Influence of Environmental Factors on Occurrence of Cyanobacteria and Abundance of Saxitoxin-Producing Cyanobacteria in a Subtropical Drinking Water Reservoir in Brazil

Blooms of cyanobacteria are frequent in Brazilian water reservoirs used for drinking water. The warning for the presence of potential toxin-producing cyanobacteria is typically based on time-consuming microscopy, rather than specific molecular detection of toxic genes in cyanobacteria. In this study, we developed a quantitative PCR assay for the detection of cyanobacteria producing the neurotoxin saxitoxin (STX). The assay targets the sxtA gene in the sxt gene cluster. Potential and dominant STX-producers in the Itupararanga reservoir were the genera Raphidiopsis, Aphanizomenon and Geitlerinema. Numbers of the sxtA gene varied from 6.76 × 103 to 7.33 × 105 cells mL−1 and correlated positively with SXT concentrations in the water. Concentrations of STX and the sxtA gene also correlated positively with TN:TP ratio and pH, but correlated negatively with inorganic nutrients and turbidity, confirming that regulation of the SXT production was impacted by environmental variables. In contrast, the occurrence of another cyanotoxin, microcystin, did not correlate with any environmental variables. The developed qPCR assay was found to be a rapid and robust approach for the specific quantification of potential STX-producing cyanobacteria and should be considered in future investigations on toxic cyanobacteria to provide an early warning of potential toxin episodes.

The effect of ice phenology exerted on submerged macrophytes through physicochemical parameters and the phytoplankton abundance

<p>The physicochemical parameters of water, the concentration of chlorophyll-<em>a</em> and the submerged aquatic vegetation (SAV) were studied to evaluate the effects of different winter seasons on the biomass of macrophytes in shallow eutrophic lakes. We hypothesised that a lack of ice cover or early ice-out can influence the physicochemical parameters of water and thus change the conditions for the development of phytoplankton and SAV. The studies were conducted in four lakes of the Western Polesie region in mid-eastern Poland after mild winters with early ice-out (MW, 2011 and 2014) and after cold winters with late ice-out (CW, 2010, 2012 and 2013). The concentrations of soluble and total nitrogen, chlorophyll-<em>a</em> and the TN:TP ratio in the lakes were considerably higher, whereas the concentration of soluble and total phosphorus and water transparency were significantly lower after the MW compared with after the CW. No differences were found in water temperature, reaction and electrolytic conductivity. Low water turbidity linked with low concentration of chlorophyll-<em>a</em> after the CW resulted in increased water transparency and the total biomass of the SAV. The negative effect of the MW on the macrophyte species was stronger on more sensitive species (<em>Myriophyllum spicatum</em>,<em> Stratiotes aloides</em>) compared with shade tolerant <em>Ceratophyllum demersum</em>. Our findings show that the ice cover phenology affected by climate warming can change the balance between phytoplankton and benthic vegetation in shallow eutrophic lakes, acting as a shift between clear and turbid water states. We speculate that various responses of macrophyte species to changes in the water quality after two winter seasons (CW and MW) could cause alterations in the vegetation biomass, particularly the expansion of shade tolerance and the decline of light-demanding species after a series of mild winters.</p>

Eutrophication and nutrient limitation in the aquatic zones around Huainan coal mine subsidence areas, Anhui, China

The eutrophication of three small lakes in the aquatic zones at the Huainan coal mine subsidence areas, designated as east site (ES), central site (CS), and west site (WS), were studied. Nutrient content, species, and nitrogen (N) to phosphorus (P) ratios were obtained through water quality analyses. Nutrient limitation was evaluated by nutrient enrichment bioassays (NEBs) in the autumn of 2012 and spring of 2013. Average annual concentrations of total phosphorus (TP) were 0.05, 0.08, and 0.10 mg/L, and total nitrogen (TN) concentrations were 0.77, 1.95, and 2.06 mg/L in the water column at CS, ES, and WS, respectively. All of the three lakes exhibited ‘meso-eutrophic’ states and the TN:TP ratio ranged from 25:1 to 74:1 with variability between seasons and sites. NEBs verified that primary productivity in the lakes at ES and WS were mainly limited by P, while N limitation or N and P co-limitation was present in the aquatic zones at CS due to unavailable dissolved inorganic nitrogen. In the studied lakes, the blue-green algae, which comprised 70% of all identified species, was the predominant taxa, while the micro-zooplankton taxa was dominant, indicating a typical trophic structure of eutrophic lakes.

Prediction ofMicrocystisBlooms Based on TN:TP Ratio and Lake Origin

We evaluated the relationship between TN:TP ratio andMicrocystisgrowth via a database that includes worldwide lakes based on four types of lake origin (dammed, tectonic, coastal, and volcanic lakes). We used microcosm and mesocosm for the nutrient elution tests with lake water and four kinds of sediment (nontreated, MgO sprinkling treated, dissolved air flotation [DAF] treated, and combined treated sediment) in order to control TN:TP ratio and to suppressMicrocystisgrowth.Microcystisgrowth was related to TN:TP ratio, with the maximum value at an optimum TN:TP ratio and the minimum values when the TN:TP ratios reached to 0 or ∞. The kurtosis of the distribution curve varied with the type of lake origin; the lowest kurtosis was found in dammed lakes, while the highest was found in volcanic lakes. The lake trophic state could affect the change in the kurtosis, providing much lower kurtosis at eutrophic lakes (dammed lakes) than that at oligotrophic lakes (volcanic lakes). The relationship between TN:TP ratio andMicrocystisgrowth could be explained by the nutrient elution tests under controlled TN:TP ratios through the various sediment treatments. A significant suppression ofMicrocystisgrowth of 70% could be achieved when the TN:TP ratios exceeded 21. Lake origin could be regarded as an index including morphological and geographical factors, and controlling the trophic state in lakes. The origin rather than trophic state for lakes could be considered as an important factor of TN:TP influences on Microcystis growth.

Use of the Morphoedaphic Index to Predict Nutrient Status and Algal Biomass in Some Canadian Lakes

The underlying assumptions of the morphoedaphic index (MEI; total dissolved solids (TDS)/mean depth), which has been used to predict fish yields in lakes, and its power for predicting biomass at lower trophic levels were examined using published data. The assumptions included the relationship between mean depth of lakes and various hydrologic characteristics (flushing rate and stratification regime), water transparency characteristics (water color and turbidity), and the stoichiometric relationship among ions (expressed as a proportion between TDS and the concentration of primary nutrients, total phosphorus (TP) and total nitrogen (TN)). Although these basic assumptions could be supported empirically, the predictive power of the MEI became progressively weakened with increasing trophic level. MEI accounted for up to 85% of the variation in TP and TN, less than 50% of the variation in [Chl a], and none of the variation in the biomass of herbivorous zooplankton. The functions relating TDS to both TP and TN were fundamentally different: as lakes increased in salinity, the TN:TP ratio decreased dramatically so that TP almost exceeded TN concentrations in extremely saline lakes. This necessitated the development of separate MEI–nutrient relationships for saline (TDS > 1000 mg/L) and nonsaline lakes.

Experimental Mesocosm Study of the Separate and Interaction Effects of Phosphorus and Mosquitofish (Gambusia affinis) on Plankton Community Structure

We examined community impacts of phosphorus and mosquitofish (Gambusia affinis) in an experimental mesocosm study of factorial design in which two levels of phosphorus addition were cross-classified with two levels of fish. Total phosphorus (TP), chlorophyll, cryptomonads, unicellular green algae, unicellular blue-green algae, colonial blue-green algae, filamentous blue-green algae, chironomid tube length, cladocerans, fish density, and fish biomass were significantly enhanced in the presence of phosphorus addition. Total nitrogen (TN), TN:TP ratio, Secchi depth, chrysophytes, and periphytic diatoms were suppressed in the presence of phosphorus addition. Diatoms, filamentous blue-green algae, chrysophytes, periphytic unicellular and colonial green algae, periphytic filamentous blue-green algae, and rotifers were enhanced in the presence of mosquitofish. Secchi depth, TN:TP ratio, cyclopoid copepodids, nauplii, cladocerans, and chironomid tubes were suppressed in the presence of mosquitofish. We found significant phosphorus × mosquitofish interaction effects for TN:TP ratio, chrysophytes, dinoflagellates, periphytic colonial green algae, cladocerans, and chironomid tubes. These results show that nutrients and fish do not act as independent regulators of plankton communities but instead have effects which can only be predicted from an understanding of their combined impacts.