Particulate Organic Matter Fractions Research Articles

What are the primary factors controlling the light fraction and particulate soil organic matter content of agricultural soils?

Particulate organic matter (POM) and light fraction organic matter (LFOM) are the fractions of soil organic matter (SOM) considered most active in terms of nutrient cycling and maintenance of soil structure. They respond quickly to changes in management and may offer insights into the long-term effect of management on SOM. However, the literature provides contradictory evidence regarding the factors which influence the amount of POM and LFOM, and there is little evidence to differentiate the relative importance of factors. Utilising data from over 150 experiments reported in the literature, we employed multiple regression to produce separate models quantifying the effect of management factors and environmental variables on POM, LFOM and total SOM; 29.3 % of the variance in the response variables was explained for POM, 28.3 % for LFOM, and 29.3 % for total SOM. Climate, organic amendments and inclusion of fallow periods were significant terms for all fractions. Climate had a larger influence on total SOM than POM or LFOM, whilst POM and LFOM were more strongly influenced by factors related to the recent history of organic matter addition; organic amendments and inclusion of fallows. Factors that were not significant variables for any of the fractions included tillage and application of N fertiliser, whilst soil texture was only a significant factor for SOM. General agreement between the total SOM, POM and LFOM models on the most important factors supports the idea that both POM and LFOM are good predictors of long-term changes to total SOM.

Brown carbon absorption linked to organic mass tracers in biomass burning particles

Abstract. Traditional gas and particle phase chemical markers used to identify the presence of biomass burning (BB) emissions were measured for a large forest fire near Boulder, Colorado. Correlation of the organic matter mass spectroscopic m/z 60 with measured particle light absorption properties found no link at 532 nm, and a strong correlation at 404 nm. Non-black carbon absorption at 404 nm was well correlated to the ratio of the mass fractions of particulate organic matter (POM) that was m/z 60 (f60) to m/z 44 (f44). The f60 to f44 ratio did not fully explain the variability in non-BC absorption, due to contributions of brown carbon (BrC) absorption and absorption due to internal mixing of POM with black carbon (BC). The absorption Ångstrom exponent (ÅAbs) showed a good correlation to f60/f44; however the best correlation resulted from the mass absorption efficiency (MAE) of BrC at 404 nm (MAEPOM-404 nm) and f60/f44. This result indicates that the absorption of POM at low visible and UV wavelengths is linked to emissions of organic matter that contribute to the m/z 60 mass fragment, although they do not contribute to 532 nm absorption. m/z 60 is often attributed to levoglucosan and related compounds. The linear relationship between MAEPOM-404 nm and f60/f44 suggests that the strength of BrC absorption for this fire can be predicted by emissions of f60-related organic matter.

Coupled and decoupled responses of continental and marine organic‐sedimentary systems through the Paleocene‐Eocene thermal maximum, New Jersey margin, USA

The flux of sediment and organic carbon from continents to the coastal ocean is an important factor governing organic burial in coastal sediments, and these systems preserve important records of environmental and biogeochemical conditions during past global change events. Burial of organic materials in coastal systems can be promoted by chemical resilience or through protection by association with mineral surfaces, but the role and influence of these processes on organic records from ancient sediments is poorly known. We studied sediment and organic matter burial as particulate organic matter (POM) and mineral‐bound organic matter (MOM) in near‐shore marine sediments from the Wilson Lake core (New Jersey, USA) that span the Paleocene‐Eocene thermal maximum (PETM), a climatic perturbation 55.9 Myr ago. Our results show that distinct POM and MOM fractions can be isolated from sediments. Both fractions appear to be dominated by terrestrial material, but POM consisted primarily of recently synthesized material whereas MOM included a significant fraction of pre‐aged organic matter from soils or ancient sediments. Variation in organic burial through the PETM is associated with changes in inorganic nitrogen burial, clay mineralogy, and clastic grain size that we associate with enhanced continental weathering, erosion and redeposition of ancient kaolinites, and eustatic sea level variation, respectively. These results provide a new perspective on factors governing carbon burial and carbon isotope records in ancient marine margin settings and offer information on rate and phasing of late Paleocene/early Eocene Earth system changes that may constrain interpretations of the cause of the PETM climate change event.

Predicting the soiling of modern glass in urban environments: A new physically-based model

This study revisits the measurements of the MULTI-ASSESS and Long Term Soiling programs for understanding physically, and modeling, the processes controlling the soiling of modern glass in polluted conditions. The results show a strong correlation between the size distribution of particles and the evolution of the mass deposited at the surface of the glass. Over observation periods covering more than 2 years, the mass deposition on glass panels sheltered from the rain is observed to accelerate regularly with time at the sites closest to the sources of particulate matter (Roadside sites). At these sites the deposit is also richer in coarse (supermicron) mineral particles than at more distant (Urban Background and Suburban) sites, where the contribution of submicron particles (among which a significant fraction of particulate organic matter) is larger. This size and compositional segregation probably explains that the mass accumulation tends to slow down with time and finally saturate after an estimated duration of more than 10 years at the Suburban sites.The analysis of the correlation between the measured accumulated mass and haze shows that the haze-creating mass efficiency of the deposit decreases progressively as the density of particles increases on the glass panels. This is interpreted as being a consequence of the increasing influence of multiple scattering. A steady-state is eventually obtained when layers of closely packed particles are formed, which occurs for surface masses of the order of a few tens of μg cm−2. After this stage is reached, the haze increases linearly with further mass deposition at a pace conditioned by the size-distribution of the deposit. The parameterization of the evolution of the deposited mass with time, and of the correlation linking this mass to the haze allows proposing a new physically-based model able to predict the development of the haze on sheltered glass. Finally, a comparison of the model predictions with the independent measurements performed at the experimental sites of the AERO program shows that the model is able to simulate correctly the development of the haze at a variety of urban sites ranging from the Suburban to Roadside categories. This predictive tool should help developing conservation strategies adapted to the real environmental conditions of the historical and modern buildings.

Corn Residue Removal Impact on Soil Aggregates in a No-Till Corn/Soybean Rotation

Many questions have surfaced regarding short- and long-term impacts of corn (Zea mays L.) residue removal for use in the biofuels industry. To address these concerns, a field study was established in eastern South Dakota in 2000 using no-till soil management within a 2-yr corn/soybean [Glycine max (L.) Merr.] rotation. The objective of this study was to examine the effects of three residue removal treatments of low (corn harvested for grain; all residues remain on soil surface), medium (corn harvested for grain; residue raked, baled, and removed), and high (aboveground corn biomass and grain removed) on soil quality, measured through particulate organic matter (POM), soil organic matter (SOM), wet aggregate stability (WAS), and dry aggregate size distribution (DASD). Following four complete rotational cycles, when residue was removed from the soil surface there was a consistent decrease in the amount of SOM and all fractions of POM regardless of aggregate size class, indicating a possible decrease in soil quality. This was further indicated by the near doubling of the erodible fraction in the high removal treatment compared to the low removal treatment. Potential further degradation of the soil structure is indicated by a shift in DASD among the residue removal treatments. Within this study, removal of corn residue had a negative impact on the soil physical and chemical properties measured, potentially illustrating the importance of crop residue to maintain our soil resource. Additional research is needed to incorporate other soil chemical and biological indicators before recommendations can be made.

Particulate organic matter, soil texture and mineralogy relations in some Eastern Cape ecotopes in South Africa

Contrasting reports have been given on the relationships between soil texture, mineralogy and particulate organic matter (POM). The objective of this study was to determine the effects of soil texture and mineralogy on aggregate POM in several ecotopes in the Eastern Cape province of South Africa. Soil from the surface 0–20 cm was collected from 14 ecotopes. Particulate organic matter was fractionated into litter POM, coarse POM and fine POM. Isolation of the POM fraction was done by dispersing the soil in 5 g l-1 sodium hexametaphosphate and passing the dispersed soil samples through a 0.053 mm sieve. Both total soil organic matter (SOM) and the POM in each fraction were determined using the weight loss on ignition procedure. Most ecotopes were either sandy loam or sandy clay loam and primary minerals especially quartz dominated the soil mineralogy. The clay content was significantly related to the total SOM (r = 0.78), hematite (r = 0.83) and quartz (r = -0.74). The results suggest that in soils that are dominated by primary minerals such as quartz, the clay content, rather than the clay plus silt content, is a better indicator of fine POM and total SOM.

Temperature sensitivity of tropical forest soil respiration increase along an altitudinal gradient with ongoing decomposition

Knowing the impact of warming on soil organic matter (SOM) is crucial for estimating future soil CO2 effluxes. Whether different soil fractions and carbon (C) complexes have different temperature sensitivities is still a matter of debate. To measure the temperature sensitivity of tropical forest soils with ongoing decomposition, we collected soil cores from three sites along an altitudinal gradient with a difference in mean annual soil temperature of about 8°C. The intact soil cores were incubated at 5, 15, 25 and 35°C, respiration rates quantified, and the soil cores reinstalled at the collection sites. This procedure was repeated after six months and after one year to quantify the impact of ongoing decomposition on the temperature sensitivity (Q10) of respiration. Changes in chemical composition were determined by infra-red spectroscopy, and C distribution was partitioned by fractionation into fine roots, particulate organic matter (POM) and mineral-associated organic matter (MOM) from soil sub-samples at the start of the experiment and after one year of decomposition. Despite the different provenances, the soils revealed the same respiration patterns with Q10 values of 1.43–1.58 at the start of the experiment and 2.02–2.21 after one year. Carbon use efficiencies were lower for more stable SOM. Chemical composition of bulk SOM did not change to a measureable extent after one year, and SOM dynamics could not be related to changes in Q10 values. Of the analysed properties, the largest impact seems to have been on the decomposition of organic matter from the POM fractions, which might have been responsible for the observed increases in Q10 values.

Does Nature and Persistence of Substrate at a Mesohabitat Scale Matter for Chironomidae Assemblages? a Study of Two Perennial Mountain Streams in Patagonia, Argentina

Chironomid substrate—specific associations regarding the nature (organic—inorganic) and stability (stable—unstable) of different habitats were investigated at two low order Patagonian streams, during high and low water periods. Nant y Fall and Glyn rivers were visited twice (October 2007 and March 2008) and seven different habitat types were identified. A total of 60 samples were collected using a Surber sampler (0.09 m -2 and 250 µm) and a set of 23 environmental descriptors including physicochemical parameters and different fractions of particulate organic matter were assessed. 35 Chironomidae taxa were recorded with Orthocladiinae (20), Chironominae (7), and Podonominae (4) being the most well—represented subfamilies. Paratrichocladius sp. 1, Parapsectrocladius sp. 2, Parametriocnemus sp. 1, Pseudochironomus sp., and Rheotanytarsus sp. were the most abundant taxa. According to the relative preference index, at least 14 taxa showed strong affinity for a particular substrate. The structurally complex macrophyte Myriophyllum quitense supported 11 taxa compared with only five taxa found on the less complex Isoetes savatieri. Generally, stable substrates (boulders, cobbles, and rooted plants) supported significantly higher chironomids richness, abundance, and diversity than unstable ones (gravel—sand). Canonical correspondence analysis revealed that detritus (leaves, seeds, and biomass), macrophyte biomass, and secondarily hydraulic variables had high explanatory power on chironomids species composition and structure. This work suggests that more complex substrates showing persistence in the temporal dimension supported a diverse array of chironomids, meaning that the maintenance of natural habitat heterogeneity is essential for the community. Land—use practices having significant effects on ecological stream attributes such as increased turbidity, sediment deposition, and runoff patterns will alter assemblages. Understanding environmental associations of the Chironomidae assemblage at the habitat scale is significant for conservation purposes and for the management of low order streams in Patagonia.

Conservation agriculture effects on soil organic matter on a Haplic Cambisol after four years of maize–oat and maize–grazing vetch rotations in South Africa

A study was conducted to determine the effects of oat (Avena sativa) and grazing vetch (Vicia dasycapa) winter cover crops and fertilization regimes on soil organic matter (SOM) in an irrigated maize-based (Zea mays L.) conservation agriculture (CA) system following four years of continuous practice. Separate plots of oat and grazing vetch cover crops were grown in winter and then maize was planted in all plots in the following summer season. The four fertilization regimes used were: (i) fertilizer applied to the cover crops and the maize crop (F1), (ii) fertilizer applied to cover crops only (F2), (iii) fertilizer applied to the maize crop only (F3) and (iv) no fertilizer applied (F4). Control plots (weedy fallows) were included and the treatments were laid out in a randomized complete block design with three replications. Soil samples from 0–5, 5–20 and 20–50cm depths were analyzed for total SOM, particulate organic matter (POM) fractions, hot water soluble C (HWC) and C-associated with water stable macro- and micro-aggregates (WSAC). While total SOM was more concentrated in the 0–5cm soil depth across treatments, a lack of maize fertilization (F2 and F4 regimes) significantly (P<0.05) reduced the stratification ratio. Oat and grazing vetch rotations produced significantly higher (P<0.05) fine POM, coarse POM and HWC than weedy fallow rotations at 0–5 and 5–20cm. When fertilized, oat was better able to support SOM sequestration in water stable aggregates at 0–20cm while grazing vetch was more effective at 20–50cm. The F3 regime had similar SOM levels as the F2. When no fertilizer was applied (F4-regime), there were significant (P<0.01) reductions in biomass input and total SOM on the oat–maize and weedy fallow–maize rotations whereas the grazing vetch–maize rotation did not respond, both at 0–5 and 5–20cm. The findings suggested that in the low fertilizer input CA system, targeting fertilizer to the winter cover crop as opposed to the maize crop could give similar SOM response, with less fertilizer invested and that grazing vetch cover crops may be better suited to low N input CA systems for SOM improvement.

Land‐use change in subalpine grassland soils: Effect on particulate organic carbon fractions and aggregation

AbstractAbandonment of mountain grassland often changes vegetation composition and litter quantity and quality, but related effects on labile soil organic matter (SOM) are largely unknown. The aim of this study was to investigate the impacts of grassland management and abandonment on soil carbon distribution in light (&lt; 1.6 g cm–3) particulate organic matter (POM) and aggregation along a gradient of management intensity including hay meadows, pastures, and abandoned grasslands. The reduction of management intensity is an interregional phenomenon throughout the European Alps. We therefore selected sites from two typical climate regions, namely at Stubai Valley, Austria (MAT: 3°C, MAP: 1097 mm) and Matsch Valley, Italy (MAT: 6.6°C, MAP: 527 mm), to evaluate effects of land‐use change in relation to climate. Free water‐floatable and free POM (wPOM, fPOM), and an occluded POM fraction (oPOM), were isolated from three water‐stable aggregate size classes (2–6.3 mm, 0.25–2 mm, &lt; 0.25 mm) using density fractionation. Aggregate mean weight diameter slightly decreased with decreasing management intensity. In contrast to absolute POM‐C, fPOM‐C increased in aggregates at both sites with abandonment. Because the oPOM‐C was less affected by abandonment, the ratio of oPOM‐C : fPOM‐C shifted from &gt; 1 to &lt; 1 from meadow to abandoned grassland in aggregates at both sites and thus independent of climate. This suggests that in differently managed mountain grasslands free and occluded POM are functionally different SOM fractions. In bulk soil, the oPOM‐C : fPOM‐C ratio is better suited as an indicator for the response of SOM to management reduction in subalpine grasslands than the total soil C, absolute or relative POM‐C content.

Contribution of Lubricating Oil to Particulate Matter Emissions from Light-Duty Gasoline Vehicles in Kansas City

The contribution of lubricating oil to particulate matter (PM) emissions representative of the in-use 2004 light-duty gasoline vehicles fleet is estimated from the Kansas City Light-Duty Vehicle Emissions Study (KCVES). PM emissions are apportioned to lubricating oil and gasoline using aerosol-phase chemical markers measured in PM samples obtained from 99 vehicles tested on the California Unified Driving Cycle. The oil contribution to fleet-weighted PM emission rates is estimated to be 25% of PM emission rates. Oil contributes primarily to the organic fraction of PM, with no detectable contribution to elemental carbon emissions. Vehicles are analyzed according to pre-1991 and 1991-2004 groups due to differences in properties of the fitting species between newer and older vehicles, and to account for the sampling design of the study. Pre-1991 vehicles contribute 13.5% of the KC vehicle population, 70% of oil-derived PM for the entire fleet, and 33% of the fuel-derived PM. The uncertainty of the contributions is calculated from a survey analysis resampling method, with 95% confidence intervals for the oil-derived PM fraction ranging from 13% to 37%. The PM is not completely apportioned to the gasoline and oil due to several contributing factors, including varied chemical composition of PM among vehicles, metal emissions, and PM measurement artifacts. Additional uncertainties include potential sorption of polycyclic aromatic hydrocarbons into the oil, contributions of semivolatile organic compounds from the oil to the PM measurements, and representing the in-use fleet with a limited number of vehicles.

Soil Organic Matter Quality in Chronosequences Of Secondary Northern Hardwood Forests In Western New England

We developed chronosequences in western New England northern hardwood forests for abandoned cultivated land (n = 10) and fields used as pasture or hay (n = 10). The top 20 cm of mineral soil was excavated using quantitative soil pits to examine particulate and potentially mineralizable organic matter as indicators of changes in soil organic matter (SOM) quality. The chronosequences were bound by land currently in agricultural use (n = 6) and native forest stands at least 250 yr in age with a history of minimal disturbance (n = 4). A 62-d incubation showed that a greater proportion of bulk soil C was potentially mineralizable in modern agricultural soils (108 g CO₂–C kg⁻¹ soil C) than at forested sites (63 g CO₂–C kg⁻¹ soil C), regardless of former use. Physical fractionation of SOM revealed that a greater proportion of bulk soil C was contained in the particulate organic matter (POM) fractions in plowed (86%) and pastured–hayed fields (49%) compared with regrowing forests 40 yr after abandonment (33–41%). Mineral-associated organic matter increased at a rate of 0.04 Mg ha⁻¹ yr⁻¹. While C/N ratios increased with forest age across the chronosequences for the bulk soil, they did not change with time for physical SOM fractions except for a weak but significant trend for the mineral-associated fraction of plowed soils (r² = 0.26, P 250 mm) was better related to climatic variables. These results suggest that the stability of SOM increases when native forests are allowed to invade abandoned agricultural fields.

Determination of organic carbon and nitrogen in particulate organic matter and particle size fractions of Brookston clay loam soil using infrared spectroscopy

The objective of this study was to determine whether models developed from infrared spectroscopy could be used to estimate organic carbon (C) content, total nitrogen (N) content and the C:N ratio in the particulate organic matter (POM) and particle size fraction samples of Brookston clay loam. The POM model was developed with 165 samples, and the particle size fraction models were developed using 221 samples. Soil organic C and total N contents in the POM and particle size fractions (sand, 2000–53 µm; silt, 53–2 µm; clay, &lt;2 µm) were determined by using dry combustion techniques. The bulk soil samples were scanned from 4000 to 400 cm−1 for mid‐infrared (MIR) spectra and from 8000 to 4000 cm−1 for near‐infrared (NIR) spectra. Partial least squares regression (PLSR) analysis and the ‘leave‐one‐out' cross‐validation procedure were used for the model calibration and validation. Organic C and N content and C:N ratio in the POM were well predicted with both MIR‐ and NIR‐PLSR models ( = 0.84–0.92; = 0.78–0.87). The predictions of organic C content in soil particle size fractions were also very good for the model calibration ( = 0.84–0.94 for MIR and = 0.86–0.92 for NIR) and model validation ( = 0.79–0.94 for MIR and = 0.84–0.91 for NIR). The prediction of MIR‐ and NIR‐PLSR models for the N content and the C:N ratio in the sand and clay fractions was also satisfactory ( = 0.73–0.88; = 0.67–0.85). However, the predictions for the N content and C:N ratio in the silt fraction were poor ( = 0.23–0.55; = 0.20–0.40). The results indicate that both MIR and NIR methods can be used as alternative methods for estimating organic C and total N in the POM and particle size fractions of soil samples. However, the NIR model is better for estimating organic C and N in POM and sand fractions than the MIR model, whereas the MIR model is superior to the NIR model for estimating organic C in silt and clay fractions and N in clay fractions.

Input related microbial carbon dynamic of soil organic matter in particle size fractions

This paper investigated the flow of carbon into different groups of soil microorganisms isolated from different particle size fractions. Two agricultural sites of contrasting organic matter input were compared. Both soils had been submitted to vegetation change from C3 (Rye/Wheat) to C4 (Maize) plants, 25 and 45 years ago. Soil carbon was separated into one fast-degrading particulate organic matter fraction (POM) and one slow-degrading organo-mineral fraction (OMF). The structure of the soil microbial community were investigated using phospholipid fatty acids (PLFA), and turnover of single PLFAs was calculated from the changes in their 13C content. Soil enzyme activities involved in the degradation of carbohydrates was determined using fluorogenic MUF (methyl-umbelliferryl phosphate) substrates.We found that fresh organic matter input drives soil organic matter dynamic. Higher annual input of fresh organic matter resulted in a higher amount of fungal biomass in the POM-fraction and shorter mean residence times. Fungal activity therefore seems essential for the decomposition and incorporation of organic matter input into the soil. As a consequence, limited litter input changed especially the fungal community favoring arbuscular mycorrhizal fungi. Altogether, supply and availability of fresh plant carbon changed the distribution of microbial biomass, the microbial community structure and enzyme activities and resulted in different priming of soil organic matter.Most interestingly we found that only at low input the OMF fraction had significantly higher calculated MRT for Gram-positive and Gram-negative bacteria suggesting high recycling of soil carbon or the use of other carbon sources. But on average all microbial groups had nearly similar carbon uptake rates in all fractions and both soils, which contrasted the turnover times of bulk carbon. Hereby the microbial carbon turnover was always faster than the soil organic carbon turnover and higher carbon input reduced the carbon storage efficiency from 51% in the low input to 20%. These findings suggest that microbial community preferentially assimilated fresh carbon sources but also used recycled existing soil carbon. However, the priming rate was drastically reduced under carbon limitation. In consequence at high carbon availability more carbon was respired to activate the existing soil carbon (priming) whereas at low carbon availability new soil carbon was formed at higher efficiencies.

Chemical Speciation and Source Assignment of Particulate (PM10) Phase Molecular Markers in Mumbai

Particulate matter (PM10) has emerged as the single most important pollutant across Indian cities, as its levels exceed the regulated standards at most places. PM10 was collected and analyzed at seven sites representing different land use patterns in Mumbai during 2007–08 for organic carbon (OC) and elemental carbon (EC). OC was further speciated for organic markers, which are useful for identifying sources. Average PAH concentration ranged from 47.84 ± 14.07 to 247.70 ± 163.19 ng/m3. n-alkanes concentration varied from 157.20 ± 35.28 to 759.13 ± 451.65 ng/m3. Hopanes and steranes showed the highest concentrations of 94.14 ± 28.66 and 32.64 ± 11.79 ng/m3 and lowest concentrations of 7.81 ± 2.00 ng/m3 and 2.83 ± 0.73 ng/m3, respectively. The values for levoglucosan varied from 0.69 ± 0.46 to 3.23 ± 2.07 µg/m3. The percentage contribution of the sum of the concentrations of these compounds to the total organic carbon varied from 1.7–5.1%. The sources contributing to particulate PAHs were identified using diagnostic ratios. Indicators like the Carbon Preference Index (CPI), Cmax and Plant Wax Number (%WNA) were used to identify the relative contributions to n-alkanes from anthropogenic and biogenic emissions. The source apportionment results and also the concentration trends for these molecular markers indicate that anthropogenic sources, especially vehicular exhaust, wood combustion and coal combustion, are mainly responsible for the organic fraction of particulate matter in Mumbai city. The sources identified qualitatively in this work can help in selecting the appropriate source profiles for estimating the quantitative contribution of these sources.

Coarse particulate organic matter in the interstitial zone of three French headwater streams

Headwater woodland streams are primarily heterotrophic: they receive substantial inputs of organic matter from the riparian vegetation, while autochthonous primary production is generally low. A substantial part of leaf litter entering running waters may be buried in the streambed because of flooding and sediment movement. Although the general significance of the hyporheic zone for stream metabolism has been reported early, organic matter storage within the sediment of streams has received less attention, with most studies only quantifying accumulations at the streambed surface and ignoring other stream compartments. In the present study, the amounts of three fractions of coarse particulate organic matter (CPOM; > 16, 4-16 and 1-4 mm) were determined in late autumn and early spring in the interstitial and benthic zones of three head- water streams of the Montagne Noire (South-Western France) differing in their substratum grain size. Our findings demonstrated that the total CPOM content in the interstitial zone can be much (up to one order of magnitude) higher than at the sediment surface. The sandy bottomed stream exhibited a higher amount of CPOM (whatever the size fraction) than the two other streams, suggesting that the sediment particle size may be a major determinant of CPOM storage. Given the large amount of organic matter stored in the interstitial zone, this compartment may play an important role for the carbon turnover and associated trophic dynamics in the stream ecosystem.

Kinetic studies on the anaerobic degradation of soluble and particulate matter in potato wastewater

The anaerobic degradation of particulate-containing potato processing wastewater using a mixed culture from an industrial anaerobic wastewater treatment plant as inoculum was characterised and modelled. Anaerobic digestion is being increasingly used for wastewater treatment, particularly those which contain high levels of biodegradable matter such as potato processing effluents. A major prerequisite for its proper modelling is a reliable wastewater characterisation with a proper discrimination of the chemical oxygen demand (COD) fractions. These wastewaters contain both soluble (S) and particulate (X) organic load that are assimilated by microorganisms at different rates. Furthermore, these wastewaters generally contain both solid (XI) and soluble (SI) inert to anaerobic degradation fractions. In this work, a procedure to determine the COD fractions of potato wastewater is developed. For the wastewater studied, the initial fraction of inert particulate organic matter ( x X I ) was negligible, while the initial fraction of inert soluble organic matter ( x S I ) was 20.94% ± 1.65. A model with first-order serial-parallel reactions system was developed for biodegradable fractions. This model has demonstrated its capability to predict the behaviour of the system and can be used for further research work or more complex reactor design.

A geostatistical approach to the field-scale pattern of heterotrophic soil CO2 emission using covariates

Soil heterotrophic respiration fluxes at field scale may exhibit a substantial spatial variability. The aim of this study was (1) to elucidate the role of soil temperature and different carbon fractions on heterotrophic soil respiration and (2) to test by which of three different statistical approaches (multiple regression, external drift kriging and simulated annealing) such influences may be best represented. Chamber-based measurements of respiration fluxes were carried out within a 180 × 40 m bare soil plot. Soil temperature was measured simultaneously to the flux measurements. Further, we recorded total soil organic carbon content, apparent electrical conductivity as well as mid-infrared spectroscopy-based carbon fractions as co-variates in addition to basic soil properties like stone content and texture. A stepwise multiple linear regression procedure was used to spatially predict bare soil respiration from the co-variates. The results showed that the particulate organic matter (POM) fraction and terrain elevation were able to explain the spatial pattern of heterotrophic soil respiration (R2 = 0.45). In a second step we applied external drift kriging to determine the improvement of using co-variates in an estimation procedure in comparison to ordinary kriging. The maximum relative improvement using the co-variates in terms of the root mean square error was 16%. In a third step we applied simulated annealing to perform stochastic simulations conditioned with external drift kriging to generate more realistic spatial patterns of heterotrophic respiration at plot scale. The conditional stochastic simulations revealed a significantly improved reproduction of the probability density function, the G-statistics value increased from 0.36 to 0.92. Further, the error in the reproduction of the semivariogram of the original point data decreased by more than one order of magnitude. All this confirmed that the mapping of soil respiration patterns may be significantly improved when considering terrain elevation and spatial heterogeneity of POM in combination with a conditional stochastic simulation.

Rock Fragments Control Size and Saturation of Organic Carbon Pools in Agricultural Topsoil

Rock fragments (RF) may severely reduce the amount of fine earth (FE) per soil volume. Here we quantified the effect of variable RF on spatial patterns of bulk soil organic carbon (SOC), particulate organic matter (POM) of three size classes, nonparticulate organic matter (nonPOM), and black carbon (BC). One hundred and twenty-nine soil samples (0-30 cm) were taken in a regular grid on an arable field nearby Selhausen (Germany). The weakly inclined site featured a strong gradient in RF, soil types covered Alfic Eutrochepts, as well as Typic and Albaquic Hapludalfs. In addition to C-pool patterns and RF we determined texture, Fe oxides, soil moisture, as well as hillslope and elevation above sea level. Additionally, 137 Cs measurements were conducted to indicate soil erosion. The reduction of SOC stocks by increasing amounts of RF on a percentage basis was smaller than attributable to mere dilution effects. Multiple regression analysis indicated BETA values of 0.65 to 0.73 between RF and FE contents of BC, nonPOM, and the finest POM fraction. The C contents of the coarse POM fractions were positively correlated with the amount of RF (R 2 = 0.72-0.78) and their spatial patterns were assumed to be caused by disproportionate input of plant litter to a reduced solum when the amount of RF increased. Statistical structure analysis and variography pointed to hierarchical C saturation of nonPOM and the finest POM fraction, which was additionally regulated by Fe oxide contents. Only the spatial distribution of BC (BETA = ―0.15) was affected by erosion.

Occurrence of the Parasite Genus Hematodinium (Alveolata: Syndinea) in the Water Column

Crustaceans worldwide are infected with alveolate parasites of the genus Hematodinium, causing substantial losses to langoustine and crab fisheries. The distinct seasonality in Hematodinium occurrence in their decapod hosts, as well as unsuccessful attempts at transmission, suggest the existence of life stages outside their benthic crustacean hosts. We used a nested polymerase chain reaction method to detect Hematodinium rDNA in the environment and in potential alternative hosts. Environmental samples from the Clyde Sea, Scotland, were screened during the April release of dinospores and during June and August, when infection prevalence is rare in benthic crustaceans. Hematodinium rDNA was amplified in 15% (14/94) of isolated langoustine larvae, and in 12% (13/111) of crab larvae. In addition, Hematodinium rDNA was present in mixed plankton samples devoid of decapod larvae, but including the 2 μm-10 mm fraction of particulate organic matter in the water column, containing phytoplankton and other zooplankton. These results indicate that Hematodinium occurs in the water column and is harboured by planktonic organisms, including larval stages of the crustacean hosts, when infections are at their lowest in adult hosts.