Status of the Guadiana Estuary (south Portugal) during 1996-1998: An ecohydrological approach

Abstract

The aims of this study were to monitor basic hydrological and ecological characteristics of the Guadiana Estuary (1996-1998) before the construction of the Alqueva dam. This work was carried out to determine how environmental factors affect seasonal and tidal variations of plankton populations in the estuary. The available information on the subcatchment of the estuary (e.g., urban, agricultural and forested areas) was integrated into a geographic information system-based software program. Mean monthly river flow varied markedly on a seasonal and yearly basis. River flow near Mértola (ca 50 km upstream from the mouth) reached 3400 2 10 6 m 3 in winter and decreased to 42 2 10 6 m 3 in summer. With respect to nutrients, nitrogen to phosphorus ratios indicated some limitation by phosphorus, except at the end of summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms usually occurred in the upper/middle estuary. Estuarine Turbidity Maximum may significantly influence the retention of zooplankton in the estuary. The fish larval life cycle, especially sensitive to environmental alterations, showed high ratios of ribonucleic to desoxyribonucleic acids indicating good physiological condition. It was concluded that an ecohydrological approach, allowing integration of different elements from the cellular to the habitat level into a geographic information system, can contribute to a better understanding of the processes that influence the aquatic biota of the estuary. The approach will be a useful assessment tool for monitoring the estuary following dam completion.

Ichthyoplankton dynamics in the Guadiana estuary and adjacent coastal area, South-East Portugal

“…The ETM is commonly located in the middle estuary, near Foz de Odeleite (st. 7) (Chícharo et al, 2001). However, seston maximum values in this study were determined in the upper estuary, near Alcoutim (st. 9).…”

Encroachment of upland Mediterranean plant species in riparian ecosystems of southern Portugal

“…The majority of watercourses are intermittent, drying during the summer. Along watercourses, the dominant riparian species are the white poplar (Populus alba), raywood ash (Fraxinus angustifolia), grey willow (Salix atrocinerea), African tamarisk (Tamarix africana), oleander (Nerium oleander) and alder (Alnus glutinosa) (Aguiar et al 2006;Chícharo et al 2001). Human activities include traditional agriculture (olive groves, vineyards, cereal production and cork extraction) and livestock production (cattle, sheep, goats and pigs), which require water extraction from neighbouring watercourses, and result in reduction of riparian vegetation by clear-cutting or grazing.…”

An analysis of the impacts of climatic variability and hydrology on the coastal fisheries, Engraulis encrasicolus and Sepia officinalis, of Portugal

“…Therefore, the significant negative relationship of E. encrasicolus with WmaG-Aut, implies that the fi sh larvae that are spawned during spring or summer, suffer higher mortality due to the unfavorable wind condition in the southern coast of Portugal. Wind magnitude may affects larvae swimming behavior during pelagic stages, and the period larvae remain in pelagic stage before settlement, and consequently long term fi shing recruitment (Chícharo et al 2001a;2001b). Moreover, these young larvae may be transported further offshore or locations where food is limiting or with other adverse environmental conditions.…”

“…However, most studies that addressed the relationship between ecohydrology and fi sheries dealt mostly with estuarine resources and particularly with river discharge (hydrology) as a single environmental variable (Chícharo et al 2001a;2006). In contrast, those works that attempt to link coastal fi sheries with climatic factors (multipressures), under the ecohydrological framework, are scarce (Chícharo et al 2001b).…”

“…This remains diffi cult because small pelagic fi shes, such as anchovy, showed important long-term natural fl uctuations in their abundance (Lluch-Belda et al 1989). Furthermore, the impact of changing freshwater fl ow from rivers into coastal waters throughout the world proved to be a crucial factor for this fi sheries (Chícharo et al 2001a;2001b;Palomera et al 2007;Bergeron et al 2010). Thus, a favorable hydrological and biological conditions is vital for successful recruitment of larvae fi sh (Wilson et al 2008) which may consequently affect fi shing yields (Hare et al 2010).…”