Because of the increasing complexity of spatial planning processes there is a need for more powerful and more intelligent planning tools. This involves the development of environmental decision support systems (EDSS), or, in a more general term, spatial decision support systems (SDSS). Their design, implementation, and application have been discussed in many articles within the last 15 years or so. A summary of the most important aspects is given here, which distinguishes between functional and structural requirements of SDSS. With regard to the latter, it is argued that, from an end user’s point of view, only a tight coupling or full integration strategy with respect to the involved software components fulfils the functional demands on SDSS. Further, the Land Use Management Support System (LUMASS) is introduced, which was developed in consideration of the functional and structural specifications discussed above. It integrates (i) the commercial GIS package ArcGISTM, (ii) ecological models focusing on soil and watercourse protection, and (iii) the Open Source Mixed Integer Linear Programming System lp_solve [Berkelaar et al., 2004] and follows a tight coupling approach. Finally, a sample application is presented that reveals the optimization of land use patterns with a view to minimizing soil erosion and sediment discharge into adjacent creeks and rivers.