Phytoplankton community structure in the Lena Delta (Siberia, Russia) in relation to hydrography

[摘要] The Lena Delta in Northern Siberia is one of the largest river deltas in theworld. During peak discharge, after the ice melt in spring, it deliversbetween 60–8000 m³ s⁻¹ of water and sediment into the Arctic Ocean. TheLena Delta and the Laptev Sea coast also constitute a continuous permafrostregion. Ongoing climate change, which is particularly pronounced in theArctic, is leading to increased rates of permafrost thaw. This has alreadyprofoundly altered the discharge rates of the Lena River. But the chemistryof the river waters which are discharged into the coastal Laptev Sea havealso been hypothesized to undergo considerable compositional changes, e.g.by increasing concentrations of inorganic nutrients such as dissolved organiccarbon (DOC) and methane. These physical and chemical changes will alsoaffect the composition of the phytoplankton communities. However, beforepotential consequences of climate change for coastal arctic phytoplanktoncommunities can be judged, the inherent status of the diversity and food webinteractions within the delta have to be established. In 2010, as part ofthe AWI Lena Delta programme, the phyto- and microzooplankton community inthree river channels of the delta (Trofimov, Bykov andOlenek) as well as four coastal transects were investigated to capturethe typical river phytoplankton communities and the transitional zone ofbrackish/marine conditions. Most CTD profiles from 23 coastal stationsshowed very strong stratification. The only exception to this was a small,shallow and mixed area running from the outflow of Bykov channel in anortherly direction parallel to the shore. Of the five stations in this area,three had a salinity of close to zero. Two further stations had salinitiesof around 2 and 5 throughout the water column. In the remaining transects, onthe other hand, salinities varied between 5 and 30 with depth. Phytoplanktoncounts from the outflow from the Lena were dominated by diatoms(Aulacoseira species) cyanobacteria (Aphanizomenon, Pseudanabaena)and chlorophytes. In contrast, in thestratified stations the plankton was mostly dominated by dinoflagellates,ciliates and nanoflagellates, with only an insignificant diatom componentfrom the genera Chaetoceros and Thalassiosira(brackish as opposed to freshwater species). Ciliateabundance was significantly coupled with the abundance of total flagellates.A pronounced partitioning in the phytoplankton community was alsodiscernible with depth, with a different community composition and abundanceabove and below the thermocline in the stratified sites. This work is afirst analysis of the phytoplankton community structure in the region whereLena River discharge enters the Laptev Sea.

[学科分类] 地球化学与岩石