GLOBAL VARIATION IN THE CHEMISTRY OF TROPICAL STREAMS

Traditionally, tropical streams and rivers have been thought of as low in nutrients and minerals and high in dissolved organic matter compared to their temperate and boreal counterparts. This characterization has been based on the belief that the typical tropical system is a blackwater river with low calcium and magnesium levels. Although some streams fit this description, a detailed assessment of the existing literature shows that in many regions, tropical streams are relatively high in nutrients and not particularly high in dissolved organic matter. In fact, some of the highest phosphate concentrations on record for relatively undisturbed forested watersheds are found in the tropics, and overall levels of nitrogen also tend to be much higher in tropical streams and rivers. I will examine the basis of the misconception regarding tropical streams, and address the biogeochemical processes that are responsible for the relatively high nutrient loads of many tropical streams.