**3.1 Cyanobacteria management in reservoirs**

Water management in the Guadiana River watershed is a complex transnational problem and has been object of negotiations between Portugal and Spain for decades now. The last bilateral Agreement assured the integrated management of water and territory, covering quantitative and qualitative features, stipulating minimum flows (under normal rainfall conditions), and foreseeing the permanent exchange of hydrologic and environmental data and information (Mendes, 2010). Environmental laws, in both countries, ensure public access to the monitoring data, allowing for international comparison of water quality in different parts of the watershed.

Normal and drought conditions in the Guadiana catchment have been modelled in multiple hydrologic studies (e.g. Brandão & Rodrigues, 2000), allowing for better management in terms of water availability. Nevertheless, water quality concerns have been mostly ignored in water reservoir management decisions. Impaired sewage treatment and agro-industrial mal-practices have been repeatedly blamed for water quality deterioration in the Guadiana river basin, both in Portugal and Spain. Official reports for the Portuguese part of the

Ecological Tools for the Management of Cyanobacteria

unexpected results (Jacquet et al., 2004).

mixing.

upstream ecology.

Blooms in the Guadiana River Watershed, Southwest Iberia 173

elimination or water column mixing (Piehler, 2008). Such techniques often bring about

The only technique used both for prevention as well as mitigation of CHABs is the reduction of water residence time, through surface water discharges. It was well known in the 1960s (Odum, 1971) that the type of water discharges, and specially the height of water column, at which they were performed, strongly influenced plankton assemblages both up- and downstream from a reservoir. While surface release mainly exports warmer water and their plankton communities, bottom discharge introduces downstream cold, nutrient enriched water, keeping the warmer plankton rich waters inside the reservoir (Wright, 1967). This means that in reservoirs with bottom water flow, slow growing picoplankton, including cyanobacteria, is given the opportunity to develop blooms, instead of being rapidly flushed downstream. Water extraction for drinking water production tends to use water at a medium height of the water column, avoiding both the surface plankton, and the bottom metal enrichment. As observed in the Algarve reservoirs (Reis, unpublished data) withdrawing cold water from the hypolimnion and maintaining a floating inoculum of warm temperature selected cyanobacteria at the surface is transforming reservoirs into bioreactors like structures, favoring the occurrence of prolonged summer blooms. This water management technique tends to enhance stratification, delaying water column

As acknowledged by increasing awareness for the need of establishing an ecological flow, reservoir water management plays a key role in downstream river ecology, but also in

Rapid changes in the water level in response to summer increased water demand seriously hinders the installation of riparian vegetation, challenging some prevention techniques. Thus, caution should be taken when applying the same ecological criteria to reservoirs as for lakes, as advocated by the European WFD. In fact, in most natural lakes excess water overflows into effluent streams, exporting phytoplankton and accumulating nutrients in bottom colder water. On the contrary, in a semi-arid region most reservoirs managers seldom let water level rise enough to cause superficial overflow, and regulate water flow by

While classifying reservoirs as Heavily Modified Water Bodies (HMWB) the WFD allows for hydro-morphological pressures upon their ecological status, pressures to which natural lakes are not subjected. Reference conditions for establishing the ecological potential of the HMWBs should be given by reference conditions for the ecological status of natural lakes of the same eco-region, but reference conditions bearing natural lakes in a semi-arid region are

In the scope of the WFD implementation, the Guadiana watershed is included in the Mediterranean Region. The Geographical Intercalibration Group for this region (Med GIG) was responsible for establishing boundary values for the Med GiG Member State classification systems. Submitted values were adopted through the European Commission

smaller continuous discharges at mid-height of the dam wall.

scarce. In fact, there are no natural lakes in Southern Portugal.

Decision of 30 October 2008 (2008/915/EC).

**3.2 Ecological tools foreseen in the European Water Frame Directive** 

watershed specifically accuse illegal sewage discharges from pig production farms and olive mills of being responsible for high nitrate concentrations (PBH, 2001) As generally accepted, the mere existence of a new dam contributes to water quality degradation, since new populations and activities are attracted to the watershed. The main water user in the Guadiana watershed is agriculture, using 90 to 95% of the consumed water (PBH, 2001). It is thus expected that newly introduced crops after the start of the Alqueva dam irrigation system, in particular the new intensive olive tree orchards, will have strong impacts in future water quality.

A diagnosis of the actual ecological status of the catchment based on reliable methods and classification indices is therefore crucial. In Spain, the Confederácion Hidrográfica del Guadiana (CHG) and, in Portugal, the Administração da Região Hidrográfica do Alentejo, conducted a diagnostic snapshot classification, based on monitoring surveys from 2005 and 2006 for the Spanish part of the catchment, and on 2009-2010 data for the Portuguese watershed. Classification results, based on multiple indices, are available online (CHG, 2006, 2007-2008, 2009; ARH Alentejo, 2011).

According to these official reports, Guadiana reservoirs fall into diverse typologies, but the majority of them behave as warm monomyctic lakes, that remain stratified during the dry season and mix the water column in winter. As expected in result of high hydraulic residence time and elevated temperatures, these freshwater reservoirs are dominated, at least in the summer, by potentially toxic cyanobacteria from the genera *Pseudanabaena, Anabaena, Planktothrix, Oscillatoria., Geitlerinema., Aphanizomenon, Merismopedia, Microcystis, Woronichinia, Synechocystis,* and *Aphanocapsa*. (CHG, 2009) Toxic species of these cyanobacteria may reach high densities forming harmful algal blooms (HABs). In fact, the term water bloom originally referred to surface scums of cyanobacteria, but has since been applied to almost any planktonic population (not even necessarily algal) with densities significantly above the normal (Reynolds, 2006).

Managing these cyanobacteria harmful algal blooms (CHABs) has become a major concern in view of the potential health impacts both through drinking water or farming products consumption (Edwards et al., 1992; Hoegar et al., 2005).

CHABs management might involve prevention actions and/or mitigation solutions. Numerous techniques have been developed for these purposes, but as stated by Perovich et al. (2008) most of them have not been explicitly evaluated and optimized for use in the control of CHABs, particularly when toxins are present.

Prevention techniques rely on CHAB association with eutrophication processes and aim to control CHAB through nutrient limitation or decreasing hydraulic residence time. These techniques include watershed protection or restoration, through adequate sewage treatment implementation, promotion of farming good practices, particularly in the use of fertilizers and pesticides; erosion control; stimulation of margin riparian vegetation as well as controlled surface water discharges. Nutrient input reduction by controlling point sources has had success in several CHABs managing cases (Piehler, 2008), but it is now acknowledge that restoration efforts seldom bring aquatic communities back to the diversity and composition they used to bear before suffering human impacts (Jacquet et al., 2004)

Mitigation enforcement, by control and removal of an installed bloom, might rely on techniques such as the addition of algicides, the introduction of fish schools, surface scums

watershed specifically accuse illegal sewage discharges from pig production farms and olive mills of being responsible for high nitrate concentrations (PBH, 2001) As generally accepted, the mere existence of a new dam contributes to water quality degradation, since new populations and activities are attracted to the watershed. The main water user in the Guadiana watershed is agriculture, using 90 to 95% of the consumed water (PBH, 2001). It is thus expected that newly introduced crops after the start of the Alqueva dam irrigation system, in particular the new intensive olive tree orchards, will have strong impacts in

A diagnosis of the actual ecological status of the catchment based on reliable methods and classification indices is therefore crucial. In Spain, the Confederácion Hidrográfica del Guadiana (CHG) and, in Portugal, the Administração da Região Hidrográfica do Alentejo, conducted a diagnostic snapshot classification, based on monitoring surveys from 2005 and 2006 for the Spanish part of the catchment, and on 2009-2010 data for the Portuguese watershed. Classification results, based on multiple indices, are available online (CHG, 2006,

According to these official reports, Guadiana reservoirs fall into diverse typologies, but the majority of them behave as warm monomyctic lakes, that remain stratified during the dry season and mix the water column in winter. As expected in result of high hydraulic residence time and elevated temperatures, these freshwater reservoirs are dominated, at least in the summer, by potentially toxic cyanobacteria from the genera *Pseudanabaena, Anabaena, Planktothrix, Oscillatoria., Geitlerinema., Aphanizomenon, Merismopedia, Microcystis, Woronichinia, Synechocystis,* and *Aphanocapsa*. (CHG, 2009) Toxic species of these cyanobacteria may reach high densities forming harmful algal blooms (HABs). In fact, the term water bloom originally referred to surface scums of cyanobacteria, but has since been applied to almost any planktonic population (not even necessarily algal) with densities

Managing these cyanobacteria harmful algal blooms (CHABs) has become a major concern in view of the potential health impacts both through drinking water or farming products

CHABs management might involve prevention actions and/or mitigation solutions. Numerous techniques have been developed for these purposes, but as stated by Perovich et al. (2008) most of them have not been explicitly evaluated and optimized for use in the

Prevention techniques rely on CHAB association with eutrophication processes and aim to control CHAB through nutrient limitation or decreasing hydraulic residence time. These techniques include watershed protection or restoration, through adequate sewage treatment implementation, promotion of farming good practices, particularly in the use of fertilizers and pesticides; erosion control; stimulation of margin riparian vegetation as well as controlled surface water discharges. Nutrient input reduction by controlling point sources has had success in several CHABs managing cases (Piehler, 2008), but it is now acknowledge that restoration efforts seldom bring aquatic communities back to the diversity and composition they used to bear before suffering human impacts (Jacquet et al., 2004)

Mitigation enforcement, by control and removal of an installed bloom, might rely on techniques such as the addition of algicides, the introduction of fish schools, surface scums

future water quality.

2007-2008, 2009; ARH Alentejo, 2011).

significantly above the normal (Reynolds, 2006).

consumption (Edwards et al., 1992; Hoegar et al., 2005).

control of CHABs, particularly when toxins are present.

elimination or water column mixing (Piehler, 2008). Such techniques often bring about unexpected results (Jacquet et al., 2004).

The only technique used both for prevention as well as mitigation of CHABs is the reduction of water residence time, through surface water discharges. It was well known in the 1960s (Odum, 1971) that the type of water discharges, and specially the height of water column, at which they were performed, strongly influenced plankton assemblages both up- and downstream from a reservoir. While surface release mainly exports warmer water and their plankton communities, bottom discharge introduces downstream cold, nutrient enriched water, keeping the warmer plankton rich waters inside the reservoir (Wright, 1967). This means that in reservoirs with bottom water flow, slow growing picoplankton, including cyanobacteria, is given the opportunity to develop blooms, instead of being rapidly flushed downstream. Water extraction for drinking water production tends to use water at a medium height of the water column, avoiding both the surface plankton, and the bottom metal enrichment. As observed in the Algarve reservoirs (Reis, unpublished data) withdrawing cold water from the hypolimnion and maintaining a floating inoculum of warm temperature selected cyanobacteria at the surface is transforming reservoirs into bioreactors like structures, favoring the occurrence of prolonged summer blooms. This water management technique tends to enhance stratification, delaying water column mixing.

As acknowledged by increasing awareness for the need of establishing an ecological flow, reservoir water management plays a key role in downstream river ecology, but also in upstream ecology.

Rapid changes in the water level in response to summer increased water demand seriously hinders the installation of riparian vegetation, challenging some prevention techniques. Thus, caution should be taken when applying the same ecological criteria to reservoirs as for lakes, as advocated by the European WFD. In fact, in most natural lakes excess water overflows into effluent streams, exporting phytoplankton and accumulating nutrients in bottom colder water. On the contrary, in a semi-arid region most reservoirs managers seldom let water level rise enough to cause superficial overflow, and regulate water flow by smaller continuous discharges at mid-height of the dam wall.

While classifying reservoirs as Heavily Modified Water Bodies (HMWB) the WFD allows for hydro-morphological pressures upon their ecological status, pressures to which natural lakes are not subjected. Reference conditions for establishing the ecological potential of the HMWBs should be given by reference conditions for the ecological status of natural lakes of the same eco-region, but reference conditions bearing natural lakes in a semi-arid region are scarce. In fact, there are no natural lakes in Southern Portugal.
