Is it possible to derive accurately Total Suspended Matter concentration or its proxy, turbidity, from remote sensing data in tropical coastal lagoon waters? To investigate this question, hyperspectral remote sensing reflectance, turbidity and chlorophyll pigment concentration were measured in three coral reef lagoons. The three sites enabled us to get data over very diverse environments: oligotrophic and sediment-poor waters in the southwest lagoon of New Caledonia, eutrophic waters in the Cienfuegos Bay (Cuba), and sediment-rich waters in the Laucala Bay (Fiji). In this paper, optical algorithms for turbidity are presented per site based on 113 stations in New Caledonia, 24 stations in Cuba and 56 stations in Fiji. Empirical algorithms are tested at satellite wavebands useful to coastal applications. Global algorithms are also derived for the merged data set (193 stations). The performances of global and local regression algorithms are compared. The best one-band algorithms on all the measurements are obtained at 681 nm using either a polynomial or a power model. The best two-band algorithms are obtained with R412/R620, R443/R670 and R510/R681. Two three-band algorithms based on Rrs620.Rrs681/Rrs412 and Rrs620.Rrs681/Rrs510 also give fair regression statistics. Finally, we propose a global algorithm based on one or three bands: turbidity is first calculated from Rrs681 and then, if < 1 FTU, it is recalculated using an algorithm based on Rrs620.Rrs681/Rrs412. On our data set, this algorithm is suitable for the 0.2-25 FTU turbidity range and for the three sites sampled (mean bias: 3.6 %, rms: 35%, mean quadratic error: 1.4 FTU). This shows that defining global empirical turbidity algorithms in tropical coastal waters is at reach.
The aim of this work was to analyze hydrological condition variations in Cienfuegos' Bay in 2011 and its possible influence in life cycle and distribution of the green mussel Perna viridis. The hydrological parameters in the bay are described according to the campaigns performed in February, May and November. Samples from two levels (surface and bottom) were taken, in order to get water temperature, salinity and dissolved oxygen. The results show the climatic seasonality influence (dry and rain) both in spatial as well as in vertical distribution of the observed parameters. The mean concentrations of the analyzed hydrological markers were in agreement with the NC 25: 1999 requirements of good quality water for fishing use. The observed hydrological variability allows the growth and development of the green mussel in Cienfuegos Bay waters.
An important consequence of eutrophication is the increased prevalence of harmful algal blooms that affect transitional and coastal waters, and ecosystems in open seas. In this work, data on phytoplankton biomass, presence of harmful/toxic algal blooms and bottom dissolved oxygen were analyzed as indicators of overall eutrophic condition in the Cienfuegos Bay, Cuba. Samples were collected every three months during the year 2009 at fifteen representative stations within the bay. In the dry and early rainy seasons, high chlorophyll a values, harmful/toxic dinoflagellate blooms and fish mortality episodes were encountered within riverine-urban wastewater discharge zones, whilst most part of the bay did not evidence symptoms of eutrophication. During the rainy season, some stations showed biological stress-hypoxia for the bottom water oxygen, and a strong increase in spatial dispersion was observed in the phytoplankton biomass, due to a substantial increment in not toxic diatom abundance, resulting in a moderate level of eutrophic conditions for chlorophyll a in the entire bay. The key factor that supports the seasonal variation in phytoplankton composition and abundance appears to be the water residence time inside the bay.
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