Suspension-feeding aquaculture systems: Effects of phytoplankton concentration and temperature on growth of the bay scallop     

William W. Kirby-Smith  Richard T. Barber 《Aquaculture (Amsterdam, Netherlands)》1974,3(2):135-145

The growth rate of the bay scallop Argopecten irradians was studied in relation to temperature and phytoplankton concentration. Results suggest that normal variations in phytoplankton concentration do not influence the growth rate of scallops in their natural habitat. Increasing the concentration of phytoplankton above natural levels did not result in increased growth rates while decreasing the phytoplankton concentration resulted in a decrease in growth rate of the scallops. Under extremely low phytoplankton concentrations, such as those that characterize ‘clean water’ effluent from a culture system, the animals ceased growing. A mathematical model of scallop growth rate as a function of phytoplankton concentration is proposed as a tool for comparing the functioning of different suspension feeders in aquaculture systems.  相似文献   

不同退化程度高寒草甸土壤磷素含量与碱性磷酸酶活性研究     

高亚君  李亚娟  姜智英  达朝玲  胡蕊梅 《草原与草坪》2022,(5):81-87

为探讨高寒草甸退化对土壤磷素、碱性磷酸酶活性及其季节动态的影响，分别在春季、夏季和冬季以典型围封草地(FG)、轻度(LD)、中度(MD)和重度退化草甸(HD)为研究对象，对不同季节不同类型草地 0~10，10~20，20~30 cm 土层全磷、有效磷和碱性磷酸酶活性进行了研究。结果表明，春季高寒草地退化对土壤磷素含量没有明显影响；相比 FG，夏季退化高寒草地 0~10 cm 土层全磷含量显著升高(P＜0. 05)，但 LD、MD 和 HD 间差异不显著；退化导致 10~20 cm 土层全磷含量显著降低(P＜ 0. 05)。同一类型草地同一土层全磷含量冬季最高，夏季最低，与夏季相比，冬季 0~10 cm 土层土壤全磷含量从 FG 到 HD 依次增加了 308. 33%、150. 00%、176. 20%、177. 30%。FG 春季 0~10 cm 土层有效磷含量为 30 mg/kg，随退化程度加剧，从 LD 到 HD 含量依次升高。FG 和 HD 季节与土层交互效应有效磷含量差异极显著，而 LD 和 MD 不显著。LD 和 MD 的土壤有效磷含量夏季最高，冬季最低，HD 则春季最高，冬季最低。春季同一退化程度高寒草地 0~10 cm 土层碱性磷酸酶活性最低，剖面 10~30 cm 土层土壤碱性磷酸酶活性在春夏两季显著升高(P＜0. 05)。相关性分析结果表明，仅在冬季土壤碱性磷酸酶活性与有效磷含量呈显著正相关，表明冬季土壤碱性磷酸酶活性可以表征土壤有效磷状况。  相似文献   

The rehabilitation of degraded soils in eastern bolivia by subsoiling and the incorporation of cover crops     

R. G. Barber  F. Navarro 《Land Degradation \u0026amp; Development》1994,5(4):247-259

A high proportion of the soils in the central zone of Santa Cruz, eastern Bolivia, are chemically and physically degraded, with low organic matter and N contents, compacted subsoil layers and a propensity to crusting, hardsetting and wind erosion. The aim of the experiment discussed in this paper was to identify suitable cover crops to be used in combination with subsoiling for the rehabilitation of degraded soils and the improvement of crop yields in eastern Bolivia. Fertilizers were not used because of their high cost. An experiment with a split complete block design, with subsoiling and no-subsoiling as the main treatments, 14 cover crops and a continuously cultivated soybean/wheat control as the subtreatments, and four replications, was established on a degraded site comprising a mosaic of two compacted siliceous isohyperthermic soils (a coarse loamy Typic Ustropept and a fine loamy Typic Haplustalf). After a two-year fallow period, the cover crops were incorporated and test crops were sown for five seasons to evaluate the effects of the treatments on subsequent crop yields. Soil samples were taken to measure changes in chemical fertility. The only significant cover crop effect on soil nutrients was an increase in exchangeable K from 0.47 to 0.56 cmol_c kg⁻¹ by Lablab; subsoiling had no effect on chemical fertility. For all treatments there was an average 24 per cent increase in soil organic matter from 13.1 g kg⁻¹ at 3 months after cover crop incorporation to 16.3 g kg⁻¹ at 19 months after incorporation. No significant differences in total N were found during this period. Test crop yields were not influenced by subsoiling, but were significantly increased by some of the cover crops as compared to the soybean/wheat control during the first three seasons only. Evidence from foliar analysis suggests that the effects of the cover crops on soybean yields were not nutritional and so presumably were physical in nature, whereas the benefits on wheat yields were possibly related to increased N availability. Panicum maximum var. Centenario and P. maximum var. Tobiatá gave the highest total yield increases over the first three cropping seasons (101 and 85 per cent, respectively), but these yield increases would not compensate the farmer for the loss of four crop harvests whilst the land was in fallow. These results highlight the difficulties of rehabilitating soil fertility and increasing crop yields through the use of subsoiling and cover crop fallows on compacted, low organic matter soils in eastern Bolivia.  相似文献   

拉萨河中下游原生动物群落物种分布格局及其驱动因素          下载免费PDF全文

达珍  张鹏  安瑞志  潘成梅  乔楠茜  巴桑 《水生态学杂志》2023,44(4):10-17

了解拉萨河中下游原生动物群落物种分布格局及其驱动因素，为拉萨河中下游生物多样性保护及可持续利用提供基础资料。选取了拉萨河中下游17个样点，于2015年5月、8月和2016年11月进行原生动物定性和定量样品采集，共采集水样153份，分析物种组成、生物多样性及其与环境因子之间的关系，确定该流域原生动物类群组成中稀有种、偶见种和常见种对物种多样性的贡献、生物多样性格局及群落与理化因子相关性，结果表明：（1）3个季节，稀有种80种，占总物种的40%；偶见种95种，占总物种的48%；常见种21种，占总物种的11%；恒见种1种，占总物种的0.5%。（2）拉萨河中下游原生动物物种类群组成中偶见种是原生动物群落物种多样性格局的重要贡献者。（3）多样性指数表明，Richness指数和Margalef指数春季和夏季高于秋季，Shannon-Wiener指数和Simpson指数春季高于秋季高于夏季。（4）基于Bray-Curtis距离的主坐标分析和相似性分析结果表明，拉萨河中下游原生动物群落结构在不同季节和不同流域均具有显著差异，且流域差异相比季节差异较大。（5）根据Mantel检验分析原生动物与环境因子的相关性，结果表明，在所测定环境因子中，水温（WT）、总溶解性固体（TDS）、盐度（Salt）、电导率（EC）、总磷（TP）及溶解氧（DO）是影响原生动物群落结构的主要环境因子。  相似文献   

基于K-means与KNN的多特征苹果在线分级     

王迎超  张婧婧  达新民  耿新雪 《新疆农业科学》2023,60(3):643-650

【目的】准确获取红富士苹果的分级指标，为实现多特征融合的苹果分级提供依据。【方法】以均值滤波、全局亮度均衡化与图像裁剪方法，预处理实验所需的苹果图像；使用K-means聚类算法、OTSU最大类间方差法，将苹果灰度图转换为二值图；利用二值图与苹果原图的异或运算，提取苹果轮廓；采用苹果的二值图计算苹果的果实区域大小；使用颜色空间转换RGB-HSV中H通道划分果实红色区域；通过构建掩膜、形态学操作判断果体是否含有缺陷及计算其面积；构建最小外接矩形计算苹果的果径及果形；利用KNN分类算法实现多特征融合的苹果在线自动分级。【结果】基于K-means聚类与KNN分类相结合的苹果在线分级方法，在优于传统图像阈值分割效果的基础上，特级果分级准确率为97.14%,一级果分级准确率为100%,二级果分级准确率为93.75%,等外果分级准确率为100%,综合分级准确率达到97%。【结论】100个苹果测试准确率达到97%,验证了该分级方法的可行性与准确性。  相似文献