Present status and changes of the phytoplankton community after invasion of Neosalanx taihuensis since 1982 in a deep oligotrophic plateau lake, Lake Fuxian in the subtropical China

Phytoplankton assemblages in the subtrophical oligotrophic Lake Fuxian, the second deepest lake in China, were investigated monthly from September 2002 to August 2003. A total of 113 species belonging to seven phyla were identified, among them, a filamentous green alga, Mougeotia sp., dominated almost throughout the study period and comprised most of the total phytoplankton biomass. Mougeotia sp. has made a substantial development during the past decades: it was absent in 1957, only occasionally present in 1983, increased substantially in 1993, and became predominant in 2002—2003. It is likely that natural invasion of the Taihu Lake noodlefish(Neosalanx taihuensis) has led to a change of dominant herbivorous zooplankton from small to large calanoid, which has increased grazing pressure on small edible algae, and thus has indirectly favored the development of the inedible filamentous Mougeotia sp.

Metabolic tuning of a stable microbial community in the surface oligotrophic Indian Ocean revealed by integrated meta-omics

Understanding the mechanisms,structuring microbial communities in oligotrophic ocean surface waters remains a major ecological endeavor.Functional redundancy and metabolic tuning are two mechanisms that have been proposed to shape microbial response to environmental forcing.However,little is known about their roles in the oligotrophic surface ocean due to less integrative characterization of community taxonomy and function.Here,we applied an integrated meta-omics-based approach,from genes to proteins,to investigate the microbial community of the oligotrophic northern Indian Ocean.Insignificant spatial variabilities of both genomic and proteomic compositions indicated a stable microbial community that was dominated by Prochlorococcus,Synechococcus,and SAR11.However,fine tuning of some metabolic functions that are mainly driven by salinity and temperature was observed.Intriguingly,a tuning divergence occurred between metabolic potential and activity in response to different environmental perturbations.Our results indicate that metabolic tuning is an important mechanism for sustaining the stability of microbial communities in oligotrophic oceans.In addition,integrated meta-omics provides a powerful tool to comprehensively understand microbial behavior and function in the ocean.

Simulation of coupled pelagic-benthic ecosystem of the Yellow Sea Cold Water Mass

A one-dimensional coupled pelagic-benthic box model for the Yellow Sea Cold Water Mass (YSCWM) is developed. The model is divided into three boxes vertically according to the depths of thermocline and euphotic layer. It simulates well the oligotrophic shelf ecosystem of the YSCWM considering effects of nu- trients deposition and microbial loop. Main features of vertical structure of various variables in ecosystem of the YSCWM were captured and seasonal variability of the ecosystem was well reconstructed. Calculation shows that the contribution of microbial loop to the zooplankton can reach up to 60%. Besides, input of inorganic nutrients from atmospheric deposition is an important mechanism of production in upper layer of the YSCWM when stratified.

Bacterial Communities in a Buried Ancient Paddy Soil from the Neolithic Age

An ancient irrigated paddy soil from the Neolithic age was excavated at Chuodunshan Site in the Yangtze River Delta, close to Suzhou, China. The soil organic matter (SOM) content in the prehistoric rice soil is comparable to the average SOM content of present rice soils in this region, but it is about 5 times higher than that in the parent materials. As possible biomarkers to indicate the presence of the prehistoric paddy soil, the bacterial communities were investigated using the techniques of aerobic and anaerobic oligotrophic bacteria enumeration, Biolog analysis, and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that in the buried soil layers, the prehistoric paddy soil had the largest number of aerobic and anaerobic oligotrophic bacteria, up to 6.12 and 5.86 log cfu g-1 dry soil, respectively. The prehistoric paddy soil displayed better carbon utilization potential and higher functional diversity compared to the parent materials and a prehistoric loess layer. The Shannon index and richness based on DGGE profiles of bacterial 16S rRNA genes were higher in prehistoric paddy soil than those in the prehistoric loess soil. It might be concluded that the prehistoric irrigated rice cultivation accumulated the SOM in plowed soil layer, and thus increased soil bacterial populations, metabolic activity, functional diversity and genetic diversity. Bacterial communities might be considered as the sensitive indicators of the presence of the prehistoric paddy soil in China's Yangtze River Delta.

The Physico-Chemical Water Quality of the Obafemi Awolowo University Teaching and Research Farm Lake, O.A.U. Campus, Ile-Ife, Southwest, Nigeria

The physico-chemical water quality of the Obafemi Awolowo University Teaching and Research Farm Lake, Ile-Ife, Nigeria, was studied over an annual cycle (September 2006 to August 2007) almost 40 years after its impoundment in 1967. This was with a view to obtaining the then current state of physico-chemical water quality parameters with their variations in time and space as well as using some of the data obtained to evaluate the aging process of the lake for the 40 years of its existence. There was no significant (p > 0.05) horizontal variation (i.e. upstream-dowstream) in the physico-chemical characteristics of the lake whereas, Apparent-color, True color, Turbidity, Total Suspended Solids (TSS), Total Solids (TS) and Total Acidity increased significantly (p < 0.05) from the lake surface towards the bottom of the lake. On the other hand, water pH, Dissolved Oxygen (DO);Dissolved Oxygen Saturation (DO% Sat.) and Biochemical Oxygen Demand (BOD5) decreased significantly (p < 0.05) from the lake surface towards the bottom of the lake. Dissolved Oxygen (DO), Dissolved Oxygen Saturation (DO% Sat.) and Nitrate ion (NO-3) were significantly higher (p < 0.05) in the dry season than in the rainy season while, True colour, pH, Conductivity, Total Hardness, Calcium ion (Ca2+), Magnesium ion (Mg2+), Potassium ion (K+) and Sulphate ion (SO2-4) were significantly higher (p < 0.05) in the rainy season than in the dry season. The lake water could be regarded as shallow, coloured, turbid, less transparent, slightly acidic, soft and well-buffered fresh-waterbodies with evidence of aging (i.e. transforming the lake from an oligotrophic status to a eutrophic waterbody). The results indicated that the lake is suitable for most of its applications with little or no adjustments as the case may be;except probably for drinking purposes where some microbial analysis may be necessary.

Role of Nutrients Input Pattern on the Growth Dynamics of Common Freshwater Microalgal Community

Most of the microalgae present in aquatic systems competed for the same available inorganic nutrients. The successful competitors would eventually dominate the rest because of their adaptive advantageous. Based on this premise, it was important to understand the effect of nutrients input rate on microalgal species-diversity and population. This was investigated in batch experiments of 14 days with pond water samples having natural ecosystem by varying nutrients dosing pattern under natural day light. Nutrients were supplied as single dose and multiple doses to the fresh water microalgal culture of fresh water. Prominent growth of many microalgal species was the key result of multiple dosing of nutrients compared to single or concentrated dosing of nutrients. Simulation towards oligotrophic condition was supporting the diverse population of microalgae. Whereas in the experiments with higher dosing of nutrients in one or two times had dominant growth of two or three microalgae and higher growth of heterotrophic bacteria. This condition resembled the eutrophic or hyper-eutrophic condition of water. This study thus showed the influence of the nutrients supply pattern on the growth and diversity of microalgae in freshwater and the nutrients added on eight, ten and twelve consecutive days from first day were considered as the effective nutrient addition pattern to promote maximum microalgal population present in a freshwater system.

The Effects of Anthropogenic Pollutants on Primary Productivity in Mtwapa Creek Waters in Kilifi, Kenya

Marine environmental pollution from urban development, tourism industry and agricultural activities affects the quality of marine and aquatic life and humans. This study established the impact of anthropogenic activities on marine water nutrient loading and primary productivity at Mtwapa Creek in Kenya. Triplicate water samples were collected twice a month from seven (7) sites on the creek to determine the levels of concentration of the three nutrients;, and in creek waters. Samples were analyzed for nutrients level using the spectrophotometric method. Primary productivity as an indication of carbon assimilation was computed using the traditional Winkler method. Quantitative one-way Analysis of Variance was used to determine the variations between sampling sites while correlation analysis was computed to establish the relationship between nutrients and carbon levels. There was spatial and temporal fluctuation of nutrients levels on the creek;however the levels of nitrates were within the oligotrophic range. Phosphate levels were not significantly different throughout the sampling period, while Ammonia levels were very significantly high in the creek waters, implying active biochemical processes affecting primary productivity with phosphates greatly influencing carbon assimilation. Strategic land based management approaches should be instituted to reduce the discharge flow into the creek waters.

Long-time precipitation reduction and nitrogen deposition increase alter soil nitrogen dynamic by influencing soil bacterial communities and functional groups

The effects of precipitation reduction and nitrogen deposition increase on soil bacterial communities and functions impact soil nitrogen cycling. Seasonal changes could modify the effects of precipitation reduction and nitrogen deposition increase on bacterial communities and functions by changing soil environments and properties. Understanding soil microbial communities and the seasonal response of functions to precipitation reduction and nitrogen deposition increase may be important for the accurate prediction of changes in the soil nitrogen dynamics. Thus, a long-term field simulation experiment of nitrogen deposition increase and throughfall exclusion was established to investigate soil bacterial communities’ response to nitrogen deposition increase and/or precipitation reduction, with no nitrogen deposition increase and no precipation reduction as a control, in a temperate forest. We examined soil bacterial communities(Illumina sequencing) under different treatments during the winter, freezing-thawing cycle periods(FTCs), and growing season. The bacterial functional groups were predicted by the FAPROTAX database. The results showed that nitrogen deposition increase, precipitation reduction, the combined effect of nitrogen deposition increase and precipitation reduction, and seasonal changes significantly altered the soil bacterial community composition.Interestingly, by combining the result of a previous study in which nitrogen deposition increase increased the nitrous oxide flux in the same experimental system, the loss of soil nitrogen was increased by the decrease in denitrification and increase of nitrification bacteria under nitrogen deposition increase,while ammonification bacteria significantly increased and N-fixing bacteria significantly decreased with precipitation reduction compared to the control. In relation to seasonal changes, the aromatic-degrading, cellulolytic, and ureolytic bacteria were lowest during FTCs, which indicated that FTCs might inhibit biodegradation. Nitrification and nitrite-oxidizing bacteria increased with nitrogen deposition increase or precipitation reduction and in FTCs compared to the control or other seasons. The interaction between treatment and season significantly changed the soil bacterial communities and functions. These results highlight that nitrogen deposition increase, precipitation reduction, seasonal changes, and their interactions might directly alter bacterial communities and indirectly alter the dynamics of soil N.

Microbial Populations,Activity and Gene Abundance in Tropical Vertisols Under Intensive Chemical Farming

There are increasing concerns on the environmental impacts of intensive chemical agriculture. The effect of high agrochemical inputs used in intensive chemical farming was assessed on soil microbiological, molecular and biochemical properties in tropical Vertisols in India. Farm field sites under normal cultivation of arable crops using high inputs of fertilizers and pesticides in chili （Capsicum annum L., 5.0× dose for fertilizers and 1.5× dose for pesticides over normal inputs） and black gram （Vigna mungo L. Hepper, 2.2× dose for fertilizers and 2.3× dose for pesticides over normal inputs） were compared with adjacent sites using normal recommended doses. Organic carbon and basal respiration showed no response to high inputs of fertilizers and pesticides in soils of both crops. Labile carbon decreased by 10% in chili soils and increased by 24% in black gram soils under high input farming system. The proportion of soil labile carbon as a fraction of soil organic carbon was unaffected by high inputs. The labile carbon mineralization coefficient （qMLc） increased by 50.0% in chili soils, indicating that the soil microorganisms were under stress due to high agochemical inputs, whereas qMLc decreased by 36.4% in black gram soils. Copiotrophs increased due to high inputs in soils of both chili （63.1%） and black gram （47.1%）. Oligotrophs increased by 10.8% in black gram soils but not in chili soils. The abundance of amoA gene reduced by 39.3% in chili soils due to high inputs and increased significantly by 110.8% in black gram soils. β-Glucosidase also increased by 27.2% and 325.0%, respectively. Acid phosphatase activity reduced by 29.2% due to high inputs in chili soils and increased by 105.0% in black gram soils. The use of high agrochemical inputs thus had adverse consequences on biological health in chili but not in black gram soils. In soils cultivated with black gram, the moderating effect of cultivating legumes and their beneficial effect on soil health were evident from the increase in soil labile carbon, lower qMLc, higher amoA gene and enzyme activities. Overall results showed that cultivation of legumes permits intensive chemical farming without deteriorating soil biological health.