Cyanobacterial blooms in natural waters in southern Portugal: a water management perspective

Abstract

This synthesis of 3 studies from 2 regions of southern Portugal (Alentejo and Algarve) was part of a workshop focusing on cyanobacteria held at the SAME 10. The first study monitored impacts of the large Alqueva dam on the Guadiana estuary since 1996, revealing changes in sediment load, nutrient regime and phytoplankton succession. Prior to dam construction, dense cyanobacterial blooms occurred in the upper estuary during summer and fall. After dam construction, chlorophyll concentration, phytoplankton diversity and abundances of cyanobacteria decreased, contrary to predictions. Mycrocystins remained at low levels in the seston and undetectable in water samples, except during summer 2003 when the particulate fraction contained 1 µg l -1 , while chlorophyll concentrations and abundances of potentially toxic cyanobacteria remained low. Algarve reservoirs studied since 2001 revealed differences in phytoplankton dynamics. In the western mesotrophic reservoirs (Bravura and Funcho), 40 to 50% of surface samples contained cyanobacterial concentrations of ≥2000 cells ml -1 , while over 80% of samples from the eastern oligotrophic reservoirs (Odeleite and Beliche) exceeded this value. Spring blooms were dominated by Oscillatoriales in Odeleite and Beliche and by Chroococcales in Bravura and Funcho. Bloom composition seemed to depend on water temperature and management strategies, while toxin concentrations reflected the increased biomass of toxic species. Finally, phytoplankton communities and microcystin production in 5 Alentejo freshwater reservoirs were studied from May to December 2005 and April to July 2006. Cyanobacterial blooms occurred, with varying intensities, not only during summer but also occasionally in winter. Microcystins were detected in 23% of the samples (n = 51), but without correlation with cyanobacterial biomass. Although Microcystis aeruginosa seemed to be the major producer of microcystins, other potentially toxic species were found. In summary, the varying pattern of cyanobacterial bloom occurrence and toxicity requires a systematic approach to monitoring programs for adequate risk assessment.

Estimation of phosphorus export from a Mediterranean agricultural catchment with scarce data

“…The results are discussed in the light of concepts and data from the literature (soft data validation). The Mediterranean catchment of the intermittent stream Enxoe, in Portugal, which discharges into a downstream reservoir that has suffered from cyanobacteria blooms in the past (Galvão et al 2008) was chosen for the case study.…”

Ecological Tools for the Management of Cyanobacteria Blooms in the Guadiana River Watershed, Southwest Iberia

“…As previously described by Galvão et al (2008), microcystin concentration were generally not correlated with cyanobacteria abundance or biomass in natural waters (freshwater reservoirs and Guadiana river, South Portugal), since different strains and/or species could produce microcystins at different rates depending on cell cycles and environmental conditions, which has also been documented in laboratory analyses (eg. Kameyama et al, 2004;Rapala et al, 1997;Saker et al, 2005).…”

“…75 %), and the recent construction of the large Alqueva dam (ca. 150 km upstream from river mouth) increased flow regulation up to 81% of the total catchment area (55 000 km 2 ) starting in 2003 (Galvão et al, 2008). Since human activity in the Guadiana watershed is mostly agriculture and the main anthropic pressure is associated to dams, the Guadiana is considered one of the best conserved but also most vulnerable estuaries of the Iberian Peninsula (Vasconcelos et al 2007).…”

“…Unusual surface and bottom DIN levels occurred in November 2006 due to exceptional water transfer from Odeleite to Beliche. As stated in Galvão et al, 2008, management of the underground channel between the two reservoirs has been associated with conditions favoring blooms through bottom sediment and nutrient resuspension. Consequent water column mixing was revealed by similar bottom and surface temperatures.…”

“…Cyanobacteria blooms have been repeatedly associated with eutrophication processes (Berg et al, 1987;Codd, 2000;Chorus, 2005;Druvietis, 1997;Pinckney et al, 1998), but they might also dominate under oligotrophic conditions (Galvão et al, 2008;Havens et al, 2003;Mez et al, 1997;Sivonen & Jones, 1999).…”