Analysis of loads, water quality and certain biological production on the Kis-Balaton Water Protection System

Wetlands are important ecosystems: they are habitats for many key species and act as natural regulators of the environment. They filter water and remove pollutants with the help of plants. Constructed wetlands are artificial wetlands built to treat mainly wastewaters. These artificial ecosystems can also be used for freshwater treatment, such as river water. The Kis-Balaton Water Protection System (KBWPS) is one of them and the main goal of the system is to treat the River Zala water before its entrance in the Lake Balaton. The two mains objectives are to avoid the eutrophication of the Lake Balaton and improve the wetland ecosystems. It is a vast constructed wetland of 71 km2, situated at Southern part of Lake Balaton, in Hungary. The goal of this thesis was to analyze the loads, water quality and biological production of the KBWPS. Interpretation of three different sets of data and field work was carried out. The first set was about inflow and outflow data, from which the removal rates of different nutrients on a long time period were computed. The second data series contained regular water quality monitoring data along the flow path and the goal was to study the inner processes happening in the KBWPS. The last data set was collected on the field and included basic water properties and some biological and physico-chemical measurements, such as primary production or tecton analysis. It allowed to differentiate the water types of the system and their properties and to better understand the inner processes, particularly the biological characteristics of the system. The interpretation of the data series gave background to understand the processes occurring within the system and it helped to characterize the actual different water groups. It drew the main lines for possible more detailed analysis. This work was partly connected to a project aiming at the development of a monitoring system that serves a better management of the KBWPS. Several conclusions can be drawn from the results found in this thesis: • General conclusions on the system, which could apply to other systems of the same type. • Specific conclusions about the operation of the system, which would refer to this system only. • Some management and monitoring suggestions for the future system.

Hydrological Importance and Water Quality Treatment Potential of a Small Freshwater Wetland in the Humid Tropics of Costa Rica

Manon Bachelin

Rapid increases in population and growing food demand are causing widespread deterioration of tropical wetlands globally, and an increased focus on the role and function of these imperiled ecosystems is required. Objectives of this study were to investigate the hydrological dynamics and water quality treatment potential of a small freshwater wetland in the humid tropics of Costa Rica. High-resolution, spatially distributed surface water and meteorological data were combined with a detailed topographical survey to quantify the wetland water balance, hydroperiod, and seasonal variability of wetland area, volume, and residence time. The water balance was dominated by precipitation and outflow, with little contribution from runoff, except during the largest storms. Over 80% of the wetland was flooded continuously; hydroperiods in remaining areas were bi-modal. Small seasonal variations in wetland area, volume, and residence times yielded high and sustained water quality treatment potential. Potential pollutant removal efficiencies were 63.6-99.8% for biological oxygen demand; 60.0-99.8% for total suspended solids; 51.1-98.5% for total nitrogen; and 34.2-99.7% for total phosphorous. The study provides insights into the hydrological functions of this and similar small Central American wetlands and provides a template for extending in-depth hydrological monitoring to other tropical wetland sites.

2011

Has the Three-Gorges Dam made the Poyang Lake wetlands wetter and drier?

David Andrew Barry

The Three-Georges Dam holds many records in the history of engineering. While the dam has produced benefits in terms of flood control, hydropower generation and increased navigation capacity of the Yangtze River, serious questions have been raised concerning its impact on both upstream and downstream ecosystems. It has been suggested that the dam operation intensifies the extremes of wet and dry conditions in the downstream Poyang Lake, and affects adversely important local wetlands. A floodgate has been proposed to maintain the lake water level by controlling the flow between the Poyang Lake and Yangtze River. Using extensive hydrological data and generalized linear statistical models, we demonstrated that the dam operation induces major changes in the downstream river discharge near the dam, including an average "water loss". The analysis also revealed considerable effects on the Poyang Lake water level, particularly a reduced level over the dry period from late summer to autumn. However, the dam impact needs to be further assessed based on long-term monitoring of the lake ecosystem, covering a wide range of parameters related to hydrological and hydraulic characteristics of the lake, water quality, geomorphological characteristics, aquatic biota and their habitat, wetland vegetation and associated fauna.

American Geophysical Union2012

Optimizing turbine withdrawal from a tropical reservoir for improved water quality in downstream wetlands

Bernhard Wehrli, Alfred Johny Wüest

Large reservoirs in the tropics act as efficient nutrient traps and often develop hypoxic conditions in the hypolimnion. Both effects may have severe implications for aquatic ecosystems, such as limited primary production in downstream riparian agriculture and in natural wetlands due to reduced nutrient loads, and, if hypolimnetic waters are withdrawn, hypoxic conditions that pose toxic risks in downstream rivers. This study using Itezhi-Tezhi Reservoir (Zambia) as a model system aims at defining optimized turbine withdrawal to prevent hypoxia and to relieve low-nutrient conditions in the downstream Kafue Flats floodplain. A biogeochemical 1-D model simulating reservoir-internal processes and water quality in the outflow was used for estimating dissolved oxygen (DO) concentrations and inorganic nitrogen and phosphorus loads in the outflow. The water depth of turbine withdrawals was varied in a set of simulations to optimize outflow water quality. Releasing hypolimnetic water was shown to result in lower average outflow DO concentrations of 4.1-6.8 mg l(-1) compared to the current 7.6 mg l(-1). More importantly, the outflow will remain hypoxic during up to 189 days. Meanwhile, withdrawing nutrient-rich hypolimnetic water compensated effectively for nutrient losses to the reservoir sediment. Both outflow DO concentrations and nutrient output could be optimized in the scenario with 50% epilimnetic turbine discharge originating from approximate to 13 m depth. In this optimal scenario, hypoxia was prevented permanently, and average DO concentrations decreased moderately to 5.2 mg l(-1). Additionally, five-times higher dissolved inorganic N and dissolved inorganic P loads resulted in comparison to the current dam operation.

American Geophysical Union2013