Search

Earthen manure storage (EMS) facilities no longer in operation present a risk to the environment, and there is limited guidance to support the planning and implementation of EMS closures. A combined dairy and feedlot in southern Alberta, Canada, had an EMS in operation for about 55 yr. The dairy portion ceased operation in 2015, and the EMS was emptied; however, no specific steps for permanent closure to minimize possible contamination were followed. The objective of this study was to document changes in shallow groundwater quality following an EMS closure. This EMS was already instrumented to assess its effect on the groundwater quality as part of a long-term study prior to closure. Eight groundwater monitoring wells were installed 2-38 m from the EMS in up- and downgradient positions in 2010 and 2011. Groundwater samples were collected about three times annually prior to and for 4 yr after the EMS closure and were analyzed for NO3 -N, NH3 -N, and Cl- . Wells screened at more than 8 m deep were not affected by the EMS prior to or after closure. However, in shallower wells, groundwater NO3 -N concentration increased to a maximum 3 yr after closure (in 2018) and then decreased afterward. In a shallow well 40 m downgradient from the EMS, the NO3 -N concentrations decreased from 31 mg L-1 in 2015 to 5 mg L-1 in 2019, and the Cl- concentration decreased from 64 to 53 mg L-1 , suggesting the contamination plume had dispersed. However, the EMS was still a source of contamination because high concentrations of NO3 -N (0.05-40 mg L-1 ) and Cl- (43-862 mg L-1 ) were present in wells adjacent to the EMS 4 yr after closure.

Leaching of nitrate (NO3-) from animal waste or fertilisers at agricultural operations can result in NO3- contamination of groundwater, lakes, and streams. Understanding the sources and fate of nitrate in groundwater systems in glacial sediments, which underlie many agricultural operations, is critical for managing impacts of human food production on the environment. Elevated NO3- concentrations in groundwater can be naturally attenuated through mixing or denitrification. Here we use isotopic enrichment of the stable isotope values of NO3- to quantify the amount of denitrification in groundwater at two confined feeding operations overlying glacial sediments in Alberta, Canada. Uncertainty in δ15NNO3 and δ18ONO3 values of the NO3- source and denitrification enrichment factors are accounted for using a Monte Carlo approach. When denitrification could be quantified, we used these values to constrain a mixing model based on NO3- and Cl− concentrations. Using this novel approach we were able to reconstruct the initial NO3−N concentration and NO3-N/Cl- ratio at the point of entry to the groundwater system. Manure filtrate had total nitrogen (TN) of up to 1820 mg L−1, which was predominantly organic N and NH3. Groundwater had up to 85 mg L−1 TN, which was predominantly NO3-. The addition of NO3- to the local groundwater system from temporary manure piles and pens equalled or exceeded NO3- additions from earthen manure storages at these sites. On-farm management of manure waste should therefore increasingly focus on limiting manure piles in direct contact with the soil and encourage storage in lined lagoons. Nitrate attenuation at both sites is attributed to a spatially variable combination of mixing and denitrification, but is dominated by denitrification. Where identified, denitrification reduced agriculturally derived NO3- concentrations by at least half and, in some wells, completely. Infiltration to groundwater systems in glacial sediments where NO3- can be naturally attenuated is likely preferable to off-farm export via runoff or drainage networks, especially if local groundwater is not used for potable water supply.

The potential effect of manure management from livestock production on groundwater quality is an issue of concern. Groundwater sampling from a regional transect in southern Alberta, Canada, was conducted to determine changes in groundwater quality with time. The study area has extensive irrigation and a high density of confined feeding operations. Nitrate-N (NO3−-N) and chloride (Cl−) concentration data from 23 groundwater-study wells were evaluated from 1994 to 2014. Twelve of these wells were water-table wells and 11 were piezometers. Of the 23 wells, 14 had significant temporal trends (increasing or decreasing) for NO3−-N and/or Cl− concentrations. On a regional basis, NO3−-N increased slightly with time while Cl− changed very little, suggesting that the effects of agricultural activities on regional groundwater quality have generally remained constant. However, concentration changes occurred on a smaller scale. Shallow groundwater in coarse-textured soils is at a relatively higher risk of contamination than groundwater in fine-textured soils, especially in locations where intensive agricultural activities occur.

During the past 50 years, winter temperatures have risen more rapidly than in summer in northern high latitudes. However, there are relatively few meteorological stations in these areas, and a better characterization of this trend is needed. This article investigates whether satellite microwave brightness temperature can be used as an indicator of near-surface air temperature over snow. The Helsinki University of Technology (HUT) snow emission model is used to generate a dry snow emissivity relationship between 19 and 37 GHz under the assumption that the air–snow interface temperatures and air temperatures (Tair ) are similar. This relationship allows the development of a near-surface air temperature retrieval model. A second empirical linear correction is also applied to reduce the residual observed bias. The comparison between retrieved near-surface air temperature and in situ air temperature for the Canadian northern regions shows a significant correlation (R 2 of 0.76) but with a root mean square erro...

Climate warming is the focus of several studies where the soil temperature plays an essential role as a state variable for the surface energy balance of the Earth. Many methods have been developed to determine summer surface temperature, but the determination in presence of snow is an ill-conditioned problem for microwave techniques because snow changes the emissivity of the surface. This project aims to improve the estimation of soil temperature, within the top 5 cm of the ground, under the snowpack using passive microwave remote sensing. Results show the potential of the passive microwave brightness temperature inversion at 10 GHz (derived from the Advanced Microwave Scanning Radiometer—Earth Observing System, AMSR-E) for the estimation of soil temperature using a physical multilayer snow–soil model (SNTHERM) coupled with a snow emission model (HUT). The snow model is driven with meteorological measurements from ground-based stations as well as data generated from reanalysis. The proposed iterative retrieval method minimizes the difference between the simulated and measured brightness temperature using the soil temperature as a free parameter given by SNTHERM. Results are validated against ground-based measurements at several sites across Canada through several winter seasons. The overall root mean square error and bias in the retrieved soil temperature is respectively 3.29 K and 0.56 K, lower than the error derived from the snow–soil model without the use of remote sensing. The accuracy in detection of frozen/unfrozen soil under the snowpack is 78%, which is improved up to 81% if the spring melting period is not considered. This original procedure constitutes a very promising tool to characterize the soil (frozen or not) under snow cover, as well as its evolution in northern remote locations where measurements are unavailable.

Possible climate warming in northern latitudes will affect stream flow in watersheds dominated by snowmelt. It is important to detect early snowmelt conditions for applications to flood forecasting and monitoring fresh water stored in snow cover. This letter presents a study to demonstrate the potential of combined active and passive microwave spaceborne observations for monitoring global to regional snow cover on a daily basis. The proposed approach uses the temporal gradient of two parameters: 1) the Ku-band QuikSCAT scatterometer backscattering coefficient variation for snow wetness detection and 2) a dual-frequency emissivity index (Δϵt) derived from the Defense Meteorological Satellite Program Special Sensor Microwave Imager brightness temperatures for snow line detection. This approach takes into account the land cover derived from satellite data on a pixel-by-pixel basis. The evolution of the backscatter and Δϵt signatures throughout the winter-spring seasonal snow cycle is compared with in situ snow and air temperature measurements and with the snow-cover maps derived from high-resolution satellite data over Eastern Canada. The results show the high potential of this approach for historical analysis, as well as for day-to-day prospective investigation (forecasting).

This work was designed to analyze the hydrogeological behavior of an alluvial aquifer in the River Mojotoro basin site in the Province of Salta, Argentina. The study area presents coarse-grained sediments with high infiltration capacity. The hydraulic conductivity field is affected by the physical heterogeneity of the medium and a geostatistical method, kriging, was used to construct this field from local measurements. The groundwater flow velocity field is computed using a hybrid mixed finite-element method and small variations in the flow directions were determined. Given the existence of a point source of chloride in the region under study, the spatial distribution of the generated plume in the saturated zone is analyzed. The advection-diffusion equation describing the transport of chloride in vertical and horizontal cross-sectional planes of the aquifer is discretized employing a method of characteristics combined with a mixed finite-element procedure, which provides an efficient method to eliminate spurious numerical oscillations and handle the convective term in the equation. The migration of chloride shows patterns, which are affected by the litologic heterogeneities of the aquifer and the regional groundwater flow.

Snow cover plays a key role in the climate system by influencing the transfer of energy and mass between the soil and the atmosphere. In particular, snow water equivalent (SWE) is of primary importance for climatological and hydrological processes and is a good indicator of climate variability and change. Efforts to quantify SWE over land from spaceborne passive microwave measurements have been conducted since the 1980s, but a more suitable method has yet to be developed for hemispheric-scale studies. Tools such as snow thermodynamic models allow for a better understanding of the snow cover and can potentially significantly improve existing snow products at the regional scale. In this study, the use of three snow models [SNOWPACK, CROCUS, and Snow Thermal Model (SNTHERM)] driven by local and reanalysis meteorological data for the simulation of SWE is investigated temporally through three winter seasons and spatially over intensively sampled sites across northern Québec. Results show that the SWE simulations are in agreement with ground measurements through three complete winter seasons (2004/05, 2005/06, and 2007/08) in southern Québec, with higher error for 2007/08. The correlation coefficients between measured and predicted SWE values ranged between 0.72 and 0.99 for the three models and three seasons evaluated in southern Québec. In subarctic regions, predicted SWE driven with the North American Regional Reanalysis (NARR) data fall within the range of measured regional variability. NARR data allow snow models to be used regionally, and this paper represents a first step for the regionalization of thermodynamic multilayered snow models driven by reanalysis data for improved global SWE evolution retrievals.

Este trabajo se refiere al modelado del flujo subterraneo y la simulacion del transporte de contaminantes en formaciones porosas saturadas. La elaboracion de un modelo matematico que describa esta situacion no solo es util para representar el estado actual de contaminacion sino para realizar un pronostico hacia el futuro. La metodologia utilizada se basa en la observacion, teorizacion y simulacion que se puede obtener en geofisica vinculando las distintas posibilidades que brinda la interrelacion de respuestas reales del comportamiento hidrologico y la matematica aplicada que proporciona la estructura logica para descifrar los efectos individuales de los fenomenos fisicos generales. La tecnica numerica TVD y el metodo iterativo mixto de caracteristicas fueron empleados para la simulacion de transporte bidimensional de contaminantes. Con el objetivo de comparar ambos metodos se planteo un caso sintetico de migracion de contaminante conservativo (cloruro) a partir de una fuente continua y puntual ubicada en la zona saturada.