Surficial Redistribution of Fallout 131iodine in a Small Temperate Catchment

Isotopes of iodine play significant environmental roles, including a limiting micronutrient (127I), an acute radiotoxin (131I), and a geochemical tracer (129I). But the cycling of iodine through terrestrial ecosystems is poorly understood, due to its complex environmental chemistry and low natural abundance. To better understand iodine transport and fate in a terrestrial ecosystem, we traced fallout 131iodine throughout a small temperate catchment following contamination by the 11 March 2011 failure of the Fukushima Daiichi nuclear power facility. We find that radioiodine fallout is actively and efficiently scavenged by the soil system, where it is continuously focused to surface soils over a period of weeks following deposition. Mobilization of historic (pre-Fukushima) 137cesium observed concurrently in these soils suggests that the focusing of iodine to surface soils may be biologically mediated. Atmospherically deposited iodine is subsequently redistributed from the soil system via fluvial processes in a manner analogous to that of the particle-reactive tracer 7beryllium, a consequence of the radionuclides’ shared sorption affinity for fine, particulate organic matter. These processes of surficial redistribution create iodine hotspots in the terrestrial environment where fine, particulate organic matter accumulates, and in this manner regulate the delivery of iodine nutrients and toxins alike from small catchments to larger river systems, lakes and estuaries

Changes in hydrologic regime by dams

Abstract Dams have major impacts on river hydrology, primarily through changes in the timing, magnitude, and frequency of low and high flows, ultimately producing a hydrologic regime differing significantly from the pre-impoundment natural flow regime. This paper presents the analysis of pre-and post-dam hydrologic changes from dams that cover the spectrum of hydrologic and climatic regimes across the United States. Our overall goals are to document the type, magnitude, and direction of hydrologic shifts because of impoundment. Using the entire database for the National Inventory of Dams (NID) for dams possessing longstanding U.S. Geological Survey (USGS) gages downstream, we identified 21 gage stations that met length-of-record criteria encompassing an array of types of dams and spanning four orders of magnitude in contributing watershed area. To assess hydrologic changes associated with dams, we applied a hydrologic model, the Indicators of Hydrologic Alteration (IHA), supplemented with orientation statistics for certain hydrograph parameters. Dams had significant impacts on the entire range of hydrologic characteristics measured by IHA. For many characteristics, the direction and significance of effects were highly consistent across the 21 sites. The most significant changes across these sites occurred in minimum and maximum flows over different durations. For low flows, the 1-day through 90-day minimum flows increased significantly following impoundment. The 1-day through 7-day maximum flows decreased significantly across the sites. At monthly scales, mean flows in April and May tend to decline while mean flows in August and September increase. Other significant adjustments included changes in annual hydrograph conditions, primarily in the number of hydrograph reversals that has generally increased for almost all sites following impoundment. The number of high pulses has increased following impoundment but the average length declines. The mean rate of hydrograph rise and fall has declined significantly. These results indicate that the major pulse of dam construction during the previous century has modified hydrologic regimes on a nationwide scale, for large and small rivers.

Science of the dammed: Expertise and knowledge claims in contested dam removals

Historically, science and its associated expert voices often serve multiple roles in the context of complex environmental conflicts: investigators of undesirable environmental conditions; guarantors of “valuefree” and de-politicised expertise and information regarding those conditions; authors of rationales that support one management decision over another; and sources of authority used to persuade sceptics or the public that a certain environmental action is logical and desirable. However, recent thinking in science and technology studies (STS) and political ecology emphasises how scientific knowledge and expertise are co-produced with the political, economic, and cultural arrangements characteristic of a given society and a given locale. In many environmental conflicts, expert knowledge is challenged on the grounds that it is out of touch and politically compromised. This paper examines the diverse scientific discourses and environmental narratives surrounding dam-removal processes in the region of New England, United States. Dam removals are increasingly seen by environmental advocacy organisations and state agencies as a means to rehabilitate degraded riverine systems, and these actors muster an array of science-based arguments in support of removal. Conversely, opponents highlight their placebased knowledge to counter the claims of removal advocates and question the motivations of expert knowledge. These competing claims feed into conflicts over dam removals in intriguing ways, and understanding how scientific knowledge and expertise are used (and misused) is crucial to understanding conflicts over river restoration and developing more participatory strategies of water governance. The question is not so much whose claims are truthful, but how such claims are inserted into, and negotiated within, controversial ecological interventions

Data from: Quantifying flooding regime in floodplain forests to guide river restoration

Determining the flooding regime needed to support distinctive floodplain forests is essential for effective river conservation under the ubiquitous human alteration of river flows characteristic of the Anthropocene Era. At over 100 sites throughout the Connecticut River basin, the largest river system in New England, we characterized species composition, valley and channel morphology, and hydrologic regime to define conditions promoting distinct floodplain forest assemblages. Species assemblages were dominated by floodplain-associated trees on surfaces experiencing flood durations between 4.5 and 91 days/year, which were generally well below the stage of the two-year recurrence interval flood, a widely-used benchmark for floodplain restoration. These tree species rarely occurred on surfaces that flooded less than 1 day/year. By contrast abundance of most woody invasive species decreased with flooding. Such flood-prone surfaces were jointly determined by characteristics of the hydrograph (high discharges of long duration) and topography (low gradient and reduced valley constraint), resulting in increased availability of floodplain habitat with increasing watershed area and/or decreasing stream gradient. Downstream mainstem reaches provided the most floodplain habitat, largely associated with low-energy features such as back swamps and point bars, and were dominated by silver maple (Acer saccharinum). However, we were able to identify a number of suitable sites in the upper part of the basin and in large tributaries, often associated with in-channel islands and bars and frequently dominated by sycamore (Platanus occidentalis) and flood disturbance-dependent species. Our results imply that restoring flows by modifying dam operations to benefit floodplain forests on existing surfaces need not conflict with flood protection in some regional settings. These results underscore the need to understand how flow, geomorphology, and species traits interact to produce characteristic patterns of floodplain vegetation, and that these interactions should form the basis of effective river restoration and conservation

HEC-RAS hydraulic model files

HEC-RAS hydraulic model files for floodplain forest research sites. The HEC-RAS software is available for free from the US Army Corps HEC at: http://www.hec.usace.army.mil/software/hec-ras/ . Model files were used to compute rating curves for each floodplain research transect as well as stream power and other flow measures

Hobo data logger daily stage data

Daily average river stage data calculated from pressure transducer measurements recorded by a Hobo data logger. Stage elevations are in the same coordinates as the vegetation elevation data in the accompanying database

GIS transect locations

ArcGIS and Google Earth files showing Connecticut River floodplain research transect locations. Please note these locations are provided for illustration and use in geographic analyses. Anyone wishing to do on the ground visits or field research at these sites needs to first obtain permission from the relevant landowners

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

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 3 rd and 4 th order streams, in low-elevation (\u3c 500 m) and low-slope (\u3c 5%) watersheds that have small to moderate upstream watershed areas (10-1000 km 2) 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