Response of Primary Producer Communities to Short-Term Nutrient Additions in a Pacific Northwest Estuarine Tidal Wetland

Abstract

While the detrimental effects of excess nutrients have been documented for tidal wetlands in many locations, the response of the primary producer community to nutrients in Pacific Northwest wetlands is unknown. We investigated the response of emergent macrophytes and sediment microalgae to 15 months of nitrogen and phosphorus addition in a Pacific Northwest estuarine tidal wetland. While both primary producer communities responded to nutrients, increased plant growth in fertilized plots resulted in less light reaching the sediment and suppressed growth of the benthic algal community. Heights of the two dominant plants, Distichlis spicata and Triglochin maritima, were significantly greater in plots fertilized with nitrogen. The relative cover of Distichlis spicata was significantly lower in fertilized plots while cover of Triglochin maritima was significantly higher in plots fertilized with nitrogen and phosphorus. Increased plant growth in fertilized plots resulted in significantly lower light levels at the sediment surface. The benthic algal community responded to these lower light levels, with biomass being significantly lower in all fertilized plots and community structure being significantly different in plots fertilized with nitrogen and phosphorus compared with all other treatments. Species richness and diversity was significantly higher in all fertilized plots. The rapid response of primary producer communities to nutrient additions indicates that Pacific Northwest tidal wetlands might be sensitive to eutrophication brought on by increased development in the coastal region.