## 3 Results and Discussion
### Delimitation of Coastal Lakes
#### 3.4.2 Coastal Lagoons--Vixan
Furthermore, _Cladium mariscus_ forms a part of a mosaic of fen communities, but the existence of a small number of specimens of this species is not sufficient to justify designation of area as this habitat [43], as occurs in the Vixan lake. The presence of _Cladium mariscus_ is not in doubt in this area (e.g., [30]), but the existence of habitat 7210 is questioned (e.g., [38; 44]), and especially of the large surface area designated in the PDRN. A large part of the area assigned to this habitat (Figure 5) was occupied by different species of Juncus (e.g., _Juncus acutus_ and _Juncus maritimus_) and _Scripus maritimus_, corresponding a typical salt marsh in the NW Iberian Peninsula. Considering the previously identified criteria and the presence of _Cladium mariscus_ in this zone, detailed analysis must be carried out to establish the presence, distribution, and extension of this species. Nevertheless, considering reports of the presence and distribution of this habitat in Spain, the presence of the species close to the Vixan lake or in the Corrubedo humid complex (LIC ESI110006) seems unlikely [44]. Based on the previous findings, all of the lake front can be considered salt marsh dominated by _Scripus maritimus_ and several species of reeds, the zone can be included in the Coastal lagoon habitat, as in the case of the reed bed, based on the Commission of the European Communities directrices [9], in which the salt marsh appears as a related habitat included in Coastal lagoons. Analysis of the temporal changes in the lake shows substantial changes in the distribution of plant communities and the surface area occupied by the sheet of water (Figures 4 and 6). The most important difference is the subdivision of reed bed in plots, which is related to the extraction of _Phragmites australis_ by the local population, for use as livestock bedding. This traditional activity was abandoned at the end of the 1980s, partly as a consequence of the environmental protection of this lake. This led to accumulation of plant biomass, which often drifts into wildfires at the end of summer (Figure 6). 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,  
Figure 5: Vixán lagoon with the main habitats defined by Plan Director Rede Natura 2000 (PDRN). Data: Xunta de Galicia ©. Areas with multiple patterns correspond with zones with various main categories. among other species. Different studies and manuals mention loss of biodiversity in relation to the increase in reed bed density and the reduction in open water [45; 46; 47; 48; 49]. Previous studies of the Vixan lake showed that the numbers of overwintering waterbirds (e.g., waterfowls, common coot, and little grebe) have decreased greatly in the last few decades as consequence of the progressive clogging of the lake and expansion of the reed bed [50; 51]. The results of the present study in relation to the water quality, as well the findings of previous studies showed that the water quality is very poor during the summer due to the high organic matter content and presence of reduced forms of N (NO\({}_{2}\)-, NH\({}_{4}\)+), which lead to fish mortality events [34; 52]. This is especially important considering that designation of the area as a Site of Community Importance (SCI) was partly related to the protection of birds (declaration of Special Protection Areas for Birds [SPAB]). Some of the values for their protection are missing due to environmental mismanagement. There are some inconsistencies in the official delimitation of the lakes considered in this study.