Proposals for inhibiting abundant phytoplankton growth at the head of a river reservoir

In a river reservoir, the Ishitegawa Dam Reservoir in Japan, sites of abundant phytoplankton growth were investigated in connection with the water movement in the reservoir from January 1982 to January 1984 by comparing the distributions of chlorophyll a, water temperature, and coliform bacteria (Project A). The results distinguished three types of phytoplankton growth, of which one type, the abundant surface growth at the head of the reservoir, was most frequently observed. This case was considered to be caused by mixing of the surface lake water with the inflowing nutrient-rich river water at the shallow lake-head. Subsequently the effects of dissolved calcium and magnesium on the chlorophyll a and phytoplanktonic particulate phosphorus concentrations at the head of the reservoir were investigated until December 1987 (Project B). A trophic index, named the Ca-Mg index, was found which correlated positively with the chlorophyll a and phytoplanktonic particulate phosphorus concentrations in a logarithmic scale and varied in relation to the changes in the same index of the inflowing river water. Based on the ecological results of these two projects, two proposals are presented for inhibiting abundant phytoplankton growth at the head of a river reservoir. Proposal A: make the head deep and, in addition, create a strong near-bottom underflow of the inflowing river water. Proposal B: make a bypass in order to cut off the inflow of river water in the case of a high Ca-Mg index.     

Detection of monsoonal phytoplankton blooms in Luzon Strait with MODIS data

The Luzon Strait experiences a seasonal surge of phytoplankton based on ocean color data. To examine the timing and position of the bloom, daily MODIS chlorophyll data (2002-2005) were acquired and analyzed. Supporting data such as MODIS SST and nLw bands, QuikSCAT wind data, river discharge, and bathymetry were also used and processed in order to investigate the possible driving forces behind the bloom occurrence. Results show that chlorophyll concentration in the Luzon Strait dramatically increases during NE monsoon reaching to approximately 2.0 mg/m³. Highest chlorophyll concentration is observed near the western slope of the Luzon Strait. The monsoonal bloom in the Luzon Strait is likely due to upwelling and can be possibly associated with the interaction of the northward flowing Luzon coastal current with the westward intrusion of Kuroshio during NE monsoon. The positive wind stress curl also contributes to this occurrence. The influence of Cagayan River is only limited within few kilometers from the river mouth.     

藻类和悬浮物的光谱识别研究

针对藻类和悬浮物浓度测量仪,利用纯种藻和混合藻种的光谱数据,通过分析研究,提出了辨识的方法和途径。     

Modelling diatom growth in turbulent waters

Algal models used as tools in the management of algal blooms may be inaccurate because representation of mixing processes is often oversimplified. A testable 3-D algal model for prediction of algal growth in turbulent surface waters was developed based on the Eulerian water quality model, HYDRO-3D. Out-door mesocosm experiments on the growth of the diatom Skeletonema costatum showed no evidence that diatom growth is significantly affected by light/dark fluctuations brought about by turbulent mixing, and no direct effects of turbulence on phytoplankton physiology were required in the algal model. The algal model was successfully calibrated and validated against mesocosm data and field data from Poplar Dock, London Docklands. Application of the model gave credible results for the hypothetical growth of S. costatum in Poplar Dock under a wide range of wind speeds and surface irradiances. However, differences between the results of a full 3-D simulation and a simplified 1-D representation of Poplar Dock were minimal, and no clear conclusions could be drawn on the superiority of 3-D models over 1-D models for simulation of complex flows in natural water bodies.     

Long-term studies (1871–2000) on acidification and recovery of lakes in the Bohemian Forest (central Europe)

This paper evaluates long-term changes in the atmospheric depositions of S and N compounds, lake water quality, and biodiversity at eight glacial lakes in the Bohemian Forest over the past 130 years. This time interval covers (i) the ‘background’ pre-acidification status of the lakes, (ii) a period of changes in the communities that can be partly explained by introduction of fish, (iii) a period of strong lake acidification with its adverse impacts on the communities, (iv) the lake reversal from acidity, which includes the recent status of the lakes. The lake water chemistry has followed—with a characteristic hysteresis—both the sharp increase and decline in the deposition trends of strong anions. Remarkable changes in biota have mirrored the changing water quality. Fish became extinct and most species of zooplankton (Crustacea) and benthos (Ephemeroptera and Plecoptera) retreated due to the lake water acidification. Independent of ongoing chemical reversal, microorganisms remain dominant in the recent plankton biomass as well as in controlling the pelagic food webs. The first signs of the forthcoming biological recovery have already been evidenced in some lakes, such as the population of Ceriodaphnia quadrangula (Cladocera) returning into the pelagial of one lake or the increase in both phytoplankton biomass and rotifer numbers in another lake.     

DEHP enrichment in the surface microlayer of a small eutrophic lake

Investigation of di-2-ethylhexyl phthalate (DEHP) in the surface microlayer (SM) and subsurface water (SSW) of a small eutrophic lake was carried out from April to June 2002. Results obtained from the field samples showed that tens to several hundred mug/L of DEHP was found in each sample of SM and SSW, indicating that the lake has been polluted by DEHP. Linear regression analysis showed that concentrations of DEHP were more strongly correlated with sampling temperature than with chlorophyll a concentrations. Correlation between DEHP concentrations and total phosphor concentrations was also obtained. Enrichment factors (EFs) of DEHP in the SM comparing with the corresponding SSW were ranging over 0.85-2.12 with an average of 1.35. DEHP EFs were significantly related to both enrichment of chlorophyll a in the SM and sampling temperature.