Abbott, Cara J.

Juncus roemerianus, the black rush, has long been used in restoration projects in south
Florida because of its unique ability to live in both freshwater and saltwater. In particular, it has
been used as an indicator of salt-water incursion due to its differing physical forms in varying
levels of salinity. When found in freshwater, it can reach heights over 2.1 meters, yet when found
in hypersaline water, it becomes dwarfed and only 1 meter in height. Because of its dramatic
differences in physical appearance due to salinity, it has provided an easy and fairly cheap
method of determining an area’s localized salinity level. Most of Juncus roemerianus’s range in
Florida lies around the coasts, which most models predict will experience significant changes
due to sea level rise in the not so distant future. The purpose of this study is to determine whether
the black rush can remain an environmental restoration indicator species in conditions influenced
by sea level rise. This study will take place in the FAU Boca greenhouse and will target
increased water levels and increased pH as the main conditions affected by sea level rise. If this
study finds that increased water levels and pH do not significantly change the appearance of
Juncus roemerianus in varying salinity, then this plant can confidently remain an indicator of
salt-water incursion in the future. Conversely, if these conditions do change the appearance of
Juncus roemerianus, then this plant may not remain an indicator species in South Florida in the
future.

The evaporation of water in the ocean can lead to hyper salinity caused by the extra substances left behind during the process. The Florida bay is surrounded by the Florida loop current and the Florida Keys, its salinity reading has been recorded as high as 70 ppt, double the normal capacity of seawater. The bay salinity depends on the amount of fresh water released from the Everglades and the magnitude of water outputted to the Gulf of Mexico and the Atlantic Ocean, as well as the ratio between the amount of water evaporated and the amount of precipitates left in the remaining water pool. For this research nine saltwater treatments from 0 to 40 ppt in increments of 5 ppt were constructed to examine how evaporation rates are affected by varying salinities. During this study, data were collected from each of the nine treatments before and after evaporation. The data recorded included salinity readings, pH levels and volume of water evaporated. The analyses of this data will determine the relationship between salinity levels and evaporation rates.

As sea levels continue to rise, the projected damage that will ensue presents a great challenge for conservation and management of coastal ecosystems in Florida. Since Juncus roemerianus is a common marsh plant throughout Florida with unique growing characteristics that make it a popular restoration plant, this study implemented a 20 week greenhouse split plot experiment to examine the effects of sea level rise on J. roemerianus and ultimately determine its tolerance ranges to salinity and inundation in a high nutrient environment. Overall, salinity level and the interaction effect of salinity level and water level had the greatest effects on measured growth parameters including average mature height, maximum height, density, basal area, root length, and biomass. An inverse relationship between increasing salinity and the measured growth variables was observed with the greatest growth and survivability in 0 ppt water, survivability and reduced growth in 20 ppt water, survivability and little growth in 30 ppt water, and nearly complete senesce in 40 ppt water. This was the first laboratory study to determine the effect of 40 ppt water on J. roemerianus. Elevated water levels resulted in higher growth variables in the 20 ppt, 30 ppt, and 40 ppt treatments while inundated water levels produced higher growth variables in the 0 ppt treatment despite previous research finding inundation to have completely adverse effects on J. roemerianus. It is likely that the high nutrient environment provided for this study is the cause for this anomaly. The results of this study have major implications for the future of coastal ecosystems that are dominated by stands of J. roemerianus in South Florida and can be used in conjunction with studies on bordering marsh plants to predict shifts in the ecosystems of Florida that are responding to sea level rise scenarios.