Morphological indices and otolith microstructure of Atlantic croaker,Micropogonias undulatus,as indicators of habitat quality along an estuarine pollution gradient

Synopsis Atlantic croaker, Micropogonias undulatus, sampled from a transect along a pollution gradient show a trend of declining growth and physical condition. This trend is apparent in the mean size of 0-group croaker, in their recent growth rate measured by marginal otolith increment widths, in longer term growth rate as indicated by relative otolith weights, and in general physical condition as measured by an index of condition of the caudal fin. We suggest that these measures are indicators of stress associated with environmental conditions. Because croaker from different positions along the pollution gradient were distinguishable, it appears that they remain for extended periods within areas of degraded environmental quality.     

Response of fishes and aquatic habitats to sand-bed stream restoration using large woody debris

Effects of habitat rehabilitation of Little Topashaw Creek, a sinuous, sand-bed stream draining 37 km² in northwest Mississippi are described. The rehabilitation project consisted of placing 72 large woody debris structures along eroding concave banks and planting 4000 willow cuttings in sandbars. Response was measured by monitoring flow, channel geometry, physical aquatic habitat, and fish populations. Initially, debris structures reduced high flow velocities at concave bank toes, preventing further erosion and inducing deposition. Physical response during the first year following construction included creation of sand berms along eroding banks and slight increases in base flow water width and depth. Fish collections showed assemblages typical of incising streams within the region, but minor initial responses to debris addition were evident. Progressive failure of the structures and renewed erosion were observed during the second year after construction.     

Assessing sedimentological connectivity using WATEM/SEDEM model in a hilly and gully watershed of the Loess Plateau,China

Sedimentological connectivity is an important issue in soil erosion and sediment transport. Landscape patterns, in combination with the rainfall regime, are known to shape such sedimentological connectivity. The quantification of sedimentological connectivity provides a link between sediment delivery and landscape pattern. There are two categories of connectivity: structural connectivity, which describes the physical coupling of landscape units, and functional connectivity, which delineates the linkage among landscape elements maintained by material transport. To quantify sedimentological connectivity, both the physical coupling of, and material transfer between, the various landscape components need to be assessed. This study quantifies the sedimentological connectivity of a headwater catchment in the Loess Plateau of China using the soil erosion and sediment delivery model (WATEM/SEDEM). Based on the model, two indicators of connectivity were developed: the area of sedimentologically effective catchment area (SEA) that contributes sediment to the sinks, and the minimum sediment output of locations on the flow path that link sources and sinks. This approach effectively represents the annual status of catchment-scale sedimentological connectivity and, furthermore, the simple structure and readily available input data make it highly practicable. However, for larger river systems in which sediment transport between sources and sinks occur over longer time scales and larger spatial scales, we suggest different techniques for quantifying the sediment flux and parameters delineating the physical coupling of landscape units.     

气候和土地利用变化影响下生态屏障带水土流失趋势研究

受气候和地形等诸多因素影响，我国"两屏三带"国家生态屏障带中的川滇-黄土高原区域和南方丘陵带水土流失十分严重，自然灾害频发。但是，针对川滇-黄土高原区域和南方丘陵带水土流失时空格局变化，特别是未来气候变化和土地利用变化影响下水土流失变化趋势的研究很少。因此，本研究以川滇-黄土高原区域和南方丘陵带为研究对象，利用修正土壤流失方程（RUSLE）定量分析了该区在2000-2015年水土流失的时空变化规律及其影响因素，并预测了在RCP2.6和RCP4.5的未来气候情景下及土地利用变化条件下水土流失的变化趋势。研究结果表明：（1）黄土高原地区在植被恢复的积极作用下，水土流失显著缓解；（2）川滇地区的西南部因植被盖度的增长和降雨的减少水土流失显著缓解，但四川省境内人口密集区农田面积增加以及降水增加造成水土流失大幅度加剧；（3）南方丘陵带受降水增加影响导致了部分区域的水土流失恶化；（4）在未来气候变化情景下，由于大部分地区降雨将减少使土壤侵蚀趋于缓解，但四川、黄土高原和南方丘陵带大部分地区仍然面临未来农田面积增加带来的水土侵蚀压力。考虑到未来气候变化情景下降雨减少的趋势，建议在黄土高原地区提高草地在土地利用类型中的占比，在减少耗水量的同时维持地表盖度，缓解水土侵蚀；此外，各区域仍需控制农田面积，而且需通过加强坡耕地上保水保土耕作措施降低农田区域的土壤侵蚀压力。     

在黄土丘陵区土质路面种草

土质道路水土流失是所有人工生态系统中最严重的土地利用类型,土壤侵蚀模数是相同条件下林地的250倍,农村道路修筑破坏了区域生态景观的完整性,为景观生态修复理论与技术研究提供了重要的实验场地。广大山区农村田间地块道路在种植和收获季节以外长期处于闲置状态,这为植物的种植和生长提供了可能。1997～2001年,以中国黄土丘陵区陕西省延安市小砭沟小流域农田道路为背景,以防止和减轻路面汇流引发的水土流失对道路的破坏和修复农村道路景观生态系统为目的,采用小区径流监测、施工统计和定点观测的方法,在路面进行了为期5a的种草实验。研究结果显示,农田作业道路路面不仅可以种草,而且具有一定生态经济价值,在条播下,胡枝子、小冠花、无芒雀麦每km年产值可达1068.88～3150.27元;同时,路面牧草可承受适度的通行压力,禾本科牧草一般可承受300t·次/a以下车辆碾压;道路种植禾本科牧草后,除有机质外,土壤中其它营养成份均有不同程度的亏损,因此有必要补充各种肥料延长路面牧草使用年限和提高牧草防蚀能力;路面种草后径流量减少46.15%～69.30%,土壤侵蚀量减少54.53%～77.80%,建设成本仅为石子路的27.69%～35.99%,维护费用仅为土质道路的30.52%,是一种经济可行的技术途径。道路种草后,路面雨季泥泞、旱季尘土飞扬的劣质景观被蜿蜒的绿色道路景观所取代,形似镶嵌在绵延山谷中的绿飘带,这无论在理论还是技术方面都是生态修复学和景观生态学研究的重要方向之一。     

Influence of market orientation on food plant diversity of farms located on Amazonian Dark Earth in the region of Manaus, Amazonas, Brazil

Homegardens may serve as reservoirs of agro-biodiversity on highly fertile, anthropogenic Amazonian Dark Earth (ADE) soils of the Amazon basin. However, as these soils are used more intensively for market-oriented agriculture, we suspected a decrease in their agro-biodiversity. We present data obtained from surveys on 16 farms where ADE was present in the region of Manaus, Amazonas, Brazil. When farms were separated into two groups by market orientation, species richness on the farms was not significantly influenced by market orientation, but there was less dominance (i.e., more diversity) for homegardens in the low-market orientation group (P < 0.1). The proportion of native species was not affected by market orientation. Hence, while the most market-oriented farms retained high species richness, homegardens located on them contained higher proportions of commercially interesting species.