The contribution of instream wood to streambed organic matter controls on microbial metabolic activity

<p>Microbial metabolic activity (MMA) in streambeds drives greenhouse gas (GHG) production and nutrient turnover. Previous research has identified that the quantity and quality of organic matter (OM) are important controls on MMA. Instream wood may make a significant contribution to the total OM content of the streambed, especially in forested streams, but it has typically been ignored or explicitly omitted in previous research. By means of an incubation experiment, we investigate the impact of streambed wood on MMA, GHG production and nutrient turnover rates. By using three geologies (sandstone, chalk and limestone) and allowing temperatures to fluctuate with environmental conditions, we observe these impacts under a range of typical scenarios. These results could have implications for estimates of GHG emissions from streams and inform catchment management, for example the impacts of direct installation of instream wood in river restoration or the indirect input as a result of riparian planting.</p>

Linking instream wood recruitment to adjacent forest development in landscapes driven by stand-replacing disturbances: a conceptual model to inform riparian and stream management

Instream wood plays an important role in stream morphology and creation of fish habitat in conifer forests throughout the temperate zone. In some regions, such as the US Pacific Northwest, many streams currently have reduced amounts of instream wood due to past management activities (timber harvest, wood removal, etc.). These reductions exist against a backdrop of naturally dynamic amounts and distributions of instream wood, which likely fluctuate over time based in part on the stage of development (disturbance and succession) in adjacent riparian forests. Despite many studies on both forest development and instream wood accumulation, the linkages between these processes have not been fully described, particularly as they relate to stream restoration needs. In this paper, we combine literature on forest development, disturbance, and processes that drive instream wood recruitment to more explicitly connect the temporal dynamics of stream wood inputs with the dynamics of adjacent riparian forests. We use moist forests of the Pacific Northwest as an exemplary system, from which to draw broadly applicable patterns for landscapes influenced by stand-replacing disturbance regimes. This conceptual model highlights a U-shaped pattern of instream wood recruitment, in which instream wood is highest after a stand-replacing disturbance and during the old-growth stage, and lowest through the middle stages of forest development (currently the most abundant stages in many landscapes as a result of past forest management practices). This mid-successional period of scarce wood is likely exacerbated in streams with a history of wood removal. The U-shaped pattern suggests that, without higher-than-average levels of disturbance, many streams in landscapes dominated by mid-successional second-growth forests (∼30–80 yr old) will be deficient of instream wood until forest stands are over 200 years old. As such, the balance between the predominant riparian conservation strategy of passive restoration (e.g., unharvested riparian reserves) and the alternative of active restoration (e.g., wood additions and (or) riparian stand treatments) should be carefully considered, depending on management objectives, site context, and potential tradeoffs over time.

Vliv říčního dřeva na morfologické a sedimentologické parametry koryta na příkladu meandrujícího toku Odry

Instream wood is a natural phenomenon that signifi cantly influences a function of the fluvial system in forested river basins and represents a natural part of this system. However, the majority of these relatios between instream wood and fluvial ecosystems were investigated in mountain streams or gravel-bed rivers and we are lacking field data from lowland meandering rivers. This study deals with the complex assessment of instream wood on morphology and sediment parameters including the content of organic material at spatially detailed scale of the selected bend of the Odra River. Within the site of interest (66.5 river km), 12 instream wood pieces were identified (lenght ≥ 1 m, diameter ≥ 10 cm). Their presence significantly affected river morphology, when they were the main initiator of pool formation. In total, 28 samples of surface bed sediments were collected from the thalweg, bars and lateral pool. In laboratory, samples were subjected to grain size analysis (sieving method) and loss on ignition (LOI) to obtain content of organic matter. The majority of bed sediment samples were coarse grained and these samples were located in the thalweg. The main component of these samples is gravel, often supplemented with admixtures of finer fractions. The analysis of data did not show the effect of instream wood on the deposition of organic matter in bed sediments. One of the reasons may be the presence of coarse grained material which generally contains a small amount of organic matter.