Dissolved organic N in shallow tropical lakes and reservoirs: Contribution to total dissolved N and relationships with eutrophication

Abstract

Dissolved organic nitrogen (DON) plays important biogeochemical and ecological roles in aquatic systems. However, little is known about its importance in small tropical lakes and reservoirs. We hypothesized that (a) DON is higher in these systems than dissolved inorganic N (DIN), and that (b) relative contributions of DON and DIN to the total dissolved nitrogen (TDN) pool decrease and increase, respectively, with trophic status. To test these hypotheses, we measured DON and DIN in six lakes and two reservoirs at the Atlantic forest‐Cerrado savanna transition in Southeast Brazil, in the rainy and the dry season. With one exception in each season, all oligo‐ and mesotrophic systems had DON:DIN ratios >1. DON:DIN ratios were negatively correlated with total phosphorus (TP). This pattern was due to high DIN, mainly ammonium, in eutrophic and hypertrophic systems. DON:DIN ratios <1 occurred at TP higher than 103 and 104 µg L−1 in the rainy and dry season, respectively. We found a general dominance of DON in near‐natural lentic systems at the Atlantic forest‐Cerrado savanna transition, which was more pronounced than that reported for other regions. Human alterations to the TDN pool may affect biological communities and ecosystem functioning of these systems.

A Kinetics Model for Predicting Microcystis Growth Based on the Synergistic Effect of Nitrogen and Phosphorus on the Growth of Microcystis densa (Cyanobacteria)

“…These results suggested that the concentration of approximately 8 mg l -1 was the maximum threshold of M. densa for N demand. This concentration was significantly higher than the N concentration in most lakes and reservoirs [35,36], which suggested that M. densa could grow rapidly in most waters and N concentrations in natural waters would not restrict the growth of M. densa.…”

Classic indicators and diel dissolved oxygen versus trend analysis in assessing eutrophication of potable‐water reservoirs

“…"> 2.Major drivers of extensive DO deficits. The metabolism of shallow turbid reservoirs under chronic eutrophication is still poorly known (Cuker et al, 1990), and improved understanding is needed to inform more protective management decisions (e.g., Andrzej et al, 2002; Boëchat et al, 2019; Dadi et al, 2017). Is the extensive anoxia/hypoxia in this system being driven primarily by present system production, and/or allochthonous carbon inputs, and/or past production (sediment consumption), or other factor(s)?…”

Spatio-temporal variability of water quality in Billings Reservoir Central Body - São Paulo, Brazil

“…Other examples of tropical reservoir that are impacted by eutrophication are: Guarapiranga reservoir, in the State of São Paulo -Brazil (Alcantara et al, 2021) and Barra Bonita reservoir, also in the State of São Paulo -Brazil (Watanabe et al, 2015). Also, Boëchat et al (2019) studied six shallow lakes and two reservoirs at the Atlantic forest in Southeastern Brazil and determined hypereutrophic state to lake Rasa and Pampulha Reservoir.…”