[1] Human activities exert global-scale impacts on our environment with significant implications for freshwater-driven services and hazards for humans and nature. Our approach to the science of hydrology needs to significantly change so that we can understand and predict these implications. Such an adjustment is a necessary prerequisite for the development of sustainable water resource management strategies and to achieve long-term water security for people and the environment. Hydrology requires a paradigm shift in which predictions of system behavior that are beyond the range of previously observed variability or that result from significant alterations of physical (structural) system characteristics become the new norm. To achieve this shift, hydrologists must become both synthesists, observing and analyzing the system as a holistic entity, and analysts, understanding the functioning of individual system components, while operating firmly within a well-designed hypothesis testing framework. Cross-disciplinary integration must become a primary characteristic of hydrologic research, catalyzing new research and nurturing new educational models. The test of our quantitative understanding across atmosphere, hydrosphere, lithosphere, biosphere, and anthroposphere will necessarily lie in new approaches to benchmark our ability to predict the regional hydrologic and connected implications of environmental change. To address these challenges and to serve as a catalyst to bring about the necessary changes to hydrologic science, we call for a long-term initiative to address the regional implications of environmental change.Citation: Wagener, T

There have been several calls made for hydrologic synthesis research: namely activities which unify diverse data sources across sites, scales and disciplines to uncover new connections and to promote a holistic understanding of water science. This paper draws on the NSF-funded Hydrological Synthesis Project (HSP) run by the University of Illinois at Urbana-Champaign to elucidate mechanisms, benefits and challenges of implementing hydrologic synthesis research from the perspectives of participants in a pilot research study. Two broadly different mechanisms of implementing synthesis were adopted in the HSP: 6-week Summer Institutes in which Ph.D. students conducted team-based research under the guidance of faculty mentors, and focused workshops which disseminated knowledge and shared experiences between scientists at many different career levels. The Summer Institutes were a test bed in which new ideas could be explored, assisted students in developing a wide range of skills, and were highly productive, but posed challenges for mentors and students because the 'new' research topics initiated during the Institutes' programmes needed to be completed in competition with students' ongoing Ph.D. research or mentor's existing research programs. The workshop-based model circumvented this conflict and was also highly productive, but did not offer the same opportunity to experiment with new ideas as part of the synthesis research. Leadership, trust, flexibility and long gestation times were all important to bringing synthesis research to a positive resolution. Funding models that embrace the exploratory aspects of synthesis and provide adequate support to mentors and students over these long timescales would facilitate future hydrologic synthesis research.

As society tackles climate change adaptation and planning, community and regional managers are turning to science for answers. The role of water, and thus hydrologists, is central to many pressing questions. Faced with concerns about water resource availability and quality degradation, society needs information on hydrologic processes at the catchment scale and smaller; although the community has significantly improved its understanding of such processes, there is a need for a new and integrative foundation of knowledge. Hydrology must not only reach beyond disciplinary boundaries but also forge broad connections with natural and social sciences to make useful water cycle predictions at regional and global scales.

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Summer hypoxia (dissolved oxygen<2 mg/L) in the bottom waters of the northern Gulf of Mexico has received considerable scientific and policy attention because of potential ecological and economic impacts. This hypoxic zone forms off the Louisiana coast each summer and has increased from an average of 8,300 km 2 in 1985-1992 to over 16,000 km 2 in 1993-2001, reaching a record 22,000 km 2 in 2002. The almost threefold increase in nitrogen load from the Mississippi River Basin (MRB) to the Gulf since the middle of the last century is the primary external driver for hypoxia.A goal of the 2001 Federal Action Plan is to reduce the 5-year running average size of the hypoxic zone to below 5,000 km 2 by 2015. After the Action Plan was developed, a new question arose as to whether sources other than the MRB may also contribute significant quantities of oxygen-demanding substances. One very visible potential source is the hundreds of offshore oil and gas platforms located within or near the hypoxic zone, many of which discharge varying volumes of produced water.The objectives of this study were to assess the incremental impacts of produced water discharges on dissolved oxygen in the northern Gulf of Mexico, and to evaluate the significance of these discharges relative to loadings from the MRB. Predictive simulations were conducted with three existing models of Gulf hypoxia using produced water loads from an industry study. Scenarios were designed that addressed loading uncertainties, settleability of suspended constituents, and different assumptions on delivery locations for the produced water loads. Model results correspond to the incremental impacts of produced water loads, relative to the original model results, which included only loads from the MRB.The predicted incremental impacts of produced water loads on dissolved oxygen in the northern Gulf of Mexico from all three models were small. Even considering the predicted ranges between lower-and upper-bound results, these impacts are likely to be within the errors of measurement for bottomwater dissolved oxygen and hypoxic area at the spatial scale of the entire hypoxic zone. ObjectivesThe objectives of this study were to assess the incremental impacts of produced water discharges on dissolved oxygen conditions in the northern Gulf of Mexico, and to evaluate the significance of these discharges relative to loadings from the MRB. This study was conducted using the three existing models of Gulf hypoxia described in Scavia et al. (2004). Results from this study will provide EPA with an initial assessment of the appropriate forward path for how to incorporate produced water discharges within the overall framework for controlling nutrient loadings to the Gulf of Mexico as a management tool for reducing the occurrence and extent of hypoxia.