posted on 2019-12-11, 11:48authored byNadia
N. Casillas-Ituarte, Audrey H. Sawyer, Kelsey M. Danner, Kevin W. King, Alexandra J. Covault
Internal phosphorus (P) in sediments plays an important
role in
the nutrient dynamics of lakes, sometimes long after external loads
have been reduced. Similarly, internal P sources may drive the nutrient
dynamics of small agricultural streams that drain to larger rivers
and lakes, despite best management practices intended to reduce external
P loads from adjacent fields. Here, internal P concentrations were
measured with sequential extraction on cores collected in spring and
summer from two small agricultural streams in the drainage basin of
Lake Erie, a large, eutrophic lake experiencing increasing SRP loads.
Average total extractable P concentrations were similar to within
5% during spring and summer, but mobile P binding fractions nearly
doubled in summer, possibly due to accelerated rates of organic matter
mineralization or iron reduction beneath suboxic, stagnant surface
waters. One site had chronically greater internal P concentrations
by 25–75%, despite the implementation of best management practices
such as grass buffers. The site also had more aquatic vegetation that
restricted the flow, less dissolved oxygen in surface water, and greater
organic matter in sediments during both seasons, suggesting that variations
in hydrology, sediment composition, and vegetation influence hot spots
of P retention throughout small agricultural streams.