Environmental Forcing of Phytoplankton in a Mediterranean Estuary (Guadiana Estuary, South-western Iberia): A Decadal Study of Anthropogenic and Climatic Influences

Abstract

Phytoplankton seasonal and interannual variability in the Guadiana upper estuary was analyzed during 1996-2005, a period that encompassed a climatic controlled reduction in river flow that was superimposed on the construction of a dam. Phytoplankton seasonal patterns revealed an alternation between a persistent light limitation and episodic nutrient limitation. Phytoplankton succession, with early spring diatom blooms and summer-early fall cyanobacterial blooms, was apparently driven by changes in nutrients, water temperature, and turbulence, clearly demonstrating the role of river flow and climate variability. Light intensity in the mixed layer was a prevalent driver of phytoplankton interannual variability, and the increased turbidity caused by the Alqueva dam construction was linked to pronounced decreases in chlorophyll a concentration, particularly at the start and end of the phytoplankton growing period. Decreases in annual maximum and average abundances of diatoms, green algae, and cyanobacteria were also detected. Furthermore, chlorophyll a decreases after dam filling and a decrease in turbidity may point to a shift from light limitation towards a more nutrient-limited mode in the near future.

Effects of warming on a Mediterranean phytoplankton community

“…In particular, phytoplankton merits special attention being generally the dominant primary producer in most aquatic ecosystems. Situated at the base of the food web, phytoplankton is linked to the biogeochemical cycles and energy flux; all changes in phytoplankton composition, abundance and distribution may have cascading effects along the trophic food web (Barbosa et al, 2010). Phytoplankton is considered to be good indicators of climate change, which may alter the structure and dynamics of aquatic ecosystems (Hays et al, 2005).…”

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

“…65% -89% of total inorganic N), showed a decreasing trend after construction of Alqueva dam (see As referred in previous studies (Barbosa et al, 2010), silicate concentration was usually correlated with rainfall and river flow, and negatively correlated to chlorophyll a. Both DSi and nitrate exhibited seasonality with higher values during winter and lower values between midspring and summer.…”

“…These authors also referred that cyanobacteria dominated the chlorophyll maximum zone in the upper estuary in late summer-early fall, due to warm waters, reduced sinking and grazing, as well as N limitation with low N:P ratio. Nitrogen limitation during summer increased in the period after Alqueva in the upper estuary (Barbosa et al, 2010). Additionally, nutrient enrichment experiments performed during 2008 clearly demonstrated that phytoplankton growth was nitrogen limited (Domingues et al, 2011).…”

“…This shift from light to nutrient limitation was probably the most determinant trend for phytoplankton observed after Alqueva (Barbosa et al, 2010). However, since chroococcoid cyanobacteria have higher affinity for nutrients due to small size, and most filamentous forms as well as some chroococcoid species have nitrogen fixing potential, these photosynthetic prokaryotes should have been less affected by lower nitrogen availability than larger non-nitrogen fixing eukaryotic phytoplankton.…”

An Innovative and High-Speed Technology for Seawater Monitoring of Asinara Gulf (Sardinia-Italy)

“…It is a sensitive bio-indicator of ecosystem general health, its nutrient status, eutrophication, pollutants, and other anthropogenic impacts in aquatic environments [3]. As primary producer, it is capable of responding to changes in nutrient and toxin input, hydrology, sedimentation, irradiance and temperature regimes over a wide range of time scales.…”