Rafael Morales-Baquero

DOES ECOSYSTEM SIZE DETERMINE AQUATIC BACTERIAL RICHNESS

With the advent of DNA-based molecular technologies, microbial ecologists now have the tools to test whether general ecological patterns apply to microorganisms. In this study, we selected 11 high-mountain lakes from Sierra Nevada (Spain) to test the predictions of island-biogeography theory in relation to ecosystem size and isolation, and to assess the influence of other factors (i.e., ecosystem productivity, resource richness, and biotic interactions) on bacterial community structure. Bacterial operational taxonomic units (OTUs), generated by denaturing-gradient gel electrophoresis of polymerase chain-reaction-amplified 16S rRNA genes, were used as a surrogate of predominant “biodiversity units.” OTU composition among lakes was heterogeneous, and the number of site-specific OTUs was near 50%. Lake remoteness did not affect the number of bacterial OTUs although the spatial distribution of the lakes significantly influenced bacterial composition. Lakes that were closer together had more similar bacterial ...

Evidence of an atmospheric forcing on bacterioplankton and phytoplankton dynamics in a high mountain lake

Abstract.We quantified dry and wet atmospheric deposition of soluble reactive phosphorus (SRP) to the Southwest Mediterranean region during one year and assessed its effect on bacterial abundance and phytoplankton specific biomass during one ice-free period in a high mountain lake located in an area highly influenced by Saharan dust outbreaks. Dry deposition of SRP represented 79% of total SRP inputs and it showed a seasonal pattern similar to Saharan dust export to this region, with maxima during spring and summer. Bacterial abundance was significantly correlated with SRP atmospheric deposition, suggesting the influence of this input on bacterioplankton dynamics. The field evidence was experimentally corroborated using bacterial regrowth cultures performed with dust-amended lake water. Dust addition significantly increased SRP concentration in lake water and it stimulated bacterial abundance. Regarding phytoplankton community, only one species, the chrysophyte Chromulina nevadensis, was significantly related to SRP inputs and, consequently, there was a significant decrease in phytoplankton species diversity after atmospheric SRP inputs. Since changes in climate will presumably lead to an alteration in dust export, these results point to the need of further studies on the potential effects of this alteration on bacterioplankton and phytoplankton dynamics in remote oligotrophic systems.

Chemical signature of Saharan dust on dry and wet atmospheric deposition in the south-western Mediterranean region

We studied if the presence of Saharan dust intrusions and the rains modify the chemical signature of the wet and dry deposition in the southern Iberian Peninsula. We have sorted the 109 sampling weeks by the presence (rainy weeks) or absence (dry weeks) of rain and by the occurrence or not of Saharan dust intrusions. Dry deposition dominated the delivery of particulate material (PM), total phosphorus (TP), soluble reactive phosphorus (SRP), Ca2+, Mg2+ and K+, whereas wet deposition dominated the delivery of Na+, total nitrogen, and . In the dry weeks, the presence of Saharan dust intrusions lead to higher inputs of PM, TP, SRP, Ca2+, Mg2+ and K+ in the dry deposition. Conversely, in the rainy weeks, there were no differences in mean values of dry deposition irrespective of the occurrence of Saharan dust intrusions. Nevertheless, in the presence of Saharan intrusions and some rain, the weekly collection of PM, TP and Ca2+ in dry deposition were significantly higher and increased as rainfall was lower. By contrast, the ions Cl– and Na+ in wet deposition were higher in absence of Saharan dust intrusion and increased as rainfall increased.

Spatiotemporal drivers of dissolved organic matter in high alpine lakes: Role of Saharan dust inputs and bacterial activity

The effects of many environmental stressors such as UV radiation are mediated by dissolved organic matter (DOM) properties. Therefore, determining the factors shaping spatial and temporal patterns is particularly essential in the most susceptible, low dissolved organic carbon (DOC) lakes. We analyzed spatiotemporal variations in dissolved organic carbon concentration and dissolved organic matter optical properties (absorption and fluorescence) in 11 transparent lakes located above tree line in the Sierra Nevada Mountains (Spain), and we assessed potential external (evaporation and atmospheric deposition) and internal (bacterial abundance, bacterial production, chlorophyll a, and catchment vegetation) drivers of DOM patterns. At spatial and temporal scales, bacteria were related to chromophoric DOM (CDOM). At the temporal scale, water soluble organic carbon (WSOC) in dust deposition and evaporation were found to have a significant influence on DOC and CDOM in two Sierra Nevada lakes studied during the ice-free periods of 2000-2002. DOC concentrations and absorption coefficients at 320 nm were strongly correlated over the spatial scale (n = 11, R(2) = 0.86; p < 0.01), but inconsistently correlated over time, indicating seasonal and interannual variability in external factors and a differential response of DOC concentration and CDOM to these factors. At the continental scale, higher mean DOC concentrations and more CDOM in lakes of the Sierra Nevada than in lakes of the Pyrenees and Alps may be due to a combination of more extreme evaporation, and greater atmospheric dust deposition.

Patterns in the composition of the rotifer communities from high mountain lakes and ponds in Sierra Nevada (Spain)

On the basis of periodic collections of rotifers from 29 lakes and ponds over 2500 m above sea level in the Sierra Nevada (Southern Spain), patterns of species richness, distribution and community composition were evaluated. Results allow us to distinguish communities which fall into two major lake types. One is defined by the presence of typically planktonic species as well as lower specific richness whereas the other includes communities of mainly benthic and periphytic species. Both lake types seem to be related to small differences in their physical and chemical characteristics. These relationships and the influence of littoral vegetation are discussed.

Reproduction strategies of Daphnia pulicaria population in a high mountain lake of Southern Spain

For three consecutive years, a population study of Daphnia pulicaria was undertaken in Río Seco Lake, a small high-mountain lake, in order to elucidate the reproductive strategies adopted by Daphnia in this system. Daphnia appears to colonize this lake every spring by hatching from ephippia and reproduce by means of subitaneous (non-diapausing) and ephippial (diapausing) eggs. D. pulicaria in this lake is an obligate parthenogenetic population. There is a short time period for subitaneous egg production and a much longer period for ephippial egg production. The contribution of subitaneous eggs to Daphnia population density and structure appears to be low. Diapause onset showed a high temporal synchronization in the three studied years in Río Seco Lake, and day-length emerged as the main cue triggering diapause onset and the main explanatory factor for the proportion of ephippial females observed. The development and reproduction of D. pulicaria in Río Seco Lake involves taking a gamble on resting forms to guarantee inter-annual Daphnia persistence in the lake, giving priority to investment in future generations.

Rotifer fauna of lakes and ponds over 2500 m above sea level in the Sierra Nevada, Spain, with description of a new subspecies

The littoral zone of lakes in the high mountains of Sierra Nevada, Spain, were sampled during the ice-free periods of 1980 and 1981. A species list is given and a new subspecies, Lepadella quinquecostata nevadensis, subsp. nov. is described. Notes on the geographical distribution of some species are also included.

Empirical evidence for a complex diurnal movement in Hexarthra bulgarica from an oligotrophic high mountain lake (La Caldera, Spain)

A detailed 24 hour sampling program has been carried out at 26 depths of 6 stations located along the two main transects of lake La Caldera. The resultant data has allowed us to define for H. bulgarica a general daily trend of movement which couples a typical nocturnal vertical migration with an ‘horizontal’ one that is particularly conspicuous at dawn and dusk when the population seemed to moved toward or away from the shore, respectively.These results confirm our previous data and suggest that light is responsible for these complex movements.

Implications of seston settling on phosphorus dynamics in three reservoirs of contrasting trophic state

We performed a comparative study in three reservoirs based on field measurements and laboratory experiments determine the impact of seston sedimentation on phosphorus dynamics. While we found a strong relationship between the trophic state and the settling flux of dry material in the study reservoirs, an increase in the trophic state did not lead to an increase in the export ratio (fraction of the primary production lost by sinking). In laboratory experiments, the analysis of biotic and abiotic contributions to phosphate (PO 4 3- ) regeneration/uptake by the sinking particles showed that an increase in the trophic state led to a significant vertical segregation in the observed patterns. Settled matter collected in both upper and lower sediment traps exhibited similar temporal patterns in the oligotrophic reservoir (Quentar), while clear spatial differences occurred in the more eutrophic systems (Cubillas and Beznar) as result of the vertical distribution of PO 4 3- characterizing warm monomictic eutrophic systems during summer thermal stratification. Chemical analysis of the settling matter in the oligotrophic reservoir (Quentar) showed that the sinking particles became richer in phosphorus during sedimentation, especially in the organic P pools. In contrast, P content in settling matter decreased with depth in the hypertrophic reservoir (Beznar), especially the org-P at the thermocline. This indicates that the mineralization of settling organic matter is important for maintaining high concentration of PO 4 3- in the deeper layers. However, no significant vertical differences in P content in settled matter were detected during the whole study period.

Saharan versus local influence on atmospheric aerosol deposition in the southern Iberian Peninsula: Significance for N and P inputs

A novel methodology was used to evaluate the contribution of Saharan dust to the atmospheric deposition of particulate material (PM), total phosphorus (TP), and total nitrogen (TN) in the southeastern Iberian Peninsula. Dry and wet aerosol depositions were measured weekly during two 1 year periods at one site and simultaneously during spring-summer of the same years at two other sites (intersite distance of ~ 40 km). Statistical relationships among depositions at the different sites permitted differentiation of Saharan dust inputs from locally derived dust. PM and TP depositions were synchronous among the three study sites; the synchrony was elevated during periods of Saharan intrusions (evaluated by air mass retrotrajectories analyses), but no temporal correlation was observed during periods without Saharan intrusions. According to analysis of variance results, PM and TP depositions were both significantly affected by Saharan intrusions. During weeks with Saharan intrusions, PM deposition increased around 85% above background levels, with no differences among the three sites, while TP deposition increased by 1.1 µmol TP m−2 d−1, i.e., 29% to 81% above background levels depending on the site. There were no correlations or differences in TN deposition among sites or as a function of Saharan intrusion periods. The annual contribution of PM and TP from Saharan dust was 75 kg ha−1 and 0.07 kg P ha−1, respectively, which can be considered a genuine input for the ecosystems in this area. This novel approach is likely to be valid in any area in the world under atmospheric deposition of long-range transported material.