Zooplankton dynamics during autumn circulation in a small, wind-sheltered, Mediterranean lake

12 pages, and tables statistics.

Managing for resilience: an information theory-based approach to assessing ecosystems

Ecosystems are complex and multivariate; hence, methods to assess the dynamics of ecosystems should have the capacity to evaluate multiple indicators simultaneously. Most research on identifying leading indicators of regime shifts has focused on univariate methods and simple models which have limited utility when evaluating real ecosystems, particularly because drivers are often unknown. We discuss some common univariate and multivariate approaches for detecting critical transitions in ecosystems and demonstrate their capabilities via case studies. Synthesis and applications. We illustrate the utility of an information theory-based index for assessing ecosystem dynamics. Trends in this inde…

Inferring the Relative Resilience of Alternative States

Ecological systems may occur in alternative states that differ in ecological structures, functions and processes. Resilience is the measure of disturbance an ecological system can absorb before changing states. However, how the intrinsic structures and processes of systems that characterize their states affects their resilience remains unclear. We analyzed time series of phytoplankton communities at three sites in a floodplain in central Spain to assess the dominant frequencies or "temporal scales" in community dynamics and compared the patterns between a wet and a dry alternative state. The identified frequencies and cross-scale structures are expected to arise from positive feedbacks that…

Daily patterns of mixing and nutrient concentrations during early autumn circulation in a small sheltered lake

17 pages, 11 figures, 1 table.-- Printed version published May 2005.

The importance of phytoplankton production for carbon budgets in a semiarid floodplain wetland

Phytoplankton production (PP) in wetlands is not measured as often as that of macrophytes. A three year-study during a period of sustained high flooding was undertaken in a central Spanish floodplain wetland (Las Tablas de Daimiel National Park) to determine net PP, its spatial heterogeneity and controlling factors, and compare it with primary production in macrophyte communities. This enabled us to estimate carbon budgets for each community. All PP variables showed high spatial and temporal variability among sites, resulting in low coherence even when flooding connected all sites. Net PP corresponded to 25- 36% of submerged plant production and 3-10% of helophyte production. Net PP was con…

We carried out enclosure experiments to assess the potential deleterious effects of the alien species common carp (Cyprinus carpio L.), mosquitofish (Gambusia holbrookii Gir.), and pumpkinseed sunfish (Lepomis gibbosus L.) on water quality and food web in a severely degraded floodplain wetland, the Spanish National Park Las Tablas de Daimiel. With addition of either carp or pumpkinseed sunfish, chlorophyll a and turbidity levels, as well as concentrations of total phosphorus and total nitrogen increased. The magnitude of this increase depended on fish species and was severest in the carp treatment. Mosquitofish did not significantly affect water quality. In the treatments with fish, cyclopo…

Long-Term Phytoplankton Dynamics in a Complex Temporal Realm

AbstractFaced with an environment of accelerated change, the long-term dynamics of biotic communities can be approached to build a consistent and causal picture of the communities’ life. We have undertaken a 25-year monthly-sampling study on the phytoplankton of a meso-oligotrophic lake, paying attention to controlling factors of overall biomass (TB) and taxonomical group biomass (TGBs). Long-term series included decreased trends of TB and TGBs, and multi-scale periodicity. A decadal TB periodicity emerged related to nitrogen concentration and Cryptophytes. Annual periodicities were mainly related to air and water temperature controlling the abundance of Chlorophytes or Dinoflagellates. Int…

Effects of overabundant nitrate and warmer temperatures on charophytes: The roles of plasticity and local adaptation

Global change effects, such as warming and increases in nitrogen loading, alter vulnerable Mediterranean aquatic systems, and charophytes can be one of the most affected groups. We addressed the possible interaction between these factors on two populations of the cosmopolitan charophytes Chara hispida and Chara vulgaris. Populations were taken from two different environments, a nitrate-poor mountain lake and a nitrate-rich Mediterranean coastal spring. The laboratory experiment had a 2 × 2 factorial design based on two nitrate levels (similar to and double the local conditions) and two temperatures. Increased temperatures favoured the growth of the four populations, but an increase in nitra…

Are there steady-state phytoplankton assemblages in the field?

The difficulty in advancing in Ecology is due, in part, to the fact that this science uses a mainly qualitative language instead of a more formal or mathematical one. Therefore, many ecologists' efforts are expended in controversies resulting from the vagueness of ecological concepts, for example: stability, equilibrium, ecosystem, community, and so on. When approaching the study of steady-state phytoplankton assemblage, the different interpretations of these concepts can paralyse fruitful discussion. In the following pages, there is an endeavour to both restrict and precise the meaning of some of the concepts related to this topic and to broaden the range of possibilities of steady-state i…

Factors controlling planktonic size spectral responses to autumnal circulation in a Mediterranean lake

14 pages, and figures, and tables statistics.

Autotrophic and Heterotrophic Picoplankton in Wetlands: Differences with Lake Patterns

This study describes the occurrence, importance and seasonal patterns of picoplankton in two wetlands (TDNP and La Safor), and compares them to a system of fifteen interconnected lakes (Ruidera). In TDNP we performed a six-year monthly study in three sites of the wetland. Bacterial abundance increased throughout time and the autotrophic picoplankton (APP) range was wide (up to 33 x 10 6 cells/ml). The annual averaged APP contribution to total picoplankton and phytoplankton biovolumes was 0.5-22% and 0.03-6% respectively. There were large differences among sites in terms of APP absolute and relative abundance and seasonal patterns. In La Safor, the APP relative contribution to picoplankton a…

Biogeochemical decoupling: how, where and when?

Research has dealt with coupling of chemical element cycles and feedback in recent years. Sometimes, this biogeochemical coupling is reversed through abiotic or biotic (including man-made) processes. It is then called biogeochemical decoupling and is a disconnection between two chemical elements whereby transformations of one affect cycling of the other, and results in asynchronical behavior of chemical elements. It appears to be more important and widespread than earlier reports suggest, and gives rise to important changes in element stoichiometry of resources. These changes in turn modify organismal stoichiometry that, if great enough, can affect biodiversity and food webs, thus altering …

Nitrogen sedimentation in a lake affected by massive nitrogen inputs: autochthonous versus allochthonous effects

12 pages, and tables statics, and figures

Effects of Changing Rainfall on the Limnology of a Mediterranean, Flowthrough-Seepage Chain of Lakes

Relationships between groundwater and lake ecology are often overlooked, but they may be strong, particularly in seepage lakes. As a result, the nature and degree of groundwater effects on lakes are usually neglected. In this study interactions among rainfall, groundwater and surface water and their limnological effects were traced seasonally for two years of changing rainfall in a Spanish flowthrough, seepage lake complex. Cumulative rainfall dictated recharge of groundwater with delays of nine months. Groundwater discharge, in turn, increased surface discharge downstream. Mediated by the geographical setting of lakes, both fluxes impinged on lake water renewal time, but effects of the lat…

Population dynamics of Cyclotella ocellata (Bacillariophyceae): endogenous and exogenous factors

Population dynamics of Cyclotella ocellata PANTOCSEK were examined from 1991 to 1993 in an oligo-mesotrophic, gravel-pit lake near Madrid (Spain). Monthly and daily sampling was carried out to track seasonal- and auxosporulation dynamics, respectively. This species was the most abundant planktonic diatom in the lake. The population increased steadily in spring until the seasonal peak (3.8.10 6 ind/ L in April) and then abundance declined slowly through late winter. Time series techniques showed that the seasonal dynamics were driven by exogenous factors: there was a relationship between Cyclotella abundance and the chemical environment, both TP (synchronic) and SRSi (with delay). Auxosporul…

Chara hispida beds as a sink of nitrogen: Evidence from growth, nitrogen uptake and decomposition

8 pages, and tables stadistics, and figures.

Nitrate uptake rates in freshwater plankton: the effect of food web structure

9 pages, 3 figure, 1 table