Technical Note: The effects of five different defaunation methods on biogeochemical properties of intertidal sediment

[摘要] Various methods have been used to remove organisms from sediments toinvestigate structure and function of faunal assemblages in intertidalhabitats. Nevertheless, little is known about how these treatments affectproperties of the sediments themselves, although changing these propertiesmay cause changes in the assemblages, independently of other hypothesesbeing tested. This study assesses the efficacy of defaunation and effect onselected biogeochemical properties of five different methods of defaunatingsoft muddy sediments in an estuary. The methods were removal and freezingof sediment, removal and oven-heating, freezing in situ with liquid N₂,spraying with formalin and spraying with hydrogen peroxide. The first fourof these methods have been used in previous studies, whilst the fifth wasconsidered to be a potentially useful defaunator because it does not leavetoxic residues. The first two methods required sediment to be brought backto the lab, disrupting the natural structure of the sediment; the last threewere done in situ, with much less disturbance.

Variables measured to assess effects of the treatments on the sediment wereamount of water, grain size, total carbohydrate, suspension index (relativeerosion rate), erosion threshold, chlorophyll a and b, colloidalcarbohydrate, F_o (minimal fluorescence) andF_v / F_m (photosynthetic yield). There were nosignificant effects of any treatment on the first four variables. For theothers, effects of defaunation varied from treatment to treatment and withtime after treatment. Generally, the greatest disturbance was to themicrophytobenthos (MPB, measured by chlorophyll and fluorescence) and relatedvariables. For most treatments, recovery was rapid, but the effects offormalin and H₂O₂ persisted for a few days. Effects on physicalproperties of the sediment were mostly minor and insignificant. Removal andfreezing or heating, however, caused major changes to the sediments becauseof the disturbances involved. Choosing the appropriate method of defaunationis very important if interpretations are not to be confounded between theeffects of defaunation per se and any effects of changes to other biota (suchas microphytobenthos) and/or the properties of sediments caused by the methodused to defaunate experimental areas.

[学科分类] 地球化学与岩石