Effects of flow scarcity on leaf-litter processing under oceanic climate conditions in calcareous streams

Abstract

Although temporary streams represent a high proportion of the total number and length of running waters, historically the study of intermittent streams has received less attention than that of perennial ones. The goal of the present study was to assess the effects of flow cessation on litter decomposition in calcareous streams under oceanic climate conditions. For this, leaf litter of alder was incubated in four streams (S1, S2, S3 and S4) with different flow regimes (S3 and S4 with zero-flow periods) from northern Spain. To distinguish the relative importance and contribution of decomposers and detritivores, fine- and coarse-mesh litter bags were used. We determined processing rates, leaf-C, -N and -P concentrations, invertebrate colonization in coarse bags and benthic invertebrates. Decomposition rates in fine bags were similar among streams. In coarse bags, only one of the intermittent streams, S4, showed a lower rate than that in the other ones as a consequence of lower invertebrate colonization. The material incubated in fine bags presented higher leaf-N and -P concentrations than those in the coarse ones, except in S4, pointing out that the decomposition in this stream was driven mainly by microorganisms. Benthic macroinvertebrate and shredder density and biomass were lower in intermittent streams than those in perennial ones. However, the bags in S3 presented a greater amount of total macroinvertebrates and shredders comparing with the benthos. The most suitable explanation is that the fauna find a food substrate in bags less affected by calcite precipitation, which is common in the streambed at this site. Decomposition rate in coarse bags was positively related to associated shredder biomass. Thus, droughts in streams under oceanic climate conditions affect mainly the macroinvertebrate detritivore activity, although macroinvertebrates may show distinct behavior imposed by the physicochemical properties of water, mainly travertine precipitation, which can override the flow intermittence effects.

Relations of interannual differences in stream litter breakdown with discharge: bioassessment implications

“…, Martínez et al. ), and small, perennial streams experiencing experimental flow reduction (Northington and Webster ). These studies demonstrated that drastic flow decreases generally slowed litter breakdown due to reduced colonization of shredders; and in the absence of surface flow, dissolution and photodegradation became the dominant mechanisms of breakdown.…”

“…Hydraulic stress-discharge relationships are potentially nonlinear and spatially heterogeneous, and are operationally difficult to establish (Kakouei et al 2017), which could limit the success in generalizing the responses of litter breakdown rates to natural hydrologic variations in perennial streams (Turner and Stewardson 2014). In contrast, hydrologic variability has clearer impacts on litter breakdown rates in drought-prone streams experiencing precipitation-induced flow intermittency (Datry et al 2011, Dieter et al 2011, Mart ınez et al 2015, and small, perennial streams experiencing experimental flow reduction (Northington and Webster 2017). These studies demonstrated that drastic flow decreases generally slowed litter breakdown due to reduced colonization of shredders; and in the absence of surface flow, dissolution and photodegradation became the dominant mechanisms of breakdown.…”

Is diversity a buffer against environmental temperature fluctuations? – A decomposition experiment with aquatic fungi

“…These studies have typically been performed under constant conditions. However, actual streams experience natural fluctuations in current, temperature and/or availability of resources, which may profoundly affect the persistence and activity of individual species and their function in the ecosystem (Riedl et al, 2013;Mart ınez et al, 2015). In fact, the functional response of communities to abiotic factor fluctuations may be dependent on the proximity of the functional optimum of the consortium: species that periodically experience their ecological optima may fully play out their ecological function, whereas species exposed to suboptimal conditions may display more reduced performances (Ruel and Ayres, 1999).…”

Effect of Small Impoundments on Leaf Litter Decomposition in Streams

“…Decomposition of leaf litter in streams is influenced by physico‐chemical variables and biotic communities such as invertebrate shredders (Suberkropp and Chauvet, ; Belančič et al . ; Martínez et al ., ). However, the studied impoundments did not have a significant effect on most physico‐chemical variables, including temperature, nutrients and oxygen concentration, though phosphates and velocity were considerably increased and decreased, respectively, in the sites IU.…”