Water Column Chemistry Research Articles

Evidence for a redox stratified Cryogenian marine basin, Datangpo Formation, South China

Here, in an effort to explore Cryogenian seawater chemistry, we present chemostratigraphic results for iron, carbon, molybdenum, and sulfur for two outcrop sections for the ca. 663–654Ma Datangpo Formation deposited between the two major Neoproterozoic glacial episodes (Sturtian and Marinoan) in the Nanhua Basin, South China. Paleogeographic reconstruction suggests that the interglacial Nanhua Basin was an emerging young ocean basin, which opened by rifting from ca. 820–630Ma. Seawater exchange with the open ocean was restricted; such interglacial conditions may have been a common feature throughout the region and the world in association with widespread rifted margins during global sea-level lowstands. Geochemical profiles generated for the shallow water Yangjiaping and deeper water Minle sections demonstrate broadly consistent stratigraphic variations and generally point to anoxic (mostly euxinic) deep water deposition for the lower black shales but increasing oxygenation for the upper siltstones deposited in shallower water at both sections. Fluctuations in water chemistry recorded in the Datangpo Formation can be explained by a stratified redox model in which water column chemistry was strongly controlled by Fe availability and other nutrient fluxes, low dissolved marine sulfate concentrations, sea level variation, and varying inputs of marine organic carbon delivered via primary production. A compilation of new and published sulfur isotope data for the Datangpo Formation indicates that the extremely 34S-enriched pyrite (up to 69‰) in the basal carbonates and shales was formed mainly in the deep waters of the Nanhua Basin. The most likely explanation is a 34S-enriched deep marine sulfate pool generated, in part, during the Sturtian glaciation by bacterial sulfate reduction in combination with severely suppressed riverine sulfate inputs and restriction of the marginal basin during a dramatic drop in sea level. This study highlights the importance of both global and local controls in determining the chemical conditions in Neoproterozoic marine basins.

Biomarkers, chemistry and microbiology show chemoautotrophy in a multilayer chemocline in the Cariaco Basin

The Cariaco Basin is the world's largest truly marine anoxic basin. We have conducted a comprehensive multidisciplinary investigation of the water column (42–750m) bracketing the redox boundary (a 250-m thick “chemocline”) of the Cariaco Basin to evaluate linkages between lipid biomarkers, distributions of major dissolved chemical species, and the microbial community and associated redox processes. Our multidimensional data set includes: hydrography, water column chemistry, microbial distributions and rates, and lipid biomarkers. Multivariant statistical analysis of this data set partitions the investigated water column into 5 distinct zones, each characterized by different chemistries, microbiologies and biomarker compositions. The core of this chemocline is a 25-m thick suboxic zone where both dissolved oxygen and sulfide were below detection limits, bacterial and archaeal cell numbers and the rate of chemoautotrophic (dark) carbon fixation are elevated, and dissolved chemical species and bacterial and archaeal lipid biomarkers are indicative of tightly coupled cycles of carbon, nitrogen, and sulfur through chemoautotrophy.

CO2 and CH4 fluxes across a Nuphar lutea (L.) Sm. stand

Floating-leaved rhizophytes can significantly alter net carbon dioxide (CO2) and methane (CH4) exchanges with the atmosphere in freshwater shallow environments. In particular, CH4 efflux can be enhanced by the aerenchyma-mediated mass flow, while CO2 release from supersaturated waters can be reversed by the plant uptake. Additionally, the floating leaves bed can hamper light penetration and oxygen (O2) diffusion from the atmosphere, thus altering the dissolved gas dynamics in the water column. In this study, net fluxes of CO2 and CH4 were measured seasonally across vegetated [Nuphar lutea (L.) Sm.] and free water surfaces in the Busatello wetland (Northern Italy). Concomitantly, dissolved gas concentrations were monitored in the water column and N. lutea leaf production was estimated by means of biomass harvesting. During the vegetative period (May-August), the yellow waterlily stand resulted a net sink for atmospheric carbon (from 97.5 to 110.6 g C-CO2 m-2), while the free water surface was a net carbon source (166.3 g C-CO2 m-2). Both vegetated and plant-free areas acted as CH4 sources, with an overall carbon release comprised between 71.6 and 113.3 g C-CH4 m-2. On the whole, water column chemistry was not affected by the presence of the floating leaves; moreover, no significant differences in CH4 efflux were evidenced between the vegetated and plant-free areas. In general, this study indicates that the colonization of shallow aquatic ecosystems by N. lutea might not have the same drastic effect reported for free-floating macrophytes.

Summer–winter transitions in Antarctic ponds: III. Chemical changes

AbstractObservations were made of water column chemistry in four Na-Cl dominated ponds on the McMurdo Ice Shelf from the end of January to early April in 2008. During that time the ponds went from ice-free to predominantly frozen, with only a small volume of residual hypoxic, saline liquid trapped at the base of each pond. Changes in the concentrations of inorganic solutes with time distinguished Na, Cl, Mg, K, SO4, As, U and Mn as ions and trace elements that behave mainly conservatively during freezing, from those which are affected by biological processes (removing HCO3) and the precipitation of mineral phases such as calcite (removing Ca and more HCO3). Dissolved Fe, Mo, Cu and Zn also show evidence of precipitation from the water column during freezing; geochemical speciation modelling predicts the formation of stable insoluble mineral phases such as Fe oxides and oxyhydroxides while conditions are oxic, and Fe-, Cu-, Mo- and Zn-sulphide minerals in the presence of H2S. Consequently, under winter conditions, residual liquid beneath the ice in such ponds is anticipated to be an anoxic Na-Cl brine with the capacity to develop high concentrations of toxic trace elements such as As and U.

Tidally driven water column hydro-geochemistry in a remediating acidic wetland

Managed tidal inundation is a newly evolved technique for remediating coastal acid sulphate soil (CASS) wetlands. However, there remains considerable uncertainty regarding the hydro-geochemical pathways and spatiotemporal dynamics of residual H+ and metal(loid) mobilisation into the tidal fringe surface waters of these uniquely iron-rich landscapes. Here, we examine the hydrology and water column chemistry across the intertidal slope of a remediating CASS wetland during several tide cycles. There was extreme spatial and temporal dynamism in water column chemistry, with pH fluctuating by ∼3 units (∼3.5–6.5) during a single tide cycle. Acute acidity was spatially confined to the upper intertidal slope, reflecting surface sediment properties, and tidal overtopping is an important pathway for mobilisation of residual H+ and Al3+ to the water column. Marine derived HCO3- was depleted from surface waters migrating across the intertidal slope and a strong gradient in HCO3- was observed from the tidal fringe to the adjacent tributary channel and nearby estuary. Tidal forcing generated oscillating hydraulic gradients in the shallow fringing aquifer, favouring ebb-tide seepage and driving rapid, heterogeneous advection of groundwater on the lower intertidal slope via surface connected macropores. A combination of diffusive and advective flux across the sediment–water interface led to persistent, elevated surface water Fe2+ (∼10–1000 μM). The geochemical processes associated with Fe2+ mobilisation displayed distinct spatial zonation, with low pH, proton-promoted desorption occurring on the upper intertidal slope, whilst circum-neutral pH, Fe(III)-reducing processes dominated the lower intertidal slope. Arsenic was also mobilised into surface waters on the lower intertidal slope under moderate pH (∼6.0) conditions and was strongly positively correlated with Fe2+. Saturation index values for aragonite were substantially depressed (−1 to −5) and significantly negatively correlated with elevation, thereby presenting a barrier to re-colonisation of the upper intertidal slope by calcifying benthic organisms. These findings highlight the spatially complex hydrological and geochemical controls on surface water quality that can occur in tidally inundated acid sulphate soil environments.

Hydrogen sulphide and methane emissions on the central Namibian shelf

Hydrogen sulphide occurs frequently in the waters of the inner shelf coastal upwelling area off central Namibia. The area affected coincides with hatching grounds of commercially important pelagic fish, whose recruitment may be severely affected by recurring toxic sulphidic episodes. Both episodic biogenic methane gas-driven advective and molecular diffusive flux of hydrogen sulphide have been implicated as transport mechanisms from the underlying organic-matter-rich diatomaceous mud. To test hypotheses on the controls of hydrogen sulphide transport from the sediments on the inner Namibian shelf, water column and sediment data were acquired from four stations between 27 and 72 m water depth over a 3 year long period. On 14 cruises, temperature, salinity, dissolved oxygen, nitrate, methane, and total dissolved sulphide were determined from water column samples, and pore water dissolved methane, total dissolved sulphide, biomass of benthic sulphide-oxidising bacteria Beggiatoa and Thiomargarita, and bacterial sulphate reduction rates were determined from sediment cores. Superimposed on a trend of synchronous changes in water column oxygen and nutrient concentrations controlled by regional hydrographic conditions were asynchronous small-scale variations at the in-shore stations that attest to localized controls on water column chemistry. Small temporal variations in sulphate reduction rates determined with 35S-labeled sulphate do not support the interpretation that variable emissions of sulphide and methane from sediments are driven by temporal changes in the degradation rates of freshly deposited organic matter. The large temporal changes in the concentrations of hydrogen sulphide and the co-occurrence of pore water sulphate and methane support an interpretation of episodic advection of methane and hydrogen sulphide from deeper sediment depths – possibly due to gas bubble transport. Effective fluxes of hydrogen sulphide and methane to the water column, and methane and sulphide concentrations in the bottom waters were decoupled, likely due to the activity of sulphide-oxidising bacteria. While the causal mechanism for the episodic fluctuations in methane and dissolved sulphide concentrations remains unclear, this data set points to the importance of alternating advective and diffusive transport of methane and hydrogen sulphide to the water column.

Dominance of a clonal green sulfur bacterial population in a stratified lake

For many years, the chemocline of the meromictic Lake Cadagno, Switzerland, was dominated by purple sulfur bacteria. However, following a major community shift in recent years, green sulfur bacteria (GSB) have come to dominate. We investigated this community by performing microbial diversity surveys using FISH cell counting and population multilocus sequence typing [clone library sequence analysis of the small subunit (SSU) rRNA locus and two loci involved in photosynthesis in GSB: fmoA and csmCA]. All bacterial populations clearly stratified according to water column chemistry. The GSB population peaked in the chemocline (c. 8 x 10(6) GSB cells mL(-1)) and constituted about 50% of all cells in the anoxic zones of the water column. At least 99.5% of these GSB cells had SSU rRNA, fmoA, and csmCA sequences essentially identical to that of the previously isolated and genome-sequenced GSB Chlorobium clathratiforme strain BU-1 (DSM 5477). This ribotype was not detected in Lake Cadagno before the bloom of GSB. These observations suggest that the C. clathratiforme population that has stabilized in Lake Cadagno is clonal. We speculate that such a clonal bloom could be caused by environmental disturbance, mutational adaptation, or invasion.

NOVEL HABITAT PREFERENCE OF AMMONIA "BECCARII" FORMA 1 IN A MACROBENTHOS COMMUNITY ON HARD SUBSTRATES IN THE OHASHI RIVER, SOUTHWEST JAPAN

Research Article| April 01, 2009 NOVEL HABITAT PREFERENCE OF AMMONIA “BECCARII” FORMA 1 IN A MACROBENTHOS COMMUNITY ON HARD SUBSTRATES IN THE OHASHI RIVER, SOUTHWEST JAPAN Hiroyuki Takata; Hiroyuki Takata 5 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, Matsue 690-8504, Japan.2Division of Earth Environmental System, Pusan National University, San 30, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Korea. 5Correspondence author. E-mail: yuu@pusan.ac.kr Search for other works by this author on: GSW Google Scholar David L. Dettman; David L. Dettman 3Geosciences Department, University of Arizona, 1040 E. Fourth Street, Tucson, AZ 85721, U.S.A. Search for other works by this author on: GSW Google Scholar Koji Seto; Koji Seto 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, Matsue 690-8504, Japan. Search for other works by this author on: GSW Google Scholar Kengo Kurata; Kengo Kurata 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, Matsue 690-8504, Japan. Search for other works by this author on: GSW Google Scholar Jun’ichi Hiratsuka; Jun’ichi Hiratsuka 4Shimane Research Group of Wildlife, 802-3 Saiwaicho, Matsue 690-0041, Japan Search for other works by this author on: GSW Google Scholar Boo-Keun Khim Boo-Keun Khim 2Division of Earth Environmental System, Pusan National University, San 30, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Korea. Search for other works by this author on: GSW Google Scholar Author and Article Information Hiroyuki Takata 5 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, Matsue 690-8504, Japan.2Division of Earth Environmental System, Pusan National University, San 30, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Korea. David L. Dettman 3Geosciences Department, University of Arizona, 1040 E. Fourth Street, Tucson, AZ 85721, U.S.A. Koji Seto 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, Matsue 690-8504, Japan. Kengo Kurata 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, Matsue 690-8504, Japan. Jun’ichi Hiratsuka 4Shimane Research Group of Wildlife, 802-3 Saiwaicho, Matsue 690-0041, Japan Boo-Keun Khim 2Division of Earth Environmental System, Pusan National University, San 30, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Korea. 5Correspondence author. E-mail: yuu@pusan.ac.kr Publisher: Cushman Foundation for Foraminiferal Research Received: 08 Aug 2008 Accepted: 14 Nov 2008 First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2009 Journal of Foraminiferal Research Journal of Foraminiferal Research (2009) 39 (2): 87–96. https://doi.org/10.2113/gsjfr.39.2.87 Article history Received: 08 Aug 2008 Accepted: 14 Nov 2008 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hiroyuki Takata, David L. Dettman, Koji Seto, Kengo Kurata, Jun’ichi Hiratsuka, Boo-Keun Khim; NOVEL HABITAT PREFERENCE OF AMMONIA “BECCARII” FORMA 1 IN A MACROBENTHOS COMMUNITY ON HARD SUBSTRATES IN THE OHASHI RIVER, SOUTHWEST JAPAN. Journal of Foraminiferal Research 2009;; 39 (2): 87–96. doi: https://doi.org/10.2113/gsjfr.39.2.87 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract We investigated the occurrence and isotope signature of Ammonia “beccarii” forma 1 on a bridge pier of the Ohashi River, southwest Japan, to elucidate the characteristics of benthic foraminifera on hard substrates in brackish water. Ammonia “beccarii” forma 1 occurred within the attached macrobenthos community on the bridge pier as well as on the bottom sediments of the nearby river and lake floor. Test morphology of bridge-pier specimens is similar to that of the surface-sediment specimens. A culturing study examining substrate preferences revealed that bridge-pier individuals of A. “beccarii” forma 1 most commonly attached to the body of hydrozoans, although many individuals established themselves in the sediments. Our observations suggest that the bridge-pier population is derived from the surface-sediment community, in particular, that from the river floor. Stable oxygen and carbon isotope ratios of specimens of A. “beccarii” forma 1 from the bridge pier have a smaller range than those in surface sediment from the Ohashi River and Lake Nakaumi. Stable isotope compositions of tests of A. “beccarii” forma 1 on and around the bridge pier have a weakly negative relationship between oxygen and carbon isotope ratios. This may reflect the influence of both saline bottom water and pore water within river sediments. The stable isotope composition of foraminiferal specimens from the bridge pier has a strong potential for environmental monitoring of water-column chemistry in local brackish environments. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Mercury Cycling in Stream Ecosystems. 1. Water Column Chemistry and Transport

We studied total mercury (THg) and methylmercury (MeHg) in eight streams, located in Oregon, Wisconsin, and Florida, that span large ranges in climate, landscape characteristics, atmospheric Hg deposition, and water chemistry. While atmospheric deposition was the source of Hg at each site, basin characteristics appeared to mediate this source by providing controls on methylation and fluvial THg and MeHg transport. Instantaneous concentrations of filtered total mercury (FTHg) and filtered methylmercury (FMeHg) exhibited strong positive correlations with both dissolved organic carbon (DOC) concentrations and streamflow for most streams, whereas mean FTHg and FMeHg concentrations were correlated with wetland density of the basins. For all streams combined, whole water concentrations (sum of filtered and particulate forms) of THg and MeHg correlated strongly with DOC and suspended sediment concentrations in the water column.

Anoxia over the western continental shelf of India: Bacterial indications of intrinsic nitrification feeding denitrification

Studies on the Arabian Sea coastal anoxia have been of immense interest, but despite its ecological significance there is sparse understanding of the microbes involved. Hence, observations were carried out off Goa (15 degrees 30'N, 72 degrees 40'E to 15 degrees 30'N, 72 degrees 59'E) to understand the processes that mediate the changes in various inorganic nitrogen species in the water column during anoxia. Water column chemistry showed a clear distinct oxic environment in the month of April and anoxic condition in October. Our study based on microbial signatures indicated that oxygen deficit appeared as a well-defined nucleus almost 40 km away from the coast during the oxic period (April) and spreads there after to the entire water column synchronizing with the water chemistry. Striking results of net changes in inorganic nitrogen species in nitrification blocked and unblocked experimental systems show that denitrification is the predominant process in the water column consuming available nitrate ( approximately 0.5 microM) to near zero levels within approximately 72 h of incubation. These observations have been supported by concomitant increase in nitrite concentration ( approximately 4 microM). Similar studies on denitrification-blocked incubations, demonstrate the potential of nitrification to feed denitrification. Nitrification could contribute almost 4.5 microM to the total nitrate pool. It was found that the relation between ammonium and total dissolved inorganic nitrogen (DIN) pool (r=0.98, p<0.001, n=122) was significant compared to the latter with nitrite and nitrate. The occurrence of high ammonium under low phosphate conditions corroborates our observations that ammonium does not appear to be locked under low oxygen regimes. It is suggested that ammonium actively produced by detrital breakdown (ammonification) is efficiently consumed through nitrification process. The three processes in concert viz. ammonification, nitrification and denitrification appear to operate in more temporal and spatial proximity than hitherto appreciated in these systems and this gives additional cues on the absence of measurable nitrate at surface waters, which was earlier attributed only to efficient algal uptake. Hence we hypothesize that the alarming nitrous oxide input into the atmosphere could be due to high productivity driven tighter nitrification-denitrification coupling, rather than denitrification driven by extraneous nitrate.

Seasonal and interannual variability in the taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake, Oregon

Taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake, Oregon, were examined during time periods between 1984 and 2000. The objectives of the study were (1) to investigate spatial and temporal patterns in species composition, chlorophyll concentration, and primary productivity relative to seasonal patterns of water circulation; (2) to explore relationships between water column chemistry and the taxonomic composition of the phytoplankton; and (3) to determine effects of primary and secondary consumers on the phytoplankton assemblage. An analysis of 690 samples obtained on 50 sampling dates from 14 depths in the water column found a total of 163 phytoplankton taxa, 134 of which were identified to genus and 101 were identified to the species or variety level of classification. Dominant species by density or biovolume included Nitzschia gracilis, Stephanodiscus hantzschii, Ankistrodesmus spiralis, Mougeotia parvula, Dinobryon sertularia, Tribonema affine, Aphanocapsa delicatissima, Synechocystis sp., Gymnodinium inversum, and Peridinium inconspicuum. When the lake was thermally stratified in late summer, some of these species exhibited a stratified vertical distribution in the water column. A cluster analysis of these data also revealed a vertical stratification of the flora from the middle of the summer through the early fall. Multivariate test statistics indicated that there was a significant relationship between the species composition of the phytoplankton and a corresponding set of chemical variables measured for samples from the water column. In this case, concentrations of total phosphorus, ammonia, total Kjeldahl nitrogen, and alkalinity were associated with interannual changes in the flora; whereas pH and concentrations of dissolved oxygen, orthophosphate, nitrate, and silicon were more closely related to spatial variation and thermal stratification. The maximum chlorophyll concentration when the lake was thermally stratified in August and September was usually between depths of 100 m and 120 m. In comparison, the depth of maximum primary production ranged from 60 m to 80 m at this time of year. Regression analysis detected a weak negative relationship between chlorophyll concentration and Secchi disk depth, a measure of lake transparency. However, interannual changes in chlorophyll concentration and the species composition of the phytoplankton could not be explained by the removal of the septic field near Rim Village or by patterns of upwelling from the deep lake. An alternative trophic hypothesis proposes that the productivity of Crater Lake is controlled primarily by long-term patterns of climatic change that regulate the supply of allochthonous nutrients.

Limnology of Two Antarctic Epishelf Lakes and their Potential to Record Periods of Ice Shelf Loss

George VI Ice Shelf is the largest ice shelf on the western side of the Antarctic Peninsula and its northern margin marks the southern most latitudinal limit of recent ice shelf retreat. As part of a project to reconstruct the long-term (Holocene) history of George VI Ice Shelf we studied two epishelf lakes impounded by the ice shelf at Ablation Point, on the east coast of Alexander Island. These lakes, Moutonnee and Ablation, are stratified water bodies with a lower marine layer and an upper freshwater layer. To determine if their sediment records could be used to detect past changes in the presence or absence of the ice shelf it was necessary to describe their present-day limnology and sedimentology. We measured water column chemistry and sampled the water column and sediments of the lakes along vertical and horizontal transects. We analysed these samples for diatoms, stable isotopes (δ18O, δ2H, δ13CDIC, δ13Corg), geochemistry (TOC, TN, C/N ratios) and physical sedimentology (grain-size). This was supplemented by chemical and biological reference data from the catchments. Results showed that the water columns of both lakes are nutrient limited and deficient in phytoplankton. Benthic productivity is low and decreases with depth. Comparison of water column chemistry with an earlier survey shows a net increase in the thickness of the freshwater layer in Moutonnee Lake between 1973 and 2001, which could indicate that George VI Ice Shelf has thinned during this period. However, a similar trend was not observed in Ablation Lake (5 km to the north) and an alternative explanation is that the changes are a seasonal phenomena. Data from the surface sediment transects identified a number of proxies that respond to the present day stratification of the water column including diatom species composition, stable isotopes and geochemistry, particularly in Moutonnee Lake. Collectively these data have been used to develop a conceptual model for determining past ice shelf configuration in epishelf lakes. Specifically, periods of past ice shelf loss, and the removal of the ice dam, would see the present stratified epishelf lake replaced by a marine embayment. It is suggested that this change would leave a clear signature in the lake sediment record, notably the deposition of an exclusively marine biological assemblage, increased ice rafted debris and δ13Corg values that are indicative of marine derived organic matter.

Redox processes in a eutrophic coal-mine lake

AbstractThe water column chemistry of lake St Eloy (St Eloy-les Mines, Allier, France) was monitored over a period of a year. This is a small stratified lake created by subsidence of an underground coal mine. The results show a permanent stratification and the development of two water bodies with contrasting chemistry. The superficial oxic layer (i.e. the upper 5 m) is of high water quality and the water, not affected by seasonal changes, is suitable as a source of drinking water. In contrast, the deeper layer is permanently anoxic and the waters have a conductivity which is six times greater than in the epilimnion. Due to density difference and the small size of the lake, no turn-over occurs and all elements that diffuse from bottom sediments are strongly concentrated in the hypolimnion. Arsenic concentrations are very low in the epilimnion, but they increase quickly with depth below the oxycline, to reach up to 7 μm below 8 m depth. Different solid phases could control the fate of arsenic in this lake such as gypsum for As(V) in the hypolimnion, mackinawite for As(V) and As(III) in the hypolimnion, and close to the oxycline, Fe(III) oxyhydroxides are possible hosts for both As(III) and As(V).

A mixed layer carbon budget for the GasEx‐2001 experiment

The GasEx‐2001 study took place aboard the NOAA Ship Ronald H. Brown in the eastern equatorial Pacific in February and March 2001. As part of this experiment, water column measurements were collected at noon each day near a drifting array of near‐surface instruments to examine the temporal evolution of the water column chemistry. These measurements were used to construct carbon mass balance estimates during this Lagrangian type study. Over a 13‐day period, the net drop in mixed layer dissolved inorganic carbon (DIC) was 6.5 μmol kg−1. The net precipitation during this period resulted in a DIC decrease of 1.2 μmol kg−1. Entrainment added 0.3 μmol kg−1 of DIC to the mixed layer from below giving a combined net physical effect that accounted for ∼14% of the total change. Biological new production removed 1.1 μmol kg−1 (17%) of DIC from the mixed layer. Air‐sea gas exchange had the largest impact on the DIC budget, accounting for 69% (4.5 μmol kg−1) of the total DIC removal from the mixed layer during this period. The estimated mean gas transfer velocity based on the DIC mass balance was 13.8 ± 3.6 cm hr−1 (K660 = 11.8 cm hr−1). The mean wind speed during this period was 6.0 ± 1.3 m s−1. This gas transfer velocity is in excellent agreement with estimates generated from atmospheric micro‐meteorological CO2 flux measurements collected on the same cruise. The agreement between the oceanic and atmospheric approaches supports the validity of the gas transfer velocities determined for the GasEx‐2001 experiment.

A modern vs. Permian black shale—the hydrography, primary productivity, and water-column chemistry of deposition

The sediment currently accumulating in the Cariaco Basin, on the continental shelf of Venezuela, has an elevated organic-carbon content of approximately 5%; is accumulating under O 2-depleted bottom-water conditions (SO 4 2− reduction); is composed dominantly of foraminiferal calcite, diatomaceous silica, clay, and silt; and is dark greenish gray in color. Upon lithification, it will become a black shale. Recent studies have established the hydrography of the basin and the level of primary productivity and bottom-water redox conditions. These properties are used to model accumulation rates of Cd, Cr, Cu, Mo, Ni, V, and Zn on the seafloor. The model rates agree closely with measured rates for the uppermost surface sediment. The model is applied to the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, a phosphate deposit of Permian age in the northwest United States. It too has all of the requisite properties of a black shale. Although the deposit is a world-class phosphorite, it is composed mostly of phosphatic mudstone and siltstone, chert, limestone, and dolomite. It has organic-carbon concentrations of up to 15%, is strongly enriched in several trace elements above a terrigenous contribution and is black. The trace-element accumulation defines a mean primary productivity in the photic zone of the Phosphoria Basin as moderate, at 500 g m −2 year −1 organic carbon, comparable to primary productivity in the Cariaco Basin. The source of nutrient-enriched water that was imported into the Phosphoria Basin, upwelled into the photic zone, and supported primary productivity was an O 2 minimum zone of the open ocean. The depth range over which the water was imported would have been between approximately 100 and 600 m. The mean residence time of bottom water in the basin was approximately 4 years vs. 100 years in the Cariaco Basin. The bottom water was O 2 depleted, but it was denitrifying, or NO 3 − reducing, rather than SO 4 2− reducing.

N2 production by the anammox reaction in the anoxic water column of Golfo Dulce, Costa Rica.

In oxygen-depleted zones of the open ocean, and in anoxic basins and fjords, denitrification (the bacterial reduction of nitrate to give N2) is recognized as the only significant process converting fixed nitrogen to gaseous N2. Primary production in the oceans is often limited by the availability of fixed nitrogen such as ammonium or nitrate, and nitrogen-removal processes consequently affect both ecosystem function and global biogeochemical cycles. It was recently discovered that the anaerobic oxidation of ammonium with nitrite--the 'anammox' reaction, performed by bacteria--was responsible for a significant fraction of N2 production in some marine sediments. Here we show that this reaction is also important in the anoxic waters of Golfo Dulce, a 200-m-deep coastal bay in Costa Rica, where it accounts for 19-35% of the total N2 formation in the water column. The water-column chemistry in Golfo Dulce is very similar to that in oxygen-depleted zones of the oceans--in which one-half to one-third of the global nitrogen removal is believed to occur. We therefore expect the anammox reaction to be a globally significant sink for oceanic nitrogen.

The influence of fish cage aquaculture on pelagic carbon flow and water chemistry in tidally dominated mangrove estuaries of peninsular Malaysia

The impact of floating net cages culturing the seabass, Lates calcarifer, on planktonic processes and water chemistry in two heavily used mangrove estuaries in Malaysia was examined. Concentrations of dissolved inorganic and particulate nutrients were usually greater in cage vs. adjacent (≈100 m) non-cage waters, although most variability in water-column chemistry related to water depth and tides. There were few consistent differences in plankton abundance, production or respiration between cage and non-cage sites. Rates of primary production were low compared with rates of pelagic mineralization reflecting high suspended loads coupled with large inputs of organic matter from mangrove forests, fishing villages, fish cages, pig farms and other industries within the catchment. Our preliminary sampling did not reveal any large-scale eutrophication due to the cages. A crude estimate of the contribution of fish cage inputs to the estuaries shows that fish cages contribute only ≈2% of C but greater percentages of N (32–36%) and P (83–99%) to these waters relative to phytoplankton and mangrove inputs. Isolating and detecting impacts of cage culture in such heavily used waterways—a situation typical of most mangrove estuaries in Southeast Asia—are constrained by a background of large, highly variable fluxes of organic material derived from extensive mangrove forests and other human activities.

Integrative assessment of benthic macroinvertebrate community impairment from metal‐contaminated waters in tributaries of the upper Powell River, Virginia, USA

Benthic macroinvertebrate communities of the North Fork Powell River (NFP), southwest Virginia, USA, appear to be impacted by aluminum (Al) and iron (Fe) from acid mine drainage (AMD) beyond the zone of pH depression. As part of a watershed restoration project, we used integrative techniques, including water column, sediment, and in situ toxicity tests; sediment and water column chemistry; and habitat assessments, to detect AMD impacts. An analysis of variance, least significant difference post hoc test, and Spearman correlations were used to test the sensitivity of these integrative techniques to detect various (acidic or neutralized) levels of AMD input and to determine the mode of impairment (metal-contaminated sediments or water) to the benthic macroinvertebrate community. Benthic macroinvertebrate indices were the most sensitive endpoint to AMD inputs and were significantly correlated (p < or = 0.05) with water column metal concentrations in in situ and water column toxicity tests. Sediment chemistry and toxicity did not detect AMD impacts and were not significantly correlated with benthic macroinvertebrate indices. These results suggest that the primary mode of impairment to the benthic macroinvertebrate communities beyond the zone of pH depression were waterborne Al and Fe.

Phytoplankton phosphorus deficiency and alkaline phosphatase activity in the McMurdo Dry Valley lakes, Antarctica

We assessed the nutrient (N, P) deficiency of phytoplankton from the perennially iceߚcovered lakes in Taylor Valley, Antarctica, with 14Cߚbased bioassays. Phytoplankton in the nearߚsurface waters from three of the four lakes displayed elevated photosynthetic carbon assimilation in the presence of added P relative to controls. Carbon assimilation in samples from deep chlorophyll layers was also enhanced by P addition in two of the lakes. No effect of N addition without simultaneous P addition was noted in any lake. Lake Bonney nearߚsurface phytoplankton consistently showed a strong response to P and N + P additions, suggesting P deficiency. The nearߚsurface phytoplankton of Lake Hoare responded to N + P but not N or P addition alone, suggesting a more general nutrient deficiency. Further investigation of phytoplankton phosphorus deficiency was carried out in the east lobe of Lake Bonney and in Lake Hoare. Water column dissolved and sestonic elemental ratios and planktonic alkaline phosphatase activity measurements corroborated the results of the bioassays. Despite the proximity of the lakes and their similarity in ice cover and watershed, a high degree of phytoplankton phosphorus deficiency was evident in Lake Bonney but not in Lake Hoare. We hypothesize that the difference in the degree of phytoplankton P deficiency between these lakes may not be due to differences in external P fluxes, but rather to differences in the internal cycling of phosphorus stemming from large differences in water column chemistry.

Sediment nutrient characteristics and aquatic macrophytes in lowland English rivers

Aquatic macrophytes play an important role in the nutrient dynamics of streams. As a result, there is much interest in their use as trophic indicators. However, the relationship between aquatic macrophytes and the trophic status of rivers is a complex one, partly because of the effects of a wide range of environmental variables and partly because submerged, rooted macrophytes can absorb nutrients from the river sediments and/or the water column. Experiments which have tried to establish the relative importance of sediments or water as sources of nutrients are inconclusive and further work is needed to establish how sediment nutrient characteristics vary within and among rivers (spatially and temporally) and the inter-relationships between sediment nutrients, water column chemistry and macrophytes. This paper presents the initial findings from a study of 17 lowland rivers in southern England which is exploring the spatial variability of sediment characteristics (total and inorganic phosphorus, total nitrogen, organic carbon, silt–clay fraction and organic matter content) and the relationship with aquatic macrophytes. The preliminary analysis indicates that although sediment characteristics are highly variable within 100-m river reaches, the variability across the 17 rivers is even greater; this is despite the limited geographic and trophic range of the study sites. The results presented in this paper also give some indication of the sediment characteristics associated with five macrophyte species but it is too early to ascribe sediment preferences for particular species.