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Experimental effects of ash deposition on macroinvertebrate assemblages in peatland streams

Johnston, K., Robson, B. J.
Marine & freshwater research 2018 v.69 no.11 pp. 1681-1691
environmental factors, macroinvertebrates, peatlands, stream channels, trays, United Kingdom
Rotational burn management has been practiced for >150 years in UK peatlands; however, little information exists on its effects on streams. An experiment investigated effects of ash input on four UK headwater streams by depositing ash onto trays filled with natural stream substrata. Before the experiment, streambed samples (SS) were taken to describe ambient macroinvertebrate assemblages. Macroinvertebrate response after 21 days was compared among SS, low (50g), high (100g) and top-up (50g + 50g dosed twice) ash-addition treatments and control trays (0g ash addition). Additions increased tray ash-free dry mass (AFDM), and by the end of the experiment, some trays retained more ash than did others (F12,72=5.15, P<0.001). Macroinvertebrate assemblages differed among streams (r=0.84, P<0.001) and treatments (r=0.23, P<0.001). SS contained fewer shredders than did other treatments (range: r=0.35–0.52, P=0.005). A significant relationship was found between assemblages and environmental conditions (Spearmans rho: 0.203, P=0.001). Stream depth and AFDM showed strongest correlations with assemblages. Ash deposition affects macroinvertebrate assemblages when deposited onto streambeds. However, the high among-stream variation in assemblage composition typical of UK headwaters is a stronger source of variation, suggesting that the effect of deposition is reasonably small in these streams.