Characterization and pollution evaluation of TOC, TN and TP in sediments of Caohai Lake, Guizhou Province, China

The study deals with the distribution of nutrients in wetland sediments, which provide the basis for revealing the wetland eutrophication processes and mechanisms of internal pollution sources. The total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) contents and distribution characteristics of sediment samples were examined. The results showed that the TOC concentration ranged from 3.81 to 15.6 g/kg, the TN concentration ranged from 0.21 to 1.18 g/kg with a mean concentration of 0.66 g/kg, and the TP concentration ranged from 0.16 to 0.35 g/kg with a mean of 0.23 g/kg. Statistical analysis showed close correlations between TOC and TN (R2 = 0.96), and TN and TP (R2 = 0.97), which indicated that the TN and TP in the sediments were from similar sources. The concentrations of TOC, TN, and TP in Longbao Lake wetland sediments were too low for eutrophication to occur. Our investigation indicated that Longbao Lake undergoes natural evolution rather than anthropogenic activities.

Spatiotemporal distribution of total nitrogen(TN),total phosphorus(TP) in sediment of Dongting lake where the 500 hm2 freshwater pearl culture system is located in Summer and Winter from 2010—2011 was observed.The relationship between these TN and TP with chlorophyll-a in the water and the content changes of TN and TP under rice ecosystem were investigated.The results showed that the contents of TN and TP in sediment decreased from the South to the North.There was no significant seasonal change in TN.The highest content of TP appeared in Summer,which was 1.64 mg/g,and the lowest TP content was in Winter,which was 0.26 mg/g.The contents of TN and TP in sediment were positively correlated to chlorophyll a content.TN and TP contents in the sediment where rice ecosystem is accessible reduced 31.6% and 45.1%,respectively,compared to those in the sediment located in the central of the culture system where rice ecosystem is inaccessible.These results suggest that three-dimensional culture and rice cultivation in the ecosystem could balance the contents of TN and TP in the sediment.

To reveal the distribution characteristics of carbon, nitrogen and phosphorus in the sediments of Zhushan Bay at Taihu Lake, sedimentary columns were collected and sliced by 2 cm vertically from ten sampling points in three sections of Zhushan Bay. The content of total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) were determined for each slice to reveal their horizontal and vertical distribution. The results showed that:spatially, the content of TN, TP, and TOC increased in the surface sediments of Zhushan Bay from the open lake area to the bay, and inside the bay these indexes were significantly higher than in the open lake area (P<0.01). The content of TN, TP, and TOC in the surface sediments in the bay (section A) were 1.53 mg·g-1, 1.55 mg·g-1, and 11.31 mg·g-1, respectively, while in the surface sediments near the open lake (section C) they were only 0.75 mg·g-1, 0.57 mg·g-1, and 6.70 mg·g-1, respectively. Vertically, a feature of surficial enrichment was shown, and the contents of carbon, nitrogen and phosphorus in all three sections showed a decreasing trend with increase of depth. The contents of TN, TP and TOC in the surface sediments are 2-3 times, 2-5 times, and 2-3 times those in the bottom sediments, respectively. Generally, the average TP content in the sediment of Zhushan Bay is 0.93 mg·g-1, suggesting an apparent heavy pollution, while the average TN content is 1.11 mg·g-1 as slight pollution. According to the organic nitrogen index and comprehensive pollution index, the northern part of Zhushan Bay is suffering from heavy pollution, where the organic pollution is relatively strong. The TP pollution index is between 1.03 and 3.87, indicating heavy pollution in Zhushan Bay.

The content of total organic carbon, total nitrogen and total phosphorus in sediments of Drug Spring Lake was detected and their vertical distribution characteristic was analysed. Results showed that there were significant changes to the content of total organic carbon, total nitrogen and total phosphorus in different depth of the columnar sediments. Their highest content both appeared in the interval of 10cm to 25cm corresponding to the period of 1980s to 1990s, when the tourism of Wudalianchi scenic area began to develop. It reflected the impact of human activities on the Drug Spring Lake. That means the regulation was still not enough, although a series of pollution control measures adopted by the government in recent years had initial success.

Sediment pollution characteristics and in situ control in a deep drinking water reservoir

To better understand the nutrient distributions in the hyporheic zone of a large shallow eutrophic lake (Lake Taihu) and the potential drivers, the total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) were investigated in March and December 2016. Spatial differences in the TN and TP contents existed in the hyporheic zone, particularly between the eastern and southern zones and the western and northern zones. The TOC/TN ratios in the western, northern, and central zones were mostly <8 and even reached 4, indicating that organic matter originated from aquatic organisms and algae, whereas those in the southern and eastern zones exhibited wide ranges, indicating complex pollution sources. The chloride depth profiles suggested that upwelling hyporheic flow potentially occurred in the southern, western, and northern zones, while alternating flow directions occurred in the eastern zone and no flow or weak flow occurred in the central zone. Compared to the 1st investigation, the TOC, TN, and TP in sediments in the 2nd investigation increased by 13%, 41%, and 87%, respectively, and these changes were mostly due to large hyporheic fluxes with high nutrient concentrations from shallow groundwater. The behavior of the hyporheic zone as an active pollution source/sink due to hyporheic flow should be considered in the comprehensive management of Lake Taihu. PRACTITIONER POINTS: Depth profiles of nutrients differed between sampling sites and between zones of Lake Taihu due to different pollution sources. Nutrients in sediment increased largely during winter compared to spring due to potential groundwater pollution through upwelling flow. No significant difference in sediment total organic carbon and ratios of C/N indicates a similar internal pollution source lake wide.

Temporal and spatial dynamics of nitrogen and phosphorus in surface water and sediments of a transboundary river located in the semi-arid region of Turkey

The water chemistry of 21 outlet brooks in undisturbed, forested catchments (0.074–38 km2) in Finland was monitored during three years (1997–1999) in order to estimate the background levels and leaching of total organic carbon (TOC), iron, nitrogen and phosphorus, and examine the relationships between catchment characteristics and brook water quality in pristine forested areas. The studied catchments are located throughout Finland except the northernmost parts of the country. The concentrations of TOC were relatively high, on average 20 mg L-1. Annual leaching of TOC ranged from 3000 to 10 000 kg km-2. The average total nitrogen concentration and annual leaching were 430 μg L-1 and 140 kg km-2, respectively. The average total phosphorus concentration and annual leaching were 15 μg L-1 and 5.4 kg km-2, respectively. On a national level temperature and discharge conditions were the most important variables for predicting total phosphorus, total nitrogen and TOC concentrations. Both total nitrogen and total phosphorus concentrationsdisplayed positive correlation with temperature, and thus the concentrations were higher in the south than in the north. Nitrogen was mainly organic and showed strong correlation with TOC. On the catchment level, both TOC and total nitrogen concentrations and export had a strongpositive correlation with the abundance of Norway spruce (Piceaabies Karsten) and a strong negative correlation with the abundance of Scots pine (Pinus sylvestris L.). Nitrate concentrations and leaching were related to average site type. The more fertile the average site type was in the catchment, the higher the nitrate concentrations and export were.

This study investigated the distribution and ecological risk of nutrient elements in the surface sediments of Jianxi watershed in northern Fujian in order to clarify the sediment environmental status of the upperstream of Minjiang River. The contents of organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in the surface sediments were considered, and the single factor pollution index was employed in the risk assessment of sediment environment. The interrelations of carbon, nitrogen, and phosphorus in sediments and their environmental significance were also discussed. The results showed that the average concentrations of TOC, TN and TP in the sediments were 3.05%, 1858.05 mg·kg-1 and 624.68 mg·kg-1, respectively, which are considered as harmless for most of aquatic organism. There were some potential ecological risks for benthonic organism with 2.0-5.8 of TOC, 2.3-4.4 of TN and 0.4-1.7 of TP using the ranges of single factor pollution index. In addition, the average values of elemental ratios (TOC/TN was 16.9, TOC/TP was 53.7 and TN/TP was 3.2) indicated that nutrient elements in the sediments of Jianxi watershed were affected by the exogenous and endogenous inputs. The output of nutrients from forestland was a mian reason for the accumulation of nutrients in the river sediments. Overall, TN in the sediments of Jianxi watershed showed the highest ecological risk for aquatic organism and was mainly affected by non-point sources in the watershed, but TOC and TP in the sediments only exhibited slight risks. Therefore, it is urgent to implement the investigation of the nitrogen pollution sources and strictly control these pollution sources so as to reduce the ecological risk of nitrogen in Jianxi watershed.

Nutrient inputs from rivers play an important role in lake eutrophication. To compare the forms characteristics of phosphorus (P) and nitrogen (N) in rivers flowing through rural and urban areas, water samples were collected seasonally from five urban rivers and six rural rivers flowing to Lake Chaohu, China. Higher total phosphorus (TP), particulate phosphorus (PP), soluble reactive phosphorus (SRP), and dissolved nonreactive phosphorus (DNP) concentrations and SRP/TP percentages were observed in urban rivers than in rural rivers, and PP/TP and DNP/TP ratios were lower in urban rivers than in rural rivers. The concentrations of total nitrogen (TN) and all N forms other than dissolved organic nitrogen (DON) were significantly higher in urban rivers than in rural rivers. NH4+/TN levels were higher in urban rivers, whereas PN/TN and DON/TN ratios were significantly lower in urban rivers compared with rural rivers. NO3−/TN and NO2−/TN levels were similar between the two groups of rivers. TP, BD-P, and NaOH-P levels in urban river surface sediments were significantly higher than those in rural rivers. NaOH-P/TP ratios were significantly elevated in urban rivers, whereas HCl-P/TP and Res-P/TP ratios were significantly lower compared with rural rivers. Urban rivers have transferred large quantities of NH4+ and SRP into Lake Chaohu, resulting in higher TP and TN levels and NH4+/TN and SRP/TP ratios. Decreasing the input of NH4+ and SRP into urban rivers is a high priority for mitigating eutrophication and algal blooms in Lake Chaohu.

Spatio-temporal changes of marine macrobenthic community in sub-tropical waters upon recovery from eutrophication. I. Sediment quality and community structure

Occurrence of phosphorus, iron, aluminum, silica, and calcium in a eutrophic lake during algae bloom sedimentation.

ABSTRACTComplex nutrient depositional processes in the Three Gorges Reservoir (TGR) are generally explained using hydrological monitoring data or shallow sediment sampling. However, an in‐depth understanding of the chronological transformations in the nutrient dynamics of deposited sediment over time is lacking. This study aims to assess the processes and underlying mechanisms of sediment‐associated carbon and nutrient deposition in the water level fluctuation zone (WLFZ) of the TGR. Sediment cores were extracted from the WLFZ close to the flood control water level (145.6 m) of the reservoir in 2013 and 2019 and analysed for particle‐size distribution (PSD), median particle size (MPS), total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP). Various nutrient ratios (C:N, C:P, N:P and C:N:P) were calculated. The sediment core chronology was determined using 137Cs activity. Daily reservoir water levels, monthly suspended sediment loads, reservoir inflow and outflow and upstream reservoir construction data were used to interpret the depositional processes and nutrient distributions. Sediment depths were 345 cm and 440 cm in 2013 and 2019, respectively. Annual and seasonal variations were observed in the sediment deposition, PSD, MPS, 137Cs, TOC, TN, TP and nutrient ratios. Mean TOC, TN and TP in 2013 were 18.6, 1.0 and 1.0 (g/kg), respectively, and 16.8, 1.1 and 0.9 (g/kg), respectively, in 2019. The average C:N:P (molar) in 2013 and 2019 were 51:2:1 and 46:3:1, respectively. The controlled flow regime, repeated inundation cycles, input sediment loads and upstream hydrological management primarily govern nutrient transportation and depositional mechanisms. Overall sedimentation decreased over time, and the deposited sediment exhibited a relative increase in fine sediment, TOC, TN and TP owing to coarse sediment retention in the upstream reservoirs. This study highlights complex geochemical alterations in reservoir ecosystems akin to large‐scale reservoir operations.

We examine surface sediment and water column total nutrient and chlorophyll a concentrations for 12 estuaries with average water depths &lt;4 m, and calculated sediment loads ranging from 0.2 to 10.8 kg m−2 year−1. Sediment total nitrogen, phosphorus and organic carbon concentrations vary inversely with sediment loads due to: (i) the influx of more mineral-rich sediment into the estuaries; and (ii) increasing sediment sulfidation. Sediment total organic carbon (TOC) : total sulfur (TS) and TS : Fe(II) ratios correlated to sediment loads because enhanced sedimentation increases burial, hence the importance of sulfate reduction in organic matter degradation. Curvilinear relationships were found between a weathering index and organic matter δ13C in sediment, and sediment load. The rising phase of the curve (increasing weathering, lighter isotopic values) at low to intermediate loads relates to soil erosion, whereas regolith or bedrock erosion probably explains the declining phase of the curve (decreasing weathering, heavier isotopic values) at higher sediment loads. The pattern of change for water column total nutrients (nitrogen and phosphorus) with sediment loads is similar to that of the weathering index. Most water quality problems occur in association with soil erosion, and at sediment loads that are intermediate for the estuaries studied. Limited evidence is presented that flushing can moderate the impact of sediment loads upon the estuaries.

Changes of soil organic carbon, nitrogen and phosphorus concentrations under different land uses in marshes of Sanjiang Plain