Large areas of nitrogen-sensitive habitats are currently estimated to be in exceedance of their critical loads (CLs) as indicators for protection from nitrogen deposition. In the UK, deposition estimates from the semi-empirical Concentration Based Estimated Deposition (CBED) model are used for official reporting of current exceed-ances. The UK Integrated Assessment Model (UKIAM) framework is designed to provide future projections of concentrations and deposition due to projected changes in emissions. UKIAM has been extended to provide alternative deposition estimates aligned with those of CBED, and the results combined with the range in habitat CL values to create an exceedance score, leading to a probabilistic evaluation of CL exceedances. The utility of the method is demonstrated by analysing a series of hypothetical scenarios. It is shown that NH3 mitigation is likely to be four times more effective in reducing CL exceedances in the UK than the mitigation of NOx emissions.

Soil organic matter (SOM) is a major ecosystem component, central to soil fertility, carbon balance and other soil functions. To advance SOM modelling, we devised a steady‐state model of topsoil SOM, with explicit descriptions of physical states and properties, and used it to simulate SOM concentration, carbon:nitrogen:phosphorus (C:N:P) stoichiometry, bulk density and radiocarbon content. The model classifies SOM by element stoichiometry (αSOM is poor in N and P, βSOM is rich), mean residence times (1–2000 years) and physical state (free, occluded, adsorbed, hypoxic). The most stable SOM is either βSOM preferentially adsorbed by mineral matter, or αSOM in strongly hypoxic zones. Soil properties were simulated for random combinations of plant litter input (amount and C:N:P stoichiometry), mineral sorption capacity, propensity for hypoxia, and bulk density of non‐adsorbed αSOM. To optimize model parameters, outputs from 5000 simulations were used to construct bivariate relations among soil variables, which were compared with those found in data for 835 survey sites, covering all common land uses. The bivariate relations, and patterns of data scatter, were reproduced, and also variations in soil radiocarbon with soil type, suggesting that apparent scatter in measured data might reflect SOM diversity. The temporal acquisition by soil of ‘bomb 14C’ could also be simulated. The steady‐state model is the basis for a dynamic version, suitable for simulating changes in SOM through time. It provides insight into the possible manipulation of soil organic carbon (SOC) sequestration; for example, increasing litter inputs might only increase moderately‐stable SOC pools, whereas encouraging the creation of βSOM by adsorption to mineral matter from deeper soil could lead to long‐term stabilization.Highlights Models of SOM should include explicit descriptions of physical states and properties. Our new topsoil SOM model is constrained by C:N:P stoichiometry, SO14C, and physical fractionation data. Simulated soil properties, randomly generated, account for measured trends and patterns of scatter in SOM data. SOM properties depend upon litter input, interactions with mineral matter, hypoxia, and bulk density.

The transport of dissolved organic matter (DOM) across the land-ocean-aquatic-continuum (LOAC), from freshwater to the ocean, is an important yet poorly understood component of the global carbon budget. Exploring and quantifying this flux is a significant challenge given the complexities of DOM cycling across these contrasting environments. We developed a new model, UniDOM, that unifies concepts, state variables and parameterisations of DOM turnover across the LOAC. Terrigenous DOM is divided into two pools, T 1 (strongly-UV-absorbing) and T 2 (non- or weakly-UV-absorbing), that exhibit contrasting responses to microbial consumption, photooxidation and flocculation. Data are presented to show that these pools are amenable to routine measurement based on specific UV absorbance (SUVA). In addition, an autochtonous DOM pool is defined to account for aquatic DOM production. A novel aspect of UniDOM is that rates of photooxidation and microbial turnover are parameterised as an inverse function of DOM age. Model results, which indicate that ~ 5% of the DOM originating in streams may penetrate into the open ocean, are sensitive to this parameterisation, as well as rates assigned to turnover of freshly-produced DOM. The predicted contribution of flocculation to DOM turnover is remarkably low, although a mechanistic representation of this process in UniDOM was considered unachievable because of the complexities involved. Our work highlights the need for ongoing research into the mechanistic understanding and rates of photooxidation, microbial consumption and flocculation of DOM across the different environments of the LOAC, along with the development of models based on unified concepts and parameterisations.

Atmospheric pollution by reactive nitrogen (N) can have profound effects on ecosystem functioning and biodiversity. Numerous mechanisms are involved, and response times vary among habitats and species. This complex picture can make it difficult to convey the benefits of controlling N pollution to policy developers and the public. In this study we evaluate pressure, midpoint, and endpoint metrics for N pollution, considering those currently in use and proposing some improved metrics. Pressure metrics that use the concept of a critical load (CL) are useful, and we propose a new integrated measure of cumulative exposure above the CL that allows for different response times in different habitats. Biodiversity endpoint metrics depend greatly on societal values and priorities and so are inevitably somewhat subjective. Species richness is readily understood, but biodiversity metrics based on habitat suitability for particular taxa may better reflect the priorities of nature conservation specialists. Midpoint metrics indicate progress towards desired endpoints – the most promising are those based on empirical evidence. Moss tissue N enrichment is responsive to lower N deposition rates, and we propose a new Moss Enrichment Index (MEI) based on species-specific ranges of tissue N content. At higher N deposition rates, mineral N leaching is an appropriate midpoint indicator. Biogeochemical models can also be used to derive midpoint metrics which illustrate the large variation in potential response times among ecosystem components. Metrics have an important role in encouraging progress towards reducing pollution, and need to be chosen accordingly.

Food security should be addressed in relation to soil sustainability and sustainable land care, and examined within the science framework of Earth's critical zone as an integrated system that includes Earth surface interactions, connected to soil functions, and ecosystem services. There is a great need to develop critical zone mathematical models that will simulate and quantify soil functions and that can be used as management tools to address soil sustainability and land care practices. The integrated critical zone model, 1D-ICZ, couples computational modules for soil organic matter dynamics, soil aggregation and structure dynamics, bioturbation, plant productivity and nutrient uptake, water flow, solute speciation and transport, and mineral weathering kinetics. The 1D-ICZ model, coupled with new pedotransfer functions to predict bulk soil properties, introduces for the first time a model that dynamically links soil structure characteristics and hydraulic soil properties by simulating their changes under varying meteorological conditions and plant growth. Field data from a Mediterranean olive grove at the Koiliaris Critical Zone Observatory (CZO) were used to simulate carbon addition to soil and agricultural management scenarios, in order to illustrate the model's ability to quantify soil management impact on soil functions and biogeochemical transformations and fluxes. The 1D-ICZ model can be used to assess, understand, and quantify the complex interactions between the different processes in the soil-plant-water system and can be applied as a tool to design sustainable agricultural management practices, taking into consideration synergy and trade-offs among soil functions.

In the next four decades, humanity needs to double food and energy production and increase the supply of clean water by over 50% while mitigating and adapting to climate change. A central element in the strategy of addressing these major environmental challenges is to maintain the central role of Earth's essential soil functions and related ecosystem services. Many soil functions are affected by soil structure in terms of particle aggregation and porosity. The objective of this work is to model soil structure and biomass dynamics, nutrients uptake, and yields using the 1D Integrated Critical Zone (1D-ICZ) model which is a mechanistic mathematical description of soil processes and functions. The 1D-ICZ model simulates the coupled processes that underpin major soil functions including water flow and storage, biomass production, carbon and nutrient sequestration, pollutant transformation, and supporting biological processes, and thus is capable of quantifying essential soil ecosystem services. The model was validated using data derived from a field experiment where tomato plants were grown using different treatments of commercial mineral fertilizers, compost, manure, and a 30% manure-70% compost amendment. Detailed data have been collected over four growing seasons on soil and soil solution chemistry, aggregate formation, and plant production. The model has been able to capture the biomass production, the temporal dynamics of the water-stable aggregate formation and the dynamics of carbon and nutrient sequestration in the different sizes aggregates as well as the variability of water filtration and transformation efficiency in the different amendment treatments. The model results demonstrate the value of applying computational simulation tools such as the 1D-ICZ model to test options for improved land management measures and to support sustainable land care practices.

Anthropogenic activity has resulted in the degradation of nearly a billion hectares of land globally either as a result of agricultural or industrial activities. This is causing the decline in many ecosystem services worldwide and is now threatening livelihoods and resulting in socioeconomic instability. Consequently, society needs to find cost-effective, socially-acceptable, and practical ways to remediate this land to restore ecosystem functioning. In this context, this article presents evidence to show how a diverse range of plants may be employed to promote ecosystem recovery. This typically involves the use of plants to remove or stabilize pollutants (e.g., heavy metals, organic chemicals, invasive weeds, microbiological contaminants) and improve various chemical, biological, and physical aspects of the soil. In addition, successful remediation relies on the correct choice of plants for the site and effective management during site restoration. Restoration schemes that are sustainable in the long term frequently use plants that both promote and accelerate natural succession processes.

Nitrogen (N) deposition is a major cause of plant biodiversity loss, with serious implications for appropriate management of protected sites. Reducing N emissions is the only long-term solution. However, on-site management has the potential to mitigate some of the adverse effects of N deposition. In this paper we review how management activities such as grazing, cutting, burning, hydrological management and soil disturbance measures can mitigate the negative impacts of N across a range of temperate habitats (acid, calcareous and neutral grasslands, sand dunes and other coastal habitats, heathlands, bogs and fens). The review focuses mainly on European habitats, which have a long history of N deposition, and it excludes forested systems. For each management type we distinguish between actions that improve habitat suitability for plant species of conservation importance, and actions that immobilize N or remove it from the system. For grasslands and heathlands we collate data on the quantity of N removal by each management type. Our findings show that while most activities improve habitat suitability, the majority do little to slow or to reduce the amount of N accumulating in soil pools at current deposition rates. Only heavy cutting/mowing with removal in grasslands, high intensity burns in heathlands and sod cutting remove more N than comes in from deposition under typical management cycles. We conclude by discussing some of the unintended consequences of managing specifically for N impacts, which can include damage to non-target species, alteration of soil processes, loss of the seedbank and loss of soil carbon.

Society requires rapid, most-probable predictions for specific and/or multifaceted questions related to environmental and geological science. In principle, models that encapsulate disciplinary knowledge are useful tools for making predictions and testing theory, but academic rewards favour disciplinary specialism and a proliferation of often insufficiently tested models. Decision makers have to assess the quality and robustness of predictions for complex environmental issues, and may prefer a model that performs accurately in a case study to a more parsimonious and generalizable model. Predictive ecosystem models tend to grow, as more processes are considered, even when a simpler model may be more appropriate and give results that are easier to interpret within a policy-relevant timeframe. Model fusion provides a practical way to combine knowledge from different disciplines, but can accelerate model growth. How then can we facilitate the evolution of useful predictive models? Coherent design is essential. When combining models it is often necessary to resolve overlapping scope, so tools need to allow for the disaggregation of model implementations as well as their fusion. Modelling software and integration frameworks can help resolve technical constraints, but to make models useful and used it is essential to involve stakeholders in their design and interpretation.

This study investigated the interactive effects of growth on drought stressed host plants and pathogen challenge with the baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) on survival and fitness-related traits using the Speckled Wood butterfly, Pararge aegeria (L.). Exposure to AcMNPV significantly reduced survival to pupation. For surviving larvae, sub-lethal infection significantly decreased daily mass acquisition rates and pupal mass. Growth on drought stressed plants increased daily mass acquisition rates resulting in heavier pupae, and increased resource allocation to adult reproduction. The interaction between host plant drought and viral exposure resulted in different resource allocation strategies, and thus different growth trajectories, between larvae. This in turn resulted in significantly different allometric relationships between larval mass (at inoculation) and both development time and investment in flight muscles. For larvae with relatively lighter masses there was a cost of resisting infection when growth occurred on drought stressed host plants, both within the larval stage (i.e. longer larval development times) and in the adult stage (i.e. lower investment in flight muscle mass). This multi-factor study highlights several potential mechanisms by which the complex interplay between low host plant nutritional quality due to drought, and pathogen exposure, may differentially influence the performance of P. aegeria individuals across multiple life stages.

Models are needed to understand how plant-soil nutrient stores and fluxes have responded to the last two centuries of widespread anthropogenic nutrient pollution and predict future change. These models need to integrate across carbon, nitrogen, and phosphorus (C, N, and P) cycles and simulate changes over suitable timescales using available driving data. It is also vital that they are constrainable against observed data to provide confidence in their outputs. To date, no models address all of these requirements. To meet this need, a new model, N14CP, is introduced, which is initially applied to Northern Hemisphere temperate and boreal ecosystems over the Holocene. N14CP is parameterized and tested using 88 northern Europe plot-scale studies, providing the most robust test of such a model to date. The model simulates long-term P weathering, based on the assumption of a starting pool of weatherable P (P-weath0, gm(-2)), which is gradually transformed into organic and sorbed pools. Nitrogen fixation (and consequently primary production) is made dependent on available P. In the absence of knowledge about the spatial variability of P-weath0, N14CP produces good average soil and plant variables but cannot simulate variations among sites. Allowing P-weath0 to vary between sites improves soil C, N, and P results greatly, suggesting that contemporary soil C, N, and P are sensitive to long-term P weathering. Most sites were found to be N limited. Anthropogenic N deposition since 1800 was calculated to have increased plant biomass substantially, in agreement with observations and consequently increased soil carbon pools.

The remarkable complexity of soil and its importance to a wide range of ecosystem services presents major challenges to the modeling of soil processes. Although major progress in soil models has occurred in the last decades, models of soil processes remain disjointed between disciplines or ecosystem services, with considerable uncertainty remaining in the quality of predictions and several challenges that remain yet to be addressed. First, there is a need to improve exchange of knowledge and experience among the different disciplines in soil science and to reach out to other Earth science communities. Second, the community needs to develop a new generation of soil models based on a systemic approach comprising relevant physical, chemical, and biological processes to address critical knowledge gaps in our understanding of soil processes and their interactions. Overcoming these challenges will facilitate exchanges between soil modeling and climate, plant, and social science modeling communities. It will allow us to contribute to preserve and improve our assessment of ecosystem services and advance our understanding of climate-change feedback mechanisms, among others, thereby facilitating and strengthening communication among scientific disciplines and society. We review the role of modeling soil processes in quantifying key soil processes that shape ecosystem services, with a focus on provisioning and regulating services. We then identify key challenges in modeling soil processes, including the systematic incorporation of heterogeneity and uncertainty, the integration of data and models, and strategies for effective integration of knowledge on physical, chemical, and biological soil processes. We discuss how the soil modeling community could best interface with modern modeling activities in other disciplines, such as climate, ecology, and plant research, and how to weave novel observation and measurement techniques into soil models. We propose the establishment of an international soil modeling consortium to coherently advance soil modeling activities and foster communication with other Earth science disciplines. Such a consortium should promote soil modeling platforms and data repository for model development, calibration and intercomparison essential for addressing contemporary challenges.

To predict ecosystem responses to anthropogenic change it is important to understand how and where plant productivity is limited by macronutrient availability. Nitrogen (N) is required in large quantities for plant growth, and is readily lost through leaching or gas fluxes, but reactive nitrogen can be obtained through dinitrogen fixation, and phosphorus (P) is often considered a more fundamental long-term constraint to growth and carbon sequestration in terrestrial ecosystems. Phosphorus limitation may be becoming more prevalent due to widespread pollution by atmospheric N. Assessments of the effects of macronutrient availability on productivity in natural ecosystems are however scarce. We measured standing biomass of bracken Pteridium aquilinum as a proxy for productivity across sites with similar climate but varied geology. Total above-ground biomass varied from 404 to 1947gm-2, yet despite 12-fold to 281-fold variation in soil macronutrient stocks these were remarkably poor at explaining variation in productivity. Soil total nitrogen, organic phosphorus, calcium, magnesium and zinc had no relationship with productivity, whether expressed as concentrations, stocks or element/C ratios, and nor did foliar N/P. Soil potassium (K) and molybdenum stocks both showed weak relationships with productivity. The stock of K in bracken biomass was considerably greater as a proportion of soil stock than for other nutrient elements, suggesting that this nutrient element can be important in determining productivity. Moisture availability, as indicated by environmental trait scores for plant species present, explained considerably more of the variation in productivity than did K stock, with less production in wetter sites. Soil N/C ratio and organic P stock were relatively unimportant in determining productivity across these bracken sites. It is possible that more-direct measures of N and P availability would explain variation in productivity, but the study shows the importance of considering other essential elements and other environmental factors when predicting productivity.

It is increasingly recognised that widespread and substantial increases in Dissolved organic carbon (DOC) concentrations in remote surface, and soil, waters in recent decades are linked to declining acid deposition. Effects of rising pH and declining ionic strength on DOC solubility have been proposed as potential dominant mechanisms. However, since DOC in these systems is derived mainly from recently-fixed carbon, and since organic matter decomposition rates are considered sensitive to temperature, uncertainty persists over the extent to which other drivers that could influence DOC production. Such potential drivers include fertilisation by nitrogen (N) and global warming. We therefore ran the dynamic soil chemistry model MADOC for a range of UK soils, for which time series data are available, to consider the likely relative importance of decreased deposition of sulphate and chloride, accumulation of reactive N, and higher temperatures, on soil DOC production in different soils. Modelled patterns of DOC change generally agreed favourably with measurements collated over 10–20years, but differed markedly between sites. While the acidifying effect of sulphur deposition appeared to be the predominant control on the observed soil water DOC trends in all the soils considered other than a blanket peat, the model suggested that over the long term, the effects of nitrogen deposition on N-limited soils may have been sufficient to raise the “acid recovery DOC baseline” significantly. In contrast, reductions in non-marine chloride deposition and effects of long term warming appeared to have been relatively unimportant. The suggestion that future DOC concentrations might exceed preindustrial levels as a consequence of nitrogen pollution has important implications for drinking water catchment management and the setting and pursuit of appropriate restoration targets, but findings still require validation from reliable centennial-scale proxy records, such as those being developed using palaeolimnological techniques.

The Effusive Eruption Modelling project undertook to determine the extent to which sulphur dioxide and sulphate aerosol might be hazardous at ground and flight levels during a future eruption scenario based on a Laki-type eruption. In order to do this the model source term was constructed and comprised five weeks of daily emissions followed by one week of no emissions. In order to sample different meteorology, the 6-week model source term is repeated eighty times over 10 years of meteorology. The scenario was run using both the NAME model, and the EME4UK model. Detailed results are presented in Witham et al. This presentation reports the results of an assessment of UK impacts of trace species and sulphur deposition.

To unravel the potential effects of climate warming on soil N availability in a high Arctic tundra ecosystem we studied temperature effects on soil mineralization, and N uptake from different soil depths (-3, -10 and -30 cm) by tundra plants. Uptake was assessed using N-15 tracer injected directly into mineral soil as (NH4Cl)-N-15 solution to specifically mimic altered N availability from enhanced mineralization. Net N mineralization rates were very low, suggesting that N is strongly limiting in this system. There was no apparent temperature effect (-2 degrees C, 5 degrees C, 10 degrees C) on mineralization, but net nitrification was strongly limited by temperature - under the -2 degrees C treatment no nitrification occurred. As a consequence of ongoing mineralization and limited nitrification under freezing conditions, mineral NH4 may accumulate during the winter season and be available for plant uptake without risk of loss via NO3- leaching immediately after snowmelt. Nitrogen uptake niches were clearly stratified by depth. Graminoids (Carex misandra and Luzula arctica) were most effective at taking up N from deep soil horizons, and recovery in graminoid biomass after one year was independent of N-15 injection depth. Recovery of N by the dwarf shrub Salix polaris was significantly higher following shallow application (-3 cm) compared to deeper treatments (-10 and -30 cm). Lichens and mosses also showed a decline in N uptake with application depth, and very little N was recovered by lichens and mosses even from -3 cm, in contrast to the strong uptake that has been observed in mosses when N is applied to the vegetation surface. The ability of graminoids to access nutrients from deeper mineral soil may give them an advantage over mosses and dwarf shrubs in warmer high Arctic tundra in acquiring limited available nutrient resources. (C) 2015 Elsevier Ltd. All rights reserved.

In response to the recent introduction of large, long-lasting gas-rich volcanic eruptions to the UK National Risk Register (risk H55) a modelling project has been conducted to improve our understanding of potential hazards to the UK from such an eruption on Iceland. A precautionary “reasonable worst case” eruption scenario based on the 1783-1784 CE Laki eruption has been determined using the results of an expert elicitation of scientists. This scenario has been simulated 80 times using two different atmospheric chemistry and transport models (NAME and EMEP4UK) over 10 years of meteorology (2003-2012). The results provide information on the range of concentrations of sulphur dioxide (SO2), sulphate aerosol (SO4) and some halogen species that might be experienced in the UK during such an eruption and the likelihood of key thresholds being exceeded and the duration of their exceedance. Data for the surface and for a range of key flight altitudes have been produced. These are evaluated against the threshold bandings of the UK’s Air Quality Index (AQI). The impact on UK ecosystems has also been considered. The data are intended to be used by UK Government Departments for further research into the impacts on the aviation, health, environmental and agricultural sectors. The results show that the prevailing meteorological conditions are the key influence on which parts of the North Atlantic and European region are affected at any time. The results demonstrate that the UK is unlikely to be affected by week after week of significantly elevated concentrations; rather there will a number of short (hours to days) pollution episodes where concentrations at the surface would be elevated bove Moderate and High air quality index levels. This pattern reflects the generally changeable nature of the weather in the UK. At the surface, consecutive exceedance durations are longer for SO4 than SO2, and can be particularly lengthy (1-2 weeks) in the Low air quality index levels, which may be of relevance to health impact assessments. The indications of potential peak concentrations and their corresponding AQI exceedance probabilities within this report serve to inform national, high-level generic risk planning. For more specific response planning, a much larger modelling study with multiple eruption scenarios and a greater number of meteorological realisations would be needed.