Trends in the Recent Evolution of Coastal Lagoons and Lakes in Galicia (NW Iberian Peninsula)

Abstract

Coastal lagoons are habitats of great environmental value. However, they are currently subject to major threats, particularly due to increasing sea levels. This study aims to identify changes—both natural and induced by anthropic activity—and their impact on the recent evolution of three different types of coastal lagoons in Galicia (Louro, Vixán, and Xuño). The application of information obtained through laser imaging detection and ranging (LiDAR) techniques suggests that the outer limits of the three lagoon systems have not experienced any relevant changes in the last 60 years (i.e., no occupation of the lagoon area has been identified). However, the internal configuration of these wetland areas has experienced some alterations. A generalized increase in the area occupied by macrophytic communities (Phragmites australis, Scirpus maritimus, Juncus maritimus, etc.) has been observed. Image interpretation by geographic information systems (GIS) and field surveys suggest that the area currently occupied by macrophytes experienced a 7% to 63% increase at the expense of the free water body. This loss of flooded area is consistent with the increase in sedimentation rates associated with the convergence of several causes, such as the abandonment of traditional macrophyte biomass harvesting and agricultural activities around the lagoons, the expansion of riparian forests, and sediment contributions by erosion due to recurrent forest fires within the drainage basins of each lagoon. Finally, water and sediment composition suggest that, of the three studied lagoons, two of them (Louro and Vixán) are included within the definition of “coastal lagoons” (habitat code 1150) by the Habitats Directive (Directive 92/43/EEC), while the Xuño lagoon should be considered a “natural eutrophic lake” (habitat code 3150).

Contribution of GIS and Geochemical Proxies to Improving Habitat Identification and Delimitation for the Natura 2000 Network: The Case of Coastal Lagoons in Galicia (NW Iberian Peninsula)

“…The total surface area of the Xuño lake is 2.3 ha and hydrophilic vegetation is currently colonizing almost all of the lake. The surface area occupied by open waters was small (0.005 ha) and decreased by more than half in the study period [15]. The lake basin is occupied by reed bed (77.5%) in the distal part and by Scirpus maritimus at the front (14.8%), with the presence of small areas occupied by Thypha latifolia (Figure 7).…”

“…The Vixán lake (42 • 32 28" N, 09 • 01 32" W), which has an approximate surface area of 15 ha, forms part of the Natural Park Complexo dunar de Corrubedo e lagoas de Carregal e Vixán (Figure 1(b3). This lake is enclosed by a well-developed dune system and its connection to the sea is almost nil [15], partly due to the long distance (~300 m) to the coastline.…”

“…Galicia (NW Iberian Peninsula) has numerous coastal lakes of various sizes, forms, and hydrodynamics (see, for example: [15][16][17][18]). This study focuses on four coastal lakes (Figure 1) with different morphological and hydrodynamics characteristics.…”

“…This unit has not suffered substantial changes in the last three decades (Figure 3), although large seasonal oscillations occur. The marked seasonal rainfall, with an important water deficit in summer, leads to a reduction of 60% in the area occupied by the sheet of water in the end of summer relative to the maximum during the winter [15].…”

“…The fires lead to substantial degradation of the water quality. Additionally, clogging of the lake promotes expansion of the reed bed to the detriment of the area of open water [15]. One of the consequences of this expansion is the disappearance of channels and, in general, the area of contact between water and vegetation, a key parameter for the conservation of multiple species of aquatic birds and passerines such as the reed warbler and sedge warbler, among other species.…”