Meteorological drivers and ENSO influence on phytoplankton biomass dynamics in a shallow subtropical lake.

Meteorological features influence the dynamics of aquatic ecosystems and consequently their biotas. This study aimed to identify the meteorological drivers of phytoplankton biomass (chlorophyll a), sampled seasonally over a period of 12 years (2001-2013) in Lake Mangueira, a large shallow subtropical lake in southern Brazil. The lake is 90 km long and 3-10 km wide with a mean depth of 3 m and is oligo-mesotrophic and highly affected by wind action. In general, non-parametric multiplicative regression analysis identified wind direction, radiation, and the Oceanic Niño Index as the main drivers of variation in chlorophyll a. Notably, ENSO periods caused changes in physical, chemical, and meteorological parameters, including conductivity, total suspended solids, total and dissolved nitrogen, alkalinity, soluble reactive silica, wind speed, and precipitation. Phytoplankton biomass showed significant differences between ENSO periods and the periods without events, occurring in the highest values during La Niña years. This study showed that meteorological variables can significantly influence productivity patterns, indicating the importance of including them in limnological studies.

Southern coastal subtropical shallow lakes skin temperature driven by climatic and non-climatic factors.

Subtropical coastal shallow lakes (SCSL) are sensitive ecosystems. The lake-skin-water temperature (LSWT) is an average lake temperature proxy and responds to changes in surroundings, affecting biological and physical lake processes. In this study, M*D11A1 products are used to develop daytime and nighttime LSWT time series for 20 SCSL in South America. The influence of climatic (air temperature, surface net solar radiation, wind speed, and wind direction) and non-climatic (latitude, lake area, perimeter, width, length, and morphology) factors are evaluated from 2001 to 2017. Pearson's coefficients (ρ) and auto- and cross-correlations are used to establish the relation between LWST and the selected factors. We identify that the dynamic of LSWT is sensitive to geomorphological factors (latitude and lake width) throughout the year, especially in summer. In winter, the LSTW regime is mainly affected by wind direction (ρ = -0.66, p value < 0.01). Linear models are fitted to the temperature series to check the trend changes in the inflection points and the warming or cooling trend for LSWT. Considering the complete series, the maximum warming rate of LSWT is 0.25 °C per decade (°C/dec). The analysis of the identified sub-periods reveals that warming and cooling can occur (significantly) in shorter periods. The average trends within sub-periods for skin temperature-daytime (± 0.0105 °C/dec), skin temperature-nighttime (0.0041 °C/dec), and air temperature (- s0.006 °C/dec; 0.007 °C/dec) are estimated. Our approach has the potential to be applied in future studies due to the expansion of knowledge about the behavior of SCSL and the understanding of the current and potential effects of climate change in association with physical and geomorphological traits.

Biological index based on epiphytic diatom assemblages is more restrictive than the physicochemical index in water assessment on an Amazon floodplain, Brazil.

Canadian Water Quality Index (CWQI) provides protection for freshwater life promoting healthy ecosystems and safeguarding human health. Biological Diatom Index (BDI) was developed to indicate the ecological status and water quality of freshwater systems. This paper evaluates the relations between the two different indices. During rising and falling, water samples were taken in the Curuai Floodplain, Brazil. CWQI was calculated using 14 physicochemical parameters and 1 microbiological parameter. The limits were established according to freshwater quality conditions and standards based on water use classes 1 and 2 determined in CONAMA 357 legislation and British Columbia. Canadian Water Quality Index categorization ranged from "marginal" to "excellent," most sampling units were "good" (71%), followed by "fair" (12%) and "excellent" (12%) water quality. Total phosphorus (38 times), chlorophyll a (20), dissolved oxygen (10), and total organic carbon (10) were the parameters that presented the most non-compliance values. Encyonema silesiacum (14%), Gomphonema parvulum (13%), and Navicula cryptotenella (12%) were the main taxa in the rising period, while G. lagenula, E. silesiacum, and Fragilaria capucina were the main taxa during the falling period. BDI ranges from I to V water quality classes. We observed "poor" to "very good" ecological status, with most sampling units "moderate" (52%) and "good" (29%). Water quality for class 2 was better than water quality for class 1, as the limits of the parameters evaluated were more restrictive in class 1 than in class 2 and the predominant uses of water require a higher degree of water purity. The biological index based on diatoms was the most restrictive index whose water classes and categorizations have shown an ecological status that could threaten the protection of aquatic communities on the Curuai floodplain. We suggest the combined use of both indices-physicochemical and biological for water quality assessment in this type of environment.

Correction: Spatial heterogeneity and hydrological fluctuations drive bacterioplankton community composition in an Amazon floodplain system.

[This corrects the article DOI: 10.1371/journal.pone.0220695.].

Spatial heterogeneity and hydrological fluctuations drive bacterioplankton community composition in an Amazon floodplain system.

Amazonian floodplains form complex hydrological networks that play relevant roles in global biogeochemical cycles, and bacterial degradation of the organic matter in these systems is key for regional carbon budget. The Amazon undergoes extreme seasonal variations in water level, which produces changes in landscape and diversifies sources of organic inputs into floodplain systems. Although these changes should affect bacterioplankton community composition (BCC), little is known about which factors drive spatial and temporal patterns of bacterioplankton in these Amazonian floodplains. We used high-throughput sequencing (Illumina MiSeq) of the V3-V4 region of the 16S rRNA gene to investigate spatial and temporal patterns of BCC of two size fractions, and their correlation with environmental variables in an Amazon floodplain lake (Lago Grande do Curuai). We found a high degree of novelty in bacterioplankton, as more than half of operational taxonomic units (OTUs) could not be classified at genus level. Spatial habitat heterogeneity and the flood pulse were the main factors shaping free-living (FL) BCC. The gradient of organic matter from transition zone-lake-Amazon River was the main driver for particle-attached (PA) BCC. The BCC reflected the complexity of the system, with more variation in space than in time, although both factors were important drivers of the BCC in this Amazon floodplain system.

Development of temporary subtropical wetlands induces higher gas production.

Temporary wetlands are short-term alternative ecosystems formed by flooding for irrigation of areas used for rice farming. The goal of this study is to describe the development cycle of rice fields as temporary wetlands in southern Brazil, evaluating how this process affect the gas production (CH4 and CO2) in soil with difference % carbon and organic matter content. Two areas adjacent to Lake Mangueira in southern Brazil were used during a rice-farming cycle. One area had soil containing 1.1% carbon and 2.4% organic matter, and the second area had soil with 2.4% carbon and 4.4% organic matter. The mean rates of gas production were 0.04 ± 0.02 mg CH4 m(-2) d(-1) and 1.18 ± 0.30 mg CO2 m(-2) d(-1) in the soil area with the lower carbon content, and 0.02 ± 0.03 mg CH4 m(-2) d(-1) and 1.38 ± 0.41 mg CO2 m(-2) d(-1) in the soil area with higher carbon content. Our results showed that mean rates of CO2 production were higher than those of CH4 in both areas. No statistically significant difference was observed for production of CH4 considering different periods and sites. For carbon dioxide (CO2), however, a Two-Way ANOVA showed statistically significant difference (p = 0.05) considering sampling time, but no difference between areas. The results obtained suggest that the carbon and organic matter contents in the soil of irrigated rice cultivation areas may have been used in different ways by soil microorganisms, leading to variations in CH4 and CO2 production.

Lower respiration in the littoral zone of a subtropical shallow lake.

Macrophytes are important sources of dissolved organic carbon (DOC) to littoral zones of lakes, but this DOC is believed to be mostly refractory to bacteria, leading to the hypothesis that bacterial metabolism is different in littoral and pelagic zones of a large subtropical shallow lake. We tested this hypothesis by three approaches: (I) dissolved inorganic carbon (DIC) accumulation in littoral and pelagic water; (II) O(2) consumption estimate for a cloud of points (n = 47) covering the entire lake; (III) measurement of O(2) consumption and CO(2) accumulation in dark bottles, pCO(2) in the water, lake-atmosphere fluxes of CO(2) (fCO(2)) and a large set of limnological variables at 19 sampling points (littoral and pelagic zones) during seven extensive campaigns. For the first two approaches, DIC and O(2) consumption were consistently lower in the littoral zone, and O(2) consumption increased marginally with the distance to the nearest shore. For the third approach, we found in the littoral zone consistently lower DOC, total phosphorus (TP), and chlorophyll a, and a higher proportion of low-molecular-weight substances. Regression trees confirmed that high respiration (O(2) consumption and CO(2) production) was associated to lower concentration of low-molecular-weight substances, while pCO(2) was associated to DOC and TP, confirming that CO(2) supersaturation occurs in an attempt to balance phosphorus deficiency of macrophyte substrates. Littoral zone fCO(2) showed a tendency to be a CO(2) sink, whereas the pelagic zone showed a tendency to act as CO(2) source to the atmosphere. The high proportion of low-molecular-weight, unreactive substances, together with lower DOC and TP may impose lower rates of respiration in littoral zones. This effect of perennial stands of macrophytes may therefore have important, but not yet quantified implications for the global carbon metabolism of these lakes, but other issues still need to be carefully addressed before rejecting the general belief that macrophytes are always beneficial to bacteria.

Genotoxicity and toxicity assessment in urban hydrographic basins.

The genotoxicity and cytotoxicity of water in small urban basins was evaluated by the Salmonella/microsome assay and micronucleus test in V79 cells. The results showed that the cytotoxic effect was the most significant response in areas with medium to heavy urban occupation for both assays evaluated. Water samples from these areas include different concentrations of chloroform, bromodichloromethane, toluene, ethylbenzene, m,p-xylene and 1,4-dichlorobenzene. As to genotoxic damage, the presence of mainly direct-acting frameshift mutagens was detected in areas with less urban concentration and showed genotoxic activity in V79 cells in more heavily urbanized areas. Water organic extracts, evaluated using a microsuspension procedure, showed frameshift mutagenic activity in the presence of hepatic metabolization that increased as the population density grow. Chronic toxicity studies of sediment samples with the microcrustacean Daphnia magna showed that, while survival was not highly affected, reproductive inhibition was found in 92% of the observations. A retrospective diagnosis of water quality using traditional physicochemical parameters that defined the differential contribution of urban wastes at the three sites was associated with the biological assays. It became clear that the biological assays were of significant benefit in the diagnosis of risks of contamination of hydrographic basins by pollutants from urban non-point sources.