Search results for "mass [rho(770)]"
showing 10 items of 416 documents
Solar PAR and UVR modify the community composition and photosynthetic activity of sea ice algae
2015
The effects of increased photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) on species diversity, biomass and photosynthetic activity were studied in fast ice algal communities. The experimental set-up consisted of nine 1.44 m(2) squares with three treatments: untreated with natural snow cover (UNT), snow-free (PAR + UVR) and snow-free ice covered with a UV screen (PAR). The total algal biomass, dominated by diatoms and dinoflagellates, increased in all treatments during the experiment. However, the smaller biomass growth in the top 10-cm layer of the PAR + UVR treatment compared with the PAR treatment indicated the negative effect of UVR. Scrippsiella complex (mainly…
Latitudinal- and local-scale variations in a rocky intertidal interaction web
2015
Natural assemblages are structured by a complex combination of positive and negative interactions, and the relative importance of each interaction can vary across spatial scales. By using a simple interaction web (barnacles-grazers-microphytobenthos) in a rocky intertidal system, we tested the hypothesis that the relative strength of positive and negative interactions would vary as a function of different environmental stress between 2 latitudinal levels and local environmental conditions. We manipulated the cover of barnacles and the presence of limpets at 2 sites in northern and southern Italy and non-destructively examined the response of microphyto - benthos (MPB) (photosynthetic biomas…
Mapping and determinism of soil microbial community distribution across an agricultural landscape.
2015
Article en open access; International audience; Despite the relevance of landscape, regarding the spatial patterning of microbial communities and the relative influence of environmental parameters versus human activities, few investigations have been conducted at this scale. Here, we used a systematic grid to characterize the distribution of soil microbial communities at 278 sites across a monitored agricultural landscape of 13km(2). Molecular microbial biomass was estimated by soil DNA recovery and bacterial diversity by 16S rRNA gene pyrosequencing. Geostatistics provided the first maps of microbial community at this scale and revealed a heterogeneous but spatially structured distribution…
Intake and milk production of goats grazing Sulla forage under different stocking rates
2010
This investigation aimed to individuate the dietary factors affecting the milk urea nitrogen (MUN) concentration in goats grazing herbaceous pasture and, particularly, to verify the relationship linking the diet crude protein (CP) content to MUN. A total of 205 individual observations regarding dietary and milk variables of 37 Girgentana goats involved in two experiments were used. Goats, averaging 154±14 days in milk and 38.1±5.4 kg of live weight, grazed on swards and received 500 g/d of barley meal. Sward biomass, herbage selected by goats and individual milk yield were measured and sampled weekly. The herbage intake and diet digestibility were estimated by the n-alkane method. Milk urea…
Advancing cyanobacteria biomass estimation from hyperspectral observations: Demonstrations with HICO and PRISMA imagery
2021
Retrieval of the phycocyanin concentration (PC), a characteristic pigment of, and proxy for, cyanobacteria biomass, from hyperspectral satellite remote sensing measurements is challenging due to uncertainties in the remote sensing reflectance (?R) resulting from atmospheric correction and instrument radiometric noise. Although several individual algorithms have been proven to capture local variations in cyanobacteria biomass in specific regions, their performance has not been assessed on hyperspectral images from satellite sensors. Our work leverages a machine-learning model, Mixture Density Networks (MDNs), trained on a large (N = 939) dataset of collocated in situ chlorophyll-a concentrat…
Potential for large-bodied zooplankton and dreissenids to alter the productivity and autotrophic structure of lakes.
2014
While limnological studies have emphasized the importance of grazers on algal biomass and primary production in pelagic habitats, few studies have examined their potential role in altering total ecosystem primary production and it's partitioning between pelagic and benthic habitats. We modified an existing ecosystem production model to include biotic feedbacks associated with two groups of large-bodied grazers of phytoplankton (large-bodied zooplankton and dreissenid mussels) and estimated their effects on total ecosystem production (TEP), and the partitioning of TEP between phytoplankton and periphyton (autotrophic structure) across large gradients in lake size and total phosphorus (TP) co…
Comparative study of phytoplankton in an oligotrophic soft water lake under different pH-phosphate ranges
1998
This work reports phytoplankton changes in a shallow, acidic and oligotrophic lake (Loch Rusky, Scotland) from two different periods: one with artificial phosphate fertilization and neutral pH (SRP 3–18 µg l-1, pH 6.6–7.8, 1972–73) and the other with low phosphate and acidic pH values (SRP <1.5 µg l-1, pH 5.6–6.9, 1985–86). Phosphate enhanced markedly total algal biomass and favoured the presence of cyanophytes, especially in the summer epilimnion, while cryptophytes dominated at this time during unfertilized periods. Anabaena sp. peaked during summer and a higher density of Ceratium hirundinella and Peridinium sp. in mid-summer was also observed during the fertilized period. Otherwise, alg…
Effects of eutrophication and organic loading on the occurrence of profundal harpacticoids in a lake in southern Finland.
1992
Harpacticoids made up 19 and 30% of the meiobenthos proper by number and 39 and 55% by biomass at maximum depths and a depth of 20 m, respectively, in Lake Paijanne. Harpacticoids accounted for higher proportions of the total meiobenthos in oligotrophic and unpolluted areas than in polluted areas. Seven species were identified, with Canthocamptus staphylinus confined to semi-lotic areas influenced by organic pollution from a pulp mill. Other species exhibited somewhat different distributions in oligotrophic and mesotrophic areas. Harpacticoid densities were most closely correlated with oxygen content and phytoplankton biomass, and correlations with environmental values were closer at maximu…
Spatial distribution of phytoplankton in the Gulf of Riga during spring and summer stages
1999
Distribution patterns of chlorophyll a, phytoplankton species and biomass were studied in the Gulf of Riga, one of the most eutrophicated areas of the Baltic Sea. Quasi-synoptic measurements were carried out during four seasonal stages (spring bloom 1995, early-summer stage 1994, cyanobacterial bloom 1994, and late summer stage 1993). For each stage, common factor analysis was used to simplify the highly correlated patterns of nutrients, salinity, temperature and the depth of mixed layer. Obtained latent variables were used to explain spatial distribution of phytoplankton. Generally, the distribution of phytoplankton variables followed closely the patterns of nutrient rich fresh water. Duri…
Plant effects on the soil community: A microcosm experiment
1999
Abstract An experiment was carried out in microcosms for testing the hypothesis that a higher level of primary production should maintain a decomposer community with higher biomass and activity. Microcosms with coniferous forest humus and a diverse microbial and faunal community were divided into three sets: (1) control without plants, (2) with birch seedlings in full illumination, and (3) with birch seedlings, shaded to reduce the net primary production. During 16 weeks of incubation at +16 °C, no treatment effects were found in numbers or biomass of taxonomic or functional groups of soil organisms, nor in the system respiration in darkness. The community structure of the shaded systems di…