Tesis doctoral de Alvaro Cabezas Beaumont
One reach in the middle ebro river (ne spain) was selected to evaluate the influence of the river disturbance regime over floodplain structure and organic matter accretion in the context of strong and repeated anthropogenic disturbances. Several spatial and temporal scales were considered for the analyses. Based on our results, we aimed to assess the ecological status of the study reach, suggesting guidelines to rehabilitate the river-floodplain system towards a more natural functioning. To that end, we considered the study reach as the larger spatial unit. For this scale, the distribution and dynamics of different landscape ecotopes was selected, in order to asses the trends during the last century. To evaluate the individual effect of different magnitude floods, we selected the hydrogeochemical features and dynamics of surface waters. Secondly, we selected an array of individual riparian wetlands to asses the effect of the river disturbance regime in a smaller spatial scale. To evaluate the effect at decadal time scale, understory diversity estimates were employed, thewhereas the structure of flooded top-sediment (0-3 cm) was used to study the influence at annual time scale. Finally, organic matter accumulation at floodplain substrates was selected as example of ecosystem function. To evaluate current patterns, we examined the top-soil (0-10 cm) on intermittently flooded habitats. Moreover, modifications of these patterns during the last century were also studied using sediment cores. according to our results, we can conclude that the river disturbance regime is the main factor explaining the floodplain structure and organic matter accretion patterns in the middle ebro river. As a result, human alterations on this regime were clearly reflected in our analyses. Such modifications exerted a direct influence on the elements of the systems which respond to river-floodplain interactions at decadal time scale (landscape, riparian understory, organic matter accretion patterns). Landscape and riparian wetland heterogeneity have markedly decreased, and mature successional stages dominate both riparian forest and aquatic habitats. Wit regards to organic matter, autogenous inputs have become to dominate over river sedimentation, what diminishes the potential of floodplain areas as carbon and nitrogen sinks. Furthermore, modifications of the river disturbance regime have to be taken into account when interpreting the results of elements responding to hydrological connectivity at shorter time scales (hydrogeochemistry, sediment composition, organic matter accretion at the top-soil of riparian forest). A diverse array of wetlands types, in terms of hydrogeochemistry and sediment composition, was found at the study reach. However, the portion of floodplain area presenting such heterogeneity is scarce, and mid-range floods (1.5 y) promote a rapid homogenization of the riverscape. With regards to organic matter at the top-soil, autochthonous inputs dominate if older habitats (>60 y) old, which present the higher budgets, whereas allochthonous does at younger patches, with lower organic matter budgets. When interpreting those results, however, it should be considered the vast extent of agricultural fields and poplar groves, about 75 % of the considered floodplain, which presented low budgets despite they are isolated from river sediments inputs. in the light of the previous analyses, it seems that ecological restoration is urgently required at the middle ebro floodplains. Basin, reach and site scale projects should be implemented to rehabilitate system components examined in this thesis. To accomplish that, periodic economic investments will be required because self-sustained restoration seems neither possible nor realistic under the current ebro basin management.
Datos académicos de la tesis doctoral «Efecto del régimen de variación de caudales en la estructura de las llanuras de inundación y la acumulación de materia orgánica en el tramo medio del ebro (ne españa)«
- Título de la tesis: Efecto del régimen de variación de caudales en la estructura de las llanuras de inundación y la acumulación de materia orgánica en el tramo medio del ebro (ne españa)
- Autor: Alvaro Cabezas Beaumont
- Universidad: León
- Fecha de lectura de la tesis: 12/12/2008
Dirección y tribunal
- Director de la tesis
- Francisco A. Comín Sebastian
- Tribunal
- Presidente del tribunal: Jesús Pozo Martinez
- diego María no Garcia de jalon de la lastra (vocal)
- alfredo Ollero ojeda (vocal)
- Andrea Butturini (vocal)