Inmaculada de Vicente

LOW PREDICTABILITY IN THE DYNAMICS OF SHALLOW LAKES: IMPLICATIONS FOR THEIR MANAGEMENT AND RESTORATION

This study was conducted in two eutrophic shallow lakes (Lake Honda LH and Lake Nueva LN) that share geographic proximity but have contrasting hydrology, meteorology, biogeochemistry, and geomorphology. Our objective was to explore the inter-annual, seasonal, and daily variability in selected biological, physical, and chemical variables of these two systems. Although the study lakes demonstrated a notable inter-annual and seasonal variation in nutrient concentrations, water transparency was the only variable that was consistently more variable in LH than LN. The reason for the greater temporal variability in water transparency of LH is its major susceptibility to wind and rain events. The impact of wind events in this lake is favored by its shallowness and by its silty surface sediment; the high ratio of catchment area to lake area is responsible for the relatively higher susceptibility of LH to rain events than LN. By contrast, in the younger and deeper LN, ground-water discharge buffers certain water chemistry parameters such as conductivity, turbidity, and alkalinity. Interestingly, differences in turbidity and ground-water discharge do not seem to affect the variability in nutrient concentrations, which was similar between the lakes, although these factors may explain differences between the lakes in nutrient concentrations. This paper reveals that the unpredictability and frequency of events in Mediterranean aquatic ecosystems makes it necessary to increase data collection frequency to obtain more accurate simulations in water quality models.

Thermal structure and energy budget in a small high mountain lake: La Caldera, Sierra Nevada, Spain

Abstract This work examines the diel change of energy storage and its associated patterns of thermal stratification during the ice‐free period in a high mountain lake (La Caldera Lake, Sierra Nevada, Spain), in response to meteorological conditions. Bihourly data have been implemented to a standard methodology of surface heat exchange calculations in lakes. Strong variations have been observed on the diverse components of the energy budget at different time scales, ranging from diel to seasonal. Additionally, time‐series analyses have been applied to reveal the underlying periodicities involved in relation to the different variables studied. The results obtained from this study provided realistic conditions for the environmental modelling of such processes, which are very sensitive in time scale.

Response of waterbirds to alternating clear and turbid water phases in two shallow Mediterranean lakes

Albufera de Adra (Southern Spain) constitutes an internationally-recognised marsh for waterbirds; important populations of some endangered species such as White-headed Duck and Red-crested Pochard overwinter and breed in its two shallow permanent lakes (Lake Honda and Lake Nueva). In a recently published article, we revealed the factors responsible for the irregular alternation between phytoplankton-dominated turbid phases and macrophyte-dominated clear water phases in Lake Honda and Lake Nueva. In this note, we try to clarify the impact of such an alternation of equilibrium states on the waterbird dynamics. Marked increments in abundance, and brood recruitment of dabbling and diving waterbirds were recorded during the clear water phases in contrast with the turbid water phases, as the increase of macrophytes associated with increased water transparency attract waterbirds for available food. Implications for ecosystem management, restoration and conservation are identified.

Interannual and between-site variability in the occurrence of clear water phases in two shallow Mediterranean lakes

It is widely accepted that clear water phases constitute a regular stage in the seasonal succession of plankton in dimictic lakes and reservoirs (i.e. PEG Model). The occurrence of such a phenomenon in Mediterranean shallow lakes is characterised by a marked interannual variability, which makes it difficult to establish reliable predictions on the dynamics and functioning of plankton in these ecosystems. In the present paper we analyse the factors influencing the occurrence of the clear water phases in the two shallow lakes of the Albufera of Adra, a coastal wetland region of south-eastern Spain: Lake Honda and Lake Nueva. Despite their geographical proximity, both lakes depicted large hydrological and limnological differences. Lake Honda is an epigenic and recharge lake that is strongly influenced by the hydrological conditions in its watershed, while Lake Nueva can be classified as a hypogenic and discharge lake and, as such, is less affected by the hydrological regime. In contrast, the morphometry, exposure and fetch of Lake Nueva make this ecosystem especially sensitive to wind forcing. Clear water phases in these shallow lakes were linked with periods of low thermal stability and the dominance of small-edible algae in the phytoplankton community, both of which allowed a Daphnia magna population to grow up and induce the algae collapse by grazing. In Lake Honda, those conditions were met during the spring of 2002 under the influence of intense rainfall-events, while in Lake Nueva the clear water phase was induced in the spring of 2003 by the occurrence of strong and frequent wind events. In both lakes, a relatively high water column thermal stability and the abundance of cyanobacteria early in the spring prevented the development of the Daphnia magna population and the occurrence of the clear water phase.

Sediment desiccation as a driver of phosphate availability in the water column of Mediterranean wetlands.

Sediment desiccation is expected to drastically affect nutrient cycling in Mediterranean wetlands as global climate change models predict that many areas will become significantly drier than they currently are. In this study, we selected two Mediterranean wetlands that clearly differ in their water chemical composition (Honda and Hituelo wetlands) in order to determine the impact of sediment desiccation on phosphate (PO₄(3-)) adsorption and desorption properties. A decrease in PO₄(3-) sorption properties was observed in transects from the littoral zone to dry land in both lakes concomitantly with a reduction in organic matter content, revealing a critical role of organic matter for sequestering P in the lake sediment. Our experiments designed to determine if drying events would lead to an enhanced P release upon re-wetting have shown that, simulating natural conditions of re-flooding (that is without adding sodium azide), PO₄(3-) concentrations were notably higher in the overlying water than those initially measured in the lake water. These results highlight the impact of drying sediment and the subsequent re-wetting on increasing P concentrations in lake water and accordingly, affecting to lake trophic state. Finally, we aimed on determining the overall effect of biotic versus abiotic activity on P release patterns observed upon re-wetting. Our results have evidenced that while in Honda, biotic processes upon re-wetting are crucial for increasing P retention in the sediment; P exchange across sediment and water upon dry sediment re-wetting is basically mediated by abiotic processes in Hituelo.

Effect of Drought Conditions on Plankton Community and on Nutrient Availability in an Oligotrophic High Mountain Lake

Abstract Natural water level fluctuations (WLFs) are an inherent characteristic of Mediterranean inland waters, which are projected to be amplified by global climate change. La Caldera (Sierra Nevada National Park, Spain) is an oligotrophic high mountain lake (3050 m a.s.l.) that has experienced large fluctuations in water volume (13–100%) during the past 20 years due to irregular annual precipitation patterns (371–1816 mm). Because of the lakes cold and dilute abiotic environment, it is likely susceptible to projected increases in global temperature and represents an ideal sentinel of global change. We analyze the effect of WLFs on water quality and on plankton community in La Caldera to better understand the potential effects of recurrent droughts (3 droughts in a 20-year period) on lake ecology. We have found significantly positive effects of WLFs on total phosphorus (TP) concentrations. There was extreme variability in TP concentrations during three recurrent droughts (1995, 1999, and 2005) reflecting sediment resuspension. However, the data also suggest that this was not the only source of phosphorus. Extremely high P-enriched atmospheric dust inputs could have maintained the abnormally high TP in-lake concentrations measured during 2005. The data indicate that recurrent droughts have reduced lake resistance to TP changes but have increased lake resistance to total nitrogen (TN) changes, which supports the idea that a P-enriched atmospheric dust inputs during 2005. An increase in dissolved inorganic nitrogen (DIN)∶TP mass ratio after 2005 was observed, revealing a higher ecosystem homeostasis of this ratio.

Selecting priority conservation areas based on zooplankton diversity: the case of Mediterranean wetlands

A set of Mediterranean wetlands has been studied in order to identify priority areas for conservation using zooplankton assemblages. We also measure the degree of nestedness to determine the best strategy for conservation of zooplankton diversity. The present study was conducted in 29 wetlands located in the south-east of the Iberian Peninsula (Spain). Two complementary approaches were used, cluster analysis and parsimony analysis of endemicity (PAE), with a presence–absence data matrix, in order to group wetlands as a function of zooplankton composition. To select conservation areas, four different criteria were used: species richness; exclusive species occurrences; the number of wetlands in which species appeared; and phylogenetic diversity. The results showed the existence of three different zones (subgroups of wetlands). Using the same method, a significant nestedness among wetlands was also observed independently of the method used to group them. The conservation proposal included 98% of the total species and 41.4% of the studied wetlands. This work confirms that zooplankton assemblages are essential for making wetland conservation decisions and for the identification of areas with connectivity (fluxes of species) in which efforts should be more intense to preserve their biodiversity.

Linking watershed land uses and crustacean assemblages in Mediterranean wetlands

The watershed land uses in Mediterranean wetlands are essential to understand the functioning of aquatic communities. This study was designed to assess the relationship between watershed land uses, wetland characteristics and zooplankton assemblages (branchiopods and copepods) in 24 Mediterranean wetlands of the southern Iberian Peninsula, which greatly differ in both wetland land uses (olive groves, pasture, scrublands, and forest) and in their morphometric and limnological features. Firstly, results from a Principal Component Analysis allowed us to classify wetlands in two categories: impacted and non-impacted. Then, one-way Analysis of Variance was performed to test differences in zooplankton species richness and a Permutational Analysis of Variance was performed to test differences in zooplankton assemblages between categories. Lastly, a Non-metric Multidimensional Scaling analysis was chosen for the lake-by-species ordination. The results support the hypothesis that zooplankton richness and composition were negatively affected by watershed land uses, mainly agriculture practices. Moreover, species zooplankton assemblages were clearly linked to the two different wetlands categories. The present study puts forward the important role of zooplankton community for testing land use effects in Mediterranean wetlands.

Chemical composition of wetland sediments as an integrator of trophic state

Because eutrophication constitutes a key problem in limnology, evaluation of trophic state is a preliminary and essential step for the conservation and management of aquatic ecosystems. Frequently, lake trophic state is expressed by using parameters measured in the water column such as water transparency, total phosphorus or chlorophyll-a concentrations. The application of these indices usually requires repeated seasonal monitoring of the system for obtaining the annual mean values. Considering that lake sediments reflect lake trophic state, in this work we show the relevance of using sediment composition (total N and organic matter content) for obtaining quantitative data related to lake trophic state (bio-production number, BPN). Our results show that the estimated values obtained with BPN (ranging from 5.23 to 6.33), in a lake with relatively low organic matter content, reflected the trophic state as estimated by traditional water-column methods. Furthermore, the reproducibility of the BPN method, which is reflected by the constant BPN values along time, means that only one sampling including the spatial heterogeneity of the surface sediment, can provide a reasonable composite measure of trophic condition in a wetland. Finally, and as it represents a less time-consuming index, we propose the BPN as an appropriate trophic state indicator for wetlands, shallow lakes, and aquatic systems showing large temporal variability.

EL PLANCTON DE LAS LAGUNAS DE SIERRA NEVADA: NECESIDAD DE ESTUDIOS TRANSDISCIPLINARES

La correcta valoracion de los procesos ecologicos, como base para el mantenimiento de la integridad ecologica del ecosistema, se ha convertido en una de las tareas de mas dificil cumplimiento en las labores de conservacion de los ecosistemas mediterraneos. La busqueda y desarrollo de herramientas en la deteccion y prevencion de alteraciones ambientales nos ha llevado a centrar la atencion en las lagunas de alta montana del Parque Nacional de Sierra Nevada, ecosistemas que presentan un singular valor ecologico dentro del ambiente mediterraneo, por su caracter oligotrofico, por su situacion a gran altitud y por la adaptacion de sus comunidades a condiciones ambientales extremas. El presente texto describe una propuesta de estudio integral en estos ecosistemas con una aproximacion basada en el analisis de las estructuras de tamano de las comunidades del plancton como herramienta descriptora y predictiva de las respuestas de esas comunidades a los cambios ambientales.