Sediment and Nutrient Assessment Program Methods
Sampling efforts at the six long-term sites (Towanda, Danville, Lewisburg, Newport, Marietta, and Conestoga) included sampling during monthly base flow conditions, monthly flow-independent conditions, and seasonal storm conditions. This resulted in two samples collected per month: one with a set date near the twelfth of each month independent of flow and one based on targeting monthly base flow conditions. The mid-monthly samples were intended to be flow independent with the intention that the data would help to quantify long-term trends. Additionally, due to the linkage of high flow and nutrient and sediment fluxes, it was necessary to target storm events for additional sampling to adequately quantify fluxes. Long-term site sampling goals included targeting one storm per season with a second storm collected during the spring season. The intention of collecting two spring storms was to have data before and after agricultural crops had been planted.
All storm samples were collected during the rising and falling limbs of the hydrograph with goals of three samples on each side and one sample as close to the peak as possible for long-term sites. Enhanced sites (those added as part of the CBPO non-tidal water quality monitoring network expansion) targeted a mid-monthly flow independent sample and two storm samples per season. Storm samples were planned to have one sample on the rising limb and one on the falling limb of the hydrograph with the goal that one of the two be as close to the peak as possible. Due to the flashiness of the hydrograph on several of the smaller streams, sometimes the two storm samples per season were taken from two different storms with the goal of having samples as close to the peak of each storm as possible.
The goal of sample collection was to collect a sample representative of the entire water column. Due to variations in stream width and depth and subsequent lack of natural mixture of the stream, it was necessary to composite several individual samples across the water column into one representative sample. The number of individual verticals at each site varied from three to ten dependent upon the stream width. Samples were collected using United States Geological Survey (USGS) isokinetic sampling methodology. Instream water quality readings were taken at each vertical to insure accurate dissolved oxygen and temperature values.
All samples were processed onsite and included whole water samples analyzed for nitrogen and phosphorus species, TOC, TSS, and SS. For enhanced sites, SS samples were only collected during storm events. Filtered samples were processed onsite to analyze for DN and DP species. Several sites included additional parameters pertinent to the natural gas industry.
Samples were either hand-delivered or shipped directly to the appropriate laboratory for analysis on the day following collection. When storm events occurred over the weekend, samples collected were analyzed on the following Monday. Samples collected in Pennsylvania and at the Octoraro Creek site near Richardsmere, Md., were delivered to PADEP’s Bureau of Laboratories in Harrisburg, Pa. Samples collected at New York sites were shipped to ALS Environmental Laboratory in Rochester, N.Y. Parameters for all samples at all sites included various nitrogen and phosphorus species, TOC, and TSS. Specific parameters, methodology, and detection limits are listed in the program’s Quality Assurance Project Plan (QAPP).
Due to the high influence of stormflow on sediment concentrations, SS samples were collected during storm events at all sites with the goal of two samples for each event and one event per quarter. Of the two samples per storm, the more sediment-laden sample was analyzed for both sediment concentration and sand/fine particle percentage. The additional sample was submitted for sediment concentration only. Sediment samples were shipped to the USGS sediment laboratory in Louisville, Ky., for analysis. Additional SS samples also were collected at long-term sites as part of each sampling round. These samples were analyzed at the Commission laboratory for sediment concentration alone. All sample results are compiled into an existing comprehensive database that includes all years of the program. All data are available under the individual site’s web page. Data were also submitted to various partners for use with models and individual analyses.