Seasonal variations in stable isotope ratios of two biomanipulation fishes and seston in a large pen culture in hypereutrophic Meiliang Bay, Lake Taihu

This paper reports on seasonal changes in stable carbon and nitrogen isotope ratios of seston and muscle tissue of silver carp and bighead carp during 2004 and 2005, focusing primarily on the carbon sources and trophic relationships among phytoplankton, zooplankton and silver carp and bighead carp in a large fish pen of Meiliang Bay (Lake Taihu, China). delta C-13 showed a minimal value in March 2005 and a maximal value in August 2005 in seston both inside and outside the pen, whereas delta N-15 of seston showed the minimum in winter and the maximum during algal blooms. A positive correlation between delta C-13 of silver carp and that of seston suggested that temporal variation Of delta C-13 in seston was preserved in fish via the food chain. The differences of delta C-13 among seston, zooplankton and muscle tissue of silver carp and bighead carp ranged only 0.2-1.7%, indicating that plankton production was the primary food source of filter-feeding fishes. According to a mass balance model, we estimated that the contributions of zooplankton to the diets of silver carp and bighead carp were 45.7% and 54.3%, respectively, based on the delta N-15 values of zooplankton and planktivorous fishes. (C) 2007 Elsevier B.V. All rights reserved

Mitigation of lake eutrophication: Loosen nitrogen control and focus on phosphorus abatement

w Traditionally, nitrogen control is generally considered an important component of reducing lake eutrophication and cyanobacteria blooms. However, this viewpoint is refuted recently by researchers in China and North America. In the present paper, the traditional viewpoint of nitrogen control is pointed out to lack a scientific basis: the N/P hypothesis is just a subjective assumption; bottle bioassay experiments fail to simulate the natural process of nitrogen fixation. Our multi-year comparative research in more than 40 Yangtze lakes indicates that phosphorus is the key factor determining phytoplankton growth regardless of nitrogen concentrations and that total phytoplankton biomass is determined by total phosphorus and not by total nitrogen concentrations. These results imply that, in the field, nitrogen control will not decrease phytoplankton biomass. This finding is supported by a long-term whole-lake experiment from North America. These outcomes can be generalized in terms that a reduction in nitrogen loading may not decrease the biomass of total phytoplankton as it can stimulate blooms of nitrogen-fixing cyanobacteria. To mitigate eutrophication, it is not nitrogen but phosphorus that should be reduced, unless nitrogen concentrations are too high to induce direct toxic impacts on human beings or other organisms. Finally, details are provided on how to reduce controls on nitrogen and how to mitigate eutrophication. (C) 2009 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Carbon and nitrogen metabolism of an eutrophication tolerative macrophyte, Potamogeton crispus, under NH4+ stress and low light availability

Submersed macrophytes in eutrophic lakes often experience high NH4+ concentration and low light availability in the water column. This study found that an NH4+-N concentration of 1 mgL(-1) in the water column apparently caused physiological stress on the macrophyte Potamogeton crispus; L The plants accumulated free amino acids (FAA) and lost soluble carbohydrates (SC) under NH4+ stress. These stressful effects of NH4+ were exacerbated under low light availability. Shading significantly increased NH4+ and FAA contents and dramatically decreased SC and starch contents in the plant shoots. At an NH4+-N concentration of 1 mg L-1 in the water column, neither growth inhibition nor NH4+ accumulation was observed in the plant tissues of P. crispus under normal light availability. The results showed that 1 mg L-1 NH4+-N in the water column was not toxic to P. crispus in a short term. To avoid NH4+ toxicity. active NH4+ transportation out of the cell may cost energy and thus result in a decline of carbohydrate. When NH4+ inescapably accumulates in the plant cell, i.e. under NH4+ Stress and shading, NH4+ is scavenged by FAA synthesis. (c) 2009 Published by Elsevier B.V.

Kinetic modelling of growth and storage molecule production in microalgae under mixotrophic and autotrophic conditions.

In order to improve algal biofuel production on a commercial-scale, an understanding of algal growth and fuel molecule accumulation is essential. A mathematical model is presented that describes biomass growth and storage molecule (TAG lipid and starch) accumulation in the freshwater microalga Chlorella vulgaris, under mixotrophic and autotrophic conditions. Biomass growth was formulated based on the Droop model, while the storage molecule production was calculated based on the carbon balance within the algal cells incorporating carbon fixation via photosynthesis, organic carbon uptake and functional biomass growth. The model was validated with experimental growth data of C. vulgaris and was found to fit the data well. Sensitivity analysis showed that the model performance was highly sensitive to variations in parameters associated with nutrient factors, photosynthesis and light intensity. The maximum productivity and biomass concentration were achieved under mixotrophic nitrogen sufficient conditions, while the maximum storage content was obtained under mixotrophic nitrogen deficient conditions.

Nitrogen dynamics in large shallow eutrophic Lake Chaohu, China

Temporal and spatial dynamics of nitrogen in lake and interstitial water were studied monthly in a large shallow, eutrophic lake in subtropical China from October 2002 to September 2003. The distribution of nitrogen was consistent with the idea that high nitrogen concentrations in the western part of the lake resulted from high levels of the nutrients from the surrounding cities through sewage-drainage systems. Nitrate was the predominant form of nitrogen in the overlying water, while ammonium was predominant in the interstitial water, indicating that strong oxidative nutrient regeneration occurred near the sediment-water interface. Nitrate could be an important dissolved inorganic matter source for phytoplankton, which in turn influenced the seasonal variations of nitrate concentrations in lake water. Significant positive correlation between ammonium fluxes and water temperature was observed and could probably be attributed to the intensified ammonification and nitrate reduction with increased temperature. Positive correlation between ammonium fluxes and algae biomass and Chl a concentrations may indicate that phytoplankton was an important factor driving ammonium fluxes in our study lake, and vice versa that higher fluxes of ammonium supported a higher biomass of the phytoplankton.

Relationships among the contents of total phenolics, soluble carbohydrate, and free amino acids of 15 aquatic macrophytes

In order to examine how carbon and nitrogen status of a macrophyte may affect its total phenolics (TP) production, the contents of free amino acids (FAA), soluble carbohydrate (SC) and TP were examined in leaves of seven submersed, four floating-leaved, and four emergent macrophytes. The floating-leaved and emergent macrophytes had much higher contents of SC and TP than the submersed macrophytes. The contents of FAA were not significantly different among the submersed, floating-leaved, and emergent macrophytes. Correlations among the contents of FAA, SC, and TP indicated that the production of TP was more dependent on the SC content than on the FAA content.

Carbon source/sink function of a subtropical, eutrophic lake determined from an overall mass balance and a gas exchange and carbon burial balance

Although studies on carbon burial in lake sediments have shown that lakes are disproportionately important carbon sinks, many studies on gaseous carbon exchange across the water-air interface have demonstrated that lakes are supersaturated with CO2 and CH4 causing a net release of CO2 and CH4 to the atmosphere. In order to more accurately estimate the net carbon source/sink function of lake ecosystems, a more comprehensive carbon budget is needed, especially for gaseous carbon exchange across the water-air interface. Using two methods, overall mass balance and gas exchange and carbon burial balance, we assessed the carbon source/sink function of Lake Donghu, a subtropical, eutrophic take, from April 2003 to March 2004. With the overall mass balance calculations, total carbon input was 14 905 t, total carbon output was 4950 1, and net carbon budget was +9955 t, suggesting that Lake Donghu was a great carbon sink. For the gas exchange and carbon burial balance, gaseous carbon (CO2 and CH4) emission across the water-air interface totaled 752 t while carbon burial in the lake sediment was 9477 t. The ratio of carbon emission into the atmosphere to carbon burial into the sediment was only 0.08. This low ratio indicates that Lake Donghu is a great carbon sink. Results showed good agreement between the two methods with both showing Lake Donghu to be a great carbon sink. This results from the high primary production of Lake Donghu, substantive allochthonous carbon inputs and intensive anthropogenic activity. Gaseous carbon emission accounted for about 15% of the total carbon output, indicating that the total output would be underestimated without including gaseous carbon exchange. (C) 2007 Elsevier Ltd. All rights reserved.

Effects of ammonium on growth, nitrogen and carbohydrate metabolism of Potamogeton maackianus A. Benn

Growth, nitrogen and carbohydrate metabolism in relation to eutrophication were studied for a submerged plant Potamogeton maackianus, a species common in East Asian shallow lakes. The plants were grown in six NH4+-N concentrations (0.05, 0.50, 1.00, 3.50, 5.00 and 10.00 mg/L) for six days. NH4+-N levels in excess of 0.50 mg/L inhibited the plant growth. The relationships between external NH4+-N availability and total nitrogen (TN), protein-N, free amino acid-N (FAA-N) and NH4+-N in plant tissues, respectively, conformed to a logarithmic model suggesting that a feedback inhibition mechanism may exist for ammonium uptake. The response of starch to NH4+-N was fitted with a negative, logarithmic curve. Detailed analysis revealed that the influx NH4+-N had been efficiently incorporated into organic-N and eventually stored as protein at the expense of starch accumulation. These data suggest that this species may be able to tolerate high levels of ammonium when dissolved oxygen is sufficient.

Differentiate performance of eight filter media in vertical flow constructed wetland: Removal of organic matter, nitrogen and phosphorus

A comparative study was conducted to reveal the differentiate effects of eight different filter media including gravel, zeolites, anthracite, shale, vermiculite, ceramic filter media, blast furnace steel slag and round ceramsite. The study mainly related to the eight different filter media's removal performances of organic matter, nitrogen and phosphorus in the vertical flow constructed wetland simulated system, which treating wastewater at hydraulic loading rate of 1000-2500 mm/d. The results indicated that the removal effects were closely related to the physical and chemical properties of medium materials. Anthracite-filled system had the highest removal rate for the total organic carbon (TOC), up to 70%, and the removal rates of other systems ranged from 20% to 30%. As for the five-day biochemical oxygen demand (BOD5), anthracite-filled and steel slag-filled systems had the highest removal rates, also up to 70%, as well as other systems all exceeded 50%. At the same time, for the total nitrogen (TN) and NH4(+)-N, the zeolites-filled and ceramic-filled systems had the best performances with the removal rates of more than 70%, the other way round, the removal rates of other systems were only about 20%. The distinguishable effects were also observed in removal performances of total phosphorus (TP) and total dissoluble phosphorus (TDP). The removal rates of TP and TDP in steel slag-filled systems were more than 90%, a much higher value, followed by that of the anthracite-filled system, more than 60%, but those of other systems being the less. Our study provided a potential mechanism to optimize the filter media design for the vertical flow constructed wetlands.

Stable isotope variations in particulate organic matter and a planktivorous fish in the Yangtze River

Temporal and spatial changes in delta(13) C and delta 15 N of particulate organic matter (POM) and Hemiculter leucisculus were studied in the Yangtze River of China. Isotopic signatures of POM showed seasonal variations, which was assumed to be associated with allochthonous organic input and autochthonous phytoplankton growth. delta C-13 of H. leucisculus was 1.1 % higher than that of POM, which suggested that the food source of H. leucisculus was mostly from the POM. A mass balance model indicated the trophic position of H. leucisculus in the food web of Yangtze River was estimated to be 2.0 - 2.1, indicating that this fish mainly feeds on planktonic organic matter, which agreed with previous gut content analysis.

Icefish (Salangidae) as an indicator of anthropogenic pollution in freshwater systems using nitrogen isotope analysis

We investigated differences in delta N-15 of seston and icefishes from seven freshwater ecosystems with different trophic states in China. An increase of seston delta N-15 values was accompanied by an increase of total nitrogen and phosphorus concentrations. Significantly positive correlations were observed between delta N-15 of icefishes and delta N-15 of seston, total nitrogen and phosphorus concentrations. This study demonstrated that icefishes could be preferred indicators of anthropogenic contamination in test systems because they integrated waste inputs over long time periods and reflected the movement of waste through the pelagic food chain.

Comparison of moment-curvature models for fiber-reinforced polymer plate-end debonding studies using global energy balance approach

This paper compares a number of different moment-curvature models for cracked concrete sections that contain both steel and external fiber-reinforced polymer (FRP) reinforcement. The question of whether to use a whole-section analysis or one that considers the FRP separately is discussed. Five existing and three new models are compared with test data for moment-curvature or load deflection behavior, and five models are compared with test results for plate-end debonding using a global energy balance approach (GEBA). A proposal is made for the use of one of the simplified models. The availability of a simplified model opens the way to the production of design aids so that the GEBA can be made available to practicing engineers through design guides and parametric studies. Copyright © 2014, American Concrete Institute.

Kinetic modelling of growth and storage molecule production in microalgae under mixotrophic and autotrophic conditions

In order to improve algal biofuel production on a commercial-scale, an understanding of algal growth and fuel molecule accumulation is essential. A mathematical model is presented that describes biomass growth and storage molecule (TAG lipid and starch) accumulation in the freshwater microalga Chlorella vulgaris, under mixotrophic and autotrophic conditions. Biomass growth was formulated based on the Droop model, while the storage molecule production was calculated based on the carbon balance within the algal cells incorporating carbon fixation via photosynthesis, organic carbon uptake and functional biomass growth. The model was validated with experimental growth data of C. vulgaris and was found to fit the data well. Sensitivity analysis showed that the model performance was highly sensitive to variations in parameters associated with nutrient factors, photosynthesis and light intensity. The maximum productivity and biomass concentration were achieved under mixotrophic nitrogen sufficient conditions, while the maximum storage content was obtained under mixotrophic nitrogen deficient conditions. © 2014 Elsevier Ltd.

Meat and bone meal replacement in diets for juvenile gibel carp (Carassius auratus gibelio): effects on growth performance, phosphorus and nitrogen loading

A 11-week growth trial was conducted in a flow-through system with juvenile gibel carp Carassius auratus gibelio to evaluate the effects of gradual replacement of fish meal (FM) by meat and bone meal (MBM) on growth performance, phosphorus (P) and nitrogen (N) loading. Six isonitrogenous (crude protein: 410 g kg(-1)) and isoenergetic (gross energy: 18 kJ g(-1)) diets were formulated. FM was used as the control protein. In the other five diets, 20, 40, 60, 80 and 100% FM protein was substituted with MBM20, MBM40, MBM60, MBM80, MBM100, respectively. Total P content in the diets ranged from 16.0 to 28.3 g kg(-1) and the available P was 5.0-6.6 g kg(-1). The results showed that the best growth was achieved with fish fed on the control diet and MBM20. Final body weight, weight gain, feed efficiency, protein retention efficiency and energy retention efficiency decreased with increased dietary MBM. No significant differences were found in the feeding rate and hepatosomatic index between the groups. Apparent digestibility coefficient (ADC) of dry matter, protein and P decreased with increase in dietary MBM, while there were no significant differences in the ADC of energy. P and N retention decreased linearly while P and N loading increased linearly with the increased dietary MBM levels. No significant differences were observed in the activity of alkaline phosphatase, aspartate aminotransferase and alanine aminotransferase, as well as pyruvate kinase in liver or in serum. Total superoxide dismutase activity in MBM20 was significantly higher than that of MBM100.