Experimental wood addition in streams: effects on organic matter storage and breakdown

Abstract

1. Channel complexity affects the physical structure, biotic communities and functioning of stream ecosystems. Large wood (LW) is a key element in the creation and maintenance of physically complex stream channels in forested areas. 2. In an attempt to enhance stream habitat quality and ecosystem functioning and to reduce inputs of organic matter to a downstream reservoir, LW was experimentally introduced into four mountain streams in the Basque Country (northern Spain), ranging in channel width from 3 to 13 m. Following a before-after/control-impact (BACI) design, streams were monitored during 1 year prior to wood addition and during 2 years after addition in one control and one experimental reach per stream. 3. Areal cover of benthic organic matter in the entire channel was measured from regular transects and the mass of stored organic matter from random Surber samples. Breakdown of organic matter was assessed in litter bag experiments performed with black alder leaves. When 50% of the initial mass in the bags remained, invertebrates associated with leaf bags were collected. 4. Wood placement produced a 2-to 70-fold increase in the storage of organic matter, especially in thick deposits upstream from wood jams, with values in excess of 2 kg AFDM per m 2 in the small streams. The accumulation of organic matter produced by wood introduction decreased with increasing stream size. 5. Despite the large increase in the availability of organic matter, litter breakdown rates were unaffected by the experimental reaches, suggesting large increases in the total amount of organic matter consumed at the reach scale. 6. Numbers of invertebrates and shredders per gram of leaf litter did not respond to wood addition. Average body mass of invertebrates associated with leaf litter showed a nonsignificant decreasing trend, which might reflect increased recruitment. 7. Although the effects of wood addition can depend on wood stability and stream size, adding LW to restore channel complexity can improve environmental conditions for invertebrate communities and affect stream ecosystem functioning, enhancing the efficiency to use organic matter inputs on a reach scale.

In the mood for wood-habitat specific colonization patterns of benthic invertebrate communities along the longitudinal gradient of an Austrian river

“…Like boulders and rocks, large wood (hereafter LW) and wood-accumulations have a strong influence on local hydraulics (e.g., Shields et al, 2001;Mutz, 2003;Manners et al, 2007;Blanckaert et al, 2014) and morphology (e.g., Gurnell et al, 1995;Keller et al, 1995;Kail, 2003;Blanckaert et al, 2014). Unlike rocks and boulders, LW also affects the nutrient budget of a river (e.g., Bilby, 1981;Hering & Reich, 1997;Gurnell et al, 2005;Flores et al, 2011) and presents an important habitat structure that increases the density and diversity of fish and benthic invertebrate species in rivers and streams (e.g., Copp, 1992;Hoffmann & Hering, 2000;Pilotto et al, 2014Pilotto et al, , 2016. Partially submerged logs serve as important land-water interfaces and oviposition sites for merolimnic insects, thereby significantly affecting their reproductive success Sweeney, 1993;Hoffmann & Hering, 2000).…”

Wood placement in river restoration: fact, fiction, and future direction

“…Once in the stream, wood affects a number of stream functions, including sediment storage and the creation of alluvial reaches in otherwise bedrock channels (Montgomery et al 1996), formation of pools (Beechie and Sibley 1997;Montgomery and Buffington 1997;Montgomery et al 1995), increased retention of organic matter and nutrients (Bilby 1981;Flores et al 2011), and island formation in large floodplain channels (Fetherston et al 1995;Gurnell et al 2001;Montgomery and Abbe 2006).…”

Reach scale ecologic influence of in-stream large wood in a Coastal Mountain range channel, Southern Chile

“…In June, in those same reaches, Ephemeroptera and Plecoptera, mainly shredders scrapers of logs and leaves respectively, were quite abundant, Elmidae (Coleoptera), Tipulidae (Diptera) and Chironomidae (Diptera), which are also consumers of soft decaying organic matter, were less abundant, while Odonata as predators appeared with very low abundance. Seemingly, Flores et al (2011) found that shredders represented 10.2% of the total invertebrates in 2006 and 26.3% in 2008, having no statistical difference between control and experimental reaches before and after wood addition; subsequently, after the introduction of wood in all streams shredders tended to increase in density.…”

“…Log jams are very important in accumulating organic matter, and Bilby & Likens (1980) report that debris dams contain nearly 75% of the standing stock of organic matter in fi rst-order streams, and this percentage reduces to 58% and 20% in second and third order streams, respectively. Flores et al (2011) report that after the incorporation of logs in stream, the CPOM in experimental reaches was 2.4-71.2 times higher than that in controls, suggesting a strong effect of wood addition on the storage of organic matter.…”