The Guadalquivir estuary in the SW of Spain plays a vital role as nursery area (fishing reserve) for several species, like anchovies, important for fisheries in the Gulf of Cádiz (Atlantic Ocean), and therefore has been monitored during the last 25 years. It is a highly anthropogenically impacted estuary, subject to dredging for navigation, high nutrient loads and reduced connection to the adjacent marshes, resulting in a high turbidity. A major part of freshwater input (80%) is controlled by a dam situated at 110 km from the estuary mouth. Temporarily high discharges can result in extreme turbidity events, while prolonged low river discharge leads to lower turbidity and higher salt intrusion into the estuary. We studied two sites in the estuary during three years with different dam discharge regimes and evaluated how these changes in environmental conditions affected phytoplankton composition, biodiversity and productivity. A prolonged period of low river discharge resulted in two chl a peaks in summer when normally only one peak is observed. It also led to a higher biodiversity and to the dominance of a previously undetected green alga. Normally, pennate diatoms comprise a considerable part of the phytoplankton, indicating that microphytobenthos may significantly contribute to the water column community. This coincided with a much higher areal gross primary production measured in the intertidal sediment compared to the water column. These data can be used to explain patterns observed in higher trophic levels.

Primary Presenter: Stefanie Van Bergeijk, (IFAPA) - Centro El Toruño (stefaniea@juntadeandalucia.es)

Authors:

Stef van Bergeijk, Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA) - Centro El Toruño  (stefaniea@juntadandalucia.es)

Silvia Meneses Gómez, Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA) - Centro El Toruño  (silvia.menesesgomez@alum.uca.es)

Emilio García-Robledo, University of Cádiz  (emilio.garcia@uca.es)

Valle Pérez Rodríguez, University of Cádiz  ()

César Vilas Fernández, Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA) - Centro El Toruño  (cesar.vilas@juntadeandalucia.es)