Seasonal variations in physico-chemical characteristics of water, sediment and soil texture in arid zone mangroves of Kachchh-Gujarat

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1 Journal of Environmental Biology September 8, 9() 7-7 (8) Triveni Enterprises, Lucknow (India) For personal use only Free paper downloaded from: www. jeb.co.in Commercial distribution of this copy is illegal Seasonal variations in physico-chemical characteristics of water, sediment and soil texture in arid zone mangroves of Kachchh-Gujarat A. Saravanakumar, M. Rajkumar*, J. Sesh Serebiah and G.A. Thivakaran Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai - 68, India Gujarat Institute of Desert Ecology, Bhuj - 7, India (Received: July 8, 6; Revised received: April, 7; Accepted: June 8, 7) Abstract: The present study was carried out to determine the physicochemical characteristics of water and sediment and the textural aspects of sediments in western mangroves of Kachchh-Gujarat, west coast of India, for a period of two years during Surface water and sediment temperatures varied from 7 o C to 7 o C and from 8. o C to 7 o C respectively. Tidal amplitude varied from.m to.78 m. Salinity varied from. to and the ph in water and sediment ranged between 7. and 8.9 and 6.9 and 8. respectively. Variation in dissolved oxygen content was from. to.8 ml l -. Concentrations of nutrients viz. nitrate (. to 7.6 µm), nitrite (. to.87µm), phosphate (. to. µm) and reactive silicate (. to 9. µm) also varied independently. Total organic carbon varied from.9% to.6% and the total inorganic phosphorus ranged between. mg g - and.97 mg g -. Total nitrogen varied from. mg g - to.9 mg g -. Sediment textures ranges in terms of % of sand, clay and silt were:.6-9.; and respectively in all the stations. The nature of soil texture is characterized by the abundance of silty loam, silty clay and silty clay loam. Kew words: Physicochemical characteristics, Water, Sediment, Soil texture, Nutrients, Mangroves, Gulf of Kachchh, Gujarat PDF of full length paper is available with author (*arunachalashivamdr@yahoo.com) Introduction Mangrove ecosystem acts as a buffer between near shore and lagoonal or estuarine environments with regard to the influence of freshwater discharge and salinity regime (Ramanathan, 997). The study of mangrove regions is necessary as they are highly productive and play an important role as breeding and nursery grounds for many commercially important fishes especially shrimps (Kathiresan and Bingham, ). Distribution of nutrients determines the fertility potential of a water mass (Panda et al., 989; Bragadeeswaran et al., 7). The regular and periodic changes in the climate synchronized with season are ultimately reflected in the environmental parameters also, which in turn have a direct or indirect influence over the planktonic population. The seasonal distribution, abiotic and biotic processes affect the nutrient cycle of different coastal environments (Choudhury and Panigrahy, 99). The magnitude and periodicity of forces such as tides, nutrients, hydro-period and stresses such as cyclones, drought, salt accumulation and frost may largely determine the energy signature in mangrove realm and the floral and faunal composition (GUIDE, ). Good quality of water resources depends on a large number of physicochemical parameters and the magnitude and source of any pollution load and to assess that monitoring of these parameters is essential (Reddi et al., 99). Assessment of water resource quality of any region is an important aspect of developmental activities of the region, because rivers, lakes and man made reservoirs are used for water supply to domestic, industrial, agricultural and fish culture (Jakher and Rawat, ). Fertility and healthiness of mangrove environment is reflected in productivity of phytoplankton and zooplankton as primary and secondary producers. They are the key players in controlling food webs in mangrove waters. Larval retention and high productivity in mangrove-lined estuaries have been attributed to the abundant food supply in comparison to adjacent marine areas (Robertson et al., 99; Robertson and Blabber, 99). Organic materials derived from decaying mangrove leaves are used as primary food source in sustaining larval and juvenile stocks. Influence of physical, chemical and biological variables on planktonic communities in mangrove waters are more pronounced than the nearshore coastal environment, resulting in seasonal changes of planktonic species composition and densities (Kannan and Vasantha, 99). However, such studies have not been attempted in the Kachchh coast of Gujarat and only little information is available on the physico-chemical aspects of the Gulf of Kachchh (Paulinose et al., 998). Although a number of authors have studied the physical and chemical characteristics of some Indian estuaries and mangroves (Mishra et al., 99; Satpathy, 996; Das et al., 997; Padma and Periakali, 999; Govindasamy et al., ; Rajesh et al., ; Rajasegar, ; Rajasekar et al., ; Sridhar et al., 6; Ajithkumar et al., 6; Anilakumary et al., 7; Asha and Diwakar, 7). Hence, the present investigation attempted to record some crucial physio-chemical variables of the mangrove milieu of western Kachchh and adjacent areas. Materials and Methods The site selection was based on their proximity to open coast and the level of anthropogenic pressure. The three selected sites are Site Jakhau Babber Creek (Lat N o 9 ; Long E 68 o 6 8 ), Site Sangi Kharo Creek (Lat o 7' 6. N; Long 68 o ' - E) and Site Medi Sinthodi Creek (Lat N o 7.8, Long E; 68 o 9.) (Fig. ) and are with - km distances Journal of Environmental Biology September, 8

2 76 Saravanakumar et al. Pakistan Fig. : Map showing the study area Kachchh District - Gujarat between each other. Seasonal collections were made to record the physico-chemical characteristics of the western mangroves of Kachchh. Rainfall data was obtained from meteorological Department of Bhuj, Kachchh, Gujarat, India. The data thus collected were grouped to represent different seasons of a calendar year viz., winter (November-February), summer (March-June) and Monsoon (July-October). Surface water and sediment samples were collected every month for a period of two years from January 999 to December in three different mangrove sites. Field data like temperature, salinity, dissolved oxygen, ph and other nutrients were collected during morning to noon. For the analysis of nutrients, surface water samples were collected in clean polypropylene/glass containers and kept in an ice box and transported immediately to the laboratory. Sediment samples were collected using a Peterson grab (size.8 m ). The water and sediment temperature were measured using standard mercury bulb thermometer of. o C accuracy. ph was measured by a calibrated ph pen (ph ep- model). Soil ph was determined by adopting the method of Jackson (98). Salinity was estimated with the help of a hand refractometer (Atago, Japan). Dissolved oxygen was estimated by the modified Winkler s method and inorganic nutrients were measured by adopting standard methods (Strickland and Parsons, 97). A total of samples were analysed for each station. Total organic carbon (TOC), and total phosphorus India content of sediment samples were estimated by the methods of El Wakeel and Riley (96) and Rochford (9). The percentage composition of sand, silt and clay in the sediment samples were determined by the combined sieving and pipette method of Krumbein and Pettijohn (98). Simple correlation (r) was made for statistical interpretation of the physico-chemical characteristics and two-way analysis of variance (ANOVA) was employed to find out variations in all hydrographic parameters between stations and seasons. Results and Discussion The total rainfall received was 67 mm during the first year 999 and 7 mm during second year (Fig. ). Comparatively, rainfall rate was higher during the first year than in the second year. Most of the rainfall occurred as downpour, confined to -9 days of the year during the months of July and August. Rainfall is the most important cyclic phenomenon in tropical countries as it brings important changes in the hydrographical characteristics of the marine and estuarine environments. In the present study, peak values of rainfall were recorded during the monsoon months of July and August. The rainfall in India is largely influenced by two monsoons viz., southwest monsoon on the west coast, northern and northeast India, and by the northeast monsoon on the southeast coast (Perumal, 99). In Gujarat, particularly in Kachchh district, the monsoon is preceded by hot dry weather during March - June. The rain sets in over most of Gujarat during late June to September, and October and November constitute the early winter period with no rain except in October (GUIDE, 999). The months of December, January and February were practically rainless. Kachchh district experiences typical Monsoon climate with rainy season confining to four months from the middle of June to September, when 9 to 98 percent of the annual rainfall occurs (GUIDE, ). The tidal amplitude in both the east and west coasts of India are influenced by tides. The tides in the study sites are mixed semi diurnal type with a large diurnal inequality and varying amplitude. Gujarat coast experiences very high tides perhaps the highest that occur anywhere along the Indian coasts (Gupta and Deshmukhe, ). However, in the study area of Kharo creek, maximum and minimum tidal amplitudes were.78 and. m respectively (Fig. ). Journal of Environmental Biology September, 8

3 Physico-chemical characteristics of water, sediment and soil texture in Gulf of Kachchh 77 Rainfall (mm) Fig. : Rainfall recorded during 999 to in the study area Tidal amplitude (m).... High tide Low tide Fig. : Seasonal variation in tidal amplitude during 999 to in the study area Salinity ( ) Fig. : Seasonal changes in salinity during 999 to at stations, and Temperature ( C) 7 6 Fig. : Seasonal changes in temperature during 999 to at stations, and Dissolved oxygen (ml/l) l - ) Fig. 6: Seasonal changes in dissolved oxygen during 999 to at stations, and The surface water temperature aried from 7 to 7 o C during winter and summer seasons. There was a steady increase in temperature from March to June, which peaked during May and low temperature of 7 o C was recorded during winter (Fig. ). All the stations showed similar trend with similar seasonal changes. Generally, surface water temperature is influenced by the intensity of solar radiation, evaporation, insolation, freshwater influx and cooling and mix up with ebb and flow from adjoining neritic waters ph Fig. 7: Seasonal changes in ph during 999 to at stations, and Nitrite (µm) Fig. 8: Seasonal changes in nitrite during 999 to at stations, and Nitrate (µm) Fig. 9: Seasonal changes in nitrate during 999 to at stations, and Silicate (µm) Fig. : Seasonal changes in silicate during 999 to at stations, and Phosphate (µm).... Fig. : Seasonal changes in phosphate during 999 to at stations, and (Govindasamy et al., ). In the present study, summer peaks and monsoonal troughs in air and water temperature were noticed, as observed earlier by several workers in the west coast of India (Desai, 99; Arthur, ). Statistical analysis showed a positive correlation between air and surface water temperature for all the three stations. Salinity varied from to during monsoon and summer seasons (Fig. ). The minimum salinity was presumably due to the Journal of Environmental Biology September, 8

4 78 Saravanakumar et al. Soil temperature ( o C) SSeries Series Series Fig. : Seasonal changes in soil temperature during 999 to at stations, and Soil ph 8 6 Fig. : Seasonal changes in soil ph during 999 to at stations, and Organic carbon (%) Fig. : Seasonal changes in organic carbon during 999 to at stations, and Total phosphorous (mg g - ) Fig. : Seasonal changes in total phosphorous during 999 to at station, and influence of heavy rainfall and the resultant river run-off, which is a regular annual event in this area during monsoon. Salinity acts as a limiting factor in the distribution of living organisms, and its variation caused by dilution and evaporation is most likely to influence the fauna in the intertidal zone (Gibson, 98). Generally, changes in salinity of brackishwater habitats such as estuaries, backwaters and mangrove are due to influx of freshwater from land run off, caused by monsoon or by tidal variations. This is further evidenced by the negative correlation (r= -. at Station, r=-. at Station and r=-. at Station ) between salinity and rainfall. Salinity showed a significant positive correlation with temperature. In the present study, salinity in all the stations was high during summer season and low during the monsoon season. Higher values during summer may be attributed to high degree of evaporation and also due to dominance of neritic water from open sea (Senthilkumar et al., Total nitrogen (mg g - ) Fig. 6: Seasonal changes in total nitrogen during 999 to at stations, and Sediment texture (%) 8 6 Sand Clay Silt Fig. 7: Monthly variations in sediment texture in Station I during 999 to Sediment texture (%) 8 6 Sand Clay Silt Fig. 8: Monthly variations in sediment texture in Station II during 999 to Sediment texture (%) 8 6 Sand Clay Silt Fig. 9: Monthly variations in sediment texture in Station III during 999 to ). On the otherhand during the monsoon season, rainfall and the consequent freshwater inflow from the land in turn would have moderately reduced the salinity. Thus the variations in salinity in the study sites were mainly influenced by the rainfall and entry of freshwater as reported earlier for Gulf of Kachchh by Vijayalaksmi et al. (99) and for Godavari estuary by Sai Sastry and Chandramohan (99). The dissolved oxygen values were high (.8 ml l - ) during the monsoon (August) and low (. ml l - ) during the summer (May) (Fig. 6). Season-wise observation of dissolved oxygen showed an inverse trend against temperature and salinity. It is well known that temperature and salinity affect dissolution of oxygen in seawater (Vijayakumar et al., ). In the present investigation, higher values of dissolved oxygen were recorded during monsoon Journal of Environmental Biology September, 8

5 Physico-chemical characteristics of water, sediment and soil texture in Gulf of Kachchh 79 Standard Trigon Station II Fig. : Variations in soil texture in the study areas months in all the stations. Relatively lower values found during winter could be mainly due to reduced agitation and turbulence of the coastal and estuarine waters. Higher dissolved oxygen concentration observed during the monsoon season might be due to the cumulative effect of higher wind velocity coupled with heavy rainfall and the resultant freshwater mixing. Das et al. (997) and Saravanakumar et al. (7) attributed seasonal variation of dissolved oxygen mainly to freshwater influx and ferruginous impact of sediments. Further, significant inverse relationship between rainfall and nutrients indicated that freshwater input constituted the main source of nutrients in the mangroves. Two way analysis of variance on the results showed that there was no significant variation between stations and seasons. The ph varied from 7. to 8.9 during monsoon and summer season (Fig. 7). Hydrogen ion concentration (ph) in surface waters remained alkaline throughout the study period in all the stations with the maximum values occurring in the summer and winter seasons and minimum values occurring in the monsoon season. Generally, fluctuations in ph values during different seasons of the year is attributed to factors like removal of CO by photosynthesis through bicarbonate degradation, dilution of seawater by freshwater influx, Station I Station III reduction of salinity and temperature and decomposition of organic matter (Upadhyay, 988 ; Rajasegar, ). Statistical analysis also revealed that salinity had highly significant negative correlation with rainfall. Nutrients are considered as one of the most important parameters in the mangrove environment influencing growth, reproduction and metabolic activities of biotic components. Distribution of nutrients is mainly based on season, tidal conditions and freshwater flow from land. In the present study, the inorganic phosphate ranged from. to. µg l - in all the three stations during 999 to (Fig. ). High concentration of inorganic phosphate observed during monsoon season might be possibly due to intrusion of upwelling seawater into the creek, which increased the level of phosphate (Nair et al.,98). Further, regeneration and release of total phosphorus from bottom mud into the water column by turbulence and mixing also contributed to the higher values during monsoon (Chandran and Ramamoorthy, 98). In the present study, influx of nutrients from hinterland appears to be negligible, apparently due to poor rainfall and numerous water harvesting structures in Kachchh, which stop even meager land runoff. Hence, the increase of nutrients Journal of Environmental Biology September, 8

6 7 Saravanakumar et al. during monsoon might be due to influx from neritic waters as inferred by Mishra et al. (99) and Ragothaman and Jaiswal (99). Nitrite and nitrate values varied from. to.87 µm and. to 7.6 µm, respectively. In general the nitrite and nitrate values were high during monsoon and low during summer seasons (Fig. 8, 9). The highest phosphate and nitrate values recorded during monsoon season may be attributed to heavy rainfall, land runoff, its autochthonous origin and weathering of rocks liberating soluble alkali metal phosphates, the bulk of which are carried into the mangrove waters (Das et al., 997 ; Gowda et al., ). Another possible way of nitrate entry is through oxidation of ammonia form of nitrogen to nitrite and then consequently to nitrate (Rajasegar, ). The low values recorded during non-monsoon period may be due to utilization by phytoplankton as evidenced by high photosynthetic activity and the dominance of neritic seawater having negligible amount of nitrate (Das et al., 997). The higher value of nitrite recorded during monsoon season may be due to various reasons including variation in phytoplankton excretion, oxidation of ammonia and reduction of nitrate and by recycling of nitrogen and bacterial decomposition of planktonic detritus present in the environment (Govindasamy et al., ) and also due to denitrification and airsea interaction exchange of chemicals (Mathew and Pillai, 99). The ranges of silicate concentration were. to 9. µm and in all the three stations (Fig. ). The silicate content was higher than that of the other nutrients (NO, NO and PO ), and the recorded high monsoon values may be due to heavy influx of freshwater derived from land drainage carrying silicate leached out from rocks and also from bottom sediments exchanging with overlying water due to the turbulent nature of water in the mangrove environment. The low concentration during summer season may be attributed to uptake of silicate by phytoplankton for their biological activity (Mishra et al., 99). A two way ANOVA on the results showed significant variations between stations (p<.) and seasons (p<.). The soil temperature ranged from 8. o C to 7 o C with the maximum during summer and the minimum during winter and monsoon similar to water temperature (Fig. ). Oceans large thermal inertia causes temperature variation due to absorption of solar energy and subsequent release to the atmosphere (Varadhachari et al., 987). During monsoon season, low value of temperature would be due to freshwater flow as stated by Varadhachari et al. (987). Soil temperature during winter decreased in tune with the atmospheric temperature. Thus, soil temperature positively correlated with water temperature and soil ph negatively correlated with rainfall, nitrate and phosphate in water. ph in sediment ranged between 6.9 and 8. (Fig. ). The sediment ph was high in summer and low during monsoon possibly due to redox changes in the sediments and water column apart from the influence of freshwater (Ramanathan, 997). Mangrove soil is always alkaline as reported by various authors (Tam et al., 99 ; Tam and Wong, 998). The low value of ph indicating acidic condition recorded during monsoon months may be due to the oxidation of FeSO and FeS to H SO (Holmer et al., 99). In addition, soil acidity may have resulted also from decomposition of mangrove litter (Lacerda et al., 99). A two way ANOVA on the results showed significant differences in ph with seasons (p<.). Total organic carbon content varied from.9% to.6% (Fig. ). The distribution of total organic carbon closely followed the distribution of sediment type i.e., sediment low in clay content was low in total organic carbon and as the clay content increased, the total organic carbon content also increased which as reported by Reddy and Hariharan (986). In the present study the total organic carbon value was low during monsoon and high during winter season. An abundant supply of organic matter in the water column, relatively rapid rate of accumulation of fine grained inorganic matter and low O content of the water immediately above the bottom sediments would favor high organic matter in the bottom sediments (Sverdrup et al., 9). A two way ANOVA on the results showed significant differences between the stations (p<.) and seasons (p<.). The organic carbon in lake sediments is derived from primary production within the aquatic ecosystem (autochthonous sources) and also from terrestrial biota (allochthonous sources) by transport of leached and eroded material into the lake (Likens, 97). In the present study high organic carbon content was recorded during winter in post monsoon. Normally, the overlying waters in the mangrove ecosystem have high organic carbon content compared to estuarine and coastal waters. Therefore, the high organic carbon in the mangrove waters may be due to the mangrove and terrestrial detritus present in the suspended matter (Jagtap, 987). In addition to this an increase in organic matter content in the sediments may be due to the fine nature of sediments (Clayey and silt sediments) and high rate of sedimentation (Raghunath and Sreedhara Murthy, 996) and decomposition of mangrove foliage and other vegetative remains in the sediments (Ramanathan, 997). Total nitrogen varied from. mg g - to.9 mg g - (Fig. 6). In the present study, total nitrogen in sediment was high during winter and summer due to the oxidation of dead plant organic matter, which has settled on the top layer. The lower value of total nitrogen during monsoon season may be ascribed to low level of organic matter. In Swartkops estuary in Africa, Dye (978) observed high nitrogen content in finer substrate and suggested that it was probably due to trapping of detritus by finer particles, resulting in an increase in bacterial population which may also be a reason for the high level of nitrogen encountered in the present study. Reddy and Hariharan (986) attributed the high values of nitrogen to release from the decay of a large number of phytoplankton in Netravathi Gurupur estuary. The sediment detritus may be a rich source of nitrogen as shown by lower C/N ratios and regular ingestion by crabs. Fragmenting leaves by crabs may be elevating the nutritional quality of the substrate detritus (Skov and Hartnoll, ). The low values of total nitrogen observed during monsoon season may be ascribed to the low level of organic matter during monsoon season along with Journal of Environmental Biology September, 8

7 Physico-chemical characteristics of water, sediment and soil texture in Gulf of Kachchh 7 high level of sand during the monsoon season. A test of two way ANOVA on the results showed significant variations between the stations (p<.) and seasons (p<.). Total inorganic phosphorus ranged between. mg g - and.97 mg g - (Fig. ). The capacity of sediment to retain or release phosphorus is one of the important factors, which influence the concentration of inorganic/organic phosphorus in the overlying waters. In the present study, high value of inorganic phosphorus was recorded during winter and low values during summer. The high values observed may be due to dead organic matter from the top layer and low values may be related to removal of top layer of sediments by heavy floods. A test of two way ANOVA showed significant differences between the stations (p<.) and seasons (p<.). Sediment texture in terms of sand, clay and silt (%) were:.6-9.; and in all the stations (Fig. 7, 8 and 9). The nature of soil textures was characterized by the abundance of silty loam, silty clay and silty clay loam (Fig. ). Soil texture revealed dominance of silty loam and silty clay in all the stations in all the months with no much variation among them. This consistently high silty loam values may be attributed to the winnowing activity of sediment transport system. Absence of perennial flow of freshwater in Kachchh district along with lack of wave induced sand transport from open sea also may be the reason for this uniformity in soil texture. The present baseline information of the physico-chemical characteristics of water, sediment and soil texture would form an useful tool for further ecological assessment and monitoring of these coastal ecosystems of western mangroves of Kachchh. Acknowledgments The authors would like to thank Gujarat State Forest Department for giving permission to carry out this study. We are grateful to Director of Gujarat Institute of Desert Ecology and Prof. T. 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