UNCORRECTED PROOF AUTHOR'S PROOFS 1 WATER QUALITY CO-EFFECTS OF GREENHOUSE GAS 2 MITIGATION IN U.S. AGRICULTURE 3 SUBHRENDU K. PATTANAYAK 1 , BRUCE A. McCARL 2 , ALLAN J. SOMMER 1∗ , 4 BRIAN C. MURRAY 1 , TIMOTHY BONDELID 1 , DHAZN GILLIG 2 5 and BENJAMIN DEANGELO 3 6 1 Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27709, U.S.A. 7 E-mail: sommer@rti.org 8 2 Texas A & M University, Texas, U.S.A. 9 3 U.S. Environmental Protection Agency, U.S.A. Q1 10 Abstract. This study develops first-order estimates of water quality co-effects of terrestrial green- 11 house gas (GHG) emission offset strategies in U.S. agriculture by linking a national level agricultural 12 sector model (ASMGHG) to a national level water quality model (NWPCAM). The simulated policy 13 scenario considers GHG mitigation incentive payments of $25 and $50 per tonne, carbon equivalent 14 to landowners for reducing emissions or enhancing the sequestration of GHG through agricultural 15 and land-use practices. ASMGHG projects that these GHG price incentives could induce widespread 16 conversion of agricultural to forested lands, along with alteration of tillage practices, crop mix on land 17 remaining in agriculture, and livestock management. This study focuses on changes in cropland use 18 and management. The results indicate that through agricultural cropland about 60 to 70 million tonnes 19 of carbon equivalent (MMTCE) emissions can be mitigated annually in the U.S. These responses also 20 lead to a 2% increase in aggregate national water quality, with substantial variation across regions. 21 Such GHG mitigation activities are found to reduce annual nitrogen loadings into the Gulf of Mexico 22 by up to one half of the reduction goals established by the national Watershed Nutrient Task Force 23 for addressing the hypoxia problem. 24 1. Introduction 25 There is growing recognition that terrestrial activities in agriculture, land-use 26 change, and forestry can play an important role in reducing the potential im- 27 pacts of climate change by mitigating greenhouse gas (GHG) emissions (Wat- 28 son et al., 2000; McCarl and Schneider, 2000). A number of economic studies 29 have focused on the cost of securing agricultural and forestry participation. 1 These 30 studies estimate the costs of carbon sequestration by calculating the foregone agri- 31 cultural returns that result from converting cultivated agricultural lands to forest, 32 and the associated costs of conversion and management. However these studies 33 have largely neglected the potential non-GHG environmental co-effects of GHG 34 mitigation. 35 The Intergovernmental Panel on Climate Change (IPCC) Special Report on Land 36 Use, Land-Use Change and Forestry suggests many land-use change and forestry 37 (LUCF) practices for GHG mitigation would likely lead to broader environmen- 38 tal benefits such as improved water quality and quantity, reduced soil erosion and Climatic Change xxx: 1–32, 2004. C  2004 Kluwer Academic Publishers. Printed in the Netherlands. TECHBOOKS Journal: CLIM MS Code: 2802 PIPS No: 5383150 DISK 1-8-2004 15:57 Pages: 32