A better evaluation?

My research needs a conceptual model. At present, I think it would be desirable to have a social dimension aside of the ecological one. Therefore, in the conceptual model, I need not only links denoting the flow of nutrient and energy, but also those representing flow of ecosystem services, which can be considered as the interface between the "human" and the "nature" parts in the system.

But "ecosystem service" would be too abstract to use even in a conceptual model. A concrete, and more desirable if universal surrogate of [these services](http://www.greenfacts.org/glossary/def/ecosystem-services.htm) is needed. I am very reluctant to use monetary measures as there are many values that cannot be underestimated using such an approach.

A search at Google Scholar gives about [200 results](http://scholar.google.com/scholar?num=50&hl=en&lr=&newwindow=1&q=%22ecosystem+service%22+surrogate&btnG=Search) using keywords "ecosystem services" and "surrogate". After a browse I cannot say that I find much enlightenment, although [this one](http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-4CC7V6J-D&_user=10&_coverDate=12%2F31%2F2004&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=52b27906458558832f14c738d40e8a95) is interesting. Non-linearity and changes should be considered when choosing the sorrogate. But it will not do if too many factors are considered, right?

Biodiversity is another often (ab-)used surrogate. But it is surely not adequate for the area I am studying, as the productivity there is so limited that it can only support a relatively simple system. The only way to achieve ``diversity'' is eutrophication, not like an option.

Or as an alternative, the energy flow combined with monetary evaluation can be used as the measure of ecosystem service?