Ierotheos Zacharias

Restoration of eutrophic freshwater by managing internal nutrient loads. A review

Eutrophication has become the primary water quality issue for most of the freshwater and coastal marine ecosystems in the world. It is one of the most visible examples of biospheres alteration due to human activities affecting aquatic ecosystems from the Arctic to the Antarctic. As eutrophication becomes frequent and many eutrophic ecosystems have difficulties meeting the EU Water Framework Directive (WFD) criteria the removal of phosphate and/or ammonium gains great importance, in water treatment. The objective of this paper is to review the restoration methods of eutrophic ecosystems, emphasizing remediation methods of internal nutrient release budget as a major factor to control eutrophication. The use of phosphate inactivation agents as a restoration tool, their capacity and application methods, as well as the individual results (in water quality, algal blooms, flora and fauna) in areas that have been implemented were also examined. Moreover, a conceptual model was conducted as a process to determine remediation technique, highlighting the need of an integrated approach to eutrophication management. The chemical lake restoration methods are not a panacea and their implementation should consist a targeted management approach as a part of an integrated management plan. The longevity of the treatment effectiveness using P-inactivation agents is reduced if not given the necessary importance in managing the external nutrient loads. The successful implementation of internal P management measures requires a site-specific study of a range of factors affecting viability of the method used, in connection with an assessment of the potential adverse effects on humans, livestock, biotic and abiotic factors.

Storage, redistribution and net export of dissolved and sediment-bound nutrients, Vejle Fjord, Denmark

Sixty three percent of the nitrogen (total transported 2041 × 103 kg y−1) and 17% of the phosphorus (total 159 × 103 kg y−1) supplied from terrestrial sources to Vejle Fjord during the period September 1988 to October 1989 is exported to the Kattegat. The sediment nutrient concentrations in the estuary are mainly governed by hydrography and resuspension. The general wind-induced circulation consists of outgoing currents along the southern side and ingoing currents along the northern side of the estuary. The sediments in shallow water on the southern side had higher concentrations of nutrients.Resuspension resulted in large differences between gross sedimentation and net sedimentation, especially in shallow water. Gross sedimentation of total-N in shallow water was 819 × 103 kg y−1 compared to a net sedimentation of 19 × 103 kg y−1. The shallow water areas in the estuary (10% of the area), had a net sedimentation of total-N which was less than 1% of the supply.Wave-induced resuspension only occurs in exposed parts of the deep water area, when wind velocities exceed 10 m s−1. The concentration of nutrients in the sediments was found to increase with distance from the river (the source) and with increasing depth, as a result of resuspension near the river mouth in the inner part of the estuary. In sheltered parts of the estuary there was no wave-induced resuspension and the net sedimentation equals gross sedimentation. The rate of sedimentation in deep water areas was 12.2 g m−2y−1 for total-N and 2.1 gm−2y−1 for total-P.

Climate change impacts on a Mediterranean river and the associated interactions with the adjacent coastal area

Abstract The Spercheios river basin—coastal marine area is a complex natural and interdependent ecosystem, highly affected by human activities and interventions. Such sensitive systems are even more vulnerable to alterations of the hydrological cycle components and it is likely to be rapidly and severely affected by climate change. In order to examine the climate change impacts on water resources of the study area, the interaction between the hydrology of the river basin and the hydrodynamic of the coastal marine area was examined using two models. Based on the results, although the irrigation needs decrease for the years 2050 and 2100 due to corresponding decrease in cultivated areas, temperature increase and precipitation decrease are both expected to influence the water resources of the Spercheios river basin, which will directly affect the Maliakos Gulf hydrodynamics. The necessity to adopt a holistic approach which will treat river basins and coastal marine areas as an integrated whole, with regard to environmental, socio-economic and political framework, is evident.

Assessing the Impact of Climate Change on Sediment Loads in a Large Mediterranean Watershed

Abstract Acheloos is the second longest and the largest, in terms of discharge, native river in Greece, supplying three hydroelectric dams along its route. The Kremasta dam, which forms the largest artificial lake in Greece, is the first dam fed by Acheloos and two other rivers. Sediment accumulation in such large reservoirs is of major concern, as it reduces storage capacity and hydropower production. In this study, the reservoir is utilized as a live record of constantly renewed sediment deposition data, which is used as a means of assessing the accumulated sediment loads originating from the watershed. The Soil and Water Assessment Tool model was combined with data from previous field surveys, which estimated the volume of deposited sediments in the reservoir. After modeling the discharge of three rivers into the Kremasta reservoir using available monthly field data from 1965 to 2001, the Soil and Water Assessment Tool was successfully calibrated against the deposited sediment mass data, accumulated at the reservoir during the first 34 years of its operation. Simulation results for a set of International Panel on Climate Change “A1B” climate change scenarios suggested a 14.6% decrease in the average rainfall on the watershed, between the 2016–2055 and 2056–2095 time periods, which induces a proportional (19.5%) decrease in flow and a milder (7.9%) decrease in the deposited sediment mass. It was also estimated that by the year 2100 the deposited sediment volume will occupy 6.1% of the effective volume of the reservoir, a value much lower than the estimated dead volume of the dam (17.4%).

Combined hydrological, rainfall–runoff, hydraulic and sediment transport modeling in Upper Acheloos River catchment

AbstractThe downstream impact of dams may solve but may also cause problems in catchment management. The present study assesses the hydrodynamic and sand transport regime of Acheloos River, focusing in the area upstream of the Kremasta Dam. Calibration and validation of water discharge presented very satisfactory coefficients of efficiency (Nash–Sutcliffe up to 85%). The proposed and applied in this study system of models and methods may be used as a water and sediment management tool in dammed or undammed catchments. The results from the present study are deemed to contribute towards improving the existing knowledge of the Acheloos hydrodynamic regime and better comprehending the sediment transport mechanisms.