DISCUSSION
Zone – I (GR-12 – GR-13) -Urban:- The present zone is located between Nadwa and Hanuman Setu. The variation of opaque phytoclast and degraded brown organic matter with fungal spores and filamentous algae suggests that the degradation is moderate to high in this zone with low oxygenation state in the sediment. The various palynofacies association has been captured and is depicted in Plate-1. The grain distribution shows very fine sand to silty sediment deposits in this zone of Gomati River indicating very low energy conditions with a unimodal depositional system in the flow regime. The statistical inference from the grain size shows that the grain are unimodal with poor sorting, negatively skewed (-0.253 and -0.418) in coarse to very coarse owing to very fine sand category, while the kurtosis suggest leptokurtic and mesokurtic statistics (Folk and Ward 1957; Blott and Pye 2001). The zone is identified with poor winnowing and variable fluvial energy conditions (Folk and Ward, 1957; Friedman 1967; Kanahaiya et al., 2016; Padhi et al., 2017, Kholia et al., 2021). The present zone is influenced by high levels of anthropogenic activity and can be held responsible for the degradation of particulate organic matter (Xenopoulos et al., 2021). Recently it has been globally recognized that human activities can modify the organic matter either in dissolved or particulate form. These can be adhered to the natural system due to land-use change, climate change, nutrient pollution, browning, wildfires, etc (Xenopoulos et al., 2021). The high opaque phytoclast percent vary effectively with slight enhancement of coarser grain fraction and is reflected in PCA biplot (Figure 6). As the river energy condition in the mature stage is low in the Gomati River, the winnowing of sediments by channel action in the flow regime with changeable energy conditions may affect the palynofacies is least anticipated. Alternatively, due to low water levels after the southwest (SW) monsoon allows high fertile sediments for agriculture practice in these parts of flood plains. The continous use of the agriculture practice since long is also one of the reasons for deterioration of palynofacies. The ratio of degraded charcoal (Dc) to burnt charcoal (Bc) ranges between 1.05-0.71 suggesting burning activity along the river channel as an evidence of human activity (Xenopoulos et al., 2021). The occurrence of opaque phytoclast (degraded or burnt) is a result of either prolonged transportation or natural/ anthropogenic fires (Mendonça Filho et al., 2011a). High encroachment of human population along the rivers is evidenced world wide and this is also a typical situation in and around the Lucknow city. Furthermore, the ratio of the cuticle (C) to tracheid (T) is 0.41-0.31 representing low vegetation in the surrounding and the present status of tracheids and cuticles may be transported by the channel as the river is perennial. Palynofacies and grain size analyses suggest that the moderate to high degradation due to anthropogenic reasons along the river banks in the urban reaches and organic matter deterioration due to development projects and encroachment on the flood plain of the Gomati River cannot be ignored. The changes in the organic matter association is also a factor of the dissolved organic matter that is subjected to the anthropogenic responses along the river channel and affects the flood plains to a great extent (Xenopoulos et al., 2021).
Zone – II (GR-8 – GR-11) - Urban Fringe:- This zone lies between Gaughat to Gaughat3. The variation of terrestrial organic matter is primarily controlled by degraded brown OM and opaque phtoclast and variable percentages of amorphous OM and Mycelium fungal hyphae. The details of the palynofacies association for the shown in Plate-2. The opaque phytoclast comprise trees/ woody material being transported onto the flood plains of the Gomati River during precipitation time. Also, the portion of opaque phytoclast shows angular to sub-angular edges suggesting low distance transport of phytoclast from nearby source. It is also noteworthy that the AOM and fungal remains show an appreciable variation reflecting slowly flowing/ near stagnant conditions and high degradation of organic matter as a consequence of post-deposition in the flood plains. The Dc/Bc ratio varies between 3-5 indicating higher degraded opaque phytoclast in the river bank as a result of post burial activity of palynofacies matter. The C/T ratio varies 0.9-2 showing high leafy remains i.e. cuticular remains and also suggest proximal region of source area. The high degradation of palynofacies may also be addressed to human practices such as agriculture along the flood banks. This zone also experiences seasonal vegetation of creeping plants and hence records of high cuticles may be a plausible explanation. The rise in land acquisition along the river is also be a probable reason for deteriorating palynofacies in this transitional part of urban suburbs. The charcoal particles have also been recorded in coarse-grained, high energy, organic-poor sediments such as distributary channel sands and point bars in the flood plains (Denison and Fowler, 1980; Parry et al., 1981; Tyson, 1995; Mendonça Filho et al., 2011a). The grain size distribution shows both silt and sand content in vaiable proportions indicating a bimodal system and suggests varying energy conditions. The negative skewness suggest fine grained deposition alongwith poor sorting, and mesokurtic and platykurtic nature of sediments in the flood plain. The incision in the channel flow has also been recognised in the Gomati channel by Thakur et al., (2009). The plausible explanation of palynofacies and grain size relatio in context to brown degraded OM and opaque phytoclast is also ascertained using the PCA analysis in PC1 and PC2 (Figure 6).
Zone – III (GR-4 – GR-7) - Urban Fringe to Sub-urban:- The localities Raitha to Ghaila marks this zone. In this zone, terrestrial organic matter is marked by a high percentage of degraded brown OM, filamentous algae, and opaque phytoclast with a small percentage of AOM that suggests low energy of the river. In order to define the fate of the palynofacies the images are captured and shown in Plate-3. Here, different palynomorphs like thecamoebians, fungal spores, and cyanobacterial remains are also recorded which indicates that this zone is low polluted and disturbed that prevented oxidation of palynofacies matter and allowed preservation in finely deposited silt and sand fraction. Based on the grain size distribution low to moderate energy conditions is interpreted. Here it can also be observed that the channel is nearly straight with minimal meandering. The negative skewness suggests fine grained sediment with platykurtic that implies mixing of sediment from two sources with poor sorting in this zone that can be attributed to channel sediments and local weathering. The zone exhibits a deposition where the natural resources are less affected by the anthropogenic activities. The Dc/Bc ratio varies between 3.05 to 6.5 suggesting high opaque phytoclast(degraded) due to the long transportation of plant material (Mendonça Filho et al., 2011a). The C/T ratio varies from 0.59 to 1.22 showing high tracheid record indicating the prevalence of woody material. The present finding agrees with the silt and very fine sand grain texture with degraded brown OM, pollen/spore, Thecamoebians, cyanobacteria, and filamentous algae explaining the highest variability in PC1 and PC2 (Figure 6). The present association of the phytoclasts is also influenced by hydrodynamic equivalence effects. Being relatively large and dense organic particles, woody debris mainly comprised of degraded brown is often concentrated in sediments rich in coarse silt and/or very fine sand (Tyson, 1993).
Zone – IV (GR-1 – GR-3) - Sub-urban:- This zone comprises the area between Atariya to Chandrika Devi. The characteristic palynofacies component comprises high proportions of the degraded brown OM followed by filamentous algae and variable proportions of opaque phytoclasts, fungal remains, and other organic matter. The major palynofacies association are shown in Plate -4 to explain the sub-urban region. The variable degree of degraded brown OM, filamentous algae and AOM points to both prolong and local transportation suggesting palynofacies deposition from autochthonous or allochthonous sources. This can be explained by the angular to sub-angular and sub-rounded opaque phytoclast. It is also noted that the high content of filamentous algae and fungal/ algal remains (Glomus sp. and Alternaria sp.) points towards clear and standing water with a low velocity of the channel and local erosion (Quamar, 2015; Sridhar et al., 2020). The variation in the AOM shows a certain degree of organic matter degradation by natural processes during transport by mechanical breakdown and further by post-deposition burial (Tyson, 1995). The grain size show negative and positive skewness suggesting fine and coarse grained sediments that are poorly sorted with platykurtic reflecting the mixing of sediment source. The palynofacies findings also go in hand-to-hand with the grain size distribution and it can be effectively postulated that the variability in palynofacies and grain size representing a bimodal system of deposition or a mixed environmental setting. The Dc/Bc ratio is of higher value i.e. 6.7-5.6 advocate major degraded charcoal deposit, at the same time, C/T ratio ranges between 0.31-1.36 showing equable recurrence of cuticle and tracheids propose high vegetation within the proximity. The association ofdegraded brown OM, filamentous algae, and AOM with fine to medium silt and fine sand is in aggreable reference in PC1 and PC2 (figure 6).
To depict the distribution and destiny of palynofacies in urban and sub-urban reaches, the various zones outlined above have also been displayed in ArcGIS to decode the spatial heterogeneity in the Gomati River flood plain in Lucknow district (Figure 7). The spatial variation shows that, in comparison to the sub-urban reaches, variability is developing more quickly throughout the urban regime. It might be argued that the increasing rate of urbanisation in the periphery areas is accelerating the degradation of sedimentary organic matter through development and concretization.