Luis F. León

Nonpoint source pollution: a distributed water quality modeling approach.

A distributed water quality model for nonpoint source pollution modeling in agricultural watersheds is described in this paper. A water quality component was developed for WATFLOOD (a flood forecast hydrological model) to deal with sediment and nutrient transport. The model uses a distributed group response unit approach for water quantity and quality modeling. Runoff, sediment yield and soluble nutrient concentrations are calculated separately for each land cover class, weighted by area and then routed downstream. With data extracted using Geographical Information Systems (GIS) technology for a local watershed, the model is calibrated for the hydrologic response and validated for the water quality component. The transferability of model parameters to other watersheds, especially those in remote areas without enough data for calibration, is a major problem in diffuse modeling. With the connection to GIS and the group response unit approach used in this paper, model portability increases substantially, which will improve nonpoint source modeling at the watershed-scale level.

Modeling as a Tool for Nutrient Management in Lake Erie: a Hydrodynamics Study

Abstract Coupled physical-biological numerical models are useful tools for understanding the relevant processes and the influence of biota and human activity on the ecological conditions in the lake, and such a suite of models has been used to assess the impact of zebra mussels on the nutrient cycling in the lake. This paper presents the hydrodynamic part of a Lake Erie modeling exercise using the 3D ELCOM model. Validation runs were performed with 1994, 2001, 2002, and 2003 data where vertical thermistor chain data are compared against model calculations and mean circulation patterns are presented for the different runs. The validated model was then used to understand the flushing of the deep water, the internal wave dynamic and the residual circulation. For example, the presence of two gyres in the west-central basin that entrain nutrient-rich western basin and Sandusky Bay water and are probably a key mechanism for retaining externally supplied nutrients in this region, contributing to variability of primary productivity and its spatial distribution in the central basin. External nutrient loads are transported eastward more quickly than would occur without gyres, and would support less extensive phytoplankton development in the west-central basin. The hydrodynamic results will eventually be used as the drivers for future simulations aimed at studying the fate and transport of nutrients.

Towards coupling a 3D hydrodynamic lake model with the Canadian Regional Climate Model: Simulation on Great Slave Lake

Recently, it has been recognized that large lakes exert considerable influence on regional climate systems and vice versa and that the Canadian Regional Climate Model (CRCM), which does not currently have a lake component, requires the development of a coupled lake sub-model. Prior to a full effort for this model development, however, studies are needed to select and assess the suitability of a lake hydrodynamic model in terms of its capability to couple with the CRCM. This paper evaluates the performance of the 3-dimensional hydrodynamic model ELCOM on Great Slave Lake, one of Canadas largest lakes in the northern climatic system. Model simulations showed dominant circulation patterns that can create relatively large spatial and temporal gradients in temperature. Simulated temperatures compared well with cross-lake temperature observations both at the surface and vertically. Sensitivity analysis was applied to determine the critical meteorological variables affecting simulations of temperature and surface heat fluxes. For example, a 10% increase in air temperature and solar radiation was found to result in a 3.1% and 8.3% increase in water surface temperature and 8.5% increase in latent heat flux. Knowledge of the model sensitivity is crucial for future research in which the hydrodynamic model coupled with the atmosphere will be forced from the CRCM output.

Integration of a Nonpoint Source Pollution Model with a Decision Support System

Abstract This paper is a progress report of an ongoing research project from which the expected final product will be an integral system to model nonpoint source pollution in surface waters. Diffuse pollution models will be included in a decision support system with a unique platform, common interfaces and GIS capabilities. This system will accommodate pre- and post-processing tools, model control and sensitivity analysis for the parameters in the models. Particularly, the construction of the interface for the AGNPS model and its link with the decision support system RAISON is presented. The model is described, including the input requirements, the development of tools and the procedures created to extract the necessary data from digital elevation model, soil type and landcover vectorized files.

The nearshore shunt and the decline of the phytoplankton spring bloom in the Laurentian Great Lakes: insights from a three-dimensional lake model

Dreissenid mussels have been hypothesized to cause selective decreases of phytoplankton in nearshore areas (nearshore shunt hypothesis) as well as the near-complete loss of the offshore phytoplankton spring bloom in some Laurentian Great Lakes. To evaluate whether mussels can reasonably be expected to mediate such changes, we extended the three-dimensional hydrodynamic-ecological model (ELCOM-CAEDYM) to include mussels as a state variable and applied it to Lake Erie (USA-Canada). Mussel-mediated decreases in mean phytoplankton biomass were highly sensitive to the assigned mussel population size in each basin. In the relatively deep east basin, mussels were predicted to decrease phytoplankton in both nearshore and offshore zones, even during periods of thermal stratification but especially during the spring phytoplankton maximum. Spatially, impacts were associated with mussel distributions but could be strong even in areas without high mussel biomass, consistent with advection from areas of higher mussel biomass. The results supported the nearshore shunt hypothesis that mussel impacts on phytoplankton should be greater in nearshore than offshore waters and also supported suggestions about the emerging importance of deep water offshore mussels. The results of this study provide an important insight into ecological role of mussels in lowering plankton productivity in some world’s largest lakes.

Watershed management modelling in Malawi: application and technology transfer

Abstract To study the possible impact on the Lake Malawi/Nyasa/Niassa water quality due to actions performed at the watershed level, a modelling project supported by the World Bank, was conducted by the United Nations University, the University of Waterloo and WL Delft Hydraulics to integrate physical and bio-chemical processes models in the lake and its basin which affect lake and river water quality. The purpose of the integration of different models was to provide a set of tools in order to analyze the impact on the lake due to actions performed in the watershed. In this paper, we present the watershed and lake box models integration and a case application to find how agricultural practices and deforestation may impact on the water quality of rivers and streams which will then lead to changes in the nutrient loading to the lake.

Modelling Changes in Stream Water Quality Due to Climate Change in a Southern Ontario Watershed

This research represents a pilot project to establish a methodology for assessing the sensitivity of watershed stream water quality to changes in water quantity caused by climate change. The pilot watershed is the Duffins Creek watershed, located 20 km east of the City of Toronto, Canada. Scenarios of climate change analyzed in this project were drawn from two internationally recognized climate models: the Canadian Centre for Climate Modelling and Analysis (CCCma) CGCM1 and the Hadley Centre HadCM2. The AGNPS (Agricultural Non-Point Source) model was used to predict changes in stream water chemistry. The results are compared to baseline conditions as well as future conditions based on 2020 land use scenarios. It was determined that 2020 land use scenarios typically result in much smaller changes in peak flows than are predicted for the climate change scenarios, especially the wet climate change scenarios. Understanding climate change responses is critical for the development of watershed plans and drinking water source protection studies. Currently, watershed studies are completed using climate information based on relatively short-term monitoring databases that reflect past weather patterns. It is widely understood that management actions advocated in watershed studies could be improved if consideration were given to the implication of climate changes.

Land use change impacts on water quality in three lake winnipeg watersheds.

Lake Winnipeg eutrophication results from excess nutrient loading due to agricultural activities across the watershed. Estimating nonpoint-source pollution and the mitigation effects of beneficial management practices (BMPs) is an important step in protecting the water quality of streams and receiving waters. The use of computer models to systematically compare different landscapes and agricultural systems across the Red-Assiniboine basin has not been attempted at watersheds of this size in Manitoba. In this study, the Soil and Water Assessment Tool was applied and calibrated for three pilot watersheds of the Lake Winnipeg basin. Monthly flow calibration yielded overall satisfactory Nash-Sutcliffe efficiency (NSE), with values above 0.7 for all simulations. Total phosphorus (TP) calibration NSE ranged from 0.64 to 0.76, total N (TN) ranged from 0.22 to 0.75, and total suspended solids (TSS) ranged from 0.29 to 0.68. Based on the assessment of the TP exceedance levels from 1993 to 2007, annual loads were above proposed objectives for the three watersheds more than half of the time. Four BMP scenarios based on land use changes were studied in the watersheds: annual cropland to hay land (ACHL), wetland restoration (WR), marginal annual cropland conversion to hay land (MACHL), and wetland restoration on marginal cropland (WRMAC). Of these land use change scenarios, ACHL had the greatest impact: TSS loads were reduced by 33 to 65%, TN by 58 to 82%, and TP by 38 to 72% over the simulation period. By analyzing unit area and percentage of load reduction, the results indicate that the WR and WRMAC scenarios had a significant impact on water quality in high loading zones in the three watersheds. Such reductions of sediment, N, and P are possible through land use change scenarios, suggesting that land conservation should be a key component of any Lake Winnipeg restoration strategy.

A Modelling Approach for Lake Malawi/Nyasa/Niassa: Integrating Hydrological and Limnological Data

This study presents a toolkit approach for linking land-and lake-based data and models to determine the impact of human activities on the water quality of rivers and lakes. The integrated modelling framework was adapted to address specific issues and scenarios. Based on the preliminary results, a hypothetical 50% re-forestation of the Linthipe Watershed in the southern part of Lake Malawi/Nyasa/Niassa may lead to a decrease in the spring peak value of total phosphorus concentration from about 15 μg/L to 10 μg/L in the top layer (0 – 40 m) of the lake’s Outlet Basin. Discussions on improvement to future modelling and monitoring programs are also presented.

Water Quality Model Integration in a Decision Support System

This paper describes an integral system to model nonpoint source pollution in surface waters. Diffuse pollution models were included in a Spatial Decision Support System (SDSS) with a unique platform, common interfaces and Geographic Information System (GIS) capabilities. This consists of pre- and post-processing tools, model control and sensitivity analysis for the parameters in the models. Particularly, the construction of the interface for WATFLOOD (flood forecast hydrological model) and its link with the decision support system RAISON (Regional Analysis by Intelligent Systems On microcomputers) is presented. A water quality component was coupled to the model in order to deal with sediment and nutrient transport. Previous work with the AGNPS (Agricultural Non-Point Source) model is used for comparison with the results from the water quality component coupled to the WATFLOOD model.