Increase In Particulate Organic Carbon Research Articles

The seasonality of the concentration of endocrine phenolic compounds in the matter attached to the surface of microplastics

Rapid biofilm formation on microplastic (MP) surfaces in marine environments and the tendency of hydrophobic pollutants to bioaccumulate may increase the exposure of organisms to ingested plastics and transport pollutants far from their sources. The role of the matter attached to MPs (MaM) in the interactions between MPs and other pollutants in marine environments is poorly understood. This paper studies pollutant sorption in MaM for three phenolic endocrine-disrupting chemicals (EDCs): bisphenol A (BPA), 4-tert-octylphenol (4-t-OP), and 4-nonylphenol (4-NP). Polypropylene (PP), expanded polystyrene (EPS), and polylactide (PLA) MPs were exposed to an environment conducive to biofouling (Vistula Lagoon, Baltic Sea) for four weeks in summer, spring, and winter. The concentrations of EDCs in MaM and the suspended particulate matter (SPM) were similar and were 2–3 orders of magnitude higher than those in water and sediment. The type and morphology of the polymers were less significant for determining the concentrations of EDCs in MaM than the season. The concentrations were higher in the growing season than in winter. EDCs increased linearly with the increase in particulate organic carbon. The relationships between organic carbon partition coefficients and octanol/water partition coefficients indicate that hydrophobic partitioning into organic matter was the dominant mechanism of 4-t-OP and 4-NP binding in MaM and in SPM. For BPA, additional sorption mechanisms seem to be significant. In addition to the direct sorption from ambient water, the binding of phytoplankton-derived particles, most probably via attachment to extracellular polymeric substances, appears to be a source of EDCs in MPs. Rough estimates showed that the largest load of particulate matter and EDCs was attached to expanded polystyrene. This study suggests that the potential negative impacts of MPs on the environment are seasonal and that low-density porous plastics can be particularly effective carriers of large EDC loads.

Low biodegradability of particulate organic carbon mobilized from thaw slumps on the Peel Plateau, NT, and possible chemosynthesis and sorption effects

Abstract. Warming and wetting in the western Canadian Arctic are accelerating thaw-driven mass wasting by permafrost thaw slumps, increasing total organic carbon (TOC) delivery to headwater streams by orders of magnitude primarily due to increases in particulate organic carbon (POC). Upon thaw, permafrost carbon entering and transported within streams may be mineralized to CO2 or re-sequestered into sediments. The balance between these processes is an important uncertainty in the permafrost–carbon–climate feedback. Using aerobic incubations of TOC from streams affected by thaw slumps we find that slump-derived organic carbon undergoes minimal (∼ 4 %) oxidation over a 1-month period, indicating that this material may be predominantly destined for sediment deposition. Simultaneous measurements of POC and dissolved organic carbon (DOC) suggest that mineralization of DOC accounted for most of the TOC loss. Our results indicate that mobilization of mineral-rich tills in this region may protect carbon from mineralization via adsorption to minerals and promote inorganic carbon sequestration via chemolithoautotrophic processes. With intensification of hillslope mass wasting across the northern permafrost zone, region-specific assessments of permafrost carbon fates and inquiries beyond organic carbon decomposition are needed to constrain drivers of carbon cycling and climate feedbacks within stream networks affected by permafrost thaw.

Deoxygenation in Marginal Seas of the Indian Ocean

This article describes oxygen distributions and recent deoxygenation trends in three marginal seas – Persian Gulf and Red Sea in the Northwestern Indian Ocean (NWIO) and Andaman Sea in the Northeastern Indian Ocean (NEIO). Vertically mixed water column in the shallow Persian Gulf is generally well-oxygenated, especially in winter. Biogeochemistry and ecosystems of Persian Gulf are being subjected to enormous anthropogenic stresses including large loading of nutrients and organic matter, enhancing oxygen demand and causing hypoxia (oxygen < 1.4 ml l–1) in central and southern Gulf in summer. The larger and deeper Red Sea is relatively less affected by human activities. Despite its deep water having remarkably uniform thermohaline characteristics, the central and southern Red Sea has a well-developed perennial oxygen minimum at mid-depths. The available data point to ongoing deoxygenation in the northern Red Sea. Model simulations show that an amplified warming in the marginal seas of the NWIO may cause an intensification of the Arabian Sea oxygen minimum zone (OMZ). Increases in particulate organic carbon and decreases in oxygen contents of the outflows may also have a similar effect. In the Andaman Sea, waters above the sill depth (∼1.4 km) have characteristics similar to those in the Bay of Bengal, including an intense OMZ. As in the case of the Bay of Bengal, oxygen concentrations within the Andaman Sea OMZ appear to have declined slightly but significantly between early 1960s and 1995. The exceedingly isothermal and isohaline water that fills the deep Andaman Basin is also remarkably homogenous in terms of its oxygen content. A very slight but statistically significant decrease in oxygen content of this water also seems to have occurred over three decades preceding 1995. New information is badly needed to assess the extent of further change that may have occurred over the past 25 years. There have been some reports of coastal “dead zones” having developed in the Indian Ocean marginal seas, but they are probably under-reported and the effects of hypoxia on the rich and diverse tropical ecosystems – coral reefs, seagrasses, and mangroves – in these seas remain to be investigated.

Divergent responses of soil organic carbon accumulation to 14 years of nitrogen addition in two typical subtropical forests

Developing an understanding of the response of soil organic carbon (SOC) to N addition is critical to quantify and predict the terrestrial carbon uptake under increasing N deposition in the future. However, results from field studies on the response of SOC content and composition to N addition are highly variable across different ecosystems. The interpretation of SOC responses to N addition are often complicated by the differences in climate, soil substrate and other factors. To address this question, we measured SOC and its components in adjacent broadleaved and coniferous subtropical forests after 14 years of N addition. SOC in the top 50 cm increased by 2.1 kg m−2, 1.8 kg m−2 and 1.2 kg m−2 for low, medium and high rates of N addition in the broadleaved forest, but did not change significantly in the coniferous forest. Increased SOC in the broadleaved forest was contributed by the significant increases in particulate organic carbon (POC), humus organic carbon (HOC) in the 0–10 cm and 30–50 cm soil layers and resistant organic carbon (ROC) in the 0–10 cm soil layer. 13C nuclear magnetic resonance (NMR) spectra of coarse SOC revealed a decrease in easily decomposed carbon (C) and a shift in recalcitrant C. The increased SOC accumulation in the broadleaved forest was largely driven by altered rates of organic matter decomposition, rather than C inputs to soil. Land-history and low nutrient availability may have contributed to the lack of significant impact of N addition on SOC in the coniferous forest. Our results suggested the different controls of SOC accumulation and less sensitivity of SOC chemical composition at the molecular level to N addition in the two subtropical forest soils.

Aggregate Stability under Long-Term Fertilization Practices: The Case of Eroded Ultisols of South-Central China

Soil aggregate stability is an important aspect of soil function and health. Fertilization could potentially alter soil properties and thereby affect aggregate stability. To determine which fertilizer is useful for improving soil fertility and stabilizing soil aggregates and thereby reducing soil erodibility, we examined three types of fertilizer, and measured how soil organic carbon, carbohydrates, and related soil properties influenced aggregate stability in eroded Ultisols. Treatments included control (CK), mineral fertilizer nitrogen (N), phosphorus (P), potassium (K) (NPK), fertilizer NPK plus straw (NPKS), and farmyard manure (FYM). Aggregate stability was tested according to Le Bissonnais method, involving three disruptive tests: fast wetting (FW), slow wetting (SW), and mechanical breakdown (WS). Total organic carbon, particulate organic carbon, mineral-associated carbon, and cold-water-soluble carbohydrate, hot-water-soluble carbohydrate, and dilute acid hydrolysable carbohydrate were measured, as well as soil intrinsic properties (including pH, bulk density, iron and aluminum oxides). The 12-year fertilization had a larger effect on aggregate stability and related soil properties in a 0–15 cm soil layer, whereas no effect was evident at a soil depth of 15–40 cm. MWD (mean weight diameter) under the three tests decreased with increasing soil depth. Fertilization, especially farmyard manure evidently improved MWDFW and MWDWS at a depth of 0–15 cm. Slaking was the main mechanism of aggregate breakdown in Ultisols studied, followed by mechanical breakdown. Correlation analysis showed that MWDFW and MWDWS at a depth of 0–15 cm increased with the increase of particulate organic carbon, total organic carbon, hot-water-soluble carbohydrate and pH. Furthermore, their interaction with amorphous iron oxides enhanced aggregate stability against slaking or, with amorphous aluminum oxides, modified aggregate stability against mechanical breakdown. Consequently, particulate organic carbon was the dominant cementing agent for aggregation in Ultisols studied, and its combination with pH, amorphous aluminum oxides, amorphous iron oxides, and free aluminum oxides play a synergetic role in stabilizing soil aggregate. Accordingly, farmyard manure or fertilizer NPK plus straw improved soil fertility and the ability to resist slaking.

Climatological temporal and spatial distributions of nutrients and particulate matter in the Ross Sea

The distributions of nutrients, chlorophyll (chl), particulate organic carbon (POC), particulate organic nitrogen (PON), and biogenic silica (BSi) were compiled from 42 cruises to the Ross Sea continental shelf to generate a monthly climatology. Nutrients were elevated in spring and removal began in early spring (November) and continued through December, at which time nitrate and phosphate removal largely ceased. Silicic acid concentrations also began to decrease in November, but continued throughout the summer. Chlorophyll concentrations increased simultaneously with nitrate removal and became maximal in December, after which time they decreased. Concentrations of chlorophyll remained relatively low and constant through February, although smaller regions remained elevated and contributed to the expected substantial spatial variability. Particulate organic carbon and nitrogen concentrations paralleled chlorophyll concentrations through the spring maximum, and also decreased in early summer. However, a notable increase in particulate organic carbon occurred later in summer that was largely independent of chlorophyll changes, resulting in a dramatic rise of POC:chl ratios. Biogenic silica concentrations were low through December but continued to increase throughout summer. We suggest that the spring pigment and particulate matter concentrations resulted from phytoplankton blooms dominated by the haptophyte Phaeocystis antarctica, consistent with repeated observations in the region. We further suggest that the late summer POC increase was due to growth of diatoms that exhibited enhanced POC:chl ratios due to iron limitation. POC concentrations in late summer were similar to those in spring, indicating that the summer bloom was substantial. Estimates of productivity from a bio-optical model using variable POC:chl ratios suggest that the summer blooms may be a significant contributor to seasonal productivity, and that estimates of productivity based on satellite pigments underestimate annual production by at least 70%. Satellite productivity estimates have substantial uncertainties in the Ross Sea and need to be constrained using in situ constituent ratios.

Carbon and nitrogen fractions and stocks under 41 years of chemical and organic fertilization in a sub-humid tropical rice soil

Effects of different fertilizers and manure on dynamics of soil organic carbon (SOC) and nitrogen fractions and their stock changes remains unclear under intensively cultivated rice soil profile. Profile soil samples in six treatments viz. control, nitrogen (N), nitrogen-phosphorus-potassium (NPK), farm yard manure (FYM), N+FYM and NPK+FYM were collected from a long term fertilizer experiment continuing since 1969 at ICAR-NRRI, Cuttack, India to study the soil organic carbon and nitrogen fractions (particulate organic carbon, POC; microbial biomass carbon, MBC; particulate organic nitrogen, PON; and microbial biomass nitrogen, MBN) and SOC sequestration. Results from the study revealed that in the control treatment, where no manure or chemical fertilizer was applied,the bulk density was highest. Balanced fertilization and combined use of chemical fertilizers and manure for 41 years increased the SOC in all the plots except the unfertilized control as compared with the initial value (6.6g/kg). Balanced fertilization (NPK) and integrated fertilization (NPK+FYM) resulted in similar increases in particulate organic carbon, carbon mineralization and microbial biomass carbon, whereas particulate organic nitrogen, nitrogen mineralization and microbial biomass nitrogen were more in integrated fertilization (NPK+FYM) compared with control treatment. Soil organic C and nitrogen stocks changed positively across the fertilizer and manure treatments over the control. In the control plot, at 0–15cm depth the soil carbon and nitrogen stock was 15.1 and 1.77Mgha−1, respectively which increased to the 19.5Mgha−1 in NPK+FYM for carbon and 2.25Mgha−1 in N+FYM for nitrogen. As compared to the initial (13.7Mgha−1), the SOC stock in 0–15cm depth increased under all the fertilized treatments during 41year period in the order: NPK+FYM>N+FYM>NPK>FYM>N>control. The rate of increase in SOC (carbon sequestration) due to fertilizer application alone varied between 57 and 89kgha−1yr−1, while for FYM addition the rate of increase was 61 to 138kgha−1yr−1, highest being in NPK+FYM. Correlation coefficients between different soil organic C and N fractions indicate differential accumulation pattern of organic C and nitrogen in different depths. Based on crop yield and C storage, integrated fertilization of chemical fertilizers and manure proved to be the best for improving crop productivity and SOC sequestration.

Influence of Major Storm Events on the Quantity and Composition of Particulate Organic Matter and the Phytoplankton Community in a Subtropical Estuary, Texas

Variations in the freshwater inflow regimes of estuaries due to perturbations, such as storm events, alter the source and composition of particulate organic matter (POM) and the phytoplankton community, which are key links in estuarine carbon and nitrogen cycling. To evaluate the impact of varying freshwater discharge on POM quantity and composition and the phytoplankton community, monthly samples of surface water were collected at four long-term monitoring stations from 2012-2015 in a subtropical estuarine system, the Mission-Aransas Estuary, Texas (USA). This system is characterized by a semiarid climate, drought, and sporadic precipitation events. We analyzed organic carbon and nitrogen content, carbon and nitrogen stable isotopes, and chlorophyll a and accessory pigments of the POM samples. Following a prolonged dry spell (2012-2015), consecutive major storm events in spring 2015 led to a dramatic freshening of the entire estuary. Large increases in particulate organic carbon (POC) concentrations and decreases in δ13C values of POC over several weeks following the storms suggest an increase in in-situ production at lower salinities as a result of increased freshwater inflow. These changes in bulk POM coincided with an increase in chlorophyll a concentration, further indicating a significant contribution by phytoplankton to the elevated POM. Concurrently, pigment biomarkers revealed a significant (10-fold) increase in the cyanobacterial pigment, zeaxanthin, and further 16S rRNA analysis showed that Cyanobium spp. was responsible for the observed bloom. The combination of environment conditions, including freshening, high temperature, and high nutrients, likely contributed to the cyanobacteria bloom. These results show that episodic rain events can substantially affect estuarine phytoplankton community composition, which impacts the available energy resources for secondary production and thus may have ecosystem-wide implications on productivity.

Horizontal and Vertical Distributions of Transparent Exopolymer Particles (TEP) in the NW Mediterranean Sea Are Linked to Chlorophyll a and O2 Variability.

Transparent Exopolymer Particles (TEP) are relevant in particle and carbon fluxes in the ocean, and have economic impact in the desalination industry affecting reverse osmosis membrane fouling. However, general models of their occurrence and dynamics are not yet possible because of the poorly known co-variations with other physical and biological variables. Here, we describe TEP distributions in the NW Mediterranean Sea during late spring 2012, along perpendicular and parallel transects to the Catalan coast. The stations in the parallel transect were sampled at the surface, while the stations in the perpendicular transect were sampled from the surface to the bathypelagic, including the bottom nepheloid layers. We also followed the short-term TEP dynamics along a 2-day cycle in offshore waters. TEP concentrations in the area ranged from 4.9 to 122.8 and averaged 31.4 ± 12.0 μg XG eq L−1. The distribution of TEP measured in transects parallel to the Catalan Coast correlated those of chlorophyll a (Chla) in May but not in June, when higher TEP-values with respect to Chla were observed. TEP horizontal variability in epipelagic waters from the coast to the open sea also correlated to that of Chla, O2 (that we interpret as a proxy of primary production) and bacterial production (BP). In contrast, the TEP vertical distributions in epipelagic waters were uncoupled from those of Chla, as TEP maxima were located above the deep chlorophyll maxima. The vertical distribution of TEP in the epipelagic zone was correlated with O2 and BP, suggesting combined phytoplankton (through primary production) and bacterial (through carbon reprocessing) TEP sources. However, no clear temporal patterns arose during the 2-day cycle. In meso- and bathypelagic waters, where phytoplanktonic sources are minor, TEP concentrations (10.1 ± 4.3 μg XG eq l−1) were half those in the epipelagic, but we observed relative TEP increments coinciding with the presence of nepheloid layers. These TEP increases were not paralleled by increases in particulate organic carbon, indicating that TEP are likely to act as aggregating agents of the mostly inorganic particles present in these bottom nepheloid layers.

Sustained Biogeochemical Impacts of Wildfire in a Mountain Lake Catchment

Wild and prescribed fires can cause severe deterioration in water quality, including increases in sediment, nutrients and dissolved organic carbon (DOC). Due to the unpredictability of wildfires, few studies have been able to employ before-after, control-intervention experimental designs, or to evaluate fire-induced water-quality changes in the context of long-term datasets. Here, we present data from a lake draining a moorland catchment in the United Kingdom, part of a 22-site, 25 year monitoring network, which experienced a major wildfire in 2011. The main water-quality response was a large, sustained increase in nitrate concentrations, sufficient to raise acidity and aluminium concentrations, effectively reversing over a decade of recovery from the effects of acid deposition. Concurrently, we observed a clear reduction in DOC concentrations, contrasting with prescribed fire studies from similar ecosystems (none based on before-after studies) that have suggested that burning causes DOC to increase. However, data from a downstream water supply reservoir do suggest a fire-induced change in DOC quality towards more soil-derived aromatic organic compounds, and lake sediment data suggest a large increase in particulate organic carbon. We conclude that the biogeochemical responses to wildfire in our moorland catchment were broadly similar to those observed in forest ecosystems elsewhere, but that historically high nitrogen deposition has made the ecosystem particularly susceptible to nitrate leaching and (re-)acidification. The observed reduction in DOC concentrations casts some doubt on the widely held view that prescribed burning in moorland systems has contributed to long-term DOC increases.

Short-term effects of grazing intensity and nitrogen fertilization on soil organic carbon pools under perennial grass pastures in the southeastern USA

Pasture management can have important implications on the amounts and long-term stability of soil organic carbon (SOC). We investigated the short-term impacts of grazing intensity and nitrogen (N) fertilization levels on C dynamics into the various SOC pools in rotationally stocked ‘Tifton 85’ bermudagrass (Cynodon spp.) pastures. Treatments consisted of three grazing intensities (based on target postgraze stubble heights of 8, 16, and 24 cm) and three levels of N fertilization (50, 150, and 250 kg N ha−1 yr−1). Soil samples (0- to 20-cm depth) were taken prior to imposing treatments and at the end of the 2-yr study. Grazing intensity and N levels had no effect on bulk SOC and N concentration and content. Greater stubble height and rate of N fertilizer resulted in a linear increase in particulate organic carbon (POC) and C and N concentration in the <53-μm particle-size fraction. Grazing intensity and N fertilization showed significant effects on δ13C values and the relative amounts of C3-C vs. C4-C. The δ13C data indicated that readily decomposable C components (C4-derived C) were lost in response to more intensive grazing (stubble height of 8 cm). Results demonstrated that POC and C associated with <53 μm particle-size fraction were sensitive indicators of short-term impacts of pasture management strategies on SOC. Further studies are warranted to examine the long-term impacts of grassland management on SOC pools in sandy soils of subtropical regions.

Evidence of prokaryotic metabolism on suspended particulate organic matter in the dark waters of the subtropical North Atlantic

The distribution of prokaryotic abundance (PA), respiratory activity (ETS), heterotrophic production (PHP), and suspended particulate (POM) and dissolved (DOM) organic matter was determined in the meso- and bathypelagic waters of the (sub)tropical North Atlantic. PA decreased by one order of magnitude from the lower euphotic zone to the bathypelagic waters, while ETS decreased by two and PHP by three orders of magnitude. On a section following the Mid-Atlantic Ridge from 35u Nt o 5uN, ETS below 1000-m depth increased southwards up to three-fold. This latitudinal gradient in the deep waters was paralleled by a six-fold increase in Particulate Organic Carbon (POC), whereas no trend was apparent in the DOM distribution. Significant correlations between POM and ETS were obtained in the water masses between 1000-m and 3000-m depth, the Antarctic Intermediate Water and the North East Atlantic Deep Water. A strong imbalance in the dark ocean was found between prokaryotic carbon demand (estimated through two different approaches) and the carbon sinking flux derived from sediment-trap records corrected with 230 Th. The imbalance was greater when deeper in the water column, suggesting that the suspended carbon pool must account for most of the carbon deficit. Our results, together with other recent findings discussed in this paper, indicate that microbial life in the dark ocean is likely more dependent on slowly sinking or buoyant, laterally advected suspended particles than hitherto assumed.

Effect of nutrient availability on carbon and nitrogen incorporation and flows through benthic algae and bacteria in near-shore sandy sediment

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 49:165-180 (2007) - DOI: https://doi.org/10.3354/ame01142 Effect of nutrient availability on carbon and nitrogen incorporation and flows through benthic algae and bacteria in near-shore sandy sediment Perran L. M. Cook1,3,*, Bart Veuger2, Simone Böer1, Jack J. Middelburg2 1Max Planck Institute for Marine Microbiology, Celsiusstr 1, Bremen 28359, Germany 2Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands 3Present address: Water Studies Centre, Monash University, Clayton, 3800 Victoria, Australia *Email: perran.cook@sci.monash.edu.au ABSTRACT: Carbon and nitrogen uptake in a microbial community comprising bacteria and microalgae in a sandy marine sediment under nutrient-limited and -replete conditions was studied using a mesocosm approach. After 2 wk of incubation, a pulse of H13CO3– and 15NH4+ was added to the mesocosms, and subsequent uptake of 13C and 15N by bacteria and microphytobenthos (MPB) was traced by analysis of 13C and 15N incorporation into hydrolysable amino acids, including the bacterial biomarker d-alanine. The results confirm that MPB communities are capable of sustained high rates of photosynthesis despite nutrient limitation. Under these conditions cellular growth stops (as defined by the synthesis of chlorophyll a and amino acids) and the carbon fixed under such conditions consists predominantly of carbohydrates produced through ‘overflow metabolism’. In the treatment with nutrient addition, algal growth was stimulated and label incorporation was more balanced, with carbohydrates accounting for a much smaller fraction of newly fixed organic carbon. There was close agreement between net C fixation based on O2 fluxes and the increase of particulate organic carbon in the sediment under both nutrient-limited and -replete conditions. This finding suggests that very little fixed C was lost to the water column as dissolved organic carbon (DOC), consistent with direct measurements of DOC release using 14C. There was a significant and rapid transfer of 13C from the MPB to bacterial biomass in both treatments within 24 h of label addition, revealing that fixed carbon excreted by MPB was rapidly utilised by bacteria. In both treatments, bacteria incorporated a significant fraction of 15N from 15NH4+, with the greatest incorporation being observed under nutrient-limited conditions. KEY WORDS: Amino acid · Isotope label · Nitrogen · Carbon · Algae · Bacteria · Sediment · Excretion Full text in pdf format PreviousNextCite this article as: Cook PLM, Veuger B, Böer S, Middelburg JJ (2007) Effect of nutrient availability on carbon and nitrogen incorporation and flows through benthic algae and bacteria in near-shore sandy sediment. Aquat Microb Ecol 49:165-180. https://doi.org/10.3354/ame01142 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 49, No. 2. Online publication date: November 15, 2007 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2007 Inter-Research.

The sensitivity of minimum oxygen concentrations in a fjord to changes in biotic and abiotic external forcing

We investigated the possible biotic and abiotic causes of the observed long‐term decrease of oxygen minimum concentrations in the deep water of Gullmar Fjord. Physical factors explained about 40% of the decreased minimum oxygen concentrations since the 1950s. The North Atlantic Oscillation and more regional climate variations account for an important part of this change. The effect of the climate variations was mainly on the timing of the renewal of the basin water. The consumption rate of oxygen in the basin water has increased by 50% since the 1950s. This biotic effect explained about 60% of the decrease in minimum oxygen concentrations. The likely dominating source of oxygen‐consuming matter was (remote) production in the Skagerrak, suggesting that there has been a long‐term increase of particulate organic carbon in the Skagerrak water.

Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment

Comparison of eight iron experiments shows that maximum Chl a, the maximum DIC removal, and the overall DIC/Fe efficiency all scale inversely with depth of the wind mixed layer (WML) defining the light environment. Moreover, lateral patch dilution, sea surface irradiance, temperature, and grazing play additional roles. The Southern Ocean experiments were most influenced by very deep WMLs. In contrast, light conditions were most favorable during SEEDS and SERIES as well as during IronEx‐2. The two extreme experiments, EisenEx and SEEDS, can be linked via EisenEx bottle incubations with shallower simulated WML depth. Large diatoms always benefit the most from Fe addition, where a remarkably small group of thriving diatom species is dominated by universal response of Pseudo‐nitzschia spp. Significant response of these moderate (10–30 μm), medium (30–60 μm), and large (&gt;60 μm) diatoms is consistent with growth physiology determined for single species in natural seawater. The minimum level of “dissolved” Fe (filtrate &lt; 0.2 μm) maintained during an experiment determines the dominant diatom size class. However, this is further complicated by continuous transfer of original truly dissolved reduced Fe(II) into the colloidal pool, which may constitute some 75% of the “dissolved” pool. Depth integration of carbon inventory changes partly compensates the adverse effects of a deep WML due to its greater integration depths, decreasing the differences in responses between the eight experiments. About half of depth‐integrated overall primary productivity is reflected in a decrease of DIC. The overall C/Fe efficiency of DIC uptake is DIC/Fe ∼ 5600 for all eight experiments. The increase of particulate organic carbon is about a quarter of the primary production, suggesting food web losses for the other three quarters. Replenishment of DIC by air/sea exchange tends to be a minor few percent of primary CO2 fixation but will continue well after observations have stopped. Export of carbon into deeper waters is difficult to assess and is until now firmly proven and quite modest in only two experiments.

Biogenic emissions and gaseous precursors to forest aerosols

Measurements of ambient monoterpenes, sulphur dioxide, nitric acid, ammonia and particulate organic carbon were made in a Scots pine forest in southern Finland as part of the BIOFOR (Biogenic aerosol formation in the boreal forest) project in the summer of 1998 and spring of 1999. Scots pine branch emission measurements were made with the chamber technique for selected days. Steady state −OH and NO·3concentrations were calculated and source terms for the production of secondary and condensable gases from the oxidation of terpenes and of SO2 were determined. The purpose of the project was to investigate the source of new particles (nucleation events) observed at the site. Forest emission rates of monoterpenes were not found to be exceptionally high prior to or during the occurrence of events. Neither the relative composition of the monoterpene emission nor that of the forest concentrations showed significant deviations prior to or during event periods. Source terms for secondary organic compounds were only slightly higher (weakly significant) on event days as compared to non-event days and did not correlate to maxima in ultra-fine particle concentrations on event days. Nucleation events were not observed during nighttime when the production of secondary organic compounds, and probably of secondary organic aerosol was greatest. Thus, we conclude that the oxidation products of the terpenes were not the nucleating species observed at Hyytiälä. Correlations between nocturnal increases in particulate organic carbon and the source term for secondary organic compounds indicate that the increase could have been due to condensation processes if the aerosol yield was at least 10–15%. Sulphur dioxide and NH3 concentrations, as well as the H2SO4 source term were significantly higher during event periods, and the H2SO4 source term together with the NH3 concentration correlated well with the daily maxima in ultra-fine particle number concentrations. The results indicate that SO2 and NH3 were involved in the mechanism for nucleation events at Hyytiälä. The H2SO4 source term was not high enough to account for the entirety of the observed growth rate of the new particles. A substantial part of the growth ought to have been due to condensation of secondary organic material from the oxidation of terpenes. The data indicate that a secondary organic aerosol yield on the order of 10% would suffice.

Biogenic emissions and gaseous precursors to forest aerosols

Measurements of ambient monoterpenes, sulphur dioxide, nitric acid, ammonia and particulate organic carbon were made in a Scots pine forest in southern Finland as part of the BIOFOR (Biogenic aerosol formation in the boreal forest) project in the summer of 1998 and spring of 1999. Scots pine branch emission measurements were made with the chamber technique for selected days. Steady state −OH and NO·3concentrations were calculated and source terms for the production of secondary and condensable gases from the oxidation of terpenes and of SO2 were determined. The purpose of the project was to investigate the source of new particles (nucleation events) observed at the site. Forest emission rates of monoterpenes were not found to be exceptionally high prior to or during the occurrence of events. Neither the relative composition of the monoterpene emission nor that of the forest concentrations showed significant deviations prior to or during event periods. Source terms for secondary organic compounds were only slightly higher (weakly significant) on event days as compared to non-event days and did not correlate to maxima in ultra-fine particle concentrations on event days. Nucleation events were not observed during nighttime when the production of secondary organic compounds, and probably of secondary organic aerosol was greatest. Thus, we conclude that the oxidation products of the terpenes were not the nucleating species observed at Hyytiälä. Correlations between nocturnal increases in particulate organic carbon and the source term for secondary organic compounds indicate that the increase could have been due to condensation processes if the aerosol yield was at least 10–15%. Sulphur dioxide and NH3 concentrations, as well as the H2SO4 source term were significantly higher during event periods, and the H2SO4 source term together with the NH3 concentration correlated well with the daily maxima in ultra-fine particle number concentrations. The results indicate that SO2 and NH3 were involved in the mechanism for nucleation events at Hyytiälä. The H2SO4 source term was not high enough to account for the entirety of the observed growth rate of the new particles. A substantial part of the growth ought to have been due to condensation of secondary organic material from the oxidation of terpenes. The data indicate that a secondary organic aerosol yield on the order of 10% would suffice.

Partition of copper between dissolved and particulate phases using aluminum oxide as an aquatic model phase: effects of pH, solids and organic matter

The sorption of copper ions from aqueous solutions onto modified aluminum oxide was investigated as a function of pH, solids concentration and both particulate and dissolved organic matter. The aluminum oxide studied was modified by adsorption of humic acid. The pH value, organic matter content, and solids concentration dominated copper adsorption onto modified aluminum oxide. The adsorption of copper increased with increasing pH. An increase in particulate organic carbon resulted in an enhanced copper uptake. The partition coefficient (Kd) of copper decreased as the solids concentration increased. Copper partitioning was maximal in the neutral pH range and decreased at either low or high pH values. There was also a decrease in copper adsorption with increasing dissolved organic matter concentration.

Trace metal associations in the water column of South San Francisco Bay, California

Spatial distributions of copper (Cu), zinc (Zn) and cadmium (Cd) were followed along a longitudinal gradient of dissolved organic carbon (DOC) in South San Francisco Bay (herein referred to as the South Bay). Dissolved Cu, Zn and Cd concentrations ranged from 24 to 66 nM, from 20 to 107 nM and from 1·2 to 4·7 nM, respectively, in samples collected on five dates beginning with the spring phytoplankton bloom and continuing through summer,1985. Dissolved Cu and Zn concentrations varied indirectly with salinity and directly with DOC concentration which ranged from 2·1 to 4·1 mg l −1. Available thermodynamic data strongly support the hypothesis that Cu speciation may be dominated by association with dissolved organic matter. Analogous control of Zn speciation by organic complexation was, however, not indicated in our computations. Computed free ion activity estimates for Cu, Zn and Cd were of the order of 10 −10, 10 −8 and 10 −10 M, respectively. The availability of these metals may be among the factors regulating the growth of certain phytoplankton species within this region of the estuary. In contrast to dissolved Cu, dissolved Cd was directly related to the concentration of suspended particulate matter, suggesting a source of dissolved Cd coincident with elevated particle concentrations in the South Bay (e.g. runoff and solute desorption). Consistent with work in other estuaries, partitioning of all three trace metals onto suspended particulates was negatively correlated with salinity and positively correlated with increases in particulate organic carbon associated with the phytoplankton bloom. These results for the South Bay indicate that sorption processes influence dissolved concentrations of these trace metals, the degree of this influence varies among metals, and processes controlling metal distribution in this estuary appear to be more element-specific than spatially- or temporally-specific.

Relations Between Annual Dredging Activities, Suspended Matter Concentrations, and the Development of the Tidal Regime in the Ems Estuary

This paper challenges Kühl and Mann's suggestion (1973) that an increase in organic matter in the Ems Estuary between 1950 and 1970 caused a five- to tenfold increase in the turbidity in that period. Their hypothesis is refuted because: (a) during that period the discharge of organic matter via both the River Ems and the River Westerwoldsche A did not change significantly; (b) the increase in particulate organic carbon in the western Dutch Wadden Sea and possibly also in the Ems Estuary resulting from eutrophication of the North Sea by the River Rhine during 1950–70 is unlikely to have been more than twofold; and (c) Secchi-disc data do not support the five- to tenfold increase in turbidity. It is suggested that dredging is probably responsible for the increase in turbidity because the volume of material dredged annually increased fourfold between 1950 and 1970. The mean annual concentration of suspended matter increased by a factor ranging from 1.3 to 2.1 between 1954 and the period 1970 to 1979. The fluctuations in concentrations of suspended matter showed a statistically significant correlation with the distance dredged annually and not with the volume dredged annually. This indicated that the relation depended more on how "extensive" rather than on how "intensive" the dredging was. The fluctuations in concentrations of suspended matter are caused by the intensified erosion and sedimentation cycle that is initiated after the local natural equilibrium between channel morphology and current pattern is disturbed. This explanation is supported by the morphological changes that occurred in part of the study area between 1975 and 1979. Further support for this hypothesis was found in the changes of the tidal regime in the estuary. It is postulated that the complete cessation of dredging would probably be accompanied by the concentrations of suspended solids falling from the 1979 levels to values nearer those obtained in 1954. The biological implications of the processes described are discussed.Key words: dredging, suspended matter, tidal regime, Ems Estuary, turbidity