Disentangling the multiple stressors acting on stream ecosystems to support restoration priorities.

Stream ecosystems may suffer from the effects of multiple stressors. Planning restoration actions without knowing the relative weight of each stressor might lead to disproportionately costly or ecologically meaningless measures. This is particularly relevant under the EU Water Framework Directive where economic considerations play a role in justifying exemptions from the overarching aim of the directive of achieving the good ecological status in all the EU water bodies by 2015. In this study, we correlated the status of macroinvertebrate assemblages with many environmental variables at 120 monitoring stations (surveyed in 2009-2011) in the streams of Lombardy, Italy. We used a combination of regression techniques to disentangle the effects of the different stressors. Furthermore, different profiles of ecological quality were associated with the dominant stressors. Finally, examples are given about how these study findings provide elements to identify restoration scenarios that maximize the effectiveness/cost ratio.

Searching for a compromise between ecological quality targets, and social and ecosystem costs for heavily modified water bodies (HMWBs): the Lambro-Seveso-Olona system case study.

The Lambro-Seveso-Olona (L-S-O) system derives from the human regulation of the natural hydrology of the territory around Milan city area. The average population density in the L-S-O area is among the highest in Italy and Europe. Industry is also highly developed in this basin: chemical, textile, paper, pulp and food industries being the most important ones. Although, at present, the L-S-O system no longer receives the untreated wastewaters of the Milan urban area, treated wastewaters constitute about half of the streamflow. Biotic communities in this river have a long history of poor quality status, having suffered great damage due to domestic and industrial discharges. Recently, new chemical quality standards for macropollutants have been set by the Italian legislation as support for the good ecological status according to the Water Framework Directive (WFD). This new index is very restrictive, and it makes it extremely challenging to achieve the water quality objectives for the L-S-O system. The aim of this study is to analyse through a modelling exercise the restoration possibilities of the L-S-O system, investigating both the source apportionment of the macropollutants, the discharge limits that should be set to achieve the good quality status and their corresponding cost.

A multivariate approach to assess habitat integrity in urban streams using benthic macroinvertebrate metrics.

Benthic macroinvertebrates are widely used as indicators of the health of freshwater ecosystems, responding both to water quality and to the hydromorphological integrity. In urban streams, evaluations can be tricky for the synergistic effects of multiple stressors and confounding factors. In these situations, the most broadly used multimetric indices can be used to assess the overall damage to the invertebrate community and, thus, the overall anthropogenic pressure, but they do not allow to understand the specific causal effects. Particularly, habitat loss due to morphological alterations can be difficult to evaluate, especially due to the often concurrent disturbance caused by water pollution. We used a multivariate approach to focus on the characteristics of the streams and rivers in an urban district and to define which macroinvertebrate metrics should be used to assess the influence of the different kinds of alteration in a severely damaged environment. Some metrics enabling the assessment of habitat loss (ratio of oligochaeta, ratio of filterers) were identified. These metrics may help to raise a better awareness in the evaluation of river restoration success and, thus, in the support of decision-making processes.

Colour removal and carbonyl by-production in high dose ozonation for effluent polishing.

Experimental tests have been conducted to investigate the efficiency and the by-product generation of high dose ozonation (10-60 mg O3 L(-1)) for complete colour removal from a treated effluent with an important component of textile dyeing wastewater. The effluent is discharged into an effluent-dominated stream where no dilution takes place, and, thus, the quality requirement for the effluents is particularly strict. 30, 60 and 90 min contact times were adopted. Colour was measured as absorbance at 426, 558 and 660 nm wavelengths. pH was monitored throughout the experiments. The experimental work showed that at 50 mg L(-1) colour removal was complete and at 60 mg O3 L(-1) the final aldehyde concentration ranged between 0.72 and 1.02 mg L(-1). Glyoxal and methylglyoxal concentrations were directly related to colour removal, whereas formaldehyde, acetaldehyde, acetone and acrolein were not. Thus, the extent of colour removal can be used to predict the increase in glyoxal and methylglyoxal concentrations. As colour removal can be assessed by a simple absorbance measurement, in contrast to the analysis of specific carbonyl compounds, which is much longer and complex, the possibility of using colour removal as an indicator for predicting the toxic potential of ozone by-products for textile effluents is of great value.