Forested wetlands in the Lower Mississippi Alluvial Valley are typically nutrient-poor ecosystems, especially where levee systems reduce the input of river sediment and nutrients. As a result, nutrient limitation leads to slower vegetation growth and ecosystem decline. However, when these wetlands are used as biological nutrient filtration systems for treated municipal effluent — also known as assimilation wetlands — baldcypress trees tend to have increased growth. In other systems, fast plant growth is associated with increased water use through transpiration and increased sensitivity to droughts. Does this phenomenon occur with baldcypress trees in effluent growing in discharge in swamps? To answer this question, Devin Schexnayder studied baldcypress trees that received effluent at the Hammond assimilation wetland in Livingston Parish and compared them to trees at the nearby Joyce Wildlife Management Area in Ponchatoula, Louisiana. Throughout the summer of 2023, he measured the trees’ transpiration rates. To accomplish this, he used sap flow probes that were inserted into the trees’ trunks and powered by floating rigs containing solar panels, car batteries and data loggers. He found that effluent discharge increased water use in trees under mild atmospheric conditions. However, when the air became hotter and drier, the water use of effluent-fed trees was more sensitive than in the trees that did not receive effluent. These results suggest that the positive effects of effluent discharge in forested wetlands may wane as air temperatures increase this century. His results were published in the journal Wetlands. Schexnayder graduated from LSU RNR in May of 2024 and is now an urban forester for the Texas Trees Foundation in Dallas, Texas.

Devin Schexnayder installs a sap flow sensor on a baldcypress tree at his study site.