44 research outputs found
Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter
Climate change and human pressures are changing the global distribution and the ex‐
tent of intermittent rivers and ephemeral streams (IRES), which comprise half of the
global river network area. IRES are characterized by periods of flow cessation, during
which channel substrates accumulate and undergo physico‐chemical changes (precon‐
ditioning), and periods of flow resumption, when these substrates are rewetted and
release pulses of dissolved nutrients and organic matter (OM). However, there are no
estimates of the amounts and quality of leached substances, nor is there information
on the underlying environmental constraints operating at the global scale. We experi‐
mentally simulated, under standard laboratory conditions, rewetting of leaves, river‐
bed sediments, and epilithic biofilms collected during the dry phase across 205 IRES
from five major climate zones. We determined the amounts and qualitative character‐
istics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds.
In addition, we evaluated the variance in leachate characteristics in relation to selected
environmental variables and substrate characteristics. We found that sediments, due
to their large quantities within riverbeds, contribute most to the overall flux of dis‐
solved substances during rewetting events (56%–98%), and that flux rates distinctly
differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contrib‐
uted most to the areal fluxes. The largest amounts of leached substances were found
in the continental climate zone, coinciding with the lowest potential bioavailability of
the leached OM. The opposite pattern was found in the arid zone. Environmental vari‐
ables expected to be modified under climate change (i.e. potential evapotranspiration,
aridity, dry period duration, land use) were correlated with the amount of leached sub‐
stances, with the strongest relationship found for sediments. These results show that
the role of IRES should be accounted for in global biogeochemical cycles, especially
because prevalence of IRES will increase due to increasing severity of drying event
Protozoa ciliates community structure in urban streams and their environmental use as indicators
Sediment respiration pulses in intermittent rivers and ephemeral streams
Intermittent rivers and ephemeral streams (IRES) may represent over half the global stream network, but their contribution to respiration and carbon dioxide (CO2) emissions is largely undetermined. In particular, little is known about the variability and drivers of respiration in IRES sediments upon rewetting, which could result in large pulses of CO2. We present a global study examining sediments from 200 dry IRES reaches spanning multiple biomes. Results from standardized assays show that mean respiration increased 32–66‐fold upon sediment rewetting. Structural equation modelling indicates that this response was driven by sediment texture and organic matter quantity and quality, which, in turn, were influenced by climate, land use and riparian plant cover. Our estimates suggest that respiration pulses resulting from rewetting of IRES sediments could contribute significantly to annual CO2 emissions from the global stream network, with a single respiration pulse potentially increasing emission by 0.2–0.7%. As the spatial and temporal extent of IRES increases globally, our results highlight the importance of recognizing the influence of wetting‐drying cycles on respiration and CO2 emissions in stream networks
A global analysis of terrestrial plant litter dynamics in non-perennial waterways
Perennial rivers and streams make a disproportionate contribution to global carbon (C) cycling. However, the contribution of intermittent rivers and ephemeral streams (IRES), which sometimes cease to flow and can dry completely, is largely ignored although they represent over half the global river network. Substantial amounts of terrestrial plant litter (TPL) accumulate in dry riverbeds and, upon rewetting, this material can undergo rapid microbial processing. We present the results of a global research collaboration that collected and analysed TPL from 212 dry riverbeds across major environmental gradients and climate zones. We assessed litter decomposability by quantifying the litter carbon-to-nitrogen ratio and oxygen (O2) consumption in standardized assays and estimated the potential short-term CO2 emissions during rewetting events. Aridity, cover of riparian vegetation, channel width and dry-phase duration explained most variability in the quantity and decomposability of plant litter in IRES. Our estimates indicate that a single pulse of CO2 emission upon litter rewetting contributes up to 10% of the daily CO2 emission from perennial rivers and stream, particularly in temperate climates. This indicates that the contributions of IRES should be included in global C-cycling assessments
Consequences of suppressing natural vegetation in drainage areas for freshwater ecosystem conservation: considerations on the new "Brazilian forest code"
Hydromorphological restoration stimulates river ecosystem metabolism
Both ecosystem structure and functioning determine ecosystem status and are
important for the provision of goods and services to society. However, there
is a paucity of research that couples functional measures with assessments of
ecosystem structure. In mid-sized and large rivers, effects of restoration on
key ecosystem processes, such as ecosystem metabolism, have rarely been
addressed and remain poorly understood. We compared three reaches of the
third-order, gravel-bed river Ruhr in Germany: two reaches restored with
moderate (R1) and substantial effort (R2) and one upstream degraded reach
(D). Hydromorphology, habitat composition, and hydrodynamics were assessed. We
estimated gross primary production (GPP) and ecosystem respiration (ER) using
the one-station open-channel diel dissolved oxygen change method over a
50-day period at the end of each reach. Moreover, we estimated metabolic
rates of the combined restored reaches (R1 + R2) using the two-station
open-channel method. Values for hydromorphological variables increased with
restoration intensity (D < R1 < R2). Restored reaches had lower
current velocity, higher longitudinal dispersion and larger transient storage
zones. However, fractions of median travel time due to transient storage were
highest in R1 and lowest in R2, with intermediate values in D. The share of
macrophyte cover of total wetted area was highest in R2 and lowest in R1,
with intermediate values in D. Station R2 had higher average GPP and ER than
R1 and D. The combined restored reaches R1 + R2 also exhibited higher GPP
and ER than the degraded upstream river (station D). Restoration increased
river autotrophy, as indicated by elevated GPP : ER, and net ecosystem production (NEP) of restored
reaches. Temporal patterns of ER closely mirrored those of GPP, pointing to
the importance of autochthonous production for ecosystem functioning. In
conclusion, high reach-scale restoration effort had considerable effects on
river hydrodynamics and ecosystem functioning, which were mainly related to
massive stands of macrophytes. High rates of metabolism and the occurrence of
dense macrophyte stands may increase the assimilation of dissolved nutrients
and the sedimentation of particulate nutrients, thereby positively affecting
water quality
An alternative fish feed based on earthworm and fruit meals.
(An alternative fish feed based on earthworm and fruit meals for tilapia and carp postlarvae). The search for alternative protein and lipid sources in the nutrition of aquatic organisms in captivity is extremely important for sustainability and ecosystem preservation. We investigated the potential of a new alternative fish feed based on fruits and earthworm and soybean meals for the nutrition of postlarvae of two high-value fish species cultivated worldwide, Nile tilapia (Oreochromis niloticus L.) and common carp (Cyprinus carpio L.). ostlarvae fed the alternative diet exhibited growth and weight gain similar to those fed a commercial fishmeal-based feed. Although concentrations of minerals and total protein were higher in the commercial than in the alternative feed, lipid concentration was higher in the latter. Tissue concentrations of minerals, protein and lipid, however, did not differ between postlarvae fed the commercial and the alternative feeds. This result suggests a high assimilation efficiency of the alternative feed compared to the commercial feed. The alternative feed tested in our study proved to be efficient in promoting growth and weight gain of carp and tilapia postlarvae. Due to its simple formulation, based on ingredients commonly found in tropical countries, the proposed alternative fish feed offers an economically viable and environmentally sound alternative for fish farmers in these countries.201
Biofilm-specific uptake does not explain differences in whole-stream DOC tracer uptake between a forest and an agricultural stream
Benthic biofilms are often assumed to control terrestrially-derived dissolved organic carbon (tDOC) uptake in streams. We tested this by comparing ¹³C-enriched ryegrass leachate uptake in an agricultural and a forest stream, hypothesizing that a greater abundance of autotrophic biofilms in the agricultural stream would cause its whole-stream tDOC uptake to be comparatively low. We measured whole-stream and biofilm tDOC tracer uptake, metabolism, bacterial and algal diversity, and nutrient status of benthic epilithic biofilms, and assessed whole-stream hydromorphology. Whole-stream uptake of tDOC was six times lower in the agricultural (3.0 mg m¯² day¯¹) than in the forest (19.0 mg m¯² day¯¹) stream, and tDOC uptake velocity indicated lower tDOC demand in the agricultural (1.2 mm min¯¹) than in the forest (1.9 mm min¯¹) stream. The agricultural stream differed from the forest stream by slightly lower transient storage capacity and higher benthic biofilm bacterial abundance and production, lower biofilm biomass and lower biofilm molar C:N, C:P, and N:P ratios. Changes in epilithic biofilms contributed little to the differences in whole-stream tDOC tracer uptake between streams, as biofilm tDOC uptake only amounted to 4% and 13% of whole-stream uptake in the forest and agricultural stream, respectively. This comparison of a forest and an agricultural stream suggests that agricultural stressors have the potential to diminish both whole-stream tDOC uptake and uptake efficiency. Furthermore, the weak link between biofilm and whole-stream tDOC uptake implies that benthic biofilms characteristics are poor predictors for human impacts on tDOC uptake in agricultural streams and that hot spots of tDOC uptake are likely situated in the hyporheic zone or in the stream water column