Efectos de la contaminación difusa sobre el perifiton de arroyos

• Autores: Carolina Vilches
• Directores de la Tesis: Adonis Giorgi (dir. tes.), María Adela Casco (codir. tes.)
• Lectura: En la Universidad Nacional de La Plata ( Argentina ) en 2012
• Idioma: español
• Enlaces
  • Tesis en acceso abierto en:  sedici.unlp.edu.ar  doi.org 
• Resumen
  • español

    El perifiton puede considerarse una comunidad clave en los cuerpos de agua lóticos pequeños ya que tiene alta producción y se considera responsable de sostener gran parte de su red trófica. Las algas que lo componen provocan cambios a nivel físicoquímico en el agua, intervienen en el almacenamiento temporario de fósforo, en la formación de sedimentos y en la reducción de la erosión de los lechos. Por otro lado, las algas constituyen refugios y favorecen la construcción del sustrato a través de las secreciones y restos de la comunidad. El perifiton responde predictiva y rápidamente a los cambios en las condiciones ambientales en un gran rango de escalas espaciales. Es una comunidad sésil que se modifica por los impactos del lugar y tiene la capacidad de absorber y concentrar sustancias contaminantes mostrando cambios en su composición y en sus características estructurales y funcionales. Por ello, puede utilizarse esta comunidad como un indicador biológico del cual se obtiene información complementaria a la suministrada por variables físicas y químicas.

    La actividad agropecuaria genera desechos que se originan a partir de fuentes puntuales (ensilado, purines, cámaras sépticas) o difusas (plaguicidas, fertilizantes, sedimentos, materia orgánica y nutrientes aportados por el ganado). Mientras que las primeras son más fáciles de detectar y controlar, las difusas son más difíciles de evaluar y manejar ya que llegan al arroyo como un complejo. Nuestra hipótesis fue que los cambios producidos por actividades agropecuarias repercutirán en las características estructurales y/o funcionales de la comunidad perifítica de acuerdo a la intensidad y tipo de contaminación difusa. El principal objetivo propuesto fue: Evaluar las modificaciones producidas por la contaminación difusa en el perifiton, considerando tanto parámetros estructurales como funcionales y elaborar un marco predictivo que describa el efecto que las distintas actividades agropecuarias producen en la comunidad perifítica. Este estudio se realizó principalmente en las cabeceras de los arroyos que dan origen al río Reconquista. La geología de la región se vincula esencialmente con los depósitos sedimentarios Cenozoicos. Las pendientes de los arroyos son sumamente bajas (0,02%) y sus aguas poseen altos contenidos de nutrientes. El río Reconquista está situado al noroeste de la región metropolitana de Buenos Aires, en una zona templada en la región pampeana.

  • English

    Periphyton can be considered a key community in small lotic water bodies because its high production and because is consider of being responsible of the maintenance of much of their food web. The algae which compose it causes changes to the physico-chemical water, interceding in the temporary phosphorus storage, in the sediment formations, and in the beds erosion reduction. On the other hand, algae provide refuges and facilitate the construction of the substrate through secretions and community remains.

    Periphyton has predictable and quick response to changes in environmental conditions in a large range of spatial scales. It is a sessile community that changes by local impacts and has the ability to absorb and concentrate pollutants showing changes in its composition as well as in its structural and functional characteristics. Therefore, this community can be used as a biological indicator in order to obtain complementary information from the provided by physical and chemical variables.

    Agricultural and livestock activities generate wastes that are originated from point sources (silage, manure, septic tanks) or diffuse sources (pesticides, fertilizers, sediment, organic matter and nutrients from livestock). While the former ones are easier to detect and control, the diffuse ones are more difficult to evaluate and manage as they reaches the stream as a complex.

    Our hypothesis was that changes produced by agricultural and livestock activities have an impact on the structural and/or functional characteristic of the periphytic community according to the intensity and type of diffuse pollution. The main objective was: To evaluate the modifications produced by diffuse pollution in the periphyton, taking into account both structural and functional parameters, and develop a predictive framework that describes the effect of different agricultural and livestock activities in the periphytic community.

    This study was carried out mainly in the headwaters of the streams that origins the Reconquista River. The geology of the region is essentially related to Cenozoic sedimentary deposits. The streams slopes are extremely low (0.02%) and their water have high content of nutrients. The Reconquista River is located northwest of the metropolitan region of Buenos Aires, in a temperate zone in the Pampean region.

    The study was carried out with both natural periphyton and artificial substrates colonized on natural environment and also with periphyton on a completely artificial environment. The use of artificial substrates allowed the incorporation of functional parameters that provide sensitive and effective measures to detect the impact on the periphyton avoiding its interaction with the natural substrate. On the other hand, the experiments in an artificial environment made possible to isolate factors that had demonstrated to be important on fieldwork results. As a result, it was possible to study its effect independently from any interaction and to make a comparison against the natural environment results. At the beginning, it was conducted a survey of the upper basin at eight sites selected according to the predominant agricultural and livestock management where physico-chemical variables were analyzed and periphyton on natural substrate (Ludwidgia peploides) was studied. Then, work was concentrated on reaches that were selected according to the intensity of farming use and the periphyton colonized on artificial substrates was analyzed. In addition to the structural characteristics, functional variables were evaluated (production and community respiration, activity of exoenzymes). Finally, three experiments were carried out in artificial streams to assess the relationship of humic substances and the concentration of phosphorus, of a fertilizer, and of an herbicide for commercial use.

    Our results revealed that the parameters that best indicate the effect of diffuse pollution on periphyton were the concentration of chlorophyll a, total phosphorus content in the periphyton, the taxonomic composition, net production and alkaline phosphatase activity. However, a combination of them is necessary to interpret the changes that we reported about. It is arguably the functional parameters serve as early warning systems of pollution due to agricultural and livestock land use, whereas the structural conditions would report the sustained good or bad water quality. In addition, it was observed that humic acids should be taken into account as a key variable in Pampean streams for the impact on the development of the communities as well as on the attenuation in the nutrients uptake.

    Finally, a general predictive scheme was made based on the possible responses of the periphytic community developed in streams with livestock or crops. The trophic status of the system, the type and the intensity of land use was taken into account to differentiate the possible impacts.