Sunlit Waters Research Articles

Formation of Silver Nanoparticles in Visible Light-Illuminated Waters: Mechanism and Possible Impacts on the Persistence of AgNPs and Bacterial Lysis

A confluence of water and silver-containing products or compounds results in unintentional or intentional discharge of silver species (including silver nanoparticles [AgNPs], free or organic matter-bound Ag+, Ag-halides, or soluble Ag-complexes) into visible light-illuminated waters. To date, little is known about the transformations of Ag species and mechanisms of AgNP formation in light-illuminated waters consisting of components such as bacteria, extracellular polymeric substances (EPS), natural organic matter (NOM), chloride, and/or nitrate. In this work, we demonstrate that in the presence of combinations of water components the transformation of ionic Ag to “new” AgNPs occurs via heterogeneous nucleation followed by (1) light-induced growth mediated by surface plasmon resonance activity of AgNPs, and (2) Ostwald ripening in the absence of light and chloride anions. Further, oxidative dissolution of AgNPs at near-neutral pH (6.8) releases Ag ions, which either complex with the components or form “new” AgNPs depending on solution chemistry. AgNP nucleation and growth on bacterial cells (e.g., Pseudomonas aeruginosa) may cause cell lysis. This study highlights that light-illuminated waters comprising common aquatic components are highly favorable for the AgNP formation over dissolution under neutral pH conditions, in which the presence of chloride accelerates AgNP formation and the reducing capacity of EPS/chloride medium may be greater than NOM (humics and fulvics). Findings of this study suggest that AgNP formation and dissolution may be a continual process and AgNPs thus formed may be stabilized by organic matter, which possibly leads to persistence of the nanoparticles in sunlit waters.

Geochemical Production of Reactive Oxygen Species From Biogeochemically Reduced Fe

The photochemical reduction of Fe(III) complexes to Fe(II) is a well-known initiation step for the production of reactive oxygen species (ROS) in sunlit waters. Here we show a geochemical mechanism for the same in dark environments based on the tidally driven, episodic movement of anoxic groundwaters through oxidized, Fe(III) rich sediments. Sediment samples were collected from the top 5 cm of sediment in a saline tidal creek in the estuary at Murrell's Inlet, South Carolina and characterized with respect to total Fe, acid volatile sulfides, and organic carbon content. These sediments were air-dried, resuspended in aerated solution, then exposed to aqueous sulfide at a range of concentrations chosen to replicate the conditions characteristic of a tidal cycle, beginning with low tide. No detectable ROS production occurred from this process in the dark until sulfide was added. Sulfide addition resulted in the rapid production of hydrogen peroxide, with maximum concentrations of 3.85 μM. The mechanism of hydrogen peroxide production was tested using a simplified three factor representation of the system based on hydrogen sulfide, Fe(II) and Fe(III). The resulting predictive model for maximum hydrogen peroxide agreed with measured hydrogen peroxide in field-derived samples at the 95% level of confidence, although with a persistent negative bias suggesting a minor undiscovered peroxide source in sediments.

Highly Dynamic PVP-Coated Silver Nanoparticles in Aquatic Environments: Chemical and Morphology Change Induced by Oxidation of Ag0 and Reduction of Ag+

The fast growing and abundant use of silver nanoparticles (AgNPs) in commercial products alerts us to be cautious of their unknown health and environmental risks. Because of the inherent redox instability of silver, AgNPs are highly dynamic in the aquatic system, and the cycle of chemical oxidation of AgNPs to release Ag(+) and reconstitution to form AgNPs is expected to occur in aquatic environments. This study investigated how inevitable environmentally relevant factors like sunlight, dissolved organic matter (DOM), pH, Ca(2+)/Mg(2+), Cl(-), and S(2-) individually or in combination affect the chemical transformation of AgNPs. It was demonstrated that simulated sunlight induced the aggregation of AgNPs, causing particle fusion or self-assembly to form larger structures and aggregates. Meanwhile, AgNPs were significantly stabilized by DOM, indicating that AgNPs may exist as single particles and be suspended in natural water for a long time or delivered far distances. Dissolution (ion release) kinetics of AgNPs in sunlit DOM-rich water showed that dissolved Ag concentration increased gradually first and then suddenly decreased with external light irradiation, along with the regeneration of new tiny AgNPs. pH variation and addition of Ca(2+) and Mg(2+) within environmental levels did not affect the tendency, showing that this phenomenon was general in real aquatic systems. Given that a great number of studies have proven the toxicity of dissolved Ag (commonly regarded as the source of AgNP toxicity) to many aquatic organisms, our finding that the effect of DOM and sunlight on AgNP dissolution can regulate AgNP toxicity under these conditions is important. The fact that the release of Ag(+) and regeneration of AgNPs could both happen in sunlit DOM-rich water implies that previous results of toxicity studies gained by focusing on the original nature of AgNPs should be reconsidered and highlights the necessity to monitor the fate and toxicity of AgNPs under more environmentally relevant conditions.

Metabolic reprogramming by viruses in the sunlit and dark ocean

BackgroundMarine ecosystem function is largely determined by matter and energy transformations mediated by microbial community interaction networks. Viral infection modulates network properties through mortality, gene transfer and metabolic reprogramming.ResultsHere we explore the nature and extent of viral metabolic reprogramming throughout the Pacific Ocean depth continuum. We describe 35 marine viral gene families with potential to reprogram metabolic flux through central metabolic pathways recovered from Pacific Ocean waters. Four of these families have been previously reported but 31 are novel. These known and new carbon pathway auxiliary metabolic genes were recovered from a total of 22 viral metagenomes in which viral auxiliary metabolic genes were differentiated from low-level cellular DNA inputs based on small subunit ribosomal RNA gene content, taxonomy, fragment recruitment and genomic context information. Auxiliary metabolic gene distribution patterns reveal that marine viruses target overlapping, but relatively distinct pathways in sunlit and dark ocean waters to redirect host carbon flux towards energy production and viral genome replication under low nutrient, niche-differentiated conditions throughout the depth continuum.ConclusionsGiven half of ocean microbes are infected by viruses at any given time, these findings of broad viral metabolic reprogramming suggest the need for renewed consideration of viruses in global ocean carbon models.

Aquatic photodegradation of sunscreen agent p-aminobenzoic acid in the presence of dissolved organic matter

Dissolved organic matter (DOM) is an important photosensitizer for the phototransformation of organic contaminants in sunlit natural waters. This article focuses on the photolysis kinetics and mechanism of sunscreen agent p-aminobenzoic acid (PABA) in the presence of four kinds of DOM; Suwannee River fulvic acid (SRFA), Suwannee River humic acid (SRHA), Nordic Lake fulvic acid (NOFA) and Nordic Lake humic acid (NOHA). It is evident that direct photolysis of PABA is highly pH-dependent because different species of PABA have different electrical densities on the ring system. The presence of four kinds of DOM inhibits the photolysis of PABA primarily due to their light screening effect. Meanwhile, a complex interaction involving energy transfer, triplet carbonyl group induced electron transfer, and amino acid induced proton abstraction between PABA and DOM is verified by competition kinetics experiments and density functional theory (DFT) computation. In addition, DOM-induced singlet oxygen (1O2) and hydroxyl radical (OH) are determined to play an insignificant role in PABA photolysis by competition dynamics method. Photoproducts identification using solid phase extraction–liquid chromatography–mass spectrometry (SPE–LC–MS) techniques reveals that the distribution of the photoproducts could not be affected by the addition of DOM. Two photodegradation pathways of PABA are temporarily proposed, in which the di(tri)-polymerization of intermediates are the dominant pathway whereas the oxidation of amino group to nitryl followed by hydroxylation is a minor process. Our findings reveal that direct photolysis is the dominant transformation pathway of PABA in natural sunlit waters, while the presence of DOM could evidently influence such process by light screening effect, energy transfer, electron transfer and proton abstraction mechanism. The findings in this study provide useful information for understanding of interaction between DOM and organic contaminants.

TRANSFORMATION AND ALLELOPATHY OF NATURAL DISSOLVED ORGANIC CARBON AND TANNIC ACID ARE AFFECTED BY SOLAR RADIATION AND BACTERIA(1).

The aim of this study was to test whether abiotic and biotic factors may affect allelopathic properties. Therefore, we investigated how solar radiation and bacteria influence allelopathic effects of the plant-derived, polyphenolic tannic acid (TA) on microalgae. Using a block design, lake water samples with and without TA were exposed to solar radiation or kept in darkness with or without bacteria for 3 weeks. Dissolved organic carbon (DOC), specific size fractions of DOC analyzed by chromatography-organic carbon detection (LC-OCD), and concentrations of total phenolic compounds (TPC) were measured to follow the fate of TA in lake water with natural DOC exposed to photolytic and microbial degradation. DOC and TPC decreased in dark-incubated lake water with TA and bacteria indicating microbial degradation. In contrast, exposure to solar radiation of lake water with TA and bacteria did not decrease DOC. Chromatographic analyses documented an accumulation of DOC mean size fraction designated as humic substances (HS) in sunlit water samples with TA. The recalcitrance of the humic fraction indicates that photolytic degradation may contribute to a DOC less available for bacterial degradation. Subsequent growth tests with Desmodesmus armatus (Chodat) E. Hegewald showed low but reproducible difference in algal growth with lower algal growth rate cultured in photolytically and microbially degraded TA in lake water than cultured in respective dark treatments. This finding highlights the importance of photolytic processes and microbial degradation influencing allelopathic effects and may explain the high potential of allelochemicals for structuring the phytoplankton community composition in naturally illuminated surface waters.

The importance of kinetics and redox in the biogeochemical cycling of iron in the surface ocean.

It is now well established that Iron (Fe) is a limiting element in many regions of the open ocean. Our current understanding of the key processes which control iron distribution in the open ocean have been largely based on thermodynamic measurements performed under the assumption of equilibrium conditions. Using this equilibrium approach, researchers have been able to detect and quantify organic complexing ligands in seawater and examine their role in increasing the overall solubility of iron. Our current knowledge about iron bioavailability to phytoplankton and bacteria is also based heavily on carefully controlled laboratory studies where it is assumed the chemical species are in equilibrium in line with the free ion association model and/or its successor the biotic ligand model. Similarly most field work on iron biogeochemistry generally consists of a single profile which is in essence a “snap-shot” in time of the system under investigation. However it is well known that the surface ocean is an extremely dynamic environment and it is unlikely if thermodynamic equilibrium between all the iron species present is ever truly achieved. In sunlit waters this is mostly due to the daily passage of the sun across the sky leading to photoredox processes which alter Fe speciation by cycling between redox states and between inorganic and organic species. Episodic deposition events, dry and wet, are also important perturbations to iron cycling as they bring in new iron to the system and alter the equilibrium between iron species and phases. Here we utilize new field data collected in the open ocean on the complexation kinetics of iron in the surface ocean to identify the important role of weak iron binding ligands (i.e., those that cannot maintain iron in solution indefinitely at seawater pH: αFeL < αFe′) in allowing transient increases in iron solubility in response to iron deposition events. Experiments with the thermal source SOTS-1 also indicate the short term impact of this species on iron solubility also with relevance to the euphotic zone. This data highlights the roles of kinetics, redox, and weaker iron binding ligands in the biogeochemical cycling of iron in the ocean.

Trimethoprim: Kinetic and mechanistic considerations in photochemical environmental fate and AOP treatment

Trimethoprim (TMP), a bacteriostatic antibiotic, has recently been detected in wastewater and surface waters. In this study the sunlight mediated photochemical fate, and treatment using advanced oxidation and reduction (free radical) processes, have been investigated with respect to their effect on TMP. Photochemical fate, in the presence of humic acid, and advanced oxidation treatment both involve the hydroxyl radical ( OH) as one of the reactive species of interest. Another reactive oxygen species, singlet oxygen ( 1O 2), may also be important in the photochemical fate of TMP. The bimolecular reaction rate constants of TMP with 1O 2 and OH were evaluated to be (3.2 ± 0.2) × 10 6 M −1 s −1 and 8.66 × 10 9 M −1 s −1, respectively. The reaction kinetics for the sub-structural moieties of TMP, 1,2,3-trimethoxybenzene (TMBz) and 2,4-diaminoprimidine (DAP), was evaluated to facilitate an understanding of the loss mechanisms. For TMBz and DAP the reaction rate constants with 1O 2 were <1.0 × 10 4 and (3.0 ± 0.1) × 10 6 M −1 s −1, while with OH they were 8.12 × 10 9 and 1.64 × 10 9 M −1 s −1, respectively. The data suggests that the 1O 2 attacks the DAP and the OH radical attacks the TMBz moiety. However, for TMP, 1O 2 and OH reactions accounted for only ∼19% and ∼6%, of its total photodegradation, respectively. Therefore, the reaction of TMP with excited state natural organic matter is postulated as a significant degradation pathway for the loss of TMP in sunlit waters containing natural organic matter. There was no effect of pH on the direct or indirect photolysis of TMP. To complete the study for reductive treatment processes, the solvated electron reaction rates for the destruction of TMP, TMBz and DAP were also evaluated. The absolute bimolecular reaction rates obtained were, (13.6 ± 0.01) × 10 9, (6.36 ± 0.11) × 10 7 and (10.1 ± 0.01) × 10 9 M −1 s −1, respectively.

Fulvic acid mediated photolysis of ibuprofen in water

Photolysis of the non-steroidal anti-inflammatory drug ibuprofen was studied by exposure to a solar simulator in solutions of fulvic acid (FA) isolated from Pony Lake, Antarctica; Suwannee River, GA, USA; and Old Woman Creek, OH, USA. At an initial concentration of 10 μM, ibuprofen degrades by direct photolysis, but the presence of FA significantly increases reaction rates. These reactions proceeded up to 6× faster in FA solutions at lower ibuprofen concentrations (0.1 μM), but the rates are highly dependent upon DOM composition. Incomplete quenching of the reaction in the presence of isopropanol suggests that the hydroxyl radical is only partially responsible for ibuprofen’s photodegradation in FA solutions, and other reactive transients likely play an important role. Liquid chromatography-quadrupole time-of-flight mass spectrometry and NMR spectroscopy reveal the formation of multiple photoproducts, with three byproducts identified as 1-(4-isobutylphenyl)ethanol, isobutylacetophenone, and a phenol derivative. Pony Lake FA significantly increases the production of the major byproduct relative to yields produced by direct photolysis and the other two FA. Thus, the photolytic fate of ibuprofen in sunlit waters is affected by its initial concentration and the source of dissolved organic matter present.

Volcaniclastic habitats for early life on Earth and Mars: A case study from ∼3.5 Ga-old rocks from the Pilbara, Australia

Within the context of present and future in situ missions to Mars to investigate its habitability and to search for traces of life, we studied the habitability and traces of past life in ∼3.5 Ga-old volcanic sands deposited in littoral environments an analogue to Noachian environments on Mars. The environmental conditions on Noachian Mars (4.1–3.7 Ga) and the Early Archaean (4.0–3.3 Ga) Earth were, in many respects, similar: presence of liquid water, dense CO 2 atmosphere, availability of carbon and bio-essential elements, and availability of energy. For this reason, information contained in Early Archaean terrestrial rocks concerning habitable conditions (on a microbial scale) and traces of past life are of relevance in defining strategies to be used to identify past habitats and past life on Mars. One such example is the 3.446 Ga-old Kitty’s Gap Chert in the Pilbara Craton, NW. Australia. This formation consists of volcanic sediments deposited in a coastal mudflat environment and is thus a relevant analogue for sediments deposited in shallow water environments on Noachian Mars. Two main types of habitat are represented, a volcanic (lithic) habitat and planar stabilized sediment surfaces in sunlit shallow waters. The sediments hosted small (<1 μm in size) microorganisms that formed colonies on volcanic particle surfaces and in pore waters within the volcanic sediments, as well as biofilms on stabilised sediment surfaces. The microorganisms included coccoids, filaments and rare rod-shaped organisms associated with microbial polymer (EPS). The preserved microbial community was apparently dominated by chemotrophic organisms but some locally transported filaments and filamentous mat fragments indicate that possibly photosynthetic mats formed nearby. Both microorganisms and sediments were silicified during very early diagenesis. There are no macroscopic traces of fossilised life in these volcanic sediments and sophisticated instrumentation and specialized sample preparation techniques are required to establish the biogenicity and syngenicity of the traces of past life. The fact that the traces of life are cryptic, and the necessity of using sophisticated instrumentation, reinforces the challenges and difficulties of in situ robotic missions to identify past life on Mars. We therefore recommend the return of samples from Mars to Earth for a definitive search for traces of life.

Differences in carbohydrate profiles in batch culture grown planktonic and biofilm cells of Amphora rostrata Wm. Sm

Diatoms are abundant in biofilms developed on surfaces immersed in sunlit waters. In both the planktonic and the biofilm mode of growth, diatoms produce carbohydrate polymers which perform several functions including motility, protection, production of macro-aggregates and detoxification. However, little is known about the differences, if any, in the production and characterization at the molecular level of carbohydrates in planktonic and biofilm cells. In order to identify the differences in these two modes of growth, the concentration of total carbohydrates, carbohydrate fractions, neutral carbohydrates, uronic acids and amino sugars in planktonic and biofilm cells of Amphora rostrata were measured. The results showed that the distribution of carbohydrate fractions, uronic acids and amino sugars was different in biofilm and planktonic cells. Cell normalized concentrations of these components were two to five times greater in planktonic cells compared with biofilm cells. The concentrations of glucose and glucosamine decreased, whereas fucose increased in planktonic cells over the period of cultivation. Conversely, the concentrations of glucose and glucosamine increased while that of fucose decreased in attached cells. The study suggests that marked differences exist between the carbohydrates of the planktonic and the biofilm cells of A. rostrata.

Optics of sunlit water drops on leaves: conditions under which sunburn is possible

*It is a widespread belief that plants must not be watered in the midday sunshine, because water drops adhering to leaves can cause leaf burn as a result of the intense focused sunlight. The problem of light focusing by water drops on plants has never been thoroughly investigated. *Here, we conducted both computational and experimental studies of this phyto-optical phenomenon in order to clarify the specific environmental conditions under which sunlit water drops can cause leaf burn. *We found that a spheroid drop at solar elevation angle theta approximately 23 degrees, corresponding to early morning or late afternoon, produces a maximum intensity of focused sunlight on the leaf outside the drop's imprint. Our experiments demonstrated that sunlit glass spheres placed on horizontal smooth Acer platanoides (maple) leaves can cause serious leaf burn on sunny summer days. *By contrast, sunlit water drops, ranging from spheroid to flat lens-shaped, on horizontal hairless leaves of Ginkgo biloba and Acer platanoides did not cause burn damage. However, we showed that highly refractive spheroid water drops held 'in focus' by hydrophobic wax hairs on leaves of Salvinia natans (floating fern) can indeed cause sunburn because of the extremely high light intensity in the focal regions, and the loss of water cooling as a result of the lack of intimate contact between drops and the leaf tissue.

Photochemical activity and characterization of the complex of humic acids with iron(III)

This study examined the effects of humic acids (HA) and Fe(III)–HA complex on the photodegradation of atrazine, one of the most widely used herbicides. It was shown that the photolysis of atrazine proceeded via first-order reaction kinetics and that atrazine photodegradation was inhibited by the presence of HA, whereas the rate for atrazine photolysis was promoted in solutions containing both HA and Fe(III). Interactions of Fe(III) with HA were characterized by SEM, EDX, UV–Vis and FTIR, revealing that Fe(III)–HA complex was formed by ligand exchange between oxygen groups of HA and Fe(III). Using fluorescence spectrometry the stability constant ( K c) and the fraction of fluorophores available for complexation ( f) were obtained as log K c = 4.28 and f = 74%. Photoformed Fe(II) by ligand-to-metal charge-transfer (LMCT) within the Fe(III)–HA complex was the most important factor involved in photolysis of atrazine, since Fe(II) was the reactant to generate hydroxyl radical. Thus, the rate of atrazine photodegradation in natural sunlit waters is dependent on both the amount of iron present and the interaction between HA and iron.

Quantifying Interactions between Singlet Oxygen and Aquatic Fulvic Acids

Singlet oxygen (1O2) is a reactive oxygen species produced by dissolved organic matter (DOM) in sunlit waters. While the production of 1O2 by DOM has been studied, little is known on interactions between 1O2 and DOM. The central objective of this work was to quantify the rate constants of reaction and quenching of 1O2 with Suwannee River and Pony Lake fulvic acids, the terrestrial and microbial end-member reference aquatic humic substances of the International Humic Substance Society. Fulvic acids were reacted with 1O2 generated through visible light irradiation of Rose Bengal. Uptake of 1O2 by the fulvic acids was followed through changes in dissolved oxygen concentrations via membrane inlet mass spectrometry (MIMS). Results from multiple diagnostic tests for 1O2-processes in solution suggested that 64-70% of the observed uptake of oxygen by the fulvic acid solutions was due to reaction with 1O2; the remaining O2 uptake was likely due to non-1O2 processes initiated by the excited-state sensitizer. The rate constants of reaction (krxn) and physical quenching (kphys) with 1O2 were determined to be 2.6 x 10(5) M-C(-1) s(-1) and 2.7 x 10(5) M-C(1-) s(-1) (krxn) and 1.5 x 10(5) M-C(1-) s(-1) and 1.3 x 10(6) M-C(1-) s(-1) (kphys) for Suwannee River and Pony Lake fulvic acids, respectively. Results from this study demonstrated that1O2 reacts with microbially and terrestrially derived DOM at rate constants comparable to phenols, naphthols, or aromatic amines, on a per carbon basis.

Mesoscale physical–biological–biogeochemical linkages in the open ocean: An introduction to the results of the E-Flux and EDDIES programs

Mesoscale currents, fronts, and eddies are ubiquitous and energetic features of ocean circulation. These phenomena, sometimes referred to as the “internal weather of the sea,” accommodate a diverse set of physical, chemical, and biological interactions that influence marine biogeochemistry on a wide range of timescales. These biogeochemical processes include the “biological pump”, i.e. the transfer or flux of biologically produced organic matter and associated elements from the surface ocean to depth (Ducklow et al., 2001; Volk and Hoffert, 1985). Within ~ 80% of the world’s oceans, the productivity and species composition of the autotrophic organisms that contribute to the biological pump are typically limited by major nutrients (e.g. nitrogen, phosphorus, and silica), or trace metals (e.g. iron). Primary production in such oligotrophic regions therefore depends mostly on intense recycling of nutrients within the surface sunlit waters, with only a small fraction supported by that entering from the atmosphere, or from the physical transport of nutrients from nutrient-rich deep waters below. Evidence that mesoscale and submesoscale phenomena play a role in the latter process dates back more than two decades (Angel and Fasham, 1983; Franks et al., 1986; Ring Group, 1981; Tranter et al., 1980; Venrick, 1990; Woods, 1988).

BROMATE IN LOS ANGELES WATER

THE CITY OF LOS ANGELES must drain 600 million gal of water—about a day’s supply—from two reservoirs after discovering high levels of bromate, a suspected carcinogen. The bromate appears to have formed in sunlit water when chlorine oxidized bromide from groundwater. The unexpected chemistry is leading to changes in water-monitoring requirements at the local and state levels and may affect nationwide policies. Bromide often occurs naturally in water supplies and is commonly oxidized to bromate during ozone disinfection of drinking water. Water treatment plants that use ozone are therefore required to test for bromate before releasing water to distribution systems. In the LA reservoirs, however, bromate was produced spontaneously in posttreatment water stored in surface reservoirs. Neither state nor federal regulations require testing for bromate in water supplies posttreatment. The LA Department of Water & Power (LADWP) learned of the problem from a laboratory conducting tests for a commercial customer. Ge...

Photostability of Kainic Acid in Seawater

The environmental degradation of a mixture of domoic acid (DA) and kainic acid (KA) in seawater with and without added transition metals is reported. The association constants for kainic acid with Fe (III) and Cu (II) were determined using (1)H nuclear magnetic resonance (NMR; K1,Fe(III) = 2.27 x 10(12), K2,Fe(III) = 8.99 x 10(8), K1,Cu(II) = 1.38 x 10(10), and K2,Cu(II) = 4.35 x 10(7)). The photochemical half-life of kainic acid has been determined to be significantly longer (40-100 h) than that of domoic acid in corresponding marine systems (12-34 h). The significance of this finding was highlighted by a comparison of the quantification of a mixture of kainic and domoic acids during photodegradation by liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques and the widely used competitive enzyme-linked immunosorbent assay (cELISA; Biosense Laboratories) method. The MS-based analysis showed that approximately 50% of the DA was photodegraded within 15 h. In contrast, the domoic acid cELISA assay reported that the concentration essentially remained unchanged over this period. The possibility of interference from naturally occurring kainic acid during cELISA measurements could lead to the overestimation of total domoic acid, especially if they occur in mixtures in sunlit waters.

Ink utilization by mesopelagic squid

Remotely operated vehicle dive video recordings of deep-sea squid ink release were examined to determine species, ink release type, release depth, and accompanying behavior/s. Ink release was commonly observed between the surface and 1,842.1 m in Monterey Bay, CA, and surrounding waters. Six ink release types were observed: pseudomorphs, pseudomorph series, ink ropes, clouds/smokescreens, diffuse puffs and mantle fills. Each species released ink throughout all or most of its depth range; inking was not limited to shallow, sunlit waters. Individuals of each species produced one ink release type more commonly than other types, however, multiple ink types could be released by individuals of all species. Common behaviors preceded and/or followed each release type; pseudomorphs and pseudomorph series were generally associated with escape behaviors, while ink ropes, clouds, and puffs normally involved the animal remaining adjacent to or amid the ink. Deep-sea squids may use ink for defensive purposes similar to those of shallow-dwelling species when they release pseudomorphs, pseudomorph series, or large clouds, and may use ink puffs in intra-specific communication. The function of ink ropes and mantle fills is unknown.

Role of dissolved organic matter composition on the photoreduction of Cr(VI) to Cr(III) in the presence of iron.

The photochemical reduction of Cr(VI) by iron and aquatic dissolved organic matter (DOM) was investigated. DOM sampled from a number of surface waters (a eutrophic wetland, a blackwater stream, and river water from a mix-use watershed) was used in this study. Moreover, a fulvic acid from Lake Fryxell, Antarctica, was also used to represent a DOM derived from a strictly autochthonous source. Cr(VI) reduction to Cr(III) at pH 5.5 was observed for all target DOMs used in this study, but rates varied widely. In general, photoreduction rates increased with increasing iron concentrations, but the type of DOM appeared to influence the kinetics to a larger degree. The rate of reduction was significantly greater for DOM derived from terrestrial systems than from predominantly autochthonous materials even if additional iron was added to the later. A positive correlation was observed between rates of Cr(VI) photoreduction and properties of the isolated DOM samples whereby faster reduction was observed for larger more aromatic substrates. On the basis of the fast rates reported for the dark reduction of Cr(VI) to Cr(III) by Fe(II)-organic ligands, we hypothesize that the rate-limiting step in these reactions is the photoreduction of Fe(III) to Fe(II) by a ligand-to-metal charge-transfer pathway after absorption of light by Fe(III)-DOM complexes or by reduction of Fe(III) by superoxide or other intermediates formed after light absorption by DOM. Thus, the rate of Cr(VI) photoreduction to Cr(III) in natural sunlit waters is dependent upon both the amount of iron present and the nature of the dissolved organic matter substrate.

Reactions of hydroxyl radical with humic substances: bleaching, mineralization, and production of bioavailable carbon substrates.

In this study, we examine the role of the hydroxyl (OH*) radical as a mechanism for the photodecomposition of chromophoric dissolved organic matter (CDOM) in sunlit surface waters. Using gamma-radiolysis of water, OH* was generated in solutions of standard humic substances in quantities comparable to those produced on time scales of days in sunlit surface waters. The second-order rate coefficients of OH* reaction with Suwannee River fulvic (SRFA; 2.7 x 10(4) s(-1) (mg of C/L)(-1)) and humic acids (SRHA; 1.9 x 10(4) s(-1) (mg of C/L)(-1)) are comparable to those observed for DOM in natural water samples and DOM isolates from other sources but decrease slightly with increasing OH* doses. OH* reactions with humic substances produced dissolved inorganic carbon (DIC) with a high efficiency of approximately 0.3 mol of CO2/mol of OH*. This efficiency stayed approximately constant from early phases of oxidation until complete mineralization of the DOM. Production rates of low molecular weight (LMW) acids including acetic, formic, malonic, and oxalic acids by reaction of SRFA and SRHA with OH* were measured using HPLC. Ratios of production rates of these acids to rates of DIC production for SRHA and for SRFA were similar to those observed upon photolysis of natural water samples. Bioassays indicated that OH* reactions with humic substances do not result in measurable formation of bioavailable carbon substrates other than the LMW acids. Bleaching of humic chromophores by OH* was relatively slow. Our results indicate that OH* reactions with humic substances are not likely to contribute significantly to observed rates of DOM photomineralization and LMW acid production in sunlit waters. They are also not likely to be a significant mechanism of photobleaching except in waters with very high OH* photoformation rates.