Land-Cover Change Trajectories in Northern Ghana

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.     

ESTIMATING NUTRIENT AND SEDIMENT THRESHOLD CRITERIA FOR BIOLOGICAL IMPAIRMENT IN PENNSYLVANIA WATERSHEDS1

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.     

Critical Impact Assessment of Organic Agriculture

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.     

Initial results from a multi-institutional collaboration to monitor harmful algal blooms in South Carolina

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.     

QUANTIFICATION OF THE WATER BUDGET AND NUTRIENT LOADING IN A SMALL PEATLAND1

ABSTRACT: Few water budgets exist for specific types of wetlands such as peatlands, even though such information provides the basis from which to investigate linkages between wetlands and upland ecosystems. In this study, we first determined the water budget and then estimated nutrient loading from an upland farm field into a 1.5 ha, kettle-block peatland. The wetland contains highly anisotropic peat and has no distinct, active layer of groundwater flow. We estimated the depth of the active layer using Fick's law of diffusion and quantified groundwater flow using a chemical mass balance model. Evapotranspiration was determined using MORECS, a semi-physical model based on the Penman-Monteith approach. Precipitation and surface outflow were measured using physical means. Groundwater provided the major inflow, 84 percent (44,418 m³) in 1993 and 88 percent (68,311 m³) in 1994. Surface outflow represented 54 percent (28,763 m³) of total outflows in 1993 and 48 percent (37,078 m³) in 1994. A comparison of several published water budgets for wetlands and lakes showed that error estimates for hydrologic components in this study are well within the range of error estimates calculated in other studies. Groundwater inflow estimates and nutrient concentrations of three springs were used to estimate agricultural nutrient loading to the site. During the study period, nutrient loading into the peatland via groundwater discharge averaged 24.74 kg K ha^-1, 1.83 kg total inorganic P ha^d, and 21.81 kg NO₃-N ha^-1.     

洞庭湖浮游植物增长的限制性营养元素研究

近20年水质监测资料表明,洞庭湖水体富营养化日趋严重。洞庭湖水体主要污染物为氮和磷,而营养盐赋存形态及其含量对浮游植物生长的影响在洞庭湖尚未见报道。2011年9月至2012年8月对洞庭湖浮游植物生物量及主要营养盐赋存形态与含量进行监测,同时利用藻类增长的生物学（NEB）评价方法对限制浮游植物增长的营养盐进行了研究,并分析了浮游植物生物量与各营养元素之间的相关性。结果表明：洞庭湖主要污染物总氮（TN）和总磷（TP）的年平均值分别为1.90 mg·L-1和0.093 mg·L-1,溶解态无机氮（DIN）平均占ρ（TN）比例为87%,溶解态总磷（DTP）平均占ρ（TP）比例为70%。洞庭湖水体中,DIN是TN的主要贡献者,且不同形态DIN的贡献大小依次为ρ（NO3--N）〉ρ（NH4＋-N）〉ρ（NO2--N）;磷形态组成中,TP主要以溶解反应性磷（SRP）存在。春季洞庭湖水体中ρ（TN）、ρ（TP）较高,这一结果可能源于春季面源污染。洞庭湖水体中ρ（Chla）与氮显著正相关,与磷显著负相关。NEB 实验结果表明氮对洞庭湖浮游植物生长有明显的促进作用,其幅度随氮浓度的增加而加强,而磷对浮游植物的生长影响不大,有时出现抑制作用,硝态氮与磷之间不存在交互作用。因此,氮可能是洞庭湖浮游植物增长的主要限制性营养因子,这一研究暗示在洞庭湖富营养化控制过程中应特别注重氮的控制。     

红壤稻田系统水分和养分转换效益研究

田间模拟施肥和水分管理模式的定位试验结果表明：施肥和水分管理模式显著地影响水分和养分的转化和生产效益。单施N的产量效应为4.5 kg/kg,而NP或NPK配施养分的产量效应分别为8.8 kg/kg和8.0 kg/kg;有机物料循环的增产率为56.5%;在有机物循环的基础上配施NPK化肥最大的增产率可达79.8%。常规灌溉年需水量为5 838 m3/hm2,田间水分分配为：蒸散占1/2,翻耕整地占1/6,植物构成占1/21,田间渗漏占1/14,其它环境耗水(维持)占1/5。晚稻灌溉占全年的71%,7～9月是灌溉需水高峰期,占全年灌溉量的68%。生产灌溉效率：生物量3.67 kg/m3,精谷量1.48 kg/m3。双季稻生产的灌溉,以早稻保持水层灌溉,晚稻按需配额灌溉的模式比较适宜。     

太湖藻源性颗粒物降解过程中营养盐转化及其生态效应

以太湖水体中藻源性颗粒有机物作为切入点,研究了不同环境条件下(有光,无光)藻源性颗粒有机物降解过程中C,N,P等营养元素的形态变化过程,分析了藻源性颗粒有机物对水体营养盐循环和浮游植物生长中的作用.实验结果显示,蓝藻水华过程中,藻源性颗粒有机物最高可占水体总C,N,P比例的81.51%,94.60%,97.47%,是水体营养元素的重要组成部分;有光组颗粒物APA显著高于无光组,说明有光组中颗粒态P降解和转化速率显著高于无光组,但有光组水体中SRP浓度低于无光组,Chl-a浓度高于无光组,说明有光组中藻源性颗粒物降解的同时伴随着藻类的生长,颗粒物释放的SRP被浮游植物吸收并转化为生物量;光照对C,N,P的降解过程有明显影响,无光组颗粒物中C,N,P降解速率是有光组的2倍,可降解比例是有光组的(2.5±0.1)倍;实验中还发现前7d各元素的降解速率要高于之后的降解速率.综上,藻源性颗粒物营养盐总量大,生物可利用性高,降解迅速,且降解产物可被浮游植物吸收,是藻类生长和水华发生重要的营养盐来源.     

水文变化条件下农田溪流营养盐滞留效应模拟

以巢湖流域某一典型农田源头溪流为对象,基于溪流水文条件的动态变化性,从水文概率密度模型与营养盐滞留率模型综合集成角度,解析较长时间尺度下营养盐滞留有效流量的动态变化特征.在对水文概率密度模型Monte Carlo随机模拟的基础上,根据先前10次野外示踪实验获得的营养盐吸收速度等数据信息,定量评估溪流营养盐滞留的总体水平,估算最有效流量和等效流量.结果表明,农田溪流渠段的NH₄⁺、PO₄^3-滞留能力总体偏低,相应的期望滞留率分别为0.0671(6.71%)和0.0541(5.41%),最有效流量分别为0.0051,0.0049m³/s,功能等效流量分别为0.044,0.043m³/s.基于溪流营养盐吸收速度明显偏低的客观现状,有必要从溪流形态和河床地貌特征的改造着手,提升溪流水体营养盐滞留能力.