ABSTRACT1. Transitional waters are ecotones between terrestrial, freshwater and marine ecosystems, being characterized by high spatial heterogeneity and temporal variability.2. The EU Water Framework Directive (WFD) posed to the scientific community the challenge to classify these ecosystems into a small number of types, while retaining a functional classification of ecosystem types.3. A niche theory approach is proposed to identify the limiting forcing factors organizing biological quality elements, i.e. the limiting niche dimensions.4. The analysis of a macro-invertebrate dataset from published papers on 36 Italian lagoons suggested a two-level typological classification of Mediterranean lagoons.5. Basic ecological theories, such as niche and island biogeography theories, have fundamental implications for the process of developing a typological classification for all aquatic ecosystems, as required by the WFD.
We studied the variation patterns of Phragmites australis detritus decomposition and derived patterns of field resource availability in three Mediterranean-type sub-basins exposed to varying degrees to summer drought events. The study was carried out during spring-summer 1998 and fall-winter 1998-1999, in 1 st to 4 th order streams. Detritus processing and macroinvertebrate body-condition were measured. Decomposition rates were significantly higher in spring-summer than in fall-winter, in relatively unperturbed than in perturbed sub-basins, and in high-order than low-order streams. The influence of disturbance decreased with increasing stream order, suggesting that higher order streams have greater resilience to drought events than lower order streams. The body condition of macroinvertebrates suggested patterns of field resource availability spatially covariant with those of detritus decay and ecosystem resilience.
Here we analyse in a 5 th order Mediterranean river (River Flumendosa, Sardinia, Italy) spatial and temporal variations of plant detritus processing, a key functional aspect of river ecosystems. Decay rates of dead leaves (Phragmites australis) were studied during the fall-winter and spring-summer seasons at 17 sites distributed among 5 stream orders. Litter decay rates varied more, and were higher in springsummer than in fall-winter. On the spatial scale, patterns of decay rate variation among sites and orders did not vary between seasons; seasonal variation was low in reaches with slow rates and high in reaches with fast rates. Data analysis showed a spatial pattern of increasing reed detritus decay rates with increasing stream order.
Benthic invertebrate communities were sampled in spring and fall, and breakdown of reed litter was measured in winter, spring, summer and fall, at 23 sites in an intermittent Mediterranean river basin (Pula, Sardinia, Italy), and their variations were related to drought frequency and other reach characteristics (altitude, order, stream channel width and depth, vegetation cover, sediment type, organic content, and water quality). 78% of the sites were affected by drought events, mainly in summer and fall. Benthic taxonomic richness was higher and most taxa were more widely distributed in spring than in fall. Canonical correspondence analysis showed that measured environmental variables accounted for 72% of the variance in invertebrate community structure. Reed decay rates varied among seasons, and during the dry season among stream orders as well. Drought events slowed down breakdown and explained 44% of spatial variability in decay rates (Stepwise multiple regression analysis), an additional 8% being explained by water chemistry. Results suggest that drought events affect ecosystem functioning (litter breakdown) more than structure (invertebrate communities).
Temporal and spatial patterns of Phragmites alrstralis leaf decomposition and the relative influence of summer droughts and abiotic features were studied in a Mediterranean-type river basin, the River Pula. Reed processing rates varied among seasons and sites, being on average significantly faster in the cold seasons (i.e., winterspring) than in the warm seasons (i. e., summer-fall) and in low rather than in high stream order reaches. On the other hand, at sites protected from summer drought events (i. e., wet sites), decay rates were faster in the warm than in the cold season. Along stream order, leaf decay rates were significantly faster at wet sites than at sites suffering from summer droughts. Summer drought events explained 44% of reed decay rate spatial variability, and major water abiotic parameters explained an additional 8%.
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