The Premature Mortality of Sabinos or Montezuma Bald Cypress (Taxodium mucronatum Ten.) in the State of Durango, Mexico

Abstract

The juniper (Taxodium mucronatum Ten. of the Cupressaceae family) is a long-lived species that forms gallery forests. Dozens of dead junipers > 100 years old have been identified in the San Pedro Mezquital watershed in Durango, Mexico. This work determines the causes of death of these specimens. The work was carried out in the field and in the laboratory, where in the former the surface of the damaged trees was identified, together with the changes observed in the watercourses. In the latter, sabino seedlings were transported to the work center and exposed for 7 days in containers with gravel to five types of wastewater generated in the region. With the above, the conditions experienced by the adult trees in the field were studied, as well as the sensitivity of the young specimens to the types of water quality, and the differences were validated with ANOVA tests. Five sites with dead junipers were found, ranging in size from 0.5 to 4 ha, with ages between 200 and 400 years. It was found that during the dry season, water is diverted to irrigated areas, leaving some areas without water for several months. The shoots survived in most of the water qualities, except the one with high salinity (3.34 mS/cm). It is concluded that the lack of water in the rivers had a stronger influence than the water quality and is the probable cause of the death of the sabino.

1. Introduction

In 1921, Taxodium mucronatum, Ten. of family Cupressaceae, commonly known as Ahuehuete, sabino, or Montezuma bald cypress [1], was recognized as the national tree of Mexico because it is found throughout the Mexican Republic [2]. Ahuehuete is derived from the Nahuatl name for the tree, āhuēhuētl, which means “upright drum in water” or “old man of the water.” It is worth mentioning that individuals over 1000 years old have been found in Querétaro, San Luis Potosí, and Durango [3]. Sabinos are part of the natural corridors between aquatic and terrestrial systems, showing great ecological dynamism [4]. Furthermore, among the vegetation of gallery forests, T. mucronatum is one of their most diverse, dynamic, and complex components [5].

T. mucronatum is widely used in popular medicine. The Aztecs used various parts of the trees as medicine. Pieces of burned bark were used on sores, burns, and skin ulcerations, and chest conditions were cured by inhaling the smoke from burning wood and branches. T. mucronatum is currently used to create infusions or ointments for the treatment of wounds, gout, heart diseases, hemorrhoids, ulcers, and varicose veins; to relieve rheumatic pain; and as an antispasmodic for the treatment of diarrhea and bronchial problems [6].

Luján-Hidalgo et al. (2012) [7] studied the chemical composition and microbial activity of T. mucronatum, finding that it obtained microbial activity on Gram-positive bacteria and yeasts, but not on Gram-negative bacteria. They also found that its main constituents are sabinene (13.16%), thujopsene (8.11%), 4-terpineol (7.66%), γ-terpinene (6.91%), and β-myrcene (6.57%). This indicates that it may have some antibiotic effects, which are still under study. Correa-Díaz et al. (2014) [8] found that although sabinos are associated with water reservoirs, they are sensitive to variations in precipitation and water quality.

Ecosystem services are the benefits that people receive from the environment [9] that contribute to human quality of life and well-being. From this perspective, riparian forests are distinguished because they form natural corridors between aquatic and terrestrial systems; they harbor a great diversity of species and are ecologically dynamic [10]. Riparian forests provide a range of ecosystem services, such as the following:

• Due to their location, they act as a filter for substances present in runoff water before it reaches the rivers, thus helping in its purification and keeping the riverbeds cleaner through the roots and small organisms that, together with the soil, retain the particles present in the water [11,12].
• The location of the trees and the geomorphology of the sites allows for the stabilization of the sediments that compose the streambanks, thus preventing excessive soil erosion [13].
• They present pleasant microclimates, where the high humidity and lower temperature than the surrounding areas allow for a great diversity of species, thus tolerating the development of local fauna, both terrestrial and aquatic, and supporting the dispersion of species because the forests are used as natural wildlife corridors [14].
• They are places that are used as recreational and relaxation areas due to their scenic beauty and microclimates [13,14].
• Due to their biodiversity, they present great ecological dynamism that supports the closing of the biogeochemical cycles of water, carbon, and nitrogen, among others [5].
• They provide food and consumption materials, among other resources.

Unfortunately, between 2000 and 2016, the integrity of the riparian forest in Durango, Mexico, was threatened, with the discovery of dead sabino trees along the banks of the Durango, Mezquital, and Poanas rivers.

Sabinos are typically found near the Durango, Mezquital, and Poanas Rivers, which belong to the higher San Pedro–Mezquital River basin [13,15], the seventh largest in Mexico and the main source of freshwater in the south of the state of Durango [14,16]. This species differs from its close relatives, such as Taxodium distichum, in that the habitat it requires for a thriving life cycle is limited to streams, surface lakes, creeks, and wet soils [17].

The death of sabinos is an anomalous situation given that they are not attacked by pests, are resistant to screwworms and bark worms, and rarely become sick [18,19,20].

Additionally, it is important to note that sabinos are sensitive to a multitude of factors, including the contamination of water and soil from chemicals and industrial waste, rising temperatures, and changes in precipitation patterns, which can alter their natural habitats, thereby affecting their ability to survive and reproduce. Additionally, deforestation and human activity can disrupt the natural patterns of riparian corridors [8,16,18].

Furthermore, Suzán-Azpiri et al. [10] found that trees in polluted rivers exhibited significantly lower radial growth and a smaller canopy than did those in the better-conditioned group and control group. Additionally, Villanueva-Díaz et al. [11] discovered that water pollution caused by industrial effluents and sewage streams resulted in mortality among sabino trees and influenced their physiological and dynamic processes.

Given the slow growth rate of sabino trees and their documented age of up to 1000 years in the area [1,13], it is crucial to acknowledge the impact of anthropogenic activities on their longevity. This recognition paves the way for the formulation of effective conservation strategies, ensuring the sustained provision of ecosystem services by these trees. The objective of this study was to establish a foundation for this.

Considering the circumstances surrounding the discovery of dead sabinos, it is reasonable to conclude that the cause of death may be attributed to either water quality, water quantity, or a combination of both. The initial stage of the investigation involved the identification of the locations where the deceased sabinos were discovered. Subsequently, an investigation was conducted to ascertain whether these sites experienced prolonged periods of water scarcity.

To ascertain the impact of water quality, wastewater from the region where the sabino seedlings were submerged was utilized, and their subsequent development was monitored.

In the juvenile phase, sabino seedlings grow under a distinct set of environmental conditions, including humidity and temperature, in comparison to those experienced by adult trees. This is attributed to the seedlings’ inherent fragility, which necessitates a period of protection and adaptation in the shade of the parent trees during their initial years of growth. Given their fragility, seedlings were selected to assess their tolerance to different water qualities. If they survive, it is likely that the adults also will. The absence of seedlings on the banks indicates additional conservation issues at these sites, but reviewing this was beyond the scope of this work.

2. Materials and Methods

The San Pedro–Mezquital River is the main source of fresh water in the south of the state of Durango. It is the seventh largest river in Mexico and part of one of the most productive and biodiversity-rich wetlands in the Pacific, the National Marshes, which houses the largest mangrove forest in the North Pacific [18].

The San Pedro–Mezquital hydrological basin (watershed) drains its waters from north to south of the State of Durango and supplies 60% of the water to the states of Durango and Zacatecas, flowing into the northern part of the state of Nayarit (National Marshes). The major rivers are shown in Figure 1, along with their lengths in kilometers.

2.1. Characteristics of the Gallery Forests of the Tunal, Durango, and Poanas Rivers

Previous diagnoses indicate that along the banks of the upper basin of the Sauceda, Tunal, and Bayacora Rivers, the riparian forests are either absent or severely degraded. Along the Durango, Poanas, and Mezquital Rivers, gallery forests with sabinos are present. Using Google Earth and field observations, the presence of dead trees was identified at these sites. Subsequently, it was identified whether there were zero flows at these sites (this means that the river remained without water for prolonged periods of time), with the help of governmental hydrometric data [19] and some other published and unpublished works (Figure 1).

2.2. Resistance of Sabinos to Water Quality

2.2.1. Collection of Sabino Seedlings and Their Adaptation in a Greenhouse

One mature sabino tree generates hundreds of seedlings in its shade, more than 99% of which are lost during the rainy season. A total of 200 seedlings were obtained from one of these sites (along Durango River) and acclimatized in a greenhouse. This process took about 42 days, during which only tap water was added until new shoots were observed. During the first several days, the leaves changed color due to the high amount of solar radiation, which necessitated the installation of a shade net.

2.2.2. Seedling Survival Evaluation

Seedlings were chosen because they are more susceptible to changes than an adult specimen. If they survive, then the adult tree will too. Three seedlings were placed in a 4 L plastic pot containing local gravel (1″ diameter, Figure 2). One seedling was considered one experimental unit, and each plastic pot had three experimental units.

Each water type was tested with 9 seedlings. A contact time of 7 days was chosen because previous work has shown that trees along different rivers can have this contact time with water [20,21]. In rivers, the flowing water can be retained in pools of different volumes, where the average residence time calculated was 7 days. This is the duration that the trees would be in contact with these types of water. The trees’ survival, growth and the presence of new leaves were recorded for each type of wastewater.

2.2.3. Types of Water Quality

The municipality of Durango is part of the state of Durango, and according to official reports [22], its industrial, service and domestic sectors contribute 7%, 1%, and 92%, respectively, to the 102 wastewater discharge points in the region [21]. Thus, the industrial and domestic effluents located in the vicinity of the study area were selected as potential pollution sources of the selected rivers.

The most deteriorated water quality is that of both domestic and industrial wastewater. A total of 4 types were put in contact with the sabino seedlings for 7 days; the eastern E-WTP is the most relevant in terms of the volume treated (1500 L/s). From it, 3 influent samples (IE-WTP) and 3 effluent samples (EE-WTP) were collected on specific dates to compare their effects on the seedlings. This wastewater treatment plant can discharge its water into the rivers.

Industrial activities are mainly concentrated in an industrial park, and their effluents are discharged through a ditch (Acequía Grande) that joins the Tunal and Durango Rivers, although a small contribution from agricultural runoff has also been reported [21]. A sample of this wastewater was collected and identified in relation to its point of collection, the San Carlos Bridge (SCB).

In addition, there are two other industries outside the industrial estate that are relevant to the present study. The first one, BioPapel (BP), has been identified as being responsible for contamination events in the Tunal River, and the second one, Holland Cheese Factory (HCF), has effluents with a high salt content that is toxic for vegetation in general. Although there are no reports of HCF effluent contamination in the rivers, a sample was obtained to investigate its effect on seedlings as a reference.

2.2.4. Experimental Design

To test the tolerance of the seedlings to the different water qualities, two experiments were designed. The first used water from the E-WTP, where samples of its influent and effluent were obtained on three occasions, and each was in contact with the seedlings for 7 days.

The second experiment used three industrial effluents from the region. The method with which they were tested is shown in Figure 3. After the experiments were completed, all seedlings were given tap water and observed for another two weeks to assess the possibility of a delayed effect caused by the different water samples.

2.2.5. Removal Efficiencies Achieved by the Presence of Seedlings

It should be remembered that plants with submerged roots release air in the root zones. This allows for them to be used by microorganisms in charge of carrying the degradation off or the components of the wastewater; in other words, the purification process of wastewater is carried out. To see the effects on this process, the quality of the water from the inlet to the outlet was measured, and the removal efficiency was established [23]

We used one-way variance analysis to validate the differences found and evaluate the effect of seedlings on changes in the water quality (removal efficiency) (Figure 3).

3. Information Analyses

3.1. Water Quality

The changes in water quality throughout the experiment were determined by measuring the pH, electrical conductivity (EC), total solids (TS), total dissolved solids (TDS), and colony-forming units of fecal coliforms (FCs).

The pH and EC values were measured with previously calibrated equipment (HACH HQ40 multi-parameter meter, Loveland, CO, USA).The contents, in mg/L, of TS and TDS were measured according to the Mexican regulation NMX-AA-034-SCFI-2015 [24]. NMX-AA-042-SCFI-2015 [25] establishes that FCs can be considered an indicator of contamination by pathogens. Accordingly, the contents of colony-forming units of fecal coliforms were quantified using a selective bile green medium. The results are reported as the most probable number (MPN) per 100 mL of water (MPN/100 mL).

3.2. Data Analysis

The effects of seedlings on changes in the water quality were evaluated using a two-way analysis of variance with a significance value of α = 0.05.

For the first experiment, the treatments were seedling + gravel + water and gravel + water on the three samplings of the influent and effluent of E-WTP.

For the second experiment, the treatments were seedling + gravel + wastewater and gravel + wastewater, using the different types of wastewaters from the region

The software used was the statistical package Statistic 7.0 [26], logarithm base 10, was applied to the fecal coliforms values, and all the data were standardized to its corresponding z value. Whenever possible, the values were compared with those established in the Mexican regulations NOM-001-SEMARNAT-2021 [27].

4. Results

4.1. Vegetation Cover

The Tunal and Bayacora Rivers displayed significant disruptions along their riverbanks, where scattered individuals of sabinos were observed [28,29]. Experts have determined that a gallery forest consists of more than 10 individuals [2,28]. Therefore, it is evident that the Tunal River does not have a gallery forest of sabinos (Figure 4).

Five sites with dead sabinos were found, with surfaces ranging from 0.5 to 4 ha. The ages of the sabinos, according to Villarreal’s work, varied between 200 and 400 years.

Table 1. Sites with dead sabinos, identifying the possible causes. The locations can be found on Google Earth.

Site	Coordinates	AMSL *	Damage in Ha	Possible Cause	Year It Dried Up	Fuente
1	24°02′01″ N 104°23′31″ W	1859	3.1	Change in the river’s course due to anthropogenic use	Before 2002	Image analysis and visits to sites
2	24°2′32.41″ N 104°21′29.92″ W	1856	1	Dry spring and zero flow	2011	Image analysis and visits to selected sites, CNA’s hydrometric data
3	23°56′50.39″ N 104°19′1.92″ W	1813	0.21	Zero flow, use of wastewater in irrigation	2000 and today	CNA’s hydrometric data
4	23°54′32″ N 104°10′51″ W	1830	4	Dry spring and zero flow	2014	Image analysis and visits to selected sites
5	23°54′0.09″ N 104°11′50″ W	1830	0.26	Dry spring	1970	Image analysis and visits to selected sites

* Above mean sea level in meters.

shows that in these places, the springs dried up, changing the direction of the watercourses, and zero flow (CNA’s hydrometric data) was recorded from the distribution of water to farmers. The deaths are associated with anthropogenic activities. Descriptive photos of each site are in the Supplementary Materials.

It is important to highlight that in several sections of the Tunal River, where no vegetation was observed, the river was completely dry. This is considered a strong indicator of damage to riparian vegetation. On the contrary, the Durango and Poanas Rivers presented the highest vegetation cover, which is coincidence with their longest distance to the City of Durango. These rivers also have zero flow at some points, but some places, such as site 4, are fed by springs, which have been drying up (Figure 4 and Figure S2).

4.2. Water Quality

4.2.1. Differences Among the Effluents Used to Assess the Survival of Seedlings

In the water samples obtained from the influent and effluent of the east domestic wastewater treatment plant (E-WTP), their FC content was studied in addition to some physicochemical factors, such as pH, electrical conductivity in µS/cm (EC), water temperature (°C), total solids (TS), and total volatile solids (TVS). The same parameters were measured in the industrial wastewater.

The results of the parameters evaluated for the water quality and their comparison with the reference values marked in the Norm Mexican are indicated in

Table 2. Average (2 repetitions) of the parameters pH, EC, TS, TVS, and FCU. The same letter means that there is no statistical difference between the means (α = 0.05).

Sample	pH	EC	TS	TVS	NH4+/NH3	log FCU/100 mL Water
		(µS/cm)	mg/L
NOM-001-SEMARNAT-2021	6–9	N. C.	N. C.	N. C.	N. C.	2.77
IEWTP Raw I	7.38 c	748 f	686 e	283 f	25	4.75
IEWTP Raw II	7.57 d	647 d	732 f	203 e	33	4.34
IEWTP Raw III	8.22 f	762 h	619 d	269 f	31	4.87
EEWTP Treated I	7.58 d	718 c	510 c	156 cd	22	2.69
EEWTP Treated II	7.26 b	731 b	485 c	180 ce	32	0.9
EEWTP Treated III	8.25 f	759 g	478 b	149 b	28	2.47
BP IV	8.50 g	1835 i	1542 g	360 g		−3
HCF IV	5.60 a	3380 j	3302 h	1427 h		4.61
SCB IV	7.57 d	746 e	511 c	175 ce		3.14
Control	7.80 e	467 a	378 a	116 a		0
AVERAGE	8	1147	979	365	29	4.33
Maximum	8.4	3381	3302	1427	33	4.87
Minimum	5.6	646	378	117	22	0
ANOVA results	F = 2770	F = 810,445	F = 1555	F = 187.5		F = 2342
	p < 0.001	p < 0.001	p < 0.001	p < 0.001		p < 0.001

Notes: N. C. = not contemplated within the Mexican regulations but known to alter water quality.

.

4.2.2. pH Values

The results in Table 2 show significant differences among the types of water (F = 2770, p < 0.001), except for EE-WTP Treated III and IE-WTP Raw III.

4.2.3. Electrical Conductivity (EC)

Regarding EC, significant differences were found among all treatments (F = 810,445, p < 0.001). Notably, the HCF and BP samples presented the highest values. Considering the criteria of water quality for irrigation [30,31], an EC of 250 µS/cm is considered excellent, that from 250 to 750 µS/cm is good, that from 750 to 2000 µS/cm is permissible, that from 2000 to 3000 µS/cm is questionable, and that equal to or greater than 3000 µS/cm is inappropriate for irrigation. Thus, the water sample from the Holland Cheese Factory is classified as inappropriate for irrigation and considered helpful as a reference for seedlings under harsh conditions. On the contrary, the lowest EC value was presented by EE-WTP Treated II, which corresponds to the effluent of the treatment plant and falls within the established standard, in terms of salt content, for use in agricultural irrigation.

4.2.4. Content of NH₄⁺/NH₃

The ammonium ion content is an indicator of the first steps of degradation of the nitrogen compounds in organic matter. It was measured in selected samples because previous studies have demonstrated its content in EE-WTP samples [24].

4.2.5. Total Solids (TS)

Regarding the TS, significant differences were found among the samples (F = 1555, p < 0.001), except for EE-WTP Treated I, EE-WTP Treated II, and SCB IV. The lowest value of total TS was presented by EE-WTP Treated II, and the water from HCF is not recommended for irrigation according to its TS value.

4.2.6. Total Volatile Solids (TVS)

Significant differences among the TVS values in the samples were observed (F = 188, p < 0.001). The total volatile solids, according to the Mexican standard NMX-AA-034-SCFI-2015 [25], refers to the amount of organic matter (including inorganic compounds) capable of volatilizing under calcination at 550 °C ± 50 °C in a period of 15 to 20 min. The TVS values obtained from the HCF sample were the least favorable for soils, plants, and surface waters. In contrast, the lowest TVS values were those of the EE-WTP Treated III sample.

4.2.7. Fecal Coliforms (FC)

Significant differences were found among the FC values (F = 2342, p < 0.001). The IE-WTP Raw III sample showed the highest value, which represents a risk to public health, even in the case of indirect contact. The EE-WTP and BP samples were within the quality limits set by NOM 001-SEMARNAT-2021 [30]

4.2.8. Water Characteristics After 7 Days with the Seedlings

The changes in water quality after 7 days in the containers with and without the seedlings can be seen in Table S1. We found statistically significant changes according to water quality, but not according to the absence or presence of trees (Figure 5).

4.2.9. Tolerance of Sabino Seedlings and Differences in Growth and Presence of New Leaves in Sabinos

During the test period of 7 days, most of the samples presented new leaves and growth (Table 2), except for the HCF group.

• In the first experiment, the water from the E-WTP, both influent and effluent, did not cause deaths. Growth occurred, and new shoots were registered in 14 of the seedlings. It should be remembered that the seedlings spent 21 days under these types of water, which are the most common and have greater volumes in the area. For decades, the wastewater from the urban area was poured into the channel that leads to the gallery forests. Since the year 2000, it has been distributed among the farmers.
• In the second experiment, it was observed that growth occurred with the water from the San Carlos Bridge (SCB). This water comes mainly from the industrial zone of the City of Durango, sometimes receiving some water from the E-WTP; growth was observed in the individuals that received it. When BP water was added, they did not die but neither did they have outbreaks. With the water from the cheese factory, although they did not die after 7 days, four individuals died 6 days after the water was withdrawn. Furthermore, in the pots with the same water and gravel, a light white layer was formed on the gravel surface, presumably made up of salts, that did not appear in any of the other pots of the other groups. This indicates that the sabinos do not tolerate the quality of water from the Holland Cheese Factory.

The different types of water had no statistically significant effect on seedling growth (Figure 6). The seedlings that survived were kept under observation for some months and maintained their perfect condition.

5. Discussion

It was observed that the riparian forests of the Durango and Poanas Rivers have been degraded and have no flow; dead sabinos were found at five sites. It was also observed that the survival and growth of the sabino saplings in contact with the different water qualities were not affected, except for those exposed to the residual water of the cheese factory. This indicates that the lack of water could be the cause of death for the specimens detected.

5.1. Riparian Quality

The San Pedro–Mezquital Rivers of the upper basin show severe damage to their banks. In most of them, their forests have been damaged to varying degrees, including to the point of elimination [28,29,32,33].

As shown in Figure 2 [28,29,33], the most degraded river is the Tunal, which is the closest to the City of Durango. The Tunal is affected by anthropogenic activities, such as the “straightening” and “rock reinforcement” of its channel, wastewater discharges, the presence of human settlements, and deforestation for pastures and agriculture (Figure S6). In addition, its water has been diverted for irrigation since 1968, when the Guadalupe Victoria Dam was built. The river is maintained by groundwater outcrops in some places, but in the lower part, it receives wastewater from the E-WTP, which has been diverted for irrigation since 2000, so there are areas with zero flow most of the year.

Regarding site 3 (Figure S3), it was found that months with zero flow have been recorded. This has been happening since 2000, according to the historical records provided by CNA and other works [21], where it is indicated that this type of event occurs for up to three consecutive months. This year coincides with the beginning of the distribution of water from the E-WTP to the farmers, indicating that if the water from the E-WTP reached this point, and now it does not, then the intermediate sites, 1 and 2, were affected by the lack of water, as was the entire riparian forest in general along this route.

The Poanas River, where sites 4 and 5 are located, is in the municipality of Nombre de Dios, the furthest from the city of Durango, which explains its characteristics as the best preserved site. This river is not only fed by runoff water, but also by underground water outcrops that have been affected because the springs that fed them have dried up, as in site 4, where 4 hectares of sabinos have been lost in the space of a year. The greatest risk of this is that there are other places that are fed in the same way and are in danger of drying up, such as the Barranca de San Quintín (Figure S7).

The degradation of riparian forests is due to the lack of recognition of the environmental services they provide, which has led to a lack of attention paid to the degradation of the riverbeds. As a result, rivers that have had water for hundreds of years are now without water for most of the year, which has led to the presence of dead sabinos with ages ranging from 200 to 400 years [32]. This paper describes five sites, but there may be more.

The above issue was addressed by the WWF in 2012, when determining the ecological flow [34], which is the minimum amount of water necessary to maintain the riparian ecosystem in operation. The first national decree was made in 2014, for the state of Durango for the San Pedro Mezquital basin [35], which considers the rivers as other users of the water for dams. However, the way to channel this water to the rivers has not yet been established, so it has not been effective in all these years, and there continues to be zero flow in the riverbeds (Figure S3).

To address this issue, academics have developed a series of actions aimed at supporting communities in the management of their natural resources. These actions include the implementation of projects in collaboration with governmental entities and non-governmental organizations (NGOs), such as the World Wildlife Fund (WWF), and the COCYTED 824 [36] and PRONACES Agua 3189562 (CONAHCYT) [37] projects.

5.2. Seedling Survival

In the state of Durango, Mexico, 95% of wastewater treatment plants discharge their water into the rivers of the area. This has been shown to cause undesirable changes in trophic levels [4]. In addition, these systems may become eutrophic due to the degradation of organic matter, and they may also receive runoff from agricultural areas [38,39].

The effluents used are statistically different according to the parameters studied, where those that can damage plants, the most are the electrical conductivity and the pH, both of which remained within the permissible limits.

The results obtained show that the seedlings survived and grew while in contact with the different qualities of water, except for the residual water from the HCF, which had the lowest pH of 5.6, due to its high contents of whey, solids, and salts [5,34]. According to NOM-001-SEMARNAT-2021 [28], the lower limit is 5.0, while the FAO has established a value below 5.5. In both cases, this level in water is considered acidic, which can lead to acidified soils and cause serious problems if it reaches aquifers or surface waters [6,35]. When the pH is below 6.5 or above 9.0, growth reductions and respiratory problems in most fish are reported [7,36]. The highest pH was found in the BP sample (8.5); however, it is within the requirements of the standard (upper limit of 10).

The HCF seedlings showed severe dehydration problems. It is believed that the amount of salts present in the water affected the osmotic processes of the plants. The dehydration process occurs as follows: when the salt concentration in the irrigation water is higher than that of the root hair cells, the water in the plant is withdrawn and lost; these results are consistent with those of previous reports [8,9,37,38]. Salinization has been identified as a determining factor in the degradation of agricultural soils and affects plants; their productivity is significantly reduced when this type of soil is cultivated [10,39].

The growth of all the seedlings was minimal over the 21 days, which is completely different from the information found in the literature on sabinos. Aguilera 2001 [11] indicated that they can grow up to 70 cm in height in eight months at the juvenile stage. The difference may be related to the growth conditions, since sabinos in their natural habitat have fewer limitations to grow, unlike the individuals used in this experiment, where the support was only gravel, and they had limited nutrients and lacked soil.

6. Conclusions

This study describes five sites, ranging in size from 0.2 to 4 hectares, where dead sabinos have been found. The evidence suggests that the most probable causes are human-induced disturbances and the lack of water. The sites have been affected either directly by the diversion of the channel or indirectly by modifications to the natural flow, which were made to meet human needs without consideration of the environmental impact. The optimal ecological flow was determined, yet this has not been implemented.

The diverse qualities of water to which the sabino seedlings were subjected did not result in mortality, suggesting that the mature trees are unlikely to suffer the same fate due to fluctuations in the quality of water they receive.

In conclusion, it is imperative that the relevant authorities and the public address the issue of the sabino forest through diagnostic studies that will allow for the development of effective strategies for its conservation and restoration. Fortunately, there are already initiatives being carried out in this direction that have provided resources for this purpose. However, it is crucial to disseminate this information among the population and ensure that it has a real impact on the decisions of the authorities.

It is also imperative to engage the local population in the conservation of these ecosystems. This entails educating them about the significance of these ecosystems and encouraging their involvement in monitoring and managing them. Furthermore, it is vital to ensure the effective implementation of ecological flow. This will require sustained and collective action to safeguard this invaluable natural heritage for future generations.