Abstract
Suspended solids are an important part of lake ecosystems, and their nitrogen and phosphorus contents have a significant effect on water quality. However, information on nitrogen and phosphorus forms in suspended solids remains limited. Therefore, a case study was conducted in Lihu Lake (China), a lake with characteristically high amounts of suspended solids. Nitrogen and phosphorus speciation in suspended solids was analyzed through a sequential extraction method. We also evaluated the sources of various forms of nitrogen and phosphorus and their different effects on eutrophication. The total nitrogen (TN) content was 758.9–3098.1 mg/kg. Moreover, the proportions of various N forms in the suspended solids of the study areas were ranked as follows: Hydrolyzable nitrogen (HN) > residual nitrogen (RN) > exchangeable nitrogen (EN). Total phosphorus (TP) ranged from 294.8 to 1066.4 mg/kg, and 58.6% of this TP was inorganic phosphorus (IP). In turn, calcium (Ca)-bound inorganic phosphorus (Ca-Pi) was the main component of IP. The correlation between various nitrogen and phosphorus forms showed that there were different sources of suspended nitrogen and phosphorus throughout Lihu Lake. Correlation analysis of water quality indices and comparative analysis with surface sediments showed that in Lihu Lake, the dissolved nitrogen and phosphorus contents in water were influenced by sediment through diffusion, while particle phosphorus content in water was influenced by suspended solids through adsorption; however, due to the higher phosphorus contents in suspended solids, we should pay more attention to the impact of suspended solids.
Highlights
Eutrophication is among the most important threats to global surface water quality
This study investigated the contents, spatial distribution, and sources of nitrogen and phosphorus forms in the suspended solids of Lihu Lake, and comparatively analyzed the different effects of suspended solids and surface sediments on water quality
The total phosphorus (TP) ranged from 294.8 to 1066.4 mg/kg, the contents of inorganic phosphorus (IP) and Organic phosphorus (OP) in suspended solids were 381.9 and 259.8 mg/kg, respectively, and Ca-Pi and NA-Po were the major components of IP and OP
Summary
Eutrophication is among the most important threats to global surface water quality. Currently, more than 75% of closed water bodies worldwide present some degree of eutrophication [1,2,3]. External inputs are the main factor leading to the eutrophication of lakes, the biochemical reaction of nitrogen and phosphorus at the sediment/suspended solid water interface has an impact on the nutrient contents in water. The degradation of nutrients in suspended solids during suspension may lead to an accelerated migration of biogenic elements into the water bodies. Previous studies on Lihu Lake mainly focused on the water quality [24], nitrogen and phosphorus forms in the sediment [25,26], etc. The study of nitrogen and phosphorus forms in suspended solids is of great significance for the further ecological restoration and environmental management of Lihu Lake. There are few studies on the forms of nitrogen and phosphorus in suspended solids of Lihu Lake. This study sought to characterize the migration and transformation of nutrients between the water–SS and SS–sediment interfaces based on the following aspects: (1) Contents and spatial distribution of nitrogen and phosphorus forms in suspended solids, (2) correlations between all of the nitrogen and phosphorus forms in overlying water, suspended solids, and surface sediments, and (3) comparison between the nitrogen and phosphorus contents in suspended solids and surface sediments
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