Evaluation of Coastal Waters Receiving Fish Processing Waste: Lota Bay as a Case Study

EVALUATION OF COASTAL WATERS RECEIVING FISH PROCESSINGWASTE: LOTA BAY AS A CASE STUDY

RAMÓN AHUMADA∗, ANNY RUDOLPH and SERGIO CONTRERASFacultad de Ciencias, Departamento de Química Ambiental, Universidad Católica de la Santísima

Concepción, Casilla 297, Concepción, Chile(∗ author for correspondence, e-mail: [email protected])

(Received 18 June 2002; accepted 20 December 2002)

Abstract. Liquid wastes from the fish meal and oil processing industries produce serious envir-onmental impacts in coastal embayments on the coasts of Chile and Peru. This article presents ananalysis of an environmental monitoring program at Lota Bay, a shallow coastal indentation in centralChile (37◦S) exposed to industrial fishing activity. The study of the environmental impact producedby waste effluents permitted making an evaluation of the bay’s capacity for seasonal recovery fromthis impact. Seasonal cruises were carried out during 1994 and in 1996, 1997, and 1998. Variablesanalyzed included salinity, temperature, dissolved oxygen, ammonium concentration and surfaceoil and grease. The hydrographic regime of Lota Bay follows a seasonal pattern, where, typical ofmost SE pacific embayments, waters from subsuperficial oxygen minimum zones moved into thebay. The percentages of dissolved oxygen were critical in the area of organic waste discharge. Theimpact of wastewater is related to the type and status of the fishery, including: (i) overloads of plantproduction lines, (ii) maintenance and cleaning of installations, and (iii) degree of shipboard fishingconservation. Major alterations were observed in summer, when the highest discharge of organicload occurred. In winter, an improvement in the re-aeration conditions reduced the impact. Remedialmeasures implemented beginning in 1997 arose from the monitoring program and had to be separatedinto two recovery factors including (a) internal management of plants and (b) treatment of planteffluents.

Keywords: Central Chile, dissolved oxygen, embayment, fisheries wastes, organic matter, waterquality

1. Introduction

Liquid industrial wastes arising from fish meal and fish oil processing industries arean environmental problem of consequence in the coastal zones of Chile and Peru(Ahumada and Rudolph, 1989; Pradenas and Rudolph, 1989; Arcos et al., 1994;Ahumada et al., 2000). The most important zones of fisheries landings in Chile arethe I and VIII Regions (Figure 1) where about 80% of the total national catch islanded (SERNAPESCA, 1996).

In the VIII Region fisheries landings are carried out at fishing ports in fourof the five bays present in the region, including Concepción Bay, San Vicente Bay,Coronel Bay, and Lota Bay (Table I). Based on this, coastal waters of these bays actin receiving washwater released in the landing of fish (in a ratio of three volumes

Environmental Monitoring and Assessment 90: 89–99, 2004.© 2004 Kluwer Academic Publishers. Printed in the Netherlands.

90 R. AHUMADA ET AL.

Figure 1. Lota Bay, Chile to show location and identification of sampling stations (numbered points)from the monitoring program carried out from 1994 to 1998.

TABLE I

Summary of fisheries activity in the VIII Region of Chile during the study period (datafrom SERNAPESCA Annual Statistics Reports 1994−1998)

Years Total fish landings Landings from Landings from Amount for fish

VIII Region, Chile industry fishery artesanal fishery meal and oil

(tons) (tons) (tons) (%)

1994 4,033,997 3,602,817 430,996 99.47

1995 3,785,580 3,560,767 224,683 91.03

1996 3,949,481 3,508,607 440,630 90.99

1997 3,302,580 2,967,914 334,107 87.63

1998 2,501,092 2,317,006 205,919 80.18

EVALUATION OF COASTAL WATERS RECEIVING FISH PROCESSING WASTE 91

of water per volume of fish landed), as well as the wastewater released from theindustrial processing of the catch. Although there has been a substantial decline infisheries activity in Chile in recent years, over 80% of the catch is directed towardthe production of fish meal and fish oil (see Table I).

The main pollutants in fisheries industry wastewater include particulate anddissolved organic matter, and oil and grease residues. High concentrations of thesepollutants produce indirect impacts as they require large amounts of oxygen fortheir oxidation. In shallow waters with little movement they may produce suboxicor even anoxic conditions (Rudolph, 1995). The particulate material, plus emulsi-fied oil and grease decrease light penetration and oxygenation of the water columnby inhibiting photosynthesis and direct oxygen exchange at the air-water interface.Particles may settle out to form areas of accumulation of organic material and redu-cing environments (Epping and Helder, 1997; Burke, 1999), with a defaunation ofthe sediments (Carrasco, 1996; Oyarzun et al., 1987). One of the products from theoxidation of organic matter is ammonium ion (NH+

4 ), the concentration of whichmay be so high as to form a useful indicator of the environmental impact of fisherieswastewaters.

The concentration of dissolved oxygen in the water column on the Chilean andPeruvian coasts is modulated by upwelling of oxygen-poor waters which reach thecoast seasonally through advective processes. This condition reduces the assimilat-ive capacities of coastal water for organic matter from fisheries waste. Evaluationof the effects on dissolved oxygen by the discharge of organic wastes from thefishing industry requires the ability to discriminate these effects from the oxygendepletion in coastal waters due to natural upwelling processes, which may bringsubsuperficial low-oxygen water shoreward from the oxygen minimum layer.

This study presents an analysis of data collected during a monitoring program inLota Bay, which is a small coastal indentation harbouring a high degree of fisheriesactivity. The objectives of the work were to determine the impact produced by thedischarge of industrial fisheries waste and to analyze the capacity of the bay forrecovery on a seasonal basis.

1.1. STUDY AREA

Lota Bay (37◦S) is approximately 914 km2 in area, with a width of 4.4 km andlength from mouth to head of about 4 km. Its average depth is about 8 m andapproximate basin volume is 7.3 × 106 m3 (Derrotero de la Costa de Chile, 1992).The mouth of the bay is oriented to the SW, with a length/width ratio of 0.7, whichplaces it within the definition of an ‘open bay’. Typical mean current velocities inthe bay are 4 cm sec−1 suggesting the residence time of water within the bay to beabout 14 hr; it has a tidal range of about 1.6 m (Ahumada, unpubl.).

92 R. AHUMADA ET AL.

2. Methods

Seasonal cruises were undertaken during 1994 prior to modernization of the fish-eries industry, and from 1996 to 1998, after installation of new fisheries plants.Before 1994 there were discharges of fisheries wastes from an obsolete plant witha production line output capacity of 12 tons hr−1. These installations were replacedby a new plant with an output capacity of 60 tons hr−1. Six hydrographic stationswere routinely occupied as shown in Figure 1. Station 1 was located at the headof the bay, and represented the area of major impact. Station 3 was located atthe entrance of the bay, and represented a dynamic sector, and Stations 4 and 6were considered as reference stations, which were chosen as representative of waterwhich would be affected by local upwelling from the continental shelf. Location ofthe stations in the field was verified using an Apelco Co. global positioning system(GPS).

Measurements of temperature and salinity were taken using a CTD probe withNeil Brown sensors, recording at 25 cm depth increments. These data were em-ployed in calculations of density and the value of oxygen saturation, and also usedas a means of verifying the origin of water entering the bay (Weiss, 1970; Rudolphet al., 2002).

Water samples obtained at the surface and at depths of 3, 5, 10 m and /or themaximum depth were taken for iodometric determination of dissolved oxygen con-centration using the Winkler method (Strickland and Parsons, 1972). Ammoniumion concentrations were determined in these samples using the method of Grasshoffet al., (1983). Chemical analysis of total oil and grease at the surface were madeusing standard methods (APHA, 1992), and water transparency was obtained usinga Secchi disc.

Data analysis included comparison of dissolved oxygen measured in the wa-ter column (integrated over depth), with the saturation value calculated from thetemperature data (Weiss, 1970). Values were integrated over depth for the watercolumn from the discrete values obtained in each station. The distribution of dis-solved oxygen from each cruise was plotted using isolines in the Surfer 7.0 program(Golden Software Inc.) with an approximation of basic radial functions.

3. Results

The hydrographic conditions of Lota Bay in the summer are presented in Figure 2in longitudinal sections of temperature and salinity. In summer, cold, high salinityand denser water was observed entering Lota bay from the Gulf of Arauco (T= <10.88 ◦C, salinity = 34.30 and density 26.50 sigma t). Winter conditions werecharacterized by weak stratification, affected by local dilution of the water, (salinity= 25.80 at the surface and 27.30 at depth) with higher temperatures, (12.78 ◦C at thesurface and 13.08 ◦C at depth). Coastal waters here represented a modification of

EVALUATION OF COASTAL WATERS RECEIVING FISH PROCESSING WASTE 93

Figure 2. Representative sections of Lota Bay (temperature, salinity, sigma t , dissolved oxygen andion ammonium concentrations) in summer ((a)–(e); 3/1998) and winter ((f)–(j); 7/1997) to showtypical values for T ◦C, salinity, sigma t , O2, and NH+

4 .

subantarctic water (ASW), which dominates the central Chilean coast (Ahumada,1992).

Dissolved oxygen and ammonia ion showed seasonal patterns during the mon-itoring programs (Figure 2). Table II shows the seasonal integrated values for thedissolved oxygen and ammonia content of the water column, as well as the oil andgrease content at the surface. Values for dissolved oxygen saturation were used asan estimate of the impact of organic matter in the bay.

In the summer the percentage saturation of dissolved oxygen in a longitudinalsection of the bay showed a distribution with values which included subsaturation(Figure 2d). The oxygen saturation value at the surface was 60% at the head ofthe bay. Lower saturations (<50%) were encountered in water near the bottom

94 R. AHUMADA ET AL.

TABLE II

Seasonal results for values of critical variables in the water column. Dissolved oxygen and ammo-nia represent integrated values for the water column at each hydrographic station and superficialdistributions of oil and grease in Lota Bay

Cruise Dissolved oxygena Ammoniaa Oil and grease

Est, 6 Est, 1 Est, 6 Est, 1 Est, 6 Est, 1

(L O2 m−2) (L O2 m−2) (mg m−2) (mg m−2) (g m−3) (g m−3)

Baseline Summer 33.33 15.38 2.95 2.55 8.0 1030.0

1994

Saturation valueb 59.18 46.44

Winter 1994 63.35a 19.80 0.87 1.23 312.0 1018.2

Saturation value 61.00 30.80

Summer 1996 45.47 11.05 4.42 1.92 38.0 832.0

Saturation value 63.13 31.00

Winter 1996 39.16 8.55 6.29 4.40 5.0 18.0

Saturation value 62.05 31.18

Spring 1996 27.44 8.41 0.59 2.52 30.0 30.0

Saturation value 59.91 29.01

Fall 1997 38.32 5.28 5.45 7.35 20.0 69.0

Saturation value 60.02 29.33

Winter 1997 59.22 36.25 1.53 191 5.4 15.2

Saturation value 62.18 38.01

Summer 1998 42.89 23.00 14.31 17.82 3.9 13.5

Saturation value 60.67 30.73

Winter 1998 61.45 26.20 5.88 7.15 18.4 17.1

Saturation value 60.91 30.71

Spring 1998 32.50 19.05 2.88 12.64 13.40 33.2

Saturation value 62.25 31.03

a = Integrated values (L O2 m−2 or mg NH+4 m−2).

b = Saturation values were estimated for integrated values of salinity and temperature at eachhydrographic station.

(Figure 2d). Different distributions were observed for oxygen values in winterconditions where these values approximated or were greater than 95% (Figure 2h).

The concentration of ammonium ion was low and relatively homogeneous inthe winter, measuring about 1 µM. In contrast, high concentrations of this ion weredetected near the bottom and towards the head of the bay in the summer (Station 1,Figure 3). In general, the concentrations of ammonium ion and dissolved oxygenappeared inversely correlated (Fröenlich et al., 1979) as when low concentrationsof oxygen were measured in the water column, high concentrations of ammonium

EVALUATION OF COASTAL WATERS RECEIVING FISH PROCESSING WASTE 95

Figure 3. Surface oil and grease concentrations in summer ((a), 3/1997) and winter ((b), 7/1997) inLota Bay.

appeared as a result of mineralization of organic matter present in bottom sedimentsin summer.

Total concentrations of oil and grease measured in 1994 (1030 g m−3) wererelated to uncontrolled fisheries activity in the area that was stopped in 1996 whentwo new industrial plants were commissioned. In 1996 oil and grease decreased inconcentration (832 g m−3), which can be related to the initiation of remedial meas-ures and elimination of the obsolete fisheries installations. Most of the elevatedvalues of these variables were concentrated at Stations 1 and 2, near wastewaterdischarge sites and near artesanal fishery activity. The surface water demonstratedan important reduction in the concentration of oil and grease at the head of thebay (>69 mg L−1) in the summer, declining to values of less than 20 mg L−1 inthe winter (Table II). In spite of this, it was possible to observe small clumps ofsaponified grease at the head of the bay at the surface during spring 1998. Watertransparency was less at the head of the bay compared with other regions, varyingfrom 0.2 m at Station 1, to 5 m at Stations 4 and 6 in the mouth of the bay.

Values for dissolved oxygen and ammonia concentrations were integrated andare presented in Table II. The concentration of dissolved oxygen in the watercolumn of this bay showed seasonal changes as listed in Table III. The values rep-resent percentages of oxygen saturation, integrated at Stations 1, 4, and 6 for eachseasonal cruise. Oxygen saturation was deficient at Station 1 at the head of the bayduring the first monitoring cruises from 1994 to 1997. Water samples showed sub-saturation to values lower than 50%, except in winter 1994. In contrast, Stations 4and 6 showed saturation values above 50%, during all of the cruises. The seasonaldifferences, with decreases in O2 occurring in the summer (Table III) representedwater with low oxygen concentration which was entering the Gulf of Arauco with

96 R. AHUMADA ET AL.

TABLE III

Percentages of dissolved oxygen by station. The theoretical equilib-rium value was taken as 100% saturation

Cruceros Station #6 Station #4 Station #1 Period

B.S.a 64% 65% 33% Summer 1994

B.W.b 100% 100% 64% Winter 1994

1 72% 50% 36% Summer 1996

2 63% 96% 27% Winter 1996

3 42% 80% 29% Spring 1996

4 68% 90% 18% Fall 1997

5 95% 105% 95% Winter 1997

6 85% 60% 74% Summer 1998

7 101% 100% 85% Winter 1998

8 52% 80% 61% Spring 1998

a B.S. = Baseline Summer.b B.W. = Baseline Winter, Monitoring Program 1994–1998.

upwelling of equatorial sub-surface waters (ESSW), as spring of 1996 at Station 6to 4.

4. Discussion

The hydrographic regime of Lota Bay shows seasonal changes which are directlyrelated to the presence on the continental shelf of subantarctic water in winter andupwelling of subsuperficial equatorial water in the summer. The exchange of waterover the continental shelf in summer is generated by the rising of higher density,oxygen poor water (ESSW) into the coastal zone (Ahumada et al., 1983). This ex-change produces a natural fluctuation in the dissolved oxygen content of the waterand thus affects the capacity for waste assimilation (oxidation of organic matter)in the local bays (Clark, 1991). Figure 3 shows the intrusion of cold, high salinity,reduced oxygen saturation (∼50%) and dense water, higher than 26.3 in sigma t , at10 m depth. This condition disappears in winter. Thus under natural conditions, theamount of oxygen available for oxidative processes is lowered during the summerperiod. In Table II, the oxygen saturation values of <70% represent summer valuesat the outer bay station (6) affected by the presence of upwelled ESSW water in theGulf of Arauco.

The record obtained in summer 1994 represents a period prior to the functioningof industrial fishing activity in the area. The loading of waste organic material inbay water is related to season, based on fisheries landings and processing, whichincrease markedly in the summer. The quality of wastewater is directly related to

EVALUATION OF COASTAL WATERS RECEIVING FISH PROCESSING WASTE 97

TABLE IV

Estimated loading of wastes discharged to Lota Bay from fisher-ies industry activities, normalized to 8 hr in 1994. Estimated as10% of the total discharge rate for Coronel-Lota Bays by Arcoset al. (1993)

Parameter measured 8 hr estimated loading Units

BOD(5) 22,853 kg O2 d−1

COD 33,556 kg O2 d−1

Ammonium ion 68.0 g NH+4 d−1

Total oil and grease 13,437 kg d−1

Total solids 307,402 kg d−1

Suspended solids 20,344 kg d−1

Filterable solids 216,476 kg d−1

Volatile solids 70,634 kg d−1

the type and status of the fishery. This quality changes: (i) if a company overloadsits production line, (ii) if the frequency of cleaning maintenance of installationsis reduced, (iii) the degree of conservation of the product, which depends on itstime of storage and storage temperature. Fisheries processing wastewater has anextremely high biochemical oxygen demand (BOD5), and high concentrations ofoil and grease, ammonium ion, and solids (Arcos et al., 1994). There have beenno measurements made on the discharge of organic matter associated with un-loading of fish catches in ports. Table IV summarizes information (Arcos et al.,1994), where organic loading may explain the impact observed in fisheries industrywaste discharge zones prior to the present study (Arcos et al., 1994; Pradena andRudolph, 1989; Rudolph, 1995).

The major alterations in dissolved oxygen concentration were observed in thewater column at the head of Lota Bay (Station 1) where the highest discharge oforganic load occurs (Figures 3 and 4). During the winter the dominance of theASW produces an improvement in the re-aeration conditions of the bay water anddecrease in ammonium ion concentrations, with the effect reaching as far as thehead of the bay (Figure 3).

In the months preceding Cruise 7 in the winter of 1997 (Table III), mitigationmeasures were implemented due to the impact produced by the industry. Someof these measures included: (i) internal management steps within the plants, andsome were made in the fishing fleet by improving the quality of the catch and,(ii) the treatment of wastewater effluents using filters for the retention of solids,and sedimentation systems for solids.

Added to these improvements two important factors were noted: (i) in Februaryand March intense sea swells occurred along the shore which mobilized uncon-

98 R. AHUMADA ET AL.

solidated muds in the zone near the mouth of the bay, and (ii) a fisheries ban wasimposed on mackerel catches which were a major component of the processing(fish meal and oil) industry. The first factor would promote oxidation of organicmatter retained in the sediments and the second would reduce the quantity of or-ganic matter at the source. Another important factor to be considered is that LotaBay water has a short residence time in its basin (14 hr) and thus may have rapidrecuperation due to its unrestricted interchange with open waters of the Gulf ofArauco.

The summation of these effects probably explains why important improvementsin oxygen conditions were observed in the water column of Lota Bay during the lastmonitoring period e.g., cruises 7–8 (Table II). However, an increase in ammoniumion has been observed as a result of suboxic reduction by the treatment of residualwaters. Anoxic reducing sediments of the Bay have continued to increase, probablydue to the accumulation of particulate organic matter from landing washwater.

5. Conclusions

The measurement of oxygen saturation in coastal waters is a sensitive and usefulparameter for water quality evaluation, as it includes the influences of variations intemperature and salinity.

Forcing functions for the recuperation of oxygen saturation levels in the interiorof Lota Bay beginning in winter 1997 probably included multiple factors such asseasonality, ocean swells, industrial mitigation strategies, and application of themackerel ban.

For a short period of time, measurable in days, the recovery of oxygen levelsin the water column could be effected by wind action over an unprotected bay,typified by Lota. Organic matter trapped in sediments exerts deleterious effects onthe oxygen balance in bay waters over longer periods (years). In the latter case, aforcing function of great importance in 1997 may have been the ocean swell (i.e.,long period wave) activity.

Finally, recuperation of water quality in Lota Bay showed unequivocal signalsthat an integral management plan must be carried out which includes all users.It is urgent that standards for waste discharge be established, and that emissionstandards be set for wastes having high organic loads.

Acknowledgement

This publication was partially supported by project DIN 05/2002, UniversidadCatólica de la Santísima Concepción.

EVALUATION OF COASTAL WATERS RECEIVING FISH PROCESSING WASTE 99

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