Morihiro Aizaki

Trophic status of Tilitso, a high altitude Himalayan lake

The trophic status and water quality of Lake Tilitso (4920 m above sea level) in a high altitude region in central Nepal were surveyed in September, 1984. The lake is rather large with a maximum depth of 95 m and a surface area of 10.2 km2. The lake water was turbid due to glacier silt and the euphotic layer was only 5 m deep. The nutrient concentration was very low with total phosphorus concentration 1–6 µg l−1, and DTN concentration 0.10–0.22 mg l−1. The phytoplankton biomass and chlorophyll-a concentration were also low. Primary production was estimated to be about 12 mg C m−2 d−1. The concentrations of particulate matter and most cations and bacterial number were higher in the epilimnion than in the hypolimnion. The trophic status of this lake was estimated as ultraoligotrophic.

HPLC fluorometric determination of natural phytoplankton phycocyanin and its usefulness as cyanobacterial biomass in highly eutrophic shallow lake

A method for HPLC determination of phycocyanin in phytoplankton samples using gelchromatography with a fluorescence detector was developed to examine the use of phycocyanin as an index of the appearance and progress of cyanobacterial blooms in highly eutrophic lake. At least two types of phycocyanin with different molecular weights, each spectroscopically different from phycoerythrin and allophycocyanin, were found in natural phytoplankton samples.Changes in phycocyanin concentrations were clearly coupled to changes in chlorophyll-a concentrations during June to October while cyanobacterial blooms were occurring. The chlorophyll-a to phycocyanin relationship was linear at chlorophyll-a concentrations of less than 250 μg L−1. The relationship between cyanobacterial carbon and phycocyanin concentration was also linear, suggesting that phycocyanin content may be a useful index of cyanobacterial biomass in highly eutrophic lakes where large cyanobacterial blooms occur.

Freshwater DOC measurements by high-temperature combustion: Comparison of differential (DTC - DIC) and DIC purging methods

Two methods were compared for the measurement of dissolved organic carbon (DOC) in waters collected from lakes, rivers and several pollution sources. Both the differential method (D-DOC method), derived from dissolved total carbon (DTC) minus DIC (dissolved inorganic carbon), and the purging method (P-DOC method), which purges DIC, were evaluated with a Shimadzu TOC-5000 with a high temperature catalytic oxidation system. Particularly in cases of gray water and/or water which had seeped through soil-layers, considerably lower concentrations were noted for P-DOC purged at around pH 2 than those measured by the D-DOC method or the P-DOC method at pH 4. DOC measurements for both field samples and specific compounds decreased due either to precipitation or flotation of colloidal organic particles insolubilized during sparging at pH 2 or 3 or to their incomplete combustion. The D-DOC method, exhibiting lower precision than the P-DOC method particularly for samples with high DIC vs DOC ratios, is, however, recommendable because of its accuracy.

Regeneration of Nutrient and Detritus Formation from Aerobic Decomposition of Natural Phytoplankton.

Respiration and short-term decomposition processes of natural phytoplankton communities collected from eutrophic Lake Kasumigaura were examined eight times in each season from 1983 to 1985 under dark and aerating conditions.The lag periods were observed for the increase of nutrient and the decrease of cell components during the initial period of the incubation. This fact suggested that most of the phytoplankters were living in the initial few days under these conditions. Since the nutrient regeneration seemed to be unrelated to the oxygen consumption rate, it was considered that the change in nutrient concentration had to be measured directly for estimation of the regeneration rate, and this measurement was useful to distinguish between decomposition and respiration processes of phytoplankton.The decomposition process could be described as a first order process in the initial period. The relative rates of decrease of the measured parameters were as follows; chlorophyll>nitrogen>carbon. Decomposition and nutrient regeneration rates seemed to be affected by water temperature and the algal species composition. Bluegreen algae easily decomposed at high temperature, but diatoms did not.About 70-90% of cell carbon and nitrogen were easily mineralized to C02 and dissolved inorganic nitrogen, and only about 10-30% changed to detritus carbon and nitrogen. About 24% of cell phosphorus was regenerated in average and the remain-der was in. the particulate form.

Relationship between nutrient loading and phytoplankton standing crop in outdoor experimental ponds with continuous flow systems

Abstract The relationship between nutrient loading and phytoplankton standing crop was studied in outdoor experimental ponds during a period from autumn 1978 to winter 1979. Throughout the experimental period, phosphate, nitrate and ammonium at 3.5, 7.0 and 10.6 mg m −2 d −1 of phosphorus, respectively were added continuously into three experimental ponds. Nitrogen loading was adjusted to about 7 times the phosphorus by weight. The apparent water residence time of each experimental pond was 20 days. The phytoplankton standing crop at steady state showed a high correlation to the nutrient loading. The relationship between phosphorus loading (P, mg m −2 d −1 ) and concentrations of chlorophyll- a (Chl- a , μg l −1 ) in the experimental ponds could be expressed by the following formula; (Chl- a ) = 18.1 (P) − 57 ( n = 14, r = 0.90). The relationship between total phosphorus and chlorophyll- a concentrations in the experimental ponds varied in each season. The slopes of the regression lines were greatest in autumn, and smallest in summer.

Phosphorus budgetary analysis of sediment–water interface in a short-term anoxic condition in shallow Lake Kasumigaura, Japan

To investigate the effective depth from the surface sediment, and phosphorus fractions related to phosphorus release under short-term anoxic conditions, varying lengths of sediment cores taken from Lake Kasumigaura, a large shallow polymictic lake in Japan, were incubated for a few weeks and then analyzed. Results showed few differences in total phosphorus (TP) amount per unit area in overlying waters irrespective of the core thickness, and sums of TP in both overlying water and 0- to 2-cm sediment layers were nearly equal before and after the experiment, indicating that phosphorus was released mainly from the 0- to 2-cm layer by dissolution. In contrast, phosphorus was decreased in pore water below a 2-cm depth, probably through sorption to sediment solids. The citrate-dithionite-bicarbonate total phosphorus (CBD-TP) and non-reactive phosphorus extracted by NaOH (NaOH-NRP) in sediment solids in the 0- to 2-cm layer decreased during the experiment. The decreases of CBD-TP were 10 times higher than those of NaOH-NRP, suggesting that the released phosphorus came mainly from the fraction bound to iron in Lake Kasumigaura.

Relationship between estimated pollutant load using GIS and observed water quality in a river flowing into Lake Kasumigaura

Lake Kasumigaura is a widely known eutrophic lake in Japan. After the Hitachigawa water gate was built in 1968, the lake water changed from brackish to fresh. Many studies have examined the water quality change in this lake. However, the water quality has nor improved over rhe last 20 years (IBARAKI PREFECTURE 1999). A water quality management plan for this lake has been devised every 5 years since 1986; numerical data only were used to devise these plans. Recently, it has become difficult to introduce effective new measures using this method. The introduction of detailed measures requires geographical data in addition to numerical data. Recently, geographic information systems (GIS) technology has made remarkable progress, and it enables the use of both numerical and geographical data ona PC (MATSUSHIGE & AIZAKI 1993). A water quality management system was constructed for several rivers flowing into L. Kasumigaura, using GIS. In the present study, the discharged pollurion load and the concentrations of chemical oxygen demand (COD), tora! nitrogen (TN), and tora! phosphorus (TP) in the Seimei River were estimated. These values were calculated from land-use data and population data for each treatment method input into GIS. The estimated concentrations were compared with the concentrations observed at the river mourh.

Influence of Fish on Dominance of Blue-green Algae: an Experimental Study Using Large Outdoor Continuous Flow-through Ponds.

Experiments using six outdoor experimental ponds equipped with a continuous flow-through system of the same influx nitrogen and phosphorus concentrations and with different fish (goldfish) densities were conducted from Aug., 1993 to Sep., 1994 to investigate the factors influencing the dominance of blue-green algae in summer. In general, blue-green algae predominated in fish ponds, in contrast to green algae in fishless ponds. Blue-green algae started to flourish after the latter half of August, when the PO4-P concentrations decreased to less than 10 μg·l-1. The difference in dominated phytoplankton between fish and fishless ponds could be explained by the reduction of total phosphorus and subsequently the depletion of PO4-P in pond water due to the feces of fish and their growth, the condition of which is advantageous for blue-green algae than others.