Agriculture Reference
In-Depth Information
Figure 11.4
. Water budget for the Augusta Creek watershed representing a year of average
precipitation. Annual fluxes are expressed as equivalent depth of water over the watershed,
and as a percentage of the annual precipitation. Shading represents the water table. Data
from Rheaume (1990).
Precipitation Chemistry
On account of air pollution, precipitation at KBS is more acidic and enriched in
nitrate (NO
3
−
) and sulfate (SO
4
2−
) than it would be otherwise (Table 11.1, Fig. 11.5),
although concentrations of these anions and the accompanying acidity have been
declining in recent years. Southwest Michigan is within a broad region of moderate to
high acid deposition rates that extends across the midwestern and northeastern United
States (Driscoll et al. 2001). High atmospheric deposition rates of NO
3
−
and SO
4
2−
in
industrialized regions result from anthropogenic N and sulfur (S) oxide emissions,
originating primarily from fossil fuel combustion. In addition, anthropogenic activi-
ties—particularly those dealing with livestock and fertilized crops—likely increase
ammonium (NH
4
+
) deposition (Konarik and Aneja 2008). From 1979 to 2010, the
mean wet deposition rates of NH
4
+
-N, NO
3
−
-N, and SO
4
2−
at KBS were 3.09, 3.44, and
20.2 kg ha
−1
yr
−1
, respectively. Sources and fluxes of organic N and P in atmospheric
deposition have not often been measured and are not well understood. Total (wet +
dry, or bulk) deposition rates of N and P were determined by Rheaume (1990) by
combining data from two National Oceanic and Atmospheric Administration stations
and two U.S. Geological Survey stations in Kalamazoo County. Rheaume estimated
total annual bulk deposition rates, which are mostly due to wet deposition, as 14.8 kg
N ha
−1
yr
−1
for total nitrogen (NO
3
−
+ NH
4
+
+ organic N) and 0.34 kg P ha
−1
yr
−1
for
total phosphorus (PO
4
3−
+ organic P). Tague (1977) reported a similar atmospheric
deposition rate for total P (0.33 kg ha
−1
yr
−1
) at KBS during 1974.
