Crop replacement by secondary forests increases soil organic carbon (OC) stocks. Quantifying this increase is subject to biases: the changes in soil compaction and, in calcareous zones, the changes ...in soil inorganic carbon (IC) content, which affect the carbon balance. How relevant are both biases, though? We studied this problem in NE Spain, subhumid Mediterranean, in a set of current crops, old forests, and new forests grown on croplands abandoned after 1956. We compared soil OC stocks on a fixed‐depth basis (30 cm), and on an equivalent‐mass basis: uppermost 425 kg m−2 of fine mineral matter (amount in crop soils). Down to 30 cm, OC stocks were lowest in crops (5.45 kg m−2) and highest in old forests (7.50 kg m−2), which gives a potential OC sequestration in the mineral soil of 2.05 kg m−2. On an equivalent‐mass basis, the potential is 2.50 kg m−2, meaning that the fixed‐depth criterion underestimates OC sequestration by more than 20%. These figures are surpassed by those of IC: crops store 17.73 kg IC m−2 down to 30 cm, old forests 12.28, suggesting a potential loss upon afforestation of 5.45 kg IC m−2. Nevertheless, the lack of negative relationships between IC losses and OC gains within a given land use suggests that the contrasting IC stocks result from past management, mainly tillage. The decarbonation is only apparent. Our results stress the need of accounting for changes in carbonate content and soil compaction in future studies about carbon sequestration in soils.
The stability of soil organic matter (SOM) depends on its degree of physical protection, biochemical quality (q), and mineralogical features such as the abundance of iron or aluminum oxyhydroxides: ...All constraints stabilize SOM, but the relevance of each is herein discussed. We studied from this point of view the stability of SOM in four grassland soils. The SOM in these profiles was characterized for its physical protection (ultrasonic dispersion + size fractionation) and its q (acid hydrolysis, carbohydrates, phenolics, and unhydrolyzable carbon). The profiles were also analyzed for free iron forms extracted with several chemicals: dithionite-citrate-bicarbonate, citric acid, oxalic-oxalate (Tamm’s solution), and DTPA. Soil horizons were incubated under optimal conditions to obtain the C lost after 33 days (Cresp33) and basal respiration rate (BRR). The microbial C was obtained at the end of the incubation. The microbial activity rate (MAR: mg C respired per g microbial C per day) was obtained from these measures. The sum soluble + microbial C was taken as the active C pool. As expected, the stability of SOM depends on its distribution between the size fractions: The higher the proportion of particulate organic matter (POM: >20 µm size), the higher the soil respiration rate. In contrast, q barely affects SOM decomposition. Both physical availability (size fractionation) and q (acid hydrolysis) affect the size of the microbial C pool, but they barely affect MAR. The effects of free iron on SOM stability are complex: While dithionite-extracted Fe negatively affected Cresp33, BRR, and MAR, the Fe extracted by smoother methods (Tamm’s reagent and DTPA) positively relates to Cresp33, BRR, and MAR. Free iron apparently modulates soil microbial metabolism because it is the only studied parameter that significantly affected MAR; however, the precise effect depends on the precise free Fe fraction. From our data, SOM stability relies on a net of constraints, including physical availability and free Fe forms, with q being of minor relevance. Our dataset suggests a role for free iron as a modulator of microbial activity, deserving future research.
Fire is a major agent involved in landscape transformation and an indirect cause of changes in species composition. Responses to fire may vary greatly depending on life histories and functional ...traits of species. We have examined the taxonomic and functional responses to fire of eight taxonomic animal groups displaying a gradient of dietary and mobility patterns: Gastropoda, Heteroptera, Formicidae, Coleoptera, Araneae, Orthoptera, Reptilia and Aves. The fieldwork was conducted in a Mediterranean protected area on 3 sites (one unburnt and two burnt with different postfire management practices) with five replicates per site. We collected information from 4606 specimens from 274 animal species. Similarity in species composition and abundance between areas was measured by the Bray-Curtis index and ANOSIM, and comparisons between animal and plant responses by Mantel tests. We analyze whether groups with the highest percentage of omnivorous species, these species being more generalist in their dietary habits, show weak responses to fire (i.e. more similarity between burnt and unburnt areas), and independent responses to changes in vegetation. We also explore how mobility, i.e. dispersal ability, influences responses to fire. Our results demonstrate that differences in species composition and abundance between burnt and unburnt areas differed among groups. We found a tendency towards presenting lower differences between areas for groups with higher percentages of omnivorous species. Moreover, taxa with a higher percentage of omnivorous species had significantly more independent responses of changes in vegetation. High- (e.g. Aves) and low-mobility (e.g. Gastropoda) groups had the strongest responses to fire (higher R scores of the ANOSIM); however, we failed to find a significant general pattern with all the groups according to their mobility. Our results partially support the idea that functional traits underlie the response of organisms to environmental changes caused by fire.
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•We estimate SOC sequestration by the fixed-depth (FD) and equivalent-mass (EM) approaches.•SOC sequestration rates are similar in both, but the amounts of sequestered SOC may ...strongly differ.•FD approach mostly underestimates SOC sequestration compared to the EM approach.•Changes in soil compaction are the main driver of the errors in SOC sequestration by the FD approach.•EM better quantifies SOC sequestration, but FD is preferable for comparison of SOC stocks worldwide.
Soil organic carbon (SOC) sequestration is often quantified through the comparison of SOC stocks down to a fixed depth, usually 30 cm. This approach gives biased estimates because SOC sequestration changes soil bulk density. To account for these biases, the comparison of SOC stocks on an equivalent mass basis is recommended. How big are the biases due to the use of a fixed-depth approach (either under- or overestimations of SOC sequestration), and whether these biases imply that the current estimates of SOC sequestration worldwide need an overhaul, are the two questions addressed in this work.
We collected from literature 140 pairs (initial-final) of plots affected by land use changes: crop to forest, crop to grassland, etc. Peatlands were excluded. The datasets were detailed enough to calculate SOC sequestration by both approaches: fixed-depth (down to 30 cm) and equivalent-mass (amount of fine mineral earth at the top 30 cm of the initial stage). Differences between both approaches were often small, but relevant in many cases: namely, when changes in soil compaction were relevant too. The fixed-depth approach overestimates SOC sequestration when soil compaction occurs, and underestimates it when soil expands. However, the average error is low, because over- and underestimations of sequestered SOC partly compensate: the fixed-depth approach underestimates SOC sequestration by about 0.326 ± 1.016 kg SOC m−2 (overall amount), or 14 g SOC m−2 yr−1 (rate). This suggest that the corrections needed by current estimates of SOC sequestration worldwide—at least, those related to the problem studied in this paper—would be low.
From our data, the equivalent-mass approach is compulsory in studies about SOC sequestration. Nevertheless, it seems less adequate than fixed-depth as an approach to compare SOC stocks worldwide. Both approaches should not be considered as opposite views, but as complementary tools for the study of carbon cycle in soils.
The usefulness of a nutrient-enriched zeolite (NEZ) obtained from simultaneous ammonium (NH4+) and phosphate (PO43−) recovery from urban wastewaters was evaluated as soil amendment through the early ...growth of sunflower (Helianthus annuus). The NEZ systems were applied to sandy (acid) and clayey (basic) soils from Mediterranean agricultural areas (Spain). Some plant growth indicators were measured: evapotranspiration, plant moisture content, plant biomass, root/shoot ratio, nitrogen and phosphorous uptake and the C/N ratio. The experimental data exhibited differences in the growth indicators for un-amended and amended soils. The addition of the NEZ system increase the plant water content of sunflowers grown on clay soils. The plant biomass of sunflower was improved by the incorporation of NEZ system in all treatments for the two soils studied. A reduction of the root/shoot ratio for the treatments of clay soil by application of NEZ systems were observed. The content of ammonium and phosphorous in tissues increased considerably with the addition of amendment material. Besides, the ammonium, nitrate and inorganic phosphorous in the post-test soils revealed that nutrients were still available for a second growth cycle. As demonstrated in previous work, the NEZ system releases nutrients continuously controlled by soil pH and mineral composition as well as the irrigation conditions provided. Therefore, this approach of amendment materials for soil seems to be a promising alternative for agricultural practice, where the dose selection must be balanced according to the plant's nutrient needs and soil properties by adjusting the growth conditions.
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•Natural clinoptilolite in its potassium form was impregnated by hydrated metal oxides (Fe, Mn, Al).•Nutrient-enriched zeolites (NEZ) obtained from wastewater treatment were used as soil amendment.•The plant growth of sunflower (Helianthus annuus) was measured in amended and non-amended soils.•Biomass production of sunflower was improved above 50% using NEZ as soil amendment.•Nutrients from the urban waste water cycle were transfer to the agriculture in a circular approach.
In this work we aim to assess the impact of a WWTP effluent overland flow on properties and nutrient concentrations of a riparian soil, in order to explore the potential of this practice as a ...nature-based treatment. We set two study zones of 150 m2 on the field, one control and one that received the WWTP effluent on its surface for one month. Samples were taken before and after the effluent overland flow system, to test the impact of the effluent on soil properties through a BACI design, and after 17 months, to evaluate the recovery of the soil. Two depths were studied: 0–5 cm and 5–20 cm. The effluent overland flow triggered an increase in exchangeable sodium percentage and a decrease in nitrate concentration in both depths, and an increase in ammonium concentration in 0–5 cm depth. After 17 months, there were not found relevant differences among zones. In conclusion, this practice could be used in the purpose to reduce the nutrient concentrations of WWTP effluents. This practice could be relevant for regions where WWTP effluents are discharged in low-flow or intermittent streams, such as semi-arid regions or the Mediterranean region.
•The WWTP effluent overland flow decreased the nitrate content of the riparian soil.•The WWTP effluent overland flow did not have a negative impact on soil properties.•The WWTP overland flow in riparian zones could be an alternative tertiary treatment.
The use of autonomous recording units (ARUs) for passive acoustic monitoring has recently gained a lot of importance. It is now widely used for scientific purposes and has been increasingly applied ...in the field of conservation biology. However, while ARUs may greatly increase cost-effectiveness in monitoring, they are not exempt from possible biases. In this study, we compared the performances of three different software in recognizing bi- and tri-syllabic bird songs and tested if their results varied significantly in a real setting. We focused on the interpretation of the relative abundance among habitats and the time of vocal activity, also using different numbers of training records to assess if the results of the software improved. Even with the quality measures of the recognizer being consistent with those of previously published studies, in several cases the results produced significantly different interpretations depending on the software used. While increasing the number of training records slightly improved the overlap in the estimates of activity among the different software, differences in the relative abundance of each song were present even with a fairly solid number of training records. Our results suggest that reliable biological interpretations might only be attained with a large number of training records and very high values of precision, recall, and the F-score. In fact, even with very high precision and F-scores, lower values for recall led not only to statistically significant differences, but also to different interpretations of relative abundance and time of activity between the two best-performing software. Thus, great caution must be taken in interpreting the results of bioacoustics studies that use automated recognition, and standards of minimum quality should be created for recognizers in scientific and technical studies.
•Automatic bird song recognition can yield different results depending on software.•Repetability of automatic bird song recognition studies can be compromised.•Increasing number of training records can improve automatic bird song recognition.•High quality measures should be demanded for automatic bird song recognition studies.
The removal of nutrients (nitrogen (N), phosphorous (P)) from waste water has become a resource recovery option in recent regulations worldwide, as observed in the European Union. Although both of ...these nutrients could be recovered from the sludge line, > 70-75% of the N and P is discharged into the water line. Efforts to improve the nutrient recovery ratios have focused on developing low-cost technologies that use sorption processes. In this study, a natural zeolite (clinoptilolite type) in its potassium (K) form was impregnated with hydrated metal oxides and used to prepare natural hybrid reactive sorbents (HRS) for the simultaneous recovery of ammonium (NH4+) and phosphate (PO43 −) from treated urban waste water. Three unfertile soils (e.g., one acidic and two basic) amended with N-P-K charged HRS were leached with deionized water (e.g. to simulate infiltration in the field) at two- and three-day time intervals over 15 different leaching cycles (equivalent to 15 bed volumes). The N-P-K leaching profiles for the three charged hybrid sorbents exhibited continuous nutrient release, with their values dependent on the composition of minerals in the soils. In the basic soil that is rich in illite and calcite, the release of potassium (K+) and ammonium (NH4+) is favoured by-ion exchange with calcium (Ca2 +) and accordingly diminishes the release of phosphate (PO43 −) due to its limited solubility in saturated calcite solutions (pH 8 to 9). The opposite is true for sandy soils that are rich in albite (both acidic and basic), whereas the release of NH4+ and K+ was limited and the values of both ions measured in the leaching solutions were below 1 mg/L. Their leaching solutions were poor in Ca2 +, and the release of PO43 − was higher (up to 12 mg P-PO43 −/L). The nutrient releases necessary for plant growth were provided continuously and were controlled primarily by the soil mineral dissolution rates fixing the soil aqueous solution composition (e.g. pH and ionic composition; in particular, the presence of calcite is a determinant for nutrient release, especially in alkaline soils). The N-P-K charged HRS sorbents that were used for soil amendment may be an alternative for avoiding nutrient leaching and reaching the goals of soil sustainability in agriculture and reducing the nutrient overloading of surface waters.
The effect of mulch soil cover on crop contamination by 137Cs was studied within the 30 km zone of Chernobyl Nuclear Power Plant. Experiments were performed with oats (Avena sativa) over a three year ...period. In 1992 soil surface was covered by a plastic net. In 1993 two straw mulch treatments were applied at a dose rate of 200 g m-2 using 137Cs contaminated and clean straw, respectively. A similar mulch treatment was applied in 1994, and two mulch doses of clean straw were tested (200 and 50 g m-2). Protection of the soil with a plastic net significantly increased crop yield and reduced crop contamination (by about 30%). When clean straw was used as a mulch layer, a significant decrease of about 30−40% in 137Cs activity concentration was observed. Mulching with 137Cs contaminated straw did not reduce crop contamination, probably due to an increase in soil available 137Cs released from the contaminated mulch. Mulching has been shown to be an effective treatment both for reducing 137Cs plant contamination and improving crop yield. Therefore, it can be considered as a potential countermeasure in a post-accident situation.
A field experiment was conducted within the 30-km zone of the Chernobyl Nuclear Power Plant to analyze whether the application of mulching reduced resuspension of 137Cs contaminated soil in oat ...(Avena sativa) crops. In 1993, we applied a mulch treatment at a dose of 200 g m-2, and soil resuspension was measured by estimating soil loadings onto plant surfaces from Ti concentrations in plants. In 1994, two mulch doses were applied, 200 and 50 g m-2, and we estimated the contribution of soil resuspension by using artificial resuspension collection devices (ARC). In the 1993 experiment between 4.6 and 34.4% of the plant's total 137Cs contamination was attributed to external soil contamination. The mean amount of soil-derived 137Cs attached to vegetation was 124.7 Bq kg-1 plant in control plots and 53.7 Bq kg-1 plant in mulched plots. In the 1994 experiment, covering the soil with a mulch layer decreased the radiocesium content in ARC by about 70%. Results obtained in these experiments suggest that soil resuspension was a significant mechanism for plant contamination and that mulching was effective in reducing that contamination.
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