EPA researches are studying the combined impacts of nitrogen loading and sea level rise that are causing the conditions of many Jamaica Bay salt marshes to worsen. The EPA is focussing on JoCo Marsh, which has been relatively stable; Black Bank, which has been deteriorating; and Big Egg, which was recently restored through dredging.
“Analyses at these three urban marshes would benefit by comparison to a pristine marsh on the eastern end of Long Island that is not exposed to the level of nutrient enhancement of Jamaica Bay,” Dr. Maher wrote in a summary of an article explaining the research by Dr. Wigand.
Dr. Davey, Dr. Maher and Dr. Wigand were out at Bass Creek on a Wednesday in late August taking core soil samples. Those cores are sent to a Rhode Island hospital to be analyzed through CAT scans. The scans provide a three-dimensional image of the marsh's below-ground composition. “These images are a good measure of how healthy the marshes are,” Dr. Wigand wrote in her article, published in the Spring 2008 Nature Conservancy newsletter. “Greater below-ground biomass often correlates with healthier marshes.”
Dr. Wigand said the CAT scan made getting an image and understanding below-ground growth processes much easier than it would be by sifting through the core samples by hand. The CAT scan can detect root structures down to a half-millimeter in diameter, Dr. Davey said.
The scans allow quantifications of coarse roots, rhizomes and peat “in a way that was not possible before,” Dr. Maher said.
Using Bass Creek as a baseline lets the scientists examine above- and below-ground processes in healthy marshes and helps them understand what might affect both processes, and by how much.
The soil and vegetation can be studied to see what nutrients they contain, to learn about where those nutrients come from and to understand how the marshes change their growth strategies as a result. For instance, if there is a lot of farm runoff, the above-ground vegetation might look lush and green, Dr. Wigand said, while the below-ground counterpart would most likely be very unhealthy. “It's sort of a negative feedback on the root system,” she added.
In Jamaica Bay, Dr. Maher said, there is much more nutrient availability from human activity than there is in Mashomack Preserve. “Without the normal bulk of below-ground root growth, the marsh surface may not be able to grow vertically fast enough to keep up with sea level rise,” Dr. Maher said. Also, “the marsh peat will not be as fibrous and tough to withstand wave energy necessary to keep it from breaking apart when exposed to storm waves.”
In order to collect samples for testing, the sample collector places a 15-centimeter ring on the marsh surface. The above-ground vegetation is cut and collected in order to compare it to the below-ground vegetation. Then a 25-centimeter long PVC pipe gets pounded into the marsh surface with a mallet and then extracted in order to keep the core sample intact. The sample is then transported for its CAT scan. Meanwhile, the hole is re-filled with sand from a nearby creek. Dr. Maher said re-vegetation in the sample area would occur within a year.
During the sample collections Dr. Wigand used another instrument to measure the marsh's soil respiration rate, a real-time measure of the carbon dioxide being released from the soil. “The actual measure is useful the same way taking the temperature of a patient is useful,” Dr. Wigand said, adding that the measure provides information on how well the soil is doing. The rates, she said, are more stable in healthier soil.
The information the EPA and Nature Conservancy is collecting, Dr. Wigand said, will help them understand the consequences of the marshes' abilities to help with flood abatement and to assist in buffering during storms. This ongoing study, Dr. Maher said, will provide information on how best to restore damaged marshes and help them regain lost elevation compared to sea level.