Organic Matter Partitioning Research Articles

Controls on labile and stabilized soil organic matter during long-term ecosystem development

A better understanding of factors controlling the distribution of soil organic matter (SOM) in differently stabilized pools in soils during ecosystem development is essential to more efficiently manage soil as a C sink and aid global warming mitigation. We, thus, investigated C and N stocks in bulk soil and differently stabilized soil fractions (free particulate organic matter (fPOM), micro- and macroaggregates, and mineral-associated organic matter (MAOM)), in seven chronosequences comprising primary and secondary successions at various locations in Europe and tested the influence of multiple environmental parameters on these C and N stocks.Best-subset multiple regression indicated that plant litter production and succession age were of minor importance. Above a certain threshold of organic matter inputs to the soil, changes in the quantity of such inputs may have little direct effect on the partitioning of organic matter to various soil fractions. Instead, biophysicochemical soil properties (such as pH and PLFA and clay contents) were the best predictors for both C and N stocks. We also found a shift in the relevance of biotic and abiotic factors from fPOM and the various aggregate fractions to MAOM, the latter being exclusively associated with pH and the clay content. This indicates that sites dominated by MAOM likely more slowly react to management interventions, such as increasing or diversifying organic matter inputs, than sites dominated by fractions more responsive to biotic factors, such as fPOM. Finally, as compared to primary successions, secondary successions were associated with higher C and N stocks in aggregate fractions, pointing towards better conditions for soil structure formation in the latter. Our results highlight the need to elucidate the form in which C and N exist in the soil for selection of proper management strategies and that soil biophysicochemical parameters may have a disparately larger impact on the partitioning of C and N to variously stabilized soil fractions than the rate of organic matter inputs.

Labile Dissolved Organic Matter Compound Characteristics Select for Divergence in Marine Bacterial Activity and Transcription.

Bacteria play a key role in the planetary carbon cycle partly because they rapidly assimilate labile dissolved organic matter (DOM) in the ocean. However, knowledge of the molecular mechanisms at work when bacterioplankton metabolize distinct components of the DOM pool is still limited. We, therefore, conducted seawater culture enrichment experiments with ecologically relevant DOM, combining both polymer and monomer model compounds for distinct compound classes. This included carbohydrates (polysaccharides vs. monosaccharides), proteins (polypeptides vs. amino acids), and nucleic acids (DNA vs. nucleotides). We noted pronounced changes in bacterial growth, activity, and transcription related to DOM characteristics. Transcriptional responses differed between compound classes, with distinct gene sets (“core genes”) distinguishing carbohydrates, proteins, and nucleic acids. Moreover, we found a strong divergence in functional transcription at the level of particular monomers and polymers (i.e., the condensation state), primarily in the carbohydrates and protein compound classes. These specific responses included a variety of cellular and metabolic processes that were mediated by distinct bacterial taxa, suggesting pronounced functional partitioning of organic matter. Collectively, our findings show that two important facets of DOM, compound class and condensation state, shape bacterial gene expression, and ultimately select for distinct bacterial (functional) groups. This emphasizes the interdependency of marine bacteria and labile carbon compounds for regulating the transformation of DOM in surface waters.

Soil sorption characteristics of benzobicyclon hydrolysate and estimated leaching risk in soils used for rice production

Environmental contextThe behaviour of herbicides in the environment is largely determined by the partitioning of the compounds between soil solids and soil solution. We determined that the rice herbicide-metabolite benzobicyclon hydrolysate partitions more into soil solution, and does so increasingly as pH increases. These results indicate that benzobicyclon hydrolysate is a risk for leaching in much of the rice-producing area in the US mid-South. AbstractBenzobicyclon hydrolysate (BH) is the major metabolite and active molecule in the pro-herbicide benzobicyclon (BZB), which is pending registration for use in US mid-Southern rice (Oryza sativa L.) production. The current study objectives were to (i) determine BH soil sorption coefficients; (ii) quantify relationships among BH sorption and soil properties; and (iii) estimate leaching potential using calculated retardation factors (RFs). Sorption coefficients for 10 representative Arkansas rice-production soils were determined by batch-equilibration experiments. Soil sorption (KD=0.25–44.3mLg−1), soil organic carbon partitioning (KOC=28.2–7480mLg−1), and soil organic matter partitioning (KOM=17.9–2580mLg−1) coefficients were negatively correlated with soil pH (r=−0.93 – −0.94). Clay and silt were significant secondary regression parameters, accounting for up to 93% of the variation in KD in combination with pH. Clay and silt effects on sorption coefficients increased when regression analyses excluded the lowest pH soil. Soil sorption coefficients were greater in soils with clay ≥27%, which may be a useful parameter for informing herbicide-use rates. Using the calculated RF’s, the estimated depth of leaching over the growing season exceeded the assumed 15-cm plough layer depth in eight of the 10 soils, and only two of the 10 soils had an estimated time to plough layer breakthrough less than the typical six-month growing season (April–September) under average water flux conditions. The results suggest that BH leaching below the plough layer is a potential risk for much of the rice-producing area in the US mid-South.

Variability in Soil Organic Carbon Fractions Relevance to Different Agricultural Practices

A field trail was conducted at The Experimental Farm, Fac. of Agric., Al-Azahar Univ., Assiut, located 375 km south of Cairo, Egypt (27° 12- 16.67= N latitude and 3° 09- 36.86= E longitude) during the growth seasons of summer 2016 and winter 2016/2017 to assess the effect of tillage and nitrogen fertilization practices on soil organic matter partitioning into the functional compartments with different dynamics. The study included three plowing manner (No plowing, NP, Minimum plowing, MP and Traditional plowing, TP) and two nitrogen sources (Urea 46.5% N as a fast nitrogen fertilizer and ureaform 40% N as a slow nitrogen fertilizer).

Direct Evidence for Temporal Molecular Fractionation of Dissolved Organic Matter at the Iron Oxyhydroxide Interface.

While the importance of organic matter adsorption onto reactive iron-bearing mineral surfaces to carbon stabilization in soils and sediments has been well-established, fundamental understanding of how compounds assemble at the mineral interface remains elusive. Organic matter is thought to layer sequentially onto the mineral surface, forming molecular architecture stratified by bond strength and compound polarity. However, prominent complexation models lack experimental backing, despite the role of such architecture in fractionated, compound-dependent persistence of organic matter and modulating future perturbations in mineral stabilization capacity. Here, we use kinetic assays and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry under high temporal frequency to directly detect the molecular partitioning of organic matter onto an iron oxyhydroxide during adsorption. We observed three sequential intervals of discrete molecular composition throughout the adsorption reaction, in which rapid primary adsorption of aromatic compounds was followed by secondary lignin-like and tertiary aliphatic compounds. These findings, paired with observed differential fractionation along formulas nitrogen and oxygen content and decreasing selective sorption with reaction time, support "zonal" assembly models. This work presents direct detection of sequential molecular assembly of organic matter at the mineral interface, an important yet abstruse regulator of carbon stabilization and composition across temporal and spatial scales.

Consistent proteinaceous organic matter partitioning into mineral and organic soil fractions during pedogenesis in diverse ecosystems

Proteinaceous compounds are critical in soil organic matter (SOM) formation and persistence, but the partitioning into mineral-associated and organic forms during hundreds and thousands of years of pedogenesis are poorly understood across multiple climates and vegetation types. We investigated the partitioning of amino acids (AA) into mineral-bound (MB) and non-mineral associated organic (NMO) soil fractions to discern whether consistent patterns during ecosystem development were observed across two different climates (cool temperate continental, USA; and moist oceanic forests, New Zealand). Although each ecosystem retained unique soil AA signatures, consistent patterns in both systems were observed with three main findings. (1) Regardless of differences in climate and vegetation between the two ecosystems, AA consistently partitioned in similar ways into MB and NMO soil fractions. For example, Thr, Ser, and Asx were relatively more dominant in the NMO fraction while Arg, Lys, Cys, and Met were relatively more dominant in the MB soil fraction. (2) AA change, showed similar trends related to chemical groupings of positively-charged, polar aromatic, sulfur containing, and non-polar AAs across both ecosystems consistent with changing patterns of soil Fe and Al bearing minerals, such as an increasing weathering index (WI; Fe dithionite/total Fe) and losses of Fe and Al from surface soils during ecosystem development. (3) The pedogenic patterns of AA change, in each system paralleled biological transitions in bacterial communities, suggesting a linkage between the AA sources and the soil sink that contributes to soil organic N. This latter point contrasts with the potential for complete change in soil AA composition that could occur upon processing and binding in soil. Overall, the consistency in the types of AAs that partition into either MB or NMO soil fractions across locations provide evidence of similar processes that contribute to soil organic N accrual across soils. Some AA also appeared to be retained in soil by electrostatic forces, and AA–organic matter interactions, that need further study. Mineral–metal complexation of AAs with sulfur side chain groups, and non-polar interactions, respectively, provide examples of these potential mechanisms for study. The results not only support mechanisms of soil proteinacous organic matter chemistry being driven by the interactions with the soil matrix, acting as a “sink”, but also draw attention to the sources of organic matter (microbes, plants) in determining the composition of organic N in soil during pedogenesis.

Chemotaxis toward phytoplankton drives organic matter partitioning among marine bacteria

The microenvironment surrounding individual phytoplankton cells is often rich in dissolved organic matter (DOM), which can attract bacteria by chemotaxis. These "phycospheres" may be prominent sources of resource heterogeneity in the ocean, affecting the growth of bacterial populations and the fate of DOM. However, these effects remain poorly quantified due to a lack of quantitative ecological frameworks. Here, we used video microscopy to dissect with unprecedented resolution the chemotactic accumulation of marine bacteria around individual Chaetoceros affinis diatoms undergoing lysis. The observed spatiotemporal distribution of bacteria was used in a resource utilization model to map the conditions under which competition between different bacterial groups favors chemotaxis. The model predicts that chemotactic, copiotrophic populations outcompete nonmotile, oligotrophic populations during diatom blooms and bloom collapse conditions, resulting in an increase in the ratio of motile to nonmotile cells and in the succession of populations. Partitioning of DOM between the two populations is strongly dependent on the overall concentration of bacteria and the diffusivity of different DOM substances, and within each population, the growth benefit from phycospheres is experienced by only a small fraction of cells. By informing a DOM utilization model with highly resolved behavioral data, the hybrid approach used here represents a new path toward the elusive goal of predicting the consequences of microscale interactions in the ocean.

Effect of elevated CO<sub>2</sub> on organic matter pools and fluxes in a summer Baltic Sea plankton community

Abstract. Ocean acidification is expected to influence plankton community structure and biogeochemical element cycles. To date, the response of plankton communities to elevated CO2 has been studied primarily during nutrient-stimulated blooms. In this CO2 manipulation study, we used large-volume (~ 55 m3) pelagic in situ mesocosms to enclose a natural summer, post-spring-bloom plankton assemblage in the Baltic Sea to investigate the response of organic matter pools to ocean acidification. The carbonate system in the six mesocosms was manipulated to yield average fCO2 ranging between 365 and ~ 1230 μatm with no adjustment of naturally available nutrient concentrations. Plankton community development and key biogeochemical element pools were subsequently followed in this nitrogen-limited ecosystem over a period of 7 weeks. We observed higher sustained chlorophyll a and particulate matter concentrations (~ 25 % higher) and lower inorganic phosphate concentrations in the water column in the highest fCO2 treatment (1231 μatm) during the final 2 weeks of the study period (Phase III), when there was low net change in particulate and dissolved matter pools. Size-fractionated phytoplankton pigment analyses indicated that these differences were driven by picophytoplankton (< 2 μm) and were already established early in the experiment during an initial warm and more productive period with overall elevated chlorophyll a and particulate matter concentrations. However, the influence of picophytoplankton on bulk organic matter pools was masked by high biomass of larger plankton until Phase III, when the contribution of the small size fraction (< 2 μm) increased to up to 90 % of chlorophyll a. In this phase, a CO2-driven increase in water column particulate carbon did not lead to enhanced sinking material flux but was instead reflected in increased dissolved organic carbon concentrations. Hence ocean acidification may induce changes in organic matter partitioning in the upper water column during the low-nitrogen summer period in the Baltic Sea.

Partitioning of organic matter in Boom Clay: Leachable vs mobile organic matter

Boom Clay (BC) is considered in Belgium as a potential host rock for nuclear waste disposal. The formation contains up to 5 wt% of natural organic matter and the presence of dissolved organic matter (DOM) may have a strong impact on radionuclide mobility. However, due to physical constraints, only a fraction of DOM is mobile through the BC layer and the extent of DOM-facilitated radionuclide transport is controlled by the distribution of OM over the mobile and immobile pools. In this work, we investigate 1/the concentration and the size distribution of leachable organic matter in BC, 2/the variability along the BC layer of the concentration and the size distribution of mobile DOM, 3/the parameters controlling the concentration and the size distribution of the leachable OM pool and of the mobile OM pool. Size exclusion chromatography with UV detection at 280 nm is chosen as the reference technique. The UV response of BC DOM is investigated as a function of MW. In pore waters, i.e for mobile DOM, the SUVA280 is dependent on the OM size/MW with the lowest value measured for low MW species (<1 kDa). The use of dynamic light scattering permits to also estimate the hydrodynamic radius (RH) distribution of BC DOM. In the investigated part of BC, the concentration of mobile DOM represents only 0.15 ± 0.8% of the total organic matter content (TOC) and is mostly <20 kDa (RH < 2.8 nm). In contrast, the OM leached from solid samples is dominated by species with MW > 50 kDa and RH > 5.3 nm and accounts for about 12 TOC%. While the concentration of the leachable OM pool is mostly controlled by the TOC content of the rock and to a lower extent by the hydrogen index of the kerogen, the mineralogy plays a significant role in the concentration and the size distribution of the mobile DOM. Filtration and sorption are promoted by clay minerals that preferentially preserves large organic species and leave only small species mobile in pore waters. Inversely, coarser minerals like silt and/or sand facilitate the transport of DOM and increase both the concentration and the MW/RH of the mobile species. The threshold of 20 kDa (RH = 2.8 nm) is considered as a cut-off over which DOM species are hardly mobile in BC. A large part of OM is showed insoluble or immobile but the distribution of OM over the mobile and immobile/insoluble pools, characterised by an average Kd¯ of 140 L kg−1 is found to rather favour the transport of radionuclides than to act as an additive sorbent phase.

Organic matter partitioning and stoichiometry in response to rising water temperature and copepod grazing

Rising ocean temperature is expected to change the balance between production and degradation of organic matter due to different temperature sensitivities of auto- and heterotrophic processes. Copepods are the most prominent zooplankton group, and elevated temperature increases their growth and grazing rates. So far, it is unknown to what extent copepods affect the partitioning and stoichiometry of organic matter in a warmer surface ocean. We therefore conducted a mesocosm experiment with 3 copepod densities and 2 temperature scenarios to determine effects on the pools of dissolved and particulate organic matter and their C:N:P ratios. Here we show that particulate organic C (POC) concentrations decreased with increasing copepod abundance. This effect was more pronounced at elevated temperature, yielding a decrease in the POC to particulate nitrogen ratio (POC:PN) from 26 to 13 and in the POC:particulate organic phosphorus (POP) ratio from 567 to 257, from low to high copepod density. Dissolved organic carbon (DOC) accumulation was positively affected by temperature. However, increasing copepod abundance decreased the accumulation of DOC at elevated temperature. Copepod grazing and egestion enhanced the recycling of N and P, thereby increasing the availability of these nutrients for autotrophs. In concert with temperature-induced shifts in the phytoplankton community composition and size, changes in copepod abundance may therefore have contributed to altering the elemental composition of seston. Our findings suggest combined effects of zooplankton grazing and temperature on the composition and recycling of organic matter that should be taken into account when simulating biogeochemical cycles in a future ocean.

Reproduction and embryonic development in two species of squaliform sharks, Centrophorus granulosus and Etmopterus princeps: Evidence of matrotrophy?

Modes of reproduction and embryonic development vary greatly among the elasmobranchs, and prior studies have suggested that the energetic toll of embryogenesis in lecithotrophic species depletes embryonic organic matter by 20% or more. Matrotrophic species experience a lesser reduction or an increase in organic matter during embryogenesis. To investigate the maternal–embryonic nutritional relationship, we measured changes in organic matter from fertilization to near-parturition in embryos of Centrophorus granulosus and Etmopterus princeps. Embryos of C. granulosus experienced a reduction of 19.5% in organic matter, while E. princeps embryos experienced a reduction of 7.7% in organic matter over the course of embryonic development, suggesting some level of matrotrophy occurs, particularly for the latter species. Uterine villi were present in both species and developed concurrently with the embryos, increasing in length and thickness while becoming progressively vascularized. Embryos of C. granulosus were dissected to track the partitioning of water, organic matter, and inorganic matter to the liver, external yolk sac, internal yolk sac, digestive tract, and evicerated body throughout development. Mating was aseasonal for both species and spatially-mediated segregation by sex and maturity stage was observed. Ovarian cycles were concurrent for C. granulosus and consecutive for E. princeps. Size at maturity for C. granulosus was determined to be 111cm TL for males and 143cm TL for females, with an average fecundity of 5.3 embryos (range=4–7). Size at maturity for E. princeps was determined to be 56.5cm TL for males and 61cm TL for females north of the Azores and 54cm TL for males and 69cm TL for females near the Charlie Gibbs Fracture Zone. Average fecundity was 11.2 embryos (range=7–18) for this species. This is the first reporting of reproductive parameters for these two species, and the information provided will be valuable for informing stock assessment models in areas where these species are fished.

Rumen Microbial Biomass Synthesis and Its Importance in Ruminant Production

Quantification of rumen microbial biomass synthesis assumes significance as rumen fermentation of feed organic matter and microbial biomass synthesis meet 70-85% of energy and 70-100% of protein needs of ruminants which necessitates understanding the feed factors influencing higher microbial biomass in the rumen. Determination of feed factors affecting microbial biomass synthesis in vivo is too expensive. Hence, the rumen in vitro gas production technique used for feed energy evaluation in ruminant feedstuffs was adopted to assess microbial biomass production potential of feedstuffs based on the concept of partitioning of fermented organic matter between microbial biomass and fermentation waste products. Diets formulated with differing in microbial biomass synthesis termed as partitioning factor (PF) and tested them for their efficiency of microbial biomass synthesis in vitro and assessed the same in vivo on feed intake, nutrient digestibility, nitrogen balance, purine excretion in urine and production performance in growing and lactating animals is compiled in this review.

Production, partitioning and stoichiometry of organic matter under variable nutrient supply during mesocosm experiments in the tropical Pacific and Atlantic Ocean

Abstract. Oxygen-deficient waters in the ocean, generally referred to as oxygen minimum zones (OMZ), are expected to expand as a consequence of global climate change. Poor oxygenation is promoting microbial loss of inorganic nitrogen (N) and increasing release of sediment-bound phosphate (P) into the water column. These intermediate water masses, nutrient-loaded but with an N deficit relative to the canonical N:P Redfield ratio of 16:1, are transported via coastal upwelling into the euphotic zone. To test the impact of nutrient supply and nutrient stoichiometry on production, partitioning and elemental composition of dissolved (DOC, DON, DOP) and particulate (POC, PON, POP) organic matter, three nutrient enrichment experiments were conducted with natural microbial communities in shipboard mesocosms, during research cruises in the tropical waters of the southeast Pacific and the northeast Atlantic. Maximum accumulation of POC and PON was observed under high N supply conditions, indicating that primary production was controlled by N availability. The stoichiometry of microbial biomass was unaffected by nutrient N:P supply during exponential growth under nutrient saturation, while it was highly variable under conditions of nutrient limitation and closely correlated to the N:P supply ratio, although PON:POP of accumulated biomass generally exceeded the supply ratio. Microbial N:P composition was constrained by a general lower limit of 5:1. Channelling of assimilated P into DOP appears to be the mechanism responsible for the consistent offset of cellular stoichiometry relative to inorganic nutrient supply and nutrient drawdown, as DOP build-up was observed to intensify under decreasing N:P supply. Low nutrient N:P conditions in coastal upwelling areas overlying O2-deficient waters seem to represent a net source for DOP, which may stimulate growth of diazotrophic phytoplankton. These results demonstrate that microbial nutrient assimilation and partitioning of organic matter between the particulate and the dissolved phase are controlled by the N:P ratio of upwelled nutrients, implying substantial consequences for nutrient cycling and organic matter pools in the course of decreasing nutrient N:P stoichiometry.

The effect of model spatial resolution on Secondary Organic Aerosol predictions: a case study at Whistler, BC, Canada

Abstract. A large fraction of submicron aerosol mass throughout the continental boundary layer consists of secondary organic aerosol (SOA) mass. As such, the ability of chemical transport models to accurately predict continental boundary layer aerosol greatly depends on their ability to predict SOA. Although there has been much recent effort to better describe SOA formation mechanisms in models, little attention has been paid to the effects of model spatial resolution on SOA predictions. The Whistler Aerosol and Cloud Study (WACS 2010), held between 22 June and 28 July 2010 and conducted at Whistler, BC, Canada provides a unique data set for testing simulated SOA predictions. The study consisted of intensive measurements of atmospheric trace gases and particles at several locations strongly influenced by biogenic sources in the region. We test the ability of the global chemical transport model GEOS-Chem to predict the aerosol concentrations during this event and throughout the campaign. Simulations were performed using three different resolutions of the model: 4° × 5° , 2° × 2.5° and 0.5° × 0.667°. Predictions of organic aerosol concentrations at Whistler were greatly dependent on the resolution; the 4° × 5° version of the model significantly under predicts organic aerosol, while the 2° × 2.5° and 0.5° × 0.667° versions are much more closely correlated with measurements. In addition, we performed a comparison between the 3 versions of the model across North America. Comparison simulations were run for both a summer case (July) and Winter case (January). For the summer case, 0.5° × 0.667° simulations predicted on average 19% more SOA than 2° × 2.5° and 32% more than 4° × 5° . For the winter case, the 0.5° × 0.667° simulations predicted 8% more SOA than the 2° × 2.5° and 23% more than the 4° × 5°. This increase in SOA with resolution is largely due to sub-grid variability of organic aerosol (OA) that leads to an increase in the partitioning of secondary organic matter to the aerosol phase at higher resolutions. SOA concentrations were further increased because the shift of secondary organic gases to SOA at higher resolutions increased the lifetime of secondary organic matter (secondary organic gases have a shorter deposition lifetime than SOA in the model). SOA precursor emissions also have smaller, but non-negligible, changes with resolution due to non-linear inputs to the MEGAN biogenic emissions scheme. These results suggest that a portion of the traditional under-prediction of SOA by global models may be due to the effects of coarse grid resolution.

Annual cycle of organic matter partitioning and its availability to bacteria across the Santa Barbara Channel continental shelf

Annual cycle of organic matter partitioning and its availability to bacteria across the Santa Barbara Channel continental shelf

Effects of rising temperature on pelagic biogeochemistry in mesocosm systems: a comparative analysis of the AQUASHIFT Kiel experiments

A comparative analysis of data, obtained during four indoor-mesocosm experiments with natural spring plankton communities from the Baltic Sea, was conducted to investigate whether biogeochemical cycling is affected by an increase in water temperature of up to 6 °C above present-day conditions. In all experiments, warming stimulated in particular heterotrophic bacterial processes and had an accelerating effect on the temporal development of phytoplankton blooms. This was also mirrored in the build-up and partitioning of organic matter between particulate and dissolved phases. Thus, warming increased both the magnitude and rate of dissolved organic carbon (DOC) build-up, whereas the accumulation of particulate organic carbon (POC) and phosphorus (POP) decreased with rising temperature. In concert, the observed temperature-mediated changes in biogeochemical components suggest strong shifts in the functioning of marine pelagic food webs and the ocean’s biological carbon pump, hence providing potential feedback mechanisms to Earth’s climate system.

Role of Biofilms in Sorptive Removal of Steroidal Hormones and 4-Nonylphenol Compounds from Streams

Stream biofilms play an important role in geochemical processing of organic matter and nutrients, however, the significance of this matrix in sorbing trace organic contaminants is less understood. This study focused on the role of stream biofilms in sorbing steroidal hormones and 4-nonylphenol compounds from surface waters using biofilms colonized in situ on artificial substrata and subsequently transferred to the laboratory for controlled batch sorption experiments. Steroidal hormones and 4-nonylphenol compounds readily sorb to stream biofilms as indicated by organic matter partition coefficients (K(om), L kg(-1)) for 17β-estradiol (10(2.5-2.8) L kg(-1)), 17α-ethynylestradiol (10(2.5-2.9) L kg(-1)), 4-nonylphenol (10(3.4-4.6) L kg(-1)), 4-nonylphenolmonoethoxylate (10(3.5-4.0) L kg(-1)), and 4-nonylphenoldiethoxylate (10(3.9-4.3) L kg(-1)). Experiments using water quality differences to induce changes in the relative composition of periphyton and heterotrophic bacteria in the stream biofilm did not significantly affect the sorptive properties of the stream biofilm, providing additional evidence that stream biofilms will sorb trace organic compounds under of variety of environmental conditions. Because sorption of the target compounds to stream biofilms was linearly correlated with organic matter content, hydrophobic partition into organic matter appears to be the dominant mechanism. An analysis of 17β-estradiol and 4-nonylphenol hydrophobic partition into water, biofilm, sediment, and dissolved organic matter matrices at mass/volume ratios typical of smaller rivers showed that the relative importance of the stream biofilm as a sorptive matrix was comparable to bed sediments. Therefore, stream biofilms play a primary role in attenuating these compounds in surface waters. Because the stream biofilm represents the base of the stream ecosystem, accumulation of steroidal hormones and 4-nonylphenol compounds in the stream biofilm may be an exposure pathway for organisms in higher trophic levels.

Can Chlorofluorocarbon Sorption to Black Carbon (Char) Affect Groundwater Age Determinations?

Although adsorption is not generally considered important in low f(oc) (fraction organic carbon) aquifers, we show that chlorofluorocarbon (CFC) adsorption to black carbon (BC) is sufficiently large to retard transport and affect groundwater ages obtained with CFCs. Sorption isotherms of CFC-11, -12, and -113 to synthetic wood char were nonlinear (Freundlich n = 0.71-0.94) while humic acid isotherms were linear. Moreover, sorption to char was 10-1000 times greater than to humic acid for all three CFCs at the lowest observed concentrations, C(w)/S approximately 10(-8)-10(-7). We used the observed isotherms for char and humic acid to represent sorption to BC and amorphous organic matter, respectively, in a dual mode model to estimate retardation factors for a low f(oc) aquifer (= 0.06% gC g(-1)). The estimated retardation factors for the char-containing aquifer (presumed BC fraction = 9% of f(oc)) were approximately 6.8-10.6 at C(w)/S = 10(-8) and >5 times those estimated assuming amorphous organic matter partitioning only. The results indicate that unless CFC adsorption to BC is evaluated in transport, the groundwater age determined may be biased toward older than true ages. The CFC data archived in BC-containing aquifers may contain information about its adsorbent properties that could be useful to predict retardation of other chlorinated organic contaminants.

Sources, transport, and partitioning of organic matter at a highly dynamic continental margin

Continental shelves play a major role as transition zone during transport of multiply-sourced organic matter into the deep sea. In order to obtain a comprehensive understanding of the origin and fractionation processes of organic matter at the NW Iberian margin, 40 surface sediment samples were analyzed for a structurally diverse range of lipid biomarkers, lignin phenols, grain size distribution, organic carbon content (TOC), its stable carbon isotopic composition ( δ 13C TOC), and the organic carbon to nitrogen ratio (TOC/TN). The biomarker inventory reflected a heterogeneous mixture of organic matter from various marine and terrestrial sources. Soil- and vascular plant-derived continental organic matter, indicated by lignin phenols and plant-derived triterpenoids, was primarily associated with the silt fraction and transported by river run-off. The spatial distribution patterns of higher plant-derived waxes, long-chain n-alkanes, n-alcohols, and n-fatty acids suggested distinct different transport mechanisms and/or sources. The branched tetraether index, a molecular proxy expressing the relative abundance of branched dialkyl tetraethers vs. crenarchaeol and considered to signal soil-derived organic matter, was not as sensitive as the other molecular indicators in detecting continental organic matter. Hydrodynamic sorting processes on the shelf resulted in a separation of different types of terrestrial organic matter; grass and leaf fragments and soil organic matter were preferentially transported offshore and deposited in areas of lower hydrodynamic energy. Algal lipid biomarker distributions indicated a complex community of marine plankton contributing to organic matter. Spatial and seasonal patterns of phytoplankton growth primarily controlled the distribution of algal organic matter components. The interplay of all of these processes controls production, distribution, and deposition of organic matter and results in three distinct provinces at the Galicia–Minho shelf: (I) fresh marine organic matter dominated the inner shelf region; (II) high inputs of terrestrial organic matter and high TOC content characterized the mid-shelf deposited mudbelt; (III) lower concentrations of relatively degraded organic matter with increased proportions of refractory terrestrial components dominated the outer shelf and continental slope.

Partitioning of organic matter in continental margin sediments among density fractions

Hydrodynamic processes sort and redistribute organic matter (OM) and minerals on continental margins. Density fractionations were conducted on sediments from diverse margins (Mexico margin, Gulf of Mexico, Mississippi River delta, Eel River margin) to investigate the nature, provenance and age of OM among density fractions. Mass, elemental (C and N), lignin, and surface area distributions, as well as stable carbon and radiocarbon isotopic compositions were measured. The lowest density fractions (< 1.6 g cm − 3 ) contained the highest organic carbon (OC) (up to 45%) and lignin concentrations (up to 8 mg g − 1 ) due to abundant woody debris, whereas high density fractions (> 2.5 g cm − 3 ) were OC-poor (%OC < 0.5) mineral material. Most sediment mass was found in the mesodensity fractions (1.6 to 2.5 g cm − 3 ) that contained the highest proportion of OC (up to ~ 75%) for each sediment. Stable carbon isotope compositions (δ 13C − 25.5‰ to − 22.9‰) show terrigenous OC as a significant component of density isolates from the river-dominated sediments (Gulf of Mexico, Mississippi River, and Eel margin), whereas the Mexico margin, least influenced by riverine input, was dominated by autochthonous marine OC (δ 13C ~ − 21.5‰). Radiocarbon compositions of density fractions indicate significant pre-aged OC (Δ 14C as low as − 900‰) in river-influenced sediments but not on the Mexico margin (Δ 14C > − 200‰). Ratios of vanillic acid to vanillin (Ad/Al)v among lignin oxidation products increase with increasing particle density suggesting variable lignin sources or selective degradation of lignin among the different density fractions.