Food webs of streams draining tropical rain forests on Costa Rica's Pacific and Caribbean coasts were examined in the 1980s via dietary analyses, and the same streams were surveyed again in 2004 to compare trophic structure based on analysis of stable isotope ratios of fish, macro-invertebrate and plant tissues. Estimates of species’ trophic positions (TP) were calculated from stomach-contents data (51 species; 5420 specimens) and compared with TP estimates derived from analysis of nitrogen isotope ratios (82 taxa; 240 samples). Coefficients of determination for TP based on dietary versus isotopic analysis ranged from 0.18 (Quebrada Camaronal, Corcovado) to 0.73 (Quebrada Estacion, Tortuguero). Consumer taxa within all four streams spanned a broad range of carbon isotope values, indicating assimilation of variable proportions of carbon from periphyton and terrestrial vegetation that in all but one of the streams had similar δ13C values. Approximately half the consumers in all four streams had carbon ratios heavier than any of the in situ production sources examined. This pattern could be explained by consumption of other production sources that were not sampled, including periphyton taxa with variable carbon isotope signatures, or migration of prey and/or consumers between these freshwater and coastal marine habitats.

Resource availability influences the flow of energy through food webs, thus affecting biomass and trophic structure of consumer communities. To assess the effect of availability of allochthonous (leaf litter) and autochthonous (periphyton) resources on the trophic structure of macroinvertebrates, we sampled monthly for a year two sites (upstream forested, downstream open canopy) of Challhuaco, a low order mountain stream in the Patagonian Andes. Leaf litter and periphyton dynamics showed the expected pattern, peaking in autumn and spring, respectively. Temporal variations of shredders and scrapers were synchronized, with the logic delay, with resource abundance. Although leaf litter mass was similar at both stream reaches, shredders were more abundant at the forest site. Periphyton biomass was higher at the forest, while scrapers were more abundant at the open site. The patterns of resource and consumer abundance, and community functional structure were mostly explained by the interaction of abiotic factors and trophic relationships.

The farmers of the Apatani tribe in Arunachal Pradesh, India have been raising a concurrent crop of fish successfully in their mountain valley rice plots for the past 40 years. They follow indigenous rice agronomy, ignoring the use of fertilizers, pesticides and even supplementary feed for the fish reared in the system. However, the yield levels of fish, ranging from 250 to 500 kg ha−1season−1, clearly support the role of other available resources within their wet rice fields. The investigation revealed that the rice itself provided the substrates for colonization and growth of periphyton. The colonized periphytic contents (1406–13513 no. cm−2 stem−1) on rice stems and other natural fish feeds within the system seem to have direct effect in this regard. The Apatani technique of rice–fish integration may be considered as one of the periphyton-based aquaculture (PBA) systems which deserve further research attention.

During 2001 - 2002, we studied periphytic biomass at 5 sites along the Agüera stream (Northern Iberian Peninsula), and comparedthe results to those from two previous researches (1990 - 1991 and 1992 - 1993). Sampling sites showed large differencesin cover, conductivity and nutrient contents, as well as some inter-annual differences, resulting from changes in discharge andin human activities. Most environmental variables showed low seasonality, main variations being produced by floods. Solarradiation changed little during 2001 - 2002, because of the coincidence of a sunny winter followed by a cloudy summer, andseasonal differences in riparian cover resulted in more sunlight reaching the streambed of closed sites during winter, and smalldifferences at the open ones. The growth and abscission of riparian leaves results in a strong light regime at the closed sites, withmore sunlight during winter, but this pattern changes from year to year, depending on the weather. Spatial differences and highestvalues of periphytic biomass were much lower than those measured in 1990 - 91, because of contrasting weather patterns.Variables controlling periphytic biomass in the Agüera change from reach to reach. At open sites flow is the main temporalcontroller, whereas at closed sites the effects of light availability prevail, thus giving more similar seasonal patterns from yearto year. Nutrients seem to play a minor role in temporal variations.

The biomass and the biochemical composition of periphyton were studied during one year in three streams of Réunion Island. The results revealed that nutritional conditions for fish development were most favourable during the dry season. The nutritive value of periphyton was highest in the Marsouins and Mât streams and remained the lowest in the Roches stream. Food availability was strongly affected by high flow, particularly during the exceptional hydrological events of February 1998 (cyclonic high flows). Study of seasonal variations of morphophysiological characteristics and biochemical composition (lipids, proteins) of the grazer gobiidae Sicyopterus lagocephalus showed that inspite of unfavourable nutritional conditions caused by hydrological disturbances, fish continue their reproduction which coincides with the summer high flow period. The significant depletion of lipid reserves which express a deterioration in animal condition is influenced by flooding period. At this time of gonad development involving an additional energy investment, fish were not able to recover a stable nutritional state after the complete achievement of the reproduction cycle. Except during this period, there is a weak participation of the reproductive physiological processes in the seasonal changes of somatic composition of this fish.

As a first step in assessing the viability of periphyton-based fish production in South Asian pond aquaculture systems, the effects of artificial substrates on development of periphyton and on water quality were evaluated. Earthen ponds (10 × 7.5 m) were provided with an artificial substrate constructed from poles of either bamboo, kanchi or hizol tree branches (1.0 m2 artificial substrate per m2 pond surface). Higher periphyton biomass, in terms of dry matter (DM) (4.9 mg cm–2) and chlorophyll a (11.5 μg cm–2) developed on hizol and bamboo, respectively. Periphyton ash content was higher on hizol (41%) than on the other two substrate types (29%). Protein content of the periphyton growing on bamboo (38% of ash-free dry matter (AFDM)) was 50% higher than that on the other two substrate types. Maximum periphyton productivities of 1.01, 1.38 and 1.03 g C m–2 d–1 were obtained for bamboo, hizol and kanchi substrates, respectively. Taxonomic composition of periphyton showed a rapid development of a relatively stable community with few differences between the substrate types. In total, 56 genera of algal periphyton and 35 genera of phytoplankton were identified. Based on a periphyton productivity estimate of 2.2–2.8 g AFDM m–2 d–1, periphyton alone can sustain an estimated fish production of 5000 kg ha–1 year–1 through the addition of a substrate area equivalent to 100% of the pond surface area.

In running water, the main natural factor of disturbance is hydraulic. Investigation of its biological impact is currently complicated by the increase of anthropogenic disturbances which tend to mask the natural functioning of rivers. Monitoring of the impacts of the artificial alterations undergone by the Middle Rhone River for some decades took place in the mid-1980s. Discharge and temperature could constitute the major events controlling the biological dynamics in terms of variations in species richness, diversity, and abundance. The between-years changes of the structure and diversity of macroinvertebrate communities were connected with the amplitude of discharge fluctuations. This was in accordance with the disturbance-diversity concept and it seems to confirm the intermediate disturbance hypothesis. The fish community mainly depended on hydroclimatic factors that influenced breeding success. Variations in nutrient input played a secondary role in controlling changes in some communities (particularly the periphyton). Therefore it appears that the study of long-term changes in river systems, including the dynamics of their biological communities, requires continuous observations and data collection that only medium- to long-term studies can provide, implying the setting up of ecological monitoring centres for the natural environment such as the Long Term Ecological Research (LTER) sites in United.

One of the agro-environmental characteristics of Brittany is the extensive use of pesticides, which leads to high concentrations of atrazine in continental water systems. Periphytic algae play a basic part in aquatic ecosystems and some of them, diatoms, are highly sensitive to environmental changes. Analyses of diatoms can thus indicate the impact of a herbicide on aquatic systems. We compared the effects of two herbicides (atrazine and nicosulfuron) on an aquatic ecosystem in 1998. This study was conducted in 15 identical ponds, each containing a holder for installing artificial substrates. The periphytic diatoms were analysed for cell density, biomass, species diversity and morphology. The general specific diversity was poor, and the diatom community was essentially dominated by Achnanthidium minutissimum. The first results showed a strong similarity between the different categories of mesocosms. Chlorophyll a concentration only seems to be affected by high herbicide concentrations.

The seasonal colonization and vertical zonation of adpressed and upright algae on Phragmites stems in Lake Belau, Germany, was investigated from November 1988 to October 1991. During the autumns and winters from 1988 to 1990 the dominant adpressed species included the diatoms Epithemia adnata, E. sorex, E. turgida and Rhopalodia gibba, while during the same seasons in 1990 and 1991, Cocconeis placentula var. euglypta was abundant. The upright diatoms were most abundant on the middle sections of the stems, whereas those epiphytes with most of their cell surfaces directly in contact with the substratum constituted the greatest part of the biomass on the lowest sections of the stems. Epithemia spp. and R. gibba attained their highest abundances near the sediment as well as buried beneath the most dense periphyton aggregations, while there were dense populations of C. placentula var. euglypta on the entire surface of the stems. Cocconeis is able to tolerate higher light intensities, with photosynthetically active radiation (PAR) values averaging 38 μmol m−2 s−1, than Epithemia and Rhopalodia, which settle at a significantly lower PAR (26 and 20 μmol m−2 s−1, respectively). The change in dominance among the adpressed species from Epithemia and Rhopalodia to Cocconeis can be explained by changes in the grazing habits of the snail Acroloxus lacustris.

Une série d'expérimentations a été réalisée afin de mesurer l'activité dénitrifiante liée aux biodermes périphytiquesse développant sur le lit de la Garonne. Cette activité et la production au sein des biodermes ont été mesurées in vitrodans des chambres photo-respiratoires.La dénitrification a été évaluée par l'accumulation de protoxyde d'azote (N2O) après l'inhibition de sa réduction parl'acétylène. Le N2O produit a été mesuré sur un chromatographe en phase gazeuse à détecteur à capture d'électrons.L'état du bioderme est caractérisé par les paramètres de biomasse, de pigments chlorophylliens et d'activité photosynthétiqueet respiratoire. La production de N2O liée aux biodermes est immédiate et linéaire. En présence de l'acétylèneet à l'obcurité, le taux horaire moyen de dénitrification atteint des valeurs de 423 µg N. g-1 M.O. h-1 dans les chambresanaérobies contre 203 µg N. g-1 M.O. h-1 dans les chambres aérées (7 mg O2 l-1). L'activité dénitrifiante est inhibée à99 % à la lumière et, en présence de l'acétylène, son taux ne dépasse guère 1 µg N. g-1 M.O. h-1.Les taux mesurés dans nos chambres photo-respiratoires, dans les conditions de température et d'éléments nutritifsproches de celles du fleuve, sont très élevés par rapport aux valeurs citées dans la littérature. Ils témoignent de l'importantecontribution qu'apportent les biodermes au processus de dénitrification et, par conséquent, à la réduction de lacharge en nitrates de l'eau de la Garonne.

La dynamique de croissance du périphyton sur des substrats artificiels immergés à l'amont et à l'aval de secteurs de cours d'eau recevant des rejets polluants a été utilisée pour évaluer le niveau de pollution. La méthode est basée sur la détermination de paramètres globaux (matières organiques, pigments chlorophylliens, respiration, photosynthèse, assimilation hétérotrophe) qui permettent de caractériser le développement des communautés photoautotrophes et hétérotrophes sur les substrats. Le taux de croissance et l'activité hétérotrophe de ces communautés évoluent au cours de la durée d'immersion des substrats selon un modèle général qui est décrit à partir de séries de données recueillies sur trois cours d'eau. Les résultats obtenus sur 22 stations montrent que ces paramètres constituent des indicateurs de pollution plus sensibles que ceux basés sur la composition spécifique des communautés de périphyton.