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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)

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The Natura 2000 network is an ambitious European project aimed at nature conservation. Nevertheless, the identification and delimitation of habitats is a complex task and simultaneously essential for correct ecosystem management. In this study we compared the current habitat delimitation and designation and the results produced by Geographic Information Systems (GIS) and geochemical proxies for the categorization of four coastal lakes in Galicia (NW Iberian Peninsula). The findings reveal important errors in the delimitation/designation. The first error is the designation of all four lakes as Coastal lagoons (habitat 1150), when geochemical data indicate that two of these lakes were always freshwater lakes and should consequently be classified as Natural eutrophic lakes (habitat 3150). Another error is of conceptual origin, because the lakes comprise a unique functional system composing of different environmental units (e.g., open water or aquatic vegetation). Subdivision into different habitats is therefore meaningless for units of negligible surface area. In addition, the designation of some habitats is very dubious according to the available data. Finally, notable changes in relation to the temporal changes of wetlands were observed. Thus, the area occupied by aquatic macrophytes increased greatly at the expense of open waters, and the increase was also reflected in the alluvial forest. This last finding indicates the importance of updating the state of Natura 2000 network in Galicia to improve habitat management.
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sciences
Article
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)
Alejandro Gómez-Pazo 1,2, Augusto Pérez-Alberti 2,3, Pedro Fraga-Santiago 2,
Martin Souto-Souto 4and X. L. Otero 2,3,5,*
1Departamento de Xeografía, Facultade de Xeografía e Historia, Universidade de Santiago de Compostela,
15782 Santiago de Compostela, Spain; a.gomez@usc.es
2CRETUS Institute, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain;
augusto.perez@usc.es (A.P.-A.); pedro.fraga@rai.usc.es (P.F.-S.)
3Departamento de Edafoloxía e Química Agrícola, Facultade de Bioloxía,
Universidade de Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, Spain
4Centro de Investigação em Biodiversidade e Recursos Genéticos, CIBIO, InBIO Laboratório Associado,
Pólo dos Açores & Faculdade de Ciências e Tecnologia da, Universidade dos Açores,
9500-321 Ponta Delgada, Portugal; martin.s.souto@uac.pt
5REBUSC, Rede de Estacións Biolóxicas da USC, Casa do Hórreo, rúa da Ribeira, 1–4,
15590 A Graña–Ferrol, Spain
*Correspondence: xl.otero@usc.es; Tel.: +34-881-813-300
Received: 4 December 2020; Accepted: 17 December 2020; Published: 18 December 2020


Abstract:
The Natura 2000 network is an ambitious European project aimed at nature conservation.
Nevertheless, the identification and delimitation of habitats is a complex task and simultaneously
essential for correct ecosystem management. In this study we compared the current habitat
delimitation and designation and the results produced by Geographic Information Systems (GIS) and
geochemical proxies for the categorization of four coastal lakes in Galicia (
NW Iberian Peninsula
).
The findings reveal important errors in the delimitation/designation. The first error is the designation
of all four lakes as Coastal lagoons (habitat 1150), when geochemical data indicate that two of these
lakes were always freshwater lakes and should consequently be classified as Natural eutrophic
lakes (habitat 3150). Another error is of conceptual origin, because the lakes comprise a unique
functional system composing of dierent environmental units (e.g., open water or aquatic vegetation).
Subdivision into dierent habitats is therefore meaningless for units of negligible surface area.
In addition, the designation of some habitats is very dubious according to the available data.
Finally, notable changes
in relation to the temporal changes of wetlands were observed.
Thus, the area
occupied by aquatic macrophytes increased greatly at the expense of open waters, and the increase
was also reflected in the alluvial forest. This last finding indicates the importance of updating the
state of Natura 2000 network in Galicia to improve habitat management.
Keywords: Habitats Directive; coastal lagoon; coastal lake; Natura 2000 network; habitats
1. Introduction
Wetland ecosystems are essential for biodiversity conservation as they are actively involved
in improving water quality and nutrient cycling, and also function as atmospheric CO
2
sinks [
1
4
].
In addition, these areas are very fragile and vulnerable to disturbance caused by human activity [
5
,
6
].
Large areas of European wetlands have been lost since the start of the 20th century and the remaining
Appl. Sci. 2020,10, 9068; doi:10.3390/app10249068 www.mdpi.com/journal/applsci
Appl. Sci. 2020,10, 9068 2 of 20
wetland habitats have been greatly altered [
7
,
8
]. In response to this situation, various dierent
initiatives and international conventions were proposed in the middle of the 20th century with the
aim of promoting the study and protection of these areas (e.g., International Waterfowl and Wetlands
Research Bureau (IWRB) and the Ramsar Convention).
In 1992, the European Union approved Council Directive 92/43/EEC (referred to here-after as the
Habitats Directive) on the conservation of natural habitats and of wild fauna and flora. This Directive
established a network of Special Areas of Conservation to protect habitats considered to be of community
importance (Annex I lists 233 natural habitats in Europe) and also wild animal and plant species that
should be protected (about 900 species, Annex II). These habitats and species formed the basis for
the creation of a network of special areas of conservation, called Natura 2000 [
9
]. The aim of the
Natura 2000 network is to ensure the long-term survival of Europe’s most valuable and threatened
species and habitats, listed in both the Birds Directive (Council Directive 79/409/EEC, 1979) and the
Habitats Directive. Member states are obliged to include in the Natura 2000 network all the natural
spaces in their territory that include habitats and species that appear in Annex I and II, especially those
considered priority spaces. Each Member State is also obliged to maintain and restore, with favorable
conservation status, natural habitats, and species of wild fauna and flora of community interest covered
in the Habitats Directive [9].
The Natura 2000 network is one of the most ambitious legislative instruments in the field of nature
conservation worldwide. However, various problems hamper the eective application of the project.
One of the main problems is related to the complexity of some articles (e.g., Art. 6) or ambiguities in
the definition of multiple habitats, which has forced the European Commission to elaborate diverse
manuals ad hoc, as [
10
]. Thus, to fully achieve the basic goals established in the Habitats Directive,
it is essential to understand the processes and the nature of the components that define each habitat
(e.g., drainage network and water composition). This is the only way of correctly designating and
delimiting habitats. Much of this information was either not available or was not used when the
Natura 2000 network was designed. Delimitation of each habitat is complicated by the method used,
as well as by the fact that many protected areas undergo substantial temporal changes in relation to
climate conditions and land use by local populations. This obliged the Member States to revise their
status within the Natura 2000 network, as established in the Habitats Directive.
Galicia has more than 2100 km of coastline [
11
], and one of the most complex littoral zones in the
Iberian Peninsula [
12
]. Coastal lakes represent one of the most unusual environments in the region.
Despite their small size, some coastal wetlands appear among the priority habitats of Annex I and
are thus included in the Spanish Natura 2000 network. As it can be dicult to establish boundaries
between habitats that appear as a continuum [
13
,
14
], in this study, we carried out a comparative
analysis of the delimitation and designation of habitats that appear in the plan developed by the Xunta
de Galicia (Government of the Autonomous Community of Galicia) for the implementation of the
Natura 2000 network, i.e., the Plan Director de la Red Natura 2000 de Galicia (PDRN) (Decree 37/2014,
Xunta de Galicia) for four lakes in the region. The information is included in the ocial cartography of
the Xunta de Galicia, which is based on the data included in Annex I of the PDRN.
The main objectives of the present study were: (1) to rethink the designation of the Galician coastal
lakes exclusively to the Coastal lagoon habitat; (2) to establish the boundaries of each lake by applying
Geographic Information System (GIS) techniques and Light Detection and Ranging (LiDAR) data
and geomorphological parameters; (3) to analyze the temporal dynamics in the coastal lakes through
remote sensing techniques; and (4) to evaluate the excessive fragmentation of these lakes in habitats
with questionable presence or limited representation. For this purpose, we used the information
provided by aerial images, orthophotographs and LiDAR data (available from the Spanish National
Geographic Institute [IGN]) and geochemical analysis of water and substrate composition in several
field surveys. This study tries to explain the need to improve the mechanism to the conservation
of nature, the aim of Nature 2000 network.
Appl. Sci. 2020,10, 9068 3 of 20
2. Materials and Methods
2.1. Study Area
Galicia (NW Iberian Peninsula) has numerous coastal lakes of various sizes, forms, and
hydrodynamics (see, for example: [
15
18
]). This study focuses on four coastal lakes (Figure 1)
with dierent morphological and hydrodynamics characteristics. The four lakes (Louro, Xuño, Vix
á
n,
and Bodeira) are located in the Atlantic coastal region of Galicia. The region has a maritime climate.
The annual average temperature is 14.6–16.2
C, and average rainfall ranges from 1211 to 1828
mm/year [
19
]. However, most (70%) of the precipitation is concentrated in the period between October
and March, generating an intense drought period in the summer that determines the water availability
in these lacustrine areas [19].
Appl. Sci. 2020, 10, 9068 3 of 19
2. Materials and Methods
2.1. Study Area
Galicia (NW Iberian Peninsula) has numerous coastal lakes of various sizes, forms, and
hydrodynamics (see, for example: [1518]). This study focuses on four coastal lakes (Figure 1) with
different morphological and hydrodynamics characteristics. The four lakes (Louro, Xuño, Vixán, and
Bodeira) are located in the Atlantic coastal region of Galicia. The region has a maritime climate. The
annual average temperature is 14.616.2 °C, and average rainfall ranges from 1211 to 1828 mm/year
[19]. However, most (70%) of the precipitation is concentrated in the period between October and
March, generating an intense drought period in the summer that determines the water availability in
these lacustrine areas [19].
Figure 1. (a,b) represents the study areas in continental and regional level, respectively. In (b) appear
the study areas represented in this figure with red dots, and the black triangles represent the main
cities/villages in this area. Numbers 1 to 4 represent the analysis zones using an ortophotography of
PNOA (Plan Nacional de Ortofotografía Aérea) captured in 2017 [20] and have the following sequence
(1) Louro, (2) Xuño, (3) Vixán, and (4) Bodeira.
The Louro lake (42°4523 N, 09°5′36 W), which has an approximate surface area of 30 ha, is
associated with a sedimentary complex with a beach and a large, well-developed dune system that
partially closes the area connecting the lake and the sea (Figure 1(a1), i.e., a temporary channel at the
NW edge [18].
The Vixán lake (42°32′28 N, 09°01′32 W), whichhas 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.
The Xuño (42°38′00 N, 09°2′19 W, Figure 1(a2)) and Bodeira (42°28′29 N, 08°54′22 W, Figure
1(b4)) lakes are both small (>3 ha) and located at the back of dune systems. In contrast to the other
lakes, these lakes are located at a higher elevation (~45 m.a.s.l). The Bodeira lake lacks a connecting
channel to the sea, while the Xuño lake the existing channel acts exclusively as an overflow channel
during periods of heavy rainfall.
2.2. Methodology
Delimitation of the different environments in each lake was carried out using different proxies.
Aerial images and Digital Elevation Models (DEMs) were used to characterize the sectors and to
Figure 1.
(
a
,
b
) represents the study areas in continental and regional level, respectively. In (
b
) appear
the study areas represented in this figure with red dots, and the black triangles represent the main
cities/villages in this area. Numbers 1 to 4 represent the analysis zones using an ortophotography of
PNOA (Plan Nacional de Ortofotograf
í
a A
é
rea) captured in 2017 [
20
] and have the following sequence
(1) Louro, (2) Xuño, (3) Vixán, and (4) Bodeira.
The Louro lake (42
45
0
23” N, 09
5
0
36” W), which has an approximate surface area of 30 ha,
is associated with a sedimentary complex with a beach and a large, well-developed dune system that
partially closes the area connecting the lake and the sea (Figure 1(a1), i.e., a temporary channel at the
NW edge [18].
The Vix
á
n lake (42
32
0
28” N, 09
01
0
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 Vix
á
n(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.
The Xuño (42
38
0
00” N, 09
2
0
19” W, Figure 1(a2)) and Bodeira (42
28
0
29” N, 08
54
0
22” W,
Figure 1(b4)) lakes are both small (>3 ha) and located at the back of dune systems. In contrast to
the other lakes, these lakes are located at a higher elevation (~4–5 m.a.s.l). The Bodeira lake lacks a
connecting channel to the sea, while the Xuño lake the existing channel acts exclusively as an overflow
channel during periods of heavy rainfall.
2.2. Methodology
Delimitation of the dierent environments in each lake was carried out using dierent proxies.
Aerial images and Digital Elevation Models (DEMs) were used to characterize the sectors and to check
Appl. Sci. 2020,10, 9068 4 of 20
the relationship with the nearby marine zone. In addition, water and sediment analyses were carried
to determine various parameters.
2.2.1. Delimitation of Temporal Changes in Coastal Lakes
The lake systems were delimited using ArcGIS 10.5 (license USC), as follow:
1.
A high resolution (1 m) Digital Surface Model (DSM) of the lake basin was generated using the
most recent LiDAR data (from 2015 [20]).
2.
The terrain ruggedness was determined using the Riley formulation [
21
]. This parameter was
then used in the delimitation by considering the mean Topographic Ruggedness Index (TRI)
as threshold.
3.
The surface area was corrected by analysis of aerial images to adapt the lake space to the
characteristics of each zone in 2017.
4.
Remote sensing techniques were used to analyze the characteristics of the areas, such as the tone
or the element size, for final delimitation of the spaces.
2.2.2. Geochemical Analysis of Water and Sediments
Lake water and sediments were sampled in dierent seasons during the period 2009–2011.
Water samples were collected in Teflon jars previously treated with HCl (5%) and rinsed several times
with Milli-Q water. Redox potential (Eh), pH and electrical conductivity (EC) were determined
in situ with a multiparameter probe (Hanna Instruments, Ann Arbor, MI, USA). Salinity was
determined with a Hanna refractometer. In the laboratory, the samples were filtered (
0.45 microns
).
Nutrient concentrations (NH
4+
, NO
3
, and PO
43+
) were determined by ion chromatography using a
Dionex 4500i system (Dionex Inc., Sunnyvale, CA, USA). DBO5 was determined by incubation in an
OxiTop Box (WTW at 20 C).
Sediment samples were obtained from the center of each lake with PVC tubes of length 150 cm
and inner diameter 80 mm. In the laboratory, sediment samples were cut into 3 to 5 cm thick
segments. The sediment samples were used to determine the influence (both present and past) of
seawater in each lake, using the concentration of pyrite (S pyrite) in sediments relative to organic C
content as a proxy measure [
22
]. The organic C/pyritic S ratio is a proxy that distinguishes anoxic
freshwater sediments (with low concentrations of pyrite, FeS
2
) from anoxic marine sediments (with high
pyrite contents) [
22
24
]. The total organic C (TOC) content was determined in ground samples in a
Leco TruSpec CHN analyzer (after removal of carbonates with 1M HCl), and the total S (TS) content
was determined in a Leco SC144DR /C element analyzer. Fe oxyhydroxides and Fe pyrite (FeS
2
)
were determined by sequential Fe extraction (for more details see [
25
,
26
]). The pyritic S content was
determined stoichiometrically from the pyritic Fe content.
3. Results and Discussion
3.1. Errors in Designation of Habitats in Annex I of the Habitats Directive
The Habitats Directive obliges EU member states to designate special areas of conservation for
habitats and species considered to be of community interest, in a network known as Natura 2000.
The Nature 2000 network aects 30% of the Spanish territory and the country has the largest area of
land included in the network in the EU. Although this is very positive from an environmental point
of view, it has led to diculties in the execution of development plans in rural areas, particularly in the
implementation of projects (e.g., wind parks and fish farms) where the location aects a Nature 2000
network space. The absence of clear guidelines for the correct, standardized interpretation of habitats
included in Annex I has generated confusion and errors during the identification of areas that should
be protected [27,28].
Appl. Sci. 2020,10, 9068 5 of 20
In Galicia, several areas degraded by anthropogenic activities were designated priority habitats.
For instance, dierent Sphagnum acid bogs (habitat 7150) were located in a zone dominated by rocky
outcrops or forest areas strongly aected by anthropogenic activities during a period of more than
30 years [
29
]. Likewise, the main Galician dune systems [
30
], which are often characterized by sediments
with more than 10% of CaCO
3
, were designated as Atlantic decalcified fixed dunes (Calluno-Ulicetea)
(priority habitat 2150) [31].
The coastal lakes, i.e., the focus of this study, represent another example of incorrect
habitat designation, as all were identified as Coastal lagoons (priority habitat 1150). This applies to
the Xuño and Bodeira lakes, but probably also applies to other coastal lakes in Galicia (e.g., Doniños),
which do not fit within this habitat category in relation to the water composition, contrary to the
definition given in the manuals published in the last few decades (e.g., [30]).
A significant weakness that appeared at the outset of the establishment of the Natura 2000 network
was the lack of standardized criteria for interpreting the habitats and the inadequate scientific-technique
knowledge of the work teams involved [
28
,
32
,
33
]. This weakness is, to a large extent, responsible for
the problems identified in the present study.
3.2. Ocial Cartography: Errors and Inconsistences in Habitat Delimitation and Designation
The analysis conducted in the present study revealed that the delimitation and designation of
habitats do not respond to clear, standardized criteria, leading to multiple inconsistences that preclude
comparative studies between dierent Natura 2000 areas with similar characteristics.
One of the most common errors observed in this project was the excessive division of natural spaces
into numerous habitats not related to the overall ecosystem functionality. In addition, incompatible
habitats sometimes appear in the same space. Table 1shows the main habitats designated as
coastal lagoons, considered by ocial sources as only including bodies of water.
Table 1.
Main, associated, and secondary habitats in the official cartography assigned to the studied lakes.
The habitats that are not marked as relevant for the conservation in the official cartography were discarded.
Source: Xunta de Galicia ©.
Code Definition
1150 Coastal lagoons
7210 Calcareous fens with Cladium mariscus and species of the Caricion davallianae
2130 Fixed coastal dunes with herbaceous vegetation (grey dunes)
2150 Atlantic decalcified fixed dunes (Calluno-Ulicetea)
3150
Natural eutrophic lake with Magnopotamion or Hydrocharition–type vegetation
5230 Arborescent matorral with Laurus nobilis
6220 Pseudo-steppe with grasses and annuals of the Thero-Brachypodietea
91E0 Alluvial forests with Alnus glutinosa and Fraxinus excelsior
In this study, we assumed that lake systems are complex habitats that include dierent
environments and plant formations such as reed beds (communities of Phragmites australis),
rushes (formation dominated by Juncus spp.) and aquatic vegetation (e.g., Ruppietea maritimae,Potametea,
Zosteretea, and Charetea). The coexistence of several formations in the same habitat is explained in the
description of coastal lagoons [9], which include salt marshes as part of these complexes.
Following on from this general framework for defining habitats in each lake in relation to the
ocial cartography, we conducted an in-depth analysis of each sector in function of the composition of
the water and sediments, as done for the delimitation.
Appl. Sci. 2020,10, 9068 6 of 20
3.3. Water and Sediment Composition
3.3.1. Water Composition and Quality
The main physiochemical characteristics of the water in the four lakes are shown in Table 2.
The water in the Louro and Vix
á
n lakes is characterized by alkaline pH (pH 8–9) and an elevated ionic
concentration (EC mean values: 10–23 dS m
1
). These results demonstrate the marine influence in
both lake systems, which coincides with the definition of Coastal lagoons (habitat 1150): “Lagoons are
expanses of shallow coastal salt water, of varying salinity and water volume, wholly or partially
separated from the sea by sand banks or shingle, or, less frequently, by rocks. Salinity may vary from
brackish water to hyper salinity depending on rainfall, evaporation and through the addition of fresh
seawater from storms, temporary flooding of the sea in winter or tidal exchange . . . ” [9].
Table 2.
Water and sediments physicochemical properties and composition, na: not analyzed.
n: number of samples.
Site pH EC DBO5 NH4+NO2NO3PO43
Water
dS cm1mg L1
Louro (n =15) 8.3 ±0.8 23.3 ±10 29 ±27 0.30 ±0.22 0.08 ±0.04 2.19 ±1.24 0.10 ±0.06
Vixán (n =18) 8.2 ±0.9 10.1 ±0.7 10 ±9.4 0.09 ±0.04 25.7 ±37.4 2.34 ±1.37 0.18 ±0.23
Xuño (n =18) 6.6 ±0.3 0.46 ±0.2 6.2 ±6.1 0.08 ±0.10 0.03 ±0.02 1.96 ±2.23 0.10 ±0.20
Bodeira (n =12) 7.2 ±0.2 0.41 ±0.1 9.1 ±11 0.08 ±0.12 0.08 ±0.07 23.5 ±42.9 0.13 ±0.13
Sediment
pH EC Eh TOC TS
Fe oxyhyd.
Fe pyrite
dS cm1mV % µmol g1
Louro (cm) (n =2) (n =2) (n =2) (n =4) (n =4) (n =4) (n =4)
0–15 6.8 24.1 124 8.6 ±1.8 2.0 ±0.2 37.0 ±15 367 ±126
40–60 6.9 20.1 110 4.2 ±0.7 1.2 ±0.1 11.9 ±5.8 197 ±13
Vixán (cm) (n =1) (n =1) (n =3) (n =4) (n =4) (n =4) (n =4)
0–15 7.8 14 78 ±9 8.7 ±2.6 0.91 ±0.4 22.5 ±1.9 131 ±55
40–60 7.3 150 ±25 1.6 ±0.3 0.20 ±0.3 23.0 ±7.0 73.9 ±3.9
90–110 na 10.8 na 4.2 ±0.8 0.92 ±0.1 na na
Xuño (cm) (n =1) (n =1) (n =1) (n =4) (n =4) (n =4) (n =4)
0–15 6.9 60 0.56 11.5 ±0.6 0.26 ±0.16 187 ±39 0.24 ±0.17
40–60 6.4 45 na 0.22 ±0.11 0.02 ±0.02 2.85 ±0.01 0.05 ±0.01
90–110 6.5 12 na 1.76 ±0.06 0.61 ±0.04 1.04 ±1.52 1.38 ±1.32
Bodeira (cm) (n =1) (n =1) (n =1) (n =4) (n =4) (n =4) (n =4)
0–15 6.1 70 0.76 24.6 ±4.6 0.72 ±0.32 89.1 ±18 0.04 ±0.03
40–60 na na na 5.30 ±1.40 0.09 ±0.04 63.4 ±15 2.54 ±1.73
90–110 7 120 na 1.61 ±0.62 0.45 ±0.02 188 ±16 2.99 ±1.78
By contrast, the water in the Xuño and Bodeira lakes was characterized by slightly acidic to neutral
pH (6.6–7.2) and a low EC (>1 dS m
1
), which indicate the strictly continental origin of these waters.
The ionic concentration only increases during the winter periods as consequence of the deposition
of marine spray [
34
]. Consequently, these lakes do not have the basic conditions established in the
definition of coastal lagoons, and they should be assigned to the category Natural eutrophic lakes with
Magnopotamion or Hydrocharition (habitat 3150).
In both types of coastal lakes, the water volume varied widely, with particularly large reductions
at the end of summer or start of autumn, coinciding with the periods of highest drought (see below).
The reduction in the volume of water in the lakes leads to a reduction in quality, due to increased
concentrations of nitrogenated forms (nitrate and ammonium), phosphates, and DBO5 (Table 2),
and thus to an increase in fish mortality events (e.g., Vix
á
n lake, [
34
]). The toxic metal contents were
very low in all the lakes under study (data not shown) [34].
Appl. Sci. 2020,10, 9068 7 of 20
3.3.2. Sedimentary Composition
The lake sediments were characterized by a predominance of the sand fraction (>75% in general
terms: data not shown, [
34
]) and low contents of inorganic colloids such as Fe oxyhydroxides (Table 2).
The organic content C was very high in the superficial part of the lake sediments (0–15 cm), with mean
values ranging between 8.6% in Louro and 24.6% in Bodeira. These values decreased with depth,
but with alternating organic C-rich and -poor layers (Table 2; see also [
18
]). The pH was close to neutral,
and the redox conditions were anoxic (Eh <200 mV; [
35
]) in all cores (Table 2). The TS content was
correlated with the TOC at depth (correlation TOC/TS, rs =0.739, p<0.001, n =41), indicating that
most of the TS is organic S. Moreover, the relationship between TOC and pyrite S (Figure 2) revealed a
clear dierence between the Xuño and Bodeira lakes and the Louro and Vix
á
n lakes. For the first pair,
the superficial and deep samples always had freshwater characteristics, while the sediment samples
from the second pair were more characteristic of marine environments. These results are consistent
with the water composition, demonstrating that the Xuño and Bodeira lakes were never salt lagoons.
Appl. Sci. 2020, 10, 9068 7 of 19
lakes. For the first pair, the superficial and deep samples always had freshwater characteristics, while
the sediment samples from the second pair were more characteristic of marine environments. These
results are consistent with the water composition, demonstrating that the Xuño and Bodeira lakes
were never salt lagoons.
Figure 2. Organic carbon vs pyrite S in lake sediments. Black solid lines represent the typical relation
for marine sediments (C/S = 2.8 ± 1.5; [23,36]), while the blue solid line represent the same relation for
freshwater environments with a reduce sulphate concentration [22]. For each location, the graph
shows the results in surficial and deep samples (up to 100110 cm in depth). The high relation C/S in
all samples indicate that Xuño and Bodeira were always freshwater lakes.
3.4. Delimitation of Coastal Lakes
The terrain ruggedness determined by the Riley formulation [21] enabled delimitation of the
maximum extension of the lake basin. The surface areas were around 5% larger than those established
with the 2017 orthophotograph (Figures 3, 4, 7, and 8). This finding indicates partial occupation of
the actual surface area of the lakes, particularly by agricultural activities. The sectors present in each
lake were estimated independently, and their characteristics are included in Table 3.
Table 3. Estimated surface in each sector follow our delimitation for the case of the second and third
column and employed the surface values included in Annex I of PDRN over the interest zone for this
study in the columns defined as “Area defined by autonomous government”. (Source: Xunta de
Galicia © ).
Lagoon/lake Area
(ha)
Free Water Surface
(ha)
Area Defined by Autonomous
Government
Coastal Lagoon
(ha)
Natural Eutrophic
Lake (ha)
33.6
19.6
23.3
-
2.3
0.005
2.3
1.7
18.0
3.4
16.4
-
1.7
0.1
1.2
0.8
Figure 2.
Organic carbon vs pyrite S in lake sediments. Black solid lines represent the typical relation
for marine sediments (C/S=2.8
±
1.5; [
23
,
36
]), while the blue solid line represent the same relation
for freshwater environments with a reduce sulphate concentration [
22
]. For each location, the graph
shows the results in surficial and deep samples (up to 100–110 cm in depth). The high relation C/S in all
samples indicate that Xuño and Bodeira were always freshwater lakes.
3.4. Delimitation of Coastal Lakes
The terrain ruggedness determined by the Riley formulation [
21
] enabled delimitation of the
maximum extension of the lake basin. The surface areas were around 5% larger than those established
with the 2017 orthophotograph (Figures 3, 4, 7, and 8). This finding indicates partial occupation of the
actual surface area of the lakes, particularly by agricultural activities. The sectors present in each lake
were estimated independently, and their characteristics are included in Table 3.
Appl. Sci. 2020,10, 9068 8 of 20
Table 3.
Estimated surface in each sector follow our delimitation for the case of the second
and third column and employed the surface values included in Annex I of PDRN over the
interest zone for this study in the columns defined as “Area defined by autonomous government”.
(Source: Xunta de Galicia ©).
Zone Lagoon/Lake Area
(ha)
Free Water Surface
(ha)
Area Defined by Autonomous
Government
Coastal Lagoon
(ha)
Natural Eutrophic
Lake (ha)
Louro 33.6 19.6 23.3 -
Xuño 2.3 0.005 2.3 1.7
Vixán 18.0 3.4 16.4 -
Bodeira 1.7 0.1 1.2 0.8
3.4.1. Coastal Lagoons—Louro
The estimated surface area of the Louro lake is 33.6 ha, distributed across three environmental units:
open water, macrophytes (especially reed beds, communities of Phragmites australis) and herbaceous
formations (Figure 3; Table 3).
1
Figure 3.
Coastal lagoon of Louro. (
a
,
b
) represent the temporal evolution of environmental units in
1989 and 2017, respectively. (
c
) shows Topographic Ruggedness Index (TRI) classification, in black,
values below mean and in white the values above mean. (
d
) Ocial cartography representing the
distribution of habitats from Annex I of Habitats Directive. The red line in all cases represent the extent
marked for the lagoon by our analysis (IGN [20]; Xunta de Galicia ©).
Open water has a total surface area of 19.6 ha, representing 58.2% of the lake. This unit
has not suered 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
Appl. Sci. 2020,10, 9068 9 of 20
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 second unit is a meadow dominated by grass (Paspalum vaginatum) and to a lesser extent by
Scirpus maritimus (association of Scirpetum maritimae) [
34
]. This plant formation occurred at the front of
the lake and occupied an area of 7.9 ha (23.6%). However, most of this formation was covered by water
during periods of maximum water availability (January–April), overlapping seasonally with the open
water sector. The reed bed, with presence of Thypha latifolia increased in the peripheral areas, located in
the distal and north part of the lake, occupying 14% of the total surface area.
In the ocial PDRN cartography, the zone was divided in three main categories. Some 75.3%
of the sector was defined as Coastal lagoon, while 12.8% was fixed coastal dunes and 11.5% was
defined as Pseudo-steppe with grasses. In this classification, the habitat distribution was closely
related to the distribution of plant units (mainly phytosociological units) and with a low weight of lake
system functionality. There was also evidence of internal inconsistences relative to the criteria used for
the habitat designation.
The main designation error in Louro resides in the inclusion of Pseudo-steppe with grasses
and annuals of the Thero-Brachypodietea (habitat 6220), which occupy 12.8% of the surface area in the
ocial cartography; the presence of these plants is very dubious based on the available information
and the habitat characteristics. These areas appear at the front of the lake, in an area that is currently
dominated by Paspalum vaginatum, a non-native species, and to a lesser extent by Scirpus maritimus,
and most of the species associated with habitat 6220 are not present (see [9]).
The environmental conditions do not correspond to the ecological requirements of the
characteristics plant communities of this habitat. This is defined as a xerophyte Mediterranean
grassland dominated by vivacious, annual grass that grows on calcareous substrates with temporal
hydromorphism [
37
]. None of these categories appeared at the front part of Louro lake.
Moreover, this habitat
was not mentioned in any zone of the Natura 2000 network in Galicia, based on
data provided by the Spanish Ministry of the Environment [
37
,
38
] or the European Environment
Agency and data obtained in previous studies in the Galician coast. In view of the foregoing and as
this unit is located in the lake basin, it should not appear in a separate category. The same applies
to the drainage channel, which cannot be considered an independent unit, because it is one of the
characteristic elements of this habitat [
39
]. The pseudo-steppe habitat with grasses should be included
as part of the lagoon.
Another important element in the Louro lake, and which appears in other lakes, is the recovery of
habitat 91E0 (Alluvial forests with Alnus glutinosa and Fraxinus excelsior, Alno-Padion,Alnion incanae,
Salicion albae), which was almost absent in 1989 and now covers a surface area of 1.4 ha. This is a
common pattern in a large portion of rivers and wetlands in Galicia and is related to the abandonment
of agricultural land in rural areas and the reduction in agricultural activity [40,41].
3.4.2. Coastal Lagoons—Vixán
The space classified as lake in Vix
á
n covered an area of 18 ha. However, it must be emphasized that
delimitation of the lake proved dicult in relation to the separation from the coastline. Between the lake
and the sea, there is a strip of land of length 300 m occupied by a transition plain with a drainage channel,
associated with a salt marsh dominated by Juncus maritimus,Juncus acutus, and Scirpus maritimus
(Figure 4). This category continues at the back of the dune system, which hampers delimitation of
the area. The main criteria used for habitat delimitation was the identification of hydrophyte vegetation
as a dominant formation.
Regarding the environmental units, most of the area was occupied by reed bed (54.9%), while open
water occupied 18.8%. In addition, an area of salt marsh occurred at the front part (26.3%).
In relation to the surface area of alluvial forest that appears in the ocial cartography, its inclusion
was ruled out, because the extension was negligible and limited to a few specimens of Alnus glutinosa
and Salix atrocinerea that did not constitute a continuous forest.
Appl. Sci. 2020,10, 9068 10 of 20
Appl. Sci. 2020, 10, 9068 9 of 19
grassland dominated by vivacious, annual grass that grows on calcareous substrates with temporal
hydromorphism [37]. None of these categories appeared at the front part of Louro lake. Moreover,
this habitat was not mentioned in any zone of the Natura 2000 network in Galicia, based on data
provided by the Spanish Ministry of the Environment [37,38] or the European Environment Agency
and data obtained in previous studies in the Galician coast. In view of the foregoing and as this unit
is located in the lake basin, it should not appear in a separate category. The same applies to the
drainage channel, which cannot be considered an independent unit, because it is one of the
characteristic elements of this habitat [39]. The pseudo-steppe habitat with grasses should be included
as part of the lagoon.
Another important element in the Louro lake, and which appears in other lakes, is the recovery
of habitat 91E0 (Alluvial forests with Alnus glutinosa and Fraxinus excelsior,Alno-Padion, Alnion incanae,
Salicion albae), which was almost absent in 1989 and now covers a surface area of 1.4 ha. This is a
common pattern in a large portion of rivers and wetlands in Galicia and is related to the abandonment
of agricultural land in rural areas and the reduction in agricultural activity [40,41].
3.4.2. Coastal LagoonsVixán
The space classified as lake in Vixán covered an area of 18 ha. However, it must be emphasized
that delimitation of the lake proved difficult in relation to the separation from the coastline. Between
the lake and the sea, there is a strip of land of length 300 m occupied by a transition plain with a
drainage channel, associated with a salt marsh dominated by Juncus maritimus, Juncus acutus, and
Scirpus maritimus (Figure 4). This category continues at the back of the dune system, which hampers
delimitation of the area. The main criteria used for habitat delimitation was the identification of
hydrophyte vegetation as a dominant formation.
Figure 4. Coastal lagoon of Vixán. (a,b) represent the temporal evolution of environmental units in
1989 and 2017, respectively. On the lagoon back appear two categories, reedbed and crops, because
this part is occupied for reedbeds and the local inhabitants using the zone for their crops. (c) shows
TRI classification, in black, values below mean and in white the values above mean. (d) Official
Figure 4.
Coastal lagoon of Vix
á
n. (
a
,
b
) represent the temporal evolution of environmental units in
1989 and 2017, respectively. On the lagoon back appear two categories, reedbed and crops, because this
part is occupied for reedbeds and the local inhabitants using the zone for their crops. (
c
) shows TRI
classification, in black, values below mean and in white the values above mean. (
d
) Ocial cartography
representing the distribution of habitats from Annex I of Habitats Directive. The red line in all cases
represent the extent marked for the lagoon by our analysis (IGN [20]; Xunta de Galicia ©).
Unlike the proposed classification, PDRN divided the Vix
á
n lake into three main habitats:
coastal lagoon (94.7% of the area), calcareous fens with Cladium mariscus and Caricion davallianae (54.7%)
and alluvial forest (45.7%). The proportions of each of these habitats indicate an important degree of
overlap between units. For instance, the area registered as alluvial forest was simultaneously identified
as coastal lagoon and calcareous fens.
Figure 5shows this habitat overlapping at the back of the lake. In this respect, the alluvial forest
was not relevant in Vix
á
n (Figure 4). The disperse trees occurred in the distal zone and occupied a
surface area (based on their canopy) of 395 m
2
, i.e., much smaller than the 76,000 m
2
registered in
the PDRN. The small area occupied, and their lack of continuity indicated that this unit should be
removed and that the zone designated as alluvial forest should be re-designated as reed bed, because
the species associated with this habitat predominate in this lake zone.
The habitat designation in the front part of the lake diered from the ocial cartography.
In the PDRN
, a zone of calcareous fens (7210) appears in this area. This habitat is associated with
water margins, flowing, or standing in hygroturb calcareous soils, with communities dominated
by Cladium mariscus. Recent studies [
34
] have shown that the substrate of the zone is acidic or
even very acidic (pH 4–6). This finding is incompatible with the term “calcareous” that defines and
characterizes this habitat. Habitat 7210 is considered by some authors as mixed habitat, defined by
the characteristics of the physical environment (substrate) and the vegetation. Several environmental
agencies consider that, although the presence of plant cover with a particular structural characteristic is
very important in the habitat definition, this should be developed in a marshy area and on calcareous
soils [42,43].
Appl. Sci. 2020,10, 9068 11 of 20
Appl. Sci. 2020, 10, 9068 10 of 19
cartography representing the distribution of habitats from Annex I of Habitats Directive. The red line
in all cases represent the extent marked for the lagoon by our analysis (IGN [20]; Xunta de Galicia © ).
Regarding the environmental units, most of the area was occupied by reed bed (54.9%), while
open water occupied 18.8%. In addition, an area of salt marsh occurred at the front part (26.3%).
In relation to the surface area of alluvial forest that appears in the official cartography, its
inclusion was ruled out, because the extension was negligible and limited to a few specimens of Alnus
glutinosa and Salix atrocinerea that did not constitute a continuous forest.
Unlike the proposed classification, PDRN divided the Vixán lake into three main habitats:
coastal lagoon (94.7% of the area), calcareous fens with Cladium mariscus and Caricion davallianae
(54.7%) and alluvial forest (45.7%). The proportions of each of these habitats indicate an important
degree of overlap between units. For instance, the area registered as alluvial forest was
simultaneously identified as coastal lagoon and calcareous fens.
Figure 5 shows this habitat overlapping at the back of the lake. In this respect, the alluvial forest
was not relevant in Vixán (Figure 4). The disperse trees occurred in the distal zone and occupied a
surface area (based on their canopy) of 395 m2, i.e., much smaller than the 76,000 m2 registered in the
PDRN. The small area occupied, and their lack of continuity indicated that this unit should be
removed and that the zone designated as alluvial forest should be re-designated as reed bed, because
the species associated with this habitat predominate in this lake zone.
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.
The habitat designation in the front part of the lake differed from the official cartography. In the
PDRN, a zone of calcareous fens (7210) appears in this area. This habitat is associated with water
margins, flowing, or standing in hygroturb calcareous soils, with communities dominated by Cladium
mariscus. Recent studies [34] have shown that the substrate of the zone is acidic or even very acidic
(pH 4–6). This finding is incompatible with the term “calcareous” that defines and characterizes this
habitat. Habitat 7210 is considered by some authors as mixed habitat, defined by the characteristics
of the physical environment (substrate) and the vegetation. Several environmental agencies consider
that, although the presence of plant cover with a particular structural characteristic is very important
in the habitat definition, this should be developed in a marshy area and on calcareous soils [42,43].
Figure 5.
Vix
á
n 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.
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 sucient to justify designation of area as this
habitat [43], as occurs in the Vixán 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 dierent species of Juncus
(e.g., Juncus acutus and Juncus maritimus) and Scirpus 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 ES1110006)
seems unlikely [
44
]. Based on the previous findings, all of the lake front can be considered salt marsh
dominated by Scirpus 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 4and 6). The most important
dierence 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,
Appl. Sci. 2020,10, 9068 12 of 20
among other species. Dierent studies and manuals mention loss of biodiversity in relation to the
increase in reed bed density and the reduction in open water [4549].
Appl. Sci. 2020, 10, 9068 11 of 19
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 Vixán 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 Scirpus 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 ES1110006) seems unlikely
[44]. Based on the previous findings, all of the lake front can be considered salt marsh dominated by
Scirpus 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.
Figure 6. Evolution of Vixan lagoon SE sector. From left to right the images correspond with
Interministerial flight (19731986); Coastal flight in October 1989 and PNOA image in June 2017. Data:
(IGN, [20]). Red polygons in 1989 represents burnt reedbed. The burning in this lagoon part was
frequent at the end of summer.
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. Different studies and manuals mention loss of biodiversity in relation
to the increase in reed bed density and the reduction in open water [4549].
Previous studies of the Vixán 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 (NO2, NH4+), which lead to fish mortality events [34,52]. This is
especially important considering that designation of the area as a Site of Community Importance
Figure 6.
Evolution of Vixan lagoon SE sector. From left to right the images correspond with
Interministerial flight (1973–1986); Coastal flight in October 1989 and PNOA image in June 2017.
Data: (IGN, [
20
]). Red polygons in 1989 represents burnt reedbed. The burning in this lagoon part was
frequent at the end of summer.
Previous studies of the Vix
á
n 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 ocial delimitation of the lakes considered in this study.
Thus, while in Vixan the reed bed surface at the back of the lake is included as part of a coastal
lagoon habitat, in the case of Louro, a similar zone is identified as an individual unit (Figures 3and 4).
3.4.3. Eutrophic Lakes—Xuño
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 limits of the Xuño lake proposed in this work are almost consistent with those established
by the PDRN. Nevertheless, in the PDRN, 99.5% of the surface area was registered as Coastal lagoon,
which appears to be an error. The Xuño lake is located at an elevation of 5 m.a.s.l. and as the channel
only acts as a drain, there is no marine influence [
15
]. This also appear clearly in the analysis of
this area, as summarized in Table 2and Figure 2.
There is also habitat division in this location, which includes coastal lagoon habitat, dune (2130)
(0.01 ha) and alluvial forest (91E0) (almost non-existent). Currently these zones are occupied by
reed bed, Scirpus maritimus and floating aquatic vegetation (Potamogeton natans,Nymphaea alba).
Appl. Sci. 2020,10, 9068 13 of 20
Appl. Sci. 2020, 10, 9068 12 of 19
(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.
Thus, while in Vixan the reed bed surface at the back of the lake is included as part of a coastal lagoon
habitat, in the case of Louro, a similar zone is identified as an individual unit (Figures 3 and 4).
3.4.3. Eutrophic LakesXuño
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).
Figure 7. Lake of Xuño. (a,b) represent the temporal evolution of environmental units in 1989 and
2017, respectively. (c) shows TRI classification, in black, values below mean and in white the values
above mean. (d) Official cartography representing the distribution of habitats from Annex I of
Habitats Directive. The red line in all cases represent the extent marked for the lagoon by our analysis
(IGN, [20]; Xunta de Galicia © ).
The limits of the Xuño lake proposed in this work are almost consistent with those established
by the PDRN. Nevertheless, in the PDRN, 99.5% of the surface area was registered as Coastal lagoon,
which appears to be an error. The Xuño lake is located at an elevation of 5 m.a.s.l. and as the channel
only acts as a drain, there is no marine influence [15]. This also appear clearly in the analysis of this
area, as summarized in Table 2 and Figure 2.
There is also habitat division in this location, which includes coastal lagoon habitat, dune (2130)
(0.01 ha) and alluvial forest (91E0) (almost non-existent). Currently these zones are occupied by reed
bed, Scirpus maritimus and floating aquatic vegetation (Potamogeton natans, Nymphaea alba).
Figure 7.
Lake of Xuño. (
a
,
b
) represent the temporal evolution of environmental units in 1989
and 2017, respectively
. (
c
) shows TRI classification, in black, values below mean and in white the
values above mean. (
d
) Ocial cartography representing the distribution of habitats from Annex I of
Habitats Directive. The red line in all cases represent the extent marked for the lagoon by our analysis
(IGN, [20]; Xunta de Galicia ©).
3.4.4. Eutrophic Lakes—Bodeira
The Bodeira lake occupies an area of 1.7 ha (Figure 8), with only 6.2% of open water. The seasonal
variation in Bodeira is more extreme than in the other lakes, as at the end of summer the lake basin
is empty of water. The aquatic vegetation and the Phragmites australis occupy 20.7 and 28.8% of
the area, respectively
. The increase in the alluvial forest mentioned in other lakes was also observed
in Bodeira, where this habitat occupied 44.4% of the area considered and has undergone a large
increase in the last few decades. The recovery of alluvial forest with Alnus glutinosa is the most
relevant characteristic of this lake. In the Bodeira area, this type of cover has increased from 0.18 ha
(in 1989) to 0.77 ha (in 2017). Outside the lake area, this habitat has increased from 0.53 ha to 6.47 ha of
continuous forest.
In the PDRN, the Bodeira lake simultaneously appears as a coastal lagoon and a natural eutrophic
lake (Figure 9), even though these habitats are not compatible. Based on the results of water and
sediment analysis, this lake should be designated as habitat 3150 (Table 2), which coincides with the
information in Ramsar Fact Sheets, in which this lake is defined as a small freshwater coastal lake.
As in Xuño, there are also small areas with other main habitats, such as alluvial forest (0.38 ha) and
pseudo-steppes (0.09 ha). This adds to the problem of the simultaneous definition as a coastal lagoon
and natural eutrophic lake.
Both lakes show important similarities (regarding the water and sedimentary composition) to
freshwater lakes separated from the sea (see Section 3.3). The high contents of nutrients (N and
P) also indicated that the lakes are eutrophic and justify inclusion of the lakes in habitat 3150 [
15
].
The inclusion in a same zone of coastal lagoons and a natural eutrophic lake (Table 3and Figure 9) is
clearly an error. The characteristics of each habitat in the same water mass and their physiochemical
Appl. Sci. 2020,10, 9068 14 of 20
parameters cannot be very dierent, as shown in Table 2. Coastal lagoon occupied a major part of
these lakes (Figure 9), and although it is the main habitat, this space cannot be considered a linked
natural eutrophic lake.
Appl. Sci. 2020, 10, 9068 13 of 19
3.4.4. Eutrophic LakesBodeira
The Bodeira lake occupies an area of 1.7 ha (Figure 8), with only 6.2% of open water. The seasonal
variation in Bodeira is more extreme than in the other lakes, as at the end of summer the lake basin
is empty of water. The aquatic vegetation and the Phragmites australis occupy 20.7 and 28.8% of the
area, respectively. The increase in the alluvial forest mentioned in other lakes was also observed in
Bodeira, where this habitat occupied 44.4% of the area considered and has undergone a large increase
in the last few decades. The recovery of alluvial forest with Alnus glutinosa is the most relevant
characteristic of this lake. In the Bodeira area, this type of cover has increased from 0.18 ha (in 1989)
to 0.77 ha (in 2017). Outside the lake area, this habitat has increased from 0.53 ha to 6.47 ha of
continuous forest.
Figure 8. Lake of Bodeira. (a,b) represent the temporal evolution of environmental units in 1989 and
2017, respectively. (c) shows TRI classification, in black, values below mean and in white the values
above mean. (d) Official cartography representing the distribution of habitats from Annex I of
Habitats Directive. The red line in all cases represent the extent marked for the lagoon by our analysis
(IGN, [20]; Xunta de Galicia © ).
In the PDRN, the Bodeira lake simultaneously appears as a coastal lagoon and a natural
eutrophic lake (Figure 9), even though these habitats are not compatible. Based on the results of water
and sediment analysis, this lake should be designated as habitat 3150 (Table 2), which coincides with
the information in Ramsar Fact Sheets, in which this lake is defined as a small freshwater coastal lake.
As in Xuño, there are also small areas with other main habitats, such as alluvial forest (0.38 ha) and
pseudo-steppes (0.09 ha). This adds to the problem of the simultaneous definition as a coastal lagoon
and natural eutrophic lake.
Figure 8.
Lake of Bodeira. (
a
,
b
) represent the temporal evolution of environmental units in 1989 and
2017, respectively. (
c
) shows TRI classification, in black, values below mean and in white the values
above mean. (
d
) Ocial cartography representing the distribution of habitats from Annex I of Habitats
Directive. The red line in all cases represent the extent marked for the lagoon by our analysis (IGN, [
20
];
Xunta de Galicia ©).
Appl. Sci. 2020, 10, 9068 14 of 19
Figure 9. (a) represent lake of Xuño and (b) represent lake of Bodeira. In both cases it shows the surface
occupied by coastal lagoon habitat (blue), and natural eutrophic lake habitat (brown). The red line in
all cases represent the extent marked for the lagoon by our analysis (IGN [20]; Xunta de Galicia © ).
Both lakes show important similarities (regarding the water and sedimentary composition) to
freshwater lakes separated from the sea (see Section 3.3). The high contents of nutrients (N and P)
also indicated that the lakes are eutrophic and justify inclusion of the lakes in habitat 3150 [15]. The
inclusion in a same zone of coastal lagoons and a natural eutrophic lake (Table 3 and Figure 9) is
clearly an error. The characteristics of each habitat in the same water mass and their physiochemical
parameters cannot be very different, as shown in Table 2. Coastal lagoon occupied a major part of
these lakes (Figure 9), and although it is the main habitat, this space cannot be considered a linked
natural eutrophic lake.
In relation to the habitat division, particularly in relation to the categorization of eutrophic lakes
by PDRN (Figures 7 and 8), in the present study it was considered that the lake basin corresponds to
a unique habitat and that division in units with a limited spatial representation does not correspond
to the functionality of wetlands. Indeed, this division appears to have arisen as the result of erroneous
land analysis using only botanic and phytosociological criteria. This highlights the need to delimit
wetlands and their habitats by using an integrated approach, including botanic, hydrological,
sedimentary, and faunistic analysis.
3.5. Anomalies in Elaboration of the Natura 2000 Network
The anomalies mentioned in previous section have led to various errors during the development of
the Natura 2000 network in Galicia. First, the absence of previous debate among experts in the different
areas (botanic, ecology, zoology, geochemistry, etc.) that would have permitted the definition of each
habitat to be adapted to the real situations in Galicia. Secondly, the interpretation and identification of
habitats to each LIC in Galicia was almost exclusively conducted by botanists. Thus, the fact that the
presence of several habitats required not only botanical knowledge (flora and vegetation) but also
knowledge about the physical environment (substrate, lithology, soils, etc.) was overlooked.
These errors have led to the current situation whereby the regional authorities must elaborate
specific studies for these complex habitats, for which dubious definitions have been made [31]. These
studies clearly show errors in designation concerning the presence and extension of the habitats, e.g.,
the classification of some zones in habitat 2150* (Atlantic decalcified fixed dunes (Calluno-Ulicetea) or
in the group 71 habitats (active raised bogs) [29].
3.6. Developmental Trends
The general trend in these coastal lake systems is for them to become clogged, through a process
that is already well advanced. The process has perhaps been further accelerated in the last 30 years
as consequence of abandonment of traditional activities such as the annual extraction of macrophytes
(sedges or reed beds). This is clearly observed in the small Xuño and Bodeira lakes, where during the
summer most of the area usually occupied by the lakes are now dry: the Bodeira lake generally
remains dry between the end of August to October (Figure 10). In order to maintain the quality of
Figure 9.
(
a
) represent lake of Xuño and (
b
) represent lake of Bodeira. In both cases it shows the surface
occupied by coastal lagoon habitat (blue), and natural eutrophic lake habitat (brown). The red line in
all cases represent the extent marked for the lagoon by our analysis (IGN [20]; Xunta de Galicia ©).
In relation to the habitat division, particularly in relation to the categorization of eutrophic lakes
by PDRN (Figures 7and 8), in the present study it was considered that the lake basin corresponds to a
unique habitat and that division in units with a limited spatial representation does not correspond to the
functionality of wetlands. Indeed, this division appears to have arisen as the result of erroneous land
Appl. Sci. 2020,10, 9068 15 of 20
analysis using only botanic and phytosociological criteria. This highlights the need to delimit wetlands
and their habitats by using an integrated approach, including botanic, hydrological, sedimentary,
and faunistic analysis.
3.5. Anomalies in Elaboration of the Natura 2000 Network
The anomalies mentioned in previous section have led to various errors during the development of
the Natura 2000 network in Galicia. First, the absence of previous debate among experts in the dierent
areas (botanic, ecology, zoology, geochemistry, etc.) that would have permitted the definition of each
habitat to be adapted to the real situations in Galicia. Secondly, the interpretation and identification
of habitats to each LIC in Galicia was almost exclusively conducted by botanists. Thus, the fact that
the presence of several habitats required not only botanical knowledge (flora and vegetation) but also
knowledge about the physical environment (substrate, lithology, soils, etc.) was overlooked.
These errors have led to the current situation whereby the regional authorities must elaborate
specific studies for these complex habitats, for which dubious definitions have been made [
31
].
These studies clearly show errors in designation concerning the presence and extension of the habitats,
e.g., the classification
of some zones in habitat 2150* (Atlantic decalcified fixed dunes (Calluno-Ulicetea)
or in the group 71 habitats (active raised bogs) [29].
3.6. Developmental Trends
The general trend in these coastal lake systems is for them to become clogged, through a process
that is already well advanced. The process has perhaps been further accelerated in the last 30 years as
consequence of abandonment of traditional activities such as the annual extraction of macrophytes
(sedges or reed beds). This is clearly observed in the small Xuño and Bodeira lakes, where during
the summer most of the area usually occupied by the lakes are now dry: the Bodeira lake generally
remains dry between the end of August to October (Figure 10). In order to maintain the quality of
these systems, as well as the natural values whereby they can be included in the Natura 2000 network,
the application of dierent management plans, such as dredging the lakes, should be considered.
Article 6 of the Habitats Directive established that this type of activity can improve the quality and
functionality of these systems. These methods have been applied through the LIFE program [
53
] in
dierent lakes included in the Natura 2000 network in Spain, Italy, Greece and Portugal. The practice
of drainage is addressed in article 17 of the Habitats Directive, which in 2007–2012 highlighted the
major threat that eutrophication represents to these lakes in relation to the associated pollution and
changes in the water level [53].
In contrast to the changes in open water surfaces, the alluvial forest (91E0) underwent an important
increase in the last three decades in Louro, Xuño, and Bodeira, which in some cases exceed 10 times the
surface area reported in 1989 (Figure 3, Figure 7, and Figure 8). This change had important eects on
the system configuration (Figure 10), simultaneously highlighting the need for an urgent review of the
current state of Natura 2000 network spaces, in relation to the presence, delimitation and distribution
of habitats [
54
,
55
]. The increase in the surface area occupied by alluvial forest is very common in
Galician lakes, in both coastal and inland areas, as a consequence of the drastic reduction in agricultural
activity in Galicia in the last 50 years [41].
Appl. Sci. 2020,10, 9068 16 of 20
Appl. Sci. 2020, 10, 9068 15 of 19
these systems, as well as the natural values whereby they can be included in the Natura 2000 network,
the application of different management plans, such as dredging the lakes, should be considered.
Article 6 of the Habitats Directive established that this type of activity can improve the quality and
functionality of these systems. These methods have been applied through the LIFE program [53] in
different lakes included in the Natura 2000 network in Spain, Italy, Greece and Portugal. The practice
of drainage is addressed in article 17 of the Habitats Directive, which in 20072012 highlighted the
major threat that eutrophication represents to these lakes in relation to the associated pollution and
changes in the water level [53].
Figure 10. (a,b) represent the evolution of Xuño coastal lake between 1989 (a) and 2017 (bd) show
the evolution of Bodeira coastal lake between 1989 (c) and 2017 (d). Data: (IGN, [20]). An important
factor to highlight in these images is the increase of alluvial forest in 2017 in relation to 1989, this
habitat rises since 0.53 ha of continuous forest to 6.75 ha.
In contrast to the changes in open water surfaces, the alluvial forest (91E0) underwent an
important increase in the last three decades in Louro, Xuño, and Bodeira, which in some cases exceed
10 times the surface area reported in 1989 (Figures 3, 7, and 8). This change had important effects on
the system configuration (Figure 10), simultaneously highlighting the need for an urgent review of
the current state of Natura 2000 network spaces, in relation to the presence, delimitation and
distribution of habitats [54,55]. The increase in the surface area occupied by alluvial forest is very
common in Galician lakes, in both coastal and inland areas, as a consequence of the drastic reduction
in agricultural activity in Galicia in the last 50 years [41].
3.7. New Technologies in Ecosystem Delimitation
LiDAR data proved to be valuable for delimiting the habitats in which the edges were associated
with variations in relief, enabling up-to-date characterization of the lake surface with an uncertainty
of around 4%, compared to remote sensing techniques, except in the case of the Louro lake. However,
lake zones should be defined by taking other data sources into account, because LiDAR analysis may
Figure 10.
(
a
,
b
) represent the evolution of Xuño coastal lake between 1989 (
a
) and 2017 (
b
d
) show the
evolution of Bodeira coastal lake between 1989 (
c
) and 2017 (
d
). Data: (IGN, [
20
]). An important factor
to highlight in these images is the increase of alluvial forest in 2017 in relation to 1989, this habitat rises
since 0.53 ha of continuous forest to 6.75 ha.
3.7. New Technologies in Ecosystem Delimitation
LiDAR data proved to be valuable for delimiting the habitats in which the edges were associated
with variations in relief, enabling up-to-date characterization of the lake surface with an uncertainty
of around 4%, compared to remote sensing techniques, except in the case of the Louro lake.
However, lake zones
should be defined by taking other data sources into account, because LiDAR
analysis may include part of the areas around the lake where there is little variation in relief [
56
].
This was clear in the Vix
á
n lake where the TRI values of the cropped area were similar to those of the
lake surface.
To improve the management of these environments, detailed studies should be conducted to
monitor the seasonal and annual variations in the lake systems. Field surveys should be carried out
to analyze water and sedimentary parameters. The use of Unmanned Aerial Vehicles (UAVs) could
be valuable for quantifying spatial variations and for estimating vegetation growth and other related
parameters [5760].
4. Conclusions
Based on the information derived from a study of these lakes, information about the vegetation
and the composition of the water and sediments, the following can be concluded:
1.
Only two of the lakes (Louro and Vix
á
n) can be considered Coastal lagoons (habitat 1150).
Both Bodeira and Xuño are natural eutrophic lakes (habitats 3150).
Appl. Sci. 2020,10, 9068 17 of 20
2.
The presence, designation and distribution of the habitats defined by PDRN should be revised
in depth. Each lake is per se a functional unit and habitat, formed by dierent environments
such as open waters, channels, salt marshes and reedbeds. Classifying each unit as a dierent
habitat contradicts the philosophy of the Habitats Directive and complicates management of the
ecosystems involved.
3.
The Vix
á
n, Xuño, and Bodeira lakes are characterized by advanced states of eutrophication and
poor water quality. Restoration of hydraulic functionality should be investigated further.
4.
The expansion of alluvial forest is an example of the rapid evolution of these systems in relation
to halting anthropogenic pressure.
5.
The delimitation of lakes should be revised by using technologies such as LiDAR and
remote sensing.
Author Contributions:
Conceptualization, A.P.-A., X.L.O.; methodology, A.G.-P., X.L.O., A.P.-A. and P.F.-S.,
formal analysis, A.P.-A., A.G.-P., M.S.-S., P.F.-S. and X.L.O.; writing-original draft preparation, A.P.-A.,
X.L.O. and A.G.-P.
; writing-review and editing, A.P.-A., X.L.O., M.S.-S. and A.G.-P. All authors have read
and agreed to the published version of the manuscript.
Funding:
This work is part of a research project entitled “Monitorizaci
ó
n de los procesos biogeoqu
í
micos en
las lagunas litorales en relaci
ó
n con su calidad ambiental y respuesta al cambio clim
á
tico” (
Xunta de Galicia
,
PGIDIT08MDS036000PR), the program for consolidation of competitive research groups (Axudas
á
consolidaci
ó
n
e estruturaci
ó
n de unidades de investigaci
ó
n competitivas do SUG del Plan Galego IDT, Ambiosol Group
ref. 2018-PG036), and Cross-Research in Environmental Technologies, CRETUS (Xunta de Galicia GRUP2015/02,
ref. 2018-PG100). A.G.-P. is supported by an FPU predoctoral contract by the Spanish government
(Ministerio de Educación, Cultura y Deporte). Grant Number: FPU16/03050.
Acknowledgments:
This work was supported by CRETUS Institute. A.G.-P. was in receipt of an FPU predoctoral
contract with reference FPU16/03050. We would like to thank Mar
í
a Santiso for her assistance with laboratory
work and Christine Francis for providing language support.
Conflicts of Interest: Authors declare no conflict of interest.
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