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841.
The rapid rate of development in the South Carolina (SC) coastal zone has heightened public concern for the condition of the state's estuaries, and alerted scientists to the potential that novel and adverse effects on estuarine ecosystems may result. Although well-developed databases from long-term monitoring programs exist for many variables valuable in predicting and following system responses, information on phytoplankton distributions in SC estuaries has lagged. Knowledge of the dynamical relationship between environmental (e.g., nutrient quantity and quality) and biological (e.g., grazing) regulation, and phytoplankton biomass and composition is critical to understanding estuarine susceptibility to eutrophication or harmful algal blooms (HABs). Recently, SC scientists from federal, state, and academic institutions established a collaborative monitoring program to assess HAB distribution and ecology statewide. The South Carolina Harmful Algal Bloom Program includes: a) intensive temporal monitoring at areas of known HAB occurrence or those exhibiting symptoms potentially related to HABs (e.g., prevalent fish lesions), b) extensive spatial monitoring in coordination with existing statewide efforts, c) a citizen volunteer monitoring network, d) nutrient response bioassays, and e) laboratory-based physiological experiments on HAB isolates. By combining trip-wire surveillance and rapid response systems, routine monitoring of environmental parameters and HAB distribution, and process-oriented studies examining the physiological functioning of HAB species, an enhanced understanding of the impact and environmental control of HABs in SC estuaries will be achieved. The application of this approach to studies on the distribution and physiological ecology of a new widespread SC red tide, and to the discovery of several potentially toxic blooms (including Pfiesteria) in SC holding ponds, are described. 相似文献
842.
Litterfall (LF) is usually collected by means of opentraps. However, this litter will be subject toleaching by the throughfall which passes through theaccumulated litter in the traps. The nutrients lostduring this leaching are not taken into account in thecalculation of LF nutrient fluxes. We report theresults from a 2-month (August–September) studycarried out in 8 northern coniferous forest stands toassess the possible importance of leaching from litterin LF traps. Compared to throughfall (TF), thelitterfall leachate (LFLgross), which includes athroughfall component, had significantly (p < 0.05)higher concentrations and fluxes of Ca, Mg, Na and S.The average net LFL (i.e., LFLnet = LFLgross-TF) fluxes were 21 (Ca), 7 (Mg), 57 (K), 10 (Na), 10 (N), and 19 (S) mg m-2 mo-1. LFLnet accounted for 42%, 37% and 50% of the LFLgross flux, and for 91%, 51% and 49% of the total litterfall flux (i.e.,LF + LFLnet) of Na, S and K, respectively. ForCa, Mg and N, the LFLnet flux accounted for 64%,58% and 29% of the LFLgross flux, and for< 14% of the total litterfall flux. Compared to TF,LF was the dominant return pathway for Ca, Mg and N tothe forest floor regardless of whether LFLnet wasincluded or not. However, for K and S, takingLFLnet into account determined whether TF or LFwas the dominant pathway. TF remained the dominantpathway for Na even when LFLnet was included. 相似文献
843.
本研究考察了厌氧-立体循环一体化氧化沟工艺(AN-IODVC)中厌氧释磷效果及诸影响因素.研究结果表明,AN-IODVC除磷脱氮系统中好氧污泥的VSS/MLSS值比厌氧污泥小,好氧污泥含磷量与厌氧污泥含磷量的差值和TP去除率、厌氧磷释放率及厌氧ORP呈良好的线性相关关系.厌氧磷释放的最佳条件为:污水COD/TP>55,维持厌氧区ORP低于-400mV. 相似文献
844.
Highland catchments in tropical regions are frequently subjected to soil erosion and the transport of chemicals downstream.
Any drastic changes in land use will increase the severity of these processes of land degradation. A simulation study using
GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) was conducted at a catchment presently under tea farming
in Cameron Highlands, Malaysia. Soil, water and nutrient transport associated with several alternative land uses was studied.
In addition, the effect of a disruptive form of land clearing on soil, water and nutrient losses was also investigated. Modelling
with GLEAMS required information from field measurements and observations, laboratory analyses, guide tables, industry records,
maps and reports published by soil survey and meteorological departments.
The most critical step in simulating soil and water movement using GLEAMS is the identification of a representative flow sequence.
In the catchment under study, the representative flow sequence was overland flow–channel 1–channel 2. Input data on soil erodibility,
porosity and surface roughness were manipulated to represent various degrees and forms of disturbance to the surface soil
layer. For all land uses studied, the highest soil loss was predicted for the overland flow area where slope gradient is high
and the soil friable. The variations in soil loss, runoff and nutrient loss between landscape elements and between land uses
were consistent with soil erosion features observed in the field. Soil and nutrient losses were substantial for crops such
as cabbage that required land shaping activities and frequent ploughing of the soil. Predicted data on enrichment ratio of
specific surface (ERSS) are consistent with nutrient enrichment processes in the field and could prove to be useful in studies
on chemical transport in highland catchments. 相似文献
845.
Land-Cover Change Trajectories in Northern Ghana 总被引:3,自引:0,他引:3
Land-cover change trajectories are an emergent property of complex human–environment systems such as the land-use system.
An understanding of the factors responsible for land change trajectories is fundamental for land-use planning and the development
of land-related policies. The aims of this study were to characterize and identify the spatial determinants of agricultural
land-cover change trajectories in northern Ghana. Land-cover change trajectories were defined using land-cover maps prepared
from Landsat Thematic Mapper dataset acquired in 1984, 1992, and 1999. Binary logistic regression was used to model the probability
of observing the trajectories as a function of spatially explicit biophysical and socioeconomic independent variables. Population
densities generally increased along the continuum of land-use intensity, whereas distance from market and roads generally
decreased along this continuum. Apparently, roads and market serve as incentives for settlement and agricultural land use.
An increase in population density is an important spatial determinant only for trajectories where the dominant change process
is agricultural extensification. A major response to population growth is an increase in cultivation frequency around the
main market. Agricultural intensification is highly sensitive to accessibility by roads. The increase in land-use intensity
is also associated with low soil quality. These results suggest the need for policies to restore soil fertility for agricultural
sustainability. The models also provide a means for identifying functional relationships for in-depth analyses of land-use
change in Ghana. 相似文献
846.
Scott A. Sheeder Barry M. Evans 《Journal of the American Water Resources Association》2004,40(4):881-888
ABSTRACT: This study employs a simple nonlinear statistical approach to establish nitrogen, phosphorus, and sediment concentration and unit area load thresholds to aid in the evaluation of aquatic biological health of watersheds within the state of Pennsylvania. Flow, nitrogen and phosphorus species, sediment, basin area, land cover, and biological assessment data were assembled for 29 Pennsylvania watersheds. For each watershed, rating curves depicting flow versus load relationships were developed using the U.S. Environmental Protection Agency's (USEPA's) storage and retrieval database (STORET) flow and concentration data, then applied to daily flow data obtained from U.S. Geological Survey (USGS) daily flow gauging stations to estimate daily load between 1989 and 1999. The load estimates and concentration data were then sorted into six sets of data: mean annual unit area nitrogen, phosphorus, and sediment loads; and average nitrogen, phosphorus, and sediment concentrations. Results of Mann‐Whitney tests conducted on each of the six datasets indicate that there is a statistically significant difference between the concentrations and unit area loads of nitrogen, phosphorus, and sediment in impaired and unimpaired watersheds. Concentration thresholds, calculated as the midpoint between the impaired and unimpaired watersheds’ 95 percent confidence interval for the median, were estimated to be 2.01 mg/L, 0.07 mg/L, and 197.27 mg/L for nitrogen, phosphorus, and sediment, respectively. Annual unit area load thresholds were estimated to be equal to 8.64 kg/ha, 0.30 kg/ha, and 785.29 kg/ha, respectively, for nitrogen, phosphorus, and sediment species. 相似文献
847.
Xie Biao Wang Xiaorong Ding Zhuhong Yang Yaping 《Journal of Agricultural and Environmental Ethics》2003,16(3):297-311
Based on its productionguideline, organic agriculture has set foritself the goals of minimizing all forms ofpollution and maintaining sustainability of thefarming system. By striving for these goals,organic farming meets the demands of anincreasing number of consumers who are criticalof conventional production methods. This papergives an overview of the present state of theart in the different issues. Possibilities ofand limitations in performing the self-aimedgoals under the basic standards of organicagriculture are discussed. Concerningenvironmental protection, in general, the riskof adverse environmental effects is lower withorganic than with conventional farming methods,though not necessarily so; with reference tosoil fertility and nutrient management, organicfarming is suited to improve soil fertility andnutrient management markedly on the farm level;regarding biodiversity, comparison studies showthat organic farming has more positive effectson biodiversity conservation; in relation toproduct quality, under the basic standards oforganic farming, there is no sufficientevidence for a system-related effect on productquality due to the production method. 相似文献
848.
Wu Gang 《环境科学学报(英文版)》1998,10(3)
The cycling characteristics of nitrogen(N), phosphorus(P) and potassium(K) of the Quercus acutissima and Pinus massoniana mixed forest, which is the most common forest type in the Three Gorge Reservoir areas in China, were systematically analyzed. The results showed that N, P and K accumulated in the plant pool and in the litter pool, while total N, P, and K were deficient in the soil pool and in the forest systems. Contents of N in the soil of depth 20-40 cm were the key factor limiting growth of trees. The biological outside cycling coefficients were 8.78, 72.5 and 11.7 times of inside cycling coefficients of N, P and K, respectively. 33.92, 10.26 and 15.88 kg of N, P and K return to the litter pool from branches, leaves and throughfall per year, but, 14.31, 1.32 and 10.48 kg of N, P and K return to the soil from litter pool per year respectively. It is clear that 58% of N, 87% of P, and 34% of K are lost by surface runoff per year. 5.49%, 1.30%, and 8.34% of N, P and K withdraw from leaves to branches, 4.99%, 1.99% and 7.30% of N, P and K withdraw from branches to trunks per year,respectively. 相似文献
849.
Nikita S. Eriksen-Hamel Joann K. Whalen 《Agriculture, ecosystems & environment》2007,120(2-4):442-448
The objective of this experiment was to determine the effects of earthworms on soil N pools and plant growth in soybean and maize agroecosystems. The species and number of individuals in earthworm communities were manipulated in plot-scale field enclosures (2.4 m × 1.2 m) by first reducing earthworm populations within enclosures with carbaryl pesticide, and then adding earthworm treatments to the enclosures. Soybean was grown in the enclosures in the first year and stover maize in the second year.The success of earthworm manipulations in field enclosures was affected by climate conditions and available food resources. The endogeic earthworm species Aporrectodea caliginosa was dominant in all enclosures, while introduced anecic Lumbricus terrestris earthworms had poor survival. In the first season, when climate conditions were favourable for earthworm survival and growth, there was a significant (P < 0.05) linear increase in soil mineral-N and microbial biomass N concentrations in the 0–15 cm depth of enclosures with more earthworms. Similarly, soybean grain and grain-N yield was significantly (P < 0.05) greater in enclosures with the largest earthworm populations than the control which had no earthworms added. In the second season, when climate conditions were less favourable, there was no effect of earthworms on soil N pools or maize plants, probably due to poor survival of introduced earthworms. 相似文献
850.