1. Introduction
In recent years, land degradation studies regarding soil and water
quality have been systematically expanded rapidly throughout the world,
with enormous health, social, and economic consequences (Kanownik 2005;
Pawlowski 2011; Frąk and Baryła 2012; Gao et al., 2014; Chiwa 2021).
Several factors influence the physicochemical quality of surface water,
namely the concentrations of nitrate, phosphate, and sulfate anions
(Akan et al., 2012), as well as sodium, potassium, calcium, and
magnesium cations (Purandara et al., 2012). In surface waters,
agricultural activity is the major cause of poor physicochemical quality
(Bedla and Misztal 2014; Halecki et al., 2019). Thus, a key objective of
water erosion assessment is to determine the physicochemical quality of
the surface water that flows out of a catchment (Robson 2014).
Specifically, soil protection research focuses on managing the terrain
such that excess rainwater can be drained to limit the amount of intense
washout in erosion-prone regions. The purpose of these procedures is to
limit the spread of surface runoff and infiltration of water into the
substratum. Furthermore, the granular composition of the soil affects
the suitability of the area for farming (Seneviratne et al., 2010;
Brocca et al., 2012). Cross-slope cultivation lessens the erosion of
soil, but the amount of annual soil loss increase with increasing slope
steepness (Vermeulen and Nieuwenhuis 2005; Kowalczyk and Twardy 2012).
Thus, various environmental engineering methods are used to manage
slopes in the Eastern Carpathian catchment (Mostowik et al., 2021).
Technical and ecological solutions are commonly sought in mountain
catchments for the design of forest roads that slow down the flushing of
soil, including polders with control devices that regulate outflow and
inflow, blockage traps, and transverse barriers (Łapuszek and Witkowska
2005). In agricultural areas on the northern slopes of the West
Carpathian, slope length is a major controlling factor for surface water
erosion in different soil and agrotechnical systems. Moreover, the
intensity of rainfall can affect the rate of soil erosion (Obi and
Salako 1995), which depends strongly on the moisture content of the soil
surface layer. Notably, runoff is one of the major determining factors
of soil degradation (Zhao et al., 2021). The valley bottom usually
contains silt in high concentrations due to surface drainage. Grazing
pastures in mountainous terrain are designed for the retention of
water-soaked clastic material (rill erosion or interrill erosion). For
example, cultivated land on the Beskid flysch slope enriches the surface
eroded material and soil surface water (Gil et al., 2021).
SWAT+ is a model used to simulate the quality of surface water in small
watersheds and river basins. The current research examined the flow of
nitrates and phosphorus in mountain streams. The study aimed to
determine the factors that affect the inorganic nutrient accumulation
and distribution based on the total suspended solids (TSS) found
upstream and downstream in the flysch catchment. Therefore, we
established the following objectives:
- Apply a new SWAT+ hydrological model in flysch watersheds affected by
human activities.
- Assess inorganic nutrient distributions in surface waters by
statistical autoregression.
- Model selected inorganic nutrients and TSS fluxes between the main
watercourse and tributaries.
- Estimate hydraulic parameters in the main stream and their effects on
inorganic nutrient concentrations in the watercourse.