Organic matter dynamics in headwater forest streams of Northern Patagonia, Argentina

ALBARIÑO, RICARDO; DÍAZ VILLANUEVA, VERÓNICA; BURIA, LEONARDO

Chile

Workshop; Final international workshop in the framework of 10 years bilateral cooperation between Ghent University (Belgium) and Universidad Austral de Chile (Chile); 2009

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:PT-BR;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> This study describes structural and functional aspects associated with detritus dynamics in a Nothofagus pumilio forest small watershed that is located in the driest extreme of the eastwardly pluvial gradient in northern Patagonia. During the study the bulk of organic matter fell between late-summer and late-autumn (stream inputs of deciduous Nothofagus leaves collected in a neighbor stream = 97-111 g AFDM m-2). Leaf litter retained in the stream bottom was higher in autumn and winter (5-30 g DM m-2) and was dominated year round by Nothofagus pumilio (lenga). Detritus accumulations had 5 to 26 times more lenga leaves than those of other species. In the water year 2006, leaf litter shed at the driest period was redistributed along headwater extensions during the first spate (May 2006). In this event, a substantial amount of lenga leaves were exported from the upper catchment and travelled more than 9 km downstream. The average of our estimated k values (0.0067 ± 0.0017, mean ± 1 s.e.) was at the lower limit of the intermediate decay rate category. Although lenga leaves seem to be of poor food quality and they dominate the benthic detrital food base in headwater streams most of the time, the community structure was dominated by detritivores (~75%) both in biomass and density with shredders representing ~50% of total biomass year round and collectors with ~50% of community density. Waterfalls act as natural physical barriers preventing the upstream settlement of the exotic rainbow trout and, in doing so, allow pristine functional and structural conditions to occur as in pre-trout introduction times.