Loss Of Base Cations Research Articles

Chemical weathering along a one-million-year soil age gradient on the Galápagos Islands

The Galápagos archipelago, a chain of islands formed by hotspot-induced volcanism on the Nazca tectonic plate, exhibits pronounced gradients of rock age and climate. Here, we investigate chemical weathering along a soil chronosequence (1.5 to 1070 ka) and under humid vs. dry conditions. Our results show considerable loss of base cations already in the early to intermediate phases of weathering under humid conditions (e.g. 95 % of Na and 78 % of Mg lost from the topsoil after 26 ka) and almost complete loss from the entire profile in soils older than 800 ka. Depletion of Si was less pronounced, with topsoil losses of 24 % and 63–68 % after 26 ka and >800 ka, respectively. Under dry conditions, weathering rates were much lower, e.g. 33 % of Na and 1.4 % of Mg lost from the topsoil after 26 ka. Indices of chemical weathering, e.g. the Chemical Index of Alteration and the Ruxton Ratio, correlated well with indicators of pedogenic development, such as solum thickness, soil pH, or the ratio of oxalate- to dithionite-extractable Fe. Total weathering flux and associated CO2 consumption rates estimated from profile-scale element losses in this study exceeded catchment-scale estimates reported for other volcanic islands or global averages during the early weathering phase, but were much lower in the intermediate and late phases. Nevertheless, total C drawdown was dominated by soil organic C sequestration (70–90 % share) rather than inorganic, weathering-induced CO2 consumption during early pedogenesis (≤4.3 ka), and the relative importance switched in the intermediate and late phases (90–95 % share of weathering-induced C drawdown at ≥166 ka). Dust deposition derived from a nearby ocean sediment core was <20 % of total basalt mass loss at the young and intermediate-aged sites, but reached 40–60 % at the older sites (>800 ka). Our results suggest that (1) young volcanic surfaces are very efficient (inorganic and organic) C sinks, (2) the development of thick soil covers at advanced pedogenic stages effectively shields the underlying rocks and decelerates weathering, and (3) dust inputs become an increasingly important biogeochemical factor in such highly weathered environments.

Chemical Weathering Rates of Soils Developed on Eocene Marls and Sandstones in a Mediterranean Catchment (Istria, Croatia)

Physical and chemical weathering, together with biological and biochemical processes, form soil from bedrock and strongly influence the chemical composition of natural waters. Erosive processes, primarily through the agents of running water and wind, remove the products of weathering from catchments. The aim was to determine the chemical weathering of minerals because of changes in land-use and natural forestation in two small neighboring catchments of the rivers Argilla and Bazuja. Agricultural land-use practice is very intense in the Argilla catchment, while the Bazuja catchment’s arable land is mostly abandoned, with progressive forestation. Chemical weathering in soils and sediments was evaluated with the aid of bulk chemistry analysis focused on major elements, trace elements, and zirconium. Weathering indices, mass balance, and strain were calculated. The abandonment of arable land and intense forestation in the Bazuja catchment caused increased chemical weathering with the loss of base cations (Ca and Mg) and enrichment of conservative elements (Zr and Ti) in surface horizons. EIC and MTF values are positive (enrichment) in areas with agricultural activities, while forested areas show negative values (loss). A comparison of the oldest and youngest parts of the overbank sediment profiles in the swallow hole zone and stream sediments shows that chemical and mechanical weathering in the Bazuja catchment was similar to present weathering in the Argilla catchment, while agriculture was active in the Bazuja catchment. The integrated knowledge gained in small catchment studies can be broadly applicable to larger systems.

Co-Composted Chicken Litter Biochar Increases Soil Nutrient Availability and Yield of Oryza sativa L.

Intensified cultivation of rice has accelerated weathering of most tropical acid soils leading to significant loss of base cations. In most developing countries, rice yield is low and this results in its production being costly because productivity versus labor is low. The objectives of this study were to (i) enhance soil chemical properties, nutrient uptake, and grain yield of rice grown on a mineral tropical acid soil using agro-wastes; (ii) determine the agro-waste (chicken manure, cow dung, forest litter, and Leucaena) that has the potential to significantly increase rice yield; and (iii) determine the residual effects of the organic soil amendments produced from the agro-wastes on soil and rice productivity. The treatments used in this three-cycle field study were (i) soil without amendments (S0); (ii) prevailing recommended rates for fertilizers (NPK-Mg); (iii) biochar–forest litter compost (OSA1); (iv) biochar–chicken litter compost (OSA2); (v) biochar–cow dung compost (OSA3); (vi) biochar–Leucaena compost (OSA4); and (vii) biochar–Leucaena–chicken litter compost (OSA5). Standard procedures were used to determine the plants’ rice growth, grain yield, plant nutrient concentrations and uptake, and selected soil chemical properties. The use of organic soil amendments (OSA1 to OSA5) significantly improved the soil chemical properties, rice plant growth, nutrient uptake, and grain yield compared with the prevailing method of cultivating rice (NPK-Mg). The application of organic soil amendments reduced the use of inorganic N, P, K, MgO, and trace elements fertilizers up to 25%, 100%, 64%, 100%, and 100%, respectively. The organic soil amendments with Leucaena significantly increased rice grain yield of OSA5 at 11.17, 13.11, and 10.06 t ha−1 in the first, second, and third cropping cycles, respectively. The residual effect of the organic soil amendments also improved rice plant growth, nutrient uptake, and rice grain yield although these were slightly reduced as compared to those of the two previous cropping cycles, the afore-stated treatments were superior to the prevailing method of cultivating rice (NPK-Mg). Transforming agro-wastes into organic soil amendments can improve tropical mineral acid soils and rice productivity.

Optimizing nitrogen management reduces mineral nitrogen leaching loss mainly by decreasing water leakage in vegetable fields under plastic-shed greenhouse

Excessive fertilization leads to high nitrogen (N) leaching under intensive plastic-shed vegetable production systems, and thereby results in the contaminations of ground or surface water. Therefore, it is urgent to develop cost-effective strategies of nitrogen management to overcome these obstacles. A 15-year experiment in annual double-cropping systems was conducted to explore impacts of N application rate and straw amendment on mineral N leaching loss in plastic-shed greenhouse. The results showed that seasonal mineral N leaching was up to 103.4–603.4 kg N ha−1, accounting for 12%–41% of total N input under conventional N fertilization management. However, optimized N application rates by 47% and straw addition obviously decreased mineral N leaching by 4%–86%, while had no negative impacts on N uptake and tomato yields. These large decreases of N leaching loss were mainly due to the reduced leachate amount and followed by N concentration in leachate, which was supported by improved soil water holding capacity after optimizing N application rates and straw addition. On average, 52% of water leachate and 55% of mineral N leaching simultaneously occurred within 40 days after planting, further indicating the dominant role of water leakage in regulating mineral N leaching loss. Moreover, decreasing mineral N leaching was beneficial for reducing leaching loss of base cations. Therefore, optimized N application rates and straw amendment effectively alleviates mineral N leaching losses mainly by controlling the water leakage without yield loss in plastic-shed greenhouse, making this strategy promising and interesting from environmental and economical viewpoints.

Soil acidification and loss of base cations in a subtropical agricultural watershed

Soil acidification along with base cations loss degrades soil quality and is a major environmental problem, especially in agroecosystems with extensive nitrogen (N) fertilization. So far, the rates of proton (H+) production and real soil acidification (loss of base cations) remain unclear in subtropical agricultural watersheds. To assess the current status and future risk of soil acidification in subtropical red soil region of China, a two-year monitoring was conducted in a typical agricultural watershed with upland, paddy fields, and orchards where high N fertilizers are applied (320 kg N ha−1 yr−1). H+ production, neutralization and base cations losses were quantified based on the inputs (rainwater, inflow of water, and fertilizer) and outputs (outflow of water, groundwater drainage, and plant uptake) of major elements (K+, Ca2+, Na+, Mg2+, Al3+, NH4+, NO3−, SO42−, Cl−, and H+). The result showed that total H+ production in the watershed was 5152 molc ha−1 yr−1. N transformation was the most important H+ source (68%), followed by excess plant uptake of cations (25%) and H+ deposition (7%). Base cations exchange and weathering of minerals (3842 molc ha−1 yr−1) dominated H+ neutralization, followed by SO42− adsorption (1081 molc ha−1 yr−1), while H+ and Al3+ leaching amounted to 431 molc ha−1 yr−1, only. These results state clearly that despite significant soil acidification, the acidification of surface waters is minor, implying that soils have buffered substantially the net H+ addition. As a result of soil buffering, there was abundant loss of base cations, whose rate is significantly higher than the previously reported weathering rate of minerals in red soils (3842 vs 230–1080 molc ha−1 yr−1). This suggests that the pool of exchangeable base cations is being depleted in the watershed, increasing the vulnerability of the watershed, and posing a serious threat to future recovery of soils from acidification.

Drivers of soil respiration in response to nitrogen addition in a Mediterranean mountain forest

Atmospheric nitrogen (N) deposition rates affect soil N dynamics, influencing soil respiration (RS) rates. However, for the Mediterranean region, the effect of changes in atmospheric N deposition on RS are not well constrained yet. We investigated the interplay between increased N deposition and tree species composition on RS at a Scots pine—Pyrenean oak ecotone in Central Spain, and whether the observed responses were mediated by changes on selected soil properties. Throughout 3 years, we simulated two N deposition rates—10 (medium) and 40 kg N ha−1 a−1 (high)—over the background deposition (control) in neighbouring stands in which tree species composition (pine or oak) shapes soil stoichiometry and microbial communities. We monitored RS on a monthly basis during 3 years; in addition, we performed targeted measurements 24 h after the N fertilization events to assess short-term soil responses. During winter and summer, RS did not respond to enhanced N deposition rates. In spring and autumn, higher RS rates were observed in the medium-fertilization, but the size and duration of this effect was tree species dependent. We suggest that climate seasonality modulates the response of RS to N availability, with tree species effects becoming relevant only when environmental conditions are adequate. RS in fertilized plots was larger from February to May and in September under pine, while under oak a response was observed only in April, probably due to differences in native soil stoichiometry under each tree species. Overall, RS showed high stability during 3 years of N enrichment in this Mediterranean ecotone area. However, we observed short-term soil responses after N fertilization events—loss of base cations, soil acidification and reduced microbial biomass—which emphasize the need to investigate consequences for the belowground C and N cycles if chronic N enrichment persists in the long run.

Road Salting Induces Regional-Scale Losses of Base Cations from Forested Watersheds

Road Salting Induces Regional-Scale Losses of Base Cations from Forested Watersheds

Quaternary record of terrestrial environmental change in response to climatic forcing and anthropogenic perturbations, in Puerto Rico

We present cospatial, contemporary archival records of biotic and abiotic terrestrial processes operating over the past ∼25 ky within the Rio Fajardo watershed, in northeastern Puerto Rico. The proxy records were derived from a 5-m-thick stratigraphic section exposed by cut bank incision. We interpreted ecosystem dynamics from changes in the stable carbon isotopic ratio of sedimentary organic material compared to δ13C ratios of contemporary carbon sources. Sedimentary organic material had δ13C values ranging from −29.715 to −15.291. We derived a record of paleo-erosion rates in the catchment from the concentration of meteoric 10Be in layers of the floodplain sediments. Paleo-erosion rates ranged from 13 to 356 mm ky−1. The chronology of the sediments was constrained with the radiocarbon ages of organic deposits, the oldest age was calibrated to ∼22.4 ky BP (thousand years before present) and retrieved at 440 cm depth. We collected grain size data, clay mineralogies, and analyzed geochemical indices including the chemical weathering index, salinization, and base cation loss down profile. This stratigraphic sequence captures major shifts in the Caribbean climate, the intensification of the El Nino-Southern Oscillation, and the arrival of humans on the island. During the last glacial and early Holocene epochs both biotic (δ13C) and abiotic proxies (10Bemet and geochemical data) indicated dynamic equilibrium with climate. The past five thousand years (ky) of record are characterized instead by pulsed responses to disturbances in both systems. Colonial-era land use drove changes that significantly exceeded natural variability in any proxy over the period of record.

Herbicide weed control increases nutrient leaching compared to mechanical weeding in a large-scale oil palm plantation

Abstract. Nutrient leaching in intensively managed oil palm plantations can diminish soil fertility and water quality. There is a need to reduce this environmental footprint without sacrificing yield. In a large-scale oil palm plantation in Acrisol soil, we quantified nutrient leaching using a full factorial experiment with two fertilization rates (260 kg N, 50 kg P, and 220 kg K ha−1 yr−1 as conventional practice and 136 kg N, 17 kg P, and 187 kg K ha−1 yr−1, equal to harvest export, as reduced management) and two weeding methods (conventional herbicide application and mechanical weeding as reduced management) replicated in four blocks. Over the course of 1 year, we collected monthly soil pore water at 1.5 m depth in three distinct management zones: palm circle, inter-row, and frond-stacked area. Nutrient leaching in the palm circle was low due to low solute concentrations and small drainage fluxes, probably resulting from large plant uptake. In contrast, nitrate and aluminum leaching losses were high in the inter-row due to the high concentrations and large drainage fluxes, possibly resulting from low plant uptake and low pH. In the frond-stacked area, base cation leaching was high, presumably from frond litter decomposition, but N leaching was low. Mechanical weeding reduced leaching losses of base cations compared to the conventional herbicide weeding probably because herbicides decreased ground vegetation and thus reduced soil nutrient retention. Reduced fertilization rates diminished the nitrate leaching losses. Leaching of total nitrogen in the mechanical weeding with reduced fertilization treatment (32±6 kg N ha−1 yr−1) was less than half of the conventional management (74±20 kg N ha−1 yr−1), whereas yields were not affected by these treatments. Our findings suggest that mechanical weeding and reduced fertilization should be included in the program by the Indonesian Ministry of Agriculture for precision farming (e.g., variable rates with plantation age), particularly for large-scale oil palm plantations. We further suggest including mechanical weeding and reduced fertilization in science-based policy recommendations, such as those endorsed by the Roundtable for Sustainable Palm Oil association.

Road salt retention and transport through vadose zone soils to shallow groundwater

Increasing background salinity in watersheds has largely been attributed to road salt retention in groundwaters due to their long residence times. However, laboratory studies demonstrate that soils temporarily store salts, either in porewater or adsorbed onto particles. Field studies of road salt retention in soils are nevertheless rare, and mechanisms of salt transport across multiple hydrological reservoirs (e.g., from soil to groundwater) are unknown. Thus, we collected roadside soil porewater and karst spring water weekly for ~1.5 yr to determine salt transport through the vadose zone into the phreatic zone. We observed dual retention mechanisms of sodium (Na+) and chloride (Cl−) in soils due to slow porewater movement, causing ion movement through the soil as slow as 1.3 cm/day, and cation exchange processes, leading to initial Na+ retention followed by later release months after application. Cation exchange processes also caused base cation loss from exchange sites into mobile porewater. Rapid Na+ and Cl− delivery to groundwater occurred through karst conduits during the winter. However, elevated background levels of salt ions in groundwater during the non-salting months indicated accumulation in the catchment due to slower porewater flow in the soil and rock matrix and delayed Na+ release from soil exchange sites.

Effects of volcanic parent materials on the acid buffering capacity of forest soils on Yakushima Island, Japan

ABSTRACT Soil acidification is a natural pedogenetic process in forest ecosystems, but is accelerated by acidic deposition. Soils on Yakushima Island, in southwestern Japan, are derived from granitic bedrock and volcanic parent materials influenced by eolian dust inputs. Acid deposition and low acid-neutralizing capacity (ANC) of granite-derived soils are hypothesized to be the cause of acidic stream water that has been widely observed on Yakushima. It remains unclear, however, whether ANCs are also limited in volcanic soils, which contain weatherable minerals and have high buffering capacities. To compare acidification rates between granite-derived soils and volcanic soils, we estimated changes in ANCs between granite and volcanic parent materials and the resulting soils at a pedogenetic timescale, using the mass balance of titanium. After 7300 years of soil development following the eruption of the Kikai caldera, decreased ANCs and total base reserves were observed in both granite-derived and volcanic soils, compared to their respective parent materials. No difference in soil ANC was observed between granite and volcanic parent materials. Different cations contribute to acid neutralization in soils: decreasing ANC results primarily from the loss of Al in granite-derived soils, while acidity is neutralized by the loss of base cations from volcanic soils. In granite-derived soils, resistance to weathering and K retention in 2:1 type silicate clays limit the loss of bases while increasing the accumulation of exchangeable Al. In volcanic soil profiles, base leaching and the sorption of organic acids onto short-range order minerals can neutralize acidity, although erosion and admixing of granite or eolian dust-derived materials lead to a reduction of ANC in surface soil horizons.

Effects of whole‐tree harvesting at thinning and subsequent compensatory nutrient additions on carbon sequestration and soil acidification in a boreal forest

AbstractResidues from forest harvesting operations may be utilized as a renewable energy source. However, the sustainability of this practice has been questioned due to the losses of nutrients and exchangeable base cations, which may impair the forest's carbon sequestration capacity and lead to soil acidification. We report the 18 year response of biomass growth, soil carbon stock and soil chemistry to whole‐tree harvest at thinning and associated compensatory measures in a Pinus sylvestris forest in northern Sweden. The whole‐tree harvest at thinning was combined with nutrient additions to compensate for the nutrient loss caused by extracting the residues. Four main treatments, stem‐only thinning, whole‐tree thinning, whole‐tree thinning with one‐time nitrogen fertilization and whole‐tree thinning with repeated nitrogen fertilization every third year were applied, with plots split for wood‐ash treatment. Eighteen years after the treatments, whole‐tree thinning that had removed 3.0 ± 0.2 Mg C/ha in residues had no effect on forest growth, soil carbon and nitrogen stocks or soil chemistry. Both nitrogen fertilization regimes increased biomass growth, but neither one resulted in a significant increase in soil carbon stock. Wood‐ash addition increased soil pH and exchangeable base cations, but did not affect carbon stock in biomass or soil. Our long‐term data suggest that utilizing harvesting residues for biofuel feedstocks is appropriate in this type of forest. Hence, any nitrogen and wood‐ash additions appear unnecessary as compensatory measures for the removal of harvesting residues, but nitrogen can be applied to increase forest growth following thinning.

Soil aggregation and aggregate-related exchangeable base cations under different aged tea (Camellia sinensis L.) plantations in the hilly regions of southern Guangxi, China

ABSTRACT As the secondary nutrients in soils, exchangeable base cations can form cationic bridges with clay particles and organic matters to promote the formation of soil aggregates, and to protect soil organic carbon (Corg) and nutrients from loss. To have a comprehensive understanding toward the dynamics of soil exchangeable base cations in the tea planting process, it requires to evaluate these cations’ distribution in soil aggregates at various sizes. In this study, soil samples (0–20 cm) from the tea plantations at various ages (8, 17, 25, and 43 yr.) in the hilly regions of southern Guangxi, China were divided into >2, 1–2, 0.25–1, and <0.25 mm aggregate fractions through a dry-sieving procedure. Then, the cation exchange capacity (CEC), total exchangeable bases (TEB), and different individual cations, such as exchangeable potassium (K+), sodium (Na+), calcium (Ca2+), and magnesium (Mg2+), in soil aggregates were detected. Our results suggested that the mean weight diameter (MWD), that is an indicator evaluating the stability of soil aggregates, in the 17-yr. tea plantations appeared to be the highest among all the tea plantations, indicating that more stable soil aggregates could be formed in the 17-yr. tea plantations in comparison with the rest plantations. During tea planting of 35 yr. (from 8 to 43 yr.), the increasing rate of soil CEC stock was 33.42 cmol m−2 yr.−1, while the loss rates of soil exchangeable K+, Na+, Ca2+, Mg2+, and TEB were 0.89, 0.52, 3.86, 1.23, and 6.51 cmol m−2 yr.−1, respectively. Interestingly, the loss rates of soil exchangeable base cations in the middle phase (from 17 to 25 yr.) were greater than those in other phases. Therefore, it is of critical importance to implement a sustainable management scheme to maintain soil aggregate stability and to minimize the loss of soil exchangeable base cations in the tea planting process, especially after 17 yr., in the hilly regions of southern Guangxi, China.

Weathering rates in Swedish forest soils

Abstract. Soil and water acidification was internationally recognised as a severe environmental problem in the late 1960s. The interest in establishing “critical loads” led to a peak in weathering research in the 1980s and 1990s, since base cation weathering is the long-term counterbalance to acidification pressure. Assessments of weathering rates and associated uncertainties have recently become an area of renewed research interest, this time due to demand for forest residues to provide renewable bioenergy. Increased demand for forest fuels increases the risk of depleting the soils of base cations produced in situ by weathering. This is the background to the research programme Quantifying Weathering Rates for Sustainable Forestry (QWARTS), which ran from 2012 to 2019. The programme involved research groups working at different scales, from laboratory experiments to modelling. The aims of this study were to (1) investigate the variation in published weathering rates of base cations from different approaches in Sweden, with consideration of the key uncertainties for each method; (2) assess the robustness of the results in relation to sustainable forestry; and (3) discuss the results in relation to new insights from the QWARTS programme and propose ways to further reduce uncertainties. In the study we found that the variation in estimated weathering rates at single-site level was large, but still most sites could be placed reliably in broader classes of weathering rates. At the regional level, the results from the different approaches were in general agreement. Comparisons with base cation losses after stem-only and whole-tree harvesting showed sites where whole-tree harvesting was clearly not sustainable and other sites where variation in weathering rates from different approaches obscured the overall balance. Clear imbalances appeared mainly after whole-tree harvesting in spruce forests in southern and central Sweden. Based on the research findings in the QWARTS programme, it was concluded that the PROFILE/ForSAFE family of models provides the most important fundamental understanding of the contribution of weathering to long-term availability of base cations to support forest growth. However, these approaches should be continually assessed against other approaches. Uncertainties in the model approaches can be further reduced, mainly by finding ways to reduce uncertainties in input data on soil texture and associated hydrological parameters but also by developing the models, e.g. to better represent biological feedbacks under the influence of climate change.

Long-term acidification of pH neutral grasslands affects soil biodiversity, fertility and function in a heathland restoration

In the wider context of heathland restoration, we investigated how field scale experimental acidification with sulphur (sulfur) affected soil biodiversity, fertility and function over a period of 17 years. A field experiment was conducted in the Isle of Purbeck, England, using ferrous sulphate and elemental sulphur as acidifying agents. We tested the effects of acidification on soil fertility, plant communities, litter decomposition, microbiology (including fungi bacteria and actinomycetes), arbuscular and ericoid mycorrhizal colonisation, and soil fauna (including earthworms, nematodes, rotifers and tardigrades). We found that elemental sulphur had a considerable and persistent effect on soil pH, lowering it to levels found in the surrounding reference acid grassland and heathland sites. A newly adapted heathland restoration index based on soil chemistry, found that elemental sulphur was by far the most successful treatment leading to soil conditions similar to the heathlands. Overall, acidification caused a loss of base cations and an increase in toxic aluminium compounds. Consequently the more mesotrophic components of soil biology were reduced by acidification during the course of the experiment. This transformed the soil biological system into one typical of acid grasslands and heathlands. Concomitant litter decomposition was similarly inhibited by acidification, with the microbiota more strongly hindered in acidified soil than the macroscopic fauna. Acidification resulted in a reduction in nematode and rotifer abundance and earthworm biomass. The vegetation community was also strongly modified by the elemental sulphur treatments and, where grazing was restricted, soil acidification allowed a restored heathland community to endure. Arbuscular mycorrhizal colonisation of grasses was reduced where heather plants were established, while ericoid mycorrhizas had developed sufficient populations in the acidified pastures to match the colonisation rate in the native heathlands.

Acid deposition induced base cation loss and different responses of soils and sediments in Taihu Lake watershed, China

Acid deposition and algae blooms have resulted in great changes in the water chemistry of Taihu Lake; however, there have been few calculated results to describe these processes. Here we used a mass balance model to estimate base cation losses and evaluate the model applicability in this intensively human-impacted watershed based on a long-term database (1985–2015). The results showed that carbonate weathering induced Ca2+ and Mg2+ losses in the watershed were responsible for the increased ion net reaction (INR) of Ca2+and Mg2+ in the lake. While the increase of K+ and Na+ were not appropriate to provide independents check on the mass balance model because they generally entered the lake as human discharges, not reflecting change of the geochemical process in the watershed as the watershed dominant bedrock is carbonate but not silicate. Acid deposition in Taihu region caused decrease in pH, lime potential, and different Ca, Mg species of surface soils. Our field measurements of sediments in the two lake parts showed that the sediment lime potential was significantly higher in the algae dominated lake area than in the hydrophyte-dominated area due to the in-lake alkalinization by algae blooms, indicating that algae blooms played a significant role in the acidification resistance. Meanwhile, the measured lime potential of the watershed soils was lower than that of the sediment, implying a potential risk of acidification in the watershed. This research helps understand the accelerated interactions between human activities and natural geochemical processes and accelerated water chemistry change at the watershed level.

Limited Ecosystem Recovery from Simulated Chronic Nitrogen Deposition

The realization that anthropogenic nitrogen (N) deposition is causing significant environmental change in many ecosystems has led to lower emissions of reactive N and deposition rates in many regions. However, the impacts of N deposition on terrestrial ecosystems can be long lasting, with significant inertia in the return of the biota and biogeochemical processes to baseline levels. To better understand patterns of recovery and the factors that may contribute to slow or no responses following declines in N deposition, we followed plant species composition, microbial abundance, N cycling rates, soil pH, and pools of NO3 - and extractable cations in an impacted alpine ecosystem following cessation of 12-yr experiment increasing N deposition rates by 0, 20, 40, and 60 kg N·ha-1 ·yr-1 . Simulated N deposition had resulted in a tripling in the cover of the nitrophilic species Carex rupestris, while the dominant sedge Kobresia myosuroides had decreased by more than half at the highest N input level. In addition, nitrification rates were elevated, soil extractable magnesium (Mg2+ ) and pH decreased, and aluminum (Al3+ ) and manganese (Mn2+ ) were elevated at the highest N treatment inputs. Over the nine years following cessation of N additions to the impacted plots, only the cover of the nitrophilic C. rupestris showed any recovery to prior levels. Abundances of both bacteria and fungi were lower with N addition in both treatment and recovery plots. Rates of nitrification and pools of NO3 - remained elevated in the recovery plots, likely contributing to the lack of biotic response to the cessation of N inputs. In addition, nutrient base cations (Ca2+ and Mg2+ ) and soil pH remained depressed, and the toxic metal cations (Al3+ and Mn2+ ) remained elevated in recovery plots, also potentially influencing biotic recovery. These results emphasize the importance of considering long-term environmental impacts of N deposition associated with legacy effects, such as elevated N cycling and losses of base cations, in determining environmental standards such as the metrics used for critical loads.

Effects of amendments on base cation and micronutrient availabilities in soils planted with tomato in a solar greenhouse

ABSTRACTIn order to obtain high tomato production, chemical fertilizers have been intensively applied in solar greenhouse in Northern China. This unreasonable use of chemical fertilizers always leads to soil degradation. One of the most serious problems is the loss of exchangeable base cations: calcium (Ca), magnesium (Mg), and potassium (K), and available micronutrients: iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn). We collected soils with different tomato cultivation durations: 0, 5, and 20 years, to investigate the effects of different fertilizers on the dynamics of soil base cations and micronutrients which extracted by 1 M ammonium acetate and 0.005 M diethylenetriaminepentaacetic acid, respectively. Five treatments were included: no fertilizer application as control (Con), chemical nitrogen, phosphorus and potassium fertilizers (CF), rice straw (FS), chicken manure (CM), and vermicompost (VM). Our results show that soil exchangeable Ca significantly decreased with the increase of cultivation duration, whereas soil exchangeable K increased due to the fertilization of K. Soil exchangeable Ca and K exhibited decreasing trends during the growth season of tomato, but not exchangeable Mg. Long-term tomato cultivation significantly increased soil available micronutrients. Soil available Fe and Mn fluctuated sharply during the growing season of tomato plant. Except Zn, fertilizers exhibited no constant significant effect on base cations and micronutrients. After long term planting of tomato, the loss of exchangeable Ca, but not Mg and micronutrients, might potentially constrain the productivity of crop under intensive chemical fertilization.

Limited ecosystem recovery from simulated chronic nitrogen deposition.

The realization that anthropogenic nitrogen (N) deposition is causing significant environmental change in many ecosystems has led to lower emissions of reactive N and deposition rates in many regions. However, the impacts of N deposition on terrestrial ecosystems can be long lasting, with significant inertia in the return of the biota and biogeochemical processes to baseline levels. To better understand patterns of recovery and the factors that may contribute to slow or no responses following declines in N deposition, we followed plant species composition, microbial abundance, N cycling rates, soil pH, and pools of NO3- and extractable cations in an impacted alpine ecosystem following cessation of 12-yr experiment increasing N deposition rates by 0, 20, 40, and 60kg N·ha-1 ·yr-1 . Simulated N deposition had resulted in a tripling in the cover of the nitrophilic species Carex rupestris, while the dominant sedge Kobresia myosuroides had decreased by more than half at the highest N input level. In addition, nitrification rates were elevated, soil extractable magnesium (Mg2+ ) and pH decreased, and aluminum (Al3+ ) and manganese (Mn2+ ) were elevated at the highest N treatment inputs. Over the nine years following cessation of N additions to the impacted plots, only the cover of the nitrophilic C.rupestris showed any recovery to prior levels. Abundances of both bacteria and fungi were lower with N addition in both treatment and recovery plots. Rates of nitrification and pools of NO3- remained elevated in the recovery plots, likely contributing to the lack of biotic response to the cessation of N inputs. In addition, nutrient base cations (Ca2+ and Mg2+ ) and soil pH remained depressed, and the toxic metal cations (Al3+ and Mn2+ ) remained elevated in recovery plots, also potentially influencing biotic recovery. These results emphasize the importance of considering long-term environmental impacts of N deposition associated with legacy effects, such as elevated N cycling and losses of base cations, in determining environmental standards such as the metrics used for critical loads.

Soil Evolution and Mass Flux of Basaltic Cinder Cones in a Cool, Semi‐Arid Climate

Core Ideas Soil development across a chronosequence of basaltic cinder cones. Elemental mass balance data were used to investigate secondary mineral formation. Elucidate rates and processes of early stage weathering. Soil developmental processes on young volcanic cinders in cool, semiarid climates are not well understood and previously under‐studied, but present a unique setting within which to study neoformation of soils under well‐dated time constraints. This study investigates the development of physical, chemical, and mineralogical soil properties on a chronosequence of basaltic cinder cones, aged approximately 2.1, 6.9, and 13.9 ka, at Craters of the Moon National Monument and Preserve in southern Idaho. Representative parent material, coarse fragments, and soil samples were analyzed using selective dissolutions and total elemental digests. Elemental mass balance data were used together with the soil physicochemical data to investigate weathering and secondary mineral formation within each soil profile. The highest degree of weathering was identified on the 13.9 ka profile, followed by the 6.9 and 2.1 ka soils. Short‐range ordered minerals, including allophane and ferrihydrite, dominate the colloidal fraction of all soils, with greatest proportions in the oldest soil. Dominant soil‐forming processes documented along the chronosequence of basalt‐derived soils are the accumulation of organic carbon, weathering of rock fragments, loss of base cations, redistribution of Fe, Al, and Ti, and the accumulation of secondary short‐range order and crystalline minerals. This study provides critical information to elucidate rates and processes of early stage weathering, dust influence, and soil evolution on cinders in cool and dry climates.