SOURCES AND DECOMPOSITION OF DISSOLVED ORGANIC MATTER IN A DESERT STREAM
In aquatic ecosystems, dissolved organic matter (DOM) is the main substrate for heterotrophic respiration. However, the molecular composition of DOM, and thus its biolability, varies depending on its source. Low terrestrial gross primary production in arid ecosystems results in a smaller input of allochthonous carbon to streams compared to those in mesic regions. This study aims to understand how in-stream primary producers (i.e., algae and wetland plants) in a desert stream influence streamwater DOM composition and benthic microbial respiration. There were significant differences in DOM composition (assessed using fluorescent and optical analyses) between two reaches that differed in dominant type of in-stream primary producer. DOM from the benthic algae-dominated reach had lower molecular weight, was less humic, and was younger than DOM in a wetland plant-dominated reach. Laboratory incubation of stream sediments with leachates derived from either algae or wetland plants demonstrated no significant difference in sediment respiration rates between leachate types. However, changes in DOM composition over the incubation period indicated a substantial microbial contribution to the DOM pool, an increase in its degree of aromaticity, and an overall loss of DOC over the course of the incubation.
Kathrine Kemmitt (Primary Presenter/Author), Arizona State University, firstname.lastname@example.org;
Nancy Grimm (Co-Presenter/Co-Author), Arizona State University, email@example.com;