Biological mechanisms driving the seasonal changes in the internal loading of phosphorus in shallow lakes

Because of the obvious importance of P as a nutrient that often accelerates growth of phytoplankton (including toxic cyanobacteria) and therefore worsens water quality, much interest has been devoted to P exchange across the sediment-water interface. Generally, the release mode of P from the sediment differed greatly between shallow and deep lakes, and much of the effort has been focused on iron and oxygen, and also on the relevant environmental factors, for example, turbulence and decomposition, but a large part of the P variation in shallow lakes remains unexplained. This paper reviews experimental and field studies on the mechanisms of P release from the sediment in the shallow temperate (in Europe) and subtropical (in the middle and lower reaches of the Yangtze River in China) lakes, and it is suggested that pH rather than DO might be more important in driving the seasonal dynamics of internal P loading in these shallow lakes, i.e., intense photosynthesis of phytoplankton increases pH of the lake water and thus may increase pH of the surface sediment, leading to enhanced release of P (especially iron-bound P) from the sediment. Based on the selective pump of P (but not N) from the sediment by algal blooms, it is concluded that photosynthesis which is closely related to eutrophication level is the driving force for the seasonal variation of internal P loading in shallow lakes. This is a new finding. Additionally, the selective pump of P from the sediment by algal blooms not only explains satisfactorily why both TP and PO4-P in the hypereutrophic Lake Donghu declined significantly since the mid-1980s when heavy cyanobacterial blooms were eliminated by the nontraditional biomanipulation (massive stocking of the filter-feeding silver and bighead carps), but also explains why TP in European lakes decreased remarkably in the spring clear-water phase with less phytoplankton during the seasonal succession of aquatic communities or when phytoplankton biomass was decreased by traditional biomanipulation. Compared with deep lakes, wax and wane of phytoplankton due to alternations in the ecosystem structure is also able to exert significant influences on the P exchange at the sediment-water interface in shallow lakes. In other words, biological activities are also able to drive P release from sediments, and such a static P release process is especially more prominent in eutrophic shallow lakes with dense phytoplankton.

Changes in the patterns of inorganic nitrogen and TN/TP ratio and the associated mechanism of biological regulation in the shallow lakes of the middle and lower reaches of the Yangtze River

The changes of NH3-N, NO3-N, NO2-N and TN/TP were studied during growth and non-growth season in 33 subtropical shallow lakes in the middle and lower reaches of the Yangtze River. There were significant positive correlations among all nutrient concentrations, and the correlations were better in growth season than in non-growth season. When TP > 0.1 mgL(-1), NH3-N increased sharply in non-growth season with increasing TP, and NO3-N increased in growth season but decreased in non-growth season with TP. These might be attributed to lower dissolved oxygen and low temperature in non-growth season of the hypereutrophic lakes, since nitrification is more sensitive to dissolved oxygen and temperature than anti nitrification. When 0.1 mgL(-1)> TP > 0.035 mgL(-1), TN and all kinds of inorganic nitrogen were lower in growth season than in non-growth season, and phytoplankton might be the vital regulating factor. When TP < 0.035 mgL(-1), inorganic nitrogen concentrations were relatively low and NH3-N, NO2-N had significant correlations with phytoplankton, indicating that NH3-N and NO2-N might be limiting factors to phytoplankton. In addition, TN/TP went down with decline in TIP concentration, and TN and inorganic nitrogen concentrations were obviously lower in growth season than in non-growth season, suggesting that decreasing nitrogen (especially NH3-N and NO3-N) was an important reason for the decreasing TN/TP in growth season. The ranges of TN/TP were closely related to trophic level in both growth and non-growth seasons, and it is apparent that in the eutrophic and hypertrophic state the TN/TP ratio was obviously lower in growth season than in non-growth season. The changes of the TN/TP ratio were closely correlated with trophic levels, and both declines of TN in the water column and TP release from the sediment were important factors for the decline of the TN/TP ratio in growth season.

Characterization of diurnal photosynthetic rhythms in the marine diatom Skeletonema costatum grown in synchronous culture under ambient and elevated CO2

Photosynthetic performance was examined in Skeletonema costatum (Greville) Cleve. under 12: 12-h light: dark (LD) cycle at ambient CO2 (350 muL L-1) and elevated CO2 (1000 muL L-1). At ambient CO2, the cellular chlorophyll a content, the light-saturated photosynthetic rate (P-m), the initial slope of the light saturation curves ( a), the photochemical efficiency of PSII (F-v/F-m), the apparent carboxylating efficiency (ACE) and the photosynthetic affinity for CO2 [1/K-m (CO2)] all showed rhythmical changes with different amplitudes during the light period. The P-m had similar changing pattern in the light period with the ACE and 1/K-m (CO2) rather than with the alpha and F-v/F-m, indicating that rhythmical changes of photosynthetic capacity may be mainly controlled by the activity of C- reduction associated with CO2 uptake during the light period. The CO2 enrichment reduced the ACE and the affinity to CO2, and increased the a, cellular chlorophyll a content and P m based on cell number. By contrast, the changing patterns of all photosynthetic parameters examined here during the light period had almost the same for cells grown at ambient CO2 and elevated CO2, suggesting that the photosynthetic rhythms of S. costatum are not affected by CO2 enrichment.

Biological evaluation of running waters in Korea, with special reference to bioassessment using the PFU system

A total of six stations in the Han River system were selected for establishing polyurethane foam units (PFUs) to collect protozoans, including phytomastigophorans, zoomastigophorans, amoebas and ciliates, in July 1993. In the bioassessment of microbial communities using the PFUs, the number of species decreased as pollution intensity increased. The diversity index values calculated at the main stations generally agreed with the pollution status of the stations. Anyang-Chon (Chon means stream) showed the lowest diversity value (1.89), and all stations, except Masok and Anyang-Chon, showed diversity index values ranging from 3.15 to 3.93. The highest heterotrophic index (HI) value was detected in Anyang-Chon followed by Masok-Chon. The number of species at the main stations reached a maximum on day 11 of being exposed to PFUs. The results of S-eq, G and T-90% all suggest that bioassessments using the PFU system were well matched with pollution status of the water. All microbial variables were significantly correlated with comprehensive chemical pollution indices, P-a and P-b, with correlation coefficients ranging from r=0.87 to r=0.96.

STUDIES ON THE PURIFICATION AND RECLAMATION OF WASTE-WATER FROM A MEDIUM-SIZED CITY BY AN INTEGRATED BIOLOGICAL POND SYSTEM

The feasibility of an inexpensive wastewater treatment system is evaluated in this study. An integrated biological pond system was operated for more than 3 years to purify the wastewater from a medium-sized city, Central China. The experiment was conducted in 3 phases with different treatment combinations for testing their purification efficiencies. The pond system was divided into 3 functional regions: influent purification, effluent upgrading and multi-utilization. These regions were further divided into several zones and subzones. Various kinds of aquatic organisms, including macrophytes, algae, microorganisms and zooplankton, were effectively cooperating in the wastewater treatment in this system. The system attained high reductions of BOD5, COD, TSS, TN, TP and other pollutants. The purification efficiencies of this system were higher than those of most traditional oxidation ponds or ordinary macrophyte ponds. The mutagenic effect and numbers of bacteria and viruses declined significantly during the process of purification. After the wastewater flowed through the upgrading zone, the concentrations of pollutants and algae evidently decreased. Plant harvesting did not yield dramatic effects on reductions of the main pollutants, though it did significantly affect the biomass productivity of the macrophytes. The effluent from this system could be utilized in irrigation and aquaculture. Some aquatic products were harvested from this system and some biomass was utilized for food, fertilizer, fodder and some other uses. The wastewater was reclaimed for various purposes.

The experimental measurement of the relative biological effectiveness of carbon ions with different qualities

The relative biological effectiveness (RBE) of carbon ions with linear energy transfer (LET) of 172 keV/mu m and 13.7 keV/mu m were determined in this study. The clonogenic survival and premature terminal differentiation were measured on normal human. broblasts AG01522C and NHDF after exposure of the cells to 250 kV X-rays and carbon ions with different qualities. RBE was determined for these two biological end points. The results showed that the measured RBE10 with a survival fraction of 10% was 3.2 for LET 172 keV/mu m, and 1.33 for LET 13.7 keV/mu m carbon ions. RBE for a doubling of post-mitotic. broblasts (PMF) in the population was 2.8 for LET 172 keV/mu m, and 1 for LET 13.7 keV/mu m carbon ions. For the carbon ion therapy, a high RBE value on the Bragg peak results in a high biological dose on the tumour. The tumour cells can be killed effectively. At the same time, the dose on healthy tissue would be reduced accordingly. This will lighten the late effect such as fibrosis on normal tissue.

Enhanced biological effect induced by a radioactive C-9-ion beam at the depths around its Bragg peak

To explore the potential of double irradiation source, radioactive C-9-ion beam, in tumor therapy, a comparative study oil the surviving effect of human salivary gland cells at different penetration depths between C-9 and C-12-ion beams has been carried out. The 9C-ion C beam, especially at the distal side of the beam came out more efficient in cell killing at the depths around its Bragg peak than the 12 Bragg peak. Compared to the C-12 beam, an increase in RBE by a factor of up to 2.13 has been observed at the depths distal to the Bragg peak of the 9C beam. The 9C beam showed an enhanced biological effect at the penetration depths around its Bragg peak, corresponding to the stopping region of the incident C-9-ions and where the delayed low-energy particles were emitted. Further analysis revealed that cell lethality by the emitted particles from the stopping C-9-ions is responsible for the excessive biological effect at the penetration depths around the Bragg peak of the C-9 beam.