Context Of Land Use Research Articles

Simulating the dynamics of cultivated land use in the farming regions of China: A social-economic-ecological system perspective

Greater comprehension of the intricate impacts of cultivated land use change on social and natural systems is of paramount importance for both immediate and long-term policy decisions and sustainable agricultural development. While prior research has examined specific elements of cultivated land use, there has been limited empirical research assessing interactions and feedback to examine the interplay among the intricacies of economic growth, social change, and their environmental impacts within a cultivated land use system. Hence, we introduce a nuanced system dynamics simulation model designed to evaluate the intricate interplay among social, economic, and ecological subsystems within the context of cultivated land use, with the Huang-Huai-Hai Plain of China serving as the case study. Our research elucidates that economic expansion tends to precipitate increased agrochemical application, highlighting that strategies to synchronize economic advancement with agricultural land conservation may alleviate the environmental stressors tied to regional land use. Furthermore, our analysis indicates that an integrative development strategy, which carefully balances economic acceleration with the reinforcement of agricultural land protection, can yield a measurable enhancement in agrarian environmental standards. This presents a feasible trajectory toward synergistic regional development.

Land use change rather than surrounding vegetation affects fungal endophyte assemblages in the African wild olive

ContextLand use change can significantly affect plant-fungal interactions.ObjectivesWe assessed how fungal endophytes within African wild olive (Olea europaea subsp. cuspidata) twigs are influenced by different levels of land use change and differences in surrounding vegetation types.MethodsTwigs were sampled in the Western Cape Province (South Africa) and their fungal endophyte assemblages were characterised using culture-independent DNA metabarcoding. We assessed the effects of land use change (natural, semi-natural and planted (completely transformed)) and differences in surrounding vegetation types (grasses/low-growing plants versus shrubs/trees versus other olives) using fungal endophyte alpha and beta diversity measures. Co-occurrence networks were constructed to assess assemblage connectivity under different scenarios and to identify OTUs of potential ecological significance.ResultsOTU richness, but not abundance, was significantly influenced by both land use change and differences in the surrounding vegetation types. Planted African olives and those surrounded by heterospecific trees harboured the highest OTU richness. Only levels of land use change significantly influenced fungal endophyte assemblage composition. Specifically, fungal assemblages from natural habitats were distinct from those in planted and semi-natural habitats, which were similar to each other. Co-occurrence network analyses revealed that cohesive and species rich networks could only be maintained within the natural habitats.ConclusionThese findings suggest that although the African olive is widespread, the identity and composition of their associated fungal assemblages are particularly sensitive to land use change. This study highlights the importance of conserving natural habitats, not just for the plants, but also for the maintenance of their associated fungal endophytes.

Runoff simulation analysis and collaborative response research based on the second Songhua River basin under the background of land use

Abstract This paper examines the context of climate change and land use in the second Songhua River basin with the goal of improving runoff. The report begins by introducing the history of watershed runoff and the study area. The differences between various land use types and land use efficiency are examined using the watershed hydrology model from previous literature. The novelty of the paper is to compare the evapotranspiration of the model in different periods with the depth data of surface runoff. The results show that the simulation analysis and collaborative response strategy proposed here can adapt to the meteorological changes in the basin. The evapotranspiration of a watershed that was converted from woodland to grassland in 1970 was 34 mm, while that of a watershed that was converted from grassland to woodland was 32 mm, according to the results of the model test. The evapotranspiration of a watershed that gone from woodland to grassland in 2010 is 45 mm, compared to 39 mm for a watershed that has gone from grassland to woodland. The second Songhua River basin's surface water yield data can therefore be used to model and study the basin's runoff in real time.

The Effect of Multi-Use Landscapes on Mammal Assemblages and Its Implication for Conservation

It has become clear that state-owned protected areas (PAs) are insufficient in preserving the world’s spatially heterogenous biodiversity. Private land conservation could contribute significantly to national conservation goals, without further burdening state resources. In South Africa, legislation has been introduced to incentivise private landowners to contribute to national biodiversity goals. In this study, we used camera trap arrays and hierarchical multi-species occupancy modelling to evaluate the impact of land-use on mammal (body mass >0.5 kg) diversity in the drylands of South Africa. Four hundred and fifty-one camera traps were deployed across a statutory PA, private PA and a neighbouring group of farmlands, covering ~2096 km2. Although trophic species richness were similar across all three land-uses, occurrence and detection probabilities of larger (>20 kg) species were low in the farmlands and highest in the private PA. In contrast, smaller species had higher occurrence probabilities in the farmlands, where large predators and megaherbivores have been extirpated. Differences in species-specific occurrence probabilities were primarily driven by land-use context, as opposed to fine-scale habitat attributes. These results highlight how a land-use matrix incorporating statutory PAs, private PAs and well-managed rangelands can benefit wildlife conservation, as long as these land-uses are included in carefully developed regional conservation planning.

Rainfall effects on vertical profiles of airborne fungi over a mixed land-use context at the Brazilian Atlantic Forest biodiversity hotspot

Whilst fungi are a large fraction of primary biological aerosol particles (PBAPs) and their impact on global climate has been widely recognised, few studies have empirically assessed fungal vertical profiles and diversity relating those with rainfall. Here, we show the results of fungal PBAPs before and after a rainfall event during a fieldwork campaign using a hot-air balloon over a mixed land-use context at the Brazilian Atlantic Forest biodiversity hotspot. Four flights of c. 1 hour each were performed in the early morning from 8th until 11th of March 2022, and data were collected at three sampling heights (0, 150 and 300 m). Rainfall estimation using IMERG data indicated the precipitation event was of 15–20 mm and ERA5/ECMWF data highlighted that most of the airborne samples were taken above the boundary layer height. After the rainfall, the concentration of fungal spores at the ground level remained unchanged, whereas it was reduced to between 2- and 2.5-fold for the 150 and the 300 m heights, respectively. This was also accompanied by a reduction in the number of Pink-CFU, indicating a major drop in fungal PBAPs at higher altitudes associated with the rain. In addition, total spore concentration indicated Cladosporium sp. as dominant at all sampling heights, accounting for more than 80% of all spores, whereas Aspergillus/Penicillium-like represented less than 20%. Our results show the effects of rainfall and altitude on the concentration of fungal PBAPs, indicating how wet removal impacts fungi vertical profiles which has knock-on-effects on cloud and precipitation formation.

Soil organic matter fractions under different land uses and soil classes in the Brazilian semi-arid region

Context Land use change (LUC) is considered one of the main factors associated with soil carbon (C) loss worldwide. Aim Evaluate changes in labile and non-labile soil organic matter (SOM) fractions in different land use systems – native vegetation (NV), agriculture with conventional cultivation (CC) and pasture (PA) – in five soil classes in the Brazilian semi-arid region. Methods Soil samples were collected to a depth of 100 cm, and soil C and nitrogen (N) content and stocks were determined and also stocks of labile (LC) and non-labile (NlC) C fractions. In addition, the Carbon Management Index (CMI) was used to evaluate soil health changes. Key results SOC stocks significantly decreased after conversion from NV to CC (by 23%; 0–30 cm) and PA (by 22%; 0–100 cm). Losses due to LUC were greater in the LC than the NlC fraction, and this was reflected in the CMI reducing by 37% for PA and 57% for CC in the 0–100 cm layer. Regarding the different soil classes, LUC reduced SOC stocks only in the Luvisol, Planosol and Leptosol classes, while in the LC fraction, changes were observed in Acrisols, Cambisols and Planosols. Conclusions Clearing NV areas for CC systems and PA reduced the SOC stocks and SOM fractions and, consequently, decreased soil quality. Implications These findings underscore the importance of considering the quality of SOM when evaluating LUC impacts on SOC stocks in the different classes of soil in the Brazilian semi-arid region.

Contexto ambiental dos processos de mudança de uso e cobertura da terra em Calimaya, Altiplano Mexicano

The convergence of conventional agriculture, real estate investments and sand and gravel mining characterize Calimaya as one of the most negatively impacted municipalities of the Mexican altiplano by anthropic activities. The objective of this work was to analyse the geographical and environmental context of land use and land cover change (LULCC) processes in this Municipality. For this, the following indicators were estimated: the cover change rate proposed by Food and Agriculture Organization of the United Nations by using the land cover classes proposed by the Intergovernmental Panel on Climate Change. LULCC in the last decade (2010-2019) were: deforestation and advancement of potato crop in the Nevado de Toluca Flora and Fauna Protection Area; decrease in the process of occupation of cropland areas by settlements; and, soil degradation in abandoned mines.

Landscape-level heterogeneity of agri-environment measures improves habitat suitability for farmland birds.

Agri-environment schemes (AESs), ecological focus areas (EFAs), and organic farming are the main tools of the common agricultural policy (CAP) to counteract the dramatic decline of farmland biodiversity in Europe. However, their effectiveness is repeatedly doubted because it seems to vary when measured at the field-versus-landscape level and to depend on the regional environmental and land-use context. Understanding the heterogeneity of their effectiveness is thus crucial to developing management recommendations that maximize their efficacy. Using ensemble species distribution models and spatially explicit field-level information on crops grown, farming practice (organic/conventional), and applied AES/EFA from the Integrated Administration and Control System, we investigated the contributions of five groups of measures (buffer areas, cover crops, extensive grassland management, fallow land, and organic farming) to habitat suitability for 15 farmland bird species in the Mulde River Basin, Germany. We used a multiscale approach to identify the scale of effect of the selected measures. Using simulated land-use scenarios, we further examined how breeding habitat suitability would change if the measures were completely removed and if their adoption by farmers increased to meet conservation-informed targets. Buffer areas, fallow land, and extensive grassland were beneficial measures for most species, but cover crops and organic farming had contrasting effects across species. While different measures acted at different spatial scales, our results highlight the importance of land-use management at the landscape level-at which most measures had the strongest effect. We found that the current level of adoption of the measures delivers only modest gains in breeding habitat suitability. However, habitat suitability improved for the majority of species when the implementation of the measures was increased, suggesting that they could be effective conservation tools if higher adoption levels were reached. The heterogeneity of responses across species and spatial scales indicated that a mix of different measures, applied widely across the agricultural landscape, would likely maximize the benefits for biodiversity. This can only be achieved if the measures in the future CAP will be cooperatively designed in a regionally targeted way to improve their attractiveness for farmers and widen their uptake.

Contrasting responses of native and introduced mammal communities to fire mosaics in a modified landscape.

Planned fire is increasingly recognized as an important tool in conservation, but other factors such as land-use change may hinder the ability of land managers to use fire for the benefit of biodiversity. The mosaic of past fires in native vegetation may interact with the mosaic of other land-cover types in human-modified landscapes, yet the effects of these interactions on mammal communities are unknown. We investigated the responses of ground-dwelling mammal community composition and species richness to interactions between land cover and post-fire vegetation growth-stage mosaics in southern Australia. This fire-prone, human-modified landscape features a fine-scale fire mosaic in native vegetation patches surrounded by pasture, horticulture, and peri-urban environments. We measured the composition of land-cover types and fire mosaics (landscape structure) at multiple scales of up to 1257 ha surrounding 129 study sites, and considered native and introduced species together and separately. Land-cover composition was the primary driver of community composition: native species favored areas with a greater proportion of native heathy woodland, whereas introduced species were associated with landscapes comprising more cleared land. The fire mosaic also influenced community composition and species richness: greater growth-stage diversity was associated with native habitat-specialist communities and fewer introduced species. In areas with more cleared land, native species richness increased when there was a greater proportion of mid-successional vegetation, demonstrating that the effect of fire mosaics on mammal diversity depended on land-cover composition. The positive relationship between introduced species richness and cleared land extent was also stronger in recently burned sites than in other growth stages, suggesting that introduced species are well suited to more modified areas of the landscape. Land managers need to consider the underlying land-cover composition and the potential interactions it may have with fire mosaics and species composition. In this landscape a greater diversity of growth stages may disadvantage introduced species yet an increase in mid-successional vegetation in more modified areas would be likely to benefit native mammal communities. Our study highlights that fire management may need to be tailored depending on the context of land use and the species of interest.

Landscape-scale drivers of pollinator communities may depend on land-use configuration.

Research into pollinators in managed landscapes has recently combined approaches of pollination ecology and landscape ecology, because key stressors are likely to interact across wide areas. While laboratory and field experiments are valuable for furthering understanding, studies are required to investigate the interacting drivers of pollinator health and diversity across a broader range of landscapes and a wider array of taxa. Here, we use a network of 96 study landscapes in six topographically diverse regions of Britain, to test the combined importance of honeybee density, insecticide loadings, floral resource availability and habitat diversity to pollinator communities. We also explore the interactions between these drivers and the cover and proximity of semi-natural habitat. We found that among our four drivers, only honeybee density was positively related to wild pollinator abundance and diversity, and the positive association between abundance and floral resources depended on insecticide loadings and habitat diversity. By contrast, our exploratory models including habitat composition metrics revealed a complex suite of interactive effects. These results demonstrate that improving pollinator community composition and health is unlikely to be achieved with general resource enhancements only. Rather, local land-use context should be considered in fine-tuning pollinator management and conservation. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Inevitability of automobility: How private car use is perpetuated in a greenfield housing estate

Ongoing advances in technologies of connectivity have strengthened our capacity to envision urban environments less dominated by private car use. Yet many cities remain attached to, and defined by, the automobile. In challenging this status quo, we must understand the complex and varied ways private car use is reinforced in different urban environments. This paper provides such an understanding in the context of a low-density, and currently car-dependent, city. It presents a detailed analysis of the system of automobility to demonstrate the way private-car use is unintentionally perpetuated through contemporary practices of planning, developing and inhabiting cities. A newly constructed suburb in Sydney, Australia, provides the case for analysis. The suburb—Oran Park—is a master-planned estate intentionally designed to encourage alternative transport modes that is rendered ostensibly car-dependent as a result of a confluence of historical and contemporary structural and practical influences. The paper combines a detailed examination of the planning, transport and land-use context of the suburb with survey data from 300 of its residents. The paper’s novel contribution is to analyze these data sources using a social practice approach. The analysis lays bare the inevitability of automobility’s reproduction in the estate—describing the litany of elements that are both infrastructural and cultural and that, in orchestration, reproduce private car use. These elements are deconstructed to inform future challenges to the hegemony of the private car.

Longitudinal modelling of housing prices with machine learning and temporal regression

Purpose The purpose of this paper is to model housing price temporal variations and to predict price trends within the context of land use–transportation interactions using machine learning methods based on longitudinal observation of housing transaction prices. Design/methodology/approach This paper examines three machine learning algorithms (linear regression machine learning (ML), random forest and decision trees) applied to housing price trends from 2001 to 2016 in the Greater Toronto and Hamilton Area, with particular interests in the role of accessibility in modelling housing price. It compares the performance of the ML algorithms with traditional temporal lagged regression models. Findings The empirical results show that the ML algorithms achieve good accuracy (R2 of 0.873 after cross-validation), and the temporal regression produces competitive results (R2 of 0.876). Temporal lag effects are found to play a key role in housing price modelling, along with physical conditions and socio-economic factors. Differences in accessibility effects on housing prices differ by mode and activity type. Originality/value Housing prices have been extensively modelled through hedonic-based spatio-temporal regression and ML approaches. However, the mutually dependent relationship between transportation and land use makes price determination a complex process, and the comparison of different longitudinal analysis methods is rarely considered. The finding presents the longitudinal dynamics of housing market variation to housing planners.

Special Issue: Challenges and opportunities in Chinese meadow grasslands: perspectives in a land-use change context

Special Issue: Challenges and opportunities in Chinese meadow grasslands: perspectives in a land-use change context

Managing yards for mammals: Mammal species richness peaks in the suburbs

Increased urbanization drives habitat loss, yet residential land-use represents significant habitat potential for mammals and could provide connectivity between patches of green spaces. Diverse mammal communities exist across urban gradients, but it is unclear how mammal community composition varies within residential lands. We conducted a camera trapping study in 36 residential yards across an urban gradient to assess the relative contributions of the degree of urbanization in the land-use context versus parcel habitat features, such as vegetation structure, on mammal community diversity and composition. We hypothesized that land-use context would more strongly influence mammal community metrics than parcel features, and that there would be species-specific differences in response. We detected 14 non-domesticated mammal species and found that species richness peaked in the suburbs and tapered off at the rural and urban ends of the gradient in accordance with patterns seen in other taxonomic groups, yet rarely quantified in mammals. Large-bodied interior forest species were associated with rural sites, urban-dwelling species were associated with urban sites, and suburban sites had an overlap of species types. Although composition of mammal species in residential yards appears to be strongly related to land-use context, which is often outside of residents’ control, management of parcel habitat features such as retention of large mature trees may facilitate connectivity between patches of habitat across urbanizing landscapes. Informed residential yard management remains an important tool for urban wildlife management in an era of global change.

Оподаткування лісогосподарських підприємств України у контексті збалансованого землекористування

Обґрунтовано залежність збалансованого використання сільськогосподарських земель від оптимального оподаткування лісогосподарських підприємств, що потребує державного регулювання. На підставі результатів дослідження запропоновано основні напрями реформування податкової політики у лісовій галузі України. Зазначено, щооптимальне оподаткування є ефективним економічним інструментом функціонування фінансово-економічного механізму забезпечення збалансованого використання лісових земель. Зауважено, що є необхідність перерозподілу напрямків та обсягів фінансових потоків у галузі використання лісових земель, що вимагає відповідних змін до податкового законодавства. Доведено, що економічні методи необхідно розглядати якорганічне доповнення до регуляторних, таким чином найбільший позитивний ефект приносить всебічне залучення всієї системи фінансово-економічного механізму. Підсумовано, що застосування світового досвіду та трансформація системи оподаткування лісових земель в Україні як одного з найважливіших економічних інструментів фінансово-економічного механізму забезпечення збалансованого землекористування повністю розкриє потенціал цього інструменту.

Depopulation impacts on ecosystem services in Mediterranean rural areas

Despite the exponential increase in human population at global scale, some rural areas have experienced a progressive abandonment over the last decades. Under particular socioecological and policy contexts, changes in demography may promote land-use changes and, consequently, alter ecosystem services (ES) supply. However, most studies on this topic have targeted urban population increase, whereas depopulation has been rarely addressed. Here, we examined how shifts in demographic variables (human population, population density, and number of villages) affect provisioning (water supply, food and biomass production) and regulating (soil retention, water and nutrient regulation) ES in Mediterranean rural areas with contrasting environmental, socioeconomic and land-use contexts. When depopulation results in underuse of socio-ecological systems, we expected a decrease of provisioning and an increase of regulating ES, whereas we expected the opposite pattern when it results in land-use intensification. To test this hypothesis, we compared demographic data and ES estimated with Soil and Water Assessment Tool (SWAT) linked to land-use changes between the 1950s and 2000s in three rural areas of Aragón (NE Spain). Generalized Additive Mixed Models and Linear Mixed-Effect Models were used to analyze demographic trends, ES changes and the relationship between them.We found severe depopulation (−42% inhabitants) and associated land-use changes in the three areas, which was particularly evident in isolated mountainous zones (−63% inhabitants). Depopulation trends significantly affected land use and, consequently, all of the ES evaluated. In mountainous depopulated areas, land abandonment and rewilding resulted in the increase in water regulation (>1000%) and soil retention (>400%). In contrast, agriculture was intensified in more fertile and easy-to-access lowland areas, boosting the food production service (>600%). Accordingly, the interactions among depopulation, crop production and regulating ES should be considered in the management schemes and policies targeting rural areas for a balanced and sustainable supply of ES in the long term.

Farmer’s agency and institutional bricolage in land use plan implementation in upland Laos

This paper looks at the (re)shaping of local institutional arrangements within the context of land use planning processes in Laos, bringing to light their dynamic and co-constitutive relationship. Taking Pa Khom village in Houaphan province as a case study, it examines how local tenure institutions are (re)produced, (re)assembled and adapted to mirror farmer’s livelihood strategies to meet households’ food security, while also conforming to the defined land use plan. Drawing on examples of changes in swidden agriculture and village grazing land arrangements introduced as part of land use planning, the paper highlights the important role played by local communities – acting autonomously, collectively and in relation to external agents – in reconfiguring the relationship between natural resources and institutional orders. It illustrates how farmers employ institutional bricolage to creatively assemble and reshape their land use arrangements to comply with the defined land use plan, thus ensuring it meets their locally embedded livelihood priorities, albeit with different distributional outcomes for various farm households. Linking farm households’ strategies with inter-household and village level institutional arrangements, the paper shows how institutional bricolage contributes to synergizing the different rationales behind land use planning processes.

Potential for Mycorrhizae-Assisted Phytoremediation of Phosphorus for Improved Water Quality.

During this 6th Great Extinction, freshwater quality is imperiled by upland terrestrial practices. Phosphorus, a macronutrient critical for life, can be a concerning contaminant when excessively present in waterways due to its stimulation of algal and cyanobacterial blooms, with consequences for ecosystem functioning, water use, and human and animal health. Landscape patterns from residential, industrial and agricultural practices release phosphorus at alarming rates and concentrations threaten watershed communities. In an effort to reconcile the anthropogenic effects of phosphorus pollution, several strategies are available to land managers. These include source reduction, contamination event prevention and interception. A total of 80% of terrestrial plants host mycorrhizae which facilitate increased phosphorus uptake and thus removal from soil and water. This symbiotic relationship between fungi and plants facilitates a several-fold increase in phosphorus uptake. It is surprising how little this relationship has been encouraged to mitigate phosphorus for water quality improvement. This paper explores how facilitating this symbiosis in different landscape and land-use contexts can help reduce the application of fertility amendments, prevent non-point source leaching and erosion, and intercept remineralized phosphorus before it enters surface water ecosystems. This literature survey offers promising insights into how mycorrhizae can aid ecological restoration to reconcile humans’ damage to Earth’s freshwater. We also identify areas where research is needed.

Surrounding landscape structures, rather than habitat age, drive genetic variation of typical calcareous grassland plant species

ContextLand use change reduced calcareous grasslands throughout Europe during the last decades. Subsequent fragmentation and habitat deterioration led, moreover, to a massive biodiversity decline. To counteract this alarming development, a clear understanding of genetic variation patterns, as fundamental level of biodiversity, becomes inevitable.ObjectivesThe aim of our study was to identify the drivers of genetic variation in common calcareous grassland plant species. More specifically, we tested whether genetic diversity or differentiation of Asperula cynanchica, Campanula rotundifolia, and Linum catharticum depend on habitat age, landscape structure, habitat quality, and/or population size.MethodsWe investigated 912 individuals, 304 per study species, from 19 calcareous grasslands across the Swabian Alb in Baden-Württemberg (Germany) using AFLP analyses.ResultsWe observed no significant influence of habitat age on genetic diversity and differentiation. Habitat quality also had no impact on genetic diversity and population size only showed weak effects. However, genetic diversity strongly depended on landscape structure represented by distance to the nearest settlement, total area of surrounding calcareous grasslands, and their connectivity.ConclusionsMigratory sheep herding is considered as main land use in calcareous grasslands on the Swabian Alb and thus, landscape structures in the study region may describe movement patterns of grazing livestock. In this study, genetic variation in calcareous grassland populations was strongly affected by surrounding landscape structures and subsequent grazing patterns. Therefore, we assume that moderate grazing intensities over the long term may increase levels of genetic diversity, whereas periods of overgrazing or abandonment could lower genetic diversity.

Land use change drives the spatio-temporal variation of ecosystem services and their interactions along an altitudinal gradient in Brazil

ContextLand use and land cover (LULC) changes may affect the provision of ecosystem services. However, little is known how LULC changes influence the spatio-temporal variation in ecosystem service and their interactions along altitudinal gradients.ObjectivesHere we assessed the spatio-temporal variation of eight ecosystem services in an altitudinal gradient between the year of 1986 and 2015, and quantified the effect of LULC transitions on the provision and interactions of ecosystems services.MethodsWe modelled and mapped eight ecosystem services in an altitudinal gradient characterized by low (< 600 m), middle (600–1200) and high altitudes (> 1200) in Zona da Mata, Minas Gerais state, Brazil. We quantified changes in ecosystem services by contrasting ecosystem service maps between 1986 and 2015, and explored how four common LULC transitions affected the variation and the interactions between the eight ecosystem services.ResultsThe spatio-temporal analysis indicated that six out of eight ecosystem services increased from 1986 to 2015, while soil erosion control and water flow regulation decreased. In areas above 1200 m, regulating services dominated, while in areas below 1200 m provisioning service were most evidenced. LULC transitions from forest to agricultural areas, and vice versa, resulted in trade-offs between provisioning and regulating ecosystem services.ConclusionsLULC changes drive the spatio-temporal variation of ecosystem services along an altitudinal gradient with contrasting biophysical conditions. Future management of ecosystem services in the landscapes should take into the account the biophysical conditions and the consequences of specific LULC transitions.