Senichi Ebise

Runoff characteristics of COD, BOD, C, N and P loadings from rivers to enclosed coastal seas

Abstract It is well known that the three nutrient elements of carbon (C), nitrogen (N) and phosphorus (P), are very important in the eutrophication in enclosed coastal seas. The major source of the C, N and P is the inflow from rivers rather than the release from sediment in the closed sea. In Japan, the environmental quality standards which indicate organic pollution in both river and sea are different from one another; in a river, it is based on BOD and in the sea, on alkaline COD M d . Therefore, these different standards lead to difficulties in obtaining consistent water quality management of the water system from rivers to enclosed coastal seas. Hinuma River observed runoff loading of alkaline COD M d , BOD, C, N and P by weekly observation in 1988 and 1989. When the flow increases, the order of increasing ratio is phosphorus, followed by carbon, and nitrogen. It was found that 88% of phosphorus runs off in the form of particulate phosphorus and 84% of nitrogen runs off in the form of dissolved nitrogen; and though nitrogen runs off in an almost constant concentration, most phosphorus runs off during the high flow stage. The behavior of the particulate phosphorus after flowing in to the enclosed coastal sea is an important factor in eutrophication.

Change in C:N:P ratios during passage of water areas from rivers to a lake

Abstract There are no detailed data concerning the carbon load of inflow rivers, in spite of carbon being one of the most important elements in closed water areas. The authors have therefore conducted weekly observations on four rivers flowing into lakes during a 1-year perod. A remarkable statistical characteristic for input loads of carbon, nitrogen and phosphorus, from the four river basins, was their dependence on discharge. Loads of three elements in the inflow rivers to Lake Kasumigaura were measured by four seasonal observations in the year. The TOC: T-N:T-P ratios of inflow nutrients were 27–45:8–32:1 using both arithmetic and discharge-weighted mean concentrations. The TOC:T-N:T-P ratios for the whole of the lake and for a bay receiving inflow from three rivers were estimated on the basis of monthly observations. Most of the inflow loads of particulate nutrients were deposited in the river mouth, whereas the inflow loads of dissolved nutrients and production-degradation processes of oganic matter largely controlled the nutrient budget in the lake water by comparison of the ratios for surface mud, phytoplankton and detritus.

Regression models for estimating storm runoff load and its application to Lake Kasumigaura

Regression models are proposed for accurate estimation of storm runoff load. Regression equations are obtained for the relationship between final cumulative load and flow during direct runoff by each storm event. The models are applied to estimate annual nutrients load by all influent rivers into the Lake Kasumigaura for a model year of average annual rainfall. The load in dry weather is calculated from observed data of all influent rivers. Total annual load for a year is the sum of loads in dry weather days and loads in wet weather days. The ratios of the load in a wet weather day to total annual loads are 29 percent for T‐N, 51 percent for T‐P, 53 percent for T‐COD, 22 percent for D‐N, 22 percent for D‐P and 30 percent for D‐COD.