Geochemical characteristics of surficial sediments in a tropical estuary, south-west India

Abstract

Geochemical characteristics of surficial sediments in the Panangad region of Cochin estuary, the largest brackish-water humid ecosystem in the south-west coast of India, were analysed. Temporal variations in nutrient stoichiometry, seasonal characteristics of redox elements Fe and S, and the phosphorus geochemistry were employed for the purpose. The stoichiometric analysis pointed towards autochthonous origin of organic matter, possibility of nitrogen limitation, and allochthonous modification of redox conditions. Seasonal variations were not statistically significant for all the geochemical parameters, whereas significant spatial variations were observed with lower values at sandy stations, suggesting that the texture of the sediments is the main factor influencing the sediment geochemistry. Significant inter-relations between the geochemical parameters also suggest a common control mechanism. Based on these geochemical characteristics, the study region can be effectively categorized into two distinct zones, viz. (1) erosion and transportation and (2) deposition zones.

Characterization of Sediments for Sustainable Development: State of the Art

“…The metal solubility is found to be strongly dependent on the redox potential (Eh) and pH of sediments, with cationic species likely to be less mobile under high pH conditions and vice-versa . It has been demonstrated that soil suspension (see Table 3) under continuous oxygen aeration for 21 days led to an increase in Eh, from 290 to 440 mV, and pH value, from 6.9 to 7.0, which is commensurate with the findings reported by Renjith and Chandramohanakumar (2007) that aerobic conditions influence the bio-availability of the elements in sediments, leading to an increase in DO from 163 to 270 mV. Incidentally, Wang et al (2001Wang et al ( , 2004 have demonstrated a strong correlation between the algal bloom in sediments based on their pH and DO values.…”

“…Physical characteristics of the sediments basically include (a) grain-size distribution characteristics (Horowitz and Elrick 1987;Chung et al 2002;Malandrino et al 2009;Grabowski et al 2011); (b) texture (Renjith and Chandramohanakumar 2007;Narayana et al 2008); (c) specific surface area (SSA) (Horowitz and Elrick 1987;Francisca et al 2005); and (d) specific gravity (G). The grain-size distribution (GSD) of the sediments can be obtained by conducting sieve analysis (American Society for Testing and Materials [ASTM] D 422-63 1994;Liu et al 2000;Chung et al 2002;Bianchini et al 2002;Kolay and Singh 2001a;Fö rster et al 2010) and Laser diffraction analysis (Bonnin et al 2005;Malandrino et al 2009;Rogers et al 2011).…”

“…Cohesive sediments are muddy and composed of clay-and silt-sized fractions (<63 mm) (Bianchini et al 2002;Bonnin et al 2005), whereas non-cohesive sediments are coarser, tend not to adhere to each other, and are primarily composed of sand-and gravel-sized fractions (>63 mm) (Bianchini et al 2002;Bonnin et al 2005). It has been reported in the literature that the texture of sediments varies from one water body to another, mainly because of their hydrodynamics, which plays a significant role in the physico-chemical processes as well as the diversity of the benthic species (Badarudeen et al 1996;Renjith and Chandramohanakumar 2007).…”

“…Quantification of the variation in this ratio within sediments has aided in determining temporal and spatial variations in organic matter (Rubio et al 2003). The organic matter of sediments having C=N < 17 is considered to be a high-energy carbon source for benthic 452 S. Sharma & D. N. Singh organisms (Renjith and Chandramohanakumar 2007). However, with increasing depth, the value of C=N decreases, which can be attributed to the lack of organic carbon.…”

“…Researchers since the early days were attracted to the presence of heavy metals in sediments due to their toxicity and bio-availability. These heavy metals have the potential to remobilize under altered environmental conditions, like a change in pH or amount of OM content (Renjith and Chandramohanakumar 2007;Kumar et al 2012). These pollutants can be either biodegradable or non-biodegradable in nature and are hence termed as xenobiotic compounds, existing mainly due to anthropogenic activities (Yang and Rose 2003;Tabrez and Ahmad 2010); they are usually present in higher concentrations than the permissible limits (NOAA 1999;USEPA 1998).…”