Driving Factors of Geosmin Appearance in a Mediterranean River Basin: The Ter River Case

In recent decades, human activity coupled with climate change has led to a deterioration in the quality of surface freshwater. This has been related to an increase in the appearance of algal blooms, which can produce organic compounds that can be toxic or can affect the organoleptic characteristics of the water, such as its taste and odor. Among these latter compounds is geosmin, a metabolite produced by certain cyanobacteria that confers an earthy taste to water and which can be detected by humans at very low concentrations (nanogram per liter). The difficulty and cost of both monitoring the presence of this compound and its treatment is a problem for drinking water treatment companies, as the appearance of geosmin affects consumer confidence in the quality of the drinking water they supply. In this field study, the evaluation of four sampling sites with different physicochemical conditions located in the upper part of the Ter River basin, a Mediterranean river located in Catalonia (NE Spain), has been carried out, with the aim of identifying the main triggers of geosmin episodes. The results, obtained from 1 year of sampling, have made it possible to find out that: (i) land uses with a higher percentage of agricultural and industrial activity are related to high nutrient conditions in river water, (ii) these higher nutrient concentrations favor the development of benthic cyanobacteria, (iii) in late winter–early spring, when these cyanobacteria are subjected to both an imbalance of the dissolved inorganic nitrogen and soluble reactive phosphorus ratio, guided by a phosphorus concentration increase, and to cold–mild temperatures close to 10°C, they produce and release geosmin, and (iv) 1–2 weeks after cyanobacteria reach a high relative presence in the whole biofilm, an increase in geosmin concentration in water is observed, probably associated with the cyanobacteria detachment from cobbles and consequent cell lysis. These results could serve as a guide for drinking water treatment companies, indicating under what conditions they can expect the appearance of geosmin episodes and implement the appropriate treatment before it reaches consumers’ tap.

Numerical assessment of climate change impact on the hydrological regime of a small Mediterranean river, Lesvos Island, Greece

Frequency of flash floods and droughts in the Mediterranean climate zone is expected to rise in the coming years due to change of its climate. The assessment of the climate change impact at a basin scale is essential for developing mitigation and adaptation plans. This study analyses the variation of the hydrologic regime of a small Mediterranean river (the Kalloni river in Lesvos Island, Greece) by the examination of possible future climate change scenarios. The hydrologic response of the basin was simulated based on Hydrologic Modeling System developed by the Hydrologic Engineering Center (HEC-HMS). Weather Generator version 6 from the Long Ashton Research Station (LARS-WG 6.0) was utilized to forecast climate data from 2021 to 2080. These forecasted climate data were then assigned as weather inputs to HEC-HMS to downscale the climate predictions of five large-scale general circulation models (GCMs) for three possible emission scenarios (such as RCP 2.6, RCP 4.5, and RCP 8.5). The alteration of the Kalloni hydrologic regime is evaluated by comparing GCMs based estimates of future streamflow and evapotranspiration with business as usual (BaU) scenario. Variation was noted in seasonal and in annual scale forecasting of long-term average discharges, which show increasing trend in autumn and decreasing in summer and there is observed a general upward trend of actual evapotranspiration losses.

Tracking the Causes of a Mass Fish Kill at a Mediterranean River within a Protected Area

In this study, an extreme event observed at the intermittent Mediterranean Bogdanas River within the territory of the protected area of the National Park of Lakes Koronia-Volvi and Macedonian Temp that led to a mass fish kill was investigated. We aimed to define the main pressures affecting water quality and biota, specifically fish. No organic poisons, pesticides or heavy metal concentrations were detected in fish tissue, while high values of BOD5, COD, TN and conductivity were measured in water samples. These results, combined with the prevailing hydroclimatic factors (high temperatures and low water flow), lead to the assumption that mass fish mortality was triggered by high organic loads discharged from an upstream point source of pollution, and in particular an active landfill.

Impact of Climate Change on Worlds Economy and Hydrological System

The Mediterranean region appears to be particularly responsive to global and climate change. The global mean temperature has increased by 0.8°C compared with preindustrial levels while Europe has warmed more than the global average, especially in the Mediterranean, the north-east region, and mountain areas. Increasingly drier conditions are observed in the Mediterranean region both in the wet and in the dry season (~20%) with an increasingly irregular precipitation in both seasons (~ 40% in the dry season). The annual river flows have also decreased in the Mediterranean region, a difference projected to exacerbate due to climate and global change, which made the Mediterranean region most prone to an increase in drought hazard and water stress. Iberian Peninsula has been already affected by several major droughts, e.g. the recent one in 2005. These driving forces of global change impacts on water availability, water quality, and ecosystem services in Mediterranean river basins of the Iberian Peninsula, as well as their impacts on the human society and economy, makes it an important issue on the EU agenda. This thesis is an approach to quantify and analyze the water quantity, hydrological ecosystem services, and water supply in temperate regions under environmental changes. A hydrological model is developed for a low flow Mediterranean river (Francolí River) to assess the water allocation situation in the river basin using MIKE BASIN. Since the Mediterranean regions are hard hit by the changes in the global climatic patterns, the hydrological model focuses on the water distribution system & flow in the region.