The mechanisms and specific sources of priming effects, i.e. short term changes of soil organic m... more The mechanisms and specific sources of priming effects, i.e. short term changes of soil organic matter (SOM) decomposition after substance addition, are still not fully understood. These uncertainties are partly method related, i.e. until now only two C sources in released CO 2 could be identified. We used a novel approach separating three carbon (C) sources in CO 2 efflux from soil. The approach is based on combination of different substances originated from C 3 or C 4 plants in different treatments and identical transformation of substances like C 3 sugar (from sugar beet) and C 4 sugar (from sugar cane). We investigated the influence of the addition of two substances having different microbial utilizability, i.e. slurry and sugar on the SOM or/and slurry decomposition in two grassland soils with different levels of C org (2.3 vs. 5.1% C). Application of slurry to the soil slightly accelerated the SOM decomposition. Addition of sugar lead to changes of SOM and slurry decomposition clearly characterized by two phases: immediately after sugar addition, the microorganisms switched from the decomposition of hardly utilizable SOM to the decomposition of easily utilizable sugar. This first phase was very short (2-3 days), hence was frequently missed in other experiments. The second phase showed a slightly increased slurry and SOM decomposition (compared to the soil without sugar). The separation of three sources in CO 2 efflux from grassland soils allowed us to conclude that the C will be utilized according to its utilizability: sugarOslurryOSOM. Additionally, decomposition of more inert C (here SOM) during the period of intensive sugar decomposition was strongly reduced (negative priming effect). We conclude that, priming effects involve a chain of mechanisms: (i) preferential substrate utilization, (ii) activation of microbial biomass by easily utilizable substrate (iii) subsequent increased utilization of following substrates according to their utilizability, and (iv) decline to initial state. q
Evidence for the movement of agricultural slurry and associated pollutants into surface waters is... more Evidence for the movement of agricultural slurry and associated pollutants into surface waters is often anecdotal, particularly with relation to its 'particulate' components which receive less attention than 'bio-available' soluble phases. To assess the extent of movement of slurry particles artificial fluorescent particles were mixed with slurry and applied to a field sub-catchment within a headwater catchment. Particles were 2-60 μm in diameter and two different densities, 2.7 and 1.2 g cm(-3) representing 'inorganic' and 'organic' material. Water samples from the field and catchment outlet were collected during two storm events following slurry application and analysed for particle and suspended sediment concentrations (SSC). SSC from the field and catchment outlet always formed clockwise hysteresis loops indicating sediment exhaustion and particles of the two densities were always found to be positively correlated. Particles from the field formed clockwise hysteresis loops during the first discharge event after slurry application, but anti-clockwise hysteresis loops during the second monitored event which indicated a depletion of readily mobilisable particles. Particles from the catchment outlet always formed anticlockwise hysteresis loops. Particle size became finer spatially, between field and catchment outlet, and temporally, between successive storm events. The results indicate that slurry particles may be readily transported within catchments but that different areas may contribute to pollutant loads long after the main peak in SSC has passed. The density of the particles did not appear to have any effect on particle transport however the size of the particles may play a more important role in the 2-60 μm range.
Despite the abundance of literature reporting both riparian and non-riparian buffer strip perform... more Despite the abundance of literature reporting both riparian and non-riparian buffer strip performance in the control of diffuse pollutants from agriculture, the spatial and temporal mechanistics of the processes involved are poorly understood. As a result, buffer zones have often been implemented incorrectly and have failed to deliver the benefits expected of them. One of the main challenges with buffer zone effectiveness has been found to be their by-passing by the passage of polluted water through sub-surface drains which in many regions of the UK has regularly been shown to greatly limit their value with regard to nutrient control [MAFF report, Leeds-Harrison 1996]. In addition, little work has been carried out on the role of additional, complementary structural buffering methods such as managed ditches and ponds, which may provide more benefits, especially if used either alongside or instead of the more conventional use of buffer strips. This paper describes a new 5 year Defra funded project*, which is using a multi-scaled approach to understand the abiotic and biotic drivers of the short-term and 'long-term' effectiveness of conventional grassed buffer strips. At the field scale, we are using high resolution monitoring methods to compare the effectiveness of other mitigation methods including buffer strips enhanced with subsurface bioreactors, managed ditches, and ponds, to control a range of water pollutants and hydrology. Each of the mitigation methods is being investigated both individually, and as part of a strategic modular network of mitigation methods in a purposely constructed and replicated experimental site.
Distributions and carbon isotope compositions of individual n-alkanes have been monitored during ... more Distributions and carbon isotope compositions of individual n-alkanes have been monitored during a 23-year decomposition experiment using litter-bags of Culluna vulgaris shoots buried in a peat bog in the Moor House Nature Reserve. After 23 years, up to 90% of weight loss had occurred for both bulk litter and for the c&Z35 n-alkane fractions. However, such extensive degradation was not accompanied by molecular carbon isotope fractionation -the 613C values of individual n-alkanes remained virtually unchanged. Biomarker n-alkane 6°C values are thereby further validated as proxies for palaeoenvironmental reconstruction and as tracers of carbon fiow in soils and sediments. '( 1997
The N2O and N2 fluxes emitted from a temperate UK grassland soil after fertiliser application (eq... more The N2O and N2 fluxes emitted from a temperate UK grassland soil after fertiliser application (equivalent to 25 and 75 kg N ha(-1)) were simultaneously measured, using a new automated soil incubation system, which replaces soil atmosphere (N2 dominated) with a He+O2 mixture. Dual isotope and isotopomer ratios of the emitted N2O were also determined. Total N2O and N2 fluxes were significantly lower (P<0.001) in the control (0 kg N) than in the 25 and 75 kg N treatments. The total N2O flux was significantly higher (P<0.001) in the 75 kg N than in the 25 kg N treatment. The general patterns of N2O and N2 fluxes were similar for both fertiliser treatments. The total gaseous N loss in the control treatment was nearly all N2, whereas in the fertiliser treatment more N2O than N2 was emitted from the soil. The ratio N2O/N2 fluxes as measured during the experiment suggested three phases in N2O production, in phase 1 nitrification>denitrification, in phase 2 denitrification>nitrification, and in phase 3 denitrification (and total denitrification)>nitrification. Dual delta15N and delta18O isotope and isotopomer (delta15Nalpha and delta15Nbeta) value ratios of emitted N2O also pointed towards an increasing dominance of the production of N2O by denitrification and total denitrification. The site preference value from the soil-emitted N2O was lower than the troposphere value. This confirmed that the enhanced troposphere N2O site preference could result from back injection of N2O from the stratosphere. The measurements of N2O/N2 flux ratio and the isotopic content of emitted N2O pointed, independently, to similar temporal trends in N2O production processes after fertiliser application to grassland soil. This confirmed that both measurements are suitable diagnostic tools to study the N2O production process in soils.
Co-deployment of two reagentless UV sensors for high temporal resolution (15 min) real time deter... more Co-deployment of two reagentless UV sensors for high temporal resolution (15 min) real time determination of wintertime DOC and nitrate-N export from a grassland lysimeter plot (North Wyke, Devon, UK) is reported. They showed rapid, transient but high impact perturbations of DOC (5.3-23 mg CL(-1)) and nitrate-N export after storm/snow melt which discontinuous sampling would not have observed. During a winter freeze/thaw cycle, DOC export (1.25 kg Cha(-1)d(-1)) was significantly higher than typical UK catchment values (maximum 0.25 kg Chad(-1)) and historical North Wyke data (0.7 kg Cha(-1)d(-1)). DOC concentrations were inversely correlated with the key DOC physico-chemical drivers of pH (January r=-0.65), and conductivity (January r=-0.64). Nitrate-N export (0.8-1.5 mg NL(-1)) was strongly correlated with DOC export (r ≥ 0.8). The DOC:NO3-N molar ratios showed that soil microbial N assimilation was not C limited and therefore high N accrual was not promoted in the River Taw, which is classified as a nitrate vulnerable zone (NVZ). The sensor was shown to be an effective sentinel device for identifying critical periods when rapid ecosystem N accumulation could be triggered by a shift in resource stoichiometry. It is therefore a useful tool to help evaluate land management strategies and impacts from climate change and intensive agriculture.
We investigated the speci®c diet and habitat of earthworms in relation to land use changes by int... more We investigated the speci®c diet and habitat of earthworms in relation to land use changes by integrating spatial and temporal scales and by using stable isotope ( 13 C and 15 N) techniques. The study involved two sites: Santiago (Northwest Spain) and North Wyke (Southwest England), both consisting of long term grassland which was partly converted to a maize crop in 1997. In 1998, the maize crop in Spain was divided into two, and one half was re-planted with maize (2 years maize) and the other half reconverted to grassland (1 year grassland); the same procedure was followed for the grassland resulting in two treatments, 2 years grassland and 1 year maize. At the English site only 2 years maize and 2 years grassland were under investigation. Within each of the four treatments in Spain and the two in England, three replicate plots were established. Random soil samples from three different depths (0±10, 10±20 and 20±30 cm), and earthworm specimens belonging to four different ecological categories (epigeic, anecic, epi/anecic and endogeic), were taken from each plot, treatment and site at the peak of the maize growth and after harvesting.
Changes in the specific diet of earthworms with time in relation to landuse changes and two diffe... more Changes in the specific diet of earthworms with time in relation to landuse changes and two different climates were studied by analysing 13C and 15N natural abundance in soils and animals. Soil samples fromthree depths (0–10, 10–20 and 20–30 cm) and earthworms were collected from two sites: Santiago (Northwest Spain) and North Wyke (Southwest England) both consisting of replicated long-term grasslands and recently converted to maize plots. Earthworms were hand-sorted in the field at the peak of the maize growth and after harvesting at both sites. In the Spanish plots, nine and eight earthworm species, all belonging to the three ecological categories (epigeic, anecic and endogeic), were found under maize and permanent pasture, whereas at the English site five and seven different species were, respectively, identified. At both sites 13C isotopic values of the earthworm tissues reflected changes in diet from C 3 to C 4 with epigeic and epi/anecic worms in the maize plots showing one delta unit difference in relation to the ones found in the grassland plots. Anecic worms seemed to be less responsive to landuse changes. The higher 13C values of the Spanish soils were also reflected in the earthworm tissues when compared with the English samples. 15N values showed no clear relationship with the cropping treatments but were clearly related to the ecological grouping, with endogeic worms reaching the highest values whereas for the epigeic and epi/anecic species the lowest values were obtained. This finding was also previously recorded by other authors1 and suggests that, in the future, stable isotope techniques could also be a useful tool in taxonomic studies.
Isotope fractionation factors associated with denitrification are still poorly examined due to co... more Isotope fractionation factors associated with denitrification are still poorly examined due to complexity of this process. The isotopologue signatures of N2O produced in course of denitrification are governed by the isotope fractionation occurring during its production (NO3- – N2O reaction step) and its reduction (N2O – N2 reaction step). Hence, for a reliable determination of fractionation factors of both N2O production and reduction, the independent data on the quantity of N2O reduction are necessary. This study is based on laboratory incubation experiments, where the N2O reduction ratio was determined using three different methods: direct N2-measurements (incubations under the N2-free atmosphere), 15N tracing (incubations with Na15NO3 addition) and reduction inhibition method (incubations with acetylene application). N2 and N2O fluxes and N2O isotopologue signatures (15NN2O, 18ON2O and SPN2O–Site Preference - difference in δ15N between the central and peripheral N positions of ...
ABSTRACT Assessing effects of organic fertilizer applications on N2O emissions is of great intere... more ABSTRACT Assessing effects of organic fertilizer applications on N2O emissions is of great interest because they can cause higher N2O emissions compared to inorganic fertilizers for a given amount of added nitrogen (N). But there are also reports about enhanced N2O reduction to climate-neutral elemental N2 after application of organic manures to soils. Factors controlling the N2O/(N2O + N2) product ratio of denitrification are interrelated, and also the ratio is difficult to study because of limitations in N2 flux measurements. In this study, we investigated N2O and N2 emissions from soil treated with organic fertilizers with different C/N ratios. An N2O isotopomer approach combined with conventional N2O and N2 flux measurements was employed to study underlying microbial pathways.
Evidence for the movement of agricultural slurry and associated pollutants into surface waters is... more Evidence for the movement of agricultural slurry and associated pollutants into surface waters is often anecdotal, particularly with relation to its 'particulate' components which receive less attention than 'bio-available' soluble phases. To assess the extent of movement of slurry particles artificial fluorescent particles were mixed with slurry and applied to a field sub-catchment within a headwater catchment. Particles were 2-60 μm in diameter and two different densities, 2.7 and 1.2 g cm(-3) representing 'inorganic' and 'organic' material. Water samples from the field and catchment outlet were collected during two storm events following slurry application and analysed for particle and suspended sediment concentrations (SSC). SSC from the field and catchment outlet always formed clockwise hysteresis loops indicating sediment exhaustion and particles of the two densities were always found to be positively correlated. Particles from the field formed clockwise hysteresis loops during the first discharge event after slurry application, but anti-clockwise hysteresis loops during the second monitored event which indicated a depletion of readily mobilisable particles. Particles from the catchment outlet always formed anticlockwise hysteresis loops. Particle size became finer spatially, between field and catchment outlet, and temporally, between successive storm events. The results indicate that slurry particles may be readily transported within catchments but that different areas may contribute to pollutant loads long after the main peak in SSC has passed. The density of the particles did not appear to have any effect on particle transport however the size of the particles may play a more important role in the 2-60 μm range.
Dryland environments are estimated to cover around 40% of the global land surface and are home to... more Dryland environments are estimated to cover around 40% of the global land surface and are home to approximately 2.5 billion people ). Many of these areas have recently experienced extensive land degradation. One such area and the focus of this project is the semi-arid US Southwest, where degradation over the past 150 years has been characterised by the invasion of woody vegetation into grasslands.
Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised b... more Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has 5 been determined in various soils, i.e. peat, forest, grassland and cropland, covered by various vegetation types, i.e., C 3 -vs. C 4 -plant type. These δ 13 C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ 13 C values of −28‰, branched GDGTs in C 3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰
The application of organic materials to agricultural lands is considered good practice to improve... more The application of organic materials to agricultural lands is considered good practice to improve soil organic matter content and recycle nutrients for crop growth. The anaerobic treatment of food waste may have environmental benefits, particularly with regard to greenhouse gases (GHGs) mitigation and enhancement of carbon sequestration. This work presents the results from a field experiment to evaluate CO(2) , CH(4) and N(2) O emissions from grassland amended with digestate produced by anaerobic fermentation of food waste. Experimental plots, located close to Rothamsted Research-North Wyke, were established using a randomized block design with three replicates and two treatments, added digestate (DG) and the unamended control (CNT). The digestate was applied on three occasions at an equivalent rate of 80 kg N ha(-1) . The application of digestate led to an increase in CO(2) emissions, especially after the 2(nd) application (74.1 kg CO(2) -C ha(-1) day(-1) ) compared with the CNT soil (36.4 kg CO(2) -C ha(-1) day(-1) ), whereas DG treatment did not affect the overall CH(4) and N(2) O emissions. The total grass yield harvested on a dry matter basis was greater in the DG treated plots (0.565 kg m(-2) ) than in the CNT plots (0.282 kg m(-2) ), as was the (15) N content in the harvest collected from the DG plots. The results suggest that the digestate can be applied to agricultural land as a fertilizer to grow crops. Our study was conducted in an exceptionally dry growing season, so conclusions about the effect of digestate on GHG emissions should take this into account, and further field trials conducted under more typical growing seasons are needed.
RATIONALE: This study aimed (i) to determine the isotopic fractionation factors associated with N... more RATIONALE: This study aimed (i) to determine the isotopic fractionation factors associated with N 2 O production and reduction during soil denitrification and (ii) to help specify the factors controlling the magnitude of the isotope effects. For the first time the isotope effects of denitrification were determined in an experiment under oxic atmosphere and using a novel approach where N 2 O production and reduction occurred simultaneously. METHODS: Soil incubations were performed under a He/O 2 atmosphere and the denitrification product ratio [N 2 O/(N 2 + N 2 O)] was determined by direct measurement of N 2 and N 2 O fluxes. N 2 O isotopocules were analyzed by mass spectrometry to determine δ 18 O, δ 15 N and 15 N site preference within the linear N 2 O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N 2 O production and reduction, taking into account emissions from two distinct soil pools. RESULTS: A clear relationship was observed between 15 N and 18 O isotope effects during N 2 O production and denitrification rates. For N 2 O reduction, diverse isotope effects were observed for the two distinct soil pools characterized by different product ratios. For moderate product ratios (from 0.1 to 1.0) the range of isotope effects given by previous studies was confirmed and refined, whereas for very low product ratios (below 0.1) the net isotope effects were much smaller. CONCLUSIONS: The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η 18 O/η 15 N ratios, previously accepted as typical for N 2 O reduction processes (i.e., higher than 2), are not valid for all conditions.
The mechanisms and specific sources of priming effects, i.e. short term changes of soil organic m... more The mechanisms and specific sources of priming effects, i.e. short term changes of soil organic matter (SOM) decomposition after substance addition, are still not fully understood. These uncertainties are partly method related, i.e. until now only two C sources in released CO 2 could be identified. We used a novel approach separating three carbon (C) sources in CO 2 efflux from soil. The approach is based on combination of different substances originated from C 3 or C 4 plants in different treatments and identical transformation of substances like C 3 sugar (from sugar beet) and C 4 sugar (from sugar cane). We investigated the influence of the addition of two substances having different microbial utilizability, i.e. slurry and sugar on the SOM or/and slurry decomposition in two grassland soils with different levels of C org (2.3 vs. 5.1% C). Application of slurry to the soil slightly accelerated the SOM decomposition. Addition of sugar lead to changes of SOM and slurry decomposition clearly characterized by two phases: immediately after sugar addition, the microorganisms switched from the decomposition of hardly utilizable SOM to the decomposition of easily utilizable sugar. This first phase was very short (2-3 days), hence was frequently missed in other experiments. The second phase showed a slightly increased slurry and SOM decomposition (compared to the soil without sugar). The separation of three sources in CO 2 efflux from grassland soils allowed us to conclude that the C will be utilized according to its utilizability: sugarOslurryOSOM. Additionally, decomposition of more inert C (here SOM) during the period of intensive sugar decomposition was strongly reduced (negative priming effect). We conclude that, priming effects involve a chain of mechanisms: (i) preferential substrate utilization, (ii) activation of microbial biomass by easily utilizable substrate (iii) subsequent increased utilization of following substrates according to their utilizability, and (iv) decline to initial state. q
Evidence for the movement of agricultural slurry and associated pollutants into surface waters is... more Evidence for the movement of agricultural slurry and associated pollutants into surface waters is often anecdotal, particularly with relation to its 'particulate' components which receive less attention than 'bio-available' soluble phases. To assess the extent of movement of slurry particles artificial fluorescent particles were mixed with slurry and applied to a field sub-catchment within a headwater catchment. Particles were 2-60 μm in diameter and two different densities, 2.7 and 1.2 g cm(-3) representing 'inorganic' and 'organic' material. Water samples from the field and catchment outlet were collected during two storm events following slurry application and analysed for particle and suspended sediment concentrations (SSC). SSC from the field and catchment outlet always formed clockwise hysteresis loops indicating sediment exhaustion and particles of the two densities were always found to be positively correlated. Particles from the field formed clockwise hysteresis loops during the first discharge event after slurry application, but anti-clockwise hysteresis loops during the second monitored event which indicated a depletion of readily mobilisable particles. Particles from the catchment outlet always formed anticlockwise hysteresis loops. Particle size became finer spatially, between field and catchment outlet, and temporally, between successive storm events. The results indicate that slurry particles may be readily transported within catchments but that different areas may contribute to pollutant loads long after the main peak in SSC has passed. The density of the particles did not appear to have any effect on particle transport however the size of the particles may play a more important role in the 2-60 μm range.
Despite the abundance of literature reporting both riparian and non-riparian buffer strip perform... more Despite the abundance of literature reporting both riparian and non-riparian buffer strip performance in the control of diffuse pollutants from agriculture, the spatial and temporal mechanistics of the processes involved are poorly understood. As a result, buffer zones have often been implemented incorrectly and have failed to deliver the benefits expected of them. One of the main challenges with buffer zone effectiveness has been found to be their by-passing by the passage of polluted water through sub-surface drains which in many regions of the UK has regularly been shown to greatly limit their value with regard to nutrient control [MAFF report, Leeds-Harrison 1996]. In addition, little work has been carried out on the role of additional, complementary structural buffering methods such as managed ditches and ponds, which may provide more benefits, especially if used either alongside or instead of the more conventional use of buffer strips. This paper describes a new 5 year Defra funded project*, which is using a multi-scaled approach to understand the abiotic and biotic drivers of the short-term and 'long-term' effectiveness of conventional grassed buffer strips. At the field scale, we are using high resolution monitoring methods to compare the effectiveness of other mitigation methods including buffer strips enhanced with subsurface bioreactors, managed ditches, and ponds, to control a range of water pollutants and hydrology. Each of the mitigation methods is being investigated both individually, and as part of a strategic modular network of mitigation methods in a purposely constructed and replicated experimental site.
Distributions and carbon isotope compositions of individual n-alkanes have been monitored during ... more Distributions and carbon isotope compositions of individual n-alkanes have been monitored during a 23-year decomposition experiment using litter-bags of Culluna vulgaris shoots buried in a peat bog in the Moor House Nature Reserve. After 23 years, up to 90% of weight loss had occurred for both bulk litter and for the c&Z35 n-alkane fractions. However, such extensive degradation was not accompanied by molecular carbon isotope fractionation -the 613C values of individual n-alkanes remained virtually unchanged. Biomarker n-alkane 6°C values are thereby further validated as proxies for palaeoenvironmental reconstruction and as tracers of carbon fiow in soils and sediments. '( 1997
The N2O and N2 fluxes emitted from a temperate UK grassland soil after fertiliser application (eq... more The N2O and N2 fluxes emitted from a temperate UK grassland soil after fertiliser application (equivalent to 25 and 75 kg N ha(-1)) were simultaneously measured, using a new automated soil incubation system, which replaces soil atmosphere (N2 dominated) with a He+O2 mixture. Dual isotope and isotopomer ratios of the emitted N2O were also determined. Total N2O and N2 fluxes were significantly lower (P<0.001) in the control (0 kg N) than in the 25 and 75 kg N treatments. The total N2O flux was significantly higher (P<0.001) in the 75 kg N than in the 25 kg N treatment. The general patterns of N2O and N2 fluxes were similar for both fertiliser treatments. The total gaseous N loss in the control treatment was nearly all N2, whereas in the fertiliser treatment more N2O than N2 was emitted from the soil. The ratio N2O/N2 fluxes as measured during the experiment suggested three phases in N2O production, in phase 1 nitrification>denitrification, in phase 2 denitrification>nitrification, and in phase 3 denitrification (and total denitrification)>nitrification. Dual delta15N and delta18O isotope and isotopomer (delta15Nalpha and delta15Nbeta) value ratios of emitted N2O also pointed towards an increasing dominance of the production of N2O by denitrification and total denitrification. The site preference value from the soil-emitted N2O was lower than the troposphere value. This confirmed that the enhanced troposphere N2O site preference could result from back injection of N2O from the stratosphere. The measurements of N2O/N2 flux ratio and the isotopic content of emitted N2O pointed, independently, to similar temporal trends in N2O production processes after fertiliser application to grassland soil. This confirmed that both measurements are suitable diagnostic tools to study the N2O production process in soils.
Co-deployment of two reagentless UV sensors for high temporal resolution (15 min) real time deter... more Co-deployment of two reagentless UV sensors for high temporal resolution (15 min) real time determination of wintertime DOC and nitrate-N export from a grassland lysimeter plot (North Wyke, Devon, UK) is reported. They showed rapid, transient but high impact perturbations of DOC (5.3-23 mg CL(-1)) and nitrate-N export after storm/snow melt which discontinuous sampling would not have observed. During a winter freeze/thaw cycle, DOC export (1.25 kg Cha(-1)d(-1)) was significantly higher than typical UK catchment values (maximum 0.25 kg Chad(-1)) and historical North Wyke data (0.7 kg Cha(-1)d(-1)). DOC concentrations were inversely correlated with the key DOC physico-chemical drivers of pH (January r=-0.65), and conductivity (January r=-0.64). Nitrate-N export (0.8-1.5 mg NL(-1)) was strongly correlated with DOC export (r ≥ 0.8). The DOC:NO3-N molar ratios showed that soil microbial N assimilation was not C limited and therefore high N accrual was not promoted in the River Taw, which is classified as a nitrate vulnerable zone (NVZ). The sensor was shown to be an effective sentinel device for identifying critical periods when rapid ecosystem N accumulation could be triggered by a shift in resource stoichiometry. It is therefore a useful tool to help evaluate land management strategies and impacts from climate change and intensive agriculture.
We investigated the speci®c diet and habitat of earthworms in relation to land use changes by int... more We investigated the speci®c diet and habitat of earthworms in relation to land use changes by integrating spatial and temporal scales and by using stable isotope ( 13 C and 15 N) techniques. The study involved two sites: Santiago (Northwest Spain) and North Wyke (Southwest England), both consisting of long term grassland which was partly converted to a maize crop in 1997. In 1998, the maize crop in Spain was divided into two, and one half was re-planted with maize (2 years maize) and the other half reconverted to grassland (1 year grassland); the same procedure was followed for the grassland resulting in two treatments, 2 years grassland and 1 year maize. At the English site only 2 years maize and 2 years grassland were under investigation. Within each of the four treatments in Spain and the two in England, three replicate plots were established. Random soil samples from three different depths (0±10, 10±20 and 20±30 cm), and earthworm specimens belonging to four different ecological categories (epigeic, anecic, epi/anecic and endogeic), were taken from each plot, treatment and site at the peak of the maize growth and after harvesting.
Changes in the specific diet of earthworms with time in relation to landuse changes and two diffe... more Changes in the specific diet of earthworms with time in relation to landuse changes and two different climates were studied by analysing 13C and 15N natural abundance in soils and animals. Soil samples fromthree depths (0–10, 10–20 and 20–30 cm) and earthworms were collected from two sites: Santiago (Northwest Spain) and North Wyke (Southwest England) both consisting of replicated long-term grasslands and recently converted to maize plots. Earthworms were hand-sorted in the field at the peak of the maize growth and after harvesting at both sites. In the Spanish plots, nine and eight earthworm species, all belonging to the three ecological categories (epigeic, anecic and endogeic), were found under maize and permanent pasture, whereas at the English site five and seven different species were, respectively, identified. At both sites 13C isotopic values of the earthworm tissues reflected changes in diet from C 3 to C 4 with epigeic and epi/anecic worms in the maize plots showing one delta unit difference in relation to the ones found in the grassland plots. Anecic worms seemed to be less responsive to landuse changes. The higher 13C values of the Spanish soils were also reflected in the earthworm tissues when compared with the English samples. 15N values showed no clear relationship with the cropping treatments but were clearly related to the ecological grouping, with endogeic worms reaching the highest values whereas for the epigeic and epi/anecic species the lowest values were obtained. This finding was also previously recorded by other authors1 and suggests that, in the future, stable isotope techniques could also be a useful tool in taxonomic studies.
Isotope fractionation factors associated with denitrification are still poorly examined due to co... more Isotope fractionation factors associated with denitrification are still poorly examined due to complexity of this process. The isotopologue signatures of N2O produced in course of denitrification are governed by the isotope fractionation occurring during its production (NO3- – N2O reaction step) and its reduction (N2O – N2 reaction step). Hence, for a reliable determination of fractionation factors of both N2O production and reduction, the independent data on the quantity of N2O reduction are necessary. This study is based on laboratory incubation experiments, where the N2O reduction ratio was determined using three different methods: direct N2-measurements (incubations under the N2-free atmosphere), 15N tracing (incubations with Na15NO3 addition) and reduction inhibition method (incubations with acetylene application). N2 and N2O fluxes and N2O isotopologue signatures (15NN2O, 18ON2O and SPN2O–Site Preference - difference in δ15N between the central and peripheral N positions of ...
ABSTRACT Assessing effects of organic fertilizer applications on N2O emissions is of great intere... more ABSTRACT Assessing effects of organic fertilizer applications on N2O emissions is of great interest because they can cause higher N2O emissions compared to inorganic fertilizers for a given amount of added nitrogen (N). But there are also reports about enhanced N2O reduction to climate-neutral elemental N2 after application of organic manures to soils. Factors controlling the N2O/(N2O + N2) product ratio of denitrification are interrelated, and also the ratio is difficult to study because of limitations in N2 flux measurements. In this study, we investigated N2O and N2 emissions from soil treated with organic fertilizers with different C/N ratios. An N2O isotopomer approach combined with conventional N2O and N2 flux measurements was employed to study underlying microbial pathways.
Evidence for the movement of agricultural slurry and associated pollutants into surface waters is... more Evidence for the movement of agricultural slurry and associated pollutants into surface waters is often anecdotal, particularly with relation to its 'particulate' components which receive less attention than 'bio-available' soluble phases. To assess the extent of movement of slurry particles artificial fluorescent particles were mixed with slurry and applied to a field sub-catchment within a headwater catchment. Particles were 2-60 μm in diameter and two different densities, 2.7 and 1.2 g cm(-3) representing 'inorganic' and 'organic' material. Water samples from the field and catchment outlet were collected during two storm events following slurry application and analysed for particle and suspended sediment concentrations (SSC). SSC from the field and catchment outlet always formed clockwise hysteresis loops indicating sediment exhaustion and particles of the two densities were always found to be positively correlated. Particles from the field formed clockwise hysteresis loops during the first discharge event after slurry application, but anti-clockwise hysteresis loops during the second monitored event which indicated a depletion of readily mobilisable particles. Particles from the catchment outlet always formed anticlockwise hysteresis loops. Particle size became finer spatially, between field and catchment outlet, and temporally, between successive storm events. The results indicate that slurry particles may be readily transported within catchments but that different areas may contribute to pollutant loads long after the main peak in SSC has passed. The density of the particles did not appear to have any effect on particle transport however the size of the particles may play a more important role in the 2-60 μm range.
Dryland environments are estimated to cover around 40% of the global land surface and are home to... more Dryland environments are estimated to cover around 40% of the global land surface and are home to approximately 2.5 billion people ). Many of these areas have recently experienced extensive land degradation. One such area and the focus of this project is the semi-arid US Southwest, where degradation over the past 150 years has been characterised by the invasion of woody vegetation into grasslands.
Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised b... more Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has 5 been determined in various soils, i.e. peat, forest, grassland and cropland, covered by various vegetation types, i.e., C 3 -vs. C 4 -plant type. These δ 13 C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ 13 C values of −28‰, branched GDGTs in C 3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰
The application of organic materials to agricultural lands is considered good practice to improve... more The application of organic materials to agricultural lands is considered good practice to improve soil organic matter content and recycle nutrients for crop growth. The anaerobic treatment of food waste may have environmental benefits, particularly with regard to greenhouse gases (GHGs) mitigation and enhancement of carbon sequestration. This work presents the results from a field experiment to evaluate CO(2) , CH(4) and N(2) O emissions from grassland amended with digestate produced by anaerobic fermentation of food waste. Experimental plots, located close to Rothamsted Research-North Wyke, were established using a randomized block design with three replicates and two treatments, added digestate (DG) and the unamended control (CNT). The digestate was applied on three occasions at an equivalent rate of 80 kg N ha(-1) . The application of digestate led to an increase in CO(2) emissions, especially after the 2(nd) application (74.1 kg CO(2) -C ha(-1) day(-1) ) compared with the CNT soil (36.4 kg CO(2) -C ha(-1) day(-1) ), whereas DG treatment did not affect the overall CH(4) and N(2) O emissions. The total grass yield harvested on a dry matter basis was greater in the DG treated plots (0.565 kg m(-2) ) than in the CNT plots (0.282 kg m(-2) ), as was the (15) N content in the harvest collected from the DG plots. The results suggest that the digestate can be applied to agricultural land as a fertilizer to grow crops. Our study was conducted in an exceptionally dry growing season, so conclusions about the effect of digestate on GHG emissions should take this into account, and further field trials conducted under more typical growing seasons are needed.
RATIONALE: This study aimed (i) to determine the isotopic fractionation factors associated with N... more RATIONALE: This study aimed (i) to determine the isotopic fractionation factors associated with N 2 O production and reduction during soil denitrification and (ii) to help specify the factors controlling the magnitude of the isotope effects. For the first time the isotope effects of denitrification were determined in an experiment under oxic atmosphere and using a novel approach where N 2 O production and reduction occurred simultaneously. METHODS: Soil incubations were performed under a He/O 2 atmosphere and the denitrification product ratio [N 2 O/(N 2 + N 2 O)] was determined by direct measurement of N 2 and N 2 O fluxes. N 2 O isotopocules were analyzed by mass spectrometry to determine δ 18 O, δ 15 N and 15 N site preference within the linear N 2 O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N 2 O production and reduction, taking into account emissions from two distinct soil pools. RESULTS: A clear relationship was observed between 15 N and 18 O isotope effects during N 2 O production and denitrification rates. For N 2 O reduction, diverse isotope effects were observed for the two distinct soil pools characterized by different product ratios. For moderate product ratios (from 0.1 to 1.0) the range of isotope effects given by previous studies was confirmed and refined, whereas for very low product ratios (below 0.1) the net isotope effects were much smaller. CONCLUSIONS: The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η 18 O/η 15 N ratios, previously accepted as typical for N 2 O reduction processes (i.e., higher than 2), are not valid for all conditions.
Uploads
Papers by R. Bol
..... ...... ....... .
..
. ...
..
.. ........... ... ..... ........ ... ...... ........ .......... ...... ... ..... .... ..........
......... .... .......... .. .... .... ......... ..... ... ...... ......... .. . ..... .... .. ..... .. ..... ... ..... .... .. ..... ...
....... .... .... ... ... .... ... .......... .... ..... .. ..... ...... ... ... ..... .... ........... .. ......... .. .... ........... ...
.... ......... ... ........ ... ... ......... ......... .. ... ........... . ..... ......... ... . .... ...... .. ... ....... .... .... .
..... ..... ... . ..... ......... .... ..... .............. ...... .... .. ... .... .......... .. ..... ... ... ... .. ........ .....
......... ..... .... ............
...... .... ....... .... ..... ......... ...... ...... ..... ... ..... .... ... ......... ......... ......... .. .... .........
.......... .......... ......... ....... .......... ... .......... .... ..... .... .... ..... ......... ... .... .. ... .... .. ... ..... ......
... ..... ...........
....... ..... ....
..
.......... ...
..
.......... .... ........ .. ... ....... ..... ..... ... .... ........ .. ... ......... .......
... ....... . ...... ............ ....... ... ..... ...... .. ... ....... ... ... ........ ...........
... .......... .. ...
..
. ...... .. ... ..... ....... .. ... ..... .... ...... .... ........ .. ..... ..... ..... ... ......... ....
...... ... ....... .... ... .......... ........ .. ... .. .. .. ...... .... ...... ....... ......... ......... ....... .. .......... .... .
.......... ... ..... .. ....... .... ..... ...... ...
......... .......... ... ... ...... ........ .. ....... ....... ........ .. ......... ........ .... ........ ....... ... ...... .....
....... ... ....... . ....... ...... .. . ...... .. ............ ....... .. ...... .... ........ .... ........... ...... .... ........ . ... .
....... ........ ........... . ........ .... .. ........ ....... ....... ... .......... ... .... ... ......... ....... ..... ...........
....... ... ........ ...... .. ... ............ ......
In the Spanish plots, nine and eight earthworm species, all belonging to the three ecological categories (epigeic, anecic and endogeic), were found under maize and permanent pasture, whereas at the English site five and seven different species were, respectively, identified. At both sites
13C isotopic values of the earthworm tissues reflected changes in diet from C 3 to C 4 with epigeic and epi/anecic worms in the maize plots showing one delta unit difference in relation to the ones found in the grassland plots. Anecic worms seemed to be less responsive to landuse changes. The higher 13C values
of the Spanish soils were also reflected in the earthworm tissues when compared with the English samples.
15N values showed no clear relationship with the cropping treatments but were clearly related to the ecological grouping, with endogeic worms reaching the highest values whereas for the epigeic and epi/anecic species the lowest values were obtained. This finding was also previously recorded by other authors1 and suggests that, in the future, stable isotope techniques could also be a useful tool in taxonomic studies.
..... ...... ....... .
..
. ...
..
.. ........... ... ..... ........ ... ...... ........ .......... ...... ... ..... .... ..........
......... .... .......... .. .... .... ......... ..... ... ...... ......... .. . ..... .... .. ..... .. ..... ... ..... .... .. ..... ...
....... .... .... ... ... .... ... .......... .... ..... .. ..... ...... ... ... ..... .... ........... .. ......... .. .... ........... ...
.... ......... ... ........ ... ... ......... ......... .. ... ........... . ..... ......... ... . .... ...... .. ... ....... .... .... .
..... ..... ... . ..... ......... .... ..... .............. ...... .... .. ... .... .......... .. ..... ... ... ... .. ........ .....
......... ..... .... ............
...... .... ....... .... ..... ......... ...... ...... ..... ... ..... .... ... ......... ......... ......... .. .... .........
.......... .......... ......... ....... .......... ... .......... .... ..... .... .... ..... ......... ... .... .. ... .... .. ... ..... ......
... ..... ...........
....... ..... ....
..
.......... ...
..
.......... .... ........ .. ... ....... ..... ..... ... .... ........ .. ... ......... .......
... ....... . ...... ............ ....... ... ..... ...... .. ... ....... ... ... ........ ...........
... .......... .. ...
..
. ...... .. ... ..... ....... .. ... ..... .... ...... .... ........ .. ..... ..... ..... ... ......... ....
...... ... ....... .... ... .......... ........ .. ... .. .. .. ...... .... ...... ....... ......... ......... ....... .. .......... .... .
.......... ... ..... .. ....... .... ..... ...... ...
......... .......... ... ... ...... ........ .. ....... ....... ........ .. ......... ........ .... ........ ....... ... ...... .....
....... ... ....... . ....... ...... .. . ...... .. ............ ....... .. ...... .... ........ .... ........... ...... .... ........ . ... .
....... ........ ........... . ........ .... .. ........ ....... ....... ... .......... ... .... ... ......... ....... ..... ...........
....... ... ........ ...... .. ... ............ ......
In the Spanish plots, nine and eight earthworm species, all belonging to the three ecological categories (epigeic, anecic and endogeic), were found under maize and permanent pasture, whereas at the English site five and seven different species were, respectively, identified. At both sites
13C isotopic values of the earthworm tissues reflected changes in diet from C 3 to C 4 with epigeic and epi/anecic worms in the maize plots showing one delta unit difference in relation to the ones found in the grassland plots. Anecic worms seemed to be less responsive to landuse changes. The higher 13C values
of the Spanish soils were also reflected in the earthworm tissues when compared with the English samples.
15N values showed no clear relationship with the cropping treatments but were clearly related to the ecological grouping, with endogeic worms reaching the highest values whereas for the epigeic and epi/anecic species the lowest values were obtained. This finding was also previously recorded by other authors1 and suggests that, in the future, stable isotope techniques could also be a useful tool in taxonomic studies.