Diatom assemblages in a reservoir sediment core track land-use changes in the watershed
Diatom assemblages in a reservoir sediment core track land-use changes in the watershed
Lauren A. Schroeder . Scott C. Martin . G. Jay Kerns . Colleen E. McLean 0 1 2 3
0 G. J. Kerns Department of Mathematics and Statistics, Youngstown State University , Youngstown, OH 44555 , USA
1 S. C. Martin Department of Civil/Environmental and Chemical Engineering, Youngstown State University , Youngstown, OH 44555 , USA
2 L. A. Schroeder (&) Department of Biological Sciences, Youngstown State University , Youngstown, OH 44555 , USA
3 C. E. McLean Department of Geological and Environmental Science, Youngstown State University , Youngstown, OH 44555 , USA
Diatom assemblages in a 144-cm sediment core reliably chronicled watershed changes and modifications of a riverine water-source reservoir in northeastern Ohio (USA) between 1932 and 2005. Non-metric Multidimensional Scaling segregated diatom assemblages into six groups that correspond to known anthropogenic modifications in the watershed and reservoir: zone I (filling, 1932-1936), zone II (high farming activity, 1937-1949), zone III (declining farm activity and increased residential development, 1950-1976), zone IV (implementation of sewage bypass, 1977-1982), reduced development activity caused by economic recession, 1983-1993), zone VI (renewed population growth and construction of a dam extension, 1994-2005). Ten watershed and reservoir environmental variables (percent farmland, population, pH, total alkalinity, total hardness, transparency, surface area, air temperature, export of suspended solids, total phosphorus) were significantly correlated with diatom aggregate distribution in ordination space. Changes in species composition, in concert with watershed and reservoir changes, implicated light, alkalinity, and littoral macrophyte development as the primary drivers of diatom aggregate structure and function. Diatom productivity did not track nutrient loading (TP) and was likely driven by factors other than nutrients. Each zone was defined by a distinct set of environmental variables that differed from all other zones. Thus, diatom aggregate structure likely was determined by a dynamic suite of factors in the watershed and reservoir that had differential effects on diatom aggregate structure through time.
Reservoir; Diatom; Watershed quality; Anthropogenic impact; Sediment core
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Riverine reservoirs provide many useful services
including water for domestic and industrial use
(Jørgensen et al. 2005). The value of these services
depends on the quality of the impounded water. Initial
water quality is determined by site conditions, i.e.
geology, climate, hydrology and morphometry.
Subsequently, water quality is subject to modification in
response to changes in watershed land use. Unlike
natural lakes, in which conditions prior to human
impacts can serve as a benchmark for determining
human impact on water quality (Bennion et al. 2011),
reservoirs are usually constructed where watersheds
have already been modified by human activities. Thus,
reservoirs have no ‘‘pristine condition’’ as a reference
for impairment. Reservoirs, from their inception, are
subject to anthropogenic stresses. As a consequence,
human activities in the watershed either improve or
degrade the quality of the reservoir water by
alleviating (Anderson et al. 2005) or intensifying stressors,
respectively (Ke˛dziora 2003). Stressors external to the
watershed may also affect water quality adversely, and
include airborne nutrients and pollutants (Woodridge
et al. 2014; Larsen 2000) and perhaps climate
warming (McGowan et al. 2012). Because the highest
standards apply to water used for domestic purposes
and recreation, reservoirs constructed to provide these
services are the most susceptible to impairment. Initial
geological conditions are relatively stable over the
lifetime of most riverine reservoirs. Therefore, with
the exception of processes like climate warming, the
magnitude and rate of degradation depends in large
part on watershed use.
Understanding the relationship between external
stressors and water quality is necessary for effective
lake and reservoir management (Battarbee and
Bennion 2011). One way to identify these linkages is
paleolimnological methods, often using diatom-based
transfer functions to reconstruct past water chemistry
and correlate such changes with shifts in land use,
atmospheric deposition or climate (Smol 1992; Wolfe
et al. 2001). Paleolimnological methods are powerful
tools that have enhanced our understanding of
ecological processes in lacustrine systems (Smol 1992,
2008; Battarbee 1999). There are, however, cases for
which paleolimnology alone is inadequate to decipher
linkages between watershed alterations and lacustrine
ecological processes (Saros 2009). Recently there has
been an appeal to integrate neo- and paleolimnological
methods to discern relationships between watershed
changes and ecological processes, and to use historical
chemical data to validate pale (...truncated)