Characteristics of Sedimentary Organic Matter and Phosphorus in Minor Rivers Discharging into Zhejiang Coast, China

: In this study, the spatial distribution of lignin-derived phenols, bulk elemental composition and di ﬀ erent phosphorus (P) species in surface sediments along six rivers discharging into Zhejiang coast, Southeast China, were investigated to improve the understanding of the carbon and P dynamics in these small river systems. The Shuang, Jiao, Ximen, Feiyun and Ao Rivers have total organic carbon (TOC) ranging from 0.29% to 2.77% and Λ (total lignin in mg / 100 mg TOC) ranging from 0.24 to 4.24; Qiantang River has the lowest Λ (0.08–0.19) but the highest TOC (1.05%–6.46%). Jiao, Ximen, Feiyun and Ao Rivers have mean the total P (TP) and bioavailable P (BAP) of 34 to 124 mg / kg and 29 to 89 mg P / kg, and mean OC / OP molar ratio of 397–917. Qiantang River has the lowest mean TP and BAP of 13 mg P / kg and 7 mg P / kg, and highest OC / OP of 18,753; whereas Shuang River has the highest mean TP and BAP of 645 mg P / kg and 559 mg P / kg, and lowest mean OC / OP of 90. The lowest Λ , TP and BAP, but highest OC / OP, in the Qiantang River could be due to tidal bore causing rapid cycling of carbon and P. Trends of slight decrease in abundance of OC, Λ , TP and BAP, but increasing ratios of vanillic acid to vanillin [(Ad / Al)v], syringic acid to syringaldehyde [(Ad / Al)s] and OC / OP farther downstream of the rivers indicate a continuous decomposition of organic matter during transport along the rivers.


Introduction
Rivers are home to various organisms, animals and plant species, providing livelihood to human and serving as a regulator of carbon and nutrient [1,2]. However, many of the world's rivers have become 'sick rivers' because of human activities such as deforestation, river engineering, overfishing and pollution [3][4][5]. The presence of dams [6] and extreme weather affect the chemical and biological compositions of river systems. As a consequence, many plant and animal species are facing extinction. Loss of buffering capacities of rivers has increased pollution in coastal zones [1]. Many studies have been carried out for larger rivers [7][8][9][10], while small rivers were given less priorities though they undergo severe degradation in recent decades and they will likely disappear first compared to large rivers.
Various studies on bulk elemental composition, stable carbon isotope and biomarkers in sediments and particulate organic matter (POM) have improved the understanding on the biogeochemistry of sedimentary organic matter in lakes [11,12], coastal zones and oceans [13][14][15], as well as river systems [9,10]. Studies have found phytoplankton to be the major source of POM downstream of the Mississippi, Colorado, Rio Grande and Columbia Rivers [16]. On the other hand, detection of

Bulk Elemental and Lignin Analysis
Dry sediment was added to an excess of 1 N HCl and let to stand overnight to remove the inorganic carbon. The residues were dried in oven at 50 °C for two days, homogenised using a mortar and pestle. They were weighed precisely into tin foil and crimped into pellets, and determined for TOC and TN using a LECO-CHN 932 elemental analyser (Elementar, Germany). BCSS-1 and NIST-1 were used as the standard reference materials. The precision for TOC and TN was <5%.
Lignin analysis was carried out based on the CuO oxidation method. Precisely 0.5 g dry sediment and 1.0 g CuO powder were weighed into a 25 mL polytetrafluoroethylene (PTFE) vessel. Precisely 10 mL of 2 M aqueous NaOH in a test tube was bubbled with N2 for 3 min. The PTFE vessels, test tubes and their contents were purged with N2 for a few minutes in a glove bag, the NaOH solution was then poured into the contents of the PTFE vessel, and the vessel was capped.  3 Shuang River, 4 Jiao River, 5 Ximen Island, 6 Feiyun River and 7 Ao River.

Bulk Elemental and Lignin Analysis
Dry sediment was added to an excess of 1 N HCl and let to stand overnight to remove the inorganic carbon. The residues were dried in oven at 50 • C for two days, homogenised using a mortar and pestle. They were weighed precisely into tin foil and crimped into pellets, and determined for TOC and TN using a LECO-CHN 932 elemental analyser (Elementar, Germany). BCSS-1 and NIST-1 were used as the standard reference materials. The precision for TOC and TN was <5%.
Lignin analysis was carried out based on the CuO oxidation method. Precisely 0.5 g dry sediment and 1.0 g CuO powder were weighed into a 25 mL polytetrafluoroethylene (PTFE) vessel. Precisely 10 mL of 2 M aqueous NaOH in a test tube was bubbled with N 2 for 3 min. The PTFE vessels, test tubes and their contents were purged with N 2 for a few minutes in a glove bag, the NaOH solution was then poured into the contents of the PTFE vessel, and the vessel was capped. The vessels were then heated from room temperature to 170 • C for 3 h and manually shaken every hour. After 3 h, the vessels were allowed to cool. The contents of the vessel were washed three times with 20 mL of 1 M NaOH and centrifuged. The supernatants were combined, acidified to pH 1 with 6 M HCl and extracted three times with 20 mL ethyl acetate. The extracts were then dried with anhydrous Na 2 SO 4 , filtered through Whatman filter paper, and spiked with 100 µL ethyl vanillin as the internal standard. This was concentrated to 1-2 mL and N 2 blown down. The oxidation product was dissolved in equal amounts of pyridine and bis-(trimethylsilyl) trifluoroacetamide with 10% trimethylchlorosilane and derivatised at 90 • C for 10 min. The solution was ready to be analysed by gas chromatography HP5880A (Agilent Technologies, USA) with flame ionisation detection. The column temperature increased from 100 • C to 300 • C at 4 • C min −1 .

Sedimentary P Species
Determination of different sedimentary P species was carried out based on the 'Standards, Measurements and Testing (SMT)' method by Ruban et al. [30,31] to elucidate different sedimentary P fractions such as NaOH-P, HCl-P, OP and IP. Precisely 200 mg of sediment was added with 20 mL of 1 M NaOH, shaken for 16 h and then centrifuged at 2000 g for 15 min and the supernatant was determined for NaOH-P or Fe/Al-P. The sediment residue was washed with 12 mL of 1 M NaCl, stirred for 5 min and centrifuged at 2500 rpm for 15 min. The supernatant from this step was discarded. After that, the residue was added with 1 M HCl, shaken for 16 h, centrifuged and the supernatant was measured for HCl-P.
Another set of dry sediment was weight to 200 mg and added with 10 mL of 1 M HCl. This was extracted by shaking for 16 h, centrifuged and the supernatant was determined for IP. The residue was washed twice with distilled water and centrifuged. The residue was then combusted at 500 • C for 6 h, added with 20 mL of 1 M HCl and extracted by shaking for 16 h. The following day, this was centrifuged and the supernatant was determined for OP. Total P was the sum of IP and OP. P was determined using the molybdate blue method at a wavelength of 885 ences 2020, 10, x FOR PEER REVIEW 4 of 24 essels were then heated from room temperature to 170 °C for 3 h and manually shaken every . After 3 h, the vessels were allowed to cool. The contents of the vessel were washed three times 20 mL of 1 M NaOH and centrifuged. The supernatants were combined, acidified to pH 1 with HCl and extracted three times with 20 mL ethyl acetate. The extracts were then dried with drous Na2SO4, filtered through Whatman filter paper, and spiked with 100 μL ethyl vanillin as ternal standard. This was concentrated to 1-2 mL and N2 blown down. The oxidation product dissolved in equal amounts of pyridine and bis-(trimethylsilyl) trifluoroacetamide with 10% thylchlorosilane and derivatised at 90 °C for 10 min. The solution was ready to be analysed by hromatography HP5880A (Agilent Technologies, USA) with flame ionisation detection. The n temperature increased from 100 °C to 300 °C at 4 °C min −1 .

Sedimentary P Species
Determination of different sedimentary P species was carried out based on the 'Standards, urements and Testing (SMT)' method by Ruban et al. [30,31] to elucidate different sedimentary tions such as NaOH-P, HCl-P, OP and IP. Precisely 200 mg of sediment was added with 20 mL NaOH, shaken for 16 h and then centrifuged at 2000 g for 15 min and the supernatant was mined for NaOH-P or Fe/Al-P. The sediment residue was washed with 12 mL of 1 M NaCl, d for 5 min and centrifuged at 2500 rpm for 15 min. The supernatant from this step was rded. After that, the residue was added with 1 M HCl, shaken for 16 h, centrifuged and the rnatant was measured for HCl-P. Another set of dry sediment was weight to 200 mg and added with 10 mL of 1 M HCl. This was cted by shaking for 16 h, centrifuged and the supernatant was determined for IP. The residue ashed twice with distilled water and centrifuged. The residue was then combusted at 500 °C h, added with 20 mL of 1 M HCl and extracted by shaking for 16 h. The following day, this was ifuged and the supernatant was determined for OP. Total P was the sum of IP and OP. P was mined using the molybdate blue method at a wavelength of 885 ɳ m. P concentration was mined based on the absorbance of the sample extract and calculated as follows: C = SV, where C centration of P in mg P/kg, S = concentration of sample obtained from the calibration curve g) and V = volume of solvent used [30,31]. All solutions were stored in plastic containers as a utionary measure. We presume there will be no silicate interference throughout the process, as the te in the working reagent could also prevent reaction between silicate and ammonium molybdate [32].

sults edimentary Organic Matter
The complete results of lignin parameters, TOC and TOC/TN molar ratios are given in ndix A (Table A2). The Qiantang River has the highest %TOC (ranged from 1.05% to 6.46%) ared to the other five rivers (0.29%-2.77%). Similarly, the percentage of TN was also the highest iantang River (0.21%-1.36%), followed by Shuang River (0.09%-0.44%) and Ao River -0.20%). Jiao, Ximen and Feiyun Rivers had a low TN content of 0.06%-0.14%. The overall /TN molar ratios varied at 5.0-11 in all the rivers. Total lignin (Λ, mg/100 mg TOC) ranged from 0.075 to 4.236. Locations along Qiantang River he lowest Λ values of 0.075-0.186. Ao and Shuang Rivers had Λ values of 0.244-1.706 and -1.909, respectively. Jiao, Ximen and Feiyun River had higher Λ values of 0.325-4.236. Similar and TOC, the S/V ratios (0.72-12.33, excluding the highest values of 21 and 37) and C/V ratios -8.000) in Qiantang River were higher than the S/V (0.250-3.500) and C/V ratios (0.02-0.692) in five rivers. The rivers in this study had a wide range of (Ad/Al)v values of 0.045-1.842 and l)s values of 0.088-2.540. The extremely high S/V, C/V, TOC, but rather low Λ, in Qiantang compared to the other five rivers is further illustrated in Figure 2. Correlation results among parameters and bulk elemental composition showed no relationship, except for the significant ive correlation between TOC and TN (Appendix A, Table A3). m. P concentration was determined based on the absorbance of the sample extract and calculated as follows: C = SV, where C = concentration of P in mg P/kg, S = concentration of sample obtained from the calibration curve (mg/kg) and V = volume of solvent used [30,31]. All solutions were stored in plastic containers as a precautionary measure. We presume there will be no silicate interference throughout the process, as the tartrate in the working reagent could also prevent reaction between silicate and ammonium molybdate [32].

Sedimentary Organic Matter
The complete results of lignin parameters, TOC and TOC/TN molar ratios are given in Appendix A (Table A2). The Qiantang River has the highest %TOC (ranged from 1.05% to 6.46%) compared to the other five rivers (0.29%-2.77%). Similarly, the percentage of TN was also the highest in Qiantang River (0.21%-1.36%), followed by Shuang River (0.09%-0.44%) and Ao River (0.09%-0.20%). Jiao, Ximen and Feiyun Rivers had a low TN content of 0.06%-0.14%. The overall TOC/TN molar ratios varied at 5.0-11 in all the rivers. elemental composition showed no relationship, except for the significant positive correlation between TOC and TN (Appendix A, Table A3).

Sedimentary P Species
The results of sedimentary P fractions are given in Appendix (Table A4). Percentages of each P fraction and bioavailable P to TP, and OC/OP molar ratios are then calculated. Table 1 shows the ranges and mean values of these parameters. The mean TP concentrations for these rivers are in the following order: Shuang (645 ± 29 mg P/kg) > Ao (124 ± 45 mg P/kg) > Jiao (81 ± 16 mg P/kg) > Feiyun (79 ± 7 mg P/kg) > Ximen (34 ± 5 mg P/kg) > Qiantang (13 ± 4 mg P/kg). Similar to TP, all P fractions were highest at Shuang River and lowest at Qiantang River. The extremely high concentrations of all P fractions of Shuang River sediments compared to the other five rivers are further illustrated in Figure 3. Bioavailable P (BAP) is the sum of NaOH-P and OP. The mean concentrations of bioavailable P are in this order: Shuang (559 mg P/kg) > Ao (89 mg P/kg) > Jiao (42 mg P/kg) > Feiyun (39 mg P/kg) > Ximen (29 mg P/kg) > Qiantang (5 mg P/kg). The percentages of bioavailable P to TP are in the following order: Shuang (87%) > Ximen (84%) > Ao (69%) > Qiantang (53%) > Jiao (50%) > Feiyun (49%). The Shuang River has the highest concentration of BAP, which was about 6 to more than 100 times higher than the other five rivers.
The mean OC/OP molar ratios are in the following order: Qiantang (18,754) > Jiao (917) > Ximen (729) > Feiyun (635) > Ao (397) > Shuang (90). Very high OC/OP ratio at Qiantang River was attributable to the highest TOC (ranged between 1.05% and 6.46%) and lowest OP (ranged from 3 to 7 mg/kg) in the Qiantang River compared to the other five rivers (TOC ranged from 0.29% to 2.77%; OP ranged from 26 to 687 mg/kg). As OP is preferentially utilized relative to OC during aerobic organic matter decomposition, higher TOC and higher OC/OP ratios indicate the presence of labile materials where the P was easily degradable [33]. Most of the sedimentary P species have significant positive correlation among one another (Appendix , Table A5).

Sedimentary P Species
The results of sedimentary P fractions are given in Appendix A (Table A4). Percentages of each P fraction and bioavailable P to TP, and OC/OP molar ratios are then calculated. Table 1 shows the ranges and mean values of these parameters. The mean TP concentrations for these rivers are in the following order: Shuang (645 ± 29 mg P/kg) > Ao (124 ± 45 mg P/kg) > Jiao (81 ± 16 mg P/kg) > Feiyun (79 ± 7 mg P/kg) > Ximen (34 ± 5 mg P/kg) > Qiantang (13 ± 4 mg P/kg). Similar to TP, all P fractions were highest at Shuang River and lowest at Qiantang River. The extremely high concentrations of all P fractions of Shuang River sediments compared to the other five rivers are further illustrated in Figure 3. Bioavailable P (BAP) is the sum of NaOH-P and OP. The mean concentrations of bioavailable P are in this order: Shuang (559 mg P/kg) > Ao (89 mg P/kg) > Jiao (42 mg P/kg) > Feiyun (39 mg P/kg) > Ximen (29 mg P/kg) > Qiantang (5 mg P/kg). The percentages of bioavailable P to TP are in the following order: Shuang (87%) > Ximen (84%) > Ao (69%) > Qiantang (53%) > Jiao (50%) > Feiyun (49%). The Shuang River has the highest concentration of BAP, which was about 6 to more than 100 times higher than the other five rivers.

Sources of Sedimentary Organic Matter
As angiosperms are composed of syringyl (S) and vanillyl (V) phenols, and gymnosperms contain vanillyl phenol, higher S/V ratios indicate the presence of more angiosperm compared to gymnosperm tissues. Higher C/V ratios indicate non-woody tissues as cinnamyl (C) phenols are The mean OC/OP molar ratios are in the following order: Qiantang (18,754) > Jiao (917) > Ximen (729) > Feiyun (635) > Ao (397) > Shuang (90). Very high OC/OP ratio at Qiantang River was attributable to the highest TOC (ranged between 1.05% and 6.46%) and lowest OP (ranged from 3 to 7 mg/kg) in the Qiantang River compared to the other five rivers (TOC ranged from 0.29% to 2.77%; OP ranged from 26 to 687 mg/kg). As OP is preferentially utilized relative to OC during aerobic organic matter decomposition, higher TOC and higher OC/OP ratios indicate the presence of labile materials where the P was easily degradable [33]. Most of the sedimentary P species have significant positive correlation among one another (Appendix A, Table A5).

Sources of Sedimentary Organic Matter
As angiosperms are composed of syringyl (S) and vanillyl (V) phenols, and gymnosperms contain vanillyl phenol, higher S/V ratios indicate the presence of more angiosperm compared to gymnosperm tissues. Higher C/V ratios indicate non-woody tissues as cinnamyl (C) phenols are found in non-woody tissues but not in woody tissues. Studies have demonstrated that S/V > 0.4 indicates the presence of angiosperm tissues and C/V > 0.2 indicates non-woody tissues [34,35]. The S/V and C/V ratios in the Shuang, Jiao, Ximen, Feiyun and Ao Rivers ranged from 0.250 to 3.500 and from 0.020 to 0.692, respectively, which showed predominance of non-woody angiosperms in these rivers, except for a few locations in Shuang and Jiao Rivers which have demonstrated the presence of some woody signal as represented by some rather low C/V ratios. The S/V and C/V compositional plot showed that most ratios fall within the range for non-woody angiosperm tissues ( Figure 4). These results are inconsistent with other locations in this region such as Changjiang Estuary [10] and salt marsh at the southwest of Hangzhou Bay [36] which had shown predominance of non-woody angiosperm tissues.
Higher TOC/TN ratios could be due to preferential loss of N components that are protein-rich, lower TOC/TN could be due to conversion of plant materials to microbial biomass [37]. Low C/N ratios have also been demonstrated for organic matter from meta-sedimentary rocks [18]. Thus, the rather low TOC/TN molar ratios (which ranged from 5 to 11) in the rivers in this study (including Qiantang River) indicate decomposed organic matter, as also supported by the elevated (Ad/Al)v and (Ad/Al)s values in these rivers, which indicate more degraded lignin materials.
Higher TOC/TN ratios could be due to preferential loss of N components that are protein-rich, lower TOC/TN could be due to conversion of plant materials to microbial biomass [37]. Low C/N ratios have also been demonstrated for organic matter from meta-sedimentary rocks [18]. Thus, the rather low TOC/TN molar ratios (which ranged from 5 to 11) in the rivers in this study (including Qiantang River) indicate decomposed organic matter, as also supported by the elevated (Ad/Al)v and (Ad/Al)s values in these rivers, which indicate more degraded lignin materials.

4.2.P Pollution
The Shuang River TP was slightly higher than the other rivers. The high NaOH-P, as well as all P contents, at the Shuang River most likely indicates P pollution from anthropogenic activities, as higher content of loosely bound-P has been associated with wastewater discharge [38]. The TP levels in rivers investigated in this study were slightly lower compared to some other locations in China such as the Min River Estuary marsh sediments which have TP ranging from 338 mg P/kg to 932 mg P/kg [39]; rivers discharging into the Bohai Sea such as Liao and Yongdingxin have TP of 219 mg P/kg and 913 mg P/kg [24]; TP in the Yellow River delta sediments was 542 mg P/kg [40]; and studies of ten major basins in China found that the average TP in sediments was around 733 mg P/kg [41].
The rivers in this study have high proportion of BAP in their sediments because of their high OP contents which constitute of 34% to 69% of TP. The percentage of NaOH-P to TP ranged from 11% to 44%, indicating that a portion of this fraction, which includes the loosely bound P and Fe-P, can be released to the aquatic environments. The BAP in these rivers were higher in comparison to some locations such as the east coast of Hainan Island (20% to 54% of BAP) [42] and the Jiazhou Bay (40%-53% BAP) [38]; rivers discharging into the Bohai Sea that were polluted with fertilizer and sewage have high abundances of NaOH-P and OP of 223 mg/kg NaOH-P (24% of TP) and 125 mg/kg OP (14% of TP), respectively [24]. These results suggest that sediments in these rivers are prone to release P to the overlying water column.

P Pollution
The Shuang River TP was slightly higher than the other rivers. The high NaOH-P, as well as all P contents, at the Shuang River most likely indicates P pollution from anthropogenic activities, as higher content of loosely bound-P has been associated with wastewater discharge [38]. The TP levels in rivers investigated in this study were slightly lower compared to some other locations in China such as the Min River Estuary marsh sediments which have TP ranging from 338 mg P/kg to 932 mg P/kg [39]; rivers discharging into the Bohai Sea such as Liao and Yongdingxin have TP of 219 mg P/kg and 913 mg P/kg [24]; TP in the Yellow River delta sediments was 542 mg P/kg [40]; and studies of ten major basins in China found that the average TP in sediments was around 733 mg P/kg [41].
The rivers in this study have high proportion of BAP in their sediments because of their high OP contents which constitute of 34% to 69% of TP. The percentage of NaOH-P to TP ranged from 11% to 44%, indicating that a portion of this fraction, which includes the loosely bound P and Fe-P, can be released to the aquatic environments. The BAP in these rivers were higher in comparison to some locations such as the east coast of Hainan Island (20% to 54% of BAP) [42] and the Jiazhou Bay (40%-53% BAP) [38]; rivers discharging into the Bohai Sea that were polluted with fertilizer and sewage have high abundances of NaOH-P and OP of 223 mg/kg NaOH-P (24% of TP) and 125 mg/kg OP (14% of TP), respectively [24]. These results suggest that sediments in these rivers are prone to release P to the overlying water column.

Dynamics of Sedimentary Organic Matter and P
Our results revealed slight decrease of Λ values along the rivers, followed by drastic increases in Λ values at some locations, especially at the river mouths. There were mixed trends of (Ad/Al)v and (Ad/Al)s values, with the locations at the river mouths usually have higher ratios ( Figure 5). TOC and TN showed slight increase along the rivers, then decrease at the river mouths, as supported by the significant negative correlation between Λ with TOC and TN (p < 0.05), indicative of contribution from anthropogenic carbon and nitrogen besides terrestrial materials farther downstream. The P forms gradually increased, followed by decreasing trend along Qiantang and Jiao Rivers; and gradual decrease along the rivers at Feiyun, Shuang and Ximen; but gradual increase along Ao Rivers ( Figure 6).
TOC and TN showed slight increase along the rivers, then decrease at the river mouths, as supported by the significant negative correlation between Λ with TOC and TN (p < 0.05), indicative of contribution from anthropogenic carbon and nitrogen besides terrestrial materials farther downstream. The P forms gradually increased, followed by decreasing trend along Qiantang and Jiao Rivers; and gradual decrease along the rivers at Feiyun, Shuang and Ximen; but gradual increase along Ao Rivers (Figure 6).      Decreasing abundance of terrestrial organic matter and P was most probably attributed to decomposition of terrestrial organic matter along the rivers. There was increased accumulation and further decomposition of terrestrial organic matter at the river mouths. Both continuous decomposition of terrestrial organic matter along the rivers and at the river mouths also indicate that these rivers most probably serve as carbon source. This is consistent with other studies which have found that rivers are carbon sources due to decomposition of fresher [43] terrestrial organic matter [44].
Increasing trends of TOC/TN ratios along the Qiantang, Shuang, Jiao, Ximen and Feiyun Rivers further supported increased organic matter decomposition farther downstream. The gradual increases of TOC/OP along the rivers indicate accumulation of terrestrial organic matter farther downstream and increased decomposition downstream. There were drastic decreases of TOC/TN ratios at the Ximen and Feiyun river mouths, this could indicate more decomposed materials, as supported by the very high (Ad/Al)v and (Ad/Al)s values here. The Qiantang River is well-known for the occurrence of tidal bore [45]. Thus, the lowest Λ values and P in the Qiantang River could be attributable to the rapid organic matter decomposition due to physical disturbances of the tidal bore facilitated mixing and resuspension, thus, further facilitated decomposition of sedimentary organic matter.  Decreasing abundance of terrestrial organic matter and P was most probably attributed to decomposition of terrestrial organic matter along the rivers. There was increased accumulation and further decomposition of terrestrial organic matter at the river mouths. Both continuous decomposition of terrestrial organic matter along the rivers and at the river mouths also indicate that these rivers most probably serve as carbon source. This is consistent with other studies which have found that rivers are carbon sources due to decomposition of fresher [43] terrestrial organic matter [44].

Conclusions
The S/V and C/V ratios in sediments of small rivers along the Zhejiang Coast of SE China indicate predominance of non-woody angiosperm tissues and the large ranges of (Ad/Al)v and (Ad/Al)s values indicate the presence of fresh to degraded lignin materials. The ranges of TOC in Shuang, Jiao, Ximen, Feiyun and Ao Rivers were 0.29%-2.77%; Qiantang River has the highest TOC of 1.05%-6.46%. Total lignin, Λ, in Shuang, Jiao, Ximen, Feiyun and Ao Rivers ranged from 0.24 to 4.24; Qiantang River has the lowest Λ of 0.08 to 0.19. TP was the highest in Shuang (645 mg P/kg), followed by the other four rivers (34-124 mg P/kg) and the lowest in Qiantang River (13 mg P/kg). On the other hand, Qiantang River has the highest OC/OP molar ratio (18,753), followed by the other four rivers (397-917) and Shuang River (90). High TOC in Qiantang River could be due to anthropogenic input. High OC/OP but low TP and Λ in Qiantang River indicates rapid recycling of organic matter and P. The high TP and low OC/OP in Shuang River could be due to the relatively higher P pollution in this river in comparison to the other rivers. Our results indicate rapid cycling of sedimentary organic matter and P along these rivers, resulting in highly degraded materials at the river mouths and low P pollution in the sediments.