benefits of preserving a wetland

An analyst wishing to estimate the benefits of preserving a wetland has combined information obtained from two methods. First, she surveyed those who visited the wetland—fishers, duck hunters, and bird-watchers—to determine their WTP for these uses. Second, she surveyed a sample of residents throughout the state about their WTP to preserve the wetland. This second survey focused exclusively on nonuse values of the wetland. She then added her estimate of use benefits to her estimate of nonuse benefits to get an estimate of the total economic value of preservation of the wetland. Is this a reasonable approach? (Note: In responding to this question assume that there was virtually no overlap in the persons contacted in the two surveys.)