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ASSESSING THE IMPACTS OF SALINITY AND NUTRIENT STRESS TO RUPPIA MARITIMA AND ZOSTERA MARINA
Citation:
Pelletier, Peg, M. Gutierrez, Rick Mckinney, AND S. Guberman. ASSESSING THE IMPACTS OF SALINITY AND NUTRIENT STRESS TO RUPPIA MARITIMA AND ZOSTERA MARINA. Coastal & Estuarine Research Federation (CERF) 23rd Biennial Conference, Portland, OR, November 08 - 12, 2015.
Impact/Purpose:
Healthy seagrass beds were once found throughout the shallow areas of Narragansett Bay, R.I. but have disappeared due to infilling, pollution and disease. Recently, there has been evidence of seagrass bed recovery in a sandy area of Greenwich Bay, a highly developed embayment within Narragansett Bay. It is possible that the area has groundwater seepage, as well as potential nutrient inputs due to septic systems in the area. The ‘new’ bed is dominated by Ruppia maritima, which is very salinity tolerant and may be nutrient tolerant rather than Zostera marina. We are conducting nutrient and salinity microcosm experiments to determine the relative salinity and nutrient tolerances of these two seagrass species. These experiments will assist in understanding the dynamics of the recovering seagrass bed in Greenwich bay and also provide dose-response data useful for the nutrient management efforts being conducted along Cape Cod.
Description:
Healthy seagrass beds were once found throughout the shallow areas of Narragansett Bay, R.I. but have disappeared due to infilling, pollution and disease. In Greenwich Bay, a highly developed embayment within Narragansett Bay, Ruppia maritima has colonized an area on the northern shore once dominated by Zostera marina. This area is sandy, which may allow groundwater seepage. Ruppia is extremely salinity tolerant, and may also be more nutrient tolerant than Zostera. A six week microcosm experiment at two salinity (20 and 30 ppt) and 4 nutrient (0, 5, 10, and 30 µM inorganic N) levels to test their relative tolerance was conducted in 2014. Treatments were renewed daily to simulate tidal flushing and the exposure water was dosed with 15N for the first week of the experiment. At the end of the experiment, the plants were weighed and measured, and dried for later isotopic analysis. In the first experiment, Ruppia had significant structural responses to both nutrients and salinity; there was a slight decline in root weight and a decrease in the total number of shoots with increasing nutrients. Average Ruppia blade length decreased with increasing nutrients and this decrease was more evident at 30 ppt. In contrast, Zostera had no significant structural differences. For both species, there were no differences in shoot or root/rhizome weights in any treatment, nor were there differences in isotopic results due to salinity. However, δ15N in the tissue increased with increasing nutrient levels for both species. For Zostera, %N also increased in the root and rhizomes. The second experiment is being run this summer (2015), with lower salinity (5 and 30 ppt) and higher nutrients (0, 30, 100, 300, and 1000 µM inorganic N). This experiment should determine Zostera’s tolerance to nutrient and salinity stress and confirm the previously observed Ruppia results.