Land-use change continues at an alarming rate in sub-Saharan Africa adversely affecting ecosystem services provided by soil. These impacts are greatly understudied, especially in biodiversity rich mountains in East Africa. The objectives of this study were to: conduct a biophysical baseline of soil and land health; assess the effects of cultivation on soil organic carbon (SOC); and develop a map of SOC at high resolution to enable farm-scale targeting of management interventions. Biophysical field surveys were conducted in a 100 km 2 landscape near Lushoto, Tanzania, with composite soil samples collected from 160 sampling plots. Soil erosion prevalence was scored, trees were counted, and current and historic land use was recorded at each plot. The results of the study showed a decline in SOC as a result of cultivation, with cultivated plots (n = 105) having mean topsoil OC of 30.6 g kg -1 , while semi-natural plots (n = 55) had 71 g OC kg -1 in topsoil. Cultivated areas were also less variable in SOC than seminatural systems. Prediction models were developed for the mapping of SOC based on RapidEye remote sensing data for January 2014, with good model performance (RMSEP cal = 8.0 g kg -1 ; RMSEP val = 10.5 g kg -1 ) and a SOC map was generated for the study. Interventions will need to focus on practices that increase SOC in order to enhance productivity and resilience of the farming system, in general. The highresolution maps can be used to spatially target interventions as well as for monitoring of changes in SOC.
Wet prairie soils in the Midwest store significant amounts of soil organic carbon (SOC) and total nitrogen (TN). Crop fields, prairie restorations of varying ages, and remnant prairies on a floodplain soil (Fine‐silty, mixed, superactive, mesic Typic Endoaquolls) in southern Wisconsin were intensively sampled to estimate changes in SOC and TN due to the conversion of native prairie to row crops and the restoration of prairie on cropped land. In the top 10 cm of soil, remnant prairies contained an additional 24 Mg SOC ha−1 and 1.7 Mg TN ha−1, compared with currently cropped fields (P < 0.05). In the top 25 cm, remnant prairies contained an additional 2.4 Mg TN ha−1 compared with currently cropped fields (P < 0.05), but a difference was not detected in SOC between unplowed remnants and cropped fields. Soil inorganic carbon (SIC) was significantly greater at all depths in cropped fields than in unplowed remnants. No differences in SOC and TN mass between annually tilled (AT) and biennially tilled (BT) fields were detected, except for greater TN in the top 10 cm of BT fields. No differences between currently cropped fields and prairie restorations less than 7 yr old were detected, however a 7‐ and 45‐yr‐old restoration had greater SOC and TN mass than crop averages. These results suggest that the loss of SOC in the A horizon of the soils on this floodplain through agriculture has likely been small. Additionally, the redistribution of SIC through the soil profile has had a significant impact on the total C stored in the plow layer, but not on the net C sequestered or released to the atmosphere through land use.
The availability of nitrogen (N) and phosphorus (P) controls the flow of carbon (C) among plants, soils, and the atmosphere, thereby shaping terrestrial ecosystem responses to global change. Soil C, N, and P cycles are linked by drivers operating at multiple spatial and temporal scales: landscape‐level variation in macroclimate and soil geochemistry, stand‐scale heterogeneity in forest composition, and microbial community dynamics at the soil pore scale. Yet in many biomes, we do not know at which scales most of the biogeochemical variation emerges, nor which processes drive cross‐scale feedbacks. Here, we examined the drivers and spatial/temporal scales of variation in soil biogeochemistry across four tropical dry forests spanning steep environmental gradients. To do so, we quantified soil C, N, and P pools, extracellular enzyme activities, and microbial community structure across wet and dry seasons in 16 plots located in Colombia, Costa Rica, Mexico, and Puerto Rico. Soil biogeochemistry exhibited marked heterogeneity across the 16 plots, with total organic C, N, and P pools varying fourfold, and inorganic nutrient pools by an order of magnitude. Most soil characteristics changed more across space (i.e., among sites and plots) than over time (between dry and wet season samplings). We observed stoichiometric decoupling among C, N, and P cycles, which may reflect their divergent biogeochemical drivers. Organic C and N pool sizes were positively correlated with the relative abundance of ectomycorrhizal trees and legumes. By contrast, the distribution of soil P pools was driven by soil geochemistry, with larger inorganic P pools in soils with P‐rich parent material. Most earth system models assume that soils within a texture class operate similarly, and ignore subgrid cell variation in soil properties. Here we reveal that soil nutrient pools and fluxes exhibit as much variation among four Neotropical dry forests as is observed across terrestrial ecosystems at the global scale. Soil biogeochemical patterns are driven not only by regional differences in soil parent material and climate, but also by local‐scale variation in plant and microbial communities. Thus, the biogeochemical patterns we observed across the Neotropical dry forest biome challenge representation of soil processes in ecosystem models.
Deep-sea ferromanganese nodules accumulate trace elements from seawater and underlying sediment porewaters during the growth of concentric mineral layers over millions of years. These trace elements have the potential to record past ocean geochemical conditions. The goal of this study was to determine whether Fe mineral alteration occurs and how the speciation of trace elements responds to alteration over 3.7 Ma of marine ferromanganese nodule (MFN) formation, a timeline constrained by estimates from 9 Be/ 10 Be concentrations in the nodule material. We determined Fe-bearing phases and Fe isotope composition in a South Pacific Gyre (SPG) nodule. Specifically, the distribution patterns and speciation of trace element uptake by these Fe phases were investigated. The time interval covered by the growth of our sample of the nodule was derived from 9 Be/ 10 Be accelerator mass spectrometry (AMS). The composition and distribution of major and trace elements were mapped at various spatial scales, using micro-X-ray fluorescence (lXRF), electron microprobe analysis (EMPA), and inductively coupled plasma mass spectrometry (ICP-MS). Fe phases were characterized by micro-extended X-ray absorption fine structure (lEXAFS) spectroscopy and micro-X-ray diffraction (lXRD). Speciation of Ti and V, associated with Fe, was measured using micro-X-ray absorption near edge structure (lXANES) spectroscopy. Iron isotope composition (d 56/54 Fe) in subsamples of 1-3 mm increments along the radius of the nodule was determined with multiplecollector ICP-MS (MC-ICP-MS). The SPG nodule formed through primarily hydrogeneous inputs at a rate of 4.0 ± 0.4 mm/Ma. The nodule exhibited a high diversity of Fe mineral phases: feroxyhite (d-FeOOH), goethite (a-FeOOH), lepidocrocite (c-FeOOH), and poorly ordered ferrihydrite-like phases. These findings provide evidence that Fe oxyhydroxides within the nodule undergo alteration to more stable phases over millions of years. Trace Ti and V were spatially correlated with Fe and found to be adsorbed to Fe-bearing minerals. Ti/Fe and V/Fe ratios, and Ti and V speciation, did not vary along the nodule radius. The d 56/54 Fe values, when averaged over sample increments representing 0.25-0.75 Ma, were homogeneous within uncertainty along the nodule radius, at 0.12 ± 0.07‰ (2sd, n = 10). Our results indicate that the Fe isotope composition of the nodule remained constant during nodule growth and that mineral alteration did not affect the primary Fe isotope composition of the nodule. Furthermore, the average d 56/54 Fe value of 0.12‰ we find is consistent with Fe sourced from continental eolian particles (dust). Despite mineral alteration, the trace element partitioning of Ti and V, and Fe isotope composition, do not appear to change within the sensitivity of our measurements. These findings suggest that Fe oxyhydroxides within hydrogenetic ferromanganese nodules are out of geochemical contact with seawater once they are covered by subsequent concentric mineral layers. Even though Febearing minerals are...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.