Search results for "plank"
showing 10 items of 578 documents
Combination of linear and nonlinear multivariate approaches effectively uncover responses of phytoplankton communities to environmental changes at re…
2022
The response of a community to environmental changes is either linear or non-linear, so that they can be investigated approximately by linear or nonlinear models. At community level, redundancy analysis (RDA) and canonical correspondence analysis (CCA), and Mantel test and Generalized Dissimilarity Modelling (GDM) are two pairs of fundamental multivariate approaches. Thus, it is necessary to determine how they are used for a given group of communities or a metacommunity. In the present study, we explored the applications of the two pairs of commonly used multivariate methods for the analysis of tropical phytoplankton communities. Phytoplankton were collected from 60 tropical reservoirs in s…
Long-term phytoplankton changes in a shallow hypertrophic lake, Albufera of Valencia (Spain)
1994
A long-term phytoplankton study was carried out in the Albufera of Valencia, a shallow hypertrophic lake (surface area 21 km2, mean depth 1 m, total inorganic nitrogen load 155 g m-2 y-1, total inorganic phosphate load 15 g m-2 y-1) from 1980 to 1988. The lake functions as a reservoir for the surrounding rice cultivation. From 1940's to 1988, its phytoplankton assemblage has been altered from a mesotrophic to a hypertrophic character, as consequence of the increasing pollution. For 1980–88, annual variations in the phytoplankton were less pronounced than seasonal changes. The hypertrophic and morphometric features of the lake favoured the stability of the phytoplankton assemblage and chloro…
Iron as a source of color in river waters.
2015
Organic chromophores of total organic carbon (TOC) and those of iron (Fe) contribute to the color of water, but the relative contributions of colored organic carbon (COC%) and Fe (Fe%) are poorly known. In this study, we unraveled Fe% and COC% in 6128 unfiltered water samples collected from 94 Finnish river sites of contrasting catchment properties. According to regression analysis focusing on TOC alone, on average 84% of the mean TOC consisted of COC, while 16% was non-colored or below the color-detection limit. COC and Fe were much more important sources of color than phytoplankton (chlorophyll a as a proxy) or non-algal particles (suspended solids as a proxy). When COC and Fe were consid…
The use of zooplankton metrics to determine the trophic status and ecological potential: An approach in a large Mediterranean watershed.
2021
In the European Water Framework Directive, zooplankton was not included as a Biological Quality Element despite its important place in the aquatic trophic web. In the present study on zooplankton abundances and biomasses, we used several metrics to test their ability to detect differences among trophic statuses and ecological potential levels, and collected a large sum of data in more than 60 reservoirs at Ebro watershed, on more than 300 sampling occasions over 10 years. Our results indicate that most zooplankton metrics are correlated to environmental variables that determine reservoirs’ trophic states, especially chlorophyll a and total phosphorus. The metrics with better sensitivity to …
Periphyton growth and diatom community structure in a cooling water pond
1982
Periphyton (Aufwuchs) accumulation was measured on artificial substrates in a pond in central Finland which receives warm cooling-water effluent from a power plant. The growth of periphyton was generally more rapid on the substrates during the first two weeks of colonization near the inflow of the warm water effluent than in the middle of the pond. The maximum accumulation of periphyton was in spring and autumn (dry weight maximum at warm effluent was in spring 3.5 mg DW cm−2,2.65 mg AFDW cm−2; chlorophyll a maximum 3.96 µg cm−2 was found in autumn at pond-middle station). During mid-winter months the growth was strongly limited by solar radiation, but the growth was also slow at both stati…
Phytoplankton primary production in a eutrophic cooling water pond
1984
The seasonal variation of phytoplankton photosynthesis was measured with 14C-method in a warmed ice-free pond in central Finland. Simultaneously with in situ measurements the photosynthesis was also measured in an incubator with different water temperatures and constant light (ca. 16 W m−2). The total annual photosynthesis was 57.2 C m−2 a−1. The portion of the winter and spring production of the annual photosynthesis was 18.4%, that of the autumn production ws 17.4%. Thus 64.3% of the total annual phytoplankton photosynthesis occurred in the three summer months. The range of the daily integrated photosynthesis per unit area was 1.9—563 mg C m−2d−1. The photosynthetic rate per unit chloroph…
How diffusivity, thermocline and incident light intensity modulate the dynamics of Deep Chlorophyll Maximum in Tyrrhenian Sea
2015
During the last few years theoretical works have shed new light and proposed new hypotheses on the mechanisms which regulate the spatio-temporal behaviour of phytoplankton communities in marine pelagic ecosystems. Despite this, relevant physical and biological issues, such as effects of the time- dependent mixing in the upper layer, competition between groups, and dynamics of non-stationary deep chlorophyll maxima, are still open questions. In this work, we analyze the spatio-temporal behaviour of five phytoplankton populations in a real marine ecosystem by using a one-dimensional reaction-diffusion-taxis model. The study is performed, taking into account the seasonal variations of environm…
Spatio-temporal dynamics of a planktonic system and chlorophyll distribution in a 2D spatial domain: matching model and data
2017
AbstractField data on chlorophyll distribution are investigated in a two-dimensional spatial domain of the Mediterranean Sea by using for phytoplankton abundances an advection-diffusion-reaction model, which includes real values for physical and biological variables. The study exploits indeed hydrological and nutrients data acquired in situ, and includes intraspecific competition for limiting factors, i.e. light intensity and phosphate concentration. As a result, the model allows to analyze how both the velocity field of marine currents and the two components of turbulent diffusivity affect the spatial distributions of phytoplankton abundances in the Modified Atlantic Water, the upper layer…
Dynamics of Two Picophytoplankton Groups in Mediterranean Sea: Analysis of the Deep Chlorophyll Maximum by a Stochastic Advection-Reaction-Diffusion …
2013
A stochastic advection-reaction-diffusion model with terms of multiplicative white Gaussian noise, valid for weakly mixed waters, is studied to obtain the vertical stationary spatial distributions of two groups of picophytoplankton, i.e., picoeukaryotes and Prochlorococcus, which account about for 60% of total chlorophyll on average in Mediterranean Sea. By numerically solving the equations of the model, we analyze the one-dimensional spatio-temporal dynamics of the total picophytoplankton biomass and nutrient concentration along the water column at different depths. In particular, we integrate the equations over a time interval long enough, obtaining the steady spatial distributions for th…
Nitrate uptake rates in freshwater plankton: the effect of food web structure
2008
9 pages, 3 figure, 1 table