Agricultural layering explains variation in sediment P dynamics in streams draining two distinct agricultural biomes

Can small stream solute–land cover relationships predict river solute concentrations?

“…Except for occasional high values, SRP was low in all streams and not related to land cover. However, for SRP it may be necessary to consider more detailed agricultural land cover (Trentman et al, 2021), including historical land use (Fraterrigo et al, 2005) and legacy inputs (e.g., Frei et al, 2021; Kreiling et al, 2020). SO 4 was only weakly related to land cover, but we believe this is because the relatively high concentrations of SO 4 due to atmospheric deposition are well above biological needs.…”

“…Point sources of solutes such as waste water treatment plants (WWTPs), feed lots, and industrial wastes usually discharge directly to larger rivers and not to small streams, and these critical sources become important at larger scales (Frei et al, 2021). Finally, large watersheds are often not geologically homogeneous, and scaling up may necessitate a consideration of geologic differences within the river's watershed (e.g., McGuire et al, 2014; Trentman et al, 2021). At even larger scales, there may be variation in precipitation inputs.…”

“…For timber harvest, the effect on stream solutes is mostly related to soil and vegetation processes, such as the lack of tree uptake and rapid decomposition of logging residue. With agriculture and urban development, inputs from subsidies, such as fertilization, waste water, and concrete weathering, are the primary causes of elevated stream solutes (e.g., Frei et al, 2021;Howarth et al, 1996Howarth et al, , 2002Trentman et al, 2021).…”

Characterizing bioavailable phosphorus concentrations in an agricultural stream during hydrologic and streambed disturbances

“…Specifically, BAP measurements in streams with larger substrate may deviate less from SRP, particularly during streambed disturbance, given that larger substrata typically contain lower bioavailable P (Logan et al 1979 ; Pacini and Gächter 1999 ). The particular land use types in the watershed may also be important, given that the proportion of agriculture or forest in a watershed can control the amount of bioavailable P in stream sediments (Trentman et al 2021 ), and would likely mediate BAP concentrations during both types of disturbances. Finally, conservation practices, such as the addition of cover crops during the winter-spring fallow period, can increase P retention on the landscape (Christopher et al 2021 ), preventing P delivery from fields to waterways.…”