Streamside Vegetation

IIt has been well documented that having trees and other vegetation around streams will help filter out sediment, nutrients, and many pollutants from entering the stream and how the overhead canopy helps cool the water allowing a more diverse assortment of aquatic plants and animals to inhabit the stream.  Another function of streamside vegetation that is not as well understood or appreciated is the value it has to the plant and animal life within the stream.  This is especially true in smaller headwater streams rather than larger water body such as the Monocacy River or Potomac River.

Larger bodies of water are influenced less by the vegetation existing on the shore than they are by the water and sediments that are being carried in from upstream sources. When flowers, leaves, branches, trees, and other plant parts fall into a waterbody they are colonized by very small micro invertebrate and larger (visible to the naked eye) macro invertebrates that help decompose this material by shredding, chewing, and filtering the material.  Once they consume this material, they release the decomposed nutrients into the water in a form that can be utilized by other aquatic creatures. The aquatic life will utilize these nutrients for growth and energy to fuel the complex interactions known as the food web.    

It is estimated that nearly 70% of the detritus that falls into streams is utilized by the local stream life.  In the spring of the year much of the input comes from pollen, flowers, branches, and seasonal plants such as skunk cabbage or trout lily.  In the fall, leaves, herbaceous plants, and branches make up most of the litter.  The largest segment of detritus that falls into a stream comes from woody sources such as twigs, branches, or sections of the tree.   All but the largest of woody vegetation is consumed in a matter of days under normal circumstances. If the stream becomes too acid then a lot of the micro and macro invertebrates will be lost or their functions impaired and nutrients are lost.  

When excess nitrogen or potassium is added via runoff the detritus is consumed very quickly so that the stream receives a flush of nutrients that can result in algae blooms and abundant aquatic plant growth all of which can reduce dissolved oxygen in the water and affect stream live.  Studies have also demonstrated that detritus coming from native plants is more readily converted into available energy than nonnative plants.  This makes sense when you consider that most of the aquatic life has evolved with native plants.  When everything is in balance the stream has a large diversity of plant and animal life, clean, cool water with adequate nutrients to fuel, but not upset the food web.

Article by FCFCDB member

Page header photo credit: Jan Barrow, Myersville, MD

Nature note for 3/8/20