ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 Critical pH Ranges of Fish rce Central mudminnov Adiro tions in streamwater are also an important bio White sucke bass NY) surface wate Arctic char acofin sols and lowering his soil depletion tributing to decreases in surface water Ca Many lakes in the considered sub-optimal for water fleas,crayfish d dac Fathead mi nose da C.Critical Loads-Acidifying Deposition Critical loads re nt the deposition Safe range,no acid-related efects occ Critca acd-reeefec ely sed rs a ific pollu Advances in understanding of chemical and biological indicators of acidification have sup ois lake che Table 2.Expected ecological effects and concern levels in freshwater ecosystems at various levels of acid neu- tralizing capacity (ANC).(Source:USEPA). Category Label ANC level (ueq/L) Expected Ecological Effects NoE9ec6em >100 exhibit expected diversity and distribution. Moderate 50-100 Fish speci ies richness beains to decline (sensitive s pe cies are lost from lakes).Brook trout tions in to e st e as spe impacted) tive to acid affected. Elevated 0-50 Fish sp esrichness is greatyreduced (more than half of loss of he ealth and re tion (f Acidic) <0 t are greati and from s The Ecological Society of America.esahg@esa.ord esa 7© The Ecological Society of America • esahq@esa.org esa 7 ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 Decreases in pH and ANC are often paral￾leled by changes in element concentrations including increases in Al+3 concentrations and decreases in Ca+2. High dissolved Al+3 concen￾trations can have toxic effects on many types of aquatic biota, and at extreme levels few aquatic species can survive (Table 1). Organic forms of Al+3 are much less toxic than inorganic forms. Emerging research suggests that Ca+2 concentra￾tions in streamwater are also an important bio￾logical indicator. Acidifying deposition has accelerated the leaching of Ca+2 from soils to surface waters gradually decreasing the avail￾able pool of Ca+2 in soils and lowering Ca+2 concentrations in runoff. This soil depletion together with decreases in leaching associated with declines in acidifying deposition is con￾tributing to decreases in surface water Ca+2. Many lakes in the boreal forest of the Canadian Shield now have Ca+2 concentrations that are considered sub-optimal for water fleas, crayfish and other crustaceans and may be limiting the species richness of lakes in this region. C. Critical Loads – Acidifying Deposition Critical loads represent the deposition rate that can occur without surpassing tipping points for a given species or ecosystem based on established indicators and effect levels. The critical load for a specific pollutant or group of pollutants will vary depending on dif￾ferences in landscape sensitivity and in the endpoints for which the critical loads are cal￾culated (e.g., forest soils, lake chemistry). Advances in understanding of chemical and biological indicators of acidification have sup￾ported the development of critical loads for sulfur and nitrogen in parts of the U.S. and Canada. Table 2. Expected ecological effects and concern levels in freshwater ecosystems at various levels of acid neu￾tralizing capacity (ANC). (Source: USEPA)a . Category Label ANC level (µeq/L) Expected Ecological Effects Low Concern >100 Fish species richness may be unaffected. Reproducing brook trout populations are (No Effect) expected where habitat is suitable. Zooplankton communities are unaffected and exhibit expected diversity and distribution. Moderate 50-100 Fish species richness begins to decline (sensitive species are lost from lakes). Brook Concern trout populations are sensitive and variable, with possible sub-lethal effects. Diversity (Minimally and distribution of zooplankton communities begin to decline as species that are sensi￾Impacted) tive to acid deposition are affected. Elevated 0–50 Fish species richness is greatly reduced (more than half of expected species are Concern missing). On average, brook trout populations experience sub-lethal effects, including (Episodically loss of health and reproduction (fitness). During episodes of high acid deposition, brook Acidic) trout populations may die. Diversity and distribution of zooplankton communities declines. Acute Concern <0 Near complete loss of fish populations is expected. Planktonic communities have (Chronically extremely low diversity and are dominated by acid-tolerant forms. The numbers of Acidic) individuals in plankton species that are present are greatly reduced. a Based on data from Southern Appalachian streams and from Shenandoah National Park. Figure 3. Critical aquatic pH ranges for fish species. (Source: Baker, J.P. and Christensen, S.W. 1991. pp. 83-106, In: Acidic Deposition and Aquatic Ecosystems: Regional Case Studies. Charles, D.F. (ed). Springer-Verlag, New York. Figure redrawn in Jenkins, J. and others 2005. Acid Rain and the Adirondacks: A Research Summary. October, 2005. Adirondack Lakes Survey Corporation, Ray Brook, NY)