Some interesting papers and websites on different footprint

lista papers
General footprint
http://www.footprintnetwork.org/en/index.php/GFN/

Water footprint
http://www.waterfootprint.org/?page=files/home
Here you could find  the most important papers on the  subject.

Nitrogen footprint
http://n-print.org/
As for water footprint this is the main website for nitrogen  footprint.

This is a list of some general papers on ecological/carbon/nitrogen/water footprint:

Ecological:

Mathis Wackernagel , Larry Onisto, Patricia Bello, Alejandro Callejas Linares,Ina Susana Lopez Falfan, Jesus Mendez Garcıa, Ana Isabel Suarez Guerrero,Ma. Guadalupe Suarez Guerrero , 1997,National natural capital accounting with the ecological footprint concept  Ecological Economics 29 (1999) 375–390
Mathis Wackemagel , William E. Rees,1997 Perceptual and structural barriers to investing in natural capital: Economics from an ecological footprint perspective ,Ecological Economics 20 (1997) 3-24
Michael Borucke, David Moore, Gemma Cranston, Kyle Graceya, Katsunori Ihaa, Joy Larsona,
Elias Lazarusa, Juan Carlos Moralesa, Mathis Wackernagel, Alessandro Galli,2012,Accounting for demand and supply of the biosphere’s regenerative capacity:The National Footprint Accounts’ underlying methodology and framework,Ecological Indicators 24 (2013) 518–533

Water:

P.W. Gerbens-Leenes , M.M. Mekonnen, A.Y. Hoek The water footprint of poultry, pork and beef: A comparative study in different countries and production systems,Water Resources and Industry 1–2 (2013) 25–36
Mesfin M. Mekonnen and Arjen Y. Hoekstra,A Global Assessment of the Water Footprint of Farm Animal Products, Ecosystems (2012) 15: 401–415

Carbon:

Norman Church,2005,Why Our Food is So Dependent on Oil
Product carbon footprinting standars in the agri-food sector International Trade Centre
Catherine Jacobsen,2008,The Food Carbon Story: A Background Paper on Carbon Accounting Practices for the Food System,Vancouver Foundation.

Nitrogen:

James N. Galloway,Zucong Cai, John R. Freney, Luiz A. Martinelli, Sybil P. Seitzinger,Mark A. Sutton, Alan R. Townsend, Jan Willem Erisman, Mateete Bekunda,  2008,Transformation of the Nitrogen Cycle: Recent Trends, Questions, and Potential Solutions, Science Vol 320
Allison M. Leach, James N. Galloway, Albert Bleeker, Jan Willem Erisman, Richard Kohn,
Justin Kitzes A nitrogen footprint model to help consumers understand their role in nitrogen losses to the
environment, Environmental Development 1 (2012) 40–66

Some different footprints togheter:

Brad R. Ewing, Troy R. Hawkinsf, Thomas O. Wiedmann, Alessandro Gallia, A. Ertug Ercine,Jan Weinzettel, Kjartan Steen-Olsenb,2012 Integrating ecological and water footprint accounting in a multi-regional input–output framework, Ecological Indicators(2012) 23  1–8

Kai Fang, Reinout Heijungs, Geert R. de Snoo,2013,Theoretical exploration for the combination of the ecological, energy,carbon, and water footprints: Overview of a footprint family, Ecological Indicators 36 (2014) 508–518 

 Hoekstra A.Y. Human appropriation of natural capital: A comparison of ecological footprint and water footprint analysis, Ecological Economics 68 (2009) 1963 – 1974 

Lidija Cucek, Jirí Jaromír Kleme , Zdravko Kravanja,2012, A Review of Footprint analysis tools for monitoring impacts on sustainability,Journal of Cleaner Production 34 (2012) 9-20
Michael Borucke, David Moore, Gemma Cranstonb, Kyle Graceya, Katsunori Ihaa, Joy Larsona,Elias Lazarusa, Juan Carlos Moralesa, Mathis Wackernagel, Alessandro Galli, 2012 Accounting for demand and supply of the biosphere’s regenerative capacity: The National Footprint Accounts’ underlying methodology and framework, Ecological Indicators(2013) 24 518–533