The chemical composition of groundwater and related surface water ecosystems can be modified by intensive agricultural activities. This is the case of the Natural Reserve of Pétrola saline lake (Albacete, SE Spain), which constitutes the discharge area of an unconfined aquifer. The extended use of fertilizers and pesticides poses a threat to ecosystem sustainability. One of the most applied herbicides worldwide has been atrazine. Despite being prohibited in Spain since 2007 by European regulations, atrazine can still be detected due to its high persistence in the environment. Atrazine degradation pathways are mediated by biological processes performed by microorganisms with adapted metabolic mechanisms that make in situ bioremediation possible. To evaluate the presence of such microorganisms in the unconfined aquifer, groundwater was collected from a flowing 37.9 m deep piezometer. DNA was extracted, and the bacterial 16S rRNA gene was amplified and cloned. Later, 93 clones were sequenced, providing the first molecular assessment of bacterial community structure in the deep zones of the aquifer. Some of these bacteria have been previously described to be involved in atrazine degradation. In addition, 14 bacteria were isolated from the groundwater samples and identified by 16S rRNA gene sequencing. DNA from these bacteria was subjected to PCR assays with primers designed for the genes involved in the atrazine degradation pathway. Positive results in the amplification were found in at least three of these bacteria (Arthrobacter sp., Nocardioides sp. and Pseudomonas sp.). The atrazine-degrading genetic potential was shown to be dependent on the trzN and atzA,B,C gene combination. These results suggest for the first time the adaptation of the bacterial population present in deep aquifer zones to atrazine exposure, even after more than 15 years of its ban in Spain. In addition, this study provides the baseline data about the bacterial communities found in deep aquifer zones from the hypersaline lake-aquifer system.

Lake Alboraj, located in southeast Spain, was declared natural Microreserve and included into European Natura-2000 Network due to its contribution to environmental heritage. Unfortunately, the ecological status of the lake has changed dramatically, mainly due to the lowering of water table caused by groundwater abstractions for irrigation. It is a permanent small karstic lake whose surface has reduced in the last decades to nearly the third part of its historical water level. The water column shows a marked seasonal oxycline, that splits an aerobic upper layer (epilimnion) from an anaerobic layer below (hypolimnion). Sequencing 16S rRNA gene amplicons and applying chemical tools at epilimnion, hypolimnion and sediment, showed a clear gradient in the bacterial community structure, which support the co-existence of assimilatory and dissimilatory microbial mediated reactions. Results allows to infer that microbial stratification could provide various physical and chemical environments at different depths in the water column related to biogeochemical reactions providing N-S-C- recycling processes.

Saline lakes are subject to numerous environmental impacts related to human activities, changing the chemical and biological natural conditions of the ecosystem. Sustainable development depends on the conservation of such delicate saline ecosystems, which may hold distinctive biodiversity. Pollution is one of the major threats to surface water bodies, for example by increasing nutrient contents and organic pollutants, including endocrine disrupting chemicals. Microbially mediated redox processes exert a fundamental control on nutrient turnover and contaminant removal. This study examines the influence of land use on the distribution of endocrine disrupting chemicals as well as on the microbial community composition in lacustrine sediments from Pétrola saline Lake (SE Spain). The lake is impacted by anthropogenic activities (agriculture, farming, mining and urban wastewater spills). Applying chemical and molecular tools (sequencing of 16S rRNA gene) showed a clear influence of land use on the chemistry and bacterial abundance of the lake sediments. The sampling points closer to wastewater outflows and mining ponds (2635, 2643 and 2650) showed fewer numbers and types of endocrine disrupting chemicals as well as a smaller number of families in the microbial community. These findings improve our understanding of how land use affects both water chemistry and the abundance of organisms responsible for biogeochemical cycles.

Saline lakes are subject to numerous environmental impacts related to human activities. Pollution is one of the major threats to water bodies, since it produces the increase of nitrogen and sulfur contents, changing the chemical and biological conditions of the ecosystem. Microbially mediated redox processes exert a fundamental control on nutrient and contaminant turnover. Therefore, the aim of this study was to determine the influence of land use on the microbial communities responsible for N and S turnover in the lacustrine sediments from Pétrola Lake (SE Spain) disturbed by anthropogenic activities (agriculture, farming, mining, and wastewaters). To reach this goal, chemical and molecular tools (sequencing of 16S rDNA gene) were applied. The results showed the influence of land use on the chemistry and microbial community structure of the sediments from the saline lake. Compared to natural conditions, wastewater and mining showed the largest differences in terms of microbial structure as a result of salinity. These findings provide better understanding of how land use affects the water chemistry and the abundance of organisms responsible for nutrient turnover.

The attenuation of atrazine in the saline water of the hypersaline Pétrola lake from a natural reserve (SE Spain) was studied to get more insight into the processes governing the fate of the contaminant in highly saline environments. In microcosms, the water column was spiked with 15.4 mg/L of atrazine for 24 days. Before atrazine amendment, the initial distribution of bacterial community was mostly composed of Proteobacteria (25.5 %), Cyanobacteria (25.2 %), Actinobacteriota (18.5 %), Verrucomicrobiota (11.5 %) and Bacteroidota (10.1 %). Within the mayor phyla, the most abundant families were identified as Cyanobiaceae (25 %), Rhodobacteraceae (10 %), Alcaligenaceae (9.9 %), Microbacteriaceae (7.3 %) and a poorly described PeM15 (6.2 %).The reduction of atrazine concentration in the water column reaches 86.9 %, which means a reduction of dissolved atrazine mass of 98.1 %. Parallel to the decrease in atrazine, the amount of its intermediate degradation metabolite, desethylatrazine, increased. Desethylatrazine was the major short-term metabolite within the first 8-12 days, indicating the potential activity by atrazine-degrading bacteria. No deisopropylatrazine was detected in the saline water above detection limit. Microbiology results showed that atrazine can be removed from the saline lake environment. After atrazine amendment, the taxonomic bacterial composition at phylum level shifted to Proteobacteria (60.8 %), Patescibacteria (9.7 %), Bacteroidota (7.3 %), Campylobacterota (6.4 %) and Actinobacteriota (2.1 %). Atrazine supplementation suggested a selective pressure on bacterial structure morphology through the emergence of different dominant groups (i.e., Campylobacterota) or even the eradication of those phyla of bacteria capable of photosynthesis (i.e., Cyanobacteria). At family level, Rhodobacteraceae (16.7 %), Burkholderiaceae (11.7 %), Thiomicrospiraceae (7.9 %), Methylophagaceae (6.7 %), Sulfurimonadaceae (4.4 %) and Solimonadaceae (3.3 %) were the most abundant in the water column at the end of the experiment.Related atrazine-degrading families established at the end of the experiment were Rhodobacteraceae, Solimonadaceae, Pseudomonadaceae, Rhizobiaceae, Chromatiaceae, Bacillaceae, Xanthomonadaceae, Caulobacteraceae, Moraxellaceae, Streptomycetaceae, Microbacteriaceae and Nannocystaceae. Related candidates such as Pseudomonas paralactis, Microbacterium sp., or Arthrobacter sp., among others, were isolated in water samples from previous studies. The bacterial candidates for atrazine degradation identified in the water column indicate that the herbicide acted as a selective pressure factor, altering the composition of the bacterial pattern. The water column would constitute a reactive environment which may govern the fate of pesticides in saline surface water bodies.

Las forestaciones en terrenos agrícolas abandonados proliferan en muchas regiones del mundo. Bajo clima mediterráneo, su arraigo puede verse comprometido por la competencia con la abundante flora arvense característica de estos ecosistemas. Nuestros objetivos fueron evaluar el potencial colonizador de la comunidad arvense en un antiguo cultivo tras 25 años de abandono, y estudiar el efecto de diferentes técnicas de control en la supervivencia y desarrollo de plantas forestales. Se muestreó el banco edáfico de semillas (métodos directo e indirecto) antes de forestar la parcela con Pinus halepensis, Quercus ilex subsp. ballota y Retama sphaerocarpa. Tras la plantación se aplicaron diferentes técnicas de control: laboreo, siega y tratamiento químico. Durante tres años se midió supervivencia, diámetro y altura. Los resultados mostraron una comunidad arvense abundante (67 taxones) con banco edáfico de semillas persistente (casi 20 000 semillas/m2), causante de elevada mortalidad principalmente en el pino. El laboreo resultó la mejor técnica el primer año para el arraigo del pino, mientras que la encina y la retama no mostraron diferencias entre tratamientos. A partir del segundo año, el tratamiento químico fue el óptimo al favorecer el crecimiento, recomendándose con las precauciones que conlleva el uso de herbicidas. Independientemente de que la respuesta de cada especie forestal a la competencia arvense pueda ser distinta, es fundamental analizar la necesidad de control de esta vegetación para incrementar el éxito de las forestaciones en ambientes tan exigentes como los mediterráneos.