Effects Of Climate Land Use And Land Management On Phosphorus Cycling And Water Quality In The Yahara Watershed

Author : Graham MacDonald
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (921 download)

DOWNLOAD NOW!

Download or read book Understanding Human Impacts on the Phosphorus Cycle written by Graham MacDonald and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Modern agriculture has led to fundamental changes in the phosphorus (P) cycle that pose agronomic and environmental challenges at all scales. Phosphorus is a non-renewable resource that is critical to food production because of its role as an essential plant nutrient. At the same time, P runoff from agricultural systems contributes to water quality degradation worldwide. Recent research has begun to illuminate the dimensions of P use in agriculture and its broader sustainability implications, yet there is limited understanding of how these disparate issues are connected across scales. In this thesis, I explore important knowledge gaps related to spatial and temporal changes in P flows due to human activity, their drivers, and some of the implications for large-scale management of soil P and water quality. With the first study, I conducted a global analysis to better understand the contemporary distribution of agronomic P use for croplands. The spatially detailed results revealed that disparities in the magnitude of P applied to cropland soils as fertilizer and manure relative to crop P use occur across most regions, but with considerable spatial variation. Although inputs of P fertilizer (14.2 Tg of P/yr) and manure (9.6 Tg of P/yr) collectively exceeded P removal by harvested crops (12.3 Tg of P/yr) at the global scale, P deficits covered almost 30% of the global cropland area. I then present a comprehensive analysis of the United States agricultural system, exploring how globalization exacerbates changes to regional P cycling. This study considered how limited national P fertilizer supplies are allocated at the interface between trade, biofuel production, and diets. Total mineral P used in the US can be traced predominantly to accumulation in domestic agricultural soils (28%), post-harvest losses (40%), or biofuel refining (10%). Only 8% of mineral P use was ultimately consumed in domestic diets, while one quarter of domestic P fertilizer use was allocated to producing exports. In turn, agriculturally-driven changes in soil P pools could have long-term ecological implications given the slow cycling of P in some soils. I conducted a comprehensive meta-analysis to assess evidence for these legacy effects throughout the world, indicated by either enriched or depleted soil labile and total P pools following agricultural abandonment. This global meta-analysis revealed potentially large and enduring legacies of past agriculture on soil P pools across different regions and soil types, but with some reduction in the magnitude of these changes over time since abandonment. Finally, I considered the roles of watershed anthropogenic and biophysical characteristics on P loading to lakes to aid in the development of large scale lake eutrophication risk models. I used a multi-faceted statistical approach with recent global land use and hydrological data to predict lakewater total phosphorus (TP) concentrations across a representative sample of >1000 lakes worldwide. Global lake TP predictions from three unique statistical methods explained from 50% to as much as 79% of the variation in observed TP, with relatively low error rates. Collectively, this work sheds new insight on agricultural modifications to the global P cycle arising from past and present nutrient management as well as how these might influence both soil P pools and water quality over time. There is growing need to balance local context (e.g., soil types, management histories, and livestock densities) with the cumulative implications these have on limited P reserves at the national or global level (e.g., closing regional P imbalances and accounting for the effects of trade). Greater attention to the spatial variation in both problems and solutions related to P, as well as their complex temporal dimensions, will be essential for advancing the science and policies needed to achieve greater P sustainability in agriculture while simultaneously ensuring healthy aquatic ecosystems." --