Abstract
Water transparency is a useful indicator of water quality or productivity and is widely used to detect long-term changes in the water quality and eutrophication of lake ecosystems. Based on short-term spatial observations in the spring, summer, and winter and on long-term site-specific observation from 1988 to 2013, the spatial, seasonal, long-term variations, and the factors affecting transparency are presented for Xin’anjiang Reservoir (China). Spatially, transparency was high in the open water but low in the bays and the inflowing river mouths, reflecting the effect of river runoff. The seasonal effects were distinct, with lower values in the summer than in the winter, most likely due to river runoff and phytoplankton biomass increases. The transparency decreased significantly with a linear slope of 0.079 m/year, indicating a 2.05 m decrease and a marked decrease in water quality. A marked increase occurred in chlorophyll a (Chla) concentration, and a significant correlation was found between the transparency and Chla concentration, indicating that phytoplankton biomass can partially explain the long-term trend of transparency in Xin’anjiang Reservoir. The river input and phytoplankton biomass increase were associated with soil erosion and nutrient loss in the catchment. Our study will support future management of water quality in Xin’anjiang Reservoir.
Highlights
Water transparency is the most straightforward way to evaluate the underwater light environment in aquatic ecosystems [1,2,3]
The first type (I) of low transparency is characteristic of river mouths, including Xin’anjiang River, Wuqiangxi River and Fuqiangxi River, which represent 60%, 20% and 10%, respectively, of the annual mean incoming runoff of Xin’anjiang Reservoir (Figure 1 and Figure 2a–c)
Transparency has been widely used to provide an integrative indicator describing a combination of eutrophication-related characteristics, together with indicators of suspended matter, phytoplankton biomass and primary production
Summary
Water transparency is the most straightforward way to evaluate the underwater light environment in aquatic ecosystems [1,2,3]. Due to its simplicity and low cost, transparency as measured by the Secchi disk depth (SDD) has been widely used by limnologists since 1865 to assess water quality [4]. Transparency plays an important role in the following four aspects of water quality. Transparency is a direct and important indicator of eutrophication and water quality assessment. In 1977, Carlson proposed a trophic state indicator for lakes based on water transparency as measured by the Secchi disk [5]. Transparency provides a highly relevant measure of the extent of the euphotic water layer where primary production is possible. Water transparency is considered an indirect major factor affecting internal nutrient release in deep lakes and reservoirs. A significant transparency decrease has been observed in many oceans, coastal and inland waters due to eutrophication and human activities [19,20,21,22]
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