Transport and decomposition of allochthonous litter in Icelandic headwater streams: Effects of forest cover

The present study was a part of a larger research project entitled ForStreams. Changes in catchment vegetation can have large impacts on stream ecosystems, especially through transport of terrestrial organic matter into them. The objectives of the present study were to compare non-forested and forested catchments in Iceland in terms of litter transport into streams and litter decomposition within them. This was the first study made in Iceland on the terrestrial-aquatic interactions in forested ecosystems. The main study consisted of nine run-off fed headwater streams in Fljótsdalshérað in eastern Iceland (N 65°01’–N 65°10’ and W 14°28’–W 14°48’). The streams either ran through treeless heathlands, birch forests (Betula pubescens Ehrh.) or conifer plantations (mainly Larix sibirica Ledeb.). The transport of terrestrial organic matter was measured with litter traps inserted into the stream banks. Decomposition of litter was measured with the litter bag method, using fine and coarse mesh litter bags to evaluate the effects on microorganism and invertebrate activity in the decomposition processes. The invertebrate fauna found within the coarse bags was also studied. Litter transport into the birch and conifer forest streams was 30–33 times higher than into the heathland streams. Hence, the litter transport increased the amount of energy available in the forest streams. Decomposition rate of birch leaves, larch needles and grass litter was 0.0033, 0.0040 and 0.0044g g-1 DM day-1, respectively. This was low compared to measured decomposition rates in comparable studies elsewhere. Grass litter had the fastest decomposition rate in the forested streams, whereas there was no difference in decomposition rate of different litter types in the heathland streams. The decomposition rate was positively correlated with the concentration of phosphorous in the water across all catchment types. It was also negatively correlated with the number of Plecoptera (shredders) found in the litter bags. This could indicate a different feeding activity of the group in Iceland and needs to be studied further. The number of taxonomic groups found in the litter bags was higher in birch than in conifer forest streams. There was no difference in the number of invertebrates found in the litter bags in different catchment types; on average 247 individuals per litter bag. The largest functional feeding groups in the litter bags were gathering collectors (44–57%) and scraping collectors (36–43%), but shredders were only 3–4% of the total number. There was no difference in the decomposition rate of litter within fine and coarse mesh bags, which was probably linked to lack of shredders in the streams. This indicated that invertebrates did not play a significant role in the decomposition process in the run-off streams, which is different from what has generally been found in forest streams elsewhere. An additional study was done on eight spring-fed headwater streams located near Mt. Hekla in southern Iceland (N 63°57’–N 64°00’ and W 19°53’–W 19°59’). There the streams ran either through birch forests or sparsely-vegetated eroded areas. There the decomposition rate of birch litter was higher in the coarse mesh litter bags than in the runoff fed streams in eastern Iceland. This shows how important it is to include different stream types when terrestrial-aquatic interactions are studied. In southern Iceland, the decomposition rate was also higher in the coarse mesh bags than in the fine mesh bags, which indicated a more important role of invertebrates in the decomposition process in the spring-fed streams. The decomposition rate in fine mesh bags did, however, not differ between southern and eastern Iceland which indicated that microbial decomposition was similar in the two stream types.

Author dc:creator

• Helena Marta Stefánsdóttir 1983-

Contributors dc:contributor

• Landbúnaðarháskóli Íslands

• Vistkerfi
• Vatnasvið
• Skógrækt

Language dc:language.iso

is

Handle dc:identifier.uri

http://hdl.handle.net/1946/7053

OAI identifier oai:identifier

oai:skemman.is:1946/7053