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  • 1
    Language: English
    In: Science of the Total Environment, 15 April 2016, Vol.550, pp.785-792
    Description: Many tropical biomes are threatened by rapid land-use change, but its catchment-wide biogeochemical effects are poorly understood. The few previous studies on DOM in tropical catchments suggest that deforestation and subsequent land use increase stream water dissolved organic carbon (DOC) concentrations, but consistent effects on DOM elemental stoichiometry have not yet been reported. Here, we studied stream water DOC concentrations, catchment DOC exports, and DOM elemental stoichiometry in 20 tropical catchments at the Cerrado–Atlantic rainforest transition, dominated by natural vegetation, pasture, intensive agriculture, and urban land cover. Streams draining pasture could be distinguished from those draining natural catchments by their lower DOC concentrations, with lower DOM C:N and C:P ratios. Catchments with intensive agriculture had higher DOC exports and lower DOM C:P ratios than natural catchments. Finally, with the highest DOC concentrations and exports, as well as the highest DOM C:P and N:P ratios, but the lowest C:N ratios among all land-use types, urbanized catchments had the strongest effects on catchment DOM. Thus, urbanization may have alleviated N limitation of heterotrophic DOM decomposition, but increased P limitation. Land use—especially urbanization—also affected the seasonality of catchment biogeochemistry. While natural catchments exhibited high DOC exports and concentrations, with high DOM C:P ratios in the rainy season only, urbanized catchments had high values in these variables throughout the year. Our results suggest that urbanization and pastoral land use exerted the strongest impacts on DOM biogeochemistry in the investigated tropical catchments and should thus be important targets for management and mitigation efforts.
    Keywords: DOM Export ; Land Use ; Pasture ; Agriculture ; Urbanization ; Organic Carbon ; Elemental Stoichiometry ; Neotropical Catchments ; Cerrado Savanna ; Atlantic Forest ; Rivers ; Streams ; Agriculture ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 2
    Language: English
    In: Journal of Applied Ecology, 1 August 2011, Vol.48(4), pp.916-925
    Description: 1. Shoreline development and the associated loss of littoral habitats represent a pervasive alteration of the ecological integrity of lakes and have been identified as major drivers for the loss of littoral biodiversity world-wide. Little is known about the effects of shoreline development on the structure of, and energy transfer in, littoral food webs, even though this information is urgently needed for management and mitigation measures. 2. We measured macroinvertebrate biomass and analysed potential food resources using stable isotopes (δ¹³C, δ¹⁵N) and mixing models to compare the complexity and the trophic base of littoral food webs between undeveloped and developed shorelines in three North German lowland lakes. 3. The lower diversity of littoral habitats found at developed shorelines was associated with lower diversity of food resources and consumers. Consequently, the number of trophic links in food webs at developed shorelines was up to one order of magnitude lower as compared with undeveloped shorelines. 4. Mixing model analysis showed that consumer biomass at undeveloped shorelines was mainly derived from the particulate organic matter (FPOM) and coarse particulate organic matter of terrestrial origin (CPOM). The contribution of CPOM to consumer biomass was twofold lower at developed shorelines, and consumer biomass was mainly derived from FPOM and suspended particulate organic matter. 5. Synthesis and application. Shoreline development impacts the flow of organic matter within littoral food webs primarily through the reduction in littoral habitat diversity. These effects are exacerbated by clearcutting of the riparian vegetation, which disrupts cross-boundary couplings between the riparian and the littoral zone. Lakeshore conservation should focus on preserving the structural integrity of the littoral zone, while restoration of coarse woody debris, reed and root habitats can be a cost-efficient measure to improve degraded lakeshores. The local effects of shoreline development demonstrated in this study might lead to whole-lake effects, but future studies are needed to derive thresholds at which shoreline development has consequences for the structure and functioning of the entire ecosystem.
    Keywords: Vegetation and Community ecology
    ISSN: 00218901
    E-ISSN: 13652664
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  • 3
    Language: English
    In: Environmental Pollution, March 2013, Vol.174, pp.204-213
    Description: We investigated the impacts of effluent discharge from small flow-through fish farms on stream water characteristics, the benthic invertebrate community, whole-system nitrate uptake, and ecosystem metabolism of three tropical headwater streams in southeastern Brazil. Effluents were moderately, i.e. up to 20-fold enriched in particulate organic matter (POM) and inorganic nutrients in comparison to stream water at reference sites. Due to high dilution with stream water, effluent discharge resulted in up to 2.0-fold increases in stream water POM and up to 1.8-fold increases in inorganic nutrients only. Moderate impacts on the benthic invertebrate community were detected at one stream only. There was no consistent pattern of effluent impact on whole-stream nitrate uptake. Ecosystem metabolism, however, was clearly affected by effluent discharge. Stream reaches impacted by effluents exhibited significantly increased community respiration and primary productivity, stressing the importance of ecologically sound best management practices for small fish farms in the tropics. ► Fish farm effluent discharge had moderate effects on stream water quality. ► Impacts on the benthic invertebrate community occurred at one stream. ► Whole-stream nitrate uptake showed no consistent impact pattern. ► Effluents caused considerable increases in stream ecosystem metabolism. ► Compliance with best management practices is important for small fish farms. Moderate water pollution by small fish farms caused considerable eutrophication responses in tropical headwater streams.
    Keywords: Aquaculture ; Eutrophication ; Nutrient Spiraling ; Gross Primary Production ; Hydrodynamics ; Otis-P ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 4
    Language: English
    In: Environmental pollution, 2013, Vol.174, pp.204-213
    Description: We investigated the impacts of effluent discharge from small flow-through fish farms on stream water characteristics, the benthic invertebrate community, whole-system nitrate uptake, and ecosystem metabolism of three tropical headwater streams in southeastern Brazil. Effluents were moderately, i.e. up to 20-fold enriched in particulate organic matter (POM) and inorganic nutrients in comparison to stream water at reference sites. Due to high dilution with stream water, effluent discharge resulted in up to 2.0-fold increases in stream water POM and up to 1.8-fold increases in inorganic nutrients only. Moderate impacts on the benthic invertebrate community were detected at one stream only. There was no consistent pattern of effluent impact on whole-stream nitrate uptake. Ecosystem metabolism, however, was clearly affected by effluent discharge. Stream reaches impacted by effluents exhibited significantly increased community respiration and primary productivity, stressing the importance of ecologically sound best management practices for small fish farms in the tropics. ; p. 204-213.
    Keywords: Nutrients ; Fish Farms ; Best Management Practices ; Metabolism ; Effluents ; Nitrates ; Streams ; Primary Productivity ; Ecosystems ; Organic Matter ; Invertebrates ; Tropics
    ISSN: 0269-7491
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 5
    Language: English
    In: Science of the Total Environment, 01 June 2018, Vol.625, pp.519-530
    Description: A large part of the organic carbon in streams is transported by pulses of terrestrial dissolved organic carbon (tDOC) during hydrological events, which is more pronounced in agricultural catchments due to their hydrological flashiness. The majority of the literature considers stationary benthic biofilms and hyporheic biofilms to dominate uptake and processing of tDOC. Here, we argue for expanding this viewpoint to planktonic bacteria, which are transported downstream together with tDOC pulses, and thus perceive them as a less variable resource relative to stationary benthic bacteria. We show that pulse DOC can contribute significantly to the annual DOC export of streams and that planktonic bacteria take up considerable labile tDOC from such pulses in a short time frame, with the DOC uptake being as high as that of benthic biofilm bacteria. Furthermore, we show that planktonic bacteria efficiently take up labile tDOC which strongly increases planktonic bacterial production and abundance. We found that the response of planktonic bacteria to tDOC pulses was stronger in smaller streams than in larger streams, which may be related to bacterial metacommunity dynamics. Furthermore, the response of planktonic bacterial abundance was influenced by soluble reactive phosphorus concentration, pointing to phosphorus limitation. Our data suggest that planktonic bacteria can efficiently utilize tDOC pulses and likely determine tDOC fate during downstream transport, influencing aquatic food webs and related biochemical cycles.
    Keywords: Terrestrial Doc ; Agricultural Catchment ; Flood Pulse ; Hydrology ; Bacteria ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 6
    In: Freshwater Biology, October 2018, Vol.63(10), pp.1240-1249
    Description: Trophic interactions are important pathways of energy and matter fluxes in food webs and are commonly quantified using stable isotopes of carbon (δ13C) and nitrogen (δ15N). An important prerequisite for this approach is knowledge on the isotopic difference between consumer and resource (trophic discrimination, Δ13C and Δ15N). The range and mechanism causing variation of trophic discrimination factors remain unclear. We conducted a controlled feeding experiment with 13 freshwater benthic invertebrate taxa fed with six resources to test if the C:N, C:P and N:P ratios of consumer, resources and consumer‐resource imbalances are significant predictors of Δ13C and Δ15N. We compiled the available literature on discrimination factors for aquatic invertebrates from controlled feeding experiments and field studies to compare the variation in trophic discrimination. Molar C:N and C:P ratios of resources as well as consumer‐resource imbalances of C:N were significantly related to Δ13C and explained more than 40% of variation of Δ13C, respectively. Resource %N was unrelated to Δ15N, but consumer N:P explained 20% of variation of Δ15N. Our data taken together with the literature compilation provide a mean Δ13C of 0.1‰ (SD = 2.2, N = 157) and a mean Δ15N of 2.6‰ (SD = 2.0, N = 155) for aquatic invertebrates to be used in mixing model analysis for estimating dietary proportions. Our study bridges the currently separated disciplines of stable isotope discrimination and ecological stoichiometry and shows that resource C:N:P and consumer‐resource imbalances are powerful predictors of invertebrate trophic discrimination. Including these stoichiometric predictors into stable isotope mixing models may improve the estimates of the contribution of organic matter sources to the diet of invertebrate consumers. The overall discrimination factors for aquatic invertebrates derived from this study may help to produce precise estimates in trophic ecology if taxon‐specific discrimination factors are unavailable.
    Keywords: Consumer‐Resource Elemental Imbalance ; Ecological Stoichiometry ; Lipids ; Macroinvertebrates ; Stable Isotopes
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 7
    In: Ecology, October 2004, Vol.85(10), pp.2818-2827
    Description: Ammonium retention was studied in 12 tropical headwater streams differing in channel morphology and hydraulic characteristics. Results from NaCl and NHCl injections combining a one‐dimensional transport model with the nutrient spiraling concept were evaluated. Transient solute storage was large in swamp reaches, with ratios of storage zone and main channel cross‐sectional area (/) of up to 18, and fractions of residence time due to transient storage () of up to 94%. Moreover, transient storage was at an intermediate level in step‐pool and meandering reaches and low in run reaches. Maximum ammonium uptake potentials () varied by a factor of 15 due to differing stream morphologies, and ammonium retention was high in swamp and step‐pool reaches, with values as high as 1.8 mg N·m·min. Between 52% and 85% of ecosystem retention occurred in storage zones. Additionally, differences in ammonium uptake efficiency in the storage zones of contrasting stream morphotypes were negligible; hence, ecosystem ammonium uptake potential was determined by storage zone size. Interestingly, surface transient storage, which is usually neglected in stream tracer studies, was both an important transient storage mechanism and a strong determinant of ammonium uptake potentials. Here, we demonstrated that channel morphology controlled transient storage and ammonium retention potentials in these tropical ecosystems.
    Keywords: Ammonium Retention ; Brazil ; Channel Morphology ; Hydraulic Characteristics ; Surface Transient Storage ; Tropical Streams ; Uptake Potential
    ISSN: 0012-9658
    E-ISSN: 1939-9170
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  • 8
    Language: English
    In: Ecological Engineering, August 2014, Vol.69, pp.134-138
    Description: Here, we compared sensor precision and drift among four commonly used dissolved oxygen (DO) sensor types under laboratory conditions, and evaluated their accuracy of measurement of stream ecosystem metabolism (EM) and subsequent assessment of stream ecosystem health in the field. Of all tested sensor types, optical sensors had the highest precision, followed by miniaturized polarographic sensors. Traditional polarographic and pulsed polarographic sensors had a lower precision. The traditional polarographic sensors were the only ones exhibiting detectable sensor drift that had to be corrected for, prior to calculations of EM. In parallel EM measurements in two rural and two pristine tropical streams, the four compared DO sensor types estimated relatively similar gross primary production (GPP), ecosystem respiration ( ) and GPP: ratios in each stream, and classified all streams as highly heterotrophic. Nonetheless, parallel GPP and estimates with different sensors had relative standard deviations of the mean between 6.2% and 34.9%, and between 7.9% and 16.3%, respectively. Thus, sensor accuracy can be a major source of variability in EM estimates. There were only minor differences in stream ecosystem health assessments among different DO sensors, compared to differences between different assessment methods. While all tested sensor types yielded useful ecosystem health classifications, the optical sensor type was the most accurate, and thus, the most suitable for functional impact assessment and monitoring.
    Keywords: Dissolved Oxygen Sensor ; Whole-Stream Metabolism ; Functional Bioindication ; Engineering ; Environmental Sciences
    ISSN: 0925-8574
    E-ISSN: 1872-6992
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  • 9
    In: Freshwater Biology, October 2009, Vol.54(10), pp.2069-2085
    Description: 1. The tropical Cerrado savannah, the second‐largest South American biome, is undergoing the most rapid land‐use change in South America, including a wholesale shift from native vegetation to pasture and cropland. However, the consequences of this development for aquatic ecosystem functioning remain unclear. In this study, we investigated how agriculture affects chemical, physical and biological characteristics of headwater streams in the Brazilian Cerrado, and how these changes relate to an important ecosystem function, i.e. ecosystem metabolism. 2. Three paired samplings of pristine and agricultural streams were conducted considering the most abundant morphotypes of Cerrado streams. Nutrient concentrations, stream morphometry and hydrodynamics, sediment transport, as well as benthic microbial biomass (BMB), and its chlorophyll (Chl‐) content were measured. In parallel, whole‐stream gross primary production (GPP) and community respiration (CR) were estimated using a diel open‐channel dissolved O change technique. 3. Agricultural streams had consistently higher nutrient concentrations, less variability in channel morphology, smaller channel cross‐sectional areas, smaller transient storage zones, higher current velocities and higher boundary shear stresses than pristine streams. At base flow, agricultural streams exhibited a midstream band of shifting sediments, while pristine streams had stable sediments. Both agricultural and pristine streams were dominated by thick microbial mats. Due to differences in hydrodynamics and sediment stability, these microbial mats covered the entire stream bed in pristine streams, but were restricted to the stream margins in agricultural streams. 4. As a result, BMB of agricultural streams was diminished by a factor of 7.5 compared to pristine streams. Interestingly, CR of agricultural streams was diminished only by a factor of 2.0, because higher BMB‐specific respiration efficiencies, potentially due to increased nutrient availability, compensated for lower BMB due to physical stress. Similarly, the 3.3‐fold elevated GPP in agricultural compared to pristine streams was only to a minor degree due to increased benthic Chl‐, but mainly a result of 2.4‐fold higher Chl‐‐specific primary production efficiencies, potentially due to increased nutrient availability. 5. In conclusion, agriculture impacted the studied Cerrado streams through two antagonistic mechanisms: physical stress resulted in decreased BMB and whole‐stream CR by preventing BMB accrual in the central streambed, but higher nutrient availability led to increased primary production and respiration efficiencies in marginal zones, as well as higher whole‐stream GPP. Finally, measures of whole‐stream metabolism were useful indicators of stream ecosystem health and allowed for the differential assessment of the effects of physical stress and eutrophication.
    Keywords: Pasture ; Primary Production ; Respiration ; Stream Ecosystem Functioning ; Stream Hydrodynamics
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 10
    Language: English
    In: Water, 01 August 2018, Vol.10(8), p.1080
    Description: Pollution abatement through phosphorus and nitrogen retention is a key ecosystem service provided by streams. Human activities have been changing in-stream nutrient concentrations, thereby altering lotic ecosystem functioning, especially in developing countries. We estimated nutrient uptake metrics (ambient uptake length, areal uptake rate, and uptake velocity) for nitrate (NO3-N), ammonium (NH4-N), and soluble reactive phosphorus (SRP) in four tropical Cerrado headwater streams during 2017, through whole-stream nutrient addition experiments. According to multiple regression models, ambient SRP concentration was an important explanatory variable of nutrient uptake. Further, best models included ambient NO3-N and water velocity (for NO3-N uptake metrics), dissolved oxygen (DO) and canopy cover (for NH4-N); and DO, discharge, water velocity, and temperature (for SRP). The best kinetic models describing nutrient uptake were efficiency-loss (R2 from 0.47-0.88) and first-order models (R2 from 0.60-0.85). NO3-N, NH4-N, and SRP uptake in these streams seemed coupled as a result of complex interactions of biotic P limitation, abiotic P cycling processes, and the preferential uptake of NH4-N among N-forms. Global change effects on these tropical streams, such as temperature increase and nutrient enrichment due to urban and agricultural expansion, may have adverse and partially unpredictable impacts on whole-stream nutrient processing.
    Keywords: Low-Order Streams ; Nutrient Retention ; Self-Purification Capacity ; Tracer Additions for Spiraling Curve Characterization ; Tropical Water Bodies ; Engineering
    E-ISSN: 2073-4441
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