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The sources of organic matter in three typical mangrove systems of Cochin estuary were assessed for the first time with help of sediment bulk parameters and fatty acid biomarkers. The C/N and δ13C analysis showed intermediate values to that of autochthonous and terrestrial inputs of organic matter, signaling to a mixed origin. The biochemical composition of sedimentary organic matter revealed a dominance of lipids over proteins and carbohydrates, indicating the nutritive or energetic value as well as the freshness of organic matter in all the systems. Fatty acids ranging from C8 to C24 were identified in the study. C20:5n-3 was one of the major fatty acids at station 1, indicating significant benthic phytoplankton contribution. The zooplankton biomarkers C20:1 and C24:1 were also present in appreciable levels, suggesting the tidal influx. Principal fatty acids at station 2 were the zooplankton biomarkers C20:1 and C24:1 implying significant estuarine contribution through tidal influx. The major fatty acids at station 3 were diatom marker C20:5n-3 and the higher plant marker C24:0. Dominant fatty acids in mangrove leaves; C18:2n-6 and C18:3n-3 were also present at station 3. The low contributions of C20:1 and C24:1 confirms the limited tidal exchange at this station. Presence of significant amount polyunsaturated fatty acids in the mangrove sediments confirms the freshness of organic matter. Thus, fatty acid biomarker study of the three mangrove systems of Cochin estuary could substantiate the bulk parameter approaches effectively; distinguishing the multiple sources of the organic matter and the observed spatial variations. [ABSTRACT FROM AUTHOR]

Fatty acids and bulk geochemical proxies were employed to understand the sources and transformation of sedimentary organic matter from surface sediments of major five mangrove systems in the northern Kerala coast. Texture, tidal rhythm and the proximity to the south eastern Arabian Sea were the main factors influencing distribution and accumulation of the organic matter in these systems. A total of 118 fatty acids were quantified and grouped into short-chain (SCFA), long-chain (LCFA), monounsaturated (MUFA), polyunsaturated (PUFA) and branched-chain (BrFA) fatty acids, hydroxy fatty acids, cyclic fatty acids, and dicarboxylic acids. The distribution of fatty acid groups was in the order SCFA > BrFA > MUFA > LCFA > PUFA. Total fatty acids (TFA) concentration exhibited profound seasonal variations and ranged from 6.25 to 580.49 lg/g (pre-monsoon > post-monsoon > monsoon except in Kadalundi which follows the reverse order). The sedimentary fatty acids in the study region reveal a wide spectrum of inputs from terrestrial, planktonic (preponderance of diatom followed by dinoflagellates along with brown algae, cyanobacteria, red algae) and bacterial sources (e.g., Desulfobulbus-type bacteria, sulfur-reducing bacteria, Sulfur-oxidizing bacteria). Significant concentrations of bacterial fatty acids suggest the functioning of an effective microbial loop and various biogeochemical pathways operating in these sediments (sulfate reduction, iron and manganese oxide reduction, etc.). [ABSTRACT FROM AUTHOR]

Aliphatic hydrocarbons in the sediments of the estuarine mangrove forests of Cochin region, Southwest coast of India were characterized to assess the sources of organic matter (OM) and to validate the effectiveness of the various geochemical indices to identify multiple OM sources and the complex geochemistry of these tropical coastal environments. The total concentration of the n-alkanes varied from 606.39 to 826.25 µg/g [dry weight (dw)] in mangrove sediments, to values between 230.10 and 287.67 µg/g in estuarine sediments. The n-alkane distribution in the study region indicated a strong odd over even predominance in both mangrove and estuarine sediments. Assessment using terrestrial OM indices such as Carbon Preference Index (CPI), Terrigenous Aquatic Ratio (TAR), and Terrestrial Marine Discriminant (TMD) suggested that a large fraction of OM in the mangrove sediments was derived from mangrove plant litter and a better preservation of mangrove OM in the sedimentary environment has occurred. These findings are supported by the higher content of total lipid, tannin, and lignin, as well as by the depleted δ13C values. Low ratios of CPI, TAR, and TMD at estuarine sites E2 and E3 indicated a mixed origin of OM. Natural or biogenic indices such as natural n-alkanes ratio (NAR), Σn-alkanes/n-C16, n-C29/n-C17, and LMW/HMW revealed that all the mangrove stations and the estuarine station E1 received OM from natural or biogenic sources, whereas a significant anthropogenic input was noticed for estuarine stations E2 and E3. Indices like Pr/Ph, Pr/n-C17, Ph/n-C18 further confirmed the mixed nature of OM accumulated under the anoxic environment. [ABSTRACT FROM AUTHOR]

Triterpenoids and fatty alcohols were identified from the sediments of five mangrove ecosystems (Kunjimangalam, Pazhayangadi, Pappinissery, Thalassery, and Kadalundi) in the northern Kerala coast, India, to illustrate the organic matter sources. Straight chain fatty alcohols in the range C12–32 were detected, and among these the long chain fatty alcohols (C20–32) were exclusively even chained compounds. Branched fatty alcohols (6,10,14-trimethyl-pentadecan-2-ol and 3,7,11,15-tetramethyl-2-hexadecanol) of bacterial origin were detected in a few observations. Twenty triterpenoids were detected from the study region in which 13 of them were sterols. Triterpenoids originated from higher plants such as stigmasterol, campesterol, β-sitosterol, taraxerol, lupeol, germanicol, β-amyrin, α-amyrin, and betulin were identified in the study. Brassicasterol, a diatom marker and dinosterol, a dinoflagellates marker were also detected in the study region. An elevated % composition of dinosterol and dissolved oxygen super-saturation were noticed in Kunjimangalam during pre-monsoon, which may suggest elevated input of algal organic matter in the mangrove system. Cholesterol transformation products such as coprostanol and epi-coprostanol were detected, which indicated the presence of fecal contamination in the sedimentary organic matter. From the ternary diagram, it was recognized that the organic matter contribution from marine algae was feeble as compared to terrestrial input. [ABSTRACT FROM AUTHOR]

The study investigated the origin, quality, composition, and trophic state of sedimentary organic matter (SOM) in core samples collected from three zones (Munambam, Vypin, Chettuva) of Central Kerala, India. The SOM exhibited enhanced levels for carbohydrate (CHO) followed by protein (PRT) and lipid (LPD); and phytopigment in the sediment followed the trend: Pheophytin (Pheo) > Carotenoid (carotend) > Chlorophyll-a (Chl-a) > Chlorophyll-b (Chl-b) > Chlorophyll-c (Chl-c). The low PRT: CHO ratio indicated a large amount of nonliving or aged organic matter in the sedimentary environment. Whereas the low Chl-a: Pheo ratio interprets the abundance of dead plant materials in the sediments. Correlation matrix showed strong association between organic matter and clay fraction of sediment. Furthermore, the strong interrelationships between biochemical components and chloropigments in all the zones suggested that SOM is strictly connected to phytodetritus deposition. Vypin zone near Vallarpadam Container Terminal revealed the presence of high biopolymeric carbon content. Besides, the PRT: CHO > 1 reflected the eutrophic condition at the same site but the low PRT: CHO ratio in the remaining stations displays the oligotrophic nature. [ABSTRACT FROM AUTHOR]

Surface sediment samples were collected from five stations along the Chitrapuzha River, during the monsoon, post-monsoon and pre-monsoon seasons, and analyzed for biochemical composition, total organic carbon (TOC), total nitrogen (TN), and stable isotopic ratios of carbon (δ13C) and nitrogen (δ15N) to identify the major sources of organic matter. Sediment grain size was found to be the key factor influencing the organic matter accumulation in surface sediments. The δ13C values vary between −27.94‰ and −26.05‰ and δ15N values ranges from −1.66‰ to −4.75‰ in surface sediments. The δ13C values indicate terrestrial inputs from higher plants, while δ15N values suggest decomposition processes in the sediments. The fraction of terrestrial organic matter (TrOM) to the total organic matter (TOM) pool ranges from 41 to 84% in the surface sediments as estimated by δ13C-based two end members mixing model. Intermediate values of TOC/TN ratios signal a combined input of both autochthonous and terrestrial organic matter sources, while protein-to-carbohydrate ratios show freshly deposited detritus in the majority of the stations. The threshold levels of protein, biopolymeric carbon, and algal contribution to biopolymeric carbon (BPC) indicate eutrophic conditions prevailing in the study area. [ABSTRACT FROM AUTHOR]