Can soil health in degraded woodlands of a semi-arid environment improve after thirty years?

In natural habitats, especially in arid and semi-arid areas that are fragile ecosystems, vegetation degradation is one of the most important factors affecting the variability of soil health. Studying physicochemical and biological parameters that serve as indicators of soil health offers important information on the potential risk of land degradation and the progression of changes in soil performance and health during recovery periods. This study specifically examines the impact of vegetation degradation on soil health indicators and the duration needed to improve the physical, chemical, and biological parameters in a semi-arid mountainous area site types with the dominance of Quercus macranthera Fisch & C.A. Mey and Carpinus orientalis Miller in northern Iran. In different years (2003, 2013, and 2023), litter and soil samples (at depths of 0-10, 10-20, and 20-30 cm) were collected in different types of degraded sites. Additionally, in 2023, a non-degraded site was chosen as a control and similar samples were collected. A total of 48 litter (12 samples for each of the study site types) and 144 soil (4 study site types × 3 depths × 12 samples) samples were collected. In order to investigate the spatial changes of soil basal respiration (or CO2 emission), which is involved in global warming, from each site type, 50 soil samples were taken along two 250-meter transects. The findings showed that litter P and Mg contents in the non-degraded site were 1.6 times higher than in degraded site types (2003). Following vegetation degradation, soil fertility indicators decreased by 2-4 times. The biota population was lower by about 80 % under the degraded site types (2003) than in the non-degraded site, and the density of fungi and bacteria in the degraded site types was almost half that of the non-degraded site types. Geostatistics showed the high variance (linear model) of CO2 emissions in areas without degradation. In addition, vegetation degradation significantly reduced soil carbon and nitrogen mineralization. Although soil health indicators under the degraded vegetation have improved over time (30 years), results showed that even thirty years is not enough for the full recovery of a degraded ecosystem, and more time is needed for the degraded area to reach the same conditions as the non-degraded site. Considering the time required for natural restoration in degraded site types, it is necessary to prioritize the conservation of vegetation and improve the ecosystem restoration process with adequate interventions.

Land degradation neutrality (LDN) in Rajasthan, Western India: a combined approach of pressure-state-response model and MODIS data products.

Land degradation has become a key concern worldwide due to changes in meteorological variables and human-caused activities. This study primarily focuses on the rate, impact, and pattern of land degradation in western India. In this instance, we evaluated the effectiveness of land degradation neutrality (LDN) between 2000 and 2020 using an integrative approach based on a PSR (pressure-state-response) model developed by the OECD-UNEP under the UNCCD framework. Here, we mainly used MODIS products (e.g., NDVI, PET, LULC, and NPP). Also, soil organic carbon (SOC) and climatic variables (e.g. precipitation, aridity index and soil moisture) were taken into account. These indicators were analysed using the Google Earth Engine (GEE) code editor platform, and post-processing was done through Q-GIS software. The analysed parameters indicate that the NDVI and NPP values are + 0.20 to + 0.3 and 4.27 × 109 to 7.74 × 109 kg Cm-2, respectively. However, overall precipitation and soil moisture depicted a positive trend, and the aridity index adeptly followed a negative trend. Hence, the land degradation rate has increased in the north-western region besides the Aravalli range and neutrality work in the southwest part of the study area. The overall land degradation trend is negative over the last two decades. Therefore, this study anticipates the policymakers and government bodies to understand about land degradation of western India.

Landfill leachate has multiple negative impacts on soil health indicators in Hyrcanian forest, northern Iran.

The storage of municipal solid wastes in unengineered landfills poses a severe threat to soil functions and health. Wastes seriously threaten human health and the terrestrial ecosystem, especially due to heavy metals. There is a general knowledge gap about the long-term impacts of storage wastes on the soil health indicators which are effective on soil functions. This investigation focuses on the examination of landfill leachate on soil health indicators from different years in the Hyrcanian forest region in northern Iran. For this purpose, soil sampling was done in the summer of 2012 and 2022 (from three depths of 0-10, 10-20, and 20-30 cm and on a surface of 30 cm × 30 cm). Soil samples were randomly collected from a polluted forest used as waste storage and a nearby unpolluted protected forest. In addition to the general soil physical, chemical and biological parameters, the amounts of cadmium (Cd) and lead (Pb) in the soil were also measured. Simultaneously with soil sampling, earthworms (from a depth of 0-30 cm) were collected and identified. Also, the concentration of Cd and Pb in the earthworm's biomass were measured in the laboratory. We found that unpolluted sites had maximum values of N, K, P, and Ca than the polluted sites. In addition, a decrease of soil aggregates stability, nutrient contents, microbial and enzyme activities, and also fauna and microflora abundance were found in the polluted sites in the period 2012-2022. Soil Cd and Pb contents were more in the polluted site in 2022 compared to the unpolluted site. Lumbricus rubellus and Lumbricus terrestris earthworms had significantly higher population in the polluted sites and higher accumulation of Cd and Pb in biomass. According to our results, soil health decreased in the order unpolluted site 2022 > unpolluted site 2012 > polluted site 2012 > polluted site 2022, which corresponds with the reduction of soil health during the release of landfill leachate. This investigation contributes to understand landfill pollution derived from leachate and its effects on soil physical, chemical and biological parameters to help managing landfill leachate. Therefore, the main issue is choosing a landfill system that minimizes the risk of pollution, installing a leachate collection system and constructing a landfill with engineering principles that can reduce the effects of urban waste pollution on soil health. We emphasize that landfilling is dangerous for the environment, so the government should implement sanitary landfilling to prevent further contamination of surface and underground waters, as well as soil in the precious Hyrcanian forest.

Soil quality cannot be improved after thirty years of land use change from forest to rangeland.

Soil quality can be assessed by measuring its physical, chemical and biological properties. In terrestrial ecosystems, the knowledge of the status of soil quality under different land use/cover can increase our understanding of processes related to soil functioning and help to properly managing ecosystems and increase their services. Conversion of the forest to rangelands is one of the most common forms of land use change having a significant effect on soil quality indicators. Here, we addressed the following objectives: (ii) to study the current status of soil physical, chemical and biological characteristics after more than thirty years of land use change from forest (dominated by Carpinus betulus and Parrotia persica) to rangeland, and (ii) to provide an overview of the spatial distributions of soil properties in forest and rangeland covers using a geostatistical method. For this, two sites (i.e., forest and rangeland) were selected in northern Iran. Within each site, 50 soil samples were collected at 0-10 cm depth along two sampling lines (250 m length) with a total of 100 soil samples for each site. Results showed that following the change of land use from forest to rangeland soil porosity, aggregate stability, pH, electrical conductivity and nutrient (i.e., total N and available P, K, Ca and Mg) contents increased, whereas soil bulk density and C/N ratio decreased. In addition, the population of soil biota (i.e., earthworms, acarina, collembola, nematode, protozoa, bacteria and fungi), microbial and enzyme activities decreased after more than thirty years of land use change from forest to rangeland. Principal component analysis confirmed that forest site had a more fertile soil and a higher biological activity than rangeland cover. Based on heat plots of soil properties, forest ecosystems created hot spots of soil quality indicators in the study area. Based on the geostatistical approach, most of the soil variables in the rangeland site followed a linear model, while in the forest site, most models were exponential and spherical. The fractal dimension values of the soil properties in the forest (1.62-1.99) had larger variations than in the rangeland (1.75-1.99) site. As a general conclusion, soil quality was not improved after more than thirty years of land use change from forest to rangeland, suggesting that degraded forest habitats should be restored by native tree species rather than converted to other land uses.

Ensemble modelling, uncertainty and robust predictions of organic carbon in long-term bare-fallow soils.

Simulation models represent soil organic carbon (SOC) dynamics in global carbon (C) cycle scenarios to support climate-change studies. It is imperative to increase confidence in long-term predictions of SOC dynamics by reducing the uncertainty in model estimates. We evaluated SOC simulated from an ensemble of 26 process-based C models by comparing simulations to experimental data from seven long-term bare-fallow (vegetation-free) plots at six sites: Denmark (two sites), France, Russia, Sweden and the United Kingdom. The decay of SOC in these plots has been monitored for decades since the last inputs of plant material, providing the opportunity to test decomposition without the continuous input of new organic material. The models were run independently over multi-year simulation periods (from 28 to 80 years) in a blind test with no calibration (Bln) and with the following three calibration scenarios, each providing different levels of information and/or allowing different levels of model fitting: (a) calibrating decomposition parameters separately at each experimental site (Spe); (b) using a generic, knowledge-based, parameterization applicable in the Central European region (Gen); and (c) using a combination of both (a) and (b) strategies (Mix). We addressed uncertainties from different modelling approaches with or without spin-up initialization of SOC. Changes in the multi-model median (MMM) of SOC were used as descriptors of the ensemble performance. On average across sites, Gen proved adequate in describing changes in SOC, with MMM equal to average SOC (and standard deviation) of 39.2 (±15.5) Mg C/ha compared to the observed mean of 36.0 (±19.7) Mg C/ha (last observed year), indicating sufficiently reliable SOC estimates. Moving to Mix (37.5 ± 16.7 Mg C/ha) and Spe (36.8 ± 19.8 Mg C/ha) provided only marginal gains in accuracy, but modellers would need to apply more knowledge and a greater calibration effort than in Gen, thereby limiting the wider applicability of models.

Projected trends of soil organic carbon stocks in Meghalaya state of Northeast Himalayas, India. Implications for a policy perspective.

Agricultural and forestry activities can affect soil organic carbon (SOC) levels and CO2 emissions from terrestrial ecosystems due to land use changes. In Northeast Himalayas, studies on the effects of forest conversion to temporary agricultural lands (jhum) on the loss of SOC and soil quality degradation have received the attention of policy makers and scientific research. Presently, local communities are now oriented towards the settled plantations systems with modern cash crops such as tea and rubber, that could act as potential SOC sinks. However, no information on SOC dynamics and simulation studies after land-use change from temporary agricultural lands (jhum) to settled cultivations and under climate change (CC) conditions are available for the Meghalaya state. Applying the RothC model, we focused on four different scenarios including the conversion from jhum to settled cultivation (rubber plantations and tea gardens), as well as continuous jhum cultivation and jhum to jhum with a period of secondary succession. Simulations under CC conditions indicated that SOC stocks significantly increased by 1.20 t C ha-1 yr-1 in tea gardens compared to rubber and jhum scenarios. Conversely, SOC stocks slightly decreased by 0.07 t C ha-1 yr-1 in rubber plantations, while the regrowth of a natural vegetation cover as secondary succession following the abandonment of the jhum fields, showed a lower SOC decrease (0.18 t C ha-1 yr-1) compared to the continuous jhum cultivation (0.24 t C ha-1 yr-1). Thus, for CC mitigation in a policy perspective, tea gardens could represent the best land use to store increasing amounts of SOC in the long-term perspective and optimize farmers' incomes, while in rubber plantations SOC storage is limited in time. Jhum cultivation can benefit in terms of productivity and profitability by extending the duration of the secondary succession period.

Is soil microbial diversity affected by soil and groundwater salinity? Evidences from a coastal system in central Italy.

Little is known about composition, diversity, and abundance of microbial communities in environments affected by primary soil salinization, such as coastal lagoon systems. The main objective of this study was to investigate the impact of lagoon salinity, soil type, and land-use on inland soil and groundwater quality, and soil microbial community structure, diversity, and gene abundance, as evaluated by T-RFLP (terminal-restriction fragment length polymorphism) and qPCR (quantitative polymerase-chain-reaction). For this purpose, four sites oriented along a groundwater salinity gradient (Fogliano lagoon, central Italy) were studied under different recreational, grazing, and land-use conditions. Spatial variability in groundwater attributes was observed depending on salinity and soil electrical conductivity, both influenced by salt intrusion. A comparison of community abundance and number of phylotypes of bacteria, archaea, and fungi across varying soil depths pointed out marked differences across soils characterized by different soil type, land-use, and salinity. The latter significantly affected the microbial population richness and diversity and showed a dominance in terms of bacteria species. Our study provides a comprehensive overview of the spatial relationship between soil microbial community and soil degradation processes along a relatively underexplored environmental gradient in a coastal system, coming to the conclusion that salinity acts differently as a driver of microbial community structure in comparison with other saline environments.

Simulating soil organic carbon stock as affected by land cover change and climate change, Hyrcanian forests (northern Iran).

Soil organic carbon (SOC) contains a considerable portion of the world's terrestrial carbon stock, and is affected by changes in land cover and climate. SOC modeling is a useful approach to assess the impact of land use, land use change and climate change on carbon (C) sequestration. This study aimed to: (i) test the performance of RothC model using data measured from different land covers in Hyrcanian forests (northern Iran); and (ii) predict changes in SOC under different climate change scenarios that may occur in the future. The following land covers were considered: Quercus castaneifolia (QC), Acer velutinum (AV), Alnus subcordata (AS), Cupressus sempervirens (CS) plantations and a natural forest (NF). For assessment of future climate change projections the Fifth Assessment IPCC report was used. These projections were generated with nine Global Climate Models (GCMs), for two Representative Concentration Pathways (RCPs) leading to very low and high greenhouse gases concentration levels (RCP 2.6 and RCP 8.5 respectively), and for four 20year-periods up to 2099 (2030s, 2050s, 2070s and 2090s). Simulated values of SOC correlated well with measured data (R2=0.64 to 0.91) indicating a good efficiency of the RothC model. Our results showed an overall decrease in SOC stocks by 2099 under all land covers and climate change scenarios, but the extent of the decrease varied with the climate models, the emissions scenarios, time periods and land covers. Acer velutinum plantation was the most sensitive land cover to future climate change (range of decrease 8.34-21.83tCha-1). Results suggest that modeling techniques can be effectively applied for evaluating SOC stocks, allowing the identification of current patterns in the soil and the prediction of future conditions.

Organic carbon pools and soil biological fertility are affected by land use intensity in Mediterranean ecosystems of Sardinia, Italy.

Soil quality is mainly studied from the chemical and physical point of view, whereas soil biochemical and microbiological parameters are relatively more scarcely explored to assess the effect of management practices. This study aimed to evaluate soil organic carbon (SOC) and its pools; soil microbial activity parameters; and the Biological Fertility Index (BFI), in six land uses characteristics of the Mediterranean basin in north-eastern Sardinia. These land uses differed in management intensity and consisted of: tilled vineyard (TV), no tilled grassed vineyard (GV), former vineyards (FV), hay crop and pasture (HC and PA), cork oak forest (CO). Significant differences among ecosystems were found in most cases in (SOC), the related pools (total extractable carbon, humic and fulvic acids, not humified, not extractable), humification parameters (degree, rate and index of humification), and soil microbial activity (microbial carbon, respiration, metabolic quotient, and mineralization quotient). Pasture and cork oak forest showed in average a better soil quality for most biochemical and microbial parameters in comparison with the other ecosystems. The index of soil biological fertility (BFI) was higher under cork oak forest which is supposed to be the most sustainable ecosystem in the long term in this environment, able to maintain soil biological fertility and microbial diversity.

Review and analysis of strengths and weaknesses of agro-ecosystem models for simulating C and N fluxes.

Biogeochemical simulation models are important tools for describing and quantifying the contribution of agricultural systems to C sequestration and GHG source/sink status. The abundance of simulation tools developed over recent decades, however, creates a difficulty because predictions from different models show large variability. Discrepancies between the conclusions of different modelling studies are often ascribed to differences in the physical and biogeochemical processes incorporated in equations of C and N cycles and their interactions. Here we review the literature to determine the state-of-the-art in modelling agricultural (crop and grassland) systems. In order to carry out this study, we selected the range of biogeochemical models used by the CN-MIP consortium of FACCE-JPI (http://www.faccejpi.com): APSIM, CERES-EGC, DayCent, DNDC, DSSAT, EPIC, PaSim, RothC and STICS. In our analysis, these models were assessed for the quality and comprehensiveness of underlying processes related to pedo-climatic conditions and management practices, but also with respect to time and space of application, and for their accuracy in multiple contexts. Overall, it emerged that there is a possible impact of ill-defined pedo-climatic conditions in the unsatisfactory performance of the models (46.2%), followed by limitations in the algorithms simulating the effects of management practices (33.1%). The multiplicity of scales in both time and space is a fundamental feature, which explains the remaining weaknesses (i.e. 20.7%). Innovative aspects have been identified for future development of C and N models. They include the explicit representation of soil microbial biomass to drive soil organic matter turnover, the effect of N shortage on SOM decomposition, the improvements related to the production and consumption of gases and an adequate simulations of gas transport in soil. On these bases, the assessment of trends and gaps in the modelling approaches currently employed to represent biogeochemical cycles in crop and grassland systems appears an essential step for future research.

Probabilistic risk assessment for linear alkylbenzene sulfonate (LAS) in sewage sludge used on agricultural soil.

Deterministic and probabilistic risk assessments were developed for commercial LAS in agricultural soil amended with sewage sludge. The procedure done according to ILSI Europe's Conceptual Framework [Schowanek, D., Carr, R., David, H., Douben, P., Hall, J., Kirchmann, H., Patria, L., Sequi, P., Smith, S., Webb, S.F., 2004. A risk-based methodology for deriving quality standards for organic contaminants in sewage sludge for use in agriculture-conceptual Framework. Regul. Toxicol. Pharmacol. 40 (3), 227-251], consists of three main steps. First, the most sensitive endpoint was determined. This was found to be the chronic ecotoxicity of LAS to soil invertebrates and plants. Additional endpoints, such as potential for plant uptake and transfer in the food chain, leaching to groundwater, surface erosion run-off, human health risk via drinking water, plant consumption and soil ingestion were also systematically evaluated but were all assessed to be of little toxicological significance. In the second step, a back-calculation was conducted from the Predicted No-Effect Concentration in soil (PNECsoil) to a safe level of LAS in sludge (here called 'Sludge Quality Standard'; SQS). The deterministic approach followed the default agricultural soil exposure scenario in the EU-Technical Guidance Document (TGD). The SQS for LAS was calculated as 49 g/kg sludge Dry Matter (DM). In order to assess the potential variability as a result of varying agricultural practices and local environmental conditions, two probabilistic exposure assessment scenarios were also developed. The mean SQS was estimated at 55 and 27.5 g/kg DM for the homogeneous soil mixing and soil injection scenarios, respectively. In the final step, the resulting SQS values were evaluated for consistency and relevance versus available information from agricultural experience and field tests. No build-up, adverse impact on soil fertility, agronomic performance, or animal/human health have been reported for agricultural fields which have received sludge with high LAS levels for up to 30 years. Distribution statistics of LAS concentrations in anaerobically digested sewage sludge measured across Europe were created (mean value: 5.56 g LAS/kg sludge DM). When compared to the above mean SQS values, adequate risk characterisation ratios of 0.08-0.2 were found. The 'ecological risk' parameter calculated for anaerobic sludge from the probabilistic approaches was below 3%. A regulatory Limit Value for LAS of 2.60 g/kg sludge DM was originally proposed in the 3rd Draft of the Working Document on Sludge [CEC, 2000b. Working Document on Sludge. Third Draft, Brussels 27 April 2000, DG. Environment, 18 p.]. The current assessment, based on an updated dataset and a refined assessment procedure, suggests that the need for a limit value for LAS in sewage sludge cannot be substantiated on a risk basis.

Heavy metals monitoring at a Mediterranean natural ecosystem of Central Italy. Trends in different environmental matrixes.

The study deals with the evaluation of the impact of heavy metal pollution on a Mediterranean natural ecosystem, and presents the results derived from a monitoring of heavy metals in different environmental matrixes (atmospheric dry depositions, suspended particulate matter (SPM) and stemflow of forest trees). Two sites in Castelporziano Presidential Estate (Rome), one internal and one near the sea-side, were chosen in order to assess the differences in pollutant load. Results showed that heavy metal contamination can arise from local anthropogenic activities, in particular road traffic, and long-range pollution, from industrial and artisan activities near Rome.

The atmospheric monitoring in a protected area.

A multi-annual research program was carried out to study the environmental quality of Castelporziano Presidential Estate (Rome, Italy). Within this program, in the field of air quality, a methodological approach was defined and applied, even by means of proper Environmental Indicators for the identification of anthropogenic contribution and the quantification of degradation. By means of mobile laboratories, macro and micro-pollutant concentrations were assessed in order to define Indexes of Atmosphere Quality and Diffuse Contamination, by relating them to possible short or long-range emission sources. Wet and dry atmospheric depositions were collected and analysed for the determination of heavy metal and acid species fluxes. Critical Load and relative Exceedance maps were elaborated, for the purpose of better underline the areas characterized by a higher environmental vulnerability.