Effects of urban and non-urban land cover on nitrogen and phosphorus runoff to Chesapeake Bay

The aim of this study was to determine the effects of catchment and riparian stream buffer-wide urban and non-urban land cover/land use (LC/LU) on total nitrogen (TN) and total phosphorus (TP) runoff to the Chesapeake Bay. The effects of the composition and configuration of LC/LU patches were explored in particular. A hybrid-statistical-process model, the SPAtially Referenced Regression On Watershed attributes (SPARROW), was calibrated with year 1997 watershed-wide, average annual TN and TP discharges to Chesapeake Bay. Two variables were predicted: (1) yield per unit watershed area and (2) mass delivered to the upper estuary. The 166,534 km² watershed was divided into 2339 catchments averaging 71 km². LC/LU was described using 16 classes applied to both the catchments and also to riparian stream buffers alone. Seven distinct landscape metrics were evaluated. In all, 167 (TN) and 168 (TP) LC/LU class metric combinations were tested in each model calibration run. Runs were made with LC/LU in six fixed riparian buffer widths (31, 62, 125, 250, 500, and 1000 meters (m)) and entire catchments. The significance of the non-point source type (land cover, manure and fertilizer application, and atmospheric deposition) and factors affecting land-to-water delivery (physiographic province and natural or artificial land surfaces) was assessed. The model with a 31 m riparian stream buffer width accounted for the highest variance of mean annual TN (r² = 0.9366) and TP (r² = 0.7503) yield (mass for a specified time normalized by drainage area). TN and TP loadings (mass for a specified time) entering the Chesapeake Bay were estimated to be 1.449 × 10⁸ and 5.367 × 10⁶ kg/yr, respectively. Five of the 167 TN and three of the 168 TP landscape metrics were shown to be significant (p-value ≤ 0.05) either for non-point sources or land-to-water delivery variables. This is the first demonstration of the significance of riparian LC/LU and landscape metrics on water quality simulation in a watershed as large as the Chesapeake Bay. Land cover metrics can therefore be expected to improve the precision of estimated TN and TP annual loadings to the Chesapeake Bay and may also suggest changes in land management that may be beneficial in control of nutrient runoff to the Chesapeake Bay and similar watersheds elsewhere.     

LiDAR derived ecological integrity indicators for riparian zones: Application to the Houille river in Southern Belgium/Northern France

Riparian zones are central landscape features providing several ecosystem services and are exceptionally rich in biodiversity. Despite their relatively low area coverage, riparian zones consequently represent a major concern for land and water resource managers confirmed within several European directives. These directives involve effective multi-scale monitoring to assess their conditions and their ability to carry out their functions. The objective of this research was to develop automated tools to provide from a single aerial LiDAR dataset new mapping tools and keystone riparian zone attributes assessing the ecological integrity of the riparian zone at a network scale (24 km).Different metrics were extracted from the original LiDAR point cloud, notably the Digital Terrain Model and Canopy Height Model rasters, allowing the extraction of riparian zones attributes such as the wetted channel (0.89 m; mean residual) and floodplain extents (6.02 m; mean residual). Different riparian forest characteristics were directly extracted from these layers (patch extent, overhanging character, longitudinal continuity, relative water level, mean and relative standard deviation of tree height). Within the riparian forest, the coniferous stands were distinguished from deciduous and isolated trees, with high accuracy (87.3%, Kappa index).Going further the mapping of the indicators, our study proposed an original approach to study the riparian zone attributes within different buffer width, from local scale (50 m long channel axis reach) to a network scale (ca. 2 km long reaches), using a disaggregation/re-agraggation process. This novel approach, combined to graphical presentations of the results allow natural resource managers to visualise the variation of upstream–downstream attributes and to identify priority action areas.In the case study, results showed a general decrease of the riparian forests when the river crosses built-up areas. They also highlighted the lower flooding frequency of riparian forest patches in habitats areas.Those results showed that LiDAR data can be used to extract indicators of ecological integrity of riparian zones in temperate climate zone. They will enable the assessment of the ecological integrity of riparian zones to be undertaken at the regional scale (13,000 km, completely covered by an aerial LIDAR survey in 2014).     

Land use disturbance indicators and water quality variability in the Biscayne Bay Watershed,Florida

Rapid land use transformations due to extensive agricultural and urban development in south Florida (USA) threaten water resources such as Biscayne Bay, an oligotrophic estuary draining the Miami metropolitan complex and South Dade Agricultural Area. Biscayne Bay is sensitive to nutrient inputs and this study evaluated watershed land use-water quality relationships from 1995 to 2004. Using eight monitoring sites, three spatial extents were considered: sub-basins, canal buffers, and site buffers. Selected sites represented agricultural, urban, and mixed land use classes. Disturbance indicators (landscape metrics; Landscape Development Intensity (LDI) index; percent imperviousness), nutrient loads (nitrate/nitrite-nitrogen (NO_X-N); total ammonia nitrogen (NH₃-N); total phosphorus (TP)), and multivariate regression models were used to determine land use factors influencing water quality variability. The sub-basin regression model was the best predictor of annual NO_X-N loads in the watershed. Both LDI and largest patch index variables were included in this model, indicating that the relative distribution of dominant land use classes influences NO_X-N loads. There were no significant regression models for total inorganic nitrogen (NO_X-N plus NH₃-N) loads. Total phosphorus loads were more closely related to disturbance indicators at a smaller spatial extent (1000 m canal buffer), which is a function of watershed nutrient transport processes. The relative proportion of directly connected impervious areas (DCIA) was not identified as a significant land use variable for regression models. Positive correlations between LDI and DCIA values suggested both indicators provided similar information regarding the intensity of human disturbance. However, the LDI index incorporates anthropogenic intensity associated with a broad range of land uses while DCIA primarily reflects the impact of watershed urbanization. Watershed managers can use the LDI index with landscape metrics that evaluate spatial patterns to link land use development to water quality parameters.     

流域尺度上河流水质与土地利用的关系

以苏子河流域内54个水质采样点为基点,生成6种尺度的河岸带缓冲区,并借助FRAGSTATS软件计算景观水平和类型水平上的8种景观指数.分别从景观空间格局与景观类型组成两方面,对景观指数与水质进行相关分析.结果表明:区域景观格局在不同缓冲区内对流域水质具有不同的效应.当缓冲区距离≤300 m时,旱地、建筑用地、水田为主要的景观类型组成,其面积比例、斑块数量、斑块密度、最大斑块指数、最大形状指数、景观斑块聚集度指数均较高,农田的连通性较高,对水质的影响较大.在距离河流较远的区域(缓冲区距离＞300 m),林地面积比例较高,林地聚集连通程度较好,对水质改善具有一定作用,但不明显.该流域耕地、建设用地等对水质有着关键的影响作用.     

农业主产区湖泊水质对湖滨带多尺度景观格局的空间响应

为分析农业主产区湖泊水环境质量对不同空间尺度上景观格局的响应关系,以洪湖为研究对象,以5种湖泊功能区为基础,利用RS和GIS软件生成7种空间尺度的湖滨带缓冲区,采用Fragstats 软件分析景观格局指数,结合冗余分析等数理统计方法与模型,研究景观格局对洪湖水质变化的空间尺度效应。结果表明: 1)景观格局在不同宽度缓冲区内对湖泊水质的影响具有空间尺度性,在200 m宽度其解释能力最大,达到86.1%,是影响水质的最有效空间尺度。2)景观配置变量(如最大斑块指数、斑块密度等)对水质的影响程度大于景观组成变量(如面积比例和均匀度指数等)。3)景观类型对水质的影响机制具有较大的差异性,农业用地受流域的地形地貌和耕作方式等因素的影响,在100～500 m小尺度的湖滨带缓冲区内对水质退化起主导作用;在远离水体的相对较大尺度(1000～5000 m),林地分布越密集、面积越大,对污染物进入水体的净化作用越明显;草地对水质的影响与林地一致;密集分布的城市用地对水质的影响与林地相反。研究结果可以从宏观尺度上为农业主产区湖泊流域水质管理和景观合理配置提供科学参考。     

A gradient analysis based on the buffer zones of urban landscape pattern of the constructed area in Guigang City, Guangxi, China

Over the last century urbanization on the landscape has increased and intensified. Urban development has a great impact on the environment at the local, regional and even global levels. As a driving force in global change, the need to understand the dynamics of urban pattern and its change in an accurate and efficient manner is ever more pressing. Based on aerial color infrared photography in 1985 and QuickBird satellite imagery in 2004 and according to the standard for plan and construction of city land use, the landscape of Guigang City was divided into 11 types. In the landscape classification maps, 31 buffer zones, each being 200 m wide, were divided. With the aid of GIS software ArcView 3.2 and landscape pattern analysis software FRAGSTATS 3.3, the landscape spatial patterns of each buffer zone were analyzed at the landscape level and class level. The landscape indices, such as patch size, patch fractal dimension, diversity index and evenness index, were calculated. The results indicated the following: The total area of the residential land and the communal land in 2004 covered 46.3% of the entire constructed area of Guigang City and the sum of the patch number of the two patch types occupied about 39.7% of the total patch number, while the percentages were respectively 48.2% and 45.4% in 1985. This showed that the mosaic landscape with the residential land and communal facilities land became increasingly unclear following urban development and landscape diversity. Based on the gradient analysis with the landscape-level index and the class-level index, there were two business and finance centers in the constructed area. One was located in the urban center with a range of 0.8 km; the other was from the 10^th to the 16^th zone. In each buffer zone, the mean patch size was larger and the landscape shape was more regular in 2004 than in 1985. Furthermore, the Shannon diversity index of each buffer zone rose in 2004 with patch richness and evenness increasing. The landscape index computed for the main landscape types (communal facilities land, industrial estate land, residential land and farmland) in the middle of the buffer zones clearly indicated the changes taking place in urbanization. The patch size and the patch number of industrial estate land and farmland also pointed to these changes, while communal facilities land and residential land assumed another similar tendency towards changes. In each gradient zone, industrial estate land had the most complex shape, the lowest area percentage of each zone and the biggest mean patch size, whereas communal facilities land and residential land were opposite to industrial estate land. Farmland had a steady percentage along the buffer zone and its continuous distribution had an important impact on the urban eco-environment. The question of how to relate the pattern of changing characteristics along the buffer zone to the urban ecological process and urban ecological planning remains to be studied further in the future.     

Landscape diversity and forest edge density regulate stream water quality in agricultural catchments

It is well known that the composition of land cover within a watershed plays a large role in regulating stream water quality. However, there remains significant uncertainty regarding the effect of spatial configuration of different types of land cover on water quality. Using periphytic algae (diatoms) as indicators of stream trophic state, we investigated the relationship between landscape configuration and water quality in a large number of watersheds (590) at varying catchment scales in Eastern Canada. Variation partitioning analysis showed that landscape configuration explained 48% of the variation in water quality. However, since the physiographic setting constrains most agricultural activities, most of the variation was attributed to the shared influence of surficial deposits, land cover and landscape configuration (34%). The results from regression models showed that the geomorphological setting of watersheds (surficial deposits and slopes) and the proportion of different land cover types (mainly forests, wetlands, crops and urban areas) have a major impact on stream water quality. Nevertheless, a few configuration metrics emerged as important factors. Landscape diversity appeared to have a negative impact on water quality, whereas forest and wetland edge densities had a positive impact. Moreover, the influence of these lanscape metrics seems to occur at certain thresholds. In areas of intensive farming, streams with a forest area that covers at least 47% of the watershed have a better water quality. Below this threshold, eutrophic and meso-eutrophic conditions are more frequent in streams and rivers. The shape and location of forested patches were also found to be relevant. Woodlands and wetlands with an edge density higher than 36 m/ha and located along streams and gullies have a positive impact on water quality. For the same proportion of forest, complex patches will be more efficient filters than large regular patches. Forest edge density seems to control the extent of the interface with the agricultural sources and thus promotes the “sink” effect of forests on nutrients.     

Validating Landsat-based landscape metrics with fine-grained land cover data

ContextModerate-grained data may not always represent landscape structure in adequate detail which could cause misleading results. Certain metrics have been shown to be predictable with changes in scale; however, no studies have verified such predictions using independent fine-grained data.ObjectivesOur objective was to use independently derived land cover datasets to assess relationships between metrics based on fine- and moderate-grained data for a range of analysis extents. We focus on metrics that previous literature has shown to have predictable relationships across scales.MethodsThe study area was located in eastern Connecticut. We compared a 1 m land cover dataset to a 30 m resampled dataset, derived from the 1 m data, as well as two Landsat-based datasets. We examined 11 metrics which included cover areas and patch metrics. Metrics were analyzed using analysis extents ranging from 100 to 1400 m in radius.ResultsThe resampled data had very strong linear relationships to the 1 m data, from which it was derived, for all metrics regardless of the analysis extent size. Landsat-based data had strong correlations for most cover area metrics but had little or no correlation for patch metrics. Increasing analysis areas improved correlations.ConclusionsRelationships between coarse- and fine-grained data tend to be much weaker when comparing independent land cover datasets. Thus, trends across scales that are found by resampling land cover are likely to be unsuitable for predicting the effects of finer-scale elements in the landscape. Nevertheless, coarser data shows promise in predicting fine-grained for cover area metrics provided the analysis area used is sufficiently large.     

Impacts of land use patterns on river water quality: the case of Dongjiang Lake Basin,China

Landscape pattern can regulate water quality, but determining the thresholds at which landscape metrics impact water quality remains a key issue. Thus, in this study, we investigated landscape metrics that affect the water quality of the rivers flowing into Dongjiang Lake, China, and their spatial and seasonal differences, were investigated using redundancy and partial redundancy analyses. Further, a raw water quality parameter-landscape metric data set was constructed. Threshold values of landscape metrics that induced sudden changes in water quality were analyzed using the bootstrap method applied to 1000 random samples extracted from data set. Finally, mechanisms of landscape patterns that affected river water quality were quantitively explored. The following results were obtained: (1) The key area of landscape that impacted water quality in the Dongjiang Lake Basin was the 400 m buffer zone; (2) Seasonal differences were observed in water quality changes, which better explained by landscape metrics in the dry season than in the wet season. Moreover, water quality was most influenced by landscape configuration metrics. The influence of landscape topographic metrics was greater than that of composition metrics in the dry season, whereas the opposite was true in the wet season; and (3) In this watershed, the largest patch index of grassland and landscape shape index of built-up land were the key metrics at the sub-basin and 400 m buffer zone, respectively. If the largest patch index of grassland was below 8.5% or the landscape shape index of built-up land exceeded 1.5, the water quality of the rivers flowing into the lake was prone to a risk of significant decline, which has an important guiding significance to the optimization of land use pattern.     

Waterbird responses to regular passage of a birdwatching tour boat: Implications for wetland management

Participation in outdoor recreation can increase support for wildlife conservation, but may also disturb wildlife. We examined responses of wintering waterbirds to the regular passage of a small boat specifically dedicated to birdwatching tours in a coastal Ramsar site in northern Spain. Disturbances were measured during two separate periods: 2006–2008 and 2012–2015. Incidence and magnitude of disturbance events were compared by grouping species based on their interest to birders (target vs. non-target) and compared across sectors of the tour route. Flight-initiation distances (FID) were used to estimate species-specific buffer zones, which can be used to manage recreational disturbance to waterbirds. We further examined relationships between species-specific traits and FID, time flying, and distance flying following disturbance. A single boat tour disturbed on average 0.3% of non-target and 2.8% of target wintering bird populations within the wetland, with the effect being more pronounced on target species due to their smaller populations. Wing loading was positively associated with distance flying after disturbance. Based on measured FIDs, we calculated an overall buffer zone for all species of 100 m, and species-specific buffer zones ranging from 41 to 211 m. Disturbance incidence and the number of birds disturbed per tour were both greatest in narrow tidal channels (<200 m), where boats were forced to pass within 100 m of waterbirds. We urge caution in allowing boat passage through tidal channels in which boat operators cannot effectively maintain recommended buffer zones between their boat and waterbirds.     

流溪河流域景观空间特征与河流水质的关联分析

人类活动影响或改变流域景观空间结构,并有可能对河流水质产生不同程度的影响,以流溪河流域为研究区,分析流域景观空间格局特征与水质指数之间的相关关系。将流域划分为27个子流域,采集水样分析水质状况,所选用的水质指标有氨氮(NH3-N)、硝态氮-亚硝态氮(NO3-N+NO2-N)、总磷(TP)、化学需氧量(CODCr)。结果表明:1)该流域土地利用结构与水质具有显著相关性,其中居住用地对水质的影响作用最强,林地对河流水质具有净化功能,与水质指标之间的关系表现为负相关,园地与水质指标关系具有不确定性;2)流域景观特征从上游到下游之间表现为城市化增强的梯度,水质状况响应这个梯度变化表现为上游优于下游,人类活动及城市化发展引起的土地利用变化及土地管理方式对水质变化有显著影响;(3)景观破碎度与水质呈现显著正相关性,是影响水质的重要指标,景观聚集程度和斑块形状复杂程度与水质有负相关关系;子流域尺度和河岸带尺度景观空间特征对水质的影响差异不明显。     

基于缓冲带的贵港市城市景观格局梯度分析

运用景观格局指数与城市建成区缓冲带划分相结合的方法,分析了广西贵港市近20a来城市建成区整体景观与主要城市景观类型（公共设施用地、工业用地、居住用地及农田）的圈层梯度变化特征.分析结果表明：贵港市城市建成区可以看作是居住用地与公共设施用地的镶嵌景观,但这种镶嵌景观随着城市化的发展,存在日趋不明显的特征;整个景观层面的指数20a来在31个梯度带内,表现出相似的变化趋势,斑块面积指数显示出贵港市城市建成区存在两个较为明显的商业金融中心;各梯度带内景观的平均面积增大,景观的形状日臻规则,景观多样性随景观类型及均匀度的增加显著上升.2004年主要城市景观类型在缓冲区中间各带能够很好的反映出格局的变化特征,其中工业用地和农田用地的斑块数和斑块密度随缓冲区梯度表现出较为一致的变化特征,而公共设施用地和居住用地的梯度变化趋势相似.各个梯度带中工业用地形状最为复杂,所占比重最低,平均斑块面积最大;公共设施和居住用地形状较为简单,在各带中所占比重较高,平均斑块面积较小;农田景观在各带中所占比例变化不大,近似连续分布,对城市生态环境的调节起到一定作用.     

Heavy metal pollution in surface water and sediment: A preliminary assessment of an urban river in a developing country

The concentration and chemical fractionation of globally alarming six heavy metals (Cr, Ni, Cu, As, Cd and Pb) were measured in surface water and sediment of an urban river in Bangladesh. The decreasing trend of metals were observed in water as Cr > Cu > As > Ni > Pb > Cd and in sediment as Cr > Ni > Cu > Pb > As > Cd. The level of studied metals exceeded the safe limits of drinking water, indicated that water from this river is not safe for drinking and/or cooking purposes. However, the investigated metals showed low mobility except for Cd and Pb which could pose a severe threat to the aquatic environment. Contamination factor (CF) and geoaccumulation index (I_geo) demonstrated that most of the sediment samples were moderately to heavily contaminated by Cr, As, Cd and Pb. The pollution load index (PLI) values were above one (>1) indicates progressive deterioration of the sediment quality. The extent of pollution by heavy metals in the river Korotoa implies that the condition is much frightening to the biota and inhabitants in the vicinity of the river as well.     

长江上游坡地景观特征对河流水质的影响

景观组成及景观格局特征决定了污染物的来源和地表景观的拦截消纳潜力，地表坡降会加剧土壤侵蚀，坡地景观特征是影响河流水质的重要因素。研究基于长江上游重庆段2015年水质监测数据和30 m空间分辨率土地利用数据，提取河岸带100 m、200 m、300 m、500 m、1000 m和子流域6种空间尺度上景观格局和景观组成，并进一步将景观组成分为总地类、缓坡地类和陡坡地类三种不同坡度尺度，再采用相关分析和冗余分析（RDA）等方法定量探讨了坡地景观特征（坡地景观组成、景观格局）对河流水质的多时空尺度影响。结果表明：坡地景观特征对2015年长江上游重庆段河流水质的影响具有空间尺度效应；坡地景观特征对河流水质的影响在河岸带尺度强于子流域尺度，其中关键尺度为河岸带100 m至300 m，最有效尺度为河岸带200 m。坡地景观特征影响水质的季节差异随空间尺度不同而变化，在河岸带100 m至300 m尺度为汛期强于非汛期，在河岸带1000 m尺度相反，在子流域尺度无季节差异。建设用地面积比与溶解氧（DO）和高锰酸盐指数（COD_Mn）正相关，耕地面积百分比与氨氮（NH₄⁺-N）参数正相关，两者为水质污染"源景观"，且缓坡耕地对水质的解释率高于总地类耕地；林地与水质参数呈负相关，对缓解水质恶化具有积极作用；集聚度（COHESION）、聚合度（AI）指标与NH₄⁺-N参数及斑块密度（PD）、边缘密度（ED）与DO、COD_Mn参数均呈正相关。在集水区尤其是河岸带300 m范围内，严格把控建设用地污水收集与处理，种植河岸带防护林，采取横坡耕种方式，并通过优化景观结构（如种植植物篱）以增强景观拦截力以减少污染物的集中输出，从而改善河流水质。     

不同空间尺度的景观格局对流溪河水质的影响

为探究不同空间尺度的景观格局对流溪河水质的影响,于2020年6月和2021年1月在流溪河干流15个采样点进行了水样的采集,测定了水温、溶解氧、pH、氨氮、硝态氮、硫酸盐和氯化物等水质指标。结合遥感解译所得的土地利用数据,提取了不同空间尺度(子流域和河岸带缓冲区)的景观格局指数,采用Bioenv分析、Mantle检验、方差分解和层次分割理论等方法揭示了景观格局对水质变化的影响。研究结果表明：氨氮是流溪河的主要污染物。土地利用结构与空间格局特征对水质的影响存在空间尺度效应。在100 m河岸带缓冲区,水域是影响水质的主要贡献源;而在其他空间尺度建设用地是影响水质的主要贡献源。在子流域尺度,林地和建设用地的斑块密度(PD指数)是影响水质变化的核心特征;而在河岸带缓冲区尺度,水域和建设用地的连通性(CONTAG指数)和林地的多样性(SHDI指数)是影响水质变化的关键特征。在各个空间尺度,土地利用与空间格局的交互作用对驱动水质变化起主导作用,尤其在1000 m河岸带缓冲区对水质的贡献率最高。因此,加强1000 m缓冲区尺度土地利用的管理和减少建设用地成片建设规划等对保护流域水质具有重要意义。     

Relationship of fish and macroinvertebrate communities in the mid-Atlantic uplands: Implications for integrated assessments

Indices developed for stream bioassessment are typically based on either fish or macroinvertebrate assemblages. These indices consist of metrics which subsume attributes of various species into aggregate measures reflecting community-level ecological responses to disturbance. However, little is known about the relationship between fish and macroinvertebrate metrics, or about how ecological health assessments are affected by assemblage-specific responses to disturbance. We used principal component analysis (PCA) and regression analysis of existing fish (n = 371) and macroinvertebrate (n = 442) stream bioassessment data from a multi-source dataset to determine broad scale, within-assemblage metric patterns, and to examine the intercorrelation of fish and macroinvertebrate metrics (n = 246) and their response to watershed area and land use/land cover gradients. Fish and macroinvertebrate metrics expressed as principal components (PCs) accounted for 72.4 and 85.4% of dataset variance, respectively, with PC-metric patterns reflecting aspects of stream impairment including water and habitat quality. Model components predicting fish metric response differed among fish PCs, with watershed area and macroinvertebrate metric response strongly correlated with the first fish PC, and remaining fish PC models consisting of watershed area, land use, and macroinvertebrate PCs. Correlation between fish and macroinvertebrate PCs, and models relating fish and macroinvertebrate PCs generally explained less variation (13–27%) than metric response models of fish (25–34%) and macroinvertebrates (8–38%) to watershed area and land use/land cover variables. Best-response models integrating fish and macroinvertebrate PCs, watershed area, and land use/land cover variables accounted for the greatest variation in fish PCs (32–50%) across sites. Because fish and macroinvertebrate metrics provide different information on ecological condition, integrated use of information from multiple groups may be appropriate when developing monitoring programs.     

Mayfly bioindicator thresholds for several anthropogenic disturbances in neotropical savanna streams

Anthropogenic disturbances are widely recognized as major threats to terrestrial and aquatic biodiversity worldwide, including areas located in non-forest ecosystems. Headwater streams in the neotropical savanna are severely threatened by large-scale landscape changes that degrade local habitat characteristics and lead to biodiversity loss. The objective of our study was to evaluate Ephemeroptera assemblages as bioindicators of catchment land use and cover, local streambed and riparian vegetation conditions, and instream water quality. To do so, we sampled mayfly nymphs in 184 stream sites across a broad disturbance gradient in four hydrologic units of the Brazilian neotropical savanna. We selected seven metrics without significant co-variation with natural variability: % catchment urban, riparian vegetation condition index (RCOND), human disturbances of the stream channel and riparian zone (W1_HALL), substrate mean embeddedness (XEMBED), dissolved oxygen (mg L⁻¹), pH, and total phosphorus (mg L⁻¹). We ran threshold indicator taxa analysis (TITAN) for each disturbance metric to detect change points in mayfly genera responses (whether sensitive or tolerant) and assemblage turnover pattern. TITAN showed that 20 of the 39 genera found were robust bioindicators (based on purity and reliability values >0.95), sixteen of them being sensitive to increased disturbance. The most sensitive genera were Tricorythopsis (Leptohyphidae) and Camelobaetidius (Baetidae), showing decreased abundance to most disturbance metrics. We found a turnover pattern of mayfly genera in response to W1_HALL in a narrow variation range. For total phosphorus, the benchmark value defined in Brazilian Federal Legislation is higher than the turnover threshold of several mayfly genera. This indicates that we will lose many sensitive genera even within the limits imposed by national environmental legislation. The indicator taxa approach, based on multiple taxa rather than univariate metrics or single indicator species, demonstrates the value of quantitative ecological information for conserving and managing freshwater ecosystems globally.     

Temporal–spatial variation and source analysis of carbon and nitrogen in a tidal wetland of Luoyuan Bay

Carbon and nitrogen are important elements in biogeochemical studies of tidal wetlands. Three wetland zones in Luoyuan Bay in the Fujian province were chosen for this study; the Spartina alterniflora flat zone with Spartina alterniflora growing, the silt zone with no Spartina alterniflora growing and the Spartina alterniflora-silt flat zone – a transition zone between the two. The spatial and seasonal variations of total organic carbon (TOC), total nitrogen (TN), stable isotopes of organic material (δ¹³C, δ¹⁵N), C/N ratio, average particle size and sediment composition in surface and vertical sediments of different ecological zones were analyzed. Carbon and nitrogen accumulation and particle size effects in the different ecological zones were discussed and the indicators of δ¹³C and C/N ratios were also compared. TOC, TN, δ¹³C contents, C/N ratios, and average particle size varied within the ranges of 0.611–1.133%, 0.053–0.090%, ?22.60 to ?18.92‰, 12.3–15.7, and 6.4–8.7 μm, respectively. Sediments were mainly silt-sized. Besides δ¹⁵N values, the other parameters, such as TOC, TN, δ¹³C contents, C/N ratios, and average particle size showed an obvious zonal distribution in surface sediments. The distribution of TOC and TN contents reflected the distribution of Spartina alterniflora within the bay. The profile and seasonal variations of these parameters in different ecological zones indicated that variations in the Spartina alterniflora flat and transition zones were complex because of the effect of Spartina alterniflora. Vertical and seasonal variations were sampled in the silt flat area. The profile and seasonal variations of TOC, TN and δ¹³C were similar in the transition zone and the Spartina alterniflora flat zone. Seasonal concentrations of TOC, TN and δ¹³C decreased from autumn > spring > winter > summer. The seasonal variation of carbon and nitrogen in the sediments may be influenced by temperature, particle size, plankton and benthos. The particle size effect was significant in the surface sediments and profile sediments of the transition zone. However, other factors had a greater effect on the distributions of TOC and TN in the Spartina alterniflora flat and silt flat zones. C/N ratios in sediments of the Spartina alterniflora flat, transition zone and silt flat were close to or > 12, indicating that the organic material source was dominated by terrestrial inputs. However, δ¹³C values decreased from the Spartina alterniflora flat zone > transition zone > silt flat zone indicating that the organic material source was predominantly from marine inputs. Thus the indications from C/N ratios and δ¹³C were different. There was no clear relationship between C/N ratios and δ¹³C values and a better relationship between δ¹³C values and TOC concentrations suggested that δ¹³C values provided a better indication of the organic source. Limited amounts of organic material came from Spartina alterniflora. This study has provided basic data for researching biogeochemical processes of biogenic elements in tidal wetlands and vegetation restoration, and has also provided a reference for assessing and protecting the environment and ecological systems in wetlands.     

艾比湖区域景观格局空间特征与地表水质的关联分析

为进一步明确区域土地利用/覆被—景观格局对河流水质影响的空间尺度。选择新疆艾比湖区域为研究对象,以25个水质采样点为中心,建立5种尺度的河流缓冲区并提取不同尺度下的土地利用/覆被-景观格局数据。首先,通过主成分分析获得水环境的主要水质变量。其次,利用冗余分析(RDA)方法探讨研究区不同宽度缓冲区土地利用/覆被—景观格局对河流水质的影响,获得水质管理的有效缓冲区。最后,引入突变点分析方法进一步寻找导致水质变量沿景观梯度突变的特定位置。结果表明:(1)土地利用/覆被—景观格局在不同宽度缓冲区内对河流水质的影响不同。4 km缓冲区土地利用/覆被—景观格局对区域水质有较强的分异解释能力,因此4 km缓冲区的景观格局合理配置对河流水质管理尤为重要。(2)通过偏RDA分析发现4 km缓冲区中,影响区域水质的主要环境变量为景观水平斑块密度、类型水平耕地斑块密度和森林聚集度。(3)在偏RDA分析的基础上,对4 km缓冲区内的景观指数进行突变点分析研究,发现区域景观水平斑块密度为90—105 m/hm~2,类型水平耕地的斑块密度ED值在90—110 m/hm~2、林草地的AI值在70%—90%,是艾比湖区域水质保护的最佳突变值,该值为艾比湖区域水质保护的阈值。本研究从多个角度对新疆艾比区域的土地利用/覆被—景观格局对区域水质的影响进行定量分析,揭示该地区景观生态变化的规律,为区域景观格局优化和土地合理规划提供理论依据,并对改善"丝绸之路经济带"生态环境、实现资源可持续利用具有重要的现实意义和理论价值。