Chauncey W. Anderson

Initial Fluvial Response to the Removal of Oregon's Marmot Dam

A temporary, 14-meter-high earthen cofferdam standing in place of Marmot Dam was breached on 19 October 2007, allowing the 80-kilometer-long Sandy River to flow freely from Mount Hood, Oregon, to the Columbia River for the first time in nearly 100 years. Marmot Dam is one of the largest dams in the Western United States (in terms of height and volume of stored sediment) to have been removed in the past 40 years, and its removal exposed approximately 730,000 cubic meters of stored sand and gravel to erosion and transport by the newly energetic mountain river. At the time, its breach represented the greatest release of sediment from any U.S. dam removal. (The subsequent March 2008 breaching of Montanas Milltown Dam exposed about 5 to 10 times as much sediment to potential erosion.) Ongoing, intensive monitoring of erosion, transport, and deposition of that sediment is providing the first detailed data from such a voluminous dam-removal sediment release, which will provide a basis for evaluating physical and numerical modeling of the effects of future dam removals from mountain rivers.

Dam removal: Listening in

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.

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 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.

Distribution Limits of Batrachochytrium dendrobatidis: A Case Study in the Rocky Mountains, USA

Knowledge of the environmental constraints on a pathogen is critical to predicting its dynamics and effects on populations. Batrachochytrium dendrobatidis (Bd), an aquatic fungus that has been linked with widespread amphibian declines, is ubiquitous in the Rocky Mountains. As part of assessing the distribution limits of Bd in our study area, we sampled the water column and sediments for Bd zoospores in 30 high-elevation water bodies that lacked amphibians. All water bodies were in areas where Bd has been documented from neighboring, lower-elevation areas. We targeted areas lacking amphibians because existence of Bd independent of amphibians would have both ecologic and management implications. We did not detect Bd, which supports the hypothesis that it does not live independently of amphibians. However, assuming a detection sensitivity of 59.5% (based on sampling of water where amphibians tested positive for Bd), we only had 95% confidence of detecting Bd if it was in ≥16% of our sites. Further investigation into potential abiotic reservoirs is needed, but our results provide a strategic step in determining the distributional and environmental limitations of Bd in our study region.

Use of Continuous Monitors and Autosamplers to Predict Unmeasured Water-Quality Constituents in Tributaries of the Tualatin River, Oregon

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Pine Lake Response to Diversion of Wetland Inflow

ABSTRACT The drainage from a wetland was diverted in fall 1988 from eutrophic Pine Lake, a small (36-ha), thermally stratified (maximum depth 11.9 m) lake in the Puget Sound region. Although the wetland contributed only 20% of the lakes annual phosphorus loading, 90% of the phosphorus was soluble and entered the lakes lighted zone during winter-spring. Furthermore, the wetland drainage fueled a spring blue-green algal bloom, which was the lakes principal water quality problem. The diversion resulted in a reduction of 36-kg TP loading (86% of total external) and greatly improved lake water quality during spring. The spring blue-greenal gal bloom was eliminated in 1989 and 1990. Spring epilimnetic mean TP declined from 27 μg· L−1 in 1980 to 16 μg · L−J in 1990 and mean chl a decreased from 18 to 6 μg· L−1, while transparency increased from 1.9 to 4.5 m. However, lake quality during late summer and fall worsened from 1980 to 1990 concomitant with a doubling in hypolimnetic TP. Metalimnetic populations of ...