Organic Matter In Suspended Sediment Research Articles

Detailing the organic matter in suspended sediments as a tool to assess the impact of land occupation in water bodies: a case of Barigui Watershed (Southern Brazil).

Suspended sediments were collected to examine the organic carbon content and n-alkanes in order to assess the impact on water bodies caused by soil and land occupation. For this, samples from distinct areas based on the level of land occupation of the Barigui Watershed and different areas under the influence of human activities were examined. The number of industries increasing along the river was also considered. Twenty-two sediment samples were collected using a time-integrated sediment sampler. Samples were extracted with dichloromethane:methanol (DCM:methanol) (2:1) in an ultrasound bath, treated and injected using gas chromatography coupled with mass spectrometry (GC-MS) for separation and quantification. Twenty-one n-alkanes were identified and were used to track both biogenic and anthropogenic inputs. The concentration of total n-alkanes varied from 38.72 to 222.76µgg-1, due to the impact of urbanization. Diagnostic indexes indicated high numbers of plants, bacteria and petroleum as n-alkanes sources. The following results were obtained using: carbon preference index (CPI), 1.96-2.22 (rainy season) and 2.12-5.80 (summer season); average chain length (ACL), 30.37-31.17 (rainy season) and 30.05-30.50 (summer season) and terrigenous aquatic ratio (TAR), 0.39-5.47 (rainy season) and 2.98-5.06 (summer season); n-alkanes had two main sources: terrestrial plant and petroleum. It is clear that the source of n-alkanes is different in each season (rainy and dry) demonstrated by n-alkanes occurrence. During the rainy season, there was an increase in organic matter of oil origin which was mainly associated with the increased runoff and rain drainage. Finally, the input of organic matter associated with land occupation and erosion can be distinguished by higher concentration in the most urbanized site (PB).

Molecular Tracing of Riverine Soil Organic Matter From the Central Himalaya

AbstractThe isomer distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils has been shown to correlate to the local mean annual temperature. Here, we explore the use of brGDGT distributions as proxy for the elevation at which soil organic carbon is preferentially mobilized in the Central Himalaya. Soil brGDGT distributions collected along an altitudinal profile, spanning elevations from 200 to 4,450 m asl, are linearly correlated to elevation. We use this calibration to trace the provenance of soil organic matter in suspended sediments of rivers draining the Himalaya. BrGDGT distributions of fluvial sediments reflect the mean elevation of the soil cover in most catchments. Inverse modeling of the brGDGT data set suggests similar relative contribution to soil organic carbon mobilization from different land covers within a factor 2. We conclude that riverine soil organic carbon export in the Himalaya mostly occurs pervasively and is at the catchment scale insensitive to anthropogenic perturbations.

The isotopic composition and fluxes of particulate organic carbon exported from the eastern margin of the Tibetan Plateau

Erosion of organic carbon from the terrestrial biosphere and sedimentary rocks plays an important role in the global carbon cycle across a range of timescales. Over geological timescales (>104 years), erosion and burial of particulate organic carbon (POC) from the terrestrial biosphere (POCbiosphere) is an important CO2 sink, while oxidation of organic carbon derived from sedimentary rocks (petrogenic, POCpetro) releases CO2 to the atmosphere. Over decadal to millennial timescales, the balance between POCbiosphere production and degradation affects atmospheric CO2 concentrations. To better constrain the controls on erosional carbon transfers, here we quantify POCbiosphere and POCpetro fluxes in a mountain range with relatively low runoff, the Longmen Shan, which drains the eastern margin of the Tibetan Plateau. We measure total organic carbon content ([OCtotal]) and the carbon isotopic compositions (13C/12C expressed as δ13C; 14C/12C expressed as fraction modern or Fmod) of organic matter in suspended sediments collected from six gauging stations on the Min Jiang, a tributary of the Yangtze River, from 2005 to 2012. We find that POCpetro has a large range of δ13C, from -26.2‰ to -13.2‰. This POCpetro mixes with POCbiosphere to set the δ13C of POC in river sediments. Binary mixing models reveal the possibility of aged POCbiosphere at two gauging stations which drain the high elevations of the eastern Tibetan Plateau, with modelled Fmod values of 0.82 ± 0.09 and 0.84 ± 0.08. This is consistent with prior suggestions of aged biospheric carbon being eroded from the Plateau. The annual POCpetro yields range from 0.04 ± 0.02 tC km-2 yr-1 to 1.69 ± 0.56 tC km-2 yr-1 across the five study catchments, with basin average yield that appears to be linked to catchment average slope as a likely proxy for erosion rate. Here, the variability in the petrogenic organic carbon content of rocks masks the signal of the weathering and oxidation of this rock-derived organic carbon. The annual POCbiosphere yields range from 0.21 ± 0.04 tC km-2 yr-1 to 3.33 ± 0.57 tC km-2 yr-1. These values are towards the lower end of those measured in mountain ranges around the world, which we suggest not only reflects the relatively low erosion rates of the Longman Shan, but also the low annual runoff (<1 m yr-1). Across this region, the river POCbiosphere discharge is related to the intensity of runoff events. Our data suggest that a wetter (and/or stormier) climate could increase the erosional export of POCbiosphere in this tectonically-active mountain range. Depending on the fate of POCbiosphere downstream in larger river systems, this could act as carbon-cycle climate feedback over geological timescales.

Combined analysis of trace elements and isotopic composition of particulate organic matter in suspended sediment to assess their origin and flux in a tropical disturbed watershed

Approximately 40% of the volume of domestic sewage generated in the São Paulo State is untreated and released into water bodies, causing serious pollution problems that affect the water quality and especially the suspended sediments transported by rivers. Thus, this paper investigates the seasonal influence on the origin and fluxes of Cu, Co, Cr, Zn, Cd, Ni, Sc and particulate organic matter (POM) in sediments transported by a disturbed watershed in the São Paulo State, i.e. the Sorocaba River basin. POM was characterized using particulate organic carbon, particulate organic nitrogen, C:N ratio and δ13C and δ15N stable isotopic composition. Eight sample collections of fine suspended sediments (FSS) were carried out at the mouth of the Sorocaba River from July 2009 to May 2010. During the study period, the discharge rate followed the seasonal variation trend of the past 25 years. Zn was the most abundant trace element in the FSS, followed by Cr, Cu, Ni, Co, Sc and Cd. There was a higher concentration of trace elements during the dry season, except for Sc and Co, which did not vary seasonally. The POM showed the same trend, with higher concentrations during the dry season. The calculated enrichment factors and geoaccumulation index indicated that most of the trace elements are of geogenic origin, except for Zn, which showed significant anthropogenic contributions (55%). The elemental and isotopic analysis of C and N and C:N ratio indicated that the anthropogenic origin of POM found in the FSS is related mainly to domestic sewage (97%), while the significant correlation found between the concentrations of Zn and POM indicates that the main anthropogenic source of Zn is related to this domestic sewage. The FSS load transported during the study period was of 373,194 t y−1, of which 87% occurred during the rainy season.

Organic matter dynamics and stable isotope signature as tracers of the sources of suspended sediment

Abstract. Suspended sediment (SS) and organic matter in rivers can harm brown trout Salmo trutta by affecting the health and fitness of free swimming fish and by causing siltation of the riverbed. The temporal and spatial dynamics of sediment, carbon (C), and nitrogen (N) during the brown trout spawning season in a small river of the Swiss Plateau were assessed and C isotopes as well as the C/N atomic ratio were used to distinguish autochthonous and allochthonous sources of organic matter in SS loads. The visual basic program IsoSource with 13Ctot and 15N as input isotopes was used to quantify the temporal and spatial sources of SS. Organic matter concentrations in the infiltrated and suspended sediment were highest during low flow periods with small sediment loads and lowest during high flow periods with high sediment loads. Peak values in nitrate and dissolved organic C were measured during high flow and high rainfall, probably due to leaching from pasture and arable land. The organic matter was of allochthonous sources as indicated by the C/N atomic ratio and δ13Corg. Organic matter in SS increased from up- to downstream due to an increase of pasture and arable land downstream of the river. The mean fraction of SS originating from upper watershed riverbed sediment decreased from up to downstream and increased during high flow at all measuring sites along the course of the river. During base flow conditions, the major sources of SS are pasture, forest and arable land. The latter increased during rainy and warmer winter periods, most likely because both triggered snow melt and thus erosion. The measured increase in DOC and nitrate concentrations during high flow support these modeling results. Enhanced soil erosion processes on pasture and arable land are expected with increasing heavy rain events and less snow during winter seasons due to climate change. Consequently, SS and organic matter in the river will increase, which will possibly affect brown trout negatively.

Monitoring soil organic carbon erosion with δ13C and δ15N on experimental field plots in the Venezuelan Andes

The question of discriminating sources of organic matter in suspended sediment transported by streams can be addressed by using total organic carbon concentration and stable isotope ( δ 13C, δ 15N) measurements when constant fluxes of organic matter supply can be assumed. However, little is known about the dynamics of organic matter release during soil erosion and the temporal stability of its isotopic composition. In this study, we have monitored soil organic carbon loss and water runoff using natural rainfall events during the 1998 rainy season on three experimental field plots with different vegetation covers (bare, maize and coffee plots), set up on slopes of a tropical mountainous watershed in NW Venezuela (Boconó watershed, 08°57′–09°31′N, 70°02′–70°34′W). Runoff and soil organic carbon losses were considerably higher for the bare field plot than for the cultivated field plots (270 and 2.2–21.0 kg C ha −1, respectively), and these findings are consistent with other soil erosion experiments. Total organic carbon concentrations, total nitrogen concentrations and the δ 13C and δ 15N composition of fine (<50 μm) size suspended sediments remain constant for high runoff periods (>30 ml s −1) and “high” suspended matter concentrations (>0.5 g l −1), closely reflecting the composition of soil organic matter from which they originate and integrating the high variability of organic carbon in top soil horizons. Because runoff and soil organic carbon loss are closely linked during most of the water flow (at the time scales covered by this study), the contribution of soil organic matter, originating from soils with different compositions, to suspended sediments in runoff can be derived using soil organic carbon erosion rates and stable ( δ 13C and δ 15N) isotope measurements.