The role of noise on the steady state distributions of phytoplankton populations

Abstract

Abstract. The spatio-temporal behaviour of total chlorophyll concentration is investigated in the middle of the Tyrrhenian Sea by using a stochastic approach. The study is based on a reaction-diusion-taxis model, which is used to analyse the dynamics of five phytoplankton groups, responsible for about 80% of the total chlorophyll a inside the euphotic zone of the water column. The analysis is performed by considering: (i) the intraspecific competition of the phytoplanktonic groups for limiting factors, i.e. light intensity and nutrient concentration, (ii) the seasonal changes of environmental variables, and (iii) the random fluctuations of the components of the velocity field and temperature. Specifically, we investigate the eects of external perturbations, both deterministic and random, on the dynamics of phytoplankton populations, by inserting a term of multiplicative noise into the dierential equation of the nutrient dynamics. the chi-square test, show that the vertical distributions of total chlorophyll concentration are in a good agreement with the experimental data. Finally, we observe that the high intensity of environmental noise strongly modifies the steady spatial distributions of two phytoplankton groups usually localized in deeper layers, causing algal blooms in surface water.

HR3DHG version 1: modelling the spatio-temporal dynamics of mercury in the Augusta Bay (southern Italy)

“…For this purpose, we incorporated the Phytoplankton MERLIN-Expo model (Pickhardt and Fischer, 2007;Radomyski and Ciffroy, 2015) to describe the mechanism of mercury uptake in 470 phytoplankton cells. Moreover, we reproduced the spatio-temporal dynamics of phytoplankton communities in seawater using a Nutrient-Phytoplankton model (Dutkiewicz et al, 2009;Morozov et al, 2010;Valenti et al, 2012;Denaro et al, 2013a, c, b;Valenti et al, 2015Valenti et al, , 2016aValenti et al, , b, c, 2017 and Hg fluxes at the boundaries of the 3D domain. The former is useful to locate the most polluted areas within the investigated basin.…”

“…In the HR3DHG model, the mercury exchange between the abiotic and biotic compartments is also taken into account. For this purpose, the spatio-temporal behavior of eukaryotes abundance is reproduced using the Nutrient-Phytoplankton (NP) 90 model (Dutkiewicz et al, 2009;Morozov et al, 2010;Valenti et al, 2012;Denaro et al, 2013a, c, b;Valenti et al, 2015Valenti et al, , 2016aValenti et al, , b, c, 2017, while the amount of Hg absorbed and released by each eukaryotic cell in seawater is calculated by using the The photochemical and biological redox transformations between Hg 0 and Hg II have been described as reaction terms with a first-order kinetic (Batrakova et al, 2014;Zhang et al, 2014;Melaku Canu et al, 2015). In particular, the rate constants of photochemical redox reactions are directly proportional to the short-wave radiation flux at sea surface then attenuated along the water column due to the dissolved organic carbon (DOC) and suspended particulate matter (SP M ) (Han et al, 2007;Zhang et al, 2014).…”

“…Finally, the biogeochemical models introduced in previous publications included neither the Nutrient-Phytoplankton model (Dutkiewicz et al, 2009;Morozov et al, 2010;Valenti et al, 2012;Denaro et al, 2013a, c, b;Valenti et al, 2015Valenti et al, , 2016aValenti et al, , b, c, 2017 nor the Phytoplankton MERLIN-Expo model for the mercury content in eukaryotes cells (Pickhardt and Fischer, 2007;Radomyski and Ciffroy, 2015).…”

Spatio-temporal dynamics of a planktonic system and chlorophyll distribution in a 2D spatial domain: matching model and data

“…Theoretical models for population dynamics allowed to reproduce the spatio-temporal distributions of phytoplankton groups in a one-dimensional spatial domain by considering the effects of heterogeneity of the limiting factors along the water column 4, 5, 11–19 . On the other side, some authors introduced two- and three-dimensional models 20, 21 , in which the habitat of planktonic groups is considered homogenous for the nutrient and the environmental parameters are fixed constant in the whole ecosystem.…”

“…In particular, these assumptions are connected with the lack of experimental data, whose availability is crucial for the estimation of some environmental variables 16, 18 , such as the light intensity, the velocity field of marine currents, the horizontal and vertical turbulent diffusivities. Moreover, unlike some one-dimensional models 4, 5, 15–18 , the numerical results for phytoplankton abundances are not converted in chlorophyll concentration, and therefore the comparison between theoretical results and experimental data can not be performed. For these reasons, the theoretical chlorophyll concentration obtained by the phytoplankton abundances has been never reproduced in the vertical water plane of the marine ecosystems.…”