bluuebunny/crossref_metadata_2025 huggingface dataset:
Stream denitrification and total nitrate uptake rates measured using a field 15N tracer addition approach
Authors: Mulholland Patrick J. , Valett H. Maurice , Webster Jackson R. , Thomas Steven A. , Cooper Lee W. , Hamilton Stephen K. , Peterson Bruce J.
Published: July 2010

We measured denitrification and total nitrate uptake rates in a small stream (East Fork of Walker Branch in eastern Tennessee) using a new field 15N tracer addition and modeling approach that quantifies these rates for entire stream reaches. The field experiment consisted of an 8‐h addition of 99 atom% K15NO3 and a conservative solute tracer. Two 15N tracer addition experiments were performed on consecutive days, the first under ambient NO3− concentrations (23 µg N L−1) and the second with a NO3− addition of approximately 500 µg N L−1. We fit first‐order NO3− uptake and two‐box denitrification models to the longitudinal measurements of tracer 15N in dissolved NO3−, N2, and N2O in stream water to determine rates. Total NO3− uptake rates were 0.028 m−1 (0.32 µg N m−2 s−1) and 0.01 m−1 (1.6 µg N m−2 s−1) under ambient NO3− and with NO3− addition, respectively. Denitrification rates were 0.0046 m−1 (uncertainty range of 0.002 to 0.008 m−1) and 9×10−5 m−1 (uncertainty range of 3 × 10−5 to 21×10−5 m−1) under ambient NO3− and with NO3− addition, respectively. Denitrification resulted almost exclusively in N2 production (>99%) and comprised about 16% (±10%) of total NO3− uptake rate under ambient NO3− concentrations and about 1% (±1%) of total NO3 uptake rate with NO3− addition. Denitrification rate expressed on a mass flux basis was about 12 µmol m−2 h−1 under ambient NO3− concentrations, a value within the range reported for other streams with low NO3− concentrations.
Interannual variation of the isotopic composition of sedimenting organic carbon and nitrogen in Lake Lugano: A long‐term sediment trap study
Authors: Lehmann Moritz F. , Bernasconi Stefano M. , Barbieri Alberto , Simona Marco , McKenzie Judith A.
Published: July 2010

We examined the evolution of δ13C and δ15N of sedimenting particulate organic matter (SPOM) in response to changes in primary productivity, nutrient loading, and plankton dynamics in Lake Lugano between 1985 and 1998. A decreasing δ13C reflects the decline of phosphorus loading in Lake Lugano, suggesting that the δ13C of SPOM is a good indicator of P availability in the lake, with phosphate being the major control on the CO2 draw‐down in the photic zone. However, annual primary production and δ13C do not correlate. The expansion of the trophogenic layer in response to lowered plankton biomass concentrations balanced the effect of reduced phosphate concentration on total primary production (per unit area) and, thus, biased the correlation of δ13C and primary productivity. Whereas a substantial decrease of total phytoplankton biomass in the late 1980s clearly affected the δ13C of SPOM, it did not seem to affect δ15N. Marked changes in the plankton population composition did not have a major effect on δ15N. If at all, the effects of primary productivity, nitrate utilization, and changes in the intensity of denitrification are superimposed on a signal dominantly derived from changes in the amount and isotopic composition of dissolved inorganic nitrogen from external sources. A marked positive shift (+3‰) in the δ15N observed in 1994/1995 corresponded to the introduction of a denitrification stage in wastewater treatment. This study demonstrates that the δ13C of exported organic matter is a useful indicator of the trophic state of lacustrine environments. The δ15N of sedimentary organic matter is unlikely to reflect nitrate utilization or denitrification if the input of external N sources dominates the N‐isotope dynamics within the lake. However, in those systems, organic matter d15N can provide information on the development of N pollution and subsequent effects of lake restoration measures.
Patterns and controls of lotic algal stable carbon isotope ratios
Authors: Finlay Jacques C.
Published: July 2010

Spatial and temporal variations in stable carbon isotope ratios (i.e., δ13C) of primary producers are common but poorly understood features of isotopic characterizations of aquatic food webs. I investigated factors that control δ13C of algae (concentration and δ13C of inorganic carbon, algal fractionation, and growth rates) in riffle habitats across a gradient in stream size and productivity in northern California. There was considerable seasonal and spatial variation in δ13C of the green alga Cladophora glomerata, microalgal‐influenced epilithic biofilms, and their herbivores. Algal and herbivore δ13C were depleted in 13C in small, unproductive tributary streams (−44‰ to −30‰) compared with more productive sites downstream (−31‰ to −23‰). The majority of variation in algal δ13C of Cladophora and epilithic biofilms was determined by dissolved CO2 (CO2aq) via effects on δ13C of CO2aq and photosynthetic fractionation. In contrast, two other taxa (the cyanobacterium Nostoc pruniforme and the red alga Lemanea sp.) showed little variation in δ13C or fractionation in response to varied inorganic carbon availability because of their distinct modes of inorganic carbon acquisition. Although variation in algal δ13C might complicate use of δ13C to resolve consumer diet sources under some circumstances, better understanding of such variation should improve the use of δ13C techniques in aquatic food web studies.
Salmon‐derived mercury and nutrients in a Lake Ontario spawning stream
Authors: Sarica José , Amyot Marc , Hare Landis , Doyon Marie-Renée , Stanfield Les William
Published: July 2010

We tested the hypothesis that concentrations of mercury species (Hg) and nutrients (NH4+, NO3−, P, and dissolved organic carbon) in abiotic and biotic components would be altered by the decomposition of salmon carcasses in streams. We investigated a tributary stream of Lake Ontario receiving spawning runs of Chinook salmon (Oncorhyncus tshawytscha) for 2 yr with contrasting bear activity. Stations with high carcass densities had significantly higher levels of aqueous total Hg, methylmercury (MeHg), particulate Hg, and nutrients than did stations with lower carcass densities. Hg levels in aquatic and terrestrial invertebrates feeding on carcasses increased by up to 25‐fold. In 2001, a bear removed most carcasses at the downstream station, and aqueous Hg and nutrient concentrations were significantly lower than during the preceding year, when no bear was active at that station. A preliminary budget for this stream shows that (1) salmon carcasses can be an important source of Hg and nutrients to aquatic and terrestrial food webs, and (2) terrestrial invertebrates and vertebrates can be important water‐to‐land vectors of Hg.
Marine diffusive boundary layers at high latitudes
Authors: Roberts Jason , McMinn Andrew
Published: July 2010

The thickness of marine diffusive boundary layers (DBLs) can be calculated from the friction velocity and the water density (a function of temperature and salinity). However, DBL thickness scales differently with temperature, depending on whether free‐stream or friction velocity is used. We show that there are advantages to using frictional velocity for experimental scaling. Low seawater temperatures in polar areas cause DBLs to be up to 32% thicker than in temperate or tropical areas. This will have a significant effect on biological processes such as photosynthesis and respiration.
Quantification of marine snow fragmentation by swimming euphausiids
Authors: Goldthwait Sarah , Yen Jeannette , Brown Jason , Alldredge Alice
Published: July 2010

Sinking of marine snow is a major mechanism of particulate carbon transport from surface waters to the seafloor. Any process altering the abundance or size of marine snow influences carbon flux and food availability to pelagic and benthic organisms. We explored whether zooplankton can alter carbon transport by a new mechanism—physical fragmentation of marine snow. The fluid stress created around the appendages of swimming Euphausia pacifica is capable of fragmenting a single aggregate into multiple, smaller aggregates. The reduced size and slower sinking rate of the daughter aggregates may increase their residence time in the water column, promoting decomposition and decreasing particle flux to depth. To determine the importance of fragmentation, tethered and free‐swimming euphausiids were videotaped in the presence of marine snow representing a range of aggregate strengths, sizes, and ages. Image analysis was used to characterize the particles prior to and following fragmentation and to determine the area of influence around a single euphausiid. Tethered euphausiids pulled in particles from an average of 6.7 mm away, and most aggregates were fragmented in either the region of the rapidly beating pleopods or in the high‐velocity jet that forms off the tail. Euphausiids were capable of fragmenting all aggregate types and produced an average of 7.3 daughter particles, with 60% of these daughter particles remaining within the marine snow size class (>0.5 mm). Thus, physical fragmentation by swimming euphausiids increases the abundance of marine snow while decreasing overall marine snow mass. This novel process, which alters particle size structure without loss of total particulate organic carbon (POC), will be important in upwelling regions where euphausiids are the dominant macrozooplankton migrators.
Seasonal and interannual particle export in an African rift valley lake: A 5‐yr record from Lake Malawi, southern East Africa
Authors: Pilskaln Cynthia H.
Published: July 2010

A time‐sequencing sediment trap was deployed at 300–350 m in Lake Malawi, East Africa, from 1987 to 1992 to measure particulate export to the deep, anoxic hypolimnion in the northern and central lake regions. The monthly settling particulate samples provide a data set of seasonal and interannual export fluxes of organic carbon, biogenic opal, calcium carbonate, and lithogenic material. Maximum total particle fluxes (~50–400 mg m−2 d−1) occurred primarily during the dry, windy season (April through October) when algal productivity is high because of wind induced upwelling of nutrient‐enriched metalimnion and hypolimnion waters. Peak‐flux particulates contained an abundance of Aulacoseira and Stephanodiscus diatom valves and chains. The total particle mass flux during the wet, austral summer months (November through March) was consistently one to three orders of magnitude less than that measured during the dry months and consisted of mineral shards, terrestrial plant debris, and scattered diatom tests. The 5‐yr trap data provide support for the claim that the light‐dark lamination couplets, abundant in northern and central lake cores, reflect seasonal delivery to the sediments of diatom‐rich particulates during the windy months and diatom‐poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Niño‐Southern Oscillation (ENSO)‐related rainfall and drought cycles, appears to exert a strong influence over the magnitude and geochemical composition of particle export to the deep hypolimnion of Lake Malawi.
Predominance of β‐proteobacteria in summer melt pools on Arctic pack ice
Authors: Brinkmeyer Robin , Glöckner Frank-Oliver , Helmke Elisabeth , Amann Rudolf
Published: July 2010

The diversity and community structure of bacteria in melt pools on Arctic pack ice floes were dominated by bproteobacteria. Thirty‐five percent of the pure cultures isolated in 1997 from pack ice floes north of Svalbard and in the Fram Strait were from the β‐proteobacteria group. Within this group, there were only two phylotypes clustering within the widespread Beta I cluster, also known as the Comamonadaceae clade. One phylotype, most closely related to Aquaspirillum arcticum (96.0‐97.3% identical), was frequent among cultures isolated from 10 melt pools. A 16S ribosomal RNA (rRNA) gene clone library, constructed from a melt pool that was sampled 2 yr later in the Fram Strait, was also dominated by β‐proteobacteria, in particular the same recurrent isolate phylotype designated “MP‐BetaI”. Fluorescence in situ hybridization of 20 melt pools corroborated the cultivation and cloning data. b‐Proteobacteria were the most abundant bacterial group, constituting ~49% of the bacteria that were stained by 4'6‐diamidino‐2‐phenylindole (DAPI). α‐ and γ‐proteobacteria accounted for only 2% each, the Cytophaga‐Flavobacterium group accounted for 9%, and the Actinobacteria spp. accounted for 9%. Approximately 63% of the β‐proteobacterial fraction that was found in the melt pools was determined with a newly developed probe to be the recurrent β‐proteobacterial MP‐BetaI phylotypes, indicating that it is particularly adapted for success in this extreme environment.
Elevated levels of dimethylated‐sulfur compounds in Lake Bonney, a poorly ventilated Antarctic lake
Authors: Lee Peter A. , Priscu John C. , DiTullio Giacomo R. , Riseman Sarah F. , Tursich Nicole , de Mora Stephen J.
Published: July 2010

Lake Bonney is a permanently ice‐covered lake in the McMurdo Dry Valleys, Antarctica. The lake has two chemically stratified lobes (referred to as the east and west lobes), each with distinct biogenic sulfur profiles. Dimethylsulfoniopropionate (DMSPp) and dimethylsulfoxide (DMSOp) exceeded 32 and 2 nmol L−1, respectively, in the photic surface waters of the lake. Maximum DMSPp levels occurred in the deep‐chlorophyll layer of both lobes, a zone dominated by chrysophytes and chlorophytes, which are thought to be the source of dimethylated sulfur in the deep waters of the lake following sedimentation and biogeochemical processing. Waters beneath the chemoclines of both lobes are cold (<0°C), saline (>3 times seawater), suboxic, and devoid of phytoplankton biomass and activity. Dimethylsulfide (DMS) levels (>330 nmol L−1) in the deep west lobe are among the highest recorded in a natural aquatic ecosystem. In contrast, saline waters of the deep east lobe contain relatively little DMS (<70 nmol L−1) but high DMSOd (270 nmol L−1), with the latter being the highest observed in any natural aquatic ecosystem. We argue that the differences in the biogenic sulfur profiles between the deep waters of the two lobes arise principally from subtle differences in the redox conditions found in each lobe.
Orthophosphate uptake by heterotrophic bacteria, cyanobacteria, and autotrophic nanoflagellates in Villefranche Bay, northwestern Mediterranean: Vertical, seasonal, and short‐term variations of the competitive relationship for phosphorus
Authors: Tanaka Tsuneo , Rassoulzadegan Fereidoun , Thingstad T. Frede
Published: July 2010

Previous studies have suggested that Mediterranean surface water becomes phosphorus limited for both bacteria and phytoplankton during stratified periods and that orthophosphate uptake in these situations was close to diffusion limitation for both cyanobacteria and autotrophic nanoflagellates. In order to better understand vertical and seasonal variations of this system, we measured orthophosphate uptake by bacteria and phytoplankton in Villefranche Bay (northwestern Mediterranean) monthly for the 0–75‐m layer and weekly or biweekly at 10 m from June to December 2002. Turnover time of orthophosphate was relatively short (<2 h) in the surface mixed layer (0–30 m) during the stratified period, and long (>30 h) in the deeper layer during the stratified period and in the whole water column during the mixing period. Short‐term fluctuations in turnover time were repeatedly observed from the stratified through the mixing periods. The dominance of PO4 uptake drastically shifted from both bacteria and cyanobacteria to cyanobacteria when there were slight increases in turnover time (1‐10 h). Compared to the theoretical maximum calculated for diffusion limitation, mean affinity constants at 10 m were similar for autotrophic nanoflagellates and greater for cyanobacteria in situations with turnover time <2 h, but observed values were much smaller than theoretical for heterotrophic bacteria even in samples with turnover time <1 h.
Effects of experimental greenhouse warming on phytoplankton and zooplankton communities in fishless alpine ponds
Authors: Strecker Angela L. , Cobb Tyler P. , Vinebrooke Rolf D.
Published: July 2010

The impacts of global warming on aquatic ecosystems are expected to be most pronounced at higher trophic levels in cold­water environments. Therefore, we hypothesized that warming of fishless alpine ponds would suppress large‐bodied consumers (e.g., cladocerans, copepods) and stimulate fast‐growing microorganisms (e.g., phytoflagellates, rotifers), thereby altering the community composition and total abundance of zooplankton and phytoplankton. This hypothesis was tested using three blocks of four experimental mesocosms (1000‐liter capacity) that were located next to alpine ponds in Banff National Park, Canada. Each block received unfiltered pond water and sediment from a pond following ice out in June 2000. A warming treatment (control vs. 3.6°C warmed) was achieved by controlling the ventilation of greenhouse canopies that were suspended over each of the mesocosms. By the end of our 50‐d experiment, warming significantly suppressed total zooplankton biomass because large cladocerans (Daphnia pulex) declined while rotifer (Keratella cochlearis, Conochilus unicornis) abundance increased during the second half of the experiment. In contrast, warming did not affect total phytoplankton biomass but significantly altered community composition by favoring phytoflagellates (Mallomonas, Synura, Trachelomonas) over larger filamentous green algae (Mougeotia, w). Warming did not significantly increase dissolved nitrogen and phosphorus concentrations. Therefore, warmer growing conditions and reduced grazer biomass best explained the increased abundance of more edible, fast‐growing phytoflagellates in the warmed mesocosms. Our findings support the hypothesis that moderate warming can destabilize plankton dynamics, thereby potentially reducing the reliability of water quality and food resources for higher trophic levels (e.g., planktivorous fish) in shallow cold‐water ecosystems.
Planktonic biodiversity: Scaling up and down
Authors: Kerfoot W Charles. , Mittelbach Gary G. , Hairston, Nelson G. , Elser James J.
Published: July 2010

In 2001, Simon Levin remarked at a National Science Foundation meeting on biocomplexity that scientific disciplines are belief systems that progressively nurture memes by establishment of societies and journals (a meme being a unit of intellectual or cultural information—a key idea—that passes from mind to mind, spreading through colleagues and over generations [Dawkins 1976]). Levin also noted that an inevitable consequence of knowledge expansion is the development of specialized jargon, which, unfortunately, creates language barriers that impede the free exchange of ideas. Occasionally, we therefore need to pause, cut through the jargon, and attempt to integrate ideas across disciplinary boundaries. According to Levin and Pacala (2003), “… it is essential to develop ways to relate processes at the level of individual organisms to the populations of which they are members, and to the communities and ecosystems in which they reside. We must learn to scale from the small to the large, from the individual to the collective to the community, from the … plant to the biosphere.”
Mechanisms, effects, and scales of dispersal in freshwater zooplankton
Authors: Havel John E. , Shurin Jonathan B.
Published: July 2010

The distribution of organisms can be regulated by local environmental factors and regional processes such as dispersal. Here, we review recent work on the role of dispersal for generating population and community structure in freshwater zooplankton. We examine evidence for different mechanisms of dispersal among lakes, for the effects of dispersal limitations on populations and communities, and for the effects of spatial scale on dispersal rates. Zooplankton move via human or animal vectors, flowing surface waters, and wind; the relative importance of the different modes of transport is poorly understood. Several lines of evidence suggest that dispersal among lakes separated over short spatial scales (<10 km) is sufficiently rapid that local interactions should limit species diversity and composition more than the supply of colonists. However, dispersal limitation over broad scales (tens to thousands of kilometers) might constrain geographic ranges and influence community structure. The current explosion in the incidence of exotic species indicates that such global‐ or continental‐scale dispersal was limiting in the past. The spread of exotic species also provides opportunities to study the scale dependence of zooplankton dispersal. We show how patterns of range expansion can be used to estimate the change in invasion likelihood with distance to a source population. Such dispersal functions provide a crucial link between small‐scale experimental studies and broad‐scale geographic patterns.
Biodiversity and ecosystem functioning: A complex adaptive systems approach
Authors: Norberg Jon
Published: July 2010

Environmental factors regulate biodiversity through species sorting processes. Species distributions in communities affect ecosystem processes and environmental factors. These dynamics are determined by the properties (traits) of species in the community. The optimal temperatures for growth, the minimal amount of resource that sustains positive mass balance, and the amount of energy allocated to predator defenses are examples of such traits. Over time, the trait distributions in communities may change in response to environmental changes, which, in turn, changes the processes and consequently the structure of the system. The result of such processes is the focus of complex adaptive systems (CAS) theory. This paper gives an overview of how CAS theory can contribute to understanding the role of biodiversity on the ability of functional groups that make up the ecosystem to change their species compositions in response to changes in the environment. Any trait that requires investment of energy, mass, or time is subjected to a tradeoff for alternative use of this resource. Such interspecies tradeoff relationships can be used to make predictions about past environmental conditions, as well as the response of the properties of a group of species, e.g., total productivity and species distributions, to future changes in the environment. The trait based framework presented here makes explicit predictions regarding the relation between the environment, trait distributions, and ecosystem processes. Trait variance, a measure of the width of the distribution of traits in the community, is proportional to the rate at which species within functional groups can replace each other in response to environmental changes. This adaptive capacity is crucial for the ecosystem's ability to maintain certain processes under times of change. Examples of empirical tradeoffs are given as well as how to formalize them to use in the CAS framework.
Biodiversity in metacommunities: Plankton as complex adaptive systems?
Authors: Leibold Mathew A. , Norberg Jon
Published: July 2010

One of the more intriguing and challenging developments in ecology and in limnology and oceanography is the expansion of the temporal and spatial scales that are being addressed by current work. Researchers are realizing that individual communities and ecosystems are not isolated from each other but rather that they are connected by exchanges of individuals (through dispersal) and materials (through spatial fluxes). From a conceptual perspective, there is a need to develop theories and hypotheses about the roles of these exchanges on different community and ecosystem attributes. Here we focus on the concept of metacommunities, to address how plankton communities are structured and how this may generate patterns of variation in planktonic ecosystems. Our premise is that planktonic systems can be understood in the framework of metacommunities and that the regulation of these metacommunities alter how they work as “complex adaptive systems.” We hypothesize that connectivity through dispersal of local communities that are embedded in aquatic metacommunities show a range of dynamic behaviors related to their capacity to respond adaptively to environmental change.
To sink or swim: Variable diapause strategies among Daphnia species
Authors: Cáceres Carla E. , Tessier Alan J.
Published: July 2010

Although dormancy is assumed to be fundamental to population persistence in temporary ponds, it has been suggested that diapause may be less frequent in populations that inhabit permanent lakes. We compared the seasonal timing and magnitude of investment in diapausing eggs and their subsequent storage in the sediment among Daphnia species from both temporary ponds (Daphnia pulex and Daphnia ephemeralis) and permanent lakes (Daphnia pulicaria and Daphnia dentifera). Species exhibited strong temporal segregation in the timing of diapausing eggs production in both temporary and permanent systems. All populations of D. ephemeralis produced ephippia in early April whereas D. pulex and D. pulicaria produced the majority of ephippia in May‐June and D. dentifera did not produce males or ephippia until autumn. Maximum investment in dormant clutches (as opposed to immediately hatching eggs) was always 100% in the temporary pond species but ranged from 3% to 100% among populations living in the lakes. The number of eggs stored in the egg bank varied within and among species but was usually lower in the temporary pond species. Our results indicate that the use of dormancy in Daphnia varies considerably among populations and species and that whether the system is temporary or permanent is not necessarily a good predictor of a populationÂ's investment in dormancy.
Nonrandom sexual reproduction and diapausing egg production in a Daphnia hybrid species complex
Authors: Keller Barbara , Spaak Piet
Published: July 2010

Sexual reproduction in Daphnia results in the production of diapausing eggs, which are enclosed in a structure called ephippium. Ephippia, accumulated by sedimentation, can be preserved for decades and offer the opportunity for microevolutionary studies as well as the study of former pelagic populations. In a Swiss subalpine lake (Greifensee), we studied the genetic structure of the pelagic Daphnia galeata × hyalina hybrid species complex. We examined sexual females, males, and ephippia production. Eggs from ephippia were hatched, and the genotypes and taxa composition of all daphnids were determined using four polymorphic allozyme loci, two of which are each diagnostic for D. galeata and D. hyalina. We found significant differences between the genetic composition and the backcross level of pelagic asexual females, sexual females, males, and ephippial eggs (Daphnia hatchlings). The asexual daphnids were dominated by hybrids. In contrast, sexual females, especially Daphnia hatched from ephippial eggs, are dominated by D. galeata. We conclude that hybrid Daphnia have a lower sexual reproductive success than the parental D. galeata. The recent hybrid dominance suggests that D. galeata that hatch from diapausing eggs are not able to alter the pelagic population. The genotypic class composition of the diapausing eggs does not reflect the extant pelagic population; therefore, Daphnia diapausing egg banks do not always represent the past lake taxa structure.
Phytoplankton nutrient competition under dynamic light regimes
Authors: Litchman Elena , Klausmeier Christopher A. , Bossard Peter
Published: July 2010

Many physiological processes in phytoplankton, including nutrient uptake, vary on a number of temporal scales. Experiments show that the daily cycle in irradiance affects nutrient uptake rates. We used a Droop‐based model of resource competition to investigate how diel variability in nutrient uptake influences phytoplankton competition and community structure. The analytical approximation we derive shows that if nutrient uptake is light dependent, the minimum nutrient requirements and, hence, nutrient competitive abilities depend on light regime in a species‐specific way. Consequently, daily variations in irradiance may slow rates of competitive exclusion or reverse the identity of the superior competitor but not allow stable coexistence. Irradiance‐induced fluctuations in the maximum nutrient uptake rate of the superior competitor can lead to fluctuations in ambient nutrient concentration and an increase in the average nutrient concentration compared to constant light conditions. This can enhance nutrient use by inferior competitors. These results may be applicable to bacteria‐phytoplankton nutrient competition as well. Depending on the costs and benefits of maintaining nutrient uptake in the dark, different strategies of nutrient use are optimal under different light regimes. Our results suggest that by mediating limiting nutrient use, fluctuations in irradiance may alter the structure of phytoplankton communities.
The effects of infaunal biodiversity on biogeochemistry of coastal marine sediments
Authors: Waldbusser George G. , Marinelli Roberta L. , Whitlatch Robert B. , Visscher Pieter T.
Published: July 2010

We tested the role of benthic infaunal functional diversity in regulating the biogeochemistry of nearshore sediments using laboratory microcosms. Single and multispecies assemblages of deposit‐feeding polychaetes (Clymenella torquata, Spio setosa, and Leitoscoloplos fragilis) were used, and fluxes of oxygen and phosphate, as well as profiles of oxygen and pH in the sediment pore water, were measured. Significant differences in flux rates were found among treatments that were unrelated to polychaete abundance or biomass alone. Multispecies assemblages had lower flux rates of both oxygen and phosphate than rates calculated from the single‐species treatments. Depth integrated oxygen and pH profiles also showed significant differences between multispecies assemblages and selected single‐species treatments. These differences were most likely from species‐specific feeding and burrowing behavior and species‐related interactions. Coefficients of variance for both oxygen and pH were highest for microcosms with no polychaetes and lowest for the assemblages, indicating a dampening effect of multispecies assemblages on porewater heterogeneity. When oxygen flux data was incorporated into a model of oxygen dynamics in Long Island Sound, results indicated that shifts in the benthic community composition could change sediment oxygen consumption rates sufficiently to disrupt the balance between the physical supply of oxygenated water and biological oxygen demand. The results of this study confirm the importance of benthic functional biodiversity to nearshore sedimentary processes and suggest that losses of functional diversity can have significant effects on ecosystem function.
Three‐dimensional modeling of lacustrine diatom habitat areas: Improving paleolimnological interpretation of planktic : benthic ratios
Authors: Robert Stone Jeffery , Fritz Sherilyn C.
Published: July 2010

Three‐dimensional modeling of lake morphometry enables the calculation of lake volume, planar surface area, and basin surface area, which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level. We have applied three‐dimensional modeling to Foy Lake, Montana, and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake. The model allows us to produce semiquantitative depth reconstructions and greatly improves lake‐level reconstruction of this morphometrically complex basin. The conceptual model also was modified to examine the influence of resuspension versus gravity redistribution of diatomaceous material on the sedimentary record. Comparison of the model results with both long and short sedimentary records from Foy Lake, Montana, suggests that planktic : benthic ratios may be a better predictor of mean lake depth than maximum lake depth. The model developed here is simple enough to be easily implemented, has few requirements, can be adapted to suit any lake basin, and can be augmented to examine a variety of different lake processes that affect habitat availability.
Gas transfer velocities of CO2 in three European estuaries (Randers Fjord,Scheldt, and Thames)
Authors: Borges Alberto Vieira , Delille Bruno , Schiettecatte Laure‐Sophie , Gazeau Frédéric , Abril Gwenaöl , Frankignoulle Michel
Published: July 2010

We measured the flux of CO2 across the air‐water interface using the floating chamber method in three European estuaries with contrasting physical characteristics (Randers Fjord, Scheldt, and Thames). We computed the gas transfer velocity of CO2 (k) from the CO2 flux and concomitant measurements of the air‐water gradient of the partial pressure of CO2 (pCO2). There was a significant linear relationship between k and wind speed for each of the three estuaries. The differences of the y‐intercept and the slope between the three sites are related to differences in the contribution of tidal currents to water turbulence at the interface and fetch limitation. The contribution to k from turbulence generated by tidal currents is negligible in microtidal estuaries such as Randers Fjord but is substantial, at low to moderate wind speeds, in macrotidal estuaries such as the Scheldt and the Thames. Our results clearly show that in estuaries a simple parameterization of k as a function of wind speed is site specific and strongly suggest that the y‐intercept of the linear relationship is mostly influenced by the contribution of tidal currents, whereas the slope is influenced by fetch limitation. This implies that substantial errors in flux computations are incurred if generic relationships of the gas transfer velocity as a function of wind speed are employed in estuarine environments for the purpose of biogas air‐water flux budgets and ecosystem metabolic studies.
Community metabolism and carbon budget along a gradient of seagrass(Cymodocea nodosa) colonization
Authors: Barrón Cristina , Marbé Nùria , Terrados Jorge , Kennedy Hilary , Duarte Carlos M.
Published: July 2010

We studied the effect of seagrass (Cymodocea nodosa) colonization on community metabolism and sediment conditions. The biomass of C. nodosa increased with time after seagrass colonization. The biomass increased steadily during the 6.1 yr of colonization to 9.1 mol C m−2. Gross primary production increased from 7 to 49.3 mmol C m−2 d−1 during the first stages of the colonization and then decreased to 20 mmol C m−2 d−1 at a time when the biomass was in excess of 6 mol C m−2. Net dissolved organic carbon (DOC) fluxes increased with time after colonization, shifting from a net uptake in patches younger than 2 yr to a net release in older patches. Community respiration (R) increased with the seagrass colonization, leading to a shift from net autotrophy in the unvegetated sediment community to net heterotrophy after C. nodosa colonization. The increase in net heterotrophy with seagrass colonization was reflected in the development of reducing conditions in the sediment. To maintain a net heterotrophic benthic metabolism and net DOC release, the C. nodosa community must receive an input of organic matter (OM) from an allochthonous source. OM inputs from sestonic material trapped by the seagrass canopy exceed 157 mmol C m−2 d−1 in developed C. nodosa communities. Thus, the seagrass community acts as an important link between the pelagic and benthic communities by trapping sestonic organic carbon.
Attachment to suspended particles may improve foraging and reduce predation risk for tintinnid ciliates
Authors: Jonsson, Per R. , Johansson, Mona , Pierce Richard W.
Published: July 2010

We describe a new behavior of planktonic ciliates. The field‐collected tintinnid Eutintinnus inquilinus attached with its lorica to a range of surfaces, including particulate aggregates. Most tintinnids remained attached with the aboral end of their lorica when well fed. On starvation, many tintinnids detached and resumed a free‐swimming life. We hypothesize that the adhesive property of the lorica has evolved as an adaptation to attach to suspended aggregates or other seston particles. Attached E. inquilinus have a feeding rate that is 80% higher than freeswimming individuals because of the change in the fluid dynamics of the feeding current for attached E. inquilinus, which leads to steeper velocity gradients and higher flow rates close to the lorica. This mechanism will also operate for swimming suspension feeders attached to smaller particles that significantly increase the hydrodynamic drag. Selection for traits that enhance the velocity gradients in feeding currents of small plankton may be common and may partly shape behavioral patterns and functional morphology. When exposed to the calanoid copepod Acartia clausi, populations of E. inquilinus were less susceptible to predation than another Eutintinnus species of similar morphology but that were entirely free swimming.
Sinking behavior of gastropod larvae (Ilyanassa obsoleta) in turbulence
Authors: Fuchs Heidi L. , Mullineaux Lauren S. , Solow Andrew R.
Published: July 2010

Larvae of coastal gastropods sink in turbulence and may use nearshore turbulence as an initial settlement cue. Our objective was to quantify the relationship between turbulence and the proportion of sinking larvae for competent mud snail veligers (Ilyanassa obsoleta). We exposed larvae to a range of field‐relevant turbulence conditions (ɛ = 8.1 × 10−3 to 2.7 × 100 cm2 s−3) in a grid‐stirred tank, holding other factors constant. We used a video plankton recorder to record larval movements in still water and in turbulence. Larval trajectories and velocity measurements were extracted using video‐image analysis. We also measured turbulent flow velocities independently, using laser Doppler velocimetry. To interpret empirical measurements in terms of larval behavior, we developed a threecomponent, normal mixture model for vertical velocity distributions of larvae in turbulence. The model was fitted to observed larval velocities by maximum likelihood, to estimate the proportions of sinking, hovering, and swimming larvae. Over the range of turbulence intensities found in typical coastal habitats, the proportion of sinking larvae increased exponentially (r2 = 0.89) with the log of the turbulence dissipation rate. The net mean behavioral velocity of the larvae shifted from positive to negative when the dissipation rate reached ~10−1 cm2 s−3. By sinking when they enter turbulent, shallow water, competent larvae could improve their chances of settling in favorable coastal habitats.
Spatial and temporal patterns in larval supply at hydrothermal vents in the northeast Pacific Ocean
Authors: Metaxas Anna
Published: July 2010

Larval supply in marine benthic invertebrates influences patterns of settlement and recruitment to adult populations. To successfully colonize newly formed or distant hydrothermal vents, which are discontinuous and ephemeral habitats, larvae of vent invertebrates must possess long‐range dispersal abilities. However, a significant proportion of locally produced larvae must remain within the adult habitat to maintain the observed dense assemblages of invertebrates. I compared spatial and temporal patterns in larval availability (flux and abundance) at hydrothermal vents within and between ridge segments in the northeast Pacific ocean at Axial Seamount and Endeavour Segment on the Juan de Fuca Ridge and at Magic Mountain on Explorer Ridge. Near‐bottom (within 50 cm) larval supply (individuals m−2 d−1) at five vents on Axial Seamount, measured with passively collecting traps in 2000 and 2001, varied temporally by an order of magnitude, but not spatially at scales of tens of meters to kilometers. The most abundant larval taxa were gastropods (particularly the limpet Lepetodrilus fucensis) and polychaetes. Larval abundance in the water column within the axial valley was measured with net tows by the remotely operated vehicle ROPOS at the three ridge segments: Axial Seamount (2000, 2001); Endeavour Segment (2001, 2002); Magic Mountain (2002). Abundance was greater by an order of magnitude at the Endeavour Segment than at Axial Seamount and Magic Mountain, and it did not differ between on‐vent (within tens of meters) and off‐vent (up to 5 km from the venting source) locations within the axial valley. The uniformly high abundance of larvae within axial valleys suggests that larval supply within a ridge segment is most likely localized, implying significant larval retention on the scale of vent fields and possibly ridge segments.
Transmission of ultraviolet radiation through the Antarctic annual sea ice and its biological effects on sea urchin embryos
Authors: Lesser Michael P. , Lamare Miles D. , Barker Michael F.
Published: July 2010

Stratospheric ozone depletion over Antarctica is expected to continue for the next 50 years, with increases in ecologically damaging ultraviolet radiation (UVR: 290–400 nm), specifically the ultraviolet‐B (UVB: 290–320 nm) portion of the spectrum. Most of coastal Antarctica is covered with 2–3 m of annual sea ice during the occurrence of the “ozone hole.” This physical barrier to UVR transmission has long been assumed to provide complete protection from the biologically damaging effects of UVR, especially for the planktonic developmental stages of the benthic invertebrate fauna. We found that short‐wavelength UVB (down to 304 nm) is transmitted through the Austral spring annual ice of McMurdo Sound, and causes significant mortality and DNA damage in the embryos of the sea urchin Sterechinus neumayeri. Although mortality of sea urchin embryos has been reported for the open waters of the Antarctic, this is the first documentation of mortality and DNA damage for embryos under the annual sea ice. The degree of mortality and DNA damage was dependent on both year and depth, with higher mortality and DNA damage at 1 m depth below the ice compared to 3 m and 5 m. Greater DNA damage occurred in 2003 compared to 2002 despite the thicker annual ice (3.1 m vs. 2.5 m). Although the thickness of the annual ice was greater, the severity of the ozone hole, 230 Dobson units (DU) versus 320 DU, and the ratio of UVB to visible radiation was greater in 2003. Embryo and larval mortality from exposure to UVR under the annual ice should be considered as another abiotic factor potentially affecting the temporally episodic recruitment of invertebrates that occur in this benthic ecosystem.
Differential uptake of dissolved and particulate organic carbon by the marine musselPerna viridis
Authors: Pan Jin-Fen , Wen-Xiong Wang
Published: July 2010

We used radiotracers in laboratory experiments to determine the organic carbon uptake by the marine mussel Perna viridis from different diets (phytoplankton and detritus) and from the dissolved phase (colloidal and low molecular weight organic carbon). Standard compounds (glucose, arginine, and leucine, and the carbohydrate macromolecular dextran with sizes ranging from 3–2,000 kDa) were used to study organic matter flux into the green mussels. Carbon absorption was significantly affected by the food type and quality. The highest absorption efficiency (AE, 80%) was from the diatom Thalassiosira pseudonana, while the AE from Chlorella autotrophica was comparable with those from three types of algal detritus (20–30%). Mussels were able to directly ingest macromolecular dextran colloidal materials. Significant accumulation of these compounds was found both in the gills and the digestive glands of the mussels within the 12–17–h exposure period. Similarly, a significant accumulation of biogenic colloidal organic carbon (COC) and low molecular weight ultrafiltered organic carbon (UOC) was found. Uptake of UOC and COC resulting from the decomposition of different algal sources was comparable, with an uptake rate constant of 6.08 × 10–−4 L g−1 dry wt h−1 and an absorption efficiency of 0.0053%. A kinetic model was subsequently applied to quantitatively evaluate the carbon contribution from dissolved and particulate sources to general organic carbon uptake by the mussels. Mussels accumulated organic carbon predominantly from the particulate phase, with very little (<0.2%) coming from the DOC. However, the apparent ingestion and accumulation of colloids suggest that they can actively participate in the food chain dynamics in marine systems.
Effects of sunlight and hydroxyl radical on dissolved organic matter: Bacterial growthefficiency and production of carboxylic acids and other substrates
Authors: Pullin Michael J. , Bertilsson Stefan , Goldstone Jared V. , Voelker Bettina M.
Published: July 2010

This study examines the importance of several possible mechanisms causing sunlight‐mediated changes in the amounts of bacterial utilization and biomass growth on dissolved organic matter (DOM) from allochthonous sources. Our results demonstrate that, while hydroxyl radical reactions with DOM can be an important process increasing its bioavailability, other photoreactions will cause most of the sunlight‐induced increases unless hydroxyl production rates are high (>~ 7 µmol L−1 d−1). Low molecular weight carboxylic acids could not account for most of the observed sunlight and hydroxyl‐induced increases in DOM bioavailability. Both sunlight and hydroxyl‐mediated reactions significantly decreased the bacterial growth efficiency of DOM, indicating that photochemical reactions affect not only the fraction of the total DOM pool available to bacteria on ecologically relevant timescales but also the substrate quality and ultimately the environmental fate of this material. Extrapolation of these results to field conditions suggests that photochemical and biochemical mineralization could be an important sink of DOC and source of bioavailable carbon in the Plum Island estuary during the summer months.
Pathways of organic carbon oxidation in a deep lacustrine sediment, Lake Michigan
Authors: Thomsen Uffe , Thamdrup Bo , Stahl David A , Canfield Donald E.
Published: July 2010

Rates of microbial iron reduction and other pathways of organic carbon (Corg) oxidation were investigated in sediment from a 100‐m deep site in Lake Michigan. Total benthic mineralization rates of 6.8 and 8.0 mmol m−2 d −1, respectively, were determined from benthic flux measurements and by summation of dissolved inorganic carbon (ΣCO2) accumulation rates measured in anoxic incubations of sediment in discrete depth intervals to 18 cm depth. Carbon oxidation rates were highest near the sediment surface and decreased asymptotically toward zero. A Corg half‐life of 0.06 yr was estimated in the oxic zone, but the half‐life increased by more than two orders of magnitude in the deep anoxic layers. Mineralization in the oxic zone (0‐2.1 cm) accounted for 37% of the total SCO2 production, whereas microbial iron reduction was the most important pathway of carbon oxidation, accounting for 44%; sulfate reduction accounted for 19%, and methanogenesis was negligible. Denitrification accounted for <3% of Corg oxidation. Sulfate reduction was suppressed in the upper 5 cm, where oxygen, manganese, and iron reduction prevailed. Below this zone, sulfate reduction peaked but coexisted with microbial iron reduction. All Mn reduction was apparently coupled to iron and sulfide oxidation in the upper 6 cm. Below that level, a transient accumulation of iron monosulfide and pyrite implied that sulfate reduction increased during the 19th century because of anthropogenic atmospheric sulfur deposition. Sediment mixing through bioturbation was crucial for the cycling of Mn, Fe, and S, and estimates of biodiffusion coefficients were 0.02‐0.3 cm2 d−1.