Sun Liying

Partitioning of water soluble organic carbon in three sediment size fractions： Effect of the humic substances

Water soluble organic carbon (WSOC) in sediments plays an important role in transference and transformation of aquatic pollutants. This article investigated the inherent mechanisms of how sediment grain size affect the partitioning coefficient (k) of WSOC. Influences of NaOH extracted humic substances were particularly focused on. Sediments were sampled from two cross-sections of the middle Yellow River and sieved into three size fractions (< 63 microm, 63-100 microm, and 100-300 microm). The total concentration of WSOC in sediments (C(WSOC)) and k were estimated using multiple water-sediment ratio experiments. Results showed that C(WSOC) ranged from 0.012 to 0.022 mg/g, while k ranged from 0.8 to 3.9 L/kg. Correlations between the spectrum characteristics of NaOH extracted humic substances and k were analyzed. Strong positive correlations are determined between k and the aromaticity indicators of NaOH extracted humic substances in different sediment size fractions. Comparing with finer fractions (< 63 pm), k is higher in larger size fractions (63-100 microm and 100-300 microm) related to higher aromaticity degree of NaOH extracted humic substances mostly. While negative relationship between k and the area ratio of fourier transform infrared spectroscopy (FT-IR) at 3400 and 1430 cm(-1) implied that the lowest k was related to the highest concentration of acidic humic groups in particles < 63 microm. WSOC in finer fractions (< 63 microm) is likely to enter into pore water, which may further accelerate the transportation of aquatic contaminants from sediment to water.

Zonal differences of runoff and sediment reduction effects for typical management small watersheds in China

Abstract In this particular study, 99 typical managed small watersheds which representing five water erosion areas in China were selected to study zonality of Runoff Reduction Efficiency (RRE) and of Sediment Reduction Efficiency (SRE). The RRE is the ratio of Effect of Runoff Reduction (ERR) by soil and water conservation measure over management degree in a watershed. And The SRE is the ratio of Effect of Sediment Reduction (ESR) by soil and water conservation measure over management degree in a watershed. First of ah, statistical analysis was applied to test the zonal effects of RRE and SRE between different water erosion regions. The results showed that the mean RRE values in northern regions were significantly greater than those of southern regions; and the mean SRE values in northern regions were significantly greater than those in southern regions. Next, the variation of RRE with runoff depth ( H ) was studied in direction of both latitude and longitude across regions influenced by East Asian Monsoon. Meanwhile, the variation of SRE with specific sediment yield ( Y ) was studied in direction of both latitude and longitude across regions influenced by East Asian Monsoon. The results showed that RRE had the inverse variation trend as H in both latitude and longitude direction and SRE had the same variation trend as Y in both latitude and longitude direction. Furthermore, the variation of unit management area Runoff Reduction Rate (RRR) with H and RRE was studied in direction of both latitude and longitude. And the variation of unit management area Sediment Reduction Rate (SRR) with Y and SRE was studied in direction of both latitude and longitude. It was found that RRR had the similar variation trend as H in latitude direction and there was critical point around 37°N greater than which RRR began to be equal to H or even larger; RRR had the similar variation trend as H in longitude direction and there was a critical point around 109°E lees than which RRR began to equal to or greater than H ; SRR had the similar variation trend as Y in latitude direction and there was critical point around 36°N greater than which SRR began to be equal to Y or even larger; SRR had the similar variation trend as Y in longitude direction and there was a critical point around 106°E lees than which SRR began to equal to or greater than Y . The zonality of RRE, RRR, SRE and SRR was determined by the combined influence of climate variation and special landform in regions controlled by East Asian Monsoon in China.