You can use the livelihoods framework developed by DFID,2001. The framework identifies a set of household 'assets' : natural capital (land and water); financial capital; physical capital (houses, equipment, animals, seeds); human capital (in terms of both labour power and capacity, or skill); and social capital (networks of trust between different social groups). References: (1) Chambers R. and Conway G. (1992). Sustainable rural livelihoods:Practical concepts for the 21st century. IDS discussion paper; no. 296, Institute of Development Studies, University of Sussex, U.K. (2) Singh, N. and Gilman, J. (1999) ‘Making livelihoods more sustainable’, International Social Science Journal, vol 51, no 4, pp539–545

It is difficult to answer. What type of wetlands you mean? Rice field is also wetland ecosystem. In this case is quite simple calculate effect in money. More difficult situation is for nature or origin wetland ecosystems. When these ecosystems exist we think that are not important for us, but without it we can record some missing ecosystem functions in our landscape. 

I think that is very crazy when everything must be recalculated for money.

Wetland contributed to the country GDP in different context i.e. by agriculture, fishing, hunting and tourism and also there is flora and fauna. If you want to know the overall contribution then used the sub sectors contribution of all the aforementioned sectors in to a single one. It will be easy for you to calculate the GDP by taking all the sub sectors in to consideration.  

The capital approach and the Use of SEM will be more suitable for the livelihood analysis.

Mark the wetland area as % of total area. Examine the type of enterprises raised on such lands (paddy, sugarcane, other water loving plants, fisheries etc), income  and employment in each enterprise, The net economic contribution can be fairly estimated in this way. Similarly cost of reclamation and other fixed and operational costs provide base for net return generated. 

There are a lot of Indicator of livelihood. You can use the improvement of five capitals of livelihood as suggested by Dauda Awoniran above. It would be very informative if you assess before and after of change in wetland, combine with with and without change. This called different in different approach. This is to ensure that the improvement of livelihood is attributable to the wetland. The improvement of five capital can be measured both using qualitative and quantitative approaches.   

To evaluate social and economic benefits of a wetland in Laos, I conducted semi-structured interviews with villagers living around the wetland. We asked them where they fished, how often, kg fish caught per day/week, fish species and price at market, fish use in terms of consumption, processing, drying, giving away etc. We also determined the relative value of fishing compared to other enterprises for income, labour and consumption. We will survey again after a fishway has been operating for a few years to bring fish back to the wetland from the Mekong River.

Respected Jiří Dušek, I means man-made wetland on a river system and wants to know its role in terms of livelihood, particularly in surrounding areas.  

today wetlands can be seen as an place of interest for tourists,besides fishing activities. wetlands attract many migratory birds. in India, Majuli river island has many wetlands where you will find hundreds of domestic as well as migratory birds, which also attract  tourists visiting majuli. beside around 3000 villagers depend on these wetlands for fishing activities.