Biogeochemical mass-balances (C, N, P, Si) in three large reservoirs of the Seine Basin (France)

Three major reservoirs (Marne, Seine and Aube), situated in the upstream basin of the river Seine represent a storage capacity of 800 10⁶ m³. In order to quantify the possible role of these reservoirs as a sink or source of nutrients and organic matter for the river system, an input/output mass-balance of suspended matter, organic carbon, inorganic nitrogen forms, phosphorus and reactive silica was established, providing reliable estimates of their retention/elimination and export. The study was carried out over 3 years (1993, 1994 and 1995) in differing hydrological conditions. The retention times varied from 0.3 to 0.8 year, depending on the reservoir and the year, but was longer in 1993 that was a drier year than 1994 and 1995, hydrologically quite similar.Regarding retention (or elimination) and export, the behaviour of the three studied reservoirs was similar. A clear loss or retention of nitrogen, phosphorus and silica was observed in the reservoirs and represented about 40% of the incoming flux of nitrate, 50% of silica, and 60% of phosphate. The retention was lower for total phosphorus than for phosphate. The reservoirs are also sites of suspended matter deposition except during the decennial drawdown, when suspended matter is exported. For inorganic nitrogen, the average amount of nitrate retained in the Seine basin reservoirs upstream from Paris is 5000 tonnes y^–1 that is almost equal to the estimated retention by deposition or denitrification in river channel sediments for the whole drainage network. The retention in the reservoirs represents about 12% of the total flux of nitrate at the outlet of the basin upstream from Paris, and 5% at the mouth of the Seine River.We also calculated inlake C, N, P, Si budgets on the basis of direct process measurements. Measurements of planktonic primary and bacterial activity production led to annual net production of 4200 and 580 tonnes of carbon, respectively. A reasonable value (450 tonnes of carbon) of grazing was calculated. Corresponding N, P, Si fluxes were drawn from appropriate C:N:P:Si ratios. Benthic fluxes were measured with bell jars. The retention of P and Si represents a small fraction of important internal fluxes of phytoplanktonic uptake and recycling, while inorganic nitrogen retention depends mostly on benthic denitrification. The behaviour of P and Si differs in that P is mainly recycled in the water column, while Si dissolution occurs at the sediment interface. Nitrogen is recycled in both the planktonic and the benthic phase.     

Effects of changes in discharge level on temperature and oxygen regimes in a new reservoir and downstream

Temperature and oxygen regimes were monitored weekly in a four-year old reservoir and downstream for ten weeks during the summer (May 15 to July 30, 1979), and monthly in the fall and winter. During the summer discharge levels were changed from top to bottom in the eighth week, back to top in the ninth, all at 0.71 m³/s (= 25 cfs), and returned to the bottom in the tenth, but at 1.14 m³/s (= 40 cfs). Changing the discharge level had little or no impact on the thermal regime within the lake or downstream at 1.14 m³/s and only a moderate impact on water in the lake near the dam at 0.71 m³/s bottom discharge by generating double thermoclines. Oxygen depletion rates were greatest near the surface of the lake, mainly due to temperature effects, but increased greatly at the 3 m depth, the level of the top discharge port, when discharge was changed from bottom to top. Discharge of anoxic waters through the bottom of the dam caused a drop in oxygen content immediately downstream but oxygen content returned to inflow values within 1 km downstream of the dam.     

A new forest cover map of continental southeast Asia derived from SPOT‐VEGETATION satellite imagery

Question: Can recent satellite imagery of coarse spatial resolution support forest cover assessment and mapping at the regional level? Location: Continental southeast Asia. Methods: Forest cover mapping was based on digital classification of SPOT4‐VEGETATION satellite images of 1 km spatial resolution from the dry seasons 1998/1999 and 1999/2000. Following a geographical stratification, the spectral clusters were visually assigned to land cover classes. The forest classes were validated by an independent set of maps, derived from interpretation of satellite imagery of high spatial resolution (Landsat TM, 30 m). Forest area estimates from the regional forest cover map were compared to the forest figures of the FAO database. Results: The regional forest cover map displays 12 forest and land cover classes. The mapping of the region's deciduous and fragmented forest cover remained challenging. A high correlation was found between forest area estimates obtained from this map and from the Landsat TM derived maps. The regional and sub‐regional forest area estimates were close to those reported by FAO. Conclusion: SPOT4‐VEGETATION satellite imagery can be used for mapping consistently and uniformly the extent and distribution of the broad forest cover types at the regional scale. The new map can be considered as an update and improvement on existing regional forest cover maps.     

Enzyme activities of aerobic lignocellulolytic bacteria isolated from wet tropical forest soils

Lignocellulolytic bacteria have promised to be a fruitful source of new enzymes for next-generation lignocellulosic biofuel production. Puerto Rican tropical forest soils were targeted because the resident microbes decompose biomass quickly and to near-completion. Isolates were initially screened based on growth on cellulose or lignin in minimal media. 75 Isolates were further tested for the following lignocellulolytic enzyme activities: phenol oxidase, peroxidase, β-d-glucosidase, cellobiohydrolase, β-xylopyranosidase, chitinase, CMCase, and xylanase. Cellulose-derived isolates possessed elevated β-d-glucosidase, CMCase, and cellobiohydrolase activity but depressed phenol oxidase and peroxidase activity, while the contrary was true of lignin isolates, suggesting that these bacteria are specialized to subsist on cellulose or lignin. Cellobiohydrolase and phenol oxidase activity rates could classify lignin and cellulose isolates with 61% accuracy, which demonstrates the utility of model degradation assays. Based on 16S rRNA gene sequencing, all isolates belonged to phyla dominant in the Puerto Rican soils, Proteobacteria, Firmicutes, and Actinobacteria, suggesting that many dominant taxa are capable of the rapid lignocellulose degradation characteristic of these soils. The isolated genera Aquitalea, Bacillus, Burkholderia, Cupriavidus, Gordonia, and Paenibacillus represent rarely or never before studied lignolytic or cellulolytic species and were undetected by metagenomic analysis of the soils. The study revealed a relationship between phylogeny and lignocellulose-degrading potential, supported by Kruskal–Wallis statistics which showed that enzyme activities of cultivated phyla and genera were different enough to be considered representatives of distinct populations. This can better inform future experiments and enzyme discovery efforts.     

大洪河水库库区土地利用变化及其社会经济驱动因素

基于农户访问,结合土地利用和社会经济指标,分析了大洪河水库邻水库区的土地利用变化及其驱动因子.结果表明,库区土地利用变化主要体现在淹没征占和移民安置征用.前者发生了土地利用类型的转化,而后者主要是打破了原有土地权属状况,并使地块更加零碎;库区人均耕地0.041 hm2,低于联合国粮农组织(FAO)警戒线.人均粮食和人均收入均较少,有30.25%的农户一年中有3个月缺粮,且35.27%的居民生活在贫困线以下;库区生态环境状况较差,健康的和较健康的生态系统所占比重较少,分别由环库区缓冲带及水田和经济林果用地生态系统组成;人口快速增长是导致库区人地关系变革的关键因素,乡村经济低下决定库区移民的生产决策,而移民信仰则在一定程度上影响库区土地利用格局,是库区土地利用格局保持稳定的诱导性力量.     

南亚热带不同营养水平水库的蓝藻组成与动态

2004年调查了广东省境内的新丰江水库和契爷石水库的蓝藻分布特征.结果表明:共检测到蓝藻18属,绝大多数为丝状体和群体种类.常见属有假鱼腥藻(Pseudanabaena)、湖生蓝丝藻(Limnothrix)、微囊藻(Microcystis)和蓝纤维藻(Dactylococcopsis).新丰江水库和契爷石水库蓝藻细胞密度分别为4～249和1 911～114 228 cells·ml-1,富营养化的契爷石水库蓝藻细胞密度比贫营养型的新丰江水库高出3个数量级;2座水库最高蓝藻细胞密度均出现在夏季,温度是引起2座水库蓝藻细胞密度的季节性变化的主要因素;在新丰江水库,微囊藻是优势蓝藻种类之一,相对丰度35%～97%,夏季细胞密度高于其它季节;在契爷石水库,虽然微囊藻细胞密度比新丰江水库高出1个数量级,但其相对丰度不超过3%;假鱼腥藻和湖生蓝丝藻是契爷石水库的优势蓝藻种类,多数情况下相对丰度超过50%;水体稳定性和由透明度主导的水体光照条件的差别可能是导致两座水库蓝藻由不同生活类型的种类占优势的主要原因.     

云南热带雨林:特征、生物地理起源与演化北大核心CSCD

云南热带雨林具有与东南亚低地热带雨林类似的群落结构、生态外貌特征和物种多样性,是亚洲热带雨林的一个类型。它的植物区系组成中有90%的属和多于80%的种为热带分布成分,其中约40%的属和70%的种为热带亚洲分布型,它含属种较多的优势科和在群落中重要值较大的科也与亚洲热带雨林相似,是亚洲热带雨林和植物区系的热带北缘类型。云南西南部、南部与东南部的热带雨林在群落结构和生态外貌上类似,但在南部与东南部之间有明显的植物区系分异,它们经历了不同的起源背景和演化历程。云南的热带雨林在很大程度上由西南季风维持。喜马拉雅隆升导致西南季风气候形成和加强,在云南热带局部地区产生了湿润气候,发育了热带雨林植被。现在的云南热带雨林里或其分布地区有落叶物种或热带落叶林存在,这不仅是季节性气候的影响,推测在晚第三纪或第四纪更新世云南热带地区曾经历了干旱气候。云南热带雨林的分布主要受制于局部生境,并非地区性气候条件。     

不同护坡草本植物的根系特征及对土壤渗透性的影响

为明确三峡库区植被边坡植物物种根系特征与土壤渗透性之间的关系,以裸地为对照,应用WinRHIZO(Pro.2004c)根系分析系统对香根草(Vetiveria zizanioides(Lin.) Nash)、百喜草(Paspalum notatum Flugge)、狗牙根(Cynodon dactylon (L) Pers.)和紫花苜蓿(Medicago sativa L.)等4种护坡草本的根系特征进行定量分析.结果表明:(1)紫花苜蓿和香根草的根长密度和根表面积密度显著大于狗牙根和百喜草;(2)不同草本类型和同一草本不同土层之间土壤渗透性存在较大差异,且各草本土壤渗透性随土层深度的增加而降低;相对于裸地而言,4种草本均能显著增强土壤渗透性,其土壤渗透性优劣表现为:香根草＞紫花苜蓿＞百喜草＞狗牙根;(3)土壤的初始入渗率、稳渗率、平均渗透率和渗透总量等各参数均随根长密度和根表面积密度增大而增强,且与直径介于0.5-5 mm不同径级的根系特征之间存在明显的相关性,故根系对土壤渗透性的增强作用主要归功于0.5-5 mm径级的根长密度和根表面积密度;(4)根长密度、根表面积密度对考斯加科夫入渗模型参数K和a有较大影响,随着根长密度和根表面积密度的增加,表征土壤初始入渗率的K值逐渐增大,而表征入渗能力衰减的参数a逐渐减小.