PARENT SESSION
Symposium 6: Anthropogenic Modification of North American Salt Marshes: Causes, Consequences and Recommendations
Organized by: B Silliman
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Chatham Ballroom C.

Changes in carbon and nitrogen cycling following Spartina alterniflora invasion of Pacific estuaries.

Tyler, Anna ^*,1, Grosholz, Edwin¹, Civille, Janie¹, Lambrinos, John¹, ¹ University of California - Davis, Davis, CA, USA

ABSTRACT- The introduction of Spartina alterniflora into Willapa Bay, WA (WB) and San Francisco Bay, CA (SFB) has impacted ecosystem primary production and the cycling of carbon (C) and nitrogen (N). S. alterniflora was introduced into WB in the early 1900s, and is currently invading mudflats dominated by microalgae and the non-native intertidal seagrass, Zostera japonica, which has been in Willapa Bay since at least the 1950s. In 1975, S. alterniflora was introduced to SFB; a subsequent hybridization with the native S. foliosa has produced an aggressive hybrid. This hybrid is now expanding into both unvegetated mudflats and native marsh vegetation. Changes in C and N cycling are most dramatic where Spartina has replaced mudflats. Sediment organic matter in unvegetated mudflats is historically low, but labile (low C:N) in comparison to the Spartina-dominated areas (high C:N). In WB, belowground C and N (living tissues only) are 10-25 times higher in S. alterniflora-dominated areas; collectively, S. alterniflora and Z. japonica have increased the C and N storage in the intertidal sediments of the estuary (23,000 ha of mudflat + marsh) by approximately 7- and 2-fold, respectively. In SFB, the impact of Spartina on C and N storage depends on the initial conditions: little change when compared to Salicornia sp.; a 2-4 fold increase compared to S. foliosa; and a 50-300 fold increase when compared to bare mudflats. Senescence of aboveground tissue results in the eventual release of 3E+05 kg N and 1E+07 kg C into WB and 2E+04 kg N and 7E+05 kg C into SFB annually. The sheer quantity of this input has profound implications for ecosystem function, including system metabolism and food web structure.

Key words: carbon, invasive species, Spartina alterniflora, nitrogen