Ana Basaguren

Afforestation with Eucalyptus globulus and leaf litter decomposition in streams of northern Spain

To test the hypothesis that decomposition of leaf species in streams is influenced by afforestation with Eucalyptus globulus, we compared decay rates, nutrient levels, fungal biomass and macroinvertebrate assemblages on alder and eucalyptus leaf litter in three streams (two headwaters under different forests, and a mid reach) of the Aguera catchment (northern Spain). Whatever the reach, alder always decomposed significantly faster than eucalyptus. Litter contents in nitrogen and phosphorus rose during breakdown at the mid reach, but not at the headwaters. No differences in fungal biomass were found between alder and eucalyptus leaves at the headwater reaches; however, at the mid reach, eucalyptus showed the highest values. Alder litter, a high quality substratum, was readily colonized by shredders, and decayed rapidly at all sites. Eucalyptus, a low quality species, had lower nutrient contents and was less favoured by shredders. Under high nutrient levels (particularly phosphorus), however, it was readily colonized by fungi, thus shifting from medium to high breakdown rates. The potentially negative impact of afforestation with eucalyptus on streams can thus be reduced in situations of high concentrations of dissolved nutrients.

Leaf-litter decomposition in headwater streams: a comparison of the process among four climatic regions

Abstract The main purpose of our work was to elucidate factors responsible for the geographical differences in leaf-litter decomposition rates in Spanish oligotrophic headwater streams. Decomposition experiments with alder (Alnus glutinosa) leaf litter were carried out in 22 headwater streams in 4 different climatic regions across the Iberian Peninsula (Cornisa Cantábrica, Cordillera Litoral Catalana, Sierra de Guadarrama, and Sierra Nevada). Streams that were similar in size, flowed mainly over siliceous substrate in catchments with scarce human settlements and activities, and fell within a range of low nutrient concentrations were chosen in each region. Breakdown rates were regionally variable and were low (0.109–0.198% ash-free dry mass [AFDM]/degree day [dd]) in the Cornisa Cantábrica, the most mesic and Atlantic region, and high (0.302–0.639% AFDM/dd) in Sierra de Guadarrama, one of the coldest and most inland areas. Temperature was not the determining factor affecting differences in breakdown rates among regions, and breakdown rates were not related to concentrations of dissolved nutrients. However, microbial reproductive activity (sporulation rates) was significantly correlated with dissolved P concentration. Breakdown rates were explained better by presence and feeding activities of detritivores than by decomposer activity. Incorporation of breakdown rates in assessment schemes of stream ecological status will be difficult because leaf processing does not respond unequivocally to environmental factors when climatic regions are considered. Thus, regional adjustments of baseline standards in reference conditions will be required.

Stream regulation by small dams affects benthic macroinvertebrate communities: from structural changes to functional implications

We studied benthic macroinvertebrate communities upstream and downstream of five small reservoirs (surface release in autumn–winters) (north Spain) to assess the effect of flow regulation on structural and functional characteristics of stream ecosystems. We based our approach on the use of structural metrics (density, biomass, richness and diversity) in combination with two functional diversity indices based on biological and ecological traits: FDPG index, related to species richness, and FDQ, which incorporates evenness across taxa. Although water physicochemical parameters were unaffected by the reservoirs during the study period (autumn–winter), macroinvertebrate metrics were lower below the dams, with detritivores (shredders and collector-gatherers) being the most affected. The alder leaf breakdown rate estimated by the litter-bag technique was related to the density, biomass, richness, diversity and FDPG index of shredders, compromising the ecosystem functioning. The most plausible origin for the observed differences in macroinvertebrate metrics between upstream and downstream reaches was the change of the flow regime caused by the impoundments at downstream sites, leading to droughts in summer in those naturally permanently flowing streams. The observed functional diversity loss might reduce the chances of the community to override natural or man-induced fluctuations in their environment with possible repercussions on important ecosystem functions and services.

Size-mass relationships of stream invertebrates in a northern Spain stream

We show the regression equations that relate the head width of 10 freshwater insect species or the length of the first thoracic segment of 2 amphipods with their dry mass in 3 reaches along a small stream in northern Spain. Spatial differences in size–mass relationships were found. Organisms stored in alcohol showed lower dry mass than those specimens that were dried immediately after collection. The use of both size measures for dry mass estimation in field samples is discussed. It is recommended that the size–mass relationships be constructed using non-preserved organisms. Furthermore, great care is required when such allometric equations are taken from the literature.

Assessing river water quality by means of multifactorial methods using macroinvertebrates. A comparative study of main water courses of Biscay.

Abstract Ninety two taxa of benthic macroinvertebrate were used to ordinate 175 sites from main water courses of Biscay (Basque Country) by means of correspondence analysis (CA). On the plane of the first two axes from CA, changes in macroinvertebrate community structure were observed between rivers due to differences in natural eutrophication and also as a result of the combined effect of industrial and urban sewage. The groups of taxa observed could be interpreted in ecological terms and were representative of headwater reaches, moderately eutrophic waters and polluted waters, respectively. This method of ordination provides more information on differences in water quality among the non-polluted sites than does a biotic index (BMWP score).

Life history, production and coexistence of two leptophlebiid mayflies in three sites along a Northern Spain stream

The life history and temporal dynamics in density, biomass, growth rate and secondary production of Habrophlebia lauta and Habroleptoides confusa were com- pared in 3 sites along the Agu era stream in northern Spain. Both species had univoltine winter life histories. Hb. lauta showed greater abundance and production at down- stream sites, while Hd. confusa did at the headwater site. The life history and temporal dynamics in population parameters differed between both species. As a result, tem- poral overlaps of abundance and, especially, production of these two mayflies were very low, which suggests that irrespective of their abundance, interspecific competi- tion between Hb. lauta and Hd. confusa was unimportant along this stream system.

Life history and production of Caenis luctuosa (Burmeister) (Ephemeroptera, Caenidae) in two nearby reaches along a small stream

Population dynamics and production of C. luctuosa were compared in two reaches of the Agüera stream (northern Spain). This species showed univoltine winter life history in both sites. However, the start of the recruitment period, and the cohort production interval differed in 1 month between reaches. Secondary production of C. luctuosa ranged from 76 mg m−2 year−1 (upper site) to 93 mg m−2 year−1 (lower site). Although annual production seemed to be mainly influenced by the biomass found at each site, changes in life history may have also been important. The need to have accurate information about life history of the analysed species at the study sites when assessing secondary production is highlighted.

Self-purification processes along a medium-sized stream

Water quality levels and loads of nutrients transported by the Agüera stream (northern Spain) were studied for a year to assess the self-purification capacity of this system. The main villages produce an increase of nutrient concentrations and a degradation of water quality. Nevertheless, the high retention capacity, especially for phosphate, allows the stream to recover its previous levels of quality after a short reach. The retention of nutrients depends on a complex combination of the flow level, hydrologic stability and the development of periphytic communities.

Leaf litter decomposition of native and introduced tree species of contrasting quality in headwater streams: how does the regional setting matter?

Terrestrial plant litter is important in sustaining stream food webs in forested headwaters. Leaf litter quality often decreases when native species are replaced by introduced species, and a lower quality of leaf litter inputs may alter litter decomposition at sites afforested with non-native species. However, since detritivore composition and resource use plasticity may depend on the prevalent litter inputs, the extent of the alteration in decomposition can vary between streams. We tested 2 hypotheses using 2 native and 3 introduced species of tree differing in quality in 4 Iberian regions with contrasting vegetational traits: 1) decomposition rates of all plant species would be higher in regions where streams normally receive litter inputs of lower rather than higher quality; 2) a higher resource-use plasticity of detritivores in regions vegetated with plants of lower litter quality will cause a greater evenness in decomposition rates among plant species compared to regions where streams normally receive higher-quality plant litter inputs. Results showed a highly consistent interspecific ranking of decomposition rates across regions driven by litter quality, and a significant regional effect. Hypothesis 1 was supported: decomposition rates of the five litter types were generally higher in streams from regions vegetated with species producing leaf litter of low quality, possibly due to the profusion of caddisfly shredders in their communities. Hypothesis 2 was not supported: the relative differences in decomposition rates among leaf litter species remained essentially unaltered across regions. Our results suggest that, even in regions where detritivores can be comparatively efficient using resources of low quality, caution is needed particularly when afforestation programs introduce plant species of lower litter quality than the native species.

Seston transport variability at different spatial and temporal scales in the Agüera watershed (North Spain)

Abstract The variability of fine particulate organic matter concentrations in the streams of a moderately disturbed catchment were studied under different spatial and temporal scales. Spatial patterns of FPOM concentrations clearly reflect the effects of disturbances imposed by human settlements and land uses, and recovery processes. Temporal changes are mainly caused by floods which disrupt the spatial variability. These sources of variation may be responsible for the lack of a significant fit between discharge and FPOM concentrations in disturbed reaches. On a diel (throughout the day) scale, FPOM transport rhythms were clear only in undisturbed headwaters. Conventional sampling designs (e.g. annual cycles) should take into account short-term variability scales. The Aguera stream shows important internal processes (e.g. self-purification trends) that mitigate the influences of human settlements and tributaries, and can control FPOM transport under low flow conditions. Examination of different temporal and spatial scales seems to be necessary to detect the main factors that control FPOM transport in streams. This organic parameter could be important in evaluating the effects of intermediate disturbances in fluvial systems.