The capacity of stream channels to retain leaf litter (retentiveness) was measured in 21 reaches of the Agüera basin (northern Spain) at different discharges, using plastic strips as leaf analogs. Strips were calibrated against seven local leaf species occurring in the area. Retention was highest for alder, followed by plastic strips, oak, beech, chestnut, eucalyptus, hazel, and sycamore. Inter-specific differences in retention were great, and not clearly related to leaf form or size. This result shows that a great deal of caution is necessary to compare results obtained by authors using different leaf species. The Agüera stream channels were highly retentive, especially Aquat. Sci. 65 (2003) 158 -166 Aquatic Sciences in the headwaters. At baseflows, the average travel distance of strips was 3.6 m in 1st-order reaches, increasing to 16.6 m in 3rd-order streams. Travel distances of strips increased twofold in 3rd-and 2nd-order reaches and 5-fold in 1st-order streams during periods of high discharge. Leaf litter retentiveness was related to channel gradient, width, and substrate. Cobbles and wood showed high retention efficiencies, and the role of wood as a retention factor increased at high discharges. Retentiveness enhances storage and subsequent utilization of organic materials in forested streams, and thus should be taken into account when managing streams.
Open-cut mining operations can form pit lakes on mine closure. These new water bodies typically have low nutrient concentrations and may have acidic and metal-contaminated waters from acid mine drainage (AMD) causing low algal biomass and algal biodiversity. A preliminary study was carried out on an acidic coal pit lake, Lake Kepwari, in Western Australia to determine which factors limited algal biomass. Water quality was monitored to obtain baseline data. pH ranged between 3.7 and 4.1, and solute concentrations were slightly elevated to levels of brackish water. Concentrations of N were highly relative to natural lakes, although concentrations of FRP (<0.01 mg/L) and C (total C 0.7-3.7 and DOC 0.7-3.5 mg/L) were very low, and as a result, algal growth was also extremely low. Microcosm experiment was conducted to test the hypothesis that nutrient enrichment will be able to stimulate algal growth regardless of water quality. Microcosms of Lake Kepwari water were amended with N, P and C nutrients with and without sediment. Nutrient amendments under microcosm conditions could not show any significant phytoplankton growth but was able to promote benthic algal growth. P amendments without sediment showed a statistically higher mean algal biomass concentration than controls or microcosms amended with phosphorus but with sediment did. Results indicated that algal biomass in acidic pit lake (Lake Kepwari) may be limited primarily by low nutrient concentrations (especially phosphorus) and not by low pH or elevated metal concentrations. Furthermore, sediment processes may also reduce the nutrient availability.
The main goal of this study was to examine the natural variability of alder (Alnus glutinosa (L.) GAERTN.) leaf processing and explore its potentiality as a functional indicator to assess the ecological status of Spanish headwater streams. Breakdown of leaf litter was studied during autumn-winter in reference headwater streams of two regions of northern Spain: the Basque Country (on the Atlantic) and Catalonia (on the Mediterranean). Spring experiments were also carried out in the Atlantic region in order to study seasonal changes. Leaf mass loss rates were slightly higher in Catalonian streams. Temperature was not the main factor for explaining differences between the two regions. In the Atlantic one, however, water temperature determined the spatial and seasonal variability of leaf litter processing. Because of the high natural variability in breakdown rates, our results highlight the difficulty in detecting moderate impairments on stream functioning through the analysis of leaf litter decomposition if this process is not accompanied by the study of other factors affecting it.
IntroductionStreams are supplied, through different pathways, by the surrounding terrestrial environments (MOLINERO and POZO, 2006). In well-oxygenated streams, aerobic bacteria, fungi and detritivores contribute to the decomposition of a significant amount of this material (ABELHO, 2001). Leaf litter breakdown is a pivotal process in stream functioning (HALL et al., 2000), which is affected by physical and chemical factors and involves the biological community; it provides an integrated measure of stream ecosystem functioning. Over two decades ago, WEBSTER and BENFIELD (1986) suggested that breakdown rates might be useful for evaluating effects of anthropogenic disturbances in streams. Since then, many studies have demonstrated that leaf litter processing is sensitive to a variety of disturbances caused by human activities in fluvial systems (e.g., land use: DANGER and ROBSON, 2004; acidification: DANGLES et al., 2004; metal pollution: CARLISLE and CLEMENTS, 2005; eutrophication: LECERF et al., 2006). However, leaf breakdown, as happens with other processes, shows 106 J. PÉREZ et al.
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