Jane L. Guentzel Enrique Portilla-Ochoa Alejandro Ortega-Argueta Blanca E. Cortina-Julio Edward O. Keith THE ALVARADO LAGOON – ENVIRONMENT, IMPACT, AND CONSERVATION In: "Lagoons: Biology, Management and Environmental Impact” Editor: Adam G. Friedman ISBN: 978-1-61761-738-6 2011 400 Oser Avenue, Suite 1600 Hauppauge, N. Y. 11788-3619 Phone (631) 231-7269 Fax (631) 231-8175 E-mail: [email protected]http://www.novapublishers.com Science Publishers, Inc. OVA N
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Jane L. Guentzel Enrique Portilla-Ochoa
Alejandro Ortega-Argueta Blanca E. Cortina-Julio
Edward O. Keith
THE ALVARADO LAGOON – ENVIRONMENT,IMPACT, AND CONSERVATION
In: "Lagoons: Biology, Management and Environmental Impact”
Editor: Adam G. Friedman
ISBN: 978-1-61761-738-6 2011
400 Oser Avenue, Suite 1600Hauppauge, N. Y. 11788-3619Phone (631) 231-7269Fax (631) 231-8175E-mail: [email protected]://www.novapublishers.com
Science Publishers, Inc.OVAN
In: Lagoons: Biology, Management and Environmental Impact ISBN: 978-1-61761-738-6
The license for this PDF is unlimited except that no part of this digital document may be reproduced, stored in a retrieval system or transmitted commercially in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services.
Jane L. Guentzel, Enrique Portilla, Alejandro Ortega-Argueta et al.
398
Over 100 fish species have been collected from the ALS, representing four ecological
guilds: marine stenohaline, marine euryhaline, estuarine, and freshwater fishes. These
assemblages have not experienced significant changes over the past 40 years, but there
has been a recent decline in diversity. Antillean manatees (Trichechus manatus manatus)
historically have occurred in the ALS but were reduced in the 1970s and 1980s by
hunting and are now considered endangered. The rescue of 6 orphan calves between 1998
and 2000 suggests that manatees are reinhabiting the ALS as a result of conservation
measures. Manatees are most commonly sighted in the Alvarado Lagoon, Acula River
and adjacent lagoons, and are rarely sighted in the Limon River and adjacent lagoons. To
protect the manatees and their habitat an educational program was developed in 1998 and
an assessment of their current status and critical habitat in the ALS was conducted. Our
manatee conservation efforts were recognized in 2001 when September 7th was officially
declared the ―National Day of the Manatee‖ in Mexico. Almost 350 species of birds
occur in the ALS, including the Mexican Duck (Anas diazi), which is undergoing a slow
but marked decline due to habitat destruction and overhunting. The largest threats to the
ALS include unsustainable sugar cane cultivation, cattle-ranching, coastal urban
development, oil and gas exploration and exploitation, water pollution by urban waste
and agricultural runoff, and increases in port and tourism industries. Despite the
establishment of government policy and measures to protect the coastal wetlands of ALS,
the identified threats continue to menace the important biodiversity and human well-
being of the region.
INTRODUCTION
The Alvarado Lagoon System (ALS) in south-central Veracruz state (Figure 1), Mexico,
is a large mangrove dominated coastal wetland located 70 km southeast of the Port of
Veracruz. It has a total area of 2800 km2 of which 258 km
2 are covered by water. The
Alvarado Lagoon (AL) is a shallow system (average depth 1.5 m) connected to the
Camaronera Lagoon by a narrow channel and to the Gulf of Mexico (GOM) via a 0.4 km
wide sea channel [Moran-Silva et al., 2005, Cruz-Escalona et al., 2007]. The AL has a
maximum width of 4.5 km and a mean surface area of 62 km2. The ALS is mainly formed by
the Alvarado, Buen Pais, Camaronera and Tlalixcoyan lagoons, but it is also associated with a
great number of smaller aquatic bodies, flood zones, and parts of the Acula, Blanco, Limon
and Papaloapan rivers. The Papaloapan River extends through the states of Oaxaca, Puebla
and Veracruz and traverses a distance of 445 km, passing through the city of Tlacotalpan and
finally emptying into the AL. The Papaloapan drainage basin covers an area of approximately
39,200 km2.
The ALS is one of the most productive estuarine-lagoon systems in the Mexican GOM
[Cruz-Escalona et al. 2007]. It is characterized by a large diversity of interactions with its
adjacent systems, particularly an extensive marsh, which contributes greatly to its biological
productivity. Seasonal changes are well pronounced and are mainly influenced by the
precipitation-drought regime conditions associated with its ecosystem. The ALS has three
separate zones based on physicochemical characteristics; Camaronera Lagoon, Buen Pais
Lagoon and the urban zone of Alvarado Lagoon, and the river zone of Alvarado Lagoon
[Moran-Silva et al., 2005].
Model studies suggest that primary production by sea grasses provides more energy input
to the ecosystem than detritus, which is the opposite of most other Mexican GOM lagoons
The Alvarado Lagoon – Environment, Impact, and Conservation
399
and estuaries. This may be a consequence of relatively rapid flushing (50 x 109 m
3 of water
each year), a short water exchange time (0.5 days), mangrove deforestation, and overfishing
[Cruz-Escalona et al., 2007]. The increase of anthropogenic activities in the surrounding
terrestrial areas coupled with limited waste management planning have contributed to both
local and regional deterioration of the hydrological characteristics of the ALS [Cruz-Escalona
et al., 2007].
Figure 1. Satellite photograph of the Alvarado Lagoon System showing the major lagoons and rivers of
the area. Image courtesy of the Consejo de Desarrollo del Papaloapan (CODEPAP, 2003), Xalapa, Ver.,
Mexico
ENVIRONMENT AND IMPACT
Mercury and Other Water Quality Parameters
We collected sediment, fish, and unfiltered water samples from the Alvarado Lagoon,
Lagoon Camaronera, and the Gulf of Mexico during the wet (September 2005) and dry
(March 2003 and 2005) seasons (Table 1). Water column pH values were slightly alkaline
(7.6-8.6) and the salinity ranged from 1-25.5 psu. Precipitation amounts for the dry season
months of March 2003 and March 2005 were 0.23 cm, and 2.79 cm, respectively, and the wet
season month of September 2005 was 272 cm. Salinity in the ALS was inversely correlated
with rainfall, with highest levels occurring in the dry season samples (March 2003 and 2005)
and lowest levels occurring in the wet season samples (September 2005) (Table 2). Our
salinity values are similar to the salinity ranges (1-14 psu) reported for the lagoon during the
2000-2001 wet, dry, and storm seasons [Moran-Silva et al., 2005]. Levels of nitrate (NO3-N
mg/L) during the 2000-2001 season ranged from 0.03-0.14 mg N/L [Moran-Silva et al.,
2005]. Our values for nitrate (NO3-N mg/L) during the 2003 dry season ranged from 0.73-2.3
Jane L. Guentzel, Enrique Portilla, Alejandro Ortega-Argueta et al.
400
mg NO3-N/L. These values are slightly higher than the 2000-2001 values and may be
indicative of increasing anthropogenic stressors within the lagoon system. Estuaries are
considered at medium risk for eutrophication when nitrate values range from 0.1-1 mg N/L
and high euthrophic risk when the values are greater than 1 mg N/L [Bricker et al., 1999]. It
has been noted that nutrient levels within the lagoon can vary seasonally and spatially as a
result of river discharge, rainfall, resuspension of sediments, and biological activity [Moran-
Silva, et al. 2005]. Concentrations of total inorganic carbon (TIC) ranged from 14.4-22.1 mg
C/L and did not vary seasonally. Levels of total organic carbon (TOC) ranged from 3.9-20.9
mg C/L, with the highest concentrations observed during the rainy season (Table 2).
Total mercury and total suspended solids (TSS) ranged from 0.92-26.1 ng Hg/L and 1-
39.2 mg TSS/L, respectively (Table 2). The strong correlation (R2=0.71; P=0.001) between
total mercury and TSS in the water column suggests that particulate matter is a carrier phase
for mercury within the Alvarado and Camaronera lagoons. A more comprehensive study of
the Alvarado Lagoon, and the Limon, Acula, Blanco, and Papaloapan rivers conducted during
the March 2003 and 2005 dry seasons and the September 2005 wet season found that mercury
concentrations were significantly correlated with total suspended solids in the water column
(R2=0.82; P<0.001) [Guentzel et al., 2007]. The mercury concentrations in the Alvarado
Lagoon, and the Blanco, Acula, and Limon rivers during the March 2003 and 2005 dry
seasons (0.9-4.9 ng Hg/L) were similar to the September 2005 wet season (1.9-4.9 ng Hg/L),
with higher Hg levels associated with higher levels of TSS. Water samples collected from the
Papaloapan River were higher in Hg (10.9-12.7 ng (Hg/L) and TSS (89.1-154.7 mg TSS/L)
during the September 2005 wet season than the March 2003 and 2005 dry seasons (0.9-2.7 ng
Hg/L; 4.8-39.7 mg TSS/L). The sites from the Papaloapan River were sampled within 12
hours of a nighttime rainfall (15cm) event during the September 2005 wet season. The
elevated Hg concentrations from this site during the wet season are likely a result of increased
particulate matter transport within the river during high flow conditions and or input of
dissolved and particulate Hg from precipitation [Guentzel et al., 2007]. A Mercury Deposition
Network (MDN) monitoring site (HD01) within this region reported a rainfall Hg
concentration of 11.4 ng Hg/L during the time period that the samples were collected from the
Papaloapan River [Mercury Deposition Network]. The water column values that we observed
for total Hg (0.92-26.1 ng/L) are below the US EPA ambient surface water quality criteria for
freshwater (0.77-1.4 µg/L) and saltwater (0.94-1.8 µg/L) (US EPA, 2006) and the Mexican
marine aquatic life criteria of 0.02 µg/L [Jimenez et al., 1999].
Table 1. Station identifications and locations for
mercury and other water quality parameters
Latitude Longitude
Station Identification (N) (W)
Alvarado Lagoon I 18 46.132 095 47.333
T 18 45.955 095 48.607
BB 18 44.995 095 44.966
Lagoon Camaronera DD 18 51.178 095 54.654
EE 18 51.589 095 55.187
FF 18 51.716 095 54.412
Gulf of Mexico AA 18 48.422 095 44.420
Table 2. Water quality parameters measured during the March 2003 and 2005
dry season and the September 2005 wet season
, Month Station Salinity
(psu)
Nitrate
NO3-N
(mg/L)
pH Total
Inorganic
Carbon
(mg C/L)
Total
Organic
Carbon
(mg C/L)
Total
Suspended
Solids
(mg/L)
Total
Mercury
(ng/L)
Alvarado Lagoon March 2003 I 9.9 2.3±0.9 8.1 14.9±4.2 5.4±2.1a 9.1±4.5a 0.92±0.05a
March 2003 T 9.8 1.35 8.0 14.4 4.7a 1a 1.78a
March 2003 BB 6.7 1.51 7.9 14.7 3.9a 14.1a 2.67a
March 2005 T 12.9 - 8.1 22.1±0.16 9.5±0.98a 9.1±5.6a 0.92±0.03a
Gulf of Mexico March 2003 AA 25.5 0.73±0.8 8.6 16.4±0.47 6.5±0.04a 1.13a 1.27±0.01a
The values for March 2003 stations I and AA, and March 2005 station T represent the mean and standard deviation of 2 replicate field samples. ―a‖ denotes that
the total organic carbon, total suspended solids and total mercury data for the Alvarado Lagoon and Gulf of Mexico are taken from Guentzel et al., 2007. ―-
― denotes that there is no data for this parameter.
Table 3. Mercury concentrations in fish, crab, shrimp, and squid and log bioconcentration
*The data for mercury concentration is taken from Guentzel et al., 2007. The log BCF is calculated as Log 10([Hg in tissue]/[Hg in water]). The average water
concentration of Hg was 1.6 ng/L. n=the number of samples.
The Alvarado Lagoon – Environment, Impact, and Conservation
403
We collected sediment from the lagoons and nearby rivers within the ALS. Total mercury
at station T in the AL ranged from 13-22 ng Hg/g-wet and the %C and %N ranged from 0.23-
0.77% and 0.31-0.37%, respectively. Total Hg from sediments in the adjacent rivers (Acula,
Limon, Blanco, and Papaloapan) ranged from 10-78 ng Hg/g wet and the %C and %N ranged
from 05-8.9% and 0.31-0.9%, respectively. There was a moderate correlation (R2=0.435,
p=0.020) between the total Hg and % carbon in the sediments from the ALS [Guentzel et al.,
2007]. The total Hg values for the sediment we collected are below the threshold effects level
of 130 ng Hg/g dry for marine sediments [Buchman 1999] and are within the US EPA
background sediment criteria of 0-300 ng Hg/g dry (US EPA 1997). Aquatic biota that
represent ~87% of the annual catch from the ALS [Cruz-Escalona et al., 2007] were collected
and analyzed for total Hg (Table 3). The total Hg concentration in the invertebrate species
(shrimp, squid, crab) ranged from 0.008-0.026 μg Hg/g wet and the vertebrate species ranged
from 0.082-0.35 μg Hg/g wet. The levels of Hg in the piscivorous and omnivorous fish
(catfish, moharra) are at or slightly above the recommended consumption level of 0.3 μg Hg/g
wet [NAS, 2000].
The log bioconcentration factors for total Hg in the organisms we collected ranged from
3.9-5.3, with no observable seasonal difference (Table 3). Activities such as biomass burning
for land clearing, mangrove deforestation, and urbanization are known stressors to the ALS.
These activities are also associated with increased mercury mobilization in aquatic and
terrestrial environments, which can result in an increase in the bioaccumulation of mercury in
biota from these systems [Friedli et al., 2003; Porvari et al., 2003; Munthe et al., 2007]. There
are a large number of indigenous riverbank communities within the ALS that rely on fishing
for comestible and economic subsistence. Reported total Hg levels in hair samples from
individuals that reside and consume fish from within the ALS ranged from 0.10-3.36 µg Hg/g
(n=47) [Guentzel et al., 2007]. Of these values, 58% are above the recommended
consumption limit of 0.1 µg Hg/kg body/day which corresponds to a hair level of 1.0 µg Hg/g
[NAS, 2000]. Anthropogenic activities that mobilize Hg could result in an increase in the
mercury content of the fish and seafood from the ALS which may ultimately lead to increased
body burdens of mercury in the indigenous peoples that reside in this region.
Vegetation
The ALS features representative and diverse ecosystems of Mexico´s Gulf coastal plain,
such as coastal dunes, reed beds of Cyperus spp., cattail Typha spp., palm forests of Sabal
mexicana, Scheelea liebmannii, and Acrocomia mexicana, oak forest of Quercus oleoides;
apompales (Pachira aquatica), and a large mangrove forest dominated by Avicenia
germinans, Laguncularia racemosa, and Rhizophora mangle [Vazques-Torres, 1998]. There
are 15 distinguishable landscape units (LU) in the area [Portilla-Ochoa et al., 1998 and Silva-
López and Portilla-Ochoa 1998]. The LU were first differentiated as areas disturbed by
agricultural activities, areas disturbed by cattle ranching, and areas where human intervention
is not yet considerable, such that natural vegetation remains the dominant landscape element.
Each LU was described in terms of land use, seasonal flooding, vegetation cover (i.e. primary
and secondary), predominant exploitation systems, the physical medium (i.e. substrate origin
and soil type), hydrologic characteristics, and other data (e.g. human settlements, main roads,