Stream Corridor Soil Phosphorus Availability in a Forested–Agricultural Mixed Land Use Watershed

Abstract

Watershed land use affects nutrient and sediment export, particularly through streambank erosion, which can add to P export and contribute to eutrophication in downstream waterbodies. We characterized P of soils from four different land uses (32 sites) along streams in the Missisquoi River basin (Vermont, USA)—silage corn (Zea mays L.), hay meadow, emergent wetlands, and forest—and their corresponding streambanks. We measured total P (TP), pH 4.8 NH4–acetate P, degree of P saturation (DPS), and soluble P. The latter three measurements were used as predictors of potential P bioavailability. Forest soils were relatively low in TP, whereas soils in corn, hay, and wetland were elevated (>1000 mg kg−1). With the exception of forests, the TP of the corresponding streambanks of each land use was statistically significantly lower than in the interior of the land use, while still higher than those in forests, suggesting a possible influence of land use on its adjacent streambank. The pH 4.8 NH4–acetate P was low in nonagricultural land uses and all streambanks of different land uses, but higher than optimum for soils in cornfields and hayfields. The DPS averaged 36% in the cornfields, but <21% in all of the streambanks. Mean soluble P was 0.14 mg kg−1 for corn‐ and hay‐associated streambanks with a DPS <10% but was as high as 3.2 mg kg−1 in the agricultural fields. The combination of low bioavailable P measurements indicates that most streambank soils are likely low contributors to P enrichment downstream. However, the elevated TP in some agricultural streambank soils suggests an accumulation of legacy P. Core Ideas Soil P concentrations varied widely among four watershed land uses. Agriculture and wetland streambank soils had less P than adjacent land uses. Streambank soils from the four different land uses had low P release potential.

Nutrients and Heavy Metals in Legacy Sediments: Concentrations, Comparisons with Upland Soils, and Implications for Water Quality

“…With such low values, we speculate that streambank legacy sediments at our sites will likely serve as sinks for inorganic P under dry, aerobic/oxic conditions and under "typical" agricultural P stream concentrations. A similar conclusion was reached by Perillo et al (2019) for streambank sediments with low P (DPS < 21%) in the Missisquoi River basin in Vermont. Alternately, if these sediments are exposed to stream waters with extremely low P concentrations, they could also desorb and release P (Sienkiewicz, 2019).…”

“…Using M3-P, M3-Al, and M3-Fe values and following Sims et al (2002), we also computed the oxalate extractable Degree of Phosphorus Saturation for the sediments (DPS %). DPS % has been used to quantify the amount of "bioavailable" P in the sediments and its potential for leaching in runoff (Perillo et al, 2019;Sims et al, 2002). DPS % was computed using the equation [(M3P/(M3Al+M3Fe))+0.019]/0.0042, where all the M3 extractable values are in molar concentrations (Figure 4a in Sims et al, 2002).…”

“…To our knowledge, this is the first study to report concentrations of M3-P and DPS for streambank legacy sediments. Although total P concentrations are important, M3-P and DPS values along with water extractable P may provide a more accurate indicator of bioavailable P in runoff (Fox et al, 2016;Perillo et al, 2019;Sims et al, 2002). While M3-P and DPS values were originally developed for agronomic assessments of upland soils (e.g., fertilizer needs and application for crops) they are increasingly being adopted to assess the P leaching potential for soils and for environmental soil P management.…”

Streambank Legacy Sediments in Surface Waters: Phosphorus Sources or Sinks?

“…In Arkansas, environmental threshold for water quality concern for M3P is higher at 150 mg kg −1 . When compared against these water quality thresholds, studies listed in Table 1 arrived at the same conclusion that streambank sediments (legacy and non-legacy) likely posed a low risk for P leaching under well oxygenated conditions and served as a net sink for P [36,[41][42][43]. All of the studies, however, did recognize that while P concentrations were low and most of the P was likely bound to metal hydro-oxides, this P could be released into solution due to the reductive dissolution of the oxides under anoxic conditions [44,45].…”

Land use and landscape position influence soil organic phosphorus speciation in a mixed land use watershed

“…Most studies have focused on changes in P concentration with land use with little regard to how P concentrations and speciation vary between the land use and its corresponding streambank. In a previous study in the Missisquoi River and its tributaries (VT, USA), we compared four types of land use (silage corn, hay meadow, emergent wetlands, and forest) and their corresponding streambanks and found that TP, soil test P (modified Morgan-extractable), and degree of P saturation (DPS) values of streambank soils varied significantly between each land use and its corresponding streambank, with the exception of forest sites (Perillo et al, 2019). However, more information about P speciation is needed to better understand P cycling in these soils.…”