Environmental set-up and tidal propagation in a tropical estuary with dual connection to the sea (SW Coast of India)

Abstract

The Kochi Backwater (KB) is the second largest wetland system in India. It is connected to the sea at Fort Kochi and Munambam (30 km north of Kochi). As the tide is forced through two openings, its propagation in the backwater system is very complicated, particularly in the northern arm of the estuary.Using synchronous water level (WL) and current measurements in the KB from a network of stations during 2007-08, it was convenient to demarcate the northern KB into two distinct regions according to the tidal forcing from the north (Pallippuram) and south (Vallarpadam). This demarcation is useful for computing the propagation speeds of the dominant tidal constituents in the northern branch of the KB with dual opening for opposing tides. WL variations indicated that M2 tide (Principal lunar semidiurnal constituent) dominated in the sea level variance, followed by the K1 constituent (Luni-solar declinational diurnal constituent). The M2 tidal influence was strongest near the mouth and decayed in the upstream direction. The propagation speed of the M2 tide in the southern estuary was ~ 3.14 m/s.The ratio of the total annual runoff to the estuarine volume is ~ 42 that indicate the estuary will be flushed 42 times in a year. KB can be classified as a monsoonal estuary where the river discharge exhibits large seasonal variation.

Heavy Metals Pollution Influence the Community Structure of Cyanobacteria in Nutrient Rich Tropical Estuary

“…The dissolved heavy metals were higher in CE during dry season, which may be attributed to changes in flushing rate. Flushing activity would be inactive in Indian estuaries during dry season, while it experiences multiple flushing in addition to heavy rain fall during wet season [38]. In concurrence with this, the level of dissolved heavy metals were found higher during dry season and lower during wet season.…”

“…The nucleic acid sequences remains limnetic during wet season due to heavy river water inflow and the influence of seawater was restricted at station S2 (salinity 9). The average river water discharge was reported to be minimum in CE from January to May in a year, it increases in June with the onset of southwest monsoon and reaches its plateau during August [29]. Accordingly the CE shifts between seawater and fresh water dominance in dry and wet season respectively.…”

“…Nutrient levels are reported to be higher in tropical estuaries during wet season, and is attributed to increased river water discharge and rainfall associated with southwest monsoon [26][27][28]. CE receives 60-70% of its annual freshwater discharge i.e., 22.41 × 10 3 Mm 3 during southwest monsoon [29], which carries the nitrogen rich effluents discharged from fertilizer and fish processing industries [30]. It is estimated that 260 million litre per day of effluents are produced in the industrial belt of Cochin and a significant fraction of it reaches CE through river Periyar [31].…”

Seasonal dynamics of the copepod community in a tropical monsoonal estuary and the role of sex ratio in their abundance pattern

“…Heavily influenced by the Indian summer monsoon, the annual precipitation of the CE is around 320 cm, of which around 75 % occurs during the summer monsoon period (June-September) (Qasim 2003). The estuary receives an influx of about 22,000 × 10 6 m 3 of freshets annually (Revichandran et al 2012) from seven perennial rivers-Periyar, Chalakudy, Pamba, Muvattupuzha, Manimala, Meenachil, and Achancoil-and their tributaries. The seasonal asymmetry in the balance between the fluvial runoff associated with the Indian summer monsoon and the tidal incursion from the Arabian Sea often evokes intense heterogeneity in the spatio-temporal characteristics of the CE.…”

“…The Cochin estuary (CE), heavily influenced by the Indian summer monsoon, differs from all other estuaries by its unsteadiness in salinity characteristics and also in its total runoff, which is many times higher than the estuarine volume (Vijith et al 2009;Revichandran et al 2012) (June-September), resulting in a possible washout during the monsoon period. This uniqueness in the estuarine features of the CE thus demands a comprehensive study for identifying the regulatory mechanisms underlying the seasonal variability in the abundance, distribution, and population maintenance of the endemic copepoda community of this estuarine ecosystem.…”