We have so far explored the six most important factors that control wetlands. If you understand these six factors, and how they affect wetland composition and functions, you have done well. Hydrology is certainly the most important, with fertility next. In spite of this you would be surprised at the number of books published on wetlands that do not even have entries for words like “nutrients” or “fertility” in the index! It is important that we put our knowledge of wetlands into the big picture – first things first.

At the same time, there are other factors that do not fit neatly into any of these six categories. As with a statistical analysis, we have extracted six main effects, but sources of variance remain. We can either ignore the rest of the variation, or consider some of the sources. The goal of this chapter is to examine a few “other factors.” Although their occurrence in this chapter means that they are regarded as being generally less important than the preceding six factors, there are local conditions where these “other factors” may become very important indeed.

Salinity

The ocean is a vast pool of saline water which has enormous effects on coastal wetlands, and produces distinctive types of wetlands (Figure 8.1). Salinity is normally measured as the conductance of water, and expressed in parts per thousand, with normal oceans having ca. 35 ppt. The major dissolved elements are sodium, chloride, sulfur, and magnesium.