The potential of agricultural headwater streams to retain soluble reactive phosphorus

Gabriele Weigelhofer

doi:10.1007/s10750-016-2789-4

Abstract

The study focuses on the capacity of agricultural headwater streams to retain soluble reactive phosphorus (SRP). In-stream phosphorus uptake was determined via short-term SRP additions in 14 reaches differing in channel morphology and riparian vegetation. In addition, zero equilibrium phosphorus concentrations (EPC0) were estimated for 8 reaches based on adsorption experiments. Average SRP uptake lengths amounted to 3.8 km in channelized sections, 1.9 km in forested sections, and 0.5 km in open meanders. Mass transfer coefficients were highest in open meanders (0.1 cm min−1), followed by forested (0.05 cm min−1) and channelized sections (0.04 cm min−1). EPC0 ranged from 20 to 1,600 µg SRP l−1 and correlated positively with inorganic P and reductant-soluble P concentrations of the sediments. In 50% of the reaches, phosphorus was released from the sediments at initial water concentrations of up to 500 µg SRP l−1, indicating a high release potential. Although EPC0 did not correlate with in-stream SRP uptake, sediments probably play a significant role for the P retention in agricultural headwater streams as they supply the benthic community with phosphorus from the subsurface. Thus, it is crucial that sediment–water interactions are considered in the restoration and management of agricultural headwater streams.

Highlights

Headwater streams have an important function in the retention and processing of dissolved and particulate organic matter and nutrients from the terrestrial surroundings (Alexander et al, 2007; Kristensen & Globevnik, 2014)
Benthic chlorophyll-a concentrations were highest in open meanders, followed by channelized and forested sections
Differences were significant between open meanders and forested sections (U test, P \ 0.01, n = 27)

Summary

Introduction

Headwater streams have an important function in the retention and processing of dissolved and particulate organic matter and nutrients from the terrestrial surroundings (Alexander et al, 2007; Kristensen & Globevnik, 2014). Comprising about two-third of the total river length in European countries and the U.S (Kavanagh & Harrison, 2014; Kristensen & Globevnik, 2014), small headwater streams are important links between the catchment and downstream reaches (Reddy et al, 1999; Dodds & Oakes, 2008) Due to their usually diverse channel morphology and their low discharge, pristine headwater streams can retain and process large amounts of nutrients and organic carbon from the catchment, thereby controlling matter transport into the remaining river system (Hall et al, 2002; Alexander et al, 2007; Hall et al, 2013). Efficient and adequate phosphorus retention within headwater reaches is, a prerequisite for the protection of European streams and rivers

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Discussion

Conclusion