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

摘要

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.