Examining the Contributions of Glacial Till Water to Storm Runoff using Two- and Three-Component Hydrograph Separations

Two- and three-component hydrograph separations based on 18O and dissolved silica are used to investigate the contributions of glacial till water to the storm runoff of a headwater stream on the Canadian Shield. Two-component isotopic hydrograph separations based on 18O indicate that the volume and flux of event water could be accounted for by direct precipitation onto saturated areas. Three-component hydrograph separations distinguish between event water, preevent soil water, and preevent till water. These results show that groundwater flow through coarse-textured glacial tills can make a significant contribution to stream discharge during runoff events (29 and 62% in this study) despite the lower hydraulic conductivities of the tills compared to the overlying soils. The three-component hydrograph separations also demonstrate that the relative contributions of preevent soil water and preevent till water changed during one runoff event such that the average water chemistry of the preevent component varied during the event. Two-component hydrograph separations using dissolved silica indicate that seasonal changes in the till water contributions also occur and are related to groundwater levels. Measurements of vertical hydraulic gradients during runoff events indicate that the increase in flow from the tills to the soils is minimal and cannot account for the large and rapid increase in till water flow into the stream. Till water that has discharged to the soils prior to the event is probably being flushed from the soils into the stream during events

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Half of the world's forest is in boreal and sub-boreal ecozones, containing large carbon stores and fluxes. Carbon lost from headwater streams in these forests is underestimated. We apply a simple stable carbon isotope idea for quantifying the CO2 loss from these small streams; it is based only on in-stream samples and integrates over a significant distance upstream. We demonstrate that conventional methods of determining CO2 loss from streams necessarily underestimate the CO2 loss with results from two catchments. Dissolved carbon export from headwater catchments is similar to CO2 loss from stream surfaces. Most of the CO2 originating in high CO2 groundwaters has been lost before typical in-stream sampling occurs. In the Harp Lake catchment in Canada, headwater streams account for 10% of catchment net CO2 uptake. In the Krycklan catchment in Sweden, this more than doubles the CO2 loss from the catchment. Thus, even when corrected for aquatic CO2 loss measured by conventional methods, boreal and sub-boreal forest carbon budgets currently overestimate carbon sequestration on the landscape

A diagnostic approach to constraining flow partitioning in hydrologic models using a multiobjective optimization framework

© American Geophysical Union: Shafii, M., Basu, N., Craig, J. R., Schiff, S. L., & Van Cappellen, P. (2017). A diagnostic approach to constraining flow partitioning in hydrologic models using a multiobjective optimization framework. Water Resources Research, 53(4), 3279–3301. https://doi.org/10.1002/2016WR019736Hydrologic models are often tasked with replicating historical hydrographs but may do so without accurately reproducing the internal hydrological functioning of the watershed, including the flow partitioning, which is critical for predicting solute movement through the catchment. Here we propose a novel partitioning-focused calibration technique that utilizes flow-partitioning coefficients developed based on the pioneering work of L'vovich (1979). Our hypothesis is that inclusion of the L'vovich partitioning relations in calibration increases model consistency and parameter identifiability and leads to superior model performance with respect to flow partitioning than using traditional hydrological signatures (e.g., flow duration curve indices) alone. The L'vovich approach partitions the annual precipitation into four components (quick flow, soil wetting, slow flow, and evapotranspiration) and has been shown to work across a range of climatic and landscape settings. A new diagnostic multicriteria model calibration methodology is proposed that first quantifies four calibration measures for watershed functions based on the L'vovich theory, and then utilizes them as calibration criteria. The proposed approach is compared with a traditional hydrologic signature-based calibration for two conceptual bucket models. Results reveal that the proposed approach not only improves flow partitioning in the model compared to signature-based calibration but is also capable of diagnosing flow-partitioning inaccuracy and suggesting relevant model improvements. Furthermore, the proposed partitioning-based calibration approach is shown to increase parameter identifiability. This model calibration approach can be readily applied to other models. Plain Language Summary Hydrologic models are often tasked with replicating historical hydrographs but may do so without accurately reproducing the internal hydrological functioning of the watershed, including the flow partitioning between low and high flows, which is critical for predicting solute movement through the catchment. Here we propose a novel model calibration framework that utilizes an empirical understanding about flow partitioning developed by L'vovich (1979) to constrain the outcomes of watershed models. Our hypothesis is that this approach increases model consistency leads to superior model performance. This method is also capable of diagnosing model structural errors (in flow partitioning) and suggesting relevant model improvements. Overall, this work is a step toward getting the right answer from hydrologic model for the right reasons.NSERC Strategic Partnership grant [STPGP-447692-2013]Canada Excellence Research Chair in Ecohydrology in the Department of Earth and Environmental Sciences at University of Waterlo

Geochemistry of Municipal Waste in Coastal Waters

Prepared with the support of Marine Ecosystems Analysis Program of the National Oceanic and Atmospheric Administration.Introduction: As we mine primary ores at an increasing rate, as we synthesize more exotic compounds in greater quantities, as we produce expanding heaps of waste, as we reroute rivers through our faucets, we are becoming an important and sometimes a dominant agent of the global geochemical cycle. Disposal of municipal wastes is a key process in this anthropic part of the elemental fluxes, for a municipal sewage system is a giant funnel which brings in one place at each instant the end products of much of the dispersed consumptive activities of a whole community. In addition to its net contribution to the flux of natural elements and to the exotic nature of some of its constituents, it is this increasingly prevalent concentration process that gives human waste its unique position in the elemental economy of the planet. Lest we should be too conceited, even in our ability to pollute, the laws of nature must have their way. Ultimately all elements in the sea must be controlled by the biogeochemical processes that govern their oceanic cycles. The question posed by the practice of municipal waste disposal into the ocean is then principally one of rates: are natural biogeochemical processes in the oceans fast enough to "assimilate" human waste? Are the dispersive and degradative mechanisms suitably rapid to maintain the concentration of all potential toxicants at acceptably low concentrations? Are the ecological processes sufficiently dynamic to buffer the impact of concentrated elemental loads, to adapt to the presence of new chemical constituents? These questions can be asked on various geographical scales, from local to global, and on various time scales from hours to centuries. On the whole we are still quite ignorant of the functioning of oceanic systems; we do not comprehend sufficiently many of the processes that govern the fate of waste constituents; we cannot answer some of our basic questions. Yet, we are in the process of learning a great deal. This chapter is an attempt at organizing some of the key known facts on the biogeochemistry of waste in coastal waters, at developing a conceptual framework for research and decision making. There are on the order of ten thousand chemical constituents in wastewaters, only about a hundred of which we know anything about. It appears that our sole hope is to develop general principles to provide, in the long run, some of the necessary answers. Municipal wastewaters are a varied lot. Although domestic sewage has a fairly uniform composition throughout the country, the industrial wastes that are often added to it do not. Metal finishing plants contribute high concentrations of some metallic compounds; chemical manufacturing processes release highly specific sets of organic constituents. In cities with combined sewers, urban storm water runoff, with its own characteristic composition, is included in the municipal sewer system. Also varied are the levels of treatment and the methods of disposal. A few cities still dispose of their raw sewage while others have added tertiary treatment to their systems. Efficient outfalls with diffusers are used in some places to carry the effluents far offshore and dilute it effectively; in many others, wastewaters are released close to shore with inefficient mixing. Barge dumping of sludge is prevalent in many areas. Just as diverse are the hydrodynamic and hydrological characteristics of the receiving waters: confined bays, harbors and estuaries in some places, open coastline in others; rapidly increasing water depth offshore on one coast, extended continental margins on the other. Current and tidal regimes which vary with time and location result in widely different waste dilution and transport processes. All this variability in effluent composition, in initial mixing, and in short and long term transport processes affects to a large degree the fate of the waste constituents. At this point, it would be a hopeless task to attempt to cover all combinations of these, to consider the problem of disposal of all types of municipal wastes in all types of receiving waters. By a fortune of sorts, one is quite limited by the available information. We have made no attempt in this chapter to be exhaustive; rather we have concentrated on these systems for which extensive data were available. In this way it is hoped that a self coherent picture will be obtained from which one may draw information to be applied to other situations. However, major caveats are clearly in order: i) the available information concerns almost exclusively the major urban centers; in some instances it may be of little relevance to small or medium size communities; ii) the Southern California Bight--which is by no means typical--has been the locus of the most intensive and extensive research efforts on the geochemistry of waste. As such it provided the data for much of this chapter. (For convenient reference on names and locations, a map of the major Southern California outfalls is provided in Fig. 0-1). One should keep in mind these demographic and geographical biases

Epilithon isotope composition as an environmental archive in rivers receiving wastewater : the case of the Grand River, Ontario, Canada

Epilithon is a complex community of autotrophic and heterotrophic organisms that includes inert, organic and inorganic material and is attached to the surface of submersed rocks. Water samples collected in the Grand River (southwestern Ontario) in April 2011 showed that ammonium concentrations decreased downstream, whereas nitrate varied, largely dependent on weather conditions (concentrations of both chemical species were higher during winter). Epilithon δ15N-TN downstream from the Kitchener wastewater treatment plant oscillated between 0.4 to 23.2‰, and δ13C-TC around -27‰. The wastewater treatment plant effluent consisted of δ15N-NO3- between 12 and 16‰, with a decreasing trend as it traveled downstream; δ15N-NH4+ became enriched downstream (as high as 31‰). Average values for δ13C-DIC were -10.1‰ and δ13C-DOC -26.8‰. It is proposed that the nitrogen and carbon isotope composition of epilithon could be used as a short- or medium-term environmental archive, as it reflects in-stream processes, such as ammonia oxidation, in a river impacted by treated wastewater. The interpretation provided here was limited due to the ample range of events and potential sources, specifically when the nitrogen isotopic composition of nitrate and ammonium was similar. Epilithon is easily collected, processed and analysed and proved to be valuable tool to describe changes in river and stream geochemistry.L’épilithon est une communauté complexe d'organismes autotrophes et hétérotrophes, qui vit conjointement avec des matériaux organiques et inorganiques attachés à la surface de rochers submergés. Des échantillons d’eau collectés dans la rivière Grand (sud de l’Ontario) en avril 2011 ont montré une diminution des concentrations d'ammonium vers l’aval, alors que les concentrations de nitrate variaient, principalement en fonction des conditions météorologiques (les concentrations des deux espèces chimiques furent plus élevées pendant l'hiver). La composition isotopique de l’épilithon en aval de l’usine de traitement des eaux usées a varié entre 0,4 et 23,2 ‰ pour l’azote ((d15N-TN) alors que pour le carbone (d13C-TC) la valeur était autour de -27 ‰. L'effluent de l'usine de traitement des eaux usées montrait des valeurs de δ15N-NO3- entre 12 et 16 ‰, avec une tendance à la baisse vers l'aval; les valeurs pour δ15N-NH4+ avait une tendance à augmenter vers l’aval (aussi élevé que 31 ‰). Les valeurs moyennes de δ13C pour le carbone inorganique étaient de 10,1 ‰ et celles pour le carbone organique (δ13C-DOC) étaient de -26,8 ‰. On propose que la composition isotopique de l’épilithon puisse être utilisée comme archive de l'environnement à court ou à moyen terme, étant donné que l’épilithon reflète les processus ayant lieu en amont, comme l’oxydation de l'ammoniac, dans une rivière touchée par le rejet d’eaux usées. Donc, δ15N-TN et δ13C-TC pourraient être utilisés comme un indicateur environnemental à court terme pour les rivières touchées par l’activité humaine, comme constaté dans la rivière Grand. L’interprétation des données actuelles était limitée en raison de la grande gamme de sources potentielles, en particulier lorsque les compositions isotopiques de l’azote étaient similaires pour le nitrate et l’ammonium. L'épilithon est facile à recueillir, à traiter et à analyser et il s'est révélé un outil précieux pour décrire les changements géochimiques se produisant dans la rivière

Large carbon dioxide fluxes from headwater boreal and sub-boreal streams

Half of the world's forest is in boreal and sub-boreal ecozones, containing large carbon stores and fluxes. Carbon lost from headwater streams in these forests is underestimated. We apply a simple stable carbon isotope idea for quantifying the CO2 loss from these small streams; it is based only on in-stream samples and integrates over a significant distance upstream. We demonstrate that conventional methods of determining CO2 loss from streams necessarily underestimate the CO2 loss with results from two catchments. Dissolved carbon export from headwater catchments is similar to CO2 loss from stream surfaces. Most of the CO2 originating in high CO2 groundwaters has been lost before typical in-stream sampling occurs. In the Harp Lake catchment in Canada, headwater streams account for 10% of catchment net CO2 uptake. In the Krycklan catchment in Sweden, this more than doubles the CO2 loss from the catchment. Thus, even when corrected for aquatic CO2 loss measured by conventional methods, boreal and sub-boreal forest carbon budgets currently overestimate carbon sequestration on the landscape

Proper interpretation of dissolved nitrous oxide isotopes, production pathways, and emissions requires a modelling approach.

Stable isotopes ([Formula: see text]15N and [Formula: see text]18O) of the greenhouse gas N2O provide information about the sources and processes leading to N2O production and emission from aquatic ecosystems to the atmosphere. In turn, this describes the fate of nitrogen in the aquatic environment since N2O is an obligate intermediate of denitrification and can be a by-product of nitrification. However, due to exchange with the atmosphere, the [Formula: see text] values at typical concentrations in aquatic ecosystems differ significantly from both the source of N2O and the N2O emitted to the atmosphere. A dynamic model, SIDNO, was developed to explore the relationship between the isotopic ratios of N2O, N2O source, and the emitted N2O. If the N2O production rate or isotopic ratios vary, then the N2O concentration and isotopic ratios may vary or be constant, not necessarily concomitantly, depending on the synchronicity of production rate and source isotopic ratios. Thus prima facie interpretation of patterns in dissolved N2O concentrations and isotopic ratios is difficult. The dynamic model may be used to correctly interpret diel field data and allows for the estimation of the gas exchange coefficient, N2O production rate, and the production-weighted [Formula: see text] values of the N2O source in aquatic ecosystems. Combining field data with these modelling efforts allows this critical piece of nitrogen cycling and N2O flux to the atmosphere to be assessed

Concentrations of 3 artificial sweeteners in the Grand River.

<p>Acesulfame (a), saccharin (b) and cyclamate (c) concentrations in the Grand River on three sampling dates; Jun 2007 (blue diamonds), Sep 2007 (red squares), Apr 2009 (green triangles). Samples plotted at y  =  “0” have concentrations less than the minimum detection limit.</p

Summary of published data on the concentration of artificial sweeteners measured in freshwater surface waters (streams and lakes) and the data from the Grand River.

<p>n  =  the number of samples; does not include our measurements in the WWTP plume.</p><p></p><p>Blank cells indicate that the parameter was not reported.</p>*<p>Maximum value reported.</p>†<p>About 50% of flow is derived from wastewater sources.</p