Environmental diagnosis of an urban basin from a social-ecological perspective.

The critical factor in restoration and conservation of urban streams and their catchments is the human population, however the most of studies of urban ecosystems do not present social descriptors as concrete variables of analysis. The objective of this study is to perform an environmental diagnosis from a social-ecological perspective by considering both ecological and urban development descriptors of an urban basin. We selected 12 sampling sites of the Langueyú upper basin where social and ecological descriptors were determined. We arranged sampling sites according to their physicochemical characteristics (pre-urban, urban and post-urban sites). An ecological index was defined from habitat and biological descriptors: vegetation cover, richness and total density of invertebrates and organic matter. The index determined that urban and post-urban sites showed similar characteristics, and pre-urban sites presented the best habitat and biological conditions. An urbanisation index was defined from urban development descriptors: distance to the stormwater drainage network, number of industries, distance to a house without sewage, impervious surface and housing density. The results showed that the pre-urban and post-urban sites share a greater similarity in relation to the urban descriptors but with different impact in ecological quality. The headwaters in the hills (pre-urban zone) still presents a very good ecological condition (although threatened by urbanisation and tourism); however, once it crosses the dense urban area, no >5 km distance, the environmental degradation is alarming. We were able to determine that the structural measures associated with greater urbanisation, added to illegally connected sewer pipes and illegally industrial connections, produce the ecological degradation of the stream. This environmental diagnosis allowed us a deep understanding of the urbanisation impact on the ecological integrity of an urban stream in a developing country which, like many others, doesn't have monitoring programs or an integrated vision of water resources.

Assessing the sensitivity of leeches as indicators of water quality.

The objective of this work was assessing the sensitivity of leeches to several water quality attributes in lowlands streams. We used occupancy modelling that account explicitly for detectability, to estimate the influence of four variables (dissolved oxygen, 5-days biochemicals oxygen demand, conductivity, and dissolved inorganic nitrogen) affecting nine species. We described the sensitivity as a change in the occupancy along the range of water quality attributes. We found at least one species of Helobdella in 81% of sites and Helobdella, as genus, was detected along the entire gradient of each attribute. However, differences in the sensitivity were observed between species. For example, if we analyse the sensitivity of the genus Helobdella to dissolved oxygen, we can say that it is very tolerant. However, if we analyse the response to dissolved oxygen of each one of the species of Helobdella, we will realize that H. michaelseni, and H. simplex showed a high occupancy at high levels of dissolved oxygen; while H. hyalina and H. triserialis lineata showed high occupancy at low levels. Describe the sensitivity of the species in terms of occupancy, offers a new methodology to understand how the species behave along a stressor gradient.

Molecular characterization of Shiga toxin-producing Escherichia coli isolated from the environment of a dairy farm.

Environmental samples were taken from ground, cattle water troughs, and feeders from a dairy farm with different STEC prevalence between animal categories (weaning calves, rearing calves, and dairy cows). Overall, 23 % of samples were positive for stx genes, stx(2) being the most prevalent type. Isolates were analyzed by PCR monoplex to confirm generic E. coli and by two multiplex PCR to investigate the presence of stx(1), stx(2), eae, saa, ehxA, and other putative virulence genes encoded in STEC plasmids: katP, espP, subA, and stcE. The toxin genes were subtyped and the strains were serotyped. The ground and the environment of the rearing calves were the sites with the highest number of STEC-positive samples; however, cattle water troughs and the environment of cows were the places with the greater chance of finding stx(2EDL933) which is a subtype associated with serious disease in humans. Several non-O157 STEC serotypes were detected. The serotypes O8:H19; O26:H11; O26:H-; O118:H2; O141:H-; and O145:H- have been asociated with human illness. Furthermore, the emergent pathogen STEC O157:H- (stx(1)-ehxA-eae) was detected in the environment of the weaning calves. These results emphasize the risk that represents the environment as source of STEC, a potential pathogen for human and suggest the importance of developing control methods designed to prevent contaminations of food products and transmission from animal to person.