bluuebunny/crossref_metadata_2025 huggingface dataset:
Amount of phosphorus inactivated by alum treatments in Washington lakes
Authors: Rydin Emil , Huser Brian , Welch Eugene B.
Published: June 2010

The effectiveness of aluminum (Al) at retaining phosphate was investigated in alum‐treated Washington lake sediments. Greater than background concentrations of Al and Al‐bound phosphorus (Al‐P) were detected in three stratified lakes (Lake Ballinger, Phantom Lake, and Medical Lake) and in three unstratified lakes (Lake Erie, Cambell Lake, and Long Lake). The ratio of added Al to P (Al:Al‐P) was approximately 11:1 by weight in all six lakes. Added Al ranged from 6 to 83 g Al m‐2 , and adsorbed P subsequently ranged from 0.5 to 7.3 g P m‐2. P bound to the added Al was apparently removed from the P cycle, as the layers of increased Al‐P due to treatment were buried in the sediment at a depth corre‐sponding to the approximate time since treatment.
Demonstration of the onshore transport of larval invertebrates by the shoreward movement of an upwelling front
Authors: Shanks Alan L. , Largier John , Brink Laura , Brubaker John , Hooff Rian
Published: June 2010

Upwelling winds off North Carolina set up upwelling fronts. As the wind forcing relaxed following such a coastal upwelling event, we observed the upwelling front move onshore. The low‐density surface water moved shoreward over the upwelled water, forming a convergence zone at the front. This shoreward‐moving front concentrated and transported larvae. Larval sergestid shrimp, spionid polychaete larvae, and the veligers of Odostomia sp. and Bittium sp. were concentrated on the seaward side of the moving convergence. Blue crab megalopae were concentrated at the surface immediately seaward of the front. These data demonstrate that a relaxing upwelling front can transport high concentrations of larvae shoreward over the inner shelf. This may be an important mechanism promoting the shoreward migration of larval invertebrates and fish.
Measurement of photosynthetic parameters in benthic organisms in situ using a SCUBA‐based fast repetition rate fluorometer
Authors: Gorbunov Maxim Y. , Falkowski Paul G. , Kolber Zbigniew S.
Published: June 2010

Benthic photoautotrophic organisms significantly contribute to the productivity of shallow tropical coastal ecosystems. However, measurements of photosynthetic light use and dissipation in benthic organisms are complicated by taxonomic diversity, spatial heterogeneity, natural variability in local nutrient, irradiance, and temperature regimes, as well as destructive sampling protocols. To help overcome these problems, we developed a SCUBA‐based fast repetition rate (FRR) fluorometer for measurements of variable chlorophyll fluorescence in corals, sea grasses, macroalgae, and algal turfs. Photosynthetic light use and electron transport can be readily calculated from variable fluorescence kinetics. Using the SCUBA‐based FRR fluorometer, changes in photosynthetic processes can be measured nondestructively in situ with high spatial and temporal resolution. Here we describe the instrument design and characteristics and present representative field results.
Calcification does not stimulate photosynthesis in the zooxanthellate scleractinian coral Stylophora pistillata
Authors: Gattuso J.‐P. , Reynaud‐Vaganay S. , Furla P. , Romaine‐Lioud S. , Jaubert J. , Bourge I. , Frankignoulle M.
Published: June 2010

The interaction between photosynthesis and calcification remains poorly known in zooxanthellate scleractinian corals. We tested whether calcification is a significant source of CO2 for photosynthesis in Stylophora pistillata. Rates of net photosynthesis, respiration, and calcification were measured on colonies incubated in synthetic seawater (SSW) controlled with respect to the inorganic carbon system and containing standard (11.40 mmol kg−1) and low (2.85 mmol kg−1) calcium concentrations. Net photosynthesis and respiration are not significantly different in standard and low‐Ca2+ SSW despite a rate of calcification 2.0–2.4 times lower in Ca2+−depleted SSW. Additional experiments carried out on the noncalcifying zooxanthellate Anthozoa Anemonia viridis demonstrate that a low calcium concentration has no direct effect on rates of photosynthesis and respiration. It is suggested that calcification is not a significant source of photosynthetic CO2 and that photosynthesis stimulates calcification rather than the opposite.
Herbivory and algal dynamics on the coral reef at Discovery Bay, Jamaica
Authors: Aronson Richard B. , Precht William F.
Published: June 2010

The cover of noncoralline macroalgae increased dramatically on Caribbean reefs during the 1980s and 1990s. A top‐down hypothesis, based largely on observations at Discovery Bay, Jamaica, is that this change was caused by reduced herbivory. Herbivory was reduced by the regional mass mortality of the echinoid Diadema antillarum in 1983‐1984 and by human exploitation of herbivorous fishes. An alternative, bottom‐up explanation is that nutrient concentrations increased past threshold levels for algal blooms. Surveys at Discovery Bay showed that Diadema reappeared on the shallow fore reef after 1996, accompanied by drastically reduced macroalgal cover. There is no evidence to suggest that nutrient levels declined at the same time. These observations corroborate predictions of the top‐down hypothesis, and they confirm the key role of herbivory in structuring shallow reef communities of the Caribbean.
Interactions of ultraviolet‐B radiation, mixing, and biological activity on photobleaching of natural chromophoric dissolved organic matter: A mesocosm study
Authors: Whitehead Robert F. , de Mora Stephen , Demers Serge , Gosselin Michel , Monfort Patrick , Mostajir Behzad
Published: June 2010

A natural planktonic assemblage from the St. Lawrence Estuary was isolated in eight 1,500‐liter outdoor meso‐cosms and subjected to combinations of fast or slow mixing regimes with natural solar radiation or natural solar radiation artificially enhanced with ultraviolet‐B (UVB, 280–320 nm) radiation. The interdependent evolution of dissolved organic carbon (DOC), absorption by chromophoric dissolved organic matter (CDOM), chlorophyll a (Chl a), particulate organic carbon (POC), and bacterial abundance in the mesocosms was followed over a 10‐d period. There was a net increase of Chl a, POC, and DOC in all systems over time; however, the slower mixing treatments had less accumulation than the systems with faster mixing. All systems displayed weak correlations of DOC with POC and Chl a. A significant effect of enhanced UVB radiation on concentrations of these bulk properties was not observed in any of the mesocosms. A strong correlation of CDOM absorbance loss (photobleaching) with absorbed radiation dose was observed in all treatments, with the fast mixing systems having larger absorbance losses and faster loss rates. Photobleaching was wavelength dependent, resulting in an increase in the spectral slope of CDOM absorption over time. Thus, although CDOM photobleaching may result in deeper penetration of light at all wavelengths, the ratios of UVB to ultraviolet‐A (UVA) and photosynthetically active radiation (PAR) are reduced. The effect of enhanced UVB radiation was unexpected, with no proportional increases in CDOM photo‐bleaching in the #x002BUVB treatments. Comparisons of the different treatments indicate that interactions of biological activity, mixing, and the in situ light field can influence CDOM absorbance properties and/or photoreactivity and that there is a possible role for UVB in the production of CDOM.
The attenuation of ultraviolet radiation in high dissolved organic carbon waters of wetlands and lakes on the northern Great Plains
Authors: Arts Michael T. , Robarts Richard D. , Kasai Fumie , Waiser Marley J. , Tumber Vijay P. , Plante Amanda J. , Rai Hakumat , de Lange Hendrika J.
Published: June 2010

We used a scanning spectroradiometer to conduct underwater optical surveys of 44 waterbodies during the ice‐free seasons of three consecutive years in wetlands and lakes in central Saskatchewan, Canada. The waterbodies ranged widely in dissolved organic carbon (DOC) concentration (4.1–156.2 mg L−1) and conductivity (270–74,300 mohms cm−1). Although penetration of UV radiation (UV‐R; 280–400 nm) in these systems was largely a function of DOC concentration, as has been reported previously, UV‐R penetrated more deeply in saline waterbodies than in freshwater systems with similar DOC concentrations. Power models representing our KdUV‐B or KdUV‐A versus DOC relationships were described by KdUV−B = 0.604DOC1.287 (r2 = 0.76, N = 23) and KdUV‐A = 0.428DOC1.136 (r2 = 0.55, N = 24) for freshwater systems and KdUV‐B = 2.207DOC0.732 (r2 = 0.40, N = 20) and KdUV‐A = 1.436DOC0.600 (r2 = 0.18, N = 20) for saline systems. Our data, when combined with data from other researchers, resulted in the more general freshwater models KdUV−B = 0.705DOC1.248 (r2 = 0.84, N = 43) and KdUV‐A = 0.470DOC1.112 (r2 = 0.70, N = 44).

UV‐B radiation (280–320 nm) is not expected to penetrate deeply (typically <50 cm) in prairie lakes and wetlands because of high intrinsic DOC concentrations. However, the central plains are characteristically windy and this, coupled with the shallowness of many of these systems, suggests that biota may still be at risk from present‐day and future‐enhanced levels of UV‐B (which may result from ozone depletion). Moreover, this risk may be exacer‐bated in saline systems. This could be significant, especially because saline waterbodies are often highly productive and represent important North American staging areas for shorebirds and waterfowl.
Continuous monitoring of surface optical properties across a geostrophic front: Biogeochemical inferences
Authors: Claustre Hervé , Fell Frank , Oubelkheir Kadija , Prieur Louis , Sciandra Antoine , Gentili Bernard , Babin Marcel
Published: June 2010

A system was designed for the continuous surface monitoring of hydrological, bio‐optical, and biogeochemical properties in the vicinity of the Almeria‐Oran jet‐front system (Northwestern Mediterranean Sea). This system included a
thermosalinograph, a fluorometer, an optical particle counter, and an absorbance‐attenuance meter (AC9), allowing the
estimation of the absorption [a(λ), (m−1)] and scattering [b(λ), (m−1)] coefficients at nine wavelengths. More than 500 multivariate records were acquired over a transect crossing the jet‐front system three times and encompassing the diversity of water types encountered in this area. A method is proposed to retrieve relevant biogeochemical or bio‐optical quantities, among which are the chlorophyll a concentration [from a(676)], the particulate carbon concentration [from b(555)], the colored dissolved organic matter [CDOM, from a(412)], and the chlorophyll‐specific scattering coefficient at 555 nm, b*(555) (m2 mg Chl a−1). The analyses of these various quantities with respect to the surface hydrodynamic fields reveal two main features. First, the particle pool displays highly dynamic quantitative variations across the frontal structure. Qualitatively, flagellate‐dominated populations are associated with moderate density waters and maximal jet velocity, while diatoms are recorded at the narrow limit between the jet‐front and the Mediterranean waters, where jet velocity is minimal. Second, the CDOM pool presents remarkable covariations with the surface‐density field. In particular, the lowest aCDOM (412) values are reproducibly associated with the highest density values, which track upwelled flow associated with the frontal circulation; accumulation of CDOM is always observed inside the frontal waters, at a density value of 27.2 kg m−3. These CDOM variations suggest that the frontal system is the place of enhanced biological activity.
Coastal food web structure, carbon storage, and nitrogen retention regulated by consumer pressure and nutrient loading
Authors: Worm Boris , Lotze Heike K. , Sommer Ulrich
Published: June 2010

By factorial field experiments we analyzed the relative effects of increased nutrient (N+P) loading and natural grazing pressure on species composition, carbon storage, and nitrogen retention in the Baltic Sea littoral food web, composed of macroalgae, grazers (snails, isopods, amphipods), and predators (shrimps, crabs, fish). Nitrogen was depleted relative to phosphorus throughout most of the year. Increasing nitrogen (6–200% over ambient concentrations) enhanced algal productivity and cover of fast‐growing annual algae, grazer, and predator densities, suggesting a three‐alevel bottom‐up effect. With increasing nitrogen loading, annual algae increasingly blocked perennial algal recruitment (65‐98% decrease) and growth. Grazers counteracted the effects of nutrient enrichment on algal species composition through selective consumption of annual algae. Grazer exclusion had equivalent negative effects on perennial recruitment as a 85% increase in nitrogen loading. Nutrient enrichment increased algal nitrogen content and decreased tissue C: N ratios in spring and summer but not in fall. Carbon storage and nitrogen retention, measured as C and N retained in plant biomass at the end of the growth season, were increased by grazers (C: 39%, N: 24%) but decreased with increasing nitrogen loading (C: –%, N: –74%). Our results emphasize the important role of grazers in buffering moderate eutrophication effects and illustrate how food web interactions and shifts in species composition are tightly linked to coastal ecosystem function.
Depth‐related cell‐specific bacterial leucine incorporation rates on particles and its biogeochemical significance in the Northwest Mediterranean
Authors: Turley C. M. , Stutt E. D.
Published: June 2010

A study of total and particle‐associated bacteria in the Northwest Mediterranean revealed notable relationships with depth. Cell‐specific leucine incorporation rates by total bacteria decreased significantly with depth (to 380 m), best fitting the power function log (rate) = 2.1–0.54 log (depth), r2 = 0.57, P = <0.001. In contrast, cell‐specific leucine incorporation rates by particle‐associated bacteria increased with depth as described by the power function log (rate) = 0.4 + 0.84 log (depth), r2 = 0.74, P = <0.01. We suggest that this relationship may reflect availability of usable dissolved organic matter (UDOM) and/or inorganic nutrients within the particle with increasing water depth. The latter relationship could also be interpreted in relation with time, i.e., be a consequence of the time taken for enzyme induction and solubilization of particulate organic matter (POM) to UDOM and the subsequent incorporation into bacterial protein during the sinking of the particle. These results may help to explain observations that sinking particles are rapidly decomposed between 100 and 500 m. Bacteria associated with particles in the Mediterranean contributed only 0.8–2.8% of total bacterial numbers but contributed 3–12% of total bacterial production in the upper 70 m. However, their contribution to total bacterial production in deeper waters was substantially higher (48% at 380 m). The activity of attached bacteria is, therefore, important and varies with depth, and this may help to explain the particularly low particle flux and hence the impoverished benthic environment found in the deeper waters of the Mediterranean.
Bacterioplankton distribution and production in deep Pacific waters: Large–scale geographic variations and possible coupling with sinking particle fluxes
Authors: Nagata Toshi , Fukuda Hideki , Fukuda Rumi , Koike Isao
Published: June 2010

Bacterial abundance and leucine incorporation rate were measured throughout the water column (depth, 4,000– 6,000 m) at stations occupied in the equatorial, subtropical, and subarctic Pacific as well as in the Bering Sea during three cruises conducted between 1993 and 1997. In general, depth‐dependent decreases of bacterial abundance and leucine incorporation in the bathypelagic layer (depth, >1,000 m) were well described by a power function with remarkably uniform exponents among distant locations: average exponents were –0.900 and –1.33 for abundance and leucine incorporation, respectively. Depth profiles of bacterial properties were complex at some subarctic stations, suggesting lateral transport of organic carbon by local eddies. Organic carbon fluxes from abyssal sediment to overlying water would explain increases in bacterial abundance and leucine incorporation in near‐bottom layers. Biomass was twofold to fourfold and the production was threefold to sevenfold greater in subarctic than in subtropical regions. This latitudinal pattern was consistent with the basin‐scale distribution of sinking fluxes of particulate organic carbon (POC) reported in the literature. Rates of bacterial carbon uptake accounted for 51% (range, 31–153) and 23% (14–58) of deep sinking POC fluxes in subarctic and subtropical regions, respectively. Average turnover time of deep bacterial assemblages was estimated to be 1–30 yr. These results suggest that deep bacterial biomass and production are generally coupled with sinking POC fluxes and that organic carbon is substantially transformed within bathypelagic environments via a sinking POC → dissolved organic carbon → bacteria pathway, as previously suggested in the mesopelagic zone.
Light scattering by viral suspensions
Authors: Balch William M. , Vaughn James , Novotny James , Drapeau David T. , Vaillancourt Robert , Lapierre Janeen , Ashe Amanda
Published: June 2010

Viruses represent one of the most abundant, ocean‐borne particle types and have significant potential for affecting optical backscattering. Experiments addressing the light‐scattering properties of viruses have heretofore not been conducted. Here we report the results of laboratory experiments in which the volume‐scattering functions of several bacterial viruses (bacteriophages) were measured at varying concentrations with a laser light‐scattering photometer using a He‐Ne and/or Argon ion laser (632.8 and 514.0 nm, respectively). Four bacterial viruses of varying size were examined, including the coliphages MS‐2 (capsid size 25–30 nm) and T‐4 (capsid size ∼100 nm), and marine phages isolated from Saco Bay, Maine (designation Y‐1, capsid size 50–80 nm) and Boothbay Harbor, Maine (designation C‐2, capsid size ∼110 nm). Volume‐scattering functions (VSFs) were fitted with the Beardsley‐Zaneveld function and then integrated in the backward direction to calculate backscattering cross section. This was compared to the virus geometric cross section as determined by transmission electron microscopy and flow‐field fractionation. Typical backscattering efficiencies varied from 20 × 10−6 to 1,000 × 10−6 . Data on particle size and backscattering efficiencies were incorporated into Mie scattering calcula‐tions to estimate refractive index of viruses. The median relative refractive index of the four viruses was ∼1.06. Results presented here suggest that viruses, while highly abundant in the sea, are not a major source of backscattering.
Hydraulic control of pore water geochemistry within the oxic‐suboxic zone of a permeable sediment
Authors: Falter James L. , Sansone Francis J.
Published: June 2010

The geochemical behavior of the top 70 cm of permeable reef flat sediments on Checker Reef, Oahu, Hawai'i was examined using spatial and temporal changes in pore water O2, NO3−, NO2−, NH4+, and N2O concentrations. The shallow depth of the sediment‐water interface relative to the height of waves propagating across the reef creates an environment in which pore water mixing and transport are dominated by wave‐induced mechanisms. Dissolved oxygen penetrated 15–50 cm in the four sites studied. The depth‐integrated concentration of dissolved oxygen was greater under larger wave conditions and in more permeable sediments, which suggests that dissolved oxygen may be a good indicator of the relationship between sediment metabolism and the physical nature of the sediment environment. The absence of any subsurface N2O maxima, limited temporal variability in pore water N2O concentrations, and vertically coherent profiles of O2, NO3−, NO2−, and N2O suggest that suboxic processes are typically restricted to spatial scales that are smaller than for oxic processes in these sediments. The geochemical response of the sediments to a natural perturbation was monitored by examining the composition of pore waters immediately following a large wave event and for several weeks thereafter. Significant changes in the depth‐integrated concentrations of O2, NO3−, NO2− and NH4+ were observed following the perturbation; however, only changes in NO3− lasted for several weeks after the event, whereas most other species returned to previous conditions within two weeks or less.
Estimation of the absorption and backscattering coefficients from inߚwater radiometric measurements
Authors: Stramska Malgorzata , Stramski Dariusz , Mitchell B. Greg , Mobley Curtis D.
Published: June 2010

Numerical simulations of radiative transfer within the ocean surface mixed layer have been used to derive a set of simple equations for estimating the absorption, a, and backscattering, bb, coefficients in the blue‐green spectral region from measurements of downwelling irradiance, Ed, upwelling irradiance, Eu, and upwelling nadir radiance, Lu. Two relationships are used in this derivation: (i) irradiance reflectance, R = Eu/Ed, is approximately proportional to bb/a and inversely proportional to the average cosine of the underwater light field, µ; and (ii) radiance reflectance, RL = Lu/Ed, is proportional to bb/a but changes little with µ. Accordingly, µ is first estimated from Lu/Eu and then the absorption coefficient is obtained from Gershun's equation. Having determined a, bb is estimated from the relation between RL and bb/a. We also show how the estimation of µ, a, and bb is improved with additional data of the beam attenuation coefficient, c. The retrieval of a and bb from Ed, Eu, and Lu has been tested using field data collected in the Southern California Bight. The a values predicted by the model show good agreement with absorption determinations from the ac‐9 instrument and on‐board spectrophotometric method, and the modeled bb agrees well with the backscattering determinations from the Hydroscat‐6 instrument. The algorithm has been derived for a broad range of the ocean inherent optical properties that do not necessarily covary with one another like in chlorophyll‐based bio‐optical models. However, the model should be used with caution if significant departure from the average Petzold particle scattering phase function is expected, for example in waters with high load of mineral particles.
The effect of ultraviolet B on phytoplankton populations in clear and brown temperate Canadian lakes
Authors: Kaczmarska Irena , Clair Thomas A. , Ehrman James M. , MacDonald Sara L. , Lean David , Day Kristin E.
Published: June 2010

Beaverskin and Pebbleloggitch lakes are located 2 km apart in Kejimkujik National Park (KNP) and share many limnetic characteristics: pH 5.0, shallow depth, and low nutrient concentrations. The lakes differ mainly in DOC concentrations, as Pebbleloggitch has 13 mg L−1 and Beaverskin 3.5 mg L−1. Consequently, 95% ultraviolet B (UV‐B) extinction occurs in relatively clear water at 50 cm, whereas in brown water it occurs at 4 cm below surface. Two treatments (UV‐B excluded with Mylar and UV‐B exposed) were used with experimental enclosures in the two lakes. In each lake, nine replicates of both treatments were sampled every 2 weeks from 2 July to 14 August 1996. Beaverskin lake phytoplankton differed fundamentally from that of the brown‐water Pebbleloggitch. The community in Beaverskin was relatively simple, consisting of few taxa, mainly cyanobacteria, dominated by Merismopedia tenuissima. Pebbleloggitch, in contrast, hosted many taxa, from all major algal divisions, e.g., Chlamydomonas angulosa, Mougeotia spp., Cryptomonas czosnowskii, Spherocystis sp., and Tabellaria quadriseptata. Phytoplankton species composition and cell densities in Beaverskin Lake did not differ significantly between the exposed and Mylar covered enclosures, except in the final week of collection. In contrast, phytoplankton populations in covered enclosures in Pebbleloggitch Lake were sharply different from those that were not covered. We attribute differences in response to the influence of the brown waters of Pebbleloggitch where the higher rates of absorbance of light by the brown waters results in slower mixing and greater damage by UV‐B radiation. This conclusion is in contrast to the generally accepted view that brown waters provide protection for phytoplankton.
Seasonal patterns of tissue biomass and densities of symbiotic dinoflagellates in reef corals and relation to coral bleaching
Authors: Fitt W. K. , McFarland F. K. , Warner M. E. , Chilcoat G. C.
Published: June 2010

Tissue biomass (ash‐free dry weight) and symbiotic dinoflagellates (density, chlorophyll a cell−1 or cm−2 of coral surface area) of five species of reef‐building corals were monitored seasonally for up to 4 yr at three different depths in the Bahamas. The lowest values of all tissue biomass and algal symbiont parameters occurred during the late summer–fall sample periods. In contrast, the highest densities and pigment content of symbionts usually occurred during the winter, whereas tissue biomass peaked most often in the spring, the time lag implying a functional relationship between these variables. Corals living in shallow water often (but not always) had higher levels of all parameters measured compared to deeper corals, except chlorophyll a content, which usually displayed the opposite trend. The results show that corals from all depths exhibited bleaching (loss of symbiotic dinoflagellates and/or their pigments) every year, regardless of whether they appeared white, tan, or mottled to the human eye. We speculate that these patterns are driven by seasonal changes in light and temperature on algal and animal physiology. Furthermore, we hypothesize that all tropical reef‐building corals, world‐wide, exhibit similar predictable cycles in their tissue biomass and symbiotic algae.
Climatic factors in the Atlantic control the oceanographic and ecological changes in the Baltic Sea
Authors: Hänninen Jari , Vuorinen Ilppo , Hjelt Pekka
Published: June 2010

Salinity changes in the Baltic Sea have been attributed to a lack of balance between irregular pulses of North Sea water penetrating the Danish Straits and the freshwater runoff to the Baltic Sea. Both pulses and runoff are controlled by climatic factors in the Atlantic. The occurrence of major pulses of oceanic water has proved unpredictable, being non‐existent during the 1980s. We used dynamic regression models to relate the response of the Baltic Sea salinity to hypothetical controlling factors: westerly winds, freshwater runoff, and, ultimately, the Northern Atlantic oscillation (NAO). Our results provided evidence for general chain‐of‐events relationship between the NAO and a subsequent weather effect over the North Sea, which was finally extended to the Baltic Sea salinity. Westerly winds followed changes in the NAO with a lag of <1 month. Total freshwater runoff to the Baltic Sea followed changes in the NAO with a lag of <2 months. Furthermore, the salinity responded to freshwater runoff with a time lag of <1 yr, and a significant decreasing trend was found in the salinity series. On the basis of the existing lags, we foresee a possibility to predict not only oceanographic, but also biological interactions in the Baltic Sea.
Cyanobacterial blooms in the Baltic Sea: Natural or human‐induced?
Authors: Bianchi Thomas S. , Engelhaupt Erika , Westman Per , Andrén Thomas , Rolff Carl , Elmgren Ragnar
Published: June 2010

Massive summer blooms of nitrogen‐fixing cyanobacteria have been documented in the Baltic Sea since the 19th century, but are reported to have increased in frequency, biomass, and duration in recent decades—presumably in response to the well‐documented anthropogenic eutrophication of the Baltic. Here, we present an 8,000‐yr record of fossil cyanobacterial pigments, diatom microfossil assemblages, and d15N variations in sediment cores from the Baltic proper. This record indicates that nitrogen‐fixing cyanobacterial blooms are nearly as old as the present brackish water phase of the Baltic Sea, starting as far back as ca. 7000 B.P.—soon after the former freshwater Ancylus Lake turned into the brackish Litorina Sea. Demonstration of cyanobacterial blooms in the Baltic prior to the greatly increased anthropogenic nutrient inputs of the 20th century is important for setting realistic goals when trying to reduce the magnitude of present blooms. Our results suggest that the presently predominating nitrogen (N) limitation of phytoplankton in the Baltic Sea proper is not man‐induced, but a natural phenomenon, which has endured for some 7,000 yr. These cyanobacterial blooms were possibly initiated by increased availability of phosphorus (P)—from inflow of P‐rich seawater and increased P release from sediments—during periods of deep‐water anoxia, caused by the establishment of salinity stratification. Efforts to restore the Baltic proper to a more oligotrophic and natural condition should take into account that nitrogen‐fixing cyanobacterial blooms are a characteristic, natural feature of this sea.
Photochemical transformation of dissolved organic matter in lakes
Authors: Bertilsson Stefan , Tranvik Lars J.
Published: June 2010

In a survey of photochemical transformation of dissolved organic matter (DOM) in lake water, we found photochemical production of dissolved inorganic carbon (DIC) and low molecular weight carboxylic acids (oxalic, malonic, formic, and acetic acid), upon simulated solar ultraviolet (UV) radiation exposure of filter‐sterilized surface water from 38 investigated lakes. Given the large variability in water chemistry of the studied systems, we suggest that these photoproducts are universally produced in sunlight exposed lake water. The measured production of carboxylic acid carbon corresponded to 34.4% (median) of the produced DIC. The production of DIC and carboxylic acids during 8 h of mild UV irradiation corresponded to an average of 4.7% (SD 2.9) of the total dissolved organic carbon pool. Hence, photochemical degradation could be a major sink for DOM in the surface layer of lakes. All photoreaction rates were strongly correlated to the total radiation absorbed during UV exposure (rs2 > 0.8), which depends mainly on amount of colored DOM in the water. The variability in DIC production after normalizing for absorbed radiation energy could partly be attributed to general water chemistry parameters (e.g., pH, iron concentration, conductivity).
Changes in composition and reactivity of allochthonous DOM in a prairie saline lake
Authors: Waiser Marley J. , Robarts Richard D.
Published: June 2010

Inland saline lakes in semiarid regions of the Canadian prairies contain some of the highest known concentrations of dissolved organic carbon (DOC). This dissolved organic matter (DOM) represents a potentially important carbon and energy source for aquatic bacteria. Redberry Lake, an oligotrophic saline lake in central Saskatchewan, is located in a hydrologically closed basin and has high levels of DOC (seasonal mean 35 mg L−1). Despite such high DOC concentrations, lake water is clear. Lake DOM is predominantly allochthonous, and enters the lake via the major inflow, Oscar Creek. Despite its origin, this DOM is compositionally much different than its creek counterpart. Approximately 73% of total lake DOM is low in molecular weight (<1000 D). XAD‐8 isolated hydrophobic organic acids (HPOA) are low in aromaticity, have high C:N ratios and a certain percentage are old (~700 years). In comparison, creek water, despite having lower DOC concentrations than the lake (14.9 mg L−1) is highly colored. Fifty‐five per cent of this DOC is low in molecular weight and isolated DOM has higher aromaticity and lower C:N ratio than lake DOM. As a result of these changes in DOM, ultraviolet light penetrates much deeper into lake water as compared to the creek. Photolysis experiments revealed that DOM in Oscar Creek and Redberry Lake is photoreactive. Changes in lake DOM are not only linked to location within a hydrologically closed basin and photochemistry, but provide the explanation for the optically different character of DOC in this geographical region. Changes in lake DOM have had an effect at the microbial level as well. Little of the lake DOM appears available for bacterial growth as a result of these photochemical changes. Creek DOM, having a shorter residence time, does not appear to have been as photochemically changed and consequently is more available for bacterial growth.
Biochemical composition of particles and dissolved organic matter along an estuarine gradient: Sources and implications for DOM reactivity
Authors: Mannino Antonio , Harvey H. Rodger
Published: June 2010

The chemical composition of high molecular weight dissolved organic matter (DOM) and particulate organic matter (POM) was examined along the salinity gradient of the Delaware Estuary. DOM was collected and frac‐tionated by tangential‐flow ultrafiltration into 1–30 kDa (HDOM; high molecular weight) and 30 kDa to 0.2 mm (VHDOM; very high molecular weight) and compared to particles collected in parallel. Polysaccharides comprised 12–43% of particulate organic carbon (POC), 30–56% of VHDOM carbon, and 7.5–19% of HDOM carbon. Hydrolyzable amino acids comprised 17–38% of POC, 5.4–12% of VHDOM carbon, and 1.5–4.2% of HDOM carbon. Only 7–43% of dissolved organic nitrogen in VHDOM and HDOM consisted of amino acids, indicating that organic nitrogen is highly modified within the dissolved pool or an unidentified pool of dissolved organic nitrogen exists. The composition of amino acids and distribution of polysaccharides are consistent with enrichment of structural biopolymers from algae and vascular plants within DOM. Proteinaceous matter released during the growth of an axenic diatom culture contains similar amino acid distributions across size fractions as in Delaware Bay samples. The source of organic matter appears to be as important as microbial processing in determining amino acid content and composition of DOM. Shifts in amino acid composition point to contrasting sources and extent of degradation for organic matter along the estuarine gradient and among size fractions. The lower amino acid and carbohydrate content and higher b‐alanine content in HDOM suggests that this fraction is more highly degraded relative to POM and VHDOM and provides geochemical evidence in support of the size‐reactivity continuum hypothesis. Spatial patterns in reactivity of organic constituents were also evident with more degraded organic matter in the turbid middle estuary and the release of fresh DOM from diatoms in the lower estuary.
Growth of marine bacteria in batch and continuous culture under carbon and nitrogen limitation
Authors: Goldman Joel C. , Dennett Mark R.
Published: June 2010

In a combination of batch and continuous culture experiments involving natural assemblages of marine bacteria we examined the impact of varying both the carbon and nitrogen substrates and the substrate C:N ratio (C:NS) on the bacterial C:N ratio (C:NB), the gross growth efficiency (GGE), and the ability of marine bacteria to cometabolize amino acids and NH4+ . We varied the C:NS ratio from 5:1 (carbon limitation) to 30:1 (nitrogen limitation) with varying combinations of glucose, glutamate, and NH4+ (and in some cases with an amino acid mixture and with other simple carbon compounds). We found that GGE was unaffected by growth rate, the C:NS ratio, or different combinations of carbon and nitrogen substrates, averaging ∼50%. However, the 95% confidence interval was as high as ±20%, suggesting that experimental error may be a common problem in determining GGE in laboratory studies and a far more serious problem in making such estimates in field studies. The C:NB ratio was invariant at ∼4.5:1 (by atoms) under all conditions when carbon was limiting growth, but increased to ∼7:1–9:1 when reaching the stationary phase during batch growth and up to 13:1 at very low growth rates in continuous culture. These results indicate that the C:NB ratio has some value as a diagnostic tool for determining the physiological state of bacterial populations, although there are some concerns about its general applicability. Finally, there was absolutely no evidence that NH4+ uptake was inhibited in the presence of amino acids. The key to NH4+ uptake is the presence of a readily assimilated carbon source to balance nitrogen uptake stoichiometrically. These findings have some bearing on the recent suggestions that gradients exist in both GGE and nitrogen preference of marine bacteria from productive inshore regions to the oligotrophic open ocean.
The effects of light and nitrate levels on the relationship between nitrate reductase activity and 15NO3− uptake: Field observations in the East China Sea
Authors: Hung Chin‐Chang , Wong George T. F. , Liu Kon‐Kee , Fuh‐Kwo Shiah , Gwo‐Ching Gong
Published: June 2010

Nitrate reductase activity (NRA) and 15NO3− uptake (NU) were determined in the East China Sea and the adjoining Kuroshio in May 1996, at six stations covering a range of hydrographic conditions: the nutrient‐rich and fresherplume of Changjiang Diluted Water along the Chinese coast, the nutrient‐rich upwelling Kuroshio Subsurface Water at the shelf edge northeast of Taiwan, the oligotrophic Kuroshio Surface Water and the mixing zones among these water masses on the shelf. The values of NRA in the surface mixed layer ranged between 16 and 0.1 nM‐N h−1, whereas those of NU ranged between 37 and 1 nM‐N h−1. Higher NRA and NU were found in the frontal zone between the coastal and shelf waters and in the upwelling zone, whereas the lowest values were found in the surface Kuroshio. The NRA/Chl a ratio increased linearly with increasing NU/primary production ratio in the sequence: Kuroshio, coastal plume, upwelling zone and mixing zones in the shelf. This is probably a reflection of the varying nutrient condition and the relative importance of NU in sustaining the biomass in these regions.

In nitrate‐ and light‐replete waters, the average NU/NRA was 1.0 ± 0.3. NRA was linearly related to NU so that NU = 1.08 (± 0.07)NRA (r2 = 0.79). Thus, NRA may be used for estimating NU in these waters. In nitrate‐deficient and light‐replete waters, the average NU/NRA was 4 ± 4. These high and variable values of NU/NRA might have been caused by an over‐estimation of NU as a result of the stimulatory effect of the added 15NO3− on phytoplankton growth. Thus, NRA may be a more reliable indicator of the rate of 15NO3− uptake in oligotrophic waters. In nitrate‐replete and light‐deficient waters, NU did not correlate well with NRA. The average NU/NRA was 0.7 ± 0.7. These low and variable values of NU/NRA suggest a possible decoupling between NRA and NU.

By using the relationship between NU and NRA in nitrate‐ and light‐replete waters and the depth‐integrated inventory of NRA in the photic zone at each station, NU in oligotrophic waters, the coastal plume, upwelling waters and shelf waters can be estimated to be 0.45, 1.55, 3.12, and 3.59 mg‐N m−2 h−1 respectively. These values fall well within the range of previously reported values in similar types of water.
Towards a complete mass balance and model for PCBs and PAHs in a small rural lake, Cumbria U.K.
Authors: Gevao Bondi , Hamilton‐Taylor John , Jones Kevin C.
Published: June 2010

This paper summarizes the processes of exchange/fluxes for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in a small well‐studied rural lake, Esthwaite Water in northwest England. Measurements of PCB and PAH concentrations have been made in rain, air, water, dated sediment cores, and sediment trap samples over a 2‐yr study period and used to determine fluxes to and from the lake. A steady state mass balance model was used to construct an input‐output budget for the chemicals and to investigate the relative importance of transport into and out of the lake. The hydraulic transport from the lake was the most important loss mechanism for both PCBs and PAHs. Volatilization, not sedimentation, is currently the dominant loss process for PCBs in the water column, whereas, sedimentation exceeds volatilization for PAHs. The data further suggest that the current sediment‐water flux is upward for PCBs and downwards for PAHs, indicating that the sediments might be acting as a secondary source for PCBs but continue to act as a sink for PAHs. Riverine, catchment runoff, or both are believed to be the most important input for PCBs and PAHs to the lake although direct aerial deposition to the lake is also important for PCBs. Differences in the mixtures of compounds in the various compartments suggests significant fractionation of PCBs and PAHs in the air‐water‐sediment system in the lake.
Light availability and variations in phytoplankton standing crops in a nutrient‐rich blackwater river
Authors: Phlips E. J. , Cichra M. , Aldridge F. J. , Jembeck J. , Hendrickson J. , Brody R.
Published: June 2010

In this paper we examine the potential role of light limitation in the regulation of phytoplankton standing crop in Florida's largest river, the St. Johns. We hypothesized that spatial and temporal patterns in standing crops of phytoplankton are strongly affected by variations in light availability in the mixed layer, particularly as they relate to river basin morphology and changes in water color, which reach high levels in the St. Johns River. This hypothesis was examined within the context of four principal research objectives: (1) Determination of the spatial and temporal patterns of phytoplankton standing crops and key environmental parameters related to nutrient concentration and light extinction, (2) Estimation of spatial and temporal patterns of mean light availability in the mixed‐layer, (3) Examination of the correlations between phytoplankton standing crops and light availability, and (4) Evaluation of the relative role of different limiting factors on the regulation of phytoplankton standing crop. The results of this study revealed a relationship between standing crops and light availability. Twelve sampling sites along a 130 km reach of the river were sampled and analyzed for phytoplankton abundance, water chemistry, and light attenuation over a three year period. Our empirical results, along with the outcome of our efforts to model light availability for planktonic production were consistent with our original hypothesis. Temporal variations in color were strongly correlated to variability in phytoplankton standing crops. Spatial trends in standing crop were most readily explained through the effects of changing basin morphology and flushing rates. The results are discussed in the context of the River Continuum Concept and variations on this theme specific to blackwater ecosystems.
Strong seasonality in phytoplankton cell lysis in the NW Mediterranean littoral
Authors: Agustí Susana , Duarte Carlos M.
Published: June 2010

The seasonality of phytoplankton cell lysis rates in the NW Mediterranean coastal waters was examined based on measurements of the dissolved esterase activity between 1995 and 1998 in the Blanes Bay (NE Spain). The temporal variability of phytoplankton biomass and gross primary production (GPP) were characterized by a late winter bloom dominated by diatoms and high GPP in summer despite the low phytoplankton biomass in this season. The phytoplankton lysis rates were found to be strongly seasonal, being highest in summer (mean ± SE = 0.41 ± 0.049 d−1) when values as high as 1.47 d−1 were attained. However, during the rest of the year, phytoplankton lysis rates remained low, particularly in winter (0.061 ± 0.005 d−1). There was a strong (R2 = 0.71, P < 0.00001) positive relationship between monthly average lysis rates and water temperature. In addition, monthly average lysis rates followed gross primary production with a maximum correlation (r = 0.65, P < 0.05) at a lag time of 1–2 months, similar to the time span from bloom initiation to bloom collapse. These results identify phytoplankton cell lysis as an important route of phytoplankton carbon flow in Blanes Bay.
Invertebrate recolonization patterns in the hyporheic zone of a gravel stream
Authors: Schmid‐Araya J. M.
Published: June 2010

Invertebrate recolonization at short‐term exposures (2–192 h) in the hyporheic zone of a gravel stream revealed significant depth‐specific differences. In the shallow hyporheic zone (0–20 cm), mean meiofaunal density increased asymptotically stabilizing within 66 h, a similar but nonsignificant pattern was found for macrofauna. Permanent meiofaunal members (e.g., rotifers, chironomids, cyclopoids) were the fastest colonizers of the traps. At the deeper hyporheos (20–50 cm) meiofauna and macrofauna entered the pipes rapidly (2 h) but neither a power curve nor an asymptotic curve described their colonization pattern. Nonlinear regression analysis indicated a significant relationship between amounts of interstitial sediment entering the pipes and abundances of macrofauna and meiofauna.
Crayfish as geomorphic agents and ecosystem engineers: Biological behavior affects sand and gravel erosion in experimental streams
Authors: Statzner Bernhard , Fièvet Eric , Champagne Jean‐Yves , Morel Robert , Herouin Eric
Published: June 2010

Effects of animals on the transport of solids (e.g., sediments) can modify earth‐surface processes and landforms (role as geomorphic agents) and resources for other organisms (role as ecosystem engineers). Therefore, we studied the impact of crayfish (Orconectes limosus) behavior on sand‐gravel erosion and bottom habitat over riffle‐pool sequences in experimental streams. We manipulated the availability of crayfish food and refugia. Refugia availability had clear effects on overall crayfish activity. The establishment of dominance hierarchies among the crayfish produced patterns in crayfish activity that differed between riffles and pools. Crayfish activity significantly affected sand and gravel erosion. High local sediment erosion averaged ≈2.8 (riffles) and ≈1.4 (pools) kg dry weight m−2 d‐1 when crayfish hierarchies were established and refugia were available. Removing the refugia increased these rates to ≈4.0 (riffles) and ≈3.2 (pools) kg dry weight m−2 d−1. This direct erosion caused by crayfish should be lower than that caused by floods. Crayfish distinctly (1) increased bedform roughness (riffles), (2) decreased sand dune height (pools), (3) shifted the transition between gravel (riffles) and sand (pools) downstream, (4) decreased sand in gravel interstices (riffles), (5) decreased filamentous algae growth on gravel (riffles), and (6) decreased biofilm cover on sand dunes (pools). These sediment changes due to crayfish activity at baseflow should have opposite effects on sediment erosion during subsequent floods. Crayfish impact on physical habitat at baseflow could largely affect population and community structure of the benthos, as well as egg survival of gravel‐breeding fish.