The Placencia Lagoon - Coastal Zone Management Authority and ...
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Characterization of a Tropical Estuarine System: <strong>The</strong> <strong>Placencia</strong> <strong>Lagoon</strong><br />
Technical Report<br />
by<br />
Eugene Ariola<br />
CZMI Water Quality Monitoring Program<br />
<strong>Coastal</strong> <strong>Zone</strong> <strong>Management</strong> <strong>Authority</strong> <strong>and</strong> Institute<br />
Princess Margaret Drive, Belize City<br />
Reference:<br />
Ariola, E. A. 2003. Characterization Of A Tropical Estuarine System: <strong>The</strong> <strong>Placencia</strong><br />
<strong>Lagoon</strong>. Report prepared under the <strong>Coastal</strong> <strong>Zone</strong> <strong>Management</strong> <strong>Authority</strong> <strong>and</strong> Institute.<br />
Work in Progress for Public Discussion.<br />
i
Table of Contents<br />
Acknowledgement iii<br />
List of Figures iv<br />
List of Tables iv<br />
List of Plates iv<br />
Abbreviations <strong>and</strong> Notations v<br />
Executive Summary 1<br />
Introduction 2<br />
Objectives 3<br />
Hypotheses 3<br />
Study Area 3<br />
Materials <strong>and</strong> Methods 5<br />
Characteristics of the terrestrial zone of influence<br />
on the <strong>Placencia</strong> <strong>Lagoon</strong> 7<br />
Characteristics of the Belize Barrier Reef <strong>Lagoon</strong><br />
(<strong>Coastal</strong> oceanographic zone of Influence) 10<br />
Importance of the <strong>Placencia</strong> <strong>Lagoon</strong>al Estuarine System 11<br />
Major L<strong>and</strong> use <strong>and</strong> Activities in the <strong>Placencia</strong> <strong>Lagoon</strong><br />
<strong>and</strong> surrounding areas 14<br />
Results 17<br />
Discussions 26<br />
Conclusions 29<br />
Recommendations 29<br />
Bibliography 30<br />
Appendices 33<br />
ii
ACKNOWLEDGEMENT<br />
<strong>The</strong> preparation of this technical report would not have been possible without the<br />
assistance of several persons. Special recognition is due to the members of the survey<br />
team especially Captain Kirk Rodriquez, Hampton Gamboa, Trenton Samuels <strong>and</strong><br />
Alex<strong>and</strong>er Garbutt. <strong>The</strong>se gentlemen worked diligently to collect confident data <strong>and</strong><br />
made each survey a memorable experience. Thanks to the CZMAI Administrative Staff<br />
especially Melissa Almendarez for providing the logistical support for the field<br />
monitoring surveys.<br />
Thanks are also due to Ian Gillett for providing assistance in resolving the software<br />
glitches that were experienced in processing <strong>and</strong> analyses of the data presented in this<br />
report.<br />
I am indebted to Natalie from the Belize National Meteorological Service <strong>and</strong> Rigoberto<br />
Quintana of the Belize Fisheries Department for providing valuable information for this<br />
report.<br />
iii
List of Figures<br />
Figure 1. Geographic location of the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 2. Extent of the terrestrial zone of Influence on the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 3. Villages in the Catchments Surrounding the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 4. Shrimp Mariculture Operations Near the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 5. Bathymetric Map of the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 6. Mean Temperatures for the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 7. Mean pH Measurements for the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 8. Mean Specific Conductivity Measurements for the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 9. Mean Salinity measurements for the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Figure 10a. Mean D.O. mg/L<br />
Figure 10b. Mean D.O. % Saturation<br />
Figure 11. Mean Turbidity Measurements for the <strong>Placencia</strong> <strong>Lagoon</strong><br />
List of Tables<br />
Table 1. Summary of the characteristics of villages in the <strong>Placencia</strong> Catchment<br />
Table 2a. Shrimp Mariculture Production & Export Data 2001.<br />
Table 2b. Shrimp Mariculture Production & Export Data 2002.<br />
Table 3. Mean Measurments of Several Parameters in the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Table 4. Variation between Surface <strong>and</strong> Bottom Salinities of the <strong>Placencia</strong> lagoon<br />
Plate 1. Photographs (a)-(h)<br />
List of Plates<br />
iv
EXECUTIVE SUMMARY<br />
<strong>The</strong>re is growing concern about the current status <strong>and</strong> fate of the <strong>Placencia</strong> <strong>Lagoon</strong><br />
amidst the changing l<strong>and</strong> use in the adjoining catchments. <strong>The</strong> destruction of natural<br />
vegetation to construct dwellings, resorts, roads, <strong>and</strong> aquaculture development is a major<br />
issue in the study area. Another issue that is frequently echoed <strong>and</strong> poorly substantiated<br />
is the contamination of the lagoon by domestic <strong>and</strong> industrial effluent.<br />
<strong>The</strong> first part of this report focuses on the <strong>Placencia</strong> <strong>Lagoon</strong> not solely from the<br />
perspective of its immediate borders but rather in the context of the catchments <strong>and</strong> the<br />
Southern Shelf <strong>Lagoon</strong> that bear influence on its health. Knowledge about the geological,<br />
hydrological, meteorological <strong>and</strong> oceanographic characteristics of the zone of influence<br />
on the <strong>Placencia</strong> <strong>Lagoon</strong> is essential to underst<strong>and</strong>ing its structure <strong>and</strong> function.<br />
Furthermore, appreciations of the biological <strong>and</strong> chemical processes that operate therein<br />
are fundamental to determine the lagoons ability to cope with the rising influx of<br />
sediment <strong>and</strong> effluent loadings. It is in this light that a conscious effort was made to<br />
characterize the lagoon.<br />
<strong>The</strong> results generated by this research substantiate that the <strong>Placencia</strong> <strong>Lagoon</strong> can be<br />
classified as a moderately stratified estuary based on its salinity distribution <strong>and</strong><br />
circulation patterns. In addition to this, there is a notably low water exchange rate<br />
between the upper section of the lagoon <strong>and</strong> the sea. <strong>The</strong>se finding signals how<br />
vulnerable the ecological <strong>and</strong> environmental conditions of the lagoon are to the impacts<br />
of developmental activities in the area of influence. Without cause for alarm, it is strongly<br />
recommended that future developments be planned to ensure the lowest possible impacts<br />
on the estuarine system.<br />
<strong>The</strong> second part of this report is an assessment of the water quality in the <strong>Placencia</strong><br />
<strong>Lagoon</strong>. Several water quality surveys were conducted in the lagoon in 2001 <strong>and</strong> 2003.<br />
Key water quality indicators used to determine the status of the <strong>Placencia</strong> <strong>Lagoon</strong> reveal<br />
that it is a healthy estuarine system. This signifies that the conditions therein are<br />
conducive to unimpaired growth <strong>and</strong> reproduction of estuarine organisms.<br />
It is envisaged that this report will stimulate public discussion about the fate of the<br />
<strong>Placencia</strong> <strong>Lagoon</strong> <strong>and</strong> trigger future monitoring, research <strong>and</strong> management initiatives in<br />
the area.<br />
1
INTRODUCTION<br />
<strong>The</strong>re are 30 coastal lagoons distributed along the mainl<strong>and</strong> coastline of Belize. Most of<br />
these lagoons remain in pristine condition. This may be attributed to the fact that most of<br />
these lagoons are remote <strong>and</strong> isolated from direct human impacts. <strong>The</strong> <strong>Placencia</strong> <strong>Lagoon</strong><br />
is one of the larger coastal lagoons in Belize. It is currently a focal area for human<br />
settlement, tourism, fisheries <strong>and</strong> aquaculture development.<br />
<strong>The</strong> rapid expansion of the human settlements in the area augments the perception of loss<br />
of critical habitats associated with destruction of natural vegetation <strong>and</strong> increase<br />
discharge of untreated domestic wastewater. <strong>The</strong> constant upgrading of roads that link<br />
one settlement with another is a potential source of sediment to the nearby waterways <strong>and</strong><br />
the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
<strong>The</strong> tourism industry is an integral component of the socio-economic situation in the<br />
communities of the <strong>Placencia</strong> Peninsula. <strong>The</strong> current trend to exp<strong>and</strong> tourism<br />
development in the area could increment economic benefits in the short term to the<br />
detriment of the fragile environs of the <strong>Placencia</strong> <strong>Lagoon</strong>. Resultant impacts of tourism<br />
development include mangrove destruction <strong>and</strong> structural modifications such as dredging<br />
<strong>and</strong> marina development. Other impacts include wastewater discharge, euthrophication<br />
<strong>and</strong> increase in boat traffic. Evidently, there is the need to for planned tourism<br />
development that is environmentally benign.<br />
Shrimp mariculture development is a viable activity around the <strong>Placencia</strong> <strong>Lagoon</strong>. Since<br />
the inception of the mariculture industry, this activity has rendered significant socioeconomic<br />
benefits to the local communities. <strong>The</strong> continued expansion of the shrimp<br />
mariculture operations around the lagoon will destroy natural vegetation <strong>and</strong> enhance the<br />
salinization of the already poor grade soils. <strong>The</strong> potential impacts to the coastal lagoon<br />
include increase loadings of nutrients <strong>and</strong> organic material, euthrophication, sediment<br />
accretion <strong>and</strong> the spread of pathogens.<br />
<strong>The</strong>re is overwhelming concern about the status of the <strong>Placencia</strong> <strong>Lagoon</strong> especially<br />
considering its intrinsic value <strong>and</strong> the fact that many coastal lagoons around the world are<br />
under threat of damage, severely damaged or already destroyed consequent to<br />
anthropogenic impacts. Thus far there is no comprehensive study that documents the<br />
status <strong>and</strong> health of the <strong>Placencia</strong> <strong>Lagoon</strong>. To this end, a new approach was undertaken to<br />
(1) collate as much information as possible regarding the physical characteristics of the<br />
entire estuarine system <strong>and</strong> (2) conduct a limited time scale water quality monitoring in<br />
the <strong>Lagoon</strong>. It is expected that the information presented in this report will be used to<br />
initiate future monitoring <strong>and</strong> research initiatives to further contribute to informed<br />
management of developmental activities in the <strong>Placencia</strong> <strong>Lagoon</strong> <strong>and</strong> its adjacent<br />
catchments.<br />
2
OBJECTIVES<br />
To identify <strong>and</strong> document the characteristics of the estuarine system of the <strong>Placencia</strong><br />
<strong>Lagoon</strong> within the context of influences from adjoining catchments <strong>and</strong> the Belize Barrier<br />
Reef <strong>Lagoon</strong>.<br />
To elucidate the vulnerability of the <strong>Placencia</strong> <strong>Lagoon</strong> to the potential impacts of l<strong>and</strong> use<br />
changes including human settlement <strong>and</strong> aquaculture development.<br />
To assess the current status of the <strong>Placencia</strong> <strong>Lagoon</strong> based on key water quality<br />
indicators.<br />
HYPOTHESIS<br />
<strong>The</strong> spatial <strong>and</strong> temporal fluxes of pollutants within the <strong>Placencia</strong> <strong>Lagoon</strong> are regimented<br />
largely by the physical characteristics of the lagoon coupled with the attributes of the<br />
terrestrial <strong>and</strong> coastal oceanographic zones of influence.<br />
Water quality deterioration <strong>and</strong> habitat degradation in the estuarine system can be<br />
accelerated by improper waste disposal <strong>and</strong> effluent discharge.<br />
STUDY AREA<br />
<strong>The</strong> <strong>Placencia</strong> <strong>Lagoon</strong> is a semi-enclosed coastal lagoon located in Southern Belize<br />
between 16°30’ <strong>and</strong> 16°40’ N latitude <strong>and</strong> 88°20 <strong>and</strong> 88°25’ W longitude (Fig. 1). <strong>The</strong><br />
<strong>Placencia</strong> <strong>Lagoon</strong> is 3.4 km wide at its widest extent, 20 km long <strong>and</strong> covers a surface<br />
area of 30 km 2 . At mean sea level (MSL), the average depth of the lagoon is about 1.5 m.<br />
<strong>The</strong> lagoon is physically influenced by the coastal oceanographic conditions of the<br />
Southern Barrier Reef <strong>Lagoon</strong> <strong>and</strong> the terrestrial conditions of the surrounding<br />
catchments.<br />
3
MATERIALS AND METHODS<br />
<strong>The</strong> <strong>Coastal</strong> <strong>Zone</strong> <strong>Management</strong> <strong>Authority</strong> <strong>and</strong> Institute provided the equipment <strong>and</strong><br />
materials that were utilized in this study. <strong>The</strong>se include the following:<br />
(a) a 28 feet skiff equipped with two 115 hp outboard engines, global positioning<br />
system (GPS) <strong>and</strong> echo sounder.<br />
(b) Two water quality multiparameter sonde [H20 <strong>and</strong> DataSonde 4a manufactured<br />
by Hydrolab Corporation].<br />
(c) A unidirectional current meter manufactured by Qualimetrics Inc.<br />
(d) Graduated PVC pipe (<strong>The</strong> measuring Pole)<br />
<strong>The</strong> objectives of this research were accomplished using the methods <strong>and</strong> data analyses<br />
described below.<br />
Comprehensive Literature Review<br />
Throughout the duration of this study, the author was fully engaged in reviewing<br />
literature pertinent to the <strong>Placencia</strong> <strong>Lagoon</strong>. This step was necessary to collate relevant<br />
information <strong>and</strong> identify the information gaps. It is believed that the existing information<br />
gaps limit our underst<strong>and</strong>ing of how the lagoon functions as a system, how it reacts to<br />
hydrological, meteorological <strong>and</strong> tidal forces. Furthermore, it is not clear how the lagoon<br />
responds ecologically to anthropogenic inputs of sediment, nutrients <strong>and</strong> pollutants.<br />
Data Collection<br />
Water Quality<br />
Four water quality surveys were conducted in the <strong>Placencia</strong> <strong>Lagoon</strong> on the following<br />
dates:<br />
Survey 1 April 5, 2001<br />
Survey 2 May 31, 2001<br />
Survey 3 March 12, 2003<br />
Survey 4 July 17,2003<br />
Sampling stations were r<strong>and</strong>omly selected in the study area on all surveys. At total of 59<br />
stations were sampled on Survey 1; 65 stations on Survey 2; 53 stations on Survey 3 <strong>and</strong><br />
25 stations on Survey 4.<br />
<strong>The</strong> water quality multiparameter sonde were used to record surface <strong>and</strong> bottom<br />
measurements of temperature, pH, Specific conductivity, salinity, dissolved Oxygen,<br />
depth <strong>and</strong> turbidity. Prior to any measurement in the field the sonde was properly<br />
calibrated in the CZMAI Laboratory. <strong>The</strong> salinity sensor was calibrated using the<br />
synthetic seawater method described in section 1.1H of Parsons et al. (1984). <strong>The</strong><br />
accuracy of the salinity sensor is ± 0.1 parts per thous<strong>and</strong>.<br />
<strong>The</strong> pH probe was calibrated using a three-point calibration procedure with pH buffers 5,<br />
7 <strong>and</strong> 10. <strong>The</strong> accuracy of the pH probe is ± 0.2 units.<br />
5
<strong>The</strong> turbidity sensor was calibrated with known concentrations of formazine solution.<br />
<strong>The</strong> accuracy of the sensor was ± 2.0 NTU.<br />
<strong>The</strong> depth sensor (a pressure transducer) was regularly calibrated in the field to<br />
compensate for changes in water level, wave height <strong>and</strong> barometric pressure.<br />
Unlike the aforementioned sensors, the temperature sensor is factory calibrated with an<br />
accuracy of ± 0.05 °C hence, there was no need to calibrate this senor in the laboratory or<br />
the field.<br />
Bathymetry<br />
A special field bathymetric survey was conducted on July 18, 2003 in which 202<br />
soundings were recorded in the <strong>Placencia</strong> <strong>Lagoon</strong>. <strong>The</strong> depth measurements were taken<br />
using the pressure transducer installed on the multiparameter sonde <strong>and</strong> the echo sounder<br />
aboard the CZMAI research vessel (Submarine 2). A graduated PVC pipe was used to<br />
measure the depths in extremely shallow but critical parts of the lagoon. As with the<br />
water quality stations, all bathymetric soundings were geo-referenced using the global<br />
positioning system.<br />
Data Analyses<br />
<strong>The</strong> data recorded on paper <strong>and</strong> on the multiparameter sondes were uploaded to<br />
Microsoft Excel worksheets. Using this software, basic mathematical operations were<br />
conducted to prepare several charts <strong>and</strong> tables. Furthermore, water quality variables were<br />
analyzed with descriptive statistics to determine means, ranges, st<strong>and</strong>ard deviation <strong>and</strong><br />
variance.<br />
A non-drift krigging interpolation method was used to create contour maps using Surfer<br />
7.0. Maps of this type illustrate the bathymetry, spatial distribution of temperature <strong>and</strong><br />
salinity within the study area. Considering that most of the data obtained in this research<br />
are geo-referenced data, the final maps <strong>and</strong> graphic illustrations were produced using<br />
ArcView GIS 3.1.<br />
6
Characteristics Of <strong>The</strong> Terrestrial <strong>Zone</strong> Of Influence On <strong>The</strong> <strong>Placencia</strong> <strong>Lagoon</strong><br />
Geology<br />
<strong>The</strong> <strong>Placencia</strong> <strong>Lagoon</strong> catchments (Santa Maria, August Creek <strong>and</strong> Big Creek) are part of<br />
the Central <strong>Coastal</strong> Plain as described by King et al. (1989). Within this portion of the<br />
coastal plain are relict marine terraces <strong>and</strong> alluvial fans (Pleistocene sediment) overlain<br />
by more recent floodplains <strong>and</strong> terraces of the Toledo Flood Plains L<strong>and</strong> System.<br />
<strong>The</strong> <strong>Placencia</strong> Peninsula, which is an appendage of the Santa Maria Creek Catchment, is<br />
a striking geomorphological feature. In fact, the peninsula is the largest s<strong>and</strong> spit along<br />
the Belize coast. This barrier spit that is comprised of few Holocene beach ridges <strong>and</strong> is<br />
only a few hundred feet wide, separates the <strong>Placencia</strong> <strong>Lagoon</strong> from the Caribbean Sea<br />
(High, 1969).<br />
Based on the geology of the area it is understood that the quaternary alluvium deposited<br />
in the terrestrial zone bearing influence on the <strong>Placencia</strong> <strong>Lagoon</strong>, is poorly consolidated<br />
<strong>and</strong> readily erodible. This could be a major source of sediment influx to the lagoon<br />
especially in light of changing l<strong>and</strong> use, deforestation <strong>and</strong> desertification.<br />
Hydrology<br />
Three catchments namely the Santa Maria Creek, August Creek <strong>and</strong> Big Creek border the<br />
lagoon (Figure 2). <strong>The</strong> Santa Maria Creek watershed has an area of 347 km 2 . <strong>The</strong> terrain<br />
is relatively low-lying with a maximum elevation of 500 meters on its westernmost<br />
boundary. Based on a flood risk analysis (Ariola et al., 2000), approximately 12.7 km 2 of<br />
the basin is permanently inundated <strong>and</strong> 32.7 km 2 is prone to flooding. Santa Maria <strong>and</strong><br />
Hemsley Creeks debouches directly into the <strong>Placencia</strong> <strong>Lagoon</strong>. However, Silver Creek<br />
<strong>and</strong> several small creeks in this watershed flow into wetl<strong>and</strong>s that display connectivity to<br />
the <strong>Placencia</strong> <strong>Lagoon</strong>. <strong>The</strong> vegetation cover within the watershed includes pine ridge<br />
savannah <strong>and</strong> mangrove swamps in the upper <strong>and</strong> lower reaches respectively.<br />
<strong>The</strong> August Creek Catchment has an area of 250 km 2 . <strong>The</strong> low relief of the catchment<br />
makes it very vulnerable to annual flooding events. Approximately 16 km 2 of the basin is<br />
permanently inundated <strong>and</strong> while 93.2 km 2 is prone to flooding during the usual rain<br />
season. <strong>The</strong> major waterways in this watershed are Mango Creek <strong>and</strong> August Creek that<br />
converge at the lower section of the catchment <strong>and</strong> flow into the <strong>Placencia</strong> <strong>Lagoon</strong>. Flour<br />
Camp Creek, Jenkins Creek <strong>and</strong> several minor waterways also contribute to the net<br />
discharge of Mango Creek. Pine ridge savannahs dominate the higher portions of the<br />
catchment. <strong>The</strong> lower portion is limited to marshl<strong>and</strong> <strong>and</strong> mangrove swamps.<br />
<strong>The</strong> Big Creek Watershed is the smallest of the three catchments adjacent to the<br />
<strong>Placencia</strong> <strong>Lagoon</strong> <strong>and</strong> has an area of 59 km 2 . Most of the l<strong>and</strong>s in this basin are less than<br />
20 meters in elevation. This basin exhibits low relief <strong>and</strong> a moderate flood risk potential.<br />
An area of approximately 5.4 km 2 is permanently inundated <strong>and</strong> 15.4 km 2 are subject to<br />
7
inundation during the rain season. <strong>The</strong> principal waterway, Big Creek, is fed by<br />
numerous small streams <strong>and</strong> debouches at the southernmost end of the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
<strong>The</strong> vegetation cover within this catchment includes marshl<strong>and</strong>s, mangroves, grass<br />
meadows <strong>and</strong> pine ridge.<br />
It is worth pointing out that none of the watercourses that flow into the <strong>Placencia</strong> <strong>Lagoon</strong><br />
are gauged, hence there are no time series on the discharge <strong>and</strong> water levels (Hydrology<br />
Service, 2003). However, Grimshaw (2000) purports that the combined low flow for<br />
August <strong>and</strong> Mango Creeks is 0.7 CMS. Furthermore the low flow for Jenkins <strong>and</strong> Flour<br />
Camp Creeks was estimated at 0.8 CMS. Silver Creek was estimated to have a low flow<br />
of 1.3 CMS.<br />
<strong>The</strong> ground water resources map of Belize divides the country into ten regions based on<br />
water availability <strong>and</strong> quality (Buckalew et al., 1998). <strong>The</strong> terrestrial zone of influence on<br />
the <strong>Placencia</strong> <strong>Lagoon</strong> falls into two of these regions.<br />
(1) <strong>The</strong> <strong>Placencia</strong> Peninsula <strong>and</strong> the western margin of the lagoon are classified as areas<br />
where small to large quantities of brackish to saline water are available. Also, meager to<br />
very small quantities of fresh water are available from quaternary alluvium <strong>and</strong> coastal<br />
deposits along the coast. Depth to water is 2 to 50 meters.<br />
(2) <strong>The</strong> wider extent of the terrestrial zone of influence is that part of the Central <strong>Coastal</strong><br />
Plain composed of s<strong>and</strong>y shales, shales, claystones, mudstones, <strong>and</strong> alluvium. <strong>The</strong>se<br />
deposits bear meager to moderated quantities of freshwater. Depth to water is generally<br />
less than 60 meters.<br />
Although, there is limited information about the ground water distribution in the<br />
terrestrial zone influencing the lagoon, it is envisaged that ground water might have some<br />
effects on the water budget of the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
Meteorology<br />
<strong>The</strong> <strong>Placencia</strong> <strong>Lagoon</strong> <strong>and</strong> adjacent catchments fall in a tropical climatic zone. Walker<br />
(1973), King et al. (1989, 1992) documented the rainfall distribution for Belize <strong>and</strong><br />
indicate that the annual rainfall for the <strong>Placencia</strong> area varies between 80 inches (2032<br />
mm) <strong>and</strong> 100 inches (3048 mm). <strong>The</strong> mean annual temperature for the region is 28°C <strong>and</strong><br />
the mean relative humidity is 80%. <strong>The</strong> predominant winds are out of the Southeast at a<br />
mean speed of 4 knots.<br />
<strong>The</strong> Belize National Meteorological Service (BNMS) has a countrywide network of<br />
climatological stations. Station 28 located at Rum Point Inn <strong>and</strong> station 29 located at the<br />
Savannah Forest Station are the stations nearest to the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
9
Characteristics Of <strong>The</strong> Belize Barrier Reef <strong>Lagoon</strong><br />
<strong>The</strong> Belize Barrier Reef <strong>Lagoon</strong> is divided into the Northern <strong>and</strong> Southern Shelf <strong>Lagoon</strong>s<br />
based on differences of physical, chemical, geological <strong>and</strong> biological characteristics of<br />
the area (Purdy et al., 1975; Purdy, 1974). <strong>The</strong> immediate coastal oceanographic zone<br />
that exerts influence on the <strong>Placencia</strong> <strong>Lagoon</strong> is that portion of the Southern Shelf<br />
<strong>Lagoon</strong> adjacent to the <strong>Placencia</strong> Peninsula.<br />
Bathymetry<br />
<strong>The</strong> bathymetry in the Southern Shelf <strong>Lagoon</strong> is very irregular due in part to the tectonic<br />
activity that formed the shelf in the first place (Lara, 1993). Subsequent growth of coral<br />
assemblages, the formation of incised valleys, channels <strong>and</strong> shoals also add to the<br />
complexity of the bathymetry of the southern Shelf. Seaward of the <strong>Placencia</strong> Peninsula<br />
is the Inner Channel with depths ranging from 10 –20 meters. East of the Inner Channel<br />
is the Victoria Channel with depths of 20- 30 meters.<br />
Sediments<br />
<strong>The</strong> Southern Shelf is comprised of both biogenic <strong>and</strong> terrigenous sediments. <strong>The</strong><br />
biogenic sediment is derived from the remains of marine organisms such as corals,<br />
coralline algae <strong>and</strong> mollusk (Purdy et al., 1975; Purdy, 1974).<br />
<strong>The</strong> terrigenous material includes quartz s<strong>and</strong>, muds, <strong>and</strong> clay minerals derived from the<br />
Maya Mountains, the Central <strong>and</strong> Southern <strong>Coastal</strong> Plains (Esker, 1998). <strong>The</strong> fact that the<br />
Southern Shelf <strong>Lagoon</strong> shows high influence of terrigenous sediment highlights the<br />
influence of terrigenous material on the <strong>Placencia</strong> <strong>Lagoon</strong>, which is in closer proximity to<br />
the Central <strong>Coastal</strong> Plain.<br />
Currents<br />
Thus far there is no comprehensive study of the current patterns near the <strong>Placencia</strong><br />
Peninsula or the <strong>Placencia</strong> <strong>Lagoon</strong>. <strong>The</strong> Watershed Reef Interconnectivity Scientific<br />
Study (2001) purports that water within the barrier reef lagoon flows predominantly from<br />
north to south at a rate of 0.05 to 0.15 m/s <strong>and</strong> rarely exceed 0.3 m/s. <strong>The</strong> Regional<br />
Monitoring <strong>and</strong> Environmental Information System component of the MBRS is in the<br />
process of completing a 3-dimensional ocean circulation model of the continental shelf of<br />
the MBRS (Ariola, 2002). In addition to this, a 2-dimensional circulation model is also<br />
being prepared. Undoubtedly, these models will enhance present knowledge about<br />
circulation patterns in Belize.<br />
Tides<br />
Tides of the Caribbean <strong>and</strong> along the Belize Barrier Reef are microtidal <strong>and</strong> of mixed<br />
semidiurnal type with a mean range of 15 cm (Kjerve, 1981). PASCO (2002) mentions<br />
that the tidal fluctuations on the windward side of the Peninsula range from 0.40 to 1.5<br />
feet.<br />
10
Salinity<br />
<strong>The</strong> salinity of the Southern Shelf <strong>Lagoon</strong> is affected on a seasonal basis by the<br />
precipitation <strong>and</strong> river discharge in the southern province. <strong>The</strong> salinity of the Southern<br />
Shelf <strong>Lagoon</strong> fluctuates range between 33 to 35 parts per thous<strong>and</strong> (Gibson et al., 1993).<br />
<strong>The</strong> Importance of the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Like most tropical <strong>and</strong> subtropical estuarine systems, the <strong>Placencia</strong> <strong>Lagoon</strong> has<br />
ecological <strong>and</strong> environmental significance. <strong>The</strong> lagoon per se has a diverse amount of<br />
planktonic life that makes it an ideal nursery ground for a myriad of marine <strong>and</strong> estuarine<br />
organisms. Many of the fish that are caught for food or fun in the higher parts of the<br />
estuary or within the Belize Barrier Reef complex depend on the <strong>Placencia</strong> <strong>Lagoon</strong> for<br />
portions of their life cycles. Furthermore, the <strong>Placencia</strong> <strong>Lagoon</strong> provides adequate<br />
ecological <strong>and</strong> environmental conditions for the endangered <strong>and</strong> threatened West Indian<br />
Manatee (Trichechus manatus). <strong>The</strong> lower portion of the lagoon is relatively shallow<br />
with extensive beds of seagrass Thalassia testudinum that these creatures feed on. In<br />
close proximity to the lagoon are the mouths of several streams that are adequate source<br />
of freshwater for the manatees to drink. <strong>The</strong> inner portions of the <strong>Placencia</strong> <strong>Lagoon</strong> have<br />
areas that are completely protected from wind <strong>and</strong> wave activity that offer a safe <strong>and</strong><br />
tranquil resting place for adult manatees <strong>and</strong> their calves.<br />
During the surveys, dolphins were sighted feeding in the middle <strong>and</strong> lower portions of the<br />
<strong>Placencia</strong> <strong>Lagoon</strong> (Plate 1). Fishers from Seine Bight Village confirmed that dolphins<br />
are sighted regularly throughout the year in the lagoon (pers. com., Javier Maritinez).<br />
Morelet’s crocodiles (Crocodylus moreletii) are also a threatened species that have been<br />
sighted in various parts of the <strong>Placencia</strong> <strong>Lagoon</strong> system. Platt et al. (1997) found no<br />
evidence of nesting activity in the <strong>Placencia</strong> <strong>Lagoon</strong> however, spoil banks in the Maya<br />
Beach area are considered potential nesting habitats. Grimshaw (2000) reported that the<br />
Morelet’s crocodiles use the habitats in the lower reaches of the <strong>Placencia</strong> <strong>Lagoon</strong> for<br />
nesting sites.<br />
<strong>The</strong> vegetation fringing the lagoon supports nesting sites for several marine birds. Quite<br />
frequently pelicans, gulls <strong>and</strong> bobbies are seen feeding in the lagoon <strong>and</strong> roosting on the<br />
natural vegetation. In addition to this, the marshl<strong>and</strong>s surrounding the <strong>Placencia</strong> <strong>Lagoon</strong><br />
serve as natural filters for sediment <strong>and</strong> pollutants. ESTAP (2000) report that the Mango<br />
Creek Special Development Area Development Plan approved in 1997, identified the<br />
need to protect the mangrove wetl<strong>and</strong>s that surround the <strong>Placencia</strong> <strong>Lagoon</strong>. <strong>The</strong> intention<br />
is to ensure that water quality in the lagoon, together with manatee <strong>and</strong> other wildlife, is<br />
not negatively affected by inappropriate development. Some residents from <strong>Placencia</strong> <strong>and</strong><br />
Seine Bight in conjunction with organizations such as BTIA <strong>and</strong> Friends of Nature<br />
express concern about the fate of the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
11
In addition to the aforementioned benefits, the lagoon also provides unparalleled<br />
recreational opportunities for residents of the nearby communities <strong>and</strong> visitors. During<br />
the storm advisories, many shallow draft watercrafts (including catamarans) are moored<br />
in the safe heaven of the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
<strong>The</strong> aesthetics of the <strong>Placencia</strong> <strong>Lagoon</strong> fringed with mangroves <strong>and</strong> coupled with its high<br />
biological diversity makes it a focal point of tourist related activities for coastal<br />
communities such as Independence, <strong>Placencia</strong>, Seine Bight <strong>and</strong> Maya Beach.<br />
Undoubtedly, there are many more benefits that could be used to elucidate the importance<br />
of the <strong>Placencia</strong> estuarine system. However it is clear that this water body could be<br />
classified as a gem that could not be replaced <strong>and</strong> hence is priceless.<br />
Plate 1. Photographs:<br />
(a) Profiling the water column with a multiparameter sonde<br />
(b) Validating ground control points for the surveys<br />
(c) Local fisherman seeking the catch of the day<br />
(d) Mangrove fringed channel of the lagoon<br />
(e) & (f) Dolphins feeding in the lagoon<br />
(f) Manatees<br />
(g) Shrimp Mariculture Operation<br />
12
Major L<strong>and</strong> Use <strong>and</strong> Activities in the <strong>Placencia</strong> Catchments<br />
Human Settlements<br />
<strong>The</strong>re are eleven villages distributed within the catchments that adjoin the <strong>Placencia</strong><br />
<strong>Lagoon</strong> (figure 3). Even though the villages located towards the westernmost boundary<br />
of the catchments might appear to be isolated from the lagoon, there is connectivity via<br />
the network of streams in the sprawl of the catchment. <strong>The</strong>refore some of the activities in<br />
<strong>and</strong> around these communities such as agriculture, logging, <strong>and</strong> improper waste disposal<br />
could have direct <strong>and</strong> indirect impacts on the lagoon.<br />
<strong>The</strong> villages in closer proximity to the lagoon are generally larger in scale <strong>and</strong> population<br />
density. <strong>The</strong> activities in these settlements including destruction of natural vegetation,<br />
improper disposal of sewage <strong>and</strong> residual water, l<strong>and</strong> reclamation, <strong>and</strong> road construction<br />
pose more direct ecological <strong>and</strong> environmental impacts to the waterway. A summary of<br />
the characteristics of the villages in the <strong>Placencia</strong> catchments is presented in table 1.<br />
Residential Development<br />
In September 2001, the wrath of Hurricane Iris devastated communities of the <strong>Placencia</strong><br />
Peninsula <strong>and</strong> surrounding areas. <strong>The</strong> National Emergency <strong>Management</strong> Organization<br />
(2001) reported significant damage to major infrastructure <strong>and</strong> natural vegetation; <strong>and</strong><br />
noted an extraordinary amount of debris scattered on the peninsula. Subsequent to this<br />
event most homes were reconstructed <strong>and</strong> new areas were also clear <strong>and</strong> filled to<br />
construct new dwellings.<br />
Currently there are several subdivisions on the <strong>Placencia</strong> Peninsula. <strong>The</strong>se subdivisions<br />
are primarily for residential areas that would provide the necessary amenities for local<br />
<strong>and</strong> foreign retired persons.<br />
14
Table 1. Summary of the Characteristics of villages in the <strong>Placencia</strong> Catchments (Source:<br />
ESTAP, 2000; Central Statistical Office, 2001)<br />
Villages Population Potable Water Waste<br />
Disposal<br />
facility<br />
Sewage Disposal Electricity<br />
Santa Rosa 185 RWS / Pumps None Latrines yes<br />
San Roman 351 RWS/ Pumps None Latrines yes<br />
Maya Mopan 427 RWS None Latrines yes<br />
Georgetown 763 RWS None Latrines yes<br />
Cowpen 399 None Latrines yes<br />
San Juan 415 RWS None Latrines yes<br />
Independence 2,881 RWS None Septic tanks /Latrines yes<br />
Maya Beach ? Cisterns None Septic tanks /Latrines yes<br />
Seine Bight 831 RWS None Septic tanks /Latrines yes<br />
<strong>Placencia</strong> 458 RWS Fair Septic tanks / latrines yes<br />
Riversdale 30 Cisterns None Latrines yes<br />
Marinas<br />
Closely linked with the major subdivisions is the need for marinas to dock <strong>and</strong> safeguard<br />
the boats. Traditionally, boat owners on the Peninsula would dock their vessels in natural<br />
<strong>and</strong> man-made channels nearest to their homes. <strong>The</strong> Department of the Environment <strong>and</strong><br />
the National Environmental Appraisal Committee are currently reviewing proposals for<br />
the construction of several marinas in the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
Shrimp Mariculture Operations<br />
<strong>Coastal</strong> lagoons in the world are recognized as suitable sites for aquaculture development<br />
(Contreras, 1993). <strong>The</strong> western margin of the <strong>Placencia</strong> <strong>Lagoon</strong> forms the nucleus of the<br />
Shrimp Mariculture Industry in Belize (Figure 4). Currently there are six shrimp farms<br />
located in this area namely Nova Laguna, Belize Aquaculture Ltd., Royal Mayan, Tex<br />
Mar Ltd., Crustaceans Ltd, <strong>and</strong> AquaMar. All the farms are functional with the exception<br />
of Nova Laguna. Collectively, these farms contributed 51 % of the total national farmed<br />
shrimp production with a corresponding export value of approximately 23 million dollars<br />
in 2001(Table 2a). It is estimated that during that same year, the farms within the<br />
<strong>Placencia</strong> <strong>Lagoon</strong> Catchments employed approximately 200 permanent staff <strong>and</strong> 230<br />
temporary staff from the nearby communities.<br />
In 2002 the collective production of the mariculture operations in the <strong>Placencia</strong> area was<br />
38 % of the total national farmed shrimp production valued at 17 million dollars (Table<br />
2b). <strong>The</strong>se farms provided approximately 231 fulltime employment <strong>and</strong> 247 part time<br />
employment to residents of communities in the vicinity.<br />
16
Table 2a. Shrimp Mariculture production <strong>and</strong> export data 2001<br />
(Data Source: Belize Fisheries Department)<br />
Mariculture Sites Production Production Export<br />
Area (acres) Heads on lbs/yr lbs of tails<br />
Nova Laguna - - -<br />
Belize Aquaculture 94 1,689,307 1,142,812<br />
Royal Mayan 324 609,535 391,000<br />
Tex Mar 158 782,000 512,000<br />
Crustaceans 116 239,509 156,000<br />
Aqua Mar 1,000 1,753,215 1,131,790<br />
Table 2b. Shrimp Mariculture production <strong>and</strong> export data 2002<br />
(Data Source: Belize Fisheries Department)<br />
Mariculture Sites Production Production Export<br />
Area (acres) Heads on lbs/yr lbs of tails<br />
Nova Laguna - - -<br />
Belize Aquaculture 180 1,612,903 369,452<br />
Royal Mayan 318 543,909 348,102<br />
Tex Mar 128 251,241 196,655<br />
Crustaceans 195 262,467 170,606<br />
Aqua Mar 1,000 1,006,884 944,768<br />
Tourism Development<br />
Tourism is the base of the economy on the <strong>Placencia</strong> Peninsula. In order to further<br />
develop this industry there is an urgent need to construct resorts <strong>and</strong> hotels with the<br />
necessary amenities to host local <strong>and</strong> international tourists. Some of these amenities<br />
include (but is not limited to) beaches, piers, marinas, <strong>and</strong> parking lots. In view of this,<br />
there is a notably higher occurrence of l<strong>and</strong> clearing, l<strong>and</strong> reclamation <strong>and</strong> dredging<br />
activities in the area.<br />
Sport fishing (Fly fishing) <strong>and</strong> recreational fishing are popular tourist activity in the<br />
<strong>Placencia</strong> <strong>Lagoon</strong>. Special tours to observe manatees, birds <strong>and</strong> crocodiles are also on the<br />
list of things to do in the <strong>Placencia</strong> <strong>Lagoon</strong>.<br />
<strong>The</strong> Department of the Environment has received several applications for Environmental<br />
Clearance to develop Jet Ski rental operations in the <strong>Placencia</strong> <strong>Lagoon</strong>. Thus far all<br />
applications of this nature have been looked at unfavorably due to the potential negative<br />
impact on wildlife.<br />
18
RESULTS<br />
Bathymetry<br />
<strong>The</strong> bathymetry of the <strong>Placencia</strong> <strong>Lagoon</strong> was computed based on 202 geo-referenced<br />
soundings that were registered within the lagoon. <strong>The</strong> depth varies from near zero at the<br />
boundaries of the lagoon to approximately 5.8 meters below MSL in the deepest channels<br />
<strong>and</strong> the mouth of the lagoon. <strong>The</strong> average depth of the lagoon is 1.5 meters (Figure 5).<br />
<strong>The</strong> water quality data from each survey was vertically <strong>and</strong> horizontally averaged to<br />
provide an initial perspective on the water quality of the lagoon. <strong>The</strong> results of the mean<br />
measurements of temperature, pH, specific conductivity, salinity, dissolved Oxygen <strong>and</strong><br />
turbidity are summarized below (Table 3).<br />
Table 3. Mean measurements of several parameters in the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Survey 1<br />
(Apr. 5, 01)<br />
Survey 2<br />
(May 31, 01)<br />
Survey 3<br />
(Mar. 12, 03)<br />
Survey 4<br />
(Jul. 17, 03)<br />
Temp<br />
°C<br />
29.42<br />
29.69<br />
29.30<br />
30.08<br />
pH<br />
units<br />
8.32<br />
8.08<br />
8.39<br />
8.57<br />
SpCond<br />
mS/cm<br />
38.86<br />
48.98<br />
41.45<br />
37.65<br />
Salinity<br />
ppt<br />
24.79<br />
32.09<br />
26.66<br />
24.00<br />
D.O.<br />
% Sat<br />
122.09<br />
92.40<br />
116.56<br />
112.54<br />
D.O<br />
mg/l<br />
8.02<br />
5.79<br />
7.58<br />
7.55<br />
Tubidity<br />
ntu<br />
5.73<br />
4.32<br />
7.89<br />
10.64<br />
Temperature<br />
<strong>The</strong> temperatures recorded in the lagoon during the four surveys varied between 29.30<br />
<strong>and</strong> 30.08 (figure 6). Although lagoonal temperatures are controlled principally by solar<br />
radiation intensity, it is usually influenced by the influx of cooler water from the adjacent<br />
catchments <strong>and</strong> the water exchange with the Belize Barrier Reef <strong>Lagoon</strong>. <strong>The</strong> spatial<br />
temperature distribution in the lagoon for the four surveys can be observed in Figures A-<br />
D in Appendix 1.<br />
19
Temperature °C<br />
30.20<br />
30.00<br />
29.80<br />
29.60<br />
29.40<br />
29.20<br />
29.00<br />
28.80<br />
29.42<br />
29.69<br />
29.30<br />
30.08<br />
APR, 01 MAY, 01 MAR, 03 JUL, 03<br />
Survey Dates<br />
Figure 6. Mean temperatures of the <strong>Placencia</strong> <strong>Lagoon</strong> during four independent surveys.<br />
pH<br />
<strong>The</strong> pH determines the acidity or alkalinity of the water by measuring the hydrogen ion<br />
activity. Pure water is described as neutral <strong>and</strong> has a pH of 7. In the <strong>Placencia</strong> <strong>Lagoon</strong><br />
the mean pH varied from 8.08 to 8.57 (figure 7).<br />
pH<br />
8.70<br />
8.60<br />
8.50<br />
8.40<br />
8.30<br />
8.20<br />
8.10<br />
8.00<br />
7.90<br />
7.80<br />
8.32<br />
APR,<br />
01<br />
8.08<br />
MAY,<br />
01<br />
8.39<br />
MAR,<br />
03<br />
Survey Dates<br />
8.57<br />
JUL, 03<br />
Figure 7. Mean pH in the <strong>Placencia</strong> <strong>Lagoon</strong> during four independent surveys.<br />
21
Specific Conductivity<br />
<strong>The</strong> specific conductivity in the <strong>Placencia</strong> <strong>Lagoon</strong> showed some variations on the<br />
surveys. <strong>The</strong> mean specific conductivities varied between 37.65 <strong>and</strong> 48.98 miliSiemens<br />
per centimeter (figure 8).<br />
Specific Conductivity mS/cm<br />
60.00<br />
50.00<br />
40.00<br />
30.00<br />
20.00<br />
10.00<br />
0.00<br />
38.86<br />
48.98<br />
41.45<br />
37.65<br />
APR, 01 MAY, 01 MAR, 03 JUL, 03<br />
Survey Dates<br />
Figure 8. Mean Specific Conductivity in the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Salinity<br />
<strong>The</strong> salinity is derived from the measurements of specific conductivity <strong>and</strong> is expressed<br />
as parts per thous<strong>and</strong> (‰). <strong>The</strong> salinity variation is between 24.00 ‰ <strong>and</strong> 32.09 ‰.<br />
(figure 9). <strong>The</strong> spatial distribution of mean surface <strong>and</strong> bottom salinities for the four<br />
water quality surveys can be observed in figures A-D in Appendix 2.<br />
Salinity ‰<br />
35.00<br />
30.00<br />
25.00<br />
20.00<br />
15.00<br />
10.00<br />
5.00<br />
0.00<br />
24.79<br />
32.09<br />
26.66<br />
24.00<br />
APR, 01 MAY, 01 MAR, 03 JUL, 03<br />
Survey Dates<br />
Figure 9. Mean Salinity in the <strong>Placencia</strong> <strong>Lagoon</strong> for four independent surveys<br />
22
<strong>The</strong> salinity measurements within the <strong>Placencia</strong> <strong>Lagoon</strong> were looked at very closely<br />
during the analysis especially since several persons report high salinity gradients <strong>and</strong><br />
stratification in the water body. Surveys 1 to 4 indicate that the difference between<br />
surface <strong>and</strong> bottom salinities were 0.31, 0.62, 0.28 <strong>and</strong> 2.87 parts per thous<strong>and</strong><br />
respectively (Table 4).<br />
Table 4. Variation between Surface <strong>and</strong> Bottom Salinities of the <strong>Placencia</strong> <strong>Lagoon</strong><br />
MONITORING SURFACE SALINITY BOTTOM SALINITY<br />
SURVEYS Average Min Max Range Average Min Max Range<br />
Survey 1<br />
(Apr. 5, 01)<br />
Survey 2<br />
(May 31, 01)<br />
Survey 3<br />
(Mar. 12, 03)<br />
Survey 4<br />
(Jul. 17, 03)<br />
24.63<br />
31.78<br />
26.52<br />
22.59<br />
21.2<br />
18.2<br />
20.5<br />
4.9<br />
35.2<br />
35.5<br />
34.2<br />
30<br />
14<br />
17.3<br />
13.7<br />
25.1<br />
24.94<br />
32.4<br />
26.80<br />
25.46<br />
21<br />
26.7<br />
20.5<br />
13.3<br />
35.1<br />
35.6<br />
34.3<br />
34<br />
14.1<br />
8.9<br />
13.8<br />
20.7<br />
23
Dissolved Oxygen<br />
<strong>The</strong> dissolved oxygen concentration in the lagoon varied between 5.79 mg/l (92.40 %<br />
saturation) <strong>and</strong> 8.02 mg/l (122.09 % sat) in the four surveys that were conducted in the<br />
lagoon. Figures 10 a, b illustrate the mean dissolved oxygen levels distributed in the<br />
<strong>Placencia</strong> <strong>Lagoon</strong>.<br />
Dissolved Oxygen mg/L<br />
9.00<br />
8.00<br />
7.00<br />
6.00<br />
5.00<br />
4.00<br />
3.00<br />
2.00<br />
1.00<br />
0.00<br />
8.02<br />
5.79<br />
7.58<br />
7.55<br />
APR, 01 MAY, 01 MAR, 03 JUL, 03<br />
Survey Dates<br />
Figure 10a. Mean dissolved oxygen concentrations (mg/L) in the <strong>Placencia</strong> <strong>Lagoon</strong><br />
Dissolved Oxygen % sat<br />
140.0<br />
120.0<br />
100.0<br />
80.0<br />
60.0<br />
40.0<br />
20.0<br />
0.0<br />
122.1<br />
92.4<br />
116.6 112.5<br />
APR, 01 MAY, 01 MAR, 03 JUL, 03<br />
Survey Dates<br />
Figure 10b. Mean dissolved oxygen concentrations (% saturation) in the <strong>Placencia</strong><br />
<strong>Lagoon</strong><br />
24
Turbidity<br />
<strong>The</strong> mean turbidity levels of the lagoon were relatively low on all the surveys ranging<br />
from 4.32 to 10.63 NTU. <strong>The</strong> following is a graphic representation of the turbidity levels<br />
in the lagoon.<br />
Turbidity [NTU]<br />
12.00<br />
10.00<br />
8.00<br />
6.00<br />
4.00<br />
2.00<br />
0.00<br />
5.73<br />
4.32<br />
7.89<br />
10 .6 4<br />
APR, 01 MAY, 01 MAR, 03 JUL, 03<br />
Survey Dates<br />
Figure 11. Mean turbidity measurements for the <strong>Placencia</strong> <strong>Lagoon</strong><br />
25
DISCUSSIONS<br />
<strong>The</strong> depth variations of the lagoon floor bring to light several depressions. It is highly<br />
probable that these depressions serve as receptacles for organic material that settle <strong>and</strong><br />
undergo decomposition within the lagoon during calm conditions. In windy <strong>and</strong> stormy<br />
conditions the depressions are perturbed <strong>and</strong> sediment <strong>and</strong> organic matter are resuspended<br />
into the water column.<br />
<strong>The</strong> water temperature is an important parameter given that it controls the rate of<br />
biological <strong>and</strong> chemical activity to some extent. Furthermore, several marine <strong>and</strong><br />
estuarine organisms synchronize important events such as reproduction <strong>and</strong> migration<br />
with optimal water temperature. <strong>The</strong> observed mean water temperatures for two distinct<br />
dry seasons in the lagoon varied between 29.30 <strong>and</strong> 30.08 °C a difference of less than<br />
1°C. Notwithst<strong>and</strong>ing the fact that the ecological composition of the lagoon was outside<br />
the scope of this study, one could infer that the nektonic <strong>and</strong> benthic organisms in the<br />
lagoon are adapted to the aforementioned temperature range. <strong>The</strong> temperature of the<br />
lagoon is dependent on natural conditions such as solar radiation, season, wind action,<br />
storms, tides, level of stratification <strong>and</strong> river discharge.<br />
Estuarine pH levels generally average from 7.0 to 7.5 in the fresher sections to 8.0 <strong>and</strong><br />
8.6 in the more saline areas. Most marine organisms prefer conditions with pH values<br />
ranging from 6.5-8.5 (U.S. EPA, 1993). <strong>The</strong> average pH conditions observed in the<br />
<strong>Placencia</strong> estuarine system varied between 8.1 <strong>and</strong> 8.6. <strong>The</strong> observed pH are well within<br />
the acceptable range for most marine organisms <strong>and</strong> healthy estuarine environment. <strong>The</strong><br />
slightly alkaline pH of this estuary could be attributed to the natural buffering from the<br />
carbonate <strong>and</strong> bicarbonate dissolved in the water.<br />
Under natural conditions, processes such as photosynthesis <strong>and</strong> respiration are known to<br />
influence pH levels. High nutrient loadings from domestic wastewater of untreated<br />
effluent could exacerbate the levels of primary productivity <strong>and</strong> respiration that could<br />
lead to drastic short-term shifts in pH. This situation can be extremely harmful for many<br />
organisms. Despite the fact that such a condition was not encountered during the<br />
monitoring surveys, it is not at all far fetched for the <strong>Placencia</strong> <strong>Lagoon</strong>. <strong>The</strong> review of all<br />
the anthropogenic activities in the <strong>Placencia</strong> catchments did not identify any potential<br />
source for long-term acidification of the lagoon.<br />
<strong>The</strong> salinity is a crucial parameter that helps to define the biological <strong>and</strong> physical<br />
character of an estuary. <strong>The</strong> salinity in combination with other critical parameters (e.g.<br />
temperature) controls the types of plants <strong>and</strong> animals that could inhabit the different<br />
zones of an estuary. <strong>The</strong> freshwater species may be restricted to the upper reaches of the<br />
estuary while the marine species inhabit the estuarine mouth. In the lower section of the<br />
<strong>Placencia</strong> <strong>Lagoon</strong> there is a high density of Thalassia testidinum that declines rapidly<br />
towards the middle portion of the lagoon. Other plant species become dominant in the<br />
middle <strong>and</strong> upper portions of the lagoon. Euryhaline fish species including snook, jack,<br />
mullet <strong>and</strong> tarpon are frequently seen in most parts of the lagoon.<br />
26
<strong>The</strong> salinity maps presented in Appendix 2 display shifts in salinity distribution within<br />
the lagoon. This could be attributed to the effects of evaporation, freshwater influx from<br />
the <strong>Placencia</strong> catchments <strong>and</strong> the net water exchange between the entire estuarine system<br />
<strong>and</strong> the sea. <strong>The</strong> fact that the salinity is a conservative parameter allows us to make<br />
certain conclusions about the character of the lagoon. For instance, the monitoring<br />
surveys in the peak of two dry seasons (2001 & 2003) indicate that the upper section of<br />
the lagoon maintains a much lower salinity relative to the mouth of the lagoon. In effect<br />
this is a clear indication that the flushing rate of the upper part of the lagoon during the<br />
dry season is very low <strong>and</strong> is strongly dependent on wind <strong>and</strong> tidal forces. This is one<br />
natural attribute of the lagoon that highlights its vulnerability to the impacts of human<br />
settlement <strong>and</strong> aquaculture developments. Hypothetically, if large volumes of wastewater<br />
or untreated effluents were discharged into the upper section of the <strong>Placencia</strong> <strong>Lagoon</strong>, its<br />
water quality would rapidly decline <strong>and</strong> affect the natural ecological balance.<br />
Another characteristic of the lagoon is that during the dry season there are minimal<br />
differences between surface <strong>and</strong> bottom salinities. Based on this observation, the<br />
<strong>Placencia</strong> <strong>Lagoon</strong> is classified as a moderately stratified estuary.<br />
Dissolved Oxygen concentration is one of the best indicators of an estuary’s health. An<br />
estuary with little or no oxygen cannot support healthy levels of animal or plant life. <strong>The</strong><br />
aerobic bacteriological decomposition of organic matter requires Oxygen. Quite often<br />
this process depletes the water of oxygen <strong>and</strong> makes the environment uninhabitable for<br />
other organisms.<br />
Most animals <strong>and</strong> plants can grow healthy <strong>and</strong> reproduce when DO levels exceed 5 mg/L.<br />
However, when DO levels falls to 3-5 mg/L living organisms may become stressed. <strong>The</strong><br />
results of the surveys indicate that the <strong>Placencia</strong> <strong>Lagoon</strong> is a healthy environment<br />
displaying a wide range of dissolved oxygen concentration (between 5.79 <strong>and</strong> 8.02<br />
mg/L).<br />
Several studies in estuaries have shown that although excess nutrients from human<br />
activities are a major cause of hypoxia <strong>and</strong> anoxia, these conditions may also occur in<br />
estuaries relatively remote from human impact. However, the severity of low DO <strong>and</strong> the<br />
length of time that low oxygen conditions persist are less extreme. This is another good<br />
reason for a proactive approach to manage the impact of anthropogenic activities in the<br />
lagoon catchments. Offsetting the balance of the healthy <strong>Placencia</strong> <strong>Lagoon</strong> towards an<br />
anoxic <strong>and</strong> unproductive environment can be avoided.<br />
During the monitoring surveys the turbidity levels in the lagoon were influenced<br />
primarily by the intensity <strong>and</strong> duration of the wave action. <strong>The</strong> amount of mixing<br />
ultimately controlled the re-suspension of silt <strong>and</strong> organic matter into the water column.<br />
<strong>The</strong> perturbation in the extremely shallow parts of the lagoon was more vigorous as<br />
opposed to deeper parts <strong>and</strong> this was reflected in the heterogeneous turbidity levels.<br />
Generally, the turbidity levels were low as indicated by the averaged values ranging<br />
between 4.32 <strong>and</strong> 10.64 NTU. During the final survey (July, 03), some parts of the<br />
27
lagoon exhibited a golden-brown coloration (Plate 1(g)). This was probably a<br />
phytoplankton bloom triggered by some runoff.<br />
High turbidity levels over prolonged periods can diminish the heath <strong>and</strong> productivity of<br />
an estuarine system. Turbid waters reduce the availability of light to underwater plants<br />
<strong>and</strong> inhibit growth. Organisms that filter feed in an estuary are usually affected by high<br />
turbidity. In such conditions, suspended particles would accumulate on the gills of the<br />
organisms <strong>and</strong> impair breathing. <strong>The</strong> ability of marine birds <strong>and</strong> some fish to sight <strong>and</strong><br />
track their prey is greatly reduced in a turbid estuary.<br />
<strong>The</strong> turbidity levels of the <strong>Placencia</strong> <strong>Lagoon</strong> could be exacerbated by agricultural runoff,<br />
aquaculture effluent, spoil from dredging <strong>and</strong> l<strong>and</strong> reclamation sites; erosion <strong>and</strong> boat<br />
traffic.<br />
Considerable attention was given to the impacts of shrimp mariculture operations in the<br />
margin of the <strong>Placencia</strong> <strong>Lagoon</strong>. At the time of this study, the upper portion of the lagoon<br />
was not affected by aquaculture effluent. Nova Toledo has been non functional for<br />
several years (Tunich Nah, 2001). On the other h<strong>and</strong>, Belize Aquaculture Ltd. is a fully<br />
functional super intensive, closed system operation with a zero effluent discharge (Boyd<br />
et al., 2002). Royal Mayan, Tex Mar <strong>and</strong> Crustaceans Ltd. are three operations that are in<br />
close proximity to each other. Each of these operations meet the settling pond<br />
requirements (10% of the production area) stipulated by the Department of the<br />
Environment. Effluents discharged from these operations are subjected to mangrove<br />
wetl<strong>and</strong>s for nutrient <strong>and</strong> sediment reduction prior to entry into the lower portions of the<br />
<strong>Placencia</strong> <strong>Lagoon</strong>. <strong>The</strong> fact that the lower portion of the lagoon has a much higher water<br />
exchange rate with the sea (as opposed to the upper portion) is the reason why there is no<br />
significant impact on the ecological <strong>and</strong> environmental conditions of the lagoon. Aqua<br />
Mar is located at the southern boundary of the lagoon <strong>and</strong> its effluents are released into<br />
wetl<strong>and</strong>s in the northeastern tip of the Sennis River Catchment. Taking into account the<br />
predominant southerly coastal currents, the impacts of this operation on the <strong>Placencia</strong><br />
<strong>Lagoon</strong> are questionable.<br />
Similarly, attention was also given to the impacts of human settlement on the <strong>Placencia</strong><br />
<strong>Lagoon</strong>. <strong>The</strong> current growth trends of the communities pose two outst<strong>and</strong>ing threats to<br />
the lagoon: (1) increasing sediment input consequent to destruction of natural vegetation<br />
<strong>and</strong> (2) increasing nutrient loadings from improper disposal of domestic wastewater.<br />
28
CONCLUSIONS<br />
<strong>The</strong> characterization of the <strong>Placencia</strong> <strong>Lagoon</strong> was essential to put into perspective all the<br />
natural <strong>and</strong> anthropogenic factors that could affect the health <strong>and</strong> function of the<br />
estuarine system.<br />
<strong>The</strong> spatial, vertical <strong>and</strong> temporal variations in salinity distribution confirms that the<br />
<strong>Placencia</strong> <strong>Lagoon</strong> may be classified as a moderately stratified estuary.<br />
<strong>The</strong> small-scale water exchange in the upper section of the lagoon brings into prominence<br />
the vulnerability of the water body’s natural ecological <strong>and</strong> environmental conditions to<br />
excessive loadings of nutrients, organic matter <strong>and</strong> sediment.<br />
<strong>The</strong> upper section of the lagoon is not impacted by direct effluent discharge from the<br />
adjacent shrimp mariculture operations.<br />
<strong>The</strong> water quality indicators assessed in this study indicate that during the dry seasons<br />
2001 <strong>and</strong> 2003 the <strong>Placencia</strong> <strong>Lagoon</strong> displayed healthy environmental conditions.<br />
<strong>The</strong> data <strong>and</strong> results obtained in this study strongly support the hypotheses postulated.<br />
However, there is the need for more research to quantify impacts in terms of budgets for<br />
conservative <strong>and</strong> non-conservative parameters.<br />
RECOMMENDATIONS<br />
Cognizant of the invaluable natural ecological services <strong>and</strong> socioeconomic benefits<br />
provided by the <strong>Placencia</strong> estuarine system, it is appropriate to make several<br />
recommendations.<br />
Firstly, a reliable environmental quality-monitoring program needs to be implemented<br />
<strong>and</strong> sustained in the <strong>Placencia</strong> <strong>Lagoon</strong>. However, most regulatory authorities are faced<br />
with both financial <strong>and</strong> human resources constraints hence, it is incumbent on the local<br />
NGOs <strong>and</strong> residents to be involved in such a program.<br />
Secondly, the local village councils should liaise closely with the Department of the<br />
Environment to ensure that the major developments are compliant with mitigatory<br />
measures <strong>and</strong> national effluent regulations.<br />
Thirdly, the environmental NGOs should assume the lead role in educational programs to<br />
heighten the residents’ awareness about the importance <strong>and</strong> also the vulnerability of the<br />
<strong>Placencia</strong> <strong>Lagoon</strong>.<br />
Lastly, in view of the low water exchange in the upper portion of the <strong>Placencia</strong> <strong>Lagoon</strong>, it<br />
is imperative that future development are planned to ensure the lowest possible impact on<br />
the estuary.<br />
29
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32
APPENDIX<br />
I<br />
Temperature Distribution for four independent surveys of the <strong>Placencia</strong> <strong>Lagoon</strong><br />
33
APPENDIX<br />
II<br />
Salinity distribution for four independent surveys of the <strong>Placencia</strong> <strong>Lagoon</strong><br />
38
Abbreviations <strong>and</strong> Notations<br />
BNMS Belize National Meteorological Service<br />
BTIA Belize Tourism Industry Association<br />
CSO Central Statistical Office<br />
CZMAI <strong>Coastal</strong> <strong>Zone</strong> <strong>Management</strong> <strong>Authority</strong> <strong>and</strong> Institute<br />
DoE Department of the Environment<br />
ESTAP Environmental & Social Technical Assistance Project<br />
FoN Friends of Nature<br />
GIS Geographic Information Systems<br />
GPS Global Positioning System<br />
MBRS Mesoamerican Barrier Reef Systems Project<br />
NEMO National Emergency <strong>Management</strong> Organization<br />
NGO Nongovernmental Organizations<br />
NTU Nephelometric Turbidity Units<br />
RWS Rudimentary Water System<br />
°C Degrees Centigrade<br />
CMS Cubic meter per second<br />
DO Dissolved Oxygen Concentration<br />
Hp Horse power<br />
mg/L Milligrams per liter<br />
mS/cm MilliSiemens per centimeter<br />
MSL Mean Sea Level<br />
% sat Percent Saturation<br />
ppt Parts per thous<strong>and</strong><br />
v