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Watershed Buffering of Legacy Phosphorus Pressure at a Regional Scale: A Comparison Across Space and Time

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  • A. S. Kusmer
  • J.-O. Goyette
  • G. K. MacDonald
  • E. M. Bennett
  • R. Maranger
  • P. J. A. Withers
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<mark>Journal publication date</mark>01/2019
<mark>Journal</mark>Ecosystems
Issue number1
Volume22
Number of pages19
Pages (from-to)91–109
Publication statusPublished
Early online date27/04/18
Original languageEnglish

Abstract

Phosphorus (P) plays a crucial role in both agricultural production and water quality. There has been growing recognition of the importance of ``legacy'' P (surplus P that has accumulated in watersheds over time) for understanding contemporary water quality outcomes; however, little is known about how different watersheds respond to cumulative pressures from surplus P. The ``buffering capacity'' concept describes the ability of watersheds to attenuate P loading to surface waters by retaining P inputs over time. To explore the role of various watershed characteristics in buffering capacity, we used historic P data to calculate indices describing long- and short-term buffering for 16 large watersheds in southern Quebec, Canada, across a 30-year time span (1981--2011). We examined the correlation between these buffering capacity indicators and a set of key geochemical, hydrological, landscape and socio-ecological variables that we hypothesized could influence P buffering dynamics. Both short- and long-term buffering metrics were most strongly correlated with hydrological characteristics. Riverine TP flux across the watersheds was most strongly correlated with long-term buffering, which could represent a dominant influence of legacy P on contemporary riverine P flux. However, short- and long-term watershed buffering indices were not correlated with each other, suggesting distinctly different timescales and mechanisms of buffering. Combining estimates of long-term P accumulation along with biophysical characteristics of the watershed (including hydrology) explained a much greater share of the variation in riverine TP flux (R2thinspace=thinspace0.69) than biophysical characteristics alone (R2thinspace=thinspace0.36). Our findings reinforce the need to consider P buffering capacity and legacy P accumulation to help guide decision making around regional water quality targets across human-dominated landscapes.

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The final publication is available at Springer via http://dx.doi.org/10.1007/s10021-018-0255-z