Estimation of long-term variation in nutrient loads from the Hii River by comparing the change in observed and calculated loads in the catchments

Abstract

To study the long-term change in nutrient loads from the Hii River to Lake Shinji, water samples were taken repeatedly over a year in 1983/1984 and again in 2001/2002. Annual total nitrogen (TN) loads, estimated from observations of water quality and river flow, increased from 860 to 920 t with a corresponding increase in NO 3 -N concentration during the cool season. In contrast, total phosphorus (TP) loads decreased from 96 to 62 t. Annual TN and TP loads, calculated using emission factors and annual statistics for the catchments, showed a tendency to decline from 1986 to 2002. No source could be identified which would result in the increase in TN in the catchments, therefore, the increase in observed TN loads was considered to originate in other areas. Atmospheric nitrogen deposition transported from long distances has elevated the sum of NH 4 -N and NO 3 -N concentration in rainwater in the cool season. Therefore, it was considered that this resulted in the increase in TN loads in the Hii River.

Robust stochastic control modeling of dam discharge to suppress overgrowth of downstream harmful algae

“…The study area is Hii River in Japan (Figure ). Environment and ecology of the river are reviewed in other works . Obara Dam with the height of 90 (m) is the largest dam installed in the river (Figure ).…”

The Effect of Charophyte Communities on Phosphorus Flow in Lake Shinji, Japan

“…These conditions favour the diffusion of phosphorus from the sediments (Kamiya et al, 2011). According to Kamiya et al (2008), the annual phosphorus inflow to the lake is 62.4 t y -1 . This is significantly less than the 95.6 t y -1 recorded when observations began in 1983, suggesting that the phosphorus inflow to the basin has decreased, mostly likely as a result of improvements to sewage systems and septic tank devices.…”

Phosphorus release and sedimentation in three contiguous shallow brackish lakes, as estimated from changes in phosphorus stock and loading from catchment

“…Coefficient variations (CVs) for a concentration of about 10 lg L -1 were about 3% for SRP and 9% for TP (Kamiya 1992). Daily TP load from the Hii River into Lake Shinji was calculated using values of daily flow rate from fiscal year (FY) 1992 (April 1992to March 1993(April 2001to March 2002 and applying the following load-flow (L-Q) equation, parameters of which were estimated by frequent water sampling in the Hii River from September 2001 to August 2002 (Kamiya et al 2008):…”

“…Values obtained by the two methods were approximately the same for these 2 years. The variation of TP loads from the catchment area of Lake Shinji was small from FY 1992 to FY 2002 (Kamiya et al 2008). We therefore assumed that TP load into Lake Shinji from 1992 to 2002 could be calculated by the L-Q equation.…”