Biological Characteristics

Types of Habitats - Lagoons

Lentic systems are epicontinental water complexes in which stagnation predominates over flow. Ecologically these systems can be differentiated into various types of lake or lagoon environments characterised, overall, by the predominance of the aquatic biotope over the hygrophitic one, due to buildup, permanent or not, of superficial water. The biogeographic peculiarities characteristic of the proposed territory have favoured the existence of a large cast of lentic systems, distributed mainly in the most depressed areas of the basin, and associated with emergences or with input from river channels.

These systems tend to the accumulation and blockage of a water layer, favoured by abnormalities in the substrate. A weakening of this trend can cause, even with persisting stagnation, to gradually reduce the waterlogged soil, causing the appearance of semi-terrestrial systems (wetlands) and finally, in a greater degree of loss, terrestrial ecosystems.

The entity of the free water layer serves as a criterion for the segregation between lakes, lagoons and ponds. A lake must have the necessary depth to show phenomena of vertical stratification in the water body. The lagoons are ecosystems with a sheet of permanent water of less importance (5-50 m) of less depth, but bigger than one hectare. The discriminating factor is a lower volume ratio of retained water and the contact surface with the banks and bottom than in a lake, which results in the absence of stable thermal stratification. The term pond is used to encompass the lagoons of small size (“lagunazo”, small lagoon, ponds, etc.), i.e., environments possessing a sheet of water of less than 5 metres of power, or covering an area of less than one hectare. During the summer period the importance of this sheet of water may persist (permanent ponds), or sometimes comes to vanish, keeping the subsurface water table (semi-permanent ponds). Semi-permanent ponds constitute an ambiguous boundary between lake and semi-terrestrial systems.

In lakes, lagoons and permanent ponds two major ecological zones can be distinguished. Externally, in contact with semi-terrestrial or even totally earthified environments, the coastline or riverbank is established, comprising the various biotopes where macrophyte and charophyte vegetation is developed. Inland there is an area of open water (pelagic), where communities of macrophytes and charophytes are absent, dominating plankton in it. Semi-permanent ponds in the dry season causes the disappearance of the pelagic zone, exposing sediments that were previously covered by water. These sediments are sometimes vegetated by ephemeral pioneer communities, dominated by amphibians or generally hygrophitic biotypes.

CHARACTERISTIC SPECIES

Weather limitations for the development of aquatic vegetation are reduced to the impact of the decrease or absence of seasonal rains, affecting the maintenance of the superficial layer of water. In slightly altered and not contaminated environments, the acidic and poorly mineralized character of the water favours the existence of submerged charophyte communities of the type Nitelletalia. However, Charetalia are poorly represented, typical of mineralized waters. Bryophyte communities are also frequent, both in aerial environments with high humidity, and completely submerged media. Prominent among the latter, we find formations of Fontinalis antipiretica, indicating reduced water mineralization.

The majority of plant biomass corresponds to cormophitic vegetation, which determines, in relation to the entity of the layer of free water, the visual perception of the lentic complex. Aquatic vegetation is characterised by a predominance of hydrophyte swimming communities (Lemnatea), adnate (Ceratophylletea), mesopleustophytes (Utricularietea) and especially radicant hydrophytes (Potametea) . Together with the strictly aquatic communities are other amphibian hygrophytes distributed mainly among Phragmitio - Magnocaricetea, Littorelletea and Isoeto-Nanojuncetea classes. As the humidity gradient decreases, we find diverse amphibian and emerged plant communities, whose major structural complexity corresponds to greater hygrophilic forests: willow, alder and birch, which are interconnected with the zonal vegetation of the territory and other azonal hydrophilic land formations (meadows and peaty heaths, sphagnum, etc). Described in detail below are the two major types of lagoon vegetation of the territory.

A. LAGOON SUBMERGED VEGETATION

The lagoon submerged vegetation, corresponding to natural stagnant water habitats, usually contains pauciespecific communities. They are made up of elements freely floating on the surface, or rooted at the bottom, so that only flowers and a part of their vegetative apparatus can be found on the surface. The components of these communities have undergone remarkable modifications in the course of evolution, both morphologically and physiologically, which confer them a high scientific interest.

The Lemnetum gibbae sintaxon includes the pooled water communities –rivers, canals, lagoons, etc.—, clean or generally eutrophized or polluted, characterised by the presence of Lemna minor and occasionally by Lemna gibba. According to Rivas-Martinez (1983), pure Lemna minor populations correspond in many cases to fragments of the Lemnetum gibbae association, which colonise polluted waters, rich in soluble ions.

The Lemnetum gibbae community can be found widely distributed in the most part of the hydrological complexes in Terra Cha, in which only Lemna minor appears. The widest representation of Lemnetum gibbae can be found in eutrophized lagoon submerged environments, as it happens in the Central Lagoon of Cospeito, where it is distributed in an irregular way along most part of the water layer, although without getting to form dense populations of considerable extent. In the rest of the complexes, their presence is barely significant, restricted to marginal zones of the lagoon surface and eutrophized canals of slow water.

The Utricularietea communities are equally monophitic, which are distributed along diverse complexes in Terra Cha, such as the Central Lagoon of Cospeito, the Lagoa of Bardancos (The Lagoon of Bardancos), the permanent pools of Fontefria –Home Morto, Pedroso, Seixas and Abelleiras—, as well as in the small temporary ponds and canals of the complexes of San Breixo, Denune and Toiral. Utricularietea communities are characteristic of shallow environments, in which even the water layer disappears of the surface during the summer months.

The communities of large Nymphoides –slightly branched stemmed plants with long petioled floating leaves— that colonise permanent aquatic habitats, relatively deep and waveless, are included in the Nymphaeion albae alliance. Within it, the Potamogeton natans community appears widely represented in those lagoonal environments which keep a water layer permanently (Fontefria –Home Morto, Cospeito, Seixas and Abelleiras and Bardancos); this has also been observed occasionally at the inlet and outlet canals of some of the lagoons (Cospeito, Fontefría – Home Morto), in areas where the course becomes slower.

Otherwise the Nymphaea alba community has a very restricted distribution in the territory. Its presence has only been testified in the lagoonal environments of two complexes, although it is relatively frequent in slow sections of the waters of the Miño River. In the Ollos of Begonte, where it constitutes a part of the neritic vegetation of both lagoons, it shows a naturalness similar to the one observed in the Lagoon of Sobrado. Besides, this community appears occasionally in the hydrological complex of the Lagoon of Cospeito, specifically in a small bend of the River Guisande, after leaving the Veiga of Anido and before its confluence with the Tamoga.

The most part of the lentic environment existing in the various hydrological complexes of Terra Cha is colonised by watermilfoil formations, constituted to a greater or lesser extent by Ceratophyllum demersum; Myriophyllum alterniflorum and Utricularia (cf. U. australis, U. vulgaris), as well as Elodea (Potamogeton natans, P. grupo pusillus), whose vegetative apparatus takes up the whole water column.

The first ones are characterised by presenting a reduced root system, as well as plenty of stems, highly branched, on which the leaves are arranged in axils. The vegetative apparatus of the watermilfoils remains floating beneath the water surface, attached to the substrate or generally free. These plants originate dense masses through propagation, which can get to completely cover the water column of surface lagoons, as it happens in the Central Lagoon of Cospeito and in the Lagoa of Ollos of Begonte. The Elodea present as well a reduced clamping system, with assimilating entire structures, generally arranged in axils or thread-like patterns.

The presence of individuals of the genus Chara spp. within the watermilfoil mass is relatively common and it has been located in the area near the mouth of the current Central Lagoon of Cospeito and the perimeter canal of the Lagoon of Bardancos, as well as in the Fuentefria permanent ponds and the temporary ones of Seixas and Denune. However, these populations do not reach under any circumstance the dimensions observed in lentic complexes fed by emergences: Lagoa of Fonmiñá, Lagoas of Pedroso, Ollos de Begonte.

The communities where watermilfoils and Eloidea prevail, with occasional presence of Nymphoides, have been included by Bellot (1966) in two organizations: Ceratophylletum demersi (CERATOPHYLLETEA), which has as its characteristic species the Ceratophyllum demersum, and Myriophylietum alterniflori (POTAMETEA), equally pauciespecific and characterised by the presence of Myriophyllum alterniflorum.

B. COASTAL VEGETATION

At the edges of lagoons, in the water courses, as well as in those areas that remain seasonally covered by a water layer, helophyte communities are installed, systematized in these classes: PHRAGMITETEA and LITORELLETE>.

Hygrophytic vegetation, consisting on helophyte or succulent herbs, occupying edges of lagoonar or river courses, as well as wetlands flooded for most of the year or at least during the winter season, is included in the PHRAGMITETEA class. Within this class, only the communities belonging to the alliance Magnocaricion have been included by the Habitat Directive, characterised by the predominance of Cladium mariscus, which sets up small pauciespecific formations at the edges of lagoons and ponds, as well as dense communities and of greater extent among hygro-peat environments. The presence of Cladium mariscus is usually related to eutrophic or mesoeutrophic environments.

In the alliance Phragmition (Phragmition communis) reedbeds and bulrushes from more or less deep waters are included, typical of lake margins and slow channels. Normally, the communities of this alliance are included in the Scirpus lacustris – Phragmitetum, although in most cases (cf. Diaz González & Fernández Prieto, 1994) they appear fragmented and very impoverished, dominated by some characteristic plants (Typha angustífolia, Scirpus lacustris, Phragmites australis, etc.) which may get to constitute monolithic communities (Scirpus lacustris community, Typha angustifolia community).

In this way, the formations with prevailing broadleaf cattail (Typha latifolia), bulrushes (Scirpus lacustris), canes or reeds (Phragmites vulgaris), colonizers of edges and channels, as well as of wetlands which keep a high amount of water on the surface or the subsurface throughout the year, to a lesser extent, are included in the Phragmition alliance. The Typha latifolia communities are abundant in the Terra Cha wetlands, especially in those whose origin is anthropogenic or which have undergone an important human variation, with large amounts of loamy and/or clayey materials, which keep a high concentration of water throughout the year (lagoons and ponds of Pedroso or the ones formed in Outeiro de Arcillá).

Bulrushes communities, Scirpus lacustris (subsp. Tabernaemontani), are less abundant in water complexes of the area of study, which appear restricted to the water complex of the Lagoon of Cospeito. The reed (Phragmites vulgaris) and the cane (Arundo donax) are present in some aquatic ecosystems heavily altered by human action in the Terra Chá.

Finally, in the Glycerio-Sparganium alliance juicy herbaceous communities, typical of some lagoon edges, brooks and rivers, with shallow, clear and well oxigenated waters are included (Glycerio declinatae - Eleocharitetum palustris, Glycerio declinate - Oenanthetum crocate, Glyceria Community sp. pl. , Helosciadetum nodiflori), or on the contrary, in shallow, quite eutrophic or polluted courses (Helosciadetum nodiflori).

The LITTORELLETEA class perennial communities, hydrophile and/or helophyte amphibia, usually with a graminoid appearance, which occupy the edges of ponds, lagoons and oligotrophic lakes subjected to seasonal flooding: Junco heterophylli - PiluIarietum globuliferae (Pilularieto – Eleocharitetum), Hyperico elodis –Potametum oblong, or the ones in which the water layer can be kept throughout the year, Eleocharitetum multicaulis.

The hetereophylli sedgePilularietum globuliflorae – is an ephemeral community, made up of small-sized perennials. It colonises inorganic sediments, usually of a clayey nature, that is left uncovered in lagoons and ponds when the free water layer is removed. This community of summer development, occasionally autumnal, is characterised by the presence of Eleocharis multicaulis, Carum verticillatum, Galium palustre, Ranunculus flammula, Veronica scutellata, highlighting also the presence of and Pilularía globulifera. These latter taxa come to constitute pauciespecific communities, whose extension is strongly conditioned by sedimentology and the environmental water regime. The communities of hetereophylli sedge —Pilularietum globuliflorae— are preferentially located at the edges of Cospeito, Seixas and Fontefría –Home Morto, as well as on the margins of the ponds of Bardancos and Riocaldo, usually colonising clayey sediments that are left uncovered after the water layer removal.

Over the clayey sediments that are subjected to temporary flooding we can find, moreover, pauciespecific communities with the prevailing presence of Eryngium viviparum, among which Cicendia filiformis, Exaculum pusiIIum, etc., are usually present, too. The clayey sediments that keep a high level of humidity on the surface during the summer time, appear colonised by Litorella uniflora monophitic communities. The scarce surface that these units take up, the habitat fragility against anthropogenic disturbances (ploughing, drainage schemes, piping, etc.) and the fact that many of the taxa that make up these communities are subjected to environmental factors that are occasionally not repeated in an annual cycle, determines its high biological interest.

On the edges of lagoons and ponds that are left uncovered when the water layer diminishes, but on whose rhizosphere is kept a high humidity level, favoured by the existence of organic or silty-clayey sediments, the Hyperlco elodis - Potametum oblongi community appears. This community is made up of small-sized hydrophytes and/or helophytes, among which Hypericum elodes, Hydrocotyle vulgaris, Potamogeton sp. pl., Baldelila ranunculoides, etc., are the ones that stand out.

The Eleocharitetum multicaulis is basically constituted by small-sized hydrophytes and/or helophytes that are established in small basins or depressed areas. During the winter season they usually get submerged by a water layer, but this one decreases and also disappears during the summer season.