Key-words:
stream, catchment, land use, nutrient enrichment, abstractionWe studied the effects of land use changes on flow regime and water chemistry of headwater streams in the highlands of Chiapas, a region in southern Mexico that has experienced high rates of deforestation in the last decades. Samples for water chemistry were collected and discharge was measured between September 2007 and August 2008 at eight streams that differed in the land uses of their riparian and catchment areas, including streams draining protected forested areas. Streams with high forest cover (>70%) in their catchments maintained flow through the year. Streams draining more disturbed catchments exhibited reduced or no flow for 4−6 months during the dry season. Nitrate concentrations were lower at streams draining forested catchments while highest concentrations were measured where conventional agriculture covered a high proportion of the catchment and riparian zone. Highest phosphorus concentrations occurred at the catchment where poultry manure was applied as fertilizer. Differences between forest streams and those draining disturbed areas were correlated with the proportion of forest and agriculture in the riparian zone. Variation in stream variables among sampling dates was lower at the forest sites than at the more disturbed study streams. Conversion of forest into agriculture and urban areas is affecting flow regime and increasing nutrient concentrations, although the magnitude of the impacts are influenced by the type of agricultural practices and the alteration of the riparian zone.
RÉSUMÉLes effets de l'utilisation des terres sur le régime d'écoulement et la composition chimique de l'eau des ruisseaux de tête de bassin des plateaux du Chiapas
Mots-clés :ruisseau, bassin versant, aménagement du territoire, Nous avons étudié l'influence des changements d'aménagement du territoire sur le régime hydrographique et la composition hydrochimique de ruisseaux des plateaux du Chiapas, une région au sud du Mexique qui a subi une déforestation de grande ampleur ces dernières décennies.
Los bosques andinos se encuentran sometidos a fuertes procesos de perturbación y fragmentación debido a la creación de pastizales y explotación de monocultivos, especialmente, cafetales. Adicionalmente, es poca la información acerca de la capacidad que tienen estos relictos de bosque para mantener su biodiversidad. Se realizó un estudio en una finca cafetalera-ganadera en el municipio de Tarso (Antioquia), Colombia, utilizando a los escarabajos coprófagos como grupo bioindicador. Se realizaron tres muestreos en tres hábitats: bosque, cafetal y pastizal, cada uno de ellos con un transecto de nueve trampas de caída, cebadas con excremento de cerdo por 48 h. Se recolectaron un total de 779 individuos, distribuidos en 13 especies y 7 géneros. Las especies: Onthophagus curvicornis (n = 196, 25,2%) y Oxysternon conspicillatum (n = 159, 20,4%) fueron las especies dominantes. No hubo diferencias significativas en la riqueza, abundancia, ni en la diversidad entre hábitats, pero si en la biomasa. El ensamblaje estuvo dominado por cavadores, algunos endocópridos y ninguna especie rodadora, evidenciando el alto grado de perturbación del bosque. El cafetal fue el hábitat que presentó la mayor diversidad, posiblemente debido a una mayor oferta alimenticia. Las diferencias entre las biomasas encontradas responden a los procesos de perturbación y fragmentación, ocasionando que el ensamblaje estuviera dominado por O. conspicillatum, lo cual sugiere que la presencia de esta especie en esta localidad sería indispensable para el mantenimiento de la funcionalidad ecosistémica.
In the present study, polymeric epoxy and polyester resin reinforced with glass fiber compounds were prepared by adding of flame retardants based on aluminum and magnesium hydroxide in order to evaluate their influence on mechanical properties. An experimental DOE design was developed with two qualitative factors: the resin and retardant type; with two levels each and a quantitative factor: volumetric composition of the retardant with three levels (3%, 6% and 9%). With all possible combinations; tensile, flexural and impact tests were carried out. The results showed that the addition of retardants in different percentages has different influence for each mechanical property. It was evidenced that the 9% HA Aluminum Hydroxide has no significant effect on the tensile strength and its modulus compared to Magnesium Hydroxide HM. Conversely; on the flexural strength, flexural modulus and rupture energy the HM has a slightly lower effect with respect to the HA. For flexural strength and its modulus, the best proportion of retardant was 6%. 3% is the recommendation for rupture energy. The data presented in this document can be used to improve the fire resistance of the existing materials studied.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.