Spartina patens Productivity and Soil Organic Matter Response to Sedimentation and Nutrient Enrichment

Abstract

Many coastal wetlands are subject to the combined effects of reduced sediment input and increased nutrient loads from watersheds. Restoration strategies focused on increasing marsh elevation and acreage can involve adding sediment through dredge sediment deposition or diversion of river water. It is unclear, however, how sediment inputs influence plant productivity in areas also receiving high nutrient loads. We tested the hypothesis that productivity of Spartina patens is greater with both nutrient and sediment addition than either or neither in a greenhouse experiment. Soil organic matter and nitrogen concentrations were predicted to increase with nutrient addition, but decrease with sediment addition. Plants experienced one of two levels of sediment deposition (control and 4 applications of 2 cm river silt) within either nutrient-enriched (6.96 N, 1.82 P, 1.82 K mg/L) or control tanks. Spartina patens exhibited nearly double the height, stem density, and aboveground biomass in nutrient treatments as compared to controls. Belowground biomass was also stimulated by nutrient-enrichment. Sedimentation reduced the emergence of new stems, but increased fine root biomass. Nutrient enrichment further stimulated root and rhizome growth into added surface sediment. Despite a large plant response to added nutrients, soil properties were unaffected by nutrient-enrichment.