共查询到20条相似文献,搜索用时 15 毫秒
1.
Thomas J. Warrner Todd V. Royer Jennifer L. Tank Natalie A. Griffiths Emma J. Rosi-Marshall Matt R. Whiles 《Biogeochemistry》2009,95(2-3):295-307
Dissolved organic carbon (DOC) in streams draining hydrologically modified and intensively farmed watersheds has not been well examined, despite the importance of these watersheds to water quality issues and the potential of agricultural soils to sequester carbon. We investigated the dynamics of DOC for 14 months during 2006 and 2007 in 6 headwater streams in a heavily agricultural and tile-drained landscape in the midwestern US. We also monitored total dissolved nitrogen (TDN) in the streams and tile drains. The concentrations of DOC in the streams and tile drains ranged from approximately 1–6 mg L?1, while concentrations of TDN, the composition of which averaged >94% nitrate, ranged from <1 to >10 mg L?1. Tile drains transported both DOC and TDN to the streams, but tile inputs of dissolved N were diluted by stream water, whereas DOC concentrations were generally greater in the streams than in tile drains. Filamentous algae were dense during summer base flow periods, but did not appear to contribute to the bulk DOC pool in the streams, based on diel monitoring. Short-term laboratory assays indicated that DOC in the streams was of low bioavailability, although DOC from tile drains in summer had bioavailability of 27%. We suggest that these nutrient-rich agricultural streams are well-suited for examining how increased inputs of DOC, a potential result of carbon sequestration in agricultural soils, could influence ecosystem processes. 相似文献
2.
Daniel Markewitz E. Conrad Lamon III Mercedes C. Bustamante Joaquin Chaves Ricardo O. Figueiredo Mark S. Johnson Alex Krusche Christopher Neill Jos�� S. O. Silva 《Biogeochemistry》2011,105(1-3):19-35
Stream discharge?Cconcentration relationships are indicators of terrestrial ecosystem function. Throughout the Amazon and Cerrado regions of Brazil rapid changes in land use and land cover may be altering these hydrochemical relationships. The current analysis focuses on factors controlling the discharge?Ccalcium (Ca) concentration relationship since previous research in these regions has demonstrated both positive and negative slopes in linear log10discharge?Clog10Ca concentration regressions. The objective of the current study was to evaluate factors controlling stream discharge?CCa concentration relationships including year, season, stream order, vegetation cover, land use, and soil classification. It was hypothesized that land use and soil class are the most critical attributes controlling discharge?CCa concentration relationships. A multilevel, linear regression approach was utilized with data from 28 streams throughout Brazil. These streams come from three distinct regions and varied broadly in watershed size (<1 to >106 ha) and discharge (10?5.7?C103.2 m3 s?1). Linear regressions of log10Ca versus log10discharge in 13 streams have a preponderance of negative slopes with only two streams having significant positive slopes. An ANOVA decomposition suggests the effect of discharge on Ca concentration is large but variable. Vegetation cover, which incorporates aspects of land use, explains the largest proportion of the variance in the effect of discharge on Ca followed by season and year. In contrast, stream order, land use, and soil class explain most of the variation in stream Ca concentration. In the current data set, soil class, which is related to lithology, has an important effect on Ca concentration but land use, likely through its effect on runoff concentration and hydrology, has a greater effect on discharge?Cconcentration relationships. 相似文献
3.
We examined patterns of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) loading to a small urban stream
during baseflow and stormflow. We hypothesized that lower DOC and TDN contributions from impervious surfaces would dilute
natural hydrologic flowpath (i.e., riparian) contributions during storm events in an urban watershed, resulting in lower concentrations
of DOC and TDN during storms. We tested these hypotheses in a small urban watershed in Portland, Oregon, over a 3-month period
during the spring of 2003. We compared baseflow and stormflow chemistry using Mann–Whitney tests (significant at p<0.05). We also applied a mass balance to the stream to compare the relative significance of impervious surface contributions
versus riparian contributions of DOC and TDN. Results showed a significant increase in stream DOC concentrations during stormflows
(median baseflow DOC = 2.00 mg l−1 vs. median stormflow DOC = 3.46 mg l−1). TDN streamwater concentrations, however, significantly decreased with stormflow (median baseflow TDN = 0.75 mg l−1 vs. median stormflow TDN = 0.56 mg l−1). During storms, remnant riparian areas contributed 70–74% of DOC export and 38–35% of TDN export to the stream. The observed
pattern of increased DOC concentrations during stormflows in this urban watershed was similar to patterns found in previous
studies of forested watersheds. Results for TDN indicated that there were relatively high baseflow nitrogen concentrations
in the lower watershed that may have partially masked the remnant riparian signal during stormflows. Remnant riparian areas
were a major source of DOC and TDN to the stream during storms. These results suggest the importance of preserving near-stream
riparian areas in cities to maintain ambient carbon and nitrogen source contributions to urban streams. 相似文献
4.
Aurea Luiza Lemes da Silva William Padilha Lemes Jssica Andriotti Mauricio Mello Petrucio Maria Joo Feio 《Austral ecology》2020,45(5):644-658
Land‐use changes such as conversion of natural forest to rural and urban areas have been considered as main drivers of ecosystem functions decline, and a large variety of indicators has been used to investigate these effects. Here, we used a replicated litter‐bag experiment to investigate the effects of land‐use changes on the leaf‐litter breakdown process and leaf‐associated invertebrates along the forest–pasture–urban gradient located in a subtropical island (Florianópolis, SC, Brazil). We identified the invertebrates and measured the litter breakdown rates using the litter bags approach. Litter bags containing 3 g of dry leaf of Alchornea triplinervia were deployed on forest rural and urban streams. Principal component analysis, based on physico‐chemical variables which, confirmed a gradient of degradation from forest to urban streams with intermediate values in rural areas. In accordance, shredder richness and abundance were lower in rural and urban than in forest streams. The land‐use changes led also to the dominance of tolerant generalist taxa (Chironomidae and Oligochaeta) reducing the taxonomic and functional diversity in these sites. Leaf‐litter breakdown rates decreased from forest to rural and finally to urban areas and were associated with changes in pH, water velocity, dissolved oxygen and abundance of leaf‐shredding invertebrates, although global decomposition rates did not differ between rural and urban streams. Overall, this study showed that land‐use changes, namely to rural and urban areas, have a strong impact on tropical streams ecosystems, in both processes and communities composition and structure. Despite of being apparently a smaller transformation of landscape, rural land use is comparable to urbanisation in terms of impact in stream functioning. It is thus critical to carefully plan urban development and maintain forest areas in the island of Florianópolis in order to preserve its natural biodiversity and aquatic ecosystems functioning. 相似文献
5.
Dissolved organic carbon (DOC) and nitrogen (DON) concentrations were quantified in urban and rural watersheds located in central Texas, USA between 2007 and 2008. The proportion of urban land use ranged from 6 to 100% in our 12 study watersheds which included nine watersheds without waste water treatment plants (WWTP) and three watersheds sampled downstream of a WWTP. Annual mean DOC concentrations ranged 20.4–52.5 mg L?1. Annual mean DON concentrations ranged 0.6–1.9 mg L?1. Only the rural watersheds without a WWTP had significantly lower DOC concentrations compared to those watersheds with a WWTP but all the streams except two had significantly reduced DON compared to those with a WWTP. Analysis of the nine watersheds without a WWTP indicated that 68% of the variability in mean annual DOC concentration was explained by urban open areas such as golf courses, sports fields and neighborhood parks under turf grass. There was no relationship between annual mean DON concentration and any land use. Urban open area also explained a significant amount of the variance in stream sodium and stream sodium adsorption ratio (SAR). Ninety-four percent of the variance in annual mean DOC concentration was explained by SAR. Irrigation of urban turf grass with domestic tap water high in sodium (>181 mg Na+ L?1) may be inducing sodic soil conditions in watershed soils in this region resulting in elevated mean annual DOC concentrations in our streams. 相似文献
6.
Ecologists have long used stream water chemistry records to infer hillslope processes, although a great deal of biogeochemical processing of soil water is known to occur both downslope and in-stream. We report the effects of forest succession on C and N export in the west central Cascades of Oregon, a region of low anthropogenic N input. In a previous study, watersheds with forests of differing ages showed a number of significant differences in stream nutrient export. This study was intended to establish whether differences in stream chemistry were due to variation in N retention by forests of different ages, and thus we measured C and N in lysimeter water draining 12 forest plots, which were categorized into four different stages of successional development. Mean total dissolved nitrogen (TDN) concentrations in deep soil solutions were 2.5 times higher than stream water TDN observed in the previous study, suggesting that denitrification and/or N uptake occurred in the streams or the riparian zone. Although there was a trend for highest soil solution N concentrations in the second youngest (stem exclusion) stage, this trend was significant only for NH4-N. We previously found that streamwater NO3-N concentrations averaged 46% of TDN export and was significantly higher in the young than in the older watersheds, however, soil solution NO3-N concentration averaged 2% of TDN concentration and did not vary with succession. Although NH4-N concentrations were very low (~5 μg L?1) in stream water, NH4-N in lysimeter samples averaged 35% of TDN. While stream water dissolved organic nitrogen (DON) concentrations averaged 30% of TDN concentrations, soil solution DON concentrations averaged 64% of TDN concentration; neither varied with succession. Even with sharp differences in both forest floor and mineral soil C:N ratios and C contents among plots, no measure of N export from the forest stands was significantly related to forest floor or mineral soil characteristics. This is most likely because forest floor C:N ratios all greatly exceeded the reported low C:N ratios required to allow significant N leakage. Taken together, these results suggest that riparian dynamics, in-stream processing, or perhaps even the presence of near-stream alders significantly alter concentrations of all N species between the soil solution and stream water. 相似文献
7.
Tamara A. Newcomer Johnson Sujay S. Kaushal Paul M. Mayer Melissa M. Grese 《Biogeochemistry》2014,121(1):81-106
Restoring urban infrastructure and managing the nitrogen cycle represent emerging challenges for urban water quality. We investigated whether stormwater control measures (SCMs), a form of green infrastructure, integrated into restored and degraded urban stream networks can influence watershed nitrogen loads. We hypothesized that hydrologically connected floodplains and SCMs are “hot spots” for nitrogen removal through denitrification because they have ample organic carbon, low dissolved oxygen levels, and extended hydrologic residence times. We tested this hypothesis by comparing nitrogen retention metrics in two urban stream networks (one restored and one urban degraded) that each contain SCMs, and a forested reference watershed at the Baltimore Long-Term Ecological Research site. We used an urban watershed continuum approach which included sampling over both space and time with a combination of: (1) longitudinal reach-scale mass balances of nitrogen and carbon conducted over 2 years during baseflow and storms (n = 24 sampling dates × 15 stream reaches = 360) and (2) 15N push–pull tracer experiments to measure in situ denitrification in SCMs and floodplain features (n = 72). The SCMs consisted of inline wetlands installed below a storm drain outfall at one urban site (restored Spring Branch) and a wetland/wet pond configured in an oxbow design to receive water during high flow events at another highly urbanized site (Gwynns Run). The SCMs significantly decreased total dissolved nitrogen (TDN) concentrations at both sites and significantly increased dissolved organic carbon concentrations at one site. At Spring Branch, TDN retention estimated by mass balance (g/day) was ~150 times higher within the stream network than the SCMs. There were no significant differences between mean in situ denitrification rates between SCMs and hydrologically connected floodplains. Longitudinal N budgets along the stream network showed that hydrologically connected floodplains were important sites for watershed nitrogen retention due to groundwater–surface water interactions. Overall, our results indicate that hydrologic variability can influence nitrogen source/sink dynamics along engineered stream networks. Our analysis also suggests that some major predictors for watershed N retention were: (1) streamwater and groundwater flux through stream restoration or stormwater management controls, (2) hydrologic residence times, and (3) surface area of hydrologically connected features. 相似文献
8.
Stephanie A. Spera Gillian L. Galford Michael T. Coe Marcia N. Macedo John F. Mustard 《Global Change Biology》2016,22(10):3405-3413
Historically, conservation‐oriented research and policy in Brazil have focused on Amazon deforestation, but a majority of Brazil's deforestation and agricultural expansion has occurred in the neighboring Cerrado biome, a biodiversity hotspot comprised of dry forests, woodland savannas, and grasslands. Resilience of rainfed agriculture in both biomes likely depends on water recycling in undisturbed Cerrado vegetation; yet little is known about how changes in land‐use and land‐cover affect regional climate feedbacks in the Cerrado. We used remote sensing techniques to map land‐use change across the Cerrado from 2003 to 2013. During this period, cropland agriculture more than doubled in area from 1.2 to 2.5 million ha, with 74% of new croplands sourced from previously intact Cerrado vegetation. We find that these changes have decreased the amount of water recycled to the atmosphere via evapotranspiration (ET) each year. In 2013 alone, cropland areas recycled 14 km3 less (?3%) water than if the land cover had been native Cerrado vegetation. ET from single‐cropping systems (e.g., soybeans) is less than from natural vegetation in all years, except in the months of January and February, the height of the growing season. In double‐cropping systems (e.g., soybeans followed by corn), ET is similar to or greater than natural vegetation throughout a majority of the wet season (December–May). As intensification and extensification of agricultural production continue in the region, the impacts on the water cycle and opportunities for mitigation warrant consideration. For example, if an environmental goal is to minimize impacts on the water cycle, double cropping (intensification) might be emphasized over extensification to maintain a landscape that behaves more akin to the natural system. 相似文献
9.
Lenize Batista Calvão Leandro Juen José Max Barbosa de Oliveira Junior Joana Darc Batista Paulo De Marco Júnior 《Journal of Insect Conservation》2018,22(5-6):675-685
The presence of riparian vegetation provides microclimatic regulation of stream conditions [e.g. luminosity (lux), air temperature (°C) and relative humidity (%)], which varies naturally throughout the day. These variables explain the diurnal behaviour patterns of ectotherms such as Odonata in natural areas. However, human land uses (e.g. pastures) modify the abiotic conditions of riparian environments, favouring the presence of disturbance-tolerant species. In this context, we assess relationships between riparian land use (control streams-natural areas and pasture), abiotic conditions habitat integrity index (in control and pastures streams), (air temperature, luminosity and humidity in control streams), and Odonata diversity (between pasture and control streams and throughout the time of day) in Brazilian savannah (Cerrado) streams. First, the control streams had higher habitat integrity index than pasture. Higher abundance and difference in composition of Odonata species were observed in streams surrounded by pasture relative to natural areas. The conversion of natural areas to pasture near streams was also accompanied by an increase in overall body size of Odonata species. Odonata species richness and abundance in natural areas varied throughout the day, but peaked around 12:00 h, coinciding with changes in air temperature and luminosity. Our study highlights that changes in the physical characteristics of streams through conversion of natural habitats to pasture will change environmental conditions and act as a filter on the distribution and persistence of Odonata species in Cerrado streams. 相似文献
10.
Peter D. Steinberg Michael T. Brett J. Scott Bechtold Jeffrey E. Richey Lauren M. Porensky Suzanne N. Smith 《Biogeochemistry》2011,106(3):415-433
Hood Canal, Washington, USA, is a poorly ventilated fjord-like sub-basin of Puget Sound that commonly experiences hypoxia.
This study examined the influence of watershed soils, vegetation, physical features, and population density on nitrogen (N)
export to Hood Canal from 43 tributaries. We also linked our watershed study to the estuary using a salinity mass balance
model that calculated the relative magnitude of N loading to Hood Canal from watershed, direct precipitation, and marine sources.
The overall flow-weighted total dissolved N (TDN) and particulate N input concentrations to Hood Canal were 152 and 49 μg l−1, respectively. Nitrate and dissolved organic N comprised 64 and 29% of TDN, respectively. The optimal regression models for
TDN concentration and areal yield included a land cover term suggesting an effect of N-fixing red alder (Alnus rubra) and a human population density term (suggesting onsite septic system (OSS) discharges). There was pronounced seasonality
in stream water TDN concentrations, particularly for catchments with a high prevalence of red alder, with the lowest concentrations
occurring in the summer and the highest occurring in November–December. Due to strong seasonality in TDN concentrations and
in particular stream flow, over 60% of the TDN export from this watershed occurred during the 3 month period of November–January.
Entrainment of marine water into the surface layer of Hood Canal accounted for ≈98% of N loading to the euphotic zone of this
estuary, and in a worst case scenario OSS N inputs contribute ≈0.5% of total N loading. Domestic wastewater discharges and
red alders appear to be a very important N source for many streams, but a minor nutrient source for the estuary as a whole. 相似文献
11.
Diego Marcel Parreira de Castro Débora Reis de Carvalho Paulo dos Santos Pompeu Marcelo Zacharias Moreira Gabriela Bielefeld Nardoto Marcos Callisto 《PloS one》2016,11(3)
It is well recognized that assemblage structure of stream macroinvertebrates changes with alterations in catchment or local land use. Our objective was to understand how the trophic ecology of benthic macroinvertebrate assemblages responds to land use changes in tropical streams. We used the isotope methodology to assess how energy flow and trophic relations among macroinvertebrates were affected in environments affected by different land uses (natural cover, pasture, sugar cane plantation). Macroinvertebrates were sampled and categorized into functional feeding groups, and available trophic resources were sampled and evaluated for the isotopic composition of 13C and 15N along streams located in the Cerrado (neotropical savanna). Streams altered by pasture or sugar cane had wider and more overlapped trophic niches, which corresponded to more generalist feeding habits. In contrast, trophic groups in streams with native vegetation had narrower trophic niches with smaller overlaps, suggesting greater specialization. Pasture sites had greater ranges of resources exploited, indicating higher trophic diversity than sites with natural cover and sugar cane plantation. We conclude that agricultural land uses appears to alter the food base and shift macroinvertebrate assemblages towards more generalist feeding behaviors and greater overlap of the trophic niches. 相似文献
12.
Sarah H. Ledford Laura K. Lautz Philippe G. Vidon John C. Stella 《Biogeochemistry》2017,133(3):317-331
Nitrate (NO3 ?) dynamics in urban streams differ from many natural streams due to stormwater runoff, sewage inputs, decreased groundwater discharge, often limited hyporheic exchange, increased primary productivity, and limited carbon input. We investigated NO3 ? dynamics in a first-order urban stream in Syracuse, NY, which has urbanized headwaters and a geomorphologically natural downstream section. Twice-monthly water sampling, NO3 ? injection tests, NO3 ? isotopic analysis, filamentous algae mat density, and riparian shading were used to identify processes regulating NO3 ? dynamics in the stream over a 12-month period. The urban headwater reach had low NO3 ? (0.006–0.2 mg N/L) in the spring through fall, with a minimum uptake length of 900 m, no canopy cover, and high algae mat density. The downstream natural reach (100% canopy cover during the summer and low algae mat density) had nitrate concentrations between 0.6 and 1.2 mg N/L from winter to summer, which decreased during autumn leaf-off. In the urban reach, autotrophic uptake by filamentous green algae is a major NO3 ? sink in summer. In the natural reach, the addition of organic matter to the stream at leaf-off led to a decrease in NO3 ? concentration followed by an increase in NO3 ? concentration in winter as gross primary productivity decreased. This study shows that the balance between autotrophy and heterotrophy in urban streams is variable and depends on an interplay of drivers such as temperature, light, and carbon inputs that are mediated by the riparian ecosystem. 相似文献
13.
The Pampean region covers a large surface in central Argentina, but despite the extensive agricultural activities and the high nutrient levels recorded in streams of the region, few authors have analysed the influence of land use on water quality. Here, we evaluated the relationships among catchment attributes (size, morphometry and land cover) and water chemistry in 23 Pampean streams in different seasons (autumn, spring and summer) and at three spatial scales: whole catchment and two scales of riparian buffers (200 and 500 m adjacent to both stream margins). Chloride concentration was positively related to catchment area and negatively related to drainage density. Nitrate level was strongly associated to cropland, but soluble phosphorus concentration showed no relationships with any type of land cover. Land cover at the buffer scale seemed to be more influential than land cover at the whole catchment for nitrogen concentration. The main impact of cropland was the increase of nitrate concentration, while cattle breeding was negatively associated to photosynthetically active radiation (PAR) in autumn and summer and to dissolved oxygen concentration in spring. Our results highlighted the importance of local land use and riparian conservation on streamwater quality. 相似文献
14.
Shuiwang Duan Katie Delaney-Newcomb Sujay S. Kaushal Stuart E. G. Findlay Kenneth T. Belt 《Biogeochemistry》2014,121(1):61-80
Leaf litter plays a critical role in regulating ecological functions in headwater forest streams, whereas the effects of leaves on water quality in urbanized streams are not fully understood. This study examined the potential importance of leaf litter for the release and transformations of organic carbon and nutrients in urban streams, and compared the effects with other types of natural organic substrates (periphyton and stream sediment). Nutrients and organic carbon were leached from senescent leaves of 6 tree species in the laboratory with deionized water, and maximal releases, leaching rate constants, composition and bioavailability of the leached dissolved organic carbon (DOC) were determined. Stream substrates (leaf debris, rocks with periphyton, and sediment) were seasonally collected from urban and forest reference streams of the NSF Baltimore Long-term Ecological Research Site and incubated with overlying stream water to estimate areal fluxes of DOC and nitrogen. Leaf litter leaching showed large ranges in maximal releases of DOC (7.0–131 mg g?1), dissolved organic nitrogen (DON; 0.07–1.39 mg g?1) and total dissolved phosphorus (TDP; 0.14–0.70 mg g?1) among tree species. DOC leaching rate constants, carbon to nitrogen ratios, and DOC bioavailability were all correlated with organic matter quality indicated by fluorescence spectroscopy. Results from substrate incubation experiments showed far higher DOC and DON release and nitrate retention with leaf debris than with sediment, or rocks with periphyton. DOC release from leaf debris was positively correlated with stream nitrate retention at residential and urban sites, with the highest values observed during the fall and lowest during the summer. This study suggests the potential importance of leaf litter quantity and quality on fostering DOC and nutrient release and transformations in urban streams. It also suggests that species-specific impacts of leaves should be considered in riparian buffer and stream restoration strategies. 相似文献
15.
Fluxes of nitrogen and phosphorus in a gallery forest in the Cerrado of central Brazil 总被引:1,自引:0,他引:1
Lucilia Maria Parron Mercedes Maria Cunha Bustamante Daniel Markewitz 《Biogeochemistry》2011,105(1-3):89-104
The Gallery forests of the Cerrado biome play a critical role in controlling stream chemistry but little information about biogeochemical processes in these ecosystems is available. This work describes the fluxes of N and P in solutions along a topographic gradient in a gallery forest. Three distinct floristic communities were identified along the gradient: a wet community nearest the stream, an upland dry community adjacent to the woodland savanna and an intermediate community between the two. Transects were marked in the three communities for sampling. Fluxes of N from bulk precipitation to these forests resulted in deposition of 12.6 kg ha?1 y?1 of total N of which 8.8 kg ha?1 was as inorganic N. The throughfall flux of total N was generally <8.4 kg ha?1 year?1. Throughfall NO3?CN fluxes were higher (7?C32%) while NH4?CN and organic N fluxes were lower (54?C69% and 5?C46%) than those in bulk precipitation. The throughfall flux was slightly lower for the wet forest community compared to other communities. Litter leachate fluxes differed among floristic communities with higher NH4?CN in the wet community. The total N flux was greater in the wet forest than in the dry forest (13.5 vs. 9.4 kg ha?1 year?1, respectively). The stream water had total N flux of 0.3 kg ha?1 year?1. The flux of total P through bulk precipitation was 0.7 kg ha?1 year?1 while the mean fluxes of total P in throughfall (0.6 kg ha?1 year?1) and litter leachate (0.5 kg ha?1 year?1) declined but did not differ between communities. The low concentrations presented in soil solution and low fluxes in stream water (0.3 and 0.1 kg ha?1 year?1 for N and P, respectively) relative to other flowpaths emphasize the conservative nutrient cycling of these forests and the importance of internal recycling processes for the maintenance and conservation of riparian and stream ecosystems in the Cerrado. 相似文献
16.
Using Diatom Assemblages to Assess Urban Stream Conditions 总被引:4,自引:0,他引:4
We characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream
conditions. Diatoms, water chemistry, and physical variables of riffles at 19 urban and 28 rural stream sites were sampled
and assessed during the summer base flow period. Near stream land use was characterized using GIS. In addition, one urban
and one rural site were sampled monthly throughout a year to assess temporal variation of diatom assemblages between the urban
and rural stream sites. Canonical correspondence analysis (CCA) showed that the 1st ordination axis distinctly separated rural
and urban sites. This axis was correlated with conductivity (r = 0.75) and % near-stream commercial/industrial land use (r = 0.55). TWINSPAN classified all sites into four groups based on diatom assemblages. These diatom-based site groups were
significantly different in water chemistry (e.g., conductivity, dissolved nutrients), physical habitat (e.g., % stream substrate
as fines), and near-stream land use. CCA on the temporal diatom data set showed that diatom assemblages had high seasonal
variation along the 2nd axis in both urban and rural sites, however, rural and urban sites were well separated along the 1st
ordination axis. Our results suggest that changes in diatom assemblages respond to urban impacts on stream conditions. 相似文献
17.
Influences of catchment and corridor imperviousness on urban stream macroinvertebrate communities at multiple spatial scales 总被引:1,自引:0,他引:1
Resolving land cover hierarchy relationships in urban settings is important for defining the scale and type of management
required to enhance stream health. We investigated associations between macroinvertebrate assemblages in urban streams of
Hamilton, New Zealand, and environmental variables measured at multiple spatial scales comprising (i) local-scale physicochemical
conditions, (ii) impervious area in multiple stream corridor widths (30, 50 and 100 m) along segments (sections of stream
between tributary nodes) and for entire upstream networks, and (iii) total impervious area in stream segment sub-catchments
and upstream catchments. Imperviousness was higher for stream segment sub-catchments than for entire catchments because of
the agricultural headwaters of some urban streams. Imperviousness declined as corridor width declined at both segment and
catchment scales reflecting the vegetated cover along most urban stream gullies. Upstream catchment imperviousness was strongly
and inversely correlated with dissolved organic carbon concentration, whereas segment and upstream corridor scales were correlated
with water temperature and pH. Corridor imperviousness appeared to be a stronger predictor than catchment imperviousness of
Ephemeroptera, Plecoptera and Trichoptera taxa richness and the Quantitative Urban Community Index specifically developed
to assess impacts of urbanisation. In contrast, imperviousness at all measured scales added only marginal improvement in assemblage-based
models over that provided by the local-scale physicochemical variables of reach width, habitat quality, macrophyte cover,
pH and dissolved oxygen concentration. These findings infer variable scales of influence affecting macroinvertebrate communities
in urban streams and suggest that it may be important to consider local and corridor factors when determining mechanisms of
urbanisation impacts and potential management options. 相似文献
18.
Longitudinal patterns in carbon and nitrogen fluxes and stream metabolism along an urban watershed continuum 总被引:1,自引:0,他引:1
Sujay S. Kaushal Katie Delaney-Newcomb Stuart E. G. Findlay Tamara A. Newcomer Shuiwang Duan Michael J. Pennino Gwendolyn M. Sivirichi Ashley M. Sides-Raley Mark R. Walbridge Kenneth T. Belt 《Biogeochemistry》2014,121(1):23-44
An urban watershed continuum framework hypothesizes that there are coupled changes in (1) carbon and nitrogen cycling, (2) groundwater-surface water interactions, and (3) ecosystem metabolism along broader hydrologic flowpaths. It expands our understanding of urban streams beyond a reach scale. We evaluated this framework by analyzing longitudinal patterns in: C and N concentrations and mass balances, groundwater-surface interactions, and stream metabolism and carbon quality from headwaters to larger order streams. 52 monitoring sites were sampled seasonally and monthly along the Gwynns Falls watershed, which drains 170 km2 of the Baltimore Long-Term Ecological Research site. Regarding our first hypothesis of coupled C and N cycles, there were significant inverse linear relationships between nitrate and dissolved organic carbon (DOC) and nitrogen longitudinally (P < 0.05). Regarding our second hypothesis of coupled groundwater-surface water interactions, groundwater seepage and leaky piped infrastructure contributed significant inputs of water and N to stream reaches based on mass balance and chloride/fluoride tracer data. Regarding our third hypothesis of coupled ecosystem metabolism and carbon quality, stream metabolism increased downstream and showed potential to enhance DOC lability (e.g., ~4 times higher mean monthly primary production in urban streams than forest streams). DOC lability also increased with distance downstream and watershed urbanization based on protein and humic-like fractions, with major implications for ecosystem metabolism, biological oxygen demand, and CO2 production and alkalinity. Overall, our results showed significant in-stream retention and release (0–100 %) of watershed C and N loads over the scale of kilometers, seldom considered when evaluating monitoring, management, and restoration effectiveness. Given dynamic transport and retention across evolving spatial scales, there is a strong need to longitudinally and synoptically expand studies of hydrologic and biogeochemical processes beyond a stream reach scale along the urban watershed continuum. 相似文献
19.
Periphyton biomass and ecological stoichiometry in streams within an urban to rural land-use gradient 总被引:2,自引:0,他引:2
This study examined the effects land use on biomass and ecological stoichiometry of periphyton in 36 streams in southeastern
New York State (USA). We quantified in-stream and land-use variables along a N–S land-use gradient at varying distances from
New York City (NYC). Streams draining different landscapes had fundamentally different physical, chemical, and biological
properties. Human population density significantly decreased (r = −0.739; P < 0.00001), while % agricultural land significantly increased (r = 0.347; P = 0.0379) with northing. Turbidity, temperature, conductivity, and dissolved Mg, Ca, SRP, pH, DOC, and Si significantly increased
in more urban locations, but NO3
− and NH4
+ did vary not significantly along the gradient. Periphyton biomass (as AFDM and Chl-a) in rural streams averaged one-third to one-fifth that measured in urban locations. Periphyton biomass in urban streams averaged
18.8 ± 6.0 g/m2 AFDM and 75.6 ± 28.5 mg/m2 Chl-a. Urban Chl-a levels ranging between 100 and 200 mg/m2, are comparable to quantities measured in polluted agricultural streams in other regions, but in our study area was not correlated
with % agricultural land. Periphyton nutrient content also varied widely; algal C varied >20-fold (0.06–1.7 μmol/mm2) while N and P content varied >6-fold among sites. Algal C, N, and P correlated negatively with distance from NYC, suggesting
that periphyton in urban streams may provide greater nutrition for benthic consumers. C:N ratios averaged 7.6 among streams,
with 91% very close to 7.5, a value suggested as the optimum for algal growth. In contrast, periphyton C:P ratios ranged from
122 to >700 (mean = 248, twice Redfield). Algal-P concentrations were significantly greater in urban streams, but data suggest
algal growth was P-limited in most streams regardless of degree of urbanization. GIS models indicate that land-use effects
did not easily fit into strict categories, but varied continuously from rural to urban conditions. We propose that the gradient
approach is the most effective method to characterize the influence of land use and urbanization on periphyton and stream
function. 相似文献
20.
Nutrient exports from soils have important implications for long-term patterns of nutrient limitation on land and resource delivery to aquatic environments. While plant–soil systems are notably efficient at retaining limiting nutrients, spatial and temporal mismatches in resource supply and demand may create opportunities for hydrologic losses to occur. Spatial mismatches may be particularly important in peat-forming landscapes, where the development of a two-layer vertical structure can isolate plant communities on the surface from resource pools that accumulate at depth. Our objectives were to test this idea in northern Sweden, where nitrogen (N) limitation of terrestrial plants is widespread, and where peat-forming, mire ecosystems are dominant features of the landscape. We quantified vertical patterns of N chemistry in a minerogenic mire, estimated the seasonal and annual hydrologic export of organic and inorganic N from this system, and evaluated the broader influence of mire cover on N chemistry across a stream network. Relatively high concentrations of ammonium (up to 2 mg l?1) were observed in groundwater several meters below the peat surface, and N was routed to the outlet stream along deep, preferential flowpaths. Areal estimates of inorganic N export from the mire were several times greater than from an adjacent, forested catchment, with markedly higher loss rates during the growing season, when plant N demand is ostensibly greatest. At broader scales, mire cover was positively correlated with long-term concentrations of inorganic and organic N in streams across the drainage network. This study provides an example of how mire formation and peat accumulation can create broad-scale heterogeneity in nutrient supply and demand across boreal landscapes. This mismatch allows for hydrologic losses of reactive N that are independent of annual plant demand and potentially important to receiving lakes and streams. 相似文献