Wetlands have long been drained for human use, thereby strongly affecting greenhouse gas fluxes, flood control, nutrient cycling and biodiversity
. Nevertheless, the global extent of natural wetland ...loss remains remarkably uncertain
. Here, we reconstruct the spatial distribution and timing of wetland loss through conversion to seven human land uses between 1700 and 2020, by combining national and subnational records of drainage and conversion with land-use maps and simulated wetland extents. We estimate that 3.4 million km
(confidence interval 2.9-3.8) of inland wetlands have been lost since 1700, primarily for conversion to croplands. This net loss of 21% (confidence interval 16-23%) of global wetland area is lower than that suggested previously by extrapolations of data disproportionately from high-loss regions. Wetland loss has been concentrated in Europe, the United States and China, and rapidly expanded during the mid-twentieth century. Our reconstruction elucidates the timing and land-use drivers of global wetland losses, providing an improved historical baseline to guide assessment of wetland loss impact on Earth system processes, conservation planning to protect remaining wetlands and prioritization of sites for wetland restoration
.
Consumption of wild-caught freshwater fish is concentrated in low-income countries, where it makes a critical contribution to food security and livelihoods. Underestimation of inland harvests in ...official statistics has long been suspected due to unmonitored subsistence fisheries. To overcome the lack of data from extensive small-scale harvests, we used household consumption surveys to estimate freshwater fish catches in 42 low- and middle-income countries between 1997 and 2014. After accounting for trade and aquaculture, these countries collectively consumed 3.6 MT (CI, 1.5–5.8) more wild-caught freshwater fish than officially reported, reflecting a net under-reporting of 64.8% (CI, 27.1–103.9%). Individual countries were more likely to underestimate (n = 31) than overestimate (n = 11) catches, despite conservative assumptions in our calculations. Extrapolating our findings suggests that the global inland catch reported as 10.3 MT in 2008 was more likely 16.6 MT (CI, 2.3–30.9), which accords with recent independent predictions for rivers and lakes. In human terms, these hidden harvests are equivalent to the total animal protein consumption of 36.9 (CI, 30.8–43.4)million people, including many who rely upon wild fish to achieve even minimal protein intake. The widespread underreporting uncovered by household consumption surveys indicates that inland fisheries contribute far more to global food security than has been recognized previously. Our findings also amplify concerns about the sustainability of intensive fishery exploitation as degradation of rivers, lakes, and wetlands continues apace.
Effect of vaccines on bacterial meningitis worldwide McIntyre, Peter B, Prof; O'Brien, Katherine L, Prof; Greenwood, Brian, Prof ...
The Lancet (British edition),
11/2012, Volume:
380, Issue:
9854
Journal Article
Peer reviewed
Three bacteria—Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis—account for most acute bacterial meningitis. Measurement of the effect of protein-polysaccharide conjugate ...vaccines is most reliable for H influenzae meningitis because one serotype and one age group account for more than 90% of cases and the incidence has been best measured in high-income countries where these vaccines have been used longest. Pneumococcal and meningococcal meningitis are caused by diverse serotypes and have a wide age distribution; measurement of their incidence is complicated by epidemics and scarcity of surveillance, especially in low-income countries. Near elimination of H influenzae meningitis has been documented after vaccine introduction. Despite greater than 90% reductions in disease attributable to vaccine serotypes, all-age pneumococcal meningitis has decreased by around 25%, with little data from low-income settings. Near elimination of serogroup C meningococcal meningitis has been documented in several high-income countries, boding well for the effect of a new serogroup A meningococcal conjugate vaccine in the African meningitis belt.
Fisheries are an essential ecosystem service, but catches from freshwaters are often overlooked. Hundreds of millions of people around the world benefit from low-cost protein, recreation, and ...commerce provided by freshwater fisheries, particularly in regions where alternative sources of nutrition and employment are scarce. Here, we derive a gridded global map of riverine fisheries and assess its implications for biodiversity conservation, fishery sustainability, and food security. Catches increase with river discharge and human population density, and 90% of global catch comes from river basins with above-average stress levels. Fish richness and catches are positively but not causally correlated, revealing that fishing pressure is most intense in rivers where potential impacts on biodiversity are highest. Merging our catch analysis with nutritional and socioeconomic data, we find that freshwater fisheries provide the equivalent of all dietary animal protein for 158 million people. Poor and undernourished populations are particularly reliant on inland fisheries compared with marine or aquaculture sources. The spatial coincidence of productive freshwater fisheries and low food security highlights the critical role of rivers and lakes in providing locally sourced, low-cost protein. At the same time, intensive fishing in regions where rivers are already degraded by other stressors may undermine efforts to conserve biodiversity. This syndrome of poverty, nutritional deficiency, fishery dependence, and extrinsic threats to biodiverse river ecosystems underscores the high stakes for improving fishery management. Our enhanced spatial data on estimated catches can facilitate the inclusion of inland fisheries in environmental planning to protect both food security and species diversity.
The metabolic theory of ecology (MTE) and ecological stoichiometry (ES) are both prominent frameworks for understanding energy and nutrient budgets of organisms. We tested their separate and joint ...power to predict nitrogen (N) and phosphorus (P) excretion rates of ectothermic aquatic invertebrate and vertebrate animals (10,534 observations worldwide). MTE variables (body size, temperature) performed better than ES variables (trophic guild, vertebrate classification, body N:P) in predicting excretion rates, but the best models included variables from both frameworks. Size scaling coefficients were significantly lower than predicted by MTE (<0.75), were lower for P than N, and varied greatly among species. Contrary to expectations under ES, vertebrates excreted both N and P at higher rates than invertebrates despite having more nutrient-rich bodies, and primary consumers excreted as much nutrients as carnivores despite having nutrient-poor diets. Accounting for body N:P hardly improved upon predictions from treating vertebrate classification categorically. We conclude that basic data on body size, water temperature, trophic guild, and vertebrate classification are sufficient to make general estimates of nutrient excretion rates for any animal taxon or aquatic ecosystem. Nonetheless, dramatic interspecific variation in size-scaling coefficients and counter-intuitive patterns with respect to diet and body composition underscore the need for field data on consumption and egestion rates. Together, MTE and ES provide a powerful conceptual basis for interpreting and predicting nutrient recycling rates of aquatic animals worldwide.
Climate change is affecting lake stratification with consequences for water quality and the benefits that lakes provide to society. Here we use long‐term temperature data (1970–2010) from 26 lakes ...around the world to show that climate change has altered lake stratification globally and that the magnitudes of lake stratification changes are primarily controlled by lake morphometry (mean depth, surface area, and volume) and mean lake temperature. Deep lakes and lakes with high average temperatures have experienced the largest changes in lake stratification even though their surface temperatures tend to be warming more slowly. These results confirm that the nonlinear relationship between water density and water temperature and the strong dependence of lake stratification on lake morphometry makes lake temperature trends relatively poor predictors of lake stratification trends.
Key Points
Lake bottom warming rates are dampened compared to surface warming rates
Stratification responses to climate controlled by lake morphometry
Tropical lake stratification is most sensitive to warming
Animals can be important in nutrient cycling through a variety of direct and indirect pathways. A high biomass of animals often represents a large pool of nutrients, leading some ecologists to argue ...that animal assemblages can represent nutrient sinks within ecosystems. The role of animals as sources vs. sinks of nutrients has been debated particularly extensively for freshwater fishes. We argue that a large pool size does not equate to a nutrient sink; rather, animals can be nutrient sinks when their biomass increases, when emigration rates are high, and/or when nutrients in animal carcasses are not remineralized. To further explore these ideas, we use a simple model to evaluate the conditions under which fish are phosphorus (P) sources or sinks at the ecosystem (lake) level, and at the habitat level (benthic and water column habitats). Our simulations suggest that, under most conditions, fish are sinks for benthic P but are net P sources to the water column. However, P source and sink strengths depend on fish feeding habits (proportion of P consumed from the benthos and water column), migration patterns, and especially the fate of carcass P. Of particular importance is the rate at which carcasses are mineralized and the relative importance of benthic vs. pelagic primary producers in taking up mineralized P (and excreted P). Higher proportional uptake of P by benthic primary producers increases the likelihood that fish are sinks for water column P. Carcass bones and scales are relatively recalcitrant and can represent a P sink even if fish biomass does not change over time. Thus, there is a need for better documentation of the fraction of carcass P that is remineralized, and the fate of this P, under natural conditions. We urge a more holistic perspective regarding the role of animals in nutrient cycling, with a focus on quantifying the rates at which animals consume, store, release, and transport nutrients under various conditions.
Warming climates are rapidly transforming lake ecosystems worldwide, but the breadth of changes in tropical lakes is poorly documented. Sustainable management of freshwater fisheries and biodiversity ...requires accounting for historical and ongoing stressors such as climate change and harvest intensity. This is problematic in tropical Africa, where records of ecosystem change are limited and local populations rely heavily on lakes for nutrition. Here, using a ∼1,500-y paleoecological record, we show that declines in fishery species and endemic molluscs began well before commercial fishing in Lake Tanganyika, Africa’s deepest and oldest lake. Paleoclimate and instrumental records demonstrate sustained warming in this lake during the last ∼150 y, which affects biota by strengthening and shallowing stratification of the water column. Reductions in lake mixing have depressed algal production and shrunk the oxygenated benthic habitat by 38% in our study areas, yielding fish and mollusc declines. Late-20th century fish fossil abundances at two of three sites were lower than at any other time in the last millennium and fell in concert with reduced diatom abundance and warming water. A negative correlation between lake temperature and fish and mollusc fossils over the last ∼500 y indicates that climate warming and intensifying stratification have almost certainly reduced potential fishery production, helping to explain ongoing declines in fish catches. Long-term declines of both benthic and pelagic species underscore the urgency of strategic efforts to sustain Lake Tanganyika’s extraordinary biodiversity and ecosystem services.
Urban streams are often severely impaired due to channelization, high loads of nutrients and contaminants, and altered land cover in the watershed. Physical restoration of stream channels is widely ...used to offset the effects of urbanization on streams, with the goal of improving ecosystem structure and function. However, these efforts are rarely guided by strategic analysis of the factors that mediate the responsiveness of stream ecosystems to restoration. Given that ecological gradients from headwater streams to mainstem rivers are ubiquitous, we posited that location within a river network could mediate the benefits of channel restoration. We studied existing stream restorations in Milwaukee, Wisconsin, to determine (1) whether restorations improve ecosystem function (e.g., nutrient uptake, whole-stream metabolism) and (2) how ecosystem responses vary by position in the urban river network.We quantified a suite of physicochemical and biological metrics in six pairs of contiguous restored and concrete channel reaches, spanning gradients in baseflow discharge (19–196 L/s) and river network position (i.e., headwater to mainstem). Hydrology differed dramatically between the restored and concrete reaches; water velocity was reduced 2- to 13-fold while water residence time was 50–5,000% greater in adjacent restored reaches. Restored reaches had shorter nutrient uptake lengths for ammonium, nitrate, and phosphate, as well as higher whole-stream metabolism. Furthermore, the majority of reaches were autotrophic (i.e., gross primary production > ecosystem respiration), which is not common in stream ecosystems. The difference in ecosystem functioning between restored and unrestored reaches was generally largest in headwaters and declined to equivalence in mainstem restorations. Our results suggest that headwater sites offer higher return on investment compared to larger downstream channels, where ecosystem responsiveness is low. If this pattern proves to be general, the scaling of ecosystem responses with river size could be integrated into planning guidelines for urban stream restorations to enhance the societal and ecological benefits of these expensive interventions.
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