Impact of a reservoir system on benthic macroinvertebrate and diatom communities of a large Mediterranean river (lower Ebro river, Catalonia, Spain)

espanolEl presente estudio incluyo las principales categorias hidrogeomorfologicas de la parte baja del rio Ebro y tuvo como objetivo detectar los patrones de distribucion de macroinvertebrados y diatomeas bentonicas aguas abajo de un sistema de embalses. Se establecio la hipotesis que las comunidades biologicas reflejan un gradiente de alteracion relacionado con la distancia al impacto (por ejemplo, las presas). Se analizaron muestreos realizados a lo largo de cinco tramos del rio de 2 Km, integrando diferentes anos y estaciones. Diversos analisis estadisticos (MDS, SIMPER, ANOSIM) fueron utilizados para evaluar las diferencias espaciales y temporales en las comunidades biologicas. Tambien se analizo la relacion entre los datos biologicos y ambientales con el test BIOENV y los patrones de asociacion de las variables abioticas se analizaron a traves de un PCA. Se encontraron diferencias significativas en la composicion de las comunidades de macroinvertebrados entre la seccion mas cercana a los embalses y el resto de las secciones de estudio; la composicion actual de estas comunidades fue muy diferente de la encontrada en estudios de los anos 80-90. En el caso de las diatomeas, solamente se encontraron diferencias significativas a nivel estacional, pero no entre secciones de estudio. Ademas, los indices para la evaluacion del estado ecologico basados en macroinvertebrados (IBMWP) y diatomeas (IPS) mostraron puntuaciones mas bajas en la seccion E5, posiblemente como resultado del impacto de las presas. Los macroinvertebrados y las diatomeas respondieron de forma diferente a los factores antropogenicos en el tramo final del rio Ebro; los macroinvertebrados fueron mas sensibles a los impactos hidromorfologicos mientras que las diatomeas fueron mas sensibles a las alteraciones de calidad de agua. EnglishThis study included the main hydrogeomorphic categories of the lower Ebro River and aimed to detect spatial and temporal patterns of macroinvertebrates and diatoms communities inhabiting downstream a reservoir system. We hypothesized that biological communities will reflect a gradient of alteration related to the distance from the impact (i.e., dams). Surveys conducted along five river sections 2 km long integrating different years and seasons were analyzed. Non-metrical Multidimensional Scaling (MDS), Similarity Percentage Analysis (SIMPER) and 1-way Analysis of Similarities (ANOSIM) were performed to assess spatial and temporal differences in community structure. The relationship between biological and environmental data was investigated with BIOENV routine and a Principal Components Analysis (PCA) was also carried out. Significant differences in the composition of the macroinvertebrate community were found between the section closest to reservoirs (E5) and the rest of the study sections; the present community was also very different of that found in previous studies carried out in the 80’s and 90’s. For the case of diatoms, significant differences in community composition were only found between seasons but not between study sections. As well, indices for ecological status assessment based on both macroinvertebrates (IBMWP) and diatoms (IPS) showed lowest scores at section E5, likely caused by the impact of dams. Macroinvertebrates and diatoms responded rather differently to anthropogenic stressors in the lower Ebro River; macroinvertebrates were more sensitive to hydromorphological impacts, while diatoms were more sensitive to water quality alteration