Seston transport and deposition in Pelorus sound,south Island,New Zealand

Transport of seston (suspended sediment) in Pelorus Sound is controlled by tides and freshwater inflow. During high freshwater inflow, a moderately stratified estuarine circulation may be superimposed on the tidal circulation, but the latter dominates and transports seston seawards and landwards with the ebb and flood phases respectively. With extreme freshwater inflow, the estuarine circulation gains impetus and most seston is rapidly transported seaward in the low saline surface layer.

Irrespective of circulation there is a persistent trend in seston concentrations. Highest values occur at the sound's head because of the influence of nearby Pelorus and Kaituna Rivers and because of resuspension of bottom sediment by strong tidal currents. Seston concentrations wane along the sound until near the entrance, where values increase as a result of greater production of biogenic seston and because additional seston is brought in from Cook Strait with the flood tide. This trend parallels variability in the thicknesses of muddy bottom sediments. Muds are thick at the head where an extensive delta extends from the river mouths; muds gradually thin seaward and then thicken markedly in the vicinity of the sound entrance.

Seston weight and composition patterns and 3.5 kHz seismic profiles indicate Pelorus Sound acts as a double‐ended sediment trap. The upper reaches receive and retain river‐derived seston, whereas the sound entrance traps seston derived from Cook Strait. This situation appears to hold for both high and extremely high influxes of sediment.     

Invertebrate recolonisation of previously dry channels in the Rakaia River

Recolonisation of previously dry channels by stream invertebrates was studied in the Rakaia River during winter 1981 and summer 1982. The winter experiment continued for 42 days, with stable low flows, whereas the summer experiment was characterised by fluctuating large flows which caused it to be abandoned after 27 days. The fauna was dominated numerically by Chironomidae, a leptophlebiid mayfly (Deleatidium), and oligochaetes during the winter, and by Deleatidium alone during the summer. Recolonisation was considered complete after 33 days in winter and 15 days in summer. Flow fluctuations were the main factor affecting colonisation rates, and it was assumed that drift was the main source of colonising animals. Small freshes during low‐flow periods in winter resulted in a rapid increase in total density of invertebrates and number of taxa present and also affected the population structure of Deleatidium larvae in colonisation baskets. Before these freshes numbers had increased steadily over a 27 day period. In summer large floods during high flow periods initially decreased benthic invertebrate numbers in samples but numbers increased rapidly once the flood had passed. This appears to be the first study of its kind on a large unstable river system.     

Critical depths for passage in braided rivers,Canterbury, New Zealand

Riffles and points of divergence of branch channels in braided rivers are critical controls upon passage of fish and recreational boats because they are points at which depths are at a minimum. Depths on randomly selected riffles were measured in braided reaches of the Ashley, Hurunui, and Rakaia Rivers and related to discharge; minimum depths encountered in extended reaches of these rivers at a range of flows have also been measured. The data can be used to predict minimum available passage depths at a specified flow, or conversely, to predict the discharge required to maintain a specified minimum passage depth. However, presently available estimates of critical minimum depths required for various instream uses (migration of salmonids, jetboating) appear excessively conservative, and minimum depth requirements must be more accurately determined before instream flow needs can be properly assessed.     

The barnacles Chirona (Striatobalanus) amaryllis (Darwin 1854) and Megabalanus coccopoma (Darwin 1854) (Crustacea,Cirripedia): two invasive species new to tropical West African waters

The collection of the barnacle Chirona (Striatobalanus) amaryllis (Darwin 1954) (Crustacea, Cirripedia) from the hull of a ship that had been operating for five months in the Gulf of Guinea and off Sierra Leone triggered a closer investigation of the cirriped fauna of the West African coast. Both C. amaryllis and Megabalanus coccopoma can now be added to the list of successful invasions in tropical West African waters. This discovery, as well as the circumstances of the findings, necessitates an update of the invertebrate faunal inventory of tropical West African marine waters.     

Recovery of benthic macroinvertebrate and epilithic communities following a large flood,in an unstable,braided, New Zealand river

Benthic macroinvertebrates and small stones were collected from a riffle in the Ashley River, North Canterbury, New Zealand, on 12 occasions within a 132‐day period following a particularly large flood in 1986. Despite the occurrence of smaller floods during this period, benthic macroinvertebrate communities and stone surface organic layers recovered rapidly. Mean concentration of stone surface organic carbon increased from 0.23 g/m² to 1.01 g/m² stone surface in the first 23 days after the flood and chlorophyll a concentration increased from 0.13 mg/m² (day 3) to 9.2 mg/m² by day 132. Minor floods during the recovery period had little effect on organic layer biomass. Mean faunal density increased from 230/m² to 7920/m² during this time and taxon richness from 7 to 21 per 5 benthic samples. Immediately after the flood and throughout the study period the fauna was dominated by larvae of Deleatidium (Ephemeroptera: Leptophlebiidae), Hydora (Coleoptera: Elmidae), and Chironomidae. Re‐establishment of Deleatidium populations in previously denuded brands was effected by oviposition, egg‐hatching, and larval immigration. Minor braids are likely to represent important epicentres from which recolonisation proceeds.     

Land‐use impacts and water quality targets in the intensive dairying catchment of the Toenepi Stream,New Zealand

Water quality monitoring in Toenepi Stream, New Zealand, started in 1995 in a study of dairy farming influences on lowland stream quality and has continued since then with brief interruptions. Surveys have provided information about changes in farm and soil management practices as they relate to environmental sustainability. Although average water quality in Toenepi Stream has changed little during 1995–2004, there have been some notable improvements. Water clarity measured by black disc has improved from 0.6m to 1.5m, and median ammonia‐N and nitrate‐N concentrations have declined by 70% and 57%, respectively. The frequency and magnitude of extreme concentrations have declined—most notably for nitrogen (N) forms, which also had decreased mean values. Specific yields for suspended solids (SS) and phosphorus (P) forms in 2002–04 were 47–67% of 1995–97 values, mainly because of lower water yields. Reduced specific yields for N forms in 2002–04 (34–37% of 1995–97 yields) were also attributable to lower mean concentrations in stream water. Faecal bacteria concentrations have not abated and are on average 2–3 times recommended guideline values for contact recreation. Fewer dairy farms and an increased proportion irrigating dairyshed effluent to land, rather than discharging it to the stream via two‐pond systems, were likely causes of improvement in water quality. Water quality targets were developed for Toenepi Stream to achieve contact recreation criteria for the Piako River (downstream) and for intrinsic habitat values for Toenepi Stream. A range of mitigation measures has been formulated to meet these targets, but substantial uptake of sustainable farming practices is needed to improve water quality in Toenepi Stream.     

亚洲夏季风各子系统主要变率相互关系初析

使用NCEP/NCAR再分析资料和CMAP月平均降水资料分析了亚洲夏季风各个子系统的相互关系。结果表明亚洲夏季风子系统之间存在显著相关。从同期强度变化可知,当东亚季风偏强时,大尺度亚洲季风、东南亚季风、南亚季风均偏弱,相关区域降水偏少;而同时大尺度亚洲季风偏强时,东南亚和南亚季风偏强,相关区域降水偏多;东南亚季风偏强时,南亚季风偏弱,南亚地区降水偏少;反之亦然。从不同周期强度变化可知各个子系统相关仍然显著。      

基于MODIS NDVI的西辽河流域主要粮食作物时空分布格局

研究以西辽河流域为案例区,以MODIS遥感数据为基础,选取2000、2005和2010年时间点,利用NDVI时间序列信息,结合西辽河流域不同作物物候历,运用决策树提取模型,获取西辽河流域春玉米、春小麦和大豆等主要作物的空间分布信息,定量揭示了10年间西辽河流域主要粮食作物的时空分布特征。研究表明：（1）2010年西辽河流域主要粮食作物播种面积为11 965.08 km2,其中春玉米播种面积约占流域主要粮食作物的92.28%,集中在西辽河流域下游地区;春小麦播种面积占比3.14%,以西辽河流域中游面积最大;大豆播种面积占比4.58%,以西辽河上游流域面积最大。（2）2000-2005年西辽河流域主要粮食作物播种面积大幅增加,涨幅达29.77%,集中在西辽河流域下游地区。其中,春玉米播种面积增长38.99%,春小麦播种面积减少39.04%,大豆播种面积增长21.27%。（3）2005-2010年西辽河流域主要粮食作物播种面积增长缓慢,涨幅为5.18%,集中在西辽河流域下游地区。春玉米播种面积呈现增加趋势,春小麦呈现减少趋势,大豆呈减少趋势。     

亚洲大陆主要活动块体的现今构造应力数值模拟

亚洲大陆晚新生代和现代构造变形以活动地块为主要特征,表现为在统一构造格局下不同地块间具有不同的运动方式和速度。为了研究这些具有不同运动学性质块体间的相互作用以及构造变形特征,基于亚洲大陆的总体构造格局构建了二维有限元模型。根据模拟结果,对比已知GPS数据、震源机制解以及地质调查数据等,定量分析了大陆内部主要活动地块构造应力场的分布特征,并探讨了影响亚洲大陆现今构造变形特征的主要因素。结果表明：在我国的西部陆块内,由于周边一系列近EW向弧形活动构造带的存在,导致其内部次级块体运动速率的衰减,从而进一步导致应力环境的变化,由青藏中部的挤压-拉张环境逐渐转变为塔里木、天山地区的完全挤压环境;在西伯利亚地块和印度板块的联合挤压作用下,华北地块上地壳的应力表现为较弱的挤压环境,而在该种应力环境下块体内部伸展构造的成因很可能与其深部的动力学环境有关;华南地块的运动方向与台湾造山带相反,从而形成一个秦岭-大别造山带以南的较强烈的挤压-拉张区;在印度-澳大利亚板块和菲律宾俯冲板块的联合挤压作用下,巽他地块作为华南地块和印支地块的逃逸窗口,表现出以婆罗洲、南海为中心近圆弧形的弱挤压区以及环绕挤压区外缘挤压-拉张区的应力分布特征。     

南亚高压强度的年代际变化及可能原因分析

利用NCEP/NCAR再分析资料和NOAA ERSST海温资料,对夏季南亚高压的年代际变化特征及其可能机制进行了分析。结果表明,南亚高压由弱到强的年代际转折发生在1970年代末,或者说南亚高压强度在1978年前后发生了年代际突变。对南亚高压偏弱和偏强两个阶段的对比分析表明,大气环流(包括风场、温度场和垂直运动场等)的异常形势和特征显著不同,几乎是相反的。夏季地表潜热通量异常的分析说明,夏季高原(特别是高原西北部)的地表热通量异常对南亚高压强度的年代际变化有重要影响;相对而言,地表感热通量异常可能对南亚高压强度的年代际变化起更重要作用。夏季热带印度洋海温的全区一致型模态在1970年代末也发生了明显的年代际变化,与南亚高压强度的年代际异常有很好的一致性,表明夏季热带印度洋海温一致型模态异常对南亚高压年代际变化有影响。