Of interest are the effects of macrophytes on water quality, such as nutrient recycling through senescense, and controls on growth and distribution of especially the nuisance submersed species, such as water milfoil and hydrilla. Much has been learned about these aspects in the past 20 years. Rooted submersed macrophytes are known to depend largely on the sediments for their nutrition. They release very little nutrient to the surrounding water via excretion, but some contribute substantially to internal nutrient loading through senescense and decay. Although sediment texture, organic and nutrient content have been shown to affect the distribution and growth of rooted macrophytes, sediment characteristics have not been effective in predicting such attributes. However, given an adequate substratum, the maximum depth of colonization can be predicted.
Most rooted macrophytes are not able to withstand too great a current and an adequate sediment deposit must exist for their rooting. Light is generally satisfactory, because rivers are usually shallow, but turbidity may still limit in some instances. Butcher has listed five types of waters, based on current