EFFECTS OF PARENT LITHOLOGY ON STREAM-GROUNDWATER EXCHANGE AND ORGANIC MATTER DECOMPOSITION IN HEADWATER STREAMS IN KYUSHU, JAPAN
Stream-groundwater exchange and organic matter decomposition in shallow streamed were studied in headwater streams flowing on 4 types of lithology; granite, pelitic schist, andesite, and welded tuff. Stream-groundwater exchange was estimated using mass loss from tracer injection. Parent lithology controls the types of substrate, as streams on pelitic schist and andesite had gravel-cobble bed, granite had gravel-sand bed, and welded tuff bedrock. As a result, the exchange rate was highest in streams flowing on pelitic schist, and lowest in streams on welded tuff. We used organic matter decomposition, as an ecological function, to examine the effects of stream-groundwater exchange. The decomposition rate was measured using the standardized cotton-strip assay method in summer of 2017. Similar to the exchange rate, the decomposition rates were highest in the streams on pelitic schist, and lowest in streams on welded tuff. Water temperature, nitrate, and DOC concentration were also measured. The decomposition rate was higher in streams with higher nitrate concentration, and the differences in decomposition rates between channel and streambed sediments became smaller as the stream-groundwater exchange increase. Thus, parent lithology controls stream-groundwater exchange, and consequently influence ecological function, such as decomposition.
Tamao Kasahara (Primary Presenter/Author), Kyusyu University, email@example.com;
Peng Ruixin (Co-Presenter/Co-Author), Kyushu University, firstname.lastname@example.org ;