Non-conservative Behavior Research Articles

An improved method for the simultaneous analysis of phenolic and steroidal estrogens in water and sediment

This paper describes an improved method for the extraction and analysis of seven endocrine disrupting chemicals with wide-ranging polarities from water and sediments using gas chromatography–tandem mass spectrometry (GC–MS/MS). The analytes were 4- tert-octylphenol, 4-nonylphenol, bisphenol A, estrone, 17β-estradiol, 17α-ethynylestradiol and 16α-hydroxyestrone. The optimised GC–MS/MS method produces increased selectivity and sensitivity compared to GC–MS, with limit of detection ranging from 0.01 to 0.49 ng L −1 in water and from 0.05 to 0.14 ng g −1 in sediment. Extraction from aqueous samples was performed by solid-phase extraction (SPE) and from sediment samples by microwave-assisted extraction (MAE). The improved method for the clean-up of sediment extracts carried out by SPE enhanced EDC recovery (86–102%) while reducing matrix interference and sample drying time. Derivatisation of final sample extracts was achieved using N, O-bis(trimethylsilyl)trifluoroacetamide and pyridine, and their stability was enhanced by reconstituting the derivatised extracts with hexane. The method was validated by spiking experiments which showed good recovery and reproducibility. The method was applied to samples taken from the Medway estuary in Kent, UK, where non-conservative behaviour of EDCs was demonstrated.

Dissolved organic matter accumulation, reactivity, and redox state in ground water of a recharge wetland

Ground water beneath the seasonal swamp of the Okavango Delta, a recharge wetland in northwestern Botswana, is known to be a sink for solutes. In this study, measurements of organic carbon and inorganic ion concentrations, as well as UV-visible and fluorescence spectroscopy, were used to examine dissolved organic matter (DOM) storage and redox state of fulvic acids in ground water beneath an island and riparian woodland. Increasing dissolved organic carbon (DOC) concentrations along the ground-water flowpath suggests an accumulation of DOM in ground water, especially beneath island centers. However, the increase in DOC concentration was relatively less than the increase in chloride and sulfate concentrations, indicating non-conservative behavior of DOM in ground water beneath wetland islands. In combination with a decrease in fulvic acid content and specific UV absorbance, this result suggests that preferential sorption or destabilization of more aromatic organic compounds may be occurring under conditions of high pH and salinity. Finally, the increase in reduced fluorescence components (semiquinone- and hydroquinone-like components) along the ground-water flowpath strongly supports the transition to reduced fulvic acids in ground water of island centers. The reactivity and potential electron-shuttling function of fulvic acids may play an important role in the dissolution of metal oxides and associated DOM-iron-arsenic interactions in ground water of this recharge wetland.

Estuarine capacity in removal of trace metals from contaminated river water, Southern Caspian Sea

AbstractIn the present investigation, the flocculation of dissolved Cd, Cu, Ni, Pb, Mn and Zn with initial concentrations of 1, 2.5 and 5 mg/L in Tadjan River water during mixing with the Caspian Sea water has been studied in order to determine estuarine capacity to remove dissolved metals in the accidental contamination of the river. The flocculation process was investigated on a series of mixtures with salinities ranging from 0.1 to 11 p.p.t. The flocculation rates were indicative of the nonconservative behaviour of Cd, Cu, Ni, Pb, Mn and Zn during estuarine mixing. The order of the final flocculation rate of dissolved metals at 1, 2.5 and 5 mg/L of initial metal concentrations in the river water is as follows:Cu (99%)>Cd (95%)>Zn (88%)>Mn (85%)>Pb (83%)>Ni (73%), Cu(95.6%)>Pb(92.4%)>Cd (90%)>Zn(88.4%)>Mn (81.6%)>Ni(78.8%) and Cd (100%)>Cu(88%)>Ni (85.2%)>Pb (84%)>Zn (83.2%)>Mn (81.2%), respectively. The results also revealed that removal of dissolved metals is not influenced by pH changes and precipitation processes. The flocculation rates revealed that the overall dissolved metal pollution loads may be reduced to about 70% up to about more than 90% during estuarine mixing of Tadjan River with the Caspian Sea water.

Sorption and desorption characteristics of the dye tracer, Brilliant Blue FCF, in sandy and clay soils

Abstract Dye tracers are widely used for tracing and visualising hydrological flow paths in soils. Despite evidence of non-conservative behaviour (i.e. sorption) in recent years, Brilliant Blue FCF continues to be used extensively for dye tracing in soil. However, previous studies have not considered hysteresis in the sorption mechanism. The objectives of this study were (1) to test the hypothesis that sorption of Brilliant Blue FCF on soils with widely contrasting textures could be described with a single sorption isotherm based solely on sorption by the clay fraction and (2) to determine whether desorption hysteresis is likely to confound the estimation of retardation factor in modelling dye transit through soil. We measured the sorption and desorption of Brilliant Blue on four soils of contrasting texture, ranging from a light sand to a heavy clay, and resolved a single Freundlich sorption isotherm for the clay fraction in all soils. An attempt to include silt and humus fractions as additional adsorbents with independent Freundlich parameters was unsuccessful. The sorption of Brilliant Blue FCF on the four soils studied was not fully reversible; there was apparent sorption–desorption hysteresis in all cases. Therefore, even though the sorption strength of Brilliant Blue in soils might be less than that of other dye tracers, it is possible that the visualised flow pathways may not accurately reflect those of water in soil. From this we suggest that Brilliant Blue may not be well suited for all forms of dye tracing in clay soils and it is therefore crucial that the specific environmental conditions, soil type, dye concentration and objectives of the study are considered each time when choosing the appropriate dye tracer.

Behavior of Cu, Zn, Pb, Ni and Mn during mixing of freshwater with the Caspian Sea water

Behavior of metals during estuarine mixing can significantly influence the chemical mass balance between rivers and seas or lakes. Present investigation describes the results of mixing of a sample of filtered (0.45 μm) Caspian Sea water with a filtered water sample taken from the Babolrud River in 9 different salinity proportions. Flocculation of colloidal size fraction of heavy metals was investigated on a series of mixtures with water salinities ranging from 1.5 to 9.5‰ during mixing of the Babolrud River with the Caspian Sea water. The flocculation trend of Cu (77.9%) > Zn (74.6%) > Mn (64.97%) > Pb (38.2%) > Ni (12.2%) indicates that Cu, Zn, Pb and Mn have non-conservative behavior and Ni has relatively conservative behavior during estuarine mixing. The highest flocculation of heavy metals occurs between the salinities of 1.5–3.5‰. Statistical analysis indicates that the flocculation of Cu is governed by pH and PO 4. The flocculation rate of the studied metals showed that the overall colloidal metal pollution loads can be reduced by various percentages (ranging from as low as 12 to as high as 78) during estuarine mixing.

Surface complexation effects on phosphate adsorption to ferric iron oxyhydroxides along pH and salinity gradients in estuaries and coastal aquifers

Non-conservative behavior of dissolved inorganic phosphate (DIP) in estuaries is generally ascribed to desorption from iron and aluminum (hydr)oxides with increasing salinity. Here, we assess this hypothesis by simulating the reversible adsorption of phosphate onto a model oxide (goethite) along physico-chemical gradients representative of surface and subsurface estuaries. The simulations are carried out using a surface complexation model (SCM), which represents the main aqueous speciation and adsorption reactions of DIP, plus the ionic strength-dependent coulombic interactions in solution and at the mineral–solution interface. According to the model calculations, variations in pH and salinity alone are unlikely to explain the often reported production of DIP in surface estuaries. In particular, increased aqueous complexation of phosphate by Mg 2+ and Ca 2+ ions with increasing salinity is offset by the formation of ternary Mg-phosphate surface complexes and the drop in electrical potential at the mineral–water interface. However, when taking into account the downstream decrease in the abundance of sorption sites, the model correctly simulates the observed release of DIP in the Scheldt estuary. The sharp increase in pH accompanying the admixing of seawater to fresh groundwater should also cause desorption of phosphate from iron oxyhydroxides during seawater intrusion in coastal aquifers. As for surface estuaries, the model calculations indicate that significant DIP release additionally requires a reduction in the phosphate sorption site density. In anoxic aquifers, this can result from the supply of seawater sulfate and the subsequent reductive dissolution of iron oxyhydroxides coupled to microbial sulfate reduction.

Iron isotope fractionation in subterranean estuaries

Dissolved Fe concentrations in subterranean estuaries, like their river-seawater counterparts, are strongly controlled by non-conservative behavior during mixing of groundwater and seawater in coastal aquifers. Previous studies at a subterranean estuary of Waquoit Bay on Cape Cod, USA demonstrate extensive precipitation of groundwater-borne dissolved ferrous iron and subsequent accumulation of iron oxides onto subsurface sands. Waquoit Bay is thus an excellent natural laboratory to assess the mechanisms of Fe-isotope fractionation in redox-stratified environments and determine potential Fe-isotope signatures of groundwater sources to coastal seawater. Here, we report Fe isotope compositions of iron-coated sands and porewaters beneath the intertidal zone of Waquoit Bay. The distribution of pore water Fe shows two distinct sources of Fe: one residing in the upward rising plume of Fe-rich groundwater and the second in the salt-wedge zone of pore water. The groundwater source has high Fe(II) concentration consistent with anoxic conditions and yield δ 56Fe values between 0.3 and −1.3‰. In contrast, sediment porewaters occurring in the mixing zone of the subterranean estuary have very low δ 56Fe values down to −5‰. These low δ 56Fe values reflect Fe-redox cycling and result from the preferential retention of heavy Fe-isotopes onto newly formed Fe-oxyhydroxides. Analysis of Fe-oxides precipitated onto subsurface sands in two cores from the subterranean estuary revealed strong δ 56Fe and Fe concentration gradients over less than 2m, yielding an overall range of δ 56Fe values between −2 and 1.5‰. The relationship between Fe concentration and δ 56Fe of Fe-rich sands can be modeled by the progressive precipitation of Fe-oxides along fluid flow through the subterranean estuary. These results demonstrate that large-scale Fe isotope fractionation (up to 5‰) can occur in subterranean estuaries, which could lead to coastal seawater characterized by very low δ 56Fe values relative to river values.

Silver in Tokyo Bay estuarine waters and Japanese rivers

Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg−1, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg−1). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients for silver throughout the estuary (log Kd > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y−1 and 15 kg y−1, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged within the Tokyo Bay estuary.

Occurrence of Contaminant Accumulation in Lead Pipe Scales from Domestic Drinking-Water Distribution Systems

Previously, contaminants, such as AI, As, and Ra, have been shown to accumulate in drinking-water distribution system solids. Accumulated contaminants could be periodically released back into the water supply causing elevated levels at consumers taps, going undetected by most current regulatory monitoring practices and consequently constituting a hidden risk. The objective of this study was to determine the occurrence of over 40 major scale constituents, regulated metals, and other potential metallic inorganic contaminants in drinking-water distribution system Pb (lead) or Pb-lined service lines. The primary method of analysis was inductively coupled plasma-atomic emission spectroscopy, following complete decomposition of scale material. Contaminants and scale constituents were categorized by their average concentrations, and many metals of potential health concern were found to occur at levels sufficient to result in elevated levels at the consumer's taps if they were to be mobilized. The data indicate distinctly nonconservative behavior for many inorganic contaminants in drinking-water distribution systems. This finding suggests an imminent need for further research into the transport and fate of contaminants throughout drinking-water distribution system pipes, as well as a re-evaluation of monitoring protocols in order to more accurately determine the scope and levels of potential consumer exposure.

Behavior of Uranium in the Yellow River Plume (Yellow River Estuary)

The Yellow River (Huanghe) is the second largest river in China and is known for its high turbidity. It also has remarkably high levels of dissolved uranium (U) concentrations (up to 38 nmol l(-1)). To examine the mixing behavior of dissolved U between river water and seawater, surface water samples were collected along a salinity gradient from the Yellow River plume during September 2004 and were measured for dissolved U concentration, U-234:U-238 activity ratio, phosphate (PO43-), and suspended particulate matter. Laboratory experiments were also conducted to simulate the mixing process in the Yellow River plume using unfiltered Yellow River water and filtered seawater. The results showed a nonconservative behavior for dissolved U at salinities < 20 with an addition of U to the plume waters estimated at about 1.4 X 10(5) mol yr(-1). A similarity between variations in dissolved U and PO43- with salinity was also found. There are two major mechanisms, desorption from suspended sediments and diffusion from interstitial waters of bottom sediments, that may cause the elevated concentrations of dissolved U and PO43- in mid-salinity waters. Mixing experiments indicate that desorption seems more responsible for the elevated dissolved U concentrations, whereas diffusion influences more the enrichment of PO43-.

How widespread and important is N2 fixation in the North Atlantic Ocean?

The spatial extent of N2 fixation in the Atlantic Ocean is examined by determining the isotopic composition of N in suspended particulate organic nitrogen (δ15N PONsusp). The samples were collected from zonal and meridional transects of the Atlantic Ocean during a 3‐year period. There is a consistent depleted δ15N PONsusp signal extending over the center of the northern subtropical gyre, which partly coincides with a region where the tracer N* increases westward following the gyre circulation. This nonconservative behavior of N* implies that N2 fixation is responsible for the depleted δ15N PONsusp. A mixing model suggests that N2 fixation over parts of the northern gyre provides up to 74% of the N utilized by phytoplankton. However, since the PONsusp represents only a small fraction of the total N pool, N2 fixation probably only plays a minor role in supplying new N to the euphotic zone in the surface waters of the northern subtropical gyre.

Depth distributions of alkalinity, TCO2 and at SEATS time-series site in the northern South China Sea

Abstract In this study, measurements of titration alkalinity (TA), total dissolved carbon dioxide (TCO2), and δ13C of TCO2 ( δ 13 C TCO 2 ) throughout the water column at the SouthEast Asian time-series study (SEATS) site were investigated in order to understand better the fundamental processes controlling their vertical distributions in the South China Sea (SCS). The linear correlations between TA and salinity in the shallow waters, as identified by the mixing line between the surface water and salinity maximum water suggested the predominant control of physical mixing on the variability of TA. In contrast, TCO2 and δ 13 C TCO 2 showed the non-conservative behavior in the respective TCO2 and δ 13 C TCO 2 vs. salinity plot due to the effect of biological production. A stoichiometric model further showed that the depth profile of NTA (=TA×salinity/35) largely reflects the increase of preformed NTA in the shallow waters, whereas carbonate dissolution was responsible for the continuous increase of NTA in the deep waters. A one-dimensional diffusion–advection model further revealed that the carbonate dissolution could account for 28% of NTCO2 (=TCO2×salinity/35) increase in deep waters, and the remaining 72% of NTCO2 was from organic decomposition. Calculation of excess TA further showed that it emerged well above the aragonite and calcite saturation depths at 600 and 2500 m, respectively, indicating that some biologically, chemically, and physically-mediated processes must be involved to provide excess TA into the shallow waters. The decrease in δ 13 C TCO 2 with depth primarily resulted from organic decomposition. The influence of anthropogenic CO2 throughout the water column was assessed with the carbon chemistry and the isotope-based approach in this study. Both methods obtained nearly the same results in which the signal of anthropogenic CO2 decreased exponentially with depth, and its penetration depth were found to be at ∼1000 m. The inventory of anthropogenic CO2 in the water column was estimated to be ∼16.6 mol C m−2, which was less than that reported in the northwest Pacific at the same latitude, presumably due to the enhanced upwelling in the SCS. Such an anthropogenic CO2 penetration had led to decreases of the saturation levels of aragonite and calcite by 17% and 14%, respectively, in the surface water, and an upward migration of aragonite saturation depth by ∼100 m since industrial revolution.

Nitrate production beneath a High Arctic glacier, Svalbard

Natural environmental isotopes of nitrate and ammonium are used in conjunction with major ion chemistry and hydrological data to establish controls upon the biogeochemical cycling of nitrogen beneath a High Arctic polythermal glacier (Midtre Lovénbreen). Here, high nitrate concentrations in subglacial meltwaters suggest that the subglacial environment may be furnishing nitrate in excess of that released from the snowpack and glacier ice. Isotopic values of δ 18O NO 3 suggest the provenance of such excess nitrate to be microbial in origin and δ 15N NO 3 indicates the source nitrogen compounds to have high δ 15N values relative to supraglacial runoff. We address the nitrification of supraglacial ammonium, the mineralization of organic nitrogen and the oxidation of geologic ammonium as potential sources of this additional nitrate. Mass fluxes of N compounds in a subglacial river and their δ 15N ratios indicate that the nitrification of supraglacial ammonium delivered to the glacier bed can account for much, but not all, of the excess nitrate. The additional source most likely involves the mineralization of organic nitrogen, although δ 15N values in rock samples suggest that the dissolution of rock-derived ammonium cannot be discounted if large fractionation effects occur during dissolution. Our results therefore agree with previous catchment scale mass balance studies at the site, which report a major internal loss of NH 4 + from the snowpack following melt. However, at the catchment scale, the NH 4 + loss is greater than the excess of NO 3 − observed in runoff, indicating that microbial assimilation of ammonia into organic matter in a range of other habitats is also likely. The identification of NH 4 +assimilation and nitrification further highlights the non-conservative behaviour of nitrogen in glacial environments and testifies to the importance of microbially-mediated reactions in the biogeochemical cycling of nitrogen in an environment that has, until recently, been regarded as biologically inert.

Flocculation of heavy metals during mixing of freshwater with Caspian Sea water

Flocculation of colloidal size fraction for Cu, Zn, Pb, Ni and Mn was investigated on a series of mixtures with water salinities ranging from 1.5 to 9.5‰ during mixing of Haraz River with the Caspian Sea water. The flocculation trend of Zn (85.5%) > Mn (55.2%) > Cu (39.6%) > Pb (33.7%) > Ni (11.3%) indicates that Cu, Zn, Pb and Mn have non-conservative behavior and Ni has relatively conservative behavior during estuarine mixing. Highest flocculation of heavy metals occurs between salinities of 1.5 and 4.5‰. Statistical analysis indicates that the flocculation of Cu, Zn and Ni is governed by pH and total nitrogen.

The tracing of riverine U in Arctic seawater with very precise 234U/ 238U measurements

The riverine flux of U that enters the deep oceans is not well constrained since the net losses during estuarine mixing are difficult to quantify. Riverine-dissolved U normally has a higher 234U/ 238U activity ratio ( 234U/ 238U ar) than the uniform value that characterizes open ocean seawater and could be used as a tracer of riverine inputs if one could resolve subtle variations in seawater composition. Using new mass spectrometry techniques we achieve a long-term reproducibility ± 0.3‰ on 234U/ 238U ar which permits the tracing of riverine U in seawater samples from the Arctic – a partially restricted basin that is ideal for such a study. We find that surface waters from the Arctic basins carry elevated 234U/ 238U ar when compared with deep ocean seawater. Samples from the Canada Basin have a significant freshwater component and provide evidence that the Mackenzie River loses ∼ 65% of its U in the Mackenzie shelf/estuary zone before entering the deeper basin. This is in contrast to samples from the Makarov Basin, which provide evidence that all of the freshwater input is derived from the major Yenisey River alone, despite the proximity of the Lena and Ob Rivers. The differing behaviour of U between the Mackenzie and Yenisey Rivers is most likely a consequence of the strong binding of U to dissolved organic matter (DOC) or secondary phases in these rivers. The Yenisey River appears to transport the majority of the DOC through the shelf and into the Makarov Basin. In contrast, the Mackenzie River appears to lose a significant amount of DOC (> 50%) in the estuary/shelf zone, which may lead to loss of associated U. These findings offer a more detailed picture of the fresh riverine water flow patterns in the Arctic Ocean when compared to other geochemical proxies. The non-conservative behaviour of U in the Mackenzie River through the shelf/estuaries has important implications for U input into oceans and the total marine budget.

Solar and Tidal Modulations of Fecal Indicator Bacteria in Coastal Waters at Huntington Beach, California

The coastal waters at many beaches in California and the United States are afflicted with fecal pollution, which poses a health risk for people exposed to the water through recreational activities such as swimming, surfing, and diving. Identifying sources of pollution is complicated by oceanographic transport/mixing processes and the nonconservative behavior of microorganisms exposed to sunlight and hostile marine conditions. This article investigates the variation of fecal indicator bacteria (FIB) concentrations in the surf zone and the adjacent coastal marsh by applying autocorrelation and cross-correlation analyses that illustrate solar and tidal modulations. A steady state bioreactor model was developed to explain solar inactivation in the surf zone, whereas a dynamic model was applied to explain tidally influenced disturbances in the coastal marsh. These models applied to intensive monitoring datasets on FIB and environmental variables have provided insights into the biologic and physical processes controlling coastal water quality, specifically the influence of sunlight and tides on bacterial levels.

The conservative and non-conservative behavior of chromophoric dissolved organic matter in Chinese estuarine waters

The spectral absorption properties of chromophoric dissolved organic matter (CDOM) and their distributions in two Chinese estuaries, the Yangtze River Estuary and the Jiulong River Estuary, were studied during August 2003 (wet season) and during different seasons between 2003−2005, respectively. The CDOM concentrations ( a 355) of fresh end members in the Jiulong River Estuary varied seasonally, while its quality remained relatively stable. However, the a 355 of the marine end members exhibited less variability. Application of a conservative mixing model indicated that CDOM behaved conservatively in the Yangtze River Estuary. No photobleaching removal was observed at high salinity region of this estuary. Although CDOM showed conservative behavior for many cruises in the Jiulong River Estuary, there was evidence for removal in the low salinity regions during some cruises. Laboratory mixing experiments and a salt addition experiment suggested that particle sorption of CDOM maybe the possible reason for the removal. These results showed that absorption properties of CDOM can be used as a tool to observe the quantitative and qualitative dynamics of DOM during estuarine mixing.

Concentration level of dissolved cadmium and its variation in surface seawater of Urasoko Bay, Ishigaki Island

From April 2005 to March 2006, the concentration of dissolved cadmium (Cd) was monitored in the surface seawater of Urasoko Bay, which is in a subtropical area of the North Pacific Ocean and is surrounded by a well-developed fringing reef. During this period, the observed salinity and Cd concentrations varied in a range of approximately 16–34.5 and 4.8–77.8 pM, respectively. The concentration range of Cd obtained in this study was considered to be too low to damage the coral species, and its variation throughout the year did not show any seasonality and was not connected with climate data. The Cd-salinity plot for all the data in the salinity range over 26 showed apparent non-conservative behavior, which suggests a possible irregular input of Cd from a solid phase through streams and groundwater, release from bottom sediments, and atmospheric deposition into the bay.

Non-conservative behaviour of molybdenum in coastal waters: Coupling geochemical, biological, and sedimentological processes

Non-conservative behaviour of dissolved Mo was observed during specific time periods in the water column of the Wadden Sea of NW Germany. In July 2005 dissolved Mo declined within 36 h from a level only slightly below seawater (82 nM) to a minimum value of 30 nM, whereas in August 2002 dissolved Mo revealed a tidal cyclicity with maximum values up to 158 nM at low tide. In contrast, cruises in August 2003 and 2004 displayed an almost conservative behaviour of Mo. The decrease in dissolved Mo during July 2005 and elevated values in August 2002 were accompanied by Mo enrichments on aggregates in the water column of the Wadden Sea. Along with Mo, dissolved Mn showed unusual concentration patterns in July 2005, with values distinctly below the common summer level (by a factor of five). A direct relation between the loss of Mo and scavenging by freshly formed MnO x phases could not be inferred from our data because both metals revealed inverse patterns. Parallel to decreasing dissolved Mo concentrations dissolved Mn showed an increasing trend while particulate Mn decreased. Such finding is compatible with the formation of oxygen-depleted zones in aggregates, which provide suitable conditions for the rapid fixation of Mo and parallel release of Mn by chemically and/or microbially mediated processes. Our assumption is supported by biological (e.g. number of aggregate-associated bacteria) and sedimentological (e.g. aggregate abundance and size) parameters. The production of organic components (e.g. TEP) during breakdown of an algae bloom in July 2005 led to the formation of larger Mo-enriched aggregates, thus depleting the water column in dissolved Mo. After deposition on and incorporation into sandy tidal flats these aggregates are rapidly decomposed by microbial activity. Pore water profiles document that during microbial decomposition of these aggregates, substantial amounts of Mo are released and may replenish and even enrich Mo in the open water column. We postulate a conceptual model for the observed non-conservative behaviour of Mo in coastal waters, which is based on the tight coupling of geochemical, biological, and sedimentological processes.

Colored dissolved organic matter in Tampa Bay, Florida

Absorption and fluorescence of colored dissolved organic matter (CDOM) and concentrations of dissolved organic carbon (DOC), chlorophyll and total suspended solids in Tampa Bay and its adjacent rivers were examined in June and October of 2004. Except in Old Tampa Bay (OTB), the spatial distribution of CDOM showed a conservative relationship with salinity in June, 2004 ( a CDOM(400) = − 0.19 × salinity + 6.78, R 2 = 0.98, n = 17, salinity range = 1.1–32.5) with little variations in absorption spectral slope and fluorescence efficiency. This indicates that CDOM distribution was dominated by mixing. In October, 2004, CDOM distribution was nonconservative with an average absorption coefficient ( a CDOM(400), ∼ 7.76 m − 1 ) about seven times higher than that in June (∼ 1.11 m − 1 ). The nonconservative behavior was caused largely by CDOM removal at intermediate salinities (e.g., a CDOM(400) removal > 15% at salinity ∼ 13.0), which likely resulted from photobleaching due to stronger stratification. The spatial and seasonal distributions of CDOM in Tampa Bay showed that the two largest rivers, the Alafia River (AR) and Hillsborough River (HR) were dominant CDOM sources to most of the bay. In OTB, however, CDOM showed distinctive differences: lower absorption coefficient, higher absorption spectral slopes, and lower ratios of CDOM absorption to DOC and higher fluorescence efficiency. These differences may have stemmed from (1) changes in CDOM composition by more intensive photobleaching due to the longer residence time of water mass in OTB; (2) other sources of CDOM than the HR/AR inputs, such as local creeks, streams, groundwater, and/or bottom re-suspension. Average CDOM absorption in Tampa Bay at 443 nm, a CDOM(443), was about five times higher in June and about ten times higher in October than phytoplankton pigment absorption, a ph(443), indicating that blue light attenuation in the water column was dominated by CDOM rather than by phytoplankton absorption throughout the year.