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Cross-system comparison of factors influencing chlorophyll-a concentration in Oregon estuaries
Citation:
White, C., C. Brown, AND TChris MochonCollura. Cross-system comparison of factors influencing chlorophyll-a concentration in Oregon estuaries. Coastal and Estuarine Research Federation, Portland, OR, November 08 - 12, 2015.
Impact/Purpose:
Water column chlorophyll-a (chla) is a proxy for phytoplankton biomass and is often used as a biological response indicator of eutrophication. Although watershed nutrient loading may influence chla concentration in estuaries, factors such as freshwater inflow, residence time, and import from the coastal ocean can also play a role. Despite the importance of chla as an indicator for ecosystem management, there is a paucity of published data for estuarine systems in the Pacific Northwest. We performed a cross-system comparison of 15 Oregon estuaries using two decades of chla, nutrient, and freshwater flow data obtained from state, federal, and tribal sources to determine principal drivers of chla in those systems.
Description:
Water column chlorophyll-a (chla) is a proxy for phytoplankton biomass and is often used as a biological response indicator of eutrophication. Although watershed nutrient loading may influence chla concentration in estuaries, factors such as freshwater inflow, residence time, and import from the coastal ocean can also play a role. Despite the importance of chla as an indicator for ecosystem management, there is a paucity of published data for estuarine systems in the Pacific Northwest. We performed a cross-system comparison of 15 Oregon estuaries using two decades of chla, nutrient, and freshwater flow data obtained from state, federal, and tribal sources to determine principal drivers of chla in those systems. Dry season (May – October) median and 90th percentile concentrations of chla were assessed. Chlorophyll a in all 15 estuaries was low compared to other systems in the U.S., with median concentrations less than 3 µg/L in nearly all systems. This difference is likely due to higher freshwater flows and strong tidal flushing; however, import of chla from the coastal ocean can lead to elevated concentrations near the mouth of some systems. Chlorophyll a levels in Oregon estuaries typically fall well below the state of Oregon’s chla standard (15 µg/L).