Settling and resuspended particles: A source or a sink of phosphate in two contrasting oligotrophic high mountain lakes?

This study focuses on two Mediterranean oligotrophic high mountain lakes located in the Sierra Nevada National Park (southern Spain): Rio Seco (RS) and La Caldera (LC). A combination of field measurements and laboratory experiments is used: (i) to quantify in situ settling fluxes; (ii) to study the soluble reactive phosphorus (SRP) release or uptake by settling and resuspended particles; and (iii) to discriminate between the biotic and abiotic contribution for such patterns. In general, all suspensions (lake water untreated and lake water enriched with settling and with resuspended matter) in both study lakes release significantly more SRP to the solution when biological activity was suppressed. Biological uptake from settling and resuspended matter is likely to be limited by the bacterial consumption of P. Despite of these similarities, this study has revealed notable differences in the effect of sediment resuspension on SRP dynamics in both study lakes, when simulating natural conditions (biotic and abiotic processes). While in LC, the enrichment of lake water with settling and with resuspended matter did not cause an increase in SRP concentrations in lake water, SRP concentrations in RS at the end of the experiment were significantly higher (probability P < 0.05) in lake water enriched with resuspended matter (3.2 μ g/l) than in natural lake water (lower than the detection limit). Accordingly, it is reasonable to expect that sediment resuspension, which occurs more frequently in RS compared with LC, affects drastically the SRP availability in the water column in RS.Original Abstract: Cette etude se concentre sur deux lacs oligotrophes de haute montagne mediterraneenne dans le Parc National Sierra Nevada dans le Sud de l'Espagne : Rio Seco (RS) et La Caldera (LC). Une serie de mesures dans les lacs et d'experiences en laboratoire ont ete utilisees : (i) pour quantifier in situ les flux de sedimentation ; (ii) pour etudier la desorption ou l'absorption du phosphate (phosphore reactif soluble [SRP]) par decantation et remise en suspension des particules ; et (iii) pour faire la distinction entre la contribution biotique et abiotique a ces processus d'echange. En general, toutes les suspensions (eau non traitee du lac et eau du lac enrichie avec des sediments decantes et avec des sediments remis en suspension) dans les deux lacs etudies liberent significativement plus de SRP dans la solution lorsque l'activite biologique est supprimee. Le prelevement biolog