Bacterial and phosphorus dynamics in profundal Lake Erken sediments following the deposition of diatoms: a laboratory study

The benthic microbial response to the deposition of naturalseston and the microbial impact on nutrient dynamics wasstudied in an experimental system using whole sediment coresequipped with flow-through systems for the overlying water. For20 days, changes in sediment bacterial activity, totalmetabolic activity (heat production), bacterial biomass,phosphorus fractions and basic chemistry were followed, as wellas the exchange of nutrients between sediment and water.Microbial activity and biomass increased immediately inresponse to the deposition of seston, peaked after seven daysand then decreased linearly over the remaining time of theexperiment. Co-settled bacteria were suggested to play animportant role in the microbial response. Changes in bacterialbiomass production, bacterial biomass and the NaOH-nrPextractable phosphorus fraction were concurrent in response toseston additions. The sediment acted as a trap for SRP from theoverlying water when bacterial activity was high and as asource when the bacterial activity decreased. Altogether, theresults suggest an important role of bacteria in theregeneration of seston P. Mineralization rates estimated fromsediment heat production showed that ca. 11% of the addedseston carbon was oxidized in the sediments during theexperiment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of hydrologic and water quality drivers on periphyton dynamics in the southern Everglades

Everglades periphyton mats are tightly-coupled autotrophic (algae and cyanobacteria) and heterotrophic (eubacteria, fungi and microinvertebrates) microbial assemblages. We investigated the effect of water column total phosphorus and nitrogen concentrations, water depth and hydroperiod on periphyton of net production, respiration, nutrient content, and biomass. Our study sites were located along four transects that extended southward with freshwater sheetflow through sawgrass-dominated marsh. The water source for two of the transects were canal-driven and anchored at canal inputs. The two other transects were rain-driven (ombrotrophic) and began in sawgrass-dominated marsh. Periphyton dynamics were examined for upstream and downstream effects within and across the four transects. Although all study sites were characterized as short hydroperiod and phosphorus-limited oligotrophic, they represent gradients of hydrologic regime, water source and water quality of the southern Everglades. Average periphyton net production of 1.08 mg C AFDW⁻¹ h⁻¹ and periphyton whole system respiration of 0.38 mg C AFDW⁻¹ h⁻¹ rates were net autotrophic. Biomass was generally highest at ombrotrophic sites and sites downstream of canal inputs. Mean biomass over all our study sites was high, 1517.30 g AFDW m⁻². Periphyton was phosphorus-limited. Average periphyton total phosphorus content was 137.15 μg P g⁻¹ and average periphyton total N:P ratio was 192:1. Periphyton N:P was a sensitive indicator of water source. Even at extremely low mean water total phosphorus concentrations ( ≤ 0.21 μmol l⁻¹), we found canal source effects on periphyton dynamics at sites adjacent to canal inputs, but not downstream of inflows. These canal source effects were most pronounced at the onset of wet season with initial rewetting. Spatial and temporal variability in periphyton dynamics could not solely be ascribed to water quality, but was often associated with both hydrology and water source.     

Organic matter distribution and retention along transects from hilltop to kettle hole within an agricultural landscape

In agricultural landscapes, the spatio-temporal distribution of organic matter (OM) varies greatly across landscape structures and soil types. We investigated patterns of organic carbon (OC) content, polyvalent cations, and isotopic values for specific OM fractions along transects spanning topographic positions from erosional to depositional areas, including aquatic sediments within a single kettle hole. We hypothesized different drivers exist at different scales. At the transect scale, we hypothesized (1) landscape form and land management to explain patterns of isotopic and OC content from different OM fractions. At the aggregate scale, (2) we expected different OM-mineral associations to explain stabilized OM. We also hypothesized, (3) that shallow sediment δ¹³C and δ¹⁵N of the kettle hole reflected different terrestrial sources. We found that distinct differences in the OM turnover rates existed between the fractions suggesting that different processes are affecting the transformation rates that are recorded in the isotopic composition patterns. Erosion along with plant productivity drive mineral-associated fractions over the transect, while microbial decomposition and slurry influence freely available and aggregated OM fractions. The type and magnitude of OM-mineral associations changed along the transect while binding OM of different decomposition status. OM in mineral-associated fractions in kettle hole sediments were derived from clay- and silt-sized particles from the field, whereas OM in freely available and aggregated fractions potentially originated from macrophytes. We conclude that kettle holes constitute important sinks for terrestrial OM across the landscape.     

Surficial sediment phosphorus fractions along a biogeochemical gradient in Nyanza (Winam) Gulf, northeastern Lake Victoria and their possible role in phosphorus recycling and internal loading

Different phosphorus fractions and metal element composition of surficial sediments were measured on three occasions in 2005 and 2006 along a transect between Nyanza Gulf and offshore Lake Victoria, in order to assess the potential for sediments to contribute to the water column P concentrations in Lake Victoria. Total phosphorus (TP), apatite phosphorus (AP), inorganic phosphorus (IP) and organic phosphorus (OP) increased in sediments along the gulf towards the main lake while the non-apatite inorganic phosphorus (NAIP) increases were less defined. The longitudinal gradient of sediment TP and its fractions in Nyanza Gulf is a result of high rates of terrigenous input and resuspension and transport of the light, phosphorus rich inorganic and organic matter towards the main lake. TP in the sediment ranged from 812.7 to 1,738 mg/kg dry weight (DW) and was highest in the Rusinga Channel, the exchange zone between the gulf and the main lake. AP was the most important TP fraction, contributing between 35 and 57.3% of TP. Ca content in the sediment was strongly associated with TP and AP in the sediment (r² = 0.92 and 0.98, respectively) in the gulf and the channel, indicating the importance of apatite in controlling P availability in these zones. In the gulf and the Rusinga Channel, the less bioavailable apatite phosphorus dominated, whereas in the deeper main lake OP was the major fraction illustrating the importance of anaerobic release of P from sediments and acceleration of internal P loading in the main lake.     

Release of sediment-phosphorus and the influence of algal growth on this process

Summary Phosphorus release from undisturbed sediment cores was studied in a continuous flow system. Various lakes and polder ditches were compared with each other. Peaty lakes exchanged their particulate phosphorus rapidly with the overlying water as compared with other sediment types. This makes them suitable for phosphorus load reduction measures. There was found to be no simple direct relation between chemically extracted phosphorus fractions and the phosphorus released during the experiment. Algal growth in the overlying water stimulated the release of phosphorus.     

Culturable bacteria community development in postglacial soils of Ecology Glacier, King George Island, Antarctica

Glacier forelands are excellent sites in which to study microbial succession because conditions change rapidly in the emerging soil. Development of the bacterial community was studied along two transects on lateral moraines of Ecology Glacier, King George Island, by culture-dependent and culture-independent approaches (denaturating gradient gel electrophoresis). Environmental conditions such as cryoturbation and soil composition affected both abundance and phylogenetic diversity of bacterial communities. Microbiocenosis structure along transect 1 (severe cryoturbation) differed markedly from that along transect 2 (minor cryoturbation). Soil physical and chemical factors changed along the chronosequence (time since exposure) and influenced the taxonomic diversity of cultivated bacteria, particularly along transect 2. Arthrobacter spp. played a pioneer role and were present in all soil samples, but were most abundant along transect 1. Cultivated bacteria isolated from transect 2 were taxonomically more diverse than those cultivated from transect 1; those from transect 1 tended to express a broader range of enzyme and assimilation activities. Our data suggest that cryoturbation is a major factor in controlling bacterial community development in postglacial soils, shed light on microbial succession in glacier forelands, and add a new parameter to models that describe succession phenomena.     

Invertebrate bioturbation can reduce the clogging of sediment: an experimental study using infiltration sediment columns

1. Invertebrate bioturbation can strongly affect water‐sediment exchanges in aquatic ecosystems. The objective of this study was to quantify the influence of invertebrates on the physical characteristics of an infiltration system clogged with fine sediment. 2. Two taxa (chironomids and tubificids) with different bioturbation activities were studied in experimental slow infiltration columns filled with sand and gravel and clogged with a 2 cm layer of fine sediment at the surface. We measured the effects of each taxon separately and combined on hydraulic head, water mobility and sediment reworking. 3. The results showed that invertebrates could reduce sediment clogging and this effect was linked to the functional mode of bioturbation of each group. Tubificid worms dug networks of galleries in the fine sediment, creating pathways for water flow, which reduced the clogging of sediment. In contrast, the U‐shaped tubes of chironomids were restricted to the superficial layer of fine sediments and did not modify the hydraulic conductivity of experimental columns. The combination of invertebrates did not show any interactive effects between tubificids and chironomids. The occurrence of 80 tubificids in the combination was enough to maintain the same hydraulic conductivity that 160 worms did in monospecific treatment. 4. The invertebrates like tubificid worms can have a great benefit on functioning of clogged interfaces by maintaining high hydraulic conductivity, which contributes to increased water‐sediment exchanges and stimulates biogeochemical and microbial processes occurring in river sediments.     

Nitrogen dynamics and microbial food web structure during a summer cyanobacterial bloom in a subtropical,shallow, well-mixed,eutrophic lake (Lake Taihu,China)

Nitrogen dynamics and microbial food web structure were characterized in subtropical, eutrophic, large (2,338 km²), shallow (1.9 m mean depth), and polymictic Lake Taihu (China) in Sept–Oct 2002 during a cyanobacterial bloom. Population growth and industrialization are factors in trophic status deterioration in Lake Taihu. Sites for investigation were selected along a transect from the Liangxihe River discharge into Meiliang Bay to the main lake. Water column nitrogen and microbial food web measurements were combined with sediment–water interface incubations to characterize and identify important processes related to system nitrogen dynamics. Results indicate a gradient from strong phosphorus limitation at the river discharge to nitrogen limitation or co-limitation in the main lake. Denitrification in Meiliang Bay may drive main lake nitrogen limitation by removing excess nitrogen before physical transport to the main lake. Five times higher nutrient mineralization rates in the water column versus sediments indicate that sediment nutrient transformations were not as important as water column processes for fueling primary production. However, sediments provide a site for denitrification, which, along with nitrogen fixation and other processes, can determine available nutrient ratios. Dissimilatory nitrate reduction to ammonium (DNRA) was important, relative to denitrification, only at the river discharge site, and nitrogen fixation was observed only in the main lake. Reflecting nitrogen cycling patterns, microbial food web structure shifted from autotrophic (phytoplankton dominated) at the river discharge to heterotrophic (bacteria dominated) in and near the main lake.     

生物扰动对沉积物中污染物环境行为的影响研究进展

生物扰动由于显著改变沉积物结构和性质,进而影响沉积物中污染物的环境行为。综述生物扰动对沉积物中氮、磷、重金属和疏水性有机污染物环境行为的影响。生物扰动促进这些污染物从沉积物向水体释放。生物扰动还对不同的污染物产生其它不同的影响。对于氮,生物扰动还影响其硝化与反硝化作用;对于磷,生物扰动不仅改变其化学形态,还提高有机磷降解。对于重金属,生物扰动还能改变其在沉积物中的分布及化学形态。对于疏水性有机污染物,生物扰动主要增强生物富集和代谢,以及提高生物降解。     

Reactivity of Iron Minerals in the Seabed Toward Microbial Reduction – A Comparison of Different Extraction Techniques

Abstract

Dissimilatory iron reduction and sulfate reduction are the most important processes for anaerobic mineralization of organic carbon in marine sediments. The thermodynamics and kinetics of microbial Fe(III) reduction depend on the characteristics of the Fe(III) minerals, which influence the potential of Fe(III)-reducers to compete with sulfate-reducers for common organic substrates. In the present study, we tested different methods to quantify and characterize microbially reducible Fe(III) in sediments from a transect in Kongsfjorden, Svalbard, using different standard sequential endpoint extractions and time-course extractions with either ascorbate or a Fe(III)-reducing microbial culture. Similar trends of increasing ‘reactive Fe’ content of the sediment along the fjord transect were found using the different extraction methods. However, the total amount of ‘reactive Fe’ extracted differed between the methods, due to different Fe dissolution mechanisms and different targeted Fe fractions. Time-course extractions additionally provided information on the reactivity and heterogeneity of the extracted Fe(III) minerals, which also impact the favorability for microbial reduction. Our results show which fractions of the existing Fe extraction protocols should be considered ‘reactive’ in the sense of being favorable for microbial Fe(III) reduction, which is important in studies on early diagenesis in marine sediments.     

Sediment microbial enzyme activity as an indicator of nutrient limitation in Great Lakes coastal wetlands

1. We compared the extracellular enzyme activity (EEA) of sediment microbial assemblages with sediment and water chemistry, gradients in agricultural nutrient loading (derived from principal component analyses), atmospheric deposition and hydrological turnover time in coastal wetlands of the Laurentian Great Lakes. 2. There were distinct increases in nutrient concentrations in the water and in atmospheric N deposition along the gradient from Lake Superior to Lake Ontario, but few differences between lakes in sediment carbon (C), nitrogen (N) or phosphorus (P). Wetland water and sediment chemistry were correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition. 3. The N : P ratio of wetland waters and sediments indicated that these coastal wetlands were N‐limited. Nutrient stoichiometry was correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition. 4. Extracellular enzyme activity was correlated with wetland sediment and water chemistry and stoichiometry, atmospheric N deposition, the agricultural stress gradient and the hydrological turnover time. The ratios of glycosidases to peptidases and phosphatases yielded estimates of nutrient limitation that agreed with those based solely on nutrient chemistry. 5. This study, the first to link microbial enzyme activities to regional‐scale anthropogenic stressors, suggests that quantities and ratios of microbial enzymes are directly related to the concentrations and ratios of limiting nutrients, and may be sensitive indicators of nutrient dynamics in wetland ecosystems, but further work is needed to elucidate these relationships.     

The nature of a shield lake sediment

The nature of the sediment of Drinking Lake in the Churchill River Basin in Canada was studied with special reference to its chemical and colloidal composition. Crystalline minerals present in the colloidal fractions of the sediment are quartz, cristobalite, feldspars, micas, amphiboles, vermiculite, chlorite and kaolinite. Sesquioxidic components and the extractable Ca and Mg are present not only in the colloidal fractions but also in the non-colloidal fractions of the sediment. Over 99% of the nitrogen in the sediment is organic and about 60% of the sediment phosphorus is inorganic. The importance of the crystalline and non-crystalline mineral components of the sediment studied in the exchange of nutrients between the sediment and its overlying water is discussed. In view of the important roles of these mineral components in affecting the transfer of nutrients, possible significant modifications of the quality of the lake water after impoundment, if a dam were constructed in the basin for a hydro-electric development, deserve close attention.     

Spatial zonation of macrobenthic fauna in Zhanjiang Mangrove Nature Reserve, Guangdong, China

The spatial zonation of macrobenthic fauna in the core region of Zhanjiang Mangrove Nature Reserve was studied with two transects vertical to the shoreline. The first transect was near Deyao Village where three faunal zones of the mangrove swamp could be divided into the following types from the high tide part to the low tide part: the Assiminea lutea-Uca arcuata-Paracleistostoma crassipilum zone, the Cleistostoma dilatatum-Macrophthalmus erato-Littoraria melanostoma zone, and the Paracleistostoma depressum-Cerithidae cingulata zone. Mollusck and crustacean exhibited the highest individual density in this transect. Mollusck mainly influenced the dynamics of community biomass as well as the species diversity index. In the second transect near Hongzhai Village, the following four faunal zones could be determined: the Littoraria melanostoma-Pseudoringicula sinensis-Ceratonereis burmensis zone, the Assiminea lutea-Cleistostoma dilatatum zone with a dominant species belonging to the Ellobiidae, Upogebia sp.-Paracleistostoma depressum zone, and the Metaplax sheni-Cerithidae cingulata zone. The crustacean showed the highest individual density in this transect. Similar to the Deyao transect, dynamics of community biomass and the species diversity index of the Hongzhai transect were mainly influenced by mollusck. By hierarchical clustering and nonmetric multidimensional scaling, the macrobenthic fauna communities could be divided into three and four groups in the Deyao and Hongzhai transects, respectively. These groups corresponded to different types of vegetation of the mangrove swamp. Taken together, our observations indicated that the spatial zonation of the macrobenthic fauna was mainly affected by the characteristics of the mangrove community, sediment characteristics and the tidal line.     

Spatial zonation of macrobenthic fauna in Zhanjiang Mangrove Nature Reserve, Guangdong, China

The spatial zonation of macrobenthic fauna in the core region of Zhanjiang Mangrove Nature Reserve was studied with two transects vertical to the shoreline. The first transect was near Deyao Village where three faunal zones of the mangrove swamp could be divided into the following types from the high tide part to the low tide part: the Assiminea lutea-Uca arcuata-Paracleistostoma crassipilum zone, the Cleistostoma dilatatum-Macrophthalmus erato-Littoraria melanostoma zone, and the Paracleistostoma depressum-Cerithidae cingulata zone. Mollusck and crustacean exhibited the highest individual density in this transect. Mollusck mainly influenced the dynamics of community biomass as well as the species diversity index. In the second transect near Hongzhai Village, the following four faunal zones could be determined: the Littoraria melanostoma-Pseudoringicula sinensis-Ceratonereis burmensis zone, the Assiminea lutea-Cleistostoma dilatatum zone with a dominant species belonging to the Ellobiidae, Upogebia sp.-Paracleistostoma depressum zone, and the Metaplax sheni-Cerithidae cingulata zone. The crustacean showed the highest individual density in this transect. Similar to the Deyao transect, dynamics of community biomass and the species diversity index of the Hongzhai transect were mainly influenced by mollusck. By hierarchical clustering and nonmetric multidimensional scaling, the macrobenthic fauna communities could be divided into three and four groups in the Deyao and Hongzhai transects, respectively. These groups corresponded to different types of vegetation of the mangrove swamp. Taken together, our observations indicated that the spatial zonation of the macrobenthic fauna was mainly affected by the characteristics of the mangrove community, sediment characteristics and the tidal line.     

Distribution and stability of sulfate-reducing prokaryotic and hydrogenotrophic methanogenic assemblages in nutrient-impacted regions of the Florida Everglades

Although the influence of phosphorus loading on the Everglades ecosystem has received a great deal of attention, most research has targeted macro indicators, such as those based on vegetation or fauna, or chemical and physical parameters involved in biogeochemical cycles. Fewer studies have addressed the role of microorganisms, and these have mainly targeted gross informative parameters such as microbial biomass, enzymatic activities, and microbial enumerations. The objectives of this study were to characterize the dynamics of sulfate-reducing and methanogenic assemblages using terminal restriction fragment length polymorphism (T-RFLP) targeting the dissimilatory sulfite reductase (dsrA) and methyl coenzyme M reductase (mcrA) genes, respectively, and assess the impact of nutrient enrichment on microbial assemblages in the northern Everglades. T-RFLP combined with principal component analysis was a powerful technique to discriminate between soils from sites with eutrophic, transitional, and oligotrophic nutrient concentrations. dsrA T-RFLP provided a higher level of discrimination between the three sites. mcrA was a relatively weaker system to distinguish between sites, since it could not categorically discriminate between eutrophic and transition soil samples, but may be useful as an early indicator of phosphorus loading which is altering hydrogenotrophic methanogenic community in the transition zones, making them more similar to eutrophic zones. Clearly, targeting a combination of different microbial communities provides greater insight into the functioning of this ecosystem and provides useful information for understanding the relationship between eutrophication effects and microbial assemblages.     

Exchange of phosphorus across the sediment-water interface

In this article, principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed. New results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water. The fractional composition of sedimentary phosphorus is discussed as a tool for interpretation of different retention mechanisms. Special emphasis is given to the impact of biological, particularly microbial, processes on phosphorus exchange across the sediment-water interface and to the significance of biologically induced CaCO₃ precipitation to phosphorus retention in calcareous lakes.     

Effects of the burrowing mud shrimp,Upogebia yokoyai,on carbon flow and microbial activity on a tidal flat

Mud shrimps, Upogebia spp., are major constituents of macrobenthic communities in tidal flats in Japan. The impact of Upogebia yokoyai on carbon flow on tidal flats was examined by comparing CO₂ emission rates from plots with and without burrows in the Kurose River estuary, Japan. In situ CO₂ emission rates from plots with burrows were significantly higher than from those without. Laboratory measurements using sediment core samples that excluded respiration of macrobenthic organisms showed similar trends. Although there were no significant differences in grain size distribution, water content, or ignition loss between the sediment cores with and without burrows, oxidation–reduction potential was significantly higher in sediment cores with burrows. Analysis of phospholipid fatty acids (PLFA) indicated that microbial biomass and community structure did not differ significantly between cores with and without burrows. However, microbial respiration activity, as indicated by CO₂ emission rates per total PLFA content, was significantly higher in sediment cores with burrows than in those without. Our results indicate that burrows of U. yokoyai change the physicochemical conditions and increase microbial activity in the sediment, significantly affecting carbon flow in the tidal flat.     

The role of sediments for phosphorus retention in the Kirinya wetland (Uganda)

Phosphorus dynamics were examined and modelled in a Cyperus papyrus and Phragmites mauritanus wetland on the Ugandan coast of Lake Victoria receiving secondary treated wastewater. Using a series of transversal transects, concentrations of nitrogen (N) and phosphorus (P) were found to decrease gradually as water moved downstream, giving nutrient retention capacities which ranged between 40% and 60%. Near-zero oxygen and nitrate concentrations were observed as well. To investigate the phosphorus retention characteristics in more detail, laboratory experiments were carried out on sediment samples and sediment cores retrieved from points along the wetland. Following a P shock load to cores of the wetland sediment, it was possible to determine a sediment P uptake rate of 0.016 day⁻¹. Sediment P adsorption studies were also performed, showing significant Freundlich and Langmuir isotherm behaviour. With these data a maximum P adsorption capacity of 4 mg P/g for the wetland sediment could be estimated. A plug-flow model was used to evaluate the phosphorus retention dynamics of the Kirinya wetland. A good correspondence between the actual and simulated P retention was observed. Comparing the daily P uptake (g/m³day) in the Kirinya wetland with the maximum sediment P uptake capacity, it can be concluded that the total P retention capacity of the wetland will only be sufficient for 30 more years under the present P loading and wetland management.     

Quantifying the impact of periphytic algae on nutrient availability for phytoplankton

SUMMARY.

• 1 Recent laboratory studies demonstrate that periphytic algae growing on the sediment surface reduce nutrient availability in the overlying water. Consequently, periphytic algae may competitively reduce growth of phytoplankton.
• 2 The aim of this study was to quantify the competitive impact of sediment-attached periphytic algae on phytoplankton in the presence of all other factors simultaneously affecting nutrient dynamics in natural systems.
• 3 In enclosure experiments, performed in three lakes of different productivity, the periphytic algal biomass was manipulated. When compared to enclosures with high biomass of periphytic algae, those with reduced biomass showed an increase in total phosphorus concentration in the water of 32–44%. Extrapolation of the experimental results to whole lakes predicts an increase in original total phosphorus concentration of between 1.5% and 8.0%. According to existing regressions between total phosphorus and phytoplankton chlorophyll, the potential increase in original phytoplankton biomass will be between 2.5% and 12.6%.
• 4 With respect to the shallow parts of lakes, my results support the conclusions revealed from laboratory studies that periphytic algae have a significant impact on the phosphorus concentration in the overlying water. However, when considering whole-lake dynamics, the competitive impact of periphytic algae on phytoplankton biomass development is probably of minor importance.
• 5 Rather, the main competitive advantage of growing on the sediment surface, compared to in the water, may be the exclusive access to nutrients in the sediment.

     

Viral and bacterial abundance and production in the Western Pacific Ocean and the relation to other oceanic realms

We completed a transect through the Western Pacific Warm Pool to examine how environmental variables may influence viral and bacterial abundance and production rates in this globally important oceanic region. Of the variables analyzed, viral abundance and production had the most significant relationship to bacterial cell abundance: viral parameters were not significantly correlated to the measured environmental variables, including temperature. Bacterial production rates were significantly correlated to temperature in open ocean waters, but not in waters close to land masses. Analyses of 16S rRNA gene by pyrosequencing indicated only minor changes in eubacterial community structure across the transect, with α-proteobacteria dominating all sampled populations. Diversity within the prokaryotic community did not correlate directly with viral abundance or activity. Comparisons to two other ocean-scale transects (> 8000 km of open ocean in total) in the Atlantic Ocean indicated that correlations between viral and bacterial abundance and production relative to environmental variables are regime dependent. In particular, correlations to temperature showed remarkable differences across the three transects. Collectively, our observations suggest that seemingly similar oceanic regions may have very different microbial community responses to environmental variables. Our observations and analyses demonstrate that ocean-scale generalizations may not apply in the case of viral ecology.