ALBERT

Description: We review the human actions, proximal stressors and ecological responses for floodplain forests Australia's largest river system—the Murray-Darling Basin. A conceptual model for the floodplain forests was built from extensive published information and some unpublished results for the system, which should provide a basis for understanding, studying and managing the ecology of floodplains that face similar environmental stresses. Since European settlement, lowlands areas of the basin have been extensively cleared for agriculture and remnant forests heavily harvested for timber. The most significant human intervention is modification of river flows, and the reduction in frequency, duration and timing of flooding, which are compounded by climate change (higher temperatures and reduced rainfall) and deteriorating groundwater conditions (depth and salinity). This has created unfavorable conditions for all life-history stages of the dominant floodplain tree (Eucalyptus camaldulensis Dehnh.). Lack of extensive flooding has led to widespread dieback across the Murray River floodplain (currently 79% by area). Management for timber resources has altered the structure of these forests from one dominated by large, widely spreading trees to mixed-aged stands of smaller pole trees. Reductions in numbers of birds and other vertebrates followed the decline in habitat quality (hollow-bearing trees, fallen timber). Restoration of these forests is dependent on substantial increases in the frequency and extent of flooding, improvements in groundwater conditions, re-establishing a diversity of forest structures, removal of grazing and consideration of these interacting stressors.

Description: Projected decreases and changes in the seasonal distribution of precipitation will have profound impacts on southeastern Australia, including its ability to generate renewable hydroelectricity. Recent decreases in precipitation over the region may be significant in the context of instrumental records, but the question of whether these decreases are within long-term natural variability remains. To help address this issue, we present December-January streamflow and dam inflow reconstructions for southeastern Australia. These reconstructions for the Tasmanian west coast are based solely on local tree-ring chronologies and span up to 1600 years. Non-parametric estimates, however, indicate good model skill for the last 458 years (streamflow) and 478 years (dam inflow). The reconstructions indicate that 20 th century conditions were well within the range of historical variability, and were in fact relatively wet. The period from ca. 1600 – 1750 CE was one of enhanced variability and a high proportion of low and high flow events occurred in the 17 th century. There are significant relationships between streamflow and inflow reconstructions and large-scale ocean-atmosphere processes such as ENSO and the Southern Annular Mode. Critically, our two reconstructions rely heavily on new tree-ring chronologies based on properties such as tracheid radial diameter, cell wall thickness and density, underscoring the importance of these different types of chronologies in reconstructions. This article is protected by copyright. All rights reserved.

Description: Agriculture must increase production for a growing population while simultaneously reducing its environmental impacts. These goals need not be in tension with one another. Here we outline a vision for improving both the productivity and environmental performance of agriculture in the U.S. Midwest, also known as the Corn Belt. Mean annual precipitation has increased throughout the region over the past 50 years, consistent with climate models that attribute the increase to a warming troposphere. Stream gauge data indicate that higher precipitation has been matched or exceeded by higher stream flows, contributing to flooding, soil loss, and excessive nutrient flux to the Gulf of Mexico. We propose increasing landscape hydrologic storage through construction of ponds and restoration of wetlands to retain water for supplemental irrigation while also reducing flood risks. Primary productivity is proportional to transpiration, and analysis shows that in the U.S. Midwest both can be sustainably increased with supplemental irrigation. The proposed strategy should reduce interannual yield variability by limiting losses due to transient drought, while facilitating adoption of cropping systems that “perennialize” the landscape to take advantage of the full potential growing season. When implemented in concert, these practices should reduce the riverine nitrogen export that is a primary cause of hypoxia in the Gulf of Mexico. Erosive sediment losses should also be reduced through the combination of enhanced hydrologic storage and increased vegetative cover. Successful implementation would require watershed-scale coordination among producers and landowners. An obvious mechanism to encourage this is governmental farm policy.

Description: The understanding of nutrient uptake in streams is impeded by limited understanding of how geomorphic setting and flow regime interact with biogeochemical processing. This study investigates these interactions as they relate to transient storage and nitrate uptake in small agricultural and urban streams. Sites were selected across a gradient of channel conditions and management modifications and included three 180-m long geomorphically distinct reaches on each of two streams in north-central Colorado. The agricultural stream has been subject to historically variable cattle-grazing practices and the urban stream exhibits various levels of stabilization and planform alteration. Reach-scale geomorphic complexity was characterized using highly detailed surveys of channel morphology, substrate, hydraulics, and habitat units. Breakthrough-curve modeling of conservative bromide (Br - ) and non-conservative nitrate (NO 3 - ) tracer injections characterized transient storage and nitrate uptake along each reach. Longitudinal roughness and flow depth were positively associated with transient storage, which was related to nitrate uptake, thus underscoring the importance of geomorphic influences on stream biogeochemical processes. Additionally, changes in geomorphic characteristics due to temporal discharge variation led to complex responses in nitrate uptake. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The application of geophysical methods, in particular, electrical resistivity measurements, may be useful for monitoring subsurface contamination. However, interpreting geophysical data without additional data and without considering the associated hydrogeochemical processes is challenging since the geophysical response is sensitive to not only heterogeneity in rock properties but also to the saturation and chemical composition of pore fluids. We present an inverse modeling framework that incorporates the simulation of hydrogeochemical processes and time-lapse electrical resistivity data and apply it to various borehole and cross-borehole data sets collected in 2008 near the S-3 Ponds at the U.S. Department of Energy's Oak Ridge Integrated Field Research Challenge site, where efforts are underway to better understand freshwater recharge and associated contaminant dilution. Our goal is to show that the coupled hydrogeochemical-geophysical modeling framework can be used to (1) develop a model that honors all the available data sets, (2) help understand the response of the geophysical data to subsurface properties and processes at the site, and (3) allow for the estimation of petrophysical parameters needed for interpreting the geophysical data. We present a series of cases involving different data sets and increasingly complex models and find that the approach provides useful information about soil properties, recharge-related transport processes, and the geophysical response. Spatial heterogeneity of the petrophysical model can be described sufficiently with two layers, and its parameters can be estimated concurrently with the hydrogeochemical parameters. For successful application of the approach, the parameters of interest must be sensitive to the available data, and the experimental conditions must be carefully modeled.

Description: Results are presented from a large-scale stated preference study designed to estimate the nonmarket benefits for households in England and Wales arising from the European Union Water Framework Directive (WFD). Multiple elicitation methods (a discrete choice experiment and two forms of contingent valuation) are employed, with the order in which they are asked randomly varied across respondents, to obtain a robust model for valuing specified WFD implementation programs applied to all of the lakes, reservoirs, rivers, canals, transitional, and coastal waters of England and Wales. The potential for subsequent policy incorporation and value transfer was enhanced by generating area-based values. These were found to vary from £2,263 to £39,168 per km2 depending on the population density around the location of the improvement, the ecological scope of that improvement, and the value elicitation method employed. While the former factors are consistent with expectations, the latter suggests that decision makers need to be aware of such methodological effects when employing derived values.

Description: Training image-based approaches for stochastic simulations have recently gained attention in surface and subsurface hydrology. This family of methods allows the creation of multiple realizations of a study domain, with a spatial continuity based on a training image (TI) that contains the variability, connectivity, and structural properties deemed realistic. A major drawback of these methods is their computational and/or memory cost, making certain applications challenging. It was found that similar methods, also based on training images or exemplars, have been proposed in computer graphics. One such method, Image Quilting (IQ), is introduced in this paper and adapted for hydrogeological applications. The main difficulty is that Image Quilting was originally not designed to produce conditional simulations and was restricted to 2D images. In this paper, the original method developed in computer graphics has been modified to accommodate conditioning data and 3D problems. This new Conditional Image Quilting method (CIQ) is patch-based, does not require constructing a pattern databases, and can be used with both categorical and continuous training images. The main concept is to optimally cut the patches such that they overlap with minimum discontinuity. The optimal cut is determined using a dynamic programming algorithm. Conditioning is accomplished by prior selection of patches that are compatible with the conditioning data. The performance of CIQ is tested for a variety of hydrogeological test cases. The results, when compared with previous Multiple-point Statistics (MPS) methods, indicate an improvement in CPU time by a factor of at least 50.

Description: Changes in the physical structure of urban streams can occur abruptly due to flashy high flow events and subsequently alter stream processes, including transient storage and nitrate uptake. We examined temporal variability in transient storage and nitrate uptake by exploring the effects of altered physical characteristics resulting from a single high flow event in three reaches of Spring Creek, an urban stream in Fort Collins, Colorado, USA. Study reaches of varying geomorphic and hydraulic characteristics were chosen to represent distinct geomorphic settings in terms of substrate size, sinuosity, bed slope, and degree of rehabilitation and structural controls. We performed detailed physical characterizations and multiple nutrient injections of Br − and NO 3 − to estimate transient storage and nitrate uptake in each reach. A comparison of pre- and post-flood data indicate that transient storage and nitrate uptake are highly context-specific and mediated by interactions between geomorphic setting and flood discharge. In the two reaches that showed significant post-flood increases in transient storage (250% to 350% increases in F med 200 ), the pool-riffle reach exhibited a significant increase in uptake velocity, while the channelized reach did not. In contrast, transient storage decreased post-flood in the third reach containing hydraulic structures. These complex responses likely reflect reach-specific differences in hyporheic vs. in-channel storage. This study shows that repeat injections are necessary to describe nutrient dynamics because transient storage and nitrate uptake can be highly variable over time (showing changes on the order of 100%) due to variation in discharge and geomorphically influential flow events. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The Southern Appalachian Mountains (SAM) are a heavily forested mid-latitude mountain region which provide an ideal location for assessing the suitability of satellite-derived snow maps and explicitly linking atmospheric circulation to the spatial patterns of new snowfall. Although a variety of synoptic-scale circulation regimes contribute to mean annual snowfall, which ranges from roughly 25 cm in the lowest valleys to over 250 cm at the highest elevations, atmospheric circulation processes have largely been absent from efforts seeking to quantify the spatial patterns of new snowfall. In this paper, we examine the suitability of fractional snow cover (FSC) maps from the Moderate Resolution Imaging Spectroradiometer (MODIS) and determine the spatial extent of snowfall according to synoptic-scale circulation. FSC maps are analyzed after 122 snow events from 2006-12 to provide a suitability analysis of MODIS products for use in the SAM. For each event, we calculate FSC distribution, total snow covered area, and compare with available in-situ observations. Results indicate that the SAM presents unique meteorological, physical, and spectral characteristics that are ideal for evaluating the suitability of MODIS for measuring snow cover. Out of 122 observed snow events, 63 are considered suitable for analysis with the FSC maps. The highest FSC values are observed after Gulf/Atlantic Lows and southeastward tracking clipper systems. We conclude that MODIS data can be successfully used to link broader atmospheric circulation processes of snowfall with the spatial patterns of snow cover. This article is protected by copyright. All rights reserved.

Description: Abstract Observatory‐scale data collection efforts allow unprecedented opportunities for integrative, multidisciplinary investigations in large, complex watersheds which can affect management decisions and policy. Through the National Science Foundation‐funded REACH (REsilience under Accelerated CHange) project, in collaboration with the Intensively Managed Landscapes‐Critical Zone Observatory, we have collected a series of multidisciplinary datasets throughout the Minnesota River Basin in south‐central Minnesota, USA, a 43,400 km2 tributary to the Upper Mississippi River. Post‐glacial incision within the Minnesota River valley created an erosional landscape highly responsive to hydrologic change, allowing for transdisciplinary research into the complex cascade of environmental changes that occur due to hydrology and land use alterations from intensive agricultural management and climate change. Datasets collected include water chemistry and biogeochemical data; geochemical fingerprinting of major sediment sources; high resolution monitoring of river bluff erosion; and repeat channel cross‐sectional and bathymetry data following major floods. The data collection efforts led to development of a series of integrative reduced complexity models that provide deeper insight into how water, sediment, and nutrients route and transform through a large channel network and respond to change. These models represent the culmination of efforts to integrate interdisciplinary datasets and science to gain new insights into watershed‐scale processes in order to advance management and decision making. The purpose of this paper is to present a synthesis of the data sets and models, disseminate them to the community for further research, and identify mechanisms used to expand the temporal and spatial extent of short‐term observatory‐scale data collection efforts.