Hydrologic versus geomorphic limitation on CPOM storage in stream ecosystems

Abstract

1. Stream ecosystems are the products of interactions between hydrology, geomorphology and ecology, but examining all three components simultaneously is difficult and rarely attempted. Frequently, either geomorphology or hydrology is treated as invariable or static. 2. To examine the validity of treating either hydrology or geomorphology as static, we studied the individual and combined effects of hydrology and channel geomorphology on coarse particulate organic matter (CPOM) storage. Using data from an experimental leaf release in a hydrologically regulated stream we created a simple numerical model. This allowed us to quantify the relative influence of CPOM trapping and CPOM retention on total long-term CPOM storage under variable regimes of flood frequency and geomorphic structure. 3. CPOM storage is a function of supply, flood frequency and the type and frequency of in-stream structures. In-stream structures perform two distinct functions, trapping and retention, whose relative importance in leaf storage changes with stream hydrology. Trapping is more important for CPOM storage in streams with few floods, while retention is more important in streams with frequent floods. Different structures (e.g. boulders, large wood, small wood) perform these functions at different efficiencies. We found that large wood trapped two to three times more leaves than the bank, but that the bank retained leaves two to three times more efficiently. 4. A modelled channel with five times the amount of large wood as the study channel (a 'wood restoration') initially stored 14% more leaves than the modelled 'natural' channel. After six floods, however, the modelled wood restoration channel stored 50% less CPOM than the natural channel as the large wood had high trapping but poor retention. The modelled natural channel contained structures that could both trap and retain. Thus, as different structures performed different functions, the structural complexity buffered the stream allochthonous energy base against changes in hydrology through its balance of trapping and retention. 5. As the frequency of floods increased, the spatial distribution of CPOM became increasingly patchy as storage was driven entirely by structures with high retention. Thus, the coupling of flood frequency and geomorphic structure influenced CPOM availability, which in turn has ramifications for the entire stream food web.

Meiofauna constitute a considerable portion of invertebrate drift among moss-rich patches within a karst hydrosystem

“…This observation diverges from many previous findings on particle transport that showed a strong positive relationship among hydrological predictors (i.e., discharge, flow velocity, shear stress) and transported PM (Maciolek 1966;Naiman & Sedell 1979;Wilcox et al 2008). Besides water column/near-bed hydrological conditions, particle transport in streams is greatly affected by initial benthic material distribution, substratum and channel (geo)morphology, complexity of in-stream retention structures, and biological activity (Cushing et al 1993;Cordova et al 2008;Small et al 2008). It appears that the crucial control mechanism of the in-stream transport capacity is the stream's ability for material retention and resuspension.…”

Assemblages of stonefly larvae (Plecoptera) in the area of small hydrological structures, in the streams of the Kamienica Nawojowska river basin (The Beskid Sądecki)

“…and, to a lesser extent, the Leuctridae family, but also in this case the largest numbers were recorded in spring and autumn. The velocity and volume of water flow in the stream influence the deposition of organic matter, bottom substrate structure, and thus the nutrient base of many substrate invertebrates and the microhabitat (Thorp, Covich, 2001, Small et al, 2008. The presence of transverse hydrological structure in the longitudinal profile of the watercourse influences the benthos (Fleituch, 2003;Santucci et al, 2005;Tiemanna et al, 2005;Vallania, Corigliano, 2007;Brown et al, 2010;Bellucci et al, 2011).…”

Formation of groupings of mayfly larvae (Ephemeroptera) in the area of small hydrological structures, in the streams of the Kamienica Nawojowska river basin (the Sądeckie Beskids, Poland)

“…The speed of flow and bottom erosion influence the structure of the bottom substrate, deposition of organic matter and thus the microhabitats and food base of many benthic invertebrates (Small et al, 2008). The structure of the flow is therefore reflected in the structure of microhabitats and groupings inhabiting them (Thorp, Covich, 2001;Parasiewicz, 2003).…”