Akanoi Bay Research Articles

Twenty Years History of Water Quality Research which is Implemented by Citizens' Initiative in Rivers Flowing into Akanoi Bay of Lake Biwa

Twenty Years History of Water Quality Research which is Implemented by Citizens' Initiative in Rivers Flowing into Akanoi Bay of Lake Biwa

Measures for the conservation of water quality in Lake Biwa and the Akanoi Bay initiative

AbstractLake Biwa is the largest lake in Japan, supplying water resources to support the lives and economic activities of 14 million people living in its downstream area. It also is one of the oldest lakes in the world, being more than 4 million years old, and ‘an ecological treasure house’ inhabited by a variety of animals and plants. In the Shiga Prefecture, to pass Lake Biwa to the next generation in a sound condition, the ‘Lake Biwa Comprehensive Conservation Plan’ (Mother Lake 21 Plan) was developed. It has been striving to achieve the comprehensive conservation of Lake Biwa, with the support of national ministries and also with the support of the people of the prefecture. This plan comprises three major areas: ‘Maintaining Water Quality’, ‘Improving the Recharge Capacity of the Soil,’ and ‘Preserving the Natural Environment and Scenic Landscapes’. The goals of the generated stages of each plan were agreed by all relevant parties. ‘The Lake Biwa Water Conservation Plans’ were settled upon in regard to preserving water quality. The Mother Lake 21 Plan represented a long‐term vision, including the development of water conservation measures. In the current 5th period plan, ‘the Akanoi Bay watershed run‐off plan Akanoi measures’ were added, as a supplement to the traditional approach, to strengthen measures for the non‐point source pollution. Akanoi Bay is a narrow, closed bay, being located in an area of the lake in which the water has been badly polluted because of the spread of the urban areas surrounding the lake, and because of the rapid influx of people. It also is the area where the people are very active in the environmental protection and is the model case study illustrating where the government and the inhabitants can work together to promote measures for addressing non‐point source pollution.

Seasonal Changes of PFOS and PFOA Concentrations in Lake Biwa Water

A survey on seasonal concentration changes of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) was performed for surface water in Lake Biwa (14 sites) from February to November in 2009. The concentrations of PFOS and PFOA were 0.8-1.6 and 7.0-10 ng/L in northern basin of Lake Biwa (eight sites), 0.9-1.7 and 8.3-13 ng/L in southern basin of Lake Biwa except Akanoi Bay (four sites), 1.4-2.8 and 9.1-17 ng/L in Akanoi Bay (8C) and 2.4-5.3 and 12-26 ng/L in Akanoi Bay (168), respectively. Seasonal changes were recognized for both of PFOS and PFOA in the two sites of Akanoi Bay but not in the other sites of the southern and northern basins of Lake Biwa. Monthly detailed surveys in the surface water were performed on the changes of PFOS and PFOA concentrations from June in 2009 to May in 2010 and further on the changes of conductivity values. The changes of PFOS and PFOA concentrations were well consistent with those of conductivity values.

Evaluation of micro‐organic pollution in lake sediments: Application to Akanoi bay, lake Biwa, Japan

The pollution of lake sediments by organic micro‐pollutants has been of growing environmental concern due to their suspected long‐term effects on both human health and the surrounding ecosystem. In this research, in order to investigate and evaluate the micro‐organic pollution in lake sediments, an analytical methodology consisting of freeze‐drying, Soxhlet extraction with dichloromethane, concentration by rotary‐evaporator, purification and fractionation by Sep‐pak florigil cartridge, and quantification by GC/MS was formulated and applied to the lake sediments of Akanoi Bay, Lake Biwa in Japan. Two polycydic aromatic hydrocarbons (PAHs) (i.e., fluoranthene and pyrene) were detected in the collected sediment samples. Based on the horizontal distribution of these two PAHs and the particle size distribution of the sediment samples, it was considered that the river inflows (the land usage in their upstream is mainly paddy field and residential) into the bay are the major pollution sources.

Characterization of suspended solids in Lake Biwa by measuring their elemental composition of Al, Si, P, S, K, Ca, Ti, Mn, and Fe

We investigated the concentrations of particulate Al, Si, P, S, K, Ca, Ti, Mn, and Fe at various areas of Lake Biwa, such as the limnetic zone in the northern basin, the offshore zone, the dredged area and Akanoi Bay in the southern basin, and reed community areas in the shore. In the wide and deep northern basin, the density of suspended solids was low, and substantial fractions of particulate Si, P, S, and Ca were biogenic matter produced by phytoplankton. In the offshore zone in the narrow and shallow southern basin, the concentration ratios of particulate Si, K, Ca, Ti, and Fe against particulate Al were almost constant throughout the year and were similar to those found in crusts. Therefore, these elements are most likely derived from terrigenous clay matter. In the dredged area where the hypolimnion became anoxic during the stratification period, the concentrations of particulate Fe, Mn, P, S, and Ca increased because of the formation of hydrous Fe and Mn oxides and Fe sulfide. In Akanoi Bay, the ratios of Mn/Al and Fe/Al were high because of the stirring of sediments enriched with Mn and Fe oxides. In the reed community areas, the concentration of suspended solids correlated well with particulate Fe and P, but not with Al or chlorophyll a; therefore these areas seem to be rich in humic organic matter enriched with P and Fe due to microbial activity. Thus, the elemental composition of suspended solids reflects the chemical, biological, and physical processes in the lake and gives us useful indices of the characteristics of the water.

Fatty acid composition as an indicator of physiological condition of the cyanobacterium Microcystis aeruginosa

The present study examined the fatty acid composition of Microcystis aeruginosa grown in a batch culture and that of Microcystis-dominated plankton collected in an experimental enclosure in a shallow, eutrophic embayment of Lake Biwa (Akanoi Bay). In pure culture, we detected 16 : 0, 18 : 2ω6, 18 : 3ω3, 18 : 3ω6, and 18 : 4ω3 acids as major fatty acids of M. aeruginosa, with trace amounts of C20 polyunsaturated fatty acids. In both pure culture and the field enclosure, the ratio of total fatty acid weight to dry weight decreased with decreasing availability of dissolved inorganic nitrogen. The ω3/ω6 ratios of C18 polyunsaturated fatty acids [(18 : 3ω3 + 18 : 4ω3)/(18 : 2ω6 + 18 : 3ω6)] varied greatly (range, 2–5) in response to the changes in physical and chemical conditions for Microcystis growth. Most notably, the ω3/ω6 fatty acid ratios were significantly positively correlated with the growth rate of cells in a batch culture. We suggest that the fatty acid composition is a useful indicator of the physiological state of Microcystis in freshwater lakes.

Effect of cyanobacterial blooms on thermal stratification

Enclosure experiments were performed at Akanoi Bay, Lake Biwa, in 1995 to determine whether the blooms of cyanobacterial algae changed thermal stratification in the lake. We used four rectangular enclosures, each 10 m × 10 m, with a volume of 200 m3, which were open to the sediments. Two enclosures, A and B, were mixed artificially by aquatic pumps from 1000 to 1400 every day, and the other two enclosures, C and D, were controls with no mixing. The experiment was conducted during late summer from August 3 to September 27. Chlorophyll a concentrations were highest in enclosure D, followed by enclosure C, both of which were controls without mixing. Enclosure A had lower concentrations than enclosures C and D, and enclosure B had the lowest concentrations. No large cyanobacterial algae blooms of Anabaena sp. and Microcystis sp. were seen in the mixed enclosures A and B. In enclosures C and D, blooms of Anabaena sp. occurred in the middle of August, and Microcystis sp. later became dominant in enclosure D at the end of August. In enclosure D, the water temperature changed over the diel cycle before August 17, with thermal stratification during the day and complete mixing at night. After August 17, as Anabaena sp. and Microcystis sp. became dominant, the temperature at the bottom of the enclosure did not change clearly over the 24-h cycle. The APE (available potential energy) density (a measure of water column stability) in the enclosures increased by almost 100% when the biovolume of Anabaena sp. + Microcystis sp. exceeded 20 mm3 l−1. These results indicate that blooms of Anabaena sp. and Microcystis sp. can increase the available potential energy in the water column and create more stable stratification for their growth.

Akanoi Bay, Lake Biwa seasonal changes in porewater phosphorus

Akanoi Bay, Lake Biwa seasonal changes in porewater phosphorus

The Influence of Wind on the Horizontal Distribution of Bloom-forming Cyanobacteria in Akanoi Bay, Lake Biwa.

In the summer of 1995, bloom-forming cyanobacteria were observed on the surface of Akanoi Bay in the South Basin of Lake Biwa. During that summer season, the horizontal distribution of chlorophyll a concentration was measured, and the cell density of phytoplankton was counted microscopically. Two different horizontal distributions of the dominant bloom-forming cyanobacteria were observed under moderate wind conditions. The colonial cyanobacteria with aggregated filaments, Anabaena of iinis, and mucilaginous clumps of Microcystis aeruginosa tended to be transported horizontally by wind, while Planktothrix agardhii with solitary filaments did not. This suggests that different cyanobacteria species may be affected by wind in different ways due to their varying physiology or morphology.

Pharyngeal Tooth Remains of the Genus Cyprinus, Including an Extinct Species, from the Akanoi Bay Ruins

Other Jomon ruins are found on the bottom of Akanoi Bay, Lake Biwa, offshore from Akanoi-cho, Moriyama City (Fig. 1). The site is dated as Early Jomon Period because it is situated immediately under the Akahoya volcanic ash layer (Hirai, 1987). Cyprinid teeth from the site are mostly crucian carps Carassius, but teeth of other cyprinids are also included. Four unbroken A2 teeth of the common carp genus, Cyprinus, are among these other teeth, identified as such because they are molariform and have grooves on the grinding surface (Chu, 1935). One of these A2 teeth is different from those of the common carp, Cyprinus carpio, and from other Cyprinus species from the site. The Cyprinus teeth are described here.

A bioassay to assess the potential effects of sediment resuspension on phytoplankton community composition

A laboratory assay (SAGA or Sediment Algal Growth Assay) was developed to assess the potential impact of sediment resuspension on the structure of phytoplankton communities, and to evaluate the effectiveness of various sediment treatments in decreasing the abundance of blue-green algae in the event of sediment resuspension during storms. In assays with sediment from eutrophic Akanoi Bay, Lake Biwa, Japan, 7–11 species of phytoplankton seeded from the sediments grew during the 3-week assay indicating that sediment resuspension has the potential to increase both phytoplankton biomass and species diversity. Treatment of sediments with Ca(NO3)2 substantially decreased phytoplankton biomass (measured as chlorophyll concentration) in assays with sediments from Akanoi Bay and the North Basin of Lake Biwa. Further, among various oxidation treatments of sediments, Ca(NO3)2 was most effective in decreasing or preventing filamentous blue-green algal growth in N- and P-replete media. In contrast, when sediments were added to P-limited phytoplankton dominated by green algae and diatoms, no growth of blue-green algae occurred regardless of sediment treatment.

Changes of Water Quality of Lake Biwa Caused by the Shortage of Water in 1994

In the late summer of 1994, the water level of Lake Biwa was reached to 123cm under the standard level by the shortage of water. The level is the lowest since measurement of the water level was begun. This shortage of water was caused by small rainfall in the rainy season and high temperature from May to middle of September. The weather condition gave various influences to the water quality of the lake. But the results were different by shape of basins in the lake. In the deep and large northern basin, NO3-N, the only detectable nutrient, was disappeared from surface layer in early stage. It brought small amount of algae and high transparency in the basin. In the shallow and small southern basin, high concentrations of COD were measured, as retention time in the basin became long and the effect of influx from the northern basin was decreased. In the more shallow and half closed water area, Akanoi Bay, extremely high concentrations of total phosphorus were measured, it caused continuous generation of water bloom of blue-green algae under the weather condition.

Metabolic rate of dissolved proteinous nitrogen in the sea and lake bottom mud.

The fate and metabolic rate of dissolved proteinous nitrogen in the sea and lake bottom mud were studied using 15N-labeled Chlorella protein. The relationship between the metabolic rate of nitrogen and bacterial flora concerning nitrogen cycle in the bottom mud was also studied. Turnover rates of dissolved proteinous nitrogen in the bottom mud were 4.0%/h in September in Mikawa Bay, 2.2%/h in March in Mikawa Bay and 2.5 %/h in November in Akanoi Bay, respectively. The 43-84% and 8-14% of metabolized proteinous nitrogen were incorporated into particulate and ammonium nitrogen, respectively.

Studies on the Release of Ammonium Nitrogen from the Bottom Sediments in Freshwater Bodies-I

In an aquatic environment, bottom mud plays an important role in the determination of the quality of water, especially in shallow freshwater bodies. A considerable amount of nutrients, originating from organic matter, are often accumulated in bottom mud and released into the water, which may cause eutrophication. From this point of view, a quantitative study has been carried out as to the release of ammonium nitrogen into the water from the bottom mud of Akanoi Bay in Lake Biwa by the use of an annular channel. The authors applied diffusion process theory in this study and obtained the diffusion coefficient of 5×10-6cm2/sec when overlying water was still and 2×10-5cm2/sec when it was moving with current velocity 1040 cm/sec. Ammonium nitrogen in mud must be considered to consist of diffusive and non-diffusive parts in order to explain the change in the vertical distribution of ammonium nitrogen in mud. The diffusive part of ammonium nitrogen in each mud sample with various ammonia concentrations was determined. The increasing rate of ammonium nitrogen with the lapse of time agrees well with the release rate estimated from the diffusion process theory.