Elsevier

Environmental Pollution

Volume 253, October 2019, Pages 516-524
Environmental Pollution

Aluminum distribution heterogeneity and relationship with nitrogen, phosphorus and humic acid content in the eutrophic lake sediment

https://doi.org/10.1016/j.envpol.2019.07.042Get rights and content

Highlights

  • Increasing amount of Al gets into water bodies due to human activities.

  • Spatial distribution heterogeneity of Al contents in sediment in eutrophic lake.

  • Higher Al contents distributed in upper layer sediment for disturbance.

  • Al contents positive correlated with TN, IP, HA, ORP, negative with OP, pH in sediment.

  • Conjugation of P-Al, HA-Al may passivate Al-salts entering eutrophic lake.

Abstract

Increasing amount of aluminum (Al) gets into aquatic ecosystem through anthropogenic activity, but the knowledge about Al migration and relationships with sediments possessing different physico-chemical properties in eutrophic lakes is limited. Here, the Al migration rule and relationships with sediment nutritions in the Hangzhou West Lake, China was investigated, where a certain amount of residual Al-salts can enter because of the pre-treatment of the Qiantang River diversion project every day. Results revealed the obvious spatial distribution heterogeneity of Al in sediment vertical direction and horizontal direction following water flow. The Al content in sediment ranged 0.463–1.154 g kg−1 in Maojiabu Lake, and ranged 9.862–40.442 g kg−1 in Xiaonanhu Lake. Higher Al content distributed in upper layer sediment in lake with more disturbance. Total nitrogen (TN) contents were higher 0.917–3.387 mg g−1 and 0.627–0.786 mg g−1 in upper layer sediment than that in lower layer in Maojiabu Lake and Xiaonanhu Lake, respectively. Total phosphorus (TP) content ranged 0.779–2.580 mg g−1, in which IP and Fe/Al-P contributed 24.9–80.8% and 17.0–51.6%, respectively. Correlations between Al content with nutrition, humic acid (HA) etc. of sediment regionally varied in Maojiabu and Xiaonanhu Lake. Spatial distribution of Al-salt in eutrophic lakes closely related with the physico-chemical characteristics of nutrients, humus, human disturbance and water division parameters. Results provides new insight into Al-salts migration and references for Al-risk evaluating in eutrophic lakes.

Introduction

Aluminum (Al), the most abundant metal element on the earth's crust, widely services in human industrial and agricultural activities (Novaes et al., 2018). More and more Al intrude into the ecosystem, leading to poison function on animal and inhibition on crop productivity (Yu et al., 2015, Chen et al., 2018, Pinheiro et al., 2018). Additionally, recent years witnessed the increasing application of Al-salt flocculants in eutrophic lake management, such as the sewage treatment, emergency control of alga bloom and controlling phosphorus (P), etc. (Welch and Cooke, 1999, Rott et al., 2017). Besides, the expansively environment acidification also facilitate the Al dissolving out from mineral and soil and inflow into the water column via surface runoff. Previous researches (Robert and Richard, 1999, Srinivasan et al., 1999, Kopacek et al., 2005, Wang et al., 2010a, Wang et al., 2010b) revealed that water soluble Al ranged 14.3–1170 μg L−1 in Norway, Britain and the USA, being higher than that in major rivers (1.7–52.9 μg L−1) and wetland lake (261–429 μg L−1) in China (Reinhardt et al., 2004, Wang, 2012). Aqueous Al will be toxic to the aquatic animal and plants when it beyond safe concentration (Xie et al., 2015).

A series of chemical reactions and physical migration, such as hydrolysis, chelation (Al bind to PO4, dissolved organic matter (DOM), etc.) (Namiesnik and Rabajczyk, 2010), flocculation and precipitation, occurred when Al-salt flocculants applied into water treatment (Kasper et al., 2005). Aqueous Al is comprised of inorganic monomer Al species and polymer species, and their proportion vary with pH, cationic/anion, P-coalition, soluble organic matter, water flow velocity (Robert and Richard, 1999, Feng et al., 2015). When Al-salts entering water, firstly, polymeric hydrolysate of Al3+ trigger the destabilization of colloidal particles through electrical neutralization, then the secondary bulky agglomerated particles rapidly settle due to its adsorption-bridging effect and eventually be removed. Meanwhile, Al3+ will adsorb and complex the harm ions (Namiesnik and Rabajczyk, 2010, Quinones et al., 2016). Al-toxicity ecological risk may occur when toxic forms of Al-salt are producted and the concentrations accumulate beyond a threshold level (Guo et al., 2012). However, previous Al-salt researches mainly focused on the terrestrial ecosystems (He et al., 2017). There has been relatively little study on the Al migration and relationships with sediments possessing different physico-chemical properties when Al-salt entering eutrophic lakes.

Eutrophic lakes are typically characterized by highly endogenous nitrogen (N), P nutrient and humus content (Paytan et al., 2017). The application of Al-sulfate in water pretreatment and lake management was originally intended to reduce excessive dissolved P in water and inhibit P release from sediments (Lin et al., 2017a), by forming Al-phosphate complexes (Babatunde and Zhao, 2010, Chu et al., 2018) and covering a floc of relatively insoluble Al(OH)3 over sediment surface (Jiri et al., 2005, Yu et al., 2018), which is pH-dependent. Besides, inorganic phosphate can also adsorb onto Al2O3 and Al(OH)3, that highly dependent on the type of Al-salts and environmental conditions (Ma et al., 2018). In addition, humic acid (HA) is important complexing agent of metal ions, which not only can reduce their content, but also can affect the toxicity and biological effectiveness of metal ions (Namiesnik and Rabajczyk, 2010, Xu et al., 2014). Humus form both weak and strong complexes with Al by the carboxylic acid functional groups (Lin et al., 2014, Jin et al., 2018). The Al-detoxifying capacity of HA is positively correlated with the relative position of OH/COOH groups in main chain and their capacity to form stable ring structure with Al (Tamer et al., 2015, Niu et al., 2018), and HA contributes to Al speciation in natural waters (Wang et al., 2010a, Wang et al., 2010b, Song et al., 2019). Besides, N is an important component of humus, and Al play important role in regulating soil N transformation and in N cycle (Zhao and Shen, 2018). Accordingly, high humus content, high N and P nutrition load and complex environmental condition, all these can affect the migration and transformation of Al-salt in the eutrophic lake systems as well as its bioavailability. Hence, it is important to reveal Al migration rule in the eutrophic lakes.

The Hangzhou West Lake, China, is famous for long culture history and urban landscape. It still faces eutrophication problem (Lin et al., 2017b). To effectively improve the water quality, 4 × 105 m3 d−1 water from the Qiantang River are diverted into the lake since 2002, by different paths after disposing through Al-salts flocculation precipitation (Jin et al., 2015). So a certain content of residual Al-salts (94–115 μg L−1) from water treatment plant flows into the lake with the pretreated water every day, and residual Al-salts could accumulated onto the sediment surface over a long period. The Al-salts from water diversion into the West Lake represents the way of exogenous Al into the eutrophic lakes. So the West Lake provides a research pilot for the study of exogenous Al-salts into the eutrophic lakes in situ.

In this study, how do Al spatio-temporal distributes when Al-salts flows into the eutrophic lake and the migration and transformation characteristics of Al-salts in different trait of sediments was investigated. Besides, the distribution characteristic of total nitrogen (TN), humus and different P species in the sediment of the West Lake was investigated for both horizontal and vertical dimensions, based on which the relationships among Al and TN, humus and different P species were analyzed. Results are of vital importance for evaluating environmental risks of Al-salt in aquatic ecosystems and helpful to eutrophic lakes management.

Section snippets

Sampling sites

The sub-lakes, Maojiabu Lake (30°14′15–24″N, 120°07′36–45″E) and Xiaonanhu Lake (30°13′41–47″N, 120°08′30–36″E), situated in west and southwest of the West Lake, Hangzhou, China, are the important direct inlets of water diversion (Fig. 1), and were chosen as the study area. The two sub-lakes are significantly different in area, division time and amount, sediment depth and moisture, and human disturbance (Table 1). There are two fixed inlets in Xiaonanhu Lake, where the division amount of Inlet

Al distribution characteristic in different sites

The spatial heterogeneity in the surface sediments was evident among the sampling sites and between the upper and lower layer, with one gradient formation. In Maojiabu Lake, the sediment Al content ranged 0.463–1.154 g kg−1 (Fig. 2). The highest Al content of upper layer and lower layer sediment (0.765 g kg−1 and 1.154 g kg−1) both located in M3, respectively being 1.65-fold and 1.25-fold to the minimum (0.463 g kg−1 and 0.924 g kg−1), which presented in M1. Conformably, the upper layer

Al distribution heterogeneity in two sub-lakes of hangzhou West Lake

Polyaluminum chloride and Al sulfate are typically applied as liquid flocculants in sewage treatment and emergency control of lakes P load (Welch and Cooke, 1999, Rott et al., 2017). Once Al-salt entering lakes, hydrolysis take place and various macromolecular complexes of a colloidal nature come into existence, which are in equilibrium with one another: Al3+ ↔ AlOH2+ ↔ Al2(OH)24+ ↔ Al3(OH)45+ ↔ Al8(OH)204+ ↔ Al13O4(OH)247+ ↔Al(OH)3 (Namiesnik and Rabajczyk, 2010). Over time, the floc will be

Conclusions

Obvious spatial distribution heterogeneity of Al in sediment vertical direction and horizontal direction following water flow existed in eutrophic lakes. Higher Al content distributed in upper layer sediment in lake with more human disturbance, which could lead the suspended particle matter containing Al-salts to resuspend. Al contents in sediment are closely related to flow field of entering the water body, and geographical location of the lake. Al contents significantly correlated with

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No.31830013), the State Key Laboratory of Freshwater Ecology and Biotechnology (2017FB05), thez Major Science and Technology Program for Water Pollution Control and Treatment in the 12th Chinese Five-Year Plan (No. 2012ZX07101007-005). We thank Jian Sun and Lai Wang from the Institute of Hydrobiology, Chinese Academy of Sciences for fieldwork and technical assistance.

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