Wetlands provide important ecosystem services by retaining and transforming nutrients in surface water. Despite decades of research on the nitrogen (N) and phosphorus (P) content of soils, plants and surface water in wetlands, we still lack a clear understanding of the constraints on nutrient retention at the ecosystem scale. Ecological stoichiometry provides an integrative framework to link biogeochemical patterns at the ecosystem scale to physiological constraints that operate at a cellular and organismal level. While there have been previous reviews of nutrient retention in wetland ecosystems, none have used a stoichiometric approach. We surveyed the literature to answer the following questions: 1) What is the variation in N:P ratios in soils, plants and surface water across different wetland ecosystems? 2) Do N:P ratios of soils, plants or water predict N or P retention among wetlands? 3) Is there a trade off between N and P retention rates across wetlands?
Results/Conclusions
Based on our literature survey we obtained nutrient data for the different components for approximately 130 wetlands. Average soil N:P molar ratio was 25 (range 2-65), plant N:P was 22 (range 14-48), and water N:P was 68 (range 3.5-176). Results to date suggest there are positive relationships between soil and vegetation N:P and surface water N:P, but the relationships have low predictive power. Average annual wetland retention was 2.1 moles N m-2 yr-1 and 0.15 moles P m-2 yr-1. There was a positive relationship between N and P retention, but the predictive power was also low. Our results suggest geology (through soil characteristics) and biota exert stoichiometric constraints on wetland nutrient retention. We suggest that these constraints should be considered when designing wetland restoration projects for water quality improvements.
