Major organic matter sources in tropical Brazilian coastal waters

DITTMAR, T.; LARA, R. J.; KATTNER, G.

Simposio; An Ocean Odyssey; 2001

Lignin-derived phenols and stable carhon isotopes were used to establish a signature for mangrove, terrestrial and marine-derived organic matter in a mangrove estuary in North Brazil. A mixing mode! was applied to calculate the contribut ion ofeach ofthe tbree sources to DOM and POM in the estuary. Best source ass ignment for POM was reached with the yield oflignin phenols and d 13C as paired indicators, while the origin ofOOM was best identified by the yield oflignin phenols and the acid to aldehyde ratio ofvanillyl phenols. Although only about 6 % ofthe fluvial eatchment area is covered by rnangroves, their contribut ion to the estua rine DOM and POM pool genera lly exceeded several t imes the terrigenic input from the hinterland. This outwe lling of mangrove-derived organic matter was enhanced during the rainy season. DOM and POM were exported from the mangrove to the estuary in similar proportions. Most mangrove-POM was removed from the water co lumn, while mangrove-DOM behaved conservatively. In contra st , terrest rial DOM was almost entirely removed in the outer part ofthe estuary, which was accompanied by a concomitant inerease in terrestria l POMA Generally a high proportion of mangrove-DOM was present in the outer part ofthe estuary, even at high tide. This indicates DOM outwelling from mangroves in adjacent bays or estuaries and points to similar driving force s controlling this process 00 a regional seale. Mangroves probably play a more important role than rivers for carhon budgets along the North Brazilian coast south of the Amazon.