Aluminum in acidic surface waters: chemistry, transport, and effects.

Abstract

Ecologically significant concentrations of Al have been reported in surface waters draining "acid-sensitive" watersheds that are receiving elevated inputs of acidic deposition. It has been hypothesized that mineral acids from atmospheric deposition have remobilized Al previously precipitated within the soil during soil development. This Al is then thought to be transported to adjacent surface waters.Dissolved mononuclear Al occurs as aquo Al, as well as OH-, F-, SO42-, and organic complexes. Although past investigations have often ignored non-hydroxide complexes of Al, it appears that organic and F complexes are the predominant forms of Al in dilute (low ionic strength) acidic surface waters. The concentration of inorganic forms of Al increases exponentially with decreases in solution pH. This response is similar to the theoretical pH dependent solubility of Al mineral phases. The concentration of organic forms of Al, however, is strongly correlated with variations in organic carbon concentration of surface waters rather than pH.Elevated concentrations of Al in dilute acidic waters are of interest because: Al is an important pH buffer; Al may influence the cycling of important elements like P, organic carbon, and trace metals; and Al is potentially toxic to aquatic organisms. An understanding of the aqueous speciation of Al is essential for an evaluation of these processes.

Effects of stream acidification and habitat on fish populations of a North American river

“…Though pH tolerance levels offer a general ranking of each species' sensitivity in acidified systems, many studies have shown that other factors such as Al im , DOC, and Ca 2+ , along with the timing and magnitude of episodic fluctuations in toxic acid and Al im concentrations, are strongly related to the degree of stream acidification and influence fish survival in natural systems (Baker et al, 1990;Gagen et al, 1993;Simonin et al, 1993;Van Sickle et al, 1996;Baldigo and Murdoch, 1997). Aluminum fractionation and Al im concentration are also directly dependent upon pH levels (Driscoll, 1985) and both acidity and Al im act in a similar manner to affect fish survival (Wood et al, 1990). These findings imply that the degree of stream acidification and related differences in stream-water chemistry may be primarily responsible for the restricted distributions of most fish-species' populations in the Neversink river, and in other similarly acidified riverine systems.…”

The effects of whole-tree clear-cutting on soil processes at the Hubbard Brook Experimental Forest, New Hampshire, USA

“…Stream acidification and mobilization of potentially toxic Al species are especially important concerns because many streams in the northeastern USA are already acidic and contain elevated Al concentrations due to acidic deposition (Driscoll, 1985;Johnson et al, 1981). The increased acidification caused by forest harvesting may therefore contribute additional stress to the aquatic ecosystem.…”

The pH-independent effect of aluminum on cultures of phytoplankton from an acidic Wisconsin lake

“…The speciation of Al was not determined in the treatments. Fluoride was negligible in the treatments, as is common for most soft- water lakes in the mid-west (Cook et al, 1986), so Al-fluoride complexes were unimportant in this experiment, although they can be the dominant form in Adirondack lakes (Driscoll, 1985). We expected that the Al bound to the ligands in the natural lake water of the treatments would mimic Al activity in lakes of similar chemistry.…”

“…However, the plankton in the treatments may have experienced the additions of Al as a toxic pulse of inorganic monomeric Al, which became less toxic as it was bound to ligands in the solution. Plankton may also experience pulses of toxic Al in the form of hydrologic events that introduce large amounts of labile monomeric Al to surface waters (Driscoll, 1985). For instance, poorly-buffered northern lakes commonly undergo a pulse of Al-rich, acidic water from spring snowmelt into their surface waters (B. WonsonLiukkonen, pers.…”

“…Substantial filamentous algal communities often dominate these acidic lakes. Free aluminum concentration and pH are strongly correlated, and the presence of this metal can inhibit the growth of some plankton species by apparently reducing the amount of available, dissolved phosphorus (Dickson, 1978;Driscoll, 1985) or by a direct toxic effect (Folsom et al, 1986). Elevated Al concentrations are detrimental to fish (Baker & Schofield, 1980;Muniz & Leivestad, 1980), but little quantitative work on algal communities has been published (but see Helliwell et al, 1983;Hmrnstrom et al, 1985, andNalewajko &Paul, 1985).…”