Abstract
The ~350 km2 water level fluctuation zone (WLFZ) in the Three Gorges Reservoir (TGR) of China, situated at the intersection of terrestrial and aquatic ecosystems, experiences a great hydrological change with prolonged winter inundation. Soil samples were collected in 12 sites pre- (September 2008) and post submergence (June 2009) in the WLFZ and analyzed for soil nutrients. Self-organizing map (SOM) and statistical analysis including multi-way ANOVA, paired-T test, and stepwise least squares multiple regression were employed to determine the spatio-temporal variations of soil nutrients in relation to submergence, and their correlations with soil physical characteristics. Results showed significant spatial variability in nutrients along ~600 km long shoreline of the TGR before and after submergence. There were higher contents of organic matter, total nitrogen (TN), and nitrate (NO3-) in the lower reach and total phosphorus (TP) in the upper reach that were primarily due to the spatial variations in soil particle size composition and anthropogenic activities. Submergence enhanced soil available potassium (K), while significantly decreased soil N, possibly due to the alterations of soil particle size composition and increase in soil pH. In addition, SOM analysis determined important roles of soil pH value, bulk density, soil particle size (i.e., silt and sand) and nutrients (TP, TK, and AK) on the spatial and temporal variations in soil quality. Our results suggest that urban sewage and agricultural runoffs are primary pollutants that affect soil nutrients in the WLFZ of TGR.
Highlights
Nutrient pollution in a watershed has a large variety of sources such as industrial and domestic wastewater, agricultural runoff, mining activities, and atmospheric deposition [1]
The concentration of Available K (AK) significantly increased, while the levels of total nitrogen (TN), NH4+, and NO3- decreased after the inundation (p < 0.001) (Fig. 2)
The changes of soil characteristics induced by inundation and anthropogenic activities understandably resulted in significant spatial variability in soil nutrients in the water level fluctuation zone (WLFZ) (p < 0.05) both before submergence (September 2008) and after submergence (June 2009) (Tables 1 and 3)
Summary
Nutrient pollution in a watershed has a large variety of sources such as industrial and domestic wastewater, agricultural runoff, mining activities, and atmospheric deposition [1]. Nutrient levels in riparian zone depend on a variety of factors, such as soil and vegetation characteristics, flooding, and anthropogenic activities [5], [6]. Soil characteristics soil pH, soil particle size composition, and redox condition have large effects on the sorptiondesorption processes and microbial activities, and regulate soil nutrient dynamics [7,8,9]. Riparian vegetation could regulate soil nutrient contents directly by uptake, decomposition and deposition of alluvial materials, and indirectly through stimulation of microbial processes in the rhizosphere [11,12,13]. Nitrate would be removed more effectively in densely vegetated riparian zones due to the plant uptake and high rates of nitrification and denitrification [2], [12], [13], [16]
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