L. Clemente

Above-ground biomass and species richness in a Mediterranean salt marsh

. Species composition, above-ground biomass and diversity of herbaceous communities were recorded in 50 sites on the upper salt marsh of the Guadalquivir delta (SW Spain). Through Canonical Correspondence Analysis relationships were shown between plant-species characteristics abundance and environmental variables. Seven community types were distinguished and related to hydro logical regime and physical and chemical soil parameters. The higher species richness was associated with moderate values of above-ground biomass (Biomass at maximum diversity, BMD = 302 g/m2). Salinity was negatively correlated with species richness. There was no significant correlation with total above-ground biomass. Water regime and soil nutrient (Ca, Mg) content were significant predictors of the community above-ground biomass.

Recent coastal evolution of the Doñana National Park (SW Spain)

Abstract Since the last Holocene sea level rise, about 6900 BP, a series of depositional littoral landforms has been generated at the outlet of the Guadalquivir River, with progradation along the predominant longshore drift (towards the east). The first coastal progradation occurred between 6900 and 4500 BP. The Donana and (perhaps) La Algaida spits, both associated with the oldest and highest marshland in the Donana National Park, are assumed to have been developed at an early stage. Originally, the Guadalquivir estuary was wider and deeper than now, and its environment was mainly marine. The oldest littoral formations have been dated as ca. 4735 BP. They show erosional events, and indicate the breaking-up of earlier spit-barriers to form inlets. The marine environment became increasingly dominant, with heavy erosion of cliffs and a retreating coastline. This period was followed by another sedimentary cycle (4200-2600 BP) that surrounded the earlier eroded barriers. The size of the estuary decreased due to the increasing marsh deposits, and a fluvial environment was born. About 2600 years ago, progradation gave way to a new period of intense erosion. The resulting morphology of littoral strands and erosional surfaces permitted the return to a marine environment. The shoreline again retreated. From 2300 BP, coastal progradation has prevailed, with an erosional interruption at 1000 BP. The present-day outlet of the Guadalquivir is an estuarine delta of inactive marshland (the Donana National Park), the dominant environment is fluvial.

Late Holocene evolution of the southwestern Doñana National Park (Guadalquivir Estuary, SW Spain): a multivariate approach

Four phases are distinguished in the Late Holocene evolution of the southwestern Donana National Park (SW Spain), based on a multidisciplinary analysis of the sediments present in drill cores. In the oldest phase (>2400–2500 cal. yr BP), a coastal lagoon (the Roman Lacus Ligustinus) was recognized in the central part of this area, partly closed by the Donana spit and limited by fluvial levees. The following phase (∼2400–2200 cal. yr BP) is characterized by high-energy events, which caused the breakthrough of the Donana spit and the creation of new littoral strands in the inner areas. In the third phase (∼2200–2050 cal. yr BP), this new outlet was closed, coinciding with the progradation of the Donana spit. The last phase (∼2050 cal. yr BP–Recent) comprises three periods: (a) an unstable period (∼2050–1950 cal. yr BP), with the deposit of cheniers over the previous levees; (b) an infilling period, with a diminution of the marine influence; and (c) the appearance of temporary ponds between the emerged levees and cheniers.

Seed storage conditions change the germination pattern of clonal growth plants in Mediterranean salt marshes

The effect of salinity level and extended exposure to different salinity and flooding conditions on germination patterns of three salt-marsh clonal growth plants (Juncus subulatus, Scirpus litoralis, and S. maritimus) was studied. Seed exposure to extended flooding and saline conditions significantly affected the outcome of the germination process in a different, though predictable, way for each species, after favorable conditions for germination were restored. Tolerance of the germination process was related to the average salinity level measured during the growth/germination season at sites where established individuals of each species dominated the species cover. No relationship was found between salinity tolerance of the germination process and seed response to extended exposure to flooding and salinity conditions. The salinity response was significantly related to the conditions prevailing in the habitats of the respective species during the unfavorable (nongrowth/nongermination) season. Our results indicate that changes in salinity and hydrology while seeds are dormant affect the outcome of the seed-bank response, even when conditions at germination are identical. Because these environmental-history-dependent responses differentially affect seed germination, seedling density, and probably sexual recruitment in the studied and related species, these influences should be considered for wetland restoration and management.

Helophyte germination in a Mediterranean salt marsh: Gut-passage by ducks changes seed response to salinity

Abstract Question: In seeds which are regularly consumed by waterbirds in the field, how does gut–passage modify their response to salinity gradients? Location: Doñana National Park salt marsh, south-west of Spain. Methods: Seeds of Scirpus litoralis and Scirpus maritimus were collected and force fed to mallards (Anas platyrhynchos). Both the ingested seeds (passage) and non-ingested seeds (controls) were exposed, in germination chambers, to a salinity range similar to that observed in the field (0–32 dS/m). After 30 days, the total percentage germination, the duration of the dormancy period and the germination speed were computed. The response of the different germination parameters to ingestion and salinity was analyzed using generalized lineal models. Recovery tests on seeds that did not germinate in the various treatments and tests of the effect of ingestion on the intrinsic variability in seed response were also performed. Results: An increase in salinity reduced germinability and increased the length of dormancy, while gut passage increased the intrinsic variability of the temporal seed response in both species. In S. litoralis there was a significant interaction between the effects of salinity and passage on germination rate. Passage increased germination rate at low salinities (≤2 dS/m) but decreased it at high salinities (≥4 dS/m). Conclusion: Gut-passage by ducks significantly changes seed response to salinity. The outcome of plant-animal interactions can be influenced by environmental gradients. Studies of germination in response to gut passage that do not take such gradients into account may produce misleading results. Abbreviation: GLM = Generalized linear model.