Permanent researchers: Anna Romaní, Sergi Sabater, Anna Vila-Gispert
Fluvial systems intervene in a key way in the cycle of carbon and nutrients through biotic processes (decomposition, incorporation, photosynthetic production) and abiotic processes (retention, adsorption). In upper and middle river sections, often wooded and closely connected with drainage basins, riverbank vegetation can act as a filter for materials. In Mediterranean rivers material entering rivers also has a significant effect for the hydrological cycle, characterised by a dry season (the summer) and strong rainfall in the autumn and spring.
Organisms that develop in the benthic substratum of the river (stones, pebbles, sand, wood, leaves) have the strongest effect on the flow of organic and inorganic materials in the upper and middle sections of rivers.
The benthic biological community is made up of autotrophic organisms (algae, cyanobacteria) and heterotrophic organisms (bacteria, fungi, micro-invertebrates and macro-invertebrates) immersed in a polymeric matrix constituting what is known as biofilm.
The main goal of this line of research is to determine how the different components of fluvial biofilm are structured depending on the entry of organic and inorganic nutrients into the river, and how the biological community contributes to the process of assimilation and/or recycling of these nutrients.Autotrophic heterotrophic biofilms are studied, as are biofilms that form part of the hiporreic sediment. Emphasis is placed on riverbank woodland as a tampon zone.
Also the decomposition of organic material is studied (basically dead leaves), along with the communities of bacteria and fungi responsible for the process of decomposition through their enzymatic capacities.
Another focus of study are the trophic and structural relations between the organisms that form the fluvial biofilm, to define the benthic microbial loop. Fieldwork represents the main types of methodology adopted, through experimental and sampling designs (addition of nutrients, colonisation of substrata), and experimental lab designs (incubations in microcosms, artificial channels).
The main methodologies used are: composition and biomass of biofilm (bacteria, algae, fungi, microfauna, macrofauna), metabolism of biofilm (extracellular enzymatic activities, photosynthesis, respiration), open metabolism (dynamics of oxygen), structure of biofilm (contents of C:N:P, polysaccharides, electronic tracking microscopes, confocal CLSM, measures with microelectrodes), trophic relations (intestinal contents), composition and biodegradability of the organic carbon dissolved (fractional separation of the DOC by molecular weight, biodegradable DOC).
Ecotoxicology of the periphyton
Managing to understand the effect of toxic matter on ecosystems is one of the main objectives of research in ecotoxicology. Within the set of exiting ecosystems as a whole, the increasing entry of xenobiotic substances in the fluvial environment has generated great concern with respect to its effects on the biota. In this context, our group has spent several years researching the effects of model toxic matter: zinc, copper and atrazine in the periphyton. We follow a field approach, based on the conviction that the presence of a toxic substance in the aquatic ecosystem has to be regarded as another environmental factor to which natural communities are exposed.
On the one hand, we use the methodology of the dose-response test in order to estimate the influence of the environmental variability in the ecotoxicological responses from natural communities (Guasch et al. 1998; Guasch and Sabater 1998, Blanck et al. 2002). On the other hand, experiments carried out in artificial rivers allow us to determine the concentration of a certain compound that can affect both the structure and the functioning of the natural community (Guasch et al. 2002). Following the same approach, studies are being carried out at basin level to assess the existing relationship between land uses and the integrity of the fluvial ecosystem. Current research also makes reference to the capture, bio-availability, bioaccumulation and/or biodegradation of toxic matter in iothic systems.
Gauging the magnitude of the effects of a spill on the fluvial ecosystem and the factors that modulate it forms the basis for assessing its capacity of self-purification and ensuring its ecological integrity, this being the ultimate goal of this line of research.
The ecotoxicology of the periphyton is also being studied in a situation where there are extreme conditions: the Mar Menor, a hypersaline coastal lagoon on Spain’s south-eastern Mediterranean coast. High concentrations of heavy metals have been measured in the sediment of this lagoon, influenced in some areas by an old mining zone. To investigate the possible transfer of metals in the aquatic trophic network, research is being conducted into the composition of the community in the periphyton, the concentration of metals and tolerance induction.
Fluvial biofilms and applications for the quality of water
Water treatment plants currently make use of sophisticated treatment methods to obtain safe water. However, the quality of the primary water currently represent a key factor, due to the increase in housing developments, industrialisation and agricultural treatments. It is therefore important to improve the quality of water prior to its treatment.
Biofilms are frequent points of biological activity in rivers and lakes, and also during the different stadiums of water treatment systems. The objective of this research is to develop the knowledge of natural biofilms in order to optimise their capacity to regulate the contents of organic matter in the water, the retention of toxic compounds and particles.
Dissolved organic carbon (DOC) and, more precisely, biodegradable DOC, is quickly used by the heterotrophic community of biofilm (bacteria, fungi, protozoa). On the other hand, self-trophic organisms (algae, cyanobacteria) can be producers of DOC and BDOC.
In certain physicochemical conditions, of high contents of nutrients, low flow and a low N/P ratio, massive growths of cyanobacteria can occur in rivers. Cyanobacteria can produce toxic substances (cyanotoxins) as well as compounds that smell (geosmin) and are given off by the water when cell lysis takes place. If these compounds are not eliminated, they reach the distribution network and users of safe water. The organisms responsible for the production of geosmina and the factors that favour its production and liberation have been researched over two years of river monitoring and lab experiments.