1. Studies on water quality, hydrographic and biodiversity at Visakhapatnam harbour and offshore Sundararajan. S, Rajaguru. S, Prince Jepa kumar, Karuppusamy, Ragumaran, Basant Kumar Jena National Institute of Ocean Technology, Ministry of Earth Sciences, Chennai
INTRODUCTION
Visakhapatnam harbour is part of the East Coast of India. It is well known for its mineral transport, ship building and other industrial cargo handling. The study area lies between ' E to ' E and 17040' N to 17043' N (Fig. 1). The Visakhapatnam harbour is protected by a high promontory known as Dolphin's nose hill on the south and Ross hill on the north of the entrance channel. The harbour consists of two parts, one is inner harbour and the other is outer harbour. The inner and outer harbour is connected through a long navigable channel. A fishing harbour is present adjunct to the outer harbour. Meghadrigedda reservoir channel enters the harbour through the central arm, which collects industrial and domestic effluents from the western areas of city. Domestic sewage from the northeastern township areas are discharged to the harbour through the south-lighter canal at the turning basin. The port activities relate to the oil refinery, fertilizer berths, Naval base, ore berths, cargo berths, coal, containers, dredging, etc. pollutes the water ecosystem. The present study deals with qualitative and quantitative level of anthropogenic pollutant and its impacts on ecosystem.
Table 3. Range of Physico-chemical characteristics of harbour and coastal waters in the study area
Table 2. Summary of Tidal Measurements
Parameters
Monsoon
Post- Monsoon
Pre-monsoon
Water Temperature (0 C)
Salilnity (ppt) pH
Total Suspended Solids (mg/L)
Dissolved Oxygen (mg/L)
Biochemical Oxygen Demand (mg/L)
AmmoniaNitrogen (mmol/L)
Nitrate Nitrogen (mmol/L)
3.6-54
Nitrite Nitrogen (mmol/L)
Total Nitrogen(mmol/L)
Inorganic Phosphate-P (mmol/L)
Total Phosphorous (mmol/L)
Chlorophyll-a ( mg/m3 )
0-4.85
Period of Study
Tidal variation (with reference to Chart Datum)
Monsoon-Phase I
1.7 m
0.08 m
0.84 m
Post-monsoon-Phase II
1.8 m
0.28 m
1.4 m
Pre-monsoon-Phase-III
1.27 m
0.04 m
0.8 m
METHODOLOGY
Water quality studies covered (physical, chemical and biological) for a period of three seasons. The tidal and current observations made using self recording automatic tide gauge and current meters. The studies were carried out during monsoon (July 1999), Post- monsoon (December 2000) and Pre-monsoon (April 2001) to obtain representative data during seasons. Previous data in that area reveals significant pollution levels in the port due to higher concentration of point source discharges. Given that the problems within the port area priority, it was decided to limit the sampling area within the port itself. Apart from the study on water quality, studies on the hydrodynamic characteristics of tides and currents were studied. Sampling stations were located to estimate the fate and transport of pollutants within the harbour area.
Tides and Currents
Three locations were selected for tide and current measurements, namely, between the south and east breakwaters, harbour channel and inner harbour. A WTS-I automatic tide gauges were deployed and the water level variation were recorded for every 10 minutes interval. The RCM-9 self recording current meters were deployed 3m from the surface to measure average speed and direction at 20 minute intervals.
Water quality
Sampling location details are provided in table 1. Station H1 was located in between the south and east break waters (that is entrance of harbour) to measure water quality, tide and current at the open boundary. Station H3 was chosen off Dolphin nose for water quality and current, serving as the other open boundary for this study. Other locations were selected to assess water quality impacts, fate and transport of pollutants in the study area.
The in-situ measurements of Water temperature, Salinity, Dissolved Oxygen and pH were carried out immediately in the onboard vessel. The water samples were collected for chemical analysis using Niskin water sampler, preserved at 4º C and transferred to laboratory for analysis. The Nutrients analysis was carried out using double beam Spectrophotometer within stipulated period. Phytoplankton and Zooplankton were collected using respective collection nets with flow meter from onboard ship, preserved and transferred to laboratory for further analysis. The benthic samples were collected using Van veen Grab sampler as per APHA .
Dissolved Oxygen (DO)
Dissolved oxygen in water depends on several factors, some of which are the salinity, temperature, reaeration, organic matter, productivity and the presence of pollutants. Lower DO values are indicating high BOD loads due to municipal and industrial wastewater discharge. During the pre-monsoon Study, high DO value of 10.6 mg/L recorded at H7. Highest Chlorophyll-a concentration (41.43 mg/m3) is detected at the same location for the same sampling run. This implies that the DO variations are also productivity related. Thus secondary treatment of municipal wastewaters may not resolve DO problems in the area.
Biochemical Oxygen Demand
Biological oxygen demand ranged from 1.1 mg/l to 10.2 mg/l during the study period. The lowest BOD values are recorded at coastal stations and the highest values are recorded at inner harbour stations during monsoon. Elevated levels in inner harbour station due to municipal wastewater discharges. BOD values have showed gradual decreasing trend from harbour stations to coastal stations. Subramaniyan et. al., (1999) also recorded high values and they concluded that phytoplankton bloom and land drainage responsible for high values of BOD.
Nutrients
Enhanced nutrient concentrations generally imply anthropogenic inputs, resulting in eutrophication with DO and nuisance problems. In general, nutrient concentrations in the seawater are very low, minor increases or decreases alter primary productivity. The concentration ranges of nutrients are shown in Table 3. Higher nutrient values in the inner harbour were recorded during all the seasons, indicating that the harbour area is polluted. Similar trends have been recorded in previous studies by Raman et a1., Satyanarayana et al., used quantitative techniques using PO4-P, NO3-N and NH4 to estimate eutrophication in Visakhapatnam harbour, with a decreasing trend towards coastal waters, culminating in mesotrophic conditions in the coastal environment.
Ammonia Nitrogen
The variations in Ammonia values are significant. Ammonia values are higher in the inner harbour locations in all the seasons when compared to the coastal stations (H1-H3). These high values indicate the presence of wastewater, which are likely to consume oxygen while being oxidized to nitrites and nitrates.
Nitrate Nitrogen
Among the three inorganic forms of Nitrogen, Nitrate Nitrogen is most abundant at all stations, as it is thermodynamically the most stable oxidation level of Nitrogen in the presence of Oxygen in seawater and would accumulate in the sediments if left unutilized by plankton or bacterial decomposition. Nitrate concentrations tend to be high at all stations during pre-monsoon and are indicative of the breakdown of municipal wastes from Ammonia to Nitrate. Highest concentration of mol/L recorded at H8 during pre-monsoon may be attributed to the release of fertilizer effluent during the time of sampling.
Nitrite Nitrogen
High concentration of Nitrite Nitrogen was recorded during post-monsoon period along all the locations. During pre-monsoon, maximum concentrations (14.7mol/L) are recorded at H8 showing the transition product from Ammonia to Nitrate.
Inorganic Phosphate Phosphorous (IRP)
In general, IRP concentrations are higher during the monsoon and low during the post-monsoon, showing minimal variations. However, the maximum concentration 162 mol/L at H8 during pre-monsoon is significant, following the trend of Nitrates. The higher IRP concentrations are attributed to the release of fertilizers effluent during the time of sampling. Similar values of IRP (173 mol/L) was recorded by Satyanarayana et. al., in 1992 in inner harbour location.
Total Nitrogen & Total Phosphorous
Higher values of Total Nitrogen were recorded during monsoon and post-monsoon seasons. Similar trends were shown in Total Phosphorous values.
Table 1. Water quality sampling locations
stations
Position
Site description
Latitude (N)
Longitude(E)
H 1
17°41'63"
83°18'41.2"
Between south and east breakwaters (harbour entrance)
H 2
17°41'7.3"
83°18'18.4"
Centre of outer harbour
H 3
17°40'43.5"
83°17'55.9"
Off Dolphin Nose
H 4
17°41'16.1"
83°17'12.5"
In between navigational channel
H 5
17°41'30.3"
83°16'54.2"
Turning basin
H 6
17°41'25.2"
83°17'5.2"
South lighter channel
H 7
17°41'36"
83°16'25"
North western arm
H 8
17°42'23"
83°16'16. I"
Western arm
H 9
17°42'14.7"
83°17'00.2"
Northern arm Outfall of industries
Fig. 1. Vishakhapatnam port and study area
RESULTS AND DISCUSSIONS
HYDRODYNAMICS
Tide
The variation of tide with respect to chart datum at Visakhapatnam harbour for the three seasons of study are presented in Table 2
Current
Variation of current speed and direction at all stations during three phases of study are between cm/s during monsoon, 0-18 cm/s during post-monsoon and 0-20 cm/s during Pre-monsoon.Variation of current direction at three stations was compared with the predicted tide from the Indian Tide Table during phase I Study. At harbour entrance (surface) there was no relationship between variations of current direction with tide. The variation in water current shows that water moves towards east and some times towards west. However, the net water flow towards east shows that water is discharging from the harbour to open sea which is expected. The predominant current direction is north east, indicating that water flows into the outer harbour from the open sea.
WATER QUALITY
Table 3. shows season wise ranges of all the physico-chemical characteristics of the coastal waters during the three phases of the Study.
Water Temperature
Temperature affects the kinetics of DO, photosynthesis, metabolic processes and other chemical and physical processes and thus controls water quality characteristics. The lowest temperature values were recorded during the post-monsoon (Table 3). Seasonal variations of 1 to 30 C are observed amongst stations.
Salinity
During monsoon, salinity at the inner harbour was low, while the inner harbour salinity in the pre-monsoon was highest (36 ppt). There is a distinct influence of freshwater in the harbour during monsoons. The inner arms of the harbour, especially H8 & H9 have significantly lower salinities for the three seasons. These sections are influenced by low salinity domestic and industrial sewage discharge. pH
The pH in the Visakhapatnam harbour and coastal waters varied from 6.3 to 8.6. The minimum and maximum values of pH for three seasons are shown in the table 3. A lowest value of pH (6.31) was recorded at northwestern arm station (H8) during post-monsoon which may be due to the discharge of acidic industrial and domestic sewage effluents through "Meghadridda stream". Similar trends are noted by Satyanarayana et. al., 1992.
Total Suspended Solids (TSS)
Total Suspended Solids varied between 12.4 mg/L to 242 mg/l during the study period. The highest concentration of TSS is found at inner harbour station (H9) during the post-monsoon (242 mg/L). High values of TSS in inner harbour stations may be due to industrial effluents and municipal waste discharges. In general TSS values are showing decreasing trend from the harbour stations towards the coastal stations.
BIOLOGICAL CHARACTERISTICS
Chlorophyll-a
Photosynthetic organisms capture light energy by means of chlorophyll pigments to fix CO2 into organic compounds. Thus concentrations of chlorophyll pigments are surrogate measurements for estimating primary production. In general low Chlorophyll-a ranges are observed during the monsoon and post monsoon Study in all stations. Maximum concentration was recorded in the inner harbour stations H4-H9 during the pre-monsoon period (41.43 mg/m3). The data indicate the influence of anthropogenic nutrient inputs through wastewater discharges.
Phytoplankton
During the present study 67 species of phytoplankton were recorded comprising species of Diatoms, Dinoflagellates and Blue green algae. Forty six species were recorded during monsoon (Phase I) and 48 species during both post-monsoon (PhaseII) and pre-monsoon (Phase III).The range of phytoplankton counts in harbour waters were found to vary between 2825 and cells/L. In harbour waters, phytoplankton population was found to be higher during monsoon season (18800 to cells/L.) when compared to pre-monsoon ( cells/L) and post-monsoon ( cells/L). Skeletonema costatum, Thalassiosira decipens and Protoperidinium sp were the dominant species in study area. Higher values recorded as a result of major industrial effluents being discharged into the Northwestern arm (Mehadri Gedda), which also receives fresh water during monsoon. Distribution of Phytoplankton is comparatively higher in the inner harbour than outer harbour during pre monsoon and post monsoon. But during monsoon, the outer harbour recorded higher phytoplankton values than the inner harbour. Sketonema costatum was found to be widely distributed in all stations irrespective of season tide, as it is most tolerant in polluted waters. This higher plankton bloom counts have been recorded by many authors in Visakhapatnam harbour area for the last several years. Raman et a.,l 1986and 1989; Subrahrnanyam et. aI., 1989.
Zooplankton
Totally 26 groups of zooplankton have been recorded at Visakhapatnam waters. Copepods was found to be the dominant group during monsoon and post-monsoon studies and Oikopleura dominated in pre-monsoon. Break waters (H1) and South channel (H5) recorded maximum population density (3456 to 3,13,135 nos/l00 m3) in the monsoon. During post monsoon season the range of zooplankton varied between 155 nos/l00 m3 to nos/l00 m3. and in pre-monsoon it ranged between 362 to nos/l00 m3. Zooplankton density was higher in inner harbour compared to the outer harbour during pre-monsoon.
Macro Benthos
Benthic organisms are higher at pre-monsoon than other seasons in harbour waters. The benthic population ranges recorded during the three phases of Study are 25 to 375 nos/m2 during monsoon , 67 to 2066-nos/ m2 during post monsoon and 2 to 100-nos/m2 during pre-monsoon. Amongst the 12 groups of benthos recorded, polychaetes are dominant. The benthic organisms were higher at outer harbour than the inner harbour during monsoon and post-monsoon and higher in inner harbour than outer harbour during pre-monsoon in contrast to the plankton trends.
CONCLUSION
Studies were carried out to determine the tides, currents, water quality and biological characteristics during three seasons i.e., monsoon, post monsoon and pre-monsoon. The transport of water in Visakhapatnam harbour is influenced by tides, freshwater discharges from canals and industrial effluents. The net movement of water is towards the Ocean. From the studies, it can be concluded that the inner harbour is significantly polluted when compared to the outer harbour locations.
The pre-monsoon Study shows poor water quality. This is important as the WLA must be done when the water temperatures are the highest, freshwater/dilution flow is lowest and during neap tides. BOD values in the inner harbour are high indicating municipal loads. Eutrophication is the second most critical water quality issue and design of the treatment/disposal must ensure that nutrient balances are in control. The option to dispose treated effluents to the outer harbour or open coastal waters must be actively considered. Secondary treatment will not remove nitrates, implying that secondary treated wastewater discharge in the inner harbour is unlikely to reduce the eutrophication problems.
Low values of dissolved oxygen (DO) were measured at the inner harbour and the northern arm. Biological oxygen demand (BOD) value is also higher at the same location indicating influences of pollutant discharge. The primary sources are sewage from Visakhapatnam City and effluents from industries and a treatment plant on a northern arm.
Fig. 2. Population density of Zoo plankton during the monsoon
Fig. 3. Seasonal variation of benthos
REFERENCES
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