Challenges and solutions in identifying agricultural pollution hotspots using gross nitrogen balances

Development of a groundwater contamination index based on the agricultural hazard and aquifer vulnerability: Application to Portugal

“…The GNB previously calculated by Serra et al (2019) at the municipality scale for the years 1999 and 2009 was used to estimate nitrate (NO 3 − ) leaching. The authors took a mass balance approach between agricultural N inputs and outputs (Eq.…”

“…If negative N balances occur, N leach and N denit were set to 0. These situations were attributed to statistical biases that affected the distribution of inorganic fertilisers in 1999 (Serra et al, 2019) and/or soil N depletion (Moklyachuk et al, 2019;Özbek and Leip, 2015). Table 1 summarizes data inputs and sources as well as the methods employed for each environmental N loss.…”

“…The extrapolated irrigated areas for 1999 were further disaggregated into different crops and irrigation systems by using the respective fractions of 2009 compared to the total irrigated area of the same year. Crop N application rates from sludge, manure and inorganic fertilisers were derived from Serra et al (2019) and distributed to crop areas under different irrigation systems.…”

“…where N app is the N-input from sludge, manure spreading, inorganic fertilisers and animal N excreted onto pastures, corrected to NH 3 losses during housing, storage and grazing (kg N ha −1 yr −1 ) and f runoff is the runoff fraction (%N app ). The latter is obtained as a function of slope (S) and land use (LU) modified according to the excess of precipitation surplus (PS; precipitation minus evapotranspiration), soil type (T) and depth to rock (DR), reclassified according to Velthof et al (2009): (Serra et al, 2019) and soil pH (Pena et al, 2015). (Serra et al, 2019).…”

Soil available nitrogen and phosphorus affected by functional bacterial community composition and diversity as ecological restoration progressed

“…For each paired sample, the gross AN and AP balance during the incubation stage was calculated as the net difference between the root-free soil (without plant root uptake) and root-soil concentrations (including plant root uptake) of AN and AP, here calculated using a method based on Serra, Cordovil, Cruz, Cameira, and Hutchings (2019) and Leip, Britz, Weiss, and de Vries (2011). First, this method is based on the assumption that ecological processes (i.e., N and P mineralization, leaching, and atmospheric N deposition), inside and outside the sample cylinders, are equivalent during each stage of cylinder incubation (Robertson et al, 1999).…”