Study on characteristics of soil and nutrient losses in Sunjiagou small watershed in cold black soil area.

Investigating the impact of different factors on soil and nutrient loss and suggesting viable control measures is currently a significant concern. This study aims to examine the variations in soil erosion, as well as nitrogen and phosphorus loss, in the core area of the typical hilly diffuse Blackland erosion control. To achieve this, runoff plots with slopes of 3° and 5° were set up in the Sunjiagou sub-basin, located in the upper reaches of the Feiketu River. These plots were subjected to various soil and water conservation measures, along with different levels of vegetation cover. This study aims to analyze the soil and nutrient loss patterns and characteristics in each runoff plot during the natural rainfall events occurring between 2020 and 2022. The results show that soil and nutrient losses are highly significantly and positively correlated with rainfall intensity. The RUSLE model demonstrates a better fit for both cross ridge tillage and bare ground. The loss of nitrogen was much more significant than that of phosphorus, and nitrate nitrogen is the main form of nitrogen loss. Nitrogen loss is mainly dominated by nitrate nitrogen (NN), which is easily soluble in water and constantly migrates with runoff due to the negatively charged NN (NN accounted for 45.2% ~ 81.8% of total nitrogen (TN)). In contrast, the positively charged ammonia nitrogen (AN) is more stable in combination with the soil; large losses only occur under severe sediment erosion. Phosphorus is easily attached to sediment, and the high sediment production leads to a more serious loss of total phosphorus (PP) in the particulate state (PP accounts for 72.7% ~ 96.2% of total phosphorus (TP)). Changing longitudinal ridge tillage to cross ridge tillage and planting vegetation with better water retention and sediment fixation as plant hedges can effectively prevent the loss of soil, runoff, nitrogen, and phosphorus.

Potential linkage between WWTPs-river-integrated area pollution risk assessment and dissolved organic matter spectral index.

The direct discharge of wastewater can cause severe damage to the water environment of the surface water. However, the influence of dissolved organic matter (DOM) present in wastewater on the allocation of DOM, nitrogen (N), and phosphorus (P) in rivers remains largely unexplored. Addressing the urgent need to monitor areas affected by direct wastewater discharge in a long-term and systematic manner is crucial. In this paper, the DOM of overlying water and sediment in the WWTPs-river-integrated area was characterized by ultraviolet-visible absorption spectroscopy (UV-vis), three-dimensional excitation-emission matrix combined with parallel factor (PARAFAC) method. The effects of WWTPs on receiving waters were investigated, and the potential link between DOM and N, P pollution was explored. The pollution risk was fitted and predicted using a spectral index. The results indicate that the improved water quality index (IWQI) is more suitable for the WWTPs-river integration zone. The DOM fraction in this region is dominated by humic-like matter, which is mainly influenced by WWTPs drainage as well as microbial activities. The DOM fractions in sediment and overlying water were extremely similar, but fluorescence intensity possessed more significant spatial differences. The increase in humic-like matter facilitates the production and preservation of P and also inhibits nitrification, thus affecting the N cycle. There is a significant correlation between DOM fraction, fluorescence index, and N, P. Fluorescence index (FI) fitting of overlying water DOM predicted IWQI and trophic level index, and a(254) fitting of sediment DOM predicted nitrogen and phosphorus pollution risk (FF) with good results. These results contribute to a better understanding of the impact of WWTPs on receiving waters and the potential link between DOM and N and P pollution and provide new ideas for monitoring the water environment in highly polluted areas.