REGION,LANDSCAPE, AND SCALE EFFECTS ON LAKE SUPERIOR TRIBUTARY WATER QUALITY1

ABSTRACT: In 1998 and 1999, third‐order watersheds in high mature forest (HMF) and low mature forest (LMF) classes were selected along gradients of watershed storage within each of two hydrogeomorphic regions in the Lake Superior Basin to evaluate threshold effects of storage on hydrologic regimes and watershed exports. Differences were detected between regions (North and South Shore) for particulates, nutrients, and pH, with all but silica values higher for South Shore streams (p < 0.05). Mature forest effects were detected for turbidity, nutrients, color, and alkalinity, with higher values in the LMF watersheds, that is, watersheds with less that 50 percent mature forest cover. Dissolved N, ammonium, N:P, organic carbon, and color increased, while suspended solids, turbidity, and dissolved P decreased as a function of storage. Few two‐way interactions were detected between region and mature forest or watershed storage, thus threshold based classification schemes could be used to extrapolate effects across regions. Both regional differences in water quality and those associated with watershed attributes were more common for third‐order streams in the western Lake Superior drainage basin as compared with second‐order streams examined in an earlier study. Use of ecoregions alone as a basis for setting regional water quality criteria would have led to misinterpretation of reference condition and assessment of impacts in the Northern Lakes and Forest Ecoregion.     

Modeling Postfire Response and Recovery using the Hydrologic Engineering Center Hydrologic Modeling System (HEC‐HMS)1

Abstract: This paper investigates application of the Army Corps of Engineers’ Hydrologic Engineering Center Hydrologic Modeling System (HEC‐HMS) to a burned watershed in San Bernardino County, California. We evaluate the HEC‐HMS’ ability to simulate discharge in prefire and postfire conditions in a semi arid watershed and the necessary parameterizations for modeling hydrologic response during the immediate, and subsequent recovery, period after a wildfire. The model is applied to City Creek watershed, which was 90% burned during the Old Fire of October 2003. An optimal spatial resolution for the HEC‐HMS model was chosen based on an initial sensitivity analysis of subbasin configurations and related model performance. Five prefire storms were calibrated for the selected model resolution, defining a set of parameters that reasonably simulate prefire conditions. Six postfire storms, two from each of the following rainy (winter) seasons were then selected to simulate postfire response and evaluate relative changes in parameter values and model behavior. There were clear trends in the postfire parameters [initial abstractions (I_a), curve number (CN), and lag time] that reveal significant (and expected) changes in watershed behavior. CN returns to prefire (baseline) values by the end of Year 2, while I_a approaches baseline by the end of the third rainy season. However, lag time remains significantly lower than prefire values throughout the three‐year study period. Our results indicate that recovery of soil conditions and related runoff response is not entirely evidenced by the end of the study period (three rainy seasons postfire). Understanding the evolution of the land surface and related hydrologic properties during the highly dynamic postfire period, and accounting for these changes in model parameterizations, will allow for more accurate and reliable discharge simulations in both the immediate, and subsequent, rainy seasons following fire.     

Bottom-up regulation of plant community structure in an aridland ecosystem

We conducted a long-term rodent exclosure experiment in native grass- and shrub-dominated vegetation to evaluate the importance of top-down and bottom-up controls on plant community structure in a low-productivity aridland ecosystem. Using multiple regressions and analysis of covariance, we assessed how bottom-up precipitation pulses cascade through vegetation to affect rodent populations, how rodent populations affect plant community structure, and how rodents alter rates of plant community change over time. Our findings showed that bottom-up pulses cascade through the system, increasing the abundances of plants and rodents, and that rodents exerted no control on plant community structure and rate of change in grass-dominated vegetation, and only limited control in shrub-dominated vegetation. These results were discussed in the context of top-down effects on plant communities across broad gradients of primary productivity. We conclude that bottom-up regulation maintains this ecosystem in a state of low primary productivity that constrains the abundance of consumers such that they exert limited influence on plant community structure and dynamics.     

Biogeochemical consequences of a changing Arctic shelf seafloor ecosystem

Unprecedented and dramatic transformations are occurring in the Arctic in response to climate change, but academic, public, and political discourse has disproportionately focussed on the most visible and direct aspects of change, including sea ice melt, permafrost thaw, the fate of charismatic megafauna, and the expansion of fisheries. Such narratives disregard the importance of less visible and indirect processes and, in particular, miss the substantive contribution of the shelf seafloor in regulating nutrients and sequestering carbon. Here, we summarise the biogeochemical functioning of the Arctic shelf seafloor before considering how climate change and regional adjustments to human activities may alter its biogeochemical and ecological dynamics, including ecosystem function, carbon burial, or nutrient recycling. We highlight the importance of the Arctic benthic system in mitigating climatic and anthropogenic change and, with a focus on the Barents Sea, offer some observations and our perspectives on future management and policy.     

Assessment of Groundwater Depletion and Implications for Management in the Denver Basin Aquifer System

The Denver Basin Aquifer System (DBAS) is a critical groundwater resource along the Colorado Front Range. Groundwater depletion has been documented over the past few decades due to the increased water use among users, presenting long‐term sustainability challenges. A spatiotemporal geostatistical analysis is used to estimate potentiometric surfaces and evaluate groundwater storage changes between 1990 and 2016 in each of the four DBAS aquifers. Several key depletion patterns and spatial water‐level changes emerge in this work. Hydraulic head changes are the largest in the west‐central side of the DBAS and have decreased in some areas by up to 180 m since 1990, while areas to the northwest show increases in hydraulic head by over 30.5 m. The Denver and Arapahoe aquifers show the largest groundwater storage losses, with the highest rates occurring in the 2000s. The results highlight uncertainty in the volumetric predictions under various storage coefficient calculations and emphasize the importance of representative aquifer characterization. The observed groundwater storage depletions are due to a combination of factors, which include population growth increasing the demand for water, variable precipitation, and drought influencing recharge, and increased groundwater pumping. The methods applied in this study are transferable to other groundwater systems and provide a framework that can help assess groundwater depletion and inform management decisions at other locations.     

Water Use for Hydraulic Fracturing of Oil and Gas in the South Platte River Basin,Colorado

Water use for oil and gas development (i.e., hydraulic fracturing) is a concern in semiarid basins where water supply is often stressed to meet demands, and oil and gas production can exacerbate the situation. Understanding the impacts of water use for hydraulic fracturing (HF) on water availability in semiarid regions is critical for management and regulatory decisions. In the current work, we quantify water use for HF at several scales — from municipal to state‐wide — using the IHS Enerdeq database for the South Platte Basin. In addition, we estimate produced water (a by‐product of oil and gas production), using data from the Colorado Oil and Gas Conservation Commission to explore reuse scenarios. The South Platte River Basin, located in northeastern Colorado, encompasses the Denver‐Metro area. The basin has one of the most productive oil and gas shale formations in Colorado, with much of the production occurring in Weld County. The basin has experienced higher horizontal drilling rates coupled with an increasing population. Results show water use for horizontal and vertical wells averages 11,000 and 1,000 m³, respectively. Water use for HF in the South Platte Basin totaled 0.63% of the basin's 2014 total water demand. For Weld County, water use for HF was 2.4% of total demand, and for the city of Greeley, water use was 7% of total demand. Produced water totaled 9.4 Mm³ in the basin for 2014, which represents 42% of the total water used for HF.     

Multilevel knowledge and team performance

We examined team performance as it was affected by organizationally supported face-to-face and technology-mediated knowledge practices. Guided by an information processing perspective, we demonstrate from a field study of over 250 teams within a global Fortune 100 technology company that team member participation in face-to-face and technology-mediated knowledge practices (e.g., community of practice (CoP) meeting attendance and use of CoP-related technologies, respectively), and team knowledge sharing practices are positively related to individual team member knowledge. We predicted that absorptive capacity would moderate tacit knowledge relationships with team performance, and that transactive memory would moderate explicit knowledge relationships with team performance. We found that the patterns of relationships differed depending on the measure of team performance. The predictions held for absorptive capacity by tacit knowledge on manager-assessed performance, and for transactive memory by explicit knowledge on customer satisfaction. Additionally, there was a significant direct effect, with no moderation, of tacit knowledge on customer satisfaction. We highlight multilevel modeling for team research and argue for joint consideration of organizational and technology practices. Copyright © 2009 John Wiley & Sons, Ltd.     

Team approaches to the development of innovative technologies and processes to facilitate remediation

The enactment of the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) created a complex liability scheme for owners, operators and prospective purchasers of contaminated properties, particularly brownfields. As the program developed, liability issues related to contiguous property, prospective purchasers, and no further action determinations became barriers to brownfield property redevelopment. The national effort on the cleanup and redevelopment of brownfield sites took on new emphasis with the passing of the federal “Small Business Liability Protection and Brownfields Revitalization Act” in January 2002. This new law provides liability clarifications as well as funding to facilitate the cleanup of brownfield sites. President Bush stated in his 2003 State of the Union address, “In this century, the greatest environmental progress will come about not through endless lawsuits or command‐and‐control regulations, but through technology and innovation.” The subject of this article is the Interstate Technology Regulatory Commission's Brownfield team, its current initiative, goals, and areas of special focus. © 2003 Wiley Periodicals, Inc.     

Mentorship and career mobility: An empirical investigation

The literature on mentorship is briefly reviewed, revealing that many studies have documented the functions that mentors provide to proteges, including vocational and psychosocial support. This study investigates the link between these functions and the career mobility outcomes of proteges. Results from a random sample of 244 manufacturing managers supports previous research on the dimensions of mentoring. Further, vocational (coaching) and psycho-social (social support) were found to be related to managers' salary level and promotions. Implications of these results for future studies of mentoring are discussed.