MEPS 283:99-112 (2004)  -  doi:10.3354/meps283099

ABSTRACT: Benthic metabolism was measured at 3 representative lagoon bottom sites in San Quintin Bay, Baja California, Mexico, during winter and summer from 1997 to 2000. At each site, and in every sampling period, three 0.5 m diameter transparent acrylic hemispherical domes were installed on bare sediment for ~24 h to determine fluxes of dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (O₂) and dissolved inorganic nutrients (NH₄, PO₄). Our results for sediment fluxes (mean ±SE; n = 63), all in mmol m^-2 d^-1, except TA in meq m^-2 d^-1 were: O₂ = -23.4 (±10.7); DIC = 31.0 (±22.9); TA = 8.1 (±8.0); NH₄ = 2.15 (±1.39); PO₄ = 0.114 (±0.140). These values fall near the median of values reported for shallow water systems. The benthic and planktonic metabolic rates were also compared. Seagrass beds were apparently responsible for ~80% of the benthic metabolism. Benthic processes dominate the metabolism at the system level, accounting for about ~70% of total primary production (PP) and respiration (R). A whole-system production to respiration ratio of ~0.9 was obtained. While recycling dominates gross metabolism, there must be an external supply of organic material to account for an excess of R over PP (net heterotrophy). We conclude that plankton external supplied from outside the system dominates this external supply. Our data agree with previous information for Tomales Bay, California, that deep sediment DIC release was about twice O₂ uptake. These results indicate that anaerobic metabolism accounted for about half the net respiration in the deep sediments.

KEY WORDS: Nutrient fluxes · Gross metabolism · Benthic-pelagic coupling · Seagrass · Temperate coastal lagoon