The fate of leaf litter in extremely acidic mining waters
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Beschreibung
This thesis comprises a number of integrative assessments and experiments conducted to investigate the long-term fate of allochthonous leaf litter in extremely acidic mining waters. It was focused to examine the possible mechanisms of leaf litter decomposition in these waters: leaching, microbial mediated decomposition and mechanical abrasion. Additionally, the potential availability of acidic conditioned litter for a local shredder was tested.
The investigations performed in the present thesis revealed incomplete leaf litter decomposition with no fragmentation. The main mechanisms of litter mass loss in these waters are leaching and microbial degradation. Indications for litter decomposition – litter mass loss and high associated microbial activity – were measured only during the initial months after entering the waters. After the initial period litter mass loss ceased while leaf associated activity decreased to the same low level as on inert substrates. Throughout the initial period the formation of massive iron precipitates (iron plaques) on leaf surfaces were observed. These plaques are likely to cause a standstill in litter decomposition by acting as a barrier against microbial attack and physical abrasion of leaf litter. There are indications that dead fungal biomass increases during leaf exposure. These findings indicate that iron plaques not only act as a barrier against microbial attack of leaf compounds but also limit the degradation of dead fungal hyphae. Besides other kinds of organic matter the dead fungal hyphae were probably the major reason for the considerable organic content of iron plaques. Since leaf litter loose approximately 15 % of mass through leaching in acidic mining waters, leaf litter leachates may provide beneficial compounds for leaf associated microorganisms. The supply of leaf leachates may probably be highest in autumn/winter during the main period of leaf abscission of deciduous trees. As laboratory experiments show, leaf litter leachates stimulate pelagic microbial processes in extremely acidic mining waters. Leachates from geogenic organic matter such as brown coal are also potential bioavailable in acidic mining waters but cause a far lower microbial response than leaf litter leachates. Laboratory feeding experiments with a local shredder (Gammarus pulex) show that, despite having a low degree of microbial conditioning, leaves coated by iron plaques are highly palatable to the shredder. The iron plaques do not function as a barrier against macroinvertebrate feeding as they do in the case of microbial leaf attack. The presence of iron plaques’ associated organic matter, e.g. enclosed dead fungal hyphae, probably increases the nutritional value for shredders. The results have to be considered in landscape construction and water management of post-mining landscapes.
Autor*in
Jeanette Schlief
Themen in »The fate of leaf litter in extremely acidic mining waters«
Fließgewässerökologie Laubabbau Tagebaugewässer acid mine drainage leaf litter decomposition stream ecology