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NITRATE RELEASE BY SALT MARSH PLANTS: AN OVERLOOKED NUTRIENT FLUX MECHANISM
Citation:
Speights, C., L. Brown, T. Estabrooks, AND Ted DeWitt. NITRATE RELEASE BY SALT MARSH PLANTS: AN OVERLOOKED NUTRIENT FLUX MECHANISM. Presented at Ocean Sciences Meeting, Honolulu, HI, February 23 - 28, 2014.
Impact/Purpose:
Salt marshes provide water purification as an important ecosystem service in part by storing, transforming and releasing nutrients. Scientists from USEPA/NHEERL/WED and collaborating institutions found that some salt marsh plants release nutrients into surface waters, which is an overlooked mechanism for nutrient delivery to surface waters. Experiments demonstrated that the vascular plant, Grindelia stricta, released nitrate into seawater during simulated tidal inundations. Rates of nitrate release increased between repeated experiments conducted over a four-week period between tidal inundation of the habitats from which the plants were collected. The scientists hypothesize that the plants exude nitrate and that this builds up over time if the plants remain dry, then are dissolved into surface waters when the plants are submerged by the high spring tides. This mechanism may also occur for other plants in other marshes, and should be considered when constructing nutrient budgets.
Description:
Salt marshes provide water purification as an important ecosystem service in part by storing, transforming and releasing nutrients. This service can be quantified by measuring nutrient fluxes between marshes and surface waters. Many processes drive these fluxes, including photosynthetic uptake by vascular plants. Nutrient flux experiments in Oregon salt marshes indicated that certain plants may release nutrients into surface waters, particularly Gindelia stricta, a high marsh forb. To test this hypothesis, we measured changes in nutrient concentration for four abundant low and high marsh plants placed in seawater to simulate tidal inundation. Nitrate concentrations increased significantly in the presence of G. stricta, but not for the other species. Additionally, nitrate release by G. stricta increased over time. We speculate that this was caused by build-up of nitrate-rich exudates on the surface of the plants between tidal inundations that were then released into surface waters during the simulated tidal inundation. This overlooked mechanism of nitrate release resulted in a change in direction of nitrate flux for high marsh habitat, and should be considered in salt marshes elsewhere.