Nutrient over-enrichment or eutrophication is a pervasive problem in streams, lakes, and estuaries, leading to algae blooms, hypoxia and fish kills. Wetlands also are susceptible to eutrophication as increased nutrients (nitrogen-N, phosphorus-P) lead to increased primary production of emergent vegetation, reduced species diversity and dominance by invasives, and alteration of carbon and nutrient cycles.
We evaluate the long-term effects of nutrient enrichment on a tidal freshwater marsh by fertilizing Zizaniopsis miliacea (giant cutgrass) plots with N, P and N+P for the past 12 years. Long-term additions of N increase Zizaniopsis above ground biomass and uptake of N and P but reduce belowground biomass and species diversity.
Our findings indicate that N is the primary limiting nutrient and, hence, the “problem” nutrient affecting tidal freshwater marshes. Considering that these and other tidal wetlands are sinks for N from the surrounding watershed, N enrichment may result in the conversion of these wetlands from a sink to a source of N, increasing the susceptibility of estuaries and shallow water bodies downstream to N eutrophication.
This work is funded by NSF.