Community plankton respiration in a salt marsh estuary and the importance of macrophytic leachates 1

Community plankton respiration (CPR) was measured in a Georgia salt marsh tidal creek and estuary. CPR ranged from 94 to 162 g 02* rnp3* yr-’ (234-978 g 02* m-l. yr-‘) inshore and was much lower in nearby coastal waters. Seasonal changes in CPR are closely associated with changes in temperature in a log-log manner (R2 = 0.60-0.85) as are many other measurements of metabolic activity in the estuary, including live biomass of Spurtina aZterni,floru. Leaching rates of dissolved organic matter by Spartina during tidal submergence were 200800 pg C*g dry wt-‘*h-l, depending on salinity and season. The release rate was lower, 21 pg C-g dry wt-‘a h-‘, when the plant was not submerged. The plankton community is capable of rapidly and cfficicntly absorbing this material, which is produced in large enough quantities to account for the observed seasonal changes in CPR. Two basic methods have been used to study the ftmctional aspects of salt marsh ecosystems. One involves an analysis of community energy flow (e.g. Teal 1962) and the other, nutrient flux (e.g. Pomeroy et al. 1972). Both methods incorporate Spartina al ternijlora as the functionally dominant influence on the biological system. Until recently, energy flow analyses have mainly dealt with the annual pulse of particulate carbon released when Spartina decays, whereas nutrient flux analyses have examined the role of living Spartina. Particulate detritus may not be the sole energy source for the estuarine waters, however; dissolved organic matter (DOM) may be leached from live Spartina during tidal submergence. Macrophyte release of DOM is a significant factor for other aquatic systems (e.g. Wetzel 1969; Khailov and Burlakova 1969). Spartina excretes salts from glands at the leaf surface (Klugh 1909; Reimold 1972; Pomeroy et al. 1972), and, as in other halophytes, this release is probably dependent on salinity stress (e.g. Ariz et al. 1955). Metabolic pools OF organic mol’ This paper is based, in part, on a Ph.D. thesis submitted to the University of Georgia, Athens. The research was supported by a National Science Folmdation predoctoral fellowship from the Duke University Cooperative Oceanographic Program, grant GA-27725, and also by grant 04-5-14812 to the Center for Wetland Resources from NOAA Office of Sea Grant. ecules may participate in balancing salt stress by increasing the cellular concentration of organic acids (Scholander et al. 1966; Williams 1969) and escape the leaf (Pollack and Waisel 1970). I report here estimates of the seasonal community respiration rates of the intertidal estuarine and coastal water community near a Georgia salt marsh and relate these rates to various environmental factors, abiotic and biotic, in an attempt to make a more precise statement of the influence of salt marsh-derived organic material on the seasonal community metabolism ot‘ these waters. To accomplish this I made a statistical analysis of the data on community plankton respiration (CPR) and other published data on community metabolism. The amount of DOM released by Spartina during tidal submergence was estimated and its incorporation into the estuarine food chain investigated. I thank L. R. Pomeroy, L. Bahr, D. Frankenberg, J. Hall, II. Jitts, R. E. Johannes, D. W. Menzel, J. E. Schindler, and W. Wiebe. Materials and methods Community plankton respiration rates -Community plankton respiration rates were determined with methods and precautions described by Pomeroy and Johannes (1966, 1968) and Turner (1978).