Spatial and Seasonal Dynamics of Inorganic Nitrogen and Phosphorous Compounds in an Orchard-Dominated Catchment with Anthropogenic Impacts

The influence of various types of agricultural activities on the dynamics of biogenic compounds of flowing water was broadly recognized in many spatial and temporal scales. However, relatively minor attention was paid to the hydrochemical functioning of horticultural catchments despite their importance and dominance in some regions of Europe. Thus, the current study investigated spatial and seasonal variations in inorganic nitrogen and phosphorous compounds in stream water in the Mogielanka River catchment, with 72% covered by apple orchards. Water samples were collected from fifteen sites distributed across the catchment in the monthly timescale from March 2020 to February 2021. Concentrations of NO3−, NO2−, NH4+, and PO43− were determined photometrically, while in situ water temperature, oxygen saturation, electrical conductivity, and pH, were measured with the use of portable devices. The impact of horticulture was mainly documented in the higher concentration of NO3− during the winter months; however, maximum values did not exceed 15 mg·dm−3 and were relatively low in comparison to catchments dominated by arable lands. The authors also found a clear impact of unstratified reservoirs and inflows from wastewater treatment plants on the dynamics of biogenic compounds. The correlations of PO43− with the sums of precipitation suggested, in turn, that increased PO43− concentration mainly results from poor sewage management. The results provided preliminary but unique and spatially extensive insight into the functioning of an orchard-dominated lowland catchment and allowed the researchers to point out the main recommendations for improving water quality in similar regions.