Abstract
The influence of dredging season on sediment properties and nutrient fluxes across the sediment–water interface remains unknown. This study collected sediment cores from two sites with different pollution levels in Meiliang Bay, Taihu Lake (China). The samples were used in simulation experiments designed to elucidated the effects of dredging on internal loading in different seasons. The results showed that dredging the upper 30 cm of sediment could effectively reduce the contents of organic matter, total nitrogen, and total phosphorus in the sediments. Total biological activity in the dredged sediment was weaker (p < 0.05) than in the undredged sediment in all seasons for both the Inner Bay and Outer Bay, but the effect of 30-cm dredging on sediment oxygen demand was negligible. Dredging had a significant controlling effect on phosphorus release in both the Inner Bay and Outer Bay, and soluble reactive phosphorus (SRP) fluxes from the dredged cores were generally lower (p < 0.05) than from the undredged cores. In contrast, NH4+-N fluxes from the dredged cores were significantly higher (p < 0.05) than from the undredged cores in all seasons for both sites, this indicates short-term risk of NH4+-N release after dredging, and this risk is greatest in seasons with higher temperatures, especially for the Inner Bay. Dredging had a limited effect on NO2−-N and NO3−-N fluxes at both sites. These results suggest that dredging could be a useful approach for decreasing internal loading in Taihu Lake, and that the seasons with low temperature (non-growing season) are suitable for performing dredging projects.
Highlights
Over the past two decades, many lakes around the world have experienced eutrophication, which has caused serious environmental problems such as frequent algal bloom outbreaks, black and foul water, and pollution [1,2,3,4]
The porosity of sediments generally decreased with depth, whereas the contents of Loss on ignition (LOI), organic carbon (OC), Total nitrogen (TN), and Total phosphorus (TP) decreased in the first tested depth and increased and decreased, showing a clear peak at depths ranging from 10 to 20 cm (Figure 2)
The present study found that 30-cm dredging could reduce the contents of organic matter (LOI) and TP in the dredged sediments (Figure 2)
Summary
Over the past two decades, many lakes around the world have experienced eutrophication, which has caused serious environmental problems such as frequent algal bloom outbreaks, black and foul water, and pollution [1,2,3,4]. Sediment can serve as a source or sink of pollutants, when sediment acts as a source, sediments are considered important sources of nutrient release to the water column, constantly replenishing nutrients and promoting the formation of algal blooms [5,6]. As a common ecoengineering technology, sediment dredging is used in many lakes to control internal nutrient loading and to rebuild the natural ecological system [12,13,14,15].
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