Spatial and temporal heterogeneity in the Alqueva reservoir, Guadiana river, Portugal

Abstract

Spatial and temporal heterogeneity in the Alqueva reservoir, Guadiana river, PortugalThis study aims to assess the physico-chemical variability of the Alqueva reservoir during its initial filling period. The dataset consists of analytical results from an 11 month survey (Mar 2003-Jan 2004 conducted in the water body, at three levels of depth in the several tributaries and in the discharge section. 21 parameters were monitored on a monthly base, in order to understand the temporal and spatial variability. Another goal of this work was to use a multivariate statistical approach to help understand the relationships between water quality parameters, to group zones according to their similarities and to distinguish between wet and dry season conditions. FA/PCA needs 6 VF/PC to point out 74 % in the wet season, and 7 VF/PC to explain 78.6 % of variance in the dry season. FA/PCA allows grouping the selected parameters according to common features. As a result, mineral content is indicated as the principal source of variability in the wet season, while oxygenation plays the main role in the dry season. DA renders an important data reduction using 10 parameters to provide 93.2 % right assignations during temporal analysis. DA assigns temporal variability to the consequences of water balance on ambient salinities, to stratification influences and to surface runoff. Also, it uses only 4 parameters to yield 71.3 % right assignations during the spatial analysis in the dry season. Conductivity declines in the lacustrine zone, while CBO5, pH and Temperature vary principally in the vertical sense. However, such a spatial pattern is not static. It can become either more defined during the dry season, or less evident during the expansion of the lotic conditions in the rainy period (late spring and summer). Seasonal processes of stratification/mixture determine the temporal changes in the lacustrine zone. The system seems to be affected by periodic pulses of modifications produced by intensive rains and drought. Thus, limnological understanding of these questions is a prerequisite for making wise judgments about reservoir management.

Spatial and temporal variability of the water and sediments quality in the Alqueva reservoir (Guadiana Basin; southern Portugal)

“…In general, high levels of this parameter occur: (i) in the absence of oxygen, due to the reduction of the nitri cation process in the water body; and/or (ii) in very enriched waters (Welch and Jacoby, 2005). The amounts of NH4-N have been increasing since 2006, as can be observed by the analysis of previous studies (Sera m et al, 2006;Morais et al, 2007;Palma et al, 2010a).…”

“…In general, the patterns of organic descriptors and nutrients in the water body (Fig. 2), presented an increment when compared with previous studies (Sera m et al, 2006;Morais et al, 2007;Palma et al, 2010a). For instance, the TNw levels (0.14-3.07 mg L 1 ) achieved/ surpassed the limit of 1 mg L 1 , in all locations, during the dry period.…”

“…These changes affect all the physical, chemical and biologic parameters with implications in the water quality of the reservoir. Further, this particular hydrology makes the tributaries to the reservoir very sensitive to anthropogenic pressure with serious implications in the status of water body (Sera m et al, 2006;Morais et al, 2007).…”

Temporal and spatial patterns in the shifting of otter diet to invasive prey after river damming

“…In this work, we analyze how the creation of a reservoir influences the diet of the otter, both at the short‐ and the long term, and whether and how this influence expands through the fluvial network, beyond the reservoir boundaries. We describe the composition of the otter diet in river systems of the area affected by the Alqueva project, which generated the largest artificial lake in Western Europe (Serafim et al, 2006). We analyze temporal and spatial variability in otter diet in three different periods (i.e., the pre‐filling phase, the immediate filling phase, and 16 years after the dam closure) and in relation to the distance to the newly created reservoir.…”

“…The Alqueva reservoir, that started flooding in 2002, is the most recent and largest among these large reservoirs, affecting the Guadiana River and several tributaries in the mid‐lower sector of the basin (Figure 1). It has a maximum storage capacity of 4,150 hm 3 and generates a flooded area of some 250 km 2 , with a coastline of more than 1,100 km (Ribeiro, Chaves, Marques, & Moreira da Costa, 2006; Serafim et al, 2006). Extending the Alqueva project, the Pedrogão dam was closed just downstream in 2006, in order to regulate the outflows from the Alqueva reservoir, generating an adjacent reservoir with a maximum capacity of 97 hm 3 (Morais, Serafim, Pinto, Ilhéu, & Ruivo, 2007).…”