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1.
Land management to protect streams requires knowing which parts of the landscape most strongly influence stream condition. Understanding how flow through landscapes and along streams affects such land-use impacts requires knowing the period of antecedent discharge that most strongly influences condition. Both considerations require determination of optimal weighting schemes for predictors of stream condition. We calculated forest cover weighted by flow-path distance to 572 urban, peri-urban, and rural sites—in the Melbourne, Australia, region—sampled for macroinvertebrates, and antecedent discharge weighted by time preceding each of 1,723 samples. Using mixed linear models that accounted for spatial dependence, we aimed to determine the weighting curve shape and length that best predicted macroinvertebrate assemblage composition. The best model was a function of mean annual discharge, weighted forest cover, weighted imperviousness, weighted antecedent discharge, and their interactions. Optimal weightings were exponential—half-decay distance 35 m overland (plausible range 26–50 m), and 1.0 km in-stream (0.75–1.3 km) for forest cover—, and linear over ≥4 year for antecedent discharge. Model plausibility was more affected by weighting distance than the shape of the weighting function. Regardless of weighting curve shape, riparian forest effects on macroinvertebrate assemblages are strongest within 10 1–10 2 m from the stream, and 10 3 m upstream. Although exponential weightings are only marginally more plausible, they are the most realistic representation of physical processes. While our conclusions should not be interpreted as recommendations for buffer widths, they provide valuable insight into the scales of influence in the region and could be used to inform management decisions. 相似文献
2.
We explored land use, fish assemblage structure, and stream habitat associations in 20 catchments in Opequon Creek watershed, West Virginia. The purpose was to determine the relative importance of urban and agriculture land use on stream biotic integrity, and to evaluate the spatial scale (i.e., whole-catchment vs riparian buffer) at which land use effects were most pronounced. We found that index of biological integrity (IBI) scores were strongly associated with extent of urban land use in individual catchments. Sites that received ratings of poor or very poor based on IBI scores had > 7% of urban land use in their respective catchments. Habitat correlations suggested that urban land use disrupted flow regime, reduced water quality, and altered stream channels. In contrast, we found no meaningful relationship between agricultural land use and IBI at either whole-catchment or riparian scales despite strong correlations between percent agriculture and several important stream habitat measures, including nitrate concentrations, proportion of fine sediments in riffles, and the abundance of fish cover. We also found that variation in gradient (channel slope) influenced responses of fish assemblages to land use. Urban land use was more disruptive to biological integrity in catchments with steeper channel slopes. Based on comparisons of our results in the topographically diverse Opequon Creek watershed with results from watersheds in flatter terrains, we hypothesize that the potential for riparian forests to mitigate effects of deleterious land uses in upland portions of the watershed is inversely related to gradient.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
3.
The biological integrity of stream ecosystems depends critically on human activities that affect land use/cover along stream
margins and possibly throughout the catchment. We evaluated stream condition using an Index of Biotic Integrity (IBI) and
a habitat index (HI), and compared these measures to landscape and riparian conditions assessed at different spatial scales
in a largely agricultural Midwestern watershed. Our goal was to determine whether land use/cover was an effective predictor
of stream integrity, and if so, at what spatial scale. Twenty-three sites in first-through third-order headwater streams were
surveyed by electrofishing and site IBIs were calculated based on ten metrics of the fish collection. Habitat features were
characterized through field observation, and site HIs calculated from nine instream and bank metrics. Field surveys, aerial
photograph interpretation, and geographic information system (GIS) analyses provided assessments of forested land and other
vegetation covers at the local, reach, and regional (catchment) scales.
The range of conditions among the 23 sites varied from poor to very good based on IBI and HI scores, and habitat and fish
assemblage measures were highly correlated. Stream biotic integrity and habitat quality were negatively correlated with the
extent of agriculture and positively correlated with extent of wetlands and forest. Correlations were strongest at the catchment
scale (IBI with % area as agriculture, r 2=0.50, HI with agriculture, r 2=0.76), and tended to become weak and non-significant at local scales. Local riparian vegetation was a weak secondary predictor
of stream integrity. In this watershed, regional land use is the primary determinant of stream conditions, able to overwhelm
the ability of local site vegetation to support high-quality habitat and biotic communities. 相似文献
4.
Large wood (LW) is critical to the structure and function of streams and forests are the main LW source to stream channels. To assess the influence of forest cover changes at different spatial scales on in-stream LW quantity, we selected eighteen catchments (2nd–4th order) in Southeastern Brazil with forests at different levels of alterations. In each catchment we quantified the pattern of forest cover (% cover and relative catchment position), the physical characteristics of catchments (elevation and slope), the characteristics of channels (wetted channel width and depth), the abundance and volume of in-stream LW, and the frequency of LW pools. We used simple and multiple linear regression to assess the response of LW variables to landscape and stream reach variables. Most of the LW was relatively small; 72 % had a diameter <20 cm, and 66 % had a length <5 m. Although percent forest cover at reach scale had substantial support to explain LW variables, the best predictors of LW variables were forest cover at broader scales (LW abundance and LW pool frequency were best predicted by forest at intermediate distance at the catchment scale and LW volume was best predicted by forest cover at the drainage network scale), suggesting that downstream transport is an important process in addition to local processes in our study area. These findings have important management implications because although low forested reaches receive less LW from local forests (or no LW in the case of deforested stream reaches), they are receiving LW from upstream forested reaches. However, the material is generally small, unstable and likely to be easily flushed. This suggests that not only should riparian forest conservation encompass the full drainage network, but forests should also be allowed to regenerate to later successional stages to provide larger, higher quality LW for natural structuring of streams. 相似文献
5.
Riparian ecosystems are interfaces between aquatic and terrestrial environments recognized for their nutrient interception
potential in agricultural landscapes. Stream network maps from a broad range of map resolutions have been employed in watershed
studies of riparian areas. However, map resolution may affect important attributes of riparian buffers, such as the connectivity
between source lands and small stream channels missing in coarse resolution maps. We sought to understand the influence of
changing stream map resolution on measures of the river network, near-stream land cover, and riparian metrics. Our objectives
were: (1) to evaluate the influence of stream map resolution on measures of the stream network, the character and extent of
near-stream zones, and riparian metrics; (2) to compare patterns of variation among different physiographic provinces; and
(3) to explore how predictions of nutrient retention potential might be affected by the resolution of a stream map. We found
that using fine resolution stream maps significantly increased our estimates of stream order, drainage density, and the proportion
of watershed area occurring near a stream. Increasing stream map resolution reduced the mean distance to source areas as well
as mean buffer width and increased the frequency of buffer gaps. Measures of percent land cover within 100 m of streams were
less sensitive to stream map resolution. Overall, increasing stream map resolution led to reduced estimates of nutrient retention
potential in riparian buffers. In some watersheds, switching from a coarse resolution to a fine resolution stream map completely
changed our perception of a stream network from well buffered to largely unbuffered. Because previous, broad-scale analyses
of riparian buffers used coarse-resolution stream maps, those studies may have overestimated landscape-level buffer prevalence
and effectiveness. We present a case study of three watersheds to demonstrate that interactions among stream map resolution
and land cover patterns make a dramatic difference in the perceived ability of riparian buffers to ameliorate effects of agricultural
activities across whole watersheds. Moreover, stream map resolution affects inferences about whether retention occurs in streams
or riparian zones. 相似文献
6.
A total of 694 streams were sampled for benthic macroinvertebrates in the autumn of 1995 as part of the Swedish national stream survey. After removal of sites considered as impacted, data from 428 streams as well as a large number of environmental variables were used to determine the relative importance of local, landscape, and large scale factors in explaining the variability in species composition of benthic stream macroinvertebrates. The environmental variables were divided into seven explanatory variable groups: local physical, local chemical, catchment land use/cover, catchment bedrock geology, Quaternary geology in catchment, regional factors (such as ecoregion) and spatial position. Partial Canonical Correspondence Analysis was used to partition the total explained variance in the species data into these variable groups. The pure (or unique) effects of the seven variable groups accounted for 69.1%, and combinations of variable groups (interaction terms) the remaining 30.9% of the total explained variability. Local scale variables such as in-stream substratum, vegetation in and near the stream (riparian zone), and some chemical variables were most strongly associated with the among-site variability. Local physical (24.4%) and local chemical (20.4%) variables explained the largest part of the among-site variability of community assemblages. These results are of importance when planning conservation and management measurements, implementing large-scale biomonitoring programs, and predicting how human alterations will affect running water ecosystems.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
7.
Determining what factors explain the distribution of non-native invasive plants that can spread in forest-dominated landscapes
could advance understanding of the invasion process and identify forest areas most susceptible to invasion. We conducted roadside
surveys to determine the presence and abundance of 15 non-native plant species known to invade forests in western North Carolina,
USA. Generalized linear models were used to examine how contemporary and historic land use, landscape context, and topography
influenced presence and abundance of the species at local and regional scales. The most commonly encountered species were
Microstegium vimineum, Rosa multiflora, Lonicera japonica, Celastrus orbiculatus, Ligustrum sinense, and Dioscorea oppositifolia. At the regional scale, distance to city center was the most important explanatory variable, with species more likely present
and more abundant in watersheds closer to Asheville, NC. Many focal species were also more common in watersheds at lower elevation
and with less forest cover. At the local scale, elevation was important for explaining the species’ presence, but forest cover
and land-use history were more important for explaining their abundance. In general, species were more common in plots with
less forest cover and more area reforested since the 1940s. Our results underscore the importance of considering both the
contemporary landscape and historic land use to understand plant invasion in forest-dominated landscapes. 相似文献
8.
Recent declines in anadromous Pacific salmonids ( Oncorhynchus spp.) have been attributed, in part, to degradation of freshwater habitat. Because riparian areas directly affect instream
habitat, assessing riparian characteristics is essential for predicting salmon habitat quality and for prioritizing restoration
projects. We quantified land use modification of anadromous fish-bearing streams in the interior Columbia River basin at multiple
resolutions. We identified riparian areas in several land use and land cover classes using remotely sensed data. We then interpreted
aerial photographs at random locations within each class to quantify riparian modifications at a local (stream reach) scale.
Riparian areas in agricultural and urban areas were significantly narrower (~30 m, median) than those in forested or shrub/grass
areas (~70 m). The largest proportion of modified riparian areas occurred in low-gradient streams with floodplains in semi-arid
ecoregions. Riparian vegetation in these areas is unlikely to provide adequate in-stream functions, making these areas a natural
starting point for restoration prioritization. We investigated how existing riparian restoration projects were spatially related
to riparian land use and found that restoration effort varied among subwatersheds. Effective strategies for restoring high
quality salmon habitat will be watershed-specific and must restore natural watershed processes. By using a hierarchical analysis
to identify regional strategies, restoration or conservation activity can be focused in specific basins and thereby increase
the likelihood that efforts will significantly improve habitat conditions for listed salmonids. 相似文献
9.
There is a pressing need to understand the consequences of human activities, such as land transformations, on watershed ecosystem
services. This is a challenging task because different indicators of water quality and yield are expected to vary in their
responsiveness to large versus local-scale heterogeneity in land use and land cover (LUC). Here we rely on water quality data
collected between 1977 and 2000 from dozens of gauge stations in Puerto Rico together with precipitation data and land cover
maps to (1) quantify impacts of spatial heterogeneity in LUC on several water quality indicators; (2) determine the spatial
scale at which this heterogeneity influences water quality; and (3) examine how antecedent precipitation modulates these impacts.
Our models explained 30–58% of observed variance in water quality metrics. Temporal variation in antecedent precipitation
and changes in LUC between measurements periods rather than spatial variation in LUC accounted for the majority of variation
in water quality. Urbanization and pasture development generally degraded water quality while agriculture and secondary forest
re-growth had mixed impacts. The spatial scale over which LUC influenced water quality differed across indicators. Turbidity
and dissolved oxygen (DO) responded to LUC in large-scale watersheds, in-stream nitrogen concentrations to LUC in riparian
buffers of large watersheds, and fecal matter content and in-stream phosphorus concentration to LUC at the sub-watershed scale.
Stream discharge modulated impacts of LUC on water quality for most of the metrics. Our findings highlight the importance
of considering multiple spatial scales for understanding the impacts of human activities on watershed ecosystem services. 相似文献
10.
ContextSpecies distributions are a function of an individual’s ability to disperse to and colonize habitat patches. These processes depend upon landscape configuration and composition.ObjectivesUsing Blanchard’s cricket frogs (Acris blanchardi), we assessed which land cover types were predictive of (1) presence at three spatial scales (pond-shed, 500 and 2500 m) and (2) genetic structure. We predicted that forested, urban, and road land covers would negatively affect cricket frogs. We also predicted that agricultural, field, and aquatic land covers would positively affect cricket frogs.MethodsWe surveyed for cricket frogs at 28 sites in southwestern Ohio, USA to determine presence across different habitats and analyze genetic structure among populations. For our first objective, we examined if land use (crop, field, forest, and urban habitat) and landscape features (ponds, streams, and roads) explained presence; for our second objective, we assessed whether these land cover types explained genetic distance between populations.ResultsLand cover did not have a strong influence on cricket frog presence. However, multiple competing models suggested effects of roads, streams, and land use. We found genetic structuring: populations were grouped into five major clusters and nine finer-scale clusters. Highways were predictive of increased genetic distance.ConclusionsBy combining a focal-patch study with landscape genetics, our study suggests that major roads and waterways are key features affecting species distributions in agricultural landscapes. We demonstrate that cricket frogs may respond to landscape features at larger spatial scales, and that presence and movement may be affected by different environmental factors. 相似文献
11.
Widespread degradation of wetlands has motivated the development of tools to evaluate wetland condition. The application of field-based tools over large regions can be prohibitively expensive; however, land cover data may provide a surrogate for intensive assessments, enabling rapid and cost-effective evaluation of wetlands throughout whole regions. Our goal was to determine if land cover data could be used to estimate the biotic integrity of wetlands in Alberta??s Beaverhills watershed. Biotic integrity was measured using both plant- and bird-based indices of biotic integrity (IBIs) in 45 wetlands. Land cover data were extracted from seven nested landscape extents (100?C3,000?m radii) and used to model IBI scores. Strong, significant predictions of IBI scores were achieved using land cover data from every spatial extent, even after factoring out the influence of location to address the spatial autocorrelation of land cover classes. Plant-based IBI scores were best predicted using data from 100?m buffers and bird-based IBI scores were best predicted using data extracted from 500?m buffers. Road cover or density and measures of the proportion of disturbed land were consistent predictors of IBI score, suggesting their universal importance to plant and bird communities. Simplified models using the proportion of undisturbed land were less accurate than more detailed models (reductions in r 2 of 0.31?C0.32). Regardless of the level of detail in land cover classification, our results emphasize the need to optimize landscape extent for the taxonomic group of interest: an issue that is typically poorly articulated in studies reporting on the development of GIS-based assessment methods. Our results also highlight the need to calibrate models in test areas before scaling up, to ensure predictive accuracy. 相似文献
12.
ContextLand use change and forest degradation have myriad effects on tropical ecosystems. Yet their consequences for low-order streams remain very poorly understood, including in the world´s largest freshwater basin, the Amazon.ObjectivesDetermine the degree to which physical and chemical characteristics of the instream habitat of low-order Amazonian streams change in response to past local- and catchment-level anthropogenic disturbances.MethodsTo do so, we collected field instream habitat (i.e., physical habitat and water quality) and landscape data from 99 stream sites in two eastern Brazilian Amazon regions. We used random forest regression trees to assess the relative importance of different predictor variables in determining changes in instream habitat response variables.ResultsMultiple drivers, operating at multiple spatial scales, were important in determining changes in the physical habitat and water quality of the sites. Although we found few similarities in modelled relationships between the two regions, we observed non-linear responses of specific instream characteristics to landscape change; for example 20 % of catchment deforestation resulted in consistently warmer streams.ConclusionsOur results highlight the importance of local riparian and catchment-scale forest cover in shaping instream physical environments, but also underscore the importance of other land use changes and activities, such as road crossings and upstream agriculture intensification. In contrast to the property-scale focus of the Brazilian Forest code, which governs environmental regulations on private land, our results reinforce the importance of catchment-wide management strategies to protect stream ecosystem integrity. 相似文献
13.
Freshwater research and management efforts could be greatly enhanced by a better understanding of the relationship between landscape-scale factors and water quality indicators. This is particularly true in urban areas, where land transformation impacts stream systems at a variety of scales. Despite advances in landscape quantification methods, several studies attempting to elucidate the relationship between land use/land cover (LULC) and water quality have resulted in mixed conclusions. However, these studies have largely relied on compositional landscape metrics. For urban and urbanizing watersheds in particular, the use of metrics that capture spatial pattern may further aid in distinguishing the effects of various urban growth patterns, as well as exploring the interplay between environmental and socioeconomic variables. However, to be truly useful for freshwater applications, pattern metrics must be optimized based on characteristic watershed properties and common water quality point sampling methods. Using a freely available LULC data set for the Santa Clara Basin, California, USA, we quantified landscape composition and configuration for subwatershed areas upstream of individual sampling sites, reducing the number of metrics based on: (1) sensitivity to changes in extent and (2) redundancy, as determined by a multivariate factor analysis. The first two factors, interpreted as (1) patch density and distribution and (2) patch shape and landscape subdivision, explained approximately 85% of the variation in the data set, and are highly reflective of the heterogeneous urban development pattern found in the study area. Although offering slightly less explanatory power, compositional metrics can provide important contextual information. 相似文献
14.
ContextAmphibians are declining worldwide and land use change to agriculture is recognized as a leading cause. Argentina is undergoing an agriculturalization process with rapid changes in landscape structure.ObjectivesWe evaluated anuran response to landscape composition and configuration in two landscapes of east-central Argentina with different degrees of agriculturalization. We identified sensitive species and evaluated landscape influence on communities and individual species at two spatial scales.MethodsWe compared anuran richness, frequency of occurrence, and activity between landscapes using call surveys data from 120 sampling points from 2007 to 2009. We evaluated anuran responses to landscape structure variables estimated within 250 and 500-m radius buffers using canonical correspondence analysis and multimodel inference from a set of candidate models.ResultsAnuran richness was lower in the landscape with greater level of agriculturalization with reduced amount of forest cover and stream length. This pattern was driven by the lower occurrence and calling activity of seven out of the sixteen recorded species. Four species responded positively to the amount of forest cover and stream habitat. Three species responded positively to forest cohesion and negatively to rural housing. Two responded negatively to crop area and diversity of cover classes.ConclusionsAnurans within agricultural landscapes of east-central Argentina are responding to landscape structure. Responses varied depending on species and study scale. Life-history traits contribute to responses differences. Our study offers a better understanding of landscape effects on anurans and can be used for land management in other areas experiencing a similar agriculturalization process. 相似文献
15.
ContextOne approach to maintain the resilience of biotic communities is to protect the variability of abiotic characteristics of Earth’s surface, i.e. geodiversity. In terrestrial environments, the relationship between geodiversity and biodiversity is well recognized. In streams, the abiotic properties of upstream catchments influence stream communities, but the relationships between catchment geodiversity and aquatic biodiversity have not been previously tested. ObjectivesThe aim was to compare the effects of local environmental and catchment variables on stream biodiversity. We specifically explored the usefulness of catchment geodiversity in explaining the species richness on stream macroinvertebrate, diatom and bacterial communities. MethodsWe used 3 geodiversity variables, 2 land use variables and 4 local habitat variables to examine species richness variation across 88 stream sites in western Finland. We used boosted regression trees to explore the effects of geodiversity and other variables on biodiversity. ResultsWe detected a clear effect of catchment geodiversity on species richness, although the traditional local habitat and land use variables were the strongest predictors. Especially soil-type richness appeared as an important factor for species richness. While variables related to stream size were the most important for macroinvertebrate richness and partly for bacterial richness, the importance of water chemistry and land use for diatom richness was notable. ConclusionsIn addition to traditional environmental variables, geodiversity may affect species richness variation in streams, for example through changes in water chemistry. Geodiversity information could be used as a proxy for predicting stream species richness and offers a supplementary tool for conservation efforts. 相似文献
16.
Widespread and increasing urbanization has resulted in the need to assess, monitor, and understand its effects on stream water
quality. Identifying relations between stream ecological condition and urban intensity indicators such as impervious surface
provides important, but insufficient information to effectively address planning and management needs in such areas. In this
study we investigate those specific landscape metrics which are functionally linked to indicators of stream ecological condition,
and in particular, identify those characteristics that exacerbate or mitigate changes in ecological condition over and above
impervious surface. The approach used addresses challenges associated with redundancy of landscape metrics, and links landscape
pattern and composition to an indicator of stream ecological condition across a broad area of the eastern United States. Macroinvertebrate
samples were collected during 2000–2001 from forty-two sites in the Delaware River Basin, and landscape data of high spatial
and thematic resolution were obtained from photointerpretation of 1999 imagery. An ordination-derived ‘biotic score’ was positively
correlated with assemblage tolerance, and with urban-related chemical characteristics such as chloride concentration and an
index of potential pesticide toxicity. Impervious surface explained 56% of the variation in biotic score, but the variation
explained increased to as high as 83% with the incorporation of a second land use, cover, or configuration metric at catchment
or riparian scales. These include land use class-specific cover metrics such as percent of urban land with tree cover, forest
fragmentation metrics such as aggregation index, riparian metrics such as percent tree cover, and metrics related to urban
aggregation. Study results indicate that these metrics will be important to monitor in urbanizing areas in addition to impervious
surface. 相似文献
17.
The distributions of freshwater mussels are controlled by landscape factors operating at multiple spatial scales. Changes
in land use/land cover (LULC) have been implicated in severe population declines and range contractions of freshwater mussels
across North America. Despite widespread recognition of multiscale influences few studies have addressed these issues when
developing distribution models. Furthermore, most studies have disregarded the role of landscape pattern in regulating aquatic
species distributions, focusing only on landscape composition. In this study, the distribution of Rabbitsfoot ( Quadrula cylindrica) in the upper Green River system (Ohio River drainage) is modeled with environmental variables from multiple scales: subcatchment,
riparian buffer, and reach buffer. Four types of landscape environment metrics are used, including: LULC pattern, LULC composition,
soil composition, and geology composition. The study shows that LULC pattern metrics are very useful in modeling the distribution
of Rabbitsfoot. Together with LULC compositional metrics, pattern metrics permit a more detailed analysis of functional linkages
between aquatic species distributions and landscape structure. Moreover, the inclusion of multiple spatial scales is necessary
to accurately model the hierarchical processes in stream systems. Geomorphic features play important roles in regulating species
distributions at intermediate and large scales while LULC variables appear more influential at proximal scales. 相似文献
18.
The potentials for the use of large wood (LW) in stream restoration projects were quantified for streams in Central Europe
(total stream length assessed 44,880 km). Two different restoration methods were investigated: recruitment (passively allowing
natural LW input) and placement (active introduction of large wood pieces into streams). The feasibility and potential effects
of each method were studied for three different scenarios, according to the land-uses to be permitted on the floodplain: (a)
only natural-non woody vegetation, forest, and fallow land occur on the floodplain, (b) including pasture and meadow, (c)
including pasture, meadow, and cropland. Hydromorphological data were used to identify stream sections where LW recruitment
or placement are feasible, and the likely effects of both restoration methods on channel hydromorphology were predicted. Passive
recruitment is feasible for only a small percentage of the total channel length in the study area (~1% for all three scenarios).
Active placement of LW can be used in much higher extent: 6.5% if only natural non-woody vegetation, forest, and fallow land
can occur on the floodplain, 20.2% if stream segments bordered by pasture and meadow are included, and 32% if cropland is
included in addition. There are differences between (1) the lower-mountainous area, where a large number of channel segments
can be restored yielding an improvement from a moderate/good to a good/excellent morphological status and (2) the lowlands,
where only a small number of channel segments can be restored yielding an improvement from a bad to a moderate morphological
state. The latter upgrading might be sufficient to reach a ‘good ecological status’ as defined by the EU Water Framework Directive.
The results of this study show the suitability of large wood recruitment and placement as appropriate methods to markedly
improve the hydromorphological state of a large proportion of the streams in the study area. 相似文献
19.
Prior studies exploring the quantitative relationship between landscape structure metrics and the ecological condition of receiving waters have used a variety of sampling units (e.g., a watershed, or a buffer around a sampling station) at a variety of spatial scales to generate landscape metrics resulting in little consensus on which scales best describe land-water relationships. Additionally, the majority of these studies have focused on freshwater systems and it is not clear whether results are transferable to estuarine and marine systems. We examined how sampling unit scale controls the relationship between landscape structure and sediment metal concentrations in small estuarine systems in the Mid-Atlantic region of the United States. We varied the spatial extent of the contributing watersheds used to calculate landscape structure and assessed linear relationships between estuarine sediment metal concentrations and the total area of developed and agricultural lands at each scale. Area of developed lands was consistently related to sediment metals while total agricultural land was not. Developed land had strongest associations with lead and copper; weakest with arsenic and chromium; and moderate associations with cadmium, mercury, and zinc. Local (i.e., less than 15−20 km from a sampling station) land uses have a greater impact than more distant land uses on the amount of toxic metals reaching estuarine sediments. 相似文献
20.
The distribution and abundance of a species may be simultaneously influenced by both local-scale habitat features and the
broader patch and landscape contexts in which these populations occur. Different factors may influence patch occupancy (presence–absence)
versus local abundance (number of individuals within patches), and at different scales, and thus ideally both occupancy and
abundance should be investigated, especially in studies that seek to understand the consequences of land management on species
persistence. Our study evaluated the relative influences of variables associated with the local habitat patch, hillside (patch
context), and landscape context on patch occupancy and abundance of the collared lizard ( Crotaphytus collaris) within tallgrass prairie managed under different fire and grazing regimes in the northern Flint Hills of Kansas, USA. Using
a multi-model information-theoretic approach that accounted for detection bias, we found that collared lizard abundance and
occupancy was influenced by factors measured at both the local habitat and landscape scales. At a local scale, collared lizard
abundance was greatest on large rock ledges that had lots of crevices, high vegetation complexity, and were located higher
up on the hillslope. At the landscape scale, collared lizard abundance and occupancy were both higher in watersheds that were
burned frequently (1–2 year intervals). Interestingly, grazing only had a significant effect on occupancy and abundance within
less frequently burned (4-year burn interval) watersheds. Our results suggest that, in addition to the obvious habitat needs
of this species (availability of suitable rock habitat), land-management practices have the potential to influence collared
lizard presence and abundance in the grasslands of the Flint Hills. Thus, mapping the availability of suitable habitat is
unlikely to be sufficient for evaluating species distributions and persistence in such cases without consideration of landscape
management and disturbance history. 相似文献
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