El Abra de Bilbao
2005/03/01 Kortabitarte Egiguren, Irati - Elhuyar Zientzia Iturria: Elhuyar aldizkaria
The Nerbioi-Ibaizabal flows into the Abra de Bilbao. It is a bay of about 23 km 2. However, in this area there is a high density of urban, industrial and service uses.
These uses have greatly altered the entire river ecosystem, that is, human activity. This is mainly because the abiotic environment suffers an excess of organic matter, oxygen shortage, large accumulations of sediments, strong water turbidity and environmental toxicity, among others.
In addition to the abiotic environment, the consequences of human activities in the biological community have been reflected in the Abra. The disappearance of structuring species, the proliferation of opportunistic species, the imbalance of flora and fauna and the reduction of species richness. In fact, wastewater from industries and/or households has enormous concentrations of organic matter, generally higher than 100 mg/l of organic carbon.
The Abra bay of Bilbao became one of the most polluted areas in Europe. For this reason, 20 years ago a comprehensive sanitation plan was launched with the support of the Bilbao Bizkaia Water Consortium and in relation to it began to conduct the first studies around the Abra bay in Bilbao. Research has continued throughout the plan to compare the initial and future situation.
Research development
All of them and more have gathered in the last twenty years around the bay of Bilbao del Abra. Biological research began in 1984. The research group Bentos of the UPV has investigated the benthic fauna and flora of the Abra bay of Bilbao in the last twenty years. These organisms, unlike fish, live on rocks, so they are a good indicator for measuring changes in water quality. Pollution produces numerous changes in the structuring of species, that is, the substitution of species unable to withstand excessive contamination by others, etc.
However, pollution reduces the number of species and the relationship between flora and fauna. The disappearance of the flora entails the disappearance of the fauna directly related to it. For example, the Cladophora pellucida algae species prefers fed waters, the waters fed by Codium decorticatum, the waters moderated by food, the clean waters by Bifurcaria bifurcata and the waters very clean by Gelidium sesquipedale.
The biological study of the Abra bay in Bilbao has been carried out since 15 observatories, eight intertidal and seven subtidal. Research follow-up was conducted every four years from 1984 to 1996. But since the changes were so numerous, between 1996 and 2004 they began to take place every two years.
Different levels or layers have been analyzed in the intertidal zones, 3 or 4 layers approximately. Five samples of 50 x 50 cm have been taken in each layer and an inventory of flora and fauna has been carried out.
In the subtidal areas, on the contrary, the study was done by cutting, that is, by joining a piece of lead to the end of a rope and taking a sample every 3 meters. In total, approximately 34 inventories have been made at each station or observatory.
Subsequently, laboratory identification of all these specimens and data has been carried out. Also the study or statistical analysis of temporal and spatial differences.
And this study highlights, on the one hand, the spectacular rise of biodiversity in the Abra bay of Bilbao. In all seasons, both animal and plant species have increased considerably. The ecosystem is increasingly complex. On the other hand, it should be noted that the subtidal vegetation of all seasons has increased considerably. For example, the Arrigunaga station in 1984 was a desert with a coverage of 0.5%. In 2004, however, the river bottoms were covered with algae.
It seems, therefore, that little by little the Bahía del Abra of Bilbao is going from being a sewer of civilization to a clean bay.
Meñakoz
In 1984 the vegetation suffered great stress, which considerably reduced the degree of diversity of the species, since the waters of the rivers were very polluted.
From 1996 appeared Stypocaulon scoparium. And what's special? Well, this species cannot live in environments with high levels of pollution, it is sensitive to pollution. It seems, therefore, that since 1996 pollution levels decreased. Along with this species, other pollution-sensitive algae have appeared in 2002, the obtuse Laurencia and the Chondracanthus acicularis.
A notable improvement in river bottoms has also been observed by finding large algae such as Codium and Saccorhiza. Therefore, it gradually takes shape of a coast without pollution.
Arrigunaga
In 1984 the intertidal zone (right figure) hardly presents flora and fauna. There were abundant sediments and the waters were very polluted, that is, the degree of toxicity of the waters was high.
In 1998, coinciding with the proliferation of cirripedes ( Chthamalus) and the entry of calcareous algae ( Corallina elongata), a notable improvement occurred.
Between 2002 and 2004 there was a slight regression in this area.
In 1984 the subtidal area (figures on the left) was practically zero, without vegetation and the rocks were covered by sediments from the estuary. As for the fauna, there were only anemones ( Actinothoe).
In 1992 the degree of water pollution was reduced and algae began to colonize river bottoms. A high level of coverage was achieved in 2002, but a new decline occurred in 2004.
However, it can be said that diversity has spread continuously.
Azkorri (intertidal zone)
As in Sopelana and Barrika, significant changes have also occurred in Azkorri.
In 1984 the area was very degraded, with very high levels of pollution. Since then, the situation in the environment has improved significantly.
For example, in 1996 the cirripeds ( Chthamalus) multiplied spectacularly. This improvement was accompanied by calcareous algae and other species sensitive to pollution.
Las Arenas (intertidal zone)
In 1984 it was an area without fauna, whose rocks were covered with silts and abundant sediments.
Since 1996 there have been numerous filter organisms such as mussels ( Mytillus) and cirripedes ( Balanus and Chthamalus). They all take the food they need from the water. Therefore, the more food the water contains, the more these species abound.
The algae flora has also had a great development. Recently the species of algae Caulacanthus ustulatus has appeared. In relation to all this, the quality of the waters of the area has improved significantly, which has allowed the marshal.
Barrika
In the vicinity of the bay of Plentzia the vegetation has been changing. On the one hand, large algae appear ( Sccorhiza, Codium) and on the other, more common algae species in clean waters ( Bifurcaria bifurcata, Stypocaulon scoparium). With the emergence of these new species, some of the contaminated areas such as Cladophora have disappeared.
There has also been a significant increase in diversity and plant cover in river bottoms. The environmental impact of this area occurred in 1998.
Comale (reference station)
Control station or reference station in the Abra estuary of Bilbao. It is a clean water area, making it an ideal place to study natural changes. In fact, any change that occurs in Kobaron can be considered natural. And the other way around, if no footprint appears in Kobaron, the impact is local.
Photos: Photos Group of Bentos researchers from the UPV.
