SALMOD, a Salinity Management Tool for Irrigated Agriculture

This paper presents an irrigation farm management tool, SALMOD (Salinity And Leaching Model for Optimal irrigation Development), that calculates the profit maximizing crop enterprise composition and irrigation management options for farm specific soil type, drainage status and irrigation system composition subject to various regional control measures and expected irrigation water salinities. After stating the water quality problem, and particularly salinisation in Southern Africa, the input data requirements and the results of SALMOD and their usefulness at farm level, are discussed. The impact of various possible regional or policy regulations are then discussed. SALMOD was developed for irrigators in the lower Vaal and Riet Rivers in South Africa. These farmers have been experiencing rapidly fluctuating salinity levels in their irrigation water, resulting in soil salinisation, yield loss and subsequent financial instability. SALMOD calculates the profit maximizing crop choice and distribution over the farm, matching the crop choice with soil type, drainage status and irrigation system, indicating the optimal leaching vs. yield reduction seasonal management options as well as calculate long term management options such as underground drainage installation, a change in irrigation system or the construction of on farm storage dams. Leaching is necessary to maintain an acceptable salt balance in the root-zone of irrigated crops. This however contributes to point and non-point source water pollution externalities if not managed correctly. Results show valuable policy information regarding the interactions between artificial drainage subsidisation, return flow restrictions and on-farm storage.Irrigation, water quality, return flows, salinisation, leaching, non-point source pollution, on-farm storage, SALMOD, linear programming, GAMS, Farm Management, Land Economics/Use,

Modelling the physical dynamics of estuaries for management purposes.

Doctoral Degree. University of KwaZulu-Natal, Durban.South African estuaries are characterised by highly variable inflows owing to the semi-arid nature of the land mass which they drain. The interaction of this variability with that of the marine environment (seasonality, high wave events, synoptic effects) gives rise to the distinctive character of South African estuaries. In general, they are small, micro-tidal, bar-built systems with strong flood tidal dominance. Approximately half of the 273 systems along the coast exhibit intermittent closure of the mouth, while a number can become hypersaline during dry periods. In view of the increasing development pressures on the rivers and estuaries of South Africa and their strong dependence on freshwater flow for the maintenance of their character and functioning, and the need for justifiable, scientifically-based decision making regarding the freshwater requirements of estuaries is evident. This study was initiated to address this issue by first developing a model to simulate the physical dynamics of South African estuaries over time scales from months to years, so enabling prediction of the medium to long term consequences of alterations in the freshwater inflow on the abiotic components of an estuary. Thereafter, the efficacy of management policies involving water releases and mouth breachings could be evaluated in terms of their success in maintaining the character and functioning of an estuary. A semi-empirical estuarine systems model incorporating seven state variables, namely water volume, salt content, stratification, circulation, tidal flushing, freshwater flushing and the height of the sill at the mouth, was formulated and implemented on two case studies. Estuarine physics concepts were incorporated dynamically in the model in a novel manner. For instance, the bulk densimetric Froude number and the Estuarine Richardson number are used in the simulation of the stratification-circulation states, while the Ackers and White sediment transport formula was modified to yield results which agreed with field observations of the closure and breaching of the mouth of the Great Brak Estuary. Additionally, tidal exchange through the mouth was modelled phenomenologically and successfully calibrated against observations for both case studies. Model results were found to be fairly robust to uncertainties in parameter values. However, most encouraging of all is that behaviour known to occur in shallow estuaries, such as modulation of the n11.:.m water level by low frequency forcing and the generation of overtides, was reproduced by the estuarine systems model although it was not specifically included in the model formulation. The model is thus considered to reliably predict the physical dynamics of South African estuaries over time scales of months to years. A number of management policies involving freshwater allocations, water releases and breachings of the mouth (where appropriate) were tested on the two case studies, namely the Great Brak Estuary, a small, temporarily open system, and the permanently open Kromme Estuary. The results indicate an increase in marine dominance as freshwater flow to the estuaries decreases. The variability in the estuarine environment declines and the systems become more inert to freshwater flooding and more sensitive to marine forcing. By applying the estuarine systems modelling approach, the performance of different management policies could be evaluated in comparison with reference policies. Accordingly, for both case studies, preferred management policies which utilize the present total annual allocations to the estuaries more beneficially could be indicated. Further management applications included the use of the estuarine systems model in a linked system of abiotic and biotic models to facilitate more comprehensive prediction of the consequences of freshwater abstraction and so more informed assessment of estuarine freshwater requirements. The estuarine systems model results were critical in enabling the prediction of the faunal and floral responses in the intermittently closed Great Brak Estuary as it is presently the only abiotic model capable of simulating the closure and breaching of the estuary mouth over a number of years. It is anticipated that further developments will occur in biological prediction in the near future and that this could require developments or adaptations to the estuarine systems model, particularly when details of the type of information required for biological prediction becomes known. Additionally, the use of the estuarine systems model in a strategic management sense is suggested. It could play a role as a screening tool for regional water resource planning, while the preliminary quantification of the extent of anthropogenic influence in expediting the movement of estuaries towards the later successionary stage of a coastal lagoon is a powerful indication of the level of prediction which could become possible in the future. Thus enhanced management decision making is now possible on a site specific basis and at a more strategic water resources planning level

Florida Bay Science Program: a synthesis of research on Florida Bay

This report documents the progress made toward the objectives established in the Strategic Plan revised in 1997 for the agencies cooperating in the program. These objectives are expressed as five questions that organized the research on the Florida Bay ecosystem: Ecosystem History What was the Florida Bay ecosystem like 50, 100, and 150 years ago? Question 1—Physical Processes How and at what rates do storms, changing freshwater flows, sea level rise, and local evaporation and precipitation influence circulation and salinity patterns within Florida Bay and exchange between the bay and adjacent waters? Question 2—Nutrient Dynamics What is the relative importance of the influx of external nutrients and of internal nutrient cycling in determining the nutrient budget for Florida Bay? What mechanisms control the sources and sinks of the bay’s nutrients? Question 3—Plankton Blooms What regulates the onset, persistence, and fate of planktonic algal blooms in Florida Bay? Question 4—Seagrass Ecology What are the causes and mechanisms for the observed changes in the seagrass community of Florida Bay? What is the effect of changing salinity, light, and nutrient regimes on these communities? Question 5—Higher Trophic Levels What is the relationship between environmental and habitat change and the recruitment, growth, and survivorship of animals in Florida Bay? Each question examines different characteristics of the Florida Bay ecosystem and the relation of these to the geomorphological setting of the bay and to processes linking the bay with adjacent systems and driving change.This report also examines the additional question of what changes have occurred in Florida Bay over the past 150 years

Trinity - San Jacinto estuary: A study of the influence of freshwater inflows

The provision of sufficient freshwater inflow to Texas bays and estuaries is a vital factor in maintaining estuarine productivity, and a factor contributing to the near-shore fisheries productivity of the Gulf of Mexico. This report analyzes the interrelationships between freshwater inflows and estuarine productivity, and established the seasonal and monthly freshwater inflow needs, for a range of alternative management policies, for the Trinity- San Jacinto estuary of Texas. Simplifying assumptions must be made in order to estimate freshwater inflow requirements necessary to maintain Texas estuarine ecosystems. A basic premise developed in this report is that freshwater inflow and estuarine productivity can be examined through analysis of certain key indicators. The key physical and chemical indicators include freshwater inflows, circulation and salinity patterns, and nutrients. Biological indicators of estuarine productivity include selected commercially important species. Useful species are generally chosen on the basis of their wide distribution throughout each estuarine system, a sensitivity to change in the system, and an appropriate life cycle to facilitate association of the organism with estuarine productivity

Effects of Wetland Management and Associated Abiotic Factors on Rare Plant Communities of Spring-fed Arid Wetlands

Spring-fed arid wetlands support high biological productivity and are hotspots for endemism and distribution of rare plants, making them areas of high conservation value. These systems are driven by complex interactions among groundwater discharge and the geomorphic and climatic features of the setting, which provide gradients of edaphic conditions, particularly soil moisture and salinity that influence the presence and abundance of rare plant communities. However, spring-fed arid wetlands are at particular risk of increases in salinity and drier hydrological regimes due to anthropogenic activities. Such alterations to abiotic conditions may jeopardize the distribution and abundance of rare plants by exceeding their tolerances during their life cycle. In this study, I evaluate how wetland management practices and associated abiotic factors affect three poorly known rare plants of spring-fed arid wetlands in Bitter Lake National Wildlife Refuge, New Mexico: the annual Pecos sunflower (Helianthus paradoxus, federally Threatened), the biennial Wright’s marsh thistle (Cirsium wrightii, proposed for listing as Threatened), and the annual Leoncita false-foxglove (Agalinis calycina, federal Species of Concern). In the lab, I used incubators to determine seed germination requirements and responses to field-derived salinities for the three species. Then, in the field, I established a series of monitoring plots equipped with groundwater wells to evaluate the hydrologic and soil factors influencing plant presence and abundance, with a particular focus on soil moisture and salinity. Pecos sunflower and Wright’s marsh thistle showed high seed germination percentages at all salinity treatments, while Leoncita false-foxglove exhibited negative responses to increasing salinities. In the field, Pecos sunflower was the most abundant and widespread of the three and was positively associated to moist-soil management. Wright’s marsh thistle and Leoncita false-foxglove occurred on permanently saturated soils associated to shallow groundwater. Reduced salinities during the spring were important for the three species. My results provide new plant life history information and insight on the abiotic processes needed to support their abundance. This information will guide management strategies to enhance their abundance and prevalence in the long term, as well as restoration efforts in areas where their populations are unstable or have been extirpated

Fifth Florida Bay Science Conference: Joint Conference on the Science and Restoration of the Greater Everglades and Florida Bay Ecosystem; Westin Innisbrook, Palm Harbor, FL; April 13-18, 2003: "From Kissimmee to the Keys"

This joint conference is to provide a forum for physical, biological, and social scientists to share their knowledge and research results concerning restoration of the Greater Everglades and Florida Bay Ecosystem

Mud crab aquaculture in Australia and Southeast Asia - Proceedings of the ACIAR Crab Aquaculture Scoping Study and Workshop 28–29 April 2003, Joondooburri Conference Centre, Bribie Island

Proceedings of the ACIAR Crab Aquaculture Scoping Study and Workshop 28–29 April 2003, Joondooburri Conference Centre, Bribie IslandCrop Production/Industries,

The Ecology and Sociology of the Mission-Aransas Estuary : An Estuarine and Watershed Profile

watershed profileThe Mission-Aransas National Estuarine Research Reserve (NERR) is one of 28 national estuarine reserves created to promote the responsible use and management of the nation's estuaries through a program combining scientific research, education, and stewardship. The purpose of this document is to provide researchers and resource managers with an adequate basis of knowledge to further development of scientific studies and applied management investigations. This document describes the different physical ecosystem components, ecological processes, habitats, and watersheds of the Reserve. The Mission-Aransas NERR is a complex of wetland, terrestrial, and marine environments. The land is primarily coastal prairie with unique oak motte habitats. The wetlands include riparian habitat, and freshwater and salt water marshes. Within the water areas, the bays are large, open, and include extensive wind tidal flats, seagrass meadows, mangroves, and oyster reefs. This site profile describes each habitat by their location, type, distribution, abundance, current status and trends, issues of concerns, and future research plans. Research within the Mission-Aransas NERR seeks to improve the understanding of the Texas coastal zone ecosystems structure and function. Current research includes: nutrient loading and transformation, estimates of community metabolism, water quality monitoring, freshwater inflow, climate change and fishery habitat. Harmful algal blooms, zooplankton, coliform bacteria, submerged aquatic vegetation, and marsh grass are monitored through the System- Wide Monitoring Program (SWMP). This document also describes the climate, hydrography and oceanography, geology, water quality, and endangered species within the Mission-AransasUniversity of Texas Marine Science InstituteMarine Scienc

Water Management Plan for the Town of Perenjori

The Rural Towns – Liquid Assets (RT–LA) project was established with the aim of integrating salinity, waterlogging and flooding control with development of new water supplies in wheatbelt towns, and where possible, finding ways of putting the excess water to commercial use. Following the identification of effective integrated water management strategies, these have been applied to the 15 Shires participating in the DAFWA led RT–LA project. This report summarises the outcomes from all scientific investigations undertaken for Perenjori. In addition it presents the water management options, a preliminary analysis of those options and the priority recommended ones. Due to the decline in rainfall over the past 10 years, Perenjori groundwater levels have shown a declining trend below the townsite since 2000, when groundwater monitoring by DAFWA in the townsite commenced. Hydrogeological studies identified groundwater pumping was not an effective solution for Perenjori to control watertable levels in the high salinity risk areas of the townsite. The studies demonstrated that only limited volumes of groundwater could be abstracted by pumping because the drawdown affects would be constrained by the geological properties. It is concluded that salinity control or water production from under the townsite via groundwater pumping is not a technically viable option. Instead, the RT–LA project has focused on surface water management options that will enable new water supplies to be developed which will also alleviate salinity, watertable, waterlogging and flooding problems. An integrated scheme such as this will provide cost effective solutions to the annual problem of irrigation water shortages. Over time, the proposed surface water diversion and harvesting schemes will reduce salinity risk by diverting and utilising runoff water which would otherwise have contributed to local recharge. Option 1, construction of a new 30ML dam in the paddock east of town belonging to Mr Jim Gilmour, is recommended as the first priority action. Along with the other options outlined in this Water Management Plan, Option 1 offers a combination of surface water engineering solutions to capture the town’s runoff and provide up to an additional 31 ML/yr, or 155 per cent of the total existing demand