Ireneo Ferrari

Nitrogen cycling networks of coastal ecosystems: influence of trophic status and primary producer form

Abstract We have used ecological network analysis to compare nitrogen cycles from five well-researched coastal ecosystems. These included a representative ricefield and two lagoons (Tancada and Encanysada lagoons) in the Ebro River delta, Spain; a region of the Sacca di Goro, a lagoon at the mouth of the Po River, Italy; and a drowned river estuary in North Carolina, USA, the Neuse River estuary. We constructed networks for the various systems and ranked them by trophic status (i.e., degree of eutrophication) using four indices. We then considered the importance of (1) trophic status, (2) growth form of dominant primary producer and (3) water residence time to the intensity and pattern of recycling and to the manner in which the systems can “filter” N. Three indices of flux (rate of import, primary producivity and total systems throughput) gave similar rankings of trophic status among ecosystems with the Italian and U.S. systems being most eutrophic, ricefields next, and then the two Spanish lagoons. Patterns of N export and of cycling within the systems were most closely related to the growth form of dominant primary producers. Phytoplankton, with their rapid turnover rate, foster rapid recycling within the water column and continuous transfer to sediments and export. Submersed and emergent aquatic vegetation and macroalgae create lags and pulses within systems by sequestering N during growth and releasing it during senescence, death and decomposition. Trends in cycling among systems relative to trophic status or water residence appear largely secondary to primary producer growth form.

Zooplankton variability related to environmental changes in a eutrophic coastal lagoon in the Po Delta

Zooplankton variability in a lagoon of the Po Delta, the Sacca di Goro, was studied in relation to changes in its hydrodynamic and hydrological features. From 1987 to 1992 the lagoon was affected each summer by severe anoxia due to the decomposition of dense and widespread beds of Ulva rigida. In August 1992 a canal was opened through the sand bank closing off the lagoon from the sea in order to improve the water circulation. This hydraulic intervention led to significant environmental changes in the lagoon: during the two subsequent years the summer dystrophic crises were brief and less severe, due to a sharp decrease in the Ulva cover. At the same time a clear increase in phytoplankton biomass values was observed. Following the opening of the channel, the most remarkable change in zooplankton was a significant density increase of calanoids, particularly of Acartia tonsa.

Ecological research on the animal communities of the Po River Delta lagoons

Abstract The main results of research on invertebrate biology and ecology in the lagoons of the Po River Delta (Sacca del Canarin, Sacca di Scardovari, Sacca di Goro) are presented and related to the more significant approaches followed in ecological research during the last two decades. The lagoons, which are intrinsically eutrophic water bodies, have recently undergone intense eutrophication due to the dramatic increase in the Po river nutrient loading. A shift towards a dystrophic state was indicated by the appearance of large Ulva rigida beds in spring and by extensive anoxia during the summer due to the decomposition of the huge macroalgal biomass. Particularly severe dystrophic crises occurred in the Sacca di Goro. Zooplankton and zoobenthos changes were analyzed according to the variations in hydrographic features as well as those in the trophic state of the water. The significance of population dynamics studies in evaluating biological responses to environmental stresses is emphasized. Investigati...

Limnological research on northern Apennine lakes (Italy) in relation to eutrophication and acidification risk

Substantial variability was found in the water chemistry of 22 northern Apennine lakes. In a group of lakes there is evidence of disturbance linked to eutrophication processes. Other lakes showed weak ion concentrations and alkalinity below the acidification risk threshold. However no acidified lakes were found. The lack of waterbodies with severely altered hydrochemistry may explain why no clear relationship between plankton community structure and water chemistry was observed.

Trophic state gradients and zooplankton and zoobenthos distribution in a Po River delta lagoon

Abstract The results of ecological research carried out in the Sacca di Scardovari, a lagoon in the Po River Delta, are reported. Clear gradients of hydrological and sedimentological characteristics from the inner zone of the lagoon to the sea mouth are evidenced. Along the same axis, marked differences in structure of the zooplankton and macrozoobenthos communities are observed. Distribution patterns of these communities are analysed in relation to the hydrodynamic features and to the variations in the main trophic state parameters in the lagoon.

Succession of cladocerans in a northern Italian ricefield

The seasonal succession of cladocerans was studied in an experimental ricefield (never treated with biocides) located on the Po River Plain (Province of Reggio Emilia) in 1982, the first year of rice cultivation, and in two later years, 1984 and 1986. A total of 26 species were identified; some of them were found in Northern Italy for the first time. The finding of Latonopsis australis Sars is discussed in detail. A trend of increasing specific diversity during the rice cultivation season was not recurrent every year. The most significant trends emerge when the three years are compared. The total number of species was 14 in 1982, 16 in 1984, and 20 in 1986. Diversity, too, increased strongly over the years: this trend was sustained chiefly by the increase in richness of Chydoridae species associated with the growth and decomposition of a large biomass of weeds and microalgae during the summer.

A Far East Moina, M. weismanni Ishikawa, 1896 found in an Italian ricefield

The study of heleoplankton samples collected in an experimental ricefield in the province of Reggio Emilia (Northern Italy) evidenced a successional pattern of cladoceran species, characterized by the dominance of Moinidae in the early phase the rice cultivation (from May to July). In particular a species new for Italy, Moina weismanni Ishikawa, 1896, typical of Far East ricefields, was found; it was probably introduced into Italy with seeds and constitutes a stable element of the heleoplankton biocoenosis. The population co-occurs with Moina brachiata, Moina affinis, and Moina micrura in the ricefield. In this short note M. weismanni is described, pointing out the morphological differences with other populations of the same species and with similar species; furthermore, life cycles in Moinidae are analysed in comparison with those of the other dominant cladocerans

Estimation of the production of Daphnia longispina in a mountain lake

Abstract The parameters characterizing the processes of birth, growth, death, reproduction and production of Daphnia longispina in Lake Santo Parmense, a mountain lake in Northern Apennines (Italy), have been estimated for the period lasting from June to the beginning of September 1973: in this period the population is mainly constituted by parthenogenetic females and presents the highest seasonal values of density and biomass. The production of D. longispina has been calculated using the compartmental model proposed by De Bernardi and Di Cola (1976) for the study of the biomass dynamics in populations with continuous recruitment. The trend of death rates of the different size classes and in particular of the classes including newborn individuals has been explained by admitting that the population receives an input of individuals hatched from resting eggs over a long period (till the end of August). The total daily production is supplied mainly by the size classes including preadult individuals, over the ...

Long-term limnological research in a quarry lake of the Po River, Italy

In recent years, many artificiallakes have been constructed in the Po River flood plain and along its triburaries, as a result of sand and gravel quarrying. However, only in a few cases have the public agencies responsible for environmental policies established regulations based on ecological criteria for rhe excavation and reclamation of rhe perifluvial areas. Consequently, most of the newly formed lakes are characterised by unsatisfactory water qualiry (VIAROLI er al. 1996, BoDINI er al. 2000). A limnological study on a quarry lake (Isola Giarola) of rhe flood plain of the Po River was started in 1991. The lake receives periodic flood waters which introduce high nutrient loads. The recovery capacity of the ecosystem following river inflows has been assessed through the analysis of trophic status parameters and the zooplankton communiry seasonal succession patterns over a l 0-year period. This long-term research aims to establish scientifically based guidelines for the construction and management of quarry lakes in rhe Po River basin, with rhe major objectives of ensuring acceptable water qualiry standards and preserving the hydraulic and biological functions of rhese aquatic environments.

Seasonal and diel variations of zooplankton populations in a lagoon of the Po river delta

Abstract Seasonal and diel variations in zooplankton structure were investigated in a small brackish lagoon of the Po river delta, the Sacca del Canarin. Zooplankton samples were collected monthly from 1977 to 1979; samples were also taken over two 24 hour cycles at spring tide, in July 1979 and July 1980. Seasonal variations were examined mainly in relation to the changes in the Po river flow. Short-term variability associated with the tides was studied with the methods of time series analysis. Hydrographic data and zooplankton density data over the two 24 hour sampling cycles were processed in order to evaluate the removal of zooplankton by the tidal currents.