Enhancement of Agricultural Policy/Environment eXtender Model (APEX) Model to Assess Effectiveness of Wetland Water Quality Functions

Amirreza Sharifi,Sangchul Lee,Megan Lang,Ali Sadeghi,Gregory Mccarty,Martin Rabenhorst,Jaehak Jeong

doi:10.3390/w11030606

Abstract

The Agricultural Policy/Environmental eXtender (APEX) model has been widely used to assess changes in agrochemical loadings in response to conservation and management led by US Department of Agriculture (USDA). However, the existing APEX model is limited in quantification of wetland water quality functions. This study improved the current model capacity to represent wetland water quality functions by addition of a new biogeochemical module into the APEX model. The performance of an enhanced APEX model was tested against five observed outgoing water quality variables (e.g., sediment, organic N, NO3, NH4 and PO4) from a wetland within the Eastern Shore of Maryland. Generalized Likelihood Uncertainty Estimation (GLUE) was implemented to assess model uncertainty. The enhanced APEX model demonstrated that it could effectively represent N and P cycling within the study wetland. Although improvement of model performance was limited, the additions of wetland biogeochemical routines to the APEX model improved our understanding of inner mass exchanges within N and P cycling for the study wetland. Overall, the updated APEX model can provide policymakers and managers with improved means for assessment of benefits delivered by wetland conservation.

Highlights

The US Department of Agriculture (USDA) Conservation Effects Assessment Project (CEAP)is a multi-agency effort with an overarching objective of assessing and quantifying the effects and effectiveness of USDA’s conservation programs and practices in agricultural landscapes across the United States [1]
The Agricultural Policy/Environmental eXtender (APEX) model is not appropriately equipped to model wetland hydrology, we found that the reservoir component within APEX can be fine-tuned to simulate hydrology of ponded wetlands
APEX shows much less sensitivity in capturing area variations and has a weaker fit compared with volume and outflow predictions

Summary

Introduction

Is a multi-agency effort with an overarching objective of assessing and quantifying the effects and effectiveness of USDA’s conservation programs and practices in agricultural landscapes across the United States [1]. Reserve Program—WRP) targets wetlands and offers landowners monetary incentives and technical support to restore, conserve and enhance wetlands and improve wildlife habitat on their property [2]. CEAP-Wetlands is one of five thematic national CEAP components, focusing on quantifying wetland ecosystem services (e.g., water quality, flood control or biodiversity) and interpreting effects/effectiveness of conservation practices on wetland functions and services through field research, data collection, model development and model application [3]. To better quantify effects of wetland conservation, there was a pressing need for a model that could be used to assess effectiveness of wetland restoration for water quality improvements, including contaminant/sediment amelioration, nutrient management and surface runoff/floodwater management. The resulting wetland model could be used for scenario analysis and for targeting wetland restoration sites that would provide maximum benefits in terms of water quality improvements

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