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1.
Sources of nutrient inputs to the Patuxent River estuary 总被引：1，自引：0，他引：1
We quantified annual nutrient inputs to the Patuxent River estuary from point and nonpoint sources and from direct atmospheric deposition. We also compared nonpoint source (NPS) discharges from Piedmont and Coastal Plain regions and from agricultural and developed lands. Using continuous automated-sampling, we measured discharges of water, nitrogen, phosphorus, organic carbon (C), and suspended solids from a total of 23 watersheds selected to represent various proportions of developed land and cropland in the Patuxent River basin and the neighboring Rhode River basin. The sampling period spanned two years that differed in annual precipitation by a factor of 1.7. Water discharge from the watershed to the Patuxent River estuary was 3.4 times higher in the wet year than in the dry year. Annual water discharges from the study watersheds increased as the proportion of developed land increased. As the proportion of cropland increased, there were increases in the annual flow-weighted mean concentrations of nitrate (NO3 ?), total nitrogen (TN), dissolved silicate (Si), total phosphate (TPO4 3?), total organic phosphorus (TOP), total P (TP), and total suspended solids (TSS) in NPS discharges. The effect of cropland on the concentrations of NO3 ? and TN was stronger for Piedmont watersheds than for Coastal Plain watersheds. As the proportion of developed land increased, there were increases in annual mean concentrations of NO3 ?, total ammonium (TNH4 +), total organic N (TON), TN, total organic C (TOC), TPO4 3?, TOP, TP, and TSS and decreases in concentrations of Si. Annual mean concentrations of TON, TOC, forms of P, and TSS were highest in the wet year. Annual mean concentrations of NO3 ?, TNH4 +, TN, and Si did not differ significantly between years. We directly measured NPS discharges from about half of the Patuxent River basin and estimated discharges from the other half of the basin using statistical models that related annual water flow and material concentrations to land cover and physiographic province. We compared NPS discharges to public data on point source (PS) discharges. We estimated direct atmospheric deposition of forms of N, P, and organic C to the Patuxent River estuary based on analysis of bulk deposition near the Rhode River. During the wet year, most of the total terrestrial and atmospheric inputs of forms of N and P came from NPS discharges. During the dry year, 53% of the TNH4 + input was from atmospheric deposition and 58% of the NO3 ? input was from PS discharges; NPS and PS discharges were about equally important in the total inputs of TN and TPO4 3?. During the entire 2-yr period, the Coastal Plain portion of the Patuxent basin delivered about 80% of the NPS water discharges to the estuary and delivered similar proportions of the NPS TNH4 +, TN, TOP, and TSS. The Coastal Plain delivered greater proportions of the NPS TON, TOC, Si, and TP (89%, 90%, 93%, and 95%, respectively) than of water, and supplied nearly all of the NPS TPO4 3? (99%). The Piedmont delivered 33% of the NPS NO3 ? while delivering only 20% of the NPS water to the stuary. We used statistical models to infer the percentages of NPS discharges supplied by croplands, developed lands, and other lands. Although cropland covers only 10% of the Patuxent River basin, it was the most important source of most materials in NPS discharge, supplying about 84% of the total NPS discharge of NO3 ?; about three quarters of the TPO4 3?, TOP, TP, and TSS; and about half of the TNH4 + and TN. Compared to developed land, cropland supplied a significantly higher percentage of the NPS discharges of NO3 ?, TN, TPO4 3?, TOP, TP, and TSS, despite the fact development land covered 12% of the basin. 相似文献
2.
Stream and watershed management and restoration can be greatly facilitated through use of physiographic landform classification to organize and communicate natural resource, hazard, and environmental information at a broad scale (1:250,000) as illustrated by the Piedmont and Coastal Plain Provinces in Maryland, or at a small scale (1:24,000) as illustrated using divisions and zones combined with a conceptual model. The conceptual model brings together geology, surficial processes, landforms and land use change information at the small watershed scale and facilitates transfer of information from one small watershed to another with similar geology and landforms. Stream flow, sediment erosion, and water quality illustrate the use of the model. 相似文献
3.
Agricultural nonpoint source (NPS) pollution at the Three Gorges reservoir area in China has been increasingly recognized as a threat to aquatic environment in recent years due to the serious eutrophication problem. Adsorbed NPS pollution is one of the major forms of NPS pollution in mountainous regions, the essential of the adsorbed NPS pollution is soil loss. Thus, simple, highly sensitive and continuous methods are required to simulate and quantify sediments yield at watershed scales. It is imperative to construct an integrated model to estimate the sediment yield and adsorbed NPS pollution load. According to the characteristics of climate, hydrology, topography, geology, geomorphology and land use types in Three Gorges reservoir area, a GIS-based dynamic-integrated-distributed model of annual adsorbed NPS load was presented in view of impacts of the rainfall intensity, sediment delivery ratio (SDR) and land management, where the temporally dynamic-continuous model of annual sediment yield was established by modifying the revised Universal Soil Loss Equation (RUSLE), and the spatially integrated-distributed model of annual adsorbed NPS load was then developed via the correlation between sediment yield and adsorbed NPS load. Furthermore, a case study of the Jialing River basin in China was applied to validate the integrated model, the dynamic-distributed coupling among GIS technology, sediment yield model, and adsorbed NPS load model was achieved successfully. The simulation results demonstrate the following: (1) runoff and sediment are influenced greatly by rainfall intensity, SDR and vegetation cover; rainfall and land management show high sensitivities to the integrated model; the average annual adsorbed TN and TP pollution loads from 2006 to 2010 decreased by 76 and 74 % compared with the previous treatment (1990), respectively. (2) Spatio-temporal variations of adsorbed NPS nitrogen and phosphorus load are mainly related to different land use types and the background level of nutriments in topsoil; different land use types have different contribution rates; the largest contribution rates of adsorbed total nitrogen (TN, 58.9 %) and total phosphorus (TP, 53 %) loads are both from the dryland cropland. (3) The identification of critical source areas can help to implement the prevention and control measures aiming at the reduction of water environmental pollution. These results will provide useful and valuable information for decision makers and planners to take sustainable land use management and soil conservation measures for the control of sediment pollution in the Three Gorges reservoir area. The application of this model in the catchment shows that the integrated model may be used as a major tool to assess sediment yield risks and adsorbed NPS pollution load at mountainous watersheds. 相似文献
4.
In the rocky mountain area of North China, soil fertility has decreased with severe soil and water losses under various land uses. Land use has been proven to affect soil fertility spatial distribution patterns at larger scales. However, less information is available about these effects in field scale plots. Soil samples were collected at 2-m intervals by grid sampling from an area (18?×?18 m) within three land use types (poplar woodland, rotation cropland with peanut and sweet potato, and peach orchard). Soil properties including soil particle composition, soil organic matter, total nitrogen (TN), nitrate nitrogen (NO3 ?-N), total phosphorus (TP), and available phosphorus (AP) were measured for each sample. The spatial variability and spatial pattern of the soil properties were assessed for the three contrasting land use types. NH4 +-N, NO3 ?-N, and AP in the peach orchard and NO3 ?-N in the poplar woodland exhibited strong variation (coefficient of variance >100 %). Other properties showed moderate variations. With annual plowing and fertilization, soil properties in the rotation cropland had less variability and greater spatial autocorrelated ranges. The spatial dependences of sand content, TN, NO3 ?-N, and SWC in both the peach orchard and the rotation cropland were weaker than those in the poplar woodland, but the spatial dependences of TP and AP in the peach orchard were stronger than those in either the rotation cropland or the poplar woodland. Human activities such as plowing, fertilization, and harvesting had obvious effects on the spatial variability and spatial pattern of soil properties. 相似文献
5.
Understanding the linkages between the biogeophysical and socio-economic processes that operate at different spatial and temporal scales is important for land cover change mitigation. This study analysed several factors that explained the forest-shrubland conversions, grassland conversions and cropland expansions in Lake Nakuru drainage basin and Eastern Mau forest reserve in Kenya from 1985 to 2011. Logistic regression models were developed using a combination of remote sensing-based land cover data, and geographical information systems-based geophysical and socio-economic data (i.e., temperature, rainfall, elevation, slope, aspect, topographic wetness, curvature, soil pH, soil cation exchange capacity (CEC), population density and distance to road, river and town). The results were varied; for example, in the period 1985–2000, forest-shrubland conversions were linked to distance to road), distance to town, soil pH, soil CEC, rainfall, topographic wetness, curvature and aspect. The same factors, in addition to slope and distance to river, also determined the likelihood of forest-shrubland conversions in the period 2000–2011. Overall, significance of the determining factors varied depending on time and nature of land cover change. For example, topographical factors influenced grassland conversions in the period 1985–2000, while soil-related factors did not. But in the period 2000–2011, the converse was true. Therefore, policies for restoration, conservation and sustainable management of critical ecosystems (e.g., forests) should be spatially targeted and time-specific. These results broaden our knowledge of land cover dynamics in this locality, and provide a base for effective environmental policy formulation, planning and management. 相似文献
6.
More than 3,200 indoor radon-222 (222Rn) measurements were made seasonally in an area of about 1,000 square kilometers of the Coastal Plain and Piedmont physiographic provinces in Virginia, U.S.A. Results of these measurements indicate that some geological units are associated, on the average, with twice as much indoor222Rn as other geological units, and that indoor222Rn varies seasonally. The Kruskal-Wallis test was used to test whether indoor222Rn concentrations for data gathered over the winter and summer seasons differ significantly by rock unit. The tests concluded that indoor222Rn concentrations for different rock units were not equal at the 5-percent significance level. The rocks associated with the highest median indoor222Rn concentration are specific rocks in the Mesozoic Culpeper basin, including shale and siltstone units with Jurassic diabase intrusives, and mica schists in the Piedmont physiographic province. The pre-Triassic Peters Creek Schist has the highest ranking in terms of indoor222Rn concentration. The rocks associated with the lowest indoor222Rn concentrations include coastal plain sediments, the Occoquan Granite, Falls Church Tonalite, Piney Branch Mafic and Ultramafic complex, and unnamed mafic and ultramafic inclusions, respectively. The rocks have been ranked according to observed222Rn concentration by transforming the average rank of indoor222Rn concentrations to z scores. 相似文献
7.
Prior to European settlement, oligohaline and mesohaline sections of Chesapeake Bay draining Piedmont saprolite supported diverse and abundant diatom and macrophyte populations. Compositional changes in diatoms and macrophytes in oligohaline sections correspond with 17th- and 19th-century deforestation and increased siltation, while effects on downstream populations were less notable. After deforestation, previously sparse diatom populations in a mesohaline estuary draining sandy Coastal Plain soils became more abundant. Fertilization of cultivated land was accompanied by increased production of both attached and free-floating diatoms. After the discharge of sewage, diatom populations increased enormously in the affected areas, followed by a dramatic decrease. The decrease suggests silica limitation after intense phosphorus enrichment. The loss of macrophytes and increase in planktonic diatoms in oligohaline areas in recent years resemble the historical sequences observed in lakes undergoing eutrophication. However, in the estuary, similar declines have also occurred in macrophyte populations in mesohaline areas where eutrophication is much less severe, but where chlorine and herbicide toxicity during the past 20 yr is similar to upstream areas. 相似文献
8.
Reprocessing and enhanced interpretation of the initial COCORP Southern Appalachians traverse 总被引：1，自引：0，他引：1
Reprocessing of the 1978–1980 COCORP Southern Appalachian seismic reflection data has produced improved images of structures related to the emplacement of the Blue Ridge–Inner Piedmont allochthon. The results enhance and extend the interpretation presented previously that the Blue Ridge and Inner Piedmont are allochthonous above a shallow, and shallow dipping, detachment that can be followed from outcrop at the Blue Ridge/Valley and Ridge transition to at least beneath the Carolina terrane. The continuity of reflections in the new images supports the interpretation that the southern Appalachian detachment is not rooted on the east side of the Inner Piedmont, but rather projects as a low-angle detachment (or zone of decoupling) to beneath the Coastal Plain. An implication of this geometry is that terranes, such as the Carolina terrane, between autochthonous North America and the Alleghanian suture beneath the Coastal Plain are detached, thin flakes. 相似文献
9.
The geological and geomorphic information preserved in the tributary valleys of the lower Mississippi River (LMR) contributes to our understanding of the lower valley's Quaternary geological history. Prominent Pleistocene terraces are preserved in the tributary valleys. Fisk first formulated his four terraces framework on the Red River. Caution needs to be followed in projecting the Red River terraces across the entire Lower Mississippi Valley (LMV). The tributary system cannot be assumed to operate in a synchronized fashion in response to changes in climate and base level. To compare the collective contribution of the tributaries of the LMR, the streams are described in terms of. (1) their characteristics, (2) geomorphic development, (3) process and response of the tributaries to and from the LMR, and (4) engineering investigations and implications. The characteristics of the tributaries are a direct function of their drainage basin size and geology. The tributary system drains portions of six physiographic provinces. Synoptically, the tributaries can be viewed as two groups: the eastern and western tributaries. All of the eastern tributaries are intra-regional, i.e., they drain only one physiographic province, the Coastal Plain, and therefore, have a restricted sediment source. Generally, the eastern tributaries are more numerous and shorter than the western tributaries. The longer western tributaries drain outside the Coastal Plain. The extra-regional nature of the western tributaries adds to the variability of discharge and sediment types. The sediment record of the tributaries reflects response to the trunk Mississippi. During glacial outwash flushes, many of the tributaries were alluvially drowned, producing alluvial cones expressed as flattened longitudinal profiles. More recently, a number of tributaries in the state of Mississippi have experienced episodes of accelerated channel erosion. The effects of navigation and flood control modification of the Mississippi River on the tributaries have not been fully studied. Therefore, fluvial geomorphic research in the tributaries is essential to understanding ways to mitigate the adverse effects of river engineering, thereby designing engineering works in balance with the alluvial architecture and processes of the stream system. 相似文献
10.
《Applied Geochemistry》1988,3(2):205-212
The distribution of Li in the environment is not well documented although its geochemistry is thought to influence human health and agriculture. This study examined the distribution of Li in the soils and surface waters of the southeastern U.S.A., contrasting the Piedmont and Coastal Plain regions. Previous studies have been limited to total, and to a lesser extent exchangeable, soil Li, usually at a single soil depth. This study evaluated more carefully the distribution of Li between the soil solution, exchange, and solid phases, and its distribution within soil profiles. Total soil Li was found to correlate strongly with clay content, and ranged from 3.74 to 59.93 mg/kg. Exchangeable Li ranged from 0.1 to 21.8 μmol/kg soil and constituted an insignificant portion of the total exchangeable cations (<0.09%) and total Li present (<1.1%) in the soils studied. Water-soluble Li ranged from 0.08 to 4.62 μg/l. Dissolved Li in 22 surface waters within the Piedmont and Coastal Plain regions of Georgia and South Carolina was also determined and ranged from 0.26 to 4.16 μg/l. The soils and surface waters of the Coastal Plain region were found to be depleted in Li relative to the Piedmont region of the southeastern U.S.A. 相似文献
11.
Philip T. King Jacqueline Michel Willard S. Moore 《Geochimica et cosmochimica acta》1982,46(7):1173-1182
228Ra, 226Ra, and 222Rn activities were determined on over 150 ground water samples collected from drilled, public water supply wells throughout South Carolina. A wide range of aquifer lithologies were sampled including the crystalline rocks of the Piedmont and sedimentary deposits of the Coastal Plain. A significant linear relationship between log 228Ra and log 226Ra (n = 182, r = 0.83) was indistinguishable between Piedmont and Coastal Plain ground water. Median activity ratios for the Piedmont, 1.2, and Coastal Plain, 1.3, ground water are close to estimated average crustal activity ratios of 1.2 to 1.5 corresponding to Th/U weight ratios of 3.5 to 4.5. A linear correlation was also found between log 222Rn and log 226Ra for Piedmont (n = 68, r = 0.62) and Coastal Plain (n = 89, r = 0.64) ground water. However, the median activity ratio for Piedmont ground water, 6100, was much higher than for Coastal Plain ground water, 230. Higher excess 222Rn activities may be due to greater retention of 226Ra by the chemically active Piedmont aquifers compared to the more inert sand aquifers sampled in the Coastal Plain. The relationship between log 228Ra and log 226Ra was used to predict total Ra () distributions in Appalachian and Atlantic and Gulf Coastal Plain ground water. Predictions estimate that 2.4% of Appalachian and 5.3% of Atlantic and Gulf Coastal Plain ground water supplies contain total Ra activities in excess of the 5 pCi/l limit established by the U.S. Environmental Protection Agency. These predictions also indicate that 40–50% of these ground water wells may be overlooked using the presently suggested screening activity of 3.0 pCi/l of 226Ra for 228Ra analysis. 相似文献
12.
Michael R. Williams Gopal Bhatt Solange Filoso Guido Yactayo 《Estuaries and Coasts》2017,40(5):1227-1246
In large part driven by total maximum daily load (TMDL) mandates, the restoration community in the Chesapeake Bay region has been implementing novel best management practices (BMPs) and stream restoration designs in urban areas, such as regenerative stream/stormwater conveyance (RSC) structures and stream-wetland complexes (SWCs). However, the nutrient and sediment reduction efficiencies of these novel designs are virtually unknown, and the possibility of increasing riverine flow in the Chesapeake Bay watershed associated with climate change this century necessitates an evaluation of their performance to develop and utilize those that optimize reductions in nutrient and sediment fluxes. We compare pre- and post-construction loads (total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS)) from RSCs (i.e., upland BMPs) and a SWC (i.e., stream restoration) constructed at the outflow of a highly developed watershed in the Coastal Plain physiographic province of Maryland. The largest of the two RSCs performed best in relation to expected nutrient and sediment reductions because of superior water retention capability. By the length of river reach restored, the SWC attained from 79 to 88% of its N reduction TMDL goal, but only 19 to 23 and 2.7 to 3.1% for TP and TSS, respectively; by watershed area, % attainments of TMDL goals were much lower. Results indicate that SWCs have the potential to curtail N loading from developed catchments, but additional water quality benefits may be limited. Climate change projections indicate that there will be an increased frequency of larger-volume storms that will result in an increase in stormflow runoff from urban areas, and increased pollutant loads will likely curtail potential gains made by efforts to achieve TMDL goals. Given the large-scale implementation of BMPs currently underway to accommodate the Chesapeake Bay TMDL, the restoration community needs to adopt a concerted strategy of building climate resilience into many types of urban BMPs to help attain and maintain loads at TMDL levels in anticipation of a progressively wetter climate throughout this century. 相似文献
13.
Zoltan Szabo Vincent T. dePaul Jeffrey M. Fischer Thomas F. Kraemer Eric Jacobsen 《Applied Geochemistry》2012
A total of 1270 raw-water samples (before treatment) were collected from 15 principal and other major aquifer systems (PAs) used for drinking water in 45 states in all major physiographic provinces of the USA and analyzed for concentrations of the Ra isotopes 224Ra, 226Ra and 228Ra establishing the framework for evaluating Ra occurrence. The US Environmental Protection Agency Maximum Contaminant Level (MCL) of 0.185 Bq/L (5 pCi/L) for combined Ra (226Ra plus 228Ra) for drinking water was exceeded in 4.02% (39 of 971) of samples for which both 226Ra and 228Ra were determined, or in 3.15% (40 of 1266) of the samples in which at least one isotope concentration (226Ra or 228Ra) was determined. The maximum concentration of combined Ra was 0.755 Bq/L (20.4 pCi/L) in water from the North Atlantic Coastal Plain quartzose sand aquifer system. All the exceedences of the MCL for combined Ra occurred in water samples from the following 7 PAs (in order of decreasing relative frequency of occurrence): the Midcontinent and Ozark Plateau Cambro-Ordovician dolomites and sandstones, the North Atlantic Coastal Plain, the Floridan, the crystalline rocks (granitic, metamorphic) of New England, the Mesozoic basins of the Appalachian Piedmont, the Gulf Coastal Plain, and the glacial sands and gravels (highest concentrations in New England). 相似文献
14.
Matthew S. Kornis Denise Breitburg Richard Balouskus Donna M. Bilkovic Lori A. Davias Steve Giordano Keira Heggie Anson H. Hines John M. Jacobs Thomas E. Jordan Ryan S. King Christopher J. Patrick Rochelle D. Seitz Heather Soulen Timothy E. Targett Donald E. Weller Dennis F. Whigham Jim UphoffJr 《Estuaries and Coasts》2017,40(5):1464-1486
Human alteration of land cover (e.g., urban and agricultural land use) and shoreline hardening (e.g., bulkheading and rip rap revetment) are intensifying due to increasing human populations and sea level rise. Fishes and crustaceans that are ecologically and economically valuable to coastal systems may be affected by these changes, but direct links between these stressors and faunal populations have been elusive at large spatial scales. We examined nearshore abundance patterns of 15 common taxa across gradients of urban and agricultural land cover as well as wetland and hardened shoreline in tributary subestuaries of the Chesapeake Bay and Delaware Coastal Bays. We used a comprehensive landscape-scale study design that included 587 sites in 39 subestuaries. Our analyses indicate shoreline hardening has predominantly negative effects on estuarine fauna in water directly adjacent to the hardened shoreline and at the larger system-scale as cumulative hardened shoreline increased in the subestuary. In contrast, abundances of 12 of 15 species increased with the proportion of shoreline comprised of wetlands. Abundances of several species were also significantly related to watershed cropland cover, submerged aquatic vegetation, and total nitrogen, suggesting land-use-mediated effects on prey and refuge habitat. Specifically, abundances of four bottom-oriented species were negatively related to cropland cover, which is correlated with elevated nitrogen and reduced submerged and wetland vegetation in the receiving subestuary. These empirical relationships raise important considerations for conservation and management strategies in coastal environments. 相似文献
15.
A summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern Appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation. The ca. 480-435 Ma Taconic event affected most of the Piedmont and Blue Ridge provinces. The ca. 380-340 Ma Acadian event was milder and was centered in the west central Piedmont and eastern Blue Ridge. The 330-230 Ma Alleghanian event exhibits an abrupt ductile deformation front in the eastern Piedmont and extends an unknown distance eastward below the Atlantic Coastal Plain. 相似文献
16.
Examination of two lines of repeated leveling in North Carolina and Georgia reveals
- 1. (1) apparent uplift at the Blue Ridge-Piedmont physiographic boundary (the AtlanticGulf drainage divide) relative to the Atlantic Coastal Plain on the east and the Valley and Ridge province to the west; and
- 2. (2) large tilts over short baselines superimposed upon the regional pattern in the vicinity of the nearby Blue Ridge—Piedmont geologic boundary (the Brevard fault zone). In the North Carolina profile a very pronounced correlation between topography and movement suggests possible systematic leveling error, but the observed movements appear to be larger than those normally attributed to leveling error. Thus, either refraction or rod errors are larger than expected, or the movement is real and strongly correlates with topography along this portion of the leveling line.
17.
The Patuxent River, Maryland, is a nutrient-overenriched tributary of the Chesapeake Bay. Nutrient inputs from sewage outfalls
and nonpoint sources (NPS) have grown substantially during the last four decades, and chlorophylla levels have increased markedly with concomitant reductions in water quality and dissolved oxygen concentrations. The Patuxent
has gained national attention because it was one of the first river basins in the U.S. for which basin-wide nutrient control
standards were developed. These included a reduction in NPS inputs and a limit on both nitrogen (N) and phosphorus (P) loadings
in sewage discharges intended to return the river to 1950s conditions. Full implementation of point source controls occurred
by 1994, but population growth and land-use changes continue to increase total nutrient loadings to the river. The present
paper provides the perspectives of scientists who participated in studies of the Patuxent River and its estuary over the last
three decades, and who interacted with policy makers as decisions were made to develop a dual nutrient control strategy. Although
nutrient control measures have not yet resulted in dramatic increases in water quality, we believe that without them, more
extensive declines in water quality would have occurred. Future reductions will have to come from more effective NPS controls
since future point source loading will be difficult to further reduce with present technology. Changing land use will present
a challenge to policy makers faced with sprawling population growth and accelerated deforestation. 相似文献
18.
Spatial variability of soil organic matter and nutrients in paddy fields at various scales in southeast China 总被引：2，自引：0，他引：2
Xingmei Liu Keli Zhao Jianming Xu Minghua Zhang Bing Si Fan Wang 《Environmental Geology》2008,53(5):1139-1147
The present study examines the spatial dependency of soil organic matter and nutrients in paddy fields at three different
scales using geostatistics and geographic information system techniques (GIS). The spatial variability of soil organic matter
(SOM), total nitrogen (TN) and available phosphorus (AP) has been characterized using a total of 460, 131 and 64 samples that
were, respectively, collected from the Hangzhou–Jiaxing–Huzhou (HJH) Plain (10 km), Pinghu county (1,000 m) and a test plot
area (100 m) within the Pinghu county, Zhejiang province of the southeast China. Semivariograms showed that the SOM and TN
had moderate spatial dependency on the large scale of HJH plain and moderate scale of Pinghu county with long spatial correlation
distances. At the moderate scale of Pinghu county and the small scale of a test plot area, the AP data did not show any spatial
correlation, but had moderate spatial dependency in HJH plain. Spherical and exponential variogram models were best fitted
to all these soil properties. Maps of SOM and TN were generated through interpolation of measured values by ordinary kriging,
and AP by lognormal kriging. This study suggests that precision management of SOM and TN is feasible at all scales, and precision
management of AP is feasible at large scales. 相似文献
19.
Land cover change over the last three centuries due to human activities: The availability of new global data sets 总被引：15，自引：0，他引：15
Land use and land cover change is an important driver of global change (Turner et al., 1993). It is recognized that land use change has important consequences for global and regional climates, the global biogeochemical cycles such as carbon, nitrogen, and water, biodiversity, etc. Nevertheless, there have been relatively few comprehensive studies of global, long-term historical changes in land cover due to land use. In this paper, we review the development of global scale data sets of land use and land cover change. Furthermore, we assess the differences between two recently developed global data sets of historical land cover change due to land use. Based on historical statistical inventories (e.g. census data, tax records, land surveys, historical geography estimates, etc) and applying different spatial analysis techniques, changes in agricultural land cover (croplands, pastures) were reconstructed for the last 300 years. The two data sets indicate that cropland areas expanded from 3–4 million km2 in 1700 to 15–18 million km2 in 1990 (mostly at the expense of forests), while grazing land area expanded from 5 million km2 in 1700 to 31 million km2 in 1990 (mostly at the expense of natural grasslands). The data sets disagree most over Latin America and Oceania, and agree best over North America. Major differences in the two data sets can be explained by the use of a fractional versus Boolean approach, different modelling assumptions, and inventory data sets. 相似文献
20.
Nutrient inputs have degraded estuaries worldwide. We investigated the sources and effects of nutrient inputs by comparing water quality at shallow (< 2m deep) nearshore (within 200 m) locations in a total of 49 Chesapeake subestuaries and Mid-Atlantic coastal bays with differing local watershed land use. During July–October, concentrations of total nitrogen (TN), dissolved ammonium, dissolved inorganic N (DIN), and chlorophyll a were positively correlated with the percentages of cropland and developed land in the local watersheds. TN, DIN, and nitrate were positively correlated with the ratio of watershed area to subestuary area. Total phosphorus (TP) and dissolved phosphate increased with cropland but were not affected by developed land. The relationships among N, P, chlorophyll a, and land use suggest N limitation of chlorophyll a production from July–October. We compared our measurements inside the subestuaries to measurements by the Chesapeake Bay Program in adjacent estuarine waters outside the subestuaries. TP and dissolved inorganic P concentrations inside the subestuaries correlated with concentrations outside the subestuaries. However, water quality inside the subestuaries generally differed from that in adjacent estuarine waters. The concentration of nitrate was lower inside the subestuaries, while the concentrations of other forms of N, TP, and chlorophyll a were higher. This suggests that shallow nearshore waters inside the subestuaries import nitrate while exporting other forms of N as well as TP and chlorophyll a. The importance of local land use and the distinct biogeochemistry of shallow waters should be considered in managing coastal systems. 相似文献