Delayed response of microbial epipelic biofilm to nutrient addition in a Pampean stream

In streams and rivers, the first organisms which directly receive and respond to nutrients are primary producers (algae, macrophytes) and microbial heterotrophs (bacteria, fungi) since they rely on available inorganic nutrients from the water column. The aim of the present study was to analyze the response of the epipelic microbial biofilm in a Pampean stream submitted to a continuous input of inorganic nutrients (nitrogen and phosphorus). For this purpose, we measured the effects of moderate nutrient addition during 14 mo on the epipelic biofilm community of a meso-eutrophic stream that runs through the Pampean plain. The effects of nutrient enrichment were tested by analyzing the difference in algal and bacterial biomass and 2 extracellular enzymatic activities (β;-glucosidase, phosphatase) at an enriched reach compared with those measured at an unmodified upstream reach. Overall, the response of the epipelon of this Pampean stream produced a slow and delayed effect on algal biomass increases, which might result in a delayed effect on the increase of bacterial densities. Neither phosphatase activity nor β;-glucosidase activity exhibited significant changes due to nutrient addition. This may be due to the fact that the phosphatase activities measured were basal activities, uninhibited by enrichment, and that the epipelic β;-glucosidase activity was regulated more by substrate availability than by any nutrient imbalance. Although changes are slow, if some of these changes were to become chronic, they would affect the functioning and services of the whole stream ecosystem.Instituto de Limnología "Dr. Raul A. Ringuelet

Delayed response of microbial epipelic biofilm to nutrient addition in a Pampean stream

In streams and rivers, the first organisms which directly receive and respond to nutrients are primary producers (algae, macrophytes) and microbial heterotrophs (bacteria, fungi) since they rely on available inorganic nutrients from the water column. The aim of the present study was to analyze the response of the epipelic microbial biofilm in a Pampean stream submitted to a continuous input of inorganic nutrients (nitrogen and phosphorus). For this purpose, we measured the effects of moderate nutrient addition during 14 mo on the epipelic biofilm community of a meso-eutrophic stream that runs through the Pampean plain. The effects of nutrient enrichment were tested by analyzing the difference in algal and bacterial biomass and 2 extracellular enzymatic activities (β;-glucosidase, phosphatase) at an enriched reach compared with those measured at an unmodified upstream reach. Overall, the response of the epipelon of this Pampean stream produced a slow and delayed effect on algal biomass increases, which might result in a delayed effect on the increase of bacterial densities. Neither phosphatase activity nor β;-glucosidase activity exhibited significant changes due to nutrient addition. This may be due to the fact that the phosphatase activities measured were basal activities, uninhibited by enrichment, and that the epipelic β;-glucosidase activity was regulated more by substrate availability than by any nutrient imbalance. Although changes are slow, if some of these changes were to become chronic, they would affect the functioning and services of the whole stream ecosystem.Instituto de Limnología "Dr. Raul A. Ringuelet

Effects of riparian vegetation removal on nutrient retention in a Mediterranean stream

We examined the effects of riparian vegetation removal on algal dynamics and stream nutrient retention efficiency by comparing NH4-N and PO4-P uptake lengths from a logged and an unlogged reach in Riera Major, a forested Mediterranean stream in northeastern Spain. From June to September 1995, we executed 6 short-term additions of N (as NH4Cl) and P (as Na2HPO4) in a 200-m section to measure nutrient uptake lengths. The study site included 2 clearly differentiated reaches in terms of canopy cover by riparian trees: the first 100 m were completely logged (i.e., the logged reach) and the remaining 100 m were left intact (i.e., the shaded reach). Trees were removed from the banks of the logged reach in the winter previous to our sampling. In the shaded reach, riparian vegetation was dominated by alders (Alnus glutinosa). The study was conducted during summer and fall months when differences in light availability between the 2 reaches were greatest because of forest canopy conditions. Algal biomass and % of stream surface covered by algae were higher in the logged than in the shaded reach, indicating that logging had a stimulatory effect on algae in the stream. Overall, nutrient retention efficiency was higher (i.e., shorter uptake lengths) in the logged than in the shaded reach, especially for PO4-P. Despite a greater increase in PO4-P retention efficiency relative to that of NH4-N following logging, retention efficiency for NH4-N was higher than for PO4-P in both study reaches. The PO4-P mass-transfer coefficient was correlated with primary production in both study reaches, indicating that algal activity plays an important role in controlling PO4-P dynamics in this stream. In contrast, the NH4-N mass-transfer coefficient showed a positive relation-ship only with % of algal coverage in the logged reach, and was not correlated with any algal-related parameter in the shaded reach. The lack of correlation with algal production suggests that mechanisms other than algal activity (i.e., microbial heterotrophic processes or abiotic mechanisms) may also influence NH4-N retention in this stream. Overall, this study shows that logging disturbances in small shaded streams may alter in-stream ecological features that lead to changes in stream nutrient retention efficiency. Moreover, it emphasizes that alteration of the tight linkage between the stream channel and the adjacent riparian zone may directly and indirectly impact biogeochemical processes with implications for stream ecosystem functioning

Delayed response of microbial epipelic biofilm to nutrient addition in a Pampean stream

In streams and rivers, the first organisms which directly receive and respond to nutrients are primary producers (algae, macrophytes) and microbial heterotrophs (bacteria, fungi) since they rely on available inorganic nutrients from the water column. The aim of the present study was to analyze the response of the epipelic microbial biofilm in a Pampean stream submitted to a continuous input of inorganic nutrients (nitrogen and phosphorus). For this purpose, we measured the effects of moderate nutrient addition during 14 mo on the epipelic biofilm community of a meso-eutrophic stream that runs through the Pampean plain. The effects of nutrient enrichment were tested by analyzing the difference in algal and bacterial biomass and 2 extracellular enzymatic activities (β;-glucosidase, phosphatase) at an enriched reach compared with those measured at an unmodified upstream reach. Overall, the response of the epipelon of this Pampean stream produced a slow and delayed effect on algal biomass increases, which might result in a delayed effect on the increase of bacterial densities. Neither phosphatase activity nor β;-glucosidase activity exhibited significant changes due to nutrient addition. This may be due to the fact that the phosphatase activities measured were basal activities, uninhibited by enrichment, and that the epipelic β;-glucosidase activity was regulated more by substrate availability than by any nutrient imbalance. Although changes are slow, if some of these changes were to become chronic, they would affect the functioning and services of the whole stream ecosystem.Instituto de Limnología "Dr. Raul A. Ringuelet

Quality and reactivity of dissolved organic matter in a Mediterranean river across hydrological and spatial gradients.

Understanding DOM transport and reactivity in rivers is essential to having a complete picture of the global carbon cycle. In this study, we explore the effects of hydrological variability and downstream transport on dissolved organic matter (DOM) dynamics in a Mediterranean river. We sampled the main stem of the river Tordera from the source to the sea, over a range of fifteen hydrological conditions including extreme events (flood and drought). By exploring spatial and temporal gradients of DOM fluorescence properties, river hydrology was found to be a significant predictor of DOM spatial heterogeneity. An additional space-resolved mass balance analysis performed on four contrasting hydrological conditions revealed that this was due to a shift in the biogeochemical function of the river. Flood conditions caused a conservative transport of DOM, generating a homogeneous, humic-like spatial profile of DOM quality. Lower flows induced a non-conservative, reactive transport of DOM, which enhanced the spatial heterogeneity of DOM properties. Moreover, the downstream evolution of DOM chemostatic behaviour revealed that the role of hydrology in regulating DOM properties increased gradually downstream, indicating an organised inter-dependency between the spatial and the temporal dimensions. Overall, our findings reveal that riverine DOM dynamics is in constant change owing to varying hydrological conditions, and emphasize that in order to fully understand the role of rivers in the global carbon cycle, it is necessary to take into account the full range of hydrological variability, from floods to droughts

Biochemical quality of basal resources in a forested stream: effects of nutrient enrichment

We studied biochemical changes in biofilm and suspended particulate and dissolved organic matter (OM) during the leaf emergence period (March-May 2008) in a forested headwater stream in response to a long-term (4 years, 2004-2008) experimental nutrient enrichment study. This study compared results from one reach upstream of the enrichment point and one reach downstream using moderate nutrient concentrations (nitrogen, N, from 388 to 765 μg L−1 and phosphorus, P, from 10 to 30 μg L−1, resulting in N:P ratios of 85-56). During the spring of 2008, we analysed the chlorophyll content, elemental composition (carbon, C, and N), bacterial density, and extracellular enzyme activities along with their biochemical composition (amino acids, fatty acids and sterols) on biofilm and OM. Nutrients caused changes in the biochemical composition of the biofilm, while changes in the OM were subtle. The C:N ratio of the biofilm decreased with nutrient enrichment likely due to the increase in protein (non-essential amino acids). The polysaccharide and total and essential fatty acid contents were higher when nutrient enrichment coincided with greater light availability. The peptidase extracellular activity was higher in the fertilised reach at early spring, while phosphatase activity decreased at late spring. The suspended and dissolved OM composition did not change due to the nutrient addition, likely due to the lower water residence time in the reach. Headwater systems are highly dynamic, and the biochemical composition of the biofilm changed in response to changes in nutrients but also to light in this study. These changes, although moderate, could influence higher trophic levels through modifications in their diet. This experiment exemplifies how small land use shifts may affect headwater streams

Drought effects on resource quality in a Mediterranean stream: fatty acids and sterols as indicators

Seasonal droughts in Mediterranean streams shape their physical, chemical, and biological characteristics. Thus, droughts have the potential to alter resources at the base of the food web, which in headwater streams are primarily allochthonous and secondarily autochthonous organic matter (OM). In the present study we assessed the quality of basal resources in a Mediterranean stream during a drought episode before and after a non-flow period (NF). Fatty acids (FA) and sterols were analyzed in the benthic substrata (leaves and sand and cobbles biofilm) and transported OM (particulate and dissolved fractions). FA and sterols were selected as indicators of resource quality because they include essential molecules for consumers and may be used as biomarkers of OM sources. The drying-rewetting process determined a general reduction in the total and essential FA of benthic substrata and transported particulate OM, and a shift from predominantly autochthonous to allochthonous OM. Furthermore, the sterol composition did not change between the drying and rewetting phases and the rewetting did not cause the leaching of FA in dissolved OM. The epilithic biofilm and leaves were the most important sources of essential FA and sterols, while the sand biofilm was the poorest source of these lipids. Our conclusions enhance the understanding of the mechanisms underlying the effects of droughts on basal resource quality in streams

Does grazing pressure modify diuron toxicity in a biofilm community?

Herbicides affect the structure and functional parameters of fluvial biofilm. Diuron is toxic to primary producers and disrupts endocrine activity. Here, we studied the interaction between this toxicant and several biological compartments in a simple food chain composed of herbivores (the snail Physella [Costatella] acuta) and biofilm. We used indoor experimental channels to which Diuron was added at a realistic concentration (2 μg/L). Bacterial survival and chlorophyll-a and photosynthetic activity were analyzed in the biofilm. We monitored biomass, mortality, reproduction, and motility as end points in the freshwater snail P. acuta. Our results showed that bacterial survival and photosynthetic activity were sensitive to Diuron. Snails were not affected by the herbicide at the concentration tested. No significant interactions between the toxicant and grazers were observed on the biofilm. Reproductive traits, however, were slightly affected, indicating a possible endocrine disruption

Bridging levels of pharmaceuticals in river water with biological community structure in the Llobregat river basin (NE Spain)

A wide range of human pharmaceuticals are present at low concentrations in freshwater systems, particularly in sections of polluted river. These compounds show high biological activity, often associated with a high stability. These characteristics imply a potential impact of these substances on aquatic biota even when present at low environmental concentrations. Low flow conditions in Mediterranean rivers, most of which flow through densely populated areas and are subjected to intensive water use, increase the environmental risk of these emergent compounds. Here, we studied whether pharmaceuticals in river water affect the local benthic community structure (diatoms and invertebrates). For this purpose, we analyzed the occurrence of pharmaceuticals along the Llobregat River and examined the benthic community structure (diatoms and invertebrates) of this system. Some pharmaceutical products in the Llobregat River registered concentrations greater than those cited in the literature. Multivariate analyses revealed a potential causal association between the concentrations of some anti-inflammatories and β-blockers and the abundance and biomass of several benthic invertebrates (Chironomus spp. and Tubifex tubifex). Further interpretation in terms of cause-and-effect relationships is discussed; however, it must be always taken with caution because other pollutants also may have significant contributions. Combined with further community experiments in the laboratory, our approach could be a desirable way to proceed in future risk management decisions

Global pressures, specific responses: effects of nutrient enrichment in streams from different biomes

Fil: Artigas, Joan. Clermont Université. Université Blaise Pascal. Laboratoire Microorganismes: Génome et Environnement; FranceFil: García-Berthou, Emili. Institute of Aquatic Ecology. University of Girona. Girona; SpainFil: Bauer, Delia Elena. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Castro, Maria I.. Department of Biology. National University of Colombia. Bogotá DC; ColombiaFil: Cochero, Joaquín. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Colautti, Darío César. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Cortelezzi, Agustina. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La PlataFil: Donato, John C.. Department of Biology. National University of Colombia. Bogotá DC; ColombiaFil: Elosegi, Arturo. Faculty of Science and Technology. The University of the Basque Country. Bilbao; SpainFil: Feijoó, Claudia S.. INEDES. Department of Basic Sciences. National University of Luján. Luján; ArgentinaFil: Giorgi, Adonis. INEDES. Department of Basic Sciences. National University of Luján. Luján; ArgentinaFil: Gómez, Nora. Institute of Aquatic Ecology. University of Girona. Girona; SpainFil: Leggieri, Leonardo. Institute of Aquatic Ecology. University of Girona. Girona; SpainFil: Muñoz, Isabel. Department of Ecology. University of Barcelona. Barcelona; SpainFil: Rodrigues Capítulo, Alberto. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Romaní, Anna M.. Institute of Aquatic Ecology. University of Girona. Girona; SpainFil: Sabater, Sergi. Catalan Institute for Water Research (ICRA). Scientific and Technological Park of the University of Girona. Girona; Spai