Spatiotemporal Variation on Water Quality and Trophic State of a Tropical Urban Reservoir: A Case Study of the Lake Paranoá-DF, Brazil

Nutrient enrichment and eutrophication are among the main problems that lead to the deterioration of water quality in lakes and reservoirs. In this study, spatial and temporal variations in the concentrations of organic and inorganic species of nitrogen and phosphorus in the water column of Lake Paranoá-DF (Brazil) were evaluated between 2016 and 2017. Seasonality was the main factor in the variations in concentrations of the investigated parameters. Additionally, we found differences in behavior for different nutrients and other variables that indicate different main sources of each nutrient as well as different biogeochemical processes predominating in each season. For example, the electrical conductivity (EC), dissolved silicon, PO43−, and NO3− showed mean concentrations significantly higher in the rainy season, indicating greater inputs in these periods (which is in part related to increasing soil leaching and runoff). Agricultural activities were the main source of NO3− and wastewater treatment plants (WWTP) proved to be the main source of nutrients, mainly NH4+ and all forms of phosphorus. These two allochthonous sources are also the determining factors of the trophic state and the degradation of the water quality of Lake Paranoá. The lake is in the transition process from a mesotrophic to a eutrophic condition.

Sponge contribution to the silicon cycle of a diatom-rich shallow bay

In coastal systems, planktonic and benthic silicifiers compete for the pool of dissolved silicon, a nutrient required to make their skeletons. The contribution of planktonic diatoms to the cycling of silicon in coastal systems is often well characterized, while that of benthic silicifiers such as sponges has rarely been quantified. Herein, silicon fluxes and stocks are quantified for the sponge fauna in the benthic communities of the Bay of Brest (France). A total of 45 siliceous sponge species living in the Bay account for a silicon standing stock of 1215 tons, while that of diatoms is only 27 tons. The silicon reservoir accumulated as sponge skeletons in the superficial sediments of the Bay rises to 1775 tons, while that of diatom skeletons is only 248 tons. These comparatively large stocks of sponge silicon were estimated to cycle two orders of magnitude slower than the diatom stocks. Sponge silicon stocks need years to decades to be renewed, while diatom turnover lasts only days. Although the sponge monitoring over the last 6 years indicates no major changes of the sponge stocks, our results do not allow to conclude if the silicon sponge budget of the Bay is at steady state, and potential scenarios are discussed. The findings buttress the idea that sponges and diatoms play contrasting roles in the marine silicon cycle. The budgets of these silicon major users need to be integrated and their connections revealed, if we aim to reach a full understanding of the silicon cycling in coastal ecosystems.

Phylogenetic and Phenogenetic Diversity of Synechococcus along a Yellow Sea Section Reveal Its Environmental Dependent Distribution and Co-Occurrence Microbial Pattern

Synechococcus is a dominant genus of the coastal phytoplankton with an effective contribution to primary productivity. Here, the phylogenetic and phenogenetic composition of Synechococcus in the coastal Yellow Sea was addressed by sequencing marker gene methods. Meanwhile, its co-occurrence pattern with bacterial and eukaryotic microbes was further investigated based on the construction of networks. The result revealed that Synechococcus abundance ranged from 9.8 × 102 cells mL−1 to 1.6 × 105 cells mL−1, which was significantly correlated to sampling depth and nutrient contents of nitrite, ammonia, and dissolved silicon. A total of eight Synechococcus phylogenetic lineages were detected, of which clade III was dominant in most of the samples. Meanwhile, clade I increased along the water column and even reached a maximum value of 76.13% at 20 m of station B. Phenogenetically, Synechococcus PT3 was always the predominant pigment type across the whole study zone. Only salinity was significantly correlated to the phenogenetic constitution. The networks revealed that Synechococcus co-occurred with 159 prokaryotes, as well as 102 eukaryotes including such possible grazers as Gymnodinium clades and Alveolata. Potential function prediction further showed that microbes co-occurring with Synechococcus were associated with diverse element cycles, but the exact mechanism needed further experimentation to verify. This research promotes exploring regularity in the genomic composition and niche position of Synechococcus in the coastal ecosystem and is significant to further discuss its potential participation in materials circulation and bottom-up effects in microbial food webs.

ZHEZHERYA V.A., ZHEZHERYA T.P., LINNIK P.M. INFLUENCE OF HIGHER AQUATIC VEGETATION ON THE CONTENT OF BIOGENIC ELEMENTS IN LIMNIC SYSTEMS OF AN URBANIZED TERRITORY

There were considered the results of studies of the content of inorganic nitrogen and its compounds, inorganic phosphorus, dissolved silicon and labile iron in the areas of the Verbne and Telbin Lakes, covered with higher aquatic vegetation and free vegetation, as well as with depth. It was found that the content of inorganic nitrogen, ammonium nitrogen, nitrate ions and in some cases inorganic phosphorus was decreased in the thickets of higher aquatic vegetation during the growing season several times compared to areas of the lake without thickets. It was found that higher aquatic vegetation during its growing season reduced the content of inorganic nitrogen in the surface layer of water by 1.1–2.0 times, and inorganic phosphorus in some cases by 1.2–1.5 times, compared with their content in sections free vegetation. The concentration of ammonium nitrogen and nitrate ions in the thickets of higher aquatic vegetation was also 1.1–3.1 and 1.3–2.5 times lower, respectively. From the beginning of the growing season, the concentration of inorganic nitrogen, phosphorus and dissolved silicon in the area of the lake without vegetation was decreased on average from 1.122 to 0.096 mg N/dm3, from 0.250 to 0.075 mg P/dm3 and from 4.1 to 0.31 mg/dm3 and in the coastal area from 1.168 to 0.073 mg N/dm3, from 0.298 to 0.063 mg P/dm3 and from 4.0 to 0.32 mg/dm3 respectively. It was found that the share of nitrate ions in the surface layer of the water of Verbne Lake increased from 9.9% to 68.3% from March to June, and in Telbin Lake nitrate ions dominated, even in March. This was due to the increase in the intensity of the nitrification process. In the first case, this was due to the supply of oxygen during photosynthesis, and in the second case, due to artificial aeration. The effect of higher aquatic vegetation on the content of dissolved silicon and labile iron were not observed. The maximum values content of inorganic nitrogen and phosphorus and dissolved silicon were observed during spring homothermia. Their content in the surface layer of water gradually decreased due to the assimilation of plant organisms with the beginning of the growing season. Direct temperature stratification led to an increase in the content of inorganic nitrogen and phosphorus, dissolved silicon and labile iron in the bottom layer of water due to their inflow from bottom sediments, especially in the absence of dissolved oxygen.