The Influence of Legacy P on Lake Water Quality in a Midwestern Agricultural Watershed

• Published in: Ecosystems (New York) 2017-12, Vol.20 (8), p.1468-1482
• Main Authors: Motew, Melissa, Chen, Xi, Booth, Eric G., Carpenter, Stephen R., Pinkas, Pavel, Zipper, Samuel C., Loheide, Steven P., Donner, Simon D., Tsuruta, Kai, Vadas, Peter A., Kucharik, Christopher J.
• Format: Article
• Language: English
• Subjects: Agricultural industry; Agricultural land; Agricultural watersheds; Agriculture; Agrochemicals; Analysis; Biomedical and Life Sciences; Climate change; Climatic changes; Climatic conditions; Computer simulation; Ecology; Ecosystem models; Environmental Management; Eutrophication; Fertilizers; Geoecology/Natural Processes; Hydrologic models; Hydrology; Hydrology/Water Resources; Indicators; International economic relations; Lakes; Life Sciences; Management; Mathematical models; Original Articles; Phosphorus; Plant Sciences; Precipitation; Quality control; Rainfall; Reduction; Sediments; Surface water; Water; Water quality; Zoology
• ISSN: 1432-9840; 1435-0629
• DOI: 10.1007/s10021-017-0125-0

Decades 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.