The lack of top-down control on Tripneustes gratilla, a sea urchin commonly known to graze on seagrass, and the bottom-up control of its feeding preference, led to the overgrazing of seagrass meadows of the species Thalassodendron ciliatum in Changuu Island (Zanzibar Archipelago). The impact of overgrazing on seagrasses was assessed by mapping the presence of grazed versus non-grazed seagrass patches in the study site, while the top-down control on T. gratilla was assessed by measuring the abundance of its fish predators. The feeding preference and distribution of T. gratilla were characterized by calculating the electivity indexes for each seagrass species and measuring sea urchin density, respectively. Approximately half of the patches of T. ciliatum were overgrazed, while predatory fishes of T. gratilla were absent from the site. The Vanderploeg and Scavia's Relativized Electivity Index indicated that T. gratilla had a feeding preference for T. ciliatum, which was also supported by higher urchin densities within T. ciliatum dominated patches. Bottom-up control of grazing activity was observed by quantifying and analyzing morphological, nutritional, and the chemical defense traits of the seagrass in relation to feeding preference and urchin density. Feeding was positively correlated to the seagrass tissue C:P ratio (ρ = 0.9), whereas urchin density showed no correlations. The bottom-up control of the feeding preference and agglomeration of T. gratilla in T. ciliatum meadows, together with the lack of evidence of substantial top-down control and the long recovery time of T. ciliatum led to the overgrazing of this species at this site. Overgrazing, therefore, was shown to be the result of multiple factors ranging from the traits of the seagrass and feeding preference of T. gratilla, to the abundance of predators in this area. 相似文献
We present a detailed analysis of the variations in spectral properties across the surface of Saturn’s satellite Dione using Cassini/VIMS data and their relationships to geological and/or morphological characteristics as seen in the Cassini/ISS images. This analysis focuses on a local region on Dione’s anti-saturnian hemisphere that was observed by VIMS with high spatial resolution during orbit 16 in October 2005. The results are incorporated into a global context provided by VIMS data acquired within Cassini’s first 50 orbits. Our results show that Dione’s surface is dominated by at least one global process. Bombardment by magnetospheric particles is consistent with the concentration of dark material and enhanced CO2 absorption on the trailing hemisphere of Dione independent of the geology. Local regions within this terrain indicate a special kind of resurfacing that probably is related to large-scale impact process. In contrast, the enhanced ice signature on the leading side is associated with the extended ejecta of the fresh impact crater Creusa (∼49°N/76°W). Although no geologically active regions could be identified, Dione’s tectonized regions observed with high spatial resolution partly show some clean H2O ice implying that tectonic processes could have continued into more recent times. 相似文献
We present several equilibrium runs under varying atmospheric CO2 concentrations using the University of Victoria Earth System Climate Model (UVic ESCM). The model shows two very different
responses: for CO2 concentrations of 400 ppm or lower, the system evolves into an equilibrium state. For CO2 concentrations of 440 ppm or higher, the system starts oscillating between a state with vigorous deep water formation in
the Southern Ocean and a state with no deep water formation in the Southern Ocean. The flushing events result in a rapid increase in atmospheric temperatures, degassing of CO2 and therefore an increase in atmospheric CO2 concentrations, and a reduction of sea ice cover in the Southern Ocean. They also cool the deep ocean worldwide. After the
flush, the deep ocean warms slowly again and CO2 is taken up by the ocean until the stratification becomes unstable again at high latitudes thousands of years later. The
existence of a threshold in CO2 concentration which places the UVic ESCM in either an oscillating or non-oscillating state makes our results intriguing.
If the UVic ESCM captures a mechanism that is present and important in the real climate system, the consequences would comprise
a rapid increase in atmospheric carbon dioxide concentrations of several tens of ppm, an increase in global surface temperature
of the order of 1–2°C, local temperature changes of the order of 6°C and a profound change in ocean stratification, deep water
temperature and sea ice cover. 相似文献
AbstractMulti-stakeholder sustainability certification schemes have become a favorite instrument for applying good governance, though studies indicate their inefficiency at the producer level. In this study, we used a mixed-method approach to first, map the institutional context of independent oil-palm smallholders in rural Sumatra while, second, reflecting upon the impact of the Smallholder Standard proposed by the Roundtable on Sustainable Palm Oil on smallholder management practices. We hold that non-recognition of micro-scale perspectives within governance processes may partially explain noncompliance with certification principles among smallholders. The Smallholder Standard appears unable to mitigate challenges important for smallholders, who in turn cannot properly comply with it, due to problems including weather instability and high management costs. We suggest that certification schemes need to work on some overlooked but essential preconditions of good governance, namely gaining micro-level visibility and acceptance. 相似文献
Climate engineering (CE) and carbon capture and storage are controversial options for addressing climate change. This study compares public perception in Germany of three specific measures: solar radiation management (SRM) via stratospheric sulphate injection, large-scale afforestation, and carbon capture and storage sub-seabed (CCS-S). In a survey experiment we find that afforestation is most readily accepted as a measure for addressing climate change, followed by CCS-S and lastly SRM, which is widely rejected. Providing additional information decreases acceptance for all measures, but their ranking remains unchanged. The acceptance of all three measures is especially influenced by the perceived seriousness of climate change and by trust in institutions. Also, respondents dislike the measures more if they perceive them as a way of shirking responsibility for emissions or as an unconscionable manipulation of nature. Women react more negatively to information than men, whereas the level of education or the degree of intuitive vs reflective decision making does not influence the reaction to information.
POLICY RELEVANCE
Current projections suggest that the use of climate engineering (CE) technologies or carbon capture and storage (CCS) is necessary if global warming is to be kept well below 2°C. Our article focuses on the perspective of the general public and thus supplements the dialogue between policymakers, interest groups, and scientists on how to address climate change. We show that in Germany public acceptance of potentially effective measures such as SRM or CCS-S is low and decreases even more when additional information is provided. This implies that lack of public acceptance may turn out to be a bottleneck for future implementation. Ongoing research and development in connection with CCS-S and SRM requires continuous communication with, and involvement of, the public in order to obtain feedback and assess the public’s reservations about the measures. The low level of acceptance also implies that emission reduction should remain a priority in climate policy. 相似文献
Reservoirs can be viewed as sentinels of their catchments and a detailed monitoring of reservoir systems informs about biogeochemical and hydrological processes at the catchment scale. We developed a comprehensive online monitoring system at Rappbode reservoir, the largest drinking water reservoir in Germany, and its inflows. The Rappbode Reservoir Observatory comprises of a set of online-sensors for the measurement of physical, chemical, and biological variables and is complemented by a biweekly limnological sampling schedule. Measurement stations are deployed at the four major inflows into the system, at the outlets of all pre-reservoirs, as well as in the main reservoir. The newly installed monitoring system serves both scientific monitoring and process studies, as well as reservoir management. Particular emphasis is paid to the monitoring of short-term dynamics and many variables are measured at high temporal resolution. As an example, we quantitatively documented a flood event which mobilised high loads of dissolved organic carbon and changed the characteristics of the receiving reservoir from eutrophic to dystrophic within a few days. This event could have been completely missed by conventional biweekly sampling programs, but is relevant for biogeochemical fluxes at the catchment scale. We also show that the high frequency data provide a deeper insight into ecosystem dynamics and lake metabolism. The Rappbode Reservoir Observatory; moreover, offers a unique study site to apply, validate, and develop state of the art lake models to improve their predictive capabilities. 相似文献
In this article, we contribute to a better understanding of contextual differences related to residential segregation. We illuminate one specific contextual factor—housing oversupply—and how it intersects with historically inherited patterns of socio-spatial differentiation and other drivers of residential segregation. The study is based on an analysis of how segregation has developed over the last 20 years in the city of Leipzig, Germany. This case offers the rare possibility of studying the impact of city-wide housing oversupply on residential segregation, rather than concentrating on decline or decay in specific areas. We examine how oversupply emerged at the meeting point of changes in market structures, housing preferences, welfare state interventions, and migration trends in the post-socialist transition. Using existing statistical data, we demonstrate how oversupply has fostered a fast and thorough reshuffling of residential patterns. After a period of resolving segregation patterns from the socialist era, oversupply acts as a catalyst for recently emerging residential segregation patterns. 相似文献