Runoff sources and land cover change in the Amazon: an end-member mixing analysis from small watersheds

The flowpaths by which water moves from watersheds to streams has important consequences for the runoff dynamics and biogeochemistry of surface waters in the Amazon Basin. The clearing of Amazon forest to cattle pasture has the potential to change runoff sources to streams by shifting runoff to more surficial flow pathways. We applied end-member mixing analysis (EMMA) to 10 small watersheds throughout the Amazon in which solute composition of streamwater and groundwater, overland flow, soil solution, throughfall and rainwater were measured, largely as part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia. We found a range in the extent to which streamwater samples fell within the mixing space determined by potential flowpath end-members, suggesting that some water sources to streams were not sampled. The contribution of overland flow as a source of stream flow was greater in pasture watersheds than in forest watersheds of comparable size. Increases in overland flow contribution to pasture streams ranged in some cases from 0% in forest to 27?C28% in pasture and were broadly consistent with results from hydrometric sampling of Amazon forest and pasture watersheds that indicate 17- to 18-fold increase in the overland flow contribution to stream flow in pastures. In forest, overland flow was an important contribution to stream flow (45?C57%) in ephemeral streams where flows were dominated by stormflow. Overland flow contribution to stream flow decreased in importance with increasing watershed area, from 21 to 57% in forest and 60?C89% in pasture watersheds of less than 10?ha to 0% in forest and 27?C28% in pastures in watersheds greater than 100?ha. Soil solution contributions to stream flow were similar across watershed area and groundwater inputs generally increased in proportion to decreases in overland flow. Application of EMMA across multiple watersheds indicated patterns across gradients of stream size and land cover that were consistent with patterns determined by detailed hydrometric sampling.     

流域景观格局与河流水质的多变量相关分析

流域内的景观格局改变是人类活动的宏观表现,会对河流水质产生显著影响,因此明确影响水质变化的关键景观因子,对于深入了解景观对水质的影响机制具有重要的研究价值。选择广东省淡水河流域为研究对象,以2007年ALOS卫星影像以及水质监测数据为基础,运用空间分析和多变量分析方法,分析淡水河流域景观格局与河流水质的相关关系。用包括流域和河岸带尺度的景观组成和空间结构信息的景观指数表征景观格局,用Spearman秩相关分析、多元线性逐步回归模型和典型相关分析(CCA)研究景观指数和水质指标的相关关系。研究结果表明:林地、城镇用地和农业用地占淡水河流域总面积超过90%,其中城镇用地超过20%。多元线性逐步回归分析和CCA结果说明水质指标受到多个景观指数的综合影响,反映了景观格局对水质的复杂影响机制。流域景观格局对河流水质有显著影响,流域尺度的景观指数比河岸带尺度的景观指数对水质影响更大。城镇用地比例是影响耗氧污染物和营养盐等污染物浓度最重要的景观指数,林地和农业用地对水质的影响较小。另外,景观破碎化对pH值、溶解氧和重金属等水质指标有显著影响。CCA的第一排序轴解释了景观指数与水质指标相关性的54.0%,前两排序轴累积能解释景观指数与水质指标相关性的87.6%,前两轴分别主要表达了城市化水平和景观破碎化水平的变化梯度。淡水河流域的景观格局特征从上游到下游呈现出城市—城乡交错—农村的景观梯度,水质变化也对应了这个梯度的变化,说明人类活动引起的流域土地覆盖及土地管理措施变化会对水质变化产生显著影响。     

黄土高原景观格局与水土流失关系研究

采用DCCA排序法对黄土高原腹地泾河流域12个子流域的景观格局与流域水土流失关系进行了定量分析.结果表明,DCCA排序的前4轴分别与农业用地比率、景观多样性指数、森林比率显著相关.各子流域的水土流失特征具有明显的梯度变异.在森林比率占65%的三水河子流域,景观相对简单、多样性低,流域年径流量大、输沙小、含沙量低,径流相对稳定;随着森林比率减小,农业用地比率增大,景观多样性升高,产流系数增高,径流深度、输沙量和含沙量增大;在森林比率很低、农业用地53.41%的洪河子流域,景观格局复杂、多样性较高,河流含沙量高、输沙率大,月输沙和径流变异极大;在农业用地比率减小,其他景观类型比率增大,景观相对简单的环江上、下游子流域,输沙量和含沙量减小,但输沙和径流的年际变化极大.排序分析结果较清晰地解释了黄土高原典型地区水土流失特征沿景观梯度的变化规律.     

SPATIAL PATTERNS AND ECOLOGICAL DETERMINANTS OF BENTHIC ALGAL ASSEMBLAGES IN MID-ATLANTIC STREAMS, USA

We attempted to identify spatial patterns and determinants for benthic algal assemblages in Mid-Atlantic streams. Periphyton, water chemistry, stream physical habitat, riparian conditions, and land cover/use in watersheds were characterized at 89 randomly selected stream sites in the Mid-Atlantic region. Cluster analysis (TWINSPAN) partitioned all sites into six groups on the basis of diatom species composition. Stepwise discriminant function analysis indicated that these diatom groups can be best separated by watershed land cover/use (percentage forest cover), water temperature, and riparian conditions (riparian agricultural activities). However, the diatom-based stream classification did not correspond to Omernik's ecoregional classification. Algal biomass measured as chl a can be related to nutrients in habitats where other factors do not constrain accumulation. A regression tree model indicated that chl a concentrations in the Mid-Atlantic streams can be best predicted by conductivity, stream slope, total phosphorus, total nitrogen, and riparian canopy coverage. Our data suggest that broad spatial patterns of benthic diatom assemblages can be predicted both by coarse-scale factors, such as land cover/use in watersheds, and by site-specific factors, such as riparian conditions. However, algal biomass measured as chl a was less predictable using a simple regression approach. The regression tree model was effective for showing that ecological determinants of chl a were hierarchical in the Mid-Atlantic streams.     

Biotelemetry of crustacean decapods: sampling design,statistical analysis,and interpretation of data

Lotic systems in many regions of the country have experienced habitat degradation and biodiversity loss due to agricultural activity and urbanization. Southeastern Michigan is no exception, as agriculture in the River Raisin watershed and increased urbanization in the Huron River watershed threatens both systems. To further understand the ecological impact of land use on trophic interactions in Midwestern streams and assess the use of a selected set of weighted, quantitative food web metrics as a tool for investigating the influence of anthropogenic disturbance on these systems we compared summer food webs for nine second-order streams. All streams were categorized as developed, undeveloped, or agricultural based on land cover data. Developed and undeveloped streams were located in the Huron River watershed and agricultural streams were located in the River Raisin watershed. Reach-level habitat quality was also assessed at each study site using the EPA’s Rapid Habitat Assessment. Fish diets (n = 410) were analyzed to create summer food webs for each site. Comparisons of food webs were made using a suite of weighted, quantitative metrics to identify differences in fish–macroinvertebrate interactions across streams with differing land cover at the sub-basin scale and habitat quality at the local scale. Although undeveloped streams had higher species richness and less habitat degradation, no significant patterns were observed in the quantitative metrics across the three stream categories or based on reach-level habitat conditions. Decapoda, terrestrial Hymenoptera, and Chironomidae were the primary prey taxa in all stream categories. Decapods accounted for the majority of biomass consumed and the pattern of this consumption strongly influenced metric scores. The suite of quantitative metrics tested in this study did not detect significant differences in fish–macroinvertebrate food webs across land use categories, likely in part due to the dominance of a large, tolerant prey taxa in fish diets, regardless of land use and local habitat quality.     

A multi-scale approach to prioritize wetland restoration for watershed-level water quality improvement

Wetland restoration is commonly presented as an important strategy for maintaining and enhancing the water quality and ecological capital of watershed-scale ecosystems. Prioritizing restoration sites on the landscape is often a haphazard process based on widely held, though often untested, assumptions about relationships between watershed characteristics and water quality. We present a framework to target and prioritize wetland restoration locations using both regional and watershed-level screening models. The regression-tree and random forest models presented in this paper identify watershed variables with the strongest relationships to a given water quality parameter, present a clear hierarchy of variable importance, and present approximate thresholds in watershed area where these variables express the greatest impact on water quality. The proportion of watersheds classified as prior-converted agricultural land was an important predictor of both ortho and total phosphorus. Fortunately because prior-converted agricultural lands were historically wetlands, they are often very suitable for wetland restoration. These sites often have poorly-drained soils requiring artificial drainage to be suitable for agriculture. These drainage systems become conduits for transporting phosphorus from agricultural field and to area streams and rivers. Maintaining natural land-cover within stream buffers is identified as another important predictor of water quality. This seems to be especially true with regard to NO₃–NO₂ concentrations. Our model results support specific management recommendations including: (a) exclusion of agricultural land-uses from riparian buffers, (b) maintaining or increasing watershed-level wetland-cover and (c) reducing wetland fragmentation.     

A global assessment of primate responses to landscape structure

Land‐use change modifies the spatial structure of terrestrial landscapes, potentially shaping the distribution, abundance and diversity of remaining species assemblages. Non‐human primates can be particularly vulnerable to landscape disturbances, but our understanding of this topic is far from complete. Here we reviewed all available studies on primates' responses to landscape structure. We found 34 studies of 71 primate species (24 genera and 10 families) that used a landscape approach. Most studies (82%) were from Neotropical forests, with howler monkeys being the most frequently studied taxon (56% of studies). All studies but one used a site‐landscape or a patch‐landscape study design, and frequently (34% of studies) measured landscape variables within a given radius from the edge of focal patches. Altogether, the 34 studies reported 188 responses to 17 landscape‐scale metrics. However, the majority of the studies (62%) quantified landscape predictors within a single spatial scale, potentially missing significant primate–landscape responses. To assess such responses accurately, landscape metrics need to be measured at the optimal scale, i.e. the spatial extent at which the primate–landscape relationship is strongest (so‐called ‘scale of effect’). Only 21% of studies calculated the scale of effect through multiscale approaches. Interestingly, the vast majority of studies that do not assess the scale of effect mainly reported null effects of landscape structure on primates, while most of the studies based on optimal scales found significant responses. These significant responses were primarily to landscape composition variables rather than landscape configuration variables. In particular, primates generally show positive responses to increasing forest cover, landscape quality indices and matrix permeability. By contrast, primates show weak responses to landscape configuration. In addition, half of the studies showing significant responses to landscape configuration metrics did not control for the effect of forest cover. As configuration metrics are often correlated with forest cover, this means that documented configuration effects may simply be driven by landscape‐scale forest loss. Our findings suggest that forest loss (not fragmentation) is a major threat to primates, and thus, preventing deforestation (e.g. through creation of reserves) and increasing forest cover through restoration is critically needed to mitigate the impact of land‐use change on our closest relatives. Increasing matrix functionality can also be critical, for instance by promoting anthropogenic land covers that are similar to primates' habitat.     

Relationship between biodiversity and landscape structure in the Gyungan stream basin,central Korea

The relationship between landscape structure and biodiversity was investigated in the Gyungan stream basin, central Korea, in order to prepare a biodiversity conservation plan. The study area was divided into upstream, midstream, downstream and Gonjiam stream sub‐watersheds based on the land use pattern of each sub‐watershed. The quality of the terrestrial landscape was assessed by connectivity and percentages of deciduous broad‐leaved forest and urbanized area. The quality of the terrestrial landscape was the highest in the downstream sub‐watershed followed by Gonjiam stream, midstream and upstream sub‐watersheds. The quality of the riparian landscape assessed by percentages of the number and the area that the wetland vegetation elements occupy in the whole area showed a similar trend to that of terrestrial landscape. The diversity of all taxa including fish, reptiles and amphibians, birds, mammals and wetland vegetation except benthic macroinvertebrates was the highest downstream. The diversity of benthic macroinvertebrates was the highest in the Gonjiam stream sub‐watershed. Thus, biodiversity was shown to be the highest in the downstream sub‐watershed, followed, in order, by Gonjiam stream, midstream and upstream sub‐watersheds in proportion to landscape quality. On the other hand, the quality of the aquatic environment based on the ecological score of benthic macroinvertebrate (ESB) index was the highest downstream, followed, in order, by upstream, Gonjiam stream and midstream areas. This trend is different from that of biodiversity. In order to improve landscape quality degraded by excessive land use and to increase biodiversity, we recommended a restoration plan that addresses both ecosystem and landscape.     

Changes in the character of DOC in streams during storms in two Midwestern watersheds with contrasting land uses

Dissolved organic carbon (DOC) dynamics in streams is important, yet few studies focus on DOC dynamics in Midwestern streams during storms. In this study, stream DOC dynamics during storms in two Midwestern watersheds with contrasting land uses, the change in character of stream DOC during storms, and the usability of DOC as a hydrologic tracer in artificially drained landscapes of the Midwest are investigated. Major cation/DOC concentrations, and DOC specific UV absorbance (SUVA) and fluorescence index (FI) were monitored at 2–4 h intervals during three spring storms. Although DOC is less aromatic in the mixed land use watershed than in the agricultural watershed, land use has little impact on stream DOC concentration during storms. For both watersheds, DOC concentration follows discharge, and SUVA and FI values indicate an increase in stream DOC aromaticity and lignin content during storms. The comparison of DOC/major cation flushing dynamics indicates that DOC is mainly exported via overland flow/macropore flow. In both watersheds, the increase in DOC concentration in the streams during storms corresponds to a shift in the source of DOC from DOC originating from mineral soil layers of the soil profile at baseflow, to DOC originating from surficial soil layers richer in aromatic substances and lignin during storms. Results also suggest that DOC, SUVA and FI could be used as hydrologic tracers in artificially drained landscapes of the Midwest. These results underscore the importance of sampling streams for DOC during high flow periods in order to understand the fate of DOC in streams.     

SWAT模型对景观格局变化的敏感性分析——以丹江口库区老灌河流域为例

景观的空间配置与类型组成能够对流域的产流、产沙及非点源污染产生影响。在以往SWAT模型研究中,往往默认水文模型考虑了该影响。为分析SWAT模型对不同景观格局变化的敏感性,根据老灌河流域2000年土地利用在各子流域的组成,模拟研究区更为破碎、复杂的景观空间配置,通过设置多套试验参数,利用SWAT模型生成基于不同景观格局的模拟结果。结果表明,SWAT模型不能反映除坡度和面积变化之外的景观水平下各斑块之间因景观空间格局改变对流域产流、产沙以及非点源污染的影响;模型通过其他参数的调整,弥补了模型分析数据的不足,使实测数据与模型部分结果高度吻合。这表明,一个能够反映流域部分水文特征的SWAT模型,未必是对研究区真实情形的模拟,而是各个参数间平衡的结果。因此,在利用SWAT模型分析模拟景观变化时,不应默认模型能够模拟景观空间格局改变对流域水文过程的影响,同时研究者可以通过划分坡度带,提高模型对不同坡度土地利用的敏感性。     

Effect of Native Vegetation Loss on Stream Ecosystem Processes: Dissolved Organic Matter Composition and Export in Agricultural Landscapes

Stream and river ecosystems are dependent on energetic inputs from their watersheds and thus shifts in land use from forest cover to agriculture will affect stream community composition and function. The disruption of forest-aquatic linkages alters the organic matter resources in agricultural streams. Dissolved organic matter (DOM) is the dominant form of organic matter in aquatic ecosystems, and a microbial energy source that is important for stream respiration. The concentrations and characteristics of DOM are regulated by both terrestrial (for example, terrestrial organic matter supply) and in-stream processes (for example, microbial respiration and periphyton production) that are influenced by land management. The effects of watershed land use and topographic, soil and climatic variables on DOM quantity (dissolved organic carbon concentration and load), source (terrestrial or in-stream) and quality (composition and lability) were measured in 14 streams across an agricultural land-use gradient. DOC concentration was positively correlated with watershed pasture cover and negatively correlated with watershed relief. No watershed variables were important correlates of DOC load. Stream DOM was primarily of terrestrial origin, but DOM in agricultural streams had a greater proportion of sources from in-stream sources. This may be due to reduced connection with riparian vegetation and increased in-stream primary production. We suggest that maintaining watershed tree cover greater than 52% and ensuring less than 10% of the length of riparian corridor is cleared for pasture could minimize changes to DOM composition. This is important to avoid flow-on effects for stream ecosystem processes that are mediated by DOM. Long-term DOM monitoring will be valuable for assessing the functional impacts of land-use change.     

Multi-scale analysis of alpine landscapes with different intensities of abandonment reveals similar spatial pattern changes: Implications for habitat conservation

The abandonment of traditional anthropogenic activities is an important driver shaping landscape patterns. Therefore, multi-scale pattern analysis over time is needed to identify appropriate scales for biodiversity conservation and monitoring of abandoned landscapes. We compared spatial and temporal changes in a pair of alpine watersheds in Italy (Cajada and Tovanella), which are similar in size, geo-climatic conditions, and land-use histories; but have had divergent anthropogenic abandonment processes since the 1950s. We hypothesize that this divergence has led to corresponding dissimilarities in multi-scale patterns of landscape change. To examine this hypothesis, we analyzed land cover maps from three years (1954, 1980/83, 2006) and described the changes using transition matrices. For each year and watershed, landscape heterogeneity and a set of class-level metrics (i.e. percentage of the landscape, area-weighted mean patch size, patch density, area-weighted mean shape index, edge density, and aggregation index) were also measured at different scales using random sampling techniques, and the results were summarized by using scalograms. Woodland expansion occurred mainly at the expenses of grasslands, meadows, and shrublands. These changes were greater during the first time-period (1954-80/83) than in the more recent period (1980/83-2006), with a mean annual value that decreased from +5.18 to +1.33 ha/year and from +4.08 to +1.96 ha/year in the abandoned and managed watersheds, respectively. Landscape heterogeneity decreased over time with a similar pattern in both watersheds, which indicates a general process of homogenization. Management regime affected the spatial-scale response of class-level metrics; these metrics showed a variety of multi-scalar responses, which were not always consistent over time and under different management regimes. When considering the response of the indices across spatial-scales for both watersheds, certain historical curves showed a scale break, representing a significant change in the shape and slope of the curve (i.e. scale divergence). The presence of scale breaks in the scalograms can potentially reveal important thresholds for biodiversity. For example, grassland and meadow patch density at small spatial scales (<200 m radius), which was found to be important for protected butterfly species, had a greater reduction over time in the managed watershed when compared to the abandoned watershed. In conclusion, the findings of this study indicate that there is good potential for understanding changes in landscape patterns under different management abandonment regimes by combining spatial and temporal analysis of class-level metrics.     

Effects of Watershed History on Dissolved Organic Matter Characteristics in Headwater Streams

Dissolved organic matter (DOM) is recognized as a major component in the global carbon cycle and is an important driver in aquatic ecosystem function. Climate, land use, and forest cover changes all impact stream DOM and alter biogeochemical cycles in terrestrial environments. We determined the temporal variation in DOM quantity and quality in headwater streams at a reference watershed (REF), a watershed clear-cut 30 years ago (CC), and a watershed converted to a white pine plantation 50 years ago (WP) at the US Forest Service, Coweeta Hydrologic Laboratory, in the Nantahala Mountains of western North Carolina, USA. Average stream dissolved organic carbon (DOC) concentrations in CC or WP were 60 and 80% of those in REF, respectively. Stream DOM composition showed that the difference was mainly due to changes in humic-like components in chromophoric DOM. In addition, excitation–emission matrix fluorescence data with parallel factor analysis indicate that although the concentration of protein-like components did not differ significantly among watersheds, their relative abundance showed an enrichment in CC and WP compared to REF. The ratio of humic acid-type to fulvic acid-type components was highest and lowest at REF and WP, respectively. Our data suggest that forest ecosystem disturbance history affects the DOM quantity and quality in headwater streams over decades as a result of changes in watershed soil organic matter characteristics due to differences in organic matter inputs.     

河流水质的景观组分阈值研究进展

土地利用/覆被变化产生的区域生态环境负面效应已引起国内外研究者的广泛关注,其中,河流水质对景观组分变化的响应已在区域及更大尺度的研究中,成为热点。探讨河流水质的景观组分阈值,可以弥补非点源污染研究在区域尺度上的景观变化影响水质问题研究中的不足,而这是当前流域水环境管理及土地利用规划与管理的主要依据之一。从景观组分指数与水质指标出发,分析了当前研究的常用指标,认为:具有明确物理意义的景观组分指数,如不透水表面指数、植被指数等,受到水质的景观组分阈值研究的青睐;在水质指标中,水化学指标应用最为广泛,同时,表征水生生态系统条件的如生物类指标、综合生物类与非生物类指标,也逐渐受到重视,方兴未艾。尽管河流水质的景观组分阈值是当前的研究重点,但在区域以及更大尺度上,阈值的差异较大。在今后的研究中,水质退化的景观组分阈值还需在研究尺度、水质指标及阈值标准等问题上进一步深化,而景观格局指数的应用将会促进对水质退化受景观组分空间配置影响的研究。对水质的景观组分阈值研究进行综述,可以为区域尺度上开展水质保护、流域水环境管理及土地利用规划提供前沿信息。     

How does forest landscape structure explain tree species richness in a Mediterranean context?

Although the strong relationship between vegetation and climatic factors is widely accepted, other landscape composition and configuration characteristics could be significantly related with vegetation diversity patterns at different scales. Variation partitioning was conducted in order to analyse to what degree forest landscape structure, compared to other spatial and environmental factors, explained forest tree species richness in 278 UTM 10 × 10 km cells in the Mediterranean region of Catalonia (NE Spain). Tree species richness variation was decomposed through linear regression into three groups of explanatory variables: forest landscape (composition and configuration), environmental (topography and climate) and spatial variables. Additionally, the forest landscape characteristics which significantly contributed to explain richness variation were identified through a multiple regression model. About 60% of tree species richness variation was explained by the whole set of variables, while their joint effects explained nearly 28%. Forest landscape variables were those with a greater pure explanatory power for tree species richness (about 15% of total variation), much larger than the pure effect of environmental or spatial variables (about 2% each). Forest canopy cover, forest area and land cover diversity were the most significant composition variables in the regression model. Landscape configuration metrics had a minor effect on forest tree species richness, with the exception of some shape complexity indices, as indicators of land use intensity and edge effects. Our results highlight the importance of considering the forest landscape structure in order to understand the distribution of vegetation diversity in strongly human-modified regions like the Mediterranean.     

The effect of landscape complexity on water quality in mountainous urbanized watersheds: a case study in Chongqing,China

The most significant feature of the landscape of mountainous urbanized watersheds is complexity. The geomorphology, composition, and configuration have strong ties with river water quality. In this study, through redundancy analysis, we examined how landscape complexity measured at both landscape and class levels related to water quality within watersheds. The results indicate that water quality is closely associated with both the relief degree of the land surface and patch density at the landscape level. The river water quality of mountainous watersheds is better if the relief degree of the land surface is larger, though river water quality degradation is associated with higher fragmentation of the landscape. At the class level, a greater proportion of non-urban land use may contribute to better river water quality, as do better connectivity and moderate degrees of aggregation. Water quality is more likely to be degraded when the shape of residential land, public service, and commercial land is more complex. We conclude that, in mountainous urbanized watersheds, river water quality can be protected through land use planning and management by regulating a set of landscape metrics for complexity measures.

     

Land-use proximity as a basis for assessing stream water quality in New York State (USA)

The influence of the proximity of urbanization and agriculture to stream water quality is often difficult to quantify. The objectives of this study were to (1) compare the influence of far-field land-use, encompassing a watershed drainage area, to a near-field, 200-m buffer on each side of the stream in an attempt to determine on which zone of influence land-use has the largest impact on water quality, and (2) incorporate the EPA's Rapid Habitat Assessment Protocol (Barbour et al., 1999) to characterize the riparian and channel characteristics of a stream that influence water quality, which can improve New York State's monitoring protocols. Impacts were assessed through biological, chemical, and physical-habitat data from 29 streams located within a variety of land-use categories. Land-use was identified through USGS National Land Cover Data (NLCD). Principal components analysis (PCA) indicated that land-use and water quality variables were associated with non-point source contaminants (e.g. nutrients and specific conductance). Using Spearman's rank correlation coefficient, significant relationships between all three land-use types and stream water quality were determined at the 200-m buffer zone of influence. At the watershed zone of influence, water quality indicators did not correlate significantly with land cover type. DO and BAP values within the 200-m buffer zone varied inversely with the percentage of urban-land cover. The stronger correlation between land cover and stream water quality at the 200-m proximity than that of the watershed suggests that the presence of a riparian buffer zone between streams and agricultural and urban areas is a significant factor in reducing contamination from non-point source loading.     

Suitability index for restoration in landscapes: An alternative proposal for restoration projects

Forest fragmentation constitutes one of the main consequences of land cover change worldwide. Through this process gaps in habitat coverage are created and the ability of populations in the remaining fragments to maintain themselves is put in doubt. Hence, two options need to be considered: conserving the remaining forest fragments, and restoring habitat in some deforested patches with the aim of reestablishing the connections among the fragments. We established a mathematical index (SIR) that describes the suitability of individual habitat patches for restoration within a landscape. The index considers classes of distances among fragments and categories of habitat quality in the areas surrounding the fragments to assess habitat quality in terms of probability of dispersal and survival of propagules (especially seeds and cutting). In the present study, we created detailed maps depicting SIR values for two periods (1988 and 2011) for Sorocaba region (São Paulo State, Brazil). We derived land cover maps from satellite images for the two years of our study, and then surveyed the transition of land cover categories and landscape metrics between years. A model for the SIR was created using a map of distance classes among fragments and also a map of habitat quality established according to each land cover category. For both 1988 and 2011, pasture was the predominant land cover category. The main land cover transitions were from pasture to urban (10.6%) and from pasture to forest fragments (13.4%). Although the land cover class “wood sites” increased, the data of SIR revealed that the areas of habitat categorized as excellent and good both decreased, while habitat classes categorized as poor and very poor increased. Our model has the potential to be applied to other regions where the forest is fragmented. Hence, local policy makers will be able to use this model to determine local patches of high value for conservation and also the most ideal locations for restoration projects.     

太湖流域河流水质状况对景观背景的响应

为探索流域水质对景观背景的响应,以太湖流域为研究对象,在0.5—24 km共9个尺度上运用冗余分析研究了土地利用、河网密度、降水量、地形等景观背景因子与河流水化学指标的关系。结果表明:2006—2010年太湖流域河流水质状况总体较差,但整体有逐渐改善的趋势,超标水质指标主要包括总磷(TP)、氨氮(AN)、生化需氧量(BOD)、化学需氧量(COD)和溶解氧(DO),上游地区主要表现为林区和平原水网区的差异,下游地区主要表现为河段上下游间的差异。河流水质受到多种景观背景因子的综合影响,并表现出尺度依赖性和区位差异性。AN、TP、DO在流域上游与聚落用地正相关,在下游则与耕地、河网密度正相关。COD、BOD在流域上游主要与自然湿地负相关,与人工湿地正相关,在下游则与坡度负相关,与河网密度正相关。总方差贡献率在上下游表现出一致的尺度依赖特征,均在较小(0.5—1 km)和较大(16 km)两个尺度上具有较高的解释能力。自然湿地和坡度,河网密度和耕地分别为上游、下游地区在较小和较大尺度上解释能力最高的景观因子。     

景观指数耦合景观格局与土壤侵蚀的有效性

景观格局分析是景观生态学中揭示景观变化及其生态效应的主要方法,而景观指数是景观格局分析中广泛使用的工具。土壤侵蚀是土壤物质在景观中的迁移和再分配过程,受地形、植被和人类活动及其空间格局的调控。运用景观格局分析揭示景观格局变化特别是土地利用/覆被格局变化对土壤侵蚀的影响是土壤侵蚀研究中应用景观生态学原理和方法的典型。在当前的研究中,斑块-廊道-基质范式下建立的景观指数对侵蚀过程的解释能力不断受到质疑,建立筛选适用的景观指数的原则和方法十分必要。以延河流域碾庄沟小流域为例,利用WATEM/SEDEM模型模拟多个年份流域侵蚀产沙和输沙量;基于土地利用/覆被数据,利用Fragstat4.2软件,计算了相应年份流域斑块、边界密度、形状、集聚与分散和斑块类型多样性4个方面的代表性景观指数。在此基础上,分析了景观指数与流域侵蚀产沙和输沙之间的关系,讨论了景观指数在土壤侵蚀研究中的有效性,在景观和斑块类型水平上分析了景观指数表达"源"、"汇"两大类景观类型的空间格局与侵蚀产沙和输沙之间的关系的一致性。结果表明:斑块-廊道-基底范式下发展的景观指数在指示景观格局的土壤侵蚀效应时存在局限。相对而言,斑块类型尺度的景观指数更能有效表达景观格局与土壤侵蚀的关系。基于景观类型在土壤侵蚀过程中的"源"、"汇"功能,提出了在土壤侵蚀研究中筛选适用的景观指数的原则:(1)对"源"、"汇"两类景观类型,景观指数与土壤侵蚀状况表征变量的相关系数符号相反;(2)对同为"源"或"汇"景观类型的多个景观类型,景观指数与土壤侵蚀表征变量的相关系数应具有符号一致性。尽管景观指数在斑块类型水平上具有一定的有效性,但用其预测景观格局变化的侵蚀效应有很大的不确定性。因此,基于土壤侵蚀过程与景观格局的作用机制发展新型的景观指数是增强景观格局分析预测土壤侵蚀过程的能力的途径。