Abstract
Fish farming has seriously influenced the aquatic environment in Sancha reservoir in SW China since 1985 and has been strongly restricted since 2005. Thus, phosphorus speciation in a sediment core dated between 1945 and 2010 at cm-resolution and in surface sediments from Sancha reservoir may allow us track how fish farming impacts phosphorus dynamics in lake sediments. Fish farming shifts the major binding forms of phosphorus in sediments from organic to residual phosphorus, which mostly originated from fish feed. Sorption to metal oxides and association with organic matters are important mechanisms for phosphorus immobilisation with low fish farming activities, whereas calcium-bound phosphorous had an essential contribution to sediment phosphorus increases under intensive fish framing. Notwithstanding the shifting, the aforementioned phosphorus fractions are usually inert in the lake environment, therefore changing phosphorus mobility little. The use of fish feed and water-purification reagents, the most important additives for fish farming, introduce not only phosphorus but also large amounts of sand-sized minerals such as quartz into the lake, to which phosphorus weakly sorbs. The sand-sized minerals as additional sorbents increase the pool of easily mobilisable phosphorus in sediments, which will slow down the recovery of reservoir water due to its rapid re-mobilisation.
Highlights
The aquatic environment in the reservoir was oligotrophic until 1985
The aquatic environment of Sancha reservoir turned intensely eutrophic with the introduction of fish farming in 1985 and other industrial activities from 2000 onwards
The large variations of fish farming activities in the history in Sancha reservoir allow us quantify the influence of fish farming on the vertical and spatial distribution, speciation and mobility of P in the lake sediments, which is the objective of this study
Summary
The aquatic environment of Sancha reservoir turned intensely eutrophic with the introduction of fish farming in 1985 and other industrial activities from 2000 onwards. There were several measures by the local government to reduce anthropogenic P input drastically for the remediation of Sancha reservoir since 2005, the aquatic environment is still eutrophic today. Fish farming in cages in Sancha reservoir expanded from the initial cage area of 1,000 m2 in the late 1980s to a peak area of 255,300 m2 in 2005 but was largely reduced in 2010. The large variations of fish farming activities in the history in Sancha reservoir allow us quantify the influence of fish farming on the vertical and spatial distribution, speciation and mobility of P in the lake sediments, which is the objective of this study. Our findings will provide scientific knowledge to improve and restore the reservoir’s ecological environment affected by fish farming
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