Michela Marchi

Invaders decrease the structural complexity of the indigenous community of Chozas Lake

Chozas Lake, a small shallow water body in Leon, NW Spain, changed from clear water conditions to turbidity in only one year. The cause was loss of abundance and richness of plants due to deliberate introduction and proliferation of the allochthonous Louisiana red swamp crayfish, Procambarus clarkii. The dynamics of this ecosystem have been studied by means of eco-exergy. Eco-exergy is a goal function introduced by S.E. Jorgensen in the 1970s and is related to conformation structures and information in nature with particular attention to evolutionary properties. Its value has been used with that of specific exergy for understanding the quality of biomass variation, seen as a change of the structural complexity of Chozas Lake. The number of crayfish increased as the ecosystem eco-exergy decreased, because the complexity of the ecosystem was higher when there was richness of macrophytes, even if the submerged aquatic vegetation is at lower level on the evolutionary scale than the invasive crustacean. There was a trophic cascade effect on the wetland ecosystem that altered the native community, with loss of invertebrates, amphibia and coots, directly related to plant destruction. However, while fish- and crayfish-eating birds seemed to increase, plant disappearance is a great threat for biodiversity in Spanish lakes because vegetation is the most abundant component of these ecosystems and so its destruction has a very important ecological role.

Greenhouse gas emissions accounting for waste management at the local scale

The administrative jurisdiction of the Province of Siena (Tuscany, central Italy) and the waste company (named Siena Ambiente S.p.A.), that operates within the provincial boundaries, have equipped themselves of the Greenhouse gas (GHG) Inventories of the solid waste disposal plants in the integrated management system with the aim to obtain a planning tool. The GHG inventories have been processed in time series (2008–2011) and include 3 landfills, 1 incinerator, 2 composting, 1 selection and valorization production lines. Results show a 12% reduction of the total GHG emissions from 2009 to 2011 due to better landfill management. Moreover, a further GHG emission reduction equal to almost 34% could be obtained if electricity from renewable resources is used (i.e. burned wastes, biogas recovery from landfills and photovoltaic panels). On this way, the consumption of the imported electricity from the national grid, which is mainly obtained by traditional thermoelectric technologies, is avoided. The present experience could be adopted as a reference model for public and private organizations, considering that the provided planning tool could suggest time series emission reduction strategies for interacting with waste disposal facilities. Territorial systems at different scales (cities, municipalities, regions and nations) might be involved in this type of analysis, so as to calibrate the waste management system according to the estimates obtained by GHG inventories, which may be verified ISO 14064 by an independent third organization in order to increase the result reliability.

Chapter 12 - Structurally Dynamic Model and Ecological Indicators to detect the crayfish invasion in a lake ecosystem

We developed a structurally dynamic model of Lake Chozas, a small shallow water body in Leon (northwest Spain). The model simulated seasonal dynamics of phosphorus concentrations in major components of the lake’s ecological network before and after 1997, the year when an invasive the allochthonous crustascean, the Louisiana red swamp crayfish (Procambarus clarkii), was introduced into the lake. The shift from clean to turbid phase, due to grazing by crayfish on submerged vegetation, caused a gradual decrease in eco-exergy, reflecting an increase in entropy. Moreover, we tested the hypotheses about the recovery of the indigenous community and water quality, when all the crayfish were removed. The recovery of Lake Chozas after the biological invasion was observed when phytoplankton dominated at total phosphorus about ≥ 200–250 mg TP/m3, and submerged vegetation returned at total phosphorus <100 mg TP/m3. To conclude the analysis, we studied health status of Lake Chozas before and after the biological invasion, compared to Lake Sentiz (a similar water body in the same district), by the joint use of different but correlated ecological indicators, supplementing the values obtained by monitoring campaigns. The joint application of different ecological indicators gives a more effective and comprehensive description of the ecosystem health status than any one considered alone.