Abstract

Solar salterns are water bodies normally situated along the coast and whose object is the obtainment of salt through the evaporation of seawater (or, in some cases, saline continental waters). They are generally composed of a system of shallow ponds with salinities exceeding that of seawater. Their location and manner of exploitation, coupled with the salinity of the ponds (particularly those situated at the end of the circuit), together set the standard for the development of environmental conditions. The elevated saline concentrations lead these systems to present extreme environmental conditions to which only a few specialized organisms have been able to adapt.

In the present doctoral thesis, an exhaustive study is carried out on the principal physicochemical parameters of these highly extreme ecosystems within the Valencian Community (the salterns of Santa Pola, La Mata-Torrevieja and Calpe), which are determined to a great extent by conditions linked to human activities:

* The Santa Pola solar saltern is a conventional flow-through system where seawater is circulated through a series of shallow ponds to obtain, via evaporation, a progressive concentration of salts, and finally their precipitation. The range of salinities in this system is very extensive, encompassing levels somewhat greater than those found in seawater to levels near the precipitation point (in the crystallizers).

* The saltern at La Mata-Torrevieja is a system composed of two large lagoons. The smaller of the pair, La Mata, presents more variable concentrations due to its role as a great heating pond. The Torrevieja lagoon exhibits very homogenous values since it acts as a great crystallizer. In addition to the water from La Mata, Torrevieja also receives saturated brines piped down from the salt deposit at El Pinoso.

* The Calpe saltern is not currently in use, although it does periodically receive influxes of seawater, which in turn maintain the water level and biodiversity in the system. Consequently, the salinity of these waters is greater than seawater, but does not exceed the levels of a heating pond.

The principal parameter considered in the study of these systems is, logically, salinity. It exhibits significant differences between solar salterns, given the particular conditions of each. Likewise studied are the behaviours of diverse physicochemical parameters (pH, ammonium, nitrite, nitrate, DIN, SRP, the ratio DIN/SRP, TP and orthosilicic acid), as well as the variations these parameters exhibit seasonally, along the saline gradient, and even in different zones within the same saltern. The different physicochemical parameters are examined to see if their status is attributable to the solar saltern exploitation system or to other causes. Additionally, the salterns are compared to determine shared behaviour patterns or, on the contrary, particularities specific to each. 

Finally, a revision is subsequently carried out of the principal criteria to be taken into account when establishing the ecological potential of the Valencian Community salterns, in application of the Water Framework Directive (2000/60/CE). This Directive establishes the European framework for the protection of surface, continental, transitional, coastal and subterranean waters so as to prevent or mitigate their contamination, promote their sustainable use, protect the environment, improve the status of aquatic ecosystems and attenuate the effects of flooding and droughts. The overall objective of the WFD is to have all water bodies achieve a “good quality status” by 2015.

Within the scope of the WFD, the solar salterns of the Valencian Community belong to the transitional-waters group, and have been designated as Heavily Modified Water Bodies (HMWB). Regarding HMWB, the WFD establishes as obligatory the determination of their “ecological potential,” and not their “ecological status.” This supposes the assumption of certain exceptional conditions, among which include the reduction of environmental requirements, maintaining at the same level the goals of protection and quality improvement.

Prior to establishing the ecological potential, an intercalibration exercise of the different proposed methodologies must first be conducted by the various Member States. To date, the intercalibration exercise for transitional waters has advanced little, as these water bodies are complex and conditioned by a large number of factors. This complexity is further exacerbated in the case of the HMWB, as their specified functions cannot be modified. Given that the intercalibration exercise remains currently undefined, the ecological potential of the solar salterns is not ready to be established. Nevertheless, a methodology is proposed in the present thesis for eventually determining the ecological potential for the Valencian saltern systems.

The proposed methodology is based on physicochemical, not biological, criteria. Given the extremely harsh conditions for life in the solar salterns, there is no biological element capable of being applied as a quality measurement of all three. For this reason, a theoretical model is proposed based on the behaviour of the P50 of TP versus the P50 of salinity. This model is applied to the Santa Pola saltern, considered the most representative saltern for its characteristics and broad saline range. A series of mitigation measures are additionally proposed to improve water quality in those salterns requiring such actions, though without altering their specified use.