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Habitat-specific nutrient removal and release in Oregon salt marshes
Citation:
DeWitt, Ted, J. Stecher, L. Brown, C. White, AND J. Moon. Habitat-specific nutrient removal and release in Oregon salt marshes. Presented at Pacific Estuarine Research Society Annual Meeting, Newport, OR, April 03 - 05, 2014.
Impact/Purpose:
Wetlands can be sources, sinks and transformers of nutrients, although it is their role in nutrient removal that is valued as a water purification ecosystem service. In order to quantify this ecosystem service for any wetland, it is important to understand the key drivers of nutrient removal within the system of interest and the variability of nutrient removal and release among systems of the same type. In this study, EPA scientists at WED measured the short-term exchange of dissolved inorganic nitrogen (N) and phosphorous (P) between surface waters and each of three salt marsh habitats (high marsh, low marsh, and tidal channel) in 20 estuaries distributed among 8 Oregon estuaries. The scientists found that patterns of nutrient exchange among habitats were consistent across all spatial scales for nitrite+nitrate (N+N) and phosphate (PO4), though there was substantial variability among marshes. In general, channel habitat had the greatest uptake of N+N and PO4, high marsh had the greatest efflux of both nutrients, while low marsh took up N+N and released PO4 but at lower rates. Thus, the net capacity of Oregon salt marshes to retain or release nutrients depends on the relative abundance of channel, low marsh, and high marsh habitats. Communities in coastal Oregon can estimate the capacity of marshes in their estuary to retain or release nutrients using these results, the area of these three marsh habitats, and the duration each habitat is tidally inundated. This same approach can be used to estimate short-term nutrient exchange rates for freshwater wetlands or salt marshes elsewhere in the US.
Description:
Wetlands can be sources, sinks and transformers of nutrients, although it is their role in nutrient removal that is valued as a water purification ecosystem service. In order to quantify that service for any wetland, it is important to understand the drivers of nutrient removal within the system of interest and its variability among systems of the same type. We compared short-term exchanges of inorganic N and P between surface water and salt marsh habitats (high marsh, low marsh, and tidal channel) measured during summer 2012 at 20 salt marshes distributed among 8 Oregon estuaries. Nutrient fluxes were estimated using open-topped chambers deployed at low tide into which nutrient-amended artificial seawater was added. Patterns of nutrient exchange among habitats were consistent across all spatial scales for nitrite+nitrate (N+N) and phosphate (PO4), though there was substantial variability among marshes. In general, channel habitat had the greatest uptake of N+N and PO4, high marsh had the greatest efflux of both nutrients, while low marsh took up N+N and released PO4 but at lower rates. Nutrient efflux in high marsh habitat was correlated with abundance of Grindelia integrifola, a native forb. We speculate that this may be due to salt excretion by these plants. We will also compare these fluxes to below-ground nutrient transformation and fluxes, the latter based on preliminary estimates of denitrification rate and sub-surface movement of tidal waters.