Export pathways of biosolid derived microplastics in soil systems - Findings from a temperate maritime climate.

The environmental fate of microplastics (MPs) added to agricultural soils remains poorly understood, particularly regarding their mobility in soils. Here we investigate the potential for MP export from soil to surface waters and groundwater in two agricultural settings with a 20-year history of biosolid treatment. A third site where biosolids had never been applied served as a reference (Field R). The potential for MP export along overland and interflow pathways to surface waters was determined from MP abundances in shallow surface cores (10 cm) along ten down-slope transects (five each for Field A and B), and through MP abundances in effluent from a sub-surface land drain. The risk of vertical MP migration was assessed from 2 m cores, and from MP abundances in groundwater sampled from the core boreholes. XRF Itrax core scanning was conducted on two of the deep cores to capture high-resolution optical and 2-D radiographic imaging. Results suggest limited MP mobility at depths >35 cm, with MPs largely recovered in surface soils characterised by lower compaction. Furthermore, abundances of MPs across the surface cores were comparable, with no evidence of MP accumulations observed. Average MP abundance in the top 10 cm of soil across Field A and B was 365 ± 302 MP kg-1, with 0.3 MP l-1 and 1.6 MP l-1 recovered from the groundwater and field drainpipe water samples, respectively. MP abundances were significantly higher in fields treated with biosolids than in Field R (90 ± 32 MP kg-1 soil). Findings suggest ploughing is the most significant driver of MP mobility in upper soil layers, however the potential for overland or interflow movement cannot be excluded, particularly for fields that may be artificially drained.

Peatland dynamics: A review of process-based models and approaches.

Despite peatlands' important feedbacks on the climate and global biogeochemical cycles, predicting their dynamics involves many uncertainties and an overwhelming variety of available models. This paper reviews the most widely used process-based models for simulating peatlands' dynamics, i.e., the exchanges of energy and mass (water, carbon, and nitrogen). 'Peatlands' here refers to mires, fens, bogs, and peat swamps both intact and degraded. Using a systematic search (involving 4900 articles), 45 models were selected that appeared at least twice in the literature. The models were classified into four categories: terrestrial ecosystem models (biogeochemical and global dynamic vegetation models, n = 21), hydrological models (n = 14), land surface models (n = 7), and eco-hydrological models (n = 3), 18 of which featured "peatland-specific" modules. By analysing their corresponding publications (n = 231), we identified their proven applicability domains (hydrology and carbon cycles dominated) for different peatland types and climate zones (northern bogs and fens dominated). The studies range in scale from small plots to global, and from single events to millennia. Following a FOSS (Free Open-Source Software) and FAIR (Findable, Accessible, Interoperable, Reusable) assessment, the number of models was reduced to 12. Then, we conducted a technical review of the approaches and associated challenges, as well as the basic aspects of each model, e.g., spatiotemporal resolution, input/output data format and modularity. Our review streamlines the process of model selection and highlights: (i) standardization and coordination are required for both data exchange and model calibration/validation to facilitate intercomparison studies; and (ii) there are overlaps in the models' scopes and approaches, making it imperative to fully optimize the strengths of existing models rather than creating redundant ones. In this regard, we provide a futuristic outlook for a 'peatland community modelling platform' and suggest an international peatland modelling intercomparison project.

Using weighted expert judgement and nonlinear data analysis to improve Bayesian belief network models for riverine ecosystem services.

Rivers are a key part of the hydrological cycle and a vital conduit of water resources, but are under increasing threat from anthropogenic pressures. Linking pressures with ecosystem services is challenging because the processes interconnecting the physico-chemical, biological and socio-economic elements are usually captured using heterogenous methods. Our objectives were, firstly, to advance an existing proof-of-principle Bayesian belief network (BBN) model for integration of ecosystem services considerations into river management. We causally linked catchment stressors with ecosystem services using weighted evidence from an expert workshop (capturing confidence among expert groups), legislation and published literature. The BBN was calibrated with analyses of national monitoring data (including non-linear relationships and ecologically meaningful breakpoints) and expert judgement. We used a novel expected index of desirability to quantify the model outputs. Secondly, we applied the BBN to three case study catchments in Ireland to demonstrate the implications of changes in stressor levels for ecosystem services in different settings. Four out of the seven significant relationships in data analyses were non-linear, highlighting that non-linearity is common in ecosystems, but rarely considered in environmental modelling. Deficiency of riparian shading was identified as a prevalent and strong influence, which should be addressed to improve a broad range of societal benefits, particularly in the catchments where riparian shading is scarce. Sediment load had a lower influence on river biology in flashy rivers where it has less potential to settle out. Sediment interacted synergistically with organic matter and phosphate where these stressors were active; tackling these stressor pairs simultaneously can yield additional societal benefits compared to the sum of their individual influences, which highlights the value of integrated management. Our BBN model can be parametrised for other Irish catchments whereas elements of our approach, including the expected index of desirability, can be adapted globally.

A Bayesian Modelling Framework for Integration of Ecosystem Services into Freshwater Resources Management.

Models of ecological response to multiple stressors and of the consequences for ecosystem services (ES) delivery are scarce. This paper describes a methodology for constructing a BBN combining catchment and water quality model output, data, and expert knowledge that can support the integration of ES into water resources management. It proposes "small group" workshop methods for elucidating expert knowledge and analyses the areas of agreement and disagreement between experts. The model was developed for four selected ES and for assessing the consequences of management options relating to no-change, riparian management, and decreasing or increasing livestock numbers. Compared with no-change, riparian management and a decrease in livestock numbers improved the ES investigated to varying degrees. Sensitivity analysis of the expert information in the BBN showed the greatest disagreements between experts were mainly for low probability situations and thus had little impact on the results. Conversely, in our applications, the best agreement between experts tended to occur for the higher probability, more likely, situations. This has implications for the practical use of this type of model to support catchment management decisions. The complexity of the relationship between management measures, the water quality and ecological responses and resulting changes in ES must not be a barrier to making decisions in the present time. The interactions of multiple stressors further complicate the situation. However, management decisions typically relate to the overall character of solutions and not their detailed design, which can follow once the nature of the solution has been chosen, for example livestock management or riparian measures or both.

Coarse sediment dynamics and low-head dams: Monitoring instantaneous bedload transport using a stationary RFID antenna.

Coarse sediment transport in fluvial systems serves an important role in determining in-stream physical habitat, spawning potential and benthic community structure. However, despite more than a decade of pressure in Europe to restore stream continuity under the Water Framework Directive (WFD), there have been relatively few empirical studies on how low-head, run-of-river structures (i.e., weirs) disrupt the processes and dynamics of bedload conveyance. In this study we present an investigation into how coarse sediment is transferred through a low-head dam via the real-time monitoring of bedload transport over a weir in southeast Ireland. Critical discharge values for particle entrainment over the structure were derived from the novel use of a stationary RFID antenna, coupled with continuous recording of water levels and sediment captured downstream using pit-style sediment traps. The stationary RFID antenna was installed along a weir crest using both 'pass-under' and 'pass-over' configurations as a means of detecting the moment bedload tracers moved over the dam crest. Results show that 10% of tracers deployed upstream were detected passing over the weir, while a further 15% that were not detected were recovered downstream. These results indicate bedload material as large as the upstream D70 (i.e., 90 mm) can move over the structure during infrequent high-flow events. However, thorough searches of the seeded area upstream of the dam also suggest that as many as 43% of the total number may have passed downstream, indicating that tracers moved over the weir after the antenna was damaged during a high-flow event, or were missed due to either particle velocity or signal collision. In addition, 30 of the tracers that remained upstream were shown to have either been buried due to the subsequent influx of sediment entering the reservoir, or were reworked though the surface material. Critical discharge values indicate size-selective transport patterns may dominate and a strong correlation between event peak discharge and total bedload captured downstream. These findings provide more evidence that low-head structures may eventually adopt a morphology that allows for the intermittent storage and later export of a channel's bedload downstream as hypothesized by other authors. Building upon these findings and those of other recent field studies, we present a set of possible schematic models that offer a basis for understanding the unique ways low-head dams can continue to disrupt sediment conveyance long after they have reached their functional storage capacity. The limitations of using a stationary RFID antenna and possible recommendations for future studies are discussed.

Effect of low-head dams on reach-scale suspended sediment dynamics in coarse-bedded streams.

River infrastructure is one of the primary threats to riverine ecosystems globally, altering hydromorphological processes and isolating habitats. Instream barriers and low-head dams can have significant effects on system connectivity, but despite this, very few empirical studies have assessed the impacts of these structures on suspended sediment transport. Through a paired turbidity study over a 20-month monitoring period we investigated the differences in suspended sediment flux above and below two low-head dams in the south-east of Ireland. Using sediment balance as a proxy for sediment storage, results showed that a net-export of sediment from the study reach occurred for 68% of the high-flow events analysed. As the primary controls on sediment dynamics at the downstream reach depend on sediment availability from upstream, we argue that these results indicate the presence of a substantial local source of sediment between monitoring stations that cannot be explained by natural intra-reach erosional processes. Here we hypothesise that as sediment supply from the catchment becomes exhausted, the structure's impounded zone (typically considered a depositional area) provides a major sediment source to the downstream reach. Our rationale is that if sediment trapped behind the weir is periodically available for transportation at the rates and frequencies observed in this study, then we can infer that both structures must be trapping sediment under lower flows.

Microplastics in brown trout (Salmo trutta Linnaeus, 1758) from an Irish riverine system.

Rivers play an important role in the overall transport of microplastic pollution (1 µm to 5 mm), with fluvial dynamics expected to influence biotic interactions, particularly for fish. So far, there have been few assessments of microplastics in freshwater salmonids. The prevalence (i.e. percentage occurrence) and burden (i.e. abundance per fish) of microplastics were assessed in the gastrointestinal tracts (GITs) and stomach contents (SCs) of 58 brown trout Salmo trutta Linnaeus, 1758 sampled at six sites along the River Slaney catchment in south-east Ireland. Sites were divided into two classifications (high and low exposure) based on proximity to microplastic pollution sources, comprising three sites each. Analysis of biological traits (e.g. fish length) and diet was performed on the same fish to determine possible factors explaining microplastic burden. Microplastics were found in 72% of fish having been recovered from 66% of GITs (1.88 ± 1.53 MPs fish⁻1) and 28% of SCs (1.31 ± 0.48 MPs fish⁻1). Fibres were the dominant particle type recovered from GITs (67%) and SCs (57%) followed by fragments. No difference in median microplastic burden was observed between fish collected in high and low exposure sites. Microplastic burden was unrelated to fish fork length, while microplastic size distribution (100 ≤ 350 µm, 350 µm to ≤ 5 mm) was unrelated to S. trutta age class estimates. Furthermore, microplastic burden was not explained by dietary intake. Though further research is necessary, this study showed the presence of microplastics in wild S. trutta collected from an Irish riverine system, which could have further implications for top-level consumers that feed on the species, including humans. Further analysis is required to determine possible trophic linkages for the species, with respect to microplastics, and to assess the suitability of S. trutta for monitoring microplastics in river systems.

Peak grain forecasts for the US High Plains amid withering waters.

Irrigated agriculture contributes 40% of total global food production. In the US High Plains, which produces more than 50 million tons per year of grain, as much as 90% of irrigation originates from groundwater resources, including the Ogallala aquifer. In parts of the High Plains, groundwater resources are being depleted so rapidly that they are considered nonrenewable, compromising food security. When groundwater becomes scarce, groundwater withdrawals peak, causing a subsequent peak in crop production. Previous descriptions of finite natural resource depletion have utilized the Hubbert curve. By coupling the dynamics of groundwater pumping, recharge, and crop production, Hubbert-like curves emerge, responding to the linked variations in groundwater pumping and grain production. On a state level, this approach predicted when groundwater withdrawal and grain production peaked and the lag between them. The lags increased with the adoption of efficient irrigation practices and higher recharge rates. Results indicate that, in Texas, withdrawals peaked in 1966, followed by a peak in grain production 9 y later. After better irrigation technologies were adopted, the lag increased to 15 y from 1997 to 2012. In Kansas, where these technologies were employed concurrently with the rise of irrigated grain production, this lag was predicted to be 24 y starting in 1994. In Nebraska, grain production is projected to continue rising through 2050 because of high recharge rates. While Texas and Nebraska had equal irrigated output in 1975, by 2050, it is projected that Nebraska will have almost 10 times the groundwater-based production of Texas.

An inspection-based assessment of obstacles to salmon, trout, eel and lamprey migration and river channel connectivity in Ireland.

Knowledge of the location, physical attributes and impacts of obstacles on river connectivity is a requirement for any mitigating action aimed at restoring the connectivity of a river system. Here, we present a study that recorded the numbers and physical diversity of obstacles in 10 river catchments in Ireland, together with the impact these structures had on overall river connectivity. A total of 372 obstacles were recorded, 3 of these were dams, and the remainder were low-head weirs/sluices, obstacles associated with road or rail crossings of rivers and natural structures. The degree of fragmentation was estimated in each catchment by calculating obstacle density and the Dendritic Connectivity Index (DCI). DCI scores were calculated for 4 native Irish fish species with different life-histories, namely diadromous (Atlantic salmon, sea trout, European eel, sea lamprey) and potamodromous (brown trout). Obstacle density ranged between 1.2 and 0.02 obstacles/km of river. Six of the 10 catchments had at least one obstacle located on the mainstem river at least 5 km from its mouth/confluence. These 6 catchments typically had the lowest connectivity scores for diadromous species and ranged between 0.6 and 44.1 (a fully connected river would receive a maximum score of 100). While there was no significant correlation between obstacle density and the DCI score for diadromous fish, a significant negative correlation was detected between obstacle density and the DCI score for potamodromous brown trout. Here, we highlight the merit of these obstacle assessments and associated challenges for decision-making relating to prioritisation of obstacles for removal or modification.

Impact of low-head dams on bedload transport rates in coarse-bedded streams.

This paper presents an empirical study that uses the movement of RFID tracers to investigate the impacts of low-head dams on solid transport dynamics in coarse-bedded streams. Here we report on the influence of two structures located in Ireland's South-East, both of which indicate that particles greater than the reach D90 can be carried through and over low-head dams. This observation suggests that both structures may have reached a state of 'transient storage' as hypothesized by previous research. However, when the data were reinterpreted as fractional transport rates using a novel application of existing empirical relations, we observed patterns consistent with supply-limited conditions downstream. Expanding on existing conceptual models and mechanisms, we illustrate how a system may continue to exhibit supply-limited conditions downstream without the need for a net attenuation of sediment to occur indefinitely. We propose that once a transient storage capacity has been reached, the system then enters a state of dynamic disconnectivity where the long-term average sediment flux equals that under reference conditions, but now with the amplitude and wavelength of these sediment fluctuations having increased. We hypothesize that the time-lag associated with the reduced frequency of events competent enough to move bedload over the structure accounts for the time necessary to complete the 'fill' phase of the transient storage dynamic; a process that will continue until both the fill and flow thresholds are again met to allow the system to reenter the 'scour' phase. This model reconciles how a system may exhibit a sediment deficit for time intervals longer than those experienced under reference conditions. As water and sediment are the drivers of channel morphology and associated habitat units, the impact a structure has on a channel's sediment regime should therefore form part of any assessment regarding the prioritization of barriers for removal or remediation.

Sources of nitrogen and phosphorus emissions to Irish rivers and coastal waters: Estimates from a nutrient load apportionment framework.

More than half of surface water bodies in Europe are at less than good ecological status according to Water Framework Directive assessments, and diffuse pollution from agriculture remains a major, but not the only, cause of this poor performance. Agri-environmental policy and land management practices have, in many areas, reduced nutrient emissions to water. However, additional measures may be required in Ireland to further decouple the relationship between agricultural productivity and emissions to water, which is of vital importance given on-going agricultural intensification. The Source Load Apportionment Model (SLAM) framework characterises sources of phosphorus (P) and nitrogen (N) emissions to water at a range of scales from sub-catchment to national. The SLAM synthesises land use and physical characteristics to predict emissions from point (wastewater, industry discharges and septic tank systems) and diffuse sources (agriculture, forestry, etc.). The predicted annual nutrient emissions were assessed against monitoring data for 16 major river catchments covering 50% of the area of Ireland. At national scale, results indicate that total average annual emissions to surface water in Ireland are over 2700tyr-1 of P and 82,000tyr-1 of N. The proportional contributions from individual sources show that the main sources of P are from municipal wastewater treatment plants and agriculture, with wide variations across the country related to local anthropogenic pressures and the hydrogeological setting. Agriculture is the main source of N emissions to water across all regions of Ireland. These policy-relevant results synthesised large amounts of information in order to identify the dominant sources of nutrients at regional and local scales, contributing to the national nutrient risk assessment of Irish water bodies.

The effect of forest windrowing on physico-chemical water quality in Ireland.

Windrowing is widely practised, across Europe and North America, in bole-only harvested coniferous forest plantations before replanting. Forest harvesting has been shown to significantly increase sediment and nutrient losses to watercourses in other studies but windrowing effects, which are as bad, have not been investigated in detail. To determine physico-chemical impacts on water quality and to help inform forest managers, the effects of windrowing were investigated in a headwater catchment. Water samples were collected from storm events pre- (PWR), during (DWR) and after windrowing (AWR). Total suspended solids (TSS), total phosphorus (TP), soluble reactive phosphorus (SRP), total ammonia, nitrate, stream discharge, water level and velocity were measured. Results showed that peak and flow weighted mean concentrations (FWMC) of TSS concentrations increased significantly during windrowing when compared to pre-windrowing concentrations. Peak TSS increased from 88 mg/l (PWR) to 502 mg/l (DWR) and decreased to 163 mg/l (one year AWR) and 225 mg/l (two years AWR). Peak and FWMC of TP also increased during windrowing when compared to pre-windrowing concentrations. Peak TP concentrations increased from 0.1 mg/l (PWR) to 0.4 mg/l (DWR) and decreased to 0.1 mg/l (AWR). SRP and nitrate concentrations increased during windrowing when compared to pre-windrowing but remained low overall. TSS and TP concentrations were highest when flows greater than 0.3 m(3)/s (exceeded 6.3% of time) were recorded in the channel. It was highlighted that high-resolution sampling of storm events is important, where precise measurements of windrowing-sourced outputs are required. Windrowing was shown to generate very high concentrations of TSS and TP, comparable to those recorded during harvesting. This research helps to identify potential impacts on physico-chemical water quality that arise during windrowing and demonstrates the need for measures to minimize impacts on surface waters as required by the EU Water Framework Directive and similar legislation elsewhere.

Improved semi-distributed model for phosphorus losses from Irish catchments.

Phosphorus (P) is one of the important limiting elements governing the quality of natural waters in Ireland. Good models that simulate the loss of P from catchments to water bodies are needed to understand the mechanism and transport of P and to assist in formulating appropriate policies and practices to control or manage the problem. In the present study, a new combined model (NCM) is developed as ahybridbetween soil and water assessment tool (SWAT) and Hydrological Simulation Program FORTRAN (HSPF) packages. The developed NCM model was tested, with the data from the Oona catchment in Ireland, and evaluated to insure it is capable of predicting flow and total P loads at the same level or better than SWAT and HSPF packages when used alone. The NCM produced better flow simulation in terms of Nash-Sutcliffe efficiency (R2) than SWAT when used alone for both calibration and validation periods when hourly time steps are used for rainfall and evapotranspiration. In addition, calibration for the total phosphorus load gave better R2 values than previously reported result for either HSPF or SWAT and showed better performance for most of the validation period. Using multi-objective optimization methods for optimizing both flow and total P loads gave better simulated results than using sequential optimization of flow followed by total phosphorus. Hence, the NCM model developed here can be used to improve the prediction of phosphorus loss to water bodies in Ireland.

Environmental consequences of a power plant shut-down: a three-dimensional water quality model of Dublin Bay.

A hydro-environmental model is used to investigate the effect of cessation of thermal discharges from a power plant on the bathing water quality of Dublin Bay. Before closing down, cooling water from the plant was mixed with sewage effluent prior to its discharge, creating a warmer, less-saline buoyant pollutant plume that adversely affects the water quality of Dublin Bay. The model, calibrated to data from the period prior to the power-plant shut-down (Scenario1), assessed the water quality following its shut-down under two scenarios; (i) Scenario2: continued abstraction of water to dilute sewage effluents before discharge, and (ii) Scnenario3: sewage effluents are discharged directly into the Estuary. Comparison between scenarios was based on distribution of Escherichia coli (E. coli), a main bathing quality indicator. Scenarios1 and 2, showed almost similar E. coli distribution patterns while Scenario3 displayed significantly higher E. coli concentrations due to the increased stratification caused by the lack of prior dilution.

Derivation of a fuzzy national phosphorus export model using 84 Irish catchments.

Implementation of appropriate management strategies to mitigate diffuse phosphorus (P) pollution at the catchment scale is vitally important for the sustainable development of water resources in Ireland. An important element in the process of implementing such strategies is the prediction of their impacts on P concentrations in a catchment using a reliable mathematical model. In this study, a state-of-the-art adaptive neuro-fuzzy inference system (ANFIS) has been used to develop a new national P model capable of estimating average annual ortho-P concentrations at un-gauged catchments. Data from 84 catchments dominated by diffuse P pollution were used in developing and testing the model. Six different split-sample scenarios were used to partition the total number of the catchments into two sets, one to calibrate and the other to validate the model. The k-means clustering algorithm was used to partition the sets into clusters of catchments with similar features. Then for each scenario and for each cluster case, 11 different models, each of which consists of a linear regression sub-model for each cluster, were formulated by using different input variables selected from among six spatially distributed variables including phosphorus desorption index (PDI), runoff risk index (RRI), geology (GEO), groundwater (GW), land use (LU), and soil (SO). The success of the new approach over the conventional lumped, empirical, modelling approach was evident from the improved results obtained for most of the cases. In addition the results highlighted the importance of using information on PDI and RRI as explanatory input variables to simulate the average annual ortho-P concentrations.

A regional examination of episodic acidification response to reduced acidic deposition and the influence of plantation forests in Irish headwater streams.

Episodic surface water acidification is common in many regions worldwide; the driving processes are dependent on a variety of physicochemical and climatic characteristics, and acid deposition pressures, which have changed significantly over the last two decades. This study provided a unique opportunity to re-examine the drivers of acidity in an environment of low anthropogenic input. In three geologically distinct acid-sensitive regions of Ireland during 2009-2010, 34 headwater streams were evaluated in peat-dominated catchments draining moorlands without forest, 20-50% (low) forest cover and >50% (high) forest cover. Results indicated episodic acidity/alkalinity loss in headwater streams, despite significant reductions in acid deposition. Both the differences in pH between base and storm-flow (∆pH) and the number of pH events≤5.5 were higher in forested streams. Dissolved organic carbon and inorganic aluminium concentrations were also higher in forested catchments. The primary driver of acidity was strong organic anions, which generally increased with increasing forest cover. Base-cation dilution was also prominent in west and southern regions, while surprisingly chlorine anion acidity from sea-salts had little or no influence on stream acidity. The contributions of excess non-marine sulphate (xSO(4)) and nitrate (NO(3)) to storm-water were low, with no observed increases in xSO(4) with increasing forest cover, although contributions of NO(3) were higher in forested catchments in the east. The results suggest that episodic acidification in Ireland is primarily driven by organic acids. However in peat dominant catchments, plantation forest, climate change and/or reductions in xSO(4) appear to also be having an effect on stream pH from increased DOC, with some forested streams previously unaffected by deposition now showing low pH (<5.5) during storm-flow. As quantified from this study, observed changes in stream acidification in Ireland may provide a better understanding of future chemical responses to declining acid deposition and climate change elsewhere.

Highway runoff quality in Ireland.

Highway runoff has been identified as a significant source of contaminants that impact on the receiving aquatic environment. Several studies have been completed documenting the characteristics of highway runoff and its implication to the receiving water in the UK and elsewhere. However, very little information is available for Ireland. The objective of this study was to determine the quality of highway runoff from major Irish roads under the current road drainage design and maintenance practice. Four sites were selected from the M4 and the M7 motorways outside Dublin. Automatic samplers and continuous monitoring devices were deployed to sample and monitor the runoff quality and quantity. More than 42 storm events were sampled and analysed for the heavy metals Cd, Cu, Pb, and Zn, 16 US EPA specified PAHs, volatile organic compounds including MTBE, and a number of conventional pollutants. All samples were analysed based on the Standard Methods. Significant quantities of solids and heavy metals were detected at all sites. PAHs were not detected very often, but when detected the values were different from quantities observed in UK highways. The heavy metal concentrations were strongly related to the total suspended solids concentrations, which has a useful implication for runoff management strategies. No strong relationship was discovered between pollutant concentrations and event characteristics such as rainfall intensity, antecedent dry days (ADD), or rainfall depth (volume). This study has demonstrated that runoff from Irish motorways was not any cleaner than in the UK although the traffic volume at the monitored sites was relatively smaller. This calls for a site specific investigation of highway runoff quality before adopting a given management strategy.

A comparison of SWAT, HSPF and SHETRAN/GOPC for modelling phosphorus export from three catchments in Ireland.

Recent extensive water quality surveys in Ireland revealed that diffuse phosphorus (P) pollution originating from agricultural land and transported by runoff and subsurface flows is the primary cause of the deterioration of surface water quality. P transport from land to water can be described by mathematical models that vary in modelling approach, complexity and scale (plot, field and catchment). Here, three mathematical models (soil water and analysis tools (SWAT), hydrological simulation program-FORTRAN (HSPF) and système hydrologique Européen TRANsport (SHETRAN)/grid oriented phosphorus component (GOPC)) of diffuse P pollution have been tested in three Irish catchments to explore their suitability in Irish conditions for future use in implementing the European Water Framework Directive. After calibrating the models, their daily flows and total phosphorus (TP) exports are compared and assessed. The HSPF model was the best at simulating the mean daily discharge while SWAT gave the best calibration results for daily TP loads. Annual TP exports for the three models and for two empirical models were compared with measured data. No single model is consistently better in estimating the annual TP export for all three catchments.