Modelling tools to analyze and assess the ecological impact of hydropower dams

We critically analyzed a set of ecological models that are used to assess the impact of hydropower dams on water quality and habitat suitability for biological communities. After a literature search, we developed an integrated conceptual model that illustrates the linkages between the main input variables, model approaches, the output variables and biotic-abiotic interactions in the ecosystems related to hydropower dams. We found that variations in water flow and water depth coupled with increased nutrient availability are major variables that contribute to structural and functional ecosystem changes. We also found that ecological models are an important tool to assess the impact of hydropower dams. For instance, model simulation of different scenarios (e.g., with and without the dam, different operation methods) can analyze and predict the related ecosystem shifts. However, one of the remaining shortcomings of these models is the limited capacity to separate dam-related impacts from other anthropogenic influences (e.g., agriculture, urbanization). Moreover, collecting sufficient high-quality data to increase the statistical power remains a challenge. The severely altered conditions (e.g., generation of very deep lakes) also lead to difficulties for standardized data collection. We see future opportunities in the integration of models to improve the understanding of the different processes affected by hydropower dam development and operation, as well as the use of remote sensing methods for data collection

Post-fire vegetation dynamics and the invasion of Paulownia tomentosa in the southern Appalachians

The last two decades have seen an increased awareness of fire’s importance in xeric southern Appalachian forest communities and an increase in its use as a management tool. In the last ten years, managers have also witnessed the invasion of Paulownia tomentosa (hereafter Paulownia) following some of these fires, and apparently as a consequence of the fires. If the pattern of Paulownia invasion is to be understood and the species targeted for control, it is essential to determine the variables that favor the spread of this exotic species into natural areas following fire and determine if it is impacting native communities or species. This work found that fire increases similarity between locations as measured by species composition and that the strength of this effect increases with fire severity. This is counter to Ryan’s Fire Severity Matrix which predicts that similarity will be negatively correlated with fire intensity. Although similarity between study sites increased after burning, each remained distinctive in ordination space and those differences increased over time as species reestablished themselves and environmental gradients shifted towards their pre-fire distributions in response to site-specific differences. This thesis also documents Paulownia seed dispersal up to 3.5 kilometers from mature individuals; distances which are orders of magnitude greater than those over which iv dispersal is generally measured. It also demonstrates that although Paulownia seeds may enter the seed-bank under appropriate conditions, they are killed by all but the least severe fires unless protected by burial. These buried seeds, even when only under 2cm of soil in the absence of litter, exhibit very limited germination. Together this demonstrates that invasion is controlled by the yearly seed rain rather than an accumulation of seeds within the seedbank. Habitat models document Paulownia’s range restriction over time as the initially prevalent high light and low competition conditions disappear with increasing native vegetation cover. Paulownia habitat is however maintained along cliff margins and narrow, shallow soiled benches suggesting that Paulownia will persist where these land forms are present. Although no significant correlation was found between Paulownia’s presence or cover and native species cover or diversity, this may not continue as Paulownia’s cover increases with stem maturity

Using Remote Sensing Techniques to Improve Hydrological Predictions in a Rapidly Changing World

Remotely sensed geophysical datasets are being produced at increasingly fast rates to monitor various aspects of the Earth system in a rapidly changing world. The efficient and innovative use of these datasets to understand hydrological processes in various climatic and vegetation regimes under anthropogenic impacts has become an important challenge, but with a wide range of research opportunities. The ten contributions in this Special Issue have addressed the following four research topics: (1) Evapotranspiration estimation; (2) rainfall monitoring and prediction; (3) flood simulations and predictions; and (4) monitoring of ecohydrological processes using remote sensing techniques. Moreover, the authors have provided broader discussions on how to capitalize on state-of-the-art remote sensing techniques to improve hydrological model simulations and predictions, to enhance their skills in reproducing processes for the fast-changing world

Earth Resources: A continuing bibliography with indexes

This bibliography lists 623 reports, articles, and other documents introduced into the NASA scientific and technical information system between April 1 and June 30, 1983. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Changes in distribution of indigenous forest in Table Mountain National Park from 1880-2012

South Africa's indigenous forest only covers 0.56% of the country's total land area. Its highly fragmented distribution and historically extensive exploitation has led it to be perceived as one of the South Africa's most vulnerable vegetation types. Despite this, forest remains one of South Africa's most under-researched ecosystems and the country has few dedicated forest ecologists. This research examines changes in distribution of Western Cape Afrotemperate Forest and Western Cape Milkwood Forest in Table Mountain National Park. Forest – Fynbos spatial ecotonal change and forest patch count was mapped from 1944 to 2008 using aerial photographs in ArcGIS 10. A full survey of species composition was undertaken and this dataset was used to produce an objective classification of the Cape Peninsula forests. Ground-based repeat photography was used to determine land cover change from 1880 to present with finer scale resolution. An analysis using transition matrices projects future land cover changes to 2050. A total of 174 forest patches were identified in Table Mountain National Park. Total indigenous forest cover has increased by 65.3% from 1944 to 2008. This increase was predominantly visible within the Peninsula's Western Cape Afrotemperate Forest and the highest expansion rates were recorded in Orange Kloof and Blinkwater Ravine on Table Mountain. Only 13 of the forest patches surveyed decreased in cover after 1944. Most of these patches were areas of Western Cape Milkwood Forest located in proximity to expanding coastal development. This trend was also reflected in the repeat photography dataset. There has also been an increase in vegetation biomass recorded at all sites. Further research is required to determine whether these changes have caused a decrease in fynbos species diversity. Non-parametric statistical analysis showed no correlation of forest change with variation in aspect, temperature, precipitation, geology, soils or fire frequency post 1975. These findings indicate that forest patches are influenced by localised ecological factors and suggests a dominant role for other drivers. Historical evidence indicates the key driver of forest expansion is vegetation recovery from past high fire frequency alongside the influence of current fire suppression policies. Increases in CO2 may also be a contributory factor although localised variation in extent of forest expansion suggests that this is not the strongest driver of change. These results hold significance for the future ecological management of Table Mountain National Park in the face of changing climate

A Riverine Ecosystem Service Cascade Model (RESCaM) framework for assessing ecosystem service provision as applied to English geomorphic river types

Riverine ecosystems are considered the lifeblood of the Earth and because of this, have been exploited for centuries for social, agricultural and industrial development, resulting in their environmental degradation and simplification. This has led to a shift in the natural processes and functions and thus their ability to provide a full range and overall high levels of regulating, provisioning and cultural ecosystem services, which humans rely on. An ecosystem service and nature-based approach is being increasingly recognised as a useful tool to help evaluate, protect and restore river ecosystems for maximising the delivery of ecosystem services sustainably. Riverine ecosystem services are derived from riverscapes whereby "hydrological, geomorphological and ecological linkages and pathways of water, sediment and biogenic matter drive the relationship between river processes and physical habitat character and ecosystem services" (Large and Gilvear, 2015; Thorp et al., 2006). Better integration of this understanding is needed to inform sustainable river management in the 21st Century and maximise ecosystem services. This research aims to develop a bespoke riverine ecosystem service assessment methodology, for rivers in England, recognising the biophysical structure of river ecosystems as the template upon which ecosystem services are generated and is useful in guiding future river management. First, I start by critically evaluating an existing river ecosystem service assessment methodology using the Google EarthTM (GE TM) platform, as proposed by Large and Gilvear (2015). The assessment is applied to a variety of rivers across England and Wales representing differing characteristics, scales and land cover uses and validated through field survey. I conclude that the L&G2015 methodology is not suitable for useful application across English and Welsh river networks and that significant advances and refinements are required. The research then focuses on developing a bespoke riverine ecosystem service assessment methodology for English and Welsh rivers that (i) accounts better for their geomorphological character, (ii) uses datasets are available in English and Welsh context and (iii) is underpinned by an evidence-based linkage matrix which recognises positive and negative linkages between riverscape attributes and land cover types, natural ecosystem functioning and ecosystem service provision. The linkages have been identified through an extensive literature review and each linkage has been assigned a confidence level. The linkages have been placed within a Riverine Ecosystem Service Cascade Model (RESCaM) framework. A geomorphic river type classification, recognising thirteen geomorphic river types commonly found in England, is further integrated within the approach to provide the template for which to evaluate ecosystem service ‘performance’ at the river reach-scale. The approach is tested across the spectrum of river types found in England and Wales and its significance for policy and river management is discussed

Process linkages in large watersheds: connecting tributary erosion to downstream channel change and floodplain forest establishment in the Yampa and Green River Basin

2022 Summer.Includes bibliographical references.It is well-understood that the physical state of a river is a combination and culmination of present processes and past trajectories. Similarly, conceptualizations of fluvial connection hold that various aspects of a given river reach – ecologic, geomorphic, hydrologic – do not operate in isolation, but rather as components within a linked system, both influencing and influenced by upstream and downstream conditions. To expand understanding of the river system as an intrinsically linked network of both process and form, here I establish connections between the processes of historical tributary erosion and distal downstream channel migration and floodplain forest establishment in the Yampa and Green River Basin. I then additionally summarize the extensive body of literature concerning the geomorphic response to sediment supply increases in low-gradient, alluvial rivers to further emphasize that the translation of sediment through the landscape can catalyze myriad responses that manifest across a continuum of scales. Concentrating initially on the investigation of historical erosion, examination of historical documents and aerial photos suggests that three key sediment contributing tributaries of the Yampa River – Sand Creek, Muddy Creek, and Sand Wash – underwent substantial historical erosion from 1880-1940. Using field investigation to determine historical channel location and field surveys of present-day dimensions, I then calculate that historical arroyo incision within the latter two tributary watersheds injected 30 x 106 tons of sediment into the mainstem Little Snake and Yampa Rivers during this time. Taking present-day annual sediment loads as an approximate background for the pre-erosion sediment regime, this represented a sizable increase in the sediment load of the Yampa River during the period of historical erosion. Moving downstream, results of dendrochronologic analysis of tree cores from three separate forest locations – Deerlodge Park on the Yampa River, Island Park and Tuxedo Bottom on the Green River – indicate that major portions of these forests established during the same time period of elevated historical erosion. Moreover, channel change analysis suggests that the channel at this time was relatively more dynamic than it has been since, and the area of forest dating to the historical period is much greater than can be explained by high flows alone. Viewed collectively, these findings suggest tributary erosion played a vital role in successful downstream forest establishment. Additional sediment fingerprinting analysis further supports this process link between geomorphic and ecologic process. Using sediment samples taken at the rooting surface of the cottonwood forest in Deerlodge Park, geochemical analysis indicates that the majority of this sediment was sourced from those tributaries – Muddy Creek and Sand Wash – that were undergoing enhanced erosion via arroyo incision during the historical period. Overall, the temporal overlap between the timing of historical tributary erosion and the establishment of substantial portions of downstream floodplain forest, in conjunction with the fact that floodplain sediment is dominantly sourced from watersheds that experienced enhanced historical erosion, together indicates a demonstrable link between the geomorphic process of historical erosion and the ecologic process of downstream floodplain forest establishment. From a summary of existing studies concerning the geomorphic adjustment of low-gradient, alluvial rivers to increased sediment supply, it is additionally clear that tributary erosion that injects substantial amounts of sediment into a river system can result in the requisite channel change necessary for successful forest establishment. The fluvial system is thus best understood as not just a physically coupled network, but a collectively connected web of processes that together regulate and are regulated by one another. Such an understanding emphasizes that management of large watersheds must be holistic and undertaken at the basin scale in order to ensure that vital riverine ecosystems endure

Soil Erosion in a Highly Dynamic, Terraced Environment - the Effect of the Three Gorges Dam in China

Worldwide, soil erosion is one of the most pressing environmental problems of present times. Particularly, soil erosion triggered by overland flow and runoff seriously affects the productivity and stability of ecosystems. The loss of fertile topsoil and soil's water storage capacity, and the discharge of sediments and associated contamination of waterbodies due to diffuse matter transport of particle-bounded agrochemicals from cropland highly elicit call a for action to combat soil erosion for a future securing of food supply and high drinking water quality. Globally, China belongs to one of those countries most affected by soil erosion. Technical problems as well as high economic off-site damages and costs resulting from reservoir siltation and thus, reduced project's lifespan due to soil erosion are typical for numerous large-scale dam projects in China. In addition to the natural disposition to soil erosion, especially, anthropogenic impacts associated to the dam construction distinctly affect the soil erosion risk potential in the adjacent ecosystems. This can be exemplarily seen at the currently worldwide largest dam project, the Three Gorges Dam at the Yangtze River in Central China. This megaproject has been controversially discussed since its planning, and most recently since its construction and full operation in 2007. It contains the largest installed hydropower capacity worldwide, and is supposed to distinctly improve the river navigation and to secure the water supply to the northern country in the long-term. The realization of the dam project has already required massive resettlements of rural and urban population of more than one million people long before its start of operation. Additionally, large-scale land use changes, e.g., land reclamation for the road and settlement construction, for small scale subsistence farming and for cash crop production as well as shifts in land uses, on the steep sloping uphill-site above the impounded area are expected to considerably foster the soil erosion in the short- to long-term. Due to their partially direct connection to the stream network agriculturally used land with high soil erosion potential affects the water quality. Precise knowledge on the quality and quantity of soil loss, and its spatial and temporal variability can help to control the soil erosion by developing an adapted land use management and identifying conducive soil conservation measures, such as contour-aligned bench terraces. Under optimum conditions, bench terraces balance the geomorphic settings and anthropogenic use and can present a fair and sound basis for economic growth in mountainous areas. The focus of the present thesis lies on the risk potential of soil erosion by water in the newly created reservoir of the Three Gorges Dam. Therefore, the central research questions aimed at the natural soil erosion risk potential and the effect of the dam-induced land use dynamics on the dimension and spatial and temporal distribution of soil losses. Due to the data scarcity and limited access to the terrain, a further focus of the research conducted lied on the data-based regionalization of soil erosion factors to use as input in soil erosion modeling. The research was conducted in the subtropical Xiangxi catchment (3,200 km²) that was considered to adequately represent the Three Gorges Area in terms of physical settings and human interventions attributing to the dam project. The Xiangxi River joins the Yangtze River as a first class tributary approximately 40 km upstream the Three Gorges Dam. Due to the dam construction, the widely terraced landscape of the Xiangxi catchments is also affected by rapid, high land use dynamics with consequences on the slope stability. Particularly, the backwater area in the southern catchment area with the impounded lower reach of the Xiangxi River is characterized by steep to extremely steep sloping terrain and predominantly shallow soils with moderate to very high soil erodibility. Additionally, the very high rainfall erosivity increases the high physical vulnerability of the entire Xiangxi catchment. Between 1987 and 2007, a governmental-driven decrease of arable land and an increase of woodland and shrubland affected the northern headwater zone of the catchment. In the immediate reservoir area, the land use change from 1987 to 2007 was mainly controlled by a distinct conversion of arable land to orange orchards. Within the framework of this thesis, methods for data survey and data processing were tested and adapted in order to evaluate the risk potential of soil erosion. In addition, comprehensive field investigations focusing on soil erosion processes and on pedological properties and further erosion-relevant factors were conducted. Relevant parameters derived from remote sensing data and land use classifications as well as the documented land use change from 1987 to 2007 were used for the parameterization of the empirical soil erosion model RUSLE. This model was applied to estimate and evaluate the spatial distribution and dynamic of the soil erosion risk potential, and to spatially localize high-risk areas. The new conceptual model TerraCE was developed and tested for the identification and spatial analysis of different terrace conditions and their causes. By means of data mining approaches, a prediction of the spatial distribution of the identified terrace conditions was computed. By integrating environmental and anthropogenic indicators on the impact of the terrain and the human influence, the causes and the strength of disturbances on the terrace conditions, and thus terrace degradation were analyzed. During the observation period from 1987 to 2007, the Xiangxi catchment is generally characterized by a decrease of average annual soil losses and their maxima due to implemented environmental programs. However, a very high soil erosion risk potential in the entire catchment must be assumed. Frequency and intensity of soil erosion mainly concentrate in the backwater area at the lower reaches of the Xiangxi River. Here, land use changes, resettlements, and infrastructure construction have the highest impact. An inadequate construction of terraces that is not adapted to the local terrain conditions and an insufficient maintenance of the farming terraces can further strongly affect the soil erosion dynamic. Moreover, rapid ecosystem changes and an associated intensification and reclamation of terraces can lead to their degradation. The tempo of the land use dynamics hardly considers available capital and labor for the cost and time-consuming restoration and maintenance of terraces, mainly cultivated with oranges. The high increase of the reclaimed area for the orange production within very short term caused a surplus production and thus, a price decline on the local and regional markets. Due to the not very profitable sale of oranges, a lack of farmers' motivation and little or no capital are made responsible for the gradual worsening of the terrace conditions. As many of the resettled peasants, that were formerly used to farm the flat valley bottoms, are often not familiar with the new and difficult terrain settings and farming techniques, there is also a lack of knowledge on adequate terrace cultivation. Subsequently, inappropriate management of those terraces leads to an increase in the soil erosion The findings of the present thesis suggest designating the terraces as important, sensitive ecosystem service as they present - if properly maintained - a very effective soil erosion control and enable for a sustainable land use in the mountainous Xiangxi catchment and throughout the entire Three Gores Area. Considering the data scarcity in terms of spatial and temporal resolution, the results further show that soil erosion factors can be successfully regionalized and used for a valid soil erosion modeling. Against the background of ongoing research within the 'Yangtze Project' as well as further projected large dam projects at the Yangtze River and worldwide, the research conducted offers an important starting point for further research on the soil erosion risk potential and associated environmental threats, such as water pollution