Land Cover Gradient Research Articles

Land-cover gradients determine alternate drivers of mammalian species richness in fragmented landscapes

ContextUnderstanding habitat fragmentation is a critical concern for nature conservation and the focus of intense debate in landscape ecology. Resolving the uncertainty around the effects of habitat fragmentation on biodiversity remains an ongoing challenge that requires the successful delineation of multiple patch-landscape interactions.ObjectivesWe carried out a regional analysis on species richness of woodland mammals to determine the relative influence of structural, compositional and functional characteristics related to woodland habitat across different land-cover gradients.MethodsWe calculated the Edge-weighted Habitat Index, an area-weighted measure of functional connectivity that incorporates a mechanistic estimate of edge-effects, for interior woodland habitat. We compared its influence on mammalian species richness to that of increasing edge and patch density, landscape diversity, and a habitat-only model, in different contexts of matrix hostility across Northern England in the UK.ResultsOur results demonstrate the relevance of alternative drivers of species richness resulting from patch-landscape interactions across gradients of matrix hostility. Evidence is provided for positive and negative effects of increasing structural (edge density), functional (connected interior habitat) and compositional (landscape diversity) attributes, varying according to matrix type and intensity. Results were sensitive to dominant land-cover types in the matrix and the scale of observation.ConclusionThis study provides new insights into fragmentation effects on biodiversity and clarifies assumptions around the relative influence of structural, compositional and functional habitat characteristics on landscape-level species richness. We highlight the presence of thresholds, related to matrix hostility, that determine alternative drivers of species richness in woodland mammals. These drivers, and related thresholds, were sensitive to the scale of observation and landscape context. Landscape decisions aimed at promoting biodiversity should consider sources of matrix hostility and homogeneity at scales relevant to ecological processes of interest.

Disentangling the Effects of Climate and Land Uses on Small Mammals in Agroecosystems of NE Spain

We analyzed the two main drivers (climate and land uses) shaping the composition of small mammal communities at 16 localities situated in the confluence of the Mediterranean and Eurosiberian regions (Barcelona, Spain). The study area represents a land use and land cover gradient showing urbanization and crop intensification in the lowlands and forest encroachment in mountain areas. We identified 2458 small mammal individuals of 12 different species from barn owl (Tyto alba) pellets. Three open-land species (Microtus duodecimcostatus, Crocidura russula, and Mus spretus) and one forest/generalist species (Apodemus sylvaticus) were dominant in the diet, accounting for 93% of prey. In order to disentangle the effects of both main drivers on the small mammal community, we used partial constrained ordination techniques, which allowed us to determine the pure effects (and shared effects) of the environmental factors. Land use predictors explained 33.4% of the variance (mostly crops), followed by 23.4% of the variance explained by the geo-climatic variables (mostly rainfall), and an additional 24.8% of the variance was shared by both groups of predictors, totaling 81.6% of environmental variance. The remaining 18.4% of variance was unexplained by environmental matrices. This pattern was consistent with expected associations of species and biotic influences at small spatial scales and highlighted that the number of species increased from the crops in the lowlands towards the highlands covered by deciduous and coniferous forests.

Mosquito Species Diversity and Abundance Patterns in Plots with Contrasting Land Use and Land Cover in Bloomington, Indiana.

Land use and land cover (LULC) gradients are associated with differences in mosquito species composition and the entomological risk of mosquito-borne disease. Here, we present results from a season-long study of mosquito species richness and abundance with samples collected at 9 locations from 2 plots with contrasting LULC, an urban farm and a forest preserve, in Bloomington, IN, a city in the midwestern USA. With a total sampling effort of 234 trap-nights, we collected 703 mosquitoes from 9 genera and 21 species. On the farm, we collected 15 species (285 mosquitoes). In the preserve, we collected 19 species (418 mosquitoes). Thirteen species were common in both study plots, 2 were exclusive to the farm, and 6 were exclusive to the forest preserve. In both plots, we collected Aedes albopictus and Ae. japonicus. In the farm, the most common mosquito species were Culex restuans/Cx. pipiens and Coquillettidia perturbans. In the preserve, Ae. japonicus and Ae. triseriatus were the 2 most common mosquito species. Time series analysis suggests that weather factors differentially affected mosquito species richness and mosquito abundance in the plots. Temperature, relative humidity (RH), and precipitation were positively associated with richness and abundance at the farm, while increases in the SD of RH decreased both richness and abundance at the preserve. Our results highlight the importance that LULC has for mosquito species diversity and abundance and confirm the presence of Ae. albopictus and Ae. japonicus in southwestern Indiana.

Dietary metabarcoding reveals the simplification of bird-pest interaction networks across a gradient of agricultural cover.

Agriculture is vital for supporting human populations, but its intensification often leads to landscape homogenization and a decline in non-provisioning ecosystem services. Ecological intensification and multifunctional landscapes are suggested as nature-based alternatives to intensive agriculture, using ecological processes like natural pest regulation to maximize food production. Birds are recognized for their role in increasing crop yields by consuming invertebrate pests in several agroecosystems. However, the understanding of how bird species, their traits and agricultural land cover influence the structure of bird-pest interactions remains limited. We sampled bird-pest interactions monthly for 1 year, at four sites within a multifunctional landscape, following a gradient of increasing agricultural land cover. We analysed 2583 droppings of 55 bird species with DNA metabarcoding and detected 225 pest species in 1139 samples of 42 bird species. As expected, bird-pest interactions were highly variable across bird species. Dietary pest richness was lower in the fully agricultural site, while predation frequency remained consistent across the agricultural land cover gradient. Network analysis revealed a reduction in the complexity of bird-pest interactions as agricultural coverage increased. Bird species abundance affected the bird's contribution to the network structure more than any of the bird traits analysed (weight, phenology, invertebrate frequency in diet and foraging strata), with more common birds being more important to network structure. Overall, our results show that increasing agricultural land cover increases the homogenization of bird-pest interactions. This shows the importance of maintaining natural patches within agricultural landscapes for biodiversity conservation and enhanced biocontrol.

Land cover, stream discharge, and wastewater effluent impacts on baseflow sediment and nutrient concentrations in SW Ohio streams

AbstractElevated nutrient and suspended sediment concentrations often result in negative environmental impacts within freshwater environments. Studies that directly compare suspended sediment and bioavailable nutrients between predominantly agricultural and predominantly urban watersheds during baseflow conditions are largely lacking. The purpose of this study was to determine the impacts of land cover, stream discharge, and wastewater treatment plant (WWTP) discharge on nutrient and sediment concentrations, across a large land cover gradient in Southwest Ohio streams. Weekly baseflow samples were collected from eight streams over 1 year from November, 2016 through November, 2017. Total suspended sediment, nitrate, and phosphate concentrations were measured. Results indicate that agricultural land cover and WWTPs increase nitrate and phosphate concentrations in the study area. Total suspended sediment and nitrate concentrations increased with discharge, and discharge was a relatively weak predictor of phosphate concentrations. Seasonal water quality trends varied by parameter and land use also had unique impacts on seasonal water quality trends. Results suggest that to improve water quality in the study area, efforts should focus on improving WWTP effluent treatment and agricultural land management.

Passive Acoustic Sampling Enhances Traditional Herpetofauna Sampling Techniques in Urban Environments

Data are needed to assess the relationships between urbanization and biodiversity to establish conservation priorities. However, many of these relationships are difficult to fully assess using traditional research methods. To address this gap and evaluate new acoustic sensors and associated data, we conducted a multimethod analysis of biodiversity in a rapidly urbanizing county: Greenville, South Carolina, USA. We conducted audio recordings at 25 points along a development gradient. At the same locations, we used refugia tubes, visual assessments, and an online database. Analysis focused on species identification of both audio and visual data at each point along the trail to determine relationships between both herpetofauna and acoustic indices (as proxies for biodiversity) and environmental gradient of land use and land cover. Our analysis suggests the use of a multitude of different sampling methods to be conducive to the completion of a more comprehensive occupancy measure. Moving forward, this research protocol can potentially be useful in the establishment of more effective wildlife occupancy indices using acoustic sensors to move toward future conservation policies and efforts concerning urbanization, forest fragmentation, and biodiversity in natural, particularly forested, ecosystems.

Constraints on avian seed dispersal reduce potential for resilience in degraded tropical forests

Abstract Seed dispersal is fundamental to tropical forest resilience. Forest loss or degradation typically leads to defaunation, altering seed transfer dynamics and impairing the ability of forested habitats to regenerate or recover from perturbation. However, the extent of defaunation, and its likely impacts on the seed dispersers needed to restore highly degraded or clear‐felled areas, remains poorly understood in tropical forest landscapes. To quantify defaunation of seed‐dispersing birds, we used field survey data from 499 transects in three forested regions of Brazil, first comparing the observed assemblages with those predicted by geographic range maps, and then assessing habitat associations of frugivores across land cover gradients. We found that current bird assemblages have lower functional diversity (FD) than predicted by species range maps in Amazonia (4%–6%), with a greater reduction in FD (28%) for the Atlantic Forest, which has been more heavily deforested for a longer period. Direct measures of seed dispersal are difficult to obtain, so we focused on potential seed transfer inferred from shared species occurrence. Of 83 predominantly frugivorous bird species recorded in relatively intact forests, we show that 10% were absent from degraded forest, and 57% absent from the surrounding matrix of agricultural land covers, including many large‐gaped species. Of 112 frugivorous species using degraded forest, 47% were absent from matrix habitats. Overall, frugivores occurring in both intact forest and matrix habitats were outnumbered by (mostly small‐gaped) frugivores occurring in both degraded forest and matrix habitats (23 additional species; 64% higher diversity). These findings suggest that birds have the potential to disperse seeds from intact and degraded forest to adjacent cleared lands, but that direct seed transfer from intact forests is limited, particularly for large‐seeded trees. Degraded forests may play a vital role in supporting natural regeneration of small‐seeded tree species as well as providing a ‘stepping‐stone’ in the regeneration pathway for large‐seeded trees. We propose that both intact and degraded forests will support the restoration potential of tropical forest landscapes, and that bird‐assisted seed dispersal can be enhanced by maintaining buffer zones of degraded or secondary forests around remaining intact forest patches. Read the free Plain Language Summary for this article on the Journal blog.

High sensitivity of Aeolus UV surface returns to surface reflectivity

Global ultraviolet (UV) surface reflectivity climatologies are all composed from daylight passive remote sensing observations of reflected UV light, generally integrated over a distribution of attainable reflection directions. We discovered the sensitivity of Aeolus lidar surface returns (LSR) to surface characteristics, providing the first evidence that active remote sensing can be effectively used for retrieving unidirectional UV surface reflectivity on global scales. LSR reproduces surface reflectivity monthly changes in Sahara, which are visible in the Lambertian Equivalent Reflectivity (LER) climatologies from TROPOMI and GOME-2. Very high correlations (r > 0.90) between gridded LSR and the LER climatologies are reported at global and regional scales for 36 different regions. Three clear land cover gradients are discerned from Aeolus LSR signal: (1) water/land, (2) vegetation/arid areas and (3) no snow/snow. The strongest LSR signal was retrieved over snow, while over vegetation, we found moderate negative agreement (r < − 0.60) between LSR and vegetation index proxy. Overall, the success of the first active remote sensing method for retrieving unidirectional UV surface reflectivity using Aeolus is demonstrated. Our approach can be effectively used to detect unresolved land and, especially, snow cover changes in high latitudes because, unlike passive instruments, Aeolus also provided nighttime observations.

Empirical evidence of climate change and urbanization impacts on warming stream temperatures

Climate change and urbanization threaten streams and the biodiversity that rely upon them worldwide. Emissions of greenhouse gases are causing air and sea surface temperatures to increase, and even small areas of urbanization are degrading stream biodiversity, water quality and hydrology. However, empirical evidence of how increasing air temperatures and urbanization together affect stream temperatures over time and their relative influence on stream temperatures is limited. This study quantifies changes in stream temperatures in a region in South-East Australia with an urban-agricultural-forest landcover gradient and where increasing air temperatures have been observed. Using Random Forest models we identify air temperature and urbanization drive increasing stream temperatures and that their combined effects are larger than their individual effects occurring alone. Furthermore, we identify potential mitigation measures useful for waterway managers and policy makers. The results show that both local and global solutions are needed to reduce future increases to stream temperature.

Effects of urban, peri-urban and rural land covers on plant functional traits around Bogotá, Colombia

AbstractThe Global South has suffered an accelerated population and urban growth. This has created multiple impacts at the regional level such as erosion, soil degradation and biodiversity loss, as well as temperature increase in the cities causing urban heat islands. Bogotá, the capital of Colombia, is one of the largest cities in the Global South and in the last five decades has undergone a rapid urban transition, impacting surrounding ecosystems. However, little is known about how urbanization affects the local flora. To understand how plants are responding and adapting to urbanization processes in the city of Bogotá, we used a land cover gradient of urban, peri-urban and rural areas, and four plant functional traits (leaf area [LA], specific leaf area [SLA], leaf dry matter content [LDMC] and wood density [WD]). We analyzed 16 species shared in at least two land covers. Although urban and peri-urban areas had higher temperatures and higher LDMC and lower SLA values than rural areas, there were no significant differences in functional traits between land covers. Some species showed significant changes between land covers, indicating that there is a species-specific response to urbanization. Considering the need for urban areas to prioritize species that promote cooling and exhibit resistance to stress, as well as the capacity to adapt to climate change, it is essential to include plants possessing different combinations of functional traits.

Nontarget Chemical Composition of Surface Waters May Reflect Ecosystem Processes More than Discrete Source Contributions.

We investigated environmental, landscape, and microbial factors that could structure the spatiotemporal variability in the nontarget chemical composition of four riverine systems in the Oregon Coast Range, USA. We hypothesized that the nontarget chemical composition in river water would be structured by broad-scale landscape gradients in each watershed. Instead, only a weak relationship existed between the nontarget chemical composition and land cover gradients. Overall, the effects of microbial communities and environmental variables on chemical composition were nearly twice as large as those of the landscape, and much of the influence of environmental variables on the chemical composition was mediated through the microbial community (i.e., environment affects microbes, which affect chemicals). Therefore, we found little evidence to support our hypothesis that chemical spatiotemporal variability was related to broad-scale landscape gradients. Instead, we found qualitative and quantitative evidence to suggest that chemical spatiotemporal variability of these rivers is controlled by changes in microbial and seasonal hydrologic processes. While the contributions of discrete chemical sources are undeniable, water chemistry is undoubtedly impacted by broad-scale continuous sources. Our results suggest that diagnostic chemical signatures can be developed to monitor ecosystem processes, which are otherwise challenging or impossible to study with existing off-the-shelf sensors.

Macroinvertebrate and diatom indicators of baseline conditions for setting targets in agricultural BMP restoration

AbstractRecovery trajectories from restoration projects are poorly understood, making it difficult to set restoration targets as part of project planning. As part of the Delaware River Watershed Initiative (DRWI), we collected baseline environmental and biological data at 84 sites in watersheds where agricultural Best Management Practices (BMPs) are being implemented and forested land is being preserved. The objective of this study was to understand which diatom and macroinvertebrate community measures best characterize biological integrity along a gradient of land cover, habitat measures, and water chemistry in order to later set targets for recovery. To this end, we ran separate Redundancy Analysis (RDA) ordinations in which environmental variables constrained (1) community metrics and (2) relative abundance (taxonomic composition) for macroinvertebrates and diatoms. To understand where along the environmental gradient the sites were represented differently by the respective biotic community measures (community metrics and taxonomic composition), the two constrained ordinations were then compared using Procrustes distance. For macroinvertebrate communities, we saw the most agreement in site characterization between the ordinations at intermediate % agricultural land, but disagreement at both high and low % agricultural land. For diatom communities, we saw the most agreement between the site characterizations at high to intermediate % agricultural land, with increasing disagreement associated with increasing % forested land cover. Use of baseline data to set targets for ecosystem recovery requires consideration of which data are most relevant for the site conditions and what amount of change is feasible based on project implementation and effectiveness. A key aspect of choosing endpoints is when the loss of information inherent to metrics makes them less useful for accurately evaluating ecological integrity, especially when looking to capture incremental changes. Based on our findings, we suggest the use of some community metrics and some key taxa to set targets of recovery in biotic communities in agricultural streams, and that these targets be adjusted to best fit the ecological conditions at a given site within a larger data set. Accordingly, monitoring must take place in the context of regional conditions and must be designed to inform target‐setting.

Response of aquatic insects to an environmental gradient in Amazonian streams

The increasing land use in the Amazon region has resulted in the widespread substitution of forest areas with pasture and bauxite mining. These land uses reduce the forest cover of streams and modify their characteristics, reducing the diversity of aquatic insect assemblages. In the present study, we aimed to identify the threshold of the assemblages of the larvae of insects of the orders Ephemeroptera, Plecoptera, and Trichoptera (collectively known as EPT), and adults of the order Odonata, along an environmental gradient of land use and land cover (LULC). We sampled 30 streams along an environmental gradient determined by the proportion of forest, pasture, and bauxite mining observed within the catchment of each stream. We identified 12 taxa associated with forest (nine positively and three negatively) and four negativelyassociated with pasture. However, no taxa were associated explicitly with the bauxite mining gradient. As forest is converted to pasture, the abundance and frequency of occurrence of the taxa sensitive to pasture are reduced, reflecting their environmental sensitivity and their potential as sentinels of preserved streams. The identification of the thresholds of the EPT and odonates taxa allowed us to determine which of these organisms are positively or negatively associated with the environmental gradient of LULC in Amazonian streams. We hope that the results of the present study can be applied in future biomonitoring programs, particularly for monitoring the response of aquatic insects to the degradation of streams.

Spatial heterogeneity of ecosystem services and their trade-offs in the Hengduan Mountain region, Southwest China

Spatial heterogeneity, which is one of the basic characteristics of ecological and geographical elements, is substantial in mountainous areas. Research on ecosystem services (ESs) increasingly considers spatial heterogeneity in environmental management-related decision-making. This study quantified the dominant ESs and ES trade-offs for the Hengduan Mountain region in Southwest China. The spatial heterogeneity was analyzed by introducing gradients of elevation, vegetation cover, and land cover. The results showed that, in addition to inverse changes in ESs, ES change rates were important for ES trade-offs. Further, land cover was identified as the main factor influencing the spatial heterogeneity of the majority of ES trade-offs. Specifically, the net primary productivity (NPP), carbon storage (C), and habitat quality (HQ) all showed inverted U-shaped trends along the elevation gradient and HQ increased thereafter, water yield (WY) presented an overall decline but increased in high-altitude areas, and soil conservation (SC) exhibited a fluctuating trend. The change rate of SC was slower than that of NPP, C, and HQ, which led to changes in the trade-offs between SC and other ESs along the elevation gradient. The higher WY in built-up land and higher HQ in forests were the main reasons for higher trade-offs. The low trade-off for unused land was attributed to the limited levels of several ESs. Along the vegetation gradient, WY first decreased then increased, whereas all other services showed increasing trends. The limited promotion effect of vegetation on SC was the primary reason for increased trade-offs. Therefore, more attention should be devoted to improving SC via engineering measures. Furthermore, vegetation degradation on unused land should be prevented to maintain SC and reduce the trade-offs among ESs.

Modeling estrogenic activity in streams throughout the Potomac and Chesapeake Bay watersheds.

Endocrine-disrupting compounds (EDCs), specifically estrogenic endocrine-disrupting compounds, vary in concentration and composition in surface waters under the influence of different landscape sources and landcover gradients. Estrogenic activity in surface waters may lead to adverse effects in aquatic species at both individual and population levels, often observed through the presence of intersex and vitellogenin induction in male fish. In the Chesapeake Bay Watershed, located on the mid-Atlantic coast of the USA, intersex has been observed in several sub-watersheds where previous studies have identified specific landscape sources of EDCs in tandem with observed fish health effects. Previous work in the Potomac River Watershed (PRW), the largest basin within the Chesapeake Bay Watershed, was leveraged to build random forest regression models to predict estrogenic activity at unsampled reaches in both the Potomac River and larger Chesapeake Bay Watersheds (CBW). Model outputs including important variables, partial dependence plots, and predicted values of estrogenic activity at unsampled reaches provide insight into drivers of estrogenic activity at different seasons and scales. Using the US Environmental Protection Agency effects-based threshold of 1.0ng/L 17 β-estradiol equivalents, catchments predicted to exceed this value were categorized as at risk for adverse effects from exposure to estrogenic compounds and evaluated relative to healthy watersheds and recreation access locations throughout the PRW. Results show immediate catchment scale models are more reliable than upstream models, and the best predictive variables differ by season and scale. A small percentage of healthy watersheds (< 13%) and public access sites were classified as at risk using the "Total" (annual) model in the CBW. This study is the first Potomac River Watershed assessment of estrogenic activity, providing a new foundation for future risk assessment and management design efforts, with additional context provided for the entire Chesapeake Bay Watershed.

The identification of wildlife-vehicle collision hotspots: Citizen science reveals spatial and temporal patterns

Linear infrastructures (e.g., roads, railways, pipelines, and powerlines) pose a serious threat to wildlife, due to the risk of wildlife-vehicle collisions (roadkills). The placement of mitigation measures, such as crossing structures, should consider species’ life cycles and ecological requirements. Such an assessment would require data collection over large areas, which may be possible by employing citizen science. In this study, we aimed to identify spatio-temporal trends of roadkill occurrence using citizen science data from one of the most urbanized and biodiversity-rich regions of Italy. Temporal trends were analyzed using generalized additive models, while landscape patterns were assessed by identifying significant thresholds over land cover gradients, related to increases in relative roadkill abundance, by employing threshold indicator taxa analysis. Our approach recorded a total of 529 roadkills, including 33 different species, comprising 13 mammal, 10 bird, 6 reptile, and 2 amphibian species. Statistical analysis indicated significant temporal trends for the red fox, the European hedgehog, the stone marten and the European badger, with peaks in roadkill occurrence between the winter and spring months. Relative roadkill abundance increased mostly in landscapes with anthropogenic land cover classes, such as complex cultivations, orchards, or urban surfaces. Our results allowed us to develop a map of potential roadkill risk that could assist in planning the placement of mitigation measures. Citizen science contributions from highly populated areas allowed data collection over a large area and a dense road network, and also directly led to the evaluation of management decisional options.

Long-term time-scale bonds between discharge regime and catchment specific landscape traits in the Spanish Pyrenees

An analysis of long-term databases with information on precipitation and discharge records was undertaken to characterize the temporal structure response of four experimental catchments, located in the Central Spanish Pyrenees, with a gradient of land-cover (from a relatively pristine forested catchment, through an abandoned cultivated catchment with progressive plant recolonization, to an afforested catchment and ending with a degraded badlands catchment). Precipitation and discharge records are non-stationary and the wavelet transform methodology was thus applied to perform a temporal scale-by-scale analysis of each catchment response to the hydroclimatic characteristics of the area. This temporal decomposition analysis illustrates how land-use and land-cover legacy control the temporal distribution of flow events occurring at different and non-similar time-scales, thus reflecting the timing, variability and physical mechanisms of water storage/transport in each catchment. Intra-annual and annual time-scales are led by climatological characteristics of the catchment sites (seasonal patterns of mountainous Pyrenees catchments). Multi-year scale is mainly shaped by land-cover and land-use legacy. Badlands catchment, with its large proportion of bare land, shows a discharge response closely synchronized with precipitation patterns for all time-scales. On the contrary, for the forested catchment the global hydrological response is mainly governed by the multi-year time-scale. Afforested catchment and abandoned cultivated catchment, which move towards a pristine forest response, are impacted by the former grazing and agriculture activities and intra-annual temporal variability still play a major role on the global discharge response of the catchment. This suggests that vegetated catchments located in the same region can show hydrological responses at different time-scales to the same climatic input. We argue that differences in land-cover and historical land-use changes are not only valuable to understand the current discharge temporal behaviour, but they will also play a significant role in characterizing the future catchment dynamics due to changing climate conditions.

Microbial Ecology of Methanotrophy in Streams Along a Gradient of CH4 Availability.

Despite the recognition of streams and rivers as sources of methane (CH4) to the atmosphere, the role of CH4 oxidation (MOX) in these ecosystems remains poorly understood to date. Here, we measured the kinetics of MOX in stream sediments of 14 sites to resolve the ecophysiology of CH4 oxidizing bacteria (MOB) communities. The streams cover a gradient of land cover and associated physicochemical parameter and differed in stream- and porewater CH4 concentrations. Michealis–Menten kinetic parameter of MOX, maximum reaction velocity (Vmax), and CH4 concentration at half Vmax (KS) increased with CH4 supply. KS values in the micromolar range matched the CH4 concentrations measured in shallow stream sediments and indicate that MOX is mostly driven by low-affinity MOB. 16S rRNA gene sequencing identified MOB classified as Methylococcaceae and particularly Crenothrix. Their relative abundance correlated with pmoA gene counts and MOX rates, underscoring their pivotal role as CH4 oxidizers in stream sediments. Building on the concept of enterotypes, we identify two distinct groups of co-occurring MOB. While there was no taxonomic difference among the members of each cluster, one cluster contained abundant and common MOB, whereas the other cluster contained rare operational taxonomic units (OTUs) specific to a subset of streams. These integrated analyses of changes in MOB community structure, gene abundance, and the corresponding ecosystem process contribute to a better understanding of the distal controls on MOX in streams.

Fire and land cover change in the Palouse Prairie\u2013forest ecotone, Washington and Idaho, USA

BackgroundPrairie–forest ecotones are ecologically important for biodiversity and ecological processes. While these ecotones cover small areas, their sharp gradients in land cover promote rich ecological interaction and high conservation value. Our objective was to understand how historical and current fire occurrences and human development influenced the Palouse Prairie–forest ecotone. We used General Land Office survey field notes about the occurrence of bearing trees to locate historical (1870s to 1880s) prairie, pine savanna, and forest at the eastern edge of the bioregion. We combined LANDFIRE Existing Vegetation classes to contrast historical land cover with current land cover. We reconstructed historical fire occurrence (1650 to 1900) from fire-scarred trees. We used fire and lightning records from 1992 to 2015 to interpret the role of people and lightning.ResultsHistorically, the ecotone was a matrix of prairie with extensive savanna and some forest. More than half of the ecotone area was prairie, which is now dominated by agriculture, with some residential development. The 16% of the landscape that was pine savanna is now forest or shrubs, agriculture, perennial vegetation under the Conservation Reserve Program, or developed; no savanna now exists. Forests covered 12% of the ecotone and these are still mostly forest. Fires were historically frequent, occurring on average every 5 to 8 years at most sites. Lightning was not frequent but could likely have been sufficient to ignite fires that could spread readily given the rolling terrain and long fire season.ConclusionsFire was far more frequent historically than currently. Conservation, restoration, and other ongoing land-use changes will likely result in more continuous vegetation and hence fuel for fires. Lightning and people may ignite fires that therefore spread readily in the future. Understanding the past and potential future of fire in the Palouse Prairie bioregion may help us live with fire while conserving ecological values here and in similar prairie–forest ecotones.

Spatial modelling of groundwater quality across a land use and land cover gradient in Limpopo Province, South Africa

The spatial variability of groundwater quality in rural Mokopane District is investigated. This was achieved by evaluating the variability in groundwater physio-chemical parameters in relation to Land Use and Land Cover (LULC)using Kriging geo-statistical technique and key groundwater physio-chemical parameters namely; ammonia, lead, Total Dissolved Solids (TDS), nitrates and chloride. Firstly, we derived the LULC from 30-m Landsat 8-OLI satellite data, with an overall accuracy of 76.67%. Water quality parameters were modelled in geographic information systems using the kriging interpolation technique. We then compared measured water quality and the drinking standards recommended by the South African Water Quality Standards (SAWS) and the World Health Organization (WHO) guideline standards for drinking water. Results indicated that there were significant differences (p < 0.05) in the levels of physio-chemical contents between borehole water and standard values according to the SAWS and WHO. For example, TDS in Mosesetjane exceeded both SAWS and WHO drinking water levels. Nitrate concentrations were also high on the first and second quarter with concentration levels of 5.56–29 mg/l and 30.9 mg/l in Mosesetjane, respectively. However, lead and ammonia were found to be evenly distributed in all the four quarters, but exhibited some slight deviations from the standard levels (±4.7 mg/l) in selected quarters. Results also indicated significant differences in TDS, chloride and nitrate concentrations across different LULC types. Subsistence farming and built-up areas were the main LULC types that were found to have high concentrations of TDS, ammonia and nitrates, exceeding the recommended standards. However, lead and ammonia, did not differ significantly (p > 0.05) and these parameters were fairly distributed, with less spatial variability . The second quarter, extending between October and December, and the fourth quarter, extending from April to June, exhibited high concentrations of nitrates, chloride and TDS during the wet season. On the other hand, the first and third quarter of the dry period were associated with low concentrations. This study indicated that LULC types and seasonal variability have influence on specific groundwater quality parameters.