Spatial and Temporal Patterns of Best Management Practice Implementation in the Chesapeake Bay Watershed, 1985–2014

Abstract

Efforts to restore water quality in Chesapeake Bay and its tributaries often include extensive Best Management Practice (BMP) implementation on agricultural and developed lands. These BMPs include a variety of methods to reduce nutrient and sediment loads, such as cover crops, conservation tillage, urban filtering systems, and other practices. Estimates of BMP implementation throughout the Chesapeake Bay watershed were provided for each year from 1985 through 2014 by the Chesapeake Bay Program (CBP). This dataset of BMP implementation is a compilation of actions reported by New York, Maryland, Pennsylvania, Delaware, West Virginia, Virginia, and the District of Columbia, and includes a wide array of management activities. Management actions vary among the jurisdictions and generally reflect the typical land use in each region. The amount of implementation also varies according to different priorities, reporting practices, and special programs within each jurisdiction. For example, extensive cover crop implementation was reported in Maryland whereas Pennsylvania, in general, has lower levels of BMP implementation reported on cropland. Pennsylvania and Maryland have higher levels of infiltration BMPs on developed land compared to those in Virginia. Conservation tillage BMPs accounted for the majority of reported agricultural BMP implementation in 1985. By 2014, however, a more diverse collection of agricultural BMPs was reported and conservation tillage BMPs accounted for a smaller proportion of overall reported agricultural BMP implementation. After the year 2000, land-use change BMPs, such as land retirement, pasture fencing, and forest buffers, were more commonly reported across the Chesapeake Bay watershed. 1U.S. Geological Survey 2Devereux Environmental Consulting, Inc. 3U.S. Environmental Protection Agency Expected changes in nutrient and sediment loads in the Chesapeake Bay watershed due to BMP implementation were estimated by use of specially designed annual scenarios of the CBP Partnership Phase 5.3.2 Watershed Model. Nitrogen loads to streams were estimated to be reduced by 11 percent from 1985 to 2014 due to the implementation of BMPs. Compared with 1985, phosphorus loads were estimated to be 19 percent lower and sediment loads were estimated to be 23 percent lower by 2014 due to the effects of BMPs. Reductions in total nitrogen from 1985 to 2014 due to BMPs varied spatially across the watershed and were estimated to be as high as 42 percent in areas of the Eastern Shore of the Chesapeake Bay. Reductions in phosphorus and sediment also varied spatially, with the largest reductions occurring in the Potomac watershed upstream of Washington, D.C. and the Eastern Shore of Maryland, according to the CBP model results. Additional model scenarios were developed to estimate the effect of individual BMP types. The largest estimated reductions in total nitrogen loads on agricultural lands in 2014 were attributed to land retirement, animal waste management systems, and conservation tillage. The largest estimated reductions in total phosphorus loads on agricultural lands were attributed to animal waste management systems, pasture fencing, and phytase feed additives in 2014. The largest estimated reduction in total sediment loads on agricultural lands was attributed to conservation tillage, pasture fencing, and conservation plans. Dry ponds, wet ponds, and constructed wetlands were reported extensively throughout the watershed. These BMPs accounted for about half of the reduction in nitrogen loads from developed land to streams, half of the phosphorus reduction, and about a third of the sediment reduction. 2 Spatial and Temporal Patterns of Best Management Practice Implementation in the Chesapeake Bay Watershed, 1985–2014 Introduction Chesapeake Bay is the largest estuary in North America and a valuable ecological and economic resource. Anthropogenic pressures, including increased urbanization and more intensive agricultural production, have led to degraded water quality conditions throughout the watershed (Phillips, 2007). The U.S. Environmental Protection Agency (EPA) has classified Chesapeake Bay as “impaired” by sediment and nutrients, and implemented Total Maximum Daily Loads (TMDLs) for nitrogen, phosphorus, and sediment (U.S. Environmental Protection Agency, 2010a). A variety of best management practices (BMPs) are often used to mitigate nutrient and sediment loadings in order to meet the TMDL regulatory requirements. These Best Management Practices (BMPs) are an important part of Chesapeake Bay restoration efforts; however, further information to quantify their effects on nutrient and sediment loads is/will be required to improve the targeting of management actions across the watershed. Whereas field-scale assessments of BMP effectiveness exist, few regional-scale estimates of the effects of BMPs on nitrogen, phosphorus, and sediment loads delivered to streams are available (Liu and others, 2017). The seven major jurisdictions in the Chesapeake Bay report BMP implementation to the Chesapeake Bay Program (CBP) annually. The major jurisdictions are New York, Maryland, Pennsylvania, Delaware, West Virginia, Virginia, and the District of Columbia (fig. 1). The CBP has agreed upon a set of BMPs that are considered effective for reducing nitrogen, phosphorus, and sediment loads. The CBP and the U.S. Geological Survey (USGS) have collaborated to develop a deterministic model (the Phase 5.3.2 Watershed Model) to quantify how water quality in the Chesapeake Bay watershed responds to changes in watershed and airshed management actions as well as changes in nutrient sources and other factors (U.S. Environmental Protection Agency, 2010b). The effectiveness of BMPs and individual BMP types has not been extensively studied or quantified in the Chesapeake Bay watershed. The evaluation of BMP implementation data, including the spatial locations, temporal patterns, and their modeled effects on nitrogen, phosphorus and sediment that is delivered to streams, provide much needed insight on the effectiveness of management strategies. The USGS has collaborated with the CBP to assess the amount of BMP implementation over time and estimate the changes in water quality attributable to these management actions. Purpose and Scope This report describes the spatial and temporal patterns of BMP implementation across the Chesapeake Bay watershed from 1985 through 2014. Methods to estimate the effect of BMP implementation on nitrogen, phosphorus, and sediment loads also are described. Additionally, the effect of individual BMP types on nutrient loads is estimated. The CBP selected 2017 as a midpoint assessment of the TMDLs. The TMDLs were designed to have all jurisdictions implement reduction strategies by 2025, so that the bay will attain its water-quality goals. The midpoint assessment period was designated to assess progress in meeting reduction strategy goals and to evaluate recent science that may indicate necessary changes to those strategies (U.S. Environmental Protection Agency, 2010a). A companion dataset to this report is available at (https:// doi.org/10.5066/P9OVU9PX) and includes detailed descriptions of BMP types as well as tables of model output at a selection of spatial scales (Devereux and others, 2018).