Impacts of Hydrological Changes on Nutrient Transport From Diffuse Sources in a Rural River Basin, Western Japan

Abstract

Increased frequency of heavy rainfall caused by climate change may affect nutrient transport from forests and agricultural lands into downstream rivers. However, little information is available on how the effects of land cover on nutrient concentrations in the downstream rivers change depending on hydrological conditions. To elucidate this, we investigated the effects of changes in precipitation and river discharge on the relationship between river nutrient concentrations (total nitrogen, total phosphorus, nitrate, and phosphate) and land cover in eight subbasins of the Hii River basin, western Japan. We hypothesized that coniferous forests and agricultural lands including poorly managed ones, which require thinning and fertilizer management, respectively, contribute to increases in nutrient concentrations in downstream rivers during storms. Linear mixed-effects model analyses based on 18-year observation data were used for testing the hypothesis. Results revealed that the slopes of the multiple regression analysis between nutrient concentrations and coniferous and broad-leaved forest area ratios were negative and decreased with increasing daily precipitation. This suggests that forests contributed to the dilution of river nutrient concentrations during storms regardless of whether they were coniferous or broad leaved. In contrast, the slope of regression between nutrient concentrations and agricultural area ratio revealed the opposite trend, indicating that even a small percentage of agricultural area makes a large contribution to increases in nutrient concentrations as precipitation increases. Our results imply that storm runoff in response to rainfall results in an elevated supply of nitrogen and phosphorus attached to arable soils to the river.

A hybrid stochastic river environmental restoration modeling with discrete and costly observations

“…This topic can also be discussed in the framework of stochastic control with partial observation, and will be addressed utilizing analytical and numerical techniques related to degenerate parabolic PDEs. From an application viewpoint, a complicated population dynamics model considering more detailed environmental dependence may be employed, 99‐101 which would be investigated along with extensive laboratorial experiments on the algae detachment. A key challenge would be how to formulate a more sophisticated model without using unnecessarily complex coefficients.…”

Combined impact of land cover, precipitation, and catchment area on discharge and phosphorus in the Mississippi basin's subcatchments

“…Jarvis, . Moreover, urban areas can contribute to P pollution because there is a positive correlation reported between P content and urban land use (Brett et al, 2005;Ide et al, 2019). Urbanization is typically associated with modifications of physical and hydrogeological characteristics of basins and creation of nutrient sources.…”

“…Yard fertilizers, septic tank drainage, domestic animal wastes, and elevated soil erosion in urban areas are commonly linked to high P content and consequently water quality degradation (Carpenter et al, 1998;Soranno, Hubler, Carpenter, & Lathrop, 1996;Tufford, McKellar, & Hussey, 1998). In contrast, Brett et al (2005) and Ide et al (2019) found that the average P concentration was negatively correlated with forest area ratio. The loss of forests in humid areas leads to minimizing the recycling of nutrients owing to declining microbial activities and plant processes that immobilize nutrients in the forest canopy, organic matter, and soil (Abelho, 2001;Wahl, McKellar, & Williams, 1997).…”

“…In many regions around the world, P inputs from chemical fertilizers and manure exceed P outputs in farm yields, thus causing surpluses of P that ultimately accumulate in soils (Carpenter et al., 1998; Foy & Withers, 1995; Haygarth, Chapman, Jarvis, & Smith, 1998). Moreover, urban areas can contribute to P pollution because there is a positive correlation reported between P content and urban land use (Brett et al., 2005; Ide et al., 2019). Urbanization is typically associated with modifications of physical and hydrogeological characteristics of basins and creation of nutrient sources.…”

Cost‐efficient monitoring of continuous‐time stochastic processes based on discrete observations

“…We focus on a mathematical modeling of monitoring a continuous‐time process representing temporal evolution of some environmental and ecological indices. We assume that the monitoring is carried out in a discrete‐time manner as in real problems of environment and ecology 12‐19 . The decision‐maker, the observer of the target process, decides a monitoring policy containing the times at which the observations are carried out.…”