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  • 1
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 36 (2000), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : We measured the base-flow stream chemistry in all the major physiographic provinces of the Chesapeake Bay drainage basin. The spatial variation of stream chemistry was closely related to differences in geology and land cover among the sampled watersheds. Some stream chemistry variables were strongly affected by geological settings in the watersheds while others were more influenced by land cover. The effects of land cover differed among chemical constituents and regions. Concentrations of Ca2+, Mg2+, pH, total alkalinity, and conductivity were mainly functions of carbonate bedrock, especially in the Great Valley. Nitrate-N and total dissolved N were closely related to cropland and increased as the percentage of cropland increased. The rate of increase varied from region to region with the highest in the Piedmont. Na+ and Cl− were mainly affected by the percentage of developed area in a watershed, especially in the Coastal Plain and Piedmont. We observed no significant effects of region or land cover on species of phosphorus because samples were collected under base flow conditions and only dissolved forms were measured. Dissolved silicate (DSi) was not related to any other water chemistry variables. DSi increased as developed area decreased and cropland increased in the Coastal Plain, but these patterns were reversed in the Piedmont. There was no consistent pattern in the spatial variation of land cover effects on the reduced forms of N, dissolved organic P, dissolved organic matter, and K+.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 35 (1999), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The purpose of this study was to determine the relationships between precipitation at the seasonal and annual scale and water discharge per surface area for seven contiguous first - and second-order tributaries of the Rhode River, a small tidal tributary to Chesapeake Bay, Maryland, USA. The goal was to quantify the effects of a wide range of precipitation, representative of inter-annual variations in weather in this region. The discharges measured included both overland storm flows and groundwater, since the aquifers were perched on a clay aquiclude. Precipitation varied from 824 to 1684 mm/yr and area-weighted Rhode River watershed discharge varied from 130 to 669 mm/yr with an average of 332 mm/yr or 29.1 percent of average precipitation. Average annual dis. charges from three first-order watersheds were significantly lower per surface area and varied from 16.0 to 21.9 percent of precipitation. Winter season precipitation varied from 125 to 541 mm. Area-weighted Rhode River winter discharge varied from 26.3 to 230 mm with an average of 115 mm or 43.9 percent of average precipitation. Spring season precipitation varied from 124 to 510 mm and watershed discharge varied from 40.0 to 321 mm with an average of 138 mm or 46.9 percent of average precipitation. In the summer and fall seasons, watershed discharge averaged 40.6 and 40.9 mm or 13.5 and 14.3 percent of average precipitation, respectively. Except in winter, the proportion of precipitation discharged in the streams increased rapidly with increasing volume of precipitation. Stream order showed a higher correlation with volume of discharge than vegetative cover on the watershed.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 33 (1997), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : We measured annual discharges of water, sediments, and nutrients from 10 watersheds with differing proportions of agricultural lands in the Piedmont physiographic province of the Chesapeake Bay drainage. Flow-weighted mean concentrations of total N, nitrate, and dissolved silicate in watershed discharges were correlated with the proportion of cropland in the watershed. In contrast, concentrations of P species did not correlate with cropland. Organic P and C correlated with the concentration of suspended particles, which differed among watersheds. Thus, the ratio of N:P:Si in discharges differed greatly among watersheds, potentially affecting N, P or Si limitation of phytoplankton growth in the receiving waters. Simple regression models of N discharge versus the percentage of cropland suggest that croplands discharge 29–42 kg N ha-1 yr-1 and other lands discharge 1.2–5.8 kg N ha-1 yr-1. We estimated net anthropogenic input of N to croplands and other lands using county level data on agriculture and N deposition from the atmosphere. For most of the study watersheds, N discharge amounted to less than half of the net anthropogenic N.
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  • 5
    ISSN: 1432-1009
    Keywords: KEY WORDS: Riparian forest buffers; Chesapeake Bay; Nonpoint source pollution; Nitrogen; Phosphorus; Sediment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Water, air & soil pollution 83 (1995), S. 263-284 
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract We studied precipitation chemistry at the Rhode River on the western shore of the Chesapeake Bay. We sampled on an event basis, beginning in 1973 for some constituents in bulk precipitation. Beginning in 1981, we also sampled wet precipitation separately from bulk precipitation. In this report, we examine temporal variability of precipitation chemistry at different time scales. Several constituents showed long-term trends. In bulk precipitation, hydronium concentration increased by 27% of its mean concentration per decade, calcium by 67%, ammonium by 28%, and nitrate by 25%, while organic nitrogen decreased by 41%, organic phosphorus by 31%, and organic carbon by 16%. In wet precipitation, ammonium increased by 33% and calcium by 100%, while magnesium decreased by 78% per decade. Concentrations differed greatly among precipitation events, increasing as the volume of precipitation decreased and as the interval since the previous event increased. Most constituents also showed marked seasonal variation. We used a regression model to predict concentrations for each event from month, precipitation volume, and the time since the previous event. We evaluated how much of the interannual variability could be explained by these factors. The event-scale model accounted for almost half of the variability among annual means for ammonium, sodium, and magnesium in bulk precipitation, and for potassium in wet precipitation. This suggests that much of the interannual variability of concentrations may result from interannual variation in the temporal distribution of precipitation.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Planta 79 (1968), S. 284-291 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Phytochrome per fresh weight in the apical 0.5 cm of the 1.5-cm coleoptile was twice that in the basal 0.5 cm; phytochrome per dry weight and phytochrome per DNA did not vary significantly from the base to the apex. Ratios of phytochrome to fresh or dry weight in the 6-cm coleoptile were nearly constant in the basal 5 cm, but increased in the two apical 0.5-cm sections. Phytochrome per DNA in the 6-cm coleoptile did not vary significantly in the apical 4 cm, but decreased by one-half in the basal 2 cm. In the 5-cm first leaf, phytochrome per fresh or dry weight was greatest in the basal 0.5 cm (zone of cell division). Phytochrome per DNA in the leaf decreased from apex to base; the phytochrome per DNA in the basal 0.5 cm (zone of cell division) was one-third as high as in the apical 0.5 cm. Pytochrome per cell was greater in all parts of the 6-cm coleoptile compared to the 1.5-cm coleoptile, although no cell division had occurred during this elongation. Phytochrome per cell was higher in the sections of the first leaf wihch were growing primarily by cell expansion rather than by cell division. Phytochrome expressed per unit dry weight was more constant than any of the other parameters studied. It was concluded (1) that the phytochrome content of all coleoptile cells is the same at any given age (length); (2) that the phytochrome content of all nondividing leaf cells is equal at any given age (but lower than that of coleoptile cells); (3) that the phytochrome content of all cells increases in direct proportion to their expansion (increase in dry weight).
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Planta 79 (1968), S. 275-283 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary During a seven-fold increase in length the content of the coleoptile in photoreversible phytochrome increased four-fold and that of the primary leaf nine-fold. The phytochrome content, during growth, expressed on a fresh- or dry-weight basis did not vary greatly for either organ. Phytochrome per mg dry weight (ΔOD730/mg=0.5) was nearly the same in the leaf as in the coleoptile. Coleoptiles studied had a constant DNA content of 4.1 μg per organ. DNA content of the leaf increased with age. Phytochrome per DNA was much higher in the coleoptile than in the primary leaf and increased with growth in each of these organs. Thus, there was not a constant amount of phytochrome per cell in either tissue with increasing age and there was not the same amount of phytochrome per cell in the coleoptile as in the primary leaf at any age.
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  • 9
    ISSN: 1573-515X
    Keywords: GIS ; GWLF ; nonpoint source pollution ; nutrient ; watershed modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We modeled nutrient export in the ChoptankRiver Basin on the coastal plain of the Chesapeakedrainage, using a modified version of alumped-parameter, hydrochemical model (GWLF).Calibration was performed using long-term (WY1980–WY1990)hydrochemistry data from a gauged site. Thecalibrated model reproduced water yields, TN, and TPexport with cumulative errors of 〈1% over the11-year calibration period and with annual RMS errorsof 10–50%. Model validation was done withindependent measurements at the same gauged site(WY1991 to WY1996) and at another nearby independentlygauged site (WY1991 to WY1995). Local adjustment ofthe groundwater recession coefficient and thedissolved N concentration in agricultural stormflowwas essential for successful application at the secondsite. GWLF appears to be a useful model for estimationof fluxes of water, N and P from ungauged areas withaccuracies of 10–50% at annual time scales.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 49 (2000), S. 217-239 
    ISSN: 1573-515X
    Keywords: ammonium ; beavers ; landscape ; nitrate ; phosphate ; silicate ; total organic-C ; total organic-N ; total organic-P ; total suspended solids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The fluxes and concentrations ofmaterials from two contiguous second-order watershedsin the Coastal Plain of Maryland, U.S.A. were measuredfor six years prior to and six years subsequent to theformation of a 1.25 ha beaver pond near the bottom ofone of the watersheds. The watersheds have a clayaquiclude and were equipped with V-notch weirs andcontinuous volume-integrating water samplers. Thebeaver pond reduced annual discharge of water,total-N, total-P, dissolved silicate, TOC, and TSS by8, 18, 21, 32, 28, and 27%, respectively. Most ofthe total-N reduction was due to increased retentionof nitrate in the winter and spring and TON in thewinter and summer. Most of the total-P reduction wasthe result of retention of both TPi and TOP in thewinter and summer. Dissolved silicate retentionpeaked in the spring, while TOC and TSS retentionpeaked in the winter. Prior to the formation of thebeaver pond, concentrations of TON, TPi, TOP, TOC, andTSS had highly significant correlations with streamdischarge, especially in the winter, but subsequent tothe pond there was little or no relationship betweenthese concentrations and stream discharge. However,concentrations of nitrate in the spring and ammoniumin the summer were highly correlated with streamdischarge both before and after the formation of thebeaver pond and regressions of discharge versusconcentrations of these nutrients explained more ofthe variation in concentrations after the formation ofthe pond.
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