Soil saturation is known to be of crucial importance to denitrification and other nitrogen cycling processes within the riparian zone. Since denitrification potential generally increases towards the soil surface, water table elevation can control the degree to which nitrate reduction is optimised. Given their topographic location and sedimentary structure, most floodplains are characterised by high water tables. However, detailed field data on water table levels, hydraulic gradients and flow patterns within the riparian zone are generally lacking. This paper presents data collected as part of a pan-European study of nitrate buffer zones, the Nitrogen Control by Landscape Structures in Agricultural Environments project (NICOLAS). An identical experimental design was employed at each site, allowing riparian zone hydrology and nitrogen cycling processes to be explored across a wide range of temperate climates; only the hydrological data are discussed here. A grid of dipwells at 10-metre spacing was installed at each site and manual measurements made at least once a month for a minimum of one year. In addition, at least one dipwell in each grid was monitored continuously using a data logger. All the riparian zones studied displayed a clear annual cycle of water table elevation, although other factors seemed equally important in influencing the range of variation. Where the riparian zone was flat, the water level in the adjoining river or lake proved more significant in controlling water table levels within the riparian zone than was originally anticipated. q

Abstract:Nutrient fluxes from developed catchments are often a significant factor in the declining water quality and ecological functioning in estuaries. Determining the relative contributions of surface water and groundwater discharge to nutrient-sensitive estuaries is required because these two pathways may be characterized by different nutrient concentrations and temporal variability, and may thus require different remedial actions. Quantifying the volumetric discharge of groundwater, which may occur via diffuse seepage or springs, remains a significant challenge. In this contribution, the total discharge of freshwater, including groundwater, to two small nutrient-sensitive estuaries in Prince Edward Island (Canada) is assessed using a unique combination of airborne thermal infrared imaging, direct discharge measurements in streams and shoreline springs, and numerical simulation of groundwater flow. The results of the thermal infrared surveys indicate that groundwater discharge occurs at discrete locations (springs) along the shoreline of both estuaries, which can be attributed to the fractured sandstone bedrock aquifer. The discharge measured at a sub-set of the springs correlates well with the area of the thermal signal attributed to each discharge location and this information was used to determine the total spring discharge to each estuary. Stream discharge is shown to be the largest volumetric contribution of freshwater to both estuaries (83% for Trout River estuary and 78% for McIntyre Creek estuary); however, groundwater discharge is significant at between 13% and 18% of the total discharge. Comparison of the results from catchment-scale groundwater flow models and the analysis of spring discharge suggest that diffuse seepage to both estuaries comprises only about 25% of the total groundwater discharge. The methods employed in this research provide a useful framework for determining the relative volumetric contributions of surface water and groundwater to small estuaries and the findings are expected to be relevant to other fractured sandstone coastal catchments in Atlantic Canada.

Baseflow separation is important for obtaining critical parameters for hydrological models. As measuring the baseflow component directly is difficult, various analytical and empirical baseflow separation methods have been developed and tested. The recursive digital filter (RDF) method is commonly used for baseflow separation due to its simplicity and low data requirement. However, parameters used in the RDF method are often determined arbitrarily, resulting in high uncertainty of the estimated baseflow rate. A more accurate method is the conductivity mass balance (CMB) method, which is established based on the differences in physical processes between baseflow and surface runoff. In this research, the output of the CMB method was used to calibrate the parameters of an RDF model, and the calibrated RDF model was used to estimate monthly, seasonal and annual baseflow rate and baseflow index for the past 19 years using streamflow discharge records. The characteristics of the baseflow hydrographs were found to be consistent with the hydrological and hydrogeological conditions of the research area. Research results indicated that the accuracy of the RDF model has been greatly enhanced after being calibrated with the CMB method so that the RDF model can provide more reliable baseflow separation results for a long‐term study. Copyright © 2012 John Wiley & Sons, Ltd.

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Abstract. In inland settings, groundwater discharge thermally modulates receiving surface water bodies and provides localized thermal refuges; however, the thermal influence of intertidal springs on coastal waters and their thermal sensitivity to climate change are not well studied. We addressed this knowledge gap with a field- and model-based study of a threatened coastal lagoon ecosystem in southeastern Canada. We paired analyses of drone-based thermal imagery with in situ thermal and hydrologic monitoring to estimate discharge to the lagoon from intertidal springs and groundwater-dominated streams in summer 2020. Results, which were generally supported by independent radon-based groundwater discharge estimates, revealed that combined summertime spring inflows (0.047 m3 s−1) were comparable to combined stream inflows (0.050 m3 s−1). Net advection values for the streams and springs were also comparable to each other but were 2 orders of magnitude less than the downwelling shortwave radiation across the lagoon. Although lagoon-scale thermal effects of groundwater inflows were small compared to atmospheric forcing, spring discharge dominated heat transfer at a local scale, creating pronounced cold-water plumes along the shoreline. A numerical model was used to interpret measured groundwater temperature data and investigate seasonal and multi-decadal groundwater temperature patterns. Modelled seasonal temperatures were used to relate measured spring temperatures to their respective aquifer source depths, while multi-decadal simulations forced by historic and projected climate data were used to assess long-term groundwater warming. Based on the 2020–2100 climate scenarios (for which 5-year-averaged air temperature increased up to 4.32∘), modelled 5-year-averaged subsurface temperatures increased 0.08–2.23∘ in shallow groundwater (4.2 m depth) and 0.32–1.42∘ in the deeper portion of the aquifer (13.9 m), indicating the depth dependency of warming. This study presents the first analysis of the thermal sensitivity of groundwater-dependent coastal ecosystems to climate change and indicates that coastal ecosystem management should consider potential impacts of groundwater warming.