Water quality estimation in consideration of pollutant runoff and internal production in Lake Biwa, Japan

2007 ◽  
Vol 55 (3) ◽  
pp. 167-175
Author(s):  
A. Ichiki ◽  
K. Nakakura ◽  
N. Sakata ◽  
A. Sasaki ◽  
Y. Tai
Keyword(s):  
Water Quality ◽  
Spatial Distribution ◽  
Water Surface ◽  
Lake Biwa ◽  
Water Quality Management ◽  
Simulation System ◽  
Quality Estimation ◽  
Limiting Nutrients ◽  
Pollutant Runoff ◽  
Internal Production

Lake Biwa is the largest lake in Japan, and water quality in the lake is heterogeneous. Therefore, it is important for water quality management that spatial distribution of water quality in the lake should be clearly understood. The objectives of this study are to show a methodology and to develop a simulation system to calculate COD distribution in Lake Biwa taking internal COD production into consideration. This study also aims to examine transition of COD in the lake using the simulation system. In the simulation system, runoff loads of COD from the Lake Biwa basin are calculated by Macro Model for each tributary. The external COD concentration in 233 inshore meshes of the Lake Biwa water surface was calculated using the runoff loads. The internal COD was calculated using relationships among limiting nutrients, chlorophyll-a and COD. Then, the spatial distribution of water quality in Lake Biwa was calculated both for the external and internal COD by spline technique. Simulations using the system were implemented for 1986–1998, and a clear difference in characteristics between a drought year and a flood year was shown. In the result, it was shown that the simulation system developed here was available to calculate COD distribution in Lake Biwa, and that it had the possibility to explain the recent phenomenon of COD increase in the lake.

Estimation of urban nonpoint source pollution in Lake Biwa Basin

1998 ◽  
Vol 38 (10) ◽  
pp. 157-163 ◽  
Author(s):  
Atsushi Ichiki ◽  
Toshiyuki Ohnishi ◽  
Kiyoshi Yamada
Keyword(s):  
Water Quality ◽  
Environmental Management ◽  
Nonpoint Source Pollution ◽  
Lake Biwa ◽  
Nonpoint Source ◽  
Storm Events ◽  
Valuable Data ◽  
Nonpoint Sources ◽  
Pollutant Runoff

This study aims to simulate pollutant runoff into Lake Biwa using the Macro Model and examine the runoff characteristics of pollutants from urban nonpoint sources. As a result of the simulations of all rivers flowing into Lake Biwa, the characteristics of urban nonpoint source pollution and the basic units of urban nonpoint pollutants in the Lake Biwa basin became clear. It was shown that the control of pollutant runoff from nonpoint sources during storm events was significant in order to protect the water quality of Lake Biwa. From these results, valuable data concerning the environmental management of the Lake Biwa basin was obtained.

Phytoplankton-based water quality metrics: feasibility of their use in a Neotropical shallow lake

2018 ◽  
Vol 69 (11) ◽  
pp. 1746 ◽  
Author(s):  
Diego Frau ◽  
Gisela Mayora ◽  
Melina Devercelli
Keyword(s):  
Water Quality ◽  
Spatial Distribution ◽  
Soluble Reactive Phosphorus ◽  
Quality Metrics ◽  
Ecological Quality ◽  
Quality Estimation ◽  
Cyanobacteria Blooms ◽  
Environmental Variations ◽  
Reactive Phosphorus ◽  
Q Index

Urban lakes constitute important recreational areas, but often they are eutrophicated. In this study we discuss the utility of 12 ecological quality metrics to test whether they: (1) can be applied to Neotropical lakes; (2) are sensitive to environmental variations throughout the year; and (3) are affected by heterogeneous spatial distribution of phytoplankton. Phytoplankton and environmental variables (including nutrients) were sampled monthly in an urban lake (four littoral and one limnetic station) throughout 1 year (n=60 samples). Twelve ecological quality metrics were tested using total phosphorus as a proxy of eutrophication through general lineal models. The best adjusted metrics were then transformed to an ecological quality ratio (EQR) to allow comparisons. The Phytoplankton Assemblage Index (Q-index) and the Cyanobacteria Bloom Index (CBI) were the most accurate. Differences in water quality estimation occurred across the year, with an overestimation of water quality in the absence of cyanobacteria blooms. There were no differences due to effects of the spatial distribution of phytoplankton. The Q-index was related to temperature and soluble reactive phosphorus, whereas the CBI was related to conductivity. We conclude that the Q-index is the most accurate metric for monitoring purposes, responding well to variations in phosphorus.

Numerical Study on the Effects of Water Surface Shield and Oxygen Injection on Water Quality in Lake Biwa

2008 ◽  
Author(s):  
Daisuke Kitazawa ◽  
Michio Kumagai
Keyword(s):  
Water Quality ◽  
Dissolved Oxygen ◽  
Water Surface ◽  
Lake Biwa ◽  
Vertical Mixing ◽  
Three Dimensional ◽  
Coupled Model ◽  
Floating Platform ◽  
Oxygen Injection ◽  
Water Bottom

Numerical simulation was carried out by means of a three-dimensional hydrostatic and ecosystem coupled model in order to predict the effects of water surface shield and oxygen injection on the water quality in Lake Biwa. Recent observations show the degradation of water quality particularly around the water bottom in Lake Biwa. One of the possible reasons of the degradation is the depletion in the vertical mixing of waters due to climate change. The meteorological observations at Hikone show that the atmospheric temperature has increased by 1°C in the recent 20 years. If the vertical mixing of waters is weakened, the waters with rich oxygen are not supplied enough around the water bottom during winter seasons, and the concentration of dissolved oxygen is hardly recovered to the saturated level. The depletion in the vertical mixing of waters has been increasingly worried since Intergovernmental Panel on Climate Change (2007) reported that the globally mean atmospheric temperature will increase by a few °C in a century. In order to cope with such problems, the present study proposes a feasible system to inject the oxygen produced by the electrolysis of water. In the proposed system, water surface is shielded by a floating platform, which blocks off the penetration of solar radiation through the water surface and generates the density-driven current due to the horizontal difference in water temperature. In addition, solar cell modules are installed on the floating platform to produce oxygen by means of the electrolysis of water. The produced oxygen is then released from the electrodes installed around the water bottom. As a result of numerical simulation using the three-dimensional hydrostatic and ecosystem coupled model, the effect of water surface shield was negligible since the surface area of the floating platform was quite smaller than that of Lake Biwa. The effect of oxygen injection was remarkable and localized in summer than in winter. The concentration of dissolved oxygen was then expected to increase by more than 0.2mg/l within 15m from the bottom surface in summer, in the cases when 730,000m3 of oxygen was injected in an year. The effect of seasonal change in the production of oxygen was negligible since little difference was found in the concentration of dissolved oxygen. As future studies, the nested grid system should be utilized to predict precisely the diffusion of oxygen both in the vicinity of the electrode and in the whole Lake Biwa.

Study on characteristics of pollutant runoff into lake biwa, Japan

1999 ◽  
Vol 39 (12) ◽  
pp. 17-25 ◽  
Author(s):  
Atsushi Ichiki ◽  
Kiyoshi Yamada
Keyword(s):  
Water Quality ◽  
Environmental Management ◽  
River Basin ◽  
Lake Biwa ◽  
Annual Runoff ◽  
Macro Model ◽  
Pollutant Runoff

This study aims to simulate pollutant runoff using the Macro Model and examine the characteristics of pollutant runoff into Lake Biwa. As a result of the simulations in all rivers flowing into Lake Biwa, annual runoff load from every river basin was shown. The characteristics of pollutant runoff into Lake Biwa were examined with consideration to characteristics of river basin and rainfalls. In the results, it was shown how we should control pollutant runoff effectively in order to protect the water quality of Lake Biwa, and some knowledge concerned with the environmental management of the Lake Biwa basin was obtained.

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