**2. Materials and Methods**

*2.1. Study Site Selection*

The Chesapeake Bay Nontidal Network is a monitoring network comprising 123 waterquality-monitoring stations throughout the Chesapeake Bay watershed that provide nutrient and sediment data [21]. The water-quality-monitoring stations are co-located with U.S. Geological Survey (USGS) streamflow gauges, allowing loads to be calculated. While streamflow data were collected at the sub-daily scale, water-quality data were collected monthly and during targeted storm events, providing 20 data points per station per year. Load data are available in the USGS database at monthly and annual time scales back to 1985; however, daily-scale data were estimated by USGS using the weighted regression on time, discharge, and season (WRTDS) load-estimation technique [21,22].

Here, we analyze eight stations from the Chesapeake Bay Nontidal Network (Table 1; Figure 1). These stations were selected because they are located in Tier 1 or Tier 2 counties in PA, which are the counties with the greatest nutrient loads to the Chesapeake Bay watershed [20]. Further, the drainage areas for each of these monitoring stations are within one county's boundaries, enabling more accurate calculation of the specific load-reduction goals that need to be met at each point (Table 1). The load reduction for TN and TP that each county needs to meet is specified in the PA Watershed Implementation Plan [20], and the load reduction needed for each selected study site was calculated based on the size of the drainage area relative to the county. For example, a drainage area that spans half of a county would need to meet half of the county's mandated load reduction.

**Table 1.** Information regarding drainage area, percentage of land use (agricultural, forested, and urban), and annual load-reduction goals for total nitrogen (TN) and total phosphorus (TP) for each selected study site in the Pennsylvania portion of the Chesapeake Bay watershed. Land use is based on USGS 2016 National Land Cover Data (https://www.mrlc.gov/data/nlcd-2016-land-cover-conus; accessed on 30 June 2020).


