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Freshwater lakes and sediments need to be monitored continuously for environmental assessment and geochemical explorations. Lake sediments are major sinks for organic matter and for all geochemical elements. In the present study, total organic matter (TOC), nitrogen (TN), and geochemical analysis of major oxides was carried out on Yercaud Lake surface sediments, located at a higher elevation in South India to infer sediment distribution pattern and source for organic matter. Particle size distribution of lake surface sediments suggests that the sediments are predominantly silty sand and sandy silt, poorly to very poorly sorted and symmetrically skewed. TOC/TN ratio (6.54–12.65) reveal that the organic matter (OM) is derived from the in situ lake sources particularly from the vascular plants and lake biota accumulation. Weathering indices that fall from [chemical index of alteration (CIA)] 88.59–93.08 values and A‐CN‐K plot reflects intense chemical weathering of the bedrock exposures in the source area, which was accelerated under warmer and humid climate conditions in the sub‐tropical regions. Al2O3/TiO2 ratio (6.94–26.62) indicates weathering particularly of the exposed charnockite rocks around the lake basin. [ABSTRACT FROM AUTHOR]

Multi-proxy analysis of lake sediments provides high-resolution and reliable palaeoclimate records. The present study aims to investigate the palaeoenvironmental changes and eutrophic evolution of the Wular Lake, Kashmir Valley spanning the last ~ 500 years. Based on the multi-proxy analysis and supported by radiocarbon chronology, two prominent environmental phases were identified. From 74 to 45 cm, the sedimentation corresponds to the late 15th to early sixteenth century suggests the influence of cold, Little Ice Age (LIA) with nutrient-poor lacustrine environmental conditions. The following climate phase (28–9 cm) reflects the 19th and early twentieth century warmer and wetter environmental conditions. Enhanced TOC and N nutrient inputs in the lake sediments observed during the top 25 cm are likely contributed by anthropogenic sources owing to rapid and sustained anthropogenic land-use of watershed environments. This increase in the lake nutrients has been caused due to intense agriculture and horticulture practices leading to the lake eutrophication. [ABSTRACT FROM AUTHOR]

Surface sediments were collected from Wular Lake, located in Bandipora district of Kashmir Valley, NW Himalaya to investigate the environmental risk assessment using trace element concentrations. The surface sediments of the lake reveal higher concentration of Cl, Cr, Ni, Cu, Co, Pb, Zn and Th. In order to estimate the impact of metal pollution on the sediments, the trace element data was quantified for enrichment factor (EF), geoaccumulation index (Igeo), pollution load index (PLI) and contamination factor (CF). The average values for Igeo reveal moderate to strong contamination of Ni, Cu, while Cr and Co exhibit moderate to strong contamination in the central part of the lake. EF reveals minor enrichment of Cu, Ni, Cr, Co and Zn in the lake surface sediments. PLI indicate moderate pollution from all the sampling sites. Spatial distribution of the metal in the lake reveals their transport through the sewage from the urbanized areas and the Jhelum river. Since metal pollution in the lake is still at nascent stage, it demands attention of the local authorities and the Lake Conservation Department to take remedial measures for the protection of this freshwater body from further contamination. [ABSTRACT FROM AUTHOR]

Paleoclimate investigations and reconstruction using the lake sediment cores of Kashmir Valley have been rarely attempted. The basin is influenced by Indian Summer Monsoon, Westerlies and the local katabatic winds. In the present study, an 80 cm undisturbed sediment core was retrieved from the Manasbal Lake situated in North western Himalaya. Sediments were dated using 14C method, and the age-depth model indicated a depositional history extending from ∼3345 yrs BP to the present. Grain size, major and trace elements, TOC, OM contents C/N ratio and diatom assemblages were applied to reconstruct the paleoenvironmental changes around the area. The A-CN-K diagram displays that the weathering intensity of the Manasbal lake sediments are moderate to highly weathered and the sediments have been derived from nearby and mixed source origin. Several wet and cold phases were identified during ∼3300 yrs BP to ∼2500 yrs BP and ∼1800 yrs BP to ∼1300 yrs BP due to intense precipitation reflect high lake level. These wet phases are marked by higher sand and silt content, C/N ratio and high allochthonous input with less abundance of diatom species, clay, OM, TOC contents and high CIA values. Consequently, low lake level and dry and cold period from ∼3345 yrs BP to ∼3300 yrs BP and ∼2500 yrs BP to ∼1800 yrs BP is observed. These inferences are corroborated with the trace elemental ratios CIA and CWI data. Our data indicate that the Westerlies and localised katabtic winds rather than the Indian summer monsoons played a major role in controlling the past climate around the Manasbal lake, Kashmir Valley. [ABSTRACT FROM AUTHOR]

In the present study, the lake floor sediments of the Karlad lake, located at higher elevation in Wayanad region of north Kerala, were analyzed for textural characteristics, organic matter, calcium carbonate, major oxides and trace elements. This study was carried out to infer the chemical composition, provenance and intensity of chemical weathering of the source rocks in the lake catchment area. Textural studies signify that lake floor sediments are predominantly as clays (38.75%) followed by sand (36.36%) and silt (25.19%) fractions. The C/N ratio of the lake sediments signify that the sediments are both autochthonous and allochthonous in origin. The major oxides average content reveals the order of abundance as follows; SiO2 > Al2O3 > Fe2O3 > TiO2 > MgO > CaO > K2O > P2O5 > Na2O > MnO. Moreover, the various weathering indices such as Chemical Index of Alteration (CIAAvg. 93.5%), PlagioclaseIndex of Alteration (PIA- Avg. 95.6%) and Chemical Index of Weathering (CIW- Avg. 95.76%) suggest an intense chemical weathering of the source area. The A-CN-K diagram is also corroborating the same. Various provenance discrimination diagrams reveal that the sediments are derived from the mafic source rocks. [ABSTRACT FROM AUTHOR]

A study involving grain size analysis was carried out from the Parsons valley lake deposit, Nilgiris, India to determine the depositional environments and paleoflood events since late Pleistocene period (∼29,838 cal yr BP). A 72 cm lacustrine core was collected from the lake and eight organic rich sediment samples were AMS radiocarbon dated. The study reveals variations in the grain size distribution chiefly influenced by regional climatic conditions. Paleoflood events have been identified by the individual sedimentary flood signatures of varying changes in the magnitude of sediment supply from the background silty sediment matrix around ∼29,838 and ∼8405 cal yr BP. [ABSTRACT FROM AUTHOR]

In this review, the shifts in organic matter (OM) accumulation and C:N ratios in lake sediments to reconstruct paleoclimate and paleo-environmental changes since the early Holocene period are presented. The C:N proxy data of total OM reflect wet climatic conditions during early Holocene (10 to 8.2 kyrs BP) due to enhanced southwest monsoon. This was followed by intermittent arid conditions during the mid and late Holocene period (8.2 to 2.8 kyr BP). Enhanced values of C:N ratio during middle to late Holocene (7.8-2.3 kyrs B.P) indicate periods with lower lake levels and minimum precipitation, while decreased C:N ratio point to stronger SW monsoon and expansion of the lakes. Further, C:N and δ13C results from the lake sediments reveal a detailed and continuous paleo-environmental changes in the relative sources of OM (allochthonous vs autochthonous). Proxy records using such natural archives have also been utilized to reconstruct past extreme events and environmental changes around the lake systems, such as causes for lake desiccation, hydrographic changes, alternations between C3 and C4 vegetation and historical disturbances in the catchment area since the early-late Holocene period coupled with the Indian summer monsoon. [ABSTRACT FROM AUTHOR]

Lakes and wetlands are dynamic geomorphic units of a landscape that hold geochemical signatures of sediment provenance and paleo-environmental shifts and are major sinks for organic matter accumulation. The source of organic matter is diverse in lake sediments and varies widely with the type and size of the lake and hence it is important to understand the source of organic carbon (terrestrial or in situ) in lake systems in order to monitor the health of the lake. Wular lake, located in north Kashmir, is one of the largest fresh water lake in India, situated at an average elevation of 1580m ASL. The lake is fed by a number of watersheds that bring a diverse type of sediments and organic matter and thus deposit them into the Wular lake basin. In order to understand sediment distribution pattern, content and source of organic matter, sediment provenance and the persisting environment in the Wular lake, 32 lake floor sediment samples covering the entire lake were collected and analyzed for organic element analysis, CaCO3, organic matter, sediment texture and diatom analysis. The results indicated that sediments in the lake are dominated by silt and silty clay. The organic carbon in the lake ranged from 0.83%-4.52% and nitrogen varied from 0.06%-0.5%. The Carbon to Nitrogen (C/N) ratios (9.04 to 22.03) indicate a mixed source of organic carbon but dominated by in situ lake sources from the vascular and lake biota accumulation. The diatom analysis revealed the occurrence of a diverse type of species along the sampling sites present within the lake. The wide distribution of the diatom species such as Cymbella, Cyclotella and Tabularia etc. in the lake indicate high organic pollution and alkaline fresh water environment prevailing in the lake. [ABSTRACT FROM AUTHOR]

This paper presents a detailed sediment chemistry investigation of the Manasbal lake, Srinagar, Jammu and Kashmir, India, which is one of the high altitude lakes in the Kashmir valley. 22 lake floor sediment samples covering the entire lake were collected and analyzed for textural characteristics, CaCO, organic matter, TOC, TN contents, C/N ratio, major and trace element chemistry. These analyses were conducted to trace the provenance of the sediments. Textural parameters reveal that the lake sediments consist predominantly clay and silt fractions. The C/N ratio of the sediments indicates a mixed source of TOC, both autochthonous and allochthonous in origin. The log (FeO/KO) Vs. log (SiO/ AlO) graph of the sediments discriminates the rock types of the catchment area that are Fe-shale, Fe-sand, wacke, shale and litharenite. The Chemical Index of Alteration (CIA) falls between 59.11 to 90.16% and Chemical Index of Weathering (CIW) between 63.97 to 99.68% and these values are higher than the Post-Archaean Australian Shale (PAAS), indicating moderate to highly chemically weathered lake floor sediments. Plagioclase Index of Alteration (PIA) values (60.74-99.63%) suggests the occurrence of plagioclase feldspars in the lake floor sediments. Geochemical characteristics signify a mixed-nature of provenance of the lake floor sediments due to the tectonic settings of the lake basin in a complex catchment area. [ABSTRACT FROM AUTHOR]

This study reports the spatial distributions of diatom assemblages and potential relationships between diatom diversity and environmental variables (C/N ratio, CaCO3%, clay mineralogy) using multivariate analyses in surface sediments of the Akkulam-Veli Lake. Surface sediment samples were collected at 19 sites throughout the lake to analyse diatom distribution, TOC, N, CaCO3%, clay mineralogy and sediment texture. The results suggest that the clay fraction is predominant in the eastern flank, whereas sand fraction is more in the western flank. TOC% and CaCO3% in the lake floor sediments are attributed to high organic activity within the lake and contributions from the vegetation around the lake margins. The results suggest that N is being added to the lake from secondary sources from catchment area leading to eutrophication of the lake. Further, clay mineralogy of the sediment samples reveals that kaolinite mineralogy dominates in clay fractions. Diatom studies show rich diversity of freshwater, marine and brackish diatoms and abundance of pollution-reflecting species such as Cyclotella sp. and Navicula sp. [ABSTRACT FROM AUTHOR]