You are what your host eats: The trophic structure and food chain length of a symbiont community are coupled with the plastic diet of the host ant.

Food chain length provides key information on the flow of nutrients and energy in ecosystems. Variation in food chain length has primarily been explained by environmental drivers such as ecosystem size and productivity. Most insights are obtained from theory or aquatic systems, but the importance of these drivers remains largely untested in terrestrial systems. We exploited red wood ant nests markedly differing in size as natural experiments to quantify the drivers of trophic structure and food chain length of their symbiont arthropod communities. Using stable isotopes, we explored the variation in the trophic positions of four symbiont species with the trophic position of the top predator as a proxy for food chain length of the symbiont community. Nest size did not affect food chain length, nor trophic distance between the symbionts. Instead, food chain length and the trophic positions of the symbionts were strongly affected by the host's foraging decisions. When the host diet shifted from predominantly herbivorous to more predacious, the trophic position of the symbionts and food chain length strongly increased. We show for the first time that a food web can be structured by biotic interactions with an engineering species rather than by abiotic environmental variables.

Organic matter processing in a [simulated] offshore wind farm ecosystem in current and future climate and aquaculture scenarios.

The rapid development of blue economy and human use of offshore space triggered the concept of co-location of marine activities and is causing diverse local pressures on the environment. These pressures add to, and interact with, global challenges such as ocean acidification and warming. This study investigates the combined pressures of climate change and the planned co-location of offshore wind farm (OWF) and aquaculture zones on the carbon flow through epifaunal communities inhabiting wind turbines in the North Sea. A 13C-labelled phytoplankton pulse-chase experiment was performed in mesocosms (4 m3) holding undisturbed hard-substrate (HS) communities, natural sediment with infauna, and mobile invertebrate predators. Carbon assimilation was quantified under current and predicted future-climate conditions (+3 °C and -0.3 pH units), as well as a future-climate co-use scenario with blue mussel (Mytilus edulis) aquaculture. Climate change induced an increase in macrofaunal carbon assimilation as well as an organic enrichment of underlying sediments. Dynamic (non-)trophic links between M. edulis and other HS epifauna resulted in shifts among the species contributing most to the phytoplankton-derived carbon flow across climate scenarios. Increased inter- and intraspecific resource competition in the presence of M. edulis aquaculture prevented a large increase in the total assimilation of phytoplankton by HS fauna. Lower individual carbon assimilation rates by both mussels and other epifauna suggest that if filter capacity by HS epifauna would approach renewal by advection/mixing, M. edulis individuals would likely grow to a smaller-than-desired commercial size. In the same scenario, benthic organic carbon mineralisation was significantly boosted due to increased organic matter deposition by the aquaculture set-up. Combining these results with in situ OWF abundance data confirmed M. edulis as the most impactful OWF AHS species in terms of (total) carbon assimilation as well as the described stress responses due to climate change and the addition of bivalve aquaculture.

Warming and redistribution of nitrogen inputs drive an increase in terrestrial nitrous oxide emission factor.

Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas N2O. Despite their importance, shifts in terrestrial N loss pathways driven by global change are highly uncertain. Here we present a coupled soil-atmosphere isotope model (IsoTONE) to quantify terrestrial N losses and N2O emission factors from 1850-2020. We find that N inputs from atmospheric deposition caused 51% of anthropogenic N2O emissions from soils in 2020. The mean effective global emission factor for N2O was 4.3 ± 0.3% in 2020 (weighted by N inputs), much higher than the surface area-weighted mean (1.1 ± 0.1%). Climate change and spatial redistribution of fertilisation N inputs have driven an increase in global emission factor over the past century, which accounts for 18% of the anthropogenic soil flux in 2020. Predicted increases in fertilisation in emerging economies will accelerate N2O-driven climate warming in coming decades, unless targeted mitigation measures are introduced.

A novel instrument for the prevention of condylar torque in bilateral sagittal ramus osteotomy when using bicortical screw fixation.

When using the bilateral sagittal split osteotomy (BSSO) technique, rigid internal fixation (RIF) remains the standard method to accurately fix the distal and proximal osteotomy fragments. A concern with the use of RIF, especially with bicortical screws, is the increased risk of condylar torque and its functional consequences. This technical note introduces a new method for preventing torque of the mandibular condyles after BSSO, using a sagittal split space maintainer.

Rapid and irreversible sorption behavior of 7Be assessed to evaluate its use as a catchment sediment tracer.

Beryllium-7 (7Be) has been used as a sediment tracer to evaluate soil redistribution rates at hillslopes and as a tool to estimate sediment residence time in river systems. A key assumption for the use of 7Be as a sediment tracer is the rapid and irreversible sorption of 7Be upon contact with the soil particles. However, recent studies have raised questions about the validity of these assumptions. Seven soil types were selected to assess the adsorption rate of 7Be on the soil particles, subsequently an extraction experiment was performed to assess the rate of desorption. Next, different treatments were applied to assess the impact of soil pH, fertilizer, humic acid and organic matter on the adsorption of Be. Finally, the influence of regularly occurring cations present on the soil complex on the adsorption of Be on pure clay minerals was evaluated. The adsorption rate experiment showed a rapid and nearly complete sorption of Be for Luvisols and Cambisols under agriculture. For a temperate climate Stagnosol under forest and two highly weathered tropical Ferralsols sorption of Be was less rapid and less complete. This may result in an incomplete adsorption of 7Be on these three soils when runoff initiates, which could lead to an overestimation of erosion rates and sediment residence time. Additional observations were made during the extraction experiment, showing a significant loss of Be from the forest Stagnosol and a stable binding of Be to the arable soils. Of the different treatments applied, only pH showed to be of influence. Finally, Ca2+ and NH4+ on the soil complex had only a limited effect on the adsorption of Be, while Al3+ in combination with a low pH inhibits the adsorption of Be on the exchange complex of the pure clay minerals. All these findings more rigorously support the use of 7Be as a soil redistribution tracer in arable soils in a temperate climate at a hillslope scale. The use of 7Be in highly weathered Ferralsols or forest rich environments should be limited to avoid overestimations of erosion rates. The spatially extended use of 7Be to evaluate residence times of sediments should be avoided in catchments with rapid changing environmental parameters as they might influence the sorption behavior of 7Be.

Denitrification and indirect N2O emissions in groundwater: hydrologic and biogeochemical influences.

Identification of specific landscape areas with high and low groundwater denitrification potential is critical for improved management of agricultural nitrogen (N) export to ground and surface waters and indirect nitrous oxide (N2O) emissions. Denitrification products together with concurrent hydrogeochemical properties were analysed over two years at three depths at two low (L) and two high (H) permeability agricultural sites in Ireland. Mean N2O-N at H sites were significantly higher than L sites, and decreased with depth. Conversely, excess N2-N were significantly higher at L sites than H sites and did not vary with depth. Denitrification was a significant pathway of nitrate (NO3⁻-N) reduction at L sites but not at H sites, reducing 46-77% and 4-8% of delivered N with resulting mean NO3⁻-N concentrations of 1-4 and 12-15 mg N L⁻¹ at L and H sites, respectively. Mean N2O-N emission factors (EF5g) were higher than the most recent Intergovernmental Panel on Climate Change (IPCC, 2006) default value and more similar to the older IPCC (1997) values. Recharge during winter increased N2O but decreased excess dinitrogen (excess N2-N) at both sites, probably due to increased dissolved oxygen (DO) coupled with low groundwater temperatures. Denitrifier functional genes were similar at all sites and depths. Data showed that highly favourable conditions prevailed for denitrification to occur--multiple electron donors, low redox potential (Eh<100 mV), low DO (<2 mg L⁻¹), low permeability (k(s)<0.005 m·d⁻¹) and a shallow unsaturated zone (<2 m). Quantification of excess N2-N in groundwater helps to close N balances at the local, regional and global scales.

Importance and functions of European grasslands.

The European agricultural policy is not simple and needs to accommodate also social and environmental requirements. Grassland will continue to be an important form of land use in Europe, but with increased diversity in management objectives and systems used. Besides its role as basic nutrient for herbivores and ruminants grasslands have opportunities for adding value by exploiting positive health characteristics in animal products from grassland and through the delivery of environmental benefits. In fact grasslands contribute to a high degree to the struggle against erosion and to the regularizing of water regimes, to the purification of fertilizers and pesticides and to biodiversity. Finally they have aesthetic role and recreational function as far as they provide public access that other agricultural uses do not allow. But even for grassland it is very difficult to create a good frame for its different tasks (1) the provision of forage for livestock, (2) protection and conservation of soil and water resources, (3) furnishing a habitat for wildlife, both flora and fauna and (4) contribution to the attractiveness of the landscape. Nevertheless it is the only crop, able to fulfil so many tasks and to fit so many requirements.

Advances in coupling a commercial total organic carbon analyser with an isotope ratio mass spectrometer to determine the isotopic signal of the total dissolved nitrogen pool.

A new method has been developed to analyse 15N of the total dissolved nitrogen (TDN) pool. The method operates on a commercial total organic carbon (TOC) analyser coupled to an elemental analyser/isotope ratio mass spectrometer (EA-IRMS). Nitrogen compounds are combusted to nitric oxide (NO) and nitrogen dioxide (NO2) by high-temperature catalytic oxidation (HTCO), after which the NOx gas is transferred to an EA-IRMS for isotopic nitrogen analysis. The system is described, including five modifications of the system in order to overcome analytical problems. First, flow paths were modified to run both systems on helium as carrier gas, while complete sample oxidation was maintained. Secondly, the catalyst structure was adapted to allow high injection volumes at the given backpressures delivered by the EA system. Thirdly, we installed a Permapure dehumidification system as the standard Peltier element did not satisfy dehumidification requirements. Finally, we prevented the inflow of atmospheric nitrogen into the system. In a final stage, we are planning to automate the coupled system in order to run a continuous batch of up to 60 samples. We have obtained satisfactory results on the accuracy and precision of 180+/-1 per thousand potassium nitrate samples (IAEA, USGS-32). Running a batch of five samples resulted in a mean isotopic value of 178.8 per thousand with a standard deviation of 2.8 per thousand. Some important issues could not yet be addressed here, and will have to be evaluated once the system is running on a continuous base. However, the results appear promising and this system has the potential to become a method for TD15N analysis. An appropriate TD15N analysis method might open new challenges in aquatic and terrestrial ecosystem nitrogen studies, including a more comprehensive study of the dissolved organic nitrogen pool.

[Physicochemical and biological factors affecting atmospheric methane oxidation in gray forest soils].

The decline of methane oxidizing activities in gray forest soil upon its conversion into arable land was shown to be caused by major changes in biotic and physicochemical properties of soil. Using the method of immune serums, methane-oxidizing bacteria were detected in both forest and agricultural soils, but their populations differed significantly in both abundance and composition. In the forest soil, the number of methanotrophs was an order of magnitude higher than in arable soil, amounting to 3.5 x 10(8) and 0.24 x 10(8) cells/g soil, respectively. All methane-oxidizing bacteria identified in the forest soil belonged to the genus Methylocystis, and 94% of these were represented by a single species, M. parvus. The arable soil was dominated by type I methanotrophs (Methylobacter and Methylomonas, 67.6%), occurring along with bacteria of the genus Methylocystis. In addition, arable soil is characterized by a low content of microbial biomass, lower porosity and water permeability of soil aggregates, and the predominance of nitrogen mineralization processes over those of nitrogen immobilization. These factors can also contribute to lower rates of methane oxidation in arable soil as compared to forest soil.

Methods to adjust for the interference of N2O on delta13C and delta18O measurements of CO2 from soil mineralization.

In this paper we present an overview of the present knowledge relating to methods that avoid interference of N2O on delta13C and delta18O measurements of CO2. The main focus of research to date has been on atmospheric samples. However, N2O is predominantly generated by soil processes. Isotope analyses related to soil trace gas emissions are often performed with continuous flow isotope ratio mass spectrometers, which do not necessarily have the high precision needed for atmospheric research. However, it was shown by using laboratory and field samples that a correction to obtain reliable delta13C and delta18O values is also required for a commercial continuous flow isotope ratio mass spectrometer. The capillary gas chromatography column of the original equipment was changed to a packed Porapak Q column. This adaptation resulted in an improved accuracy and precision of delta13C (standard deviation(Ghent): from 0.2 to 0.08 per thousand; standard deviation(Lincoln): from 0.2 to 0.13 per thousand) of CO2 for N2O/CO2 ratios up to 0.1. For delta18O there was an improvement for the standard deviation measured at Ghent University (0.13 to 0.08 per thousand) but not for the measurements at Lincoln University (0.08 to 0.23 per thousand). The benefits of using the packed Porapak Q column compared with the theoretical correction method meant that samples were not limited to small N(2)O concentrations, they did not require an extra N2O concentration measurement, and measurements were independent of the variable isotopic composition of N2O from soil.

[Seasonal dynamics of atmospheric methane oxidation in gray forest soils]. / Sezonnaia dinamika okisleniia atmosfernogo metana v serykh lesnykh pochvakh.

Seasonal fluctuations in the methane flow in the soil-atmosphere system were determined for gray forest soils of Central Russia. Consumption of atmospheric methane was found to exceed methane emission in gray forest soils under forest and in agrocenosis. The average annual rates of atmospheric methane consumption by the soil under forest and in agrocenosis were 0.026 and 0.008 mg CH4-C/(m2 h), respectively. The annual rate of atmospheric methane oxidation in the gray forest soils of Moscow oblast was estimated to be 0.68 kton. Seasonal fluctuations in the methane oxidation activity were due to changes in the hydrothermal conditions and in the reserves of readily decomposable organic matter and mineral nitrogen, as well as to changes in the activity of methane oxidizers.

Nitrogen removal from sludge reject water by a two-stage oxygen-limited autotrophic nitrification denitrification process.

Nitrogen removal from sludge reject water was obtained by oxygen-limited partial nitritation resulting in nitrite accumulation in a first stage, followed by autotrophic denitrification of nitrite with ammonium as electron donor (similar to anaerobic ammonium oxidation) in a second stage. Two membrane-assisted bioreactors (MBRs) were used in series to operate with high sludge ages and subsequent high volumetric loading rates, achieving 1.45 kg N m(-3) day(-1) for the partial nitritation MBR and 1.1 kg N m(-3) day(-1) for the anaerobic ammonium oxidation MBR. Biomass retention in the nitritation stage ensured flexibility towards loading rate and operating temperature. Nitrite oxidisers were out-competed at low oxygen and high free ammonia concentration. Biomass retention in the second MBR prevented wash-out of the slowly growing bacteria. Nitrite and ammonium were converted to dinitrogen gas in a reaction ratio of 1.05, thereby maintaining nitrite limitation to assure process stability. The anoxic consortium catalysing the autotrophic denitrification process consisted of Nitrosomonas-like aerobic ammonium oxidizers and anaerobic ammonium oxidizing bacteria closely related to Kuenenia stuttgartiensis. The overall removal efficiency of the combined process was 82% of the incoming ammonium according to a total nitrogen removal rate of 0.55 kg N m(-3) day(-1), without adding extra carbon source.

Oxygen-limited nitrogen removal in a lab-scale rotating biological contactor treating an ammonium-rich wastewater.

A lab-scale Rotating Biological Contactor (RBC) was operated with the purpose of oxygen-limited (autotrophic) nitrification-denitrification of an ammonium-rich synthetic wastewater without Chemical Oxygen Demand (COD). Based on the field observations that RBCs receiving anaerobic effluents come to anoxic ammonium removal, the RBC was inoculated with methanogenic sludge. Some 100 days after the addition of the anaerobic sludge to the reactor as a possible means of a rapid initiation of the nitrogen (N) removal process, a maximum ammonium removal of 1,550 mg N m(-2) d(-1) was achieved. Batch tests with 15N labeled ammonium and nitrite indicated that a large part of that N was removed via oxygen-limited oxidation of ammonium with nitrite as the electron acceptor. The other part was removed via conventional denitrification, presumably with COD released from lysis of cells. Species identification of the most abundant microorganisms revealed that Nitrosomonas spp. were the dominant ammonium-oxidizers in the sludge. Thus far, the molecular characterization of the sludge could not show the presence of Planctomycetes among the most dominant species. Overall this experiment confirms the property of the RBC system to remove ammonium to nitrogen gas without the use of heterotrophic carbon source.

In situ net mineralization rates in a heterogeneous mixed deciduous forest receiving elevated n deposition.

In situ net mineralization was studied at 6 locations (E, Eb, Ec, F1, F2, F3) of a heterogeneous mixed deciduous forest ("De Gulkeputten") with oak (Quercus robur L., Quercus rubra) and birch (Betula pendula) as dominant species. Net nitrogen mineralization was determined by means of a sequential in situ incubation experiment using intact soil cores. For all incubations, the net mineralization rates of the organic (F+H) layer varied between -0.4 and 2.0 g N m(-2) month(-1), while the net nitrification rates varied between -0.6 and 0.7 g NO3- -N m(-2) month(-1). The net mineralization and nitrification rates of the mineral (0-30 cm) layer ranged from 4.5 g N m(-2) month(-1)to 8.8 g N m(-2) month(-1)and from -1.0 to 4.9 g NO3- -N m(-2) month(-1) respectively. In general, net mineralization rates increased from August 1998 to October 1998. Net mineralization rates were positively correlated with the gravimetrical moisture content and mineralization and nitrification rates were mutually positively correlated.

Flux estimates from soil methanogenesis and methanotrophy: Landfills, rice paddies, natural wetlands and aerobic soils.

Present and future annual methane flux estimates out of landfills, rice paddies and natural wetlands, as well as the sorption capacity of aerobic soils for atmospheric methane, are assessed. The controlling factors and uncertainties with regard to soil methanogenesis and methanotrophy are also briefly discussed.The actual methane emission rate out of landfills is estimated at about 40 Tg yr(-1). Changes in waste generation, waste disposal and landfill management could have important consequences on future methane emissions from waste dumps. If all mitigating options can be achieved towards the year 2015, the CH4 emission rate could be reduced to 13 Tg yr(-1). Otherwise, the emission rate from landfills could increase to 63 Tg yr(-1) by the year 2025. Methane emission from rice paddies is estimated at 60 Tg yr(-1). The predicted increase of rice production between the years 1990 and 2025 could cause an increase of the CH4 emission rate to 78 Tg yr(-1) by the year 2025. When mitigating options are taken, the emission rate could be limited to 56 Tg yr(-1). The methane emission rate from natural wetlands is about 110 Tg yr(-1). Because changes in the expanse of natural wetland area are difficult to assess, it is assumed that methane emission from natural wetlands would remain constant during the next 100 years. Because of uncertainties with regard to large potential soil sink areas (e.g. savanna, tundra and desert), the global sorption capacity of aerobic soils for atmospheric methane is not completely clear. The actual estimate is 30 Tg yr(-1).In general, the net contribution of soils and landfills to atmospheric methane is estimated at 180 Tg yr(-1) (210 Tg yr(-1) emission, 30 Tg yr(-1) sorption). This is 36% of the global annual methane flux (500 Tg yr(-1)).