bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral light attenuation and the absorption of UV and blue light in natural waters
Authors: Markager Stiig , Vincent Warwick F.
Published: June 2010

The spectral pattern of light attenuation in the ultraviolet (UV) and blue region (360–500 nm) was analyzed for seven high Arctic lakes. The best description of Kd versus wavelength was obtained with an exponential model similar to the model used for absorption by chromophoric dissolved organic compounds (CDOM), but with an additional parameter (Kback) that accounts for background scattering:
urn:x-wiley:19395590:media:lno20004530642:lno20004530642-math-0001
where Kd(λ) is the diffuse vertical attenuation coefficient at wavelength λ and S is the exponential slope parameter that characterizes the decrease in attenuation with increasing wavelength. The inclusion of the background parameter gave a significantly better fit and eliminated the systematic deviations over the spectrum that occur in the absence of Kback. The resultant S values (mean = 17.4 µm−1) were on average 47% higher than values calculated without a background parameter, and were more sensitive to between‐lake differences. The same pattern was found when S was estimated from spectral Kd values in three literature data sets, so the new equation will generally increase the estimated values of S based on Kd and provide a more accurate guide to intersystem variability. A compilation of literature data for S (based on Kd and the new equation or on absorbance) showed that its mean value (±SE) is significantly higher in freshwaters (17.1 ± 0.7 µm−1) than in the sea (14.0 ± 0.4 µm−1). The variability in S was highest for low values of Kd or a (340 nm values below 3 m−1). This pattern may be due to instrument‐related problems or more likely represents the real variability in the optical properties of CDOM in low colored systems. The analysis showed that S can vary significantly between and within systems (overall range = 9.2–36.2 µm−1) and that the value obtained also depends on the method of calculation, the wavelength range, and the type of optical measurement.
Spatial and temporal variability of picocyanobacteria Synechococcus sp. in San Francisco Bay
Authors: Ning Xiuren , Cloern James E. , Cole Brian E.
Published: June 2010

We collected samples monthly, from April to August 1998, to measure the abundance of autotrophic picoplankton in San Francisco Bay. Samples taken along a 160‐km transect showed that picocyanobacteria (Synechococcus sp.) was a persistent component of the San Francisco Bay phytoplankton in all the estuarine habitats, from freshwater to seawater and during all months of the spring‐summer transition. Abundance ranged from 4.6 × 106 to 5.2 ×8 cells L−1, with peak abundance during the spring bloom (April and May) and during July with a persistent spatial pattern of smallest abundance near the coastal ocean and highest abundance in the landward domains of the estuary. The picocyanobacterial component (as estimated percentage of chlorophyll a concentration) was, on average, 15% of total phytoplankton biomass during the summer–autumn nonbloom periods and only 2% of chlorophyll biomass during the spring bloom. This result is consistent with the emerging concept of a gradient of increasing importance of picocyanobacteria along the gradient of decreasing nutrient concentrations from estuaries to the open ocean.
Biological accumulation of 226Ra in a groundwater‐augmented Florida lake
Authors: Brenner Mark , Smoak Joseph M. , Allen Micheal S. , Schelske Claire L. , Leeper Douglas A.
Published: June 2010

Round Lake, Hillsborough County, Florida (U.S.A.) has been augmented with 226Ra‐rich (6.2 dpm L−1) groundwater from the Floridan aquifer for more than 30 years. Water column 226Ra activity in Round Lake is 3.4 dpm L−1, about one third of the U.S. drinking water standard value. Radionuclide measurements in biota and sediment cores from the lake indicate high 226Ra activities in plants, mollusc shells and tissues, fish bones, and recent sediments. Unionid mussels bioaccumulate 226Ra and display very high activities in soft tissues (219.9–454.8 dpm g−1 dry). Throughout Florida, groundwaters are increasingly pumped for agricultural irrigation, as well as residential and industrial use. Biological accumulation of 226Ra by filter‐feeding pelecypods in aquatic ecosystems is an important pathway for transfer of the radionuclide to higher trophic levels of both aquatic and terrestrial food webs. Radionuclide analysis of soft tissues from aquatic bivalves provides a rapid means of identifying waterbodies that receive substantial inputs of dissolved 226Ra.
Distribution and turnover of dissolved DMSP and its relationship with bacterial production and dimethylsulfide in the Gulf of Mexico
Authors: Kiene Ronald P. , Linn Laura J.
Published: June 2010

We measured the distribution of particulate and dissolved pools of the phytoplankton osmolyte dimethylsulfoniopropionate (DMSP) in the euphotic zone at a series of shelf (<40 m total water depth) and oceanic (>500 m depth) stations in the northern Gulf of Mexico. We also measured turnover rates of the dissolved DMSP pools (DMSPd) with tracer additions of 35S‐DMSPd and short‐term (<1 h) incubations, with the aim of examining the relationship between DMSPd turnover and bacterial production. Particulate DMSP concentrations were relatively low (<25 nM) throughout the study area with about twofold higher mean concentration at the shelf sites (15 nM) compared with the oligotrophic oceanic sites (7 nM). DMSPd concentrations averaged 3.0 nM in shelf waters and 1.3 nM in oceanic waters. Concentrations of dimethylsulfide (DMS), a degradation product of DMSP, also were low throughout the Gulf, averaging 2.0 nM for all depths sampled and 2.5 nM in surface waters. Microbial assem‐blages metabolized 35S‐DMSPd with the sulfur being incorporated into biomass, volatile compounds (DMS and methanethiol), and other dissolved products. DMSPd turnover was relatively slow (mean of 3.8 nM d−1) in oligotrophic oceanic waters and averaged 10‐fold higher (39 nM d−1) in mesotrophic shelf waters. DMS concentrations ranged from 0.2 to 5.1 nM in oceanic waters and appeared to be weakly related to DMSP turnover. In contrast, DMS concentrations in shelf waters fell within a narrow range (0.8–2.8 nM) and showed no relationship at all with DMSPd turnover. DMSPd turnover rates were high enough to sustain the measured concentrations and estimated turnover of DMS, even if the conversion efficiency of DMSPd into DMS was only 10%. DMSPd turnover was significantly correlated with bacterial production (as measured by 3H‐thymidine incorporation) and we estimate that DMSPd turnover contributed a mean of 3.4% of the carbon and ~100% of the sulfur required for bacterial growth in Gulf of Mexico surface waters. In addition to its role as a precursor of DMS, DMSP deserves attention as an important substrate for bacterioplankton in the euphotic zone.
Microbial biomass and production associated with decaying leaf litter of the emergent macrophyte Juncus effusus
Authors: Kuehn K. A. , Lemke M. J. , Suberkropp K. , Wetzel R.G.
Published: June 2010

Emergent macrophytes are a major source of organic matter production in freshwater wetlands, and often represent the bulk of
the plant material entering the detrital pool. We examined the decomposition and microbial dynamics associated with litter of the
emergent macrophyte, Juncus effusus (soft rush), during its movement from an aerial standing dead to a submerged decay
environment. Standing dead leaves of J. effusus were collected after an initial period of standing litter microbial decay,
placed in 1‐mm mesh litter bags, and submerged in a wetland. Litter bags were retrieved periodically over 268 d and
analyzed for microbial (fungal and bacterial) biomass and production, ATP concentrations, litter mass loss, and quality (C:N:P and
plant fiber). Submerged litter decay of J. effusus was slow (k = 0.0010 d−1), with only 23% weight loss
after 268 d. Both fungal and bacterial biomass and production decreased significantly soon after standing plant litter was
submerged in the wetland surface waters. Despite decreases in microbial biomass and production, fungal decomposers remained the
dominant microbial assemblage associated with decaying plant litter, accounting for 99% and 91% of the total microbial biomass and
production, respectively. Mean fungal production ranged from 73–2,836 mg C g−1 AFDM d−1
(AFDM: ash‐free dry mass remaining) during the study period, whereas attached bacterial production ranged from 4–32
mg C g−1 AFDM d−1. Patterns of litter ATP and nutrient concentrations (N and P) were similar
to those observed for fungal and bacterial biomass, suggesting that at least a portion of the detrital N and P may have been
incorporated into microbial biomass. Significant changes in microbial colonization and activity associated with emergent
macrophyte litter can occur following the collapse of standing dead plant matter to the water or surface sediments. Furthermore,
our findings suggest that fungi are significant contributors to the decay of coarse particulate plant matter in wetland ecosystems.
Effect of growth conditions on flow‐induced inhibition of population growth of a red‐tide dinoflagellate
Authors: Juhl Andrew R. , Velazquez Vivianna , Latz Michael I.
Published: June 2010

The population growth of some dinoflagellates is known to be reduced by exposure to fluid flow. The red‐tide dinoflagellate Lingulodinium polyedrum was used to examine the effect of growth conditions on flow‐induced inhibition of population growth. Three factors were tested: time of exposure relative to the light:dark (LD) cycle, illumination level, and culture growth phase (early vs. late exponential phase). Cultures maintained on a 12:12 h LD cycle were exposed to one of two flow conditions: quantified laminar shear produced by Couette flow or unquantified flow generated in shaken flasks. The duration of exposure to flow was 1 h d−1 for 5–8 d in all experiments; the shear stress in Couette shear experiments was 0.004 N m−2. There were many qualitative similarities in the pattern of response to flow in the two hydrodynamic conditions. In both cases, exposure to flow in the last hour of the dark phase resulted in greater reduction of net growth than exposure during the light phase. Cultures grown under lower illumination had proportionally greater reductions in net growth than cultures under higher light. Finally, late exponential phase cultures exhibited much greater reductions in net growth following a given flow exposure than early exponential phase cultures. The higher sensitivity of late exponential phase cultures did not appear to be linked to nutrient limitation or changes in pH of the medium; it may be partially attributed to exudates from late exponential phase cells. These results suggest that the response of red‐tide dinoflagellate population growth to in situ turbulence may depend on both environmental conditions and the physiological state of the cells.
A novel chemical method to quantify fish debris in marine sediments
Authors: Schenau S. J. , De Lange G. J.
Published: June 2010

Burial of fish bones, which consist primarily of hydroxyapatite, has been recognized as a mechanism to remove reactive phosphorus from the oceans. In this study, a new method is presented, which differentiates P associated with biogenous apatite (Pfish) from other P fractions. The method, consisting of a sequential chemical extraction with 2 M NH4Cl, has been successfully tested on standard materials. It enables us, for the first time, to quantify fish debris in sediment records and to assess their importance for the marine phosphorus cycle.

The NH4Cl extraction has been applied to sediment samples from the Arabian Sea. Preservation of fish debris is significantly higher in sediments located above 1,200 m water depth than it is for deeper sediments. The distribution of Pfish contents in surface sediments is predominantly governed by the extent of fish debris regeneration, which is related to differences in water depth and sedimentation rates. In addition, a good correlation between high sedimentary Pfish contents and low oxygen bottom water concentrations suggests that the presence of the intense oxygen minimum zone may account for the enhanced preservation of fish debris in continental slope sediments.
The physical regime and the respective biogeochemical processes in the lower water mass of Lake Kinneret
Authors: Nishri A. , Imberger J. , Eckert W. , Ostrovsky I. , Geifman Y.
Published: June 2010

Physical measurements made in Lake Kinneret, during the stratified period, indicate that the lower water mass (LWM) consists of two layers: a turbulent benthic boundary layer (BBL) and a hypolimnetic layer overlying the BBL. The water in the LWM moves in response to vertical mode one seiching of the metalimnion; this movement is accentuated near the perimeter of the metalimnion due to shoaling of the seiche and breaking of internal waves. The motion associated with this phenomena induce a well mixed benthic boundary layer (BBL) adjacent to the lake bottom. The BBL and hypolimnion were distinguished chemically because transport of solutes between these water bodies was very small. Compared to the hypolimnion, the BBL was characterized by more intensive biomineralisation processes as indicated by the faster depletion of DO and NO3, by higher levels of NH4,H2S, and soluble reactive phosphorus (SRP) and by lower pH values. SRP levels in the hypolimnion were particularly low, suggesting that phosphorus was either preferentially removed by sedimentation from the hypolimnion, or it was not released from particles. As a result NH4 over SRP ratios in the hypolimnion were significantly higher than in the BBL and diffusional fluxes of both nutrients from the LWM to the trophogenic epipelagic water, should therefore be characterized by relatively high N/P ratios.
Efficiency of water‐column light utilization in the subarctic northwestern Pacific
Authors: Akihiro Shiomoto
Published: June 2010

Efficiency of water‐column light utilization in the upper 2% light depth ( c) tended to be high during spring and summer (means: 0.75 and 0.96 g C g Chla−1 mol quanta−1 m2) and low during autumn and winter (means: 0.33 and 0.53 g C g Chla−1 mol quanta−1 m2). Higher phi values were probably due to an increase in the phytoplankton growth rate in the blooms. With the exception of bloom conditions, the phi tended to increase with a decrease of the daily photosynthetically active radiation (PAR), and variations in the phi in relation to the daily PAR were within the range of those summarized by Falkowski and Raven (1997). The water‐column light utilization efficiency in the subarctic northwestern Pacific at the bloom times was noticed to be by far the highest in the world oceans.
Muscle fatty acids as indicators of niche and habitat in Malawian cichlids
Authors: Kuusipalo Liisa , Käkelä Reijo
Published: June 2010

Fatty acid composition in the muscle of eight endemic haplochromine cichlids and one tilapiine cichlid from Lake Malawi was studied by gas‐liquid chromatography. The species studied represent a wide variety of niches: Algae combing, shell crushing, feeding on littoral and semipelagic zooplankton, detecting invertebrates hidden in the sediment using expanded lateral line canals, and fish predation in littoral and bathypelagic zones. The sampling was done during the early rainy season. The analysis of fatty acid composition suggests that, despite the reported plasticity in feeding, the niches of the species studied are established and stable. The proportion of eicosapentaenoic acid (20:5n‐3) in relation to arachidonic acid (20:4n‐6) illustrated the position of these species in the foodweb: equal proportions in algae feeders and clear 20: 4n‐6 dominance in species feeding on benthic prey. Although the number of replicates was small, discriminant analysis with 31 fatty acids separated the specimens into dense centers according to species. These results encourage the use of chemometric methods for studying ecological relationships among freshwater fauna and ongoing evolutionary processes.
Effects of nutrient enrichment and small predator density on seagrass ecosystems: An experimental assessment
Authors: Heck K. L. , Pennock J. R. , Valentine J. F. , Coen L. D. , Sklenar S. A.
Published: June 2010

We used a field experiment to assess the individual and combined effects of removing top predators and enriching water column nutrients (nitrogen‐N and phosphorus‐P) on seagrass ecosystem structure and function. Experiments were conducted in turtlegrass (Thalassia testudinum) habitats in St. Joseph Bay, FL, an aquatic preserve in the northern Gulf of Mexico that exhibits low ambient nutrient concentrations and contains abundant populations of small crustacean and gastropod mesograzers. We stocked 7.0 m 2 enclosures with elevated (≈4ࢤ8× ambient) densities of juvenile pinfish (Lagodon rhomboides), the dominant fish species in local seagrass habitats, to simulate the first‐order effects of large predator reductions, and we used an in situ delivery system to supplement N and P to ≈3× ambient levels in nutrient addition treatments. Monthly determinations of water column nutrients and Chl a, along with measurements of the biomass and abundance of leaf epiphytes and seagrass production, biomass, and shoot and leaf densities were used to evaluate the relative effects of manipulating nutrient supply and altering food web structure.

In contrast to our expectations, results showed few significant nutrient effects, or fish × nutrient enrichment effects on any of the parameters measured. However, there were many significant fish effects, most of which were unexpected. As predicted, increased pinfish density reduced mesograzer numbers significantly. Not anticipated, however, was the reduced epiphyte biomass in fish enclosure treatments, apparently brought about by the pinfish consuming significant amounts of epiphytes as well as mesograzers. This reduction in epiphyte biomass produced positive indirect effects on seagrass biomass, shoot number, and rates of primary productivity in pinfish enclosure treatments.

Our results also showed important top‐down effects in determining the composition and abundance of seagrass‐associated plants and animals in this pristine environment. Although we did not observe simple trophic cascades, most likely because pinfish fed at more than one trophic level, and because the dense seagrass prevented small grazers from being reduced to low numbers, pinfish produced important changes in the epibiota as well as the seagrasses themselves. These data, while contrasting with studies reporting significant negative nutrient enrichment effects on seagrasses, support the results of recent experimental studies in showing that: (1) small grazers can often control the abundance of epiphytes; and (2) it is unlikely that a full understanding of the consequences of nutrient enrichment for seagrass ecosystems can be gained without knowing how grazer population are regulated.
Climate‐driven changes in spring plankton dynamics and the sensitivity of shallow polymictic lakes to the North Atlantic Oscillation
Authors: Gerten Dieter , Adrian Rita
Published: June 2010

Climate is increasingly recognized as a major factor driving long‐term changes in plankton communities in both marine and limnetic ecosystems. In a shallow and polymictic lake, marked changes in the dynamics of phytoplankton and in the timing of distinctive successional events in spring were observed during two recent decades. We studied whether and how these changes were linked to a series of uncommonly warm winter and spring seasons, focusing on the predictive power of a macroscale atmospheric circulation pattern, the North Atlantic Oscillation (NAO). In the warm period 1988‐1998, phytoplankton developed about 1 month earlier than in the cool period 1979‐1987, and high total phytoplankton biomass was recorded in early spring. These changes were significantly related to the NAO, which explained about 35% of the variance, and can be attributed to a shortening or lack of ice cover periods in winter. Zooplankton (Keratella, Bosmina, Daphnia) developed about 2 weeks earlie in the warm period, consequently leading to an early establishment of the clearwater phase. The shift in the timing of the daphnid peak and of the clearwater phase required an additional warming trend in late April and early May and was not significantly correlated with the winter situation. The memory effect of the NAO was restricted to a rather short postwinter period and was overtaken by the prevailing weather in April. Our results suggest that assessments of potential impacts of climate warming on biological processes in freshwater ecosystems demand basic knowledge about the relationships between global climate indices, local meteorological conditions, and the thermal response of various lake type .
Electron flow in an iron‐rich acidic sediment—evidence for an acidity‐driven iron cycle
Authors: Peine Ariane , Tritschler Andrea , Küsel Kirsten , Peiffer Stefan
Published: June 2010

The anoxic sediment of an acidic (pH ∼3) iron‐ and sulfate‐rich lake and its pore water was studied with respect to the turnover rates of solid and dissolved iron and sulfur species. High sedimentation rates of iron (570 g m−2 a−1) lead to an enrichment of the upper (0–5 cm) acidic sediment zone (pH < 4) with schwertmannite (Fe8O8(OH)x(SO4)y (∼ 350 g kg−1). Microbial iron‐reduction rates measured by closed vessel incubation technique were highest close to the sediment‐water interface (250 nmol cm−3 d−1), sulfate reduction measured by the 35S‐tracer technique was not detectable in this zone. The absence of sulfide allowed complete reoxidation of dissolved Fe(II) diffusing into oxic parts of the lake water. Thus, an iron cycle is established where acidity generation through this process (1.0–4.7 mol m−2 a−1) balanced the alkalinity gain through microbial iron reduction in this zone (0.65–4.0 mol m−2 a−1). Predominance of iron over sulfate reduction under acidic conditions is further stabilized by the transformation of schwertmannite to goethite at a depth of 3–5 cm, which releases acidity at a rate of 3.5 mol m−2 a−1. Below, pore‐water pH increased to values between 5 and 6, sulfate reduction occurred with a maximum rate of 14 nmol cm−3 d−1), sulfate reduction measured by the 35S‐tracer technique was at 9 cm depth. Release of Fe(II) and a short turnover time of reduced sulfur relative to the sediment age implies that most of the sulfide formed seemed to be recycled to sulfate at this depth, presumably coupled to the reduction of iron. Consequently, net alkalinity is generated at low rates only (0.12 mol m−2 a−1).
Interactions between trace elements and dissolved organic matter in the stagnant anoxic deep layer of a meromictic lake
Authors: Albéric Patrick , Voillier Eric , Jézéquel Didier , Grosbois Cécile , Michard Gil
Published: June 2010

About 80% and more than 90% of the dissolved organic carbon (DOC) in the bottom water of Lake Pavin were isolated, respectively, on Amberlite XAD and Spherodex DEAE resins. Trace element concentrations in the fractions isolated were analyzed by using ICP‐MS. Uranium, molybdenum, and antimony were found to be about 40% associated with fulvic and hydrophilic acids adsorbed on XAD resins at pH 2, the metal‐organic association being not dissociated. Much higher percentages of the same elements, plus vanadium, were adsorbed on the DEAE resin at the pH of natural water, possibly because of the better preservation of acid labile organic complexes or of the supplementary adsorption of inorganic compounds. Ultrafiltration and dialysis made it possible to exclude colloidal fractions together with much U (78%), Mo (80%), V (55%), and DOC (65%). These elements and many others (including barium) were previously found to be quite reactive at the bottom of the lake, (apparently being scavenged by settling particles, which are mostly diatoms, then dissolved at the sediment‐water interface). Conversely, trace elements with a conservative behavior in the bottom layer (such as lithium and cesium) were not found associated with dissolved organic mater (DOM). Barium was not strongly associated with the extractable DOM, which may argue for a direct interaction with inorganic particles or the existence of very labile complexes. Our work suggests the existence of relatively stable (nonacid labile) U and Mo–DOM colloidal associations in the anoxic bottom waters of the lake and their importance in the scavenging of those metals.
Accessory pigments versus chlorophyll a concentrations within the euphotic zone: A ubiquitous relationship
Authors: Trees Charles C. , Clark Dennis K. , Bidigare Robert R. , Ondrusek Michael E. , Mueller James L.
Published: June 2010

Remotely sensed chlorophyll a (Chl a) concentrations are determined by the ratio of upwelled radiances within the Soret band of Chl a (443 nm) and at 550 nm. Absorption at wavelengths outside this band (>460 nm) is dominated by accessory pigments and for the successful measurement of Chl a (e.g., 490:550 nm and 520:550 nm ratios) early Coastal Zone Color Scanner investigators speculated that these accessory pigments must covary with Chl a, although routine methods to measure these pigments had not yet been developed. Nearly 7,000 (high performance liquid chromatography) pigment samples, collected within the euphotic zone, were measured to test the consistency of the relationship between accessory pigments and Chl a. Despite the various sampling periods (1985–1998) and numerous geographic locations, consistent patterns have emerged in the ratios of the log accessory pigments to log total Chl a (TCHLA = Chl a, Chl a allomer, Chl a epimer, and chlorophyllide a). There were strong log‐linear relationships within cruises for these ratios with an average r2 of 0.889. An even more impressive relationship was observed on a global scale when all the data were combined. Individual relationships were also calculated for case I and case II waters, as well as for the first optical depth (Κ−1), termed the remote sensing depth. There were some statistical differences between these relationships, yet on a practical sense many could be combined. Despite a wide range of environments sampled, the overall slope of the log accessory pigments:log TCHLA was found to be 0.934 with a relative‐difference root‐mean‐square error of 28% in log accessory pigment concentrations. This global log‐linearity largely explains the success in remotely sensed Chl a algorithms, even though phytoplankton populations can vary in their composition and suite of pigments.
The nutritional quality of P‐limited algae for Daphnia
Authors: Boersma Maarten
Published: June 2010

This paper details results of experiments intended to clarify the relative effects of mineral versus biochemical limitations of algae on the food quality for herbivorous zooplankton. Phosphorus limited algae (Scenedesmus) were fed to Daphnia magna and the somatic growth rates of the animals were measured. The animals showed an increase in growth rate when phosphorus (P) was added to P‐limited algae, especially when the animals were older. The addition of highly unsaturated fatty acids only resulted in an increase in growth rates when the algae had a C:P ratio of less then 300. The main conclusion of this work is that both mineral and biochemical limitations of their food play a role in the growth and population dynamics of zooplankters, but that mineral requirements need to be met first.
Functional responses of the rotifers Brachionus calyciflorus and Brachionus rubens feeding on armored and unarmored ciliates
Authors: Mohr Silvia , Adrian Rita
Published: June 2010

Density dependent grazing experiments were performed to investigate the feeding behaviour of the rotifers B. calyciflorus and Brachionus rubens on the ciliates Coleps sp. and Tetrahymena pyriformis. The ciliates are similar sized but differ in their body surface texture. The surface of Coleps sp. consists of calcareous plates while T. pyriformis is a soft bodied ciliate. The two rotifers, which differ in their body size, were allowed to feed for 4 h on the ciliates, and the clearance and ingestion rates were calculated to fit functional response models. For B. calyciflorus fed with Coleps sp., the curvilinear functional response Type 2 gave the best fit to the data (maximal clearance and ingestion rate of 30 μl rotifer−1 h−1 and 5.7 ciliates rotifer−1 h−1), whereas the functional response for the ciliate T. pyriformis changed to the rectilinear Type 1 model (maximal clearance and ingestion rate of 8.5 μl rotifer−1 h−1 and 4.2 ciliates rotifer−1 h−1). In contrast, B. rubens could not eat Coleps sp., but when fed with T. pyriformis a functional response Type 2 was observed (maximal clearance and ingestion rate of 8 ml rotifer−1 h−1 and 3.3 ciliates rotifer−1 h−1). There is evidence that the surface texture of prey organisms influences the type of functional response. The change from a Type 2 (Coleps sp.) to a Type 1 model (T. pyriformis) for B. calyciflorus suggests that the handling time for the armored Coleps sp. is longer than for the soft bodied T. pyriformis. The smaller rotifer B. rubens, which generally prefers smaller food items than B. calyciflorus, was able to ingest the soft bodied T. pyriformis but needed a longer handling time for this ciliate than did B. calyciflorus. The hard surface texture of Coleps sp. probably prevented its ingestion by B. rubens.
The exopolymer secretions (EPS) layer surrounding Aureoumbra lagunensis cells affects growth, grazing, and behavior of protozoa
Authors: Liu Hongbin , Buskey Edward J.
Published: June 2010

“Texas brown tide”, a nuisance algal bloom formed by the marine pelagophyte Aureoumbra lagunensis, persisted without interruption from 1990–1997 in Laguna Madre, Texas. We hypothesize that, in addition to other factors, the presence of a mucus layer of exopolymer secretions (EPS) outside its cell wall may have played a role in reducing microzooplankton grazing on A. lagunensis, and therefore contributing to the persistence of the brown tide bloom. Three protozoan species common to the bloom waters fed A. lagunensis with low or high EPS showed significantly reduced growth rates with a high EPS diet. An additional experiment with the ciliate Aspidisca sp. revealed that the lower growth rate was caused by a reduced grazing rate on A. lagunensis with high EPS. A. lagunensis cells with high EPS might be unpalatable to Aspidisca, hence forced it to feed on bacteria as an alternate food source. Also, the EPS mucus might have affected the feeding mechanics of ciliates by adhering to their cilia and clogging their feeding apparatus. Motion analysis of swimming behavior of Aspidisca fed high and low EPS A. lagunensis revealed altered behavior in the presence of high EPS that could affect their grazing efficiency.
Carbon loss and optical property changes during long‐term photochemical and biological degradation of estuarine dissolved organic matter
Authors: Moran Mary Ann , Sheldon Wade M. , Zepp Richard G.
Published: June 2010

Terrestrially derived dissolved organic matter (DOM) impacts the optical properties of coastal seawater and affects carbon cycling on a global scale. We studied sequential long‐term photochemical and biological degradation of estuarine dissolved organic matter from the Satilla River, an estuary in the southeastern United States that is dominated by vascular plant‐derived organic matter. During photodegradation, dissolved organic carbon (DOC) loss (amounting to 31% of the initial DOC) was much less extensive than colored dissolved organic matter (CDOM) or fluorescent dissolved organic matter (FDOM) loss (50% and 56% of the initial CDOM and FDOM), and analysis of kinetics suggested a reservoir of DOC that was resistant to photodegradation. In contrast, CDOM photodegradation closely followed first‐order kinetics over two half‐lives with no indication of a nondegradable component. FDOM loss was slightly biased toward fluorophores considered representative of terrestrial humic substances. Additional changes in optical properties included increases in spectral slope and shifts in fluorescence excitation/emission maxima that were generally consistent with previous observations from field studies of photobleached DOM. Biological degradation of photobleached DOM was more rapid than that of unbleached material, and this net positive effect was evident even for extensively photodegraded material. Bacterial degradation caused shifts in the opposite direction from photochemical degradation for both spectral slope and excitation/emission maxima and thus dampened but did not eliminate changes in optical properties caused by photobleaching.
Hydrodynamics is a major determinant of streambed biofilm activity: From the sediment to the reach scale
Authors: Battin Tom J.
Published: June 2010

The effects of hydrodynamics and organic matter on sediment biofilm esterase activity and [3H]thymidine incorporation were investigated at several depths in the streambed and riparian zone of the alpine stream Oberer Seebach (Austria). On the sediment scale, microbial activity increased with both upwelling and downwelling Darcian velocities of interstitial water and was minimal when the surface/subsurface water exchange decreased. As revealed by stepwise multiple regression analyses, sediment carbohydrates and chlorophyll a explained a considerable percentage (up to 97% in summer) of the variance of biofilm esterase activity and [3H]thymidine incorporation, whereas pore‐water temperature and concentrations of dissolved organic carbon (DOC) and dissolved oxygen (DO) were poor predictors of biofilm activity. DOC and DO fluxes, however, accounted for a considerable percentage of the variance in [3H]thymidine incorporation, which points toward the importance of flow in biofilm functioning. On the reach scale, the ratio of surface water travel length to the subsurface travel length, which is an index of the surface/subsurface water exchange frequency, determined average reach biofilm activity. Downstream routing along predominantly subsurface flow paths increased streambed esterase activity, whereas elevated surface travel lengths reduced esterase activity. Esterase activity and [3H]thymidine incorporation were also positively related to the streambed DOC retention efficiency, which underscores the role of biofilms in solute retention. These results highlight the coupling between streambed hydrodynamics and microbial activity and link sediment‐scale and reach‐scale processes.
Elements of a theory for the mechanisms controlling abundance, diversity, and biogeochemical role of lytic bacterial viruses in aquatic systems
Authors: Thingstad T. Frede
Published: June 2010

Mechanisms controlling virus abundance and partitioning of loss of bacterial production between viral lysis and protozoan predation are discussed within the framework of an idealized Lotka‐Volterra–type model. This combines nonselective protozoan predation with host‐selective viral lysis of bacteria. The analysis leads to a reciprocal relationship between bacterial diversity and viruses, in which coexistence of competing bacterial species is ensured by the presence of viruses that ‘kill the winner,’ whereas the differences in substrate affinity between the coexisting bacterial species determine viral abundance. The ability of the model to reproduce published observations, such as an approximate 1:10 ratio between bacterial and viral abundance, and the ability of viral lysis to account for 10–50% of bacterial loss are discussed.
A fine‐scale record of 130 years of organic carbon deposition in an anoxic fjord, Saanich Inlet, British Columbia
Authors: Tunnicliffe Verena
Published: June 2010

A varved sediment sequence from an anoxic temperate fjord is examined for a 130‐yr record of organic carbon content and stable carbon isotope composition. Saanich Inlet, British Columbia, receives most detrital input from a logged and reforested watershed. Winter and summer laminae differences are significant and are isotopically depleted with respect to water column organic carbon. Within the core, organic carbon content increased from 2.5% in the 1860s to 3.3% in the 1990s, whereas carbon isotopes become depleted by 1.2‰ toward the late 1990s. Homogenization of large sample volumes yields the most repeatable carbon results. Overlaid on the trends are cycles of roughly a 38‐yr period for both records. River outflow has not changed, but logging rates that peaked midcentury in the watershed match the organic carbon shifts. This influence, plus the interdecadal Pacific‐climate oscillation, likely explain the periodicity observed.
Turbulent kinetic energy balance as a tool for estimating vertical diffusivity in wind‐forced stratified waters
Authors: Wüest Alfred , Piepke Gabriel , Van Senden David C.
Published: June 2010

Based on microstructure measurements in a simply shaped lake basin, the sources of vertical mixing in the stratified part of the water body were identified and estimates of their relative importance obtained by balancing turbulent kinetic energy introduced by the wind. It was found that (1) ∼1.9% of the vertical wind energy flux P10 (∼39 mW m−2), estimated 10 m above the lake surface, was available for turbulent mixing in the entire lake water body; (2) ∼1.5% of P10 was dissipated by turbulence in the weakly stratified surface layer (epilimnion ;6 m deep), and ∼0.42% of P10 reached the stratified deep water (hypolimnion) as turbulent kinetic energy via internal seiching; (3) ∼90% of the turbulent kinetic energy in the stratified water (i.e., 0.38% of P10 ) was dissipated within the bottom boundary layer of a few meters thickness, whereas only ∼10% was lost in the interior (away from the boundary; 0.04% of P10); and (4) as a consequence mixing within the bottom boundary was found to be the main source of vertical mixing for the deep waters of the whole lake. The ratio of buoyancy flux to dissipation (i.e., the mixing efficiency) was found to be ϒmix ∼ 0.15, leading to agreement between the Osborn‐Cox microstructure diffusivities and basin‐wide tracer diffusivities.

Comparison with turbulent kinetic energy balances, performed in five other lakes, demonstrates that this analysis is representative for many enclosed water bodies, as long as wind is the dominant source of turbulent energy (i.e., if other processes, such as convective mixing, double diffusion, or riverine intrusions can be neglected). Although the lakes under consideration were very different in size and shape and although the currents in Lake Baikal were inertial rather than seiching related as in the other lakes, the turbulent kinetic energy balance was very similar and the mixing efficiency was identical. Typically, 0.3 ± 0.1% of P10 is transferred as turbulent kinetic energy into the stratified part of the water body, and 0.04 ± 0.02% of P10 is stored as potential energy in the stratification. This analysis provides a tool for estimating vertical diffusivity for wind‐driven hypolimnetic mixing within a factor of two based on stratification and wind measurements alone.
In vivo estimation of the photosystem II photochemical efficiency of individual microphytobenthic cells using high‐resolution imaging of chlorophyll a fluorescence
Authors: Oxborough K. , Hanlon A. R. M. , Underwood G. J. C. , Baker N. R.
Published: June 2010

Rates of primary production by intertidal microphytobenthos within biofilms have been shown to be very high. An essential step toward assessing the contribution of individual species to this level of production is the in vivo measurement of photosynthetic efficiency from individual cells. A strong relationship between photosystem II photochemical efficiency and the fluorescence parameter Fq'/Fm′ (where Fq′ = Fm′ − F′) has been established within higher plants and unicellular algae. Calculation of Fq′/Fm′ requires measurement under constant light (at the F′ level of fluorescence) and during a pulse of saturating light (at the Fm′ level of fluorescence). High‐resolution imaging of chlorophyll fluorescence at the F′ and Fm′ levels has allowed the construction of Fq′/Fm′ images from individual cells of several species of diatom and Euglena sp. within intact biofilms. No species differences in the values of Fq′/Fm′ were observed at low levels of incident light. However, Euglena sp. showed significantly higher Fq′/Fm′ values at moderate to high incident light levels than all of the diatom species. Endogenous rhythms of vertical migration during tidal exposure and peaks in photosystem II photochemical efficiency at low tide could also be followed using this technique. Clear differences were observed in the migration of individual taxa to the surface of the biofilm. Images of Fq′/Fm′ were also used to assess the scale of heterogeneity for this parameter. Overall, these data demonstrate that high‐resolution imaging of chlorophyll fluorescence is a valuable technique that allows for determination of the photosystem II photochemical efficiency from different microphytobenthic taxa within biofilms.
Infection of the single‐celled diatom Stephanodiscus alpinus by the chytrid Zygorhizidium: Parasite distribution within host population, changes in host cell size, and host–parasite size relationship
Authors: Holfeld Harald
Published: June 2010

An epidemic caused by a Zygorhizidium species infecting the single‐celled planktonic centric diatom Stephanodiscus alpinus was analyzed for parasite distribution within the host population, final parasite size relative to host cell size, and size changes of infected and uninfected S. alpinus cells. Infections in the lake occurred at random within the whole host population. There was no evidence for aggregated or even distribution of the parasite individuals, indicating that the infections occur independently of each other. In enclosures in which light was enhanced compared to the lake, there tended to be an even parasite distribution within the host population, irrespective of whether plant nutrients were added. This suggests that infected host cells were negatively selected by the parasite zoospores under these conditions. Final parasite sporangium size and host cell size were positively correlated. Thus, parasite fecundity was limited by host cell size. Infected S. alpinus cells tended to be larger than uninfected cells, and the mean size of host cells within the population decreased during the epidemic. This might be due to selective infection of larger host cells or to the peculiar mode of cell division in diatoms.
Organic matter in Bolivian tributaries of the Amazon River: A comparison to the lower mainstream
Authors: Hedges John I. , Mayorga Emilio , Tsamakis Elizabeth , McClain Michael E. , Aufdenkampe Anthony , Quay Paul , Richey Jeffrey E. , Benner Ron , Opsahl Steve , Black Brenda , Pimentel Tania , Quintanilla Jorge , Maurice Laurence
Published: June 2010

We determined the concentrations and compositions of coarse particulate (>63 µm), fine particulate (0.1–63 µm), and dissolved (0.001–0.1 µm) organic matter collected along a river reach extending from a first‐order stream in the Bolivian Andes, through the Beni River system, to the lower Madeira and Amazon Rivers. Dissolved organic carbon (DOC) concentrations increased down the total reach from ~80 to 350 µM. The percentage of total DOC with a molecular weight greater than ~1,000 atomic mass units that could be isolated by ultrafiltration also increased downstream from 40 to 80%. Weight percentages of organic carbon in the ultrafiltered isolates also grew downstream from 5% at the uppermost station to 37% in the Amazon mainstem. Organic carbon composed only 0.4–1.2 weight percentage of the total mass of the fine particulate fraction, which accounted for 70–80% of the total organic carbon (TOC) in transport through the highly turbid (~600–2000 mg L−1) Beni sequence. Observed compositional differences were related primarily to the size fractions in which the organic matter occurred. On average, coarse particulate organic material exhibited an atomic C:N of 24, whereas ultrafiltered DOM was nitrogen poor, (C:N)a = 34, and fine particulate material was nitrogen rich, (C:N)a = 15. The lignin and stable‐carbon isotopic compositions of these fractions indicate tree leaves and other nonwoody tissues from C3 land plants as predominant sources. Three molecular parameters demonstrate that the coarse, fine, and dissolved fractions of individual water samples are increasingly degraded downstream. Elemental nitrogen, amino acids, and basic amino acids are all preferentially associated with fine minerals. Observed geographical patterns included more positive δ13C values in particulate organic matter from high altitude sites and an increase in the abundance and degradation of ultrafiltered dissolved organic matter down the drainage system. Many of these compositional patterns are imprinted within materials carried by low‐order, high‐altitude tributaries and appear to reflect processes occurring on the landscape.
Effect of Zn, Mn, and Fe on Cd accumulation in phytoplankton: Implications for oceanic Cd cycling
Authors: Sunda William G. , Huntsman Susan A.
Published: June 2010

Cd and phosphate concentrations in seawater are closely related, suggesting that Cd distributions, like those of PO4, are controlled by algal uptake and regeneration. But the factors that control Cd levels in phytoplankton and their influence on oceanic Cd versus PO4 relationships are poorly known. We examined the effect of important controlling factors (free ion concentrations of Cd, Zn, and Mn and Fe limitation of growth rate) on Cd accumulation by an oceanic diatom (Thalassiosira oceanica). More limited comparative experiments were also conducted with a coastal diatom (T. weissflogii) and an oceanic coccolithophore (Emiliania huxleyi). Cellular Cd:C ratios increased with increasing Cd ion concentrations and decreasing Zn ion concentrations in all species and with decreasing ionic Mn in the diatoms. The effects of Mn and Zn apparently are related to the uptake of Cd by the cells' Mn and Cd/Co transport systems, which are under negative feedback regulation by cellular Mn and Zn. Cd:C ratios were determined in the oceanic diatom as functions of free ion concentrations of Cd, Zn, and Mn over the oceanic range of these metal ions. The data were combined with estimates of free ion concentrations of these metals in seawater to construct models of Cd:C and Cd:P ratios in oceanic phytoplankton. The modeled Cd:P ratios showed good agreement with slopes of Cd versus P relationships in different oceanic regimes. The models suggest that the high Cd versus phosphate slopes found in iron‐depleted waters of the Southern Ocean and subarctic Pacific result from unusually high levels of zinc depletion in these waters. The resulting low zinc ion concentrations induce high levels of Cd uptake by phytoplankton, yielding high algal Cd:P ratios. The heavy depletion of zinc may be linked to elevated Zn:C and Zn:P ratios in iron‐limited diatoms, as observed in experiments we conducted with T. oceanica.
The incorporation of zinc and iron into the frustule of the marine diatom Thalassiosira pseudonana
Authors: Ellwood Michael J. , Hunter Keith A.
Published: June 2010

Zinc and iron uptake experiments were conducted with the marine diatom Thalassosira pseudonana, to investigate whether Zn and Fe are incorporated into the frustule of this diatom. Our results show that the uptake and deposition of Zn into opal has a sigmoidal relationship with the free Zn2+ concentration of the culture medium. The amount of Zn incorporated into the opal represents only 1–3% of the total amount of Zn taken up by the diatom; however, the exact reasons for Zn incorporation into the opal are not known. Even so, the consistent relationship between Zn levels in the opal and the culture medium suggests that fossil diatoms may be used as a recorder for historical changes in oceanic free Zn2+ concentrations. These results also demonstrate that the Zn:Si(OH)4 relationship observed in the Pacific and Antarctic Oceans is not a result of Zn released from biogenic opal. Fe uptake experiments also revealed that Fe is incorporated into diatom opal; however, the amount incorporated appears to be regulated by the diatom and did not increase with increasing Fe concentration within the diatom culture medium. This therefore eliminates the use of Fe incorporated within diatom opal as a possible proxy for dissolved Fe concentrations.