Evidence-based indicator approach to guide preliminary environmental impact assessments of hydropower development.

Global expansion of hydropower resources has increased in recent years to meet growing energy demands and fill worldwide gaps in electricity supply. However, hydropower induces significant environmental impacts on river ecosystems - impacts that are addressed through environmental impact assessment (EIA) processes. The need for effective EIA processes is increasing as environmental regulations are either stressed in developing countries undertaking rapid expansion of hydropower capacity or time- and resource-intensive in developed countries. Part of the challenge in implementing EIAs lies in reaching a consensus among stakeholders regarding the most important environmental factors as the focus of impact studies. To help address this gap, we developed a weight-of-evidence approach (and toolkit) as a preliminary and coarse assessment of the most relevant impacts of hydropower on primary components of the river ecosystem, as identified using river function indicators. Through a science-based questionnaire and predictive model, users identify which environmental indicators may be impacted during hydropower development as well as those indicators that have the highest levels of uncertainty and require further investigation. Furthermore, an assessment tool visualizes inter-dependent indicator relationships, which help formulate hypotheses about causal relationships explored through environmental studies. We apply these tools to four existing hydropower projects and one hypothetical new hydropower project of varying sizes and environmental contexts. We observed consistencies between the output of our tools and the Federal Energy Regulatory Commission licensing process (inclusive of EIAs) but also important differences arising from holistic scientific evaluations (our toolkit) versus regulatory policies. The tools presented herein are aimed at increasing the efficiency of the EIA processes that engender environmental studies without loss of rigor or transparency of rationale necessary for understanding, considering, and mitigating the environmental consequences of hydropower.

Uranyl peroxide closed clusters containing topological squares.

Four self-assembling clusters of uranyl peroxide polyhedra have been formed in alkaline aqueous solutions and structurally characterized. These clusters consist of 28, 30, 36 and 44 uranyl polyhedra and exhibit complex new topologies. Each has a structure that contains topological squares, pentagons and hexagons. Analysis of possible topologies within boundary constraints indicates a tendency for adoption of higher symmetry topologies in these cases. Small angle X-ray scattering data demonstrated that crystals of one of these clusters can be dissolved in ultrapure water and that the clusters remain intact for at least several days.

Expanding the crystal chemistry of actinyl peroxides: mu-eta2:eta1 peroxide coordination in trimers of U6+ polyhedra.

Uranyl peroxides have been intensively studied recently because they form topologically complex structures including spherical clusters containing tens of uranyl polyhedra. In all uranyl peroxides reported to date, the coordination of U(6+) cations by peroxide is bidentate. The compound K(2)(Mg(H(2)O)(6))(4)[(UO(2))(3)(O(2))(8)].2H(2)O has been synthesized and characterized and contains a trimer of linked uranyl peroxide polyhedra. The central U(6+) cation is linked to two peroxide groups in a mu-eta(2):eta(1) configuration. Inclusion of this mode of linkage could dramatically increase the flexibility and topological complexity of uranyl peroxide nanoscale clusters.