Assessment of nutrient entry pathways and dominating hydrological processes in lowland catchments

International audienceThe achievement of a good water quality in all water bodies until 2015 is legally regulated since December 2000 for all European Union member states by the European Water Framework Directive (EU, 2000). The aim of this project is to detect nutrient entry pathways and to assess the dominating hydrological processes in complex mesoscale catchments. The investigated Treene catchment is located in Northern Germany as a part of a lowland area. Sandy, loamy and peat soils are characteristic for this area. Land use is dominated by agriculture and pasture. Drainage changed the natural water balance. In a nested approach we examined two catchment areas: a) Treene catchment 517 km2, b) Kielstau catchment 50 km2. The nested approach assists to improve the process understanding by using data of different scales. Therefore these catchments serve not only as an example but the results are transferable to other lowland catchment areas. In a first step the river basin scale model SWAT (Soil and Water Assessment Tool, Arnold et al., 1998) was used successfully to model the water balance. Furthermore the water quality was analysed to distinguish the impact of point and diffuse sources. The results show that the tributaries in the Kielstau catchment contribute high amounts of nutrients, mainly nitrate and ammonium. For the parameters nitrate, ammonium and phosphorus it was observed as a tendency that the annual loads were increasing along the river profile of the Kielstau

Estimation of ungauged Bahr el Jebel flows based on upstream water levels and large scale spatial rainfall data

The study derives Bahr el Jebel flow data at Mongalla, combining upstream flow from Lake Albert and torrential runoff derived from the Collaborative Historical African Rainfall Model (CHARM) rainfall data in the catchment between Lake Albert and Mongalla using GIS techniques. The results provide an updated rating curve for Lake Albert outflows and currently unavailable flow data at Mongalla, the entry to the Sudd swamp, with a high level of confidence for the period after 1983; data which are essential for detailed hydrological assessments of the swamp system with its significant importance for the economies and lives of people in the area

Advances and visions in large-scale hydrological modelling: findings from the 11th Workshop on Large-Scale Hydrological Modelling

Large-scale hydrological modelling has become increasingly wide-spread during the last decade. An annual workshop series on large-scale hydrological modelling has provided, since 1997, a forum to the German-speaking community for discussing recent developments and achievements in this research area. In this paper we present the findings from the 2007 workshop which focused on advances and visions in large-scale hydrological modelling. We identify the state of the art, difficulties and research perspectives with respect to the themes "sensitivity of model results", "integrated modelling" and "coupling of processes in hydrosphere, atmosphere and biosphere". Some achievements in large-scale hydrological modelling during the last ten years are presented together with a selection of remaining challenges for the future

Application of a virtual watershed in academic education

International audienceHydrologic models of watersheds often represent complex systems which are difficult to understand regarding to their structure and dynamics. Virtual watersheds, i.e. watersheds which exist only in the virtual reality of a computer system, are an approach to simplify access to this real-world complexity. In this study we present the virtual watershed KIELSHED-1, a 117 km2 v-shaped valley with grassland on a "Cambisol" soil type. Two weather scenarios are delivered with the watershed: a simplified artificial weather scenario based on long-term data of a German weather station as well as an unmodified data record. The input data and parameters are compiled according to the conventions of the SWAT 2000 hydrological model. KIELSHED-1 is mainly used for education, and illustrative application examples, i.e. calculation of water balance, model calibration, development of land use scenarios, give an insight to the capabilities of the virtual watershed

Using residual analysis, auto- and cross-correlations to identify key processes for the calibration of the SWAT model in a data scarce region

Hydrological modeling poses a particular challenge in data scarce regions, which are often subject to dynamic change and thus of specific interest to hydrological modeling studies. When a small amount of data available for a catchment is opposed by extensive data requirements by the chosen hydrologic model, ways have to be found to extract as much information from the available data as possible. In a study conducted in the Xiangxi Catchment in the Three Gorges Region in China, the use of residual analysis as well as auto- and cross-correlations for enhanced model evaluation and for the identification of key processes governing the hydrological behavior of the catchment prior to model calibration was tested. The residuals were plotted versus various variables such as time, discharge and precipitation. Also, auto-correlations were calculated for measured and simulated discharge and cross-correlations of measured and simulated discharge with precipitation were analyzed. Results show that the analysis of residuals as well as auto- and cross-correlations can provide valuable information about the catchment response to rainfall events, which can be very helpful for calibration of hydrologic models in data scarce regions

SRTM DEM levels over papyrus swamp vegetation – a correction approach

The SRTM DEM, a digital elevation model based on the Shuttle Radar Topography Mission of February 2000 is a source of elevation data with nearly worldwide coverage. It has proven its usefulness in various regions but problems persist for densely vegetated areas where, caused by the organic matter and water content of the vegetation, the radar signal is reflected at some level between the vegetation canopy and the ground level. This level varies with different types and densities of vegetation cover and has so far not been assessed for papyrus areas. The paper describes the approach and establishment of a correction factor for a pilot area in the Sudd swamps of southern Sudan based on comparison of SRTM reference levels and ground control points collected during field surveys between 2004 and 2006. Results show a correction factor between the sensed and the real surface of 4.66 m and a average penetration depth of the radar signal into the dense papyrus vegetation of 0.34 m

Training hydrologists to be ecohydrologists and play a leading role in environmental problem solving

Ecohydrology is a relatively new and rapidly growing subject area in the hydrology curriculum. It is a trans-disciplinary science derived from the larger earth systems science movement and examining mutual interactions of the hydrological cycle and ecosystems. It is also an applied science focused on problem solving and providing sound guidance to catchment-scale integrated land and water resources management. The principle spheres of ecohydrology include (i) climate-soil-vegetation-groundwater interactions at the land surface with special implications for land use, food production and climate change; (ii) riparian runoff, flooding, and flow regime dynamics in river corridors with special implications for water supply, water quality, and inland fisheries; and (iii) fluvial and groundwater inputs to lakes/reservoirs, estuaries, and coastal zones with special implications for water quality and fisheries. We propose an educational vision focused on the development of professional and personal competencies to impart a depth of scientific knowledge in the theory and practice of ecohydrology and a breadth of cross-cutting knowledge and skills to enable ecohydrologists to effectively collaborate with associated scientists and communicate results to resource managers, policy-makers, and other stakeholders. In-depth knowledge in hydrology, ecology, and biogeochemistry is emphasized, as well as technical skills in data collection, modeling, and statistical analysis. Cross-cutting knowledge is framed in the context of integrated water resources management. Personal competencies to be fostered in educational programs include creative thinking, cooperation, communication, and leadership. We consider a life-long learning context but highlight the importance of master's level training in the professional formation of ecohydrologists.Facultad de Ingenierí

Impacts of cascade run-of-river dams on benthic diatoms in the Xiangxi River, China

The ecological effects of small run-of-river dams on aquatic ecosystems are poorly understood, especially on downstream benthic algal communities. We examined impacts of such dams on the benthic diatom community at a regional scale in the Xiangxi River, China. A total of 90 sites were visited, which were divided into five habitats (H1-H5) according to impact extent of each dam. Using partial least squares (PLS) modeling, we developed two predictive models (diatom species richness and total diatom density) based on environmental variables of an unregulated habitat (H1). These models were then used to predict species richness and total densities at impacted habitats (H2-H5) and residuals, i.e. the differences between observed and predicted values, were used to evaluate impact strength of flow regulation. Significant impacts of flow regulation on diatom species richness were detected at three impacted habitats (H3-H5), where observed species richness were significantly higher-70.6, 63.9 and 46.6%, respectively-than predicted values. Then, possible mechanisms for observed impacts were discussed. Further research is necessary to address the potential negative impacts of cascade run-of-river dams on other aquatic organisms in different seasons, and to explore more appropriate mechanisms for such impacts, which may lead to sustainable management strategies and help to determine the optimal ecological water requirement for the Xiangxi River

Land use change impacts on floods at the catchment scale: Challenges and opportunities for future research

Research gaps in understanding flood changes at the catchment scale caused by changes in forest management, agricultural practices, artificial drainage and terracing are identified. Potential strategies in addressing these gaps are proposed, such as complex systems approaches to link processes across time scales, long-term experiments on physical-chemical-biological process interactions, and a focus on connectivity and patterns across spatial scales. It is suggested that these strategies will stimulate new research that coherently addresses the issues across hydrology, soil and agricultural sciences, forest engineering, forest ecology and geomorphology