Greetings from the Powell Center: Your browser is currently running on Internet Explorer (IE) 8 or lower version. To better view this Web site we recommend updating your browser to the most current IE Version.

John Wesley Powell Center for Analysis and Synthesis

Powell Center Products

Tropical rainforest carbon sink declines during El Niño as a result of reduced photosynthesis and increased respiration rates

Powell Center Working Group Products - Fri, 08/18/2017 - 09:23
Summary
  • Changes in tropical forest carbon sink strength during El Niño Southern Oscillation (ENSO) events can indicate future behavior under climate change. Previous studies revealed ˜6 Mg C ha-1 yr-1 lower net ecosystem production (NEP) during ENSO year 1998 compared with non-ENSO year 2000 in a Costa Rican tropical rainforest. We explored environmental drivers of this change and examined the contributions of ecosystem respiration (RE) and gross primary production (GPP) to this weakened carbon sink.
  • For 1998-2000, we estimated RE using chamber-based respiration measurements, and we estimated GPP in two ways: using (1) the canopy process model MAESTRA, and (2) combined eddy covariance and chamber respiration data. MAESTRA-estimated GPP did not statistically differ from GPP estimated using approach 2, but was ˜ 28% greater than published GPP estimates for the same site and years using eddy covariance data only.
  • A 7% increase in RE (primarily increased soil respiration) and a 10% reduction in GPP contributed equally to the difference in NEP between ENSO year 1998 and non-ENSO year 2000.
  • A warming and drying climate for tropical forests may yield a weakened carbon sink from both decreased GPP and increased RE. Understanding physiological acclimation will be critical for the large carbon stores in these ecosystems.

Dam removal: Listening in

Powell Center Working Group Products - Mon, 07/31/2017 - 15:35
Abstract

Dam removal is widely used as an approach for river restoration in the United States. The increase in dam removals--particularly large dams--and associated dam-removal studies over the last few decades motivated a working group at the USGS John Wesley Powell Center for Analysis and Synthesis to review and synthesize available studies of dam removals and their findings. Based on dam removals thus far, some general conclusions have emerged: (1) physical responses are typically fast, with the rate of sediment erosion largely dependent on sediment characteristics and dam-removal strategy; (2) ecological responses to dam removal differ among the affected upstream, downstream, and reservoir reaches; (3) dam removal tends to quickly reestablish connectivity, restoring the movement of material and organisms between upstream and downstream river reaches; (4) geographic context, river history, and land use significantly influence river restoration trajectories and recovery potential because they control broader physical and ecological processes and conditions; and (5) quantitative modeling capability is improving, particularly for physical and broad-scale ecological effects, and gives managers information needed to understand and predict long-term effects of dam removal on riverine ecosystems. Although these studies collectively enhance our understanding of how riverine ecosystems respond to dam removal, knowledge gaps remain because most studies have been short (< 5 years) and do not adequately represent the diversity of dam types, watershed conditions, and dam-removal methods in the U.S.

A Synoptic View of the Third Uniform California Earthquake Rupture Forecast (UCERF3)

Powell Center Working Group Products - Wed, 07/12/2017 - 10:46
ABSTRACT

Probabilistic forecasting of earthquake‐producing fault ruptures informs all major decisions aimed at reducing seismic risk and improving earthquake resilience. Earthquake forecasting models rely on two scales of hazard evolution: long‐term (decades to centuries) probabilities of fault rupture, constrained by stress renewal statistics, and short‐term (hours to years) probabilities of distributed seismicity, constrained by earthquake‐clustering statistics. Comprehensive datasets on both hazard scales have been integrated into the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3). UCERF3 is the first model to provide self‐consistent rupture probabilities over forecasting intervals from less than an hour to more than a century, and it is the first capable of evaluating the short‐term hazards that result from multievent sequences of complex faulting. This article gives an overview of UCERF3, illustrates the short‐term probabilities with aftershock scenarios, and draws some valuable scientific conclusions from the modeling results. In particular, seismic, geologic, and geodetic data, when combined in the UCERF3 framework, reject two types of fault‐based models: long-term forecasts constrained to have local Gutenberg-Richter scaling, and short‐term forecasts that lack stress relaxation by elastic rebound.

Integrating geographically isolated wetlands into land management decisions

Powell Center Working Group Products - Wed, 07/12/2017 - 09:59
Abstract

Wetlands across the globe provide extensive ecosystem services. However, many wetlands - especially those surrounded by uplands, often referred to as geographically isolated wetlands (GIWs) - remain poorly protected. Protection and restoration of wetlands frequently requires information on their hydrologic connectivity to other surface waters, and their cumulative watershed-scale effects. The integration of measurements and models can supply this information. However, the types of measurements and models that should be integrated are dependent on management questions and information compatibility. We summarize the importance of GIWs in watersheds and discuss what wetland connectivity means in both science and management contexts. We then describe the latest tools available to quantify GIW connectivity and explore crucial next steps to enhancing and integrating such tools. These advancements will ensure that appropriate tools are used in GIW decision making and maintaining the important ecosystem services that these wetlands support.

In a nutshell:
  • Wetlands in general receive insufficient protection and this is particularly true for geographically isolated wetlands (GIWs), which are completely surrounded by upland areas
  • GIWs have recently gained policy attention because they provide important ecosystem services, but like most wetlands, their loss and degradation continues
  • Knowledge of the hydrologic connections of GIWs to downstream waters is necessary for their management, particularly under US federal law
  • We synthesize data and modeling tools to quantify GIW connectivity and assess consequent individual and cumulative effects on downstream waters
  • The most defensible management decisions are based on knowledge from a combination of measured, modeled, and hypothesized GIW connections

A global multiproxy database for temperature reconstructions of the Common Era

Powell Center Working Group Products - Tue, 07/11/2017 - 10:55
Abstract

Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850-2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.

Landscape context and the biophysical response of rivers to dam removal in the United States

Powell Center Working Group Products - Tue, 07/11/2017 - 10:36
Abstract

Dams have been a fundamental part of the U.S. national agenda over the past two hundred years. Recently, however, dam removal has emerged as a strategy for addressing aging, obsolete infrastructure and more than 1,100 dams have been removed since the 1970s. However, only 130 of these removals had any ecological or geomorphic assessments, and fewer than half of those included before- and after-removal (BAR) studies. In addition, this growing, but limited collection of dam-removal studies is limited to distinct landscape settings. We conducted a meta-analysis to compare the landscape context of existing and removed dams and assessed the biophysical responses to dam removal for 63 BAR studies. The highest concentration of removed dams was in the Northeast and Upper Midwest, and most have been removed from 3rd and 4th order streams, in low-elevation (< 500 m) and low-slope (< 5%) watersheds that have small to moderate upstream watershed areas (10-1000 km2) with a low risk of habitat degradation. Many of the BAR-studied removals also have these characteristics, suggesting that our understanding of responses to dam removals is based on a limited range of landscape settings, which limits predictive capacity in other environmental settings. Biophysical responses to dam removal varied by landscape cluster, indicating that landscape features are likely to affect biophysical responses to dam removal. However, biophysical data were not equally distributed across variables or clusters, making it difficult to determine which landscape features have the strongest effect on dam-removal response. To address the inconsistencies across dam-removal studies, we provide suggestions for prioritizing and standardizing data collection associated with dam removal activities.

Grand challenges for integrated USGS science—A workshop report

Powell Center Working Group Products - Mon, 07/03/2017 - 09:59
Executive Summary

The U.S. Geological Survey (USGS) has a long history of advancing the traditional Earth science disciplines and identifying opportunities to integrate USGS science across disciplines to address complex societal problems. The USGS science strategy for 2007-2017 laid out key challenges in disciplinary and interdisciplinary arenas, culminating in a call for increased focus on a number of crosscutting science directions. Ten years on, to further the goal of integrated science and at the request of the Executive Leadership Team (ELT), a workshop with three dozen invited scientists spanning different disciplines and career stages in the Bureau convened on February 7-10, 2017, at the USGS John Wesley Powell Center for Analysis and Synthesis in Fort Collins, Colorado.

The workshop focused on identifying “grand challenges” for integrated USGS science. Individual participants identified nearly 70 potential grand challenges before the workshop and through workshop discussions. After discussion, four overarching grand challenges emerged:

  • Natural resource security,
  • Societal risk from existing and emerging threats,
  • Smart infrastructure development, and
  • Anticipatory science for changing landscapes.

Participants also identified a “comprehensive science challenge” that highlights the development of integrative science, data, models, and tools--all interacting in a modular framework--that can be used to address these and other future grand challenges:

  • Earth Monitoring, Analyses, and Projections (EarthMAP)

EarthMAP is our long-term vision for an integrated scientific framework that spans traditional scientific boundaries and disciplines, and integrates the full portfolio of USGS science: research, monitoring, assessment, analysis, and information delivery.

The Department of Interior, and the Nation in general, have a vast array of information needs. The USGS meets these needs by having a broadly trained and agile scientific workforce. Encouraging and supporting cross-discipline engagement would position the USGS to tackle complex and multifaceted scientific and societal challenges in the 21st Century.

Synthesis Centers as Critical Research Infrastructure

Powell Center Working Group Products - Mon, 06/19/2017 - 10:51
Synthesis centers offer a unique amalgam of culture, infrastructure, leadership, and support that facilitates creative discovery on issues crucial to science and society. The combination of logistical support, postdoctoral or senior fellowships, complex data management, informatics and computing capability or expertise, and most of all, opportunity for group discussion and reflection lowers the “activation energy” necessary to promote creativity and the cross-fertilization of ideas. Synthesis centers are explicitly created and operated as community-oriented infrastructure, with scholarly directions driven by the ever-changing interests and needs of an open and inclusive scientific community. The last decade has seen a rise in the number of synthesis centers globally but also the end of core federal funding for several, challenging the sustainability of the infrastructure for this key research strategy. Here, we present the history and rationale for supporting synthesis centers, integrate insights arising from two decades of experience, and explore the challenges and opportunities for long-term sustainability.

Geomorphic Responses to Dam Removal in the United States – a Two-Decade Perspective

Powell Center Working Group Products - Mon, 05/22/2017 - 11:26
Recent decades have seen a marked increase in the number of dams removed in the United States. Investigations following a number of removals are beginning to inform how, and how fast, rivers and their ecosystems respond to released sediment. Though only a few tens of studies detail physical responses to removals, common findings have begun to emerge. They include: (1) Rivers are resilient and respond quickly to dam removals, especially when removals are sudden rather than prolonged. Rivers can swiftly evacuate large fractions of reservoir sediment (≥50% within one year), especially when sediment is coarse grained (sand and gravel). The channel downstream typically takes months to years--not decades--to achieve a degree of stability within its range of natural variability. (2) Modest streamflows (<2-year return interval flows) can erode and transport large amounts of reservoir sediment. Greater streamflows commonly are needed to access remnant reservoir sediment and transport it downstream. (3) Dam height, sediment volume, and sediment caliber strongly influence downstream response to dam removal. Removals of large dams (≥10 m tall) have had longer-lasting and more widespread downstream effects than more common removals of small dams. (4) Downstream valley morphology and position of a dam within a watershed influence the distribution of released sediment. Valley confinement, downstream channel gradient, locations and depths of channel pools, locations and geometries of extant channel bars, and locations of other reservoirs all influence the downstream fate of released sediment.

Accessibility FOIA Privacy Policies and Notices

USA.gov logo U.S. Department of the Interior | U.S. Geological Survey | DOI Inspector General
URL: http://powellcenter.usgs.gov/aggregator/categories/1
Page Contact Information: Ask USGS
Page Last Modified: December 19, 2013
Site Team