New Insights Into Legacy Phosphorus From Fractionation of Streambed Sediment

Abstract

Streambed and lake sediment was studied in Sävjaån, a eutrophic mesoscale catchment (722 km 2) in central Sweden. Triplicate sediment cores from five lakes and nine streams, ranging from headwater to fourth order, were sampled. The sediment was analyzed with a sequential extraction method, where six different phosphorus (P) fractions were measured. The results showed that streambed sediments store considerable amounts of P and in some cases have comparable P contents (g/kg DW) to lake sediment. Land use, soil type, and drainage area (location in the catchment) had a significant effect on the different P fractions found in surficial sediments. Sediment from lakes and forested headwater streams generally had high proportions of organic P and iron bound P. In larger streams located in agricultural areas on clay soils closer to the catchment outlet, with dense sediment and a relatively low proportion of organic matter, P was to a larger extent bound to calcium. Streambed sediment may be an important catchment scale P store and should be considered when modeling catchment P dynamics. The large stores of streambed legacy P should also be considered when performing ditch maintenance to avoid unnecessary mobilization of bioavailable P.

Spatial Persistence of Water Chemistry Patterns Across Flow Conditions in a Mesoscale Agricultural Catchment

“…The SP of more biologically reactive parameters (i.e., SRP, NO 3 − , and DOC) decreased earlier than less reactive parameters (i.e., TDP, PP, and DIC) (Figure 3), which showed spatial reorganization as discharge decreased. These seasonally lagged spatial rearrangements in chemistry suggest parameter‐specific dynamics, potentially associated with stoichiometrically regulated biological uptake and release, or complex multi‐flow path sources (Casquin et al., 2020; Frei et al., 2020; Helton et al., 2015; Lannergård et al., 2020).…”

The influence of landscape spatial configuration on nitrogen and phosphorus exports in agricultural catchments

“…During the lowflow dates, the correlations with LCI-TP were not significant: different sources and sinks likely dominate the influence of agricultural areas and their configuration, which predominates during the flow period. Leaks from septic tanks or animal buildings and desorption from sediments are the most likely sources of P during this ecologically sensitive period, while hydrological disconnection, uptake, and sedimentation can be sinks of P (Lannergård et al 2020;Sandstrom et al 2020).…”

Variability in fluvial suspended and streambed sediment phosphorus fractions among small agricultural streams

“…Calcium‐bound P is usually contained in mineral lattices and hence is usually nonavailable or even considered inert (Lukkari et al., 2007). There is a need for further studies on the effect of environmental conditions on potential P bioavailability in FSS and streambed sediment in headwater streams because the environmental conditions affecting P release in headwater streams can differ from larger rivers as well as lakes (Lannergård et al., 2020).…”

“…Historical land management practices have caused accumulation of legacy P in soils and freshwater sediments (Kleinman et al., 2011; Sharpley et al., 2013) where biogeochemical processes can transform recalcitrant P fractions to more bioavailable forms (Lannergård et al., 2020). Although streambed sediments are important sources and sinks for P cycling (Ezzati et al., 2020; Jarvie et al., 2005; Owens & Walling, 2002; Weigelhofer et al., 2018), the role of fluvial suspended sediment (FSS) in P cycling is rarely investigated despite its potential significance.…”

“…Most schemes define operational P fractions, including loosely sorbed P, metal‐associated P (e.g., iron [Fe] and aluminum [Al]), and calcium (Ca)‐bound P (Condron & Newman, 2011). Numerous studies exist on P fractions in lake sediment (Agstam‐Norlin et al., 2020; Kaiserli et al., 2002; O'Connell et al., 2020; Pettersson, 1998), and there are a few studies of P fractions in streambed sediment (Audette et al., 2018; Lannergård et al., 2020; SanClements et al., 2009). However, studies of FSS are rare (Ballantine et al., 2008; Nguyen & Sukias, 2002), and knowledge about seasonal variations is needed.…”