal Ca sink in the system is sufficient to precipitate 60,000 t of CaCO3 yr−1.Stream delivery of P, mainly as particulate material, is largely sequestered in the sediments (~100 t yr−1). At least 1,100 1 yr−1 of N, primarily as NO3− delivered by streams, are apparently lost to denitrification, while only 200 t yr−1 are sedimented. Cycling of N and P within the lake dominates over throughput in controlling standing stocks. Vertical mixing within the lake may play a dominating role in this cycling. Cycling of Pin the lake can be regarded as “closed”—a sediment‐water column turnover of materials with only minor hydrographic loss from the system. By contrast, N cycling is “open,” with an important net loss to the atmosphere.
Surface pigments, algal biomass profiles, and potential production of the euphotic layer: Relationships reinvestigated in view of remote‐sensing applications
Authors: Morel André , Berthon Jean‐François 
Published: April 2010

Maps of surface chlorophyllous pigment (Chl a + Pheo a) are currently produced from ocean color sensors. Transforming such maps into maps of primary production can be reliably done only by using light‐production models in conjunction with additional information about the column‐integrated pigment content and its vertical distribution.As a preliminary effort in this direction, ∼4,000 vertical profiles of pigment (Chl a + Pheo a) determined only in oceanic Case 1 waters have been statistically analyzed. They were scaled according to dimensionless depths (actual depth divided by the depth of the euphotic layer, Ze) and expressed as dimensionless concentrations (actual concentration divided by the mean concentration within the euphotic layer). The depth Ze, generally unknown, was computed with a previously developed bio‐optical model. Highly significant relationships were found allowing 〈C〉tot the pigment content of the euphotic layer, to be inferred from the surface concentration, C&#x0304;pd, observed within the layer of one penetration depth. According to their C&#x0304;d values (ranging from 0.01 to >10 mg m−3), we categorized the profiles into seven trophic situations and computed a mean vertical profile for each. Between a quasi‐uniform profile in eutrophic waters and a profile with a strong deep maximum in oligotrophic waters, the shape evolves rather regularly. The well‐mixed cold waters, essentially in the Antarctic zone, have been separately examined. On average, their profiles are featureless, without deep maxima, whatever their trophic state. Averaged values of ρ, the ratio of Chl a to (Chl a + Pheo a), have also been obtained for each trophic category.The energy stored by photosynthesizing algae, once normalized with respect to the integrated chlorophyll biomass 〈C〉tot is proportional to the available photosynthetic energy at the surface via a parameter ψ*, which is the cross‐section for photosynthesis per unit of areal chlorophyll. By taking advantage of the relative stability of ψ*, we can compute primary production from ocean color data acquired from space. For such a computation, inputs are the irradiance field at the ocean surface, the “surface” pigment from which 〈C〉tot can be derived, the mean ρ value pertinent to the trophic situation as depicted by the C&#x0304;pd or 〈C〉tot values, and the cross‐section ψ*. Instead of a constant ψ* value, the mean profiles can be used; they allow the climatological field of the ψ* parameter to be adjusted through the parallel use of a spectral light‐production model.
Surface water‐quality studies in the interior marine environment of Denmark
Authors: Højerslev Niels K. 
Published: April 2010

Suspended matter in terms of light scattering and gelbstoff in terms of fluorescence, temperature, and salinity have been measured on surface samples taken from the Øre Sund, the Kattegat, the Store Bælt, and the Baltic in January and August 1975 during the Danish Belt Project.For the area investigated, the average surface concentration of suspended matter about doubled between January and August 1975, whereas the average surface gelbstoff concentration remained approximately unchanged.The overall horizontal variation of the surface concentration of suspended matter attained its maximum in January 1975, being of the order of 10 times. For August 1975, this variation dropped appreciably, to the order of two times.The overall horizontal variation of the surface gelbstoff concentration was about the same for January and August 1975, being of the order of two times. This suggests that biological activities such as primary production and organic decay are unrelated to the formation of gelbstoff in the sea.Two older surface maps based on light scattering measurements similar to those above from the Øre Sund in April 1957 and November 1953 suggest that the surface concentration of suspended matter has more than tripled during the period 1953–1975.