Elsevier

Environmental Pollution

Volume 176, May 2013, Pages 267-274
Environmental Pollution

Aluminum sulfate (alum) application interactions with coupled metal and nutrient cycling in a hypereutrophic lake ecosystem

https://doi.org/10.1016/j.envpol.2013.01.048Get rights and content

Abstract

Many lake ecosystems worldwide experience severe eutrophication and associated harmful blooms of cyanobacteria due to high loadings of phosphorus (P). While aluminum sulfate (alum) has been used for decades as chemical treatment of eutrophic waters, the ecological effects of alum on coupled metal and nutrient cycling are not well known. The objective of our study was to investigate the effects of an in-situ alum treatment on aluminum and nutrient (P, N, and S) cycling in a hypereutrophic lake ecosystem. Our results indicate that the addition of alum along with sodium aluminate (as a buffer) increased dissolved aluminum and sulfate in the surface and pore waters, and altered nitrogen cycling by increasing nitrous oxide (N2O) concentrations in the surface water. The increase of aluminum and sulfate may potentially feedback to alter benthic community dynamics. These results enhance our understanding of the unintended ecological consequences of alum treatments in hypereutrophic freshwater ecosystems.

Highlights

► Alum addition increased dissolved aluminum and sulfate of a hypereutrophic lake. ► Alum also altered nitrogen cycling by increasing nitrous oxide in surface water. ► Such effects of alum may potentially feedback to alter benthic community dynamics.

Introduction

Cultural eutrophication, defined as excessive phytoplankton growth stimulated by unnaturally high nutrient levels, is the predominant challenge to aquatic resource management (Smith and Schindler, 2009). Harmful (i.e., toxin-producing) algal blooms (HABs) are one potential consequence of eutrophication. HABs are increasing due to a variety of factors including increased nutrient loadings and climatic changes (Paerl et al., 2011; Elliott, 2012). Reducing availability of nutrients, and primarily phosphorus (P), via chemical alteration of the water is often the most effective short-term solution to combat HABs (Jancula and Marsalek, 2011). Aluminum sulfate (alum) has been used for decades in the chemical treatment of eutrophic waters because it can complex P in a solid phase and form a “cap” on the sediments, inhibiting benthic remobilization of P (Kennedy and Cooke, 1982; Cooke et al., 2005). While effects of aquatic alum treatment on P and plankton growth are well known, only a few studies have focused on the effects of alum on nutrient cycling and sediment biogeochemical responses (Reitzel et al., 2005; Egemose et al., 2011). Most published studies have neglected to: 1) examine potential unintended consequences of alum treatment beyond the chemical and biological responses of interest (e.g., P and chlorophyll), 2) use concurrent replication within the study system, particularly in ecosystem scale studies, and 3) measure sediment biogeochemical responses (i.e., most studies focus solely on surface water changes). The overarching goal of this study was to understand the direct and indirect effects of alum treatment on coupled metal and nutrient cycling in the surface waters and sediments of a hypereutrophic lake.

Alum addition is a popular restoration practice to control eutrophication in P-enriched lakes. It is estimated that hundreds of lakes worldwide have been treated with alum since the first reported applications in the early 1970's (see references in Cooke et al., 2005). When added to buffered, circumneutral water, alum (Al2(SO4)3·14H2O) hydrolyzes to form an amorphous floc of Al(OH)3(s) that has a high adsorption affinity for P (Huang et al., 2002) and can react with PO43 to form insoluble AlPO4(s). Although alum has been used worldwide during the past 40 years in an attempt to inactivate P in eutrophic and hypereutrophic ecosystems, the solubility and chemistry of Al after an alum treatment remain not well known (Kennedy and Cooke, 1982; Gensemer and Playle, 1999). Water pH largely controls Al speciation: Al(OH)4 is dominant at high pH (>9), Al(OH)3(s) between 6 and 8, and free Al3+ at low pH (<5) (Kennedy and Cooke, 1982). Al3+ is highly toxic to aquatic organisms (see review by Gensemer and Playle, 1999). To combat pH reduction during alum hydrolysis, sodium aluminate (NaAl(OH4)) is commonly added with alum treatments and can therefore influence the efficacy of alum treatment and toxicity to aquatic organisms (Kennedy and Cooke, 1982; Cooke et al., 2005).

While a connection between increased aqueous Al concentration and alum treatment is apparent, it is less clear how alum additions may alter coupled biogeochemical cycles. Alum additions may increase sulfate (SO42) levels at the sediment–water interface. Sulfate is reduced in anoxic sediment to sulfide, which can react with ferrous iron and form insoluble iron sulfide (FeS). Precipitation of iron sulfides can attenuate the capacity of iron to bind phosphate in sediment and contribute to its release to overlying water (Caraco et al., 1993). Finally, even less is known about the potential adverse effects of alum on cycling of nitrogen (N). Alum has been added to poultry manure to lower the pH and inhibit formation of toxic levels of ammonia (Moore et al., 1999, 1995). Dissolution and hydrolysis of alum produces H+, which converts ammonia to nonvolatile ammonium (NH4+) that can complex sulfate to form ammonium sulfate (DeLaune et al., 2004; Moore et al., 2000). In a laboratory microcosm study, Gibbs et al. (2011) found that alum treatment could induce adverse non-targeted effects by temporarily suppressing coupled nitrification–denitrification in oxic sediments and suggested minimizing alum application in lake littoral zones. However, the ecological effects of alum treatments on Al, S, and N cycling are overlooked because most studies of alum-treated ecosystems have focused on short- and long-term effectiveness in reducing P levels in surface water and sediments (Lewandowski et al., 2003; Steinman et al., 2004; Steinman and Ogdahl, 2008).

The objective of this study was to examine the short-term, direct and indirect effects of alum additions on nutrient and metal cycling in a hypereutrophic lake ecosystem. Grand Lake Saint Mary's (GLSM) is Ohio's largest inland lake (52.4 km2, Fig. 1). It is shallow (zmax = 2 m) and has a large watershed (240 km2) dominated by agriculture and livestock operations that have resulted in high P loadings to the lake (up to 1000 μg L−1 of total P in inlet water; Hoorman et al., 2008). Excessive loadings of P to GLSM have resulted in blooms of toxic cyanobacteria and water quality degradation, causing the State of Ohio to issue “no-contact” orders with the lake for two subsequent summers (2009 and 2010). In September 2010, the Ohio Environmental Protection Agency conducted a pilot study of alum treatment in three small bays of GLSM to examine its efficacy in controlling planktonic growth (Tetra Tech, 2010). Three weeks after alum additions, we conducted a field study of the same three treatment sites and three matched reference (non-alum amended) sites in the lake. Surface water and sediments from each alum treatment and reference site were analyzed for physicochemical parameters, dissolved ions, aluminum, and dissolved gases. We predicted that alum treatment would: 1) increase Al concentrations in the water and near-surface sediments, 2) increase sulfate levels in the lake, which may negatively affect benthic communities, and 3) affect N cycling by altering the distribution of N species through chemical and biological reactions in the alum-treated sites of GLSM.

Section snippets

Materials and methods

Alum and sodium aluminate (buffer) were added to three enclosed bays (Harmon, Otterbein, and West Bank) located along the shore of GLSM on September 20, 2010 (Fig. 1). Nominal loadings of total Al were 38, 47, and 58 g m−2 in Harmon, Otterbein, and West Bank bays, respectively (Tetra Tech, 2010). Each alum-treated bay was cordoned off from the open lake by installation of a barrier curtain, which minimized dilution of the alum with untreated lake water. This experiment was the predecessor to an

In-situ measurements

Alum treatment affected the physicochemistry of water in each of the three bays. Alum + buffer application resulted in increased pH and decreased turbidity, chlorophyll, and redox potential in all three treated bays compared to the reference sites (Table 1). Surface water at the alum-treated sites of Otterbein and West Bank bays had very high pH (8.81 and 9.79, respectively) compared to their matched reference sites (8.17 and 8.84, respectively).

Surface water analyses

TSS, SRP, total particulate P, and total

Discussion

The addition of alum to surface waters of a hypereutrophic lake resulted in expected and well-documented effects on the target or “direct” chemical and biological responses (e.g., forms of P, chlorophyll concentration). However, alum application also affected untargeted or “indirect” elemental cycling, and in many cases resulted in negative responses. We elaborate on these lines of evidence below, which are summarized in Fig. 6.

Acknowledgments

We thank the following individuals who assisted with either sample collection or analysis: Sara Harvey, Erin Cull, James Detraz, Melanie Stall, Jaclyn Klaus, Deepthi Nalluri, Dan Marsh, Astrea Taylor, Bob Hiskey, and Robbie Weller. We also thank two anonymous referees for their valuable comments to the manuscript and their constructive suggestions. This research was supported by the Ohio Water Resources Center 104b program (grant number 668386).

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    Present address: Annis Water Resources Institute, Grand Valley State University, 740 West Shoreline Drive, Muskegon, MI 49441, USA.

    2

    Present address: School of Natural Resources, University of Nebraska, 412 Hardin Hall, 3310 Holdrege Ave., Lincoln, NE 68583, USA.

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