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. el:osystems (Weizel 1983). Of the four gross compartments into. aquatic...


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Chapter 3 SEASONAL & TIDAL VARIATION OF ORGANIC COMPOUNDS & NUTRIENTS 3.1 Particulate organic carbon 3.2 Chlorophyll 3.3 Nutrients 3.4 Protein Nitrate Nitrite Phosphate 3.5 Carbohydrates
Chapter 3 SEASONAL & TIDAL VARIATION OF ORGANIC COMPOUNDS & NUTRIENTS 3.1 Particulate organic carbon 3.2 Chlorophyll 3.3 Nutrients 3.4 Protein Nitrate Nitrite Phosphate 3.5 Carbohydrates 3.(, Tannin & 1. Ignm. 3.7 Tidal variations Chapter 3 Coastal waters throughout the world are being affected b anthropogenic inputs of nutrient elements, of organic matter that underg ) Oei bacterial degradation consuming dissolved oxygen and releasing nutrients and of potentially toxic trace metals. These inputs are related directly ~ increases in human population density, agriculture and industri~ development in coastal regions. Considering the global carbon cycle and the major role played by the ocean, it seems that the coastal zone must be considered as a specially important area (Wollast 1991). Thougn representing only a small surface of marine realm (about 8%), it is the most productive area of the ocean (more than 25% of total marine production. Nienhuis, 1981). The cycling and ultimate sequesteration of organic matter in estuaries and coastal zone is controlled by different processes, among which microbiological ones play a key role with regard to production. degradation and mineralization of organic matter (Hoch & Kirchman, 1993) The importance of dissolved and particulate organic detrital matter to the metabolism of aquatic ecosystems has not been fully explored (Boon et al 1982). Dissolved organic matter comprises most of the reduced carbon in aquatic ecosystems and provides energy and carbon sources for the metabolism of heterotrophic bacteria. It is known that humic substances dominate the dissolved organic matter of the stream water and it has been suggested that humic substances play an important role in ecosystem metabolism. Saline marsh contained 2.2 and 4.2 times more organic matter and mineral matter than inactive fresh marsh (Nyman et ai, 1990). The high productivity of the coastal zone is mainly related to the influence of the river inputs, enriching the coastal waters in nutrients and organic matter, and to the close coupling between the water and sedime~ assuring a rapid reutilization of regenerated eleml ts. The type of flora, in the water shed. the distribution and abundance of wetland and littoral plants, and the pathways of release of detrital organic material into the water body have. different effects on overall rates of eutrophication and development oj 43 ----. el:osystems (Weizel 1983). Of the four gross compartments into Seasonal & Tidal Variation of Organic Compounds & Nutrients aquatic..... h marine matter may be categonzed (morgamc/orgamc, particulate/ WhlC 1 d. c:.. h 1. Ived) the disso ve orgamc lractlon remams t e east well understood. dlsso ' tudies argued the case for major flows of carbon, nitrogen and Eary I S hosphate through the dissolved organic pool. Four main groups of organic ~ompounds formed by the decomposition of organic matter are; (a) Nitrogen -free organic matter, (b) Nitrogenous substances, (c) Fatlike substances, (d) complex substances resulting from the groups (a) & (c) 3.1 Particulate Organic Carbon The particulate matter carried by the river can be divided into four parts; detrital inorganic matter, non- algal organic matter, phyto planktonic organic material and autochtonous calcite particles. Organic carbon generally falls under two categories. It is either in a particulate ( 0.45 )lm) or in a dissolved state «0.45 )lm). The size of the organic carbon depends on a number of factors and the quantities of each usually depend on the stage of decomposition. The particulate and dissolved organic carbon together constitute a minor fraction of total organic carbon of sea water, yet they are very important components in the transformation of carbon. Since the majority of mangrove production goes into the formation of new leaves and since mangroves lose their leaves on a regular or event-driven (high winds, etc.) basis, leaf litter is considered to be one of the biggest losses in mangroves. Once these leaves fall, they begin to be degraded by a number of bacterial, fungal, and meiofaunal organisms. Particulate organic carbon occurs in degradable and refractory forms, the latter is mainly constituted by carbon present in humic material. Further Poe can be of living or non living (detrital) nature where the latter fraction may contain the refractory subst~ces that result either from recycled marine m tt a er or from terrestrial sourc~s. 44 Chapter 3 Table 3.1 Seasonal variation of Particulate Organic Carbon (mg [I) Stations Pre Mon IH H 3.34 ll L Mon Post-man Ell Pre-Mon Mon o Post-mon IH 2H IL 2L J Stations Fig 3.1 Seasolfal variation of particulate organi,: carbolf (mgr l ) Monthly data are given in the appendix and seasonal variation is depict~ in the Fig 3.1. poe values of the forests varied from 5.75 mg I 1 to 27.89rng 1 between the forests 5 and 1 L.during pre monsoon. The concentration of po( was higher in all forests than in the canals during this season. But duri!1 ~ monsoon the concentration of the forests fluctuated between 1.96mg 1 - I - 37. ---.1 mong the forests 3 and 1 L. POC was less in the forest 3 than in the Seasonal & Tidal Variation of Organic Compounds & Nutrients Illg I a When stations 5 & 6 were compared, the forest 5 showed a high value cana 14. the canal 6. Among the forests the maximum amount of POC was than ll d. I.... ~ IH observ ed in the forest unng post-monsoon. n this season, all loft!sts, L 3 & 5 exhibited high values for POC than the canals. The values in the I, 1 forest were 9.23, 19.35, 3.5 & 3.47 mg l' respectively. Table 3. la Earlier reported values of poc (mg [1) No System Range Reference I. Bay of Bengal 0.84 x x 10-3 Sarojini et ai, Ross Sea 0.48 Gardner et ai, Arabian Sea Sardessai et ai, Amazon Basin 1-3 Jeffrey et ai, 1990 Analysis of data of POC shows that the observed concentration is very high when compared to the reported values (Table 3.1a). POC transport is to a large extent depend on the physical processes governing sediment dynamics. The erosion and deposition cycles can mobilize POC can be deduced from the concurrent patterns of the flux anomalies for POC and bulk suspended sediments (Meade et ai, 1985). During the temporary residence of sediment deposited on the flood plain, carbon new to the river could be added through local primary production with the enriched particles cycled back into the river through flooding and erosion The POC is potentially labile, non woody vascular plant debris. High salinity, the shallow and turbid nature of water around the ecosystems led to the accumulation of particulate organic carbon during pre-monsoon. Less dense plant debri s se t t I'd es more slowly than san, therefore concentrates. In SUSpension When the river velocity decreases. But in monsoon, the increased terr.. pes tnal runoff as well as plant remains in the plain contribute to the hike In QC Will . A summer increase of POC in coastal areas was reported by su I~rns (1995). Higher primary productivity due to increased convection stains h' h Ig er POC in coastal areas during monsoon. Sardessai et al (1999) Chapter 3 reported that the relatively higher POC values observed in Arabian during pre-monsoon could have been due to abundant bacterial populatio ~ n. 3.2 Chlorophyll Viewed from orbiting satellites earth is a green and blue plan e! Almost all of the pigmentation outside polar and desert areas is due t( plants. Regional events such as droughts, the onset of the rainy season o' autumn bring about marked changes in the coloration of vegetation. At thl' global level much of the greater contribution comes from one group 0: pigments- the chlorophyll. It has been estimated that each year, the toi4 chlorophyll production globally exceeds 10 9 tonnes 75% from terrestria plants and the remainder from aquatic organisms, largely marint phytoplankton. In order to grow the plants must be able to convert energ: from the sun into a useful form. Humans produce pigments in their skin tha: protect them from harmful effects of solar radiation; in contrast, exposure 0: plants to light stimulates them to produce pigments that absorb and utilizt energy. In higher plants, the final product of photosynthesis are sucrose, anc starch or fructose but in algae wide variety of sugar a1cohols and glucose polymers have been found as products of photosynthesis. There are three classes of photosynthetic pigments in photosynthetic organisms; the chlorophylls, the phycobilins and the carotenoids. The chlorophyll molecule consists of a porphyrin ring with a dense cloud 0: ITelectrons. They are actually cyclic tetrapyrroles. In the cyclic form, these tetrapyrroles are usually porphyrins. The chlorophylls have a charactersl ic pattern. The absorption of a photon of light promotes the molecule to aj: excited state. The long chain lipophilic terpenoid side group unique Il1 chlorophyll a and b may provide hydrophcoic bonding component~ foi association within the thylalkaloid membrane or with proteins. 47 ---- I J 2 Seasonal variation ojchlorophyll (Ile [I) Tab l. Stations Pre-Mon Mon IL L SeAsonal & Tidal Variation o/organic Compounds & Nutrients Post-mon [] Pre-Mm...'on o Post-mon 1H 2H 1l 2l 3 4 Stations 5 6 ;?ig 3.2 Seasonal variation of Chlorophyll (J.1g [I) Monthly variations of chloroph 'li a in the three mangrove systems andlheircon. nectmg ' cana I are given.. h d SI. In I e appen IX. easona vanatlons are given in F 3 2 a m. Ig.. The concentration of chlorophyll of the forests varied from ax. 1fnum of 11.6 ~Ig 1-1 in station IL 10 a minimum of J,1g I - 1 in 48 Chapter 3 station 5 during pre-monsoon. All forests were rich in chlorophyll than canals except 3. But in monsoon, canals exhibited higher values ~ chlorophyll than the forests except ll. Chlorophyll was high in the canalso r & 6 compared to the forests 3 & 4. In post -monsoon, the amount vari~ from 4.44 ~grl to 8.51 ~grl between the forests 5 & IH. During this seas on also, canals were chlorophyll rich than the forests except 1 L. According to Bianchi et al (1997) high POC: chlorophyll a ratio) «1463) during pre monsoon indicated that most of the chlorophyll Was degraded. These high ratios could not be from autochthonous water column production (phytoplankton). The predominantly low chlorophyll a concentrations observed were primarily by inputs of degraded vascular plan! detritus with minor contribution from periphyton and phytoplankton. During the high inflow periods, the high values observed could be due to phytoplankton. Even though the concentration of chlorophyll in these ecosystems is less when compared to the reported values, it is well within that in the Schedt estuary (Table 3.2a). Table 3.2a Earlier reported values o/chlorophyll (J,Lg (1) No System Range Reference l. Algae of Arabian Sea. 42mg m- 2 Rao et ai, Alton. Water. Saffolk UK Perkins et ai, Scheldt Estuary 1-93 Gons et ai, Georges Bank 4-5 Townsend et al Cochin Harbour Area Rasheed et al Coastal areas of Orissa Panigrahy et al Eastern Arabian sea Pillai et al Bay of Bengal 8-24 Subramaniam et al Nutrients Seasonal & Tidal Variation of Organic Compounds & Nutrients Most of the nitrogen in earth is present as molecular dinitrogen in the h ere The oceanic nitrogen reservoir is also dominated by N2 atmosp. I d by nitrate which comprises about 6% of sea water nitrogen. The folowe world ocean appears to be experiencing a net loss of Nitrogen. The magnitude of the input to the sea from rivers, biological fixation and recipitation accounts for about 70 % of the losses by denitrification plus ~urial. The nitrogen cycle involves electron shifts between the most oxidised form N03- and the most reduced NH/. Uptake by Nutrients are affected by a variety of processes in inter tidal sediments (Klump& Martens 1989). There are many bio physical disturbances that impact on inter tidal sediments. These are tides, waves, storms, runoff events and sediment movements which result from the above, bioturbation, bioirrigation and anthropogenic factors such as fishing and dredging. The disturbances occur over a wide range of time scales and influence processes over different space scales. But the net effect is to produce an environment that, although structured, is patchy and dynamic. The productivity of coastal waters was maintained by storing and regenerating nutrients on a seasonal basis allowing the development of significant fisheries. The main inputs of nutrients are now land derived due to the impact of human activities. Intertidal areas may now be acting as a buffer which, while maintaining the productivity of coastal waters, acts to ameliorate inputs of nutrients to the coastal waters. The main nutrients involved in this study were N0 2 -, N0 3 - and PO/. Their distributions and variations during different seasons is discussed below Nitrate Th', b IS IS the most oxidised form of N2. In order for mangrove forests to e both. n ' net exporters of particulate nitrogen to coastal ecosystems and Itrogen 'k -., ' ' SIn s WIthIn the estuaries, there must be SIgnIficant transfol111ations Chapter 3 within mangroves (Twilley et ai., 1986). Over the past decade, studies tidally borne fluxes of particulate and dissolved materials to and froin Of tropical mangrove system in northern Australia have indicated that nitrog~ is iargely recycled within the system (Boto & Wellington, 1988). Nitrogen was present in low concentrations in particulate materials (mainly intact mangrove plant detritus) which were exported from the system through tidal action. Hence, despite the considerable total quantities of particulate matter losses of nitrogen were relatively small, in the order of 3.7 g Nm -2y- 1, which is equivalent to 13% of average annual forest net primary production nitrogen requirements (Boto & Bunt, 1982). Concentrations of dissolved organic and inorganic forms of nitrogen in the mangrove and near-shore waters were also consistently low in this tidally dominated system,which receives virtually no fresh water or terrestrial influence. Information on rates of nitrogen fixation in mangrove forests is limited, especially estimates of the importance of this process on a whole- forest scale. Table 3.3 Seasonal variation of Nitrate (J.lg-at [1) Stations Pre-mon Mon Post-mon IH H L L - Sellsonal & Tidal Variation ojorgallic Compoullds &' Nutritmts 1H 2H ll 2L Stations Fig 3.3 Seasonal variation of Nitrate (JJg-af rl) Distribution of nitrate during different months are given in the appendix and the seasonal variations are depicted in Fig 3.3. Analysis of the seasonal distribution of the dissolved nitrate concentrations showed a hike in the monsoon season in all stations. Since this is the high inflow period, the source can be land run off. But the concentration was high in the forests than m the canals except in station 4. The values varied from t 1.86 ug-at/i to 38.68ug-atll among the forests. High concentration of nitrate was noted in stations 2H, 1 L & 2l during postmonsoon and the values were 51.91, 38.2 & 38.2ug-atll res~tive l y. Comparatively lower values were observed during pre-monsoon. Dunng this season also higher values wt're noted in forests except in station 4. ),j. ~ a~lmum Was noted in station 1 H during high tide and the minimum m talion 3. Th e va I ue ranged between 34.72ug-at I ' _ 3.44 ug-at I - Chapter 3 Table 3.3a Earlier reported values of Nitrate-N (J.1g- at (1) No. System Range Reference l. Kusheswarasthan Wetland Manish et ai, Kuttanad Wetlands Lizen mathews, Bay of Bengal 1-30 Subramaniam et ai, Veli mangroves George et ai, Cochin Backwaters Nair, Cochin Estuary Anirudhan, Nitrate concentrations in these mangroves are low when compared to the values reported in the Cochin backwaters. Nair (1990) reported 1-70 ug. at I -I in Cochin backwaters. Usually high values are expected in mangroves, but not observed. The main sources of nutrients in this area are the leaf litter and the tidal water. But nitrogen was present in low concentrations in particulate materials mainly intact mangrove plant detritus which were exported from the system through tidal action. Concentrations of dissolved organic and inorganic forms of nitrogen in the mangrove and near -shore waters were also consistently low in a tidally dominated mangrove ecosystem in the Hichinbrook island, Australia which receives virtually no fresh water or terrestrial influence (Boto & Willington!988). Although the previous studies of this forest have strongly indicated that nitrogen supply is growth limiting, years of observation of the system have given no indication of any long term, continuous degradation of the nitrogen nutritional status, According to Simpson et al (1997) under low flow conditions the river discharge entering the estuary is exported by evapotranspiration through the mangrove system and that net flow discharge from the estuary is small. This is reflected in the premonsoon values. FI.x studies in mangrove stdim ents of Termino Lagoon, Mexico indicated that dissolved inorganic J' in tidal waters is trapped in the first centimeters of the sediment surface (Riveria' Monroy et al. 1995a). High inorganic N demand in decomposing leaf litter 3 may regulate an efficient recycling of nitrogen that could serve as 53 --- hanism Seasonal & Tidal Variation of Organic Compounds & Nutrients for nutrient conservatiol1 (Twilley et ai, 1986b; Twilley 1988; rnec Alongi et al.i992) Nitrite Nitrite is the intermediate form of nitrogen in the nitrogen cycle. Nitrite is highly reactive, so its amount will be generally low in the aquatic s stems. N02- may occur in waters as a result of biological decompositions :r proteinaceous material and is an index of organic pollution. In oxygen poor conditions, autotrophic organisms are able to take oxygen from the reduction ofn03- to N02-. Table 3.4 Seasonal variation of Nitrite (J,J.g-at 1-1) Stations Pre-Mon Mon Post-moo IH H ll L Fig 3.4 shows the seasonal variation of this species and the table comprising monthly data is given in the appendix. Seasonal variation showed a maximum peak in the monsoon in all stations. Maximum concentration of nitrite was observed in all forests during all seasons except In station 4 where high amount was observed in the canal. During low tide, the concentration was high in both forest and the canal. The value varied be~een 0.97 ug-at rlin station 3 and 22.1 Jlg-at rl in station ll. This vanation observed may be due to river runoff. Abnormal high values were observed '..... In station I L & 2L. Not much VarIatIOns are noted during prernons d. -1 oon an post monsoon. The values varied between 0.75Jlg-at I - ~C~ha~p~tn~3~ 1.60J.1g-at rl among the forests during postrnonsoon and between O.94ug. ill rl ug-at r1during pee-monsoon. C Pro-M on. Mon o Post-man IH 2H IL 2L 3 Stations Fig 3.4 Seasonal variatioll of Nitrite {M-at ( I) Table 3. 4a Earlier reported values of NO] (JJg_alr l ) No System Range Reft!rence I. Bay of Bengal Sarojini et ai, Kuttanad Wetlands Lizen mathews, Kayamkulam Padma, Cochin Backwaters Nair et ai, Cochir, Estuary Anirudhan, Earlier reported values are giv.. n in the Table 3.4a. ComparativelY high values were observed in stations 11 & 2L.Thomas et al ( ) hypothesized that high nitrate and nitrite values at low tide are caused by nitrification within the tidal water or tidal creek sediments. The shall O \\' 55 Seasonal & Tidal Variation of Organic Compounds & Nutrients ---C ter ehara, conditions favourable. for anaerobic diagensis contributed to the. ase in the concentration at 1 L & 2L. mere Phosphate Phosphorus is an essential nutrient for the marine ecosystem. On eological time scales the bioavailability of dissolved phosphorus is thought ~o control biological productivity (TyrrelI 1999). Only a small fraction of articulate phosphorus produced in the euphotic zone is ultimately burried in the sediment, while the remainder is remobilized and reutilized by the marine ecosystem (Brocker and Peng 1982). Table
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