The prolonged history of industrialization, flood control, and hydropower production has led to the construction of 80,000 dams across the U.S. generating significant hydrologic, ecological, and social adjustments. With the increased ecological attention on re-establishing riverine connectivity, dam removal is becoming an important part of large-scale river restoration nationally, especially in New England, due to its early European settlement and history of waterpower-based industry. To capture the broader dimensions of dam removal, we constructed a GIS database of all inventoried dams in New England irrespective of size and reservoir volume to document the magnitude of fragmentation. We compared the characteristics of these existing dams to the attributes of all removed dams over the last ∼25 years. Our results reveal that the National Inventory of Dams significantly underestimates the actual number of dams (4,000 compared to >14,000). To combat the effects of these ecological barriers, dam removal in New England has been robust with 127 dams having been removed between ca. 1990–2013. These removed dams range in size, with the largest number (30%) ranging between 2–4 m high, but 22% of the removed dams were between 4–6 m. They are not isolated to small drainage basins: most drained watersheds between 100–1,000 km2. Regionally, dam removal has re-connected ∼3% (3,770 river km) of the regional river network although primarily through a few select dams where abundant barrier-free river lengths occur, suggesting that a more strategic removal approach has the opportunity to enhance the magnitude and rate of river re-connection. Given the regional-scale restoration of forest cover and water quality over the past century, dam removal offers a significant opportunity to capitalize on these efforts, providing watershed scale restoration and enhancing watershed resilience in the face of significant regional and global anthropogenic changes.

We compared long-term change in two lake districts, one in a forested rural setting and the other in an urbanizing agricultural region, using lakes a

The rapid drainage of supraglacial lakes introduces large pulses of meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction of water to the subglacial system has been shown to affect ice flow, and modeling suggests that variability in water supply and delivery to the subsurface play an important role in the development of the subglacial hydrologic system and its ability to enhance or mitigate ice flow. We developed a fully automated method for tracking meltwater and rapid drainages in large (> 0.125 km²) perennial lakes and applied it to a 10 yr time series of ETM+ and MODIS imagery of an outlet glacier flow band in West Greenland. Results indicate interannual variability in maximum coverage and spatial evolution of total lake area. We identify 238 rapid drainage events, occurring most often at low (< 900 m) and middle (900–1200 m) elevations during periods of net filling or peak lake coverage. We observe a general progression of both lake filling and draining from lower to higher elevations but note that the timing of filling onset, peak coverage, and dissipation are also variable. Lake coverage is sensitive to air temperature, and warm years exhibit greater variability in both coverage evolution and rapid drainage. Mid-elevation drainages in 2011 coincide with large surface velocity increases at nearby GPS sites, though the relationships between ice-shed-scale dynamics and meltwater input are still unclear.

Landsat thematic mapper (TM) and enhanced thematic mapper plus (ETM+) images are being used to map lake water clarity region-wide in the Upper Midwest states of Minnesota, Wisconsin, and Michigan using a standardized image processing protocol. In Wisconsin, lake clarity estimates have been produced for 8645 lakes in the 1999-2001 time period. In addition to satellite imagery, the protocol relies on Secchi disk data collected by a network of citizen volunteers for development and validation of models. The most significant term in the regression model relating the satellite imagery to the field data is the ratio of spectral radiance values in the blue and red bands (ratio of Landsat band 1 to Landsat band 3). The resulting database of satellite-derived lake water clarity estimates represents an important new resource for lake managers in the region, and for those studying the linkages between lakes and their surrounding landscapes. Les images Landsat-TM et ETM+ sont utilisées pour cartographier la transparence de l'eau de lac à l'échelle régionale dans les états du Minnesota, du Wisconsin et du Michigan, dans le Upper Midwest, à l'aide d'un protocole standard de traitement d'images. Au Wisconsin, des estimations de la transparence de l'eau de lac ont été produites pour 8645 lacs au cours de la période 1999-2001. En plus d'images satellitaires, le protocole repose aussi sur des données de disque Secchi collectées par un réseau de citoyens volontaires pour le développement et la validation des modèles. Le terme le plus significatif dans le modèle de régression reliant les images satellitaires aux données de terrain est le rapport des valeurs de la radiance spectrale dans les bandes du bleu et du rouge (rapport bande 1 / bande 3 de Landsat). La base de données résultante d'estimations de la transparence de l'eau de lac dérivées des données satellitaires représente une nouvelle ressource importante pour les gestionnaires de lacs dans la...

The water balance of the Arctic tundra is shifting as permafrost stability, seasonality, and the ratio of precipitation to evaporation respond to amplified Arctic warming. While in some northern tundra locations there has been a notable increase in the number of water bodies, generally, the tundra landscape has experienced a decline in the number and area of lakes. We analyzed changes in small lake count (10,000 m²), and lake surface area across the periglacial tundra of western Greenland, using historical satellite and aerial imagery and weather data from the late 1960s to present. Overall, we found a decrease in lake count (21%) and surface area (2%) across our study region. Specifically, smaller ponds were particularly prone to change, with decreases of 28% in count and 15% in surface area. Shrinking lakes often became revegetated by both emergent aquatic and terrestrial vegetation, which captures potential successional trajectories following Arctic lake drying. Additionally, while annual precipitation may be increasing, it occurred primarily during the winter months in the form of snow, which may or may not contribute to the overall growing season water budget. Conversely, the peak growing season months of June, July, and August all have experienced significant increases in potential evaporation rates, thus likely creating a water deficit for much of the growing season. These results suggest that a large section of deglaciated Greenland appears likely to become drier in the summer months, which may result in widespread ecological consequences.