Anthropogenic and Climate-Exacerbated Landscape Disturbances Converge to Alter Phosphorus Bioavailability in an Oligotrophic River

Caitlin Watt,Monica B Emelko,Adrian L Collins,Uldis Silins,Micheal Stone

doi:10.3390/w13223151

Caitlin Watt, Monica B Emelko + Show 3 more

Open Access

https://doi.org/10.3390/w13223151

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Abstract

Cumulative effects of landscape disturbance in forested source water regions can alter the storage of fine sediment and associated phosphorus in riverbeds, shift nutrient dynamics and degrade water quality. Here, we examine longitudinal changes in major element chemistry and particulate phosphorus (PP) fractions of riverbed sediment in an oligotrophic river during environmentally sensitive low flow conditions. Study sites along 50 km of the Crowsnest River were located below tributary inflows from sub-watersheds and represent a gradient of increasing cumulative sediment pressures across a range of land disturbance types (harvesting, wildfire, and municipal wastewater discharges). Major elements (Si2O, Al2O3, Fe2O3, MnO, CaO, MgO, Na2O, K2O, Ti2O, V2O5, P2O5), loss on ignition (LOI), PP fractions (NH4CI-RP, BD-RP, NaOH-RP, HCI-RP and NaOH(85)-RP), and absolute particle size were evaluated for sediments collected in 2016 and 2017. While total PP concentrations were similar across all sites, bioavailable PP fractions (BD-RP, NaOH-RP) increased downstream with increased concentrations of Al2O3 and MnO and levels of landscape disturbance. This study highlights the longitudinal water quality impacts of increasing landscape disturbance on bioavailable PP in fine riverbed sediments and shows how the convergence of climate (wildfire) and anthropogenic (sewage effluent, harvesting, agriculture) drivers can produce legacy effects on nutrients.

Highlights

The quantity, composition, storage, and remobilization of fine sediment and associated phosphorus (P) can be substantially altered in rivers flowing through forested regions that experience increased levels of natural and anthropogenic landscape disturbance, such as wildfire [1] and harvesting [2]
Concentrations of Total PP (TPP) stored in the gravel-bed matrix of the Crowsnest River ranged from 469.9 to 734.1 μg g−1
Mean TPP concentrations across the study sites ranged from 601.7 μg g−1 at S1 to 708.6 μg g−1 at S2

Summary

Introduction

The quantity, composition, storage, and remobilization of fine sediment and associated phosphorus (P) can be substantially altered in rivers flowing through forested regions that experience increased levels of natural and anthropogenic landscape disturbance, such as wildfire [1] and harvesting [2]. Remobilization of riverbed PP from previous disturbances, or “legacy P” [3], is a critical source of potentially bioavailable P that can promote the growth of nuisance algae including cyanobacteria [4], pose significant challenges to water treatment [5,6,7], and degrade the health of aquatic ecosystems for decades [8,9]. Because the bioavailable PP forms that comprise NAIP are typically found adsorbed to mineral surfaces in aquatic systems, fine sediment geochemistry is a key abiotic driver of aquatic ecosystem change and must be considered in any evaluation of landscape disturbance impacts on water quality, eutrophication, or habitat degradation [3,21,22]

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