Agriculture Reference
In-Depth Information
Surface-derived contaminants other than NO 3 do not yet appear to be an
extensive problem in local groundwaters around KBS, and a survey of a wide
suite of organic contaminants and trace elements in wells and streams through-
out Kalamazoo County revealed little contamination in the rural areas (Rheaume
1990). Hydrogeological characteristics indicate, however, that most of the area sur-
rounding KBS is moderately to highly susceptible to groundwater contamination
from surface sources (Rheaume 1990). In the glacial deposits of Barry County, a
rural area just north of KBS, Kehew and Brewer (1992) did find evidence of sur-
face-derived contamination from human activity in water samples collected from
domestic water-supply wells. About 25% of those wells had not only elevated con-
centrations of NO 3 (>1 mg N L −1 ) but also NH 4 + (>0.5 mg N L −1 ) and/or chloride
(≥10 mg L −1 ), the latter likely originating from the use of de-icing salts on roads
and probably also the addition of potash (most commonly composed of KCl) to
agricultural fields.
Arsenic is a common health concern in well water, including wells around KBS.
In Michigan its origin is thought to be largely from native minerals, but mobiliza-
tion of arsenic could be related to human activities, including increased loading of
soluble cations (e.g., Ca 2+ and Mg 2+ associated with NO 3 leaching, as discussed
above). Anthropogenic increases in cation loading can cause arsenic to be released
from ion exchange sites in soils, potentially resulting in arsenic accumulation
downstream in groundwater flow paths (Böhlke 2002).
Surface Waters
Streams and Rivers
Streams and rivers are important in the transformation and retention of nutrients,
often reducing the nutrient load in water passing through them (Alexander et  al.
2009, Mulholland et al. 2008). Alterations in surface flow paths—by draining wet-
lands and straightening streams—prevent water from passing through soil and wet-
land filters that naturally retain nutrients and sediments, and result in degraded
water quality downstream (NRC 1995). There has been less wetland drainage in the
immediate vicinity of KBS than in most other parts of southern Michigan and the
rest of the upper Midwest (Prince 1997) because it is difficult to drain the abundant
isolated depression wetlands.
Streams around KBS resemble the groundwater in their total ionic content
because they derive most of their annual discharge from groundwater (Fig. 11.2).
The stream example depicted in Fig, 11.9 is for Prairieville Creek (Fig. 11.1),
a tributary to Gull Lake that originates from a complex of groundwater springs
and drains a largely agricultural watershed. Streams with lower conductance than
groundwater tend to be outflows from larger lakes and wetlands that capture more
direct precipitation that dilutes groundwater inflows. The few streams in the region
around KBS that have significantly higher conductance than groundwater tend to
be in urban areas and likely receive pollution, particularly Na + and Cl . Overland
flow from storm runoff or snow melt also tends to dilute the total ion content. When
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