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Ocean & Coastal Management 47 (2004) 625–639
www.elsevier.com/locate/ocecoaman
Coastal water quality assessment in the Yucatan
Peninsula: management implications
Jorge A. Herrera-Silveiraa,, Francisco A. Cominb,
Nancy Aranda-Cirerola, Luis Troccolic, Luis Capurroa
a
Marine Resource Department, CINVESTAV-IPN Unidad Merida, Carretera Antigua a Progreso km.
6,97310 Merida Yucatan, C.P., Mexico
b
Instituto Pirenaico de Ecologı´a-CSIC, Zaragoza Spain
c
Universidad de Oriente, Venezuela
Abstract
The coastal zone of Yucatan Peninsula has been recognized as the most important
environment to the economic development of this region. Different projects have been
conducted in this area, including harbors, tourist, commercial, and aquaculture infrastructure,
among others. However, there is no information available on what are ‘‘normal’’
concentrations of dissolved inorganic nutrients (DIN) and chlorophyll-a (Chl-a) for these
regions. In order to establish the base-lines of selected water quality parameters four coastal
areas of the north of Yucatan Peninsula (SE, Mexico) a monitoring program has been
conducted since 1999 in four localities of the north of Yucatan which show differences on the
kind and intensity of anthropogenic impacts. The results show that Dzilam is the site with the
best water quality conditions and a conservation program must be implemented, while Sisal
and Progreso are the ports with the worst water quality and where different strategies must be
implemented, such as water management of the shrimp farm effluents through constructed
wetlands in Sisal, or water waste treatment and facilitation of water circulation in the Progreso
port. Other results from phytoplankton community and submerged aquatic vegetation
indicate that these components must be incorporated into water quality programs in order to
effectively identify the problems and monitor the success of management strategies. These
results can be used to understand the linkages between stressors from the activities and
Corresponding author. Tel.: +52 99 99 812960; fax: +52 99 99 812334.
E-mail address: [email protected] (J.A. Herrera-Silveira).
0964-5691/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ocecoaman.2004.12.005
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attributes of the water quality. A joint state-federal and academic effort to improve the
conditions and increase the sustainability of the coastal zone is favored.
r 2005 Elsevier Ltd. All rights reserved.
1. Introduction
The Yucatan Peninsula (YP), with 1500 km of coast line, includes the
Mexican States of Campeche, Yucatan and Quintana Roo. It had a population of
4 million in 2000 and an annual birth rate of 2.2%, which is greater than the national
average of 1.7%. Its coastal zone is a region which provides enormous natural,
economic, and public health benefits. This region includes the watersheds, shores,
estuaries, coastal lagoons, bays and the exclusive economic zone (EEZ), where
important economic activities take place such as oil exploitation, fisheries, port
operation and tourism, all of which create environmental pressures that threaten the
very resources that make the coast desirable. These pressures include wetland loss,
changes in water circulation, increased nutrient load, and release of toxic chemicals
and pathogens.
From the above, it is clear that water quality is a major issue when dealing with
problems of human health, eutrophication, harmful algal blooms, fish kills, seagrass
loss, coral reef destruction, and even marine mammal and seabird mortality.
Therefore, it is of major importance to recognize the spatial and temporal
variability of the water characteristics in coastal aquatic ecosystems as a key point to
establish indicators of water quality which may be used for its management [1]. In
many cases, region specific features, rather than a single common general rule,
should be considered.
It should be noted that the hydrographic basin of the YP shows some particular
features such as a karstic type of soil which favors rainwater infiltration to the
aquifer, and an important web of groundwater discharge in the coastal zone through
springs and non-point sources amounting 9 million m3 yr1 km of coast [2]. The
region does not have any rivers and has little to no topographic elevation.
These general features of the entire coastal zone of the YP contrast with the
differences observed on the kind and intensity of the anthropogenic impacts as the
following sites.
Progreso has the highest coastal population, with 50,000 residents and a similar
amount occupying the beach houses during tourist season (July–August). It has the
most important port of the region, moving 120 ton day1; however, due the
shallowness of the area (o5 m), it was necessary to build an 8 km seaway to reach a
depth of 5–6 m. About 70% of this structure prevents the east–west water flow
modifying the hydrodynamics of the zone. Sisal is a fisherman-town of less than 5000
inhabitants, with shrimp-farms, in an area of 480 ha and still growing. Celestún, is
another fisherman-town (5000 inhabitants), where both fish-trawling in shallow
areas (o2 m depth) and growing local tourism are important activities. Finally,
Dzilam is another fishery-town (o3,000 inhabitants) characterized by great amounts
of groundwater discharge through coastal springs, more than 100 of which have been
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recorded in 3 km2. All the sites do not have wastewater treatment; houses, tourist
facilities and fishery industries generally have septic tanks.
Therefore, we assume that the water quality is affected in different levels related to
the kind and intensity of the anthropogenic impacts. The purpose of this study is to
identify the spatial and temporal heterogeneity of water characteristics in the YP
using non-conventional instrumentation and data analysis, and to discuss the value
of reference water quality characteristics and indexes for monitoring programs and
their utility for management strategies.
2. Material and methods
Samples were taken along four lines parallel to the coast, with a total of 12 stations
on a 4 km2 sampled area at each locality (Fig. 1). They were covered bimonthly from
September 1999 to August 2001. At each station in situ measurements of
temperature, salinity, and dissolved oxygen were made using a YSI 85 multiparameter sound. Water samples were collected with a 2.5 l Van Dorn bottle for
nutrient and chlorophyll-a (Chl-a) analyses following standard methods [3,4].
In order to establish reference conditions for water quality, information of the
water characteristics should cover different temporal and spatial scales.
2.1. Single variables
Each variable was analyzed through a non-parametric variance analysis using box
and whisker diagrams in order to evaluate differences between sites. The mean is
Fig. 1. Map of the Yucatan Peninsula showing the sampling sites.
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represented by a triangle and median by the horizontal line into the box, 25th and
75th percentiles are top and bottom of the box, while the 5th and 95th are located on
the tips of the whiskers. The median notch is the 95% confidence interval of the
estimate. When notches between boxes do not overlap, the medians are considered to
be significantly different.
2.2. Combined variables
In order to provide means of exploring the multivariate nature of the data set, an
ordination analysis (principal components analysis—PCA) was done to identify the
key variables with the greatest influence in the hydrological behavior of each site.
2.3. Spatial and temporal variability
Spatial variability of the lagoon under different weather conditions was measured
with an instrument system for high-speed mapping of temperature, salinity,
chlorophyll-a and transparency called DataFlows.[5]. This instrument is adapted
for flow-through sampling of the shallow coastal environment using a small boat
with a flexible intake and equipped with sensors interfaced with a data-logger to
automate the measurement of multiple variables in a spatial context through
integrated GPS. The continuous trip in each run can be observed in the Fig. 2; more
than 2000 data points of each variable were recorded for each period.
The collected data were analyzed to estimate the variability index (VI), which
produced an average percentage of change of each variable from nearest neighbor
for each point in the transect.
1 Zx; y ;
VI ¼ 1 Zx 1; y 1
where Z ¼ parameter, x ¼ lat., y ¼ long.
2.3.1. Trophic status
The sampling sites of the YP are enriched with nutrients from natural and cultural
discharges; therefore, for the evaluation of water quality it was necessary to use an
index of trophic status. In this case the nutrient eutrophication index applied was
TI ¼
C
þ log A;
C log x
where TI is the nutrient eutrophication index, C is the log of the total loading of a
given nutrient in an area and x is the total concentration of this nutrient at certain
station. The values generated provide a continuous assessment of water quality and
give a value to the degree of eutrophication. The significance of the nutrient
eutrophication index is that a TI is higher than 5 indicates eutrophic waters; for
mesotrophic waters the TI ranges from 5 to 3, and for oligotrophic waters the TI is
lower than 3 [20]. This dimensionless index was designed to be specific for each
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40
36
Salinity, psu
Temperature, ˚C
35
30
25
32
28
24
20
20
DZ
PR
(A)
SI
CE
Site
DZ
PR
(B)
SI
CE
SI
CE
Site
9
12
10
8.5
8
pH
Dissol. Oxygen, mg/l
629
6
4
8
7.5
2
7
0
DZ
(C)
PR
SI
Site
CE
DZ
(D)
PR
Site
Fig. 2. Box and whiskers plots of temperature, salinity dissolved oxygen and pH, for each sampling site.
nutrient, with application to various types of water, sensitive to stressful effects of
eutrophication and simple for gathering data and for calculation.
In order to establish seasonal variability, comparison of the hydrographical
variables between sites and seasons was done with the heterogeneity index [6], which
results from the sum of the Euclidian distances of each station (12) of each site (4)
from the PCA biplot.
To get a first approach of site classification as a function of water quality, cluster
analysis was done with the significant variables provided by PCA. This analysis was
done using data agglomeration techniques applied to calculation of the squares of
their Euclidean distances.
3. Results
3.1. Single variables
Variance analysis showed significant differences (po0.05) among the study areas
with respect to salinity, dissolved oxygen, pH, nitrate, nitrite, silicate and Chl-a. The
lowest and highest water temperatures were observed in Dzilam (21–33.8 1C)
(Fig. 2A). The median salinity was comparatively lower in Dzilam than in the other
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Table 1
Median, lower and upper quartile of water quality variables for each study area (n ¼ 850)
Temperature
1C
Salinity
Psu
Dissol. Oxygen
Mg/l
PH
Nitrate
mmol/l
Nitrite
mmol/l
Ammonium
mmol/l
Phosphate
mmol/l
Silicate
mmol/l
Chl-a
Mg/m3
a
Dzilam
Progreso
Sisal
Celestun
EC CNAa
27
25–29
36
34–37
5.3
4–6
8.3
8.1–8.3
5.2
3.2–9.4
0.51
0.2–0.9
4.2
3–6
0.62
0.3–0.9
8.8
6–13
1.14
0.8–2
26.3
24–28.6
38.3
37–39
5.2
4.5–6
8.3
8.2–8.4
1.2
0.5–2
0.79
0.5–1
5.2
4–6
0.46
0.2–0.7
4.3
3–6
1.7
1–3
26.4
25–28.4
37.4
36–38
5.7
5.5–6.5
8.2
8.1–8.3
4.8
3.2–7
1.01
0.5–1.5
4.5
1.2–7.7
0.51
0.3–0.8
7.1
4–11
3.2
1.6–6
26.5
24.8–28
37.6
36–38
5.7
5–6.5
8.2
8.1–8.3
1.7
0.5–3.2
0.49
0.2–0.9
5.2
3.7–8.7
0.46
0.3–0.7
7.5
5–11
2.5
1.4–5
NAb
NA
5
NA
0.6
0.04
0.55
0.02
NA
NA
EC-CNA: Ecological Criteria, Comision Nacional del Agua.
NA: not applicable.
b
sites (Table 1). Nevertheless, in Sisal the lowest values (20.5 psu) (Fig. 2B) registered
corresponding to the effluent of a shrimp farm.
Dissolved oxygen shows hypoxic (o2 mg/l) levels in Dzilam, Progreso and Sisal;
however, the median values (Table 1) indicate general conditions of a well
oxygenated water column in all sites. The pH is less variable in Progreso and was
significantly lower in Sisal (Fig. 2D).
Ammonium was higher in Sisal and Progreso, with most values above 3 mmol/l
(Fig. 3A). In Sisal, concentrations above 80 mmol/l were observed near the discharge
of the shrimp farm effluents, while in Progreso high values (430 mmol/l) were
registered during the periods of major human occupation of the summer houses.
Nitrate was significantly high (Po0.05) in Dzilam and Sisal (Fig. 3B). The highest
concentrations in Dzilam (450 mmol/l) correspond to areas around the groundwater
discharges, while in Sisal high concentrations were observed near the effluent of the
shrimp farm (4100 mmol/l)
Nitrite was significantly higher (Po0.05) in Sisal and Progreso (Fig. 3C),
following the same pattern as ammonium with respect to sources and time.
Phosphate median was significantly different among sites (Fig. 3D),
however, relevant values (45 mmol/l) were observed in Sisal in the shrimp farm
effluent area.
Silicate was significantly higher (Po0.05) in Dzilam and Sisal (6.61 mM) (Fig. 3E).
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10
80
100
8
60
40
20
0
60
40
20
3
2
1
0
60
40
20
0
DZ
PR
SI
Site
CE
2
120
90
60
30
0
DZ
(E)
4
150
80
Chl-a, mg/m3
Silicate. µmol/l
4
6
(C)
100
5
631
0
(B)
6
Phosphate, µmol/l
80
0
(A)
(D)
Nitrate, µmol/l
100
Nitrate, µmol/l
Ammonium, µmol/l
J.A. Herrera-Silveira et al. / Ocean & Coastal Management 47 (2004) 625–639
PR
SI
Site
CE
DZ
(F)
PR
SI
CE
Site
Fig. 3. Box and whiskers plots of ammonium, nitrate, nitrite, phosphate, silicate and chlorophyll-a for
each sampling site.
Chlorophyll-a was significantly higher (po0.05) in Sisal and Celestun.
Minimum values were observed in Dzilam (o0.5–1.5 mg/m3) and maximum in Sisal
(4120 mg/m3) (Fig. 3F) near the shrimp farm effluent.
3.2. Combined variables
Principal component analysis of the hydrological variables showed that 60% of
the total variance is in the first three components for all study zones (Table 2). In
Dzilam, salinity, silicate, nitrate and dissolved oxygen have a significant correlation
with the first two components, suggesting association with groundwater discharges.
Ammonium and Chl-a are correlated with the third component related aquatic
production.
With respect to Progreso, PCA showed nitrite, phosphate and ammonium related
to Component I, likely from eutrophication processes. Salinity and dissolved oxygen
are related to Component II, meaning groundwater discharges, as the third
component correlates with silicate.
In Sisal, salinity, Chl-a and silicate have a significant correlation with the first
Component while the second one is correlated with nitrate, ammonium and
phosphate, indicating that the shrimp farm effluent is an important source of
variation to the hydrological pattern.
In the case of Celestun, PCA showed salinity and nitrate correlated to Component
I (groundwater discharges) while silicate and Chl-a are correlated with Component
II, suggesting aquatic production.
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Table 2
Percentage of total explained variance and critical variables of the three first components in study area
Site
Component
Explained variance
Critic variables
Dzilam
I
II
III
32
17
12
Salinity, nitrite, silicate
Nitrate, dissolved oxygen
Chl-a, ammonium
Progreso
I
II
III
25
20
15
Phosphate, nitrite, ammonium
Dissolved oxygen, salinity
Silicate
Sisal
I
II
III
45
13
12
Salinity, Chl-a, silicate
Nitrate, ammonium, phosphate
Nitrite, pH
Celestun
I
II
III
27
24
11
Salinity, nitrate
Chl-a, silicate
Dissolved oxygen, pH
Heterogeneity index
12
11.9
11.8
11.7
11.6
11.5
11.4
NORTES
DZILAM
DRY
SEASON
PROGRESO
SISAL
RAINY
CELESTUN
Fig. 4. Comparison of spatial and temporal variability from date of the DataFlow system: Exempla with
fluorescence.
3.3. Spatial and temporal variability
The high resolution of the spatial data collected with the DataFlow system can be
used to estimate the variability of each zone and comparison among sites and
seasons for each variable (Fig. 4) or for all variables (Table 3).
The major variability of salinity and temperature was observed in Dzilam where
the groundwater springs are abundant and where mean depth is lowest (2.3 m).
The long-term variability of each site was determined after the annual trends of
the trophic index (Fig 5). Dzilam showed a uniform oligotrophic behavior while the
other sites showed a tendency to increase their trophic status. Progreso and Celestun
changed from oligotrophic to lightly mesotrophic in three years, while in Sisal the
major changes were from mesotrophic to almost eutrophic.
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Table 3
Total and individual Variability Index the data from DataFlow system
Variable site
Salinity
Temperature
Transparency
Fluorescence
Total
Dzilam
Progreso
Sisal
Celestun
0.86
0.75
0.78
0.72
0.72
0.68
0.68
0.63
0.53
0.73
0.82
0.66
0.64
0.76
0.87
0.71
2.75
2.92
3.15
2.72
6
Disimilarity
5
4
3
2
1
0
DZILAM
CELESTUN
PROGRESO
SISAL
Fig. 5. Values of Trophic Index for each sampling site.
6
5
TROPHIC INDEX
Eutrophic
1999
2000
2001
4
Mesotrophic
3
2
Oligotrophic
1
0
Dzilam
Progreso
Sisal
Celestun
SITES
Fig. 6. Heterogeneity Index calculated by each sampling site.
3.4. Classification of sites
The heterogeneity index from hydrographic variables showed seasonal changes.
During the Nortes (northern winds) season, Celestun had the greatest heterogeneity,
followed by Dzilam, while in Sisal and Progreso high heterogeneity happened
during the dry and rainy seasons, respectively (Fig 6). In accordance with their
hydrographic similarities there are two groups in the dendrogram (Fig. 7A,B and C,D):
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(1) Dzilam and Celestún and Progreso and Sisal, however, as seen in the distance value,
the sites of the second group are more similar between them.
4. Discussion
The studied coastal aquatic ecosystems of Yucatan showed a high spatial
variability of their water characteristics at small (meters) (Fig. 4, Table 3) and
medium (km) (Figs. 2 and 3) scales. The same high spatial variability was observed at
short (seasonal) (Fig. 6) and medium (interannual) (Fig. 5) temporal scales. This is a
common characteristic in many coastal zones [7] because of the ecological gradients
established as a consequence of the land-ocean energy exchanges, mixing of fresh
and marine waters, and human disturbances. As a consequence, quality criteria and
monitoring of the water characteristics of these coastal aquatic ecosystems should be
done covering their spatial and temporal variability.
Fig. 7. Classification analysis of the sampling sites.
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Fig. 7. (Continued)
The data from this study were analyzed according to EPA [8] recommendations
showing strong differences between sites (Table 1), which indicates that water quality
characteristics are strongly dependent on landscape features, particularly those
related to human activities. As a consequence, specific criteria may be required for
different sites to establish quality criteria and monitoring programs. Table 1 also
shows that the official water quality criteria used in Mexico [9] are inappropriate,
because they are applied in general to waters in the Gulf of Mexico, Caribbean and
Pacific Seas, which have very different hydrographic and biogeochemical characteristics. Accepting the application of those common criteria for such different seas
implies that human activities must have similar qualitative and quantitative impacts
in all of them. As an example, all localities studied should be labeled as ‘‘poor’’ for
support of aquatic life since the average nitrate concentration observed during this
study is higher than the official designated value (0.06 mmol/l). The same is valid for
nitrite, phosphate and ammonium. Again, reference criteria should be reviewed
according to specific site characteristics and the monitoring and comparative
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program should be extended to cover the range of spatial and temporal data
variability observed.
This approach has additional advantages for implementing management actions.
Figs. 2 and 3 show that temperature variability was higher in Dzilam, which is the
coastal zone with the highest number of springs and the shallowest zone [10]. Salinity
variability was high in Dzilam, Sisal, and Progreso and reached relatively low values
in these three zones related to spring groundwater discharges, shrimp farm effluents,
and non-point groundwater discharges, respectively (12).
Salinity in Dzilam and Sisal was more variable, and reached the lowest values, the
first related to the groundwater discharge and the second to the shrimp farm effluent,
while Progreso showed the highest median value, suggesting input from groundwater
seepage [11]
The wide range of variation of dissolved oxygen indicates intense metabolic
activity in the water column; nevertheless, the hypoxic values observed in Dzilam,
Progreso and Sisal suggest that they may be more vulnerable to increasing loading of
dissolved nutrients and organic matter [12].
Ammonium, nitrite and phosphate were good indicators of anthropogenic
impacts. In Progreso the loading of nutrients comes from seepages [10,11] and are
higher during the summer season, which is the time with the major human
occupation of the coast by local tourism. The highest concentrations of nutrients and
Chl-a in Sisal are related with the shrimp farm and harbor effluents. In Celestun,
trawling fishing in shallow (o2 m) areas induce water-sediment processes favoring
high ammonium and Chl-a levels. Phytoplankton is dominated by benthic
diatoms. [13], suggesting resuspension as an important agent to the biogeochemistry
of this site.
Nitrate and silicate were higher in Dzilam and Sisal, the former from groundwater
discharges recognized as nitrate and silicate source [14], the latter from the shrimp
farm and harbor effluents. Shrimp ponds are fertilized with nitrates and silica to
favor the growth of diatoms, while in the harbor two springs fertilize the coastal
area.
As part of a major project, phytoplankton and submerged aquatic
vegetation (SAV) have been recorded in some sites in order to incorporate biological
indicators of water quality. As for phytoplankton, Progreso is dominated by
dinoflagellates and has been reported harmful species as Dinophysis caudata,
Gymnodinium sanguı´neum, Gambierdiscus toxicus, Prorocentrum mexicanum, Prorocentrum mı´nimum, Heterocapsa circularisquama, Prorocentrum lima, and Pyrodinium bahamense v. compressum, while in Dzilam diatoms dominate the community
[10,13], this algal dominance changes is recognized as a primary symptom of
eutrophication [15].
With respect to SAV, Dzilam is the site with highest coverage of seagrasses, with
Progreso and Sisal being the lowest. These two sites have been experiencing loss of
SAV and substitution of seagrasses by macroalgae [16]; these changes are recognized
as secondary symptoms of eutrophication [15]. In Celestun, trawling fishing’s
mechanical damage to SAV and increases water turbidity, both of which have
negative impacts to SAV growth.
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Incorporation of water quality biological indicators in a coastal zone management
program may seem expensive and time-consuming; however, their utility in evaluate
the consequences of eutrophication, chemical pollution, and impacts to human
health [17,18], as well as to evaluate the successes of the management strategies can
not be questioned.
The analysis of each variable is the first step to determine the water quality of the
coastal zone; however, to optimize the value of this information in costal zone
management, it is necessary the repeat measurements over time and space and to
conduct integral analysis in order to learn patterns and trends of water quality.
Multivariate statistical techniques and indexes can be useful in order to capture the
variance of the original dataset and extract general patterns.
In Dzilam, PCA results (Table 2) indicate that groundwater discharges and
resuspension are the most important process as to control water quality patterns.
Spatial variability is also related to groundwater discharge and their general
characteristics, including the human activities, result in a oligotrophic condition with
respect to the other sites, suggesting that conservation strategies should be included
in a management coastal zone program of this area.
In Progreso, the critical variables (Table 2) suggest that domestic sewage seepage
and changes in water movement by the harbor are the major factor affecting water
quality; its spatial variability and trophic status are reflected in phytoplankton and
SAV communities. Therefore, a sewage treatment plant and improvement of the
harbor water circulation should be the first step in a management strategy.
In Sisal, it is clear that the shrimp farm effluent is responsible for the spatial
variability and temporal trophic changes, showing that mariculture is an activity that
must be strictly regulated by local legislation. A new water pond management must
be developed considering the wetlands use as waste treatment [19].
In Celestun, critical variables, spatial variability and trophic status show a healthy
water body classified in the same group of Dzilam. However, some management
strategies should be implemented to stop trawling fishing in shallow areas (o2 m),
improve the septic tanks systems in the tourist infrastructure, and promote the water
circulation in the fisherman port.
It can be concluded that eutrophication is a major concern of the Yucatan
Peninsula coastal zone, and in accordance with the present economic development
(e.g., ports, tourism) of the region, its impact on the water quality, biological
integrity, and human health could be enormous and could negatively affect any
management program.
In conclusion, it is recommended that sustainable coastal zone management
include an efficient water quality program for each area or zone (reference values),
incorporating measurements (physical, chemical and biological) of a group of
environmental variables in a space–time context. These measurements should be
analyzed following approaches to integrate the collected data (e.g., through
multivariate statistics and indexes) in order to develop the capacity to determine
localization and intensity of the problems and trends of management actions. Water
quality should be used as a reference point for the coastal zone management
procedure.
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Acknowledgments
We thank the staff of the Primary Production Laboratory of CINVESTAV-IPN
Unidad Merida, in special to J. Ramirez, A. Zaldivar, C. Alvarez, M. Agüayo,
J. Trejo, C. Vallejo, I. Medina, M. Reyes and Z. Chi. This work was supported by
CONACYT-32356-T and CONACYT G-34709-T.
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