Natural Runoff Nitrogen and Phosphorus data

This data set contains NO3-N, NH4-N, PO4-P, and Total Nitrogen (TN) concentration (mg/L) measurements from liquid runoff samples collected after natural precipitation events. The surface runoff analyzed in this dataset was collected in Beltsville, MD at the Central Maryland Research and Education Center (CMREC) (39°00'46.0"N 76°49'35.7"W). Maryland has a temperate climate with humid dry summers and wet cold winters. The data was collected during the wet cold months (Nov-May) when the potential for surface runoff is the greatest. This was done over two sample years: November 2021-May 2022 and November 2022-May 2023. During each sampling year, surface runoff was collected from 24 in field locations using mini-erosion weirs. Each weir collects runoff from a 0.29 m^2 area into an 8L receptacle jug. The jugs were checked for samples after each runoff producing precipitation event (>12.7mm precipitation). However, not all 24 weirs collected surface runoff during each runoff producing rain event due many reasons: natural slope of the land, infiltration rate, intensity and duration of the precipitation. The runoff collection was part of a greater experiment utilizing three different cover crop treatments (No Cover, 3-Way, and Rye) in two different cash crop residues (Corn and Soybean). During each sample year there were eight weirs in each of the three cover crop treatments and 12 weirs in each cash crop residue. When runoff samples were collected, the jugs were brought back to the lab at the University of Maryland College Park. A 100mL sub-sample of each jug was filtered using a 0.45um membrane. After filtration the inorganic N concentrations, NO3-N and NH4-N, were determined colorimetrically using the Salicylate Method and the Endol Blue Method respectively. The inorganic P concentration, PO4-P, was determined using the Molybdate colorimetric test. The filtrate was also analyzed for the TN concentration by mixing the filtrate with a strong alkaline persulfate solution and heating the mixture for 1hr at 120 deg C under 16kpa in an autoclave. Following this, the mixture was analyzed for NO3-N and using the respective NO3-N colorimetric methods, giving the total dissolved N concentration. All colorimetric analysis was performed using a DU 7000 Series Beckman Coulter Spectrophotometer and absorbance readings were converted into concentration (mg/L) using equations derived from the standard curves. 

NO3-N (mg/L) = 135.5*absorbance

NH4-N (mg/L) = 55.7*absorbance

TN (mg/L) = 146.7*absorbance - 1.447

PO4-P (mg/L) = 1.764*absorbance + 0.007

This data set also contains NO3-N, NH4-N, PO4-P, and TN concentration (mg/L) measurements of the soil surrounding each of the 24 weirs. Six shallow soil cores were taken around each of the 24 weirs in November 2021, November 2022, and May 2023.The six cores were combined into two composite samples per weir; 0-2.5cm and 2.5-15cm. In the lab the soil cores were air dried, ground using a 1mm sieve, and extracted using 0.1M CaCl2 solution. The extract was filtered through 0.45um filter paper and then the filtrate was analyzed for NO3-N, NH4-N, PO4-P, and TN concentrations (mg/L) using the same methods mentioned above.