Eva M. Mockler

Understanding hydrological flow paths in conceptual catchment models using uncertainty and sensitivity analysis

Increasing pressures on water quality due to intensification of agriculture have raised demands for environmental modeling to accurately simulate the movement of diffuse (nonpoint) nutrients in catchments. As hydrological flows drive the movement and attenuation of nutrients, individual hydrological processes in models should be adequately represented for water quality simulations to be meaningful. In particular, the relative contribution of groundwater and surface runoff to rivers is of interest, as increasing nitrate concentrations are linked to higher groundwater discharges. These requirements for hydrological modeling of groundwater contribution to rivers initiated this assessment of internal flow path partitioning in conceptual hydrological models.In this study, a variance based sensitivity analysis method was used to investigate parameter sensitivities and flow partitioning of three conceptual hydrological models simulating 31 Irish catchments. We compared two established conceptual hydrological models (NAM and SMARG) and a new model (SMART), produced especially for water quality modeling. In addition to the criteria that assess streamflow simulations, a ratio of average groundwater contribution to total streamflow was calculated for all simulations over the 16 year study period. As observations time-series of groundwater contributions to streamflow are not available at catchment scale, the groundwater ratios were evaluated against average annual indices of base flow and deep groundwater flow for each catchment. The exploration of sensitivities of internal flow path partitioning was a specific focus to assist in evaluating model performances. Results highlight that model structure has a strong impact on simulated groundwater flow paths. Sensitivity to the internal pathways in the models are not reflected in the performance criteria results. This demonstrates that simulated groundwater contribution should be constrained by independent data to ensure results within realistic bounds if such models are to be used in the broader environmental sustainability decision making context. Groundwater simulations and parameter sensitivities for 3 models were compared.Of 3 models calibrated to total flow, SMART captured groundwater contribution best.Internal flow partitioning varies greatly between models and parameter sets.Independent data on flow paths should inform calibration of conceptual models.

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.

Modeling the pathways and attenuation of nutrients from domestic wastewater treatment systems at a catchment scale

Domestic Wastewater Treatment Systems (DWTS) are often cited as significant sources of pollution in rural catchments. A mass balance based model has been developed to determine annual nutrient loading from individual DWTS into rivers in Ireland. The transport and attenuation of nitrogen and phosphorus in DWTS effluent to groundwater and surface water has been formulated using the results from field research in Ireland, as well as being informed by other international studies. Conceptually the model splits the transport of nutrients to the river into three pathways: direct to surface water (for areas of inadequate percolation), a near surface (subsoil) pathway, and a groundwater pathway. The model quantifies the net nutrient contribution for each DWTS and has been incorporated into a broader source load apportionment catchment model which includes agricultural inputs, thereby enabling the relative risk of nutrient pollution from DWTS in a catchment to be defined. Mass balance based model to determine annual nutrient loading from DWTS to rivers.Model splits the transport of nutrients to the river into three distinct pathways.Transport and attenuation of nutrients determined by local subsoil permeability.Model incorporated into a broader source load apportionment catchment model.Relative risk of nutrient pollution from DWTS in a catchment can be identified.

Nutrient Load Apportionment to Support the Identification of Appropriate Water Framework Directive Measures

A model for predicting the sources of nutrient loads (phosphorus and nitrogen) to water has been developed to support Water Framework Directive (WFD) implementation. The Source Load Apportionment Model (SLAM) framework described in this paper integrates catchment data and pressure information from point discharges and diffuse sources to enable characterisation of source pathway receptor relationships. Hydrogeological controls have a strong impact on nutrient fluxes, particularly in agricultural catchments, and have been incorporated into the diffuse agricultural model (the CCT). Results for the Suir catchment matched the measured loads of nitrogen and phosphorus well, and showed that pasture is the dominant source of nitrogen. The main sources of phosphorus in sub-catchments varied between diffuse agriculture, wastewater and industrial discharges. A relatively small proportion (13%) of the Suir catchment area requires a reduction in phosphorus emissions to achieve Good status. In these areas, model results can be used in conjunction with local knowledge gathered through the WFD characterisation process to identify significant pressures that contribute excessive nutrient loads. An example of assessing load reduction scenarios is presented to illustrate how modelling can support catchment scientists in identifying appropriate measures.

Development of a Catchment Management Tool to Assess Environmental Risk from Nutrient Loadings Using Open Source GIS

A Catchment Management Tool (CMT) is being developed for the Irish Environmental Protection Agency (EPA) that will allow River Basin Managers to evaluate the environmental risk from organic and inorganic nutrient loadings due to various land uses and human activities. The CMT was built using Open Source GIS (Geographical Information System) software, to facilitate development and widen the research user-base of the tool. The user interface of the CMT is designed to be flexible to allow local knowledge to be included in the system as well as the possibility to try what-if scenarios in relation to environmental assessment. Contaminant loadings are calculated from publicly available data and hydrogeologically susceptible areas (HSAs) are formed by combining soil and geological GIS layers. Further combinations of Loadings and HSAs allow Critical Source Areas to be delineated that identify areas contributing significant amounts of a given contaminant to any selected water body.

Minimal climate change impacts on natural organic matter forecasted for a potable water supply in Ireland

Natural organic matter poses an increasing challenge to water managers because of its potential adverse impacts on water treatment and distribution, and subsequently human health. Projections were made of impacts of climate change on dissolved organic carbon (DOC) in the primarily agricultural Boyne catchment which is used as a potable water supply in Ireland. The results indicated that excluding a potential rise in extreme precipitation, future projected loads are not dissimilar to those observed under current conditions. This is because projected increases in DOC concentrations are offset by corresponding decreases in precipitation and hence river flow. However, the results presented assume no changes in land use and highlight the predicted increase in DOC loads from abstracted waters at water treatment plants.

Water at the Centre of Environmental Issues – Research at the UCD Dooge Centre for Water Resources Research

Since 1988, the UCD Dooge Centre for Water Resources Research has been conducting research in a wide range of water topics including hydraulics, hydrology, coastal dynamics and wastewater with an emphasis on multi-disciplinary collaboration. This paper presents an overview of this research, both past and present, and provides an outlook to the future research directions of the Centre.