Planning for the extraction of aggregates is typically dealt with at a case to case basis, without assessing environmental impacts strategically. In this study we assess the impact of sand mining in Poyang Lake, where dredging began in 2001 after sand mining in the Yangtze River had been banned. In April 2008 concern over the impact on the biodiversity led to a ban on sand mining in Poyang Lake until further plans could be developed. Planning will require consideration of both sand extraction in relation to available sediment resources and also environmental impacts within the context of future demand for sand in the lower Yangtze Valley. We used pairs of near-infrared (NIR) Aster satellite imagery to estimate the number of vessels leaving the lake. Based on this we calculated a rate of sand extraction of 236 million m 3 year -1 in [2005][2006]. This corresponds to 9% of the total Chinese demand for sand. It qualifies Poyang Lake as probably the largest sand mining operation in the world. It also indicates that sand extraction currently dominates the sediment balance of the lower Yangtze River. A positive relation between demand for sand and GDP, revealed by historic data from the USA, suggests that the current per capita demand for sand in China might increase in the near future from 2 to 4 m 3 year -1 . We review various environmental impacts and question whether it will be possible to preserve the rich biodiversity of the lake, while continuing at the same time satisfying the increasing Chinese demand for sand. Finally we review alternative options for sand mining, in order to relieve the pressure from the Poyang Lake ecosystem.

SummaryFollowing an abnormal flood in 2010 at China’s Poyang Lake, we observed wintering Siberian Cranes Leucogeranus leucogeranus switch from foraging in the shallow-water wetlands they typically use to grassland habitats. These previously undocumented habitat selection patterns raised questions whether differences in crane behaviour such as foraging success existed between the two habitats and how those differences might affect this critically endangered species. Over two winters, we used the density of customary food items (tubers of Vallisneria spp.) obtained from long-term monitoring efforts, Siberian Cranes flock behaviours, individual foraging success and estimated total flock foraging effort across both habitats. Novel foraging patterns by Siberian Cranes were associated with low densities of Vallisneria tubers across multiple sub-lakes within Poyang Lake National Nature Reserve (PLNR). Foraging success was higher in grasslands than in wetlands in winter 2010–2011, but higher in wetlands following a recovery of Vallisneria in 2011–2012. Subsequent to upland foraging during the winter of 2010–2011, we observed lower juvenile to adult ratio of Siberian Cranes at a fall migratory stopover location in north-eastern China despite indications of average environmental conditions in the nesting areas from 2010 to 2012. While grasslands adjacent to shallow-water habitats may be important refugia for wintering Siberian Cranes when Vallisneria is absent or inaccessible, and should be included in protected areas, multi-year dependence on grasslands for foraging could negatively impact population levels. Eliminating crab farming in protected areas and extending protection to shallow water areas sheltered from flooding by dykes could also help secure high quality foraging habitat under a variety of hydrological regimes. Novel foraging patterns by wintering Siberian Cranes represent a new challenge to the conservation efforts for this species that focus on shallow-water wetlands, and may be indicative of broader changes within Poyang’s ecosystem.

Poyang Lake is a very important wintering place for cranes in China and East Asia. Two crane surveys were conducted at Poyang Lake during the 2011/2012 winter, the first on 18-19 December 2011 and the second on 18-19 February 2012. The survey covered the entire Poyang Lake basin, as well as two main lakes in Jiujiang (Saicheng Hu and Chi Hu), i.e., a total of 85 sub-lakes were surveyed. Both surveys recorded four species of cranes. The first survey on 18-19 December 2011 recorded 4577 Siberian Cranes (Grus leucogeranus), mostly in Bang Hu, Sha Hu and Dahu Chi, 302 Hooded Cranes (G. monacha), 885 White-naped Cranes (G. vipio) and 8408 Eurasian Cranes (G. grus), for the most part in the center of the lake basin. The second survey on 18-19 February 2012 recorded 3335 Siberian Cranes (mostly in Poyang Lake National Nature Reserve (PLNR) and its surrounding areas), 110 Hooded Cranes (largely in PLNR and its surrounding areas), 283 White-naped Cranes (86% in Bang Hu) and 2205 Eurasian Cranes (particularly in Duchang and Nanjishan NNR). The number of Siberian Cranes enumerated in December was 1000 more than the second count in February 2012. It is not possible to rule out double counting due to the close proximity of the main sites of the Siberian Cranes. During winters from 1998 to 2009, the average of the highest counts each winter was 3091, ranging from 2345 in 1996 to 4004 in 2002. By comparison with counts taken at other times, we therefore estimate a wintering population of Siberian Cranes of ~3800-4000 at Poyang Lake. Additional evidence will be needed to raise the world population estimate. Our more recent surveys indicate a continuing decline in the number of White-naped Cranes and an increase in Eurasian Cranes.

Poyang Lake, the largest freshwater wetland in China, provides critical habitat for wintering waterbirds from the East Asian Flyway; however, landscape drivers of non-uniform bird diversity and abundance are not yet well understood. Using a winter 2006 waterbird survey, we examined the relationships among metrics of bird community diversity and abundance and landscape characteristics of 51 wetland sub-lakes derived by an object-based classification of Landsat satellite data. Relative importance of predictors and their sets was assessed using information-theoretic model selection and the Akaike Information Criterion. Ordinary least squares regression models were diagnosed and corrected for spatial autocorrelation using spatial autoregressive lag and error models. The strongest and most consistent landscape predictors included Normalized Difference Vegetation Index for mudflat (negative effect) and emergent grassland (positive effect), total sub-lake area (positive effect), and proportion of submerged vegetation (negative effect). Significant spatial autocorrelation in linear regression was associated with local clustering of response and predictor variables, and should be further explored for selection of wetland sampling units and management of protected areas. Overall, results corroborate the utility of remote sensing to elucidate potential indicators of waterbird diversity that complement logistically challenging ground observations and offer new hypotheses on factors underlying community distributions.

Poyang and Dongting Lakes, major water resources and key elements for natural flood control and reduction within the Yangtze River middle basin, were monitored from 2000 to 2008, with a re-visiting period of 10 days, using ENVISAT ASAR, and completed by MODIS data, validated by Beijing 1 time series. GPCP and TRMM time series were utilized to derive regional meteorological indicators. At the lake scale as well as their subdivisions ones, results allowed the characterization of lake behaviors. Even if the Dongting and Poyang lakes mechanisms are substantially different, their water surface areas and water level variations exhibit a good similarity, including the same year of major flooding (2002) and the same year of lowest extent of inundation (2001). Both lakes present astonishingly low water levels and low surface areas in summer of 2006, being associated with a very early draw-off. Few reasons could explained it: (i) a rainfall deficit at the sub-watershed level; (ii) a hydrological event in the upper stream part, namely a possible closure of the Three Gorges Dam (TGD) gates; or (iii) a global climate change effect at the regional scale. The reasons for the dramatic water dropdown are neither a local rain deficit nor a change in the TGD management. The smallest water extent for wet season observed in 2006, appeared to be linked with a severe drought within the upper stream part of the Yangtze River basin. In addition, an impressive decreasing tendency of water surface and level is observed in the middle reaches of the Yangtze River, linked with relatively constant decreasing precipitations over the last decade. This synergistic utilization of data from earth observation systems and in situ data provide valuable information on water resource management at the scale of the middle Yangtze River watershed.

Le lac Poyang, première réserve d'eau douce de Chine, est un lac de moussons présentant de fortes variations de surfaces en eau entre la saison sèche, novembre-mars, et la saison humide juin-septembre. Les surfaces en eau passent ainsi de plus de 3000 km2 en été, à moins de 1000 km2 en hiver, cela correspondant à une variation inter annuelle de la hauteur de l'eau de 8 à 12 mètres. En saison sèche, la dépression du Poyang comprend une cuvette centrale en eau de taille réduite, et des lacs déconnectés entourés de vastes zones enherbées plus ou moins hautes. Lorsque le niveau d'eau augmente, la grande dépression centrale se remplit, puis au fur et à mesure du remplissage, comme une marée montante, l'eau arrive au niveau des lacs, les submerge et l'ensemble forme alors une petite mer intérieure d'eau douce. Cette dynamique et cette amplitude de variations ont de nombreuses implications en termes de ressources en eau, de santé publique (bilharziose), et mais aussi de richesse de la biodiversité.Le lac Poyang est un des milieux les plus riches et les plus importants en termes de biodiversité en Asie du Sud Est. Il s'agit d'une zone d'hivernage essentielle pour toute l'avifaune de l'Asie et de Sibérie. Plus de trois cents espèces d'oiseaux dépendent de cet habitat unique dont plus d'une douzaine d'espèces considérées en danger. Les plus emblématiques sont les grues de Sibérie et les cigognes blanches orientales dont la quasi-totalité, 98% de la population mondiale (moins de 3000 individus) viennent hiverner au Poyang. Cette de grande diversité d'oiseaux d'eau migrateurs est une conséquence directe de l'hydrologie complexe du lac Poyang.La forte variabilité intra et interannuelle du remplissage du Poyang, est un phénomène difficile à qualifier, c'est pourquoi un suivi temporel à relative haute fréquence est nécessaire. Dans le cadre de la RTU Pléiades HR, des acquisitions sur une base mensuelle ont été programmées au cours de l'année 2013 couvrant la partie la plus riche et sensible de la Reserve Naturelle du lac Poyang (PLNR). L'exploitation des données a porté sur plusieurs axes. Tout d'abord la caractérisation, à une échelle fine, des trajets de l'eau et de la dynamique de remplissage et de vidange des lacs, mettant en évidence un remplissage plutôt tardif et peu important au regard des observations réalisées les 12 dernières années, et surtout une vidange très précoce (fin juillet, entrainant par exemple la vidange totale du Bang Hu, principal site d'accueil des grues sibériennes). Les travaux ont également portés sur l'autre principale composant du milieu naturel, la végétation et sa dynamique inverse de l'eau. A partir des relevés terrain, le long de quatorze de transects, des indices de végétation ont été exploités afin de réaliser la cartographie de la végétation de ce secteur clé du lac Poyang. Les travaux ont également portes portés sur l'impact des activités anthropiques sur le milieu avec deux atteintes fortes, la mise en place de zones de cultures au sein du Parc national, et l'exploitation du lac Poyang comme carrière de sable se traduisant par un fort retrait des berges et un creusement des lits mineurs. Enfin, l'exploitation des données Pléiades HR, associées à des données CSK a permis de lever la première carte des filets de pêche au sein de la Reserve naturelle. De plus, deux triplets stéréo ont été acquis lors de périodes de basses hautes en en mars et septembre 2013, permettant la génération de modèles numériques de surfaces très précis et très détaillés.Les résultats obtenus suite à l'exploitation des images Pléiades HR, transmis à l'administration en charge de la gestion du Parc et à une ONG, l'International Crane Fondation, montrent l'apport des données Pléiades HR pour le suivi environnemental et aussi tout l'intérêt de séries temporelles très haute résolution pour la connaissance, et par la même, la protection des milieux.

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