The Susquehanna River Basin Commission implemented a five-year nutrient-monitoring program in October 1984 to establish a database for estimating nutrient and suspended sediment loads in the Susquehanna River Basin. This monitoring effort, conducted as part of the Chesapeake Bay Restoration Program, consisted of monthly base flow sampling and periodic sampling throughout the high flow hydrograph for a minimum of five storms per year.
Initially, 12 sampling sites were established. This sampling network included a series of mainstem and major tributary sites, and a series of sites located on smaller watersheds that had significant areas of specific land use, or representative combinations of land uses. Collection of data at stations on the mainstem and major tributaries was necessary to enable accurate allocation of nutrient and suspended sediment loads to the main river reaches and to major subbasins. Data were collected for the Susquehanna River at Danville and Harrisburg, the West Branch Susquehanna River at Lewisburg, the Juniata River at Newport, the Swatara Creek near Hershey, the West Conewago Creek near Manchester, and the Conestoga River at Conestoga, Pennsylvania, to confirm the Chesapeake Bay Program watershed model load allocations and provide the basis for refining the model outputs for these areas. Each site represented large areas having significant differences and levels of complexity in terms of geological setting and combinations of land uses.
The stations located on relatively small watersheds of varying geologic settings provided a range of land uses or representative combinations of land uses. The sites represent: (1) a total wilderness area--Stony Creek at Water Tank Trail near Dauphin, Pa., (2) a sparsely populated forest/cropland watershed with no areas of concentrated residential development--Sherman Creek at Shermans Dale, Pa., (3) a small watershed of intense suburban development throughout its headwaters area--Paxton Creek near Penbrook, Pa., (4) a complex area that drains extensive cropland with a number of fairly large reservoirs--Codorus Creek near York, Pa., and (5) a suburban and urban development--Codorus Creek at Pleasureville. These watersheds were considered to be representative of many areas throughout the basin and would provide detailed information for: (1) refining the Bay watershed model, (2) identifying problems related to specific land uses and combinations of land uses, and (3) identifying future management actions in the area.
In 1987, an additional site was added on the Susquehanna River at Marietta, Pa., to provide a better estimate of the nutrient and suspended sediment loads transported by the Susquehanna River prior to entering the hydropower reservoirs in the lower river. In 1989, another sampling site was established on the Susquehanna River at Towanda, Pa., to provide an estimate of nutrient and suspended sediment loads from New York State.
The initial five-year program was concluded at the end of December 1989, and five of the twelve original sites were selected for continued long-term monitoring. The Susquehanna River at Towanda, Danville and Marietta, and the West Branch Susquehanna River at Lewisburg were selected to provide long-term data to evaluate trends in nutrient and suspended sediment transport from the major subbasin. The fifth site, the Conestoga River at Conestoga was selected to provide long-term data from a major tributary watershed with intensive agricultural activity and increasing development. Implementation of Best Management Practices is also being actively pursued. In October 1993, a sixth site, the Juniata River at Newport was re-established for long-term monitoring.
In October of 2004, 13 additional sites were added to the monitoring network as part of the Chesapeake Bay Programís Non-tidal Monitoring Network. Additional sites were added in 2005 and 2012. This effort was conducted by the CBP Non-Tidal Water Quality Workgroup based on the following objectives:
These new sites were chosen with the following priorities:
The current monitoring sites for the SNAP are listed below.
Group A Sites (Long-term sites):
Group B sites (Enhanced sites):
Data from the original sites are being used to compute annual loads of nutrients and suspended sediment at each of the sites. The initial five-year intensive sampling program provides baseline data that can be used to evaluate changes in water quality as management practices are installed. Data from the long-term monitoring sites also have been used for statistical trend analysis.