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Researchers from Sweden extrapolated the laboratory results from data collected from mineral weathering rates in the laboratory and in the field, with the field data having lower rates. Data from the Aitik site in northern Sweden was used as a model to investigate the scale-dependence of weathering rates.

This study develops a general quantification framework for consistent intermodel and intercatchment comparison of the nutrient and pollutant mass loading from multiple sources in a catchment area to downstream surface and coastal waters. The framework accounts for the wide spectrum of different transport pathways and travel times through the subsurface (soil, groundwater, sediment) and the linked surface (streams, lakes, wetlands) water systems of a catchment. The account is based on key flow partitioning and mass delivery fractions, which can be quantified differently by different flow and transport and reaction models. The framework application is exemplified for two Swedish catchment cases with regard to the transport of phosphorus and of a generic attenuating solute. The results show essential differences in model quantifications of transport pathways and temporal spreading, with important implications for our understanding of cause and effect in the catchment-scale nutrient and pollutant loading to downstream waters. [ABSTRACT FROM AUTHOR]

Environmental policies for water quality and ecosystem management do not commonly require explicit stochastic accounts of uncertainty and risk associated with the quantification and prediction of waterborne pollutant loads and abatement effects. In this study, we formulate and investigate a possible environmental policy that does require an explicit stochastic uncertainty account We compare both the environmental and economic resource allocation performance of such an uncertainty-accounting environmental policy with that of deterministic, risk-prone and risk- averse environmental policies under a range of different hypothetical, yet still possible, scenarios. The comparison indicates that a stochastic uncertainty-accounting policy may perform better than deterministic policies over a range of different scenarios. Even in the absence of reliable site-specific data, reported literature values appear to be useful for such a stochastic account of uncertainty. [ABSTRACT FROM AUTHOR]

We simulate and analyze long-term dynamics of coastal nitrogen (N) loading and the inland source changes and processes that may have determined its development over the past 60-year period and may govern its possible future responses to various N source management scenarios. With regard to processes, the results show that average basin-scale N delivery fractions to the coast may not be representative of the coastal impacts of either diffuse or point inland sources. The effects of inland source changes may be greatly redistributed in space-time and delayed by slow N transport and mass transfer processes in the subsurface water system of coastal catchments. Extrapolation of current N transport-attenuation conditions for quantification of future abatement effects may therefore be misleading if the extrapolation models do not realistically represent delayed long-term influences of slow subsurface processes. With regard to policy, the results show that and why national Swedish and international Baltic Sea region policies for coastal N load abatement may be difficult or impossible to achieve by inland source abatement only. Large mitigation of both point and diffuse sources may be necessary to achieve targeted coastal N load reductions fast and maintain them also in the long term. [ABSTRACT FROM AUTHOR]

Modeling of the spatial distribution of nitrogen transport and attenuation from various inland sources and along different hydrological pathways to coastal waters is needed for relevant decisions on effective allocation of measures for coastal nitrogen load abatement. We identify, classify, and quantify uncertainties associated with main discrepancies between spatial process representations in different catchment-scale nitrogen transport-attenuation models. The results show important model differences, indicating scientific disagreement on the realistic spatial process understanding, representation, and quantification in nitrogen transport-attenuation modeling. By further developing solutions for economic optimization of spatially differentiated nitrogen source abatement in coastal catchments, we find this disagreement to considerably affect the economic efficiency of coastal nitrogen load reduction. It may also lead to stakeholder mistrust and conflict and needs to be recognized and handled in environmental policy. [ABSTRACT FROM AUTHOR]

Human water use and anthropogenic water pollution and ecosystem deterioration have increased so much that it is now a strategic challenge to maximize benefits from various possible water uses, white ensuring that basic human needs are met and the environment is protected. We propose and develop a novel use of input-output flow analysis as a relatively simple, compact and powerful tool for quantification of coupled natural and cross-sectoral flows of water, nutrients, and pollutants in catchments. The tool quantifies implications of various environmental regulation and management scenarios for both natural water systems and engineered-economic systems and sectors that use and impact natural waters for meeting human needs. Specific case study application to water and nitrogen flows in the Swedish Norrstrŏm drainage basin indicates considerable nitrogen toad contributions to surface and coastal waters from slow groundwater flow paths and legacies of accumulated nitrogen in subsurface and immobile water pools. This implies that effective nitrogen load abatement cannot focus only on active sources but must also include downstream measures, which can capture and abate nitrogen/pollutant loading from different types of known and yet unknown point and diffuse sources within associated catchments. [ABSTRACT FROM AUTHOR]

Eutrophication problems in coastal and marine waters worldwide emphasize the significance, for the scientific community as well as the whole society, of relevant quantification of catchment-scale nitrogen transport from land to coast. Different catchment-scale nitrogen budget models use, and base management recommendations on, quite different process representations of and spatial resolution approaches to in-stream nitrogen attenuation. We compare three different spatial resolution approaches to modeling nitrogen loss rates in streams of the same drainage basin. Results show that commonly used spatial model aggregation may lead to artificial decrease of calibrated nitrogen loss rates with increasing stream depth (or flow), in addition to any such dependences that may prevail in independently measurable reality. Coastal nitrogen impact predictions and practical management implications of large-scale model aggregation of nitrogen attenuation rates may further differ considerably from those based on rates from finer resolution modeling or independent measurements. [ABSTRACT FROM AUTHOR]

Many environmental problems require assessment of extensive reaction systems within natural subsurface flow systems exhibiting large physical and biogeochemical heterogeneity. We present an approach to couple stochastic advective-reactive modeling of physical solute transport (LaSAR) with the geochemical model PHREEQC for modeling solute concentrations in systems with variable flow velocity and multicomponent reactions. PHREEQC allows for general and flexible quantification of a multitude of linear and nonlinear geochemical processes, while LaSAR efficiently handles field-scale solute spreading in stochastic heterogeneous flow fields. The combined LaSAR- PHREEGC approach requires very modest computational efforts, thereby allowing a large number of reactive transport problems to be readily assessed and facilitating handling of quantifiable uncertainty in environmental model applications. Computational efficiency and explicit handling of field-scale dispersion without introduction of excessive fluid mixing that may impair model results are general advantages of the LaSAR compared with alternative solute transport modeling approaches. The LaSAR-PHREEQC approach is restricted to steady or unidirectional flow fields, and our specific application examples are limited to homogeneous reaction systems without local or transverse dispersion-diffusion, although these are not general methodological limitations. As a comprehensive application example, we simulate the spreading of acid mine drainage in a groundwater focusing on Zn2+ and including relevant major-component geochemistry. Model results show that Zn2+ may be substantially attenuated by both sorption and precipitation, with flow heterogeneity greatly affecting expected solute concentrations downstream of the mine waste deposit in both cases. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the comment made by Richard B. Alexander and colleagues on the article "In-Stream Nitrogen Attenuation: Model-Aggregation Effects and Implications for Coastal Nitrogen Impacts," by A. Darracq and G. Destouni in a 2005 issue.

Eutrophication problems in coastal and marine waters worldwide emphasize the significance, for the scientific community as well as the whole society, of relevant quantification of catchment-scale nitrogen transport from land to coast. Different catchment-scale nitrogen budget models use, and base management recommendations on, quite different process representations of and spatial resolution approaches to in-stream nitrogen attenuation. We compare three different spatial resolution approaches to modeling nitrogen loss rates in streams of the same drainage basin. Results show that commonly used spatial model aggregation may lead to artificial decrease of calibrated nitrogen loss rates with increasing stream depth (or flow), in addition to any such dependences that may prevail in independently measurable reality. Coastal nitrogen impact predictions and practical management implications of large-scale model aggregation of nitrogen attenuation rates may further differ considerably from those based on rates from finer resolution modeling or independent measurements.