Long-term Effects of the Clean Air Act on Water Toxicity and Brook Trout Survival in Acidified Streams of the Southwestern Adirondacks, 1984-2017

Background

Forested watersheds in the southwestern Adirondack Mountains of New York received some of the most acidic deposition in North America from the 1970s through much of the 1990s (NADP 2005). Thus it is not surprising that associated effects on surface-water quality and ecosystems in lakes and streams of the southwestern Adirondack Mountains of New York were investigated to various extents over the past 35 years; first to document acidification effects and then to evaluate potential recovery. In fact, evidence of adverse impacts on water quality and aquatic ecosystems across the region provided much support for implementation of the Clean Air Act (CAA) of 1990. Although the underlying effect mechanisms were not well understood, the chemical and biological impacts of chronic and episodic acidification were quantified during the 1980s. Though most early studies focused on lakes, a few investigated acidification of streams.  Additional studies during the 1980s and early 1990s assessed the effects of chronic and episodic acidification on mortality of brook trout (Salvelinus fontinalis) and found that mortality was generally attributed to elevated concentrations of Alim. During the 1990s, regional studies waned and were limited to a set of trout species and strain tests in 1997 and a survey of fish communities in 36 streams during fall 1999. During a 2001-05 study of 200 streams in the western Adirondacks, Lawrence and others showed that about half of streams become seasonally toxic to biota (Alim levels surpassed 1.0 mmol L-1) when base-cation surplus (BCS) became negative, and found that current levels of BCS and Alim adversely effected macroinvertebrate assemblages in 44-56% of a subset of streams sampled in the same region. During the same period (2001-03), Baldigo and others assessed brook trout survival in six local streams and determined that mortality differed little from that observed in some of the same streams during 1984-85, 1988-90, and 1997 tests. These results generally indicate that the benefits of the CCA (decreasing SOx and NOx emissions) to aquatic ecosystems across the region between 1990 and the mid-2000s have been either unperceivable or much smaller than anticipated.

Significant changes in dissolved organic carbon (DOC) levels have possibly improved the biological-recovery story. Over the past decade, air temperatures and dissolved organic carbon (DOC) levels in some waters have increased, possibly related to climate change. Lawrence and others demonstrated that DOC has a significant effect on stream pH, BCS, and Alim concentrations. Thus, long-term increases in DOC could be interacting with decreases in acidity to increase organic monomeric Al (Alom) fractions and theoretically reduce biologically available (and toxic) Alim concentrations and water toxicity. Decreases in trout mortality and water toxicity were not discernable in local streams during 2001-03, however, it is not known if increasing DOC levels are interacting with decreasing acidity and Alim levels to reduce contemporary toxicity levels in streams of the region beyond a point that emission reductions alone (related to the CAA) could not have attained.

Objective

The primary objective of this study is to determine how the CAA and climate factors may have interacted to alter watershed and stream geochemistry (increased DOC and pH and decreased Alim concentrations in surface waters) beyond a threshold that may permit native brook trout to survive for extended periods in formerly acidified streams in the southwestern Adirondacks. Contemporary (2015-17) toxicity tests are proposed in the same streams where tests were done during four prior periods (1984-85, 1988-90, 1997, and 2001-03) specifically to determine: 

1. if water toxicity (and brook trout mortality) has decreased significantly between 1984 and present;
2. if mortality levels reflect recognized Alim-toxicity thresholds for survival of brook trout (and other aquatic biota);
3. how the relations between pH, ANC, BSC, Ca, DOC, and Alim levels may have changed over time, and;
4. what the implications of any changes in water quality may have for trout populations and fish communities in the six study streams and in other acid-sensitive streams of the region.

Approach

The U.S. Geological Survey (USGS) in cooperation with the New York State Department of Environmental Conservation (NYSDEC) propose a 3-year study to quantify mortality responses of juvenile brook trout in six streams where morality rates were defined from prior toxicity tests. Streamflow, stream chemistry, and mortality of brook trout will be assessed using 30d toxicity tests done annually between April 15 and June 1, 2015, 2016, and 2017 at six study streams/sites near Inlet, NY, (Fig. 1); the sites will include Buck Creek (BUC), Pancake Hall Creek (PAN), Moss Lake Inlet (MLI), Bald Mountain Brook (BMB), Fly Pond Outlet (FPO), and Wheeler Creek (WHE). Fly Pond Outlet will serve as a control stream because it is well buffered at all flows. Trout-mortality and water-chemistry data from toxicity tests done in these six streams during 2001-03 and in nearby Townsend Pond Outlet (TPO), West Pond Outlet (WPO), Squash Pond Outlet (SPO), and Seventh lake Inlet (SLI) assessed at least once during 1984-1985, 1988-1990, and 1997 will be summarized and analyzed to assess potential changes in toxicity and trout survival over time. All ten streams (Fig. 1) are tributaries to the Moose River, which feeds into the Black River, which in turn empties into Lake Ontario..

Newly collected (2015-17) data on trout mortality, water chemistry, and exposure duration will be analyzed to address the main study objective and related goals. First, daily cumulative mortality, 15 min discharge data, and all pH, ANC, Alim data from each test period will be evaluated graphically to qualify likely sources of toxicity in each stream; and regression equations will be developed between trout mortality at the end of each test and median Alim concentrations during each test to define the existing relationship in all streams. Second, trout mortality at the end of each test and median Alim concentrations will be assessed to determine whether low, moderate, and high mortality rates correspond to widely recognized Alim thresholds for mortality of brook trout and other aquatic biota. Third, the relations between median Alim concentration and exposure duration, or the number of days until mortality reached 20, 50, and 90% during the 2001-03 tests will be examined to evaluate the temporal mortality response above the Alim-mortality thresholds. Fourth, the relations between Alim concentration and discharge at BUC will be examined to identify a surrogate discharge that corresponded to both Alim -mortality thresholds. The resulting data will be then used to develop cumulative flow-duration curves for each toxicity-test period and year (2015-17) at BUC and to assess the duration or number of days (percentage of total exposure time) during which discharge exceeded the thresholds during each period. These data approximate test-period and total annual exposure to acutely toxic conditions and thereby help predict the effects on brook trout mortality, brook trout populations, and the entire fish community within BUC. Continuous Alim concentrations will be interpolated for each of the other five streams and used to create Alim concentration-duration curves, estimate the percentage of time that Alim concentrations exceeded Alim-mortality thresholds, and predict potential effects on brook trout populations and the entire fish community within each stream.

Project
Location by County

St. Lawrence County, NY, Herkimer County, NY, Hamilton County, NY, Lewis County, NY, Oneida County, NY