02495nas a2200253   4500008004100000020001400041245009100055210006900146260001100215300001100226520172200237100001901959700001301978700002001991700002702011700001802038700002302056700002402079700002202103700001702125700002102142700003002163856004802193       2017                        eng d  a1435-062900aThe Influence of Legacy P on Lake Water Quality in a Midwestern Agricultural Watershed0 aInfluence of Legacy P on Lake Water Quality in a Midwestern Agri  c2017//  a1 - 153 aDecades of fertilizer and manure applications have led to a buildup of phosphorus (P) in agricultural soils and sediments, commonly referred to as legacy P. Legacy P can provide a long-term source of P to surface waters where it causes eutrophication. Using a suite of numerical models, we investigated the influence of legacy P on water quality in the Yahara Watershed of southern Wisconsin, USA. The suite included Agro-IBIS, a terrestrial ecosystem model; THMB, a hydrologic and nutrient routing model; and the Yahara Water Quality Model which estimates water quality indicators in the Yahara chain of lakes. Using five alternative scenarios of antecedent P storage (legacy P) in soils and channels under historical climate conditions, we simulated outcomes of P yield from the landscape, lake P loading, and three lake water quality indicators. Legacy P had a significant effect on lake loads and water quality. Across the five scenarios for Lake Mendota, the largest and most upstream lake, average P yield (kg ha−1) varied by −41 to +22%, P load (kg y−1) by −35 to +14%, summer total P (TP) concentration (mg l−1) by −25 to +12%, Secchi depth (m) by −7 to +3%, and the probability of hypereutrophy by −67 to +34%, relative to baseline conditions. The minimum storage scenario showed that a 35% reduction in present-day loads to Lake Mendota corresponded with a 25% reduction in summer TP and smaller reductions in the downstream lakes. Water quality was more vulnerable to heavy rainfall events at higher amounts of P storage and less so at lower amounts. Increases in heavy precipitation are expected with climate change; therefore, water quality could be protected by decreasing P reserves.1 aMotew, Melissa1 aChen, Xi1 aBooth, Eric, G.1 aCarpenter, Stephen, R.1 aPinkas, Pavel1 aZipper, Samuel, C.1 aLoheide, Steven, P.1 aDonner, Simon, D.1 aTsuruta, Kai1 aVadas, Peter, A.1 aKucharik, Christopher, J.  uhttp://dx.doi.org/10.1007/s10021-017-0125-0