Open ocean carbon monoxide photo-production

Sunlight-initiated photolysis of chromophoric dissolved organic matter (CDOM) is the dominant source of carbon monoxide (CO) in the open-ocean. A modelling study was conducted to constrain this source. Spectral solar irradiance was obtained from two models (GCSOLAR and SMARTS2). Water-column CDOM and total light absorption were modelled using spectra collected along a Meridional transect of the Atlantic ocean using a 200-cm pathlength liquid waveguide UV-visible spectrophotometer. Apparent quantum yields for the production of CO (AQYCO) from CDOM were obtained from a parameterisation describing the relationship between CDOM light absorption coefficient and AQYCO and the CDOM spectra collected. The sensitivity of predicted rates to variations in model parameters (solar irradiance, cloud cover, surface-water reflectance, CDOM and whole water light absorbance, and AQYCO was assessed. The model\u27s best estimate of open-ocean CO photoproduction was 47 +/- 7 Tg CO-C yr-1, with lower and upper limits of 38 and 84 Tg CO-C yr-1, as indicated by sensitivity analysis considering variations in AQYs, CDOM absorbance, and spectral irradiance. These results represent significant constraint of open-ocean CO photoproduction at the lower limit of previous estimates. Based on these results, and their extrapolation to total photochemical organic carbon mineralisation, we recommend a downsizing of the role of photochemistry in the open-ocean carbon cycle. (c) 2006 Elsevier Ltd. All rights reserved

Effects of Salinity Changes on the Photodegradation and Ultraviolet-Visible Absorbance of Terrestrial Dissolved Organic Matter

We performed laboratory studies to determine the effects of salinity on the photodegradation of dissolved organic matter (DOM) from the Great Dismal Swamp, Virginia, an important source of terrestrial DOM to the lower Chesapeake Bay. Samples were created by mixing Great Dismal Swamp water (ionic strength approximate to 0 mol L-1) with modified artificial seawater solutions of differing salinities while keeping the final dissolved organic carbon (DOC) concentration constant. These samples were then irradiated for 24 h in a light box providing ultraviolet (UV) light similar to that of natural sunlight. Light absorbance and DOC concentrations decreased after photoexposure, whereas dissolved inorganic carbon (DIC) concentrations increased. Variations in salinity affected both DIC production and UV absorption, with the higher salinity samples showing lower DIC production and less photobleaching. Addition of an iron chelator eliminated the relationship between photochemistry and salinity by reducing both photobleaching and DIC production at low salinities. As terrigenous DOM transits through an estuary, its photochemical reactivity and optical properties may change significantly as a function of salinity, probably as a result of changes in DOM conformation or changes in iron-DOM photochemistry, or both

A Preliminary Examination of an in situ Dual Dye Approach to Measuring Light Fluxes in Lotic Systems

Light is a critical parameter in aquatic ecosystems, affecting primary production and in situ photochemistry. However, measuring light exposure for suspended particles or dissolved components in a dynamic water column can be challenging with existing Eulerian approaches. Here, we assess the simultaneous deployment of two dyes differing in photolability (rhodamine WT and fluorescein) as a Lagrangian measure of sunlight exposure in a lotic system. Fluorescein is sensitive to light exposure; rhodamine WT is relatively photostable. We examined dye fluorescence at various pH, salinity, and temperature conditions. We also tested dye photolability as a function of pH and wavelength range. In conjunction with this laboratory work, we performed initial field testing of the dual-dye approach in a stream on the north shore of Lake Superior, USA. Irradiation of the dyes using long-pass filters identified wavelengths \u3e= 420 nm as responsible for the vast majority of the loss of fluorescein fluorescence, with rhodamine appearing relatively photostable in these short-term studies across the wavelength ranges tested. Dye response to irradiation is pH-sensitive; the dual-dye approach will require additional calibration for acidic or basic waters and should be used with caution in aquatic systems undergoing strong (several pH unit) changes in pH. Field testing showed that the fluorescein to rhodamine WT ratio decreased approximately linearly with light exposure. The dual-dye methodology shows promise as an in situ light sensor applicable to water column species in lotic systems if temperature is recorded, and the pH range is measured and relatively stable (e.g., varies by \u3c 1 unit)

Absorption Spectral Slopes and Slope Ratios as Indicators of Molecular Weight, Source, and Photobleaching of Chromophoric Dissolved Organic Matter

A new approach for parameterizing dissolved organic matter ( DOM) ultraviolet-visible absorption spectra is presented. Two distinct spectral slope regions ( 275-295 nm and 350-400 nm) within log-transformed absorption spectra were used to compare DOM from contrasting water types, ranging from wetlands (Great Dismal Swamp and Suwannee River) to photobleached oceanic water ( Atlantic Ocean). On the basis of DOM size-fractionation studies ( ultrafiltration and gel filtration chromatography), the slope of the 275-295- nm region and the ratio of these slopes (SR; 275-295- nm slope : 350-400- nm slope) were related to DOM molecular weight ( MW) and to photochemically induced shifts in MW. Dark aerobic microbial alteration of chromophoric DOM ( CDOM) resulted in spectral slope changes opposite of those caused by photochemistry. Along an axial transect in the Delaware Estuary, large variations in SR were measured, probably due to mixing, photodegradation, and microbial alteration of CDOM as terrestrially derived DOM transited through the estuary. Further, SR varied by over a factor of 13 between DOM-rich wetland waters and Sargasso Sea surface waters. Currently, there is no consensus on a wavelength range for log-transformed absorption spectra. We propose that the 275-295- nm slope be routinely reported in future DOM studies, as it can be measured with high precision, it facilitates comparison among dissimilar water types including CDOM-rich wetland and CDOM-poor marine waters, and it appears to be a good proxy for DOM MW. © 2008, by the American Society of Limnology and Oceanography, Inc

Temporal and spatial variability of dissolved organic and inorganic phosphorus, and metrics of phosphorus bioavailability in an upwelling-dominated coastal system

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 110 (2005): C10S13, doi:10.1029/2004JC002837.High-frequency temporal and spatial shifts in the various dissolved P pools (total, inorganic, and organic) are linked to upwelling/relaxation events and to phytoplankton bloom dynamics in the upwelling-dominated Oregon coastal system. The presence and regulation of alkaline phosphatase activity (APA) is apparent in the bulk phytoplankton population and in studies of cell-specific APA using Enzyme Labeled Fluorescence (ELF®). Spatial and temporal variability are also evident in phytoplankton community composition and in APA. The spatial pattern of dissolved phosphorus and APA variability can be explained by bottom-controlled patterns of upwelling, and flushing times of different regions within the study area. The presence of APA in eukaryotic taxa indicates that dissolved organic phosphorus (DOP) may contribute to phytoplankton P nutrition in this system, highlighting the need for a more complete understanding of P cycling and bioavailability in the coastal ocean.KCR acknowledges WHOI for rapid-response funding that made possible participation on this first COAST cruise, and NSF-OCE grant 0119134 for support of subsequent work on these and other COAST samples

Indirect interaction between two native thistles mediated by an invasive exotic floral herbivore

Spatial and temporal variation in insect floral herbivory is common and often important. Yet, the determinants of such variation remain incompletely understood. Using 12 years of flowering data and 4 years of biweekly insect counts, we evaluated four hypotheses to explain variation in damage by the Eurasian flower head weevil, Rhinocyllus conicus, to the native North American wavyleaf thistle, Cirsium undulatum. The four factors hypothesized to influence weevil impact were variations in climate, weevil abundance, phenological synchrony, and number of flower heads available, either on wavyleaf thistle or on the other co-occurring, acquired native host plant (Platte thistle, Cirsium canescens), or on both. Climate did not contribute significantly to an explanation of variation in R. conicus damage to wavyleaf thistle. However, climate did influence weevil synchrony with wavyleaf flower head initiation, and phenological synchrony was important in determining R. conicus oviposition levels on wavyleaf thistle. The earlier R. conicus was active, the less it oviposited on wavyleaf thistle, even when weevils were abundant. Neither weevil abundance nor availability of wavyleaf flower heads predicted R. conicus egg load. Instead, the strongest predictor of R. conicus egg load on wavyleaf thistle was the availability of flower heads on Platte thistle, the more common, earlier flowering native thistle in the sand prairie. Egg load on wavyleaf thistle decreased as the number of Platte thistle flower heads at a site increased. Thus, wavyleaf thistle experienced associational defense in the presence of flowering by its now declining native congener, Platte thistle. These results demonstrate that prediction of damage to a native plant by an exotic insect may require knowledge of both likely phenological synchrony and total resource availability to the herbivore, including resources provided by other nontarget native species

Environmental and Climatic Determinants of Molecular Diversity and Genetic Population Structure in a Coenagrionid Damselfly

Identifying environmental factors that structure intraspecific genetic diversity is of interest for both habitat preservation and biodiversity conservation. Recent advances in statistical and geographical genetics make it possible to investigate how environmental factors affect geographic organisation and population structure of molecular genetic diversity within species. Here we present a study on a common and wide ranging insect, the blue tailed damselfly Ischnuraelegans, which has been the target of many ecological and evolutionary studies. We addressed the following questions: (i) Is the population structure affected by longitudinal or latitudinal gradients?; (ii) Do geographic boundaries limit gene flow?; (iii) Does geographic distance affect connectivity and is there a signature of past bottlenecks?; (iv) Is there evidence of a recent range expansion and (vi) what is the effect of geography and climatic factors on population structure? We found low to moderate genetic sub-structuring between populations (mean FST = 0.06, Dest = 0.12), and an effect of longitude, but not latitude, on genetic diversity. No significant effects of geographic boundaries (e.g. water bodies) were found. FST-and Dest-values increased with geographic distance; however, there was no evidence for recent bottlenecks. Finally, we did not detect any molecular signatures of range expansions or an effect of geographic suitability, although local precipitation had a strong effect on genetic differentiation. The population structure of this small insect has probably been shaped by ecological factors that are correlated with longitudinal gradients, geographic distances, and local precipitation. The relatively weak global population structure and high degree of genetic variation within populations suggest that I. elegans has high dispersal ability, which is consistent with this species being an effective and early coloniser of new habitats

Predictors of Ips confusus Outbreaks During a Record Drought in Southwestern USA: Implications for Monitoring and Management

In many ecosystems the effects of disturbance can be cryptic and disturbance may vary in subtle spatiotemporal ways. For instance, we know that bark beetle outbreaks are more frequent in temperate forests during droughts; however, we have little idea about why they occur in some locations and not others. Understanding biotic and abiotic factors promoting bark beetle outbreaks can be critical to predicting and responding to pest outbreaks. Here we address the environmental factors which are associated with Ips confusus outbreaks during the 2002 widespread drought within the distribution range of pinyon pine woodlands in Arizona. We used univariate statistics to test if whether tree characteristics, other herbivores, stand properties, soil type, wind, and topography were associated with I. confusus outbreak, and logistic regression to create a predictive model for the outbreaks. We found that I. confusus attacks occur in low elevation stands on steeper slopes, where favorable winds for I. confusus dispersion occur. I. confusus select larger trees, in high density stands with understory shrubs that exhibit phenotypic traits characteristic of resistance to stem-boring moths. The model was highly accurate, and explained 95% of the variability in occurrence (98% of the absences and 95% of the presences). Accurate prediction of the impacts of disturbance allow us to anticipate, minimize or mitigate for and eventually counteract its effects, especially those affecting diversity and ecosystem function. Identification of outbreak risk areas can guide regional and national management towards the reduction of infestation risk and enhancing conservation of pinyon-juniper woodlands

The Passive Yet Successful Way of Planktonic Life: Genomic and Experimental Analysis of the Ecology of a Free-Living Polynucleobacter Population

Background: The bacterial taxon Polynucleobacter necessarius subspecies asymbioticus represents a group of planktonic freshwater bacteria with cosmopolitan and ubiquitous distribution in standing freshwater habitats. These bacteria comprise,1 % to 70 % (on average about 20%) of total bacterioplankton cells in various freshwater habitats. The ubiquity of this taxon was recently explained by intra-taxon ecological diversification, i.e. specialization of lineages to specific environmental conditions; however, details on specific adaptations are not known. Here we investigated by means of genomic and experimental analyses the ecological adaptation of a persistent population dwelling in a small acidic pond. Findings: The investigated population (F10 lineage) contributed on average 11 % to total bacterioplankton in the pond during the vegetation periods (ice-free period, usually May to November). Only a low degree of genetic diversification of the population could be revealed. These bacteria are characterized by a small genome size (2.1 Mb), a relatively small number of genes involved in transduction of environmental signals, and the lack of motility and quorum sensing. Experiments indicated that these bacteria live as chemoorganotrophs by mainly utilizing low-molecular-weight substrates derived from photooxidation of humic substances. Conclusions: Evolutionary genome streamlining resulted in a highly passive lifestyle so far only known among free-living bacteria from pelagic marine taxa dwelling in environmentally stable nutrient-poor off-shore systems. Surprisingly, such a lifestyle is also successful in a highly dynamic and nutrient-richer environment such as the water column of the investigate