107 Evaluation of the state of conservation of shallow lakes in the province of Leon (Northwest Spain) using botanical criteria M. FernÆndez AlÆez, C. FernÆndez AlÆez, S. Rodrguez & E. BØcares Area de Ecologa. Universidad de Len. Campus de Vegazana, 24071 Len. E-mail: degmfa@unileon.es ABSTRACT The floristic richness of the aquatic and hygrophytic vegetation of 27 permanent and temporary small lakes located in the Len province was analyzed. The evaluation of these wetlands was carried out specifying their significance at a European, national and regional level. The main factors related to species richness were size of the water body and alterations due to pollution and shore degradation. Samplings in 1981 and 1994 were compared. Highly significant differences in genera and species richness were found between years in all lakes. The richness of hygrophytic flora was much larger in the latter sampling. This was rela- ted to large interannual variations in mean water levels. Botanical criteria for assessing shallow lake ecological importance use indices based on the abundance of hydrophytes and on floristic richness of sites. We conclude that four of the 27 lakes and wetlands studied here are of European interest, while 10 are of national significance. Key words: Macrophytes, species richness, temporary lakes, shallow lakes, conservation. RESUMEN Se analiza la riqueza florstica de la vegetacin acuÆtica e higrfila de 27 formaciones palustres permanentes o con ritmos de inundacin temporal en el cuadrante suroriental de la provincia de Len, y se realiza la valoracin de estos humedales, especificando su significado en los contextos europeo, nacional y regional. Los factores que parecen estar relacionados con la riqueza de especies y de gØneros en las lagunas son: su extensin, y las alteraciones que experimentan por contaminacin y degradacin de la orilla. Se comparan los resultados obtenidos en muestreos efectuados en 1981 y 1994. Cuando se con- sidera la riqueza de gØneros y especies de cada laguna las diferencias son muy significativas, aumentando especialmente la riqueza de la flora higrfila en el muestreo mÆs reciente debido probablemente a las variaciones interanuales de la disponi- bilidad de agua. De acuerdo con la valoracin de las lagunas segœn criterios botÆnicos, que utilizan ndices basados en la importancia de los hidrfitos y en la diversidad florstica de cada enclave, y que reflejan la madurez del sistema y grado de conservacin, se deduce que tienen importancia en el contexto europeo 4 lagunas y 10 en el Æmbito nacional. Palabras clave: Macrfitos, riqueza de especies, lagunas temporales, conservacin. Limnetica 17: 107-117 (1999) ' Asociacin Espaæola de Limnologa, Madrid. Spain. ISSN: 0213-8409 INTRODUCTION The number of references to temporary waters is not in accord with their widespread ocurrence, ecological importance and limnological interest (Williams, 1987). In the southeast of Len there is a number of water bodies, usually shallow, fos- tered by overland water inflows and groundwater flows. These water bodies are rarely permanent, though water is retained enough time for macro- phytic communities to grow. Such communities were described by FernÆndez AlÆez et al (1984, 1986a, 1986b, 1988) from a sampling carried out in 1981. Unusual weather patterns in the past years and intensification of agriculture in recent decades have adversely affected many shallow