Eutrophication in the newly built Laohutan Reservoir during the initial impoundment period: the role of nutrient loading

Abstract

The purpose of this study was to elucidate the role of nutrient loading played in the eutrophication of newly built reservoirs. Taking the Laohutan Reservoir as an example, field monitoring and laboratory experiments were conducted before and after the reservoir impoundment. According to the results, the Laohutan Reservoir was eutrophicated 4 months after its impoundment, since nutrient loading played an important role. Riverine inputs were found to be the major source of nutrients, with the contribution of greater than 72 %. Nutrients from soil were also influential during the first 20 days. Its release was gradually weakened by the routine operations of the reservoir. The release patterns of nutrients from the four main land-use types of soil (forest, bamboo groves, paddy and construction sites) were similar, but their influence to the reservoir water quality varied dramatically. And the atmosphere was also an important source of nutrients, especially nitrogen. Meanwhile, by a comparison, the Laohutan Reservoir to an older one located nearby, the newer with relatively lower trophic levels underwent a cyanobacteria bloom, while there was none in the older. It verified that new reservoirs were more prone to eutrophication than the older, and high nutrient loading is a necessary but not sufficient condition for eutrophication. The fragility of the new reservoir's ecosystem accelerated water environment deterioration, and resulted in the eutrophication and cyanobacteria bloom during the initial impoundment period.

Changes in Water and Sediment Quality of a River Being Impounded and Differences Among Functional Zones of the New Large Tropical Hydroelectric Reservoir

“…The low chl a concentration, however, coincided with low nutrient concentration, suggesting that nutrients were the limitation for phytoplankton in the lacustrine zone. Chl a concentration in the transitional zone of Murum Reservoir (≈ 15.5 mg/m 3 ) was relatively higher than that reported in Laohutan Reservoir [4], where it ranged from 1 to 10 mg/m 3 ; whereas chl a concentration in the lacustrine zone (≈ 4.4 mg/m 3 ) was within the reported range during its initial impoundment period. The higher chl a concentration in the present study could be due to the considerably higher TP concentration in Murum Reservoir (≈ 0.51 mg/L) than in Laohutan Reservoir (0.013-0.073 mg/L), as phosphorus is often considered the limiting factor in phytoplankton growth.…”

“…Again, the high organic matter coupled with low DO led to the accumulation of TAN. Similarly, Zhu et al [4] reported higher TN and TP concentrations at bottom water than those at surface water of the newly built Laohutan Reservoir during the initial impoundment period where the authors attributed the nutrient stratification to the release of soil nutrients.…”

“…The present study demonstrates that water quality of Murum Reservoir is different in different functional zones during the filling phase. The inflow from the riverine zone into the reservoir is often responsible for the longitudinal patterns observed in the reservoir transitional-lacustrine zone [4,7]. Both upstream and downstream riverine zones of Murum Reservoir were higher in pH, DO, and conductivity, but lower in chl a concentration than those in the transitional and lacustrine zones.…”

“…Impoundment and its associated negative impacts on the river have been well documented [1][2][3]. Studies have shown that a new reservoir is even more prone to eutrophication than an old one [4]. As the condition of a new reservoir significantly influences its functions in the future and has impacts on the surrounding environment, research conducted on a new reservoir is novel and necessary, particularly a large reservoir in a tropical area like Malaysia, which has a higher potential for environmental degradation given the higher propensity to hypoxia in the deeper layers [5].…”

Influencia de los suelos en la dinámica de transferencia de nutrientes en la interfase suelo-agua en un embalse tropical

“…Como consecuencia de la oxidación de la materia orgánica contenida en el suelo, en los embalses nuevos se generan condiciones anóxicas que favorecen la liberación de nutrientes [7]- [9]. De esta manera, los suelos contribuyen a la contaminación del agua y, en conjunto con otras fuentes, a la eutrofización de los embalses [10].…”