Abstract
Planktonic primary production and respiration rates were estimated in a subtropical coastal lake dominated by Cyanobacteria in order to investigate the temporal and vertical variation in this lake and to evaluate its relationships with limnological variables and phytoplankton. Light and dark bottles were incubated at four different depths in the central part of the lake and were performed bimonthly from June/2009 to December/2010. No significant difference was evident among depths in relation to phytoplankton, limnological variables and metabolic rates. However, the highest production rates were recorded at the surface, and decreased towards the bottom, coupled with phytoplanktonic photosynthetic capacity. Wind induced mixing in Peri Lake played an important role in nutrient and phytoplankton redistribution, characterizing this lake as polymictic. According to density and biovolume, the phytoplankton community was dominated by filamentous Cyanobacteria, especially Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba-Raju. This study has shown that both water temperature and nutrient availability drive phytoplankton growth and consequently the temporal variation in metabolic rates, where respiration is higher than primary production.
Highlights
Primary production studies in the tropics and subtropics are scarce, but are essential for understanding energy and nutrient flows
Some Cyanobacteria species are capable of regulating their position in the water column through gas vesicles in order to improve their photosynthetic efficiency (Moura et al, 2011)
Considering the temporal variation the increase in water temperature in December/2009 and February/2010 coincides with the maximal chlorophyll a, the minimal dissolved oxygen concentrations, and the total nitrogen (TN):total phosphorus (TP) ratio (Figure 2)
Summary
Primary production studies in the tropics and subtropics are scarce, but are essential for understanding energy and nutrient flows. Previous studies reveal that high temperature and light availability, in the tropics, favors high planktonic primary production and respiration, which promotes the fastest nutrient cycling, and maintains metabolic rates constant along the time (Berman et al, 1995; Amarasinghe and Vijverberg, 2002). Production and respiration in a subtropical lake. Phytoplankton productivity is sensitive to nutrient, especially phosphorus availability (Tadonléke, 2010; Kerimoglu et al, 2013). Phosphorus enrichment and light availability sustain the pelagic chlorophyll a and primary production, while in oligotrophic lakes phytoplanktonic growth and production are frequently constrained by nutrient limitation (Carpenter et al, 2001; Liboriussen and Jeppesen, 2003)
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