Agriculture Reference
In-Depth Information
removed by co-precipitation with calcite and sedimentation. As a result, primary
production in local streams and other groundwater-fed surface waters tends to be
strongly limited by the availability of P (Wetzel 1989, Hamilton et al. 2009).
Augusta Creek discharges into the Kalamazoo River, and further downstream in
the Kalamazoo River system nutrient concentrations increase considerably. This river
system has several reservoirs, and the largest and most downstream reservoir (Lake
Allegan; Fig. 11.1) has a history of poor water quality ascribed mainly to eutrophica-
tion by high P loading. Reid and Hamilton (2007) presented evidence for shifting
patterns of nutrient limitation in these reservoirs, with N, P and Si all potentially
important as limiting factors for algal growth, but only at times of low river discharge
and reservoir flushing. Phosphorus contributions from the various subwatersheds of
the Kalamazoo River and the transport and transformation of P and other elements
through the river system were subsequently quantified in greater detail through inten-
sive monitoring and modeling (Baas 2009). This work documented the importance
of nonpoint (diffuse) sources of P loading to the river system, including the release
of sediment P from a reservoir (Morrow Lake) upstream of the City of Kalamazoo to
river water, possibly reflecting a legacy of high sediment loading rates.
Wetlands
Wetlands are generally recognized for their positive effects on water quality, for
example, nutrient removal and sediment trapping (NRC 1995). Wetlands are abun-
dant in the landscape around KBS, covering 10% of the four townships in the vicin-
ity (Fig. 11.1). The National Wetland Inventory (U.S. Fish and Wildlife Service)
provides maps and information on the general types of wetlands and their spatial
patterns (
http://www.fws.gov/wetlands/Data/index.html)
. The present vegetation
and, to some extent, the hydrology of local wetlands has been strongly influenced
by the history of land use since settlement in the 1830s (Rich 1970). Logging, graz-
ing, farming, construction of ponds and drainage channels, and mining of peat and
calcium carbonate were common practices in local wetlands. And the effects of
these activities on the geomorphology, hydrology, and vegetation still persist today.
The abundance and diversity of wetlands near KBS make this landscape ideal
for comparative studies. The wide range in specific conductance of wetland
waters shows that they are the most hydrochemically variable surface waters in
the landscape (Fig. 11.2). This is because wetlands have highly variable hydrau-
lic connectivity with groundwater: they span the range from receiving negligible
groundwater inputs to having their water budgets dominated by groundwater
through-flow (Kehew et al. 1998).
Thobaben and Hamilton (2014) surveyed wetland hydrology across a diverse
set of 24 wetlands around KBS. They estimated the relative importance of ground-
water as a source of water to the wetlands by comparing solute composition and
found—consistent with previous studies in lakes—that dissolved Mg
2+
is the best
tracer of groundwater in this landscape (Wetzel and Otsuki 1974, Stauffer 1985).
This is because (1) concentrations are negligible in precipitation but consistently
high in groundwater in contact with dolomite minerals in the glacial deposits, (2)
biological activity has no detectable effect on Mg
2+
concentrations, and (3) Mg
2+
