Non-Point Source Pollution Modelling: An Overview

The objective of this paper is to provide a critical evaluation of the data available from existing studies concerning non-point source pollution (NPS). NPS pollution is complex and difficult to detect and manage when compared with point source pollution. To tackle its risk, it is vital to have precise simulations and estimations of NPS pollutants. Different modelling techniques applied to NPS pollution were reviewed and classified as either physically-based models or empirical. The physically-based models (White box models) can be used both for long-term and daily time steps. They require initial model data as well as watershed morphological and physiographic, which makes them complex and not easy to use. Empirical models on the other hand are called black-box models or metric models and can be used for both long-term, daily time steps with minimal data requirement and requires less skill to operate. Although their results are easy to interpret, these types of models are only suitable within the boundary of a certain domain. The findings of this review will serve as a guide to water resource planners in identifying the type of NPS model they need to apply to a particular catchment for a particular problem

Dynamic transport of the sediment and nutrient in the Mekong River Basin and the role of the Tonle Sap Lake : Assessment coupling data and modelling approaches

The Asian river basins are great contributors to sediments and nutrient to the seas. These rivers are subject to the influence of climate variability and human activities, which alter the nutrient transport and fate of water quality. The Mekong River is a transboundary river in Southeast Asia and plays an important role in economy, agriculture and also by contributing fluxes into the Mekong delta and into the sea. Within the Mekong basin, the Tonle Sap area is a complex system with a unique reverse flow between Tonle Sap Lake and the Mekong River. Sediment and nutrient in the Mekong River are important to sustain the geomorphology of the floodplains and particularly the Tonle Sap Lake. At the same time, Tonle Sap Lake are contributing the sediment and nutrient for the Mekong delta. Therefore, the sediment and nutrient assessment in the Mekong River and its linkage between the Mekong mainstream and the Tonle Sap Lake would be necessary to evaluate. The study was to assess the dynamic transport of sediment and nutrient in the Mekong River Basin and evaluate the role of the Tonle Sap to the Mekong River through the coupling data and modelling approaches. The physical-based SWAT model was used upstream of the Mekong delta to simulate the water regime and suspended sediment and nutrient flux of the Mekong River. The SWAT model was calibrated based on observed discharge at eight gauge stations, suspended sediment load at six stations and nutrient data at five stations from 1995 to 2016 at a monthly time step. To understand the role of Tonle Sap Lake in sediment and nutrient to Mekong River, the study considered the balanced of the Tonle Sap reverse system at seasonal and annual scales. Before entering the confluence of Mekong and Tonle Sap Lake and delta, the sediment load is found 72±26 Mt/year with a decreasing annual trend from 1995 to 2018. The annual sediment yield of the upper 80% Mekong River basin (310 t/km2/year) is comparable with sediment yields reported for other world major rivers. The Mekong annual average riverine nitrate yield was 202 kg/km2/year with 361.8±83.5 kt/year from 1985-2016 of annual nitrate flux before entering the Mekong delta. The sediment loads variability of the Mekong River and Tonle Sap system presented in this study helps clarify the exchange annual discharge and sediment load toward the Mekong delta. The study also highlighted that the fact that Tonle Sap is the sediment sink (1.35±0.7 Mt annually) in the Mekong basin lead to a reduction in sediment supply, which compounds the threat to the delta from accelerated subsidence and sea-level rise. The study has emphasized the interaction role of Tonle Sap Lake and Mekong in nutrient supply for the Mekong delta. On the annual scale, it is worth discussing these interesting results revealed Tonle Sap Lake contributed 34 kt/year of nitrate and 6.6 kt/year of total phosphorus to the Mekong system or Mekong Delta. In contrast, the Mekong River shared nitrate flux 35.8 kt/year and 8.7 kt/year of total phosphorus to Tonle Sap Lake and its floodplain during the high flow season. Future studies of hydrology together with sediment and nutrients can be carried on based on this model with scenarios of global changes, such as climate changes and land-use changes and include the sediment and nutrient input to Tonle Sap Lake system from the lake tributaries and interconnect with the Mekong River basin model

Studies on Water Management Issues

This book shares knowledge gained through water management related research. It describes a broad range of approaches and technologies, of which have been developed and used by researchers for managing water resource problems. This multidisciplinary book covers water management issues under surface water management, groundwater management, water quality management, and water resource planning management subtopics. The main objective of this book is to enable a better understanding of these perspectives relating to water management practices. This book is expected to be useful to researchers, policy-makers, and non-governmental organizations working on water related projects in countries worldwide

Modelling transport and fate of heavy metals at the watershed scale: state-of-the-art and future directions

A predictive understanding of the source-specific (e.g., point and diffuse sources) land-to-river heavy metal (HM) loads and HM dynamics in rivers is essential for mitigating river pollution and developing effective river basin management strategies. Developing such strategies requires adequate monitoring and comprehensive models based on a solid scientific understanding of the watershed system. However, a comprehensive review of existing studies on the watershed-scale HM fate and transport modeling is lacking. In this review, we synthesize the recent developments in the current generation of watershed-scale HM models, which cover a wide range of functionalities, capabilities, and spatial and temporal scales (resolutions). Existing models, constructed at various levels of complexity, have their strengths and weaknesses in supporting diverse intended uses. Additionally, current challenges in the application of watershed HM modeling are covered, including the representation of in-stream processes, organic matter/carbon dynamics and mitigation practices, the issues of model calibration and uncertainty analysis, and the balance between model complexity and available data. Finally, we outline future research requirements regarding modeling, strategic monitoring, and their combined use to enhance model capabilities. In particular, we envisage a flexible framework for future watershed-scale HM models with varying degrees of complexity to accommodate the available data and specific applications

Flood Forecasting Using Machine Learning Methods

This book is a printed edition of the Special Issue Flood Forecasting Using Machine Learning Methods that was published in Wate

The study of agricultural non-point source pollution control policy system

As the agricultural non-point source pollution(ANPSP) has become the most significant threat for water environmental deterioration and lake eutrophication in China, more and more scientists and technologists are focusing on the control countermeasure and pollution mechanism of agricultural non-point source pollution. The unreasonable rural production structure and limited scientific management measures are the main reasons for acute ANSPS problems in China. At present, the problem for pollution control is a lack of specific regulations, which affects the government\u27s management efficiency. According to these characteristics and problems, this paper puts forward some corresponding policies. The status of the agricultural non-point source pollution of China is analyzed, and ANSPS prevention and control model is provided based on governance policy, environmental legislation, technical system and subsidy policy. At last, the case analysis of Qiandao Lake is given, and an economic policy is adopted based on its situation

Impacts of Anthropogenic Activities on Watersheds in a Changing Climate

The immediate goal of this Special Issue was the characterization of land uses and occupations (LULC) in watersheds and the assessment of impacts caused by anthropogenic activities. The goal was immediate because the ultimate purpose was to help bring disturbed watersheds to a better condition or a utopian sustainable status. The steps followed to attain this objective included publishing studies on the understanding of factors and variables that control hydrology and water quality changes in response to human activities. Following this first step, the Special Issue selected work that described adaption measures capable of improving the watershed condition (water availability and quality), namely LULC conversions (e.g., monocultures into agro-forestry systems). Concerning the LULC measures, however, efficacy was questioned unless supported by public programs that force consumers to participate in concomitant costs, because conversions may be viewed as an environmental service

Numerical modeling of thermal bar and stratification pattern in Lake Ontario using the EFDC model

Thermal bar is an important phenomenon in large, temperate lakes like Lake Ontario. Spring thermal bar formation reduces horizontal mixing, which in turn, inhibits the exchange of nutrients. Evolution of the spring thermal bar through Lake Ontario is simulated using the 3D hydrodynamic model Environmental Fluid Dynamics Code (EFDC). The model is forced with the hourly meteorological data from weather stations around the lake, flow data for Niagara and St. Lawrence rivers, and lake bathymetry. The simulation is performed from April to July, 2011; on a 2-km grid. The numerical model has been calibrated by specifying: appropriate initial temperature and solar radiation attenuation coefficients. The existing evaporation algorithm in EFDC is updated to modified mass transfer approach to ensure correct simulation of evaporation rate and latent heatflux. Reasonable values for mixing coefficients are specified based on sensitivity analyses. The model simulates overall surface temperature profiles well (RMSEs between 1-2°C). The vertical temperature profiles during the lake mixed phase are captured well (RMSEs < 0.5°C), indicating that the model sufficiently replicates the thermal bar evolution process. An update of vertical mixing coefficients is under investigation to improve the summer thermal stratification pattern. Keywords: Hydrodynamics, Thermal BAR, Lake Ontario, GIS

Water Resource Variability and Climate Change

Climate change affects global and regional water cycling, as well as surficial and subsurface water availability. These changes have increased the vulnerabilities of ecosystems and of human society. Understanding how climate change has affected water resource variability in the past and how climate change is leading to rapid changes in contemporary systems is of critical importance for sustainable development in different parts of the world. This Special Issue focuses on “Water Resource Variability and Climate Change” and aims to present a collection of articles addressing various aspects of water resource variability as well as how such variabilities are affected by changing climates. Potential topics include the reconstruction of historic moisture fluctuations, based on various proxies (such as tree rings, sediment cores, and landform features), the empirical monitoring of water variability based on field survey and remote sensing techniques, and the projection of future water cycling using numerical model simulations