Search

An integrated modeling approach was used to connect socioeconomic factors and nutrient management to river export of nitrogen, phosphorus, silica and carbon based on an updated Global NEWS model. Past trends (1970-2000) and four future scenarios were analyzed. Differences among the scenarios for nutrient management in agriculture were a key factor affecting the magnitude and direction of change of future DIN river export. In contrast, connectivity and level of sewage treatment and P detergent use were more important for differences in DIP river export. Global particulate nutrient export was calculated to decrease for all scenarios, in part due to increases in dams for hydropower. Small changes in dissolved silica and dissolved organics were calculated for all scenarios at the global scale. Population changes were an important underlying factor for river export of all nutrients in all scenarios. Substantial regional differences were calculated for all nutrient elements and forms. South Asia alone accounted for over half of the global increase in DIN and DIP river export between 1970 and 2000 and in the subsequent 30 years under the Global Orchestration scenario (globally connected with reactive approach to environmental problems); DIN river export decreased in the Adapting Mosaic (globally connected with proactive approach) scenario by 2030, although DIP continued to increase. Risks for coastal eutrophication will likely continue to increase in many world regions for the foreseeable future due to both increases in magnitude and changes in nutrient ratios in river export. [ABSTRACT FROM AUTHOR]

This paper presents a new reconstruction of the 20th century global hydrography using fully coupled water balance and transport model in a flexible modeling framework. The modeling framework allows a high level of configurability both in terms of input forcings and model structure. Spatial and temporal trends in hydrological cycle components are assessed under "pre-industrial" conditions (without modern-day human activities) and contemporary conditions (incorporating the effects of irrigation and reservoir operations). The two sets of simulations allow the isolation of the trends arising from variations in the climate input driver alone and from human interventions. The sensitivity of the results to variations in input data was tested by using three global gridded datasets of precipitation. Our findings confirm that the expansion of irrigation and the construction of reservoirs has significantly and gradually impacted hydrological components in individual river basins. Variations in the volume of water entering the oceans annually, however, are governed primarily by variations in the climate signal alone with human activities playing a minor role. Globally, we do not find a significant trend in the terrestrial discharge over the last century. The largest impact of human intervention on the hydrological cycle arises from the operation of reservoirs that drastically changes the seasonal pattern of horizontal water transport in the river system and thereby directly and indirectly affects a number of processes such as ability to decompose organic matter or the cycling of nutrients in the river system. [ABSTRACT FROM AUTHOR]

This paper presents a new reconstruction of the 20th Century global hydrography using fully coupled water balance and transport model in a flexible modeling framework. The modeling framework allows a high level of configurability both in terms of input forcings and model structure. Spatial and temporal trends in hydrological cycle components are assessed under "pre-industrial" conditions (without modern-day human activities) and contemporary conditions (incorporating the effects of irrigation and reservoir operations). The two sets of simulations allow the isolation of the trends arising from variations in the climate input driver alone and from human interventions. Our findings confirm that the expansion of irrigation and the construction has significantly and gradually impacted hydrological components in individual river basins. Variations in the volume of water entering the oceans, however, are governed by variations in the climate signal alone with human activities playing secondary role. Globally, we do find a significant trend in the terrestrial discharge over the last century. The largest impact of human intervention on the hydrological cycle arises from the operation of reservoirs that drastically changes the seasonal pattern of horizontal water transport in the river system and thereby directly and indirectly affects a number of processes. [ABSTRACT FROM AUTHOR]

In this study we analyze the scope and potential impact of reservoirconstruction on the world's river systems. Water storage behind the global population of large dams represents a 700% increase in the standing stock of natural river water, with residence times for individual impoundments spanning less than one day to several years. The imprint of such storage persists downstream. The mouths of several large rivers show a reservoir-induced aging of continental runoff that exceeds three months. Globally, the mean age of river water has likely tripled to well over one month. From both case studies and global synthesis, we find that this aging can lead to significant changes in net water balance, flow regime, reoxygenation of surface waters, and sediment transport. The pandemic construction of large reservoirs represents an important component of the terrestrial water cycle and one that merits due consideration in future global change studies. [ABSTRACT FROM AUTHOR]