Resumen de Temporal variation in benthic macroinvertebrate community from impaired streams
During the last century global population has experienced immense growth leading to huge changes in land use planning to cope with its own sustentation. More in detail, world population has shifted from an agriculture-based economy to an industrial society, which has pushed the population to move from rural to urban areas. The development of urban areas has led to changes in the physical structure of the environment (i.e. water bodies and surrounding area) being responsible for water quality changes by diffuse and point pollution and alterations in hydrological features such as flow magnitude and frequency. As a consequence of the physical and chemical alterations, instream community structure and composition has been altered and, hence, the ecological integrity of rivers has been jeopardized.
Despite efforts to restore the natural state and functioning of the river systems there is still a lack of knowledge on three questions that I sought to explain in this dissertation: (i) is the variation of macroinvertebrate community inherent to the impairment of the river or is there a natural fluctuations that guides long-term variation?;
(ii) how do rivers respond to restoration activities when biological communities may already be adapted to such impaired conditions?; and (iii) which are the most successful restoration measures at improving the biological condition of the river.
To answer these questions I studied impaired river systems in Canada and Italy.
Interannual variability of macroinvertebrate community from eight Canadian rivers, representing a gradient of anthropogenic water quality pressures and variable hydrological regimes, were studied over a period of 20 years, focusing on the relationship between water quality, hydrologic variables and sampling features. In Italy the process of restoration of an urban river was followed over a period of 3 years studying the relationship between environmental variables and macroinvertebrate community, focusing on the hydromorphological improvements.
Results of the Partial Least Square (PLS) Regressions on data from the long-term study demonstrated that the benthic community assemblage was not driven by any of the measured environmental variables (i.e. water quality, hydrologic variables, sampling features), while at a short-term benthic community responded to water quality and hydrometric features, but did not show significant responses to restoration measures.
The temporal stability of the studied benthic communities to variations in environmental and anthropogenic conditions may be reflective of the limited pool of tolerant taxa within these systems.
