Development of regional characterization factors for aquatic eutrophication

Life cycle assessment (LCA) has traditionally been considered a site-independent tool, but nowadays, there is a trend towards making LCA more site-dependent. Site-dependent characterization factors have been calculated for regional impact categories such as acidification, terrestrial and aquatic eutrophication, and smog. Specifically, for aquatic eutrophication, characterization factors have been proposed for large geographical areas (mainly European and North American countries). Those factors are not detailed enough for countries which present large geographical, climatic, and economical variability such as Spain. Therefore, this work aims to calculate the characterization factors and the normalization reference for aquatic eutrophication at a regional level, using Galicia (NW Spain), a region with increasing problems of eutrophication, as a case study. Finally, the comparison of the factors obtained here with literature values will be used to analyze the influence of spatial differentiation with increasing coverage of the causality chain.

Particular ecological and economic reasons justify the estimation of characterization factors in Galicia taking into account the specific characteristics of three different ecosystems: Atlantic Ocean, freshwaters, and rias (a specific ecosystem that takes place when a river valley is submerged by a rise in sea level). Taking into account that the state of the art does not allow the calculation of an exhaustive effect factor, the work was focused on the calculation of transport and equivalency factors.

Both the principal pathways of transport and the sources of nitrogen (N) and phosphorus (P) were considered to calculate the characterization factors, and from them, the normalization reference was also obtained. An analysis on uncertainty identified the estimations of fractions of NH_x–N and NO_x–N deposited on maritime waters, land, and freshwaters and the fraction of N and P deposited in the soil that reaches water ecosystems, as the more uncertain values.

As the rias are both N- and P-limited ecosystems, which is a characteristic of coastal and brackish waters in general, the approximation followed in this study to establish characterization factors for the rias can be applied to these types of ecosystems elsewhere (e.g., fiords in Norway) in order to better define aquatic eutrophication impact. By comparing the results obtained with those available in the literature, it is clear that the application of transport factors in the calculation of characterization factors leads to a more realistic definition of aquatic eutrophication, especially when P inputs to the soil are present. When varying the spatial differentiation (continent, country, or region), characterization factors do not vary significantly; however, this variation is likely to increase as long as the definition of the causality chain is improved as it has been reported for other impact categories. In this sense, the equations used in this study can be adapted when those effect factors became available, being flexible and suitable for future applications in other regions.

This study describes the process to calculate aquatic eutrophication characterization factors at a more detailed scale than country, with the particularity of differentiating three different aquatic ecosystems, considering for the first time the rias. The results show the importance of including transport factors in the calculation of characterization factors for aquatic eutrophication, while spatial differentiation is less important at this level of sophistication in terms of coverage of the causality chain.

The estimation of effect and damage factors is regarded as the next step in the sophistication of this category. On the other hand, the significance of transport factors makes their estimation for other regions than Europe and North America (the only available at the moment) also desirable.