Real Science for Real People

What Playing In The Mud Can Reveal

 

Editor’s note: Beth Ravit has been contributing science-related articles to Hackensack Tidelines for years. In light of her recent achievement—the attainment of her doctorate degree in environmental science—she was asked to focus this issue’s “Real Science” on her own Meadowlands research.

 

By Dr. Beth Ravit

(aka The Mud-slinger)

 

I love to play in the mud. During the past four years I have been an environmental science graduate student at Rutgers University, and on June 30, 2004, I successfully defended my Ph.D. thesis. Since the majority of my thesis research took place in the Hackensack Meadowlands, I thought I would take this opportunity to tell you about my work.

 

I am very interested in ecosystem functions such as the movement of carbon (C) and nitrogen (N) through the environment [sort of like how water moves through the water cycle]. These cycling processes are critically important due to the global increase in the release of carbon dioxide (CO2) and N. Salt marshes are important components of these cycles.

 

Plants absorb CO2, which is used in photosynthesis to produce more biomass (living tissue). In salt marshes, over 50% of the plant biomass is below ground in the root system. When the plant dies, microbes living in the sediment decompose the root tissues. These decomposition processes release (CO2) and methane (CH4), both of which are potent greenhouse gases. However, also living in the sediments are different microbes that are able to take up these greenhouse gases, and so under natural conditions the C cycle remains in balance. Salt marshes are also important in N cycling because under the anaerobic (no oxygen) conditions that are found in flooded sediments, microbes transform nitrate (a form of nitrogen) to inert N2 gas. The N2 gas is then released back into the atmosphere.

 

My research addressed two questions: 1) Are there different sediment microbial communities associated with Phragmites versus Spartina grasses? and 2) Are there differences in sediment microbial communities in a disturbed marsh ecosystem versus an undisturbed marsh ecosystem?

 

I analyzed sediment microbial community structure (which microbes live there) and function (what can they do), and had some very interesting results. Using sediment taken from both disturbed and undisturbed systems, I added a brominated flame retardant contaminant (see Tidelines, Winter 2004) and then incubated the samples anaerobically in the laboratory. Spartina sediments from both sites biotransformed the contaminant more quickly than either Phragmites sediments or unvegetated mud. We're not exactly sure why this happens, but I am setting up new experiments to try and find out what is different about the Spartina root zone.

 

I also found differences in how the sediments responded to the addition of C and N compounds. Sediments from the undisturbed salt marsh systems (Mullica and Maurice River estuaries) had more microbial activity related to C and N cycling than did the sediments from the Meadowlands. We think this is because the Mullica and Maurice Rivers drain the Pinelands, which is a low nutrient system. Under low nutrient conditions the microbial community would respond quickly to nutrient inputs. The lower response in Meadowlands sediments suggests that nutrient loads are higher in the Hackensack than in the Mullica or Maurice Rivers.

 

I hope that the work I'm doing can ultimately be incorporated into salt marsh restoration projects, so when we restore damaged estuarine systems we set goals for the sediment restoration as well as for above ground habitats. It is in the mud that critical microbial processes are occurring, and these processes have the potential to affect the cycling of C and N, which at this point in time has global consequences.