Producción CyT
Tesis
Autoría
Fecha
12/03/2019
Resumen
Información suministrada por el agente en
SIGEVA
Rivers and streams are among the most threatened ecosystems worldwide. The increase in industralization and agricultural production, along with changes in land use associated to urbanization, are among the main threats that lead to detriments in the ecological quality of these ecosystems. Besides, lowland streams such as the ones in the Pampean ecoregion, are modified by river engineering works to better drain their surrounding lands. These streams are characterized, among other attributes, by ...
Rivers and streams are among the most threatened ecosystems worldwide. The increase in industralization and agricultural production, along with changes in land use associated to urbanization, are among the main threats that lead to detriments in the ecological quality of these ecosystems. Besides, lowland streams such as the ones in the Pampean ecoregion, are modified by river engineering works to better drain their surrounding lands. These streams are characterized, among other attributes, by their low or absent riverine vegetation, which allows a high incidence of solar radiation allowing a diverse and abundant macrophyte assemblage to develop. These macrophytes have a fundamental role in habitat structuring for macroinvertebrates. They also increase the site’s complexity, which is positively correlated to the amount of taxa and individuals present, since the increase of leaf sections increases the number of available shelters for invertebrates. Rehabilitation efforts have the main goal to counteract the ecological degradation of rivers and streams, and has become an urgent necessity throughout the world; an example of these techniques is the transplanting of macrophyte. This technique involves the reintroduction (transplanting) of macrophytes from nearby streams to reaches that had been altered by river engineering works, such as dredging. To achieve a successful macrophyte reintroduction in an environment, a detailed understanding is needed of how these plant species respond to the physical-chemical and hydrogeomorphological characteristics, along with their interaction with hervibores. The main objective of this thesis was to analyze the role of macrophytes in the assessment and rehabilitation of Pampean streams. The study of the factors that affect macrophyte distribution, seasonal variation, macroinvertebrate and their interaction with herbivores, will allow a more detailed understanding of their role in ecosystem rehabilitation after hydrological engineering works have been conducted in streams. The Pampean streams selected for this thesis were the Martín and Carnaval Streams, both tributaries to the Río de la Plata estuary. Seven sites were sampled (4 in the Martín stream and 4 in the Carnaval Stream) for two years in the following dates: May 2004 (fall-F1), August 2014 (winter-F2), November 2014 (spring-F3), March 2015 (summer-F4), June 2015 (winter-F5) and November 2015 (spring-F6). At each date, the following physicalchemical and hydrogeomorfological parameters were measured: dissolved oxygen, conductivity, pH, temperature, turbidity, water velocity, mean depth width and flow. Also water and sediment samples were collected; the former were analyzed for nitrites, nitrates, ammonium, phosphate, biochemical oxygen demand (BOD5) and chemical oxygen demand (COD). Sediment samples were analyzed for organic matter content and granulometry. The macrophyte assemblage was analyzed by calculating specific coverage and life form classification. To sample the macroinvertebrates present in the aquatic vegetation, those species that were frequently found in most sites throughout the entire study were selected: Ludwigia peploides (Kunth) P. H. Raven (Onagraceae, free floating; LUD), Gymnocoronis spilanthoides (Don) DC. (Asteraceae, emergent; GYM), Egeria densa Planch (Hydrocharitaceae, submerged; EGE), Schoenoplectus californicus (C. A. Meyer) Soják (Cyperaceae, emergent; SCH), Hydrocotyle ranunculoides L. (Umbelliferae, floatingleaved; HYD), Polygonum punctatum Elliot (Polygonacea, emergent; POL). To analyze the interactions between macrophytes and hervibores, the snail Pomacea canaliculata (Lamark) was selected to conduct consumption and trophic preference studies using three of the aforementioned plants (LUD, GYM and EGE). Samples of these species were also collected to determine their content of dry matter and ashes, and their concentration of phosphorous, nitrogen, carbon and phenols. Besides, a transplanting experiment of three species of macrophytes (LUD, GYM and EGE) was conducted. Two sampling sites were established for experimental purposes, one was located upstream where macrophytes were collected (SND); this site had not been affected by the river engineering work. The other site, which was downstream (SD), had been recently dredged, rectified, widened, and the aquatic plants removed. The growth and coverage of the transplanted macrophytes was measured, along Pomacea canaliculata individuals and egg masses throughout the experiment. Also, epiphytic biofilm samples were collected from the macrophytes. The physical-chemical variables analyzed showed that the stream reaches are representative of the typical Pampean streams. From the RDA analysis conducted, sites were separated in three groups: a) a first group, composed by the middle reach of the Martín Stream, with a higher ammonium concentration; b) a second group, composed by the streams sources, with a naturally high phosphorous concentration, and; c) a third group consisting of the middle reach of the Carnaval Stream, with a low phosphorous concentration and high organic matter content. A total of 13 macrophyte species were recorded, being the ones with greater coverage: Hydrocotyle ranuncloides (24.3±23.0), Tipha latifolia (18.2±5.9), L. peploides (16.8±11.8), Polygonum punctatum (8.3±20.0), G. spilanthoides (6.8±5.6), Senecio bonariensis (6.2±12.0), Nasturtium officinale (9.8±9.4) y S. californicus (3.9±4.2). Both GYM and LUD were registered in most study sites, and were well represented in all sampling dates. Due to their high frequency and coverage in the studied streams, they might represent a suitable alternative in rehabilitation projects. Also, an RDA biplot analysis of the macrophyte species and the significant physicalchemical variables was performed. The species that were better represented in the sites with high ammonium concentrations were N. officinale, E. densa and H. ranunculoides, while Eleocharis montana and P. punctatum were abundant in sites C1 and C2, that were defined by their high phosphorous concentrations. Regarding GYM, the species was associated with high concentrations of organic matter. Regarding the macroinvertebrate analysis present in the different macrophyte species, the mixed lineal models analyses using the Shannon-Wiener index, species richness, density and evenness indicated that there were significant differences associated to the macrophyte species. As for functional feeding groups present in the different macrophyte species, the results were similar: despite the different proportion of species, the collector-gatherers were the most represented group through the study. A global analysis of the macroinvertebrate assemblage present in the macrophytes showed that LUD and GYM presented similar associations, and so did EGE, HYD and POL, while the assemblage present in SCH was significantly different from all the others. Consumption analyses were conducted to assess the relative consumption rate (RCR) of Pomacea canaliculata of LUD, GYM and EGE, and showed that the snail has a lower RCR in EGE when compared to the other two macrophyte species. As for preference, no significant differences were found, and the RCR was only related to the dry organic matter content in the macrophyte’s tissues.
Ver más
Ver menos
Palabras Clave
TrasplanteMacroinvertebradosRehabilitacion
Descargue o solicite el texto completo