Urban catchment hydrology overwhelms reach scale effects of riparian vegetation on organic matter dynamics

1. Urbanisation severely affects stream hydrology, biotic integrity and water quality, but relatively little is known about effects on organic matter dynamics. Coarse particulate organic matter (CPOM) is a source of energy and nutrients in aquatic systems, and its availability has implications for ecosystem productivity and aquatic communities. In undisturbed environments, allochthonous inputs from riparian zones provide critical energy subsidies, but the extent to which this occurs in urbanised streams is poorly understood. 2. We investigated CPOM inputs, standing stocks, retention rates and retention mechanisms in urban and peri‐urban streams in Melbourne, Australia. Six streams were chosen along a gradient of catchment urbanisation, with the presence of reach scale riparian canopy cover as a second factor. CPOM retention was assessed at baseflow via replicate releases of marked Eucalyptus leaves where the retention distance and mechanism were recorded. CPOM and small wood (>1 cm diameter) storage were measured via cores and direct counts, respectively, while lateral and horizontal CPOM inputs were assessed using riparian litter traps. Stream discharge, velocity, depth and width were also measured. 3. CPOM inputs were not correlated with urbanisation, but were significantly higher in ‘closed’ canopy reaches. Urbanisation and riparian cover altered CPOM retention mechanisms, but not retention distances. Urban streams showed greater retention by rocks; while in less urban streams, retention by small wood was considerably higher. CPOM and small wood storage were significantly lower in more urban streams, but we found only a weak effect of riparian cover. 4. These findings suggest that while riparian vegetation increases CPOM inputs and has modest/weak effects on storage, catchment scale urbanisation decreases organic matter availability. Using an organic matter budget approach, it appears likely that the increased frequency and magnitude of high flows associated with catchment urbanisation exerts an overriding influence on organic matter availability. 5. We conclude that to maintain both organic matter inputs and storage, the restoration and protection of streams in urban or rapidly urbanising environments relies on the management of both riparian vegetation and catchment hydrology.     

Growth, production and bioenergetics of brown trout in upland streams with contrasting riparian vegetation

1. A series of laboratory-based equations on trout growth and bioenergetics developed by J.M. Elliott were applied to data collected for brown trout ( Salmo trutta L.) under field conditions in Co. Mayo, Western Ireland. Fish were collected by electrofishing eight upland streams with contrasting riparian vegetation; grassland, open canopy and closed canopy deciduous.
2. Stream temperatures, one of the main influencing factors on fish growth and energetics, did not differ significantly between riparian types.
3. Observed growth rates were lower than the predicted maximum growth rates and were not influenced by riparian vegetation type. Growth ranged between 0.66% day⁻¹ for 0 + trout to 0.08% day⁻¹ for 2 + trout.
4. Production estimates showed no clear difference between riparian vegetation types over the growing season.
5. Fish densities and biomass tended to be greater in closed canopy streams particularly in summer.
6. Actual ration sizes calculated for trout were similar to the ration required for maintenance metabolism and were only 45–63% of the maximum potential rations. Although there was an ontogenetic increase in ration size with increasing fish age, the proportion of ration available for growth (i.e. the difference between actual and maintenance rations) did not differ between age classes but was greatest in summer. 1+ and 2+ trout show greatest ration available for growth in grassland streams.
7. Trout growth did not differ between riparian vegetation types but did vary seasonally with greatest attainment in summer. Growth was limited in the present study possibly due to combined effects of reduced prey available to fish and low stream temperatures reducing metabolic requirements. In such food limited systems, terrestrial invertebrate energy subsidies could have significant benefits to brown trout growth, production and bioenergetics.     

Effect of drift sampler exposure time and net mesh size on invertebrate drift density in the Njoro River,Kenya

Although invertebrate drift is an important ecological process in lotic ecosystems, very little is known about it in Kenyan rivers. The primary aim of this study was to investigate the effect of driftnet mesh size and exposure duration on drift density in 2017. Drift samples were dominated by Chironomidae, Baetidae, Simuliidae, Caenidae and Culicidae. The 100 µm mesh driftnet had the highest mean invertebrate density, followed by the 250 µm and 500 µm nets. Invertebrate drift densities decreased with increased exposure time. This study demonstrates that sampler mesh size and exposure time should be taken into account when characterising invertebrate drift in streams. Future studies should consider sampling different biotopes and during different seasons.     

Development, maintenance and role of riparian vegetation in the river landscape

1. Riparian structure and function were considered from a longitudinal perspective in order to identify multiscale couplings with adjacent ecosystems and to identify research needs. 2. We characterized functional zones (with respect to vegetation development in association with various biogeochemical processes) within geomorphological settings using a delineation based upon erosional, transitional and depositional properties. 3. Vegetation dynamics within the riparian corridor are clearly influenced substantially by hydrological disturbance regimes. In turn, we suggest that vegetation productivity and diversity may widely influence riverine biogeochemical processes, especially as related to the consequences of changing redox conditions occurring from upstream to downstream. 4. However, surface and groundwater linkages are the predominant controls of landscape connectivity within riparian systems. 5. The importance of riparian zones as sources and sinks of matter and energy was examined in context of structural and functional attributes, such as sequestering or cycling of nutrients in sediments, retention of water in vegetation, and retention, diffusion or dispersal of biota. 6. The consequences of interactions between different communities (e.g. animals and plants, micro-organisms and plants) on biogeochemical processes are notably in need of research, especially with respect to control of landscape features. Multiscale approaches, coupling regional and local factors in all three spatial dimensions, are needed in order to understand more synthetically and to model biogeochemical and community processes within the river-riparian-upland landscape of catchments.     

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

• 1 The seasonal dynamics of the benthic macroinvertebrate assemblage, and the subset of this assemblage colonising naturally formed detritus accumulations, was investigated in two streams in south‐west Ireland, one draining a conifer plantation (Streamhill West) and the other with deciduous riparian vegetation (Glenfinish). The streams differed in the quantity, quality and diversity of allochthonous detritus and in hydrochemistry, the conifer stream being more acid at high discharge. We expected the macroinvertebrate assemblage colonising detritus to differ in the two streams, due to differences in the diversity and quantity of detrital inputs.
• 2 Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period.
• 3 Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos.
• 4 Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage.
• 5 Within‐stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between‐stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.

     

Development of a stable isotope index to assess decadal-scale vegetation change and application to woodlands of the Burdekin catchment, Australia

Forty-four study sites were established in remnant woodland in the Burdekin River catchment in tropical north-east Queensland, Australia, to assess recent (decadal) vegetation change. The aim of this study was further to evaluate whether wide-scale vegetation ‘thickening’ (proliferation of woody plants in formerly more open woodlands) had occurred during the last century, coinciding with significant changes in land management. Soil samples from several depth intervals were size separated into different soil organic carbon (SOC) fractions, which differed from one another by chemical composition and turnover times. Tropical (C₄) grasses dominate in the Burdekin catchment, and thus δ¹³C analyses of SOC fractions with different turnover times can be used to assess whether the relative proportion of trees (C₃) and grasses (C₄) had changed over time. However, a method was required to permit standardized assessment of the δ¹³C data for the individual sites within the 13 Mha catchment, which varied in soil and vegetation characteristics. Thus, an index was developed using data from three detailed study sites and global literature to standardize individual isotopic data from different soil depths and SOC fractions to reflect only the changed proportion of trees (C₃) to grasses (C₄) over decadal timescales. When applied to the 44 individual sites distributed throughout the Burdekin catchment, 64% of the sites were shown to have experienced decadal vegetation thickening, while 29% had remained stable and the remaining 7% had thinned. Thus, the development of this index enabled regional scale assessment and comparison of decadal vegetation patterns without having to rely on prior knowledge of vegetation changes or aerial photography.     

The distribution of Austrocrangonyx new species (Crustacea: Amphipoda) on the eastern New England plateau, Australia, with reference to riparian clearing

The amphipod Austrocrangonyx n.sp. livesin forested streams above 1165m on the easternNew England plateau in NSW. Classification andRegression Tree (CART) analysis and principalcomponent biplots showed low streamtemperatures and high levels of coarseparticulate organic matter (CPOM), among manyenvironmental factors measured, were the mainfactors associated with its distribution andabundance. Riparian clearing, which increaseswater temperature and greatly reduces CPOM, isassociated with local extinction ofAustrocrangonyx. Secondary reafforestation isnot accompanied by return of the amphipod.     

Ectomycorrhizas associated with a relict population of Dryas octopetala in the Burren, western Ireland. I. Distribution of ectomycorrhizas in relation to vegetation and soil characteristics

The distribution of ectomycorrhizas on Dryas octopetala L in grass heaths of the 450 km² karst region known as the Burren in Western Ireland was examined in relation to soil factors and vegetation type. Ectomycorrhizas were identified or characterised from 56 soil cores from 30 sites, and the occurrence of each ectomycorrhizal (EM) type was quantified by estimating the total length of mycorrhizal tips of each type. Soil organic matter, total nitrogen, extractable phosphorus, pH and depth were the soil factors determined. In total, 24 EM types were recorded. The EM community of Dryas roots was significantly more species-rich in one vegetation type—Hyperico-Dryadetum—than in others (Arctostaphylo-Dryadetum or Asperulo-Seslerietum). Multiple linear regression analyses indicated that soil organic matter and soil depth explained a significant portion of the variation in EM abundance, while soil organic matter and extractable phosphorus explained a significant portion of the variation in EM diversity. Canonical correspondence analysis showed that some individual EM types (e.g. Craterellus lutescens, Cenococcum geophilum, Tomentella sp., Boletus sp.) exhibited distinct soil preferences, most markedly in relation to soil organic matter, which, in this analysis, was the main significant soil variable distinguishing the three vegetation types.     

Fish community characteristics of the lower Gambia River floodplains: a study in the last major undisturbed West African river

1. The Gambia River is the last major West African river that has not been impounded. However, a hydroelectric dam is being constructed and substantial changes to the hydrology and ecology of the system are expected. 2. Little information is available on the impact of water impoundments in semi‐arid regions on downstream floodplain fish communities, due to the scarcity of pre‐intervention data. Because profound impacts on physical habitat, salinity and nutrient transport can occur downstream of such impoundments, a knowledge of the species‐habitat associations of biota such as fishes is necessary for understanding likely changes and how to limit them. 3. Fish were sampled using cast and hand nets along two transects on the floodplain, and with fyke nets in two ‘bolongs’ (creeks) from May to November 2005 and 2006 in the lower reaches of the Gambia River, close to the salt water front where ecological changes due to the construction of the dam are likely to be pronounced. 4. Greatest fish species richness was associated with low conductivity, low pH and deep water. Bolongs held greater species richness compared with other floodplain habitats, probably because they acted as conduits for fish moving on and off the floodplain. Species richness and catch biomass increased rapidly following the first rains and then declined. 5. Using a multivariate analysis, three main species groups were identified on the floodplain; one associated with deeper water, one with less brackish water and one with shallow, open water. Tilapia guineensis was the commonest species on the floodplains. 6. The floodplains provide nursery habitats as many fish captured were immature, particularly for species where adults are mainly encountered in the main channel. Several small‐sized floodplain specialists were also represented by a high proportion of mature individuals. 7. Impoundment is expected to reduce seasonal flooding of the floodplain in the lower Gambia River, downstream of the impoundment, resulting in reduced occurrence of aquatic habitats, especially bolongs, together with lower dissolved oxygen and increased salinity, leading to alteration of the floodplain fish communities, benefiting salt‐tolerant species, reducing overall species richness and probably reducing floodplain fish production.     

River continuum relationships in an 8th-order river reach: Analyses of polar ordination,functional groups,and organic matter parameters

Data on macroinvertebrate functional groups and benthic and suspended organic matter were examined using polar ordination techniques to test for distribution patterns in relation to stream size along an extended section of the Salmon River, Idaho (U.S.A.). Responses over a 200-km 8th-order section were studied in autumn 1978 and the succeeding summer. Overall trends and those of individual parameters comprising the three categories studied were used to examine aspects of the River Continuum Concept of Vannoteet al. (1980). Community composition of functional groups changed in an orderly fashion as a function of stream size (measured as link magnitude) along the 8th-order section in autumn but not in summer.Likewise, the composition of transported and combined (benthic plus transported) organic matter was a statistically significant function of stream size in autumn but not in summer. Only selected, individual functional groups and organic matter parameters demonstrated significant river continuum patterns; again, these were more prevalent in autumn than in summer. We conclude that continuum relationships within a segment of a given order are discerned better through analysis of compositional trends based on polar ordination than a focus on individual parameters.     

Monitoring vegetation change caused by trampling: a study in the Cairngorms,Scotland

Summary

A study was made in the Cairngorms, Scotland to make recommendations for a monitoring scheme capable of detecting changes in the vegetation caused by recreational pressure following the development of a funicular railway. Four methods were used in field trials to assess percentage cover of plant species and gravel, rock and bare ground, where appropriate, in two vegetation types (open and closed). The methods used were visual estimates in 50 × 40 cm quadrats (Q), the mean of visual estimates in twenty 10 × 10 cm sub-quadrats of the 50 × 40 cm quadrats (Q₂₀), a modified point intercept method (RL) and photography. Variances between observers and between-quadrats were estimated for the different methods. The sampling design for detecting change was based on a model of variance, constructed from field trial data.

Between-observer and between-quadrat variances were related to mean percentage cover and approximated to a binomial distribution. The between-quadrat variance was larger than observer variance. The Q₂₀ method achieved appreciably better precision than the other methods. Analysis of half of the 10 × 10 cmsub-quadrats (1/2Q₂₀) selected in a checker board design achieved a relative efficiency of 78% compared with the Q₂₀. This result suggests that comparable precision to the Q₂₀ method could be achieved by choosing about 14 sub-quadrats in a larger quadrat, thus saving some time. Variation between quadrats also suggested that the Q₂₀ method was the one of choice for maximising precision. The precision of the photographic method was based on fewer data points, so is less accurate than other estimates.

Minimum sample sizes were estimated for detecting a 10% relative change of a species in open vegetation with 30% cover (i.e. a change from 30% to <27 or to >33% cover). With a 10 % Type II error rate and 5 % Type I error rate the minimum sample sizes were 47 quadrats for Q, 18 for Q ₂₀, 43 for RL, and 23 for the means of ten 10 × 10 cm sub-quadrats in open vegetation.

The most time-efficient field recording appeared to be the use of Q despite the required sample size being 2.6 times higher than that of Q₂₀. The far lower time requirement per quadrat, however, compensated for the higher numbers. The number of quadrats would depend on the specified change in percentage cover and on the statistical significance level used. For example, to detect a 10% absolute change in cover (i.e. from 30% to either <20 % or >40 % cover) at 95 % probability the net effective recording time is estimated at 5 h per vegetation type while to detect a 5 % change at 99 % probability would require c. 25 h. Larger samples may be required for other species or for species with a low initial cover.     

Interactions of the bacterial assemblages of a prairie stream with dissolved organic carbon from riparian vegetation

The zonation of riparian vegetation on the Konza Prairie Research Natural Area of Kansas (tallgrass prairie ecosystem) provided a situation where the influences on uptake rates of the different DOC qualities could be measured in the field. Leachates from grasses disappeared rapidly from stream water in in situ chambers at upstream sites in grassland reaches and at downstream sites in forested reaches. The reverse observation, uptake of leachates from trees, revealed that DOC disappeared rapidly from chambers placed in the forested reaches but bacteria in the grassland reaches did not utilize tree leachate as rapidly. The pattern varies seasonally. The interpretation of these observations was aided by aseptic laboratory culture on the different substrate types and by measurements in poisoned chambers to evaluate abiotic uptake.     

Ecosystem respiration and organic carbon processing in a large,tidally influenced river: the Hudson River

We estimated whole-ecosystem rates of respiration over a 40-km stretch of the tidally influenced freshwater Hudson River every 2 to 3 weeks from May through November. We measured in situ concentrations of oxygen over depth at dusk and dawn at 10 stations spaced over this interval. The use of multiple stations allowed for the consideration of the influence of tidal advection of water masses. Respiration was estimated from the decrease in oxygen overnight with a correction for diffusive exchange of oxygen with the atmosphere. We estimated this flux of oxygen to or from the atmosphere using the measured oxygen gradient and a transfer velocity model which is a function of wind velocity.Integration of the data for the period of May through November yields an estimate of whole-ecosystem respiration of 591 g C m^–2 (S.E. = 66). That the standard error of this estimate is relatively low (11% of the estimate) indicates that the use of multiple stations adequately deals with error introduced through the advection of water between stations. The logarithm of average daily respiration rate was correlated with average daily temperature (p = 0.007;r² = 0.62). We used this temperature-respiration relationship to derive an estimate of the annual respiration rate of 755 g C m^–2 yr^–1 (S.E. = 72). This estimate is moderately sensitive to the estimated flux of oxygen between the atmosphere and water; using the lower and upper 95% confidence limits of our model relating the transfer velocity of oxygen to wind speed gives a range of annual respiration estimates from 665 g C m^–2 yr^–1 to 984 g C m^–2 yr^–1.The river is strongly heterotrophic, with most respiration driven by allochthonous inputs of organic matter from terrestrial ecosystems. The majority of the allochthonous inputs to the river (over 60%) are apparently metabolized within the river. Any change in allochthonous inputs due to changes in land use or climate patterns would be expected to alter the oxygen dynamics and energy flow within this tidally influenced river.     

Impact of Anthropogenic Organic Matter on the Distribution Patterns of Sediment Microbial Community from the Yangtze River,China

Abstract

How microbes respond to substantial and increasing anthropogenic disturbance remains an open question in river systems. We tested the hypothesis that the source and distribution of anthropogenic organic matter (OM) were significant factors affecting the spatial variation of the microbial community composition of the Yangtze River sediments. Bulk geochemical proxies and lignin phenols suggested a general decrease of terrestrial C3 plants or soil OM input from the middle to the lower reaches. Fecal sterols inferred higher sewage contamination levels in the middle reaches. Polycyclic aromatic hydrocarbons (PAHs) distribution indicated a dominant biomass and coal combustion signal in the middle reaches, whereas a mixed source including petroleum combustion in the lower reaches. Phylogenetic analysis revealed a large portion of Methanobacteria and Verrucomicrobia enriched in the middle reaches, whereas OM-degrading bacteria, including Flavobacteria, Acidobacteria, and Alphaproteobacteria were dominant in the lower reaches. Quantitative PCR analyses and multivariate analysis further demonstrated that sources and distribution of OM had combined effects in shaping alpha and beta-diversity of sediment microbial communities. Sewage discharge and incomplete OM combustion, respectively, were associated with Methylococcaceae, Chloroflexi, and Bacteroidetes groups. This study provides a foundation for further understanding of the river sediment microbial composition, considering the continued increase of anthropogenic influences.     

A study on the relationship between vegetation pattern and environment in the upstream of Minjiang River, China

The vegetation pattern in the upstream of Minjiang River, and its relationship with environment factors, such as landscape position (elevation, slope, aspect), precipitation and temperature and soil are analyzed in this paper. The data used in this paper were based on the landscape map derived from 1994 TM imagery. The results were as follows: 1) dominant landscape types were forest, shrub land and grassland, which were very similar in terms of area ratio (32.87%, 31.85% and 28.44%, respectively); 2) the patch shape of conifer forest and mixed forest was complicated while that of broad-leaved forest and cultivated land was simple; 3) the fragmentation of conifer forest and mixed forest was serious in contrast with low fragmentation of broad-leaved forest and cultivated land; and 4) closed scrub and grassland had a high contagion and good connectivity while mixed forest had a lower contagion and bad connectivity. In addition, the vegetation distribution pattern of upstream of Minjiang River was closely related with elevation and temperature, but the relationship between vegetation and precipitation was not statistically significant. __________ Translated from Journal of Beijing Normal University (Natural Science), 2005,41(4) [译自: 北京师范大学学报(自然科学版), 2005,41(4)]     

Deposition of sediments during a flood event on seasonally flooded forests of the lower Orinoco River and two of its black-water tributaries, Venezuela

Deposition of suspended sediments andtheir associated nutrients were estimated during theflood event of 1995 in the seasonally flooded forestsof the Mapire and Caura Rivers, two black-watertributaries of lower Orinoco, and on two islands ofthis white-water river. The deposition spanned a widerange from 0.07 kg m^–2 in the depositional barforests of the Mapire River to 73.60 kg m^–2 onthe flooded forests of the Orinoco Island site calledJarizo. This variation is associated with the dynamicnature of sediment mobilization, transport anddeposition, as well as with the different geomorphicenvironments and erosion processes upstream from thestudy sites. The deposited sediment in all the studyareas was highly quartzitic with a relatively highcontent of kaolinite and goethite. Only in thesediment of the Orinoco Islands was mica (illite)identified in a relatively high proportion. Thesemineralogical results reflect the intense weatheringprocesses in the catchment areas of the study rivers.The chemical composition of the deposited sedimentsshowed a great variability among the different studyareas, which is in part related to the mineralcomposition of the sediments and their particle sizedistribution. The highest concentrations of K, Caand Mg were found on the clay sediments of the Orinocoagricultural island. The total amount of depositednutrients varied over a wide range, which isinfluenced by the amount of deposited sediments. Inthe Jarizo Island site of lower Orinoco were depositedthe largest amount of nutrients. In the floodedforests of the Mapire River, the nutrient contributionby the deposited sediments to the nutrient cycling isrelatively low in the depositional-bar forests andpractically nonexistent in the forests sites onterraces.