Macronutrients along the sediment profile in a subtropical monsoonal wetland in India |
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Authors: | B Anjan Kumar Prusty Rachna Chandra P A Azeez |
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Institution: | 1.Environmental Impact Assessment Division,Sálim Ali Centre for Ornithology and Natural History (SACON),Coimbatore,India;2.Gujarat Institute of Desert Ecology (GUIDE),Bhuj,India |
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Abstract: | We analyzed 144 composite sediment samples to appraise the seasonal variation in select major nutrients in the bed sediments
of Keoladeo National Park (KNP), Bharatpur, a subtropical monsoonal wetland system in India, from September 2003 to July 2005.
Total organic carbon (TOC, %) and total nitrogen (TN, %) in the sediments were in the range of 0.61–14.01 and 0.26–0.68, respectively.
The total available phosphorus (TAP, %) and total available sulphur (TAS, %) ranged from 0.001 to 0.034 and from 0.001 to
0.012, respectively. While C:N ratio was within a narrow range (1.38–13.56), C:P ratios varied widely (18.81–5995.83). Similar
wide variations were seen in C:S ratio (352.2–3929.5) as well as N:P ratio (9.34–56.6). All the parameters except TAS showed
depth-wise declines along the sediment profile. In contrast, the pH gradually increased along the depth. Most of the parameters
significantly varied across months and sediment layers. A positive correlation (Two-tailed, P < 0.05) existed between TOC and all the nutrients and their ratios except TAP and N:P. TAP was positively correlated with
electrical conductivity (EC) and water soluble substances (WSS), suggesting the contribution of phosphate to the dissolved
salts. During certain months elements such as P were comparatively low in concentration, in spite of input through agricultural
runoff and large scale bird droppings, probably due to its higher uptake by macrophytes growing luxuriantly in the wetland.
Organic materials appear to decay at a faster rate during the drier periods as indicated by the fall in TOC and the rise in
TN. Principal Component Analysis (PCA) shows that three components contributed to 68.9% of the total variance. The first component
that accounted for 26.4% of the total variance reflects the importance of total organic carbon in wetland sediments and the
ratio of carbon to other nutrients. The second one accounting for 23.7% of the variance correlated with water soluble substances
(EC, WSS and TAS). The third component accounting for 18.7% of the variance reflects the influence of two major nutrients,
nitrogen and phosphorus, in sediments those affect the biogeochemical processes in wetlands. Thus, the three PCA components
can be characterized as ‘sediment organic carbon and its ratios with other elements’, ‘WSS, TAS’ and ‘the limiting nutrients
such as N and P’, respectively. |
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