Abstract
Stream biofilms are among the first to react to environmental degradation, since their structural and functional characteristics are tightly linked to the physicochemical variables in the water and sediment. The objectives of this research were to study the differences in chlorophyll-a, bacterial density and metabolism endpoints of epipelic biofilms in nutrient-rich streams under different physical-chemical conditions in the stream water in relation to changes in urbanization, and to measure the short-term responses (up to 72 h) in the biofilm when translocated to more urbanized sites. For these purposes, chlorophyll-a, bacterial density, biofilm respiration (electron transfer activity) and O2 consumption were measured in epipelic biofilms in nutrient-rich streams exposed to different levels of urbanization after a 30 day colonization. Afterward, biofilms were translocated downstream to more polluted sites, and sampled to identify any fast occurring changes to be considered as potential indicators of environmental degradation. Results show that in the nutrient-rich streams studied, the structural characteristics of the biofilm were linked to urbanization, and even after a short time following the translocation, chlorophyll-a and bacterial density varied, reflecting the environmental degradation. On the other hand, metabolic variables were highly variable and produced inconsistent results when representing an increase in urbanization.
Highlights
Stream biofilms are among the first to react to environmental degradation, since their structural and functional characteristics are tightly linked to the physicochemical variables in the water and sediment
The objectives of this research were to study the differences in chlorophyll-a, bacterial density and metabolism endpoints of epipelic biofilms in nutrient-rich streams under different physical-chemical conditions in the stream water in relation to changes in urbanization, and to measure the short-term responses in the biofilm when translocated to more urbanized sites
The results show that the structural and metabolic variables measured in the biofilm responded to the physical-chemical characteristics of the water, they did not represent suitable indicators of shortterm environmental degradation during the translocation experiment
Summary
Stream biofilms are among the first to react to environmental degradation, since their structural and functional characteristics are tightly linked to the physicochemical variables in the water and sediment. Fluvial biofilms (Lock 1981) have been used to monitor physical and chemical water quality changes since the short life cycle of the microorganisms and the trophic interactions between the microbiota allow for the detection of both short and longterm impacts These communities are among the first to be affected by the impacts associated to urbanization, including nutrient enrichments (Guasch et al 1995, Rier & Stevenson 2002, Olapade & Leff 2005), heavy metals (Ramelow et al 1987, Medley & Clements 1998, Giorgi & Malacalza 2002), herbicides and pesticides (Dorigo et al 2007, Tlili et al 2008, Ricart et al 2010) and pharmaceutical components (Proia 2012). No studies have been conducted in epipelic biofilm from lowland streams, where the predominant substrate are sediments with large contents of silts and clay, that measure their short-term responses to water quality detriments linked to urbanization
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