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The effectiveness of measures to mitigate nitrate concentrations in surface and groundwater depends not only on their suitability for reducing nitrate leaching, but also on characteristics of groundwater transport that may cause a lag in achieving recovery. The recovery of a catchment within a Nitrate Vulnerable Zone in the east of Scotland has been assessed using a combined monitoring and modelling approach. Understanding of the dominant hydrological processes was developed through a programme of monitoring of surface and groundwater bodies. Age dating of groundwater samples, using dissolved atmospheric trace gases (CFCs and SF6) underpinned the conceptualisation of groundwater transport and a lumped dispersion model was applied to the data to estimate mean solute transit times. High spatial variability in the groundwater dating made it difficult to estimate catchment means, but the range was estimated to lie between 15 and 60 years. A catchment hydrology and nitrate model was used to explore the effect of simple changes in land management on reducing nitrate concentrations, as well as associated time scales of recovery. The study has helped improve understanding of the role of groundwater in catchment recovery and given an indication of the scale of agricultural changes required to achieve different levels of pollution mitigation. [ABSTRACT FROM AUTHOR]

Better knowledge of spatial and temporal delivery of dissolved organic carbon (DOC) in small catchments is required to understand the mechanisms behind reported long-term changes in C fluxes from some peatlands. We monitored two storms with contrasting seasons and antecedent conditions in a small upland UK moorland catchment. We examined DOC concentrations and specific UV absorbance (SUVA at 285 nm), together with solute concentrations required to undertake end-member mixing analyses to define dominant flow paths contributing to stream flow. This was combined with laboratory soil-solution equilibrations. We aimed to resolve how seasonal biogeochemical processing of DOC and flowpath changes in organo-mineral soils combine to affect DOC exported via the stream. An August storm following a dry period gave maximum DOC concentration of 10mg l-1. Small DOC:DON ratios (16-28) and SUVA (2.7-3.6 l mg-1 m-1) was attributed to filtration of aromatic compounds associated with up to 53% B horizon flow contributions. This selective filtration of high SUVA DOC was reproduced in the experimental batch equilibration system. For a November storm, wetter antecedent soil conditions led to enhanced soil connectivity with the stream and seven times greater DOC stream-load (maximum concentration 16mg l-1). This storm had a 63% O horizon flow contribution at its peak, limited B horizon buffering and consequently more aromatic DOC (SUVA 3.9-4.5 l mg-1 m-1 and DOC:DON ratio 35-43). We suggest that simple mixing of waters from different flow paths cannot alone explain the differences in DOC compositions between August and November and biogeochemical processing of DOC is required to fully explain the observed stream DOC dynamics. This preliminary evidence is in contrast to other studies proposing hydrological controls on the nature of DOC delivered to streams. Although our study is based only on two storms of very different hydrological and biogeochemical periods, this should promote wider study of DOC biogeochemical alteration in headwaters so that this be better incorporated in modelling to predict the impacts of changes in DOC delivery to, and fate in, aquatic systems. [ABSTRACT FROM AUTHOR]

The article focuses on the study regarding the transit time distributions (TTDs) of conceptual hydrological and tracer transport model, storage residence time and mixing (STREAM), applied to a catchment of the Lunan Water in Scotland. It says that daily precipitation and stream water samples were examined for isotope content. It reveals that the model TTDs do not conform to any statistical function and their characteristics could be altered depending on how the model is set up.

The article presents a study which aims to develop rainfall-runoff models for conceptualization of hydrologic processes in upland watersheds by multi-criteria calibration and tracers. It mentions that the study was conducted in Girnock Burn, a stream in River Dee in Scotland. Model calibration was used to evaluate efficiency of proposed runoff models. Moreover, analysis of Model I, II and III runoff models shows that Model II represents well the hydrologic conditions of Girnock.

The article presents a study on the isotope hydrology of a set of nested sub-catchments in the north-east of Scotland to evaluate the mixing processes and residence times of water in the catchments. It states that hydrochemical mixing analyses indicated that groundwater contributes between 62 and 90% of the streamflow in all sub-catchments, while model analysis demonstrated that the δ18O in stream water is indicative of a highly mixed system in which near surface runoff appears to be mixed with groundwater, within the soil profile, before being released from the catchment.

The author focuses on the impact of technological-driven improvements in data collection methods on the development of hydrology as a geoscience. Emerging issues regarding the new approaches to data collection aid process conceptualization are discussed. It mentions the ability of light detecting and ranging (LiDAR) to resolve catchment land surfaces scale of a few centimeters in Data Traffic Management System (DTMS) and real-time characterization of inputs in weather radar. Information on the model-guided data collection and mining existing data sets is presented.

The authors comment on the conceptualization process in catchment hydrology. An overview of the latest progress in process conceptualization is provided. The authors suggest that, despite the ongoing progress in conceptualization, the need for better coordination in research and collaborative comparative studies continues.

Tracer investigations were combined with a geographical information system (GIS) analysis of the 31 km² Gimock catchment (Cairngorm Mountains, Scotland) in order to understand hydrological functioning by identifying dominant runoff sources and estimating mean residence times. The catchment has a complex geology, soil cover and topography. Gran alkalinity was used to demonstrate that catchment geology has a dominant influence on baseflow chemistry, but flow paths originating in acidic horizons in the upper soil profiles controlled stormflow alkalinity. Chemically based hydrograph separations at the catchment scale indicated that ∼30% of annual runoff was derived from groundwater sources. Similar contributions (23-36%) were estimated for virtually all major sub-basins. δ18O of precipitation (mean: -9.4‰ range: -16.1 to -5.0‰) and stream waters (mean: -9.1‰ range: -11.6 to -7.4‰ were used to assess mean catchment and sub-basin residence times, which were in the order ∼4-6 months. GIS analysis showed that these tracer-based diagnostic features of catchment functioning were consistent with the landscape organization of the catchment. Soil and HOST (Hydrology of Soil Type) maps indicated that the catchment and individual sub-basins were dominated by hydrologically responsive soils, such as peats (Histosol), peaty gleys (Histic Gleysols) and rankers (Umbric Leptosols and Histosols). Soil cover tin combination with a topographic index) predicted extensive areas of saturation that probably expand during hydrological events, thus providing a high degree of hydrological connectivity between catchment hillslopes and stream channel network. This was validated by aerial photographic interpretation and groundtruthing. These characteristics of hydrological functioning (i.e. dominance of responsive hydrological pathways and short residence times) dictate that the catchment is sensitive to land use change impacts on the quality and quantity of streamflows. It is suggested that such conceptualization of hydrological functioning using tracer-validated GIS analysis can play an important role in the sustainable management of river basins. [ABSTRACT FROM AUTHOR]