Mapping ecosystem services: The supply and demand of flood regulation services in Europe

Ecosystem services (ES) feature highly distinctive spatial and temporal patterns of distribution, quantity, and flows. The flow of ecosystem goods and services to beneficiaries plays a decisive role in the valuation of ES and the successful implementation of the ES concept in environmental planning. This is particularly relevant to regulating services where demands emerge often spatially separated from supply. However, spatial patterns of both supply and demand are rarely incorporated in ES assessments on continental scales. In this paper, we present an ES modeling approach with low data demand, fit to be employed in scenario analysis and on multiple scales. We analyze flood regulation services at a European scale by explicitly addressing the spatial distribution of ES demand. A flood regulation supply indicator is developed based on scenario runs with a hydrological model in representative river catchments, incorporating detailed information on land, cover, land use and management. Land use sensitive flood damage estimates in the European Union (EU) are employed to develop a spatial indicator for flood regulation demand. Findings are transferred to the EU territory to create a map of the current supply of flood regulation and the potential supply under conditions of natural vegetation. Regions with a high capacity to provide flood regulation are mainly characterized by large patches of natural vegetation or extensive agriculture. The main factor limiting supply on a continental scale is a low water holding capacity of the soil. Flood regulation demand is highest in central Europe, at the foothills of the Alps and upstream of agglomerations. We were able to identify areas with a high potential capacity to provide flood regulation in conjunction with land use modifications. When combined with spatial patterns of current supply and demand, we could identify priority areas for investments in ES flood regulation supply through conservation and land use planning. We found that only in a fraction of the EU river catchments exhibiting a high demand, significant increases in flood regulation supply are achievable by means of land use modifications.     

A national approach for mapping and quantifying habitat-based biodiversity metrics across multiple spatial scales

Ecosystem services, i.e., services provided to humans from ecological systems have become a key issue of this century in resource management, conservation planning, and environmental decision analysis. Mapping and quantifying ecosystem services have become strategic national interests for integrating ecology with economics to help understand the effects of human policies and actions and their subsequent impacts on both ecosystem function and human well-being. Some aspects of biodiversity are valued by humans in varied ways, and thus are important to include in any assessment that seeks to identify and quantify the benefits of ecosystems to humans. Some biodiversity metrics clearly reflect ecosystem services (e.g., abundance and diversity of harvestable species), whereas others may reflect indirect and difficult to quantify relationships to services (e.g., relevance of species diversity to ecosystem resilience, cultural value of native species). Wildlife habitat has been modeled at broad spatial scales and can be used to map a number of biodiversity metrics. In the present study, we present an approach that (1) identifies mappable biodiversity metrics that are related to ecosystem services or other stakeholder concerns, (2) maps these metrics throughout a large multi-state region, and (3) compares the metric values obtained for selected watersheds within the regional context. The broader focus is to design a flexible approach for mapping metrics to produce a national-scale product. We map 20 biodiversity metrics reflecting ecosystem services or other aspects of biodiversity for all vertebrate species except fish. Metrics include species richness for all vertebrates, specific taxon groups, harvestable species (i.e., upland game, waterfowl, furbearers, small game, and big game), threatened and endangered species, and state-designated species of greatest conservation need, and also a metric for ecosystem (i.e., land cover) diversity. The project is being conducted at multiple scales in a phased approach, starting with place-based studies, then multi-state regional areas, culminating into a national-level atlas. As an example of this incremental approach, we provide results for the southwestern United States (i.e., states of Arizona, New Mexico, Nevada, Utah, and Colorado) and portions of two watersheds within this region: the San Pedro River (Arizona) and Rio Grande River (New Mexico). Geographic patterns differed considerably among metrics across the southwestern study area, but metric values for the two watershed study areas were generally greater than those for the southwestern region as a whole.     

The contribution of persistent soil seed banks and flooding to the restoration of alluvial meadows

Restoration of species-rich flood meadows impoverished by agricultural intensification is an important challenge. The relationships between flooding regime and soil seed bank were compared in three successive meadow communities (hygrophilic, mesohygrophilic and mesophilic) distinguished along a topographic and hydric gradient. Differences in flood duration and frequency between the three associations allowed the study of the contribution of floods to soil seed bank richness and density. No significant difference was found in species richness among the three soil seed banks, whereas the densities were significantly higher in the wettest community. The three seed bank compositions were clearly distinguished along the hydric gradient. In fact, the three seed bank types constituted a species poor version of the meadow communities to which they belong. Flood contributions appear to play a minor role in seed bank enrichment. Thus, seed dispersal by flood water would probably be insufficient to enable the restoration of alluvial meadows.     

The Influence of Land Use on Lake Nutrients Varies with Watershed Transport Capacity

Nutrient loading to lakes depends on both the availability of nutrients in a watershed and their potential for movement to a lake. Many studies have demonstrated that variation in watershed land use can translate to differences in lake water quality by affecting nutrient availability. There have been few attempts, however, to understand how loading to surface waters is affected by land use when there are differences in watershed transport capacity. We compared the relationship between land use/cover and lake nutrients in lakes draining watersheds that exhibited high and low transport capacity using a 5 year (2001–2005) dataset describing the chemistry of 101 lakes and reservoirs in a region of intensive agriculture. We measured watershed transport capacity by compositing the hydrologic, geologic, and topographic variables correlated with interannual variability in lake total nitrogen (TN) or phosphorus (TP) because the hydrologic permeability of watersheds amplifies downstream responses to rainfall events. Factors describing watershed transport capacity differed for TN and TP, consistent with differences in nutrient mobility and biogeochemistry. Partial least squares regression revealed that watershed transport capacity influenced the nature of the association between land use/cover and lake chemistry. In watersheds with low transport capacity, in-lake processes and near-shore land use/cover tended to be more influential, whereas, in watersheds with high transport capacity, land use/cover across the entire watershed was important for explaining lake chemistry. Thus, although land use is a key driver of nutrient loading to lakes, the extent to which it influences water quality can vary with watershed transport capacity. JMF conceived the study and analyzed the data. JAD collected the data. JMF and JAD wrote the paper.     

湖泊-流域生态系统管理的内容与方法

在流域生态系统管理研究综述的基础上,对湖泊一流域生态系统管理的概念进行了界定,对水环境管理、综合流域管理与流域生态系统管理之间的差异进行了对比分析。确定了生态系统生态学、流域生态学、生态系统健康和流域方法为湖泊．流域生态系统管理的理论基础,生态系统方法和流域分析为其方法学基础。在上述分析的基础上,提出了湖泊．流域生态系统管理的6个主要步骤：研究范围界定、基础信息收集与基本生态学问题的分析和评价、管理目标设定、系统综合、生态系统综合评价、适应性管理;识别出湖泊-流域生态系统管理中的3个关键问题：①生态系统管理中的不确定性和障碍分析;②流域土地利用变化对湖泊水质和生态系统的影响;③流域生态子系统与社会子系统的关联。     

Effects of the 2000 southern Mozambique floods on a marginal coral community: the case at Xai-Xai

In early 2000 the southern part of Mozambique suffered the worst flooding in 50 years, causing fatalities and considerable material loss. This study aimed to investigate the impact of this flood on the coral communities in Xai-Xai lagoon. Benthic cover was assessed in January 2000 (before the floods) and September 2000 (after the floods) using the line intercept transect technique. A decrease in hard coral cover of the order of 58.5% was observed. The soft coral community was significantly affected, with a decrease in percentage cover of 90.4%. Coralline algae also decreased by 85.1%. All other categories increased in percentage cover: turf algae (164.4%), other invertebrates (e.g. sponges, sea urchins — 111.1%), fleshy algae (80.4%), rubble (34.4%) and dead coral (379.0%). The main causes of this degradation were the reduced water salinity and the large amount of sediment discharged by the Limpopo River. Some massive (e.g. Porites, Favia, Favites and Goniopora) and encrusting (e.g. Echinopora) hard coral genera seemed less affected, suggesting an elevated capacity to cope with this kind of stress through mucus-sheet formation. The extent of the flood effect on other reefs on the southern Mozambique coast is discussed and a monitoring programme is proposed.     

The influence of floods and precipitation on <Emphasis Type="Italic">Tamarix</Emphasis> establishment in Grand Canyon,Arizona: consequences for flow regime restoration

Decoupling of climate and hydrology combined with introduction of non-native species creates novel abiotic and biotic conditions along highly regulated rivers. Tamarix, a non-native shrub, dominates riparian assemblages along many waterways in the American Southwest, including the Colorado River through Grand Canyon. We conducted a tree-ring study to determine the relative influences of climate and hydrology on Tamarix establishment in Grand Canyon. Riparian vegetation was sparse and annually scoured by large floods until completion of Glen Canyon Dam, which allowed pioneer species, including Tamarix, to expand. Post-dam floods in the mid-1980s were associated with high Tamarix mortality but also initiated a large establishment event. Subsequent establishment has been low but continuous with some exceptions. From 1984 to 2006 establishment increased during years of high, late-summer flows followed by years of low precipitation. This combination provided moist surfaces for Tamarix establishment and may have caused reduced erosion of seedlings or reduced competition from native plants. Attempts to mimic pre-dam floods for ecosystem restoration through planned flood releases also have affected Tamarix establishment. Early (March 1996) and late (November 2004) restoration floods limited establishment, but a small restoration flood in May 2000 followed by steady summer flows permitted widespread establishment. Flood restoration is not expected to prevent Tamarix spread in this system because historic flood timing in May–July coincides with seed release. To decrease future Tamarix establishment, river managers should avoid floods during peak Tamarix seed release, which encompasses the historic spring and early summer flooding period. Tamarix dominance may be reduced by early spring floods that initiate asexual reproduction of clonal shrubs (e.g., Salix exigua, Pluchea sericea).     

Diverse water quality responses to extreme climate events: an introduction

We synthesize and summarize main findings from a special issue examining the origins, evolution, and resilience of diverse water quality responses to extreme climate events resulting from a Chapman Conference of the American Geophysical Union (AGU). Origins refer to sequences of interactive disturbances and antecedent conditions that influence diversification of water quality responses to extreme events. Evolution refers to the amplification, intensification, and persistence of water quality signals across space and time in watersheds. Resilience refers to strategies for managing and minimizing extreme water quality impacts and ecosystem recovery. The contributions of this special issue, taken together, highlight the following: (1) there is diversification in the origins of water quality responses to extreme climate events based on the intensity, duration, and magnitude of the event mediated by previous historical conditions; (2) interactions between climate variability and watershed disturbances (e.g., channelization of river networks, land use change, and deforestation) amplify water quality ‘pulses,’ which can manifest as large changes in chemical concentrations and fluxes over relatively short time periods. In the context of the evolution of water quality responses, results highlight: (3) there are high intensity and long-term climate events, which can generate unique sequences in water quality, which have differential impacts on persistence of water quality problems and ecosystem recovery rates; and (4) ‘chemical cocktails’ or novel mixtures of elements and compounds are transported and transformed during extreme climate events. The main findings regarding resilience to extreme climate events are that: (5) river restoration strategies for reducing pollution from extreme events can be improved by preserving and restoring floodplains, wetlands, and oxbow ponds, which enhance hydrologic and biogeochemical retention, and lengthen the distribution of hydrologic residence times; and (6) the biogeochemical capacity for stream and river ecosystems to retain and transform pollution from landscapes can become “saturated” during floods unless watershed pollution sources are reduced. Finally, the unpredictable occurrence of extreme climate events argues for wider deployment of high-frequency, in situ sensors for monitoring, managing, and modeling diverse water quality responses. These sensors can be used to develop robust proxies for chemical cocktails, detect water quality violations following extreme climate events, and effectively trace the trajectory of water quality recovery in response to managing ecosystem resilience.     

Using simplified watershed hydrology to define spatially explicit ‘zones of influence’

Riparian areas represent dynamic spatial gradients characterized by a varying degree of terrestrial–aquatic interaction. Many studies have considered riparian zones to be discrete watershed sub-portions (e.g., 100-m riparian buffers), whereas I introduce ‘zones of influence’ that are subsets of the riparian zone. The purpose of this study is to introduce the concept of hydrologically defined influence zones using a simple hydrologic model to delimit land-cover. I describe a method for identifying zones of influence using watershed hydrologic patterns to delimit zones along a near-stream continuum between a downstream point (e.g., sample reach) and the watershed boundary. Using hydrologic modeling equations and GIS, travel time was calculated for every 30 × 30-m cell in 10 watersheds providing spatially explicit estimates of watershed hydrology and enabling us to calculate the travel time required for rainfall in any watershed cell to reach the watershed terminus. Shorter-duration travel times (i.e., 30–60 min) described smaller areas than longer-duration travel times (i.e., 210–300 min). This method is an alternative method to delimit near stream areas when quantifying watershed influence. Handling editor: K. Martens     

Relationships between vegetation patterns and hydroperiod on the Roanoke River floodplain,North Carolina

This study quantified relationships between forest composition and flooding gradients on the Roanoke River floodplain, North Carolina. Because flooding is highly variable in time and space, the research was designed to determine the specific hydrological parameters that control woody species abundance on the landscape scale. I specifically tested the importance of spring vs. yearly flood duration, as well as flood duration during hydrologically wet vs. dry years. Field vegetation samples of woody species composition were integrated with spatial data from a Landsat Thematic Mapper (TM) classification and a flood simulation model derived in part from synthetic aperture radar (SAR) imagery. Flood simulations were output and summarized for the periods 1912–1950 (before dams were constructed on the river) and 1965–1996 (after all of the dams were completed). Tenth percentile (dry), median, and 90th percentile (wet) hydroperiod (flood duration) regimes were generated for the spring and year, both pre- and post-dam. Detrended correspondence analysis (DCA) was used to ordinate the plot data, and correlation/regression between ordination axis scores and the flood variables were used to explore the relationships between flooding and species composition. Nineteenth percentile hydroperiod (i.e., wet conditions) correlated most strongly with DCA axis 1 (r>0.9), indicating that inundation during extremely wet years strongly controls species composition on the floodplain. The results were used to quantitatively determine the niche width for both species and mapped vegetation classes in terms of number of days flooded annually and during the spring growth period. The results suggest that spring hydroperiod is an important mechanism that may drive competitive sorting along the flooding gradient, especially during the early years of succession (i.e., pre-dam, which represents the period during which most of the forests sampled were established), and that annual hydroperiod affects the relative dominance of species as the forests mature.     

Watershed ‘chemical cocktails’: forming novel elemental combinations in Anthropocene fresh waters

In the Anthropocene, watershed chemical transport is increasingly dominated by novel combinations of elements, which are hydrologically linked together as ‘chemical cocktails.’ Chemical cocktails are novel because human activities greatly enhance elemental concentrations and their probability for biogeochemical interactions and shared transport along hydrologic flowpaths. A new chemical cocktail approach advances our ability to: trace contaminant mixtures in watersheds, develop chemical proxies with high-resolution sensor data, and manage multiple water quality problems. We explore the following questions: (1) Can we classify elemental transport in watersheds as chemical cocktails using a new approach? (2) What is the role of climate and land use in enhancing the formation and transport of chemical cocktails in watersheds? To address these questions, we first analyze trends in concentrations of carbon, nutrients, metals, and salts in fresh waters over 100 years. Next, we explore how climate and land use enhance the probability of formation of chemical cocktails of carbon, nutrients, metals, and salts. Ultimately, we classify transport of chemical cocktails based on solubility, mobility, reactivity, and dominant phases: (1) sieved chemical cocktails (e.g., particulate forms of nutrients, metals and organic matter); (2) filtered chemical cocktails (e.g., dissolved organic matter and associated metal complexes); (3) chromatographic chemical cocktails (e.g., ions eluted from soil exchange sites); and (4) reactive chemical cocktails (e.g., limiting nutrients and redox sensitive elements). Typically, contaminants are regulated and managed one element at a time, even though combinations of elements interact to influence many water quality problems such as toxicity to life, eutrophication, infrastructure corrosion, and water treatment. A chemical cocktail approach significantly expands evaluations of water quality signatures and impacts beyond single elements to mixtures. High-frequency sensor data (pH, specific conductance, turbidity, etc.) can serve as proxies for chemical cocktails and improve real-time analyses of water quality violations, identify regulatory needs, and track water quality recovery following storms and extreme climate events. Ultimately, a watershed chemical cocktail approach is necessary for effectively co-managing groups of contaminants and provides a more holistic approach for studying, monitoring, and managing water quality in the Anthropocene.     

长江流域生态系统水文调节服务空间特征及影响因素:基于子流域尺度分析

水文调节服务是流域生态系统所提供的重要服务之一,认识流域生态系统水文调节服务空间变异规律及其驱动力,对于流域生态系统保护与恢复、合理开发利用水资源具有重要意义。以洪涝灾害频发的长江流域为对象,运用变异系数法和多元统计方法,在子流域尺度上研究了长江流域生态系统水文调节服务空间特征及影响因素。结果表明,长江流域子流域生态系统水文调节服务呈现出明显的空间异质性,水利工程密集、自然植被覆盖率高达71%的金沙江和汉江水系各子流域水文调节服务最强,降雨与径流变异系数差为0.477;农田和人口密集的嘉陵江水系各子流域水文调节服务最弱,降雨与径流变异系数差为-0.474,其他子流域水文调节服务作用不明显。影响水文调节服务的主要因素是:水库库容、自然植被面积比例、农田面积比例、单位面积人口数,其中:水库库容和自然植被面积比例对水文调节服务具有正向促进作用,农田面积比例和单位面积人口对水文调节服务的作用正好相反。水库库容对子流域生态系统水文调节服务空间异质性的贡献最大(58.85%)。上述结果有助于科学认识长江流域生态系统水文调节服务空间分异规律,可为制定不同子流域生态保护与恢复措施、提升子流域生态系统水文调节服务提供科学依据。     

The impact of flooding on aquatic ecosystem services

Flooding is a major disturbance that impacts aquatic ecosystems and the ecosystem services that they provide. Predicted increases in global flood risk due to land use change and water cycle intensification will likely only increase the frequency and severity of these impacts. Extreme flooding events can cause loss of life and significant destruction to property and infrastructure, effects that are easily recognized and frequently reported in the media. However, flooding also has many other effects on people through freshwater aquatic ecosystem services, which often go unrecognized because they are less evident and can be difficult to evaluate. Here, we identify the effects that small magnitude frequently occurring floods (<?10-year recurrence interval) and extreme floods (>?100-year recurrence interval) have on ten aquatic ecosystem services through a systematic literature review. We focused on ecosystem services considered by the Millennium Ecosystem Assessment including: (1) supporting services (primary production, soil formation), (2) regulating services (water regulation, water quality, disease regulation, climate regulation), (3) provisioning services (drinking water, food supply), and (4) cultural services (aesthetic value, recreation and tourism). The literature search resulted in 117 studies and each of the ten ecosystem services was represented by an average of 12?±?4 studies. Extreme floods resulted in losses in almost every ecosystem service considered in this study. However, small floods had neutral or positive effects on half of the ecosystem services we considered. For example, small floods led to increases in primary production, water regulation, and recreation and tourism. Decision-making that preserves small floods while reducing the impacts of extreme floods can increase ecosystem service provision and minimize losses.     

黄土高原不同植被覆盖对流域水文的影响

以山西省吉县蔡家川流域为对象,研究了植被覆盖类型对流域水文的影响.结果表明:不同植被覆盖的流域年径流系数分别为:林地流域1.6%～2.3%,以农、牧为主的流域3.1%～3.9%;各流域基流系数差异显著,人工林流域为零,次生林为主的流域1.0%～1.5%,以农、牧为主的流域2.5%～2.8%;在雨季人工林流域的径流总量是次生林流域的3.37倍、农地流域的1.9倍,而农地流域的基流量是次生林流域的2.2倍;短历时高强度降雨条件下,人工林流域、次生林流域地表径流量分别是农地流域的10.8倍和2.2倍;在历时较长的暴雨条件下,人工林流域单位面积上的洪峰流量是农地流域的3.4倍,次生林流域的6.9倍;在长历时、大雨量条件下,农地流域的径流量是次生林流域的1.8倍.水平梯田的水源涵养功能与次生林植被相当,次生林植被的水源涵养功能远好于人工植被,在水资源短缺的黄土高原应提倡植被的自然恢复.     

A comment on “Changing estuaries,changing views”

The provision of flood safety is of paramount importance in densely populated deltaic regions. The Dutch rely on flood defences to protect their lives and livelihoods from large-scale floods. The paper “Changing estuaries, changing views” (Smits et al., Hydrobiologica 565:339–355, 2006) criticizes this strategy and presents an alternative that could be summarized as a proposal to leave deltas untouched and to rely on natural sedimentation to reduce the impact of floods. It seems questionable, however, whether such a strategy will often be compatible with population pressures and efforts to stimulate economic growth. Moreover, it presupposes morphological conditions that seem highly unrealistic, not just in the Netherlands but also in many other sediment-starved coastal systems. Other than recommending countries not to implement the Dutch flood protection strategy and to leave deltas untouched, it should be recommended that solutions be tailored to local circumstances. The choice of a flood protection strategy should be based on a balanced evaluation of alternatives, including a realistic assessment of physical conditions.

浑太流域洪涝灾害及其治理方略

抚顺、鞍山、辽阳等在内的中部城市群提供年用水量７．０×１０９ｍ３的７０％［５］,对辽宁经济发展与生态环境建设具有至关重要的作用．本文试图剖析浑河、太子河洪涝灾害问题,找出其成因与特点,从生态与工程结合角度提出治理方略,为防洪减灾,振兴经济服务．２　洪涝灾害成因分析２．１　洪涝灾害的一般分析　　洪涝灾害是天降暴雨和下垫面综合作用的结果．它通常依赖气象、水文地理和生态环境三方面因素．气象因素主要指暴雨,包括雨量、雨强和降雨落区．暴雨主要受大气环境制约,目前人类难以左右．然而,通过人工控制增减局地降雨…     

COMPARISON OF SIMPLE AND MULTIMETRIC DIATOM‐BASED INDICES FOR GREAT LAKES COASTLINE DISTURBANCE1

Because diatom communities are subject to the prevailing water quality in the Great Lakes coastal environment, diatom‐based indices can be used to support coastal‐monitoring programs and paleoecological studies. Diatom samples were collected from Great Lakes coastal wetlands, embayments, and high‐energy sites (155 sites), and assemblages were characterized to the species level. We defined 42 metrics on the basis of autecological and functional properties of species assemblages, including species diversity, motile species, planktonic species, proportion dominant taxon, taxonomic metrics (e.g., proportion Stephanodiscoid taxa), and diatom‐inferred (DI) water quality (e.g., DI chloride [Cl]). Redundant metrics were eliminated, and a diatom‐based multimetric index (MMDI) to infer coastline disturbance was developed. Anthropogenic stresses in adjacent coastal watersheds were characterized using geographic information system (GIS) data related to agricultural and urban land cover and atmospheric deposition. Fourteen independent diatom metrics had significant regressions with watershed stressor data; these metrics were selected for inclusion in the MMDI. The final MMDI was developed as the weighted sum of the selected metric scores with weights based on a metric’s ability to reflect anthropogenic stressors in the adjacent watersheds. Despite careful development of the multimetric approach, verification using a test set of sites indicated that the MMDI was not able to predict watershed stressors better than some of the component metrics. From this investigation, it was determined that simpler, more traditional diatom‐based metrics (e.g., DI Cl, proportion Cl‐tolerant species, and DI total phosphorus [TP]) provide superior prediction of overall stressor influence at coastal locales.     

Application of watershed analyses and ecosystem modeling to investigate land–water nutrient coupling processes in the Guadalupe Estuary, Texas

Estuarine nutrient enrichment is thought to be controlled by land use patterns in coastal watersheds. Hence, the objective of this work was to conduct a watershed analysis in two adjacent river basins with different land use characteristics to determine their influence on estuarine ecosystem response in the Guadalupe Estuary, Texas, U.S.A. All data sources for this study were available electronically on the Internet; the data were mined, managed, analyzed and transformed to simulate the estuarine ecosystem response to watershed-derived nutrient loads. Between 1992 and 2001, developed land use/land cover increased the most while forest cover decreased the most in both basins. Two hydrologic units nearest the coast were responsible for the greatest change in land cover. Nutrient concentrations and loads were significantly higher in the San Antonio River Basin than in the Guadalupe River Basin. Both river basins exhibited the highest flows ever recorded in 1992, however the magnitude of difference in loads between the two coastal hydrologic units for a wet and dry year was much greater in the Guadalupe River Basin (GRB) than in the San Antonio River Basin (SARB); this difference supports the concept that the GRB is a nonpoint source dominated system and SARB is a point source dominated system. There was a strong correlation between developed land use and nutrient concentrations in river water; the GRB had less developed land use and lower nutrient concentrations while the SARB had more developed land use and higher nutrient concentrations. Estuarine ecosystem response differed in the timing, duration and magnitude of DIN, phytoplankton and zooplankton when nitrogen loads from the Lower Guadalupe River were used as opposed to the Lower San Antonio. The two basins studied differ in their fundamental characteristics, i.e. precipitation, flow, human population density, etc., resulting in different drivers of nitrogen loading, point sources in the San Antonio River Basin and nonpoint sources in the Guadalupe River Basin, therefore, differing estuarine ecosystem responses.     

Threats and opportunities for freshwater conservation under future land use change scenarios in the United States

Freshwater ecosystems provide vital resources for humans and support high levels of biodiversity, yet are severely threatened throughout the world. The expansion of human land uses, such as urban and crop cover, typically degrades water quality and reduces freshwater biodiversity, thereby jeopardizing both biodiversity and ecosystem services. Identifying and mitigating future threats to freshwater ecosystems requires forecasting where land use changes are most likely. Our goal was to evaluate the potential consequences of future land use on freshwater ecosystems in the coterminous United States by comparing alternative scenarios of land use change (2001–2051) with current patterns of freshwater biodiversity and water quality risk. Using an econometric model, each of our land use scenarios projected greater changes in watersheds of the eastern half of the country, where freshwater ecosystems already experience higher stress from human activities. Future urban expansion emerged as a major threat in regions with high freshwater biodiversity (e.g., the Southeast) or severe water quality problems (e.g., the Midwest). Our scenarios reflecting environmentally oriented policies had some positive effects. Subsidizing afforestation for carbon sequestration reduced crop cover and increased natural vegetation in areas that are currently stressed by low water quality, while discouraging urban sprawl diminished urban expansion in areas of high biodiversity. On the other hand, we found that increases in crop commodity prices could lead to increased agricultural threats in areas of high freshwater biodiversity. Our analyses illustrate the potential for policy changes and market factors to influence future land use trends in certain regions of the country, with important consequences for freshwater ecosystems. Successful conservation of aquatic biodiversity and ecosystem services in the United States into the future will require attending to the potential threats and opportunities arising from policies and market changes affecting land use.     

场次暴雨条件下降雨和植被变化对洪水影响的定量评估——以彭冲涧小流域为例

降雨和植被是影响流域洪水的两个关键性因素,定量研究二者对洪水影响的贡献率,对流域的植被建设及水资源管理具有重要的科学意义。本研究以南方红壤区的彭冲涧小流域为对象,基于1983—2014年的地理信息数据和水文气象数据,利用Mann-Kendall检验法、累积距平法、HEC-HMS模型等分析该流域的暴雨和洪水特征,并定量评估降雨和植被变化对洪水影响的贡献率。结果表明: 1983—2014年间,彭冲涧小流域的暴雨量和洪水总量分别呈非显著上升和下降趋势。HEC-HMS模型对场次暴雨洪水的模拟效果较好,评价结果均在误差范围内。无论是对洪水总量,还是对洪峰流量,不同场次暴雨洪水的降雨和植被变化贡献率均存在差异。降雨和植被变化对洪水总量的平均贡献率分别为66.5%和33.5%,对洪峰流量的平均贡献率分别为58.9%和41.1%。本研究成果可为小流域洪水评价、植被建设和水土流失综合治理提供科学依据。