Lake/watershed sulfur budgets and their response to decreases in atmospheric sulfur deposition: watershed and climate controls

Abstract

Abstract:Atmospheric sulfur (S) emissions peaked in North America in the early 1970s followed by declines in S deposition and sulfate (SO 4 2À ) concentrations in surface waters. Changes in S biogeochemistry affect the mobilization of toxic (Al +3 , H + ) and nutrient (Ca 2+ , Mg 2+ , K + ) cations, and the acid-base status of ecosystems. We focused on lake/watersheds in the Adirondack Mountains of New York, USA, one of the most acid-sensitive and acid-impacted regions in North America. We used 16 of the 17 original Adirondack Long-Term Monitoring Lakes from 1984 through 2010 and found significant declines (À2.14 mmol c l À1 year À1 ) in SO 4 2À concentrations. There were significant declines (À0.28 kg S ha À1 year À1 ) in total S deposition for all lake/watersheds. We constructed S mass balances for 14 lakes/watersheds from wet and dry S deposition and SO 4 2À loss from drainage and found a comparable decline (À0.26 kg S ha À1 year À1 ) in lake SO 4 2À export. There was a discrepancy (mean 2.34 kg S ha À1 year À1 ) between atmospheric S deposition and watershed S loss due to internal S sources. Using major solute chemistry including dissolved silica and watershed characteristics, it was evident that the watershed S budget discrepancy increased with thickness of surficial deposits. The annual discrepancies in S mass balances were strongly linked with annual watershed discharge. These results suggest that internal S sources are becoming increasingly important as atmospheric S inputs have declined. The internal SO 4 2À supply of watersheds decreased concomitantly with lake acid neutralizing capacity (ANC). These findings suggest that the limited contributions from internal sources of SO 4 2À will facilitate the recovery of ANC from those lake/watersheds with the lowest ANC. With long-term decreases in atmospheric S deposition, the effects of climate, especially increases in precipitation, will play an increasingly important role in regulating S budgets and the amount of SO 4 2À mobilized from internal watershed sources.

Development of a total maximum daily load (TMDL) for acid-impaired lakes in the Adirondack region of New York

“…Also shown are ANC targets of 11 meq L À1 and 20 meq L À1 . till watersheds, because thin till watersheds have less capacity to neutralize and retain SO 4 2À , therefore atmospheric SO 4 2À deposition is largely transported to surface waters (Mitchell et al, 2013). Moreover, since medium or thick till watersheds exhibit greater supply of acid neutralizing base cations and retain atmospheric inputs of SO 4 2À and NO 3 À lakes adjacent to these watersheds experienced less severe historical acidification in response to elevated acid deposition and will recover more slowly compared to lakes with thin till watersheds.…”

Acid-base characteristics of the Grass Pond watershed in the Adirondack Mountains of New York State, USA: interactions among soil, vegetation and surface waters

“…6). Other research has also found that the basal area of acid-tolerant tree species was inversely correlated with nitrification rates due to leaf litter nutrient concentrations and associated C : N ratios (Christ et al, 2002;Finzi et al, 1998;Mitchell et al, 2003;Ross et al, 2009). Within the upper elevations of Grass Pond subwatershed 5 where black cherry groves were identified, fresh black bear scat loaded with black cherry seeds was observed during early October field sampling, indicating a bear den in the area.…”

“…The associations between sugar maple basal area and high stream water high ANC and low stream water DOC indicates deep sub-surface hydrological flow paths through thick mineral soil layers and parent material (Fig. 6) (Chen et al, 1984;Mitchell et al, 2013;Driscoll and Peters, 1987). In general, sites with thick soil layers with relatively high soil pH and Ca concentrations are more likely to be colonized by sugar maple trees than other less suitable more acidic sites because of the relatively high nutrient demands of this tree species (Bailey et al, 2004;Burns and Honkala, 1990;Christopher et al, 2006;Van Breemen et al, 1997).…”

“…It is generally recognized that within the northern hardwood forests, sugar maple (Acer saccharum) and other species such as American basswood (Tilia americana), eastern hophornbeam (Ostrya virginiana) and white ash (Fraxinus americana) require base-rich soils and are acid intolerant, while American beech (Fagus grandifolia), and red spruce (Picea rubens) are acid-tolerant species (Christopher et al, 2006;Duchesne et al, 2005;Fujinuma et al, 2005;Mitchell et al, 2003). Sugar maple often grows poorly in soils that are low in Ca and Mg, high in Al and have a low pH (Burns and Honkala, 1990;Van Breemen et al, 1997).…”

Mapping the relative risk of surface water acidification based on cumulative acid deposition over the past 25 years in Japan

“…In addition, enhanced NO 3 -leaching has been reported in forested watersheds exposed to chronic atmospheric N deposition, suggesting an excess of N in these ecosystems (e.g., Aber 1992;Fenn et al 1998). SO 4 2-leaching might be accelerated by the mobilization of the S that has accumulated in the soil for the past several decades (Mitchell et al 2013). Surface water acidification via leaching of strong acids affects aquatic organisms, whose distributions vary widely according to their sensitivities to acidification (Schindler 1988).…”