PARENT SESSION
Oral Session # 61: Biogeochemistry IV: Al, Ca, P, and DOC.
Presiding: R Fitzhugh
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 205.

Factors influencing dissolved organic matter and dissolved inorganic nutrients in a mangrove forest near Braganca (Para, Brazil).

Schwendenmann, Luitgard¹, Lara, Ruben ², ¹ Institute of Soil Science and Forest Nutrition, University of Goettingen, Goettingen, Lower Saxony, Germany² Center for Tropical Marine Ecology, Bremen, Bremen, Germany

ABSTRACT- This study focused on depth distribution and seasonal variation of dissolved organic carbon and nitrogen, dissolved inorganic nutrients (ammonium, nitrate, nitrite, ortho-phosphate and silicate) and salinity of waters from a mangrove forest and an adjacent tidal creek located at the northeast coast of Para (Brazil). Water samples were taken at different depth from boreholes and piezometers located within the mangrove forest and from the tidal creek at neap and spring tides during dry and rainy season, respectively. In addition, sediment from the mangrove forest has been analyzed for carbon, nitrogen, salinity and hydraulic properties. As surface and groundwater inflow from neighboring areas is impeded, depth distribution and seasonal changes of organic matter, nutrients and salinity can only be attributed to the in/output of these elements via tidal creek, rainwater and to biological, biogeochemical and physical processes within the sediment. Compared with creek water, mangrove water was enriched in dissolved organic carbon and nitrogen, dissolved inorganic nitrogen and silicate because of the input of organic matter and subsequent biological transformation. Thus, these mangrove forests may act as a source for carbon and nitrogen to the adjacent tidal creek and estuary. The subsurface distribution of organic matter and inorganic nutrients was mainly governed by biological and geochemical processes, but vertical and lateral transport processes also seemed to play a role. Both processes were strongly influenced by physical sediment characteristics in the different profile layers. Whereas dissolved organic matter, silicate and salinity showed a distinct seasonal pattern, dissolved inorganic nitrogen and ortho-P were invariant to seasonal changes.

Key words: dissolved organic matter, seasonal variation, Brazilian mangrove ecosystem, dissolved inorganic nutrients