José Ramón Díez

Inputs of Particulate Organic Matter to Streams with Different Riparian Vegetation

To test whether afforestation with eucalyptus affects the amount, quality, and timing of litter inputs, we evaluated the inputs of coarse particulate organic matter (CPOM) to 2 headwater streams, one flowing through a mixed deciduous forest and one through a plantation of Eucalyptus globulus. Vertical and lateral traps were sampled at least monthly, and the material collected was sorted into 4 main categories: fallen leaves (several species), fruits and flowers, twigs and bark, and debris. The eucalyptus plantation resulted in a reduction of 32% of total litter inputs, and 73% of lateral inputs, compared to the mixed deciduous forest. It also had a less marked seasonal pattern of inputs, and different timing of peak litterfall, the peak in the deciduous forest occurring in autumn, whereas in the eucalyptus plantation the peak occurred in summer. Similarly, leaf diversity was greatly reduced under the eucalyptus, with 98% of the leaf litter mass from 1 species, resulting in broad changes in litter quality. Litter inputs in the eucalyptus plantations contributed 67% less nitrogen and 65% less phosphorus to the stream than in the deciduous forest. Although eucalyptus plantations result in broad changes in organic inputs, no drastic impacts on the structure or function of benthic communities are evident so far in the Agüera stream. Nevertheless, caution suggests maintaining the quantity and timing of allochthonous inputs by keeping buffer strips of native riparian forest.

Effect of removal of wood on streambed stability and retention of organic matter

We tested the hypothesis that wood influences stream channel morphology, sediment composition, retention, and storage of organic matter by experimentally removing all wood from 2 first-order reaches (ca 90 m length) of 2 neighboring tributaries (Salderrey and Cuchillo streams) in the Agüera catchment (Basque Country, Spain). We established 2 control reaches upstream from these treatment reaches. We completed maps of substrate, fill/scour transects, and wood surveys in 1997 (prior) and 1998 (after) wood removal. We measured monthly inputs of fine wood to the treatment reaches. In addition, we measured seston every 2 wk, benthic coarse organic particulate matter (CPOM) every 2 mo, and the retention capacity of reaches every 3 mo. All reaches were scoured during the study period, but the volume of sediment lost was higher in the treatment reaches (53 m3) than in the controls (14.2 m3 in Salderrey, 2.7 m3 in Cuchillo). As a result, the area of coarse substrate increased in the treatments, but remained unaltered in the controls. The capacity of the reaches to retain CPOM decreased after the treatment, but affected neither seston concentration nor the benthic storage of CPOM. Wood is an important constituent of Basque streams, and removal of wood significantly impacts channel structure and organic matter storage.

Does it make economic sense to restore rivers for their ecosystem services

Temperate forests managed to maximize sustainable yield of wood products can reduce the availability of dead wood on the forest floor and in adjacent streams, which in turn can impair ecological processes such as retention and transformation of organic matter. Lack of tools to link ecological processes with their effects on human well-being leads forest managers to ignore the cost on other services from terrestrial and aquatic ecosystems. We examine how adding dead wood to restore stream channel complexity affects the provision and value of selected ecosystem services, mainly related to the retention and transformation of matter and cycling of nutrients, as well as to the effects on aquatic biota. Specifically, we evaluated the cost-effectiveness of stream restoration through a comparative analysis of four reach-scale projects in streams flowing through temperate forest and into a drinking water reservoir and two scenarios of active and passive restoration at the basin scale. Results indicate that the lack of dead wood in streams has an important economic cost because of the effects on fish provisioning, opportunities for recreation and tourism, water purification and erosion control. Active reach-scale restoration resulted in a 10- to 100-fold increase in the monetary benefits provided by streams, accounting as much as 1·8 € per metre of restored river length each year. Results of the reach-scale cost-benefit analyses estimated that the time required to recover the active restoration investment ranged from 15 to 20 years in low- to middle-order streams. Synthesis and applications. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services

Leaf retention in streams of the Agüera basin (northern Spain)

Abstract. 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 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.

Assessing the effects of multiple stressors on the functioning of Mediterranean rivers using poplar wood breakdown

Mediterranean rivers in the Iberian Peninsula are being increasingly affected by human activities, which threaten their ecological status. A clear picture of how do these multiple stressors affect river ecosystem functioning is still lacking. We addressed this question by measuring a key ecosystem process, namely breakdown of organic matter, at 66 sites distributed across Mediterranean Spain. We performed breakdown experiments by measuring the mass lost by wood sticks for 54 to 106 days. Additionally, we gathered data on physico-chemical, biological and geomorphological characteristics of study sites. Study sites spanned a broad range of environmental characteristics and breakdown rates varied fiftyfold across sites. No clear geographic patterns were found between or within basins. 90th quantile regressions performed to link breakdown rates with environmental characteristics included the following 7 variables in the model, in decreasing order of importance: altitude, water content in phosphorus, catchment area, toxicity, invertebrate-based biotic index, riparian buffer width, and diatom-based quality index. Breakdown rate was systematically low in high-altitude rivers with few human impacts, but showed a high variability in areas affected by human activity. This increase in variability is the result of the influence of multiple stressors acting simultaneously, as some of these can promote whereas others slow down the breakdown of organic matter. Therefore, stick breakdown gives information on the intensity of a key ecosystem process, which would otherwise be very difficult to predict based on environmental variables.