The Minho is an international river in the West Iberian Coast, more than 300 Km long, which drains a basin of 17.080 Km2, with a mean flow higher than 300 m3 s– 1, presenting a mesotidal partially mixed estuary, with a maximum width of 2 Km. During high floods it tends towards a salt wedge estuary, with the influence of spring tides extending for about 40 Km upstream. The estuary, which is still relatively low impacted by human activities, has high socio-economic importance, providing goods and services to 80.000 people, and high ecological value, presenting large diversity of habitats and biodiversity (included in Natura 2000; “Zona de Protecção Especial para Aves” (ZEP); Important Bird Area (IBA); CORINE Biotope).
Its biological communities have been studied at least since the 40s. However, regular and quantitative studies published in international journals took place mostly in the last two decades, mainly focusing on the benthic macroinvertebrates, namely molluscs, and fish communities. Illustrative publications addressing the most relevant aspects: Antunes et al., 1994; Antunes & Weber, 1996; Cabral et al., 2007; Guimarães et al., 2009; Sousa et al., 2005 ; 2006; 2007a;b; 2008 a; b; c; d; e; Vasconcelos et al., 2009).
The Mondego River drains a basin of approximately 6670 Km2 and its valley is considerably steep in upstream sections, forming a large alluvial plain consisting of good agricultural land in downstream areas. Since the 1960s, the Mondego catchment area underwent a large scale morphological modification, involving the construction of stone walls, to regulate the river water flow and enlarge harbour facilities, and water reservoirs to control floods, improve the uses of water resources, and produce electric power, which modified the riverbed topography and changed the system hydrodynamics. The river contributes presently with a high anthropogenic loading of nutrients and several chemicals into its relatively small estuary (1600 ha, splitting in two arms separated by an island in the terminal part), causing eutrophication. Besides, the estuary - Western coast of Portugal - North Atlantic Ocean Eco-region - supports industrial activities, salt-works, and aquaculture farms, and is the location of Figueira da Foz, a harbour and a centre of seasonal touristic activity.
A comprehensive study on the Mondego estuary environmental quality has been carried out during the last two decades, focusing on water quality, hydraulics and sediments dynamics, plankton communities (phyto, zoo, and ichtyoplankton), the term evolution of the benthic communities (intertidal and subtidal), and the changes in macrophytes’ beds (Zostera noltei) and green macroalgae distribution in relation to morphological alterations. Illustrative publications addressing the most relevant aspects: Cardoso et al., 2004; Dolbet et al., 2003; Lopes et al., 2005, Marques et al., 1997; 2003; Martins et al, 2001; Patrício & Marques, 2006; Patrício et al., 2009; Teixeira et al., 2008; 2009).
The Mira estuary, located in the south-west coast of Portugal, is a narrow entrenched system, with a length of more than 40 km and a mean depth of about 6 m. Until 2007 near the river mouth the estuary presented ecologically important macrophytes’ beds in the intertidal and shallow subtidal areas, which during 2008 collapsed due to unknown causes. Despite this, this estuary is considered well preserved, namely because the river basin has low human population densities and scarce industry, although some of its areas show a slight contamination by heavy metals, probably related to rice cultivation in its upper and middle reaches. In general, the system exhibits minor hydromorphological changes, mainly built for irrigation purposes, and touristic development appears presently to be the major threat, which is related to the fact that the Mira estuary is entirely included in a nature protected area (Parque Natural do Sudoeste Alentejano e Costa Vicentina).
The Mira estuary has been monitored for the physicochemical characteristics and biological communities, namely the fishes’ community, since the 1980s. Illustrative publications addressing the most relevant aspects: Adão, 2004; Adão et al, 2009; Andrade, 1986; Almeida, 1988; Chainho et al., 2008; Costa et al., 1994; 2008; Marques & Bellan-Santini, 1987).
Estuaries Minho, Mondego and Mira
Portugal LTER site